Textbook of Radiology And Imaging [1, 8 ed.] 9788131259634, 8131259633

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Textbook of Radiology & Imaging Edition 8 Volume 1 David Sutton Rodney Reznek, Janet Murfitt Adaptation Editor Bharat Aggarwal Director, Radiology Services, Max Healthcare, New Delhi, India Adjunct Professor, Koita Centre for Digital Health (KCDH) of Indian Institute of Technology, Bombay

Associate Editors Amit Kumar Sahu Consultant

Department of Radiology Max Superspeciality Hospital, Saket

New Delhi, India

Akshay D. Baheti Professor Department of Radiodiagnosis Tata Memorial Center and Homi Bhabha National University Mumbai, Maharashtra, India

Varsha Joshi Senior Consultant Radiologist Vijaya Diagnostic Centers Hyderabad, Telangana, India

Section Editors Girish Gandikota Professor and Vice Chair of Radiology

University of Chapel Hill, North Carolina

Adjunct Professor, Radiology and Rheumatology

University of Michigan Ann Arbor, MI, United States

Mukesh Harisinghani Professor of Radiology Harvard Medical School, Massachusetts General Hospital

Boston, MA, United States

Puneet Bhargava Professor, Director

Gastrointestinal Imaging

Abdominal Imaging Radiologist, University of Washington School of Medicine Hospitals, Seattle, WA, United States

Sandeep S. Hedgire Assistant Clinical Director

Cardiovascular Division, Director, Vascular Imaging

Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States

Subba R. Digumarthy Associate Professor of Radiology

Harvard Medical School

Boston, MA, United States Head of Thoracic Oncology Imaging Division of Thoracic Imaging and Intervention

Massachusetts General Hospital Boston, MA, United States

Sujit Vaidya Consultant Radiologist

The Royal London Hospital, Barts Health NHS Trust

Queen Mary University of London, London, United Kingdom

Suresh K. Mukerji

Professor of Radiology & Radiation Oncology

University of Louisville & University of Illinois, Robert Wood Johnson Medical School, Rutgers University, New Brunswick, NJ, United States. Faculty, Otolaryngology Head Neck Surgery, Michigan State University National Director of Head & Neck Radiology; Pro

Scan Imaging

Bruce Bradley Fellow; The Leapfrog Group

Suyash Mohan Associate Professor of Radiology & Neurosurgery, Perelman School of Medicine at the University of Pennsylvania

Philadelphia, PA, United States

Formerly, Clinical Lecturer-II University of Michigan, Ann Arbor, MI, United States

Copyright Elsevier

RELX India Pvt. Ltd. Registered Office: 818, 8th floor, Indraprakash Building, 21, Barakhamba Road, New Delhi-110 001 Corporate Office: 14th Floor, Building No. 10B, DLF Cyber City, Phase II, Gurgaon-122 002, Haryana, India Textbook of Radiology & Imaging, 2 Volume Set, 7e, David Sutton, Rodney Reznek, Janet Murfitt. Copyright © 2005 by Churchill Livingstone, an imprint of Elsevier Ltd. Previous editions copyrighted 2005, 1998, 1993, 1987, 1980, 1975, 1969. All rights reserved. ISBN: 978-0-443-07109-6 The right of David Sutton to be identified as author of this work has been asserted by him in accordance with the copyright, Design and Patents Act 1998. This adaptation of Textbook of Radiology & Imaging, 2 Volume Set, 7e, by David Sutton, Rodney Reznek, Janet Murfitt was undertaken by RELX India Private Limited and is published by arrangement with Elsevier Ltd. Textbook of Radiology & Imaging, 2 Volume Set, 8e by David Sutton, Rodney Reznek, Janet Murfitt.Adaptation Editor: Bharat Aggarwal Copyright © 2024 by RELX India Pvt. Ltd. Adaptation ISBN: 978-81-312-5960-3 Adaptation e-ISBN: 978-81-312-5963-4

Set ISBN: 978-81-312-5959-7 Set e-ISBN: 978-81-312-5962-7 All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notice The adaptation has been undertaken by RELX India Pvt. Ltd and its sole responsibility. Medical Students, radiology residents, practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds or experiments described herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made. To the fullest extent of the law, no responsibility is assumed by Elsevier, authors, editors or contributors in relation to the adaptation or for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Although all advertising material is expected to conform to ethical (medical) standards, inclusion in this publication does not constitute a guarantee or endorsement of the quality or value of such product or of the claims made of it by its manufacturer. Authorised Territory for Print form only is India, Pakistan, Bangladesh, Nepal, Srilanka, Bhutan, Maldives, Singapore, Malaysia, Brunei, Indonesia, Philippines, Thailand, Vietnam, Cambodia, Laos and Myanmar.Publisher’s `e-book’ shall have `World’ rights for selling globally through 3PP websites as approved by Proprietor. Content Strategist: Mrinalini Bakshi

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Foreword When I was a resident in the late 1980s, the only general radiology textbook we referred to was Dr. David Sutton’s Textbook of Radiology. My copy was heavily underlined and annotated and dog-eared and had multiple short, “xeroxed” pages of newer information from journals stuck to the original pages by tape or gum, increasing the weight of the textbook significantly. Even though in the later years, other textbooks became popular, Sutton was always the first book that would come to mind when we wanted residents to read up on a specific topic. In those days, with no Internet, no Pubmed, no Radiopaedia, and no other online resources, our only avenues to learn were general radiology and specialty textbooks and the popular grey and yellow journals, which in India, we would receive only about 6-9 months after publication. Dr. Sutton died in 2002. The last (7th) edition of his book was also published in 2002. Given its immense popularity, it is no wonder that Elsevier has decided to resurrect an 8th edition of this book, in a new avatar, especially for a South Asian audience. This is no mean task. Radiology has advanced by leaps and bounds since the time Dr. Sutton updated his book. Residents, fellows, and consultants now have access to a large number of online teaching resources, some very good, many free, and some behind paywalls, but all available at the click of a mouse or the touch of a thumb. The large language models such as Chat-GPT4 are also increasing access to textual knowledge, especially for specifically structured questions. Textbooks therefore now face significant competition for eyeballs and money. Elsevier was wise and I would say lucky to find and choose my friend Dr. Bharat Aggarwal to helm this project to bring to life this 8th edition. A third-generation radiologist, Bharat is one of the finest radiologists I have

known over the last 30 years. He understands the nuances of the subject, is widely read and traveled, and hence has been able to put together an enviable roster of renowned radiologists of Indian origin, both in India and from the US and the UK, as Associate and Section Editors. His Associate Editors, Drs. Amit Sahu, Akshay Baheti, and Varsha Joshi are radiologists I have known for the last many years, all of them passionate teachers and educators. His Section Editors are all internationally renowned experts in their field. Drs. Suyash Mohan, Suresh Mukherji, Sandeep Hedgire, Mukesh Harisinghani, Sujit Vaidya, Subba Digamurthy, Girish Gandikota, and Puneet Bhargava have all put tremendous effort into their individual sections to bring the book to fruition. It has taken about 4 years, two of which were during the challenging COVID-19 times, to make sure that each chapter in the book is as good, if not better than any online resource, with new images, algorithms, flowcharts, and tables. Some new sections have been added including Women’s, Pediatric Imaging, and Interventional Radiology. It is a complete textbook that would give residents most of the information they need during their residency days and clear their examinations. It has taken a lot of effort to maintain the flavor, language, and flow of the original book, while still ensuring that every statement of fact has been vetted and that all information is current up to the date of publication. I congratulate Dr. Bharat Aggarwal and his team for this effort and I am sure that the book will serve as a popular and invaluable resource, not only for residents, but even for consultants, who can use this as a quick reference resource when stuck on a specific subject. Dr Bhavin Jankharia

Preface Radiology is a continuously evolving field. With each passing year, advancements in technology enable greater precision and improved safety. The adoption of digital tools, artificial intelligence and machine learning, coupled with a better understanding of the molecular basis of disease, has enabled the introduction of new therapies and altered decision pathways for patient care. The role of the radiologist is now central to treatment planning and disease monitoring, therefore making it vital for radiologists to not only provide diagnoses but also actively contribute to decision-making in patient care. The modern radiologist now, more than ever before, must have a strong foundational knowledge while adapting to the evolving technological advances. It is with this premise that we have adapted this new edition of Sutton’s Textbook of Radiology. It has been an honor to be invited by Elsevier to edit and update Sutton’s Textbook of Radiology, the gold standard and a key reference book for practicing radiologists over multiple generations. I have attempted to share my experiences as a radiologist, a journey that began when I learned radiology from my father, Dr. Sudarshan K. Aggarwal, perhaps one of the greatest visionaries of Indian Radiology. The Diwan Chand Aggarwal Imaging Center, started by my grandfather in 1924 and taken forward by my uncle Dr. Satyapal Aggarwal, was scaled to an institution under the stewardship of my father, and managed under one core tenet—patient first. This created an academic environment and pushed the institute to be a teaching center from where over 100 radiology residents completed their training and are now leading radiologists across the globe. I continue to follow this philosophy of combining high-quality clinical care and academic pursuit in my ongoing tenure at Max Healthcare, one of the largest healthcare providers in India.

Despite the fact that the last revision of this book was in 2002, it has continued to be a favorite textbook among radiology residents, mainly because of the comprehensive coverage of each topic and the presentation style. We have preserved the unique style of the textbook and retained material that continues to be relevant even two decades later. This edition of Sutton is aimed at recreating an exhaustive resource and reference text for radiologists to solve diverse clinical scenarios using the latest and most appropriate technology, and develop a sound process-driven approach. New sections on radiology physics and techniques, pediatric radiology, interventional radiology, and emergency radiology have been added to make the book comprehensive. The first section includes chapters on quality assurance, structured reporting, information technology in radiology, and a primer in artificial intelligence—knowledge of which is now extremely important to practicing radiologists. The remaining sections have been reorganized to emphasize the need for sub-specialty radiology. Chapters on nuclear medicine and dental radiology provide the practicing radiologist with an understanding of all imaging-based diagnostic techniques available today. The evolving radiology lexicons that radiologists should use in their daily practice to communicate their findings for consistent care have also been incorporated into the book. This book was put together through the COVID-19 pandemic, the biggest medical calamity faced by our generation. I want to extend my heartfelt gratitude to all the contributors who, despite being personally and professionally impacted by COVID-19 at the frontlines during the pandemic, stood true to their commitment and contributed high-quality material that will lay the foundation for the careers of the radiologists of the future. I acknowledge the proactivity, guidance, and support extended by the section editors, all of whom are leaders in their fields—a big thanks to Dr. Suresh Mukherji, Dr. Suyash Mohan, Dr. Girish Gandikota, Dr. Sandeep Hedgire, Dr. Mukesh Harisinghani, Dr. Sujit Vaidya, Dr. Puneet Bhargava, and Dr. Subba Digumarthy. I would also like to thank Dr. Rajesh Gothi and Dr. Shivani Khanna for editorial support, and the management of Max Healthcare for their support. I would have been unable to complete this project without the commitment shown by my associate editors, Dr. Amit Sahu and Dr.

Akshay Baheti, right from the acceptance of this challenge to its planning and smooth execution, along with Dr. Varsha Joshi. Most importantly I thank the patient community that my family has served over almost a century, for shaping my professional career and encouraging me to be a better doctor. There are absolutely no words to describe the encouragement and support I have received from my wife, Suman, and children, Samir and Divya, in this extended, almost four-year journey of editing Sutton and the endless personal time ungrudgingly shared. This book is my contribution to the legacy of my family and to the specialty of Radiology. Dr Bharat Aggarwal

Contributors Abraham Fourie Bezuidenhout

Faculty

Department of Radiology

Beth Israel Deaconess Medical Center

Boston, MA, United States Adriano Basso Dias

Assistant Professor

University of Toronto

Division of Abdominal Imaging, Joint Department of Medical Imaging

University Health Network Mount Sinai Hospital – Women’s College Hospital, University of Toronto

Toronto, ON, Canada Alireza B. Abadi

Resident Physician

Department of Radiology

University of Washington

Seattle, WA, United States Alpana Joshi

Consultant & Director

Thane Ultrasound Centre

Thane, Maharashtra, India Ameya S. Kawthalkar

Department of Radiology

KIMS Kingsway Hospital

Nagpur, Maharashtra, India

Amna Zafar

Assistant Professor of Medicine

Co-Director of Cardio-Oncology

Division of Cardiovascular Diseases and Hypertension

Rutgers Robert Wood Johnson School of Medicine

New Brunswick, NJ, United States Amrin Israrahmed

Associate Consultant

Department of Intervention Radiology

Medanta Hospital

Gurgaon, Haryana, India Anderson H. Kuo

Midland Memorial Hospital

Midland, TX, United States Anisha Gehani

Junior Consultant

Tata Medical Center

Kolkata, West Bengal, India Anto Ramesh

Founder

Chairman & Managing Director

Radblox Healthcare Services

Bengaluru, Karnataka, India Anu Eapen

Professor

Christian Medical College

Vellore, Tamil Nadu, India Anupam Bam

Clinical Research Medical Advisor

Novartis, Mumbai, Maharashtra, India Anuradha Chandramohan

Professor and Clinical Lead of Abdominal Imaging Service Department of Radiology

Christian Medical College

Vellore, Tamil Nadu, India Aparna Katdare

Associate Professor

Department of Radiodiagnosis

Tata Memorial Hospital

Mumbai, Maharashtra, India Argha Chatterjee

Gastroradiology

Associate Consultant

Department of Radiology

Tata Medical Center

Kolkata, West Bengal, India Ashok Mithra

Senior Consultant Radiologist & Head of Radiology

Naruvi Hospitals

Vellore, Tamil Nadu, India Atif Zaheer

Professor

Radiology

Johns Hopkins University School of Medicine

Director

Cross-sectional Body Imaging Fellowship Program

Baltimore, MD, United States Avinash Bansal

Consultant

Thane Ultrasound Center

Thane, Maharashtra, India Avinash Kambadakone

Associate Professor

Harvard Medical School

Boston, MA, United States Benjamin Strnad

Instructor

Radiology

Division of Diagnostic Radiology

Abdominal Imaging Section

Abdominal Imaging Fellow

Mallinckrodt Institute of Radiology and Washington University in St. Louis School of Medicine

St. Louis, MO, United States Bharat Gupta

Consultant

Rajiv Gandhi Cancer Institute and Research Center

New Delhi, India Bojan Kovacina

Radiologist

Jewish General Hospital

Assistant Professor of Radiology

McGill University

Montreal, QC, Canada Brian B. Ghoshhajra

Service Chief

Cardiovascular Imaging

MAS; Clinical Fellow Carlos S. Restrepo

Professor of Radiology

Vice-Chair of Education

Director of Cardio-Thoracic Radiology

University of Texas Health Science Center at San Antonio

San Antonio, TX, United States Charissa Kim

Interventional Radiology Resident

Department of Radiology

Beth Israel Deaconess Medical Center

Boston, MA, United States Ciara O’Brien

Assistant Professor

University of Toronto

Division of Abdominal Imaging

Joint Department of Medical Imaging

University Health Network Mount Sinai Hospital – Women’s College Hospital

University of Toronto

Toronto, ON, Canada Dayanand Lingegowda

Senior Consultant

Department of Radiology

Tata Medical Center

Kolkata, West Bengal, India Dexter Mendoza

Assistant Professor of Radiology

Icahn School of Medicine at Mount Sinai

New York, NY, United States Dhiraj Baruah

Director

Thoracic Imaging

Medical University of South Carolina

Charleston, SC, United States Eric W. Zhang

Fellowship Director

Thoracic Imaging

Thoracic and Cardiovascular Imaging

Assistant Professor of Radiology

McGill University Health Centre (MUHC)

Montreal, Quebec, Canada Isha D. Atre

Harvard Medical School

Boston, MA, United States Jena N. Depetris

Assistant Clinical Professor

Department of Radiology

Ronald Reagan UCLA Medical Center and UCLA Santa Monica Medical Center

Los Angeles, CA, United States John E. Kirsch

Department of Radiology

Harvard Medical School

Boston, MA, United States Kanthan Amin

Assistant Professor

University of Washington

Seattle, WA, United States Kiran Batra

Associate Professor

UT Southwestern Medical Center

Dallas, TX, United States Krishan Patel

Piedmont Medical Center

Atlanta, GA, United States Krishna Shanbhogue

Professor of Radiology

NYU Langone Health

New York, NY, United States Luke Ginocchio

Assistant Professor

Department of Radiology

New York University Grossman School of Medicine

New York, NY, United States Madeleine Sertic

Department of Abdominal Imaging

Massachusetts General Hospital

Instructor

Harvard Medical School

Boston, MA, United States

Maria Zulfiqar

Assistant Professor of Radiology

Mayo Clinic ArizonaPhoenix

AZ, United States Markus Y. Wu

Assistant Professor

Department of Radiology

University of Colorado-School of Medicine

Aurora, CO, United States Michael Steigner

Director

Vascular CT/MRI

Medical Director, 3D Lab

Brigham and Women’s Hospital

Assistant Professor of Radiology

Harvard Medical School

Boston, MA, United States Milind D. Dhamankar

Senior Clinical Affairs

Specialist at Siemens Healthineers

Malvern, Pennsylvania, United States Mrudula Bapat

Presently, Director

Dhanvantari Diagnostics and Bapat Urology Centre

Thane, Maharashtra, India Muhammad Usman Aziz

Assistant Professor

Sections of Cardiopulmonary and Abdominal Radiology

University of Alabama at Birmingham Hospital (UAB)

Birmingham, AL, United States Mukesh G. Harisinghani

Professor Harvard Medical School

Massachusetts General Hospital

Boston, MA, United States

Neeraj Kaur

Radiologist

Scarborough Health Network

Toronto, Canada Nikita Nanwani

Assistant Professor Kiran Medical College & Hospital

Surat, Gujarat, India Nitin Chaubal

Director Thane Ultrasound Centre

Thane, Maharashtra, India Palak Popat

Professor

Department of Radiodiagnosis

Tata Memorial Hospital

Mumbai, Maharashtra, India Pooja Punjani Vyas

Fellowship in Fetal Medicine Mediscan Systems

Chennai, Tamil Nadu, India Prabhakar Rajiah

Professor of Radiology

Mayo Clinic

Rochester, MN, United States Prashant Nagpal

Section Chief

Cardiovascular Imaging

Cardiovascular and Thoracic Imaging

Associate Professor of Radiology

University of Wisconsin–Madison

School of Medicine and Public Health

Madison, WI, United States Priya Pathak

Assistant Professor of Radiology

University of Minnesota

Minneapolis, MN, United States

Puneet Bhargava

Professor

Body Imaging Section

Department of Radiology

University of Washington Medical Center

Seattle, WA, United States Rajas Chaubal

Secretary

Musculoskeletal Ultrasound Society, India Ramandeep Singh

Clinical Fellow in Radiology

Massachusetts General Hospital

Harvard Medical School

Boston, MA, United States Reetu John

Professor

Department of Radiology

Christian Medical College

Vellore, Tamil Nadu, India Rohit Takhar

CARPL.ai Pvt. Ltd.

New Delhi, India Rory L. Cochran

Massachusetts General Hospital

Harvard Medical School

Boston, MA, United States Ruchi Rastogi

Principal Consultant Max Superspeciality Hospital

New Delhi, India Sachin S. Saboo

Radiologist

South Texas Radiology Group

San Antonio, TX, United States

Sandeep S. Hedgire

Assistant Clinical Director CV Division

MAS

Fellow

Cardiovascular imaging

MAS

Clinical Fellow Sandhya Vinu-Nair

Associate Professor

Radiology

Section Director

Emergency Radiology

University of Texas Health Science Center at San Antonio

San Antonio, TX, United States Sangeet Ghai

Associate Professor

University of Toronto

Toronto, ON, Canada Sanjeeva P. Kalva

Chief

Interventional Radiology

Massachusetts General Hospital

Professor of Radiology

Harvard Medical School

Boston, MA, United States Sarv Priya

Clinical Assistant Professor

Radiology

University of Iowa Hospitals & Clinics

Iowa City, IA, United States Satinder Singh

Professor of Radiology and Medicine (Division of CV Diseases) University of Alabama at Birmingham Hospital (UAB)

Birmingham, AL, United States

Saugata Sen

Senior Consultant

Department of Radiology and Imaging Sciences

Tata Medical Center Kolkata

Kolkata, West Bengal, India Seema Kembhavi

SMO Radiology

Mackay Hospital and Health Services

Mackay

QLD, Australia Shalini Govil

Senior Advisor Radiology Quality

Naruvi Hospital

Vellore, Tamil Nadu, India Sharad Maheshwari

Consultant Radiologist

Kokilaben Hospital Mumbai, Maharashtra, India Shyamkumar N. Keshava

Professor and Head

Department of Interventional Radiology

Division of Clinical Radiology Smita Esther Raju

Consultant Radiologist & Director of Training

Clinical Radiology

Royal Adelaide Hospital

Adelaide, SA, Australia Somesh Singh

Consultant

Department of Radiodiagnosis

Medanta Hospital

Gurgaon, Haryana, India Sourav Panda

Consultant Radiologist

Healthworld Hospital

Durgapur, West Bengal, India Srinivasa R. Prasad

Professor

University of Texas MD Anderson Cancer Center

Houston, TX, United States Subba R. Digumarthy

Associate Professor of Radiology

Harvard Medical School

Boston, MA, United States Sumit Gupta

Instructor in Radiology

Brigham and Women’s Hospital Department of Radiology Boston, MA, United States Sumit Mukhopadhyay

Senior Consultant

Department of Radiology

Tata Medical Center

Kolkata, West Bengal, India Sunaina Yadav

Imperial College London, United Kingdom Swati Garekar

Consultant Pediatric Cardiologist

Fortis Hospital Mulund Mumbai, Maharashtra, India Tejas Kapadia

Consultant Paediatric Radiologist

Royal Manchester Children’s Hospital

Manchester, United Kingdom Udo Hoffmann

Chief Scientific Officer

Cleerly Inc

New York, NY, United States

Vaibhav Nichat

Pediatric Radiology Fellow Department of Radiodiagnosis and Imaging

Postgraduate Institute of Medical Education and Research

Chandigarh, Punjab, India Vasantha Kumar Venugopal

CARPL.ai Pvt. Ltd.

New Delhi, India Venkat Katabathina

Associate Professor

University of Texas Health Science Center at San Antonio

San Antonio, TX, United States Venkateswar R. Surabhi

Professor of Radiology

Department of Abdominal Imaging

Division of Diagnostic Imaging

The University of Texas MD Anderson Cancer Center

Houston, TX, United States Vidur Mahajan

CARPL.ai Pvt. Ltd.

New Delhi, India Viky S. Loescher

Cardiovascular-Cardiothoracic Radiologist

Mount Sinai Medical Center

Miami Beach, FL, United States Zainab Vora

Consultant Radiologist

Apple Imaging

New Delhi, India

Table of Contents Cover Image Title Page Copyright Foreword Preface Contributors Table of Contents

Section A Imaging Physics and Principles of Imaging 1 X-ray Physics Discovery of X-rays

Atomic Structure Electromagnetic Spectrum X-ray Imaging Film-screen Radiography Digital Radiography Fluoroscopy Suggested Readings References 2 Ultrasound Physics Introduction Principle of Ultrasound Properties of Sound Pulse Echo Instrumentation Image Quality B-Mode Imaging Artifacts Doppler Practical Tips and Image Optimization Summary Special Imaging Modes Suggested Readings References

3 Computed Tomography Physics Introduction Components of a Computed Tomography Machine Computed Tomography Generations Parameters for Image Acquisition and Modes of Scanning Scanned Projection Radiograph Axial and Helical Acquisition Image Reconstruction Techniques Basic Image Display and Processing Image Quality Noise Artifacts Dosimetry Dose Optimization and Factors Affecting Patient Dose Automatic Exposure Control (AEC) Overbeaming and Overranging Advanced Computed Tomography Applications Suggested Readings References 4 Principles of MRI Physics

Introduction Fundamentals of MRI MRI Hardware MRI Pulse Sequences and Applications Using Different Schemes in k-Space Manipulations Using Artifact Reduction Techniques Diffusion-Weighted Imaging and Diffusion Tensor Imaging Susceptibility-Weighted Imaging Magnetic Resonance Angiography MR Spectroscopy Perfusion-Weighted Imaging Advanced Applications MRI and Artificial Intelligence (AI) MR Artifacts MRI Safety Suggested Readings References 5 Concepts in Radiation, Contrast and Safety Radiation Sources of Radiation

Effects of Radiation Linear No-Threshold Model and Its Limitations Principles of Radiation Protection Practical Aspects of Radiation Protection Radiation Risks and Radiophobia Contrast Media Iodinated Contrast Media Contrast Reactions Gadolinium-Based Contrast Media MRI Safety Imaging in Pregnancy Suggested Readings References 6 Information Technology in Radiology Introduction Terminologies Used in IT RIS, PACS, and Radiology Workflow DICOM Postprocessing and Advanced Image Visualization Radiology Workstations and Monitors

Teleradiology Suggested Readings References 7 Quality Assurance and Structured Reporting Introduction The Quality Improvement Program Sequential Steps in The Quality Improvement Process Essential Ingredients of a Quality Improvement Program Patient Safety and Communication Diagnostic Errors Performance Monitoring: Accuracy Audit Performance Monitoring: Productivity Audit Performance Improvement: Training “As-You-Go” Physician Scorecard and the Total Quality Score (TQS) Accreditation by Regulatory Bodies The New Structured Radiology Report Equipment Quality Control Suggested Readings References

8 Artificial Intelligence in Radiology What is Artificial Intelligence? Creating an AI Algorithm? Broad use Cases of AI AI in the Radiology Workflow Challenges and Limitations Suggested Readings References 9 Introduction to Methods in Research Introduction Avenues in Radiology Research Creating a Research Framework Measuring Impact Conclusion Suggested Reading References 10 Approach to Oncoimaging Introduction Basics of Oncology

Imaging in Cancer Response Evaluation Beyond “Tumor Assessment” in the Post-Treatment Setting Newer Advances and the Road Ahead Personalized Oncology and Personalized Radiology Suggested Readings References

Section B Respiratory System 11 Normal Chest Introduction Chest Radiography Computed Tomography PET-CT and PET-MRI MRI Ultrasound Anatomy Chest Radiograph Summary Suggested Readings

References 12 Differential Diagnosis in Chest Imaging Introduction Hyperlucent Hemithorax Opacified Hemithorax Elevated Hemidiaphragm Widened Superior Mediastinum Hilar Enlargement Airways Pulmonary Nodules Patterns of Lung Disease Cystic Lung Disease Mediastinum Pleura Miscellaneous Suggested Readings References 13 Mediastinum Anatomy

Clinical Presentation of Mediastinal Disease Imaging Workup of Mediastinal Disease Clinical Applications Suggested Readings References 14 Pleura, Diaphragm, and Chest Wall Anatomy Physiology Imaging Appearance of Normal Pleura, Diaphragm, and Chest Wall Pleural Fluid Pneumothorax Bronchopleural Fistula Pleural Thickening Pleural Calcification Pleural Tumors The Diaphragm Chest Wall Suggested Readings References

15 Pulmonary Infections Introduction Role of Radiological Techniques in Pulmonary Infection Clinical Classification Patterns of Pulmonary Infections Radiographic and CT Imaging of CAP Lung Necrosis, Lung Abscess, and Cavity Bacterial Pneumonias Atypical Pneumonia Viral Pneumonias Chlamydial and Rickettsial Pneumonias Pulmonary Tuberculosis Pulmonary Infections in Congenital Disorders, Genetic Disorders, and Primary Immunodeficiency Disorders Pulmonary Infections in Immunocompromised Patients Bacterial Pneumonia Fungal Infection Immune Reconstitution Inflammatory Syndrome (IRIS) Differential Diagnosis and Radiologic Approach to InfectionRelated Various Nodules Based on the Type of Immunosuppression (Aids versus Hematological Cell Transplant)

Suggested Readings References 16 Lung Tumors Introduction Benign Lung Tumors Chondroma Malignant Lung Tumors Suggested Readings References 17 Diseases of Airways Tracheal Diseases Bronchial Diseases Airway Diseases Collapse or Atelectasis Suggested Readings References 18 Diffuse Lung Disease Introduction Idiopathic Interstitial Pneumonias

Connective Tissue Diseases Hypersensitivity Pneumonitis Eosinophilic Lung Disease Drug-Related Lung Diseases Pneumoconioses Sarcoidosis Amyloidosis Diffuse Cystic Lung Diseases Other Diffuse Lung Diseases Suggested Readings References 19 Miscellaneous Conditions of Chest Thoracic Trauma Postoperative Chest Thoracic Lines, Tubes, and Devices Suggested Readings References

Section C Cardiovascular System

20 Normal Heart Introduction Pericardium Cardiac Chambers Valves Coronary Anatomy Cardiac Venous Anatomy Multimodality Imaging Suggested Readings References 21 Chest Radiograph in Acquired Heart Disease Introduction Heart Size and Shape Approach to Acquired Heart Disease on Chest Radiograph Individual Cardiac Chamber Enlargement Pulmonary Vascular Pattern Pulmonary Hypertension Pulmonary Venous Hypertension Pulmonary Plethora Pulmonary Oligemia

Right Ventricular Failure/Right Ventricular Dysfunction Thoracic Osseous Radiographic Features Associated with Cardiovascular Disease The General Postoperative Chest Radiograph Postcardiac Surgery Implants Coronary Heart Disease Acute Myocardial Infarction Cardiac Valves Pericardium Thoracic Aorta Pulmonary Embolism Pulmonary Artery Aneurysm Pulmonary Arteriovenous Malformation Heart Transplantation Cardiac Devices on Chest X-Ray Suggested Readings References 22 Coronary Artery Disease Introduction

Coronary Artery Calcification Stenosis and Plaque Evaluation Cardiac Manifestations of Ischemia Coronary CT Fractional Flow Reserve Overall Approach Sample Report Templates Suggested readings References 23 Noncoronary Artery Heart Disease Introduction Valvular Heart Disease Imaging of Cardiomyopathies Cardiac Tumors Suggested Readings References 24 Pericardium Introduction Imaging Techniques Normal Pericardial Anatomy

Pericardial Disorders Medical Devices in the Pericardium Overall Approach to the Pericardium/Take Home Points Suggested Readings References 25 Diseases of Arteries General Concepts Aorta Abdomen Pelvic Arteries Lower Extremity Upper Extremity Suggested Readings References 26 Diseases of Veins and Lymphatics Part I: Diseases of Veins Vascular Imaging Techniques Upper Extremity Venous System Pelvic and Lower Extremity Venous System

Inferior Vena Cava Renal Veins Hepatic Veins Porto–Mesenteric–Splenic Venous System Gonadal Veins Adrenal Veins Central Thoracic Veins Pulmonary Veins Part II: Diseases of Lymphatics and Vascular Malformations Lymph System Anatomy and Variants Lymphatic Imaging Lymphorrhea Lymphedema Vascular Malformations Suggested Readings References

Section D Abdomen and Gastrointestinal Tract 27 Conventional Abdominal Radiology Introduction

Imaging Techniques Chest X-Ray Abdominal Radiographs Fluoroscopy Normal Anatomy on Abdominal Radiographs Pathology on Abdominal Radiographs Suggested Readings References 28 Esophagus and Stomach Normal Anatomy Imaging Techniques Anomalies Esophagus: Inflammatory Processes Esophageal Vascular Disease Mechanical Esophageal Disease Esophageal Trauma and Foreign Bodies Esophageal Neoplasms Stomach—Inflammatory Conditions Vascular Mechanical Gastric Disease

Gastric Trauma Miscellaneous Gastric Processes Gastric Neoplasms Postsurgical Stomach Summary Suggested Readings References 29 Imaging of Small and Large Bowel Anatomy Imaging Techniques General Causes of Non-neoplastic Bowel Wall Thickening Specific Small Bowel Abnormalities Specific Large Bowel Abnormalities Imaging of Lower Gastrointestinal Tract Bleeding Imaging of Postoperative Bowel Perianal Fistulas Defecography Systematic Approach to Small and Large Bowel Evaluation on Contrast-enhanced Computed Tomography Suggested Readings

References 30 Liver Anatomy and Variants Introduction Imaging Techniques External Anatomy Vascular Anatomy and Variants Pseudolesions Suggested Readings References Chapter 31 Noncirrhotic Liver Introduction Imaging Techniques Focal Hepatic Lesions Overall Approach and Common Clinical Scenarios Suggested Readings References Chapter 32 Diffuse Liver Disease Hepatic Steatosis Hepatic Iron Deposition

Genetic and Metabolic Diseases Hepatic Fibrosis and Cirrhosis Conclusion Suggested Readings References Chapter 33 Cirrhotic Liver Introduction Imaging Diagnosis and Staging of Fibrosis Imaging the Morphology of Cirrhosis Complications of Cirrhosis Hepatocellular Carcinoma Liver Transplant Conclusion Suggested Readings References Chapter 34 Spleen Normal Anatomy Imaging Techniques Normal Imaging Appearance

Splenic Abnormalities and Diseases Benign Neoplasms Malignant Neoplasms Miscellaneous Overall Approach and Common Clinical Scenarios Suggested Readings References Chapter 35 Gallbladder and Biliary Tree Anatomy Methods of Investigation Developmental Anomalies Gallbladder Bile Ducts Approach to a Case of Right Upper Quadrant Pain Suggested Readings References Chapter 36 Pancreas Introduction Overview of Imaging Techniques

Pseudotumors Congenital Anomalies Acute Pancreatitis (AP) Chronic Pancreatitis (CP) Pancreatic Neoplasms Cystic Pancreatic Neoplasms Suggested Readings References Chapter 37 Peritoneum, Retroperitoneum, and Abdominal Wall Anatomy of Peritoneum, Omentum, and Mesentery Imaging Techniques Developmental Lesions Nonpancreatic Pseudocysts Infectious, Inflammatory, and Ischemic Disorders Intraperitoneal Collections Neoplastic Disorders Miscellaneous Overall Clinical Approach for Diagnosis of Peritoneal Lesions Retroperitoneum Abdominal Wall

Suggested Readings References

Section E Genitourinary Tract Chapter 38 Urinary Tract: Anatomy, Conventional Radiology, and Ultrasonography Introduction Anatomy Imaging Introduction to IVU Interpretation Congenital Lesions and Variants Inflammatory Disease Reflux Nephropathy Rare Inflammatory Conditions Tumors Renal Vascular Disease Calculi and Obstruction Upper Urinary Tract Trauma Suggested Readings References

Chapter 39 Urinary Tract: Nontumorous Diseases Introduction Infections and Inflammatory Conditions Calculi and Obstruction Diffuse Multifocal and Renal Parenchymal Abnormalities Pretransplant Evaluation in Renal Donors Postrenal Transplant Imaging Renal Transplant Complications Genitourinary Trauma Suggested Readings References Chapter 40 Urinary Tract: Tumors Solid Renal Tumors Benign Tumors Malignant Tumors Other Tumors Staging RCC Other Malignant Tumors Management Approach to Renal Masses

Cystic Masses of the Kidney Bosniak Classification Upper Urinary Tract Tumors Imaging of Urinary Bladder Cancer Conclusion Suggested Readings References Chapter 41 Adrenals Introduction Adrenal Imaging Adrenal Diseases Suggested Readings References Chapter 42 Prostate Introduction Anatomy Diseases Suggested Readings References

Chapter 43 Male Genital Tract Male Urethra Scrotum and Testes Extratesticular Disorders Testicular Disorders Testicular Malignancies and Related Conditions Penile Disorders Radionuclide Imaging of the Testis Role of Radiology in Andrology Disorders Suggested Readings References

Section F Women's Imaging Chapter 44 Uterus and Cervix Introduction Imaging Techniques Normal Anatomy, Physiology, and Imaging Appearance of the Uterus and Cervix Benign Conditions of the Uterus and Cervix Malignant Conditions of the Uterus and Cervix

Suggested Readings References Chapter 45 Ovaries and Adnexae Anatomy and Imaging Appearance Physiology Imaging Techniques History, Clinical Examination, and Biomarkers Lexicon for Reporting Adnexal Lesions Specific Adnexal Lesions Ovarian Cancer Screening Radiological Approach to Adnexal Lesions Suggested Readings References Chapter 46 Miscellaneous Gynecological Conditions Endometriosis Mullerian Duct Anomalies Infertility Benign and Malignant Conditions of Vagina and Vulva Suggested Readings

References Chapter 47 Obstetrics: First Trimester Introduction First-Trimester USG Early First-Trimester Fetal Evaluation Late First-Trimester Fetal Evaluation First-Trimester Screening for Preeclampsia Suggested Readings References Chapter 48 Obstetrics: Second Trimester Introduction Central Nervous System Anomalies Spine Face Chest Gastrointestinal Tract Genitourinary System Skeletal Fetal Infections and Genetic Screening

Suggested Readings References Chapter 49 Obstetrics: Third Trimester Introduction Fetal Growth Restriction Fetal Environment Twins Summary Suggested Readings References Chapter 50 Obstetrics: Fetal Echocardiography and Interventions Section 1: Fetal Echocardiography Section 2: Fetal Interventions Suggested Readings References 51 Breast The Basics: Normal Anatomy and Histology Brief Introduction to Pathology of Epithelial Changes in Breast Mammography Equipment and Physics

Language of Reporting Breast Ultrasonography Breast Magnetic Resonance Imaging Newer & Emerging Imaging Techniques Common Conditions and Diseases of the Breast With Clinical Radiology–Pathology Correlation Image-Guided Procedures Suggested Readings References Index

SECTION A

Imaging Physics and Principles of Imaging

1

X-ray Physics Tejas Kapadia, Zainab Vora, Nikita Nanwani

Discovery of X-rays On a Friday afternoon (November 8, 1895), an experiment conducted by Sir Wilhelm Conrad Roentgen, a German physicist, led to the discovery of mysterious rays. In his experiment on the then recently invented Crooke's tube (invented in 1870 by Sir William Crookes), Roentgen found that a sheet of barium platino-cyanide placed at a distance was glowing even when the tube was covered by black cardboard. He repeated this experiment, furthering the sheet to a distance more than 6 m when no other known rays from the tube could reach that far. He concluded that these mysterious invisible rays were able to penetrate the cardboard and travel farther than the cathode rays, and he named these invisible rays “x-rays.” His discovery changed the practice of medicine forever. The famous radiograph of his wife's

hand was taken on December 22, 1895, a week before his first “provisional” communication, titled “On a New Kind of Rays,” in the Proceedings of the Würzburg Physico-Medical Society [1]. Sir Roentgen was awarded the first Nobel Prize in Physics in 1901.

Atomic Structure All matter is made of atoms, and understanding the structure of atoms is key to learning the fundamentals of x-ray physics. An atom is made up of a central nucleus and electrons orbiting around it in shells. The nucleus of an atom consists of nucleons made up of positively charged protons (p) and neutrons (n) having no charge. The electrons orbiting around the nucleus have a negative charge, and the atom as a whole is electrically neutral (i.e., with an equal number of protons and electrons). The positively charged protons in nucleus repulse because they are of the same charge. However, they are held together by short-range forces. Neutrons help in reducing the repulsive forces by spacing out protons. ■ The atomic number (Z) is the number of protons in the nucleus; it is unique to each element

(e.g., the Z for oxygen is 8, for iodine is 53, and for tungsten is 74) ■ The atomic mass number (A) is the number of protons and neutrons Electrons orbit in energy shells around the nucleus and have specific shell-binding energy depending on their proximity to the nucleus. The closer the shell to the nucleus, the higher is the shell binding energy. In the Bohr model, the innermost shell is labeled as the K shell, and subsequent outer shells are labeled L, M, N, O, etc. (Similarly, the inner shell is assigned a principal quantum number of n = 1 and subsequent shells as 2, 3, 4, 5, etc.) Each shell can contain a maximum of 2n2 number of electrons; for example, the K shell with n = 1 can contain two electrons, and the L shell with n = 2 can contain a maximum of 8 electrons (Fig. 1.1).

Figure 1.1 Atomic structure of carbon (Z = 6) with two K-shell electrons and four L-shell electrons. (From: D Graham, P Cloke, M Vosper, Principles and Applications of Radiological Physics, sixth ed, 119, Churchill Livingstone, Evolve Elsevier, 2012, UK.) Electrons are bound in orbits by electrostatic force from the nucleus, which is equal to amount of energy required by electron to escape from the field of nucleus, also called electron-binding energy, measured in electron volts (eV). Binding energy is specific for each electron shell of each element. Electrons in the innermost shells have highest binding

energies in thousands of electron volts (keV) for most elements compared with just few electron volts for outer-shell electrons. The K shell is the most desirable for electrons, and if an electron is removed from the K shell, an outershell electron falls into its space with release of energy. K-shell binding energy increases with the atomic number (Z) of the element; for example, the K-shell binding energy for molybdenum (Z = 42) is 20 KeV compared with 70 KeV for tungsten (Z = 74). ■ Electron-binding energy (eV) is the amount of energy required to expel an electron from the field of nucleus. It increases with an increase in atomic number of the elements ■ Inner-shell electrons have higher binding energies

Electromagnetic Spectrum X-rays are electromagnetic waves having both electric and magnetic properties. Electromagnetic waves are transverse waves in which the electric and magnetic fields oscillate perpendicular to each other

and to the direction of the wave. Electromagnetic waves travel in a straight line with the speed of light (3 × 108 m/sec in a vacuum) and require no medium to travel (i.e., they can travel in a vacuum). The velocity (c) of the wave can be calculated by the product of frequency (f) and wavelength (λ) as

X-rays are made up of photons, which can behave as both waves and particles. The photon energy (E) is directly proportional to frequency (E = h × f), in which h is the Plank's constant. The electromagnetic waves above the visible light of energy spectrum (ultraviolet rays, x-rays, and γ-rays) are classified as ionizing because they are capable of displacing an electron from the atom.

X-ray Units Energy produced at source and energy deposited or absorbed by tissues is measurable (Table 1.1). Kerma was developed to measure the amount of kinetic energy released in matter per unit mass. Dose is used to quantify the energy deposited or absorbed by an

object. Energy passing through a cross section (sum of energies of all photons) per unit area measured per unit time gives the energy fluence rate or beam intensity (signifies beam quality). Intensity is a measure of energy in a cross-section area and is mostly dependent on the number of x-ray photons (quantity). Table 1.1 Units of Radiation Dose SI Conventiona Term Description Uni l Unit t Exposu Amount of ionization Roentgen C/ re produced per unit of kg mass of air Kerma

Kinetic energy released in matter per unit mass

Rad

Gr ay (G y) or J/k g

Term

Description

Dose

Energy absorbed per unit mass

SI Conventiona Uni l Unit t Rad Gr ay (G y) or J/k g

Intensit Number of photons × KeV/cm2 y photon energy per unit area

J/ m2

SI, International System of Units.

X-ray Imaging X-ray Tube An X-ray tube is made up of two oppositely charged electrodes (cathode and anode) capable of producing x-rays when a current is passed through it. When fastmoving electrons are bombarded on a metal target,

the kinetic energy of the electrons is converted mainly into heat (>99%) and x-rays ( This can be reduced by reducing the patient surface area to be irradiated and can be achieved by ■ Using collimation in the form of a light beam diaphragm or cones or cylinders. The light beam diaphragm is integrated with the x-ray tube system in all modern equipment. Cones and cylinders are

additional collimation devices that can be attached to the x-ray tube to limit the field of exposure and to image specific areas of interest (e.g., the coned view of the lumbosacral junction as part of a series of spine imaging in adults) ■ Tissue compression reduces the thickness and helps in reducing scatter as well as patient dose Limiting scatter from reaching the detector Scatter reaching the detector can be reduced by using the use of grids or by using the air-gap technique. Secondary radiation grid A grid is a device placed between the patient and the image receptor to prevent scatter radiation from reaching the receptor, which reduces the scatter by 90%, thus improving image contrast (Fig. 1.15). Grids were first developed by Gustave Bucky in 1913, and 7 years later Hollis Potter developed the moving grid. Therefore, today the moving grids are called Potter-Bucky grids.

Figure 1.15 The grid interposed between the patient and the receptor absorbs about 90% of scatter radiation. (From: SC Bushong, Scatter radiation. In: Radiologic Science for Technologists, eleventh ed, 195, Elsevier, 2017, Canada.) Grids are made of strips of high atomic number material (usually lead of 0.05–0.07mm width)

sandwiched between thicker strips of low atomic number material (usually a low atomic number material, such as carbon fiber). Only the rays passing straight through the interspace material reach the detector, and those passing obliquely are absorbed by the lead grid strips. The transmitted incident rays usually pass the interspace material and contribute to image formation. The scatter radiation is usually at an angle and gets absorbed by the lead strips; however, if the angle of scatter is small, it can match the angle of acceptance of the grid and can reach the image receptor, contributing to noise. Grid ratio: This is an important parameter that describes the attenuation capacity of the grid. It is defined as a ratio of the height (h) of the lead strips to the width (D) between them (Fig. 1.16).

Figure 1.16 Grid ratio. D, thickness of the interspace material; h, height of the strip; T, thickness of the lead strip. (From: SC Bushong, Scatter radiation. In: Radiologic Science for Technologists, eleventh ed, 195, Elsevier, 2017, Canada.) The higher the grid ratio, the better the ability to remove scatter, and it improves image contrast. But this also increases the radiation dose to the patient because it requires increasing the energy of the x-ray beam to achieve adequate exposure of the image detector. Contrast improvement factor: This is used to calculate grid performance.

A contrast improvement factor (K) of 1 indicates no improvement. Grids in use generally have K values in the range of 1.5 to 3 (usually double the contrast); this is higher for high-ratio grids. Bucky factor: Increasing the grid ratio reduces the total amount of radiation reaching the image detector and thus can affect the image quality. To compensate, the radiation energy has to be increased, which also increases the patient dose. This increased dose to the patient can be calculated by the Bucky factor, which is a ratio of

The Bucky factor (patient dose) increases with an increase in grid ratio and with an increase in kVp.

Grid factor: Using a grid necessitates increasing mAs and thus increases the patient exposure. This can be measured by a parameter called the grid factor, which is measured as

The grid factor is generally in the range of 3 to 5, and this shows how much the exposure and patient dose increase because of the grid. It depends on the thickness of patient, grid ratio, and the kV used. Focused and unfocused grids Grids with parallel orientation of the lead strips are call unfocused grids, and they tend to absorb some of the useful transmitted radiation because of divergent nature of the x-ray beams that travel obliquely at the periphery of the image (Fig. 1.17A). To counter this, focused grids were developed in which the lead strips are tilted at an angle from the center to the periphery to align toward the tube focus (Fig. 1.17B).

Figure 1.17 A. parallel unfocused grid (A) and a focused grid with tilted lead strips (B). (From: SC Bushong, Scatter radiation. In: Radiologic Science for Technologists, eleventh ed, 198, 200, Elsevier, 2017, Canada.) Moving grid The grid can sometimes be seen on the radiographic image as grid lines. This can be negated by moving the grid at the time of exposure. Most of the newer equipment has moving grids to counter image artifacts caused by grid lines. Sometimes motion blur can occur because of the moving mechanism of the grid, but this outweighs the obvious benefits of the moving grid. Grid cut-off

Numerous factors should be considered while using grids, and failure to follow the steps correctly can cause significant image quality compromise (Fig. 1.18). The tube needs to be at a specified distance and well centered for focused grids. The focused grid cannot be placed upside down, or the direction of its movement cannot be changed; this will lead to cut-off of the primary beam and thus significant artifacts on the image, prompting repeat imaging.

Figure 1.18 (A) Proper position of the focused grid well oriented to the focus. (B) Off-level grid. The grid is not perpendicular to the central axis (grid cut-off across the image; this is an underexposed, light image). (C) Off-center grid. This is a focused grid positioned off center (grid cut-off across the image; this is an underexposed, light image). (D) Off-focus grid

(focused grid is not positioned at the focal distance required; grid cut-off toward the edge of the image). (E) Upside-down grid (severe grid cut-off toward the edge of the image). (From: SC Bushong, Scatter radiation. In: Radiologic Science for Technologists, eleventh ed, 202, Elsevier, 2017, Canada.)

Figure 1.19 Characteristic curve showing the graphical relationship between optical density and radiation exposure. (From: SC Bushong, Scatter radiation. In: Radiologic Science for

Technologists, eleventh ed, 312, Elsevier, 2017, Canada.) Practical aspects of using a grid Grid greatly improves image quality by reducing scatter radiation reaching the image receptor but has a major disadvantage of necessitating an increase in patient dose. ■ Grid is generally used for imaging thick body sections (e.g., the chest or abdomen) and when higher than 60 kVp is used ■ For general radiology, a grid with ratio of 10:1 or 12:1 works well in balancing the patient dose and image quality ■ For mammography and mobile radiography, a lower grid ratio is used ■ A moving grid is part of the Bucky setup and is preferable and commonly used for body radiographs ■ Stationary grids can cause artifacts on the image, appearing as grid lines, and are generally used for mobile radiography when a moving grid setup is not possible

■ Moving grids are generally focused grids, and parallel or unfocused grids are used for mobile imaging and fluoroscopy Air-gap technique Increasing the gap between the patient and detector without an interposing grid is called an air-gap technique. The distance is increased by about 10 to 15 cm, and this reduces the amount of scatter reaching the detector to a similar extent to that with a grid. However, the scanning parameters have to be changed, which increases the patient dose compared with a technique without a grid. The patient dose with the air-gap technique is similar to the dose caused by a radiograph taken with grid. There are a few disadvantages with the air-gap technique, including image magnification caused by increased distance (similar to a shadow cast against light). Also, air-gap technique causes some geometric blur affecting image quality.

Film-screen Radiography

Film radiography and film-screen radiography were used to capture the radiographic image for decades since the use of x-rays in medicine. Similar to the impact of digitization in photography, the use of both has drastically reduced globally with digital capture of the radiographic image almost completely replacing this technique. It will be described here briefly because it lays the foundation of currently used digital techniques in radiography.

Radiographic Film The radiographic film is the photographic receptor used to decode the information carried by the attenuated x-ray beam, serving as the primary medium to convert the invisible radiation to an image. The radiographic film is 150 to 300 μm thick and is composed of three layers: the base, the emulsion, and the supercoat [3]. The base is a thick, translucent layer made up of polyester, which serves as the foundation of the radiographic film, with an intrinsic property to maintain its shape without distortion, referred to as dimensional stability. The emulsion is the most

important part of the film interacting with the x-rays, contributing to the latent image formation. It is a 3- to 5-μm-thick layer composed of silver halide crystals dispersed in a gelatin base. The halide is 90% to 99% silver bromide (AgBr) and 1% to 10% silver iodide (AgI), forming silver iodo-bromide crystal, which is precipitated and emulsified in the crystal lattice. The emulsion is coated on both sides of the base and called double-emulsion film (most common). However, in a few cases such as mammography, the emulsion is coated only on one side to reduce the parallax effects, referred to as a single-emulsion film. The emulsion and base are separated by a thin material, referred to as subbing or adhesive layer, that ensures proper contact and integrity of the emulsion to the base during processing of the film. The emulsion is covered by a thin layer of gelatin called the overcoat or supercoat. The functions of this layer are to protect the sensitive emulsion from scratches, pressure, and contamination and to provide suitable surface characteristics. Radiographic films can be classified into direct exposure and indirect exposure films based on their

use without or with an intensifying screen, respectively. The direct exposure films need higher exposure doses. These are mainly used for dental, extremity, and orbital radiography. The indirect exposure film (most common) is used with an intensifying screen, wherein the emulsion interacts with visible light as described in the next section.

Intensifying Screen An intensifying screen is a device used to amplify the effect of x-rays that reach the screen–film combination. The intensifying screen converts the energy of the x-rays to visible light, which then interacts with the emulsion to form the latent image. The advantages include a 1. reduced radiation dose to the patient, and 2. shorter exposure times that reduce motionrelated artifacts. The disadvantages include 1. higher image noise and blurring, and 2. lower spatial resolution of the resultant image.

In usual practice, the double-emulsion radiographic film is sandwiched between two intensifying screens, so that the emulsion on each side is exposed to the light from its respective screen. This entire system is enclosed in a cassette. The intensifying screen is made up of four layers: the base, reflective layer, protective coating, and the heart of the intensifying screen, which is the radiographically active layer of phosphor. ■ The base is the made up of an approximately 1mm-thick layer of polyester, providing mechanical support to the active phosphor ■ The reflective layer lies between the phosphor and the base, made up of magnesium oxide or titanium dioxide, which demonstrates isotropic emission. Isotropic Emission refers to the property of these compounds to emit light produced by the interaction of x-rays with the phosphor with equal intensity in all directions and in turn increases the efficiency of the screen–film combination ■ The protective coating is the thin outermost transparent plastic layer of the intensifying screen, which is closest to the radiographic film. The most important layer of the intensifying screen is the

phosphor, which converts the x-ray beam to light; this process is called luminescence. Originally, crystalline calcium tungstate (CaWO4) was used as the phosphor layer, which was then replaced by rare earth elements such as gadolinium, lanthanum, and yttrium, which have discrete emissions near the green-yellow region and provide a higher efficiency, faster speed, and lower patient dose Characteristic Curve The characteristic curve is a measure of the optical density with respect to the x-ray exposure to the film. This is credited to Ferdinand Hurter and Charles Driffield and hence is referred to as the H & D curve. The characteristic curve is a graphical representation of the film's response to light and is made by plotting the optical density on the y-axis against the log of exposure given (log-E) on the x-axis. The characteristic curve is used to compare different types of films and screens. Radiographic films have an optical density in the range of 0 to 4. The shape of the curve (Fig. 1.19) is

representative of the film response to a different range of exposures. As the slope of the curve decreases, the ability of the film to measure the contrast between different exposures decreases. At low and high radiation exposures, high variations in the exposure result in only a small change in the optical density. These portions of the curve are referred to as the toe and shoulder, respectively. The toe portion begins at the threshold and continues to the straight-line portion. It includes the base and fog density, usually up to 0.2. The point at which the curve just begins to turn up is called the threshold. It represents the first response of the material to radiation. At the middle part, or the straight line or linear portion, there is a linear relationship between density and log-exposure (log-E) of the curve. Hence, any small changes in exposure lead to large changes in the optical density. Exposure in this area results in the best image contrast. The shoulder refers to the portion beyond the linear curve. With increasing exposure, the rate of density increase gradually declines until the maximum density is reached; beyond this point, exposure variability cannot be recorded. This maximum density is referred to as

Dmax. It depends on the amount of silver halide coating and processing conditions. The latitude is the range of exposure required to have an acceptable image. As a general rule, films with higher latitudes make the exposure less critical. Factors determining quality of intensifying screen The most important properties of the intensifying screen include the screen speed, intensification factor, spatial resolution, and image blur. 1. Screen speed The efficiency of the intensifying screen to convert xrays to visible light is measured by the screen efficiency. The following properties determine the speed of the intensifying screen: a. Phosphor material: The calcium tungstate screens are considered the reference and assigned a value of 100. The rare earth screens having higher efficiency have speeds up to 1200.

b. Thickness of phosphor layer: The higher the thickness, the higher the detective quantum efficiency and the higher the speed. c. Reflective layer: The presence of a reflective layer increases the screen speed. d. Crystal size: The larger individual phosphor crystals produce more light per x-ray interaction and increase the speed. e. Concentration of phosphor crystals: A higher crystal concentration increases the screen speed. 2. Dyes: Light-absorbing dyes are added to films to control (reduce) the speed of light and improve spatial resolution. Intensification factor The intensification factor is defined as the ratio of the exposure required to produce the same density on a film with and without the screen. 3. Image noise

An intensifying screen has many advantages, as described, but one of the major disadvantages is its contribution to the image noise and reduction of image contrast. It is higher in fast screens and highkVp techniques. An important concept contributing to image noise is light crossover wherein light emitted from an intensifying screen exposes not only the adjacent film emulsion but also crosses over to the emulsion on the other side of the base. 4. Spatial resolution Another disadvantage that may be attributed to the intensifying screens is of lower spatial resolution when compared with direct-exposure radiographs. Spatial resolution is represented by the number of line pairs per millimeter (lp/mm) that may be imaged. Operational Problems With Intensifying Screens The intensifying screen has to be handled with utmost care because even the slightest of damage, especially from fingernails, can produce artifacts and degrade the resultant image. Dirty or damaged screens cause white spots on the image. Poor screen contact, which

may be caused by worn-out contact felt, loose or broken hinges, or warped screen, results in areas of cloudy images.

Processing of Film Production of the Latent Image The first step in processing the film is production of latent image by the interaction of image-forming xrays exiting the patient with the intensifying screen– film combination. During exposure of the film, photoelectrons are formed by the interaction of light photons with the bromide ions. The emulsion, as discussed previously, has various defects and impurities that provide it a crystal lattice referred to as point defects or Frankel defects, which attract these photoelectrons. The electron at the point defect then attracts a positively charged silver ion and neutralizes it to form a silver atom. This phenomenon is repeated many times over, and the result is an area of the crystal with several neutral silver atoms on the surface, which constitutes the latent image. For the latent image to be developable, 4 to 10 silver atoms must be collected at a point defect.

Development of the Latent Image The following steps are performed for the development of the latent image. The steps are performed either in an automatic processor, which takes around 90 seconds, or the older manual processing done previously in which each film took around 10 to 15 minutes to be processed. The latent image is converted to a visible image by a reducing alkaline agent, most commonly consisting of phenidone and hydroquinone, wherein the crystals with a latent image in them allow the rest of the silver ions form a dark silver grain speck on the film while they remain crystalline and inactive. The developer contains alkali compounds such as sodium carbonate and sodium hydroxide that act as buffering agents and control the pH of the solution. Potassium bromide and potassium iodide are added as restrainers, which allow only the crystals with the latent image to be processed. If the developing agent is too strong or the developing temperature is too high, it will develop the crystals in which no latent image is present and produces a low level of blackening called fog.

Fixation After development, the film is fixed and hardened in a weakly acid solution, most commonly made of acetic acid, usually referred to as activator, which neutralizes the pH of the emulsion and stops developer action. Sodium or ammonium thiosulfate, referred to as hypo, is used as a fixing agent to remove undeveloped silver halide crystals from the emulsion. An artifact, that results from the use of the fixer is referred to as hyporetention, wherein fixer is retained within the emulsion, which combines with silver to form silver sulfide, which appears as yellowbrown stains. The fixer also contains a hardener, which causes the emulsion to shrink and become more rigid. The chemicals commonly used are potassium alum, aluminum chloride, and chromium alum. Washing and Drying Vigorous washing of the film to remove all the chemicals from the previous step is performed.

Finally, the film is dried to make it acceptable for viewing and reporting. Screen-film Radiographic Artifacts Artifacts are undesirable optical densities or blemishes on a medical image that may cause wrongful interpretation. These may be classified into 1. Exposure-related artifacts Improper screen–film matching or contact results in obscuration of the images. Patient movement can lead to blur (Fig. 1.20), and reusage of casettes lead to double exposure. These are among the most common causes of reexaminations. 2. Processing and handling artifacts

Figure 1.20 Lateral radiograph of lumbar spine shows blurring artifact caused by patient movement. Most of these artifacts are noted because of the defective parts of the processors. Fogging or “pi lines” (Fig. 1.21) can be seen because of stains in the rollers. Inadequate or excessive usage of chemical scan result in chemical fogging referred to as dichroic stain and curtain effect, respectively. Improper temperature or humidity can also lead to improper exposure.

Figure 1.21 Pi lines. These are linear lines in the uniform gap in a radiograph of the hand caused by a stain in the roller.

Digital Radiography Significant developments in computer technology have resulted in conventional screen-film radiography systems being replaced by DR systems, which are now the standard of care all over the world. DR is defined as the technique by which digital detectors are used to capture information produced by the interaction of x-ray photons with an object. The

images are produced in a digital format that can be stored and processed on a computer. There are two types of DR systems classified based on the type of detector used: CR and direct or indirect DR.

Computed Radiography Computed radiography uses photostimulable phosphors (PSPs) to capture a latent image on the imaging plate (IP). When the emission of light is delayed, allowing x-ray energy to be temporarily stored in a phosphor screen to be read-out later, it is called phosphorescence. Image Receptor The image receptor of CR, referred to as PSP, is composed of barium fluoro-halide activated with divalent europium (BaFX: Eu2+ in which the halide X is typically bromine or iodine) embedded in a polymer binder with a protective overcoat (Fig. 1.22). There is a black reflective layer that sends the light in a forward direction, preventing scatter of stimulating and emitted light.

■ Interaction of PSP with x-ray photons results in the excitation of electrons into a metastable state. With the addition of europium, the PSP crystals develop a tiny defect called metastable sites of F centers (derived from German Farbzentren, or color centers). These F centers can trap the electrons for a longer time ■ During reading out of the image, a red laser scans and exposes the IP. The photon energy of the red laser light is absorbed by the trapped electrons, which return to their ground state ■ During this deexcitation, energy is released in the form of blue-green light. The intensity of the bluegreen light is recorded and converted to a pixel value

Figure 1.22 Parts of an Imaging plate in computed radiography. The image receptor is composed of barium fluorohalides activated with divalent europium embedded in a polymer binder with a protective overcoat and a reflective layer that prevents scatter of light. PSP, photostimulable phosphor. (From: SC Bushong, Scatter radiation. In: Radiologic Science for Technologists, eleventh ed, 285, Elsevier, 2017, Canada.) The spatial resolution is determined by the phosphor layer thickness, diameter of the readout laser beam, and the pixel size. In contrast to film-screen radiography, which has a spatial resolution of approximately 10 lp/mm, CR has a lower spatial resolution of 2.5 to 5 lp/mm.

Computed Radiography Reader A CR reader is a compact mechanical, optical, and computer assembly with drive mechanisms that automatically transport the IP through different processes. The time taken for scanning an IP is

approximately 40 to 90 seconds depending on the PSP size, resolution desired, and dual- or single-side readout. The modern CR systems that use line scanning techniques can reduce the image readout time to as low as 20 seconds. Image formation: The sequence of events in producing an image with CR begins with the interaction of x-ray photons with the IP. 1. Latent image formation X-ray photons are absorbed by the phosphor, resulting in the excitation of electrons in a metastable state. The electrons become temporarily trapped at specific sites throughout the layer of phosphor crystals producing the latent image 2. Stimulation with laser The IP is scanned with a finely focused beam of red laser. The diameter of this laser beam is an important determinant of the spatial resolution of the image.

The smaller the diameter, the higher the spatial resolution. 3. Detection of the emitted light Upon stimulation with a laser beam, the electrons return to the ground state with the emission of a shorter wavelength light in the blue region of the visible spectrum. The light photons are directed through a light-channeling guide onto a photocathode layer on the input side of a photomultiplier tube, which amplifies the signal from the light photons. The sampling rate of this emitted light also determines the spatial resolution of the image. The output is an analog signal that is converted digitally into an electrical signal by an analog-to-digital converter (ADC) and used to form an image that is transmitted to a computer system and transferred to a workstation for interpretation. A picture element or pixel is a quantized value and represents the smallest area in the digital image. The CR image consists of multiple rows and columns of pixels representing at different locations. 4. Erasing imaging plate

To reuse an IP, all the residual excited metastable electrons need to be removed. If the residual latent image remains, it will lead to ghosting on subsequent use. This is done by flooding the PSP with very intense white light. Recent developments in computed radiography ■ Dual-sided reading: The CR reader is equipped with two sets of detectors that can detect and capture light from the PSP upon stimulation with a laser beam. This results in a higher signal-to-noise ratio (SNR) in these systems. ■ Solid-state semiconductor laser diodes: These are more durable than the helium–neon gas lasers, resulting in longer shelf lives of the equipment. ■ Line scan reader: These have a laser line source with a shaping lens that refine the beam into a fine line rather than a point fed to a charged-coupled device (CCD) photodetector array, resulting in an increased speed of processing. Advantages of computed radiography 1. Improved contrast resolution: The PSP receptors in CR have an excellent linear optical density

response to the intensity of x-ray, in contrast to the classic sigmoid-shaped curve of the conventional film-screen combination. The CR therefore produces good contrast over a much wider range of exposures. 2. Dose reduction: The wide latitude allows low radiation exposure without a drop in quality. 3. Repeat rate reduction: The wide dynamic range leads to reduced rates of failed x-ray exposure. 4. Compatible with a conventional X-ray imaging system: It can be retrofitted and used in existing xray systems. 5. Use in picture archiving and communications system: This is the biggest advantage of all forms of digital imaging over conventional film-screen radiography. Disadvantages of computed radiography 1. It is a time-consuming technique because of the handling, transporting, and loading of individual IPs in the reader. 2. Loss of latent image happens immediately and decays with time, making it a time-bound technique.

3. It has a lower spatial resolution than film-screen radiography. 4. Separate read-out electronics contribute to noise.

Digital Radiography Digital radiography is the technique of converting xray into electrical charges using combined image capture and image readout process followed by analog-to-digital conversion to produce a final digital radiograph. Unlike CR, there is no handling and processing of a cassette because the image is produced directly from the image detector and displayed on screen in a matter of seconds. This may be done by direct or indirect means. 1. Indirect DR Indirect conversion is a two-step process for x-ray detection using scintillators that convert x-ray energy to visible light. The visible light is then converted into an electric charge using photodetectors. Thalliumdoped cesium iodide (CsI) is the most commonly used phosphor material as the scintillator. Another material that some systems use is gadolinium

oxysulfide or Gadox (Gd2O2S), which has an amorphous structure that results in the spread of light produced by x-ray absorption, leading to a poorer spatial resolution Indirect digital radiography X-ray → Scintillator → Stored electrons → Light photons → Photodiode → Charge → ADC 2. Direct DR Direct-conversion is a single-step process, wherein photoconductors directly convert x-ray photons into an electric charge (Fig. 1.23). Direct digital radiography X-ray → Photoconductor → Charge → ADC

Figure 1.23 The image acquisition process of a direct capture digital radiography system. TFT, thin-film transistor. (From: C Carter, Introduction to Digital Radiography and PACS, first ed, Mosby Elsevier, 2007, Canada.) The photoconductor materials used commonly include amorphous selenium (a-Se) and lead iodide. A-Se is most commonly used because of its excellent x-ray detection and high intrinsic spatial resolution. Because selenium has a relatively low atomic number, which results in less x-ray absorption in the general radiography kV range, the K-edge of selenium is

better suited for the diagnostic kV range used in mammography. The readout can be done by two systems: a selenium drum or a thin film transistor array. The readout is by gating each row of thin-film transistor (TFT) switches, corresponding to 1 pixel, similar to indirect DR. The resulting electrical signal is then digitized and transferred to the system computer. Postprocessing Following the readout of the image in direct and indirect DR, the image data will be processed before display, and this forms the most influential final step that reflects the way a radiologist sees the end product. Postprocessing, in general, improves the image quality by optimizing contrast, reducing image noise and technical artifacts. The factor that cannot be adjusted by postprocessing is spatial resolution. ■ A technique called low-pass spatial filtering is performed, by which a weighted average of grayscale value is stored in each pixel and the value of the neighboring pixels is generated to

remove image noise. The effect smoothens the final image; however, it blurs small details or edges ■ Another filter called high-pass edge enhancement does the opposite by adding a proportion of the difference in grayscale values between neighboring pixels to heighten the contrast resolution Recent Developments in Digital Radiography ■ Mobile DR: A portable DR system, allowing imaging of critical patients, is performed most commonly with a mobile 17- × 14-inch flat-panel detector (FPD) ■ Wireless DR systems: A wireless portable DR system can transfer image data wirelessly to the monitor. This has the advantage that the cables do not interfere with surrounding machines, allowing radiography of difficult regions of the body such as trauma settings or limbs with limited mobility, axilla, the temporomandibular joint, etc. ■ Image stitching: Automatic image reconstruction is possible after multiple sequential exposures, which is especially useful for wholespine imaging and scannogram

■ Dual-energy imaging: Separate generation of bones and soft tissue structures from two exposures with different kilo voltage techniques. Finds application in better characterization of pulmonary nodules, calcified pleural plaques, coronary artery calcification, etc. ■ Tomosynthesis: Multiple low-dose exposures at various angles are taken during an arc motion of the x-ray tube with a stationary detector. Using pixel shift, many projections are created after adding these low-dose images. It is now used predominantly for mammography. It is also used for better delineation of bronchiectasis in cases of cystic fibrosis ■ Computer-aided diagnosis: This is a useful tool that marks suspicious areas for review by the radiologist, preventing overlooking significant findings Image Quality Determinants of Digital Radiography The major determinants of the image quality are as follows:

1. Spatial resolution Spatial resolution in DR determined by the focal spot size and pixel size. Spatial resolution is inversely proportional to the pixel size. The pixel is expressed in length and width. It is represented as line pairs per millimeters. 2. Contrast resolution Contrast resolution is the measure of grayscale differentiation in an image measured dynamic range. Dynamic range, or the bit depth, is the number of possible grey shades an image can reproduce. Digital imaging systems have much better contrast resolution than conventional screen-film radiography. In digital detectors, a wide and linear dynamic range is seen, with four to five orders of magnitude. The other major advantage of digital imaging is the ability of postprocessing that allows us to exploit the complete dynamic range by windowing. 3. Modulation transfer function Modulation transfer function (MTF) measures the ability of a system to modulate input signal. It takes

into account both the spatial and contrast resolution. The ideal imaging system with an MTF of 1 would produce an image that appears exactly like the object. 4. Detective quantum efficiency (DQE) Detective quantum efficiency (DQE) is a measure of the efficiency of x-ray absorption and represents the probability that an x-ray will interact with the image receptor. It is calculated by measuring the SNR at the detector output. It is primarily determined by the absorption coefficient of the compound in the image receptor. The DQE of DR is higher than the filmscreen radiography, which contributes to a lower patient dose in the former (Fig. 1.24).

Figure 1.24 Detective quantum efficiency as a function of x-ray energy for various image receptors in computed radiography (CR) and digital radiography (DR). (From: SC Bushong, Scatter radiation. In: Radiologic Science for Technologists, eleventh ed, 319, Elsevier, 2017, Canada.) Digital Radiography Artifacts These may be classified into the following: 1. Patient-related factors. Patient motion and improper positioning leading to artifacts are common to screen-film and DR. Because the IP is very sensitive to scatter radiation, primary beam collimation is of utmost important. If the image collimation is not parallel to the IP, it hampers the image quality. 2. Image receptor–related factors. These are usually encountered in CR wherein incomplete erasure of the IPs results in overwriting

and ghost artifacts (Fig. 1.25). Cracks resulting from aging of the IP also produce superimposed focal artifactual opacities. 3. Software-related factors. Artifacts associated with image transmission errors can be caused by either communication errors or data cable malfunctioning, which will result in corrupted or incomplete images.

Figure 1.25 Ghost artifact. Incomplete erasure of the image from the previous exposure (arrow) in a chest radiograph leads to a double image. The pelvic bones from a prior exposure can be seen superimposed on the heart and upper abdomen.

Fluoroscopy Technique of Fluoroscopy Whereas general radiography provides single, discrete images, fluoroscopy provides real-time dynamic viewing of anatomic structures. Thus, fluoroscopy is used for examination of moving internal structures and fluids. Fluoroscopy is used for various diagnostic and interventional procedures. I. General fluoroscopy room A. Any barium study such as barium swallow and upper gastrointestinal (GI) series. B. Iodinated studies such as hysterosalpingography and urology procedures such as micturating cystourethrography.

II. Interventional radiology. III. Operating room (OR): during procedures for alignment of bones, surgical fixation, etc. Types of equipment [4] I. Radiography/fluoroscopy (R/F) units with undertable x-ray tubes: The x-ray tube and collimator are mounted below the table. The image intensifier tower is mounted above the table on a carriage that can be panned over the patient. II. R/F units with over-table x-ray tube: Radiography can be performed with the same x-ray tube and Bucky. III. Fixed C-arm positioners: These are ceiling- or floor-mounted models. There is a floating tabletop that allows for easy patient movement. IV. Biplane system (two C-arm units): One is floor mounted, and the other is ceiling mounted. One of the two or both can be used during the examination. It carries the advantage of the ability to see two projections without delay because of Carm movement. It is used in dedicated cardiac, neuroangiography, and interventional radiology suites.

V. Mobile C-arm positioners: These are useful during orthopedic and vascular surgical procedures in the OR.

Fluoroscopic Imaging Chain [4] A typical fluoroscopic imaging chain consists of a generator, x-ray tube, collimator, filter, grid, image intensifier, and video camera system. In modern fluoroscopy systems, FPDs are replacing the image intensifier. Fluoroscopy can be performed in a continuous manner or can be pulsed. The advantages of pulsed fluoroscopy are improved temporal resolution (which reduces motion blur) and reduced radiation dose. The disadvantages of pulsed fluoroscopy include an increase in noise perception, flicker effect, and reduced visibility of fine catheters and guidewires. Fluoroscopic Detector Systems Fluoroscope was invented by Thomas Edison in 1898 [5]. In the original fluoroscope, a fluorescent screen was placed in the x-ray beam directly above the

patient. The radiologist had to stare directly into the screen, and a dark room was required because the image was dim. The image intensifier was developed in the 1950s and eliminated the need for a dark room and allowed cone vision to be used for image visualization. Fluoroscopic images are now viewed on a television or flat-panel monitor. Image Intensifier–based Fluoroscopy Systems (Fig. 1.26)

Figure 1.26 Image intensifier. (From: Bushberg, The Essential Physics of Medical Imaging.) The main function of an image intensifier is to amplify and convert incident x-rays into visible light. The important components include an input phosphor, photocathode, electrostatic focusing lenses, accelerating anodes, and output phosphor. ■ The input phosphor is made up of cesium iodide and emits part of absorbed x-ray photons as a large number of light photons. Because the K-shell binding energies of Cs and I are approximately 35 keV, it efficiently absorbs x-rays ■ The photocathode absorbs these light photons and converts them into photoelectrons ■ The electrostatic lens focuses these photoelectrons to the output phosphor. At the same time, these photoelectrons are accelerated by an accelerating voltage of approximately 30 keV ■ These energetic electrons are absorbed by the output phosphor, which converts them into large numbers of light photons. The output phosphor is made up of silver-activated ZnCdS (zinc– cadmium–sulphide)

■ The output phosphor is coupled to the camera or CCD ■ The light image on the output of image intensifier is several thousand times brighter than that of input phosphor. This increase in brightness at the output phosphor relative to input phosphor is called brightness gain.

in which minification gain is the ratio of the area of output phosphor to input phosphor, which is equal to the square of ratio of diameters. Flux gain is the number of photons generated by the output phosphor for every photon generated by the input phosphor. Instead of brightness gain, modern systems use a “conversion factor” for expressing the intensification by an image intensifier:

Limitations of image intensifiers

1. Lag is transient persistence of previously acquired image caused by continued luminescence at the output phosphor even after the x-ray stimulation is stopped. 2. Geometric distortion occurs because of projection of a curved input phosphor to a flat output phosphor. The input phosphor is curved to allow focusing of electrons and to minimize stress from the vacuum. 3. Pin-cushion distortion is magnification and stretching at the periphery of an image. 4. S-distortion is caused by local magnetic fields. 5. Vignetting is fall-off of brightness at the periphery. 6. Veiling glare is caused by light scattered within the output phosphor, which decreases the contrast. Digital Fluoroscopy System To overcome the limitations of conventional fluoroscopy, digital fluoroscopy was developed. Flat-panel detectors

One major advance in modern fluoroscopy units is the introduction of FPD arrays, similar to DR. FPD replaces the image intensifier, lens, and camera system. It directly records the real-time fluoroscopic image sequence. Unlike CCD cameras, FPD systems do not need a video system. FPD directly or indirectly converts incident x-ray photons into electronic signals, which are displayed on the monitor. ■ FPD consists of TFT arrays of individual detector elements (dexels or DEL) arranged in a square or rectangle ■ Each detector element has a capacitor and a transistor ■ The capacitor accumulates and stores the signal as electrical charge, and the transistor functions as a switch ■ Indirect x-ray conversion modes are used more commonly than direct ones in fluoroscopy. In indirect TFT, x-rays are first converted to light by phosphor, and then this light is converted into charge by photodiode ■ The charge stored in capacitor is dependent on the incident x-ray flux on the detector element

■ Reading the array discharges the capacitor and makes them ready for next frame acquisition Advantages of FPDs are the smaller equipment size, thereby increasing flexibility; better dynamic range; improved coverage of corners because of a square or rectangular field (circular field in II); better stability; lower radiation dose rates because of improved DQE; and lack of glare and geometric distortions. Disadvantages include the higher cost and lower spatial resolution with a very small or very large field of view. The only similarity between an image intensifier and FPD is the use of a scintillator. In FPD, pixel binning (combining of adjacent pixels) can be used to reduce noise. Binning also helps in allowing fast frame rate imaging. The image distortion artifacts seen with image intensifiers are not seen with FPD. Postprocessing techniques [6] 1. Last image hold: This permits visualization of the last image even when the x-ray beam is

switched off. This image helps in guidance without additional radiation to the patient or medical staff. 2. Grayscale processing adjusts brightness and contrast depending on the region of interest. 3. Temporal frame averaging: Two or more successive images are averaged to form a single image with noise reduction. 4. Measurement of distance is possible because of digital image and calibration. Recording fluoroscopic images Various methods of image recording can be used during fluoroscopy: direct film recording, indirect recording, and recording motion.

Digital Subtraction Angiography Image subtraction technique is used in digital subtraction angiography (DSA) to remove the effects of stationary anatomic structures (especially bones) from the images of contrast-enhanced blood vessels. Thus, precontrast mask image is subtracted from the postcontrast image to reveal only the contrastenhanced vessel (Fig. 1.27). The various subtraction

techniques include temporal subtraction, energy subtraction, and hybrid subtraction. ■ Temporal subtraction can be done using the mask mode or time-interval difference (TID) mode. Mask mode results in successive subtraction images of contrast-filled vessels. TID mode produces subtracted images from progressive masks and following frames ■ Energy subtraction is based on the abrupt change in photoelectric absorption at the K-edge of contrast media compared with that for soft tissue and bone ■ Hybrid subtraction is a combination of temporal and energy subtraction

Figure 1.27 Digital subtraction angiography. (A) Postcontrast image of a venolymphatic malformation around the knee. (B) Subtracted image. The precontrast image (not provided) is subtracted from the postcontrast image to reveal only the contrast enhanced vessels. (Courtesy: Dr. Sagar Tyagi.) A special technique used in DSA that helps in placement of catheters and guidewires is the roadmap (Fig. 1.28). Here, the mask image used is a subtracted fluoroscopic image with maximum contrast opacification of vessel. The subsequent fluoroscopic

images are subtracted from this mask image, highlighting the vessel of interest [3]. Other techniques that can be used for DSA include fluoroscopy fade, stepping technique, and threedimensional (3D) rotational angiography.

Figure 1.28 Roadmap technique for uterine artery digital subtraction angiography (DSA), which helps in catheter and guidewire placement. (A) DSA is performed. (B) Subtracted fluoroscopic image with maximum contrast opacification of vessel is selected as the mask image. (C) The subsequent fluoroscopic image is subtracted from the roadmap mask. This gives live fluoroscopic images of the inserted catheter or wire overlaid on a static image of the vasculature with subtraction of

distracting underlying tissue. (Courtesy: Dr. Sagar Tyagi.) A new combined angiography/computed tomography (CT) suite has been developed that uses FPD technology and allows obtaining 3D rotational DSA or cone-beam volume CT interchangeably with the same FPD C-arm motion without patient transfer. This is especially useful in immediate detection or exclusion of intracranial complication that might have occurred during neurovascular procedures without patient transfer to the CT scanner [7]. Digital subtraction angiography is susceptible to patient motion, which can be corrected by computer manipulation of digitally stored images. This can be done by spatial displacement of mask image (mask pixel shift technique), which allows re-registration or by remasking (selecting recent image as new mask image). Other postprocessing techniques include image summation and landmarking. Summation helps in adding up frames to allow visualization of vessel as a complete structure. Landmarking allows anatomic landmarks to be added to subtraction image by adding

a lesser intensity area of original image to the subtracted image.

Suggested Readings • SC Bushong, Radiologic Science for Technologists: Physics, Biology, and Protection, 2018. • S BA, The AAPM/RSNA physics tutorial for residents: general overview of fluoroscopic imaging. Radiographics 20 (4) (2000): 1115–1126. [Internet] [cited 2021 Aug 13]. Available from: https://pubmed.ncbi.nlm.nih.gov/10903700/. • SC Bushong, Radiologic Science for Technologists: Physics, Biology, and Protection, 2017.

References [1] OWC Glasser, Roentgen and the discovery of the Roentgen rays. AJR Am J Roentgenol [Internet]. 1995 [cited 2021 Jul 30];165(5):1033–40. Available from: https://pubmed.ncbi.nlm.nih.gov/7572472/

[2] Radiographic Imaging and Exposure, Elsevier Health [Internet]. [cited 2021 Aug 13]. Available from: https://www.uk.elsevierhealth.com/radiographicimaging-and-exposure-9780323661393.html? gclid=CjwKCAjwsNiIBhBdEiwAJK4khg8jW431vQ BX4rtoGd_4SfES5WnQEdbhBUL2x2Y7ux1nKNAIi eSrEhoC8MsQAvD_BwE&gclsrc=aw.ds [3] SC BushongRadiologic Science for Technologists, Binder Ready: Physics, Biology, and Protection. Evolve Elsevier, Canada, 2018. [4] BA S. The AAPM/RSNA physics tutorial for residents: general overview of fluoroscopic imaging. Radiographics [Internet]. 2000 [cited 2021 Aug 13];20(4):1115–26. Available from: https://pubmed.ncbi.nlm.nih.gov/10903700/ [5] SC BushongRadiologic Science for Technologists: Physics, Biology, and Protection, Evolve Elsevier, Canada, 2017. [6] R Pizzutiello, Review of Radiologic Physics. 4th Edition. Walter Huda, Author. Philadelphia: Lippincott Williams & Wilkins, 2016. Softcover:

336pp. Price: $74.99. ISBN 9781496325082. Medical Physics [Internet]. 46 (5) (2019) 2539. Available fromhttps://aapm.onlinelibrary.wiley.com/doi/full/10. 1002/mp.13473. [7] Heran NS, Song JK, Namba K, Smith W, Niimi Y, Berenstein A. The utility of dynaCT in neuroendovascular procedures. AJR Am J Roentgenol [Internet]. 2006 Feb [cited 2021 Aug 13];27(2):330. Available from: https://pmc/articles/PMC8148775/

2

Ultrasound Physics Nikita Nanwani, Vaibhav Nichat

Introduction Ultrasound is sound waves with frequency greater than the human audible range (20–20k Hz). Ultrasound devices in medical fields use sound waves in the range of 1 to 20 MHz. Ultrasound imaging and Doppler ultrasound detect sound waves reflected from the body and display it in the form of images. The various modes of image display in ultrasonography (USG) are A- mode, B-mode (most commonly used), M-mode, and Doppler mode. A (amplitude) mode is 1D representation of structures and is used in ophthalmology to measure the axial length of the eyeball. B (brightness) mode displays twodimensional (2D) images in which echo amplitude is depicted as dots of different brightness. The routine grayscale ultrasound examination is a B-mode USG. M (motion) mode shows movement as a function of time and is used in cardiac imaging. Doppler mode is used to measure blood flow and velocity.

Principle of Ultrasound Ultrasound works on the pulse echo principle (Fig. 2.1), which is facilitated by piezoelectric material in ultrasound probe

crystal. When a piezoelectric crystal is electrically pulsed, it changes shape and vibrates, producing a sound beam that propagates through tissues. The reflected echoes reach the transducer causing its vibrations which produces electrical voltage comparable to returning echo.

Figure 2.1 The pulse-echo principle. Piezoelectric crystal in the transducer converts electric voltage to ultrasound pulse (A) and converts received echoes (B) into electric voltage pulses.

Properties of Sound Unlike x-rays, sound is mechanical energy, requires a medium for travel, has tissue-dependent velocity, and does not cause

ionization. Sound travels as a longitudinal wave with peaks and troughs (Fig. 2.2).

Figure 2.2 Anatomy of sound wave with areas of compression (peaks) and rarefaction (trough). Wavelength (λ) = Distance between corresponding points on the time– pressure curve. Period (T) = Time (T) to complete a single cycle. Frequency ( f ) = Number of complete cycles in a unit of time = 1/T. The propagation velocity depends on tissue and is constant for a particular tissue (Table 2.1). It is inversely proportional to the compressibility and density of tissue and directly proportional to the stiffness of tissue. Thus, the velocity of sound is less in air (330 m/sec), which has high compressibility; in soft tissue, it is 1540 m/sec. Thus, to get the best images of soft tissues, USG machines are calibrated to this speed (1540 m/sec). Table 2.1

Ultrasound Velocities of Interest in Ultrasound Imaging [1] Speed of Sound Material (m/sec) Air 330 Fat

1450

Water

1480

Soft tissue (average)

1540

Bone

4080

Piezoelectric crystal

4000

Acoustic Impedance The resistance offered by tissues to the movement of particles caused by ultrasound waves is called the acoustic impedance (Z). Z = ρc, in which ρ is the density of tissue and c is the speed of the ultrasound wave in the tissue.

◾ Unit: Rayl, which is kg/(m s) 2

Thus, acoustic impedance is directly proportional to the density, rigidity of tissue, and speed of sound in a material. (Analogy: A high jumper landing on a foam mattress [soft and light] will find

that it yields to his body much more readily than concrete [solid and heavy].) Acoustic impedance mismatch is the difference in acoustic impedance at interface of two tissues and determines the amount of energy reflected at the interface, which in turn is detected and displayed as images in ultrasound imaging. If the mismatch is high (e.g., air–bone interface), almost 100% sound is reflected back with almost no transmission. If mismatch is low (e.g., fat–muscle interface), there is better sound transmission with decreased reflection. Piezoelectric crystals at the transducer head have very high acoustic impedances compared with skin. Therefore, the matching layer is used in front of the piezoelectric crystal to reduce this difference and allow for better sound transmission into the body (discussed later under transducers). Interaction With Tissue There are four mechanisms by which sound can interact with tissues: absorption, reflection, refraction, and scatter. Absorption Major mechanism. The higher the frequency, the greater the absorption. Reflection The higher the acoustic impedance mismatch, the greater the reflection. Thus, to decrease the acoustic impedance mismatch and thereby allow better sound transmission between the

transducer and the skin, ultrasound gel is used. Gel also decreases the amount of trapped air between the transducer and the skin. The other practical application is when examining the pelvis, the urinary bladder should be as full as possible to lift the intestine out of the way. Ultrasound reflection also depends on the size and surface features of the interface. Reflecting surfaces can be specular or diffuse (Fig. 2.3).

◾ A specular reflector is large and smooth like a mirror and forms an image only when the incident sound is perpendicular to the surface because with an oblique incident sound, the reflected sound is reflected away from the transducer, and no image is formed. Examples of specular reflector are the diaphragm, fetal skull, and vessel wall (see Fig. 2.3A) A diffuse reflector is more frequently encountered and is made up of small interfaces, each being much smaller than the incident sound wavelength. Echo is scattered in all directions with only a portion of reflected waves reaching the transducer and forming an image. The characteristic echo pattern of solid organs and tissues such as the liver (see Fig. 2.3B) is attributable to diffuse reflection

◾

Figure 2.3 (A) The diaphragm as a specular reflector. (B) The liver parenchyma as a diffuse reflector. Refraction Change in velocity and angle as beam crosses an interface. Scatter Small surfaces scatter sound in many directions because of reflection and refraction. Examples are the liver and kidney parenchyma. Based on the amount of scatter compared with background signal, a tissue or lesion is categorized as hyperechoic, hypoechoic, or anechoic when the amount of scatter is more, less, or no scatter at all, respectively. The result of all interactions is sound attenuation, that is, the decrease in the intensity of the ultrasound waves as they pass through tissues, similar to sound that becomes fainter when one moves further away from it. Attenuation is measured in decibels per centimeter. Attenuation is directly related to the sound

frequency. Thus, for deeper tissues, lower frequency transducers (3.5 MHz) should be used to allow adequate penetration without attenuation, but for superficial organ scanning in adults or for children, 5 MHz or greater is best.

Pulse Echo Instrumentation Components of an ultrasound system: 1. Transducer (described later): forms the ultrasound pulse. 2. Transmitter or pulsar: energizes the transducer. 3. Receiver or signal processor: performs functions of preamplification, amplification, compensation, compression, demodulation, and rejection. 4. Transmit and receive switch: ensures the electrical signals travel in the correct direction. 5. Scan converter: part of the machine that makes grayscale imaging possible and is responsible for storage of the image data. The older systems were based on analog, but the current systems are digital. 6. Display. 7. Master synchronizer: part of the machine responsible for controlling the timing of the echoes. It ensures that a new pulse is not sent out until the previous pulse has returned. Transducer Most clinical applications use pulsed ultrasound, in which brief bursts of acoustic energy are transmitted into the body. The source of these pulses is the ultrasound transducer. A transducer

is any device that converts one form of energy to another. In USG, the transducer with piezoelectric crystals converts electrical energy to mechanical (sound) energy and vice versa. It acts as both a transmitter and receiver of sound. The returning echoes are represented as points of brightness in B-mode imaging. Key Terms Related to Transducers Bandwidth: The range of frequencies produced by a given transducer is termed its bandwidth. Bandwidth determines the purity of frequency emitted and pulse length. A narrow-bandwidth transducer emits relatively pure frequency sound and longer pulse length. However, the resolution is less. Quality factor:

Quality factor describes the amount of ringing the crystals undergo when power is applied to the transducer. (Analogy: When a church bell is struck, it vibrates rapidly, and then the vibration gradually stops.) Thus, decreasing quality factor decreases ringing in the transducer and improves its performance. When the bandwidth is wide, the Q factor is low as in pulse-wave transducers. When the bandwidth is narrow, the Q factor is high as in continuous-wave transducers and therapeutic USG. Frequency of transducers:

The resonant frequency of the transducer is determined by its thickness (inversely related). Generally, thickness (t) of crystal is equal to one-half of the wavelength (λ) (i.e., t = λ/2). Transducer frequency can vary from 2.0 MHz to 50.0 MHz and its selection is primarily based upon the patient’s body habitus and the region to be scanned. Pulse repetition frequency:

Each pulse of a transmitter contains a transmit and a receive phase. The ultrasound pulses must be spaced with enough time between the pulses to permit the sound to travel to the depth of interest and return before the next pulse is sent. Pulse repetition frequency (PRF) is the number of pulses of ultrasound sent out by the transducer per second. It depends on the velocity of sound and depth of tissue being imaged. The deeper the tissue, the lower the PRF because the echo takes a longer time to travel. Construction of an Ultrasound Transducer or Probe (Fig. 2.4)

Figure 2.4 Ultrasound transducer–probe construction. 1. Crystal or piezoelectric material A transducer or probe can have a single element in the form of disc or multiple elements, called as transducer array. The number, size, shape, and arrangement of transducer elements vary according to the transducer type and application. Whereas older systems used natural piezoelectric material quartz, most used material nowadays is artificial lead (Pb) zirconate titanate (PZT). PZT is created by heating it to Curie point, which is the temperature at which an ultrasound transducer gains its piezoelectric properties. While being heated, the PZT is placed into a magnetic field, which causes dipoles in the PZT to align themselves

in relation to the magnetic field. Finally, the material is cooled, and it gains its piezoelectric effect. If the transducer is heated again above Curie point, it loses its piezoelectricity. Therefore, ultrasound transducers must never be heat sterilized. Emerging technology for transducer material includes silicon-based capacitive micro-machined ultrasound transducers, polyvinylidene fluoride, and single-crystal technology [2]. 2. Electrodes Electrodes enable electrical connection. Positive electrode is at the back of the element, and ground electrode is on the front. 3. Damping or backing block The damping or backing block is adhered to the back of the crystal behind the positive electrode and stops vibrations reverberating back into the piezoelectric material. Thus, it determines the length of the ultrasound pulse by determining how much it is dampened via the Qvalue. (Analogy: If a bell is grabbed while it is ringing, it decreases the ringing time of the bell.) Color wave transducers do not have backing material and subsequent narrow-bandwidth, high Q-factors. Pulsed-wave transducers have typically low Q-factors because they need damping to make the pulse short. 4. Matching layer The matching layer is the part that comes in contact with the patient’s skin and is placed in front of piezoelectric crystal. It consists of a material with acoustic impedance between the soft tissue and the transducer material. Thus,

it allows close to 100% transmission of the ultrasound from the element into the tissues by decreasing the impedance mismatch. The matching layer thickness is one-fourth the wavelength of sound in that material and is referred to as quarter-wave matching [2]. 5. Housing Housing is the electrical insulation and protection of element, consisting of a plastic case, metal shield, and acoustic insulator. 6. Lens The lens helps in focusing the beam and is usually incorporated after the matching layer. In array transducers, it is usual for one large lens to extend across all the transducer elements. Modern transducers use electronic focusing. 7. Wire Wire is used to transfer electrical signals to and from the transducer. Modern scan heads often contain more than 100 individual transducer elements, each of which is supplied with electrical energy via a wire. Beam Formation and Focusing In the case of pulsed ultrasound, the term beam means the width of the pulse as it travels away from the transducer. According to Huygen’s principle, the beam starts out as small wavelets at the face of the transducer. The interference of the wavelets produces a propagation sound beam. The direction in which the beam travels is perpendicular to the wavefront.

An ultrasound beam consists of near and far zones (Fig. 2.5). The near or Fresnel zone is the region between the transducer and the minimum beam width. This is the most useful part of the beam. The far or Fraunhofer zone is the region beyond the minimum beam width. The focal length or focal distance is the distance between the transducer surface and end of near zone length (i.e., where the beam is narrowest).

Figure 2.5 Ultrasound beam profile with near and far zones. Near zone length (NZL) = d2/4λ, in which d = diameter of transducer and λ = wavelength. Thus, to get as long a near-zone length as possible, we would have to make the transducer wider. However, the resolution will be reduced, and the width of the whole transducer array will be much larger. To overcome this, a stepped linear array is used (discussed later). Beam focusing improves resolution by decreasing the minimum beam width compared with that produced without focusing. However, well beyond the focal region, the width of the focused beam is greater than that of the unfocused beam. Focusing decreases the near-zone length as it moves the end of near zone toward the transducer. Various methods to achieve beam

focusing are by using the lens; using curved transducer elements rather than flat elements; and electronic focusing, which is achieved by using a curved pattern of phased delays. Types of Transducers (Fig. 2.6)

Figure 2.6 Types of transducers. Ultrasound transducers typically consist of 128 to 512 [3] piezoelectric elements arranged in linear or curvilinear arrays. Each element is individually insulated. Mechanical Transducers:

The beam is steered mechanically by spinning or rotating element or array housed in an acoustic coupling liquid. It could be single element transducer with fixed focus that were used in early ultrasound scanners, or it could consist of annular arrays of

elements with electronically controlled focus which are used in 3D USG. Electronic Transducers:

Electronic transducers have multiple active elements that form an array. An array is formed by slicing down a single slab of PZT into multiple subelements. Each subelement has its own wire and can fire independently. Thus, the elements can be excited selectively as needed to shape and steer the beam. There are two broad types of arrays, sequenced and phased (discussed later). Key Concepts in Understanding Working Mechanism of Different Types of Electronic Transducers Beam Formation by Sequencing in a Linear Array (Fig. 2.7):

In a linear array, elements are placed next to each other and activated as a group. The initial elements are then inactivated, and the next group of elements is activated. This moves the beam along. Thus, wide beams can be produced in a smaller space than can be produced with wide transducers activated individually. Longer near-field distance can be achieved.

Figure 2.7 Linear sequenced array. A voltage pulse is applied simultaneously to all elements in a small group, first to elements 1 to 4 (for example) as a group (A), then to elements 2 to 5 (B), etc. across the transducer assembly (C–E). The process is then repeated (F). Beam Focusing by Phasing in a Linear Sequenced Array:

The transmitted beam can be focused to a specific point by phasing (i.e., activating outermost transducers first, then the inner two, then the innermost, etc.). Similarly, during reception of echoes, dynamic focusing can be done (i.e., preferentially receiving echoes from a particular depth). This is what happens when the focus is set on the ultrasound machine. Beam Steering by Phasing in a Phased Array (Fig. 2.8):

Phasing implies changing the timing of excitation of elements to shape and steer the beam. In contrast to linear and curved arrays,

all the elements work together in a phased array (see Fig. 2.8).

Figure 2.8 (A) Phased transducer. (B) Beam formation without phase delay. (C) Beam steering by phasing. Compared with a nonphased array, a phased array has smaller transducer footprint, requires a small acoustic window, and can do precise beam focusing and steering. Thus, the major advantage is that very broad image field can be visualized at larger depths that too with a narrow transducer footprint. Phased-array transducers are widely used in cardiac scanning because these transducers fit easily between the ribs. An endovaginal transducer is also a phased-array transducer. Hybrid Beam-Stepping and Beam-Steering Transducers These are linear arrays in which both beam stepping and beam steering are used. Trapezoidal or Virtual Curvilinear Scanning (Fig. 2.9A):

This is a linear array with the image format of a curvilinear array but with a flat top (hence, virtual curvilinear). Being a linear array, it overcomes the high pressure required for a

convex array to maintain contact. The image shape is trapezoidal. This is achieved by steering the scan lines situated toward the ends of the transducer progressively outward. Thus, the image is widened in the far zone similar to a curvilinear array, giving the advantage of a large field of view.

Figure 2.9 Hybrid transducers. (A) Trapezoidal transducer. (B) Steered linear array transducer. (C) Compound scanning. Steered Linear-Array Transducers (Fig. 2.9B):

This is a linear array with the ability to steer all transmit and receive beams to the right or left. Thus, the image is parallelogram shaped (Fig. 2.9B). It is useful in Doppler imaging and to view vessels in difficult areas, such as under the angle of the jaw. Compound Scanning (Fig. 2.9C):

Compound scanning superimposes several angled views in a single “compound” scan. The gray level of each pixel is the average of the values for that pixel in the several superimposed views. It is an extension of the steered linear array technique. It can be done using both linear and curvilinear arrays.

Table 2.2 summarizes the properties of commonly used transducers. Table 2.2 Summary of Properties and Functioning of Commonly Used Transducers Vector or Convex Trapezoida Linear Phased Property Transduce l Transducer Transducer r Transduce r Array (Phased) (Phased) (Linear) (Phased terminolo linear convex phased and gy: words (sequenced (sequenc array sequence in ) array ed) array d) (linear) parenthes vector es are array implied in abbreviate d common terminolo gy Category

Beamstepping array

Beamstepping array

Beamsteering array

Hybrid beamstepping and beamsteering array

Vector or Convex Trapezoida Linear Phased Property Transduce l Transducer Transducer r Transduce r Shape of Rectangle Sector; Sector; Sector; the image or curved pointed flat top parallelogr top top am (when (because steered), the flat top elements are arranged in an arc) Beam scanned by

Sequencin g: sequential scans of a subset of transducer elements

Sequenci ng

Phasing: scans of entire set of transducer elements by applying sequential electronic delays

Sequenci ng and phasing

Beam focused by

Phasing

Phasing

Phasing

Phasing

Property

Use

Vector or Convex Trapezoida Linear Phased Transduce l Transducer Transducer r Transduce r Vascular Abdomin Cardiac, Abdomin and highal and neonatal al, resolution gynecolo brain, cardiac, imaging gy and endocavit Doppler obstetrics ary imaging transducer s

Three- and Four-Dimensional Transducers These are used to create 3D image and volume scanning. Three ways to generate a 3D image are a freehand technique, an automated 3D technique using a mechanical transducer, and electronic using a 2D array or matrix array technology.

◾ In the freehand or manual technique, the operator moves the transducer steadily across the path to gather 2D slices. The 2D slices, after being converted to 3D format, may then be sliced to view coronal, sagittal, and axial planes. The limitation of this technique is the need for steady transducer movement, so it is highly operator dependent The mechanical or automated 3D technique uses a mechanical transducer. It uses sequenced array transducers mounted onto a motor that sweeps the image plane from side

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to side. It permits measurement on the screen of the 3D image as well as real-time 3D or four-dimensional (4D) imaging, the frame rate of which is governed by the speed of the motor The newest technique is electronic using latest 2D array or matrix array technology [2]. It acquires real-time volumes using transducers containing as many as up to 10,000 elements compared with 12 to 512 elements in standard transducers [2]. The arrays could be linear or annular arrays. Whereas linear arrays allow electronic beam steering by phasing, annular arrays have to be steered mechanically. The advantages are linear arrays enable precise focusing because of use of multiple elements, and the beam can be focused in both the elevation plane and lateral plane

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Ultrasound Gel and Acoustic Coupling Agents [4,5] Gel is needed to remove pockets of air between probe and the patient’s skin, which would otherwise prevent sound transmission into patient’s body. Thus, ultrasound gel acts as a medium to transmit sound and as a lubricant. Liquids such as water and alcohols are suitable media; however, being volatile and having low viscosity, they are inappropriate. That is why specific gels have been developed. Hydrogel is preferred over Lipogel because it can be easily removed by tissue or a towel. Ingredients of ultrasound gel include distilled water, carbomer, ethylenediaminetetraacetic acid (EDTA), propylene glycol, glycerin, and trolamine. Occasionally, colorant is used, usually a blue color.

In case of a patient having an open wound, a skin rash, or any other risk of infection, the transducer or patient’s skin should be covered with plastic, and gel should be used on both sides of the plastic. The transducer must be cleaned after every patient.

Image Quality The quality of an ultrasound image is determined by spatial resolution, contrast resolution, temporal resolution, and absence of certain artifacts. Spatial Resolution Spatial resolution is the ability to differentiate two closely situated objects as distinct structures. It is considered in three planes, with different determinants of resolution for each. Resolution along the axis of the ultrasound beam is axial resolution (see Fig. 2.10A), resolution in the plane perpendicular to the beam and parallel to the transducer is lateral resolution, and resolution in the plane perpendicular to the beam and to the transducer is azimuth or elevational resolution or slice thickness (see Fig. 2.10B).

Figure 2.10 (A) Axial resolution. (B) Lateral (L) and elevation (E) resolution.

◾ Axial resolution is the ability to separate two objects lying along the axis of the beam. It can be improved by a shorter wavelength (higher frequency) and shorter length of pulse (lower Q-value of backing material). But the problem with high-frequency transducers is poor penetration Lateral resolution is the ability to resolve two adjacent objects and is best achieved within the focal zone. Its key determinant is width of the ultrasound beam, which can be altered by focusing the beam, usually by electronic phasing. It can be improved by using focused transducers, adjusting focal position, and using multiple focal lengths. However, this reduces frame rate Azimuth, elevational resolution, and slice thickness are directly related to transducer height and are fixed for standard 2D transducers

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Temporal Resolution Temporal resolution is the ability of the system to display events occurring at different times as separate images and is measured in frames per second. Factors that decrease temporal resolution include a greater number of focal zones, having Doppler on, imaging a deeper object (echo takes longer to return), and large sector width (more space to scan). Contrast Resolution

Contrast resolution is the ability of a grayscale display to distinguish between echoes of slightly different intensities. Contrast resolution depends on the number of bits per pixel in the image memory and can be improved by increasing the number of bits per pixel (more gray shades) [6].

B-Mode Imaging Artifacts Artifacts are incorrect representations of anatomy or function that can enhance or degrade the diagnostic value of the ultrasound image. The causes are machine and operator related, as well as intrinsic to the characteristics and interaction of ultrasound with the tissues. Remedying these potentially avoidable artifacts is important for maximizing image quality and thereby increasing diagnostic accuracy. Assumptions in Ultrasound Imaging Sonographic instruments are based on following assumptions, violation of which results in artifact. 1. Velocity of sound: Sound travels at uniform speed of 1540 m/sec throughout the tissues. Alteration in the velocity results in propagation velocity artifact. It is also assumed that the longer the roundtrip travel time of ultrasound wave, the deeper the object or target is situated. 2. Attenuation of sound: Sound waves decrease in intensity at a constant rate as they travel through tissues. If the wave travels through tissues that do not attenuate much or attenuate more, then artifacts such as increased through

transmission, enhancement, and shadowing arise, respectively. 3. Path of sound: Sound waves travel in a straight line; are reflected off a reflector only once; return directly back to the probe at the same angle, exactly to the point from which they left the probe; and echo originate only from objects located along the beam axis. If the sound waves undergo more than one reflection, then artifacts such as mirror image, reverberation, or comet-tail artifacts occur. And if the direction of the beam or its echo is altered, refraction or anisotropy artifact may be produced. 4. Beam profile: Sound beam generated by the transducer is a narrow line. Violation results in side lobe or grating lobe artifacts. Classification of Ultrasound Artifacts We shall classify the artifacts based on these assumptions and their violation into following groups: propagation velocity artifact, attenuation errors, path of sound-related artifacts, beam profile–related artifacts, and miscellaneous. Propagation Velocity Artifact or Misregistration Artifact In the case of a fatty lesion, the slower speed of propagation (∼1450 m/sec) means that the echo will take longer to return to the transducer; thus, the lesion is displayed deeper in the image than its true location. This can be minimized by using multibeam (spatial compounding) features and improved signal processing.

Attenuation Artifacts (Fig. 2.11)

Figure 2.11 Attenuation artefacts. (A) Shadowing deep to renal calculus. (B) Edge shadowing of the fetal skull. This is caused by beam bending at a curved surface with resultant loss in intensity, producing a shadow. (C) Acoustic enhancement artifact is seen in the renal parenchyma deep to a simple renal cyst. Although most artifacts degrade the ultrasound image and impede interpretation, shadowing and enhancement are of clinical value. Shadowing (see Fig. 2.11A) results when there is a marked reduction in the intensity of the ultrasound deep to a strong reflector, attenuator, or refractor; consequently, no information is received from the area behind the structure. Clean, dark shadows are seen behind calcified objects when the focal zone is at or just below the structure. Edge shadowing (see Fig. 2.11B) is caused by excessive refraction and commonly occurs from the edges of vessels, cystic structures, and bones. Converse to shadowing is enhancement or increased throughtransmission artifact. Enhancement (see Fig. 2.11C) is seen when then there is less attenuating object compared with

surrounding tissues. Consequently, increased amplitude of the beam reaches and is returned from the area deep to this object compared with surrounding tissues. Therefore, this area appears bright compared with surrounding tissues. The enhancement artifact is commonly encountered deep into fluid collections such as cysts, the urinary bladder, or ascites. Thus, it helps in confirming the fluid nature of the object. One has to be wary of misinterpretation as well. For example, kidneys scanned through ascites fluid can appear echogenic because of the enhancement artifact, raising false suspicion for medical renal disease. Path of Sound-Related Artifacts Mirror image artifacts and multipath artifacts:

The ultrasound beam encounters a highly reflective surface. The reflected echoes then encounter another reflective structure on their way back and are reflected back toward the reflective interface before being reflected to the transducer, where they are detected. The display shows a duplicated structure equidistant but on the opposite side of the reflector, creating a mirror image. This most often happens at the diaphragm, where the liver is seen in the chest cavity because of sound waves being reflected off the diaphragm (Fig. 2.12).

Figure 2.12 Grayscale image showing artifactual mirror image of the liver (asterisk) deep to the diaphragm caused by specular reflection from the diaphragm. Reverberation artifacts:

Reverberation artifacts arise when the ultrasound signal reflects repeatedly between highly reflective interfaces near the transducer, resulting in delayed echo return to the transducer. This appears in the image as a series of regularly spaced echoes at increasing depth. It can be reduced by changing the scanning angle or placing transducer in such a way so as to avoid the parallel interface that contribute to artifact. Reverberation may be helpful in identification of a specific type of reflector, such as a surgical clip or needle during biopsy.

Two types of reverberation artifacts are comet-tail and ringdown artifacts.

◾ In comet-tail artifact, the repetitive reflections occur within very small structures, such as tiny cysts in the case of von Meyenburg complexes and tiny crypts in the wall of the gallbladder in the case of adenomyomatosis (Fig. 2.13). Accordingly, the reverberated echoes may not be individually visible. The tapered, comet-tail appearance is caused by the decreasing amplitude of each reverberation as a result of beam attenuation Ring-down artifact occurs when the ultrasound waves cause oscillation within fluid trapped by a tetrahedron of gas bubbles

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Figure 2.13 Comet-tail artifact in gallbladder adenomyomatosis. Refraction:

When an ultrasound beam is incident on a boundary between two tissues at an angle other than 90 degrees and if these tissues do not have the same speed of sound, there is a change in the direction of the ultrasound beam (refraction) This results in artifactual representation of objects on the display even when they are not truly in the scanned field of view Thus, refraction can cause object position misregistration, duplication, or lateral defocusing at the edge of curved structures. This artifact is most often observed in pelvic structures deep to the rectus muscles and midline fat. It can be minimized by increasing the scan angle so that sound waves travel perpendicular to the interface. Anisotropy (Fig. 2.14):

Figure 2.14 Anisotropy. Short-axis image of the supraspinatus tendon. Artifactual hypoechogenicity (arrow) may simulate tendinosis or a tear.

Anisotropy is an artifact caused by structures that are composed of bundles of highly reflective fibers running parallel to each other, such as tendons and ligaments. If the sound beam hits the tendon or ligament fibers perpendicular to their length, it is reflected directly back, resulting in an echogenic appearance. But if the angle of insonation is not perpendicular to the tendon fibers, the beam is reflected away from the transducer, leading to the generation of an image with artifactual hypoechogenicity within the tendon. Beam Profile–Related Artifacts Beam width artifacts and side-lobe and grating-lobe artifacts (Fig. 2.15):

Figure 2.15 (A) Along with main central beam (M), the side lobes are also generated. (B) Side lobe artifact caused by soft tissue close to the urinary bladder wall (red arrow) leading to an artifactual appearance of soft tissue mass in the urinary bladder lumen. Although most of the energy generated by a transducer is emitted in a beam along the central axis of the transducer (M in

Fig. 2.15A), some energy is also emitted at the periphery of the primary beam. These are called side lobes (B in 14A) and grating lobe” (C in Fig. 2.15A) and are lower in intensity than the primary beam. Side lobes or grating lobes may interact with strong reflectors that lie outside of the scan plane and produce artifacts that are displayed in the ultrasound image (see Fig. 2.15B). They are more evident when the misplaced echoes overlap an expected anechoic structure. They can be minimized by placing the transducer at the center of the object of interest and adjusting the focal zone to the appropriate depth. Miscellaneous Artifacts Speckle artifacts:

Closely spaced, very small objects or reflectors, as in solid organs such as the liver and kidney, generate echoes that cannot be resolved. This results in speckle with resultant granularity and noise in the image. Speckle can be reduced by newer imaging techniques such as spatial compounding. Tips to Avoid Artifacts

◾ Know the pitfalls ◾ Know the anatomy ◾ Beware of strong reflections ◾ Use multiple views. Every ultrasound examination is a search and is incomplete if it does not provide 3D

information about the area of interest and all the neighboring organs. Hence, do not hesitate to toggle the transducer manually, sweep the organ, and take multiple scans. If you cannot see what is needed, turn the patient over to each side, make the patient oblique, or examine the patient while she or he is standing Remember that artifacts are inconsistent

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Doppler Doppler ultrasound is based on Doppler effect (i.e., the shift or change of frequency in an ultrasound wave caused by a moving reflector, such as blood cells in the vasculature). The difference between the incident and returning frequencies is called the Doppler shift frequency. This is the same effect that causes a siren on a fire truck to sound high pitched as the truck approaches the listener (the wavelength is compressed) and a shift to a lower pitch sound as it passes by and continues on (the wavelength is expanded). The moving reflectors in the body are the blood cells. By comparing the incident ultrasound frequency with the reflected ultrasound frequency from the blood cells, it is possible to discern the velocity of the blood. The Doppler effect can also be used to measure tissue motion. The relationship of the returning ultrasound frequency to the velocity of the reflector is described by the Doppler equation, as follows:

The Doppler frequency shift is ΔF, FR is the frequency of sound reflected from the moving target, FT is the frequency of sound emitted from the transducer, v is the velocity of the target toward the transducer, and c is the velocity of sound in the medium. The Doppler frequency shift (ΔF) applies only if the target is moving directly toward or away from the transducer. In most clinical settings, the ultrasound beam usually approaches the moving target at an angle designated as the Doppler angle. In this case, ΔF is reduced in proportion to the cosine of this angle, as follows:

in which θ is the angle between the axis of flow and the incident ultrasound beam. In practice, Doppler angles should be less than 60 degrees because at angles greater than 60 degrees, the cosine value changes rapidly. Because cos (90) is zero, no Doppler shift is produced when the motion is perpendicular to the sound beam. The maximum frequency shift occurs when the reflector is moving directly toward the detector (i.e., θ is equal to 0 degrees) or directly away from the detector (i.e., θ is equal to 180 degrees). Types of Doppler Continuous-Wave Doppler

As the term says, these transmit and receive sound waves continuously; thus, they need to contain two separate elements for transmitting and receiving. The Doppler effect is emitted as audible sound as the Doppler shift is in the audible sound range. The higher the sound pitch, the higher the velocity, and the harsher the sound, the greater the turbulence. These are usually dedicated handheld devices (e.g., cardiotocogram for the fetal heart).

◾ Advantages are it is cheap, easy to use, and sensitive to flow ◾ Limitations are the inability to objectively measure velocity, depth, and output generally is a combination of arterial and venous signals because all vessels in the beam path are insonated until the beam is attenuated and arteries and veins lie close together

Pulsed-Wave Doppler Unlike continuous-wave doppler, in pulsed-wave Doppler, the same elements are used for transmitting and receiving, Brief pulses of ultrasound energy are emitted. Only returning echoes at specific depths can be accepted by using range gating. Duplex involves Doppler imaging overlaid over B-mode imaging. Three types of pulsed wave Doppler are color, power, and spectral Doppler. Color Doppler (Fig. 2.16A):

Figure 2.16 (A) Color Doppler. (B) Power doppler. (C) Spectral doppler. A, peak systolic velocity; B, enddiastolic velocity. Color Doppler provides a 2D visual display of moving blood. Color Doppler information is displayed on top of the B-mode image. The measured Doppler frequency shifts are encoded as colors. Colors are assigned dependent on motion toward or away from the transducer. Red signifies motion toward the transducer, whereas blue signifies motion away from the transducer. Turbulent flow may be displayed as green or yellow. Color intensity varies with flow velocity.

◾ Advantages are the ability to provide information in the direction and magnitude of the flow over a large region of

interest, it can detect flow in vessels too small to see by imaging alone, and it allows complex blood flow to be visualized Disadvantages are angle dependence, aliasing, inability to display entire Doppler spectrum in the image, and artifacts caused by noise

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Power Doppler (Fig. 2.16B):

Figure 2.17 (A) High-resistance vessel femoral artery spectral Doppler showing sharp upstroke and narrow range of velocities. (B) Low-resistance vessel internal carotid artery Doppler showing low pulsatility with a large range of velocities. Power Doppler images map only the power or amplitude of the Doppler signal without any indication of the velocity because it is based on Doppler signal strength alone without taking Doppler shift into consideration. Unlike Color Doppler, in which positive and negative velocities of the same magnitude from a given region would be cancelled out, in power Doppler, these

are summed up. Thus, in power Doppler, the main emphasis is on the quantity of blood flow.

◾ Advantages are less dependence on insonation angle; very low flow rates can be detected because noise is reduced, allowing higher gain settings (vs color Doppler in which noise appears across the entire frequency spectrum); and aliasing is not a limiting factor Disadvantages are flow direction is not displayed and artifacts can occur because of tissue motion

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Spectral Doppler (Fig. 2.16C):

As the term says, spectral Doppler displays the range of Doppler frequencies or velocities returned (along the y-axis) over time (along the x-axis) in the form of a spectrum. Whereas velocities above horizontal axis suggest flow in one direction, those below horizontal axes suggest flow in the opposite direction. Different spectral traces are produced depending on differences in vessel wall resistance. These peripheral resistances are indicated by Doppler flow indices: 1. S/D ratio = Peak systolic velocity (PSV)/End-diastolic velocity (EDV). 2. Resistive index (RI) = PSV - EDV/PSV. RI increases with vessel narrowing and increased resistance to blood flow. 3. Pulsatility index (PI) = Peak systolic velocity - Minimum diastolic velocity/Mean velocity. It is used to assess resistance in a pulsatile vascular system, along with RI.

High-resistance vessels such as peripheral vessels (femoral artery) show highly pulsatile spectrum with sharp upstroke and narrow range of velocities (Fig. 2.17A), but low-resistance vessels such as vital organs and blood vessels (e.g., the internal carotid artery) that need flow even during diastole show low pulsatility with a large range of velocities (Fig. 2.17B). Doppler Artifacts Major Sources of Doppler Imaging Artifacts Doppler frequency:

An increase in transducer frequency increases Doppler sensitivity, but at the same time, it increases attenuation, resulting in diminished penetration. Wall filters:

Wall filters are used to remove low-frequency signals form adjacent tissue motion. These remove signals that fall below a given frequency limit. But at the same time, this may also remove signals from low-velocity blood flow. In general, the filter should be kept at the lowest practical level, usually 50 to 100 Hz. Pulse repetition frequency:

As discussed earlier, PRF is dependent on depth, with lower PRF required for greater depth. If PRF is less than twice the maximum frequency shift produced by movement of the target

(Nyquist limit), aliasing results. In these cases, lower frequency shifts than are actually present are displayed. Doppler angle:

As discussed earlier, the Doppler angle should be less than 60 degrees. Sample volume size:

Large sample volume increases vessel wall noise. Thus, the sample volume must be adjusted to exclude vessel walls, which lead to unwanted clutter. Doppler gain:

An increase in gain increases the noise appearing at all frequencies. Excessive or insufficient Doppler gain results in over- or underestimation of velocity, respectively. The right approach to setting Doppler gain is to place the sample volume in the vessel and increase Doppler gain to a level at which noise is visible in the image. Then the gain should be gradually reduced to a point at which noise first disappears completely. Doppler Artifacts Spectral broadening artifacts (Fig. 2.18):

Figure 2.18 Spectral broadening in internal carotid artery Doppler caused by stenosis. The spectral broadening artifact occurs when there is an increase in the range of flow velocities within a sample volume, as in stenosis. Artifactual spectral broadening can occur because of improper positioning of the sample volume near the vessel wall, use of an excessively large sample volume, or excessive system gain. Artifactual vascular flow (Fig. 2.19):

Figure 2.19 Artifactual vascular flow. This is used to advantage to show flow from each ureteric orifice in the urinary bladder, which is seen as color Doppler jets. The Doppler effect (shift) is not specific to vascular flow and occurs with movement of any reflector toward or away from the ultrasound beam. Fluid or solid tissue motion can mimic vascular flow. Transmitted pulsations, especially close to the heart or major arteries, can therefore result in artifactual appearance of flow within thrombosed veins or avascular areas. Artifactual vascular flow can also be visualized if the color gain is too high or the color-write priority is too high. Aliasing and velocity scale errors (Fig. 2.20):

In Doppler imaging, the velocity scale setting in the machine is crucial for accurate signal display. When the velocity scale range is set too high, low-flow states may not be represented. Conversely, when the range is set too low, aliasing artifact occurs. Clinically, aliasing is most often encountered in abrupt transition to high-flow states such as vascular stenosis. The Nyquist limit states that the sampling frequency must be greater than twice the highest frequency of the input signal to be able to accurately represent the image Nyquist limit = PRF/2. If the velocity of the flow is greater than the Nyquist limit, the Doppler shift exceeds the scale, and “wrap-around” occurs (see Fig. 2.20).

Figure 2.20 Aliasing caused by undersampling (lower pulse repetition frequency) in spectral Doppler. Aliasing is seen as a “wraparound” of the higher frequencies that are displayed below the baseline. In color Doppler, aliasing is

seen as wraparound of the frequency color map from one flow direction to the opposite direction without transition of unsaturated color that is seen in true change in flow direction. Aliasing can be avoided by increasing the velocity scale range (which also increases the pulse repetition frequency), increasing the Doppler angle, or using a lower frequency transducer. Blooming artifacts:

Blooming artifact occurs when color reaches beyond the vessel wall, making the vessels look larger than expected. It is dependent on gain, wall filter, and color overwrite. Lowering the gain and increasing the wall filter decrease the artifact. Twinkle artifacts (Fig. 2.21):

Figure 2.21 Appearance of twinkle artifact on color Doppler. Twinkle artifact is the artifactual depiction of color signal on crystalline materials in the body. This artifact occurs just deep to strong reflectors with rough surfaces and appears as a closely spaced band of randomly alternating Doppler signals. The spectral tracing is flat. The twinkle artifact is quite useful clinically because it can aid in the detection of small stones, calcifications, and other crystalline material within the body. Direction ambiguity artifact:

The direction ambiguity artifact is primarily caused by operator error in using the hardware. When the ultrasound beam intercepts a vessel at or close to 90-degree angle, with the beam side lobes interrogating flow both upstream and downstream, the resulting signal is manifested as a spectral tracing both above and below the baseline. Clinically, this artifact is most often seen when evaluating flow in solid organs such as the liver, where the vessels can course in multiple planes and directions. Simply altering the transducer position to change the beam angle away from perpendicular will correct for the direction ambiguity. This should be distinguished from true bidirectional flow (e.g., neck of pseudoaneurysm) in which the flow is never simultaneously symmetric above and below the baseline.

Practical Tips and Image Optimization Summary

1. Select the most appropriate anatomic area presets. Application specialists can assist in the customization of presets in clinical practice. 2. Appropriate transducer selection is governed by anatomic size and location (depth). The highest frequency should be used without compromising penetration. 3. A small sector width or scan area increases the image quality and frame rate. 4. Gain: signal amplification a. Gain control: regulates the overall gain. b. Time gain compensation (TGC): Compared with gain control, TGC adjusts gain at specified depth. The bottom control adjusts gain at the bottom of the image and the top control at the top of the image. Because ultrasound lines have minimum density at the bottom of the image, TGC is increased at the bottom, and the TGC at the top of the image is generally kept at low levels. This compensates for attenuation that occurs at the depth. 5. An appropriately positioned focus and number of focal zones are generally indicated on the side of the image. 6. Use a small Doppler box because a small box means a greater frame rate, which means more real-time images. 7. Use low Doppler PRF for low flow. 8. Use an appropriate Doppler angle ( color Doppler > B-mode USG) [1] Cavitation: This is the action of an acoustic field within a fluid to generate bubbles. The pressure changes cause microbubbles in a liquid to expand increasingly and then collapse. There is an increased risk of cavitation in • gas-containing structures (e.g., bowel, lung), • low-frequency pulses (i.e., longer wavelengths), • higher power or intensity of pulses, and • use of ultrasound contrast agents. Mechanical damage to cell membranes

◾

◾

Suggested Readings • P Hoskins, K Martin, A Thrush, Diagnostic Ultrasound: Physics and Equipment, third Edition, CRC Press, Boca Raton, FL, 2019. • K Frederick, Sonography Principles and Instruments, Elsevier, 2022. • M Rumack Carol, Diagnostic Ultrasound, Elsevier/Mosby, 2018.

References

[1] W McDicken, T Anderson, Basic Physics of Medical Ultrasound, 2011. [2] SM Penny, FTB. Examination Review for Ultrasound. Sonographic Principles and Instrumentation (SPI), 2018. [3] JT Bushberg, JA Seibert, EM Leidholdt, JM Boone, The Essential Physics of Medical Imaging, 1030. [4] Sekar M, AASGMVJJYPA. Formulation and evaluation of natural ultrasound gel for physiotherapy treatment. Indo Am J Pharm Sci. 2017 ; [5] PES Palmer, Manual of Diagnostic Ultrasound, World Health Organization, 1995. [6] W Frederick, Sonography: Principles and Instruments, 2016 [7] CM Rumack, D Levine. Diagnostic Ultrasound, fifth ed. [8] American Institute of Ultrasound in Medicine, Statement on Mammalian Biological Effects of Heat. [9] Hoskins PR. Diagnostic Ultrasound: Physics and Equipment. 3rd ed. CRC Press/Taylor & Francis Group; 2019.

3

Computed Tomography Physics Vaibhav Nichat, Nikita Nanawani

Introduction Computed tomography (CT) or computerized axial tomography was invented by Sir Godfrey Newbold Hounsfield in 1967 [1]. Hounsfield was an electric engineer with special interest in computers. While working as a senior researcher, he thought it could be possible to image an object with its internal constituents by acquiring x-rays at various angles. Later, he began working on computer software that could convert x-rays into images and eventually invented computed tomography, which was first used clinically in England in 1971. Hounsfield was felicitated with the Noble Prize in 1979 for his remarkable contribution in developing this new diagnostic technique [2]. CT technology has undergone many evolutions and advancements since then and is now one of the mainstay investigations in

radiology, with approximately 75 million scans performed per year in the United States alone [3]. The standard CT attenuation value is called the Hounsfield unit (HU) in honor of its inventor. The HU value is a dimensionless universally accepted unit of CT used to express CT numbers in a standardized and convenient form [4]. HU values are derived from linear transformation of the measured attenuation coefficients and can be calculated using the following formula [5]: HU value = 1000 × (µmeasured – µwater)/µwater [Attenuation coefficient (µ) of water is 0.192] Hounsfield unit values of various substances and organs are listed in Table 3.1 [6]. Table 3.1 Hounsfield Unit Values of Various Substances and Organs Substances HU Value Air −1000 Lung

−500

Substances Fat

HU Value −50 to −100

Water

0

Cerebrospinal fluid

15

Kidney

30

Blood

30–45

Muscle

10–40

Gray matter

37−45

White matter

20–30

Liver

40–60

Calcification

>80

Contrast

100–300

Cancellous bone

700

Cortical bone

3000

The basic concepts of a CT scan are very similar to those of x-rays. An object essentially consists of multiple substances with different attenuation coefficients. X-rays from various angles are projected on the object. The attenuation values of the

transmitted radiations are measured. Using various mathematical algorithms, a final reconstructed image is generated from these projections. Various methods of image reconstruction have been devised over a period of time to reduce image artifacts and to get a true image of an object, which will be discussed later in this chapter [5,7].

Components of a Computed Tomography Machine Knowledge of various components of a CT machine is important to understand its functioning. Different components of CT scanners are described in Fig. 3.1. Their synchronous work generates an image spontaneously [5]. Before studying various components of a CT machine, we must know the orientation of the various axes used in CT. The z-axis is along the long axis of a patient lying on the tabletop, the y-axis is along the ground-ceiling plane, and the x-axis passes transversely across the patient, perpendicular to both the y- and z-axes [8].

Figure 3.1 Schematic representation of a multidetector computed tomography scanner hardware and its parts.

X-Ray Source The basic design of a CT tube is similar to that of an x-ray machine. The main difference lies in the fact that the CT tube operates at a high mA and kV and a very high heat capacity (∼4 MJ), with good heat dissipation. The tube voltage can fluctuate with a range of 80–140 kV, and the current can go up to 1000 mA. Power loading can reach up to a 100 kW. Cooling of the x-ray source happens by oil and air [9].

The tube rotates perpendicular to the z-axis of the patient. The arrangement of the x-ray tube in CT is made in such a way that anode–cathode axis lies parallel to the rotational axis to reduce the anode heel effect. Two sizes of focal spots are used in the CT xray tube—small for less power loading (0.6 mm for high-resolution CT scans) and large for higher power loading (∼1 mm for other purposes). Depending on the movement of x-ray tube, scan time, and number of detectors, CT scanning has evolved across various generations, which are discussed subsequently [10].

Filter The main purpose of the filter is to remove unwanted low-energy x-rays and reduce the direct patient dose. These low energy x-rays do not contribute to image generation. Filters also help in the formation of monochromatic beams and increase the mean energy of x-rays (beam hardening effect). A bow-tie filter is a special type of filter used in the newer generation CT scanners. It has a thinner portion in the center and a thicker portion at the periphery. The aims of this filter are to reduce unnecessary radiation dose to the

periphery and make the dose evenly distributed in the center and peripheral part of the tissue [11].

Collimator The collimator is a beam restrictor device allowing sufficient x-rays to pass through the patient to cover only the scanning area. The purpose of the collimator is to reduce scatter radiation [12].

Detector Ionization chamber detectors were used previously in old CT scanners. Solid-state scintillating detectors are used in all modern CT scanners. They convert xrays into light. Rare earth screen materials are used to improve intensification conversion factors and detector efficiency. All the detectors are mounted on an electronic array along with photomultiplier tubes, which provide power signals and simultaneously collect electronic information from them. These electronic signals are processed, amplified, and converted to digital forms and stored. Multidetectors are used in modern scanners. Slice thickness and resolution are determined by the detector size.

Multiple detectors with smaller widths give better resolution. Five-millimater width detectors either give 5-mm thickness of slices or 10-mm thickness of slices [13]. Ideal properties of the detector also include stability, noise-free response, wide dynamic range, low cost, small size, and negligible afterglow [10].

Generator The generator provides constant and stable power supply to the CT x-ray tube and detector array. It helps in maintaining stable current and voltage over wide ranges, resulting in faster rotation of tube with reduction in scan time. Because of the heavy weight of the generator, the gantry can only be tilted by up to 30 degrees [5].

Patient Table The patient lies on the table as it moves through the gantry aperture while scanning. It is machine driven and manufactured to sustain heavy weights of greater than 200 kg in some modern scanners [10].

Console The CT room is equipped with one to three console monitors for imaging, postprocessing of images, and viewing of images. Patient entry, details, protocol selection, optimizing technical factors, postprocessing of the images, and filming can be done on the console. It can be connected with the online software Radiology Information System (RIS) and picture archiving and communication system (PACS) network [9].

Computed Tomography Generations Multidetector and slip-ring technology are the newest advances in CT scanners that have enabled faster acquisition of image data, allowing for diversifying the use across a number of high-end applications in different body systems [9]. In the earlier generation CT scanners, electric cables were connected from a stationary x-ray generator to a rotating x-ray tube and likewise from a rotating detector system to the reconstruction computer system. As a result, the

gantry had to rotate back to prevent entanglement and overstretching of electric cables, reducing the speed of acquisition. To solve this limitation, slip-ring technology was developed to allow free movement of the x-ray tube and gantry without any coiling of electric cables. The slip ring has two parts, a metal ring and a connector. The metal ring is mounted on the outer part of the gantry. Detector arrays are connected to this metal ring with a connector. This helps in smooth transfer of collected data from detector arrays to the metal ring with continuous, unidirectional motion of the gantry while also maintaining electrical contact with the stationary generator component [8]. This being the basic electro-mechanical building block for modern CT led to sequential improvements in CT technology, reducing scan times and helping parallelly transmit continuous data for image reconstruction [12]. Improvement in various technologies in the CT scan led to evolution of different generations of scanners as listed in Table 3.2. Table 3.2 Various Generations of Computed Tomography

Scanners

First generati on

◾ Translate and rotate type ◾ Single source and detector with fixed coupling ◾ Source and detector work as an assembly. They first move together and later rotate to image a single slice.

Second generati on

◾ Uses pencil beam x-ray ◾ Moves 1 degree at a time (to image a slice, it would take 180 degree rotation) ◾ Longer scan time (∼30 min) [5] ◾ Translate and rotate type ◾ Single source with multiple detectors (∼30) ◾ Uses a fan beam ◾

Third generati on

Fourth generati on

◾ Shorter scan time (∼90 sec) [5] ◾ Rotate and rotate type (no translator motion) ◾ Single source with multiple detectors (∼300–700) ◾ Uses a fan beam ◾ Moves with more arc coverage ◾ Shorter scan time (4–9 sec) ◾ Better image quality [14] ◾ Rotate and fixed type (rotator x-ray tube and stationary row of circular detectors)

◾ Single x-ray source and multiple detectors in range of thousands ◾ Wider fan beam ◾

◾ Scan time is further shortened ◾ Disadvantage: less spatial separation than third-generation computed tomography (CT) scanners [19] Fifth generati on

◾ Stationary and stationary type (source and detectors are both fixed) ◾ Also known as ultrafast CT or electron-beam CT ◾ Used for cardiac imaging ◾ Very short scan time in milliseconds [16]

Sixth generati on

◾ Combination of helical scanning, third- or fourth-generation scanner, and slip-ring technology

◾ Allows three- and fourthdimensional imaging protocol acquisitions in one breath hold [17]

Seventh generati on

◾ Multiple array of detectors ◾ Uses cone beam ◾ Disadvantage: Increased scatter radiation because of the cone beam [17]

In the first- and second-generation CT scanners, the source and detector were rigidly coupled with each other; in the translate and rotate type of scanners, the source and detector were located on the opposite sides of the patient. Each projection was acquired during a translation motion, after which the source and detector assembly would have to rotate to acquire the next projection using another translate motion. Multiple such projections would then be used to create an image for that cross section. The patient table would then move to acquire the next set of projections to create the next image. The firstgeneration scanners used a pencil beam and a single detector system and had a longer scan acquisition time of approximately 30 minutes. The secondgeneration scanners reduced scan acquisition time

using a thin fan beam of x-rays with multiple detectors arranged in a linear array along the x–y axis [5]. The translate–rotate scanners were replaced by the rotate–rotate type in subsequent CT generations. The introduction of third-generation scanners removed the translator motion and covered the whole cross section of patient in a single rotation by mounting multiple detectors in an arc fashion, helping in continuous data acquisition [14]. In the fourth-generation scanners, the detector elements were removed from the rotating gantry and placed as a stationary layer of detectors outside the arc of the x-ray tube [15]. Fig. 3.2 illustrates the designs of first- to fourth-generation CT scanners.

Figure 3.2 (A–D) Schematic diagrams showing various types of computed tomography generations. Fifth-generation CT (electron-beam CT) was invented to remove the mechanical component of the CT machine, and it replaced the x-ray tube with an electron-beam scanner that was deflected around the

patient onto a half-circle tungsten target to generate the x-rays, which were detected by a detector ring on the opposite side. Because of the high cost of running this equipment, it was discontinued shortly after a few years of usage [16]. The sixth-generation helical CT scanners allowed continuous x-ray generation because of the ability of the table to continuously rotate around the patient and allowing table movement to happen simultaneously. This created an image in a helical or spiral pattern and allowed whole-body scanning in a matter of seconds. It is the most widely used CT scanner with the basic design of a third- or fourthgeneration scanner along with the addition of slipring technology [17]. The method of generation of the x-ray beam has also undergone advances with cone beam now used in modern seventh-generation CT scanners. This allows having multiple rows of detectors and allowing larger z-axis coverage per rotation. Dual-energy and dual-source CT scanners use the same principle of tube and detector assemblies [15,18]. Helical scan

acquisition with multiple rows of detectors is also known as multidetector CT or multislice CT.

Parameters for Image Acquisition and Modes of Scanning There are some basic parameters that a radiologist should be aware of that impact the quality of scanning, speed of acquisition, and radiation dose. The radiologist can modify these parameters to optimize scanning for different body areas. The manufacturers of CT equipment provide preset scanning protocols for different body areas and applications. Depending on the institution’s own policies, processes, and experience, these can be modified and stored on the console as institutionspecific protocols. Rotation time is the time taken by the x-ray tube to complete one rotation around a patient. A faster scan helps to minimize motion artifacts with good spatial resolution [15]. Pitch is defined as the distance traveled by the table during a single rotation divided by the total

width of simultaneously acquired slices. Pitch is an important entity that decides the scan time and resolution. There are two methods to calculate pitch in a multislice scanner [15]. In a single-slice CT scanner, pitch is the table distance traveled in a single 360-degree rotation divided by the width of the slice Multislice scanner pitch (also known as beam pitch) is the table distance traveled in a single 360-degree gantry rotation divided by the total thickness of all simultaneously acquired slices

◾ ◾

Increasing the pitch will decrease scan time and reduce the spatial resolution of image with loss of data and vice versa. A higher pitch also has a reduced radiation dose [14]. Slice thickness is the axial resolution of an image. Slice thickness in a single-slice CT scanner is determined by pre- and postpatient beam collimation but is limited by detector width. However, in a multislice CT scanner, slice thickness is determined by the width of the smallest detector array rows and not by beam collimation.

Smaller detectors lead to thinner slices. However, thicker slices are not affected by detector thickness. The smaller the slice thickness, the better the resolution. For example, if a machine has 1-mm thickness of detectors, then the scanner can generate slice thickness of 1 mm or more by adding data from adjacent detectors [15].

Scanned Projection Radiograph Also known as a topogram, scanogram, or scout, this is a radiograph taken at a stationary (single) projection angle. It may be obtained as an anteroposterior, posteroanterior, or lateral projection. A scanogram is the first image obtained for planning the CT study. It has reduced spatial resolution but less scatter [20].

Axial and Helical Acquisition Axial acquisition is a scanning mode in which the table stops at the scanning position and the tube rotates around the patient to acquire an image (Fig. 3.3). In helical acquisition, the patient is

continuously moving in the z-axis direction, and the x-ray tube keeps rotating around the patient with simultaneous image acquisition (Fig. 3.4) [12]. Further differences are tabulated in Table 3.3. Table 3.3 Differences Between Axial and Helical Scanners Axial Acquisition Helical Acquisition Also known as Also known as sequential scanning spiral scanning

◾ ◾ Step-and-shoot approach: one slice is

◾ ◾ Slices are imaged continuously when the

imaged, and then the gantry steps farther and again images next slice.

table moves through the gantry aperture.

◾ X-rays are switched ◾ X-rays are emitted off in between imaging continuously. slices.

◾ Manual control over ◾ Technical imaging technical imaging parameters vary parameters

according to the thickness of the body part being examined.

Axial Acquisition

◾ Less radiation exposure

◾

Helical Acquisition More radiation exposure

◾ Longer scan time ◾ Shorter scan time ◾ Data loss in between ◾ No data loss in sections caused by between sections switching off x-rays in between imaging slices

Figure 3.3 Axial acquisition.

Figure 3.4 Helical acquisition.

Image Reconstruction Techniques A pixel is defined as the smallest area of information on an image that is a two-dimensional (2D) representation of a tissue volume [21]. Rows and columns of pixels form a matrix. The matrix helps in formation of the CT image. A pixel can be calculated by the dividing field of view by the matrix size [21]. A voxel is the three-dimensional (3D) structure (tissue volume) represented by a pixel on a CT image. It can be calculated by multiplying the pixel area by the section thickness, the resolution of the image being inversely proportional to the slice thickness [21].

After x-rays are transmitted through the subject with multiple projections at various angles, the emerging x-rays are collected by rows of detectors. A single CT image generally requires multiple projections in single rotation of the x-ray source. With the acquired data, the linear attenuation coefficient of each and every pixel is calculated. With complex mathematical equations, the final CT image is generated (Fig. 3.5). The rate-limiting step in image reconstruction is rapid processing of data and immediate generation of the CT image. Complex mathematical algorithms and reconstruction techniques to generate CT images have evolved over the past decades [17,22]. Three basic reconstruction techniques used are as follows.

Figure 3.5 Schematic diagram showing the sequence of image generation and display. CT,

computed tomography; PACS, picture archiving and communication system. 1. Simple back projection Simple back projection is the oldest and easiest method for image reconstruction and is the basis of all new reconstruction techniques [12]. It is also known as the addition method or summation method. When an object is exposed with x-rays in two directions, the final summed linear attenuation coefficient value is averaged out and projected back in each row and column. Averaged values of the linear attenuation coefficient in each row and column are then added to get the final CT image (Fig. 3.6). Advanced CT scanners do not use this technique because the linear attenuation coefficient within a particular voxel is affected by the linear attenuation coefficient in the adjacent voxel, producing image blurring and image quality deterioration [23]. 2. Filtered back projection Filtered back projection was the most widely used method of image reconstruction in previous

generations of CT scanners. Its basic mechanism is the same as that of simple back projection except that in this technique, the resultant image is filtered so that unwanted frequencies producing image blurring are eliminated. It is better than simple back projection because of its ability to detect lowcontrast objects, better spatial resolution, and decreased blur. The final CT image is nearly similar to the object that is scanned. Convolution and deconvolution are the mathematical algorithms used in filtered back projection to reduce image blurring. Different types of filters are used in this technique depending on resolution and noise. Bony filters are used when high resolution is required. Soft tissue filters are used when less noise is required [22]. 3. Iterative reconstruction Iterative reconstruction is an advanced reconstruction algorithm used in the current generations of scanners with the ability of reducing patient dose and faster generation of CT images. Two types of data are used in this reconstruction, simulated data and measured data. It is a

successive approximation method in which attenuation coefficient values of simulated data are approximated with measured data [22].

◾ It starts with comparison of simulated data with the measured data. ◾ Correction is made in these two data values, and the resultant data are calculated until the simulated data matches the measured data. ◾ This process is repeated until the simulated data and measured data are equal or nearly equal (Fig. 3.7). ◾ CT artifacts and noise are significantly reduced with this technique without any impact on spatial and temporal resolution, with radiation exposure reduced substantially up to 50% [24].

Figure 3.6 Simple back projection. Twodimensional reconstruction of an object that is scanned from two sides (x-ray 1 and x-ray 2 in A). The projection images from variable attenuation of the thicknesses of the object (O in A) are seen as steps on images B and C with the degree of darkness proportionate to the length of the object resulting in higher attenuation and therefore the greater darkness in the central step in both projects (asterisk in B and C) in attenuation. On superimposition of the individual projections, there is a crude reproduction (I in D) of the original object.

(Adapted from TS Curry, JE Dowdey, RC Murry, EE Christensen, Christensen’s Physics of Diagnostic Radiology, fourth ed., Lea & Febiger, Philadelphia, 1990.)

Figure 3.7 Illustration of a ray-by-ray iterative reconstruction for a four-element square. Horizontal, vertical, and diagonal ray sums are shown in the adjacent blocks. In the first step, the two horizontal ray sums (16 and 6 in the hatched blocks) are divided equally among the

two elements in the ray. If the ray sums had represented 10 elements, the sum would have been divided equally among all 10 elements. Next, the new numbers in the vertical row are added to produce the new ray sums (11 and 11 in the shaded blocks) and compared with the original measured ray sums (also in shaded blocks). The difference between the original and new ray sums (10 – 11 = –1 and 12 – 11 = +1) is divided by the number of elements in the ray (– 1 ÷ 2 = –0.5 and +1 ÷ 2 = +0.5). These differences are algebraically added to each element (8 – 0.5 = 7.5, 3 – 0.5 = 2.5, 8 + 0.5 = 8.5, and 3 + 0.5 = 3.5). The process is repeated for diagonal ray sums to complete the first iteration. In this example, the first iteration produces a perfect reconstruction. With more complex data, iterations may have to be repeated 6 to 12 times to reach an acceptable level of agreement between the calculated and measured values.

Basic Image Display and Processing

To display any image that allows the human eye to discern different structures, there is a requirement to convert the wide range of attenuation values into an image that can match the grayscale contrast of the human eye. It is important to image tissue properly to minimize loss of information. Attenuation values in a tissue can range from –1000 to +3000 (total, 4000 shades of gray), but the human eye is capable of differentiating not more than 50 shades of gray. If a particular CT number is given to a particular pixel in a matrix, then there will be thousands of shades of gray, which will be impossible for the human eye to differentiate from each other [25]. To simplify this, CT numbers are averaged out with a specific shade of gray for a particular tissue in the body. Various tissues of the body have different ranges of CT numbers (HU values); for example, muscle has CT numbers ranging from 40 to 60 HU and fat from –60 to –150 HU [26]. Window level is defined as the center (median) of CT number in an image. Window width is defined as the range of CT numbers above and below the window level. A narrower window width produces higher tissue contrast than a wider window width (Fig. 3.8). The benefit of window

width is that maximum possible information and findings can be derived from a single image [27].

Figure 3.8 Left frontoparietal infarct with loss of gray and white matter differentiation. A narrower window width in B has better tissue contrast than the wider window width in A, helping in confident diagnosis of a left frontoparietal infarct. The various commonly used basic postprocessing techniques are described next. Sagittal and coronal reformation: Normal axial images are reconstructed in x and y directions. Sagittal and coronal reformations are routinely performed in y- and z-axis directions and in x- and

z-axis directions, respectively. (To reconstruct images in various planes, the data acquired in modern scanners are isotropic. Reformatted images from data that are anisotropic can appear distorted because of various artifacts such as stairstep [28].) Oblique reformation: Several organs such as the aorta are not well visualized in routine sagittal and coronal reconstructions because of their curved anatomy, and oblique reformation can be used in such situations [29]. Maximum intensity projection (MIP): Only the maximum attenuation values of rays are retained from a selectable width of scanned tissue image in any plane for a 2D display on screen to generate MIP (Fig. 3.9A). It is commonly used to visualize high attenuation structures like bones and contrast filled vessels on angiograms. Minimum intensity projection (MinIP) is used to image low-attenuation structures (Fig. 3.9B). Minimum values of rays are retained from a selectable width of scanned tissue in any plane for a 2D display on screen by computer to generate MinIP. It is useful when analyzing hypodense structures like the tracheobronchial tree, cystic

lung disease, mosaic attenuation, and the pancreaticobiliary tree [30]. Curved multiplanar reformation is used to image curved structures such as the coronary arteries and other tortuous vessels, the bowel, and the ureters (Fig. 3.10) [31]. Volume rendering is a process in which 3D sample data are displayed in two dimensions. CT numbers that make up a particular structure are expressed as a picture in different colors and different transparency levels (Fig. 3.11). It is helpful for referring surgeons to plan and execute surgery [32]. Surface rendering: Voxels present on the edge of the structure are identified and marked with displaying of its CT numbers as a surface rendering (Fig. 3.12). The rest of the voxels are made invisible. This is useful in CT bronchoscopy and CT colonoscopy [33].

Figure 3.9 (A) Maximum intensity projection (MIP) view showing branches of celiac axis of computed tomography angiography of the abdominal aorta. (B) MIP view showing the tracheobronchial tree in computed tomography chest.

Figure 3.10 Curved multiplanar reformatted image showing the left anterior descending artery in computed tomography coronary angiography.

Figure 3.11 Volume-rendered image of the head and neck vessels in computed tomography angiography of the head and neck.

Figure 3.12 Surface-rendered image of the colon in computed tomography colonoscopy.

Image Quality Image quality control and improvement in CT can be objectively calibrated and measured using CT phantoms (Fig. 3.13) [27,34]. Two important factors affecting image quality are resolution and noise.

Figure 3.13 Computed tomography (CT) phantom. A quality control test is carried out using this CT phantom. Several different composite materials of variable but known density (CT number) are placed in various positions in the water phantom. Calibration helps in monitoring the accuracy of the CT number of each material and water. If the CT number of a particular material varies more than 5 HU, then rectification action and servicing of the machine should be performed.

Resolution

There are three components of image resolution: spatial, contrast, and temporal resolution [27].

◾ Spatial resolution is the ability to differentiate two closely situated objects as different ◾ Contrast resolution is the ability to differentiate two objects with nearly similar HU as different ◾ Temporal resolution is the ability of a CT scanner to produce motion-free images and therefore is measured in milliseconds. Temporal resolution holds particular importance in imaging moving structures such as the heart and is determined by the rapidity with which data is acquired. It can be improved by increasing the speed of gantry rotation, number of detector channels in the system, and speed of recording rapidly changing signals by the system. Resolution and noise are interconnected with each other

Spatial resolution is measured in line pairs per centimeter (lp/cm). Resolution of CT ranges between 5 and 10 lp/cm [35]. Factors affecting resolution are discussed in Tables 3.4 and 3.5 [27,34].

Table 3.4 Factors Affecting Spatial Resolution Spatial resolution can be increased by

◾ Decreasing pixel size: Pixel size is directly proportional to the field of view (FOV) and inversely proportional to the matrix size.

◾ Decreasing FOV: A smaller FOV leads to smaller pixel size and increased spatial resolution. ◾ Increasing matrix: Pixel size decreases by increasing the matrix size. ◾ Type of algorithm: High-resolution algorithms such as bony algorithms have higher spatial resolution. Soft tissue kernels have less spatial resolution.

◾ Small size of detector: A smaller thickness of the detector means that the detector has to cover a smaller area of interest, leading to increase in spatial resolution.

◾

◾ Smaller focal spot size: The smaller the width of the x-ray projection path, the greater the spatial resolution.

◾ Increasing sampling frequency: It gives finer resolution of an image because of increasing details of tissue acquired.

◾ Decreasing slice thickness: The thinner the section thickness, the higher the resolution. It also helps in mitigating partial-volume effects.

◾ Decreasing pitch: Resolution is increased by decreasing pitch. ◾ Decreased patient motion: Patient motion degrades spatial resolution. ◾ Isometric imaging: Increases spatial resolution in all planes. Table 3.5 Factors Affecting Contrast Resolution Contrast resolution can be increased by

◾

◾ Decreasing kV: Increasing kV increases the mean energy of the x-ray beam, leading to increased penetrating power through tissue and decreasing contrast resolution.

◾ Increasing tube current and decreasing noise: Noise is decreased by increasing the tube current, increasing the contrast resolution.

◾ Tissue characteristics: Tissues having greater difference in linear attenuation coefficient have more contrast resolution. For example, it is very easy to differentiate between calcium and fat.

◾ Contrast media: Both oral and intravenous contrast media increase contrast resolution. Noise

Noise is defined as the graininess of an image and results from a deviation from uniformity of homogenous CT numbers. It is also called mottle. Images with more noise ultimately reduce the image quality and degrade diagnostic performance and

contrast resolution (Fig. 3.14). Noise can be produced by three sources [34]:

◾ Quantum noise is the most significant one and is caused by a lack of photons reaching the detectors ◾ Electronic noise is random and an unwanted fluctuation in electric signals associated with the system and is not significant ◾ Structural noise is associated with the reconstruction algorithm of the scanner

Figure 3.14 (A) An image with noise. (B) An image without noise. Noise is decreased by increasing the number of photons, tube current, kilovoltage, rotation time of

the gantry, and slice thickness and by using advanced reconstruction algorithms [34].

Artifacts Computed tomography artifacts are deviation of HU values of tissue in the reconstructed image from their actual HU values. Artifacts deteriorate image quality and can obscure or imitate pathologies. Depending on the source of origin, they are divided into the following four types [36,37]. 1. Patient-related artifacts: Various subtypes of patient-related artifacts, their causes, and correction techniques are discussed in Table 3.6 [36] 2. Physics-related artifacts: These are caused by processes involved in CT scanning and recovering data. The types of physics-related artifacts with correction techniques are discussed in Table 3.7 [36] 3. Hardware-related artifacts: These are the result of errors, imbalances, calibration drifts, malfunctions, and measurement inaccuracies in

hardware design. They are discussed in Table 3.8 [36] 4. Helical- and multisection-related artifacts: These arise because of reconstruction algorithms. Table 3.9 describes subtypes of helical- and multisection-related artifacts along with their causes and correction techniques [36,37] Table 3.6 Patient-Related Artifacts Correction Subtype Causes Techniques Motion artifact: Reducing scan It happens Respirator time because of y chest voluntary or Helical movement involuntary acquisition movements of the s patient. This can Cardiac lead to electrocardiograp Cardiac misregistration of pulsations hic gating data and manifests as Proper breath directional holding Vascular

◾ ◾

◾ ◾ ◾

◾

◾

shading and Subtype streaking in reconstructed images. The streaks occur between highcontrast edges and the x-ray tube position when motion occurs (Fig. 3.15).

pulsations Causes

Correction Techniques Proper patient Swallowin instructions on the g need to stay still mechanis m Use of positioning supports Unconscio us Specialized movement motion correction s software

◾ ◾

◾ ◾ ◾

◾ Sedation and immobilization may be used in pediatric and unconscious or uncooperative patients

Subtype Metallic artifact: Artifacts are more with elements that have high atomic numbers than those with low atomic numbers (Fig. 3.16).

Causes

Correction Techniques

◾ Metal ◾ Removing all objects removable metal within the region of interest

items before scanning

◾ Angulating the gantry to

◾ Earrings avoid metal objects within the ◾ Dental scanning field braces ◾ Increasing kV ◾ Metal to increase clips penetration ◾ Body ◾ Metal artifact implants reduction software on newer scanners

Subtype Incomplete projection: Artifacts are produced by objects lying outside the region of interest of scanning (Fig. 3.17).

Causes

Correction Techniques Proper positioning so that nothing lies outside the field of the scan

◾ ◾ Artifacts of the hands lying by the side of body in chest and abdomen scans

Table 3.7 Physics-Related Artifacts Subtype

Causes

Correction Techniques

Subtype

◾

Causes

Cupping When artifact polychromatic x-rays pass through the center of the cylinder, rays get hardened more than when they pass through the peripheral part of the cylinder. When these hardened beams pass through an object, attenuation of an object gets altered compared with the original attenuation.

Correction Techniques

◾ Tilting the gantry ◾ Appropriate calibration

◾ Use of a bow-tie filter ◾ Iterative reconstructio n algorithms using software correction

Subtype Steak and dark bands: It is also a type of beamhardenin g artifact (Fig. 3.18).

Causes

Correction Techniques

◾ When the x-ray ◾ Beambeam passes between hardening two dense objects, streak and dark bands are generated.

◾ Artifact is seen in scans with dense bony regions or high-density intravenous contrast.

correction software

◾ Use of a prehardened beam by the filter

◾ Calibration of machine

Subtype

Causes

◾ ◾ ◾

Partial Blurring of image volume: The CT Size overestimation number of a Inadequate spatial particular resolution voxel is the average of CT numbers of all the tissue in that voxel (Fig. 3.19).

◾

Photon When the x-ray starvatio beam has to pass n (Fig. through an area of large 3.20) thickness, most of the photons get removed,

Correction Techniques

◾ Thinner acquisition ◾ Iterative reconstructio n

◾ Increased reconstructio n filter

◾ Increased tube potential

◾ Automated tube current modulation, which helps

Subtype

and only a few photons Causes are left to image the remaining structures, producing noise and streak like artifact caused by photon starvation.

Correction Techniques in increasing photon release when the beam has to pass through a larger thickness of tissue than a narrow portion

◾ Adaptive filtration software smoothens out the image in the region of photon starvation and reduces noise.

Subtype Table 3.8

Causes

Correction Techniques

Hardware-Related Artifact Subtype Ring artifact: This artifact is more common in solidstate detectors than xenon gas detectors. They rarely simulate any pathology (Fig. 3.21).

Causes

Correction Techniques

◾ Uniform ◾ Repair circular or of faulty semicircular artifact is produced at every rotation due to faulty detector.

detector

◾ Recalibrati on of machine

◾ Software correction Table 3.9 Helical- and Multisection-Related Artifacts

Subtyp e Helica l artifa ct (Fig. 3.22)

Causes

Correction Techniques

◾ Helical artifact is seen ◾ during image generation Correction

and reconstruction, causing distortion of image software due to rapid anatomic change in structure along the z-axis when the gantry Advanced rotates around the patient. reconstructio n algorithms

◾

Subtyp Causes e ConeWider collimation beam helps in collecting larger artifa data because of an ct increased number of slices per rotation in the cone beam. Artifacts are more for the outer row of detectors because of offcenter positioning of objects leading to apparent elongation of data. Artifacts are more common in 64-slice scanners than 32-slice scanners.

◾

Correction Techniques New reconstructio n techniques

◾

Subtyp e Stairstep artifa ct (Fig. 3.23)

Causes

Correction Techniques

◾ It is seen on ◾ Thin reformatted images after slice scanning at wide interval in between two projections.

◾ It can be identified around the corners of the scanned object.

acquisition

◾ Overlapping image reconstructio ns

◾ Multidetecto r CT scanners eliminate this artifact

Subtyp Correction Causes e Techniques Zebra It is seen caused by Thin artifa helical interpolation of the collimation ct data process producing Longer noise inhomogeneity along scan duration the z-axis.

◾

◾ ◾

◾ Thin dark lines are seen at regular intervals in reformatted images with helical multisection scans.

◾ Noise is generated in reformatted images that are reconstructed from helical scans.

Dosimetry Radiation originating from CT examinations is a major contributor of radiation dose to the patient population from medical purposes. There is a concern

regarding radiation doses because of these examinations in both children and adults; this is discussed in more detail in Chapter 5. CT is used for diagnostic and intervention imaging as well as radiation planning, and monitoring radiation exposure is important [12]. The CT dose index is a universal standardized unit used to measure the radiation dose output of a CT scanner machine. Various dose indices have been developed over a period of time to measure radiation exposure caused by CT and are discussed in Table 3.10. These are automatically provided by CT machines for every scan [12]. Table 3.10 Computed Tomography Dose Indices CT dose It is a dose calculated from single index (CTDI) rotation of gantry using a pencil ionization chamber.

◾

◾ Unit: mGy [13] ◾

CTDI100

◾ It is the dose calculated over a length of 100 mm using a pencil ionization chamber.

◾ Unit: mGy [13] ◾ It is the weighted average dose of the central and peripheral parts of the

CTDIw (weighte d average) organ covered in the scan.

◾ It is an adjusted dose for spatial variation because the dose at the periphery is more than at the center.

◾ CTDI  = 1/3 CTDI of central part + 2/3 CTDI of peripheral part ◾ Unit: mGy [40] ◾ It is the radiation dose calculated for the volume of the scanned organ. ◾ CTDI  = CTDI /pitch ◾ w

100

100

CTDIvol

vol

w

◾ To keep uniformity in radiation dose measurement, CTDI is widely used. ◾ Unit: mGy [41] ◾ DLP can be calculated by multiplying the length of the scan (cm) vol

Doselength product (DLP)

Effectiv e dose

with the CTDIvol.

◾ Unit: mGycm [41] ◾ It can be derived by multiplying the DLP with organ-specific conversion factors.

◾ Different tissues have differing sensitivities to radiation, so the tissueweighing factor of each organ can be used to calculate the effective dose.

◾ Conversion factors for the chest and abdomen are 0.014 and 0.015, respectively.

◾

◾ Unit: mSv [41] ◾ It is an average dose calculated over multiple scans over an interval length

Multiple -scan average [41]. dose (MSAD )

◾

SizeIt can be estimated from CTDIvol, specific measurements of the patient’s size and estimate conversion factors [42]. d dose Dose reference levels of various types of adult CT scans are displayed in the tabulated format in Table 3.11 [38]. Almost all the CT scanners calculate and display these values as a part of patient information at the end of scan as mentioned in Fig. 3.24 [39]. Table 3.11 European Dose References Levels for an Adult Patient for Various Computed Tomography Scans

Dose Reference Levels CT of the head

CTDIvol DLP Effective (mGy) (mGycm) Dose (mSv) 60

1050

2

CT of the chest

30

650

12

CT of the abdomen

35

780

13

CT of the pelvis

35

570

10

CTDIvol, computed tomography dose index volume; CT, computed tomography; DLP, dose-length product.

Figure 3.15 Noncontrast computed tomography head showing a motion artifact.

Figure 3.16 (A) Metallic artifact caused by a femur implant. (B) Neutralization of the artifact using metal artifact reduction software.

Figure 3.17 (A) CT topograph of chest showing both the arms lying by the side of body. (B) Asymmetrical linear low-density bands seen

over the liver and spleen because of incomplete projection of the arms lying by the side of body, causing degradation of image quality.

Figure 3.18 Streak and dark bands artifact. Multiple alternate hyperdense and hypodense bands are seen because of anterior communicating artery aneurysm coiling.

Figure 3.19 Partial-volume artifact of temporal bone seen as a calcific focus (arrow) in the right frontal lobe.

Figure 3.20 Computed tomography scan of the shoulder region shows that attenuation is much higher in the lateral direction than the anteroposterior (AP) direction. Projections in the lateral direction are “photon starved” and show higher noise than those in the AP direction, resulting in photon starvation artifact in the lateral direction (arrows).

Figure 3.21 Ring artifact caused by a defective detector.

Figure 3.22 A to C, Helical artifact. Contrastenhanced computed tomography scan of abdomen at the liver sections shows helical

curved low-attenuation areas at the margins of liver as indicated by the white arrows.

Figure 3.23 Stair-step artifact. Sagittal reformatted image of computed tomography (CT) head scanning at a 5-mm reconstruction interval. In modern imaging, these are usually seen with a lower row multidetector CT.

Figure 3.24 Triple-phase computed tomography (CT) scan of an abdomen done for gastrointestinal bleed. The dose chart shows the CT dose index and dose-length product (DLP) of various phases. The effective dose can be calculated by adding the individual DLP (total DLP, 736 mGycm) and then multiplying it with conversion factor of abdomen (0.015). The effective dose in this scan is 11.04 mSv.

Dose Optimization and Factors Affecting Patient Dose Computed tomography scanner manufacturers have been striving to develop various optimization techniques to reduce radiation doses to patients while at the same time generating quality images for diagnosis. Radiologists should make every effort to

decrease the radiation dose and follow the principle of ALARA (as low as reasonable achievable) while maintaining image quality.

◾ Minimizing the scan range of CT scan is a straightforward way to achieve this goal ◾ For multiphase CT protocols, the number of required phases should be minimized ◾ Noncontrast scan should be obtained only when needed ◾ Clinical indication and protocol of CT perfusion should be determined because of the associated substantial radiation dose

Other useful dose optimizing strategies are discussed in the following section [43]. Body size–adapted CT protocols: This is a principal part of optimizing CT doses. Optimal tube voltage and current should be determined for patients of each body size to obtain a diagnostic range of images by keeping radiation doses to the minimum. To reduce image noise, higher tube current should be used along with low CT voltage [44].

Tube current modulation: Tube current modulation according to body size, shape, and attenuation parameters contributes to dose optimization without hampering image quality. Approximately 25% to 50% of the radiation dose can be reduced by tube current modulation [45]. To avoid faulty tube current modulation, the patient should be positioned at the isocenter on the gantry table [44]. Optimization of tube voltage: This is done by selecting the most dose efficient tube voltage. A lower tube voltage is used for contrast-enhanced CT examination [45]. Scan modes: A low-dose scan mode is used to reduce the dose involved in CT examinations such as in a prospective electrocardiography (ECG)gated sequential scan for cardiac imaging [46]. Iterative reconstruction: This reduces the quantum noise of an image without hampering image quality such as spatial and temporal resolution. It uses less projection and low-dose data. This helps in reduction of radiation dose to the patient with a reduction in noise. This benefit is most apparent in low-dose CT acquisitions in

which noise obscures visualization of clinically relevant information [24].

Automatic Exposure Control (AEC) The optimal dose requirement is different for different tissues. For example, the same kV and mA are not sufficient to image both the chest and abdomen appropriately. Instead, the dose varies from slice to slice, especially in spiral acquisition. Dynamic modulation (angular adjustment) of the tube current is done by the x-ray source while spiral scans are acquired. For example, more current is used during lateral acquisition because of increased thickness of tissue compared with the anteroposterior direction. All modern CT scanners use this technology to optimize radiation exposure [47]. The mechanism behind AEC depends on the x-ray numbers and energies reaching the detectors. The detectors accordingly give feedback to the tube to modulate current according to the size and attenuation properties of the tissue being imaged. As attenuation increases, tube current also increases

and vice versa. While imaging varying thickness of tissue, current modulation is done by the data collected during the scanogram. Up to 50% of radiation can be reduced with this technology. While imaging pediatric patients, kV should be reduced because AEC only deals with current modulation [48].

Overbeaming and Overranging In a single-slice CT scanner, the fan beam width corresponds exactly to or less than the detector width. In a multidetector CT scanner, the width of the fan beam is always greater than the detector width because all the effective operating detectors should be covered by it. During this process, the fan beam projects outside the effective operating row of detectors, resulting in excessive radiation dose to the patient and simultaneously not contributing to image generation. This effect is known as overbeaming (Fig. 3.25). Although it may appear as a small dose over a single slice, it adds up over the length of the scan and increases the overall radiation dose to the patient [49].

Figure 3.25 Schematic self-explanatory diagram showing the effect of overbeaming and overranging in computed tomography with adaptive collimation. Because of the need for reconstruction of images, spiral CT machines scan patients a little more at the ends of the area of interest. To interpolate the data, this extra scanning at the beginning and end of area of interest is necessary. This excessive scanning at the end of area of interest is not wasted as in overbeaming; it is used for reconstruction of images. This is called overranging (see Fig. 3.25). Modern

CT scanners use adaptive or dynamic collimation to reduce the radiation dose to patients by up to 40% at the beginning and end of scanning. Dynamic collimators are mechanical blades that move inward and outward of the radiation field to reduce overranging [50]. The approach and techniques to reduce radiation dose are described in Table 3.12 [51,52]. Table 3.12 Factors Affecting Computed Tomography Radiation Dose 1. Justification or appropriateness: CT should be performed only for a valid indication. 2. kV: Radiation dose increases with increase in kV. 120 kV is the routine tube potential used in CT scanners. 3. mA: The dose is directly proportional to the mA. It is a key parameter while scanning a patient.

4. Rotation time: The dose is directly proportional to the rotation time. 5. Patient size: Oversized patients undergoing CT receive significantly higher doses than small patients. 6. Pitch: The dose is inversely related to the pitch. 7. Noncontrast phase: Virtual noncontrast images can be generated with dual-energy CT. 8. Multiphase protocol: Multiphase scanning should be performed only if indicated for a specific purpose. 9. Topography: Posterior-anterior topography is preferred than anteroposterior topography; this reduces radiation dose to structures such as the gonads, thyroid, and breast. 10. Isocenter positioning: Positioning the patient properly at the center of the table reduces unwanted radiation exposure to the periphery according to the inverse square law.

11. Reducing overbeaming and overranging (discussed in the text) decreases the radiation dose. 12. AEC and iterative reconstruction techniques reduce radiation exposure. 13. Bow-tie filters: Beam hardening causes elimination of low-energy x-rays, which are sources of the radiation dose. 14. Cardiac imaging: Use of prospective gating has significantly lower radiation dose than retrospective gating. 15. Section thickness: An increased radiation dose is associated with thinner collimation. 16. Scan length: The radiation dose is directly proportional to the scan length. 17. Dual source CT: Dual-source CT can produce good image quality at a similar or lower radiation dose than single-source CT. AEC, automatic exposure control.

Advanced Computed Tomography Applications With a great demand to assess functional and molecular information in addition to anatomic information, multiple advances have happened in CT scanners. A few of these are discussed here in brief [53]. Readers can read more details in the individual chapters pertaining to these topics.

Cardiac Computed Tomography It is now possible to image the heart and coronary arteries because of improved spatial and temporal resolution of CT scanners enabled by ECG gating. High-resolution cardiac images can be reconstructed at any phase because of ECG-gating and breath-hold technique. ECG gating can be prospective or retrospective. In retrospective gating, a scan is acquired during a complete cardiac cycle, and cardiac function can also be calculated. In prospective gating, the scan is specially acquired during the end diastole phase to reduce the radiation exposure to the patient [54].

Computed Tomography Perfusion The same body part is scanned repeatedly after contrast administration over a defined period of time in perfusion CT. Different organs have different acquisition times for perfusion scanning; for example, myocardial perfusion takes around 30 seconds, and brain perfusion takes 40–60 seconds. Various parameters are calculated in perfusion studies such as mean transit time, time to peak, blood flow, and blood volume and are plotted graphically or on color-coded maps (Fig. 3.26). Radiation dose is an issue in CT perfusion caused by repeated and continuous scanning of a particular organ; the radiation dose is generally five times higher than in a routine scan. A few current and evolving applications of CT perfusion techniques are listed below [55].

Figure 3.26 Computed tomography perfusion done in a patient with right hemiplegia. Altered perfusion parameters are seen in the left middle cerebral artery territory suggestive of infarct. Cerebral Blood Volume image shows blue color in left middle cerebral artery territory corresponding to decreased volume of blood supplied to brain parenchyma. Cerebral Blood Flow image also shows blue color suggestive of

decreased volume of blood passing through a given amount of brain tissue per unit of time. Time to Drain and Mean Transit Time images show yellow/red color indicating prolonged perfusion.

◾ To evaluate acute stroke [56] ◾ To identify occult malignancies [57] ◾ To characterize lesions into benign and malignant [57] ◾ To monitor therapeutic response of various treatment regimes on tumors [57] Dual-Energy Computed Tomography X-rays interact with matter via the photoelectric effect and Compton effect. The Compton effect produces the majority of the scatter radiations. The photoelectric effect deals with K-edge electrons, producing photoelectrons, positive ions, and energy. Different tissues and materials have different atomic numbers and different K-shell energies. However, one cannot separate soft tissues with similar HU values from each other on single-energy CT scans. For example, it is difficult to separate and classify

iodinated contrast from other materials such as bone that have similar HU values in single-energy CT scans. These materials are, however, governed by different atomic numbers, different K-shell energies, and different linear attenuation coefficients at highand low-energy levels [58]. Dual-energy CT is an advanced CT technique in which materials with different K-edge energy characteristics can be separated by different x-ray energy spectra. Unlike the single energy dataset produced by routine conventional single-energy CT, dual-energy CT scanners produce two energy datasets. Various materials have characteristic attenuation values at different energy levels because of their linear attenuation coefficients and can hence be identified accurately based on their appearance on the two different data sets. Dual-energy CT can thus be used to delineate and differentiate any tissue when imaged with both low- and high-energy x-ray beams. The various types of scanners used for dualenergy imaging are summarized in Table 3.13 [59]. Table 3.13

Designs of Dual-Energy Computed Tomography Scanners DualEnergy Dual Dual-Energy Single Source Source SplitRapid kV Dual-Layer Filter Switching Detectors Twin Beam

◾ Two xray sources

◾ A ◾ A single ◾ A single xx-ray source single x-

ray source function produces independent rapidly ly of each alternating other and low- and work at highlow-energy energy (80 kVp) rays and high = (Fig. 3.31 energy B). (140k Vp) levels (Fig. 3.31A ).

operates at high tube kilovoltage (Fig. 3.31C).

ray source operates at high tube kilovolta ge (Fig. 3.31D).

◾ Two ◾ Single ◾ Dual detector rapid layered

◾ Two filters at

arrays are positioned opposite to two x-ray sources at right angles to each other.

the tube end (gold and tin) split the beam into highand lowenergy spectra before it reaches the patient.

response detector array

detector array to separate low and high energy x-ray photons. The top yttrium layer absorbs lowenergy data, and the bottom gadolinium layer absorbs high-energy data.

Images in dual-energy CTs are most commonly obtained at 80 and 140 kV. Weighted average images are usually reconstructed in all dual-energy CT scanners. They represent a linear blend of data obtained from low- and high-energy spectra. Usually

20% to 30% of low-energy data and 70% to 80% of high-energy data are used to construct weighted average images. These data are similar in appearance to the data acquired by a routine 120kVp single-energy CT scanner. Radiation exposure is similar or less than in the conventional single-energy CT because of iterative reconstruction and automated current modulation techniques. Apart from the “regular” image set, various image reconstructions are possible with these two energy datasets, such as monoenergetic images, virtual noncontrast images, iodine concentration maps, and weighted average images (Fig. 3.27) [60]. This technique can also be used for metal artifact reduction. By acquiring CT at high- and low-energy spectra, it is possible to perform greater degree of material decomposition (separation) based on differences in attenuation at different energies. Material decomposition is used to accurately differentiate materials that have identical appearance on single-energy CT such as calcium, iodinated contrast, and hemorrhage. One such example is the use of dual-energy CT to differentiate the types of

renal calculi by using the ratio of low-energy versus high-energy attenuation (Fig.3.28) [58].

Figure 3.27 Set of images show types of image data generated with dual-energy computed tomography (CT). (A) Routine contrastenhanced CT. (B) A virtual noncontrast image. (C) and (D) Material differentiation iodine reconstruction images on grayscale and color maps, respectively, which help in deriving quantitative and qualitative iodine uptake.

Figure 3.28 (A) Blue color coding of the left renal lower pole calculus. (B) Various parameters after placing the stone marker on the desired stone, which are very accurate in classification of various stones. (C) Graphical representation of the location of the marker in the various categories. Dual-energy computed tomography is extremely rapid and helps to characterize the stone. Similarly, because we know that iodine attenuation is higher at 80 kVp than 120 kVp, it is possible to create virtual nonenhanced images by identifying and subtracting iodine content. This obviates the need to obtain a noncontrast phase in most patients, thus decreasing the radiation dose (Fig. 3.27B) [60]. Dual-energy CT can also be used to remove calcium from atherosclerotic blood vessels or to reduce artifacts of metals in stents and implants [61]. Using the same principle, one can also display iodine content as a pure iodine map, quantifying the exact amount of concentration of iodine in every voxel. Iodine overlay maps that superimpose the colored iodine content on top of grayscale virtual noncontrast images can also be created [59].

A few important applications of dual-energy CT scanners are listed below. Central Nervous System

◾ Calcium removal from carotid arteries in head and neck angiography along with bone removal ◾ Easy identification of intracranial hemorrhage using virtual noncontrast images for those who undergo CT angiography of the head ◾ Bone removal in CT angiography [60]

Cardiovascular System

◾ To assess myocardial viability and myocardial perfusion (Fig. 3.29) ◾ To detect myocardial iron deposition ◾ To evaluate coronary stents ◾ To characterize and remove calcified plaques from peripheral vessels and coronary arteries ◾ To look for aortic endoleaks after treatment [62]

Figure 3.29 (A) The 17-segment model of heart. (B) Good perfusion of the left anterior descending artery territory and right coronary artery territory in red color. B also demonstrates that there is widespread decreased perfusion of left circumflex artery territory, giving green, blue, and yellow colors. Thoracic System

◾ To perform pulmonary perfusion: to accurately diagnose subtle tiny peripheral pulmonary thromboembolism by detecting perfusion deficit and iodine maps To characterize solitary pulmonary nodules: Dual-energy CT quantitatively measures the degree of accumulation of iodine concentration in

◾

the solitary pulmonary nodule, which correlates with the risk of malignancy [63] Gastrointestinal System

◾ CT colonography: Colonic masses and polyps enhance by 40 to 50 HU on postcontrast images; thus, iodine density maps help in distinguishing colonic masses and polyps from stools To detect liver steatosis: The material decomposition technique helps in generating monoenergetic fat-weighted images. Dual-energy CT accurately quantifies the amount of fat deposited in the liver using fat-weighted images To detect iron deposition in the liver To detect gallstones [59]

◾ ◾ ◾

Urinary System

◾ To detect and characterize renal stones: Uric acid stones can be treated with oral medications by dissolving them. Struvite calculi are treated by lithotripsy. Calcium oxalate and cystine stones are resistant to lithotripsy

◾

◾ To characterize renal cysts: Dual-energy CT helps to distinguish hyperdense cysts from enhancing cysts without acquiring noncontrast images [64] Musculoskeletal System

◾ To detect gout and pseudogout crystals and to differentiate the two pathologies (Fig. 3.30) ◾ To reduce artifacts when imaging implants ◾ Dual-energy CT helps in superior differentiation of marrow edema from trabecular bone network, leading to easy detection of fractures and marrow lesions To visualize tendons and ligaments: It is easier to image tendons and ligaments with dual energy than with single-energy CT. The dual-energy CT material decomposition technique is a valuable tool to display tendons and ligaments [65]

◾

Figure 3.30 Volume-rendered image of dualenergy computed tomography of the ankle showing green color crystal posterior to the fibula suggestive of gout.

Figure 3.31 Types of dual-energy computed tomography (CT). (A) Dual-source CT scanner. (B) Single-source CT scanner with rapid kV switching technique. (C) Single-source CT scanner with dual layer detectors. (D) Singlesource CT scanner with a split-filter twin beam.

Photon-Counting Computed Tomography

Photon-counting CT is based on direct conversion technology and converts x-ray photons directly into electronic signals and was launched in end of 2021. Cadmium-based semiconductor material is used in the detectors that precisely measure the number of reaching x-ray photons and calculate the accurate energy of each photon. This mechanism helps in better signal-to-noise ratio, spatial resolution, contrast resolution, and reduced noise. Accuracy is also increased with reduction in CT artifacts by calculating the exact concentration of materials within the voxel (e.g., iodine, calcium). Photoncounting detectors have practically zero electronic noise [66].

Suggested Readings P Allisy-Roberts, J Williams, Farr’s Physics for Medical Imaging, second ed., 2007, 1. TS Curry, JE Dowdey, RC Murry, EE Christensen, Christensen’s Physics of Diagnostic Radiology, fourth ed., Lea & Febiger, Philadelphia, 1990. JT Bushberg, The Essential Physics of Medical Imaging, second ed., Lippincott Williams &

Wilkins, Philadelphia, 2002. N DeMaio Daniel, Mosby’s Exam Review for Computed Tomography, third ed., Elsevier, 2018. R Haaga John, CT and MRI of the Whole Body, fifth ed., 2-Vol. set., 2009.

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4

Principles of MRI Physics Milind D. Dhamankar, John E. Kirsch

Introduction It can be emphatically stated that radiologists have broadened their contribution to patient management due to the versatility and innovations of magnetic resonance imaging (MRI). Advances in imaging technology are expanding the capabilities of MRI to support precision medicine [1]. MRI is a prescription device that is ordered by a physician to get insights into a specific patient condition so that the radiologist can provide actionable steps for the management of the patient. Personalization of the magnetic resonance (MR) exam starts at the time of the first scan. The scanner calibrates to the patient’s physiology and body condition. Better differentiation between normal and abnormal tissues can be achieved with MRI scans of various tissue contrasts. Interrogation and quantification of biochemical composition of tissues is possible with MRI. Insights into functional and pathophysiological mechanisms of the body can be achieved using MRI techniques. Multiparametric MRI [2] imaging is becoming common place where high spatial resolution scans with minimal motion artifacts are acquired along with other scans that provide additional insights about the disease and/or the body. All of this is accomplished in shorter MRI scan times and a more comfortable patient experience. Major developments in MRI scanner hardware, image acquisition software and techniques, computational speed, postprocessing techniques, quantification, and artificial intelligence (AI) algorithms have significantly improved the quality of MR images, the diagnostic value the radiologists can glean from them, and operational workflow [3]. More recently, deep learning algorithms are being deployed to assist radiologists in reporting these increasingly larger and complex datasets.

Fundamentals of MRI

An MR image displayed on a monitor or on a film is a representation of sectional anatomy acquired by a complex cascade of events during an MR examination. Generally, a well-defined MR “protocol” is planned for the examination with respect to slice orientation, tissue contrast, and specific image parameters that need to be acquired for a diagnostic study. After “registering” the patient in the MR system software, the patient is positioned into the MRI scanner (i.e., the magnet) with an appropriate pickup coil (i.e., an antenna) for the anatomy to be examined. The technologist will run a series of MR scans known as “pulse sequences” that transmit radiofrequency (RF) waves into the patient’s body for a short period of time. Simultaneously, the MR system software orchestrates coordination with various MR system hardware components to spatially encode and collect the signal emitted from the patient. This signal is then received by the coil, digitized and stored in a raw data matrix (known as “k space”), and later converted by reconstruction methods to produce an MR image. It is critical for every scan performed that the technologist selects the right scan strategy (correct MR sequence/s and sequence parameters) with respect to three parameters: the total scan time to acquire the desired tissue contrast (time of acquisition, TA), the spatial resolution and the overall signal-to-noise ratio (SNR) including contrast-to-noise ratio (CNR) (Fig. 4.1). These three parameters need to be balanced for every scan to maximize scan efficiency optimizing image quality and diagnostic information. i. TA represents the time to acquire the images of a desired contrast. TA depends on many factors that determine the speed by which the raw data matrix, or k space, gets sampled as well as the size of that matrix ii. Spatial resolution is the ability to distinguish closely spaced structures. Spatial resolution is dependent on matrix size, field-of-view (FOV), and slice thickness iii. SNR is the ratio of wanted/desired signal to background noise. CNR is the difference of SNR between adjacent structures to help differentiate normal from abnormal tissues

Figure 4.1 Three parameters need to be considered for every scan to maximize scan efficiency and diagnostic information: scan time, spatial resolution, and signal-to-noise ratio (SNR). TA, SNR, and resolution depend on many scan parameters that will be discussed later in this chapter. Attention to those dependencies will also help the reader mitigate some image artifacts. Since these factors are all interrelated, the technologist must constantly balance among them by adjusting parameters, personalizing them to the patient’s condition to acquire diagnostic images in a reasonable time while providing the desired diagnostic information that was protocoled.

B0, Magnetization, and RF MRI is based on probing hydrogen protons in the body. The hydrogen nucleus, a single proton, is like a little spinning magnet (Fig. 4.2), performing a precessional motion that resembles the wobbling of a spinning top. When the patient is positioned in the magnet, the protons in the body align themselves either parallel or antiparallel (Fig. 4.3) to the external magnetic field of the magnet known as the static B0 field. There are slightly more protons in the parallel state, collectively leading to a bulk magnetization that initially aligns in the direction of B0 (known as the state of thermal equilibrium). Essentially, the

patient’s body becomes magnetized. This bulk magnetization will ultimately contribute to the MR signal.

Figure 4.2 The hydrogen nucleus, which consists of a single proton, is like a little spinning magnet.

Figure 4.3 In the presence of an external magnetic field, hydrogen protons in the body align themselves either parallel or antiparallel to the field, also referred to as the static B0 field. Because the initial net longitudinal magnetization is parallel to the external magnetic field (conventionally known as the “z” direction), it cannot be detected. However, it spins at a characteristic rate called the Larmor frequency which is directly proportional to the magnetic field strength. The proportionality constant, known as the gyromagnetic ratio, is unique to the nucleus being probed. For hydrogen, it is equal to 42.57 MHz/T. Therefore, at a B0 field strength of 1.5T, the magnetization spins at a frequency of approximately 64 MHz. When RF waves are transmitted into the patient, a temporal magnetic field perpendicular to the z direction, known as B1+, is created (Fig. 4.4). If the frequency of this transmission matches the Larmor frequency of the magnetization (known as the resonance condition), it rotates the net magnetization out of the longitudinal z direction, creating a perpendicular component of magnetization (transverse magnetization) in the x–y plane that rotates at the Larmor frequency. This rotating magnetic field, known as B1−, induces an electric current in an antenna also referred to as an MR receiver coil (Fig. 4.5). This signal is then picked up, digitally sampled, and processed.

Figure 4.4 RF transmission waves create a B1+ field that is perpendicular to the direction of the static B0 field. This then rotates the magnetization out of the direction of B0 by a flip angle theta.

Figure 4.5 When rotated out of the direction of B0, the net magnetization has a longitudinal (z) component and a transverse (xy) component that then can be detected by an MR receiver coil. B1– is related to the transverse component of the magnetization.

T1, T2, and T2* Relaxation The moment the RF pulse is switched off, the magnetization begins to “relax” and starts returning to its original position along the longitudinal z direction of B0. The longitudinal component of the magnetization grows back to its original magnitude at thermal equilibrium. Fig. 4.6 demonstrates the exponential growth of longitudinal magnetization over time. The characteristic time constant that represents the time it takes for the longitudinal magnetization to recover to 63% of its original value is known as T1, the longitudinal (also known as spin-lattice) relaxation time, and has a unique value associated with each type of tissue.

Figure 4.6 Exponential growth of longitudinal magnetization to thermal equilibrium. The rate of growth is determined by the T1 relaxation of the tissue. Simultaneously, the transverse component of magnetization decreases after the RF pulse is switched off because the magnetization loses phase coherence and the protons that comprise the magnetization collectively progress out of phase (known as “spin dephasing”). Fig. 4.7 shows the exponential decay of transverse magnetization over time. The characteristic time constant that represents the time it takes for the transverse magnetization to decay to 37% of its original value is known as T2, the transverse (also known as spin-spin) relaxation time, and has a unique value associated with each type of tissue.

Figure 4.7 Exponential decay of transverse magnetization. The rate of decay is determined by the T2 and T2* relaxation of the tissue. In addition to the irreversible T2 relaxation process, faster decay known as T2* relaxation represents an additional but reversible dephasing process that further reduces T2 (i.e., T2* < T2). This is based on other aspects that can produce spin dephasing, including magnetic susceptibility which is not a part of the T2 process. T1 and T2 relaxation times are unique characteristics of the various tissues in the body (Table 4.1). Water has a relatively long T1 and T2 time, while fat has a relatively short T1 and T2 time. All tissues will have unique combinations of T1, T2, and T2* relaxation, which ultimately produces the exquisite tissue contrast

that is so unique to MRI. These properties are dependent on field strength where T1 tends to increase with B0 while T2 changes to a lesser extent. Table 4.1 Approximate Values of T1 and T2 at 1.5T Tissue T1 T2 (ms) (ms) Water (CSF)

4000

2000

Fat

250

70

Gray matter

900

90

Muscle

900

50

Liver

500

40

The values are “typical.” Numerous papers have been published about T1 and T2, and values vary significantly at times due to methodology and statistics. (Source: http://mriquestions.com.)

Spatial Encoding Spatial encoding of the signal is necessary to produce the image. MRI exploits the fact that the frequency at which the transverse magnetization rotates about the x–y plane is directly proportional to the magnetic field strength according to the Larmor equation. At the main static magnetic field strength (B0) that is spatially uniform and homogeneous there is no distinction in spatial location of the signal that would get detected. However, if a gradient magnetic field (G) is applied, superimposed on the B0 field such that the total magnetic field varies linearly in space, then a one-to-one relation between frequency and space exists (Fig. 4.8). This forms the basis for spatial encoding in MRI.

Figure 4.8 The gradient magnetic field (G). When applied, it creates spatially varying B0 magnetic field that produces a one-to-one relation between the magnetization Larmor frequency and space, and is the basis for spatial encoding of the MRI signal. Since the signal must come from a point within the body, there are three independent G fields representing the three physical directions in space, namely X, Y, and Z axes. During the time when the RF is applied, a G field can selectively “excite” a slice at a physical location in space that rotates the magnetization out of the longitudinal z direction and creates a transverse component in the x–y plane. After this plane of excitation, a G field within that plane can then be applied to uniquely spatially encode the transverse magnetization in one direction also referred to as phase encoding. Finally, at the time the signal is detected, the third G field in the other perpendicular direction in that excited plane would be applied (referred to as frequency encoding) to complete the spatial encoding of that slice. In summary, the complete MRI process involves applying a combination of multiple magnetic fields. A main B0 magnetic field magnetizes the body and creates the initial bulk magnetization. A perpendicular B1+ magnetic field rotates that magnetization, and spatially varying G magnetic fields encode the signal that produces the image from a specific location in physical space. T1 and T2

relaxation are the two primary MRI relevant properties of the tissues. And it is the timing of everything combined that ultimately produces the unique contrast and resolution of the MRI image (Fig. 4.9).

Figure 4.9 Three fundamental types of the tissue contrast in MRI that exploit tissue differences in T1 and T2 relaxation. Axial images of the brain with the tissue contrast of (A) proton density weighting (PDw), (B) T1 weighting (T1w), and (C) T2 weighting (T2w).

MRI Hardware The clinical MRI scanner consists of the following main hardware components (Fig. 4.10B): 1. Magnet and shim coils 2. Gradient system including X, Y, and Z gradient coils, gradient amplifier, and electronics 3. RF system including transmit and receive coils and electronics 4. Host computer, image processor, operator console, display monitor 5. Patient table

Figure 4.10 Typical layout of an MRI system. (A) The suite consists of the exam room, console room, and equipment room. (B) The system consists of the magnet, patient table, gradient coil, transmission coil, receiver coil, and computer for measurement control and image display. A typical layout of an MRI system is shown in Fig. 4.10A. The magnet or gantry is usually housed inside an RF-shielded cabin and is typically called the magnet or examination room because the patient lies on the patient table and is initially positioned in the magnet for the MR examination (Fig. 4.10B). Since the scanner usually operates in the MHz frequency range, the RF shield prevents outside interference from adulterating the MR signal and helps reduce artifacts in the image. It also prevents the emission of RF from the magnet room. A technologist operates the MR scanner from the control room at a computer console. Remaining electronics are typically located in an adjacent equipment room. Workflow of an MRI Examination: An MR image displayed on the console monitor is a representation of anatomy after a series of events. First, the patient is reclined on the patient table and positioned inside the magnet with an appropriate receiver coil (antennae) for the anatomy to be examined (Fig. 4.10A). Second, the operator/technologist plans the exam protocol with different measurements and runs those scans on the patient. For each scan, RF waves are transmitted into the patient. X, Y, and Z direction gradients are switched on and off to spatially localize the signal coming from the patient, which gets picked up by the coil receiver. This is then digitized, stored, and processed to generate images of various anatomical orientations and of different tissue contrasts. Magnets (B0): The main role of the magnet in an MRI scanner is to provide a strong static B0 magnetic field (typically ranging from 0.2 to 3.0 Tesla for clinical systems, with 7 Tesla systems now also introduced in some larger institutions) to essentially magnetize the body and establish the initial MR thermal equilibrium condition. It must therefore be stable over time and spatially uniform (or homogeneous) across a large volume of space so that good image quality can be obtained particularly for techniques that are sensitive to spatial variations in B0, such as spectral fat suppression or spectroscopy. Contemporary actively shielded magnets have counterrunning coil windings surrounding the main field windings

to reduce stray fields thereby producing smaller magnet footprints facilitating more compact installations. There are three types of magnets used for MRI scanners: permanent, resistive, and superconducting. Permanent magnets: Generally, these are used in low-field strength (1 cm) showing APHE without washout or a nodule without definite APHE but with definite washout showing >1 cm of interval growth can be labeled as HCC with features of progression

Table 10.6 mRECIST Response Assessment Criteria Response Criteria Comple te respons e (CR)

■ Disappearance of intralesional enhancing components in all target lesions

Partial respons e (PR)

■ At least 30% decrease in total sum of viable components of all target lesions (measured on arterial phase)

Progres sive disease (PD) Stable disease (SD)

■ At least 20% increase in total sum of viable components of all target lesions (measured on arterial phase) compared with nadir. OR ■ Unequivocal appearance of new HCC foci ■ Not meeting any of the criteria described earlier

FIGURE 10.13 mRECIST and LI-RADS tumor response assessment. (A and B) Response in HCC. There is reduction in longest dimension of enhancing component on post-TACE imaging with increase of necrotic areas. (C and D) Progression in HCC. Appearance of new arterially enhancing foci (arrows) in a patient on sorafenib suggests progressive disease. TACE, trans arterial chemoembolization.

Response Assessment for Bone Lesions Response assessment of bony metastases has always been challenging as bone is a very dynamic organ and skeletal lesions behave differently after treatment and may respond with increased sclerosis rather than a decrease in size. Some tumors may have metastases only to bones with no other sites of metastases (commonly seen with carcinoma breast or carcinoma prostate). RECIST and RECIST 1.1 did not address assessment of skeletal lesions unless there was a soft-tissue component present as well. Hamaoka et al. (MD Anderson Cancer Center) [32] proposed a bone lesion assessment criteria based on the WHO criteria for breast cancer patients, which incorporated all techniques such as radiographs, scintigraphy, CT, PET-CT, and MRI (Table 10.7). Although not commonly used, the principles behind these criteria are very useful in assessing bone lesions in routine clinical practice (Fig. 10.14).

Table 10.7 MD Anderson Response Assessment Criteria for Bone Lesions Response Criteria Complet e response (CR)

■ Complete sclerosis of lytic lesion on radiograph/CT, OR ■ Complete disappearance of “hot spots” on skeletal scintigraphy, OR ■ Complete disappearance of tumor signal on MRI, OR ■ Normalization of bone density on radiograph/CT

Partial response (PR)

■ Appearance of a sclerotic rim or partial sclerosis around lytic lesions on radiograph/CT, OR ■ Sclerosis of previously undetected lesion, OR ■ ≥50% decrease of measurable component on radiograph/CT/MRI (such as extraosseous soft-tissue component), OR ■ ≥50% subjective decrease of tracer uptake on scintigraphy, OR ■ ≥50% decrease in size of osteoblastic lesions on radiograph/CT

Progress ive disease (PD)

■ ≥25% increase of measurable component on radiograph/CT/MRI (such as extraosseous soft-tissue component), OR ■ ≥25% subjective increase of tracer uptake on scintigraphy, OR ■ New bone metastases on scintigraphy/radiograph/CT/MRI

Stable disease (SD)

■ No change is size, number, or morphology of lesions, OR ■ 9% has been used in the literature to indicate the presence of normal thymus or thymic hyperplasia [13,15].

Figure 13.14 In-phase (A) and out-of-phase (B) T1-weighted MRI chest in a 22-year-old male demonstrating significant signal intensity dropout in a pyramidal lesion situated in the upper prevascular mediastinum (asterisk). The signal intensity index equals ~53%, which is greater than the 9% threshold corresponding to the presence of microscopic fat content and indicating the presence of normal thymus or thymic hyperplasia.

It is important to keep in mind that not all thymus glands and thymic hyperplasia suppress on OOP imaging. In cases when normal thymus or thymic hyperplasia is suspected based on morphology, but where there is nonsuppressing tissue on OOP imaging, follow-up MRI

imaging is indicated to document either stability or regression of thymic tissue over time. Thymic Hyperplasia: The thymus gland can enlarge due to several reasons. One of the most common reasons for thymic enlargement is thymic hyperplasia. Thymic hyperplasia is defined by an increase in thymic size past what is expected for a patient’s age and clinical condition [13,14,16]. On pathology, there is an influx of reactive B cells with otherwise normal thymus gland architecture. There are two forms of thymic hyperplasia: true hyperplasia and lymphoid follicular hyperplasia. True hyperplasia can be idiopathic or related to recent physiologic stress, also known as thymic rebound hyperplasia (Fig. 13.15). Rebound hyperplasia can be seen in the setting of systemic infections, chemotherapy, radiotherapy, surgery, burns, and corticosteroid therapy, and is itself of no clinical significance.

Figure 13.15 Axial CT chest pre- (A) and post- (B) bilateral mastectomy and chemoradiation for breast cancer (asterisk). Notice the interval enlargement of the triangular soft-tissue density in the prevascular mediastinum (arrows), corresponding to rebound thymic hyperplasia. There are no unusual heterogeneity or lobulation to the contours to suggest an underlying thymic neoplasm. Thymic lymphoid hyperplasia is characterized on pathology by increased number of germinal centers and is most frequently associated with myasthenia gravis [15]. Thymic lymphoid hyperplasia may also be idiopathic or associated with a variety of autoimmune conditions including systemic lupus erythematosus (SLE), rheumatoid arthritis, polyarthritis nodosa, Hashimoto thyroiditis, Graves disease, and Behcet disease. Thymic lymphoid hyperplasia can also be seen in the setting of HIV infection.

On CT, thymic hyperplasia can appear as an enlarged thickened gland to a degree that is unexpected for the age of the patient. Hyperplastic thymus can also present as a focal mass and can be confused with thymic neoplasms. As with a normal thymus gland, chemical shift MRI can be useful in differentiating thymic hyperplasia from thymic neoplasms by taking advantage of the presence of microscopic fat that is usually seen in hyperplastic thymic tissue and not present in thymic neoplasms. Therefore, both CSR and SII can be used for confirmation of thymic hyperplasia [13,15,16]. The utility of PET is limited since thymic hyperplasia can be PET-positive. True and lymphoid thymic hyperplasias have similar appearances and differentiation usually depends on clinical context and histopathology. Thymic Cyst: Thymic cysts are rare benign cystic lesions, making up only 1–3% of all mediastinal masses. Thymic cysts can be either congenital or acquired [17–19]. Congenital thymic cysts are derived from a patent thyropharyngeal duct, whereas acquired thymic cysts can occur secondary to thoracic surgery, after chemoradiotherapy, or associated with inflammatory conditions such as myasthenia gravis, SLE, aplastic anemia, and Sjogren

syndrome. Congenital cysts are usually unilocular thinwalled simple cysts containing low-attenuation fluid (0– 20 HU). There is usually no evidence of associated inflammation or complication. In contrast, acquired cysts can be multilocular with varying degree of wall thickness and often demonstrate pathologic evidence of inflammation. Radiographically, thymic cysts appear as a circumscribed mass in the anterior mediastinum [13,17– 19]. On CT, a congenital thymic cyst will usually appear as a well-circumscribed round or oval water-attenuation lesion with a thin barely perceptible wall (Fig. 13.16). On MRI, congenital thymic cysts will usually be homogeneously T1 hypointense and T2 hyperintense, with no internal contrast enhancement. Acquired cysts will be more often multiloculated and complicated by hemorrhage or infection, which appears as higher attenuation on CT with or without calcification in its wall. Complicated cysts on MRI can appear as highsignal intensity on both T1- and T2-weighted images related to hemorrhage or proteinaceous fluid, with varying degrees of peripheral wall enhancement related to inflammation.

Figure 13.16 Example of a simple thymic cyst. Axial CT chest (A) demonstrating a wellcircumscribed fluid-attenuation lesion in the prevascular mediastinum. Corresponding T2weighted MRI chest (B) of the lesion demonstrates homogeneousT2 hyperintense signal intensity with a thin imperceptible peripheral wall. Corresponding fat-saturated T1-weighted MRI chest pre- (C) and post- (D) gadolinium injection demonstrate no significant enhancement within the lesion or the peripheral wall. Thymolipoma: Thymolipomas are rare circumscribed fat-containing lesions composed of mature adipose tissue and normal thymic gland architecture [20]. Thymolipomas are benign, usually found in early adulthood (ages 20–30), and are associated with autoimmune conditions including myasthenia gravis, aplastic anemia,

hypogammaglobulinemia, and Graves disease. Thymolipomas can be differentiated from simple lipomas by the presence of thymic tissue and, unlike atrophic thymic glands, are encapsulated and massforming. Thymolipomas present usually as large anterior mediastinal masses. Due to their fatty composition, they often conform or mold to adjacent organs and can extend into the cardiophrenic angles. On frontal radiographs, they simulate cardiomegaly extend to the hemidiaphragm. Large thymolipomas can also mold to the adjacent mediastinal structures and diaphragm, simulating diaphragmatic elevation or lobar collapse on chest radiograph. CT and MRI imaging usually demonstrates a mixed attenuation lesion with both macroscopic fat component and soft-tissue thymic component (Fig. 13.17).

Figure 13.17 Example of a biopsy-proved thymolipoma. Note the mixed attenuation ovoid lesion in the prevascular mediastinum with clear macroscopic fat component interspersed by softtissue thymic component. Thymic Epithelial Neoplasms: Thymic epithelial tumors encompass a histopathologic continuum ranging from thymomas and thymic carcinomas [19,21–24]. The histopathologic classification as defined by the World Health Organization is based on distinct pathologic features, degree of invasiveness, and clinical prognosis (Table

13.3). Thymomas are classified based on the degree of epithelial cell atypia, relative proportion of tumoral lymphocyte, and distortion from normal thymic anatomy. Thymomas can be histologically heterogeneous and a tumor can be composed of different types of thymomas, which can lead to undersampling with percutaneous biopsies. The Masaoka–Koga staging system, based on surgical findings, is often used to predict prognosis and dictate the treatment approach (Table 13.4). Table 13.3 World Health Organization Histopathological Classification of Thymic Epithelial Tumors Tenyear Invasivenes Disease Type Pathological Features s (%) -free Surviva l (%)

Tenyear Invasivenes Disease Type Pathological Features s (%) -free Surviva l (%) Type A 10–40 100 Spindle or thymom polygonal cell a without atypia

◾

◾ Paucity of immature thymocytes ◾ Contains both type A (lymphocyte-

Type AB thymom poor) and type B a (lymphocyte-rich) cells

30–40

100

Type Thymoma B1 resembling cortical thymom thymus a

45–50

100

◾

Tenyear Invasivenes Disease Type Pathological Features s (%) -free Surviva l (%) Type Increasing 65–70 85 B2 epithelial/lymphocyte thymom ratio and atypia a

◾ ◾

Type 85–90 Increasing B3 thymom epithelial/lymphocyte ratio and atypia a

◾ Mature lymphocytes

35

Tenyear Invasivenes Disease Type Pathological Features s (%) -free Surviva l (%) Thymic 90–95 15 Epithelial cell carcino atypia and infiltration ma

◾ ◾ Absence of immature lymphocytes

◾ CD5/KIT expression Table 13.4 Masaoka–Koga International Thymic Malignancy Interest Group Staging System for Thymoma Stag Findings e 1 Completely encapsulated 2

◾ ◾Invasion of tumor capsule

Stag e 3 4A 4B

Findings

◾Invasion of neighboring organs ◾Pleural or pericardial implants ◾ Distant (extrathoracic) hematogenous or lymphogenous metastasis

Thymomas are the most common primary neoplasms of the anterior mediastinum, with the majority arising from the upper anterior mediastinum near the ascending aorta and pulmonary artery. They are typically seen in adulthood and are rarely found in children. Although often asymptomatic, thymomas can be associated with myasthenia gravis, hypogammaglobulinemia, and aplastic anemia. About 25–50% of patients with thymoma have myasthenia gravis while 10–25% of patients with myasthenia have a thymoma. Many thymomas can be seen on chest radiograph, usually manifesting as a lobulated or ovoid circumscribed mass projecting unilaterally in the mediastinum [21,22]. However, depending on the size and location of the tumor, chest radiographs can also be normal or have very subtle distortions of the anterior junction line. Thickening of the anterior junction line usually indicates the presence of an anterior mediastinal

mass. The lateral radiograph can also help detect the presence of thymomas in the retrosternal space. CT imaging has increased sensitivity for detecting thymomas and help assess local invasion and aid surgical planning [19,21,22,24]. Thymomas usually appear as well-defined round or oval soft-tissue density masses on CT, usually projecting on one side of the anterior mediastinum (Fig. 13.18). Thymomas may contain curvilinear or nodular calcification and are usually homogeneous, enhancing with intravenous contrast. Nonetheless, some thymomas can present as more heterogeneous masses with cystic, necrotic, and hemorrhagic areas. Heterogeneity of tumors is associated with higher tumor grade and is often seen in thymic carcinomas, but this feature alone is not specific for a degree of invasiveness, as low-grade tumors may also demonstrate heterogeneity. Intravenous contrast is useful in delineating vascular encasement and invasion of neighboring organs. CT is also helpful in detecting the presence of intra- and extrathoracic metastasis, which if found, will upstage a patient and change management. Unlike lung cancer, thymomas rarely present with lymphadenopathy, pleural effusion, and pulmonary metastases. In contrast, thymic carcinomas will exhibit more aggressive behavior and can often present with both intra- and extrathoracic metastases

(Fig. 13.19). Common areas for intrathoracic metastatic involvement in thymic carcinomas include pleural drop metastasis and invasion of contiguous mediastinal structures such as pericardium and great vessels.

Figure 13.18 Biopsy-proved AB-type thymoma. Enhanced CT chest in axial (A) and sagittal (B) views demonstrating a round prevascular mass with mildly heterogeneous attenuation adjacent to the pericardium. No local metastases at the time of the scan.

Figure 13.19 Biopsy-proved high-grade thymic carcinoma. Enhanced axial CT chest (A) demonstrating an irregular heterogeneous mass in the prevascular mediastinum. Accompanying 18FFDG PET at the same level (B) shows peripheral intense radiotracer uptake within the mass, which has a central necrotic core. At the level of the upper abdomen (C), there are several areas of intense radiotracer uptake, concerning distant metastases. On MRI, thymomas are nonspecific and can have intermediate T1 signal and hyperintense T2 signal (Fig. 13.20). Unlike thymic hyperplasia, thymomas will not demonstrate evidence of microscopic fat on OOP images. Dynamic enhancement MRI cannot accurately differentiate a thymoma from other anterior mediastinal masses including thymic carcinoma, lymphoma, or germ cell tumors. Furthermore, heterogeneity by itself is not an accurate assessment of the invasiveness of thymoma. MRI can help differentiate a proteinaceous and hemorrhagic thymic cyst from a solid mass.

Figure 13.20 Biopsy-proved AB-type thymoma. Fat-saturated T1-weighted MRI chest pre- (A), 1 minute (B), and 5 minutes (C) postgadolinium injection demonstrating asymmetric nodular enhancement. Germ Cell Tumors Germ cell tumors in the anterior mediastinum derive from primordial germ cell rests left behind during their embryological migration to the urogenital ridge [17,18,25]. Germ cell tumors are usually found along the median line of the body and the anterior mediastinum is the most common location for extragonadal germ cell tumors. Other common areas where germ cell tumors can be found include the pineal gland, the sacrum/coccyx, and the neurohypophysis. Most germ cell tumors, including dermoid cysts or mature teratomas, are benign. However, as many as 30% of

germ cell tumors are malignant and include entities such as seminoma, choriocarcinoma, yolk sac tumors, and embryonal cell carcinoma. The World Health Organization classifies germ cell tumors into either seminomas or nonseminomatous tumors. Nonseminomatous germ cell tumors include teratomas, embryonal carcinoma, yolk sac carcinoma, and choriocarcinoma. Mixed tumors have features of more than one histologic subtype. Germ cell tumors are classically discovered incidentally on chest radiograph and usually seen in young male adults. Although many tumors are asymptomatic, some can produce cough, chest pain, and dyspnea. Teratomas are tumors containing elements of all three germ cell layers including the ectoderm, mesoderm, and ectoderm [17,18,25]. Teratomas can be either mature or immature and are the most common mediastinal germ cell tumors. Mature teratomas are benign, wellcircumscribed, predominantly cystic masses. The majority of mature teratomas contain sebaceous fat. Calcification is another characteristic of mature teratomas, seen in about half of mature teratomas. Mature teratomas contain solid components of different histologic elements called Rokitansky protuberances. Diagnosis can be confirmed by CT or MRI by the presence of a cystic mass containing macroscopic fat,

calcification, and soft-tissue components (Fig. 13.21). MRI is particularly useful in delineating the presence of fat, which is hyperintense on T1-weighted images and creates a chemical shift between cystic and fatty components of the tumor. Fat-fluid levels can be delineated within mature teratomas and is a specific feature for mature teratomas. Rokitansky protuberances can also sometimes be seen on MRI, manifesting as layering palm tree-like protrusions.

Figure 13.21 Surgically removed mediastinal mature teratoma. Enhanced CT chest in coronal (A) and axial (B) views demonstrating a welldelineated predominantly cystic mass in the prevascular mediastinum with internal soft-tissue attenuation septations of varying thickness and high-attenuation foci of calcification (arrows).

In comparison, immature teratomas are predominantly solid tumors containing immature neural elements. Whereas mature teratomas are benign and are surgically curative, immature teratomas can recur and have malignant potential. Distinguishing immature from mature teratomas can be difficult on imaging, as immature teratomas can also contain fat and calcification. The presence of significant solid components can suggest immature teratoma, although mature teratomas can contain solid components as well. Increased serum alpha-fetoprotein levels are also more associated with immature teratomas. Unlike teratomas, malignant germ cell tumors including seminomas and nonseminomatous tumors do not contain macroscopic fat [17,18,25]. Seminomas usually present as lobulated well-circumscribed homogeneous masses on CT and MR images. A minority of mediastinal seminomas demonstrate high levels of B-human chorionic gonadotropin. On MRI, seminomas can demonstrate T2-hypointense fibrovascular septa, and calcification or cystic components are rare. In contrast, nonseminomatous germ cell tumors, such as yolk sac tumors or choriocarcinomas, are usually more heterogeneous with more frequently seen internal necrosis or hemorrhage. Other features of malignancy

can be seen including lymphadenopathy and metastatic disease. Lymphangioma Lymphangiomas are rare and benign fluid-filled congenital malformations related to the failure of communication between the lymphatic system with the venous system during embryological development [17,18,26]. The classification of lymphangiomas is based upon the size of lymphatic channels. Small lymphatic channel lesions are termed simple-capillary malformations, cavernous malformations have dilated lymphatic channels, and cystic lymphangiomas (otherwise known as cystic hygromas) demonstrate the presence of cystic lymphatic collections. Lymphangiomas are primarily seen in children under the age of 2 years and are usually found in the cervical and axillary regions, with or without mediastinal extension. Less than 1% of lymphangiomas are found isolated in the mediastinum and these are often discovered incidentally on chest radiographs in children. Lymphangiomas are not confined to the anterior mediastinum and can be found in the posterior mediastinum as well. Large mediastinal lymphangiomas can cause symptoms based on the mass effect on

adjacent anatomy. Lymphangiomas can be complicated by hemorrhage, infection, and rupture with chylothorax or chylopericardium. Lymphangiomas are well-defined lobulated masses on chest radiographs with distortion of normal radiographic anatomy and are sometimes associated with chylous pleural effusions [17,18,26]. On CT, lymphangiomas appear as thin-walled cystic lobulated masses of varying size, with low-attenuation fluid (0–20 HU) and thin internal septae (Fig. 13.22). These features can also be well seen on MRI, where lymphangiomas demonstrate high T2 signal intensity in keeping with cystic fluid content. It is uncommon for lymphangiomas to calcify and there is usually no enhancing component. Large lymphangiomas tend to conform or mold around adjacent structures such as the heart and trachea. If complicated by hemorrhage, the internal fluid will demonstrate higher density on CT and can be difficult to distinguish from solid masses. In cases when lesions are equivocal on CT, dynamic-enhanced MRI with subtraction is useful to confirm the presence of hemorrhage or proteinaceous fluid (variable T1weighted signal), without internal enhancing solid component.

Figure 13.22 Surgically removed mediastinal lymphangioma. Enhanced axial CT chest (A) demonstrating a well-defined lobulated lowattenuation mass invaginating around the heart. On the corresponding T2-weighted MRI chest (B), the mass is uniformly hyperintense with thin internal septae. Pleuropericardial Cyst Pleuropericardial cysts are benign congenital thin-walled mesothelial cysts containing simple fluid [17,18]. They are usually seen in the anterior mediastinum at the right cardiophrenic angle, although a minority can also be found in the left anterior cardiophrenic angle or middle mediastinum. Most patients are asymptomatic, and they are often discovered incidentally on chest radiographs in

adult patients. They are usually seen as a wellcircumscribed, oval, or round mass, which can deform and change shape during the respiratory cycle (Fig. 13.23). The presence of low-attenuation fluid on CT (0– 20 HU) or high-signal intensity of T2-weighted MRI is usually confirmatory of the diagnosis.

Figure 13.23 Axial-unenhanced CT chest demonstrating a round circumscribed lowattenuation cystic lesion adjacent to the right pericardium with thin imperceptible wall, likely a small pericardial cyst. Lipomatous Lesions

Lipoma: Lipomas are rare mesenchymal tumors, which usually occur in the anterior mediastinum adjacent to the diaphragm [27,28]. Lipomas can also be found in other mediastinal compartments. Histologically, lipomas are composed of mature adipocytes that resemble normal fat. Most lipomas are encapsulated. They are considered benign tumors, although there are extremely rare reports of malignant degeneration in the literature. Radiographically, lipomas are usually found incidentally as a mass in the anterior mediastinum. CT imaging (Fig. 13.24) demonstrates a characteristic well-defined round or oval mass with homogeneous fat attenuation (−50 to −130 HU), no soft-tissue nodularity, and no internal contrast enhancement, although thin (2 mm), nonlipomatous soft-tissue components, and marked septal enhancement.

Figure 13.25 Example of a de-differentiated liposarcoma in a 45-year-old female. Frontal chest radiograph (A) and corresponding coronalenhanced CT chest (B) demonstrating a bulky and heterogeneous mediastinal mass exerting mass effect on the adjacent structures. Multiple lymphadenopathies (arrows) are noted in the AP window, right axilla, and lower neck in keeping with nodal metastases. Epipericardial Fat Necrosis:

Epipericardial fat necrosis is an underrecognized and uncommon benign, self-limited condition, which usually presents as an acute pleuritic chest pain in otherwise healthy individuals [29]. Given the symptoms, it is often confused with acute myocardial infarction, pericarditis, or pulmonary embolism and is usually discovered incidentally on CT imaging. Epipericardial fat necrosis is characterized by focal inflammation and necrosis of the epipericardial fat, which connects the pericardium to the anterior chest wall. The condition is idiopathic and analogous to epiploic appendagitis seen in the abdomen. Radiographically, the findings are nonspecific, sometimes normal, and other times demonstrating an illdefined opacity near the cardiophrenic angle, with or without unilateral pleural effusion. CT demonstrates accurately the presence of a round, encapsulated fatty lesion with surrounding fat stranding in the anterior mediastinum with thickening of the adjacent pericardium and pleural effusions in many cases (Fig. 13.26). Given this condition is self-limited, treatment is conservative and entails usually symptomatic relief with nonsteroidal anti-inflammatory drugs.

Figure 13.26 Example of epipericardial fat necrosis in a 38-year-old previously healthy male presenting with acute chest pain. Note the round, encapsulated fatty lesion in the prevascular mediastinum with surrounding fat stranding (arrow) and the unilateral left pleural effusion (asterisk). The patient was treated conservatively with NSAIDs and recovered with no complication. Pericardial/Epicardial Fat Pad: Prominent pericardial fat pad is an incidental finding commonly seen at the cardiophrenic angles on chest radiographs, related to fat deposition in between the parietal pericardium and parietal pleura [30]. Enlargement of pericardial fat pads can be seen in

normal individuals, as well as in obesity, Cushing’s syndrome, and chronic steroid use. Radiographically, it can often be mistaken for an anterior mediastinal mass or focal pneumonia, although they are usually more radiographically lucent than real masses (Fig. 13.27). Pericardial fat pads can easily be distinguished on CT and MRI as nonencapsulated fat deposition in the anterior mediastinum adjacent to the heart and hemidiaphragm. Serial follow-up radiographs will demonstrate stability over time, providing evidence for the presence of a benign pericardial fat pad.

Figure 13.27 Example of prominent pericardial fat pads on frontal chest radiograph. Note the smooth contours and relative lucency of the opacities noted at the bilateral cardiophrenic angles.

Mediastinal Lipomatosis: Mediastinal lipomatosis involves excessive accumulation of fatty tissue within the mediastinum [28]. It is usually seen in the setting of obesity or exogenous steroid use. High levels of endogenous steroids such as in Cushing syndrome can also lead to increased fat deposition in the mediastinum. Importantly, lipomatosis involves the deposition of unencapsulated fat, which symmetrically accumulates in the upper anterior compartment and may simulate a mass on the radiograph (Fig. 13.28). CT imaging and MRI will demonstrate increased fat deposition around normal anatomic structures without evidence of compression or invasion. Unlike lipomatous tumors, no capsule, internal septation, soft-tissue component, or contrast enhancement is noted.

Figure 13.28 Example of mediastinal lipomatosis. Frontal chest radiograph (A) demonstrating relatively symmetric and smooth widening of the upper mediastinum. Corresponding unenhanced axial CT chest (B) revealing increased unencapsulated fat attenuation throughout the upper mediastinum. Herniation Omental herniation into the anterior mediastinum can occur through the Morgagni foramen or through an acquired postsurgical or post-traumatic defect [31]. The foramen of Morgagni is a persistent developmental defect in the anterior diaphragm. Omental herniation is usually discovered incidentally as a mass in the anterior mediastinum on a chest radiograph. In rare cases, symptoms can occur related to the infarction of herniated fat, compression of the lungs, and intestinal obstruction/strangulation. Radiographically, most Morgagni hernias are usually located in the right anterior cardiophrenic angle. Larger hernias can contain gasfilled loops of bowel (Fig. 13.29). The diagnosis can be confirmed on CT and MRI by demonstrating the presence of omental fat, colon, and other upper

abdominal organs herniating through an anterior diaphragmatic defect.

Figure 13.29 Example of a Morgagni hernia. Lateral chest radiograph (A) and corresponding enhanced coronal CT chest (B) demonstrating a focal defect in the anterior mediastinum with herniation of air-filled bowel loops in the thoracic cavity.

Middle Mediastinum Congenital Mediastinal Cysts Congenital cysts arising from the middle mediastinum encompasses foregut duplication cysts comprising of

bronchogenic and esophageal duplication cysts [17,18]. Bronchogenic cysts derive from abnormal budding of the tracheobronchial tree during embryological development and are lined by respiratory ciliated pseudostratified columnar epithelial cells. They may contain clear serous fluid or thick mucoid material. Bronchogenic cysts are uncommonly associated with other congenital pulmonary malformations such as lobar emphysema or sequestration. Bronchogenic cysts can be complicated by hemorrhage or infection and expand rapidly in size. However, most bronchogenic cysts are asymptomatic, producing occasional symptoms from compression of adjacent structures. Radiographically, bronchogenic cysts appear usually as a well-defined solitary mass located inferior and on either side of the carina. On CT, they appear usually as nonenhancing, unilocular cystic lesions with thin imperceptible walls and homogeneous internal attenuation ranging from simple fluid (0–20 HU) to as high as 100 HU in a setting of hemorrhage or proteinaceous fluid (Fig. 13.30). T2weighted MRI will demonstrate high signal with variable T1-weighted signal related to internal fluid content and without enhancement after IV gadolinium.

Figure 13.30 Examples of bronchogenic cysts. Enhanced axial CT chest (A) demonstrates a simple bronchogenic cyst arising in the paratracheal region with a thin imperceptible wall and homogeneous internal fluid attenuation. In contrast, an unenhanced axial CT chest (B) in a separate patient demonstrates a complicated bronchogenic cyst arising inferior to the carina with a clear fluid–fluid level within the cyst, corresponding to hemorrhagic material. Note the walls of the cyst are thicker and more ill-defined secondary to inflammatory changes. Esophageal duplication cysts are uncommon developmental foregut cysts that are most commonly found in infants and children [17,18]. As with bronchogenic cysts, they may also hemorrhage or become superinfected. Their imaging appearance is

usually undiscernible from bronchogenic cysts, although some may demonstrate a thicker wall related to underlying mural smooth muscle. Unlike bronchogenic cysts, esophageal duplication cysts will occur along the esophagus (Fig. 13.31). Tc-99m sodium pertechnetate scan can be useful in highlighting the presence of ectopic gastric mucosa, which is present in up to 50% of thoracic duplication cysts.

Figure 13.31 Esophageal duplication cyst. (A) Barium swallow showing smooth indentation and narrowing of esophagus. (B) Contrast CT image shows well circumscribed simple cystic lesion adjacent to the esophagus with a thin imperceptible wall. Mediastinal Lymphadenopathy

Lymphadenopathy can be found in all compartments of the mediastinum but is most often occur in the middle compartment along the paratracheal, subcarinal, and hilar stations [2,5,33]. The differential diagnosis of mediastinal lymphadenopathy is vast, and includes metastatic disease, lymphoma, sarcoidosis, silicosis, and tuberculosis. Reactive lymphadenopathy can be seen in a wide range of infections and inflammatory conditions. Fungal infections such as histoplasmosis, coccidioidomycosis, actinomycosis, and blastomycosis can produce isolated hilar and paratracheal lymphadenopathy without pulmonary involvement. Reactive lymphadenopathy can also be seen in the setting of congestive heart failure and cystic fibrosis. On chest radiograph, mediastinal lymphadenopathy can appear as widening of the right paratracheal stripe, lateral displacement of the azygoesophageal recess, irregular widening of the mediastinal, lobulated mass in the hilar region, and as a mass in the aortopulmonary window (Fig. 13.32). Calcified lymphadenopathy can be noted as increased radiodensity on chest radiographs and can be noted in many different conditions (Table 13.5) [32]. Peripheral calcification, also known as eggshell calcification, can be seen in sarcoidosis, silicosis, amyloidosis, treated lymphoma, scleroderma, coal

worker’s pneumoconiosis, and histoplasmosis (Fig. 13.33).

Figure 13.32 Examples of sarcoidosis in a 28-yearold female. Frontal chest radiograph (A) demonstrates bilateral perihilar and paratracheal opacities corresponding to extensive bilateral hilar (white arrows) and mediastinal lymphadenopathy on coronal-enhanced CT chest (B). Note the relative symmetric distribution of the lymphadenopathy. Table 13.5 Causes of Calcified Lymphadenopathy Tuberculosis Sarcoidosis Silicosis and other pneumoconiosis

Histoplasmosis Postradiation lymphoma Metastasis: mucin-secreting adenocarcinoma; papillary and medullary thyroid carcinoma; osteogenic sarcoma Scleroderma Amyloidosis Castleman’s disease

Figure 13.33 Examples of calcified lymphadenopathy on frontal chest radiograph (A) and unenhanced axial CT chest (B) related to previous histoplasmosis exposure. Note the radiodense opacity at the right hilar station (arrows) and additional calcified subcarinal lymph node.

Diagnosis of mediastinal lymphadenopathy is easily confirmed on CT imaging, which demonstrates the presence of multiple soft-tissue masses in the mediastinum [33]. In general, 10-mm short-axis diameter is considered the upper limit of normal on CT. Unlike normal lymph nodes, abnormal lymphadenopathy will usually be round or irregular in shape and not demonstrate a fatty hilum (Fig. 13.34). On MRI, lymphadenopathy is usually seen as intermediate signal intensity on T1-weighted imaging with variable enhancement and usually missing normal fatty hilum.

Figure 13.34 Examples of malignant lymphadenopathy. Enhanced axial CT chest (A) in a 78-year-old male with B-cell lymphoma and diffuse mediastinal lymphadenopathy. Enhanced axial CT chest (B) in a 67-year-old male with

primary lung adenocarcinoma and extensive mediastinal and hilar lymphadenopathy. Lymphadenopathy can be necrotic or cystic, which manifests as low internal attenuation on CT and high T2-weighted signal on MRI. Low-attenuation lymphadenopathy can be seen in a variety of conditions including tuberculosis, nontuberculous mycobacterial infection, histoplasmosis, treated lymphoma, Whipple disease, and metastases including testicular cancer and squamous cell carcinoma. Castleman’s disease is an idiopathic benign lymphoproliferative condition characterized by avidly enhancing mediastinal lymphadenopathy on CT and MRI (Fig. 13.35). Other causes for hypervascular lymphadenopathy include metastasis from hypervascular tumors such as renal cell carcinoma, melanoma, Kaposi sarcoma, and thyroid carcinoma.

Figure 13.35 Example of biopsy-proved Castleman’s disease in a 57-year-old female.

Frontal chest radiograph (A) demonstrates a welldefined ovoid opacity in the AP window. Corresponding axial T1-weighted unenhanced MRI chest (B) and postgadolinium T1-weighted subtraction image (C) demonstrates intensely avid enhancement of the large conglomerate lymphadenopathy. Esophageal Pathologies Esophagitis: Inflammation of the esophagus can occur from a range of infectious (HIV, CMV, Candida, Herpes) and noninfectious causes (gastroesophageal reflux, caustic ingestion, medication-induced, radiation-induced) [34,35]. Double-contrast esophagography and endoscopy are the primary diagnostic techniques for evaluating the esophagus. On CT imaging and MRI esophagitis usually manifests as focal or segmental circumferential wall thickening and mural enhancement and edema. Esophagitis can also appear as a target sign on CT, which is caused by a combination of mucosal enhancement and edematous hypodense submucosa. Nonetheless, cross-sectional imaging is limited by

underdistension of the esophagus, which can mimic wall thickening and a lack of specificity. Esophageal Dysmotility: Esophageal dysmotility encompasses a wide range of pathologies, which involve the disruption of normal movement of the esophagus in transporting food from the oropharynx to the stomach [35]. Achalasia a primary form of esophageal dysmotility defined by the failure of organized peristalsis caused by impaired relaxation of the lower esophageal sphincter. Radiographically, achalasia (Fig. 13.36) can be seen as a convex opacity overlapping the right mediastinum indicating the presence of dilated esophagus. The presence of an air– fluid level in the esophagus due to stasis is suggestive of achalasia. A dilated thin-walled esophagus filled with fluid and debris can be seen on CT and MRI. In all cases of esophageal dilation, it is important to exclude secondary achalasia caused by an obstructing esophageal or gastric tumor.

Figure 13.36 Achalasia cardia. (A) PA chest radiograph shows double density shadow (thin arrows) with normal appearing outer cardiac shadow. Splenic flexure shadow (thick arrow) is visualized in left subdiaphragmatic region with the absence of normal gastric fundal shadow. (B) Barium swallow shows the inner density to be dilated esophagus which is abruptly narrowed at the gastroesophageal junction (arrow). A fixed or irreducible hiatus hernia is one of the commonest causes of a mediastinal abnormality and is usually seen as an incidental posterior mediastinal mass on a chest radiograph in an elderly patient. The hernia is often asymptomatic, but can produce dyspnea,

retrosternal chest pain, epigastric discomfort, and iron deficiency anemia. Incarceration of the stomach is uncommon. A hiatus hernia appears as a round soft-tissue mass often containing either gas or an air–fluid level behind the heart, and usually lies to the left of the midline in the posterior mediastinum (Fig. 13.37). The larger hernias can also contain small intestine, colon, and liver.

Figure 13.37 Hiatus hernia. PA chest radiograph shows round soft-tissue mass (thin arrows) with air–fluid level (arrow head). The diagnosis is readily confirmed by a lateral film, or a barium meal, which shows the stomach above the diaphragm. The diagnosis is also often confirmed by CT

which shows the stomach above the diaphragm with surrounding fatty tissue. Esophageal Malignancy: Esophageal cancer is usually associated with alcohol and tobacco abuse [36]. Other risk factors for esophageal carcinoma include chronic gastroesophageal reflux disease, achalasia, and celiac disease. Patients with esophageal malignancies often present with dysphagia, which is seen in the setting of advanced cancers [36]. Double-contrast barium studies and upper endoscopy are usually performed to assess for dysphagia and make the diagnosis of primary esophageal malignancy. On CT and MRI, esophageal malignancies are seen as irregular asymmetric wall thickening and/or soft-tissue masses extending past the margins of the normal esophagus (Fig. 13.38). Interpretation on crosssectional imaging can be difficult, owing to the underdistension of the esophagus, which may mimic wall thickening. The primary use of cross-sectional imaging is for accurate staging of disease, including regional and distant metastases. CT and MRI imaging cannot reliably delineate the involvement of the individual layers of the esophageal wall. However, CT

and MRI are useful for assessing for invasion into the adjacent periesophageal fat and mediastinum as well as lymphadenopathy.

Figure 13.38 Example of biopsy-proved esophageal carcinoma in the mid esophagus in a 62-year-old male on axial (A) and coronal (B) enhanced CT chest. Note the irregular heterogeneous mass bulging antidependently into a distended esophagus. The proximal esophagus is significantly dilated. Fibrosing Mediastinitis Fibrosing mediastinitis is a rare and benign condition characterized by the proliferation of fibrotic tissue in the mediastinum [37]. Fibrosing mediastinitis can be focal or diffuse. The focal form of the disease is the most

common and often associated with granulomatous infections such as histoplasmosis and tuberculosis. Diffuse fibrosing mediastinitis can be idiopathic or associated with autoimmune diseases such as sarcoidosis, SLE, rheumatoid arthritis, IgG-4-related diseases, and Behcet’s disease. Diffuse nongranulomatous fibrosing mediastinitis can also be seen after radiation therapy or as a complication of methysergide treatment. Radiographically, fibrosing mediastinitis will present as abnormal widening of the mediastinum [37]. The presence of calcification can be observed. Due to fibrosis and compression of bronchovascular structures, there can often be findings of secondary volume loss and venous congestion. On CT and MRI, an irregular infiltrating soft-tissue mass can often be seen in focal granulomatous fibrosing mediastinitis, often with calcifications (Fig. 13.39). In the nongranulomatous diffuse variant of the disease, there is a more widespread extent of the infiltrative soft tissue throughout the mediastinum (Fig. 13.40). In both variants, there is often compression, encasement, and sometimes obliteration of the mediastinal and hilar bronchovascular structures. Positron emission tomography (PET)/CT is not a reliable technique for assessing fibrosing mediastinitis, which can demonstrate variable FDG avidity.

Figure 13.39 Example of focal fibrosing mediastinitis on enhanced axial (A) and coronal CT chest in soft-tissue (B) and lung (C) windows. Note the irregular soft-tissue mass infiltrating the left hilum, which is narrowing the left-sided bronchovasculature with significant linear scarring and volume in the left lower lung. Multiple highattenuation calcifications are noted throughout (arrows).

Figure 13.40 Example of diffuse fibrosing mediastinitis on enhanced coronal CT chest in softtissue (A) and bone (B) windows. Note the irregular soft-tissue attenuation infiltrating the entire mediastinum and bilateral hilum. Due to the fibrotic encasement and narrowing of the segmental pulmonary arteries, vascular stents were placed to keep the vasculature open (arrows). A right pleural effusion is also noted, likely related to congestion on the pulmonary venous blood return. Acute Mediastinitis Acute mediastinitis results from infection of the mediastinum and can be devastating for patients with high morbidity and mortality [38,39]. They can happen spontaneously or be associated with other infections such as pharyngitis, pneumonia, epiglottis, or bronchitis. Primary cases of acute mediastinitis are rare and the vast majority of acute mediastinitis arise secondarily from head and neck infections, iatrogenic procedures, esophageal perforations, or postoperatively. Classically, infection within the head and neck can move through the prevascular space or can break through the alar fascia and enter the retrovisceral space (also known as the danger space) to reach the mediastinum. Clinically,

patients with acute mediastinitis are septic and will present with dyspnea, pain, high-grade fevers, and leukocytosis. Radiographically, acute mediastinitis can demonstrate widening and poor definition of the superior mediastinal borders [38,39]. In advanced cases, pneumomediastinum and subcutaneous air within the soft tissues of the neck can sometimes be seen. Nonetheless, CT imaging is recommended technique for assessing acute mediastinitis owing to its superior spatial resolution and ability to detect the presence of a mediastinal abscess (Fig. 13.41). On CT, it is common to find inflammatory fat stranding, loculated fluid collections or abscesses, pneumomediastinum, as well as pleural effusions and/or empyema. In the event of an esophageal perforation, a large perforation can often be identified. In the postoperative period, CT imaging is also helpful for assessing postoperative changes, hematoma formation, and sternal dehiscence. Percutaneous aspiration or drainages can also be done under CT guidance.

Figure 13.41 Example of acute mediastinitis and mediastinal abscess formation (arrow) on axialenhanced CT chest in a patient status—after median sternotomy. The abscess is extending from the site of sternal dehiscence to the anterior mediastinum. Note the small locule of free air within the abscess and the surrounding fat stranding. Vascular Anomalies Vascular disease is common in mediastinum and includes arterial and venous causes. Common arterial

causes are thoracic aorta aneurysm, aortic dissection, tortuous innominate artery, dilatation of the main pulmonary artery, and coarctation of aorta. The mediastinal venous abnormalities include dilated superior vena cava, persistent left-sided superior vena cava, superior vena cava obstruction, and dilated azygos vein. Tracheal Pathology Lesions in the trachea usually present with either cough or dyspnea due to recurrent chest infections or stridor in children and adult patients. Tracheal lesions can produce narrowing or widening of the trachea or a mass within its lumen on the chest radiograph. Malignant tracheal tumors such as squamous cell carcinoma and adenoid cystic carcinoma or cylindroma, benign tracheal tumors such as hamartoma and chondroma, and other lesions such as tracheobronchial papillomatosis and amyloidosis can produce a soft-tissue mass in the trachea. Widening of the trachea is seen in tracheobronchiomegaly or the Mounier–Kuhn syndrome, which is associated with the Ehlers–Danlos

syndrome. Narrowing of the trachea is seen in the sabre sheath trachea of chronic obstructive pulmonary disease, relapsing polychondritis, Wegener’s granuloma, sarcoidosis, tuberculosis, trauma, tracheopathia osteochondroplastica, and tracheomalacia. The diagnosis of all tracheal lesions is confirmed by CT which shows the narrowed or widened trachea, intraluminal softtissue masses, a thick-walled trachea or extrinsic mediastinal disease. Tracheal lesions are discussed in more detail in Chapter 17.

Posterior Mediastinum Neurenteric Cyst Neurenteric cysts are rare congenital cysts along the spinal axis, made up of heterotopic endodermal tissue [40]. Patients are usually diagnosed during the second and third decades of life. Depending on the size and location of the lesion, neurenteric cysts can present with progressive focal spinal pain, radicular symptoms, paresthesia, or focal weakness. Radiographically, neurenteric cysts present as a space-occupying mass along the posterior mediastinum distorting the paraspinal lines. MRI provides superior delineation of the anatomic relation of the cyst with the spinal cord compared with

CT. Nonetheless, CT imaging is useful in evaluating adjacent associated osseous malformations. On CT, neurenteric cysts appear usually as a solitary welldefined cyst with a thin imperceptible wall. On MRI, neurenteric cysts are nonenhancing lesions, which are hyperintense on T2-weighted images and hypo-toisointense on T1-weighted images. Similar to other congenital mediastinal cysts, neurenteric cysts do not have enhancing mural nodules, which helps differentiate these cysts from spinal neoplasms. Meningoceles Thoracic meningoceles arise from focal protrusions of the meninges in the spine and may be congenital or iatrogenic in nature [40]. Lateral thoracic meningoceles are most often associated with neurofibromatosis type 1. Iatrogenic meningoceles can result from trauma or as a complication from spinal surgeries. Radiographically, meningoceles are seen as well-delineated paraspinal masses along the posterior mediastinum, often with smooth scalloping of the adjacent osseous structures. CT and MRI will demonstrate a well-circumscribed homogenous mass of fluid attenuation and intensity with a thin wall and no mural nodularity. Meningoceles will demonstrate a connection with the spinal subarachnoid

space and the fluid they contain will follow the attenuation and intensity of cerebrospinal fluid. Neurogenic Tumors Neurogenic tumors are among the most common tumors found in the posterior mediastinum and encompasses nerve sheath tumors, autonomic ganglion tumors, and paragangliomas [41]. Nerve sheath tumors include benign tumors such as schwannomas and neurofibromas, as well as malignant peripheral nerve sheath tumors (MPNSTs). Tumors of the autonomic ganglion include a histopathologic continuum ranging from low-grade ganglioneuromas, intermediate-grade ganglioneuroblastomas, and highly malignant neuroblastomas. Paragangliomas are rare neuroectodermal tumors arising from the sympathetic or parasympathetic chain. Differentiation of the different neurogenic tumors involves the integration of demographics, clinical information, and imaging features. Ganglioneuroma: Ganglioneuromas are low-grade tumors made up of well-differentiated large ganglion cells, Schwann cells,

and nerve fibers [41]. They are usually slow-growing tumors, discovered commonly in children older than 10 years of age and found more commonly in males than females. Given their origin, they are usually attached to an intercoastal or sympathetic nerve. On CT, ganglioneuromas usually are circumscribed elongated masses with low internal attenuation compared with muscle, related to an abundance of myxoid content. On MRI, ganglioneuromas usually have homogenous intermediate signal on all sequences and demonstrate enhancement. On occasion, low-signal intensity curvilinear or nodular bands can be seen on T1- and T2weighted imaging. Ganglioneuroblastoma: Ganglioneuroblastoma makes an intermediate-grade tumor in between more benign ganglioneuromas and more malignant neuroblastomas [41]. They are usually discovered in children younger than 10 years of age with equal sex predominance. On imaging, these tumors are usually encapsulated and range in appearance from wellcircumscribed enhancing solid masses to more irregular and cystic heterogeneous masses. Local invasion and metastasis at the time of diagnosis are not uncommon.

Neuroblastoma: Neuroblastomas are most commonly seen in young children under the age of 3 years. They comprise the most common extracranial solid malignancy of childhood [41]. Histologically, neuroblastomas are made up of small round cells with little stroma and no capsule. Given they are often associated with hemorrhage and necrotic degeneration; they can appear as irregular masses with internal low-attenuation and heterogeneity. Radiographically, neuroblastomas can present as a paravertebral mass with or without internal calcification. Local invasion and metastatic disease can be noted on imaging. On CT, half of neuroblastomas will demonstrate internal stippled or curvilinear calcifications. Enhancement can be homogeneous or heterogeneous, depending on the degree of necrosis (Fig. 13.42). MRI is preferable to CT in assessing the extent of tumor involvement and metastatic disease in the bone marrow and liver, to avoid radiation.

Figure 13.42 Example of biopsy-proved neuroblastoma on axial-enhanced CT chest (A) and corresponding postgadolinium-enhanced T1weighted MRI chest (B). Note the heterogeneity of the mass on the MRI with avidly enhancing peripheral components and necrotic degeneration in the center. Also, note the component widening the left neuroforamen and eroding the adjacent vertebral body. Schwannoma: Schwannomas are the most common nerve sheath tumors, frequently found associated with an intercostal nerve or spinal nerve root [41]. Most schwannomas are solitary and sporadic (Fig. 13.43), although multiple schwannomas can be found associated with neurofibromatosis type 2. Radiographically, schwannomas appear as well-circumscribed ovoid

paraspinal mass. On CT, schwannomas are well-defined, noninfiltrating masses, which can displace the surrounding fat (termed “split fat” sign). Schwannomas are uncommonly calcified. Although not invasive, schwannomas can cause smooth erosion of adjacent bony structures over time. On MRI, schwannomas are hypo-to-isointense on T1-weighted images, hyperintense on T2-weighted images, and demonstrate avid enhancement of solid components. Large schwannomas can have cystic degeneration and hemorrhage and will appear more heterogeneous.

Figure 13.43 Example of peripheral nerve sheath tumor (schwannoma). On coronal (A) and axial (B) CT chest, note the well-defined ovoid noncalcified paraspinal mass (arrows) centered at the expected location of the left intercostal neurovascular bundle. On corresponding T1-weighted nonfatsaturated (C) and T1-weighted fat-saturated postcontrast (D) MRI chest, note the smooth encapsulated mass with relatively homogeneous

and avid enhancement. The adjacent bone marrow signal is normal. Neurofibroma: Neurofibromas [41] are usually found in adulthood, between the third and fifth decades. The presence of plexiform neurofibromas is considered pathognomonic with neurofibromatosis type 1. On CT, neurofibromas appear as smooth well-delineated homogeneous masses, sometimes with a split fat sign. Unlike schwannomas, cystic degeneration is uncommon and calcifications and bony changes are also more frequently associated with neurofibromas. On MRI, neurofibromas are low to intermediate signal on T1-weighted images and usually demonstrate homogeneous enhancement. On T2weighted MRI, neurofibromas can demonstrate lower central intensity and higher peripheral zone intensity, termed “target” sign (Fig. 13.44).

Figure 13.44 Example of a neurofibroma on axial T2-weighted image of the chest demonstrating well-circumscribed, mildly lobulated mass with internal areas of T2 hypointensity (target sign) centered within the extrapleural fat of the right lateral chest wall. Malignant Peripheral Nerve Sheath Tumor: MPNSTs are aggressive peripheral nerve sheath tumors characterized by large size (greater than 5 cm), irregular borders, and fast rate growth [41]. Most tumors are solitary and sporadic, although 20–30% are associated with neurofibromatosis type 1. MPNSTs usually present

in the fourth to fifth decades of life and without gender predisposition. A rapidly enlarging mass in the posterior mediastinum with associated pain and neurologic deficits raise the suspicion of an MPNST. Histologically, MPNSTs demonstrate spindle cells with nuclear atypia, increased mitosis, and areas of necrosis. On imaging, they appear as large heterogeneous soft-tissue masses with an invasion of adjacent structures including bone, muscle, and pleura. CT and MRI appearance depend on the degree of internal cysts, necrosis, and hemorrhage. Paraganglioma: Thoracic paragangliomas are rare highly vascular tumors of the mediastinum, mostly arising in adulthood between 40 and 50 years of age [41]. They may be associated with syndromes including multiple endocrine neoplasias and von Hippel–Lindau disease. Paragangliomas arise from chemoreceptor paraganglionic cells and, when active, can secrete catecholamines and cause hypertension, headaches, and blushing. Paragangliomas are not confined to the posterior mediastinum and can be found in any of the three mediastinal compartments. Paragangliomas can be found in the paravertebral space, aortic arch, along the sympathetic nerve chain, along the pericardium, along the vagus nerve, and within the

interatrial septum. Radiographically, paragangliomas appear as nonspecific mediastinal masses. On CT and MRI, thoracic paragangliomas present as avidly enhancing soft-tissue masses, some with extensive hemorrhagic or cystic degeneration. Paragangliomas are usually intermediate intensity on T1-weighted images and hyperintense on T2-weighted images. Large masses are usually supplied by multiple feeding vessels and demonstrate a salt-and-pepper appearance on T2weighted MRI, owing to the presence of vessel signal flow void amidst the hyperintense mass. Bochdalek Hernia Bochdalek hernia arises from herniation of abdominal contents through the foramen of Bochdalek, a persistent congenital defect in the posterior diaphragm [31]. In most cases, Bochdalek hernia is asymptomatic, although rarely strangulation of herniating bowel can occur. Most commonly Bochdalek hernias are found in the left hemidiaphragm, given the presence of the liver on the right. Small hernias can appear on the chest radiograph as a focal opacity in the posterior costophrenic angle. Large hernias containing small bowel and colon can appear as gas-filled structures in the left hemithorax and those containing solid viscera such as kidneys are of

soft-tissue density. CT imaging is usually confirmatory, demonstrating the presence of the congenital defect in the posterior diaphragm (Fig. 13.45).

Figure 13.45 Sagittal-enhanced CT chest demonstrating example of a small right Bochdalek hernia with protrusion of fat into the thoracic cavity. Extramedullary Hematopoiesis Extramedullary hematopoiesis are rare centers of hemopoiesis occurring outside of the principal sites of hemopoiesis such as the long bones, ribs, and vertebral

bodies [42]. This condition is associated with diseases such as myelofibrosis, where the primary sites of hemopoiesis fail or are destroyed, and in hemoglobinopathies such as sickle cell disease and thalassemia. In the thorax, extramedullary hematopoiesis appears as oval circumscribed paravertebral masses along with an expansion of ribs. Extramedullary hematopoiesis can also occur in other areas of the body, including in the liver, spleen, perirenal space, and retroperitoneum. Imaging features on CT and MRI are nonspecific (Fig. 13.46). Although usually bilateral, extramedullary hematopoiesis can sometimes be unilateral. The presence of macroscopic fat can suggest a diagnosis of extramedullary hematopoiesis. However, many of these soft-tissue masses do not contain fat, making the diagnosis difficult, and often requiring biopsy for confirmation.

Figure 13.46 Example of biopsy-proved extramedullary hematopoiesis in a 59-year-old male with beta-thalassemia. Axial-enhanced CT chest demonstrates bilateral ovoid smoothly marginated and homogeneous soft-tissue masses in the paravertebral space.

Suggested Readings • BW Carter, MF Benveniste, R Madan, MC Godoy, PM de Groot, MT Truong, et al., ITMIG classification of mediastinal compartments and multidisciplinary approach to mediastinal masses, Radiographics 37 (2) (2017) 413–436.

• MY Jeung, B Gasser, A Gangi, A Bogorin, D Charneau, JM Wihlm, et al., Imaging of cystic masses of the mediastinum, Radiographics 22 (Spec No) (2002) S79–S93. • CS Nin, VV de Souza, RH do Amaral, NR Schuhmacher, GR Alves, E Marchiori, et al., Thoracic lymphadenopathy in benign diseases: A state of the art review, Respir Med 112 (2016) 10–17. • JD Pavlus, BW Carter, MD Tolley, ES Keung, L Khorashadi, JP Lichtenberger, 3rd, Imaging of thoracic neurogenic tumors, AJR Am J Roentgenol 207 (3) (2016) 552–561. • AS Roberts, AS Shetty, VM Mellnick, PJ Pickhardt, S Bhalla, CO Menias, Extramedullary haematopoiesis: radiological imaging features, Clin Radiol 71 (9) (2016) 807–814.

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14

Pleura, Diaphragm, and Chest Wall Dhiraj Baruah, Sachin S. Saboo, Kiran Batra

Anatomy Pleura is a thin membrane of fibrous tissue lined by the mesothelium which covers the lung surface (visceral pleura) and lines inner surface of the chest wall (parietal pleura) [1]. The visceral pleura is along the lung surface and fissures. Pulmonary arteries and veins supply the visceral pleura and systemic vasculatures are for the parietal pleura. There are four parts of the parietal pleura—along the ribs and intercostal spaces is “costal part,” along hemidiaphragm is “diaphragmatic part,” along mediastinum is “mediastinal part,” and along the cervical extension is “cervical part.” Mediastinal part of the parietal pleura is continuous with the visceral pleura and extends inferiorly to form the inferior pulmonary ligament. Pleural cavity is the potential space between visceral and parietal pleura and is lined by a thin layer of approximately 5 mL lubricating physiologic fluid. The pleural cavity is developed between the fourth and seventh weeks of the embryonic life. Pleura is permeable to both air and fluid; however, no air is normally seen in the pleural space. Pleural fluid is dynamic with approximately 100 mL of fluid produced per hour and is absorbed by the lymphatic system in the parietal pleura draining ultimately into the thoracic duct [1]. The diaphragm is a dome-shaped muscular septum surrounding a central tendon which is a physical barrier between the thoracic and abdominal cavities. Phrenic nerves are the primary innervation of the diaphragm; however, some part of the lateral diaphragm is often supplied by intercostal nerves. Third to fifth cervical roots contribute to the phrenic nerves and the nerve passes along the lateral pericardial border to reach the diaphragm [2]. The bony rib cage is supported by chest wall musculatures and provides a protective barrier for internal vital organs and also takes part in the respiration.

Physiology Mechanical coupling between the lung and chest wall helps maintaining lung inflation [3]. As the lung has a natural tendency to collapse toward its hilum, similar magnitude of chest wall force is required to keep it expanded. With accumulation of abnormal amount of fluid (pleural effusion/empyema/hemothorax) or air (pneumothorax) in the pleural space this outward force decreases leading to collapse of a part of or whole lung depending on amount of collection. This passive collapse also depends on underlying condition of the lung and presence or absence of pleural adhesions. Sometimes, the lung may not completely collapse (e.g., fibrosis, emphysema, and consolidation) and with adhesions in the pleural space distribution of air and fluid may vary. Pleural fluid and air distribution can also vary in double lung transplant patients where a single pleural layer is used to cover both lungs. Primary function of diaphragm and chest wall musculatures is to help in respiration with the diaphragm being the primary muscle of respiration and accessory muscles of respiration are external intercostal, sternocleidomastoid, and scalene muscles. Contraction of diaphragm along with accessory muscles of respiration expands the thoracic cavity which decreases intrathoracic pressure and draws air into the airways and lungs. In expiration, elastic recoil of the lungs during diaphragmatic relaxation pushes air out from the lung. During inspiration, the diaphragm closes the gastroesophageal junction preventing reflux and enlarges inferior vena cava (IVC) hiatus pumping deoxygenated blood to the right atrium. By increasing intra-abdominal pressure the diaphragm also helps in emesis, urination, and defecation.

Imaging Appearance of Normal Pleura, Diaphragm, and Chest Wall Pleura is not visible normally on radiographs, however, it is often visible where two layers of pleura are outlined by the aerated lung. These places are horizontal fissure of the right lung which is often seen on a frontal radiograph and oblique fissures in both lungs often seen on the lateral radiograph (Fig. 14.1). Some common accessory fissures are inferior accessory fissure of the right lower lobe and azygos fissure (Fig. 14.2).

FIGURE 14.1 Normal fissures. Frontal and lateral radiographs showing right horizontal fissure (arrow in A) and bilateral oblique fissures (arrows in B).

FIGURE 14.2 Accessory fissures. Plain radiograph and axial computed tomography images showing azygos fissure (arrows in A and B) and accessory right lower lobe fissure (arrow in C).

On a plain radiograph, diaphragmatic outline is visible between the air containing lung and opaque abdomen. Normally, the right hemidiaphragm is higher than the left because of the liver in the right upper quadrant of the abdomen (Fig. 14.3). Posterior and lateral portions of the diaphragm are usually lower than the anterior and medial portions. Motion of the diaphragm with respiration is commonly assessed using dynamic imaging like fluoroscopy, ultrasound, or magnetic resonance imaging (MRI). There are openings in the diaphragm that

allow structures to pass between the chest and abdominal cavities and these openings can be seen in cross-sectional imaging. These openings are called diaphragmatic hiatuses and there are three important hiatuses (Fig. 14.4A). In the midportion of the central tendon is the hiatus for IVC, which is at the T8 vertebral level and contains IVC and right phrenic nerve (Fig. 14.4B). At the T10 vertebral level is the esophageal hiatus which allows passage of esophagus along with vagus nerve and sympathetic nerve branches (Fig. 14.4C). The third important hiatus is the aortic hiatus at T12 vertebral level which contains descending thoracic aorta along with thoracic duct, hemiazygos, and azygos veins (Fig. 14.4D).

FIGURE 14.3 Normal diaphragmatic outline on frontal (A) and lateral (B) plain radiographs. The right hemidiaphragm (arrows) is slightly at a higher level compared to the left (curved arrows) because of liver under the hemidiaphragm on right.

FIGURE 14.4 Diaphragmatic hiatuses. Diagrammatic representation of diaphragm and openings for inferior vena cava (IVC), esophagus, and aorta (A). CT images showing the IVC hiatus located at T8 vertebral level and contains IVC (arrow in B) and right phrenic nerve branches (not visualized). CT image at T10 vertebral level showing the esophageal hiatus that contains esophagus, vagus nerve, and branches of the sympathetic plexus. This hiatus is formed by crossing of the muscle fibers of the right diaphragmatic crus (arrow in C). CT image showing aortic hiatus at T12 vertebral level bounded by the diaphragmatic crura (arrows in D) and contains aorta (curved arrow in D), thoracic duct, azygos, and hemiazygos veins.

Pleural Fluid Normal thin layer of lubricating fluid in the pleural space helps transmitting transpleural forces developed during normal breathing. This fluid will accumulate within the pleural cavity if the rate of production (increased microvascular pressure in the lungs like in heart failure, decreased plasma oncotic pressure with hypoproteinemia, increased permeability with pleural inflammation, fluid from another space like ascites) is more than its rate of absorption (decreased pleural lymphatic drainage like in lymphangitis). Fluid in pleural effusion can be simple

(transudative) or complex (exudative) like pus (empyema), blood (hemothorax), chyle (chylothorax), neoplastic involvement, etc. (Table 14.1). Table 14.1 Types of Pleural Effusion Types of Pleural Effusion Transudat ive

Causes Left ventricular failure Constrictive pericarditis Hepatic cirrhosis Renal failure Peritoneal dialysis Superior vena cava obstruction Myxedema

Exudative

Empyema

Bacterial infection Fungal infection Tuberculosis infection Parasitic infection Viral infection

Hemothorax

Trauma Iatrogenic Neoplastic Catamenial/endometriosis

Chylothorax

Trauma Iatrogenic

Neoplastic involvement

Mesothelioma Metastasis

Types of Pleural Effusion Others

Causes Connective tissue diseases Pulmonary embolism Gastrointestinal diseases

Plain radiograph helps to identify presence or absence of pleural effusion. Cross-sectional imaging like computed tomography (CT) and MRI can help identify simple or complex fluid. CT, MRI, and positron emission tomography (PET) imaging are also helpful to identify pleural tumor involvement, however, direct evaluation of pleural fluid is often necessary to have a definitive diagnosis. Simple pleural fluid collection (hydrothorax) can be seen with different etiologies and one common etiology is heart failure, where effusion often starts in the right and then becomes bilateral. Other causes include hypoproteinemia (renal failure, cirrhosis, and anemia), constrictive pericarditis, Meigs’ syndrome, and myxedema. Some frequently encountered causes of exudative pleural collection are bacterial pneumonia, pulmonary tuberculosis, lung cancer, lung infarction, and pleural metastasis. Other less common causes are connective tissue diseases (particularly systemic lupus erythematosus and rheumatoid arthritis), nonbacterial pneumonias, postmyocardial infarction syndrome, acute pancreatitis, abdominal infection, and mesothelioma. Most common cause of hemothorax is trauma, including open or closed chest trauma. Other conditions with bleeding tendencies (including hemophilia and excessive anticoagulation) can rarely lead to hemothorax. Iatrogenic bleeding into the pleural space can occur in lung biopsy or interventional procedures. Pulmonary infarction, lung cancer, and pleural metastasis can also lead to blood stained pleural fluid. Chylothorax is due to accumulation of a milky fluid (containing fat and fatty acids) mostly due to injury or obstruction to the thoracic lymphatic channels. Iatrogenic trauma during surgery is a common cause. Other etiologies include nonsurgical trauma, lung cancer, lymphoma, filariasis, and rarely lymphangiomyomatosis.

Imaging Appearance of Pleural Fluid Free Fluid Pleural fluid appears as a homogenous opacity on plain radiograph [4,5]. Location of this opacity depends on position of the patient, presence or absence of pleural adhesions, and radiographic technique. Pleural fluid initially accumulates in the

posterior costophrenic angle, which is the most dependent pleural recess and can be seen as blunting of this angle on frontal radiograph (Fig. 14.5). At least 50 mL of pleural fluid is necessary for blunting of the posterior costophrenic angle. Approximately 100–200 mL of fluid is needed to fill this recess to be able to see the fluid above the diaphragm on frontal radiograph (Fig. 14.6). A very small effusion can be seen with decubitus view (placing the abnormal side dependent), ultrasound, CT, or MRI (Fig. 14.7). At least 10 mL of fluid is minimum to be detected on a decubitus view. With increasing pleural fluid lateral costophrenic angle on the frontal radiograph opacifies and gradually obscures the hemidiaphragm and lung base and often tracks along the fissures. On crosssectional imaging, pleural effusion occupying less than one fourth of anteroposterior dimension of the hemithorax in the midclavicular line corresponds to less than 300 mL of pleural fluid. Pleural effusions occupying more than half of the hemithorax on cross-sectional imaging have more than 1 L of pleural fluid. Complete opacification of a hemithorax can be seen with a massive pleural effusion. Mass effect due to massive effusion can displace the mediastinum toward the contralateral side. Mediastinal deviation may be absent if the underlying lung is completely collapsed.

FIGURE 14.5 Tiny left pleural effusion. There is slight blunting of the left lateral costophrenic angle (arrow in A) and a small amount of fluid is seen in the CT image (curved arrow in B).

FIGURE 14.6 Bilateral pleural effusions. Frontal and lateral radiographs showing homogeneous opacification blunting the lateral (arrows in A) and posterior costophrenic angles (arrows in B).

FIGURE 14.7 Small bilateral pleural effusions. Man aged 34, renal transplant patient with cytomegalovirus pneumonia. The effusions probably relate to renal failure rather than the pneumonia. Posterior anterior (PA) film shows subtle filling in of both costophrenic angles (A). Horizontal-beam right and left lateral decubitus films show obvious free pleural effusions collecting along the dependent lateral costal margins (arrowheads in B and C).

Distribution of pleural fluid is often atypical leading to different appearances on conventional chest radiographs. A significant amount of pleural fluid may be hidden between the lung and the hemidiaphragm (subpulmonic effusion) leading to inadequate quantification on chest radiographs compared to ultrasound and CT. Subpulmonic effusion can appear as elevated hemidiaphragm on a chest radiograph (Fig. 14.8). Some useful hint to indicate subpulmonic effusion is apex of the “apparent” elevated hemidiaphragm is more lateral than usual, and usually

there is associated blunting of the costophrenic angle and often thickened fissure indicating fluid tracking along the fissure. Pleural fluid can collect between the lung surface and visceral pleura sparing the costophrenic angle, known as the lamellar effusion [4]. Sometimes a significant amount of pleural fluid can collect in the azygoesophageal recess mimicking a retrocardiac mass (Fig. 14.9).

FIGURE 14.8 A 15-year-old male with Adriamycin-induced cardiomyopathy and recently increasing shortness of breath. Erect PA film shows a large heart and apparent elevation of the right hemidiaphragm due to a large subpulmonic effusion (A). Lateral film shows fluid tracking up the posterior chest wall and blunting the posterior costophrenic recess (B). Supine chest radiograph obtained shortly afterward showing redistribution of pleural fluid (C). The appearances are now typical of a large supine pleural effusion with increased density of the right hemithorax. Ultrasound of the right lung base reveals a large anechoic space consistent with an uncomplicated pleural effusion (D).

FIGURE 14.9 Moderate-size pleural effusion in a 56-year-old woman. Effusion of unknown etiology. PA film demonstrates typical pleural opacity with concave upper border, slightly higher laterally, and obscuring the diaphragm and underlying lung. Fluid is extending into the fissure (arrows) and also into the azygoesophageal recess, producing a retrocardiac opacity (arrowheads).

Loculated Fluid Loculation of pleural fluid can be seen when there is a fusion of parietal and visceral pleural layers mostly due to old pleural processes. A few diagnostic features can help in differentiating loculated pleural fluid from lung parenchymal abnormality, extrapleural opacity, and mediastinal mass [6]. Loculated pleural fluid is often associated with free fluid along the costophrenic angle or the fissure (Fig. 14.10A, B). Encapsulated pleural fluid appears like a “biconvex lens” with comparatively little depth and considerable width and the appearance varies with radiographic projections. Sharp outline helps to identify opacity outside the pleura (extrapleural) often with tapered, sometimes concave edges at the point of chest wall contact [7,8]. An air bronchogram helps to differentiate peripheral lung abnormality from pleural fluid. Often, cross-sectional imaging is needed to

differentiate loculated pleural fluid from other conditions (Fig. 14.10C, D). Sometimes it may be difficult to differentiate loculated from free pleural fluid on CT and imaging in a different position (prone or decubitus) or with ultrasound can help solving the problem.

FIGURE 14.10 Loculated pleural fluid. Frontal and lateral radiographs showing loculated left pleural effusion with loculated posterior fissural components (arrows in A and B). Coronal and sagittal reconstructed CT images showing loculated fissural fluid (arrows in C and D). Loculated fluid is also seen in the left lower chest laterally and mid and lower chest anteromedially.

Pleural fluid can be loculated in the fissures and can be seen in patients with heart failure. Radiographic appearance depends on location and amount of loculated fissural fluid. Small amount of fluid in the fissures appear as fissural

thickening. Loculated fluid in the horizontal fissure appears as a well-defined lenticular opacity in both frontal and lateral radiographs. Loculated fluid in the oblique fissure is often poorly defined on frontal radiograph and lenticular appearance is seen on the lateral radiograph (Fig. 14.11A, B). Loculated fissural fluid can be confused with a mass lesion on a chest radiograph. However, they disappear rapidly following treatment, and hence are known as “pseudo-” or “vanishing” tumor (Fig. 14.12A, B).

FIGURE 14.11 Loculated fissural fluid in the oblique fissure. Frontal (arrows in A) and lateral (arrow in B) radiographs showing loculated pleural fluid in the right oblique fissure anteriorly.

FIGURE 14.12 Pseudotumor. Frontal radiograph showing loculated fissural fluid on right (A) which disappeared after a few days of chest tube placement (B).

Empyema Plain radiographs are often limited in differentiating simple pleural fluid from empyema. A fluid–fluid level due to difference in density of pleural fluid on a plain radiograph may suggest a complex effusion including empyema. However, cross-sectional imaging is often necessary to make a confident diagnosis of empyema (Fig. 14.13). Empyema commonly appears as a lenticular pleural fluid collection with or without air compressing adjacent lung parenchyma. Both layers of pleura are often thickened and show enhancement on postcontrast imaging. Early diagnosis of empyema on imaging is important as drainage with small caliber catheter is often not successful and when becomes chronic with significant pleural thickening surgical decortication may be necessary for the proper lung expansion [7]. Multiple septations are usually present in a complex pleural collection like empyema and instillation of fibrinolytic agents (e.g., urokinase) is often necessary for optimal drainage (Fig. 14.14).

FIGURE 14.13 Empyema. Patient with right pleural effusion with an air–fluid level in the right apex suggesting loculated complex pleural effusion (arrow in A). CT showing loculated complex right lower lateral and apical pleural fluid collections with enhancing thick pleura and multiple air foci in the right apical pleural collection (arrow in B). In appropriate clinical setting, this is an appearance of empyema.

FIGURE 14.14 Series of chest radiographs in a patient with a loculated parapneumonic pleural effusion successfully treated with intrapleural urokinase. The initial chest radiograph demonstrates a large right pleural effusion (A) which an ultrasound scan (B) shows to be heavily loculated. PA radiograph 24 hours after fine-bore catheter insertion and instillation of streptokinase (C). PA chest radiograph 5 months later (D).

Ultrasound is a commonly used imaging technique to diagnose, localize, and aspirate pleural fluid [9]. Ultrasound-guided aspiration can be diagnostic or therapeutic. Simple pleural fluid is anechoic and particulate material with or without septations can be seen in complicated pleural fluid. Ultrasound is also helpful to identify pleural thickening and masses (Fig. 14.15). Ultrasound can help guiding needle track in pleural mass biopsy (Fig. 14.16).

FIGURE 14.15 A 5-year-old female with shortness of breath. Complete opacification of right hemithorax on frontal chest radiograph with mild mediastinal deviation toward left (A). Ultrasound images showing multilobulated pleural homogeneous echoic soft-tissue mass with complex multiseptated right pleural effusion (B). Axial contrast-enhanced CT image showing multilobulated enhancing soft-tissue pleural lesions with large right pleural effusion (C). Of note, pleural septations are better visualized on real time ultrasound. Surgical biopsy revealed pleural Ewing’s sarcoma.

FIGURE 14.16 Usefulness of ultrasound in detecting pleural mass and guiding needle for biopsy. Positron emission tomography computed tomography image showing intense uptake of diffuse pleural nodularity/masses (A). Ultrasoundguided needle placement for biopsy—note the linear echogenic needle within the soft-tissue pleural mass (B).

CT is often helpful in localizing and characterizing pleural fluid when plain radiographic and ultrasound findings are confusing, and CT can help identify the cause of pleural fluid collection in certain situation. Pleural fluid is hypodense on CT and pleural thickening is somewhat higher attenuation than fluid. However, complex pleural fluid collection like acute hemothorax can have high attenuation. Pleural effusion on CT with associated pleural thickening and enhancement suggest an exudative pleural effusion.

Pleural fluid collection can be sometimes be difficult to differentiate from peripheral lung abscess, extrapleural fluid collection, or even ascites. A few signs can help suggesting pleural fluid on CT as described below [5,6,10–12].

◾differentiating Split pleura sign: pleural fluid displaces both visceral and parietal pleura and this helps pleural fluid collection from peripheral lung abscess (Fig. 14.17A) ◾anteriorly Displaced crus sign: pleural fluid collect posterior to the diaphragmatic crus and displaces it and ascites collects anterior to the crus and displaces it posteriorly (Fig. 14.17B) ◾dome Diaphragm sign: fluid exterior to the dome of the diaphragm is in the pleura and that is within the is ascitic fluid (Fig. 14.17C) ◾these Interface sign: ascites being in close contact with liver and spleen will have a sharp interface with organs as compared to pleural fluid (Fig. 14.17D) ◾coronary Bare area sign: ascitic fluid cannot extend to the bare area of the liver which is bounded by ligament. So, fluid over the posterior surface of the liver is usually pleural fluid than ascites (Fig. 14.17C)

FIGURE 14.17 CT signs which may help diagnosing pleural effusion from peripheral lung abscess or ascites. Split pleura sign: Pleural fluid separates parietal and visceral pleura and this differentiates pleural fluid from peripheral lung abscess (A). Displaced crus sign: The right pleural effusion collects posterior to the right crus of the diaphragm (arrows) and displaces it anteriorly (B). Diaphragm sign: The pleural fluid (p) is over the outer surface of the dome of the diaphragm, whereas the ascitic fluid (a) is within the dome (C). Interface sign: The interface (white arrow) between the liver and ascites is usually sharper than between liver and pleural fluid (black arrow in D) (D). Bare area sign: Peritoneal reflections prevent ascitic fluid from extending over the entire posterior surface of the liver (white arrow in C), in contrast with pleural fluid in the posterior costophrenic recess (p in C).

Pneumothorax

Collection of air in the pleural cavity is pneumothorax. Pneumothorax can occur when air enters the pleural space through a defect in the parietal or visceral pleura. There are different etiologies of pneumothorax including trauma, spontaneous, iatrogenic, etc. As pleural effusion, pneumothorax maybe localized if there are pleural adhesions. If free pleural air moves in and out with breathing it is called an open pneumothorax. When air enters in inspiration and remains there in expiration it is called a valvular pneumothorax. Increase in intrapleural pressure in a valvular pneumothorax leads to tension pneumothorax [5–8].

Etiology Most common pneumothorax is spontaneous pneumothorax, usually occurs in young tall men and due to rupture of apical congenital pleural blebs. Paraseptal emphysematous bullous lesions are common factor in older individual. Other causes of spontaneous pneumothorax include chronic bronchitis, asthma, rupture of air containing lung cyst or cavity (tuberculosis, staphylococcal pneumonia, and malignancy), and interstitial pulmonary fibrosis (cystic fibrosis, histiocytosis, tuberous sclerosis, sarcoidosis, and pneumoconiosis). Both blunt and penetrating trauma can lead to pneumothorax. Usual traumatic causes of pneumothorax are penetrating trauma, closed chest trauma (mostly due to bronchial rupture), rib fracture, pleural/lung interventional procedure, bronchoscopy, positive pressure ventilation, and thoracic surgery. Diagnostic pneumothorax to diagnose pleural condition and artificial pneumothorax to treat pulmonary tuberculosis are of historical interest only. However, artificial pneumothorax can help gaining access in some chest biopsies including biopsy of mediastinal lesions.

Imaging Appearance of Pneumothorax A small free pneumothorax in an erect patient tends to collect in the apex [6,7]. Lung adjacent to the pneumothorax retracts toward the hilum and on a frontal radiograph a sharp radiopaque line of the visceral pleura separates air containing radiolucent avascular pleural space from lucent lung parenchyma with lung markings (Fig. 14.18A–C). A skin fold can often appear as a pneumothorax, however, unlike pneumothorax the line due to skinfold often does not follow the expected course of visceral pleura, the line is usually a thick white line compared to thin visceral pleural line and lung markings are visible outside the curvilinear shadow (Fig. 14.18D).

FIGURE 14.18 Woman aged 22 with a spontaneous pneumothorax. PA radiograph showing apical pneumothorax. The visceral pleura (arrowheads) separates aerated lung from the radiolucent pleural space (A). AP chest radiograph and CT scan in a patient with Pneumocystis carinii pneumonia complicated by bilateral pneumothoraces and extensive mediastinal and surgical emphysema (B and C). Supine chest radiograph of an intubated patient. There is a skin fold projected over the right lung apex simulating a pneumothorax (arrows). Close inspection reveals lung markings extending beyond the skin fold, and no fine pleural line that should be visible with a genuine pneumothorax (D).

A small pneumothorax may be easily missed, and it is important to look for it carefully and with image magnification. In closed pneumothorax, pleural air volume is not changed in respiration and an expiratory radiograph will make it easier to see due to decrease in lung volume. A lateral decubitus radiograph with the nondependent abnormal side can help detecting small pleural air. This is particularly helpful in AP radiographs in infants and patients in the intensive care unit where a small pneumothorax is often difficult to visualize due to its accumulation anteriorly and medially (Fig. 14.19A, B) [13]. Another technique is

horizontal beam “shoot-through” lateral radiograph which might help identifying anterior pneumothorax in a supine patient. With pneumothorax, a small amount of normal pleural fluid may cause blunting of the costophrenic angle. With hydropneumothorax, a horizontal fluid level is noted separating dependent fluid and nondependent air (Fig. 14.20). In patients with double lung transplant using a single pleural covering pleural effusion or pneumothorax can shift from one side to the other depending on patients position and can extend along the midline (Fig. 14.21).

FIGURE 14.19 Anteromedial pneumothorax. AP radiograph in an intubated patient showing pneumothorax anteromedially (A). The pneumothorax is seen anteromedially on same day CT (B).

FIGURE 14.20 Air–fluid level. Horizontal air–fluid level separating dependent fluid and nondependent air in hydropneumothorax (A). Plain radiograph and CT showing horizontal air–fluid level in a patient postpneumonectomy (B and C).

FIGURE 14.21 Pneumothorax in double lung transplant. Pneumothorax extending along the midline in a patient with double lung transplant with single pleural covering, also known as buffalo chest.

Amount of collapse of the lung due to pneumothorax depends on amount of air, rapidity of development, and underlying lung condition. A large pneumothorax can lead to complete lung relaxation toward the hilum with mediastinal shift to contralateral side, which increases in expiration.

Tension Pneumothorax Large or rapid accumulation of pleural air can lead to significant displacement of mediastinum with kinking of the great veins and acute cardiorespiratory decompensation [4]. On plain radiographs, the signs of tension pneumothorax are significant contralateral mediastinal deviation, collapsed lung maybe squashed against the mediastinum or displaced toward contralateral side and depression of ipsilateral hemidiaphragm (Fig. 14.22). Fluoroscopy can show contralateral mediastinal displacement greatest on inspiration, differentiating tension pneumothorax from large pneumothorax without tension.

FIGURE 14.22 Tension pneumothorax following a transbronchial lung biopsy. There is inversion of the right hemidiaphragm, and deviation of the mediastinum to the opposite side (A). Following insertion of a right-sided chest drain the diaphragm and mediastinum have returned to a normal position (B). The diffuse bilateral infiltrate is due to pre-existing pulmonary hemorrhage.

Loculated Pneumothorax Similar to loculated pleural effusion, pleural adhesions can also lead to loculated or encysted pneumothorax [7]. Loculated pneumothorax appears as an ovoid air collection close to the chest wall and may be difficult to differentiate from thinwalled subpleural lung cavity, cyst, or bulla radiographically. Pleural adhesions extend between two pleural layers and appear as a line shadow (Fig. 14.23). Rupture of an adhesion can lead to hemopneumothorax and discharge from an underlying infected subpleural lesion can lead to pyopneumothorax.

FIGURE 14.23 Septation in loculated pneumothorax. A 29-year-old male with known lacrimal gland cancer with multiple bilateral lung metastasis. Bilateral loculated pneumothoraces seen on frontal and lateral plain radiographs (A and B) and on coronal reformatted CT (C). Septations are nicely seen on CT (black arrows).

Re-expansion Pulmonary Edema Rapid re-expansion of a lung following drainage of a large pleural effusion or pneumothorax may be associated with a condition called re-expansion pulmonary edema with development of extensive consolidative opacities in the ipsilateral lung (Fig. 14.24) [14]. Re-expansion edema usually resolves within a day or two.

FIGURE 14.24 Re-expansion edema. Initial frontal radiograph in this 36-yearold female showing large right pleural effusion with underlying collapse and mediastinal deviation toward left (A). Radiograph after pleural fluid drainage showing opacification of right lung likely representing re-expansion edema (B) which was improving gradually (C). Large right pleural effusion on another patient (D). Right lung ground glass opacities after drainage of pleural fluid is likely due to re-expansion edema (E).

Bronchopleural Fistula A communication between the airway and pleural space is called bronchopleural fistula (Fig. 14.25). This is a known complication following complete or partial pneumonectomy and is discussed in detail in the chapter describing postoperative complication. Other causes include bronchial carcinoma, ruptured lung abscess, and trauma. A nonresolving pneumothorax or hydropneumothorax in appropriate clinical situation raises possibility of bronchopleural fistula.

FIGURE 14.25 Bronchopleural fistula. A wide fistulous tract is seen connecting the pleural cavity (arrow in A) with the central airway (arrow in B). Note persistence of right pneumothorax even with a chest tube in place.

Pleural Thickening Localized pleural thickening commonly results in bilateral apical opacification and blunting of costophrenic angle [15]. Localized pleural thickening usually results from a previous pleuritis, which is often subclinical. In the asymptomatic patient without any other radiological abnormality blunting of the costophrenic angle due to pleural thickening is of no significance. However, this may mimic a small pleural effusion and comparison with old radiographs is helpful. Otherwise, a lateral decubitus radiograph or ultrasound correlation is necessary to rule out a small amount of pleural fluid depending on clinical presentation. Biapical pleural thickening is also a common finding, often seen in elderly and not always due to tuberculosis. Symmetrical apical homogenous opacities on plain radiographs are due to benign pleural thickening or prominent extrapleural fat (Fig.  14.26). Asymmetrical or unilateral apical pleural thickening maybe of a pathological significance if associated with symptoms like pain. Pancoast tumor can appear as unilateral apical thickening and it is important to look at adjacent ribs and spine for any evidence of malignant destruction (Fig. 14.27). As bony destruction almost always suggest malignancy, these patients were evaluated with penetrated radiographs and tomography in earlier days and now with CT. Apical pleural thickening can also be seen with postradiation treatment, particularly for head and neck malignancies.

FIGURE 14.26 Bilateral apical pleural thickening. The apical pleural shadowing (arrows) is symmetrical with well-defined edges.

FIGURE 14.27 Unilateral apical pleural thickening on plain radiograph. Man aged 46 with pain in the right side of the neck and right arm. Dense pleural shadowing is present at the right (A). The left apex is clear. An AP view of the cervical spine demonstrates absence of the right pedicle of T3 (arrow in B). CT demonstrates a right apical mass infiltrating the third thoracic vertebra (C). Histology: anaplastic carcinoma.

Both benign and malignant causes can lead to extensive unilateral pleural thickening. Previous thoracotomy, complicated pleural effusion and rarely chronic pneumothorax can lead to unilateral pleural thickening. Fibrothorax is a condition when the entire lung is surrounded by a fibrotic pleura. Surgical decortication may be necessary in fibrothorax when it causes significant ventilatory restriction of the affected lung.

Bilateral pleural thickening and calcification are common manifestations of prior asbestos exposure [16]. The term asbestosis is only used if pulmonary fibrosis is present in a patient with asbestos-related pleural thickening or calcification.

Pleural Calcification Pleural calcifications are usually due to benign etiologies and conditions causing pleural thickening can also lead to pleural calcification (Table 14.2). Unilateral pleural calcification can be seen with previous empyema, hemothorax, pleurisy, and postradiation treatment. Bilateral calcifications typically occur after asbestos exposure and some other pneumoconiosis [16]. Similar to pleural thickening pleural calcification may be incidental and patient may not remember any previous chest disease. Table 14.2 Causes of Pleural Calcifications

◾ Asbestos related ◾ Prior hemothorax ◾ Prior empyema ◾ Tuberculosis ◾ Radiation ◾ Chronic renal failure ◾ Prior chest surgery ◾ Rheumatoid arthritis ◾ Calcifying fibrous pseudotumor

Pleural calcification with previous pleurisy, empyema, or hemothorax involves the visceral pleura and almost always there is associated pleural thickening. The pleural calcification in this scenario may appear as continuous sheet or in discrete plaques. On imaging, visceral pleural calcification produces dense, coarse, irregular opacities, which is often sharply demarcated laterally (Fig. 14.28). If a plaque is viewed en face on plain radiograph, it may mimic a pulmonary nodule and often radiograph in another projection helps localizing it to the pleura.

FIGURE 14.28 Pleural calcification in a middle-aged woman with a history of recurrent episodes of pleurisy, presumed to be tuberculosis. Extensive plaques of pleural calcification surround both lungs (A). Bilateral calcified pleural plaques seen in face over both lungs due to exposure to asbestos (B).

Asbestos-related pleural calcification is usually more delicate and bilateral and involves the parietal pleura. Common locations are along the diaphragm and adjacent to the axillae. CT is most sensitive technique for detection of pleural calcification (Fig. 14.29).

FIGURE 14.29 Asbestos-related pleural calcification. CT is helpful for detecting small pleural plaque. Axial CT images showing classic distribution of pleural plaques along 3 and 9 o’clock positions and along the hemidiaphragms (arrows).

Pleural Tumors Pleural tumors are relatively rare compared to lung and mediastinum. Common benign pleural tumors include localized fibrous tumor (fibroma) and lipoma. Commonest malignant pleural tumor is metastasis (Fig. 14.30) with most frequent primary sites being the lung and breast. Primary malignant tumor or the pleura (malignant mesothelioma) is usually associated with prior asbestos exposure. On plain radiographs, loculated pleural fluid in the fissure can appear as a mass lesion, known as pseudotumor (Fig. 14.12A, B).

FIGURE 14.30 Pleural metastasis. Plain radiograph showing bilateral nodular lung metastasis with elevated right hemidiaphragm likely due to subpulmonic effusion (A). Ultrasound showing right pleural effusion with soft-tissue nodule (B). Axial contrast-enhanced CT and fat-saturated contrast-enhanced MRI showing right pleural effusion with enhancing nodule (C and D).

Pleural fibromas are often incidental on a chest radiograph in an asymptomatic patient. Paraneoplastic conditions associated with pleural fibroma are finger clubbing, hypertrophic osteoarthropathy, and hypoglycemia. They are slow growing tumors and usually benign, but malignant features can also be seen. On a plain radiograph, they appear as well-defined lobulated mass adjacent to the chest wall, mediastinum, diaphragm, or along the fissures (Fig. 14.31A, B). Size may be small or large enough to occupy the entire hemithorax. When small, crosssectional imaging shows homogenously enhancing pleural tumor and with large tumor there are often nonenhancing areas suggesting intratumoral necrosis [17]. Cross-sectional imaging including CT and MRI is helpful in characterizing the tumor and showing the extent (Fig. 14.31C–F).

FIGURE 14.31 Solitary fibrous tumor of the pleura. Frontal and lateral plain radiographs showing lobulated mass along the posterior left hemidiaphragm (arrows in A and B). Axial and coronal CT images showing homogeneous pleural mass lesion with foci of calcification (C and D). T2 and fat-saturated postcontrast T1-weighted MRI showing heterogenous tumor with multiple areas of heterogenous enhancement (E and F).

Subpleural or pleural lipomas appear as well-defined rounded peripheral masses on a plain radiograph. As they are soft tumors, they can change their shape with breathing. CT and MRI are diagnostic detecting fat within these tumors (Fig. 14.32).

FIGURE 14.32 Pleural lipoma. Frontal and lateral plain radiographs showing well-defined rounded lesion in the right lateral chest with incomplete border suggesting pleural/extra-pleural origin (A and B). Coronal CT image showing fat containing well-defined lesion along the right lateral pleura (C). The lesion is homogeneously hyperintense on nonfat-saturated MRI image (D) and hypointense on fat-saturated image (E).

Malignant mesothelioma is usually due to a long-term exposure to asbestos particles, particularly the crocidolite with a latent period from exposure to asbestos and development of mesothelioma is typically 20–40 years. Patients usually present with nonspecific mild chest symptoms with significant disease on imaging. Symptoms include chest pain, cough, hoarseness, dyspnea, night sweats, fatigue, weight loss, etc. On imaging, malignant mesothelioma appears as nodular pleural thickening around all or part of the lung (Fig. 14.33) often with hemorrhagic pleural effusion. Lung changes of asbestosis are not always present. Associated pleural effusion may obscure the underlying mass on a plain radiograph or noncontrast-enhanced CT. Though rib destruction can be seen with mesothelioma, most common cause of pleural mass with adjacent rib destruction is metastatic or primary tumor involving the bone. Cross-sectional imagings including CT, MRI, or PET are necessary for treatment planning of malignant mesothelioma [18–20]. Although all patients with mesothelioma receive some form of chemotherapy, staging helps in identifying patients who can benefit from surgery. Clinical staging with imaging is performed first which often underestimates disease burden. Surgical staging is performed after clinical staging if patient is eligible for surgery after clinical staging. There are multiple staging

systems for mesothelioma and most commonly used staging system is eighth edition of the TNM (tumor, node, metastasis) system. Early-stage disease (Stage I and II) involves pleura and may involve lung parenchyma or diaphragmatic muscle, however without involvement of lymph nodes or distant organs. In this eighth edition locally advanced disease is included in the Stage III. Stage IV includes only patients with distant metastasis. Features suggesting malignant versus benign pleural thickening are nodularity, thickening extending along the mediastinal surface or fissures, lung encasement, and loss of ipsilateral lung volume. MRI is superior to CT for detecting mediastinal and chest wall extension and involvement of cardiovascular structures. Percutaneous or surgical needle biopsy is necessary to make a final diagnosis. Tumor seeding of malignant mesothelioma is reported along the biopsy or chest drainage tracts (Fig. 14.34). Lymphoma can also involve pleura, usually with systemic disease and isolated pleural involvement is rare. Another rare tumor that can arise from pleura is a neuroectodermal tumor called the Askin tumor.

FIGURE 14.33 Mesothelioma. Abnormal chest radiograph shows lobulated right pleural opacities (A). CT scan through the mid thorax demonstrates encasement of the right lung by nodular pleural tumor (B).

FIGURE 14.34 CT scan through the lower thorax of a patient with malignant mesothelioma. There is metastatic tumor seeding along the biopsy tract (white arrows). Note the fleck of pleural calcification (curved arrow).

The Diaphragm The normal diaphragm is 2–3 mm thick [21]. On the left side where the gastric bubble lies beneath the diaphragm, the stomach wall and diaphragm form a linear density 5–8 mm thick. However on the right side thickness cannot be assessed unless the inferior surface is outlined by free intraperitoneal gas. Thickening may be a normal variant but occurs with tumors of the diaphragm, stomach and pleura, subpulmonary fluid, diaphragm humps, and abdominal lesions including subphrenic abscess, hepatomegaly, and splenomegaly.

Normal Variants

◾predominantly Scalloping (Fig. 14.35): short curves of diaphragm convex upward are seen and this occurs on the right side ◾emphysema. Muscle slips (Fig. 14.35): these are most commonly seen in tall, thin patients, and in those with They appear as small curved lines, concave upward, and are more common on the right

[21] ◾side Diaphragm humps and dromedary diaphragm (Fig. 14.35): these variants are probably mild forms of eventration with incomplete muscularization of the hemidiaphragm but no muscle defect. They arise anteriorly and are usually right sided, containing liver. There is no diaphragm defect. On the PA film the hump appears as a shadow in the right cardiophrenic angle and must be distinguished from a fat pad, lipoma, pericardial cyst, and Morgagni hernia. On the lateral film the hump overlies the cardiac shadow and should not be confused with middle lobe consolidation. The dromedary diaphragm is a more severe form of diaphragm hump appearing as a double contour on the PA view Accessory diaphragm: this rare condition is asymptomatic and usually right sided. The hemithorax is partitioned by the accessory diaphragm running parallel to the oblique fissure and resembling a thickened fissure. Its blood supply is often anomalous. Reported associations are other congenital lesions of the lungs such as anomalous venous drainage and lobar hypoplasia

◾

FIGURE 14.35 Normal variants of the diaphragm. (A) Scalloping (B) Muscle slips (C–F) Diaphragm hump.

Diaphragmatic Dysfunction It is more commonly being unilateral and often presents on a chest radiograph as an elevation of one of the hemidiaphragm. Patients with unilateral diaphragmatic dysfunction are often asymptomatic and detected incidentally and symptomatic patients’ usual clinical presentations are dyspnea on exertion and orthopnea. Eventration is the term used when a portion of the diaphragm is elevated due to congenital thinning (Fig. 14.36). Anteromedial portion of the right hemidiaphragm is the commonest location of diaphragmatic eventration [21]. Focal bulge due to eventration can be diagnosed on plain radiograph or CT and

differential includes focal diaphragmatic hernia (see below). Functional evaluation of diaphragmatic movement is commonly performed with fluoroscopic “sniff” test. Both hemidiaphragms normally move downward in deep inspiration and normal excursion is at least one intercostal space width in adults. In patients with diaphragmatic paralysis, this normal movement is absent and there may be paradoxical motion in inspiration which is more obvious with sniffing (Fig. 14.37). However paradoxical movement is also seen in a small number of normal subjects. Reduced excursion of the diaphragm frequently occurs with inflammatory processes either above or below the diaphragm; examples are subphrenic abscess and basal pneumonia. Treatment of diaphragmatic dysfunction depends on clinical severity and etiology. Asymptomatic patients with unilateral dysfunction are managed conservatively and patients with respiratory distress due to paralysis of both hemidiaphragm often require long-term positive pressure ventilation. Diaphragmatic plication is reserved for symptomatic patients with irreversible phrenic nerve damage. Phrenic nerve stimulation by surgically implanting an electrode is helpful when phrenic nerve is intact, for example, in cases with high cervical spine injuries.

FIGURE 14.36 Plain radiograph (A) and coronal reconstructed CT (B) images of a patient with eventration of right hemidiaphragm.

FIGURE 14.37 Left diaphragmatic paralysis. A 7-year-old male with prior history of cardiac surgery and left phrenic nerve injury showing paradoxical motion of the left hemidiaphragm (elevation during inspiration and depression during expiration). Normal motion of the right hemidiaphragm.

The Elevated Diaphragm (Box 14.1) Box 14.1

Causes of Elevation of the Diaphragm Bilateral Reduced pulmonary compliance, e.g., fibrosing alveolitis, lymphangitis, carcinomatosis Technical Supine film, expiratory film Postoperative pain Subdiaphragmatic Ascites, obesity Abdominal mass, pregnancy Bowel distension Unilateral Paralysis Surgery and trauma Idiopathic Radiotherapy Neoplastic Diabetes mellitus Infections, TB glands, herpes zoster Congenital Eventration and humps Pulmonary Pulmonary and lobar collapse Pulmonary hypoplasia Pneumonectomy Pulmonary embolism Basal pneumonia Pleural Thickening Pleurisy

Subpulmonary effusion Bony Scoliosis Rib fractures Subdiaphragmatic Gas-distended viscus Subphrenic abscess Pancreatitis Abdominal mass Hepatomegaly Splenomegaly

Frequently no cause can be found to explain an elevated hemidiaphragm. The clinical history is important. It is essential to exclude an active lesion, particularly malignancy, by carefully assessing the lung fields, hila, and mediastinum.

◾ Eventration may be associated with marked cardiac displacement ◾obliteration Pleural thickening is often accompanied by tenting of the diaphragm, with loss of definition and or blunting of the costophrenic angles and thickened fissures ◾straighter Subpulmonary fluid may be difficult to distinguish from an elevated diaphragm. Typically it has a upper border and will change shape with patient position if it is not loculated ◾films. Loculated subpulmonary effusions are very difficult to distinguish from a high diaphragm on plain Ultrasound is the definitive diagnostic investigation ◾pneumonia, Splinting of the diaphragm occurs with upper abdominal inflammatory processes, basal and embolism

Determining whether diaphragm elevation is due to paralysis or an abdominal mass elevating the diaphragm may be difficult on the plain film. The position of the liver edge should be noted. If the liver edge is low then there is probably a mass within or between the liver and diaphragm, whereas a normally positioned or high liver edge favors paralysis as a cause. On the left side the gastric bubble is assessed using the same principles. A depressed diaphragm is seen with pulmonary hyperinflation and large pleural effusions.

Subphrenic Abscess These are often associated with recent surgery or sepsis. A subphrenic abscess is more common on the right than the left side. Ultrasound and CT are the investigations of choice with percutaneous drainage if appropriate. Plain film signs of a subphrenic abscess include:

◾ Ipsilateral basal atelectasis and pleural effusion ◾ Elevated hemidiaphragm with paradoxical or decreased movement ◾14.38); Abnormal gas shadow beneath the diaphragm due to infection with gas-forming organisms (Fig. horizontal beam films improve visualization of the abscess cavity ◾ Depression of the liver edge or gastric fundus

FIGURE 14.38 Right subphrenic abscess following cholecystectomy. A large gas shadow with an air–fluid level is seen below the right hemidiaphragm (arrow). There are bilateral effusions with patchy shadowing at the right base.

Tumors of the Diaphragm Tumors of the diaphragm are rare. Benign lesions include lipomas, neurofibromas, fibromas, and cysts. Sarcomas commonly present with a pleural effusion. Diaphragm tumors may appear as smooth or lobulated masses and need to be differentiated from lung and liver masses, hernias, and diaphragm humps. CT is the most helpful investigation.

Hernias of the Diaphragm

The classic appearance of a hiatus hernia, with a fluid level superimposed on the cardiac shadow on the PA film, is well known (Fig. 14.39). A Bochdalek hernia (Fig. 14.40) arises posterolaterally through the pleuroperitoneal canal and is usually congenital, presenting at birth as respiratory distress. Ninety percent are left sided. The hernia may contain omentum, fat, spleen, kidney, and bowel, in which case a gas shadow is seen within the mass. The ipsilateral lung is invariably hypoplastic with deviation of the mediastinum away from the side of the hernia. In the neonate, this condition needs to be distinguished from cystic adenomatoid malformation of the lung.

FIGURE 14.39 Hiatus hernia. A large soft tissue is seen superimposed on cardiac shadow with air–fluid level (arrow).

FIGURE 14.40 Axial and coronal CT images showing large right diaphragmatic hernia (Bochdalek hernia) containing omentum and nonobstructed bowel loops.

The Morgagni hernia is usually asymptomatic, presenting in adults as an incidental finding on a chest film. It is right sided and anterior, appearing as a homogeneous shadow in the cardiophrenic angle. The hernia contains fat or occasionally bowel and liver (Fig. 14.41).

FIGURE 14.41 Morgagni hernia. Lateral radiograph showing focal bulge along the anterior hemidiaphragm (arrows in A). Ultrasound image showing herniated liver along the anterior hemidiaphragm with wasting/mushroom configuration of the herniated liver segment (arrow in B).

Rupture of the Diaphragm This usually results from trauma but may be idiopathic or related to previous surgery. Presentation is commonly acute but may be delayed, in which case bowel strangulation may occur. Some 80% of cases are left sided. Herniation of the stomach with gastric obstruction is common and must be distinguished from a pneumothorax and eventration. The gastric wall rarely abuts all the borders of the thoracic cage but if there is a diagnostic problem passage of a nasogastric tube or oral contrast should be helpful. Herniation of colon, spleen, and kidney is less common. Appearances on the PA film may be normal if there is rupture without herniation, or the diaphragm may be elevated with an abnormal outline. CT and ultrasound may be helpful.

Chest Wall The Bones The Clavicles

Old healed fractures are frequent findings. Erosion of the outer ends of the clavicles is associated with rheumatoid arthritis and hyperparathyroidism. Hypoplastic clavicles may be seen with the Holt-Oram syndrome and cleidocranial dysostosis.

Sternum Developmental abnormalities such as perforation, fissures, and agenesis are rare. Several sternal abnormalities are associated with congenital heart disease; examples include sternal agenesis, premature obliteration of the ossification centers, and pigeon chest, which are found with ventricular septal defects, and depressed sternum, associated with atrial septal defects and the Marfan’s syndrome. Delayed epiphyseal fusion is a feature of cretinism, and double ossification centers in the manubrium commonly occur in the Down’s syndrome. One of the commonest bony developmental abnormality of the sternum is pectus excavatum or funnel chest where the sternum is depressed and anterior ribs project outward more than the sternum itself. The heart is displaced to the left and posteriorly and appears enlarged with a straight left border and indistinct right border, with prominent lung markings and ill-defined shadowing in the right cardiophrenic angle. This should not be confused with middle lobe consolidation. The lower thoracic spine is clearly seen through the heart. Lateral plain radiograph shows the degree of sternal depression and CT is often used to quantify the severity with a measurement called “Haller index” (Fig. 14.42). This index is derived by dividing the transverse diameter of the chest by AP diameter with a normal value of 2.56 (±0.35 SD) with a value more than 3.25 often requiring surgical correction. Pectus carinatum is the deformity where the sternum protrudes outward and often described in patients with congenital cyanotic heart diseases (Fig. 14.43).

FIGURE 14.42 Pectus excavatum. Depressed sternum decreasing anteroposterior diameter with CT measurement of Hellers index. Note the right paracardiac haziness on the frontal radiograph—which is commonly seen in patients with Pectus excavatum.

FIGURE 14.43 Pectus carinatum. Protrusion of the sternum is noted anteriorly in this lateral radiograph of a 12-year-old asymptomatic female without known congenital heart disease.

Erosion of the sternum may occur with adjacent anterior mediastinal lymphadenopathy or tumors, aortic aneurysms, and infective processes. Primary tumors are rare and usually cartilaginous. The sternum may be the site of metastases, lymphoma, and myeloma. Sternal fractures are often due to a steering wheel injury, with injury of the thoracic spine being commonly associated.

The Ribs Rib notching may affect the superior or inferior surface of the rib and be unilateral or bilateral.

◾patients Superior notching (Fig. 14.44) may be a normal finding in the elderly but has been reported in with rheumatoid arthritis, SLE, hyperparathyroidism, Marfan’s syndrome, neurofibromatosis, and in paraplegics and polio victims ◾neurogenic Inferior notching (Fig. 14.45) develops as a result of hypertrophy of the intercostal vessels or with tumors (Box 14.2). Obstruction of the aorta results in reversed blood flow through the intercostal and internal mammary arteries. With coarctation the first and second intercostal arteries and ribs are not affected because they arise proximally from the costocervical trunk. The lower ribs are not affected unless the lower abdominal aorta is also involved. A preductal coarctation does not produce rib notching

FIGURE 14.44 Superior rib notching in a patient with a long history of paralysis following poliomyelitis.

FIGURE 14.45 Inferior rib notching. An elderly man who presented with hypertension. Coarctation of the aorta with rib notching most prominent in the fourth to eighth ribs.

Box 14.2

Causes of Inferior Rib Notching Unilateral Blalock–Taussig operation Subclavian artery occlusion Aortic coarctation involving left subclavian artery or anomalous right subclavian artery Bilateral Aorta—coarctation, occlusion, aortitis Subclavian—Takayasu’s disease, atheroma Pulmonary oligemia—Fallot’s tetralogy; pulmonary atresia, stenosis; truncus type IV

Venous—SVC, IVC obstruction Shunts—intercostal–pulmonary fistula; pulmonary–intercostal arteriovenous fistula Others—hyperparathyroidism; neurogenic; idiopathic

Congenital rib anomalies such as hypoplasia, bridging, and bifid ribs are common. Hypoplastic first ribs, arising from T1, are distinguished from cervical ribs. Cervical rib arises from a cervical transverse process which is usually a horizontally directed transverse process as compared to upward sloping thoracic transverse process (Fig. 14.46). Cervical ribs have an incidence of 1–2% and are usually bilateral but frequently asymmetrical. Patients with cervical rib are often asymptomatic and a symptomatic patient can present with thoracic outlet syndrome due to neurovascular bundle compression.

FIGURE 14.46 Cervical rib. Bilateral cervical ribs in this asymptomatic patient who was evaluated for trauma. The left cervical rib is longer. Note that the cervical transverse process is horizontally oriented compared to thoracic transverse process which is oriented upward.

With Down’s syndrome there are often only 11 pairs of ribs. In Tietze’s syndrome the anterior ends of the ribs are usually normal but are occasionally

enlarged or have a spotty appearance. An intrathoracic rib is uncommon and it appears as a ribbon-like shadow near to the spine attached by one or both ends. Soft-tissue masses such as a lipoma or neurofibroma may displace adjacent ribs and create a defect from pressure erosion. Crowding of the ribs occurs with a scoliosis and major pulmonary collapse, particularly in children. It is an early sign of a mesothelioma. Hyperinflation results in the ribs having a horizontal lie. Fractures are often difficult to spot on the high kilo volt peak film. There may be an accompanying extrapleural hematoma, a pneumothorax or surgical emphysema. Callus may simulate a lung mass. The sixth to ninth ribs in the axillary line are the common sites for cough fractures. Stress fractures usually affect the first ribs. Pathological fractures may be due to a local rib lesion or to a generalized reduction in bone mass as occurs with senile osteoporosis, myeloma, Cushing’s disease and other endocrine disorders, steroid therapy, and diffuse metastases. Cushing’s disease is associated with abundant callus formation. The Looser’s zones, or pseudofractures, of osteomalacia represent areas of uncalcified osteoid and the resulting rib deformity creates a bell-shaped thorax. Rib sclerosis occurs with generalized disorders such as osteopetrosis, myelofibrosis, fluorosis, and metastases, or with localized lesions such as the Paget’s disease (Fig. 14.47), in which bony enlargement is characteristic. Postirradiation necrosis results in un-united rib fractures, bony sclerosis or an abnormal trabecular pattern and soft-tissue calcification, and is often associated with a mastectomy.

FIGURE 14.47 Paget’s disease. An enlarged sixth rib with a coarse trabecular pattern and of increased density.

Localized rib expansion occurs with fibrous dysplasia, myeloma, Gaucher’s disease, and benign tumors such as eosinophilic granuloma, hemangioma, chondroma, the brown tumors of hyperparathyroidism, and aneurysmal bone cyst. In Hurler’s syndrome there is generalized expansion of the ribs, sparing the proximal ends, whereas in thalassemia expansion is most marked proximally and the trabecular pattern abnormal. Widening of the ribs is seen with rickets (Fig. 14.48) and scurvy. Rib destruction due to an infection or tumor of the soft tissues, lung, or pleura is usually accompanied by an extrapleural mass. Characteristically actinomycosis infection is associated with a wavy periostitis of the ribs. Many malignant processes including metastases, lymphoma, and myeloma commonly destroy the ribs.

FIGURE 14.48 Rickets. Enlargement and cupping of the anterior ends of the ribs (large arrow). Note the metaphyseal changes in the humeri (small arrows).

Thoracic Spine A survey is made to check for abnormal curvature or alignment, bone and disk destruction, sclerosis, paravertebral soft-tissue masses, and congenital lesions such as a butterfly vertebrae. Scoliosis and Klippel–Feil syndrome are associated with an increased incidence of congenital heart disease. With a severe scoliosis, when the curve exceeds 60°, cardiorespiratory complications are common in adults. With the straight back syndrome, the normal kyphosis is reduced so that the sternum and spine are virtually parallel, resulting in compression of the mediastinum. Characteristically on the PA film the heart appears enlarged, is displaced to the left of midline and has a prominent left atrial appendage and aorta. On auscultation there is an ejection systolic murmur with accentuation on expiration.

Anterior erosion of the vertebral bodies sparing the disk spaces may occur with aneurysms of the descending aorta, vascular tumors, gross left atrial enlargement, and neurofibromatosis, which may also cause posterior scalloping of the vertebral bodies and enlarged intervertebral foramina. Destruction of a pedicle is typical of metastatic disease. A single dense vertebra, the ivory vertebra, is the classical appearance of lymphoma but is also seen with other conditions such as Paget’s disease and metastases. Destruction of the disk with adjacent bony involvement is characteristic of an infective process. Disk calcification may be idiopathic or post-traumatic and occurs in ochronosis and ankylosing spondylitis.

Soft Tissues Artifacts Hair plaits and fasteners, buttons, clothing, and jewelry, etc., overlying the lungs may simulate a lung lesion. Tracing the edges of a lesion will show whether it extends beyond the lung margins, in which case the lesion is nonpulmonary. The suprasternal fossa, particularly in the elderly, may appear as a large translucency overlying the supraclavicular spine and should not be mistaken for a pharyngeal pouch. Skin Lesions Skin lesions including nevi and lipomas may simulate lung tumors. Multiple nodules occur with neurofibromatosis (Fig.  14.49). Pedunculated lesions have well-defined edges, being surrounded by air, and lung markings should be visible through the lesion. It is most helpful to examine the patient.

FIGURE 14.49 Neurofibromatosis. Multiple soft-tissue lesions, those overlying the lung fields simulating intrapulmonary nodules.

The Breast Mastectomy is one of the commonest causes of a translucent hemithorax. With a simple mastectomy the axillary fold is normal, but following a radical mastectomy the normal downward curve of the axillary fold is replaced by a dense ascending line due to the absence of pectoralis major (Fig. 14.50). In addition, there may be a congenital absence of pectoralis major and minor, sometimes associated with syndactyly and rib abnormalities (Poland’s syndrome) [22]. It appears as a unilateral hyperlucency of the affected side on chest radiograph and absence of the muscle is easily diagnosed on cross-sectional imaging (Fig. 14.51).

FIGURE 14.50 Left mastectomy in two different patients. (A) Left breast shadow is absent and the left lung is hypertransradiant. (B) Left mastectomy. Note the abnormal left axillary fold passing cranially (arrows). The left lung is hypertransradiant at its base. Note radiation necrosis of the upper ribs and softtissue calcification.

FIGURE 14.51 Poland syndrome. Axial (A) and coronal (B) CT images of this 11-year-old male showing absence of right pectoralis major muscle.

Surgical Emphysema This often accompanies a pneumothorax and pneumomediastinum (Fig. 14.52). After surgery an increase in the amount of emphysema on serial films suggests the development of a bronchopleural fistula.

FIGURE 14.52 Surgical emphysema in a patient of COVID-19 infection. Note the presence of left side pneumothorax (asterisk) and pneumomediastinum (arrow).

Miscellaneous Calcified nodes and parasites such as cysticercosis may overlie the lung fields.

Suggested Readings • C Charalampos, Y Andrianna, L George, et al., Pleura space anatomy, J Thorac Dis 7(Suppl 1), (2015) S27-S32. doi:10.3978/j.issn.2072-1439.2015.01.48. • DM Hansell, DA Lynch, HP McAdams, AA Bankier, Imaging of Diseases of the Chest, fifth ed., Mosby, 2009. • LR Goodman, Felson’s Principles of Chest Roentgenology, A Programmed Text, Elsevier, fifth edition, 2020. • AN Leung, NL Müller, RR Miller, CT in differential diagnosis of diffuse pleural disease, Am J Roentgenol 154 (1990) 487–492.

References [1] C. Charalampidis, A. Youroukou, G. Lazaridis, S. Baka, I. Mpoukovinas, V. Karavasilis, I. Kioumis, G. Pitsiou, A. Papaiwannou, A. Karavergou, K. Tsakiridis, N. Katsikogiannis, E. Sarika, K. Kapanidis, L. Sakkas, I. Korantzis, S. Lampaki, K. Zarogoulidis, P. Zarogoulidis. Pleura space anatomy. J. Thorac Dis. 2015; 7(Suppl 1): S27–S32. doi: 10.3978/j.issn.2072-1439.2015.01.48. [2] J.D. Rives, DD. Baker Anatomy of the attachments of the diaphragm: their relation to the problems of the surgery of diaphragmatic hernia. Ann. Surg. 1942; 115(5):745–55. [3] C. Charalampidis, A. Youroukou, G. Lazaridis, S. Baka, I. Mpoukovinas, V. Karavasilis, I. Kioumis, G. Pitsiou, A. Papaiwannou, A. Karavergou, K. Tsakiridis, N. Katsikogiannis, E. Sarika, K. Kapanidis, L. Sakkas, I. Korantzis, S. Lampaki, K. Zarogoulidis, P. Zarogoulidis. Physiology of the pleural space. J. Thorac Dis. 2015; 7(Suppl 1): S33– S37. [4] D.M. Hansell, D.A. Lynch, H.P. McAdams, AA. Bankier (2009) Imaging of diseases of the chest, 5th ed. Mosby. [5] L.R. Goodman (2020) Felson's principles of chest roentgenology, a programmed text. Elsevier; 5th ed.. [6] SR. Digumarthy, S. Abbara, J.H. Chung (2020). Problem solving in chest imaging, 1st ed., Elsevier. [7] RS Fraser, NL Muller, N Colman, PD Pare, Fraser and Pare’s Diagnosis of Diseases of the Chest, fourth ed., Philadelphia: PA: W.B. Saunders, 1999. [8] G Simon, Principles of chest X-ray Diagnosis, fourth ed., London: Butterworths, 1978. [9] T.C. McLeod, C.D.R. Flower (1991) Imaging the pleura: sonography, CT and MR imaging. Am. J. Roentgenol., 156, 1145–53. [10] C.I. Henschke, S.D. Davis, P.M. Romano, D.F. Yankelvitz (1989) The pathogenesis, radiological evaluation and therapy of pleural effusions. Radiol. Clin. North Am., 27, 1241–1255. [11] N.L. Müller (1993) Imaging of the pleura. Radiology, 186, 297–309. [12] B.N. Rasch, E.W. Carsky, E.T. Lane, J.P.O. Callaghan, E.R. Heitzman (1982) Pleural effusion: explanation of some atypical appearances. Am. J. Roentgenol., 139, 899–904. [13] P.S. Moskowitz, N.T. Griscom (1976) The medial pneumothorax. Radiology, 120, 143–147. [14] J.H. Baik, M.I. Ahn, Y.A. Park, SH. Park High resolution CT findings of re-expansion pulmonary edema. Korean J. Radiol.. 2010;11:164–8. doi:

10.3348/kjr.2010.11.2.164. [15] A.N. Leung, N.L. Müller, R.R. Miller (1990) CT in differential diagnosis of diffuse pleural disease. Am. J. Roentgenol., 154, 487–492. [16] S.M. Albelda, D.M. Epstein, W.B. Gefter, W.T. Miller (1982) Pleural thickening: its signiଁcance and relationship to asbestos dust exposure. Am. Rev. Respir. Dis., 126, 621–624. [17] T.S. Desser, P. Stark (1998) Pictorial essay: solitary ଁbrous tumor of the pleura. J. Thorac. Imaging, 13, 27–35. [18] G. Hillerdal (1983) Malignant mesothelioma 1982: review of 4710 published cases. Br. J. Dis. Chest, 71, 321–343. [19] A. Kawashima, H.I. Libshitz (1990) Malignant pleural mesothelioma: CT manifestations in 50 cases. Am. J. Roentgenol., 155, 965–969. [20] B.H. Miller, M.L. Rosado-de-Christenson, A.C. Mason, et al (1996) From the archives of the AFIP: malignant pleural mesothelioma: radiological–pathological correlation. Radiographic, 16, 613–644. [21] L.K. Nason, C.M. Walker, M.F. McNeeley, W. Burivong, C.L. Fligner, J. David Godwin. Imaging of the diaphragm: anatomy and function. Radiographics. 2012;32(2):E51-70. doi: 10.1148/rg.322115127. [22] M. Pearl, T.F. Chow, E. Friedman. Poland's syndrome. Radiology 101:619-623, 1971.

15

Pulmonary Infections Neeraj Kaur, Prashant Nagpal, Sachin S. Saboo

Introduction Inflammatory disease of the lung may be referred to as either pneumonia or pneumonitis. Although these terms are interchangeable, pneumonia usually implies an infection by pathogenic organisms resulting in consolidation of lung, whereas pneumonitis tends to refer to those inflammatory processes that primarily involve the alveolar wall, for example, fibrosing alveolitis in the United Kingdom or usual interstitial pneumonia in the United States. Typically, pneumonia is characterized by a newly recognized lung infiltrate on chest imaging together with fever, cough, sputum production, shortness of breath, physical findings of consolidation, and leukocytosis [1].

Role of Radiological Techniques in Pulmonary Infection Radiograph Chest radiograph (CXR) is the initial screening technique for any patient presenting with chest complaints. Standard 2 view radiographs include frontal and lateral radiographs. CXR define the extent of pneumonia, laterality of the infection, detect complications such as pleural effusion, pneumothorax, empyema, lung abscess, and identify alternative diagnosis such as underlying malignancy. Common radiographic features of pulmonary infection include consolidative opacities, ground-glass opacity (GGO) or reticulonodular opacity. Less commonly seen radiographic findings include lymphadenopathy (hilar or mediastinal), pleural effusion, cavitation, or pneumatoceles [2]. CXR are sufficiently accurate to diagnose community-acquired pneumonia (CAP) in most immunocompetent patients; however, accuracy is diminished in patients with chronic obstructive pulmonary disease, atelectasis, or congestive heart failure. The pace of radiographic improvement is related to patient age as well as initial pneumonia extent and it often lacks the clinical improvement. The accuracy of CXR for the detection of hospital-acquired pneumonia (HAP) and ventilatoracquired pneumonia (VAP) is less than that for CAP, because of confounding opacities caused by atelectasis and pleural effusions [3–6].

Computed Tomography Three major computed tomography (CT) techniques are used for the imaging of the chest: spiral CT, high-resolution CT (HRCT), and CT angiography (CTA). CT is the imaging technique of choice for assessing patients with suspected pulmonary infections [7] and volumetric thin-section spiral CT with thin detectors (0.5–0.625 mm) has become the routine in many institutions in evaluation of patients with clinical suspicion of infection and normal or nonspecific radiographic appearance [8]. HRCT is typically used for the assessment of interstitial lung diseases and is useful in the detection of subtle pulmonary infectious abnormalities. CT leads to early detection of the pulmonary infections compared with CXR by a lead time of at least 5 days and helps in differential diagnosis.

CT can be helpful in differentiating atelectasis or cardiogenic pulmonary edema from pneumonia and detecting radiographically occult infectious bronchiolitis [4]. CT plays a major role in the identification of complications such as cavitation, abscess, empyema, chest wall, and other thoracic and upper abdominal organ extension of the infection. CTA chest helps to delineate the vascular structures and is needed for the evaluation of the pulmonary and bronchial vasculature in the pulmonary infections. This is particularly useful for the assessment of the bronchial arteries before embolization in a patient presenting with clinical symptoms of hemoptysis. Nuclear medicine imaging: Nuclear medicine imaging is used sometimes for the pulmonary infections such as pneumocystis jirovecii pneumonia (PJP) in the acquired immunodeficiency syndrome (AIDS) patients. The combination of a positive thallium-201 scan and a negative gallium67 scan can be specific for the diagnosis of Kaposi sarcoma [9]. Pneumonias can be classified based on the clinical presentation, imaging morphological appearance, and etiology.

Clinical Classification Community-Acquired Pneumonia CAP indicates acute lung infection in patients who do not satisfy the criteria for HAP or healthcareassociated pneumonia (HCAP), and it is associated with at least some symptoms of acute lung infection, along with the presence of an acute lung opacity on a chest imaging (Fig. 15.1) [10–12]. Pulmonary opacities are radiographically seen within 12 hours of the onset of symptoms.

FIGURE 15.1 Community-acquired streptococcal pneumonia-related acute chest syndrome in sickle cell disease with worsened anemia and acute chest syndrome (ACS). There is a right lower lobe round consolidative opacity (arrow) suggestive of a round pneumonia. There is cardiomegaly due to hyperdynamic circulation.

The common pathogens are Streptococcus pneumonia, Haemophilus influenzae, Staphylococcus aureus, Moraxella catarrhalis, Pseudomonas aeruginosa, atypical organisms (mycoplasma, viral, chlamydia), Legionella, Klebsiella, and other gram-negative bacteria. Recently, new pathogens such as avian influenza A viruses (H5N1), coronavirus associated with severe acute respiratory syndrome (SARS), Middle-East respiratory syndrome (MERS), swine flu (H1N1), and COVID-19 are increasingly recognized as a cause for CAP. Despite exhaustive testing, no organism is found in about 30–65% of cases. CAP is the most common type of pneumonia, whereas the VAP is the least common [1,12,13]. Disease severity in CAP is used to indicate prognosis and to guide management and the most commonly used scores for such assessment are pneumonia severity index, the CURB65, the SMART-COP score, the major and minor criteria recommended by the American Thoracic Society/Infectious Disease Society of America and quick Sepsis Organ Failure score. Pleural effusion, multilobar involvement, and empyema are the most frequent pulmonary complications in CAP [14].

Hospital-Acquired Pneumonia HAP is pneumonia acquired after admission to the hospital, with infection neither present nor in the incubation period at the time of the hospital admission. Nosocomial or HAP leads the cause of death from hospital-acquired infections. This is seen in intensive care patients and those requiring mechanical ventilation. The most common organisms implicated are Pseudomonas and S. aureus [10,12,15].

Healthcare-Associated Pneumonia

HCAP is pneumonia related to risk from healthcare-related risk factors of recent hospitalization for 20 or more days in the past 90 days of infection, dialysis, nursing home residents, residents of longterm care facilities, and immunocompromised states. Pathological organisms are similar to the HAP including Pseudomonas and S. aureus. The use of the term HCAP was discontinued in the latest management guidelines [10,12,16].

Ventilator-Associated Pneumonia Pneumonia within 2–3 days after recent endotracheal intubation-related ventilation. VAPs are typically caused by Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacteriaceae [10,12].

Pneumonia in the Immunocompromised Patient All of the previously mentioned pneumonias can occur in an immunocompromised individual. However, certain infections are specifically seen in the immunocompromised states and thus are referred to as opportunistic infections. These include fungal infections such as Aspergillus, Nocardia, and viral pathogens such as CMV, HHV 8, and parasitic infection such as pneumocystis jirovecii, etc. [12,17].

Patterns of Pulmonary Infections Pulmonary infections can be broadly divided into three types:

◾ affecting the pulmonary parenchyma called as pneumonia, ◾ the small airways called as bronchiolitis, ◾ affecting affecting the center airways called as tracheobronchitis.

Pneumonia further can be characterized into lobar pneumonia, bronchopneumonia, and interstitial pneumonia; however, it should be remembered that differentiation among different patterns is often difficult and unreliable in suggesting a particular pathogen.

Radiographic and CT Imaging of CAP The radiographic and CT patterns of CAP can be traced to the causative agent. The lower respiratory tract (LRT) infection/pneumonia acquired by way of the airways and confined to the lung parenchyma and airways manifests radiographically and on CT through either of the three patterns: 1. Focal nonsegmental or lobar pneumonia 2. Multifocal bronchopneumonia or lobular pneumonia 3. Focal or diffuse “interstitial” pneumonia [2,18]

Lobar Pneumonia Lobar pneumonia refers to the consolidation of partial or complete segments of lung or less commonly an entire lobe. This is the most common presentation of the CAPs and is often bacterial in origin. Common causes of lobar consolidation are Legionella species, Streptococcus pneumoniae (Fig. 15.2), Klebsiella pneumonia, and Mycoplasma pneumoniae [11]. Specific radiological signs include air bronchogram sign (due to the patency of the larger bronchioles), bulging fissure sign (typically seen in the Klebsiella pneumonia), and no significant volume loss of the involved segment or lobe [2,11].

FIGURE 15.2 Streptococcus pneumonia. Frontal radiograph of the chest in a middle-aged man with COPD presenting with cough, fever, chills and underlying reveals right upper lobe pneumonia-related consolidation bound inferiorly by the minor fissure (arrows) along with multifocal airspace opacities in the right middle and lower lobe due to bronchopneumonia.

Bronchopneumonia (Lobular Pneumonia) Bronchopneumonia is defined by the peribronchiolar inflammation and characterized radiologically as poorly marginated airspace nodules. Unlike lobar consolidation, air bronchograms are absent. On radiographs, these cause a typical patchy distribution of large heterogeneous scattered poorly defined airspace opacities which become more homogeneous with progression of disease (Fig. 15.3). Most common organisms causing this pattern of disease are S. aureus, H. influenzae, P. aeruginosa, anaerobic bacteria, and fungi. CT shows poorly defined centrilobular nodules, airspace nodules, linear, branching airspace opacities, and multifocal lobular areas of consolidation [2,11]. Infectious disease-related cellular bronchiolitis and centrilobular nodules can be seen on CT with endobronchial spread of tuberculosis (TB) and nontuberculous mycobacteria (NTMB), viral bronchiolitis, bacterial and fungal pneumonia, and allergic bronchopulmonary aspergillosis (ABPA) [8].

FIGURE 15.3 Bronchopneumonia. Frontal chest radiograph shows extensive, bilateral, diffusely distributed ill-defined nodular solid and ground-glass opacities (arrows) in both lungs representing bronchopneumonia pattern, which in this case was due to bacterial etiology. An area of confluence is seen in the right upper lobe.

Interstitial Pneumonia/Atypical Pneumonia Interstitial pneumonia is secondary to the infection of the peribronchial tissue and interstitial tissues and manifests radiologically as heterogeneous opacities, best described as extensive peribronchial thickening, reticular, or reticulonodular opacities distributed in a focal or diffuse distribution on radiograph. These correlate with bronchial wall thickening and bronchiolitis (centrilobular nodules) appearance on CT. These can be associated with patchy subsegmental or plate-like atelectasis. It is commonly caused by viral and atypical organisms such as mycoplasma, chlamydia, or PJP (Fig. 15.4) [2,11].

FIGURE 15.4 Pneumocystis jirovecii pneumonia (PJP). Axial lung window chest CT image in a 45-year-old woman with shortness of breath after chemotherapy for breast malignancy shows diffuse multifocal patchy ground-glass opacities (arrows) in both lungs which were confirmed to be due to PJP on bronchoalveolar lavage (BAL).

Round Pneumonia Round pneumonia is seen typically in children, can occur in adults and is believed to be due to the incomplete development of pores of Kohn. This leads to the confinement of the infection and presents as a rounded mass-like opacity. The common causative organism is Streptococcus pneumoniae (Fig. 15.1) [2,11]. Table 15.1 lists differential diagnosis and approach to common CT-based signs of lung infection from other important noninfectious causes. Table 15.1 CT Patterns Caused by Infectious Etiologies and Its Noninfectious Mimics in an Immunocompetent Host CT Pulmonary Pulmonary Noninfection Cause Appearance Infection Linear and groundglass opacitie s

Uncommon (interstitial pneumonia)

Centrilo bular nodules

Common (bronchopneu monia)

Interstitial pulmonary edema, pulmonary hemorrhage, hypersensitivity pneumonitis, organizing pneumonia, alveolar proteinosis, and drug reaction

Respiratory bronchiolitis, acute hypersensitivity pneumonitis (HP)

CT Pulmonary Appearance Infection

Pulmonary Noninfection Cause

Tree-inbud nodules

Common (endobronchial spread of infection)

Aspiration, pulmonary artery metastasis (rare)

Rando m nodules

Uncommon (ex: disseminated fungal infections and miliary TB)

Metastases

Lobular GGO or consoli dation

Common

Pulmonary edema, pulmonary hemorrhage, chronic infiltrative lung diseases, drug toxicity

Nonseg mental consoli dation

Common

Atelectasis

Segmen tal consoli dation

Common

Pulmonary infarction

Ex, example.

Some signs common to lung infections and noninfective etiologies are as follows:

◾ Halo sign, typical of early invasive fungal infection in immunosuppressed host, can also be seen with hemorrhagic metastasis in an immunocompetent host ◾ Reverse halo sign indicative of early invasive fungal infection in immunosuppressed host, can also be seen with pulmonary infarct and organizing pneumonia in an immunocompetent host ◾ Crescent sign suggests resolving invasive fungus infection with overall normal underlying lung in immunosuppressed host while this sign is suggestive of aspergilloma colonizing preexisting cavity in an immunocompetent host [3,4]

Lung Necrosis, Lung Abscess, and Cavity On radiograph, lung necrosis appears as focal lucency within an area of consolidation typically later in the course of the disease. On CT, lung necrosis appears as geographic areas of nonenhancing lung parenchyma, some of which progress to discrete lung abscesses. Lung abscess is defined as an inflammatory mass within the lung parenchyma, the central part of which has undergone purulent liquefaction, necrosis, and pus-filled cavitation secondary to infection by pyogenic bacteria. CT shows air–fluid levels in three-fourth of cases and adjacent parenchymal consolidation in half of the cases (Fig. 15.5) [11]. A variety of organisms may be responsible, and anaerobic bacteria (most commonly Fusobacterium nucleatum [Fig. 15.6] and Bacteroides species), S. aureus, P. aeruginosa, and K. pneumoniae are the common causes. Other causes include septic pulmonary emboli, mycobacteria, fungi, parasites, trauma, and rarely, viral infections. Suppuration and necrosis of pulmonary tissue with secondary abscess may also occur due to malignant tumor and infected cysts [3,4].

◾ Onindicates radiograph, an abscess appears as irregular masses with the ill-defined outer aspect. Appearance of an air–fluid level that a communication with the airways has developed [19]. The wall of the abscess may be thick at first, but with further necrosis and coughing up of infected material it becomes thinner ◾ Onadjacent CT, lung abscess is typically round or oval, low fluid attenuation lesion (Fig. 15.7), forming acute angles with pleura, have irregular densely enhancing inner wall contour in acute stage with varying wall thickness (Fig. 15.5). This needs to be differentiated from empyema which typically has smooth inner wall contour with uniform wall

thickness (Fig. 15.8). Lung abscess typically cause truncation of adjacent bronchi and pulmonary vessels which may also be seen entering an abscess wall [3,4]. Treatment-related healing of lung abscess result in thinning and more sharply defined wall of an abscess along with reduction in the size and fluid contents of the abscess

FIGURE 15.5 Complicated pyogenic lung abscess. Coronal chest soft-tissue window image in a 48-year-old man with history of achalasia cardia presenting with fever and difficulty swallowing shows right upper lobe pyogenic lung abscess with air–fluid level (bold arrow) as a sequelae of aspiration. There is adjacent focal mediastinal pleural thickening with air-filled outpouching extending into the adjacent mediastinum (dotted arrow), consistent with fistula of the lung abscess with adjacent mediastinum and focal mediastinitis. Note the dilated, food, and air-filled esophagus (double arrow) due to achalasia cardia. Star denotes trachea.

FIGURE 15.6 Organizing pneumonia due to Fusobacterium necrophorum Axial chest CT lung window image in a 58-year-old woman with high fever, weakness, and cough for 2 months shows a peripheral pleural-based cavitary nodular opacity in the left lower lobe (arrow).

FIGURE 15.7 Mycoplasma pneumonia complicated by lung abscess and pleural effusion. Axial soft-tissue window in a 26-year-old woman with mycoplasma pneumonia-related partial collapse and consolidation of the left lower lobe and lingula (black arrows) complicated by focal left lower lobe lung abscess (white arrow). There is secondary left parapneumonic effusion and inflammatory mild linear enhancing left pleural thickening. Multifocal ground-glass opacities were seen in both lungs (not shown).

FIGURE 15.8 Klebsiella pneumonia complicated by lung abscess and empyema. Sagittal soft-tissue window chest CT image in a 43-year-old diabetic woman with new onset hemoptysis, cough, left-sided rib pain. Partially enhancing moderate to large left lower empyema (white arrows) containing scattered foci of air. There is a small thick-walled lung abscess along the lateral inferior lingular lobe (black arrow). Note pneumonia-related heterogeneously enhancing consolidative opacities involving most of the left lower lobe, with associated volume loss.

Lung cavity is an air-filled space, appearing as a lucency or low-attenuation area, within a nodule, mass, or area of parenchymal consolidation with clearly defined wall >4-mm thick. Cavities can be classified into acute and subacute cavities if they are 12 weeks old. Acute and subacute cavities are typically due to acute infection (lung abscess, necrotizing pneumonia, septic emboli, fungal infection, and nocardia), whereas chronic or indolent evolution of cavities suggests chronic infections (TB, NTMB, fungal, parasitic, and viral), autoimmune conditions (rheumatoid arthritis, granulomatosis with polyangiitis), or malignancy (primary lung cancer, metastatic lung disease) [20].

Aspiration Pneumonias Aspiration of particulate or liquid foreign material into the lungs can result in mechanical bronchial obstruction and inflammation. When the cough reflex is suppressed by stupor, alcohol, or drugs; aspiration of food from the stomach during vomiting is likely to occur. The inflammatory response excited by vegetable matter is intense and commonly followed by secondary infection with commensals and anaerobic organisms. Aspiration of infected material from nasal and oral sepsis is a common cause of lung abscess. Radiologically, this aspiration manifests as atelectasis or suppurative bronchitis and pneumonia (Fig. 15.9). Metallic or inorganic particles typically cause mechanical effects of uncomplicated

atelectasis or obstructive emphysema and they may remain undetected for long periods. Aspiration of bland substances such as water, blood, or neutralized gastric contents result in little inflammation manifesting radiologically with consolidation in dependent portions of lung while inflammatory pulmonary edema result from aspiration of acidic gastric contents. Pleural effusion is uncommon with aspiration unless complicated by pneumonia (Fig. 15.9).

FIGURE 15.9 Aspiration pneumonia. Diffuse bilateral centrilobular ground-glass nodules and tree-in-bud opacities in the right middle lobe and bilateral lower lobes with peripheral consolidation, due to aspiration pneumonia. The high-density opacities, favored to represent aspirated barium contrast (arrows) from recent upper GI study. Note esophageal stent in the mid to lower thoracic esophagus placed for the treatment of bronchoesophageal fistula to the right lower lobe bronchus.

Exogenous lipoid pneumonia develops when lipid-containing substances of mineral, animal, or vegetable origin travel to the LRT, most commonly through aspiration of nasally applied or ingested material, or less commonly, through inhalation. The prolonged use of liquid paraffin for constipation is the usual cause and a precipitating factor is chronic esophageal obstruction. The oil is almost inert and the reaction is indolent, granulomatous, and fibrotic; any lung damage is permanent. Radiographically, there are dense well-defined tumor-like masses or an extensive bilateral opacity spreading outward from the hilar regions. On CT, bilateral consolidative and GGOs, crazy-paving pattern are the most common radiologic findings, with fatty attenuation of lesions (Fig. 15.10) in less than 50% of patients. Bronchiectasis and fibrosis result with chronicity [21]. Vegetable oils and animal fats such as milk induce a greater inflammatory response and the opacities are ill defined and bronchopneumonic [22].

FIGURE 15.10 Lipoid pneumonia. Axial soft-tissue window (left) and coronal lung window (right) chest CT images in a 67-year-old man with cough, mild fever, and chest discomfort shows mixed consolidative (black arrow) and ground-glass (white arrows) opacities in the right lower lobe with some areas demonstrating fat component with mean attenuation of −31.4 HU (left image) consistent with lipoid pneumonia due to acute on chronic mineral oil aspiration.

Influenced by gravity, the lesions of aspiration and inhalation are found predominantly in the posterior parts of the lungs. Small aspirates are common in the elderly from incompetence of the closing mechanism of the larynx. These recurrent aspirations produce coarse peribronchial thickening, small patches of pneumonia, and eventually fibrosis and bronchiectasis.

Bacterial Pneumonias Streptococcus Pneumoniae Streptococcus pneumoniae/pneumococcus is the most commonly identified cause of CAP, however, its frequency has declined, and it is now detected in only about 10–15% of inpatient cases in the United States [1]. It is also responsible for most of the pneumonia in all age groups. Classic radiographic and CT feature of acute pneumococcal pneumonia consists of a homogeneous nonsegmental consolidation that can evolve into lobar pneumonia. The lobar pattern can mimic Klebsiella pneumonia except that volume of the consolidated lung remains normal. It can also present with bronchopneumonia pattern-related patchy, multifocal GGO, and consolidative opacity (Fig. 15.2). Rarely, it can appear as a spherical focal mass-like consolidation/round pneumonia (Fig. 15.1). Pleural effusion is common. Resolution is usually complete and complications like cavitation and abscess formation are unusual if treated immediately [10,11,13,23].

Staphylococcus Aureus S. aureus is a common cause of pneumonia. In debilitated patients, nosocomial pneumonia and may also cause superinfection in influenza. Hematogenous infection of S. aureus to the lungs/septic emboli is a common complication of intravenous drug abuse and bacterial tricuspid valve

endocarditis which appears as multiple poorly defined rounded solid pulmonary nodules that cavitate (Fig. 15.11) over a period of several days and are usually peripherally located and predominate in the lower lobes. Wedge-shaped areas of peripheral consolidation are common with septic embolization.

FIGURE 15.11 Pulmonary methicillin-resistant Staphylococcus aureus (MRSA) infection. A composite image with posteroanterior (left) zoomed chest radiograph and axial CT lung window image (right) in a young patient with left thumb abscess after injury, reveals right upper lobe partly cavitary peripheral nodular opacity in the right upper lobe (arrow).

Infection may also result from inhalation, typically leading to bronchopneumonia which appears on CT as bilateral patchy often multifocal consolidative opacities, often associated with centrilobular nodules or tree-in-bud opacity. The “feeding vessel sign,” due to hematogenously disseminated of disease to the lung, can be seen with septic emboli (Fig. 15.12). Other features are areas of atelectasis, cavitation, abscess formation pneumatoceles, pleural effusions, empyema, spontaneous pneumothorax, and progression to diffuse alveolar damage (Fig. 15.13) [10,11,13,23].

FIGURE 15.12 Pulmonary methicillin sensitive Staphylococcus aureus (MSSA) bacteremia. Coronal CT lung window image in MSSA bacteremia with sepsis associated with catheter line infection presenting with hypoxic respiratory failure shows multifocal pneumonia in the form of solid and cavitary pulmonary nodules in the predominant peripheral and peribronchial distribution, many manifesting the feeding vessel sign (arrow) (nodules are often closely associated with pulmonary vasculature) due to septic emboli. Also noted are bilateral loculated pleural effusions.

FIGURE 15.13 Acute interstitial pneumonia (AIP)/diffuse alveolar damage due to MRSA. Axial chest CT lung window image in a 50-year-old man presenting with shortness of breath shows multifocal patchy and geographic interstitial and airspace ground-glass and consolidative opacities with crazy-paving appearance in both lungs and gradient in the bilateral lower lobes from anterior to posterior portion. The anterior portions revealing groundglass changes and posterior portion revealing consolidation consistent with acute interstitial pneumonia which in this case was related to MRSA.

Klebsiella Pneumonia K. pneumoniae is the cause and usually occurs in elderly debilitated men. It usually causes lobar consolidation with air bronchograms, causing the volume of the affected lobe to be maintained or increased (bulging fissure sign). This frequently involves upper lobe and more often on right side. CT shows GGOs, consolidation, and intralobular reticular opacity and sharp margins of the advancing border of the pneumonic opacities. A bronchopneumonic pattern may occur. Complications of cavitation (Fig. 15.14), pulmonary abscess, pleural effusion, and empyema (Fig. 15.8) are common. Healing with fibrosis can mimic chronic fibrocavitory form of TB [11,23].

FIGURE 15.14 Klebsiella pneumonia. There is a large cavity in the right lower lobe after cavitation of pneumonic consolidation. An aortic valve replacement is present.

Legionnaire’s Disease Since first identified in early 1977, Legionella pneumophila bacteria are recognized as a common cause of CAP. The organism is ubiquitous in water, multiplying in water coolers, air conditioners and showers, and infection takes place from inhalation of an aerosol mist. It is prone to attack smokers, the debilitated and older men. Radiographically, it presents as spreading peripheral focal consolidation like S. pneumoniae pneumonia, and although it may be confined to one lobe (lobar pneumonia) initially, it soon extends to several lobes (Fig. 15.15), to the opposite lung and in severe cases results in respiratory failure with diffuse alveolar damage. Cavitation occurs frequently in immunocompromised patients. Small pleural effusions are common; abscess and pneumatocele formation are rare [24]. A characteristic feature is the slow radiographic resolution over several weeks compared with other bacterial pneumonias, but this is usually complete [25].

FIGURE 15.15 Legionella pneumonia. Axial chest CT image in a 60-year-old man with alcohol abuse with high-grade fever and chills shows right lower lobe consolidation with mild surrounding ground-glass opacities (arrows) crossing the fissure (dotted arrow) extending into the posterior segment of the right upper lobe suggesting aggressive infection and was proved to be Legionella pneumonia on positive urine test.

Haemophilus Influenzae H. influenzae pneumonia is predisposed by immunodeficiency and debilitated status. CXR and CT usually show nonspecific bronchopneumonic pattern of multifocal, multilobar patchy with segmental, lobar or bilateral consolidation. Centrilobular nodules or tree-in-bud nodules can be seen on CT. Pleural effusions is common; however, cavitation and empyema are uncommon [26,27].

Gram-Negative Bacilli Pneumonia The main causes of gram-negative pneumonias are Klebsiella pneumoniae, Enterobacter sp., Serratiamarcescens, Escherichia coli, Proteus sp., and Pseudomonas aeruginosa. Patients typically have underlying debilitating chronic medical or pulmonary condition and pneumonia normally results from inhalation but may also be hematogenous in origin. They have lower lobes predominance of affection. The radiographic and CT appearances are bronchopneumonia pattern with cavitation, pleural effusions, and empyema formation like that seen with S. aureus infections in adults. Escherichia coli accounts for 4% of cases of CAP and 5–20% of cases of HAP or HCAP. Pseudomonas aeruginosa is the most common cause of nosocomial pulmonary infection that causes confluent (Fig. 15.16) and extensive bronchopneumonia with frequent cavitation.

FIGURE 15.16 Pseudomonal pneumonia. Frontal radiograph of the chest and axial chest CT image in a middle-aged man on immunomodulator therapy for Crohn’s disease and DM reveals large right upper lobe consolidation (black arrows) with bulging right transverse fissure (white arrow) on x-ray and major fissure on CT.

Melioidosis Melioidosis, a disease of tropical countries of the East, is caused by Pseudomonas pseudomallei. It may manifest years after the patient has left an endemic area. It can present with a septicemic disseminate infection with necrotizing lesions, a chronic apical pneumonia which breaks down to form a thin-walled cavity [28], lobulated heterogeneously enhancing anterior mediastinal lymph nodal mass [29] or as lung consolidative mass with pleural and pericardial effusion, and mediastinal lymph node thus can mimic lung cancer [30].

Tularemia Infection is usually acquired by contact with infected animals with aerobic gram-negative bacillus Francisella tularensis and occurs through inhalation, intradermal injection, or oral ingestion. A nonspecific airspace multifocal unilateral or bilateral consolidative opacity due to pneumonia is most common finding in patients with tularemia and occurs typically in rural settings. Pleural effusion and hilar or mediastinal lymphadenopathy due to granulomatous lymphadenitis are seen in 50–90% of affected patients [31].

Atypical Pneumonia The term “atypical pneumonia” is imprecise and arguably outdated; however, the concept of atypical pathogens is still accepted. Atypical pneumonia term was originally characterized by initial mild symptoms and scant sputum production, with progression to an illness of varying severity, extrapulmonary systemic involvement, and lack of response to penicillin therapy. “Atypical” denotes acute febrile illness characterized by acute inflammatory changes centered within the alveolar walls and interstitium and the lack of the alveolar exudate evident in most pneumonic infections [32]. The lack of typical findings of lobar consolidation on CXRs and failure to isolate a pathogen using routine bacteriologic testing methods are also common features of this group of microorganisms. Infections with Mycoplasma pneumoniae, C. pneumoniae, Legionella pneumoniae are the most common nonzoonotic causes, while the most common zoonotic bacteria that cause atypical pneumonias are Chlamydia psittaci (psittacosis), F. tularensis, and Coxiella burnetti (Q fever). Influenza virus types A and B, parainfluenza virus, respiratory syncytial virus (RSV), adenovirus, and human metapneumovirus are among the most common viruses causing atypical pneumonia and responsible for CAP in humans [33]. The term atypical pneumonia in the radiologic

reports should be carefully used by providing mention in the report if the radiographic pattern observed is commonly seen with certain infections or if it raises the possibility of alternative diagnosis [33].

Mycoplasma Pneumoniae This is the only member of the mycoplasma group that is commonly pathogenic in man. Although classed as bacteria these organisms are unlike other common bacterial species, being smaller and lacking rigid cell walls containing peptidoglycan. Patients with M. pneumoniae can develop neurologic syndromes, venous thrombosis, pericarditis, and myocarditis. The earliest chest radiographic signs are interstitial opacities in the form off-line reticular or nodular shadows followed by the consolidation pattern, which may be segmental or lobar. CT typically shows consolidation in patchy, segmental, and lobular pattern, centrilobular nodules, or GGOs (Fig. 15.17). Cavitation, lymph node enlargement and pleural effusion are uncommon (Fig. 15.7). Mosaic attenuation and air trapping may be seen due to small airway obstruction. Adults may be more likely to present with this bronchiolitis–bronchopneumonia pattern than children in whom segmental and lobar pneumonia may be more common similar to that of bacterial lobar pneumonia [34].

FIGURE 15.17 Mycoplasma pulmonary infection. Axial lung window chest CT image in a 56year-old man with antisynthetase syndrome shows multifocal patchy diffuse ground-glass opacities and streaky linear opacities related to atypical mycoplasma pulmonary infection along with few lung cysts.

Viral Pneumonias Viral pneumonia is traditionally uncommon in adults, unless the patient is immunocompromised. Most pneumonia that complicate viral infections in adults are due to bacterial superinfection. However, viral pneumonias are not rare in infants and children. CT is currently the imaging technique of choice for the evaluation of pulmonary viral infections even though its features are usually nonspecific [8]. Clinically, viral pneumonia in adults can be divided into atypical pneumonia in an immunocompetent hosts and viral pneumonia in immunocompromised hosts.

Influenza virus types A and B account for most viral pneumonias in immunocompetent adults [35]. Viral pneumonia usually commences in distal bronchi and bronchioles as an interstitial process with destruction of the epithelium, edema, and lymphocytic infiltration. There may also be focal inflammation of the terminal bronchioles and alveoli and progression to hemorrhagic pulmonary edema. The radiographic appearances of a viral pneumonia are very varied, but often include peribronchial opacities, reticulonodular opacities, and patchy or extensive consolidation. CT appearances reflect various histopathologic features seen in viral pneumonia such as diffuse alveolar damage, intra-alveolar hemorrhage, and interstitial intrapulmonary or airway inflammation. CT appearances of various viral pneumonias have been summarized in Table 15.2 [36]. Table 15.2 CT Findings in Viral Pneumonia Pulmonary Pulmonary GroundNodules, Etiology of Glass Micronodule Viral Opacities s, and TreePneumonia and In-Bud Consolidati Opacities on

Interlobul ar Septal Thickenin g

Bronchial and Bronchiol Miscellaneous ar Wall Findings Thickenin g

Adeno virus

+++

None

None

+++

Sequalae: bronchiect asis, bronchiolit is obliterans, and unilateral hyperluce nt lung

Herpe s simple x virus

+++

++

None

None

Solid lung nodules with halo sign

Varice lla

+++

+++

None

None

Solid lung nodules with halo sign, nodule calcificati on

CMV (Fig. 15.19)

+++

++

None

None

Solid lung nodules with halo sign

Systemic Findings

Gingivosto matitis, pharyngitis

Pulmonary GroundEtiology of Glass Viral Opacities Pneumonia and Consolidati on

Pulmonary Nodules, Micronodule s, and TreeIn-Bud Opacities

Interlobul ar Septal Thickenin g

Bronchial and Bronchiol Miscellaneous ar Wall Findings Thickenin g

Systemic Findings

EBV

+++

+

+

None

Solid lung nodules with halo sign

Infectious mononucle osis Mediastin al lymphade nopathy

Influe nza A

+++

+++

None

++

DAD

Avian flu (H5N1): pneumatoc ele, pleural effusion

Parain fluenz a 1–4

+++

+++

None

None

RSV

+++

+++

None

++

Centrilobu lar nodules

HMP V

+++

+++

None

++

Centrilobu lar nodules

Measl es

+++

+++

++

++

Centrilobu lar nodules, pleural effusion, lymphade nopathy

Gastroente ritis

Hanta virus (HCP S)

+++

++

+++

None

Pulmonary edema

Shock

Pulmonary GroundEtiology of Glass Viral Opacities Pneumonia and Consolidati on

Pulmonary Nodules, Micronodule s, and TreeIn-Bud Opacities

Interlobul ar Septal Thickenin g

Bronchial and Bronchiol Miscellaneous ar Wall Findings Thickenin g

Coron avirus (SAR SCoV2, SARS -CoV1, MER SCoV

+++

Rare

+++

Unco mmo n

HPIV

+

+

None

++

Mump s

++

None

None

Rare

Rhino virus (Fig. 15.66)

++

+

None

Unco mmo n

Systemic Findings

Peripheral, multifocal opacities, crazypaving lung pattern Pleural effusion rare

Parotid gland involved

DAD, diffuse alveolar damage; GGO, ground-glass opacity; HMPV. human metapneumovirus; HCPS, Hantavirus cardiopulmonary syndrome; plus signs indicate the relative frequency of the findings from lowest (+) to highest (+++). SARS-CoV, severe acute respiratory syndrome coronavirus; MERS-CoV, Middle East respiratory syndrome coronavirus; HMPV, human metapneumovirus; HSV, herpes simplex virus; RSV, respiratory syncytial virus.

Influenza Virus Influenza outbreaks occur typically in winters due to influenza type A virus.

◾ Pneumonia as a complication of influenza is normally due to secondary bacterial infection, often Staphylococcus aureus, Streptococcus pneumoniae, or Haemophilus in which case changing pattern of radiographic findings and lobar consolidation are helpful in the diagnosis of bacterial-superimposed infection ◾ Adolescents, elderly, and debilitated patients may develop a primary viral influenza pneumonia-related tracheobronchitis and bronchopneumonia which appear on radiograph as lower lobe predominant bilateral reticulonodular opacities and/or multifocal consolidations ◾ Ill-defined patchy or nodular consolidations on radiograph and CT that become confluent are also seen secondary to diffuse alveolar damage or superinfection that typically subside in 3 weeks ◾ Ill-defined small nodules and patchy GGOs due to influenza are reported in patients with underlying hematological malignancies [37]

Patients can progress to hemorrhagic pneumonia, acute respiratory distress syndrome, or organizing pneumonia. If the patient survives, extensive pulmonary fibrosis may develop. The swine-origin influenza A (H1N1) virus emerged in Mexico in April 2009 and become global pandemic with the dominant CT findings being GGOs, patchy consolidation, or a mixed pattern of GGOs and areas of consolidation, frequently in bilateral, peripheral subpleural, and peribronchovascular distribution [38]. Avian flu is caused by H5N1 subtype of influenza type A through contacts with birds and can show additional findings of centrilobular nodules, pneumatocele, pseudocavitation, and lymphadenopathy on CT [38,39].

Herpes Varicella Zoster Varicella pneumonia/chickenpox occurs more often in adults than in children.

◾ Inconfluent the acute phase of infection, the CXR and CT may show widespread random distribution multiple ill-defined, nodular opacities up to 1 cm in diameter with halo sign due to multicentric hemorrhage and necrosis centered on airways, and clinically the pneumonia will be concurrent with the typical skin rash ◾ After recovery a small proportion of these nodules calcify and may produce a characteristic radiographic and CT appearance of randomly distributed 2–3 mm densely calcified nodules (Fig. 15.18) [40]

FIGURE 15.18 Multiple calcified varicella scars.

FIGURE 15.19 Cytomegalovirus (CMV) pulmonary infection. Coronal chest CT lung window image in a young man presenting with acute hypoxemic respiratory failure shows multifocal ground-glass opacities with areas of crazy-paving appearance in both upper lobes proved on PCR to be due to CMV.

Disseminated varicella zoster virus infection is seen with underlying immunocompromised status [8].

Measles Giant Cell Pneumonia Measles virus infections are frequently reported in adults and children and severe cases present with pneumonia, gastroenteritis and encephalitis especially in pregnant females and immunocompromised patients. Bronchitis and/or bronchiolitis and interstitial pneumonia due to measles manifest radiologically with reticular nodular opacities, interlobular septal thickening, and peribronchial nodular opacities as well as mediastinal and hilar lymphadenopathy and pleural effusion while CT additionally shows centrilobular nodules and GGOs. Remarkably swift resolution can take place, over the course of a few days however follow-up CT may demonstrate residual fibrosis [41].

EBV Pneumonia Epstein-Barr virus (EBV) causes intrathoracic lymphadenopathy and splenomegaly as a manifestation of infectious mononucleosis and pneumonia is rare manifestation. The CT manifestations of EBV pneumonia are similar to those of other viral pneumonias producing lobar consolidation, parenchymal diffuse and focal hazy opacities, reticular opacities, and miliary nodules or halo sign [42].

Coronaviridae SARS-CoV-1, MERS Coronavirus, and SARS-CoV-2 Human coronaviruses can cause upper and LRT infections (pneumonia and bronchiolitis) with a potential to progress to acute respiratory distress syndrome, multiorgan failure, and death. A

worldwide outbreak of SARS coronavirus (SARS-CoV-1), occurred in 2002–2003 with origin of the outbreak traced to the Guangdong Province of China and mortality close to 50% for patients older than 60. The animal hosts were the masked palm civet, raccoon dogs, and the Chinese ferret-badger. Another corona virus named MERS coronavirus was first identified in September 2012, in Riyadh, Saudi Arabia in Dromedary camels and bats. A new coronavirus, novel coronavirus (2019-nCoV)/SARS coronavirus 2 (SARS-CoV-2) responsible for coronavirus disease 2019 (COVID-19) was initially identified in Wuhan, Hubei Province, China, in early December 2019, with the mortality rate of 3 to 5–10%. About 754 million cases and 6.83 million deaths of COVID-19 have been reported worldwide as of February 8th, 2023 (https://covid19.who.int/). Angiotensin-converting enzyme 2 is a potential SARS virus receptor; and immunopathologic mechanism, endothelial damage, and thromboinflammation may be responsible for the progression of disease severity and involvement of multiple body systems. The main modes of disease transmission were droplet and contact transmission with possible occasional airborne transmission. A diagnosis is made based by the positive reverse transcription-polymerase chain reaction test of an upper respiratory tract specimen [43]. Patient with mild symptoms of COVID-19 does not require chest CT examination. However, after confirming SARS-CoV-2 infection, chest CT may be used in moderate to severe cases to evaluate disease severity, and establishing the next management strategies. CT severity score is a semiquantitative scoring system to quantitatively estimate the pulmonary involvement by COVID19 on the basis of the area involved. Each of the five lung lobes are visually scored on a scale of 0– 5, with 0 indicating no involvement; 1, less than 5% involvement; 2, 5–25% involvement; 3, 26– 49% involvement; 4, 50–75% involvement; and 5, more than 75% involvement. The total CT score is the sum of the individual lobar scores and ranges from 0 (no involvement) to 25 (maximum involvement) [44]. The initial CXRs may be normal or nonspecific pulmonary opacities with rapid progression to multifocal airspace opacities predominantly in the peripheral lower lung zones.

◾ Normal chest CT can be seen up to 2 days after onset of flu-like symptoms in up to 50% of patients with COVID-19 infection. CT may show lung abnormalities even with an initially negative reverse transcription-polymerase chain ◾ CTreaction pulmonary findings caused by SARS-CoV-2 are similar to those findings of other human coronaviruses. The most common CT finding for SARS-CoV-2 pneumonia is GGO followed by consolidation ◾ The most common CT features are bilateral peripheral subpleural multifocal posterior, and diffuse or lower lobe predominant GGOs (Fig. 15.20), consolidation and reticulations related to organizing pneumonia or capillary ◾ ◾

permeability pulmonary edema-related mechanism of lung injury. The round morphology or a reversed halo or atoll sign of opacities resemble the organizing pneumonia [45] A reversed halo sign, halo sign, reticulation, or nodules are rare and usually manifest later in the disease course. Less commonly seen atypical findings are cavitation, isolated lobar, or segmental consolidation without GGOs lymphadenopathy, spontaneous pneumothorax, pneumomediastinum (Fig. 15.21), and pleural effusions. On CT, fine reticular opacity and pulmonary artery enlargement/thick vessel sign within pulmonary opacities and regional mosaic perfusion patterns are also commonly found in COVID-19 pneumonia compared with other viral pneumonia Peak pulmonary disease manifests as crazy-paving, new or worsening lung consolidative opacities, and higher rates of multilobar and bilateral involvement (Fig. 15.21)

FIGURE 15.20 SARS-CoV-2/COVID-19 acute pulmonary infection. Coronal CT lung window image shows extensive predominantly peripheral and perilobular ground-glass opacities (arrows) in both lungs due to SARS-CoV-2.

FIGURE 15.21 SARS-CoV-2/COVID-19 pulmonary infection complicated by pneumomediastinum and subcutaneous emphysema. Axial chest CT lung window image shows diffuse ground-glass opacities (bold arrow) in both lungs with bilateral lower lobe peribronchovascular and peripheral consolidative opacities (dotted arrow) due to COVID pneumonia with large pneumomediastinum and right subcutaneous emphysema. Note that patients with COVID-19 who require mechanical ventilation are at increased risk of barotrauma compared with ARDS alone.

Resolution of the lung findings may take close to a month or so. Follow-up CT obtained during recovery after 2 weeks from initial symptom onset showed a gradual decrease in consolidation, with residual GGOs [8,36,46]. Interstitial lung fibrosis can remain after the recovery in some of these patients based on the initial severity of disease with lung fibrotic changes in more than one-third of patients who survived COVID-19 pneumonia [47,48]. Hypercoagulable state in COVID-19 disease is multifactorial in nature and result in both venous and arterial thromboembolism and result in deep venous thrombosis, PE, limb ischemia, stroke, and myocardial infarction [43].

Chlamydial and Rickettsial Pneumonias Psittacosis/Ornithosis Psittacosis is a systemic disease that can cause an atypical pneumonia. This infection is due to Chlamydia psittaci and usually acquired by contact with sick parrots or pet birds and poultry. The pneumonia usually presents as patchy or lobar consolidation, although nodular shadows may be seen. There is often hilar lymphadenopathy. The radiographic changes may take several weeks to resolve [49].

Q Fever This rickettsial gram-negative aerobic bacterial pneumonia is usually acquired by contact with farm livestock, cattle, or sheep and is due to Coxiella burnetii. The pneumonia presents on CXRs and CT as rounded areas multifocal, peripheral predominant areas of consolidation in both lungs due to interstitial and alveolar inflammation. In the early stages of the disease, CXRs might be normal. Single or multiple irregular nodules with halo sign, consolidation in patchy, segmental, or lobar distribution, necrotizing pneumonia or linear atelectasis are also known imaging findings. Pleural

effusion or lymph node enlargement is not known [50]. The radiographic changes may take a month or more to resolve [2,51].

Rocky Mountain Spotted Fever This tick-borne disease caused by Rickettsia rickettsii is endemic to the southern United States as well as the Rocky Mountains. It may cause patchy consolidation, pleural effusions, and be complicated by secondary bacterial pneumonia. Overall there is a 3–4% mortality and has reduced due to antibiotics [52]. Scrub typhus: This rickettsial disease is an acute febrile illness caused by the Orientia tsugamushi, which is transmitted by the bites of infected chigger mites and is endemic in the countries of the Asia-Pacific, and causes pulmonary abnormalities in approximately 10% of cases. The radiographic pattern is diverse and takes the form of interstitial, lobar, or widespread pulmonary opacities due to pneumonia and can develop complications of acute respiratory distress syndrome, acute kidney injury, hepatitis, meningoencephalitis, myocarditis, and shock [53].

Pulmonary Tuberculosis Pulmonary tuberculosis (PTB) is a common lung infection worldwide, with heterogeneous incidence geographically. The prevalence of tuberculosis has continued to decline in the United States, however, with relatively higher prevalence of tuberculosis in some states and in certain immigrant populations from developing countries from Asia and Africa. Mycobacterium tuberculosis (MTB) is the most common cause of tuberculosis; less than 5% of cases are caused by atypical mycobacteria. Normally, infection occurs by inhalation of organisms from open case of the disease. Transmission is by droplet inhalation. Other factors that predispose to PTB are poor nutrition, alcoholism, silicosis, diabetes, pregnancy, old age, malignancy, and immunosuppression, especially by the human immunodeficiency virus (HIV) infection. In general, the occupational risk of hospital personnel is minimal and only a pre-employment CXR is needed. Reactivation of previous infected foci is a cause in most cases of postprimary infection, and it often appears many years after first infection. Rarely, a primary infection progresses into the postprimary phase, without a latent period of intervention. Radiologically, it can be difficult to differentiate primary from postprimary tuberculosis due to their overlapping manifestations [54].

Primary Pulmonary Tuberculosis Primary PTB occurs due to a first-time exposure to MTB and is typically seen in infants and children. Its frequency is increasing in adulthood and represents about 23–34% of all adult cases of TB [2,54]. Although CXRs are commonly used in diagnosis, they may be normal in 15% of cases of primary PTB. The four imaging manifestations of primary PTB include: 1. Lymphadenopathy 2. Parenchymal disease 3. Pleural effusion 4. Miliary disease [9]

◾ Lymphadenopathy is the most common manifestation of PTB in children and can present with or without pneumonia. In adults hilar or mediastinal lymphadenopathy is less common. The most common sites of nodal involvement include right

◾

paratracheal and hilar lymph nodes (Figs. 15.22 and 15.23) with CT being more sensitive than CXR. These nodes are often larger than 2 cm, with characteristic “rim sign” due to low-density center related to caseous necrosis, and peripheral enhancing rim from granulomatous inflammation [55]. After healing the nodes involved can calcify. Lymphadenopathy is usually unilateral but may be bilateral, in which case the differential diagnosis includes sarcoidosis and lymphoma. Adjacent airways may get pressed by enlarged lymph nodes (Fig. 15.23), which cause pulmonary collapse or air trapping with hyperinflation. Caseating nodes may also erode into vessels causing miliary infection and into airways, causing bronchopneumonia [55]. Cavitation is uncommon, occurring mainly with progression of the disease Nonspecific focal or lobar dense and homogeneous consolidation as a manifestation of parenchymal involvement involves in any part of the lung, with predominance in the lower and middle lobes typically in adults [54,56,57]. This can be differentiated from bacterial pneumonia based on the presence of lymphadenopathy and the lack of response to conventional antibiotics

◾ Infection can also appear as a well-defined nodule or nodules. Healing is often complete in approximately two-thirds of cases without any sequelae on the CXR although fibrosis and calcification may occur in the remaining cases. Less than 10% of cases might have residual mass-like opacities due to tuberculomas [54,56,57]. Ranke complex is commonly the only imaging evidence to suggest previous PTB and consists of the combination of a calcified or noncalcified lung parenchymal scarring (Ghon lesion; Fig. 15.22) and calcified hilar and/or paratracheal lymph nodes [54,56,57]. These lesions may contain dormant bacilli, which might convert into postprimary TB. In rare cases of primary uncontrolled PTB, a progressive disease with multilobar involvement and cavitation may develop [58] Pleural effusion can be sole finding in teenagers and young adults [2,54]. The effusion may be large and relatively asymptomatic. The effusion is typically unilateral, and its complications such as empyema formation, fistulization, and rib osteomyelitis are uncommon. Ultrasonography often reveals a complex septated pleural effusion. It resolves with treatment without complication. Residual pleural thickening and calcification can remain [54,56,57] Miliary tuberculosis is due to hematogenous spread of infection and can be found in both primary and postprimary PTB. Clinically significant miliary disease affects between 1% and 7% of patients with all forms of tuberculosis. In primary TB, the patient is often a child, and in the postprimary cases the patients are often elderly, debilitated, or immunocompromised At first, the CXR may be normal, and hyperinflation may be the earliest feature Subsequently typical radiographic findings of small, discrete nodules of 1–2 mm in diameter, become apparent, evenly distributed throughout; both lungs are seen (Fig. 15.24). Contrarily, tree-in-bud nodules are poorly defined and have a patchy distribution Chest CT is more sensitive than radiographs and reveals the random distribution of these tiny miliary pulmonary nodules. These nodules may enlarge and coalesce to form focal or diffuse consolidation, but they slowly resolve within 2– 6 months with adequate treatment without scarring or calcification [54,57,59]

◾ ◾

FIGURE 15.22 Primary pulmonary Mycobacterium TB (MTB) infection. A composite image with posteroanterior chest radiograph (left) and coronal CT lung window image (right) in an asymptomatic 12-year-old boy reveals right upper lobe peribronchial nodular opacities and thickening (Ghon’s focus) with right hilar lymphadenopathy. The combination of the lung parenchymal infection (Ghon’s focus) and lymph node MTB infection has been termed the Ranke complex.

FIGURE 15.23 Tuberculous lymphadenopathy. There is mediastinal and left hilar lymph node enlargement causing severe narrowing of the left main bronchus (arrows).

FIGURE 15.24 Miliary spread of Mycobacterium tuberculosis infection. Frontal chest radiograph shows innumerable, bilateral, diffusely distributed small nodules representing miliary hematogenous spread of MTB infection. Note small right pleural effusion (arrow).

A tuberculoma is a localized granuloma/localized parenchymal disease that alternately activates and heals and may occur in the setting of primary or postprimary PTB. It is a well-defined, solitary nodule, with a diameter of up to 5 cm. It frequently remains stable for years with calcification being common, but cavitation is rare.

Postprimary Pulmonary Tuberculosis (PostprimaryPTB)/(Reactivation, Secondary, or Adulthood PT) Postprimary-PTB typically occurs in adolescence and adulthood and most cases are due to reactivation of quiescent lesions, but occasionally due to new TB infection from an exogenous source. Primary tuberculosis is usually self-limiting, whereas postprimary PTB is progressive, with cavitation as its characteristics finding, which can result in hematogenous dissemination and endobronchial spread of TB leading to the CT features of tree-in-bud opacities. Although the imaging manifestations of primary and postprimary PTB might overlap; the differentiating features of postprimary PTB include a predilection for the upper lobes and the presence of cavitation. Lymphadenopathy is often seen in the Indian population. The three radiological manifestations include parenchymal disease, airway involvement, and pleural extension [54,56,57,59]. Parenchymal Changes

◾ Parenchymal disease manifests early with patchy, ill-defined, and nodular consolidation, particularly in the apical and posterior segments of the upper lobes or superior segment of the lower lobe (Fig. 15.25A). Bilateral disease seen in onethird to two-thirds of cases. Progressive infection is indicated by the extension and coalescence of consolidation areas, and cavity development (Fig. 15.26). The typical pulmonary cavities have thick, irregular walls, which evolve into smooth and thin as a response to treatment. Cavities are typically multiple and occur within regions of consolidation (Fig. 15.26). Tuberculous bronchopneumonia may occur in both primary and postprimary infection, causing patchy, often nodular, areas of consolidation. Cavitary superinfection by other bacteria should be suspected when the air–fluid level is considerable

◾ After antituberculous treatment healing leads to fibrosis and calcification. Resolution of pulmonary abnormalities is achieved after 3 months of treatment in most cases [58]. Fibrosis and volume loss may occur at the same time as ◾

consolidation, indicating healing. Fluid levels can sometimes be seen in cavities which can indicate the presence of superinfection. With fibrosis, cavities are often obliterated. Moreover, larger cavities may persist, and areas of bronchiectasis and emphysema can occur. Healed lesions mostly calcify. Often there is evidence of severe volume loss and pleural thickening, trachea being pulled away from the midline, elevation of the hila and distortion of the lung parenchyma (Fig. 15.25B) Aspergillus and other fungi often colonize the chronic cavities, and mycetomas may develop. Progression of disease is monitored by periodic radiographs, with the formation of new lesions or the extension of old ones indicating continued activity, whereas the contraction indicating response to treatment [54,56,57,59]. Once the radiographic signs have stabilized, any subsequent size or density changes should raise concern for complication of reactivation, fungal invasion, or neoplasm. Lymphadenopathy and pneumothorax are seen in only about 5% of patients [57]. Other rare complications include broncholithiasis

FIGURE 15.25 (A) Pulmonary tuberculosis (PTB) showing typical nodular opacities in the upper and mid zones of both lungs (white arrows) with areas of fibrosis. Another patient (B) with more long-standing disease shows collapse of the left lung, with bronchiectatic cavities within the collapsed lung. There is ipsilateral mediastinal shift and elevation of the left dome inferred by a higher position of the gastric fundus air shadow. Fibrotic changes and volume loss are also seen in the right upper lobe.

FIGURE 15.26 Postprimary pulmonary tuberculosis (PTB). Coronal chest CT lung window image in a 50-year-old man presenting with shortness of breath shows innumerable bilateral solid pulmonary nodular opacities (bold black arrows), centrilobular nodules and tree-in-bud opacities involving all the lobes of both lungs as well as a few areas of consolidative opacity most prominent in the left upper lobe (dotted arrows) and both upper lobe predominant thickwalled pulmonary cavities (white arrow) consistent with endobronchial spread of tuberculosis.

Pleural Changes Pleural effusion complicating primary PTB may be large and relatively asymptomatic, but they are generally small and associated with parenchymal disease in cases of postprimary PTB. The effusions are usually septated. CT shows fluid in the pleural cavity and with enhancement of the pleural layers after contrast administration. Effusion frequently transforms to empyema with thickened enhancing pleura and complex pleural effusion. Healing leads to residual pleural thickening and often calcification. Complications of tuberculous empyema are pleurocutaneous fistula, bronchopleural fistula, and osteitis of a rib. Secondary infection is rare. Previous thoracoplasty can also make the radiographic appearance more complicated. Apical tuberculosis is associated with the apical pleural thickening/apical cap due to chronic pleural inflammation on radiographs. CT can reveal it to be mainly due to thickened layer of extrapleural fat. Pneumothorax may complicate subpleural cavitary disease [54,56,57,59]. Empyema necessitates is an uncommon late complication of TB empyema in which pleura collection spontaneously erodes into chest wall resulting in abscess in the chest wall (Fig. 15.27) [58].

FIGURE 15.27 Empyema necessitans due to TB. Frontal chest radiograph shows right-sided pyopneumothorax with extension of the air (arrow) and fluid (not perceptible on radiograph) beyond the right lower ribs, indicating chest wall extension and is called empyema necessitans. Note sequealae of TB with the left upper lobe reticulonodular fibrotic opacities and variable volume loss bilaterally.

(Courtesy: Dr Amy Mumbower.)

Airway Involvement Airway involvement could be secondary to lymphadenopathy or endobronchial infection, therefore may complicate both primary and postprimary disease. Central airways compressed by enlarged nodes (Fig. 15.23) may cause pulmonary collapse or hyperinflation related to air trapping, obstructive pneumonia, and mucoid impaction. Bronchial stenosis is seen in up to 40% of patients with active tuberculosis [60] and appears on CT as long segment irregular wall thickening and luminal narrowing, luminal obstruction, and extrinsic compression. Endobronchial infection results in tree-in-bud opacities as well as traction bronchiectasis, particularly of the upper lobes. A Rasmussen aneurysm (Fig. 15.28) is a rare deadly complication of cavitary tuberculosis caused by granulomatous weakening of a pulmonary arterial wall [58]. Fibrosing mediastinitis is a late sequela of tuberculosis, manifest on CT as localized mediastinal soft-tissue mass with calcification.

FIGURE 15.28 Pulmonary tuberculosis (PTB) complicated by Rasmussen pseudoaneurysm. A composite image with axial contrast-enhanced chest CT soft-tissue window (left) and coronal pulmonary artery catheter image (right) in a young patient reveals pulmonary artery enhancing pseudoaneurysm (arrows) along right upper lobe segmental pulmonary artery related to right upper lobe cavitary consolidative opacities due to pulmonary tuberculosis. Note enlarged enhancing mediastinal lymph nodes due to TB.

(Courtesy: Dr Amy Mumbower.)

Active Versus Inactive PTB Postprimary TB heals with parenchymal scarring and nodules and CXRs can determine the stability of the lesion, but stable lesions can contain active bacilli. CT features can help to differentiate active from inactive PTB. Active PTB typically presents with centrilobular nodules, tree-in-bud opacities, thick-walled cavities, consolidation, miliary nodules, pleural effusions, or necrotic lymphadenopathy [54,56]. Inactive PTB can reveal conversion of thick-walled cavities into thin-walled relatively smaller smooth cavities, the development of pulmonary fibrotic opacities, and parenchymal, nodal, or pleural calcifications [54,56]. Active disease on CT must be confirmed by analysis of sputum for the presence of bacilli [58].

Nontuberculous Mycobacteria/Atypical Mycobacteria NTMB include at least 20 organisms that potentially cause human disease of which the most common cause of human pulmonary disease are Mycobacterium avium-intracellulare complex (mac), M. kansasii, and mycobacterium abscessus. Most NTMB are inhabitants of natural water sources. Many patients who develop NTMB infections are chronically ill and older with risk factors include chronic obstructive pulmonary disease, bronchiectasis, silicosis, cystic fibrosis, and AIDS. The pathologic patterns of most NTMB infections are similar to that of MTB infection. The most common chest CT findings of NTMB pulmonary infection irrespective of the specific species are bilateral small pulmonary nodules, cylindrical bronchiectasis, and branching centrilobular nodules (Fig. 15.29) [61]. Four imaging patterns of NTMB include: 1. Apical fibrocavitary pattern/classic pattern similar to postprimary MTB causing upper lobe consolidation, cavitation, fibrosis, apical pleural thickening, and endobronchial spread of infection-related small nodules 2. Bronchiectasis and centrilobular nodules with predominance in the right middle lobe and lingula 3. Findings mimicking hypersensitivity pneumonitis, with poorly defined ground-glass centrilobular nodules, and air trapping 4. Asymptomatic single or multiple pulmonary nodules without distant satellite nodules

FIGURE 15.29 Pulmonary nontuberculous Mycobacterium avium infection (non-TB-MAI). Axial chest lung window image in a 43-year-old man shows layering fluid/debris in the large septated cyst in the left lower lobe (arrow) consistent with Bullaitis. Extensive bronchiectasis, bronchial wall thickening with tree-in-bud opacities and architectural distortion particularly in the right middle lobe, lingula, and both lower lobes due to endobronchial spread of non-TBMAI.

Pleural effusion, lymph node enlargement, and miliary disease are rare in NTMB. However, in an individual case, these differences are not sufficient to distinguish NTMB from M. tuberculosis infections [62].

Actinomyces The actinomyces (nocardia and actinomyces) are fungi morphologically, however, they respond to antibiotics as they are appropriately considered bacteria. Actinomycosis: Actinomyces israelii is a commensal of the oropharynx and may rarely cause pulmonary infection by aspiration or direct extension from mediastinum or esophagus. Pulmonary actinomycosis has peak incidence in the fourth and fifth decades and CT is better at evaluating extent. Classically, it causes lower lobe peripheral airspace consolidation with areas of low attenuation, abscess formation, pleural invasion with pleural thickening, pleural effusions, and osteomyelitis of ribs, sinuses to the chest wall. Apical disease may mimic tuberculosis, and patchy pneumonia can develop occasionally. The mass-like consolidation with cavitation may even resemble lung cancer [63]. Nocardiosis: Nocardia asteroides is a saprophyte found worldwide in soil and infection usually occurs through inhalation of the organism particularly in debilitated immunosuppressed individuals but may occur in otherwise healthy individuals. Nocardia asteroides infection may complicate alveolar proteinosis. CXR and CT most commonly show nonsegmental, cavitating consolidative pneumonia (Fig. 15.30), bronchopneumonia (Fig. 15.31), often with empyema or pleural effusion. It may also present as a solitary pulmonary nodule, with or without cavitation, and sometimes with hilar lymphadenopathy. Multiple nodules may be seen, particularly in immunosuppressed patients [64].

FIGURE 15.30 Pulmonary Nocardia infection. Axial CT lung window image shows nodular consolidation with areas of cavitation and surrounding ground-glass opacities (arrow) in the left lower lobe related to Nocardia infection.

FIGURE 15.31 Disseminated Nocardia pulmonary infection. Axial lung window CT image shows multifocal diffuse ground-glass (bold arrows) and peripheral consolidative opacities (dotted arrow) in both lungs with areas of crazy-paving appearance due to disseminated nocardia infection proved with BAL fluid analysis.

Histoplasmosis Histoplasma capsulatum infection normally results from inhalation of soil or dust contaminated with bat or bird excreta and is most commonly seen in Ohio and Mississippi River valleys of the United States. The radiologic manifestations of histoplasmosis occur in parallel with the clinical syndromes. Infection is usually subclinical and heals spontaneously, sometimes leaving small, calcified pulmonary nodules and calcified mediastinal nodes or hilar nodes.

◾ CXR appears normal in most of the patients with histoplasma capsulatum infection ◾ imaging in acute disease, smaller or larger pulmonary nodules (Figs. 15.32–15.34) will be seen ◾ OnDisseminated disease may show a miliary or diffuse reticulonodular pattern/bronchopenumonia pattern that rapidly progresses to diffuse airspace opacification. When many nodules are scattered throughout the lungs (Fig. 15.33), they closely resemble the nodules of varicella pneumonia or miliary tuberculosis except they tend to be slightly more variable ◾ Hilar node enlargement is common and sometimes may be the only visible manifestation (Figs. 15.32 and 15.35) ◾ Inwithchronic state, fibrosis and cavitation with focally distorted lung in the apicoposterior distribution is seen on imaging similar appearance to postprimary tuberculosis [65,66] ◾ Acentral histoplasma may resemble a tuberculoma, being round, usually well circumscribed up to 3-cm nodule and often with calcification. Adjacent satellite nodules can be present ◾ Hematogenous spread and pleural disease are rare ◾ Fibrosing mediastinitis is an uncommon late manifestation of mediastinal histoplasmosis due to nodal fibrosis which can cause stenosis of the superior vena cava, esophagus, trachea, bronchi, or pulmonary arteries or veins. The CXR reveals widened mediastinum along with large hilar opacities extending into the lungs along with interstitial opacities, whereas chest CT reveals soft-tissue or calcified masses (Fig. 15.36) in the distribution of lymph node locations [65,66]

FIGURE 15.32 Acute histoplasmosis. Axial lung window (left image) and soft-tissue window (right image) chest CT images in a 23-year-old woman with recent history of travel currently presenting with fever and cough show clustered right upper lobe peribronchial dominant softtissue nodule (black arrow) and associated ipsilateral right hilar lymphadenopathy (white arrow). Differential diagnosis for such pattern includes tuberculosis, sarcoidosis, and other fungal infections. Follow-up 6-month CT chest showed development of diffuse amorphous calcification within the same right hilar node (not shown) due to post-treatment healing changes.

(Courtesy: Dr Carlos S Restrepo.)

FIGURE 15.33 Pulmonary histoplasmosis. Coronal chest lung window image in a 45-yearold man with cough and dyspnea on exertion shows numerous small, sharply defined, random solid diffuse, and uniform in distribution miliary nodules with few thick-walled pulmonary cavities (arrow). Differential diagnosis of military nodules includes metastases, miliary tuberculosis, fungal infection, sarcoidosis, Langerhans histiocytosis, silicosis, and coal worker’s pneumoconiosis.

FIGURE 15.34 Acute histoplasmosis after massive exposure while visiting a bat-infested cave. There are widespread bilateral well-defined 3–5-mm nodules.

FIGURE 15.35 Coronal chest CT image in a 38-year-old nonsmoker man from endemic histoplasma region presenting with fever and SOB shows a lobulated right lower lobe solid nodule (dotted arrow) with enlarged hilar and subcarinal lymph nodes (bold arrows) mimicking lung cancer.

FIGURE 15.36 Histoplasmosis-related fibrosing mediastinitis. Axial soft tissue and lung window chest CT images in a middle age man with hemoptysis showing partly calcified left hilar ill-defined soft tissue with near complete occlusion of the pulmonary artery, bronchus, and pulmonary vein on the left side with resultant interstitial thickening in the upper lung lobe and severe pulmonary hypertension-related main pulmonary artery dilation.

Coccidioidomycosis

Coccidioides immitis causes endemic disease in parts of the south west United States, Northern Mexico, and areas of Central and South America. Approximately 60% of infections are asymptomatic with the most common radiographic feature is a nodule which calcifies with healing. The radiologic manifestations of coccidioidomycosis occur in parallel with the clinical syndromes.

◾ Acute coccidioidomycosis may cause a pneumonic illness and manifests on CXR and CT, as multifocal nodules (Fig. 15.37), segmental or lobar consolidation (Fig. 15.38), or peribronchial thickening and may be associated with hilar or mediastinal adenopathy or pleural effusion ◾ Pulmonary nodules up to the size of 3 cm in diameter can occur, and these nodules have a tendency to form thin- or thick-walled cavities (Fig. 15.39) with persistent primary infection. Although healing of lung lesion may result in a solitary nodule or coccidioidomycoma [65,66] ◾ Chronic coccidioidomycosis manifests as persistent or progressive consolidation, cavitation, adenopathy, effusion, multiple nodules, fibrosis, or bronchiectasis (Fig. 15.40) similar to postprimary tuberculosis. Coccidioidal cavities can be ◾

complicated by rupture into the pleural space, resulting in a spontaneous pneumothorax or a persistent bronchopleural fistula Disseminated coccidioidomycosis occurs most commonly in immunocompromised patients with a miliary pattern on chest imaging, usually accompanied by hilar or mediastinal lymphadenopathy and extrathoracic spread [65,66]

FIGURE 15.37 Coccidioidomycosis. Axial lung window (left) and axial soft-tissue window (right) in an 81-year-old woman with incidentally identified right upper lobe noncavitary, noncalcified peripheral soft-tissue nodule (arrow) closely abutting the pleura.

FIGURE 15.38 Acute coccidioidal consolidative infection. Axial CT lung window image shows confluent mixed consolidative and ground-glass opacity within the right upper lobe in a central peribronchovascular distribution (arrow).

(Courtesy: Dr Carlos S Restrepo.)

FIGURE 15.39 Acute coccidioidal cavitary infection. Sagittal CT lung window image shows a thick-walled cavity (arrow) in the posterior segment of the right upper lobe with surrounding ground-glass nodules and opacities.

FIGURE 15.40 Chronic coccidioidal fibrocavitary infection. Coronal CT lung window image shows multifocal thick-walled cavitary lesions (arrow), peribronchovascular nodules, tree-inbud opacities, and irregular fibrosis throughout the right lung, most pronounced within the right upper lobe due to chronic coccidioidal infection. Dominant cavity within the medial aspect of the right lung extending between the right upper and lower lobes with internal rounded soft tissue related to complication from mycetoma formation (arrow). Note honeycombing in basal segments of both lungs due to underlying UIP pattern of pulmonary fibrosis.

North American Blastomycosis Pulmonary blastomycosis refers to respiratory infection due to Blastomyces dermatitidis and is found in parts of the central and south east United States.

◾ Radiologic findings include an asymptomatic solitary nodule, a pneumonic illness with acute or chronic consolidation in focal or bronchopneumonia pattern, single or multiple pulmonary nodules, lymphadenopathy, focal mass-like opacity ◾

mimicking lung cancer (Fig. 15.41) with satellite nodules, or miliary disease with fibronodular disease. Cavitation is occasionally seen, but calcification is rare Unlike histoplasmosis and coccidioidomycosis, fibrosis is uncommon, and once lesions have healed, scars are frequently inconspicuous [65,66]

FIGURE 15.41 Pulmonary blastomycosis. Axial lung window (left) and coronal soft-tissue window (right) in a 67-year-old man with fever and weight loss shows peripheral lingular lobe lobular mass-like consolidation. Lung cancer was suspected, and patient underwent FNAC which showed blastomycosis. Differential diagnosis includes lung cancer: Can be difficult to differentiate as in the index case; Pneumonia: No response to conventional antibiotic therapy should raise possibility of atypical infections in endemic areas; and Rounded atelectasis: Mass-like appearance, comet-tail appearance, and adjacent pleural thickening.

Radiologic Features to Differentiate Endemic Fungi on Imaging The radiologic findings of an acute fungal pneumonia due to these organisms are usually nonspecific.

◾present Acute blastomycosis and coccidioidomycosis are more likely than acute histoplasmosis to as a lobar consolidation ◾ Cavitary consolidation is suggestive of acute coccidioidomycosis ◾acute Although hilar adenopathy is common in all, but mediastinal adenopathy is rare except in coccidioidomycosis ◾ Pleural effusions are overall uncommon ◾ Persistent nodules are most common due to previous histoplasmosis or coccidioidomycosis ◾ Calcification is suggestive of previous H. capsulatum infection ◾clinically Chronic infection with these organisms typically mimics postprimary tuberculosis both and radiologically in the form of upper lobe fibrocavitary disease, satellite nodules, fibrosis, and bronchiectasis [65,66]. Fibrosis is uncommon in blastomycosis

Cryptococcosis (torulosis) Cryptococcus neoformans is a yeast form of fungus found worldwide in soil, particularly abundant in pigeon excreta and is the most common etiologic agent resulting in cryptococcosis. Infection is

mostly subclinical, but is important in debilitated patients. In an otherwise healthy individual, cryptococcal pulmonary infection usually manifests as single lung mass (mimicking lung cancer) or multiple peripheral pulmonary nodules, generally without cavitation (Fig. 15.42), and uncommonly with consolidation. In patients with AIDS, diffuse interstitial opacities or bronchopneumonia pattern can be seen. Miliary nodules, single or multiple pulmonary nodules, occasionally with cavitation can also be seen. Lymphadenopathy and pleural effusion are rare. Systemic spread particularly to brain and meninges is common in AIDS and immunocompromised patients [4,17,65–68].

FIGURE 15.42 Cryptococcosis. Axial lung window chest CT image in a 76-year-old man with Hodgkin lymphoma on chemotherapy currently presenting with fever and chest pain shows multiple ill-defined soft-tissue nodular opacities in the right lower lobe (arrows) with minimal surrounding ground-glass opacities.

Candidiasis Candida albicans is a normal mouth commensal and is rarely invasive unless the patient is immunocompromised. Pulmonary candida infection occurs most commonly from hematogenous spread with multiorgan involvement in the setting of immunosuppression, where it manifests with miliary nodules or multiple larger nodules in a centrilobular or random distribution. The second uncommon form results from aspiration of contaminated oropharyngeal secretions and results in bronchopneumonia with patchy bilateral consolidation in a peribronchovascular distribution. In immunosuppressed patients, the CXR and CT findings of pulmonary candidiasis are small or large diffuse multiple pulmonary nodules (Figs. 15.43 and 15.44) with our without “CT halo sign” along with GGOs and nonspecific focal or multilobar patchy consolidation (Fig. 15.44). Pleural effusion, cavitation (Fig. 15.43), and lymphadenopathy are uncommon.

FIGURE 15.43 Candida fungemia. Axial chest CT image in a 36-year-old man with diabetes mellitus, fever, and chills shows multiple predominantly peripherally distributed solid pulmonary nodules (arrows) with some nodules showing cavitation (arrow in right lower lobe).

FIGURE 15.44 Disseminated candidiasis. Axial lung window chest CT image in a 10-year-old child with acute lymphocytic leukemia on chemotherapy with febrile neutropenia. CT shows innumerable tiny bilateral solid pulmonary nodules (arrows), focal consolidation, and small left pleural effusion.

The infectious causes of CT halo sign include fungal infections such as candida, mucormycosis, actinomycosis, bacterial infections such as Pseudomonas and Legionella and viral infections such as herpes simplex virus and cytomegalovirus [17,69–71].

Mucormycosis/Mucor Infection

Pulmonary mucormycosis (PM) is rare fatal fungal infection caused by members of the genus Rhizopus or Mucor due to inhalation of infected spores, most often seen in immunocompromised patients, and can progress rapidly in neutropenic patients.

◾ Lobar and segmental consolidation (Figs. 15.45–15.47) is the most common finding on CXR with multilobar and bilateral distribution in some patients. Single or multiple nodules and masses are common ◾ CTnodules, shows nonspecific findings of peribronchial GGO in early phase while disease progression reveals consolidation, or masses with ground-glass halo (Fig. 15.45). Pseudoaneurysm formation (Fig. 15.46) and abrupt termination of a pulmonary artery branch/vascular cut-off sign are known with PM. The reverse halo sign (Fig. 15.47), pleural effusions and more than 10 nodules, is more common in PM than with invasive pulmonary aspergillosis (IPA). PM can involve pleura (pleural thickening or effusion), chest wall (air in the intercostal space or subcutaneous soft tissues), mediastinum, and diaphragm. The reverse halo sign differential diagnosis includes organizing pneumonia, bland pulmonary infarct, and lung cancer [72]

FIGURE 15.45 Acute mucor infection. Coronal lung window chest CT image in a 58-year-old man with AML on chemotherapy shows aggressive consolidation containing mottled ground glass in center and rim of consolidation in right lung (“reverse halo sign”) crossing the transverse fissure (black arrow) with in right lung. Note left lower lobe solid nodule also due to mucor infection.

FIGURE 15.46 Mucormycosis pneumonia complicated by pulmonary artery pseudoaneurysm. A composite image with axial soft-tissue window (left) and axial CT lung window image (right) in a young patient reveals mycotic pulmonary artery enhancing pseudoaneurysm (bold arrows) along right lower lobe segmental pulmonary artery related to right lower lobe consolidative opacities due to mucor pneumonia (dotted arrows).

FIGURE 15.47 Pulmonary mucormycosis. Sagittal chest CT lung window image in a middleaged man presenting with nonresponding fever shows right middle lobe necrotizing consolidation with cavity formation with lack of parenchymal normal vascularity. The right upper lobe reveals reverse halo sign/atoll sign characterized by central heterogeneous mixed ground-glass and consolidative opacification, crazy-paving appearance, and peripheral consolidative rim due to angioinvasive mucormycosis. This was proved on lung lobectomy specimen.

Aspergillosis Aspergillus fumigatus is widespread in the atmosphere and it is inevitable that man inhales the spores from time to time. It can multiply when conditions are favorable in the air passages. The pulmonary manifestations are grouped into following categories [73]: 1. Aspergilloma 2. Allergic bronchopulmonary aspergillosis 3. Invasive aspergillosis: a) Angioinvasive b) Airway invasive aspergillosis (Aspergillus bronchopneumonia) c) Acute tracheobronchitis 4. Subacute invasive pulmonary aspergillosis (formerly called chronic necrotizing pulmonary aspergillosis) [2,4,20,23,69, 74– 76]

Aspergilloma/Mycetoma Any chronic pulmonary cavity may be colonized by this fungus. Such cavities are mostly secondary to tuberculosis, histoplasmosis, sarcoidosis, with rare causes including bullae, abscesses, and bronchiectasis. These are, therefore, typically found in the upper lobes. The fungal hyphae form a ball or mycetoma that lies free in the cavity and patients with mycetoma generally have normal immunity. The CXR and CT could show a round or oval mass surrounded by air within a cavity producing the typical air crescent sign (Fig. 15.48). The ball is seen to be mobile by altering the position of the patient on radiograph or CT to decubitus position. CT may also reveal thin fungal strands bridging the fungus ball and the cavity wall (Fig. 15.49) as well as demonstrate foci of increased attenuation within the fungal ball likely due to calcium. There is almost always pleural thickening related to the

mycetoma. An air–fluid level is usually not present within the cavity. The cavity is generally thin walled. The differential diagnosis of a mycetoma in a cavity includes lung abscess, blood clot, hydatid cyst, and cavitating tumor.

FIGURE 15.48 Aspergilloma of lung. Composite image of left upper hemithorax chest radiograph (left) and axial lung window (right) in a 34-year-old man with chronic asthma on steroids shows soft-tissue nodule in the dilated left upper lobe bronchus with peripheral air lucency related to air crescent sign (arrows) and associated adjacent pleural thickening.

FIGURE 15.49 Pulmonary aspergillomas. Coronal chest CT lung window image in a 48-yearold man presenting with hemoptysis and previous granulomatous disease shows two dominant both upper lobe cavitary lesions with intracavitary lobulated soft tissue (arrows) due to mycetomas which was related to aspergillomas. Note cylindrical bronchiectasis and multifocal scarring in both upper lobes.

The “air crescent” sign can also be seen in angioinvasive and chronic necrotizing aspergillosis patients who are immunosuppressed patient in which case, there are no pre-existing cavities; radiological findings appearing within a few days in the angioinvasive forms and within several weeks or months in the chronic necrotizing forms of Aspergillus infection. Mycetomas are associated with the development of vascular granulation tissue in the cavity wall, which may bleed [2,4,20,23, 69,74–76]. Allergic Bronchopulmonary Aspergillosis ABPA occurs due to Type III hypersensitivity to Aspergillus fumigatus and typically always affects patients with asthma or cystic fibrosis in whom the fungus has colonized the segmental and lobar central airways causing bronchial dilatation with predominance in the upper lung.

◾ The CXR in the acute phase shows patchy consolidation, often in the upper zones. With appropriate treatment, the appearances will return back to normal. Nodules, tram-track opacities, toothpaste/finger-in-glove opacities (Fig. 15.50A) ◾ ◾ ◾

due to dilated mucus-filled bronchi, lobar collapse and migrating opacities, and large lung volumes may be seen in longstanding cases. Pleuropulmonary fibrosis and bronchiectasis (parallel line and ring shadows) can occur with repeated attacks CT typically reveals bronchial wall thickening, central bronchiectasis, filled by mucoid impactions with a Y- or V-shaped finger-in-glove opacities, usually involving segmental or subsegmental bronchi (Fig. 15.50B). High attenuation of impacted mucus (typically >100 HU) with density greater than that of paraspinal muscles is a pathognomonic finding of ABPA (Fig. 15.50C and D). Hyperattenuating mucus is due to calcium, iron, and manganese metals or desiccated mucus similar to seen in sinusitis Mosaic perfusion and air trapping may be seen Rarely lobar or segmental atelectasis, pleural effusion, or spontaneous pneumothorax can be seen

FIGURE 15.50 Allergic bronchopulmonary aspergillosis (ABPA). Frontal radiograph (A) shows typical finger-in-glove opacities due to mucus-filled dilated bronchi in the right upper lobe (arrow). Axial lung window chest CT images (B) in another 36-year-old steroid-dependent asthmatic patient with cough and shortness of breath shows extensive cylindrical bronchiectasis (arrows) with patchy areas of mucoid impaction and scattered centrilobular and tree-in-bud nodules due to endobronchial spread of infection. Axial mediastinal (C) and lung window (D) of a different patient with ABPA show hyperdense impacted mucus (arrow in C) within the dilated bronchi (arrow in D).

Eventually, fibrosis can cause volume loss, cavitation, bullae, focal emphysema, and eventually end-stage upper lobe fibrosis thus may mimic previous chronic pulmonary infection including tuberculosis [2–4,7,17,23,65,66,69,70,73,75,76]. Invasive Aspergillosis Due to underlying neutropenia in immunosuppressed individuals, Aspergillus may cause primary infection of the lung and airways. a) Angioinvasive aspergillosis accounts for majority of cases of invasive aspergillosis causing pulmonary vasculature thrombosis, pulmonary hemorrhage, and infarction. This may be in the form of multiple nodules, or lobar consolidation. On CT, a highly suggestive finding of AIA is a halo of GGO surrounding a denser central nodule (halo sign) (Fig. 15.51), which corresponds to hemorrhagic inflammation surrounding a region of septic infarction/necrosis.

FIGURE 15.51 Invasive pulmonary aspergillosis. Axial lung window chest CT image in a 54year-old man with AML, status after stem cell transplant 1 year ago currently presenting with febrile neutropenia shows solid pulmonary nodules with surrounding ground-glass opacities (halo sign) arrow in both upper lobes. Surrounding ground-glass opacities usually represent alveolar hemorrhage due to fungal invasion of small vessels.

Candida, herpes simplex, and cytomegalovirus infections; Wegener granulomatosis, hemorrhagic metastases, and Kaposi sarcoma should be considered in the differential diagnoses of “halo sign” in neutropenic patients [2– 4,7,17,23,65,66,69,70, 73,75,76]. Cavitation (crescent sign) of such pulmonary lesions (retracted, infarcted lung/mycotic lung sequestrum), and is seen in immunocompromised patients, is normal and often happens when the white blood cell count recovers about 2 weeks after the onset of invasive aspergillosis infection and thus mimic an intracavitatory mycetoma. b) Airway invasive Aspergillus appears on radiographs and CT as nonspecific bronchopneumonia pattern with patchy airspace opacities and small nodules in peribronchiolar distribution and also as bronchiolitis pattern with patchy centrilobular nodules with tree-in-bud appearance. c) Aspergillus acute tracheobronchitis is rare and appears on CT as tracheal or bronchial irregular multifocal wall thickening, which are occasionally high in attenuation due to the ability of Aspergillus to fix calcium [2– 4,7,17,23,65,66,69,70,73,75, 76].

Subacute IPA (formerly called chronic necrotizing pulmonary aspergillosis): It is uncommon and poorly understood form of locally invasive aspergillosis, which typically occurs in patients with moderately immunocompromised status and in patients with chronic lung pathology, is a more rapidly progressive infection (1 hour Palmar telangiectasia Raynaud's phenomenon Unexplained digital edema Unexplained fixed rash on the extensor surfaces of the digits (Gottron's sign) B. Serologic domain ANA ≥ 1:320 titer with diffuse, speckled, or homogeneous patterns; or any titer with either nucleolar or centromere pattern Rheumatoid factor ≥ 2 times the upper limit of normal Presence of one or more antibodies: Anti-CCP Anti-dsDNA Anti-Ro (SS-A) Anti-La (SS-B) Anti-RNP Anti-Smith Anti-topoisomerase (Scl-70) Anti-tRNA synthetase (e.g., Jo-1, PL-7, PL-12) Anti-PM-Scl Anti-MDA-5 C. Morphologic HRCT patterns NSIP

OP NSIP with OP overlap LIP Histopathology patterns NSIP OP NSIP with OP overlap LIP Interstitial lymphoid aggregates with germinal centers Diffuse lymphoblastic infiltration with or without lymphoid follicles Multicompartment involvement in addition to interstitial pneumonia Unexplained pleural effusion or thickening Unexplained pericardial effusion or thickening Unexplained intrinsic airways disease Unexplained pulmonary vasculopathy HRCT, high-resolution computed tomography; LIP, lymphocytic interstitial pneumonia; NSIP, nonspecific interstitial pneumonitis; Op, organizing pneumonia. Adapted from A Fischer, KM Antoniou, KK Brown, et al. An official European Respiratory Society/American Thoracic Society research statement: interstitial pneumonia with autoimmune features, Eur Respir J 46 (2015) 976–987.

The CT patterns identified in interstitial pneumonia with autoimmune features are most commonly UIP, NSIP, HP, and OP. When a UIP pattern is present, three features have been reported to be associated with a higher likelihood of an underlying CTD [17]: 1. Significant anterior upper lobe fibrosis 2. Exuberant honeycombing 3. “Straight edge” sign

Hypersensitivity Pneumonitis Hypersensitivity Pneumonitis (HP), also referred to as extrinsic allergic alveolitis, is an immune-mediated lung disease resulting from intense and often prolonged exposure to a variety of antigens from inhaled organic dusts. Classical HP syndromes include farmer's lung resulting from exposure to thermophilic actinomycetes, bird fancier's lung from avian proteins, and hot

tub lung from mycobacterium avium complex, among others. Up to 40% of cases, however, do not have an identifiable exposure despite careful assessment [23]. HP most commonly affects middle-aged adults and may be more commonly seen in nonsmokers than smokers. This is thought to be due to the immunosuppressive effects of tobacco smoking. Regardless of the type of allergen exposure, the clinical, pathologic, and radiologic manifestations of HP are similar and can be classified into acute, subacute, and chronic, all of which can occur concurrently.

Acute Hypersensitivity Pneumonitis Acute HP occurs following exposure to large amounts of antigen in susceptible individuals. It is characterized by alveolar infiltration with neutrophilic exudate with severe cases resulting in DAD with pulmonary edema or hemorrhage. Depending on the severity, imaging may be normal or may demonstrate as diffuse ground-glass opacities, multifocal ill-defined consolidations, and centrilobular nodules.

Subacute Hypersensitivity Pneumonitis Continued exposure to offending agents can result in progressive symptoms over several weeks to months. Histologically, subacute HP is characterized by alveolitis, small, ill-defined granulomas, and cellular bronchiolitis. These findings are reflected on CT as patchy ground-glass opacity and small illdefined centrilobular nodules, and focal areas of mosaic attenuation and airtrapping as confirmed on expiratory phase imaging (Fig. 18.11). The combination of focal areas of increased attenuation (ground-glass), decreased attenuation (mosaic attenuation), and normal lung parenchyma results in the “headcheese” sign, which is nearly pathognomonic of HP (Fig. 18.11). These findings may be reversible with treatment and removal of the offending agent.

FIGURE 18.11 Subacute hypersensitivity pneumonitis. (A) Axial CT image demonstrates diffuse centrilobular ground-glass nodules bilaterally with small, scattered lobular areas of increased lucencies suggestive of air-trapping. (B) Coronal CT image demonstrates relative sparing of the lower lobes. (C) Expiratory-phase axial CT image in a different patient with subacute HP demonstrates the “headcheese” sign with three distinct lung attenuations representing areas of air trapping, ground-glass opacities, and normal lung parenchyma.

Chronic Hypersensitivity Pneumonitis Long-standing exposure to the antigen can result in progression of symptoms and ultimately result in pulmonary fibrosis, which can develop over months and years. Imaging findings include reticulation, architectural distortion, volume loss, traction bronchiectasis and bronchiolectasis, and honeycombing with areas of air trapping (Fig. 18.12) [24]. The distribution of the fibrotic findings is variable and may be mid, lower, upper, or no distinct lung predominance. When honeycombing is present, however, it is more commonly upper lung predominant. Findings of subacute HP are often superimposed on these findings and are valuable in distinguishing it from other causes of fibrosis.

FIGURE 18.12 Chronic hypersensitivity pneumonitis. (A) Coronal CT image demonstrates upper lobe predominant fibrotic changes with subpleural reticulation, traction bronchiectasis, and architectural distortion. (B) Axial CT image demonstrates fibrotic changes in the upper lobes, right greater than left, with superimposed mosaic attenuation. (C) Expiratory-phase axial CT image confirmed areas of air trapping.

Eosinophilic Lung Disease Eosinophilic diseases of the lung are a heterogeneous group of disorders characterized by eosinophilic infiltration of the pulmonary interstitium and alveolar spaces, with or without associated peripheral (blood) eosinophilia [25].

Simple Pulmonary Eosinophilia (Loeffler's Syndrome) Simple pulmonary eosinophilia (SPE) is characterized by fleeting lung opacities associated with blood eosinophilia. It can be idiopathic or be secondary to drug toxicity or parasitic infection (e.g., Ascaris lumbricoides). Most patients are asymptomatic or have self-limited, mild symptoms. The most common CT findings are randomly distributed ground-glass opacities and consolidations, which may fluctuate and ultimately resolved over days without treatment.

Chronic Eosinophilic Pneumonia Chronic eosinophilic pneumonia is an idiopathic disorder characterized by extensive interstitial and alveolar infiltration by mixed inflammatory cells, predominantly eosinophils. It is commonly accompanied by peripheral eosinophilia. Unlike SPE, patients with chronic eosinophilic pneumonia are typically symptomatic, presenting with cough, shortness of breath, fever, and malaise. As much as half of those affected have a history of asthma or atopy. On radiographs, it may present with peripheral consolidations with perihilar

sparing, resulting in the “photographic negative of pulmonary edema” or “reverse batwing” lung opacities (Fig. 18.13) [26]. On CT, it is characterized by patchy, peripheral-predominant consolidations, and ground-glass opacities (Fig. 18.13). Unlike SPE, the findings of chronic eosinophilic pneumonia are persistent and typically respond well to corticosteroid therapy.

FIGURE 18.13 Chronic eosinophilic pneumonia. (A) Frontal chest radiograph demonstrates peripheral-predominant consolidation with relative sparing of the perihilar region with appearance of “photographic negative of pulmonary edema” or “reverse batwing.” (B) Axial and (C) coronal CT images demonstrate dense, multifocal peripheral consolidation with associated ground-glass opacities.

Acute Eosinophilic Pneumonia Acute eosinophilic pneumonia is an acute febrile illness presenting with rapid onset shortness of breath and respiratory failure. It is typically diagnosed by the presence of marked eosinophilia (>25%) in bronchoalveolar lavage fluid. It has been associated with recent history of smoking or a change in smoking habit. Although the presentation can be severe, it responds promptly to corticosteroid therapy. Typical CT findings include diffuse ground-glass opacities, interlobular septal thickening, and pleural effusions, with or without consolidations. The ground-glass opacities and septal thickening result in a “crazy paving” appearance. Unlike in pulmonary edema, the cardiac chambers are typically normal in size.

Hypereosinophilic Syndrome Hypereosinophilic syndrome is a rare condition characterized by marked peripheral eosinophilia (absolute eosinophil count >1500/mm3) and tissue eosinophilia resulting in organ dysfunction. Cardiac involvement is the leading cause of death in affected individuals. Lung involvement occurs in

up to 40% of patients and is typically related to cardiogenic pulmonary edema. Pulmonary nodules may be present and are typically associated with peripheral ground-glass halos.

Eosinophilic Granulomatosis with Polyangiitis (Churg–Strauss Syndrome) Eosinophilic granulomatosis with polyangiitis (eGPA), also known as Churg–Strauss syndrome and allergic granulomatous angiitis) is a rare multisystem disorder typically presenting with the triad of asthma, hypereosinophilia, and vasculitis. Imaging findings of eGPA including transient ground-glass opacities and consolidations, which may be peripheral or patchy in distribution. Other manifestations include pulmonary masses and/or nodules, pulmonary edema, and pulmonary hemorrhage. Unlike granulomatosis with polyangiitis, the masses and nodules seen in eGPA do not typically cavitate [27].

Drug-Related Lung Diseases Certain drugs have been associated with lung toxicity, which can manifest in a variety of ways depending on the agent (Table 18.4). Common lung manifestations related to drugs include pulmonary edema, DAD, pulmonary hemorrhage, OP, hypersensitivity reactions, and chronic interstitial pneumonitis with fibrosis [28]. Table 18.4 Patterns of Lung Injury Related to Drugs Amiodarone Chronic interstitial pneumonitis and fibrosis Peripheral (high-attenuation) consolidations and/or nodules Diffuse alveolar damage (ARDS) Bleomycin Pulmonary fibrosis (resembling UIP) Checkpoint inhibitors (immunotherapy) NSIP

OP Diffuse alveolar damage (ARDS) Sarcoid-like reaction Cyclosporin Lung masses/nodules (with or without lymphadenopathy) Interferon Sarcoid-like reaction Nitrofurantoin Pulmonary eosinophilia Organizing pneumonia Pulmonary fibrosis Crack cocaine Diffuse alveolar damage (ARDS) Diffuse alveolar hemorrhage Heroin Noncardiogenic pulmonary edema Intravenous crushed pills Excipient lung disease Vaping Organizing pneumonia Diffuse alveolar damage (ARDS) Acute eosinophilic pneumonia Diffuse alveolar hemorrhage ARDS, acute respiratory distress syndrome; UIP, usual interstitial pneumonia.

Amiodarone Amiodarone is an iodinated drug used in the treatment of refractory ventricular arrhythmias. It can accumulate in the liver and the lungs, with pulmonary toxicity seen in up to 5% of patients. Lung involvement may

occur in the form of DAD, OP, or chronic interstitial pneumonitis resulting in fibrosis. Classical CT findings include consolidations, which are hyperattenuating due to the accumulation of iodine (Fig. 18.14). Hyperattenuating liver is often seen in the setting of amiodarone lung toxicity.

FIGURE 18.14 Amiodarone toxicity. (A) Axial CT image on lung window demonstrates patchy mixed consolidative and ground-glass opacities bilaterally. (B) Corresponding axial CT image on soft tissue window demonstrates relative hyperattenuation of the consolidations. (C) Axial CT images through the upper abdomen demonstrate hyperattenuation of the liver.

Bleomycin Bleomycin is a cytotoxic drug used in the treatment of lymphoma and certain carcinomas, particularly testicular, ovarian, and cervical cancers. Pulmonary toxicity can be seen in less than 5% of patients. A wide variety of lung manifestations have been reported with bleomycin toxicity including pulmonary edema, DAD, OP, hypersensitivity reactions, and chronic pneumonitis with fibrosis. Chronic pneumonitis with fibrosis typically presents with progressive shortness of breath and cough 1–2 months following initiation of bleomycin therapy. Imaging shows lower lobe predominant reticulations and groundglass opacities, with or without consolidations. Bleomycin can also characteristically result in development of pulmonary nodules representing foci of OP, which can mimic metastases.

Cyclophosphamide Cyclophosphamide is an alkylating, immunosuppressive chemotherapeutic agent used in the treatment of a wide variety of malignancies and autoimmune disorders. Lung toxicity occurs in less than 1% of patients and

can manifest as chronic pneumonitis with fibrosis, OP, DAD, and pulmonary edema.

Methotrexate Methotrexate is a commonly used antifolate agent for the treatment of a variety of malignancies and inflammatory disorders. It can cause lung toxicity in as much as 10% of patients receiving treatment, typically as a hypersensitivity reaction. Eosinophilia can be seen in up to half of patients with lung toxicity. Common imaging features include basal-predominant consolidations and ground-glass opacities, which typically resolve following cessation of treatment. Pulmonary fibrosis can occur but is rare.

Nitrofurantoin Nitrofurantoin is an antibiotic most commonly used in the treatment of urinary tract infections. Nitrofurantoin-related lung toxicity can be acute or chronic. Acute toxicity can present as eosinophilic lung disease similar to idiopathic simple or acute eosinophilic pneumonia, which resolves following discontinuation of the medication. Long-standing nitrofurantoin use can result in chronic toxicity in the form of basal-predominant fibrosis.

Immune Checkpoint Inhibitors Immune checkpoint inhibitors (ICIs) are a type of immunotherapy used in the treatment of a variety of cancers, including melanoma, lung cancer, urothelial cancers, head and neck cancers, and lymphoma. Commonly used ICIs include atezolizumab, durvalumab, ipilimumab, nivolumab, and pembrolizumab. They work by preventing the deactivation of T cells, allowing them to attack and kill cancer cells. This T cell activation, however, may also result in multisystemic adverse reactions. ICI-related pneumonitis is estimated to affect 3–6% of patients under therapy with increased frequency in patients with lung cancer and those receiving combination ICI therapy. Most patients present with dyspnea and cough, with some patients presenting with chest pain and fever. Grading of the severity of ICI-related pneumonitis is largely based on symptoms (Table 18.5), ranging from Grade I, which is only clinically or radiographically observed but without symptoms to life-threatening respiratory failure (Grade IV) and death (Grade V) [29]. Table 18.5

Common Terminology Criteria for Adverse Events (CTACE) in the Setting of Immune Checkpoint Inhibitor-Related Pneumonitis Gra Definition de G r a d e 1

Radiographically apparent but without symptoms

G r a d e 2

Mild to moderate symptoms limiting instrumental ADL and requiring treatment

G r a d e 3

Severe symptoms limiting self-care ADL, typically requiring oxygen supplementation

G r a d e 4

Life-threatening respiratory compromise requiring urgent intervention

G r a d e 5

Respiratory failure and death

ADL, activities of daily living.

The imaging patterns of ICI-related pneumonitis are variable. Findings on radiographs are nonspecific and may have unilateral or bilateral hazy opacities and consolidations. On CT, several typical patterns have been

observed, including OP pattern, NSIP pattern, HP pattern, AIP/ARDS pattern, and sarcoid-like reaction (Fig. 18.15). “Radiation recall” can also occur wherein lung abnormalities are limited to previously irradiated sites [30].

FIGURE 18.15 Various patterns of pneumonitis related to immune checkpoint inhibitors. Axial CT images of different patients on a variety of immune checkpoint inhibitors for the treatment of malignancy demonstrate (A) Multifocal peribronchovascular ground-glass opacities consistent with organizing pneumonia pattern. (B) Dense, confluent peribronchovascular consolidations are also consistent with organizing pneumonia pattern. (C) Basal-predominant subpleural ground-glass opacities are consistent with NSIP pattern. (D) Bilateral geographic reticular and ground-glass opacities in the paramediastinal lungs (arrows) in a patient with a remote history of mediastinal radiation are consistent with “radiation recall” pattern of pneumonitis. (E) Diffuse tiny 1- to 2-mm nodules with a perilymphatic distribution are consistent with a sarcoid-like reaction.

Recreational Drugs Cocaine and its derivative crack are sympathomimetic agents that can cause pulmonary edema by inducing cardiac dysfunction from ischemia or arrhythmia or cause acute lung injury with resultant noncardiogenic (highpermeability) pulmonary edema, pulmonary hemorrhage, or a combination thereof. CT commonly shows diffuse or multifocal ground-glass opacities with interlobular septal thickening or dense consolidations (Fig. 18.16).

FIGURE 18.16 Diffuse alveolar damage related to crack cocaine use. (A) Frontal chest radiograph demonstrates diffuse, confluent hazy opacities bilaterally. (B) Axial and (C) Coronal CT images demonstrate dense ground-glass opacities with interlobular septal thickening with consolidations in the dependent lower lobes. Layering pleural effusions are also present.

Excipient lung disease, sometimes referred to as pulmonary talc granulomatosis, results from intravenous injection of inert fillers contained in crushed oral tablets (e.g., methadone) or other particulate matter in illicit street drugs. This results in an angiocentric granulomatous response that typically presents as centrilobular or tree-in-bud nodules on CT (Fig. 18.17). Acute pulmonary hypertension with right heart strain presenting as pulmonary arterial and right ventricular dilation may be present [31].

FIGURE 18.17 Excipient lung disease in a patient with history of intravenous injection of crushed prescription drugs. Axial CT image demonstrates diffuse centrilobular and tree-in-bud nodules bilaterally.

Vaping-associated lung disease (also known as E-cigarette or vapingassociated lung injury) is a pattern of lung injury resulting from use of electronic cigarettes and vape pens. A majority of these cases have been connected to the use of tetrahydrocannabinol-containing products containing vitamin E acetate, which is used as a thickening agent. Several histological patterns have been reported including lipoid pneumonia, DAD, diffuse alveolar hemorrhage, acute eosinophilic pneumonia, OP, and HP. The most common CT findings are diffuse, bilateral ground-glass opacities, sometimes with subpleural sparing (Fig. 18.18) [32].

FIGURE 18.18 Vaping-associated lung injury. (A) Frontal chest radiograph demonstrates low lung volumes with diffuse hazy opacities bilaterally. (B) Axial CT image demonstrates diffuse ground-glass opacities with septal thickening and superimposed consolidation in the right lower lobe. Note the areas of subpleural sparing, frequently reported with vaping-associated lung injury.

Pneumoconioses Pneumoconioses are a group of lung diseases related to inhalation of dust particles (Table 18.6) [33]. These particles may be fibrogenic and result in eventual pulmonary fibrosis and respiratory dysfunction or may be nonfibrogenic (inert) and cause minimal or no dysfunction. Table 18.6 Causative Agents and Related Exposures in Pneumoconiosis Agent Disease Exposure Fibrogenic Alu minu m

Aluminosis

Explosives manufacturing

Asbe stos

Asbestosis

Construction, mining, shipbuilding, textile

Bery llium

Berylliosis

Aerospace, ceramic manufacturing

Coal

Coal-worker's pneumoconiosis

Coal mining

Agent

Disease

Exposure

Silic a

Silicosis

Ceramic, drilling, glass manufacturing, mining, sandblasting

Talc

Talcosis

Ceramic/paint/paper manufacturing, cosmetics

Nonfibrogenic Bari um

Baritosis

Glass and paper manufacturing

Iron

Siderosis

Foundry work, mining, welding

Tin

Stannosis

Mining, welding

Asbestos-Related Diseases and Asbestosis Asbestos refers to a group of naturally occurring fibrous silicate minerals, which was widely used as a building material due to its great durability, tensile strength, and heat resistance. It is now a known hazardous material, prompting restrictions in its mainstream use. Intense or prolonged asbestos exposure can result in pleural and lung parenchymal diseases and is a risk factor for malignancy, which typically present decades following exposure. Common pleural manifestations of asbestos exposure include pleural effusions, pleural thickening, and calcified and noncalcified pleural plaques [34]. The plaques are characteristically distributed in the lower thorax and the diaphragmatic surfaces. CXR can detect most pleural effusions and pleural plaques when calcified or extensive (Fig. 18.19). Viewed en face, the pleural plaques typically have irregular, uneven borders resembling a holly leaf (“holly leaf sign”). When nodular these plaques may be mistaken for lung nodules. CT is much sensitive and can better characterize these pleural findings.

FIGURE 18.19 Asbestos-related pleural disease. (A) Frontal chest radiograph demonstrates bilateral pleural calcifications. Calcified plaques seen en face have irregular, uneven borders resulting in a “holly leaf” appearance (arrows). (B) Lateral chest radiograph shows preponderance of calcifications along the basal and posterior pleural surfaces (arrows). (C) Axial CT image demonstrates extensive calcified pleural plaques bilaterally.

Rounded atelectasis frequently occurs with asbestos-related pleural disease and is known as Blesovsky disease. Rounded atelectasis results in characteristic imaging features on CT and presents as a rounded subpleural opacity with associated volume loss and tethering of the adjacent bronchovascular bundles resulting in the characteristic “comet tail sign.” There is typically associated pleural abnormality in the form of an effusion or thickening (Fig. 18.20). Asbestos-related pleural diseases and rounded atelectasis are typically asymptomatic and are commonly found incidentally.

FIGURE 18.20 Rounded atelectasis resulting from prior asbestos exposure. (A) Axial, lung window CT image demonstrates rounded and wedge-shaped subpleural opacities in the right middle and bilateral lower lobes. Note tethering and swirling of the adjacent bronchovascular bundles resulting in a “comet-tail” appearance. (B) Axial, soft tissue window CT image demonstrates homogenous enhancement of the opacities. Note the adjacent pleural thickening, effusion, and calcification.

Asbestosis is another parenchymal manifestation of asbestos exposure resulting in a diffuse, chronic fibrosing ILD, which develops as much as 20– 30 years after exposure but may be accelerated in cases of intense exposure. On CXR, findings include lower lobe predominant reticular opacities with volume loss and honeycombing in advanced cases. On CT (Fig. 18.21), asbestosis presents as subpleural, lower lobe predominant fibrosis with reticulation, subpleural curvilinear opacities often paralleling the chest wall, 2- to 5-cm parenchymal bands extending to the pleural surface, traction bronchiectasis, and honeycombing in advanced stages. It may resemble and be indistinguishable from UIP. Findings of pleural disease, which is seen in up to 80% of patients with asbestosis and a history of prior asbestos exposure, are clues to asbestosis as the underlying cause for pulmonary fibrosis.

FIGURE 18.21 Asbestosis. (A) Frontal chest radiograph demonstrates low lung volumes with basal and peripheral-predominant reticular opacities. (B) Axial CT image demonstrates subpleural reticulation with architectural distortion with scattered parenchymal bands. (C) Axial CT image at the lung bases demonstrates extensive traction bronchiectasis and bronchiolectasis and apparent areas of honeycombing. (D) Sagittal CT image demonstrates the basal predominance of the abnormalities. Calcified pleural plaques consistent with prior asbestos exposure are also present (arrows).

Asbestosis is typically symptomatic with patients commonly presenting with progressive shortness of breath. While most patients have stable disease for years, some progress into end-stage pulmonary fibrosis, with eventual respiratory failure and death when left untreated. Asbestos exposure is also a known risk factor for the development of lung cancer and malignant mesothelioma. These are discussed separately.

Silicosis Silicosis is the most common occupational lung disease and is caused by inhalation of dust containing silica. Exposure to silica is common in mining and quarrying, construction, sandblasting, and glass manufacturing. Silicosis can present as acute, classic, or accelerated. Acute silicosis (also known as silicoproteinosis) is primarily seen in sandblasters and results from exposure to large amounts of silica over a relatively short time period. It presents shortly after exposure and can progress rapidly into respiratory failure. CT features include ground-glass opacities with septal thickening (“crazy paving” pattern), central or diffuse consolidations, and diffuse centrilobular nodules. Classic (or chronic) silicosis usually presents 10–20 years following longstanding exposure to levels of silica. Simple, uncomplicated cases are typically asymptomatic and characterized on imaging as multiple small pulmonary nodules, which may calcify. Lymphadenopathy, which may have eggshell classifications is common (Fig. 18.22) and may precede parenchymal findings.

FIGURE 18.22 Simple, uncomplicated silicosis in a patient who previously worked as a sandblaster. (A and B) Axial CT images demonstrate multiple clustered small pulmonary nodules predominantly with a peribronchovascular distribution. (C) Coronal CT image high attenuation lymph nodes (C, arrows) suggestive of developing calcifications.

Classic silicosis can be complicated and may result in progressive massive fibrosis (Fig. 18.23) wherein the small nodules coalesce into larger opacities, eventually resulting in upper lobe predominant fibrosis, with volume loss and architectural distortion. Larger masses may have central necrosis and cavitation. Complicated silicosis can result in significant respiratory dysfunction and failure in some patients. Accelerated silicosis has similar imaging findings as classic silicosis but presents and progresses more rapidly, usually in 4–8 years.

FIGURE 18.23 Progressive massive fibrosis due to silicosis in a former foundry worker. (A) Frontal chest radiograph demonstrates confluent opacities in the upper lobes with associated superior retraction of the bilateral hila. An incidental hiatus hernia is also seen as a retrocardiac opacity with air–fluid level. (B) Axial and (C) Coronal CT images demonstrate confluent areas of fibrosis in the upper lobes with resultant mass-like opacities. Note the associated volume loss and adjacent architectural distortion and traction bronchiectasis.

Coal-Workers Pneumoconiosis Coal-workers pneumoconiosis (CWP) results from inhalation of coal dust. The clinical presentation and imaging findings of CWP overlap considerably

with and may be indistinguishable from those of silicosis and can only be differentiated by exposure history. Caplan syndrome (also known as rheumatoid pneumoconiosis) is the cooccurrence of RA and a pneumoconiosis, more commonly CWP but also with silicosis. On imaging, it is characterized by superimposition of larger necrobiotic (rheumatoid) nodules on the smaller nodules seen with the pneumoconiosis (Fig. 18.24).

FIGURE 18.24 Caplan syndrome. (A) Frontal chest radiograph demonstrates multiple rounded opacities are present (some partly calcified). (B) Axial CT image shows a left lower lobe cavitary mass corresponding to a necrobiotic (rheumatoid) nodule (arrows) superimposed on multiple additional smaller nodules corresponding to underlying pneumoconiosis.

Talcosis Lung disease related to talc may result from either inhalation of dust particles or intravenous injection of crushed oral drugs. Commercially available talc is usually contaminated with other minerals, such as asbestos or silica, and may resemble asbestosis or silicosis, respectively. Findings are typically less severe compared to the other pneumoconioses. Injection of crushed oral medications can result in talc granulomatosis, a type of excipient lung disease as discussed earlier.

Berylliosis Beryllium exposure has historically been seen in fluorescent lamp workers but is now more commonly seen in those working in aeronautic, computer, and electronics manufacturing. Acute, high-dose exposure can result in chemical pneumonitis that presents as pulmonary edema. Chronic berylliosis from long-standing exposures results in a multisystemic granulomatous disease with imaging features indistinguishable from those of sarcoid, including mediastinal and hilar lymphadenopathy, small perilymphatic nodules, and upper lobe predominant confluent opacities and fibrosis in advanced cases.

Nonfibrogenic Pneumoconioses Siderosis results from dust containing iron, often associated with welding. Inhaled iron particles may accumulate and result in small hyperdense nodules or consolidations in more advanced cases. Stannosis results from tin inhalation, often by miners or metal refiners. It can result in ill-defined dense nodules or thin, dense branching opacities.

Sarcoidosis Sarcoidosis is a multisystem inflammatory disorder of unknown etiology, characterized by formation of noncaseating granulomas. It can involve almost any organ, but pulmonary involvement, which is seen in 90% of patients, results in the most morbidity and mortality. Up to 50% of patients are asymptomatic and are incidentally detected on imaging. Common presenting symptoms are dyspnea, weight loss, fatigue, fever, and night sweats. Stages of sarcoidosis have been described based on radiographic findings: Stage 0: No visible abnormalities. Stage 1: Hilar and/or mediastinal lymphadenopathy without lung parenchymal abnormalities. Stage 2: Hilar and/or mediastinal lymphadenopathy with visible lung disease. Stage 3: Diffuse lung disease without lymphadenopathy. Stage 4: End-stage fibrosis. The major thoracic abnormalities associated with sarcoidosis can be categorized into lymph node abnormalities, airway abnormalities, and lung parenchymal abnormalities. Nodal abnormalities are seen in up to 90% of patients at some point in the course of the disease. Nodal enlargement typically involves hilar and

mediastinal lymph nodes. Typical CXR findings are symmetric mediastinal and hilar lymphadenopathy (Fig. 18.25). The presence of right paratracheal, right hilar, and left hilar enlargement results in the 1–2–3 pattern [35]. The presence of enlarged aortopulmonary lymph nodes in addition to this is sometimes referred to as the 1–2–3–4 pattern. Enlarged internal mammary, paravertebral, and retrocrural lymph nodes can be seen but are less common. CT is more sensitive in the detection of nodal enlargement and clearly demonstrates symmetric lymphadenopathy. Lymph nodes in sarcoidosis may have calcifications, which are also more easily detected on CT.

FIGURE 18.25 Mediastinal and hilar lymphadenopathy in sarcoid. (A) Frontal chest radiograph demonstrates 1–2–3–4 sign (arrows) denoting lymphadenopathy in the right paratracheal region [1], bilateral hila [2] and [3], and aortopulmonary window [4]. (B) Lateral chest radiograph confirms lymphadenopathy including in the subcarinal region and behind the bronchus intermedius resulting in a “donut” configuration (arrows). (C) Coronal CT image confirms extensive mediastinal and hilar lymphadenopathy.

Airway involvement is common in sarcoidosis and most commonly manifests as nodular bronchial wall thickening. Small endobronchial granulomas may also be present. Endobronchial or peribronchial granulomas may result in airway obstruction and result in atelectasis. It may also result in air-trapping, which is demonstrated on expiratory phase imaging. The lung parenchymal abnormalities in sarcoidosis are variable. Small nodules in a perilymphatic distribution are common (Fig. 18.26), particularly in the active phase of the disease. These nodules are typically a few millimeters in size but tend to be well-defined despite their size. The perilymphatic distribution of the nodules is apparent, with nodules predominating the central peribronchovascular interstitium, the interlobar fissures, and subpleural regions. When extensive the nodules may appear diffuse and miliary in distribution [36]. Like the lymph nodes, these nodules may calcify.

FIGURE 18.26 Variable imaging appearance of pulmonary sarcoidosis. (A) Axial CT image demonstrates tiny, 1–2 mm nodules in the upper lobes, right greater than left, with a predominantly peribronchovascular and perifissural distribution. Clustered submillimeter nodules result in apparent ground-glass attenuation (arrows). (B) Axial CT images show diffuse, upper lobe predominant peribronchovascular nodules with associated architectural distortion and volume loss. Coalescent small nodules can result in larger nodules as seen in the left upper lobe (arrow). (C) Axial CT image shows mass-like consolidation in the right upper lobe with innumerable smaller satellite nodules consistent with the “galaxy sign” (arrows). Additional smaller nodules are seen in the other lobes bilaterally. (D) Axial CT image demonstrates dense, mass-like consolidation with surrounding groundglass and associated volume loss and architectural distortion consistent with progressive massive fibrosis, which is often ascribed to pneumoconioses but can also be seen with sarcoid.

These nodules often coalesce into larger nodules and mass like consolidations sometimes referred to as alveolar sarcoidosis. Many of these abnormalities resolve over time, but in some patients areas of fibrosis may persist. Small satellite nodules are often present giving the appearance of the “galaxy sign” (Fig. 18.26) [37]. Groups of very tiny nodules may also result in ground-glass appearance. While most of the parenchymal abnormalities in sarcoidosis resolve over time, some patients may have persistent and progressive fibrosis. Fibrosis is usually upper lobe predominant and results in upward hilar retraction (Fig. 18.27). Progression of fibrosis may also result in conglomerate mass-like opacities, similar to progressive massive fibrosis seen with silicosis. Paracicatricial emphysema, cystic bronchiectasis, and other air-filled cysts are common. Honeycombing can be infrequently seen. Fungus balls (aspergilloma) can develop within the cystic spaces.

FIGURE 18.27 Advanced, fibrotic pulmonary sarcoid. (A) Frontal chest radiograph demonstrates upper lung predominant fibrosis with confluent perihilar opacities with associated volume loss and architectural distortion resulting in superior hilar retraction bilaterally. (B) Axial CT image demonstrates geographic bilateral perihilar consolidative opacities with volume loss and intrinsic traction bronchiectasis and surround architectural distortion. There are also calcified hilar lymph nodes bilaterally (arrows). (C) Coronal CT image demonstrated upper lobe predominant fibrotic changes and multiple calcified mediastinal and hilar lymph nodes.

Amyloidosis Amyloidosis is a heterogeneous group of diseases characterized by extracellular deposition of abnormal protein fibrils (amyloid). Pulmonary manifestations of amyloidosis can be classified into (1) diffuse amyloidosis, (2) localized nodular amyloidosis, and (3) tracheobronchial amyloidosis [38]. Diffuse amyloidosis (also referred to as alveolar septal amyloidosis) is most often related to primary systemic amyloidosis and typically presents with respiratory symptoms. Findings on imaging are variable and include multiple small (2–4 mm) nodules, interlobular septal thickening, and focal consolidations. Calcification may be seen within the nodules and consolidations (Fig. 18.28). Lymphadenopathy is common. Findings can progress over time and result in respiratory failure.

FIGURE 18.28 Diffuse pulmonary amyloidosis. (A) Axial CT image demonstrates subpleural consolidations predominantly in the lower lobes with larger mass-like consolidations in the right paravertebral and left paramediastinal lower lobes (A, arrows). There are associated diffuse ground-glass opacities with interlobular septal thickening. (B) Sagittal CT image through the right lung demonstrates extensive septal thickening and ground-glass opacities with a large consolidative opacity in the posterior basal right lower lobe. (C) Corresponding sagittal CT image in soft-tissue window shows dense calcifications within the consolidation.

Localized nodular amyloidosis is usually asymptomatic and present on imaging as single or multiple, round, well-defined lung nodules or masses, which can enlarge over time. Calcifications are seen in half of the cases. Cysts may also be present. Tracheobronchial amyloidosis may involve the larynx, trachea, and central bronchi. Amyloid deposits may be focal or diffuse and typically manifest on imaging as focal nodular or diffuse airway thickening, with or without calcifications.

Diffuse Cystic Lung Diseases The Fleishner society defines a cyst as “a round parenchymal lucency or low-attenuating area with a well-defined interface with normal lung.” They are typically thin-walled (20%) for cardiovascular event will likely benefit from therapy and those with low risk (540), coronary CTA has been found to be often inconclusive [20]. In that series, 93% of the patients with inconclusive coronary CTA are found to require subsequent coronary revascularization. The issue of luminal visualization in heavily calcified coronary arteries is partially alleviated by using dual-energy CT (DECT) with subtraction [21] or deblooming algorithm [22]. However, these techniques are still undergoing active research and refinement with limited current use in the clinical arena.

FIGURE 22.7 Poor delineation of calcification from opacified vessel lumen. When the arterial contrast opacification is robust, calcified plaques (arrow) may be difficult to detect. This issue is circumvented by comparison with the noncontrast or calcium scoring scan.

Repeat Calcium Scoring The utility of repeat calcium score testing is equally poorly established. Literature documents that development/progression of coronary calcifications between scans is associated with increased hazard for cardiovascular events [23]. However, studies also suggest that the progression/development of coronary calcium score may be reasonably predicted using the baseline score and available clinical parameters [24]. Further, analysis shows inclusion of calcium score progression in large cohort studies adds little to risk prediction [25]. Adding to the issue is rescan reproducibility, which varies by about 20 points for the Agatston method [26]. Combined, these findings indicate routinely repeat calcium scoring is of very questionable clinical benefit at this time.

Summary—Calcium Scoring In summary, calcium scoring is performed in asymptomatic patients with intermediate risk for coronary artery disease since the risk/benefit of preventive treatment may be further stratified. Because the result is viewed in light of existing literature with specified acquisition parameters, care is needed to ensure the scanning protocol allows for valid interpretation. A numeric result is given, with higher values corresponding to higher all-cause mortality. Currently, there is no clear benefit of calcium scoring in symptomatic patients or repeat testing.

Stenosis and Plaque Evaluation Advancement in imaging techniques has led to improving capability of CTA in noninvasive evaluation of the coronary arteries. In contrast to calcium scoring, where only calcified plaques are assessed, coronary CTA allows direct assessment of both calcified and noncalcified plaques, luminal narrowing, and plaque characteristics as well as more subtle aspects of anatomy.

Technical Considerations in Coronary CT Angiography Coronary CTA represents the pinnacle of CT imaging in terms of technical demands. In contrast to most body parts, spatial resolution, temporal resolution, and contrast resolution all need to be addressed. Spatial Resolution With the importance of luminal narrowing quantification in mind, the constraint imposed by spatial limitation is first considered. With 0.5 mm isovolumetric CT acquisition, a 3 mm coronary artery is represented by 6 voxels in profile and 28 voxels in cross section. In contrast, a 1.5 mm coronary artery is represented by 3 voxels in profile and 7 voxels in cross section. With increasing voxel size, this insufficient voxel representation worsens. Consequently, Society of Cardiovascular Computed Tomography guideline recommends a slice width of at most 1.0 mm and slice increment of 50%, although thinner slice width is preferred [27]. Also because of this limitation, it should be kept in mind that a vessel under 1.5 mm in size may be visible if patent but rarely adequately displayed for narrowing assessment on CT. In aiding with the issue of spatial resolution, coronary CTA may be performed following administration of nitroglycerin, which results in significant coronary artery vasodilation, increases the number of evaluable

artery segments, and improves the diagnostic accuracy of the exam [28]. Sublingual tablet, sublingual spray, and dermal patch have all been used with success, albeit with differences in timing and duration [29]. Side effects of nitroglycerin are generally mild and transient, which may include headache, dizziness, flushing, and hypotension. Contraindications should be kept in mind (Table 22.1). To avoid inadequate display of the voxels due to image matrix size limitation, a small field-of-view reconstruction (200–250 mm) is recommended as is a larger (512 × 512) default image matrix size [27]. Table 22.1 Contraindications to nitroglycerin Contraindications of nitroglycerin Hypotension (SBP 1 (180° tube rotation for complete image or 90° with dual source scanners)

1.5 cm ◾proximal Higher distal attenuation gradient (denser opacification distal to the occlusion compared to to the occlusion) ◾vessel Distal reverse attenuation gradient (denser opacification in the terminal portion of the compared to just after the occlusion) ◾ Increased number of side branches ◾ Blunted stump ◾ calcification >50% ◾ Cross-sectional Presence of significant collateralizing vessels

FIGURE 22.11 Total vessel occlusion. In an occluded artery, the segment of involvement is often long (>1.5 cm). A blunted stump (solid arrow) is suggestive. Distal to the occlusion, reverse contrast gradient may be seen, where the distal segment (dashed arrow) opacifies more strongly than the proximal segment (dotted arrow), a result of backward collateralization flow.

FIGURE 22.12 Subtotal vessel occlusion/severe narrowing. An apparent very short segment of occlusion (arrow) is likely to have residual contrast flow on follow-up angiography. This configuration is thus more appropriately termed subtotal occlusion/severe narrowing.

Plaque Characterization In addition to luminal narrowing, the plaque should be examined for highrisk/vulnerable features. Because acute coronary events, as mentioned, are thought to be the result of plaque rupture and thrombosis more than half of the time [38], identification of such factors prompts consideration of treatment even in the absence of significant luminal narrowing. Further, the ability to evaluate the extraluminal structures is a distinct advantage of CT over routine catheter angiography, an added value that should not be overlooked. Our understanding of plaque vulnerability is coupled to studies examining the natural course of coronary atherosclerosis (Fig. 22.1). The advanced atherosclerotic lesion with a lipid/necrotic core and thin smooth muscle fibrous cap, the so-called thin-cap-fibroatheroma (TCFA), is found most vulnerable to rupture. In fact, by histology, TCFA is differentiated from

ruptured plaque only by the integrity of the overlying cap. Unfortunately, the spatial and contrast resolution of clinical CT precludes direct identification of TCFA. Instead, a few findings that are associated with TCFA and acute coronary events [39–41] are:

◾TCFA Low-density plaque, defined by 70% stenosis [56].

Kawasaki disease is classically aneurysmal (Fig. 22.30) compared to other vasculitis, in which ectasia is more common. Congenital disease and shunting constitute the last major cause and must be considered when the dilatation is diffuse and smooth in morphology (Fig. 22.31). Notably, conditions included in this category include coronary-pulmonary fistula, coronary-cameral fistula, and anomalous coronary artery arising from pulmonary artery, as well as extensive collateralization that occurs as result of proximal vessel occlusion. Other rarer causes include connective tissue disorder and other inflammatory diseases.

FIGURE 22.29 Coronary artery aneurysm in atherosclerosis. Coronary artery aneurysms may be the result of advanced atherosclerosis. In this case, fusiform aneurysms (arrows) are seen distal to foci of severe narrowing (dashed arrows). The arteries are typically diffusely diseased. Note presence of luminal thrombus (dotted arrow) within the inferior aneurysm, a common finding.

FIGURE 22.30 Coronary artery aneurysm in Kawasaki disease. In Kawasaki disease, the aneurysm (arrow) is typically seen without the background of diffuse atherosclerosis. Single or multiple aneurysms may be seen. The age of presentation is an additional important factor to consider.

FIGURE 22.31 Coronary artery ectasia in congenital heart disease. If identified, coronary artery ectasia should prompt consideration of vascular shunting or anomalous vascular connection. In this case, ectasia of both the right coronary artery (A) and left coronary arteries (B) is shown in a patient with anomalous left coronary artery from the pulmonary artery (arrow, ALCAPA, Bland–White–Garland syndrome).

The differentiation of pseudoaneurysm from aneurysm is a pathologic one. An aneurysm is contained by three-layer vessel wall, whereas the tunica intima and media of a pseudoaneurysm are ruptured or incomplete. This distinction on imaging is often difficult and more readily suggested by etiology. Coronary artery dilatations in the setting of traumatic injury, following catheter-based interventions, infection, and drug use (notably cocaine) are most commonly pseudoaneurysms (Fig. 22.32), as the intima and media are rarely intact in acute dilatation. Nonetheless, any true aneurysm that enlarges sufficiently may rupture and, when contained, become a pseudoaneurysm. Perivascular soft tissue stranding/inflammation and associated fluid collection are rarely seen with uncomplicated aneurysm and suggestive of pseudoaneurysm formation.

FIGURE 22.32 Coronary artery pseudoaneurysm. Coronary artery pseudoaneurysms may be difficult to differentiate from aneurysms. Most commonly, the etiology of the finding helps to discriminate, with pseudoaneurysms being more commonly the result of trauma (accidental or iatrogenic) or infection. The acute onset, surrounding soft tissue stranding, and wall irregularity can provide additional clue. In this case, a pseudoaneurysm (arrows) is seen arising from the proximal right coronary artery that is the result of recent intervention.

In addition to the dilatation, important features to identify in imaging include presence or absence of luminal thrombus (Fig. 22.29), which is reported in up to 67% of the aneurysms in a small series [57]. To avoid confusing uneven contrast opacification with luminal thrombus, delayed phase images are helpful. The location of the aneurysm should be discussed in conjunction with distance of the aneurysm sac to the artery ostium or large branch vessel and presence of proximal narrowing in anticipation for possible catheter-based intervention. Attention needs to be paid to look for focal outer wall irregularity, which may hint to impending rupture/pseudoaneurysm formation. Similarly, any fat stranding around the dilated vessel should be viewed with suspicion. Comparison to prior studies

is essential. It is worth noting that Kawasaki disease and dilatation secondary to shunting may regress with appropriate treatment. The prognosis of patients with coronary artery dilatation is dependent on the etiology. In the largest international registry to date with 1565 patients and a median follow-up of 37 months, 31% of patients with coronary artery aneurysms displayed a major cardiovascular event and 15% died [55]. However, this poor prognosis may reflect the underlying atherosclerotic disease burden and not additional risk conferred by presence of aneurysm per se. In Kawasaki disease, the size and location of the aneurysm may be used for risk stratification [58]. Prognosis of patients with coronary ectasia due to vascular shunting is favorable barring underlying complex pathology [59]. The natural history in other vasculitis and connective tissue disorders is not well established due to their rarity. Mycotic and drug use-related pseudoaneurysms have a higher chance for complications and should be closely monitored, especially in the acute period.

Myocardial Bridging Myocardial bridging is discussed here due to its effects on coronary artery atherosclerosis. Myocardial bridging refers to anomalous course of the coronary artery through the myocardium instead of the normal epicardial space, also termed intramyocardial, intramural, or intramuscular coronary artery. This congenital anomaly is common, estimated at roughly 40% in frequency by both autopsy and CT series, although a wide range of values has been reported [60]. The mid segment of the LAD artery is the most common site, followed by its distal segment. The intramyocardial segment (termed tunneled segment) may be of varying length and depth. The overlying myocardium (termed myocardial bridge) may provide a complete or partial covering. Clinical Significance The clinical significance of myocardial bridging is debated. Earlier reports suggest an association of myocardial bridging with various cardiac complications such as arrhythmia, angina, myocardial infarction, and sudden cardiac death. However, its high prevalence on later studies has led others to consider it as a benign anatomic variant. This view is perhaps supported by the classic teaching that coronary perfusion occurs in diastole, but compression of the tunneled artery is mainly a systolic phenomenon. Nevertheless, a recent meta-analysis inclusive of 21 prior studies finds that myocardial bridging is in fact associated with myocardial ischemia and major adverse cardiac events [61]. Together, these findings suggest that there is likely only a small subpopulation of the patients in which this common finding has pathologic consequences. The morphology and degree of

narrowing are presumed influencing factors. However, there is currently no consensus on what constitutes pathologic bridging. Pathology The pathology of myocardial bridging is now believed to extend beyond systolic artery compression [62]. In some patients, the arterial compression persists into early diastole, shortening the perfusion window. Moreover, the early diastolic relaxation and dilatation generate transient negative pressure and a “sucking phenomenon” that disrupts normal coronary blood flow [63]. The hemodynamic alterations are likely further compounded by the angulation of the tunneling and resurfacing vessel. The locoregional endothelial function of the tunneled segment is impaired [64], predisposing to vasospasm [65]. Not surprisingly, the degree of narrowing and duration of compression are dependent on cardiac effort. In some cases, the associated flow dysregulation is evident only under exercise or pharmacologic stress. An important consequence to the altered physiology is that myocardial bridging predisposes the coronary artery segment proximal to the bridge to atherosclerosis but spares the tunneled and more distal segments. The atherosclerotic changes may be seen earlier in life than normally expected and contribute to the association to myocardial ischemia. This accelerated atherosclerosis is typical at the junction of the proximal and mid segments of the LAD, given the mid segment is the most common location of myocardial bridging and bifurcation points are already susceptible to the development of atherosclerosis. Systolic narrowing or compression of the tunneled segment is thought to protect against lipid and infiltrate deposition and should not be mistaken for atherosclerotic narrowing. In young patients where no other etiology for myocardial ischemia is identified, myocardial bridging may warrant consideration particularly if the tunneled segment is long and deep. In patients where coronary artery bypass grafts are planned, myocardial bridging should be mentioned to reduce the possibility of intraoperative confusion. Imaging Contrast-enhanced coronary CTA has high sensitivity in detection of myocardial bridging. On CT, myocardial bridging is best shown on MPRs and MIP images, where the traversing artery can be clearly viewed in relation to the myocardium and epicardial fat (Fig. 22.33). As mentioned, close attention should be paid to the artery segment proximal to the bridge for atherosclerotic narrowing. The inability to assess physiology is a weakness of CT, and suspected cases of pathologic bridging typically undergo physiologic testing. It should also be noted that measurement of artery compression/narrowing extent is best avoided on CT due to spatial resolution limitation, image noise (especially when ECG dose

modulation/pulsing is used), and common use of beta-adrenergic blockade in heart rate control that may lessen the compression. The inability to visualize extraluminal structures makes catheter angiography less sensitive in the detection of myocardial bridging. Instead, the dynamic change in caliber of the vessel (“milking effect”) and in course/angulation of the tunneling and resurfacing segments (“step down–step up phenomenon”) are examined.

FIGURE 22.33 Myocardial bridging with proximal atherosclerosis. In myocardial bridging, the coronary artery dives into the myocardium for a distance before re-emergence. Note the tunneled segment (arrow) underlying the outer myocardial wall (dashed arrow) and the normal epicardial position of the artery (dotted arrow). While the tunneled segment is thought to be protected against atherosclerosis, the segment proximal to the myocardial bridge is at an increased risk, as in this case.

Coronary Artery Intervention Upon identification of coronary artery atherosclerosis, therapeutic options consist of (a) medical therapy that aim at symptomatic control and halting or

even reversing plaque progression and (b) revascularization via percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG). Here, we describe the postprocedural appearance of the coronary system that may be encountered. Coronary Artery Bypass Grafts

Types of Bypass Grafts: In CABG, revascularization is achieved by creation of collateral supply using either a venous or an arterial conduit. In venous bypass, a segment of the saphenous vein is harvested from the lower extremity. This venous segment is then reversed in direction or valvectomized and used to connect the ascending aorta to the obstructed coronary artery. Radio-opaque graft anastomosis markers are sometimes placed to help identify the bypass graft ostia on follow-up. In arterial bypass, the arterial segment may be either used as an in situ graft or a free graft. In an in situ graft, a noncoronary artery near the heart is mobilized without disruption of its origin and anastomosed to the diseased artery. Most commonly, the left internal mammary artery (internal thoracic artery) is used due to its normal course in close proximity to the anterior cardiac wall. The right internal mammary artery may be used in the same fashion, although more often anastomosing to the RCA or inferior aspect of the heart. Very rarely, the right gastroepiploic artery or the inferior epigastric artery are utilized. In a free graft, the arterial segment (most commonly the radial artery, although internal mammary arteries are also used in decent frequency) is transplanted to create the aortocoronary connection. Occasionally, a single graft is used for reperfusion of two native arteries in a “jumped” or sequential graft by a mid-graft side-to-side anastomosis and an end-graft end-to-side anastomosis (Fig. 22.34).

FIGURE 22.34 Sequential coronary artery bypass graft. In a sequential or “jumped” graft, a single bypass artery is used to provide blood flow to two diseased arteries. Here, a left internal mammary artery bypass graft (solid arrow) is seen anastomosing to both the first diagonal artery (dashed arrow) and the mid-distal left anterior descending artery (dotted arrow).

Imaging: On radiographs, radio-opaque markers provide easy clue to prior CABG if present (Fig. 22.35). Surgical clips from internal mammary artery harvest are sometimes visible. However, changes of sternotomy may be the only provided sign. On CT, internal mammary grafts can be identified by examining the expected course of the arteries, where the mobilized artery is seen displaced posteriorly (Fig. 22.36). Venous grafts and free arterial grafts are seen as anomalous vessels arising from the ascending aorta if patent (Fig. 22.37). If occluded, focal outpouching/irregularity of the ascending aorta is suggestive of the remnant anastomotic ostium (Fig. 22.38). Care needs to be paid to safeguard against mistaking the cannulation site used for cardiopulmonary bypass for an occluded graft by searching for the

hyperdense felt pledget on noncontrast images (Fig. 22.39). In addition to luminal narrowing and occlusion, the grafts should be evaluated for malpositioning and kinking (Fig. 22.40).

FIGURE 22.35 Coronary bypass graft anastomosis markers. On radiograph (A), changes of prior coronary artery bypass grafting may be identified by the presence of radio-opaque anastomosis markers (arrow). Sternotomy wires (dotted arrow) and pacer/ICD leads (dashed arrow) are partially seen. On CT (B), the radio-opaque marker is identified on the anterior aspect of the ascending aorta (arrow). Note that several markers are in use with variable appearance. Occasionally, the ostia may be marked impromptu using surgical wires.

FIGURE 22.36 Arterial in situ coronary bypass graft. On CT (A), in situ arterial coronary bypass grafts are easily identified by the abnormal positioning of the redirected internal mammary artery (arrow), which can be followed to the coronary anastomosis. Note the normal positioning of the internal mammary artery on the contralateral side (dashed arrow). Corresponding volumetric rendering (B) shows the typical course of the left internal mammary graft (arrow). Also note a partially seen venous bypass graft (dashed arrow).

FIGURE 22.37 Patent venous coronary bypass graft. In a venous coronary bypass grafts (and free arterial bypass grafts, which have a very similar appearance), the aortic anastomosis is typically identified in the anterior aspect of the ascending aorta instead of the sinuses of Valsalva. Inevitably, the graft displays a course in the prevascular space (arrows), where it can be identified. Note a concurrent in situ left internal mammary bypass graft (dashed arrow) as well as focal irregularity of the right anterolateral ascending aorta (dotted arrow), representing a partially visualized ostium of an additional bypass graft.

FIGURE 22.38 Occluded venous coronary bypass graft. When occluded, venous and free arterial bypass grafts can be difficult to identify. In some cases, the graft occludes just distal to the ostium, facilitating its detection (arrow). Surgical clips around the course of the bypass graft may also provide a clue. The area should be evaluated on noncontrast images as to not misidentify prior aortic cannulation site as patent ostium of an occluded graft.

FIGURE 22.39 Cardiopulmonary bypass cannulation site. In patients who underwent prior cardiopulmonary bypass, the aortic cannulation site is most often closed and reinforced with hyperdense felt pledgets (arrow), which may be mistaken for pseudoaneurysm or ostium of an occluded graft on contrast-enhanced images (A). Examining area on noncontrast images (B) helps correctly identify as neither pseudoaneurysm nor ostium should appear hyperdense before contrast administration.

FIGURE 22.40 Focal coronary artery bypass graft kinking. Occasionally, focal kinking of the arterial bypass graft results in hemodynamically significant narrowing. Here, there is subtotal occlusion of a venous bypass graft (arrow) as a result of focal kinking.

Similar to the native coronary arteries, the bypass grafts are examined for narrowing and occlusion in their entirety. In the case of in situ internal mammary artery grafts, the field of view is extended to the clavicular heads to ensure adequate coverage of the artery origin (Fig. 22.41). Three etiologies of graft stenosis and occlusion include graft thrombosis, neointimal hyperplasia, and atherosclerosis. Similar in appearance, these complications are best distinguished by differences in time course of their occurrence. Graft thrombosis is an acute complication of bypass surgery that occurs predominantly within the first month postsurgery. Neointimal hyperplasia is a result of smooth muscle proliferation and extracellular matrix deposition that occurs within the first year. Atherosclerosis, although may initiate early, is typically not sufficiently visualized or obstructive until after the first year. Also similar to native coronary arteries, the bypass grafts may develop aneurysm and pseudoaneurysm. Pseudoaneurysm is generally considered a surgical complication that is seen in the acute period. Akin to

that of native coronary artery, a graft aneurysm is a result of atherosclerosis, a late complication.

FIGURE 22.41 Origin of the internal mammary artery graft. In the evaluation of coronary bypass grafts, the field of view should be extended to the level of the clavicular heads in the case of an in situ internal mammary graft. Here, focal severe narrowing of the left internal mammary artery origin is seen (arrow) secondary to atherosclerotic changes.

Percutaneous Coronary Intervention In PCI, the diseased arterial segment is accessed via a transcatheter approach. The stenosis or occlusion is crossed and balloon angioplasty performed to re-establish blood flow. Because prior clinical trials have demonstrated improved clinical and angiographic outcome by the addition of stents [66], coronary stents are now deployed as standard of care. In-Stent-Restenosis

On imaging, coronary artery stents appear as hyperdense geometric structures, which may be easily mistaken for coronary artery calcifications (Fig. 22.6). Appropriate clinical history is key to its identification. ISR represents a feared complication that results from either thrombus organization or neointimal proliferation and subsequent narrowing or occlusion of the stent lumen (Fig. 22.42). Unfortunately, the high density of the stent material and adjacent bulky calcification often result in obscuration of the stent lumen, which limits evaluation. There is general consensus based on studies that stents of 2.5–3 mm or more are evaluable, more so than stents of smaller sizes [67]. Using 64-slice CT, 93% of the stents ≥2.5 mm are deemed evaluable with ISR sensitivity of 95% [68]. In practice, the evaluability of the stent should be judged on a case by case basis and clearly conveyed.

FIGURE 22.42 Coronary artery stent occlusion. Because metallic artifacts may obscure the in-stent lumen, lack of contrast opacification is alone not a sufficient sign of in-stent-restenosis unless both an opacified segment (solid arrow) and a nonopacified segment (dashed arrow) are seen. In occluded cases, lack of contrast flow distal to the stent is helpful in making the diagnosis.

Stent Fracture and Protrusion Rarely, a coronary artery stent may be fractured (Fig. 22.43), requiring targeted revascularization in the case of flow compromise. In the absence of obstruction, the clinical significance of this abnormality is not clear nor studied in detail due to its rarity. This finding should not be confused with overlapping or serial stents. The distinction between the two is best made by clinical history and comparison to prior exam. Last, extracoronary positioning of a stent should be described. Most commonly, the coronary artery stent protrudes slightly into the aortic lumen, which may be purposefully positioned in treating ostial stenosis (Fig. 22.44). However, this placement may interfere with future procedures such as transcatheter replacement of the aortic valve and is thus worth noting. Rarely,

extraluminal stent migration occurs, which is potentially devastating. Thankfully, this finding is rarely a diagnostic challenge.

FIGURE 22.43 Fracture coronary artery stent. Stent fracture (arrow) is an uncommon complication that may be suggested on CT images by discontinuity of the stent wall or separation of the components. Clinical history should be examined as to not mistaken serial stents as a fracture. Also note the mild kinking of the proximal stent component.

FIGURE 22.44 Protruding coronary artery stent. In ostial disease and narrowing, the coronary stent may be placed such that the proximal component protrudes partially into the aorta. This configuration may cause confusion or complication with future procedure if not identified.

Coronary CT Fractional Flow Reserve Computed tomography derived fractional flow reserve (FFR) is a promising technique with growing interest that has not yet reached widespread clinical use. This topic is briefly mentioned here for completeness as it addresses a major weakness of CT imaging in coronary atherosclerosis. As discussed above, CT provides anatomic description of the arteries. While powerful, it has been noted that not all cases of significant narrowing on CT is associated with functional myocardial ischemia even when confirmed on catheter angiography. That is to say, regular coronary CTA overestimates the clinical significance of narrowing if taken at face value because it does not assess physiology. In catheter angiography, this disadvantage is addressed with a measure termed FFR.

In FFR, a catheter with an attached pressure transducer is maneuvered across a stenotic lesion to obtain proximal and distal pressure readings after pharmacologic (adenosine) induction of hyperemia to serve as a suitable surrogate for the blood flow reduction. Calculated as the ratio of distal coronary pressure to proximal pressure, FFR is reduced in the presence of a pressure gradient. Studies show that FFR reliably discriminates functionally significant lesions: a lesion with FFR >0.80 is rarely clinically important whereas FFR 0.75 is used to defer versus perform PCI in patients with intermediate lesions, long-term (15 year) follow-up indicates this deferral is safe and associated with lower rate of myocardial infarction compared to the stented group [70]. Studies like this have cemented the use of FFR in angiography, which is now considered standard of care. A relatively newly established measurement using similar principle, instant wave-free ratio, may be obtained without use of hyperemic agent [71]. The advent of computational modeling in the last decades has led to the possibility of a similar measurement to be obtained using CT imaging. In essence, a simplified closed-loop model of the cardiovascular system is constructed to enable estimation of the hemodynamic properties including FFR at each location, giving rise to computational fluid dynamics models [72]. The result of the process is a 3D, personalized, dynamic model that may be interpreted alongside the structural images (Fig. 22.45). The noninvasive acquisition is a major advantage, which may be performed using the coronary CTA dataset if certain requirements are achieved. The technical complexity and lack of widespread availability represent its major weaknesses. Currently, HeartFlow FFRCT (processing algorithm by commercial company HeartFlow, Redwood City, CA) is the only clinical CT FFR tool approved for use in the United States.

FIGURE 22.45 CT fractional flow reserve. In the mid LAD, a focus of moderate narrowing by partially calcified plaque is seen (A, arrow), which may or may not be functionally significant. Using HeartFlow FFRCT (HeartFlow, Redwood City, CA), CT FFR is computed throughout the entire coronary tree (B). The associated concurrent drop in CT FFR to less 0.75 indicates the lesion is likely hemodynamically significant (arrow). On catheter angiography (C), the moderate stenosis is redemonstrated (arrow) and iFR recapitulated a similar drop across the lesion (not shown).

(Courtesy: Dr. Praveen G. Ranganath, Massachusetts General Hospital Boston, MA, USA.)

Overall Approach 1. Calcium scoring is used for risk stratification in asymptomatic patients with intermediate to high risk for coronary artery atherosclerosis. 2. Coronary CTA is mainly used to evaluate symptomatic patients with intermediate risk/pretest probability for significant/obstructive coronary artery obstruction. 3. In performing coronary CTA, spatial, temporal, and contrast resolutions all need to be considered. Nitroglycerin may be given to induce coronary artery dilatation and increase the number of evaluable segments. Beta adrenergic blockade helps with heart rate control but is becoming less critical with improving scanner temporal resolution. Adequate contrast opacification is achieved with injection of high concentration contrast at a high rate, necessitating a relatively large bore access line. 4. In interpreting coronary CTA, both extent of atherosclerotic narrowing and plaque features should be assessed (keeping in mind that acute coronary events are more frequently the result of plaque rupture than narrowing). 5. CAD-RADS allows for standardized reporting that provides the referring physician with interpretation and management suggestions. 6. Coronary artery dissection is a major differential for atherosclerotic disease that is distinguished by patient demographic, risk factors, and global atherosclerotic disease burden. Visualization of a dissection flap, although possible, is a rare finding. 7. Coronary artery aneurysm and ectasia are predominantly the result of atherosclerosis, Kawasaki disease, and vascular shunting. Coronary artery pseudoaneurysms are more frequently the result of trauma and infection. 8. Myocardial bridging is a very common anomaly that is pathologic in only a very small proportion of the patients. The arterial segment proximal to the bridge is prone to develop atherosclerosis, whereas the tunneled segment is protected against atherosclerosis. 9. Interpreting coronary CTA in patients with prior bypass without proper clinical history is illfated as occluded grafts may be very difficult to detect. Similarly, clinical history is key to avoid misidentification of coronary artery stent as dense calcific plaque.

10. CT FFR is a promising technique that assesses physiology using structural data that is not yet widely used.

Sample Report Templates Coronary Calcium Score EXAM: CORONARY CALCIUM SCORE CT CLINICAL HISTORY: [ ] COMPARISON: [ ] TECHNIQUE: Scout images of the chest were obtained. Noncontrast CT of the heart was then performed with parameters specified by the Agatston method. The scan was acquired using prospective ECG-triggering and under breath-holding using a [scanner type]. Calcium scoring was completed by manual segmentation and according to the Agatston method. HEART RATE AND RHYTHM: The patient was in [sinus rhythm] with heart rate of approximately [ ] beats per minute at the time of acquisition. QUALITY: [Excellent, with no artifacts; Good, with minor artifact of no consequences; Fair, with moderate artifacts but diagnostic quality; Poor, with severe artifacts that limit evaluation]. FINDINGS: Coronary arteries: The Agatston calcium score is [ ], corresponding to [ ] percentile for subjects of the same age, sex, and ethnicity who are free of clinical cardiovascular disease and treated diabetes. The calcium score distribution is as follows: left main coronary artery: [ ]; left anterior descending artery: [ ]; left circumflex artery: [ ]; right coronary artery: [ ]. The coronary arteries are [normal in origin and course]. There is [right; left; co-] coronary artery dominance. Cardiac morphology: The atria and ventricles are [normal in morphology and size], allowing for limitations of a noncontrast study. Cardiac valves: There is [no significant calcifications] of the aortic and mitral valves. Pericardium: There is [no significant pericardial effusion or calcifications]. Extracardiac findings: [There are no significant extracardiac findings in the limited views of the great vessels, lungs, mediastinum, and upper abdomen.] IMPRESSION: 1. [No evidence of coronary atherosclerosis, coronary calcium score 0; Coronary atherosclerosis, calcium score __]. 2. [Other important findings.]

Coronary CT angiography EXAM: CORONARY CT ANGIOGRAPHY CLINICAL HISTORY: [ ] COMPARISON: [ ] TECHNIQUE: Scout images of the chest were obtained followed by noncontrast CT of the heart. Following administration of intravenous contrast, [0.6] mm collimated images were obtained through the coronary arteries. Delayed images [were; were not] obtained. The scan was acquired using [prospective; retrospective] ECG-triggering and under breath-holding using a [scanner type]. 3D reconstructions including curved MPRs were performed. MEDICATIONS IF APPLICABLE: Dose and route of administration such as beta blocker and nitroglycerine The patient experienced [no significant side effects or complications]. HEART RATE AND RHYTHM: The patient was in [sinus rhythm] with heart rate of approximately [ ] beats per minute at the time of acquisition. QUALITY: [Excellent, with no artifacts; Good, with minor artifact of no consequences; Fair, with moderate artifacts but diagnostic quality; Poor, with severe artifacts that limit evaluation]. FINDINGS: Coronary arteries (description can be altered to document presence, characteristics of plague and degree of luminal narrowing when present) For example the following description refers to reporting template for CADRADS 0: The coronary arteries are [normal in origin and course]. There is [right; left; co-] coronary artery dominance. Left main coronary artery: The left main coronary artery is a [small; medium; large] sized vessel with [bifurcation; trifurcation]. It is [patent without evidence of plaque or stenosis]. [The ramus intermedius is patent without evidence of plaque or stenosis.] Left anterior descending artery: The LAD is [patent with no evidence of plaque or stenosis]. Its evaluable major branches are [patent without evidence of plaque or stenosis]. [A __ mm segment of myocardial bridging is seen in the mid; distal LAD.] The distal LAD terminates [before; at; around] the apex. Left circumflex artery (LCx): The LCx is [patent with no evidence of plaque or stenosis]. Its evaluable major branches are [patent without evidence of plaque or stenosis]. [It gives off a patent posterior descending artery and a patent posterior left ventricular branch.] Right coronary artery: The RCA is [patent with no evidence of plaque or stenosis]. Its evaluable major branches are [patent without evidence of

plaque or stenosis]. [It gives off a patent posterior descending artery and a patent posterior left ventricular branch.] [No vulnerable plaques were identified.] [There were no evidence of dissection or abnormal dilatation.] [No bypass grafts or stents were seen.] [The Agatston calcium score is __, corresponding to __ percentile for subjects of the same age, sex, and ethnicity who are free of clinical cardiovascular disease and treated diabetes. The calcium score distribution is as follows: left main coronary artery: __; LAD: __; LCx: __; RCA: __.] Cardiac morphology and function: The atria and ventricles are [normal in morphology and size]. The cardiac function is [normal without evidence of focal wall motion deficit]. Cardiac valves: There is [no significant thickening or calcifications] in the aortic and mitral valves. Pericardium: The pericardial contour is [preserved]. There is [no significant pericardial effusion, thickening, or calcifications]. Extracardiac findings: [There are no significant extracardiac findings in the limited views of the great vessels, lungs, mediastinum, and upper abdomen.] IMPRESSION: 1. CAD-RADS [0- no plaque or stenosis by coronary CT angiography]. [Consider nonatherosclerotic causes of chest pain.] 2. [Other important findings.]

Suggested readings • P Greenland, MJ Blaha, MJ Budoff, R Erbel, KE Watson, Coronary calcium score and cardiovascular risk, J Am Coll Cardiol 72 (2018) 434– 447. • RC Cury, S Abbara, S Achenbach, A Agatston, DS Berman, MJ Budoff, et al., Coronary Artery Disease – Reporting and Data System (CAD-RADS): an expert consensus document of SCCT, ACR and NASCI: endorsed by the ACC, JACC, Cardiovasc Imaging 9 (2016) 1099–1113. • F Saremi, S Achenbach, Coronary plaque characterization using CT, Am J Roentgenol 204 (2015) W249–W260. • SN Hayes, CESH Kim, J Saw, D Adlam, C Arslanian-Engoren, KE Economy, et al., Spontaneous coronary artery dissection: current state of the science: a scientific statement from the American Heart Association, Circulation 137 (19) (2018) e523–e557. • S Abou Sherif, O Ozden Tok, Ö Taşköylü, O Goktekin, ID Kilic, Coronary artery aneurysms: a review of the epidemiology, pathophysiology, diagnosis, and treatment, Front Cardiovasc Med 4 (2017).

• G Murtaza, D Mukherjee, SM Gharacholou, A Nanjundappa, CJ Lavie, AA Khan, et al., An updated review on myocardial bridging, Cardiovasc Revascul Med 21 (9) (2020) 1169–1179.

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23

Noncoronary Artery Heart Disease Muhammad Usman Aziz, Prabhakar Rajiah, Satinder Singh

Introduction Nonischemic heart disease accounts for nearly half of the cardiac deaths and includes heterogenous diseases, including valvular heart disease, cardiomyopathies, cardiac masses, and pericardial diseases. Noninvasive imaging techniques have increased the diagnostic accuracy for all these diseases and consequent decrease in invasive procedures. In this section, we will review valvular heart disease, cardiomyopathy, and cardiac tumors emphasizing the current and evolving role of noninvasive imaging techniques.

Valvular Heart Disease Valvular heart disease is common and is one of the leading causes of hospitalization and mortality worldwide [1]. With prevalence of 2.5%, it accounts for up to 20% of all cardiac surgeries performed in the United States [2,3]. Most common cause of valvular heart disease now is degenerative in the western world (rheumatic heart disease remains the most common cause in developing countries). Often these are diagnosed in early stages with echocardiography; hence chest radiographic findings are minimal to nil. Echocardiography remains the initial technique of choice for  diagnosis due to its noninvasive nature, accessibility, well-established strong evidence-based data, no radiation exposure, and high temporal resolution enabling excellent visualization of cardiac valves. It is, however, limited by limited field of view due to obesity, chest deformity, or scarring from prior surgery, artifacts, and operator skill. Cardiac magnetic resonance imaging (MRI) and computed tomography (CT) are used if echo is suboptimal and in select patients requiring additional risk

assessment [4]. Cardiac MRI offers excellent contrast and temporal resolution and is often the second choice after echocardiography. It can, however, be timeconsuming, is susceptible to hardware artifacts and cannot be performed in patients with claustrophobia. Newer CT scanners have excellent spatial resolution and much improved temporal resolution for evaluation of heart structures. It is also fast, widely available, not restricted by hardware and is less limited by claustrophobia. Nonetheless, it does require intravenous iodinated contrast administration, and there is exposure to radiation. The latter, however, has decreased in the latest generation of scanners due to low kVp imaging, iterative and model-based reconstructions, EKG dose modulation and newer techniques like high pitch scanning available on dual source CT machines. The purpose of this section is to review the major cardiac valvular abnormalities, their pathophysiology, and appearance on different imaging techniques.

Echocardiography Echocardiography is widely used in the diagnosis of valve disease, assessment of valve morphology, and assessing the morphology and function of both ventricles. In patients scheduled for surgery, echo is used preoperatively, intraoperative transesophageal echo (TEE), perioperative, and for postoperative surveillance.

MRI of Cardiac Valves Valves can be difficult to visualize on MRI due to their low proton density, especially on the traditional “black blood” spin-echo sequences. The balanced steady state free precession (b-SSFP) sequence has replaced the previously commonly utilized spoiled gradient echo imaging as the mainstay of MRI assessment of the valves [5]. In stenosis and regurgitation, dephasing from turbulent flow appears as dark or black jets in the forward (stenosis) and backward (regurgitation) directions [6,7] (Table 23.1). Table 23.1 Sample MR Cardiac Protocol for Valvular Assessment Plane Sequence Axial

Black blood-gated HASTE/SSFSE through chest

Axial

White blood SSFP through chest

Plane

Sequence

2 Chamber

Vertical long axis—cine SSFP

4 Chamber

Horizontal long axis—cine SSFP

3 Chamber

LVOT view—cine SSFP

Short axis

Stack of cine SSFP cine through entire heart

Aorta/PA flow

Mid ascending aorta phase contrast flow

Optional/Selective Postcontrast Sequences Short axis

Look locker sequence for assessment of inversion recovery time

Short axis/2 chamber/3 chamber/4 chamber

10 minutes postcontrast magnitude or phase sensitive inversion recovery (late gadolinium enhanced)

MR can also readily identify ventricular response to valve disease: chamber hypertrophy in valve stenosis, and dilatation from increased volumes in regurgitation. Ventricular contour tracing on dedicated software allows calculation of ventricular volume and mass, which can be indexed to the patient's body surface area and compared to reference values to assess severity of the valve disease affecting management, including surgical intervention. The severity of stenosis and regurgitation can be subjectively assessed from signal loss on cine images. Regurgitant fraction can also be indirectly calculated by comparing the ventricular volumes and stroke volumes but this method can be limited by presence of shunting. Direct flow assessment with acquisition of velocity encoded cine (VENC) magnitude and phase contrast sequences is the most accurate MR method in assessing the severity of the stenosis or regurgitation. Voxel grayscale encoding can display flow velocity and direction on the phase contrast images and in cases of stenosis, can help calculate pressures across the valve plane. The resultant values can then be compared to the reference tables for grading. Similarly, in cases of regurgitation, flow velocities from each phase of the cardiac cycle are multiplied by the region of interest area, and the resultant flow is divided by forward flow to get regurgitant fraction.

CT of the Cardiac Valves CT is often considered when additional information is needed or when echocardiography and MRI cannot be performed or are suboptimal due to reasons

listed earlier. CT is also used preoperatively to evaluate coronary arteries in patients with valvular endocarditis to avoid dislodging vegetation with catheter. CT is the technique of choice to evaluate suspected obstruction from thrombosis or pannus in post-transcatheter aortic valve replacement (TAVR) and even postsurgical valve replacement (SVR) population where echo cannot evaluate the valve apparatus optimally (Box 23.1). Box 23.1

Sample Cardiac CT Technique for Valvular Assessment Noncontrast CTA for Aortic Calcium Score Slice thickness (mm)

2.5–3

Field of view (mm)

From carina to cardiac apex

EKG gating

Prospective

Dedicated 3D postprocessing for evaluation of aortic valvular calcium Contrast CTA for Valve Assessment Slice thickness (mm)

1.5–2

Field of view (mm)

From carina to cardiac apex (may be extended up to the aortic arch if required; for assessment of associated findings)

EKG gating

Retrospective or prospective

IV access

Optimally 18-gauge caliber

Contrast

Dual or triphasic injection—contrast, contrast + saline,

injection and flow rate

saline

Flow rate of 4–5 cc/s Acquisitio n parameters

Slice thickness of 0.5–0.9 mm (vendor dependent)

Postproces sing

Phase reconstruction from the entire R-R cycle (0– 90%); typically at 10% intervals

Dedicated 3D postprocessing for valvular evaluation

Aortic valve calcification scoring obtained from a noncontrast EKG-gated cardiac CT is known to correlate directly with severity of aortic valve stenosis and is now routinely done in all patients who are being evaluated for TAVR [8].

Aortic Stenosis Degenerative aortic stenosis (AS) with valve leaflet thickening and calcification is the most common cause of AS especially in elderly in the developed world with prevalence of 2–5%. Rheumatic fever is a less common cause in developed countries. Bicuspid aortic valve is the most common cause of AS in younger patients. Aortic valvular calcification is thought to be present in up to 25% of individuals at 65 years of age [9]. AS can occur at the supra-, sub-, or at the valvular levels. Valvular stenosis is the most common type (Boxes 23.2–23.4). Box 23.2

Causes of Aortic Stenosis Causes of Aortic Stenosis

Valvular ■ Congenital; bicuspid, unicuspid, or tricuspid partially fused valves

■ Acquired; degenerative calcific, rheumatic, infective endocarditis

Subvalvular ■ Subaortic stenosis from muscular or membranous diaphragm ■ Hypertrophic cardiomyopathy with LVOT obstruction

Supravalvular ■ Diffuse aortic hypoplasia or interrupted aortic arch ■ Membrane above the aortic root ■ Williams' (Beuren) syndrome

Box 23.3

Bicuspid Aortic Valve ■ Most common congenital cardiac malformation (0.5–2.0% of population) ■ Most common cause of aortic stenosis in younger patients ■ Associations: coarctation of aorta (Turner syndrome) ■ Can be treated surgically or by TAVR

Box 23.4

Williams Syndrome ■ Hypercalcemia in infancy ■ Elfin faces with low nose bridge ■ Supravalvular aortic stenosis; produces hour glass narrowing ■ Stenosis in peripheral pulmonary arteries, hypoplasia of thoracic and abdominal aorta, isolated stenosis in arch vessels, renal or celiac or superior mesenteric artery ■ Dilated and tortuous coronary arteries due to subjection to elevated left ventricular systolic pressure

AS is a slowly progressive disease and therefore remains asymptomatic for a long duration before clinical presentation. However, once it becomes symptomatic, there is rapid decline associated with high mortality if not treated. Most common symptoms include chest pain, dyspnea, and syncope. Heart failure develops in later stages with an elevated risk of sudden death. On physical examination, a systolic murmur may be heard in the right second intercostal space on auscultation. Aortic valve calcification can be seen on lateral radiograph as faint speckled calcification (Fig. 23.1). Dilatation of ascending aorta may be present in longstanding AS (Fig. 23.2), but it correlates poorly with severity of AS. There is also cardiomegaly with rounding of the LV apex due to hypertrophy (Fig. 23.2). In congenital AS presenting in infancy, chest radiograph shows pulmonary edema with cardiomegaly.

FIGURE 23.1 Aortic valve calcification. (A) Lateral chest radiograph shows speckled calcification of the aortic valve (arrows) and confirmed on noncontrast chest CT (B).

FIGURE 23.2 Chronic aortic stenosis frontal chest radiograph. The left ventricle is dilated with apex shifted downward and to the left (star). There is also dilatation of the ascending aorta (arrows).

Echocardiography can determine aortic valve area, its restricted opening, leaflet thickening, and calcification as well as elevated velocity and pressure gradient across the stenotic valve (Figs. 23.3A–C). Severity of AS has been described on echocardiography (Box 23.5) [10]. It also provides ventricular systolic and diastolic function and morphology. In select patients with asymptomatic severe AS, exercise or dobutamine stress echocardiography has a role in selection for surgery; (1) if patient develops symptoms, (2) fall in blood pressure from baseline, or (3) increased mean gradient of >20 mm Hg.

FIGURE 23.3 Bicuspid aortic stenosis. (A) TTE showing aortic valve area of 0.84 cm2 and Vmax 419 cm/s. (B, C) TEE. Bicuspid aortic valve leaflets are thickened and calcified with severe aortic stenosis, AVA of 0.8 cm2 and a mean pressure gradient of 43 mm Hg. (D, E) Aortic valve and coronal SSFP cine images through the aortic valve and ascending aorta show thickened stenotic aortic valve with fusion of the right and noncoronary cusps (D). Systolic dephasing in the ascending aorta (dotted arrow) from stenotic flow into the aorta. (F, G) Axial and coronal CT in a different patient with severely calcified bicuspid aortic stenosis. Ao, aorta; LV, left ventricle; LVOT, left ventricular outflow tract.

Box 23.5

Severity of Aortic Stenosis on Echocardiography Mil d

Valve area of 1.5 cm2 or greater, peak velocity of less than 3 m/s, pressure gradient of less than 25 mm Hg

Mo der ate

Valve area between 1.0 and 1.5 cm2, peak velocity between 3 and 4 m/s, pressure gradient between 25 and 40 mm Hg

Sev ere

Valve area less than 1.0 cm2, peak velocity greater than 4 m/s, pressure gradient of greater than 40 mm Hg

MRI also shows valve thickening, susceptibility from valve calcification, limited mobility, and reduced aortic valve orifice area. Geometric aortic valve area measured by planimetry on MR tends to underestimate in comparison with TEE [11]. Systolic flow void is seen extending into the aorta in systole representing dephasing from flow jet (Figs. 23.3D–E). On phase contrast flow sequences, peak velocity and flow can be quantified. Adjustment of the VENC may be required in cases of aliasing secondary to very high velocities. From an optimal aortic root plane, the peak transaortic velocity can be obtained and using Bernoulli equation (4V2), peak gradient can be estimated. On postcontrast imaging, patchy and subendocardial late gadolinium enhancement (LGE) can be seen in up to one-third of patients indicating presence of fibrosis and carries poor prognosis [12]. On T1 mapping there are higher native T1 values in severe AS. Myocardial tagging assessing myocardial contraction has shown increased twisting of the left ventricle leading to increased torsion in cases of AS, with improvement noted 1 year after valve replacement [13,14]. CT is not first line investigation but can provide valve area, left ventricular (LV) volume and function, ascending aortic measurements, and quantification of aortic calcification (Figs. 23.3F–G, 23.4). On postcontrast cardiac CT, valve leaflet thickening of greater than 2 mm, fixation, limited mobility, and calcification are noted. Decreased aortic valvular orifice area, LV wall thickening of more than 12 mm indicating hypertrophy, and poststenotic ascending aortic dilation in longstanding AS can be seen (Fig. 23.5).

FIGURE 23.4 Tricuspid aortic calcific stenosis. Thickened calcified aortic leaflets show restricted systolic opening suggesting aortic stenosis (A) and incomplete cooptation in diastole suggesting concomitant presence of aortic regurgitation (B). Systolic images are noisier due to EKG modulation where the radiation exposure is maximum in diastole and reduced in systole. Ideally for TAVR CT where annulus measurements are done in systole, the EKG modulation if used should be reversed, that is, regular radiation in systole and decreased radiation in diastole.

FIGURE 23.5 Isolated supravalvular aortic stenosis. (A, B) Coronal and 3D volume rendered reconstruction images from a gated cardiac CTA. An 11-yearold male with supraaortic stenosis (white arrows) due to elastin gene mutation and abnormal array CGH analysis result consistent with a 5p14.1 duplication. Similar imaging findings are seen in patients' with Williams syndrome. In this patient, the aortic valve was tricuspid but was deformed and thickened. Ao, aorta; LV, left ventricle.

CT is the technique of choice and essential for pre-TAVR planning as well as post-TAVR evaluation for thrombosis or pannus. Aortic valve calcification has association with subclinical atherosclerosis without known coronary artery disease and has a high correlation with stroke and cardiovascular events. Severe CT aortic calcium score of 1274–1377 Agatston units (AU) in women, and 2062–2065 AU in men have shown a high reproducibility and predict severe disease [8]. This is of particular value in cases with discordant echocardiography pressure gradients— low-flow, low-gradient AS. Traditionally, SVR has been the definitive treatment in advanced symptomatic AS with a survival rate of greater than 80% after 10 years [15]. More recently, TAVR is now being used more commonly in high, intermediate and even low risk patients [16] and has shown similar or better postoperative outcomes in comparison to SVR.

Aortic Regurgitation Aortic regurgitation is commonly seen in males with prevalence increasing with age (Box 23.6). Presentation includes gradually worsening signs and symptoms of heart failure. There is high mortality (25%) in patients with advanced heart

failure. Patients with type A aortic dissection or infective endocarditis (IE) can present acutely (Box 23.7). Box 23.6

Causes of Aortic Regurgitation A. Leaflet abnormality ■ Rheumatic valvular disease ■ Bicuspid aortic valve with thickening and calcification ■ Valvular endocarditis ■ Aortic valve leaflet prolapse in Marfan's syndrome or patients with perimembranous VSD B. Ascending aortic dilatation ■ Systemic hypertension ■ Annuloaortic aneurysm in Marfan's syndrome ■ Ehlers–Danlos syndrome ■ Aortitis in rheumatoid arthritis, ankylosing spondylitis, giant cell aortitis C. Aortic root abnormality ■ Type A dissection ■ Sinus of Valsalva aneurysm ■ Trauma (rare)

Box 23.7

Consequences of Aortic Valve Infective Endocarditis ■ Aortic regurgitation ■ Left ventricular failure from aortic regurgitation or coronary emboli ■ Aortic root/periaortic root abscesses ■ Systemic embolization ■ Mycotic aneurysms, splenomegaly and infarction, and renal failure

Chest radiograph may be normal in acute cases. In chronic cases, there is often significant LV dilatation. Incomplete coaptation of the valve leaflets, delayed opening, and premature closure are readily visualized on echocardiography. LV dilation can be seen in chronic cases. Color Doppler evaluation shows regurgitant jet which can be central or eccentric (Fig. 23.6).

FIGURE 23.6 Doppler transthoracic echocardiographic images showing severe aortic regurgitation with the regurgitant jet (white arrows) reaching up to the left ventricular apex. LA, left atrium; LV, left ventricle.

AR is identified as backward diastolic flow into the LV outflow track on SSFP cine MR imaging, especially in left ventricular outflow tract (LVOT) or threechamber view (Fig. 23.7A). Phase contrast velocity encoding is the most accurate way of regurgitation quantification, preferably in double oblique planes to ensure complete visualization of the flow void (jet) (Fig. 23.7B–C). VENC may need to be adjusted depending on the concomitant presence of AS. Grading of regurgitation on MRI have been proposed [17] based on regurgitating fraction; 30% for mild, 30–49% for moderate, and greater than 50% for severe AR. It has also been proposed that regurgitant fraction on MR may be a more accurate prognostic parameter than left ventricular volumes.

FIGURE 23.7 Aortic regurgitation. (A) Cine SSFP sequence LVOT view shows severe aortic regurgitation with a large eccentric dephasing jet extending into the left ventricular cavity and originating from the aortic valvular plane (white arrow). (B, C) Through plane phase contrast images acquired just above the level of the aortic valve show dephasing on the phase contrast image (C) in the ascending aorta (white arrow) due to significant regurgitation. Calculated regurgitant fraction was of 48% consistent with severe aortic regurgitation. Ao, aorta; LA, left atrium; LV, left ventricle.

Role of CT is limited, but if performed for other reasons such as coronary artery evaluation, a retrospective-gated CT can provide information about aortic valve morphology and malcoaptation of the valve leaflet (Fig. 23.4B), which has high sensitivity and specificity for detecting moderate to severe aortic regurgitation compared to transthoracic echocardiography [18]. Conservative management of AR includes control of arrhythmias and vasodilators. Antibiotic prophylaxis may be required to prevent superimposed infections and endocarditis. In acute cases, conservative measures are employed as a bridge to surgical management. Surgical intervention has a better outcome before advanced left heart failure develops with a 5-year survival rate of 85% in patients with a higher than 45% LV ejection fraction.

Mitral Stenosis Rheumatic heart disease is the most common cause. Other causes include degeneration, endocarditis, tumors, and rarely congenital (Box 23.8). Thickening and calcification of the valve leaflets result in restricted opening leading to a decrease in the normal cross-sectional valve area of 4–6 cm2. Obstruction at the level of the inflow tract of the left ventricle results in inadequate diastolic LV filling. Left atrial dilation, pulmonary hypertension, and arrhythmias may occur, with atrial fibrillation being most common. Box 23.8

Causes of Mitral Stenosis Acquired

■ Rheumatic heart disease (most common) ■ Prolapse of left atrial tumor or rarely thrombus through the mitral valve ■ Leaflet carcinoid, valve vegetation Congenital (rare) ■ Part of hypoplastic left heart syndrome ■ Obstructing large papillary muscles ■ Parachute mitral valve deformity

Symptoms typically develop 5–10 years after the initial acute rheumatic fever in younger age. Patients, usually present with dyspnea. Shortness of breath and cough may also develop due to pulmonary edema. Thrombi may form due to atrial fibrillation, with added risk of stroke. Ten-year survival rates vary from about 60% to less than 15%, in asymptomatic patients at diagnosis or patients with severe symptoms at presentation, respectively [19]. Left atrial enlargement seen as retrocardiac increased density with double right cardiac border, splaying of the carina, and upward displacement of left main bronchus on frontal view and posterior bulge of upper cardiac margin on lateral view (Figs. 23.8A–B). Features of pulmonary venous hypertension such as upper lobe redistribution of blood flow, peribronchial, and septal thickening (Kerley B lines) may be present. In later stages, features of pulmonary artery hypertension may be seen as dilated pulmonary arteries with right ventricle (RV) enlargement. Rarely nodular calcifications of the mitral valve may be seen. In long-standing chronic cases with atrial fibrillation eccentric thrombus with calcification may be seen in the dilated left atrium (Fig. 23.8C) and rarely hemosiderosis may be seen as dense tiny nodular densities in the lungs.

FIGURE 23.8 Mitral stenosis. (A, B) Left atrial enlargement seen as double density along right cardiac margin (white arrows) on frontal view and as bulge along upper heart border on lateral view displacing the left upper lobe bronchus posteriorly (yellow arrow). There is also upper lobe vascular redistribution due to pulmonary venous hypertension (PVH). (C) In chronic mitral stenosis, there can be calcification in left atrial wall or in the mural thrombus seen as curvilinear arrows on lateral view (black arrows).

Rheumatic mitral stenosis on echocardiography has typical appearance with thickened leaflets and commissural fusion resulting in bowing deformity of leaflets mimicking hockey stick (Figs. 23.9 and 23.10A–B). Valve planimetry is done in mid diastolic phase and Doppler across the valve provides the mean transmittal gradient. Patients with severe symptoms but only moderate mitral stenosis on echo may also benefit from exercise echocardiography.

FIGURE 23.9 Mitral stenosis. (A, B) TEE shows thickened mitral leaflets, restricted opening, stenotic turbulence and increased velocities across mitral valve and hockey stick appearance (arrows). There is dilatation of the left atrium. LA, left atrium; LV, left ventricle.

FIGURE 23.10 Rheumatic mitral stenosis and regurgitation. (A, B) TEE shows irregularly thickened and calcified mitral valve leaflets (arrows) with turbulent flow across the stenotic valve along with backward flow. (C) Chordae tendineae thickening and fusion (arrows) is also common in as seen in the axial color rendered CT image. LA, left atrium; LV, left ventricle.

Due to the presence of atrial fibrillation and problem with EKG gating, cardiac MR is not routinely used. Signal loss occurs due to the presence of calcification. Restriction motion of the leaflets, fish mouth appearance due to fused commissures, bowing of the anterior leaflet, dephasing from increased velocity flow across the narrow orifice can be seen with measurements of the velocities

with phase contrast imaging (Fig. 23.11). Secondary findings may include chamber dilatation and back pressure changes from pulmonary hypertension.

FIGURE 23.11 (A) LVOT view cardiac MR shows the dephasing jet (yellow arrow) in the left ventricle from mitral valvular stenosis. (B) Mitral insufficiency was also present as shown in four-chamber view (white arrow). LA, left atrium; LV, left ventricle.

Due to its high spatial resolution, CT is particularly useful in detecting calcification in the mitral apparatus. CT can also provide orifice area in addition to left atrial size, detect left atrial appendage thrombus, pulmonary edema, pulmonary hypertension, and right ventricular hypertrophy. Chordae tendineae may also be thickened and matted together (Fig. 23.10C). Medical therapy includes anticoagulation for arrhythmias and reducing cardiac effort. More invasive treatment options include balloon valvuloplasty with excellent survival rate, and surgical replacement. Lately, robotic replacement of mitral valve has gained grounds with decreased postoperative morbidity and fast recovery leading to increased patient acceptance.

Mitral Regurgitation Mitral valve regurgitation represents backward flow into the left atrium from the left ventricle during systole and is the most common valvular abnormality in the United States. Multiple etiologies can result in valve degeneration, leaflet retraction, and incomplete coaptation resulting in regurgitation (Box 23.9). Myxomatous degeneration of the mitral leaflets results in prolapse (Barlow's disease)—which is a billowing of the leaflet into the left atrium of more than 2

mm. “Flail” leaflet can occur secondary to chordal thinning and rupture in advanced disease. Chronic regurgitation can result in chamber dilation. In patients with inferior wall myocardial infarction (MI) acute papillary muscle rupture often present as acute atypical pulmonary edema. Box 23.9

Causes of Mitral Regurgitation Primary A. Leaflet Rheumatic endocarditis, mitral Valve Prolapse, left atrial myxoma or thrombus, tumor deposit B. Chordae tendineae Rupture from endocarditis, cystic medial necrosis or trauma C. Papillary muscle Infarction Secondary (Functional) Mitral annulus dilatation due to LV dysfunction (ischemic heart disease, dilated cardiomyopathy, hypertension)

Mitral valve prolapse affects 1–3% of general population and usually presents in the second to fourth decades of life [20]. The variable clinical outcome depends on patient age, degree of mitral regurgitation, LV ejection fraction, atrial diameter, and ventricular arrhythmia. Although MVP may remain asymptomatic, it can lead to significant MR and heart failure, increases risk for IE and ventricular arrhythmia including sudden cardiac death (SCD). The ventricular arrhythmia related to MVP tend to occur more often in young females who also tend to have bileaflet prolapse and more valve thickening. Characteristic T-wave abnormality (biphasic or inverted T-waves in inferior leads II, III, and aVF) are seen in majority of patients with MVP-related SCD and its presence should prompt further investigation. Due to mechanical traction exerted by the prolapsing leaflet a localized area of myocardial fibrosis seen as delayed enhancement on MRI can be seen in inferolateral wall of LV or the papillary muscles. In acute presentation, heart size is often normal with pulmonary edema present. In acute posteromedial papillary muscle rupture due to acute inferior wall MI, there can be focal right upper lobe edema due to direction of acute MR jet and this can mimic pneumonia on chest radiograph. In chronic cases, enlarged cardiac silhouette is present with or without pulmonary hypertension (Fig. 23.12).

FIGURE 23.12 Mitral regurgitation. PA radiograph of the chest demonstrating left ventricular and atrial dilation. Note presence of mitral annular calcifications (white arrows) and double right heart border (secondary to atrial dilation—red arrow).

Due to excellent evaluation of mitral valve apparatus, echocardiography can detect underlying cause for mitral regurgitation. Color Doppler can detect and quantify severity of MR from the width of vena contracta (the high velocity central color Doppler jet from the regurgitating flow occurring at or just below the level of the valve orifice) or effective regurgitant orifice area. MR is considered severe if the vena contracta width is >7 mm with peak transmitral velocity >1.5 m/s and mitral velocity time integral: aortic velocity time integral ratio >1.34 [21]. TEE provides better anatomical and quantitative evaluation of the complex mitral valve abnormalities (Fig. 23.13A–B).

FIGURE 23.13 Severe mitral regurgitation due to infective endocarditis. (A, B) Transesophageal echo shows dilated left atrium (LA) with a 0.9 × 0.5 cm vegetation at the P3 scallop (white arrow). (C) Eccentric mitral regurgitation jet is directed anteriorly (white arrows). There was also systolic flow reversal in the right pulmonary veins (not shown) consistent with severe MR. LA, left atrium; LV, left ventricle.

MR is seen as loss of signal across the mitral valve due to flow turbulence on SSFP and GE sequences and has good correlation with echocardiographic grading (Fig. 23.14A). Direct visualization of the leaflet prolapse, and incomplete coaptation on MRI is possible. Regurgitant fraction can be quantified using volume measurements, and phase contrast velocity flow measurements. The regurgitant fraction is calculated as the (RVol/LV stroke volume) × 100 [22]. Direct mapping at the mitral valve annulus is another method to assess degree of regurgitation. MRI is useful in serial assessment of the LV function as reduced survival has been shown in patients with an ejection fraction of less than 60% before surgical repair is undertaken [23].

FIGURE 23.14 (A) Four-chamber cine SSFP sequence cardiac MRI demonstrating mitral valve prolapse (white arrow) with dephasing artifacts from mitral regurgitation (dashed arrow). (B) Four-chamber view from a retrospectively gated cardiac CTA demonstrating gross prolapse of the posterior leaflets of the mitral valve into the left atrium (white arrow). Note left atrial dilation, and streak artifacts from right heart AICD leads. LA, left atrium; LV, left ventricle.

Direct visualization of mitral regurgitation is difficult on contrast CT; however, prolapse of the mitral valve leaflets is well seen in retrospectively gated cardiac CT (Fig. 23.14B). Incomplete leaflet coaptation, mitral valve length and calcification, chordae tendineae calcification, and secondary signs of regurgitation including left atrial dilation, presence of pulmonary edema in acute MR, and pulmonary hypertension in chronic cases can be detected on cardiac CT. Medical management is dependent on symptoms, and includes treating heart failure, edema, or thrombi. Surgical management is considered the definitive treatment. Transcatheter mitral valve clip and valve replacement are options in surgically high-risk patients. Transcatheter Mitral Valve Replacement There is an evolving role of transcatheter interventions in symptomatic patients with mitral regurgitation where medical therapy has failed and patients are at very high risk to undergo surgery. Patients with degenerative prosthetic mitral valves or annuloplasty rings are also high risk for reoperation and could benefit from percutaneous valve in valve treatment. Transcatheter mitral valve replacement (TMVR) is more challenging due to more complex mitral valve pathology involving the leaflets and sometimes annulus and its proximity to the aortic valve and LVOT. There are additional technical challenges including potential of LV outflow obstruction, foreshortening of left atrium, device anchoring, and paravalvular leaks. Preprocedural cardiac CT evaluation of the three-dimensional

relationship between the aortic and mitral valve is critical in measuring the saddleshaped mitral valve annulus, selecting appropriate size valve, and predicting LVOT obstruction by the anterior leaflet of mitral valve or device after TMVR. The latter can be assessed with the CT simulation of final valve positioning via 3D segmentation techniques available on postprocessing software [24]. Most of the TMVR devices are still under clinical investigation; therefore, information about their durability, structural deterioration, and comparison with surgery is not available. Currently, the transcatheter mitral valve leaflet edge-toedge percutaneous repair with Mitraclip device (Abbott Vascular: Abbott Park, IL) is the only percutaneous technique approved by the FDA. More recently Tendyne (Abbott Vascular: Santa Clare, CA) is the first transcatheter mitral valve implantation system approved in Europe among several other devices under investigation. The Tendyne MV system is a self-expanding trileaflet porcine pericardial valve, mounted on a nitinol double-frame stent, implanted via transapical approach, is completely retrievable and can be repositioned.

Pulmonic Stenosis Pulmonic stenosis (PS) can be at valvular, subvalvular, or supravalvular level (Box 23.10). The most common cause of valvular PS is congenital and majority of such patients have a membrane with central hole and fused commissures. The valves can be bicuspid or tricuspid and have domed appearance in systole. In contrast, in approximately 10–15% patients, the valves are dysplastic with thick cusps and often associated dysplasia of the pulmonary annulus. The thick and stiff valve leaflets often are immobile throughout the cardiac cycle with asymmetric oriented orifice in systole. Box 23.10

Causes of Pulmonary Stenosis A. Valvular ■ Congenital a Commissural fusion (90%) b Dysplastic valve with thickened and nonfused commissures (10%) ■ Acquired a Carcinoid and rheumatic heart disease B. Subvalvular ■ Usually Congenital

a Component of tetralogy of Fallot due to hypoplastic crista supraventricularis b Double chambered right ventricle ■ Acquired from compression by tumor, right ventricular hypertrophy C. Supravalvular ■ Congenital a Williams' Syndrome b TOF ■ Acquired a Takayasu arteritis b Behcet's disease c Carcinoid d Surgical banding e Tumor or thrombus

Patients with mild PS are often asymptomatic. More severe stenosis can lead to symptoms of congestive heart failure from systemic venous backpressure due to upstream obstruction. The cardiac silhouette is normal or there is dilatation of the main and left pulmonary artery due to stenotic jet directed toward main and left PA. These findings are better appreciated on cross-sectional imaging such as cardiac CT or cardiac MR (Fig. 23.15).

FIGURE 23.15 Valvular pulmonary stenosis. Multiplanar MPR (A, B) and cross-section images (C) show thickened stenotic pulmonary valves (red arrows) with dilatation of main (MPA) and left pulmonary artery (LPA). Ao, aorta; LPA, left pulmonary artery; LV, left ventricle; MPA, main pulmonary artery; RPA, right pulmonary artery; RV, right ventricle.

PS commonly associated with congenital heart disease such as TOF is often subvalvular infundibular stenosis due to hypoplasia of crista supraventricularis (Figs. 23.16A–B). The pulmonary valve is also stenotic in about half of TOF patients with small pulmonary annulus (Fig. 23.16C). PS has association with Noonan and LEOPARD (lentigines, electrocardiographic anomalies, ocular hypertelorism, pulmonary stenosis, abnormalities of genitalia, retardation of growth, and deafness) syndromes.

FIGURE 23.16 A 64-year-old female with prior Blalock–Taussig palliation for tetralogy of Fallot. (A) Oblique coronal 3D volume rendered CT reconstruction demonstrating right ventricular (RV) hypertrophy, overriding aorta (Ao), and subaortic VSD (asterisk). (B) 3D volume rendered reconstruction illustrating the right ventricular outflow tract obstruction (white arrow). (C) Another patient with infundibular narrowing (red star) as well as hypoplasia of pulmonary annulus (yellow arrow). Ao, aorta; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.

The severity of PS can be graded on echo by peak gradient; less than 36 mm Hg for mild PS, 36–64 mm Hg for moderate and greater than 64 mm Hg for severe disease or by peak velocity; less than 3 m/s for mild, 3 to 4 m/s for moderate and greater than 4 m/s for severe PS. Leaflets are thickened or calcified with reduced excursion of leaflets associated with increased transpulmonary flow velocity gradient on color Doppler imaging [25]. Restricted opening of the leaflet can be seen from valve leaflet thickening and fusion. Turbulent dephasing flow from increased velocity can be seen across the pulmonary valve on SSFP cine imaging (Fig. 23.17). Quantification of chamber volumes and function and any associated complex congenital heart defects can also be evaluated.

FIGURE 23.17 (A, B) Phase contrast sequence image through the pulmonary valve showing restricted opening of the pulmonary valve leaflets. Aliasing is seen due to increased velocity flow through the narrow orifice (white arrow). PA, pulmonary artery.

CT can show valvular leaflet thickening, reduced valvular annular opening area, right ventricular hypertrophy, and dilation. Flattening or bulge of the interventricular septum toward the left ventricle due to increased right cardiac pressures. Main and left pulmonary artery are usually more dilated due to poststenotic flow directed more into the left branch due to more acute angulation of the right branch of the pulmonary artery (Fig. 23.15). Various congenital cardiac anomalies associated with pulmonary stenosis can be well assessed on a gated cardiac CT performed with optimal contrast opacification of both systemic and pulmonic cardiac chambers (Fig. 23.18).

FIGURE 23.18 (A–C) Follow-up TOF patient with bioprosthetic valve replacement. Multiplanar reconstruction (MPR) images (A, B) showing narrowing at the level of the pulmonic valve (dashed arrows) with restricted leaflet opening (white arrow) suggesting pulmonary valve stenosis. (C) Right atrial and ventricular dilation and flattening of interventricular septum due to pressure overload are seen on the four-chamber cardiac CTA. Optimal contrast opacification of both ventricles as in this patient is critical in evaluation of biventricular function. Ao, aorta; LV, left ventricle; MPA, main pulmonary artery; RV, right ventricle.

In symptomatic congenital valvular PS, balloon angioplasty shows good results. However, patients with dysplastic pulmonary valve with thick and stiff leaflets usually do not respond to percutaneous balloon valvuloplasty and often require surgical valvotomy.

Pulmonic Regurgitation Trivial or mild pulmonic regurgitation (PR) is common in patients with normal heart and usually is of no clinical significance. More commonly PR results from surgical repair of TOF (Box 23.11). Transannular patching with pericardium, Dacron or polytetrafluoroethylene provide excellent relief of right ventricle outflow tract (RVOT) obstruction but invariably lead to PR, hypokinesis, aneurysm of the RVOT (Fig. 23.19), and fibrosis. Box 23.11

Causes of Pulmonary Regurgitation A. Acquired (more common) ■ After repair of TOF ■ PV endocarditis ■ Pulmonary HTN causing annulus dilatation B. Congenital

■ Absent pulmonary valve in TOF

FIGURE 23.19 Surgically corrected TOF now with significant biventricular dysfunction by echo. Cardiac MR could not be performed due to the presence of non-MR compatible AICD. A gated cardiac CTA was done and the coronal oblique reformat bone window image shows aneurysmal dilatation of the RVOT patch repair (white arrows). Surgical sutures are also seen at the site of VSD closure (yellow arrow). The indexed RV end diastolic volume was 230 mL/m2 and RVEF was 25%, both suggesting need for pulmonary valve replacement. Ao, aorta; RV, right ventricle; RVOT, right ventricular outflow tract.

Echocardiogram is used for surveillance follow-up after corrective surgery of TOF. Color Doppler can show a jet directed into the RV during ventricular systole, can calculate pressure half time to determine the severity of PR.

Cardiac MR is the technique of choice to evaluate PR especially in post-treated TOF patients to determine the degree of PR, severity of RV dilatation and dysfunction which help in determining the optimal timing for intervention. Artifacts from the reversed flow into the RV are readily visualized using cine MRI sequences (Fig. 23.20). Phase contrast MR sequence using VENC can quantify the regurgitant fraction; up to 25% is mild, 25–35% moderate, and greater than 35% is considered severe. Right ventricular function and volume assessment using MRI is of utmost importance in determining time to intervene. A cut off ranging from a right ventricular end diastolic volume of 150–170 mL/m2 is usually considered optimal for pulmonary valve replacement (Box 23.12) [26,27].

FIGURE 23.20 Pulmonary regurgitation. Right ventricular outflow tract (RVOT) view from cine SSFP sequence from two different cardiac MRIs (A, B) showing dephasing artifacts from pulmonary regurgitation (white arrows). PA, pulmonary artery; RV, right ventricle.

Box 23.12

MR Criteria for Pulmonary Intervention [24,25] ■ Indexed RVED volume >150 mL/m2 ■ Indexed RVES volume >80 mL/m2 ■ RV function 7 mm, peak velocity >1 m/s, and prominent flow reversal in hepatic veins. RV may be normal in size but hyperdynamic in patients with compensated severe TR but it gradually dilates and becomes hypokinetic with time. Symptoms from TR vary from being asymptomatic in mild cases, to symptoms of right heart failure. Significant TR or tricuspid insufficiency can be identified as turbulent flow across the tricuspid valve into dilated right atrium (Fig. 23.21A). Quantification of the regurgitant fraction is possible by assessment of the pulmonary artery flow, and subtraction of the right ventricular stroke volume. Direct measurement is possible by 4D flow technique.

FIGURE 23.21 Tricuspid insufficiency. (A) Functional TR due to tricuspid annulus dilatation from RV dilatation. (B) Ebstein's anomaly with apically displaced septal tricuspid leaflet along with valve dysplasia (black arrows) leading to TR. The portion of RV up to displaced leaflet is atrialized (star). LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Annuloplasy is the most common surgical intervention for TR, however, it is associated with significant residual regurgitation. Surgical tricuspid valve replacement carries 70% 5-year survival. Transcatheter Tricuspid Valve Replacement Transcatheter tricuspid valve replacement is in its early stages of development due to complex tricuspid valve apparatus. The tricuspid annulus is less fibrous compared to the mitral valve, the right coronary artery is in close proximity to the parietal attachment of the valve, the conduction system is in close proximity to the valve and the valve is a nonplanar dynamic structure which changes its size and shape throughout the cardiac cycle making it very challenging to evaluate with noninvasive imaging. The large size of the tricuspid valve requires a large caliber venous access system either via jugular or femoral approach. Ebstein's anomaly is a developmental anomaly of tricuspid valve in which the septal hypoplastic leaflet is displaced toward the RV apex while the anterior larger leaflets maintain its normal attachment site but are often dysplastic. The RV is divided into two portions, a proximal dilated atrialized part and smaller more distal RV with limited pumping capacity. The right cardiac chambers are enlarged but pulmonary artery is of normal size or small. Increased volume in right chamber lead to septal bowing of interventricular septum which can cause decreased diastolic LV volume (Fig. 23.21B). Depending on the severity of RV dysfunction and TR, patients can remain asymptomatic into adulthood. Symptoms

often develop from conduction abnormalities, most common of which is Wolf– Parkinson–White syndrome and right bundle branch block. This anomaly can be easily identified on Echo, cardiac CT or cardiac MR (Fig. 23.21B). Currently, MR is the technique of choice and is especially useful in determining leaflet size and location, annulus and atrial size along with RV function, findings which help in deciding type of surgical repair.

Prosthetic Valves Prosthetic valves can be mechanical or bioprosthetic (Box 23.14). Patients with prosthetic heart valve require follow up with clinical assessment and imaging to detect rare but life threatening complications. Box 23.14

Types of Prosthetic Valves A. Mechanical valves—made of carbon, plastic, or metal. Ball in cage, tilting disk, bileaflet More durable, requires lifelong anticoagulation. Bileaflet most common mechanical valve used. Indicated in younger patients (less than 50 years of age); in repeat replacements or with concomitant aortic root placement

B. Bioprosthetic valves—made of pericardium, bovine, or porcine tissue Less durable, do not require lifelong anticoagulation—better safety profile. Preferred treatment choice in elderly patients and in patients planning pregnancy [25]

C. Transcatheter valve replacement Less invasive, lower complications Aortic (TAVR)

Edward-SAPIEN—balloon expandable valve, a stainless steel frame and leaflets from bovine pericardium Medtronic core valve—self-expanding, contain leaflets from porcine pericardium attached to an alloy stent made from nitinol Mitral and Tricuspid (TMVR, TTVR) (experimental at few centers)

Prosthetic valve localization on a radiograph can be done by drawing an imaginary line from the left atrial appendage to the right cardio phrenic angle on a frontal projection, and from carina to the cardiac apex on a lateral view. Aortic and pulmonic valves typically lie above these lines, and mitral and tricuspid below, with the tricuspid being more anterior on the lateral view (Figs. 23.22 and 23.23). Cine fluoroscopy is commonly used for assessment of leaflet motion, but is limited in evaluating leaflet thickening or determining the cause of dysfunction.

FIGURE 23.22 (A, B). An example of valve localization using the imaginary lines on frontal and lateral views. Mitral (white arrow) and tricuspid (dashed arrow) repaired valves are seen. Note more anterior position of tricuspid valve on lateral view. A left atrial appendage clip is also seen (red arrows).

FIGURE 23.23 Chest radiographs, lateral (A) and frontal (B) views demonstrating multiple bioprosthetic valves in pulmonic (white arrow), aortic (dashed arrow), and mitral (curved arrow) locations. Note the respective locations of the valves in relation to the imaginary localization planes on frontal and lateral views.

Transthoracic echocardiography is often the first imaging technique used but can be limited by artifacts from metallic valve components. Latest generation of multidetector CT (MDCT) can evaluate prosthetic valve with minimal beam hardening artifacts. Retrospective-gated contrast cardiac CT scanning can readily access the dynamic motion of the leaflets and their opening and closing angles, presence of thrombus or pannus, and valve dehiscence (Figs. 23.24A–C).

FIGURE 23.24 (A, B) Coronal oblique images from a retrospectively gated cardiac CTA demonstrating normal opening and closing of the metallic aortic valve. (C) MPR reconstruction from a retrospective cardiac CTA demonstrating immobile aortic metallic valve leaflet (dotted arrow). Note presence of thrombus along the aortic surface of the leaflet (white arrow). Ao, aorta; LV, left ventricle.

In patients with suspected infected valve prosthesis, SPECT/CT with indium 111 oxime, or technetium 99m hexamethyl propylene amine oxime and F-18 FDG PET/CT may show increased activity with infection (Fig. 23.25A–B).

FIGURE 23.25 (A, B) A 71-year-old female s/p TAVR with CORE valve presented with fever and blood culture positive for coagulase positive staphylococcus bacteremia (MRSA) despite IV antibiotics. CTA chest showed a heterogenous attenuating fluid collection around the ascending aorta just above the core valve (white arrow). A subsequent FDG PET showed intense uptake in the corresponding area suggesting this to be the infective nidus. Ao, aorta; PA, pulmonary artery.

Transcatheter Aortic Valve Replacement With careful patient selection, increasing operative experience, advances in imaging evaluation and technical refinements, the outcome from TAVR has significantly improved. Symptomatic patients with AS are first evaluated with transthoracic echo (TTE) to determine if they meet the criteria for severe AS. A pre-TAVR CTA of the heart and chest, abdomen, pelvis is done for annulus measurements and to determine appropriate access site (Boxes 23.15 and 23.16, Table 23.2) [29]. In patients with renal insufficiency, oral or intravenous hydration along with lower amount of intravenous contrast is used to limit renal damage. Post-TAVR follow-up usually involves clinical assessment and TTE to determine any change in transaortic gradient. In patients with increasing gradient further evaluation with a retrospective-gated cardiac CTA and/or TEE is indicated to determine presence of valve thrombosis and leaflet motion restriction (Box 23.17) (Fig. 23.26). Pannus is defined as a linear hypodensity on the ventricular side of the valve and appears contiguous with the adjacent LVOT walls. In contrast, thrombus is usually located on the aortic side of the prosthetic valve and can result in pressure gradients on echocardiography (Box 23.18). This may also be nodular in appearance. Hypoattenuating leaflet thickening (HALT) is a manifestation of subclinical thrombosis appearing as thin centrifugal hypodensities without a pressure gradient or increased velocities on echocardiography. HALT with restricted motion is termed hypoattenuation affecting motion. Box 23.15

MDCT TAVR Protocol ■ Noncontrast CT for aortic valve calcification ■ Systolic prospective or retrospective-gated CTA for heart, nongated for chest, abdomen & pelvis ■ Contrast: single injection, usual 60–100 (based on BMI), renal insufficiency 30–40 cc ■ If no contrast could be given: noncontrast CT or noncontrast MR; supplemented with TEE or IVUS ■ Single breath hold imaging: 4–8 seconds ■ Postprocessing of images (systolic phase): dedicated workstation

Box 23.16

MDCT TAVR CT Annulus Evaluation ■ Done in systolic phase using phase with maximal valve opening ■ Use double oblique method ■ To define basal ring and accurate measurements the plane must be balanced so that all three leaflets come to view when scrolling cephalad at the same time ■ When the inferior aspect of all three aortic cusps are identified in the same plane a true double oblique transverse image of the root is achieved ■ Measure annulus diameter and area/perimeter ■ Annulus to LM and RCA distance ■ Mitral annular calcification especially anterior near the anterior mitral leaflet ■ LVOT size and status of outlet septal thickness ■ Optimal deployment angle ■ Other findings: Lung nodule/mass, PTE, mediastinal adenopathy, interstitial lung disease or COPD, degree of thoracic aortic atherosclerotic disease, radiation fibrosis in patients with known lung cancer

Box 23.17

Role of CT in TAVR-Related Complications ■ Vascular access related (arterial injury at access, problems with closure, LV apex injury) ■ Aortic injury during procedure ■ Coronary artery obstruction ■ Myocardial injury in transapical approach leading to pseudoaneurysm formation ■ Valve thrombosis during postprocedure follow-up

Box 23.18

Post-TAVR Valve Thrombosis ■ Post-TAVR thrombosis is underdiagnosed in asymptomatic patients

■ Increase in valve hemodynamic deterioration (VHD) should raise concern ■ Gated CTA can detect thrombus as hypoattenuation along valves (HALT) ■ Reversible with anticoagulation

Table 23.2 TAVR Valve Sizes and Normal Measurement Ranges Edwards LifeSciences Sapien 20 mm 23 mm Valve Sizes

26 mm

29 mm

Native annulus area (mm2)

273–345

338–430

43 0– 54 6

54 0– 68 3

Area-derived diameter (mm)

18.6– 21.0

20.7– 23.4

23 .4 – 26 .4

26 .2 – 29 .5

Valve height (mm)

15.5

18

20

22 .5

Ilio-femoral vessel diameter

≥5.5 mm

≥6.0 mm

Edwards eSheath introducer set

14F or equivale nt

16F or equivale nt

FIGURE 23.26 Post-TAVR thrombosis. A 52-year-old male with severe aortic stenosis underwent TAVR and at 6-month F/U echo transaortic gradient increased from 13 to 26 mm Hg. (A, B) A retrospective-gated CTA done showed hypodense thrombus (red arrows) in the right and left coronary cusps. Ao, aorta.

Infective Endocarditis IE is a complex, deadly disease which involves heart and associated multiorgan complications. Its prognosis depends on prompt detection leading to aggressive treatment with appropriate antibiotics and early SVR when indicated. Up to 40% of patients with endocarditis have prosthetic valves (Box 23.19). In patients with prosthetic heart valve, IE is most common in first 5 years after surgery. Staphylococcus epidermidis and S. aureus infection from devices, surgery, and skin wound are the causative organisms within 2 months of surgery. After 2 months, Streptococcus is the most common organism spread via hematogenous route. Box 23.19

Predisposing Factors to Infective Endocarditis ■ Presence of prosthetic valves ■ H/O prior endocarditis ■ Cyanotic congenital heart disease ■ Degenerative valve disease

■ H/O intravenous drug abuse ■ Nosocomial bacteremia ■ Indwelling leads or pacemakers

Patients present with fever, shortness of breath, and other signs of heart failure. Fluctuating cardiac murmurs may be present. Right-sided IE may present with septic emboli in lungs while left-sided IE from systemic spread to brain, abdominal viscera, mesenteric ischemia, joint infection, spondylodiscitis, and mycotic aneurysms (Figs. 23.27 and 23.28).

FIGURE 23.27 A 69-year-old male with a PMH of CAD, CVA, HTN, hyperlipidemia, s/p CABGx1, Asc Ao and transverse arch replacement, and AVR (tissue) in 2017. He presented for increasing confusion and difficulty ambulating. TTE revealed a large thrombus on the aortic valve. A subsequent Cardiac CT was done for further evaluation of coronary arteries before surgery which showed aortic valve endocarditis. There was also acute septic embolism of SMA branch. Blood culture grew Staph. epidermidis. (A) TTE: There is an echogenic mass in the aortic valve orifice (yellow arrow). (B) CTA LVOT view shows an irregular soft tissue-filling defect across the prosthetic aortic valve. In addition there was a small extra luminal contrast along the right cusp (red arrow) suggesting small perivalvular abscess. (C) Acute thrombus in the distal portion of the right lower quadrant SMA with surrounding stranding due to septic emboli (green arrow). (D) Diffusion restriction of pre- and postcentral gyri

(arrow) compatible with acute infarction, in a distribution concerning for embolic etiology. Ao, aorta; LA, left atrium; LV, left ventricle.

FIGURE 23.28 Tricuspid valve endocarditis with septic embolism. (A) TTE image showing vegetation along the tricuspid annulus (white arrows). (B) Mediastinal and (C) lung window images from nongated CT examination showing large vegetation at the tricuspid valve (black arrow). Note multiple cavitary lesions in both lungs—septic emboli. Ao, aorta; LV, left ventricle; RA, right atrium; RV, right ventricle.

Echocardiography remains the first imaging technique for diagnosis, assessing severity, risk for embolization (size and mobility), and follow-up serial evaluations. Echo features suggesting IE include presence of vegetation on valve, valve perforation, perivalvular abscess or pseudoaneurysm, or presence of intracardiac fistula. TEE is more sensitive in detecting small vegetations, perivalvular abscess, and evaluating prosthetic valves (Fig. 23.29C). Retrospectively, EKG-gated cardiac CTA can assess both native and prosthetic valve along with any perivalvular lesion. The sensitivity and specificity of CT to detect perivalvular abscess and pseudoaneurysm compared to surgical findings is very high (>95%) especially in the aortic valve [30] (Figs. 23.29A and 23.30). Cardiac CT also allows noninvasive evaluation of coronary arteries preoperatively in patients undergoing valve surgery as catheter angiography is often contraindicated. CT can also detect extra cardiac IE-related lesions in both right and left-sided endocarditis. MR is of limited value (Fig. 23.29B) in some cases.

FIGURE 23.29 Pseudoaneurysm due to infective mitral valve endocarditis. Gated CTA (A) and four-chamber SSFP image from cardiac MRI (B) showing a large contrast filled cavity (pseudoaneurysm— red star) communicating with the left ventricle cavity (white arrow) with dephasing artifact from the flow through the narrow neck. (C) TEE confirmed the large patent PSA (red star) near the left AV valve with a large defect along the mitral annulus (white arrow) communicating with LV. LA, left atrium; LV, left ventricle.

FIGURE 23.30 Preoperative-gated cardiac CTA in patient with aortic valve endocarditis. Axial (A) and coronal (B) images show a large irregular extraluminal contrast collection (yellow star) along the left cusp abutting the LM and LAD consistent with aortic root abscess and pseudoaneurysm. Patient underwent successful surgical aortic root homograft and aortic valve replacement. Ao, aorta; LV, left ventricle; PA, pulmonary artery.

FDG-PET/CT or radiolabeled leukocyte SPECT/CT may show abnormal increased activity/uptake especially around the prosthetic valves [31,32] (Fig. 23.25).

Carcinoid Syndrome Approximately half of all patients with carcinoid syndrome develop cardiac involvement. Thickening of the right-sided heart valves with retraction and fibrosis of the valve leaflets and papillary muscles result in dysfunction including incomplete coaptation and restricted opening. In a minority of cases, involvement of the left-sided cardiac valves is possible when a right to left shunts or left-sided bronchial carcinoids are present. Secretion of the vasoactive substances results in clinical symptoms with flushing being the most common symptom. Signs of heart failure can be seen in advanced stages. Diagnosis is based on urinary and plasma 5-hydroxy indoleacetic acid levels. Both MR and CT can show leaflet thickening, restricted leaflet motion, incomplete coaptation, carcinoid deposit, and secondary chamber dilation (Fig. 23.31). SPECT imaging using radiolabeled octreotide and specific tracer somatostatin agents including DOTATE PET/CT have excellent sensitivity (Fig. 23.32).

FIGURE 23.31 (A, B) Cardiac CTA in a patient with history of metastatic carcinoid disease to the liver demonstrating dilated right atrium and ventricle consistent with carcinoid heart disease. (C) Different patient with metastatic carcinoid disease shows enhancing nodule (118 HU) along the tricuspid valve within the right ventricle in early arterial enhanced phase imaging (black arrow) consistent with a metastatic deposit. There are multiple enhancing liver metastasis (white arrow). RA, right atrium; RV, right ventricle.

FIGURE 23.32 (A–C) A 43-year-old male with metastatic neuroendocrine tumor presents for initial staging and subsequent treatment planning. PET CT DOTATATE performed shows increased tracer activity in interventricular septum thick (thick white arrow in A,C), several nodes in the mediastinum (thin white arrow C), liver metastases (B,C) and peritoneal nodules (yellow arrows C).

Somatostatin agents and serotonin inhibitors are the main treatment options along with symptomatic treatment for right heart failure. More invasive options may include balloon angioplasty in advanced cases of stenosis, or surgical treatment in cases of severe regurgitation.

Radiation-Induced Valvular Disease Rare, usually develops decades after significant mediastinal radiation treatment usually >30 Gy [24]. In one autopsy survey, up to 81% of valves were involved by radiation-induced damage [33]. Vast majority of patients are asymptomatic and

valve disease is incidentally detected, often with development of coronary artery disease-related symptoms. Cardiac CT can show valve leaflet fibrosis and calcification, along with aortic or pulmonary artery calcifications (Fig. 23.33).

FIGURE 23.33 (A) TTE image in a 57-year-old patient with history of Hodgkin's disease and radiation to mediastinum at 6 years of age, showing severe pulmonic stenosis with mean gradient of 15–17 mm Hg. (B) Noncontrast cardiac CT image showing severe calcifications along the RVOT and pulmonic valve annulus. (C, D, E) Retrospective-gated cardiac CT images showing leaflet thickening and calcifications (white arrows) and restricted opening (dashed arrows). PA, pulmonary artery; RV, right ventricle.

Imaging of Cardiomyopathies Cardiomyopathies refer to a diverse group of diseases of the myocardium that result in mechanical and/or electrical dysfunction. Inappropriate myocardial hypertrophy or dilation is seen, without associated hypertension, coronary artery disease, congenital heart disease, or valvular heart disease. Approximately 6.5 million people are affected with heart failure in the United States, with almost 25,000 deaths annually [1,34]. Cardiomyopathy can be either primary or secondary to other systemic diseases. Morphologically, it can be classified as hypertrophic, restrictive, dilated, arrhythmogenic, and inflammatory types, all of which can be either primary or secondary [34]. Recently a MOGE(s) classification

has been proposed, which describes the morphofunctional phenotype (M), organ (O), genetics (G), etiology (E), and functional status (S) [35]. Cardiomyopathies can clinically present in several ways, typically with heart failure, arrhythmia, SCD, or chest pain. Symptoms include dyspnea, fatigue, edema, ascites, chest pain, palpitations, and syncope. Cardiomyopathy is the underlying etiology for cardiac failure in 2–15% of patients. Imaging plays an important role in the evaluation of cardiomyopathies [36]. The specific imaging approach depends on the initial presentation. For those patients who present with heart failure, imaging is necessary to establish the diagnosis of heart failure, quantify the function (i.e., ejection fraction) and to distinguish patients who present with reduced EF from those with preserved EF [37]. The next important step is to establish the etiology of the cardiomyopathy, since the treatment strategies can vary significantly depending on the etiology [38]. Broadly, cardiomyopathies are classified as ischemic and nonischemic.

Imaging Techniques Several imaging techniques are used in the evaluation of cardiomyopathies (Table 23.3). Chest radiograph has a limited use as an initial imaging technique to evaluate heart failure and associated vascular abnormalities [37]. Enlargement of the cardiac silhouette may be seen in some cardiomyopathies. Heart failure manifests as pulmonary congestion, blurred margins of vessels, dilated of pulmonary veins, septal lines, pleural effusions, and alveolar opacities (Fig. 23.34). Dilated pulmonary arteries can be seen with pulmonary hypertension. Echocardiography is often the initial cross-sectional imaging technique that is used to evaluate cardiac failure and cardiomyopathy. Echocardiography provides information on ventricular function and volumes, myocardial mass, wall motion abnormalities, and valvular function. Echocardiography can also evaluate diastolic dysfunction, which is seen in the early stages of cardiac abnormalities. Using contrast improves the quantification of ventricular volumes and function. Echocardiography is widely available, portable and noninvasive, but limitations include operator dependence and limited acoustic windows which limit its ability to visualize the RV and apical regions. Echocardiography is also limited in tissue characterization [37,38]. Table 23.3 Role of Imaging in Cardiomyopathies Technique Utilities Limitations

Technique

Utilities

Limitations

Radiograph y

Evaluation of heart failure

Low sensitivity and specificity Cannot characterize abnormality

Echocardiog raphy

Ventricular function (global, regional) and volumes Myocardial mass Regional wall motion abnormalities Diastolic function Valvular function

Operator dependence Limited acoustic windowsespecially in large patients and COPD; particularly for RV and apical regions Cannot characterize cardiomyopathies

Nuclear medicine

Quantification of ventricular function Myocardial ischemia Sarcoidosis Amyloidosis

Magnetic resonance imaging

Ventricular function (global, regional) and volumes Myocardial mass Regional wall motion abnormalities Valvular function Characterization

Contraindications including metallic devices and claustrophobia Artifacts in patients with metallic devices

Technique

Utilities

Computed tomography

Alternative to MRI in patients who cannot have it or expected artifacts Morphological evaluation Qualitative global and regional ventricular function Functional quantification Myocardial ischemia Delayed enhancement

Cardiac catheterizati on

Hemodynamics Constrictive pericarditis Coronary arterial morphology and function

Limitations Potentially nephrotoxic iodinated contrast media Ionizing radiation

FIGURE 23.34 Chest radiograph of cardiomyopathy. PA chest radiograph shows enlargement of the cardiac silhouette with perihilar congestion (dashed arrows) and dilated veins (white arrow), consistent with cardiac failure.

MRI is a valuable imaging technique in the evaluation of cardiomyopathies (Tables 23.4). It can provide morphological information that is superior to echocardiography due to its ability to visualize the entire heart, including RV and LV apical and lateral regions as well as surrounding structures. MRI is considered the gold standard in the quantification of cardiac volumes and function, with high accuracy and reproducibility. In addition, MRI also has the ability to characterize tissues which helps in narrowing the specific etiology of cardiomyopathy. Using different sequences, several specific features can be extracted. Cine SSFP sequence is used to evaluate morphology and qualitative assessment of ventricular and valvular function. This sequence is also used for accurate and reproducible quantification of ventricular volumes. Cine sequence in real-time mode is used to evaluate the respiratory changes of the ventricular septum, which is useful in evaluation of constrictive pericarditis which can be clinically confused with restrictive cardiomyopathy. Strain imaging provides an evaluation of regional myocardial function, which is often deranged earlier than ejection fraction in

several cardiac diseases. Parametric mapping techniques provide quantitative assessment of intrinsic myocardial properties such as T1, T2, and T2*, with the pixels color-coded based on these values. Native T1-mapping is used for evaluation of myocardial fibrosis, edema, infiltration, and iron. T2 mapping is used for evaluation of myocardial edema, seen in acute myocarditis and MI. Extracellular volume (ECV) maps are obtained from pre- and postcontrast T1 values of the myocardium and blood pool along with hematocrit. T2* is used for evaluation of myocardial iron deposition. T2-weighted images with fat suppression are used for evaluation of myocardial edema. Following contrast, first-pass perfusion images, both at stress and rest can be used for identification of myocardial ischemia. Early gadolinium enhancement is obtained in the first few minutes after contrast administration. Abnormal enhancement in these images can be seen due to capillary hyperemia in acute myocarditis as well as in acute MI. LGE is an important sequence which allows characterization of cardiomyopathies based on the pattern of enhancement. This sequence is obtained 7–10 minutes following administration of intravenous gadolinium-based contrast media with an inversion recovery pulse. Contrast washes away from normal myocardium by this time, whereas it is retained in scar/fibrotic tissue. LGE also is a predictor of future adverse events, including the development of ventricular arrhythmia and SCD [39,40]. The salient imaging features of key cardiomyopathies and differential diagnosis for LGE of myocardium are listed in Tables 23.5A and 23.5B. Table 23.4 MRI Sequences and Utility in the Evaluation of Cardiomyopathies Sequence Utility Cine steady state free precession

Morphological evaluation Global and regional function Quantification of function Qualitative valvular function

Real-time cine imaging

Pericardial function

Strain imaging

Regional myocardial function

First-pass perfusion imaging

Ischemia

Sequence

Utility

Early gadolinium enhancement

Capillary hyperemia in myocarditis Microvascular obstruction in myocardial infarction

T2-weighted fat suppressed images

Myocardial edema

Late gadolinium enhancement

Characterization of cardiomyopathies based on pattern of enhancement Prognosis and risk stratification

T1 mapping

Edema, fibrosis, infiltration

T2 mapping

Edema

Extracellular volume mapping

Fibrosis, scarring

T2* images and mapping

Myocardial iron

Phase contrast

Quantification of flow and stenosis

Table 23.5A Salient Imaging Findings of Key Cardiomyopathies Cardiomyopathy Key Findings Ischemic

Regional wall motion abnormalities in vascular distribution Subendocardial or transmural perfusion defect in vascular distribution Subendocardial or transmural LGE in vascular distribution Ventricle may be dilated Global systolic dysfunction may be seen

Dilated nonischemic

Dilated ventricle Global systolic dysfunction Linear mid-myocardial LGE in the septum may be seen

Cardiomyopathy

Key Findings

Amyloidosis

Concentric ventricular thickening Biatrial enlargement Diffuse subendocardial to transmural LGE High native T1, extracellular volume

Sarcoidosis

Ventricle—May be dilated or thickened Global/regional hypokinesis Mid-myocardial/subepicardial LGE Mid-myocardial/subepicardial edema in acute phase

Hypertrophic cardiomyopathy

Classic type—Asymmetric hypertrophy of the basal ventricular septum Systolic anterior motion of the mitral valve may be seen Mitral regurgitation may be seen Left ventricular outflow tract obstruction may be present Patchy mid-myocardial, RV insertion, or diffuse LGE Elevated native T1 and ECV

Myocarditis

Global/regional hypokinesis Mid-myocardial/subepicardial LGE Mid-myocardial/subepicardial edema in acute phase Elevated T1, T2, and ECV may be seen Ventricle dilation or global systolic dysfunction may be seen Pericardial effusion may be associated

Iron deposition

Concentric thickening Dark signal of myocardium in gradient echo images Low myocardial T2* (2.3 Ventricle dilation or global systolic dysfunction may be seen

Cardiomyopathy

Key Findings

Arrhythmogenic right ventricular cardiomyopathy

Major wall motion abnormalities of the RV— Aneurysm, akinesia, dyssynchrony along with either RV dilation or RV dysfunction Fat or LGE may be seen in the RV myocardium

Stress-induced cardiomyopathy

Classic type—Apical ballooning (akinesis) with hyperkinesis of basal segments Edema may be seen in the apical segments No abnormal LGE

Table 23.5B Patterns of Late Gadolinium Enhancement Pattern Etiology Subendocardial in vascular distribution

Myocardial infarction

Subendocardial—Diffuse

Cardiac amyloidosis Hypereosinophilic syndrome Systemic sclerosis Cardiac transplant

Mid-myocardial—Linear

Idiopathic dilated cardiomyopathy Myocarditis

Mid-myocardial—Patchy

Myocarditis Sarcoidosis Chagas disease Fabry's disease

Mid-myocardial—RV insertion points

Hypertrophic cardiomyopathy RV pressure overload

Subepicardial

Myocarditis Sarcoidosis Chagas disease Fabry's disease

Pattern

Etiology

Transmural

Myocardial infarction (vascular distribution) Cardiac amyloidosis Chronic/severe myocarditis Chronic/severe sarcoidosis

CT scan has a limited role in the evaluation of cardiomyopathies. Its main utility is in the exclusion of coronary artery disease in a patient who presents with heart failure and/or dilated cardiomyopathy. CT has high accuracy and negative predictive value in the exclusion of coronary artery disease. CT is also valuable in patients who cannot get an MRI due to contraindications including claustrophobia and metallic devices or due to expected artifacts from such devices. Using retrospective ECG-gating, that is, acquisition of data throughout the cardiac cycle, ventricular function, and volumes can be obtained with accuracy comparable with MRI. Regional wall motion abnormalities can also be calculated. CT can provide morphological evaluation of valves, but cannot provide quantification of valvular function. CT perfusion, both at rest and stress can be used to evaluate myocardial ischemia. CT can also be used to evaluate delayed enhancement, but this is limited by the low contrast-to-noise ratio of this technique [41]. Several scintigraphic techniques are also used in the evaluation of cardiomyopathies. Myocardial ischemia following stress and rest are evaluated either using SPECT (thallium-201, Tc-99m-sestamibi/tetrofosmin) or PET (Rb82) techniques. Gallium-67, thallium-201, and 18F-FDG PET are useful in the evaluation of cardiac sarcoidosis. Several isotopes such as Tc-pyrophosphate, tcDPD (3,3,0 diphosphon-1,2 propanodicarboxylic acid), I-123 serum amyloid P component, Pittsburgh compound B, and 18F-florbeapir are useful in diagnosing cardiac amyloidosis. Cardiac function can also be quantified using Tc- labeled human albumin serum or red blood radionuclide ventriculography or using SPECT with Tc-sestamibi/tetrofosmin or thallium-201 [38,42]. Cardiac catheterization is an invasive technique that provides hemodynamic information and prognostic value, particularly for the evaluation of pulmonary hypertension and constrictive pericarditis. Coronary angiography is also the gold standard in the evaluation of coronary arteries with invasive fractional flow reserve used for lesion-specific ischemia. Endomyocardial biopsy can also be performed to obtain confirmatory diagnosis [38].

Ischemic Cardiomyopathy

Most of the classification systems of cardiomyopathies exclude ischemia as a type of cardiomyopathy. However, this remains the most common cause of dilated cardiomyopathy and cardiac failure. Ischemic cardiomyopathy is secondary to coronary artery disease, which decreases blood flow to the myocardium. This can eventually culminate as MI that progress as a wavefront from subendocardium to the subepicardium. Diagnosing ischemic etiology is important, since this can be treated using medicines and revascularization procedures. Patients can present with symptoms of cardiac failure. Echocardiography may show ventricular dilation and global systolic dysfunction. Regional wall motion abnormalities are seen in a vascular distribution. In patients with suspected ischemic cardiomyopathy, a coronary CTA can be performed to evaluate for coronary artery disease as an etiology for cardiomyopathy. This obviates the need for an invasive angiographic procedure. On MRI, the ventricle is dilated and there may be global systolic dysfunction. Regional motion abnormalities, such as hypokinesis, akinesis, or dyskinesis are seen in a vascular distribution. For example, left anterior descending artery supplies the basal and mid anterior, anteroseptum, and most of the apical segments; the left circumflex artery supplies the lateral wall; and the right coronary artery supplies the basal and mid inferoseptum, inferior segments, and apical inferior segment. On first-pass perfusion images, myocardial ischemia is seen as a subendocardial or transmural perfusion defect on stress, but not on rest images (Figs. 23.35A–B), whereas MI is seen as perfusion defect in both stress and rest images [37]. Subendocardial to transmural LGE can be seen in patients with MI (Figs. 23.36). If the LGE involves 75% indicates that the myocardium is not viable and unlikely to recover function. LGE 50–75% is indeterminate [43]. In acute MI, myocardial edema is seen as high signal in STIR images with elevated T2 values (>50 milliseconds) and T1 values. The edema is usually more extensive than the LGE, and the difference between the two represents the myocardium that can be salvaged with revascularization. Acute microvascular obstruction is seen as a dark filling defect within a bright scar tissue. Complications of MI can also be evaluated with MRI, including thrombus, aneurysm, pseudoaneurysm, rupture (free wall or septum), pericarditis, and mitral regurgitation. Ischemia can also be evaluated by scintigraphic techniques, including SPECT and PET-CT [44]. In ischemic cardiomyopathies, AICD is placed for prevention of SCD in New York Heart Association (NYHA) class II or III heart failure despite medical therapy and LV EF ≤ 35% of NYHA class I heart failure and LV EF ≤ 30%, at least 40 days post-MI and 90 days postrevascularization, if meaningful survival of >1 year is expected [45].

FIGURE 23.35 Myocardial ischemia. (A) First-pass perfusion MRI at rest shows normal perfusion of the myocardium. (B) First-pass perfusion MRI obtained after injection of IV regadenoson shows a subendocardial perfusion defect in the basal inferior wall (arrow), consistent with inducible ischemia.

FIGURE 23.36 Myocardial infarction. (A) Four-chamber cine balanced steadystate free precession (b-SSFP) image shows dilation of the left ventricle with apical thinning and aneurysm (arrow). (B) Four-chamber postcontrast inversion recovery image shows full-thickness late gadolinium enhancement (LGE) of the LV apical region (arrow), consistent with an established infarction in the left anterior descending (LAD) artery territory. (C) Short-axis postcontrast inversion recovery image in the same patient shows the myocardial infarction as a full thickness late gadolinium enhancement (arrow). The involvement of full thickness of the myocardium makes this nonviable and will not benefit from a revascularization procedure.

Dilated Nonischemic Cardiomyopathy Dilated cardiomyopathy can also be idiopathic or due to toxins, familial, infections, infiltrative disorders, autoimmune diseases, metabolic abnormalities, and arrhythmias. This is characterized by dilation of the left ventricle with global systolic dysfunction (Fig. 23.37A). Typically, no regional wall motion abnormalities are seen. Note that dilation of the heart can been in other causes of cardiac failure and also with valvular regurgitation and shunts. This is usually a diagnosis of exclusion, after coronary artery disease has been excluded. In the absence of any specific etiology, it is considered to be idiopathic. Most of these cases do not have any LGE. A linear mid-myocardial enhancement can be seen, particularly in the ventricular septum (Fig. 23.37B). This is due to replacement fibrosis and associated with poor prognosis. Nevertheless, the main role of imaging, particularly MRI is to exclude coronary artery disease as a cause of dilated cardiomyopathy [36,38]. In nonischemic cardiomyopathies, AICD is placed for primary of SCD in NYHA class II or III heart failure and LV EF ≤ 35%, if meaningful survival of >1 year is expected [45]. In patients with SCD due to VT/VF or hemodynamically unstable VT or stable sustained VT, it is placed for secondary prevention [45].

FIGURE 23.37 Dilated nonischemic cardiomyopathy. (A) Four-chamber cine SSFP image shows severe dilation of the left ventricle (LV). There was also severe global systolic dysfunction with ejection fraction of 21%. There is also moderate central mitral regurgitation (curved arrow) secondary to mitral annular dilation from LV enlargement. Note also the large circumferential pericardial effusion (straight arrow). (B) Four-chamber postcontrast inversion recovery image shows a linear mid-myocardial LGE in the ventricular septum (arrow), which is frequently seen in nonischemic dilated cardiomyopathy.

Hypertrophic Cardiomyopathy Hypertrophic cardiomyopathy is generally an inherited disease characterized by inappropriate myocardial hypertrophy. Clinical manifestations include dyspnea, syncope, arrhythmias, and SCD. Myocardium is considered to be thickened when the end-diastolic diameter is >15 mm. MRI is accurate in measurement of myocardial thickness and evaluation of morphology. The most common morphological type is the asymmetric basal type, in which the basal septum is hypertrophied (Fig. 23.38A). This may produce obstruction of the LVOT, which is seen as a dark jet in the LVOT (Fig. 23.38B). This obstruction provides a Venturi effect and systolic anterior motion of the mitral valve, which results in mitral regurgitation. LGE may be seen in a mid-myocardial pattern, especially in hypertrophied segments and at the insertion points of the right into left ventricle (Fig. 23.38A). MRI also shows abnormalities of the papillary muscles, which may contribute to LVOT obstruction. In the apical variant HCM, the hypertrophy involves the apical segments and there is ace-of-spade appearance of the LV cavity (Fig. 23.39A–B). This may be complicated by apical aneurysm and thrombosis. Other variants include mid-ventricle type, mass-like type, concentric and spiral types. Concentric type of HCM may be challenging to distinguish from

other etiologies such as hypertension, AS, and athlete's heart. In systemic hypertension, the thickening is milder, EF can be lower, ventricle can be dilated, LGE is absent or minimal. There is increased LV wall stress and lower anteroseptal systolic strain. In AS, restricted opening of the aortic valve in systole and flow acceleration can be seen in MRI. In athlete's heart, there is mild concentric hypertrophy, with mild LV dilation (end-diastolic diameter 10% or a reduction of EF >5% in symptomatic individuals in patients who are on chemotherapy. Early diagnosis of this entity can be made with abnormal myocardial strain, increased LV mass, high signal in T2-w images, high T1, T2, and ECV values. LGE in mid-myocardial to subepicardial distribution can be seen [57]. Peripartum cardiomyopathy is seen in late stages of pregnancy or in the first 5 months after pregnancy. LGE can be seen in subepicardial to mid-myocardial distribution. Chagas disease is caused by the parasite, Trypanosoma cruzi, which is endemic in South and Central America. Cardiac involvement may present with heart failure, arrhythmia, sudden death, and thromboembolism. Global systolic dysfunction, regional wall motion abnormalities, LV dilation, aneurysm, and

thrombus may be seen. LGE is commonly seen, typically in apical and basal inferolateral segments, either in a subendocardial, transmural, mid-myocardial, or subepicardial pattern [58]. Endomyocardial fibrosis is the most common cause of restrictive cardiomyopathy worldwide, which is a spectrum of hypereosinophilic syndrome. This has necrotic, thrombotic, and fibrotic phases. Apical thickening may be seen. A three-layered pattern of LGE may be seen, with an inner layer of dark thrombus, middle layer of subendocardial enhancement from fibrosis, and outer dark layer of normal myocardium. Scleroderma may show linear mid-myocardial LGE, either in the septum or LV free wall [38].

Cardiac Tumors Cardiac masses are rare and can be divided as neoplastic versus nonneoplastic. The neoplastic lesions can be primary or secondary tumors (Table 23.6). The primary tumors of the heart are rare with necropsy incidence of only 0.05% while the secondary tumors are much more common, seen in 1% of postmortem examinations [59]. Table 23.6 Cardiac Masses Benign

Malignant

Tumor-Like Masses

Myxoma

Metastasis

Thrombus, vegetation

Lipoma

Sarcoma (angiosarcoma, liomyosarcoma, rhabdomyosarcoma, undifferentiated sarcoma, osteosarcoma, malignant fibrous histiocytoma)

Prominent crista terminalis

Papillary fibroelast oma

Primary cardiac lymphoma

Lipomatous hypertrophy of IAS

Benign Fibroma

Malignant Mesothelioma

Tumor-Like Masses Caseous necrosis of mitral annular calcificatio n

Rhabdom yoma Hemangi oma Paragang lioma Teratoma

Up to 90% of primary cardiac tumors are benign and can arise from the myocardium or the pericardium [60]. The secondary cardiac tumors are much more common and are mostly malignant [61]. In an autopsy series, metastatic involvement of heart is seen in up to one in five patients dying from cancer [59– 63].

Clinical Presentations Cardiac tumors may be asymptomatic and found incidentally during evaluation of an unrelated problem or can be symptomatic. Symptoms include dyspnea, chest discomfort, syncope or presyncope and can be due to mass effect on the myocardial function or blood flow, arrhythmias, interference with heart valves causing stenosis or regurgitation or due to pericardial involvement leading to effusion or even tamponade. Tumors may also present due to embolic events either due to pulmonary thromboembolism from right chamber masses or systemic thromboembolism from left-sided chamber masses [62,64]. Lastly, there can be systemic manifestation in the form of constitutional symptoms such as fever, fatigue, arthralgia, weight loss, and paraneoplastic syndromes. Goals of imaging in patients with suspected cardiac mass are 1. to establish if a cardiac tumor is present or not, 2. determine location of the mass in the heart, 3. characterization of the mass to determine if it is benign or malignant, and

4. evaluate effect of the mass on the adjacent structures.

Echocardiography is often the first technique as it is widely available, noninvasive and can be done bedside. It can easily identify and locate the mass in a cardiac chamber, determine its mobility and obstructive effect on adjacent valve. Echo can also determine if the myocardium or pericardium is involved. When TTE evaluation is limited due to poor acoustic window, TEE though invasive usually provides excellent evaluation of a cardiac mass. Cardiac MRI is often the second technique of choice to evaluate cardiac mass. In addition to determining its location, mobility, and obstructive effects on valves, MR can also characterize a mass using T1-, T2-weighted, and postcontrast imaging (Table 23.7) [65]. CMRI is limited by its less wide availability, long exam time, claustrophobia, and inability to scan due to an incompatible cardiac hardware. Cardiac CT is an excellent technique with high spatial and temporal resolution, widely available and fast which can be performed in patients with cardiac hardware. In clinical practice, due to their complementary nature often more than one technique is used to evaluate a suspected cardiac mass. Table 23.7 MR Tissue Characteristics of Common Cardiac Tumors Cardiac Postcontrast (Delayed T1 T2 Tumor Enhancement) Myxoma

Isointense

High

Heterogenous

Lipoma

High

High

None

Fibroma

Isointense

Low

Yes

Angiosar coma

Heterogenous

Heterog enous

Heterogenous

Lympho ma

Isointense

Isointen se

Minimal to none

Metastas is

Low (melanoma: high)

High

Heterogenous

Cardiac Myxoma

The most common benign primary cardiac tumor derived from mesenchymal cell precursors. Most commonly found in the left atrium though can also occur in the right atrium and rarely in the ventricles and great vessels (Figs. 23.48 and 23.49) [66]. In the left atrium, they are most commonly attached by a stalk to the interatrial septum near the fossa ovalis. The right atrial myxoma is more common in children. The majority of these tumors occur in women and mean-age at diagnosis is 50s. Tumors vary in size from 1 to 15 cm in diameter [66].

FIGURE 23.48 RA myxoma. (A, B) Echocardiogram four-chamber view shows a large slightly heterogeneous mass in the right atrium attached to the interatrial septum. (C–F) Four-chamber bright blood gradient echo, triple inversion, postcontrast first pass and delayed images of cardiac MR confirm the echo findings and also shows vascularity in the tumor in first pass images (red arrow) and enhancement on delayed images (yellow arrow). LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

FIGURE 23.49 LA myxoma. (A–C) Axial, coronal, and sagittal contrastenhanced CT images show a large well-circumscribed homogenous mass (black arrows) seen in the left atrium attached to the interatrial septum with calcification (white arrows). LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Morphologically, two types of myxomas are described: polypoid and papillary. The polypoid myxomas when large enough can prolapse into the mitral valve thereby causing mitral stenosis symptoms. The papillary variety is more often associated with embolic phenomena [67,68]. Rarely, constitutional symptoms including fever, fatigue, and weight loss have been described. In approximately 7% of patients, cardiac myxomas can occur in association with multiple endocrine neoplasia and hyperpigmentation of skin (lentiginosis syndrome); also known as Carney complex [66,69], not to be confused with Carney's triad (gastrointestinal stromal tumors, pulmonary chondroma, and extra adrenal paraganglioma) or Carney Statakis syndrome (GISTs and paragangliomas; Box 23.20). Box 23.20

Carney Complex ■ Autosomal dominant ■ Multiple myxomas; often diagnosed at earlier age, increased tendency to recur ■ Schwannomas ■ Endocrine tumors ■ Pigmented lentigines and blue nevi on face, trunk, and neck

On echocardiography, seen as variable echogenicity mobile mass in the left atrium attached by a stalk along the interatrial septum near the fossa ovalis (Fig.

23.48A–B). On CT they are often low attenuating masses attached to the interatrial septum with smooth or slightly irregular surface (Fig. 23.49). In up to 15% of patients, these masses are calcified and calcification is more commonly seen in the right atrial myxomas [65,66,68]. These tumors often demonstrate heterogeneous enhancement only recognized on delayed CT images [70]. On cardiac MR, the tumors demonstrate heterogeneous signal intensity on T1- and T2-weighted images due to the presence of grading amount of hemorrhagic, myxoid, necrotic, and ossific tissue. There is often patchy delayed enhancement after gadolinium administration (Figs. 23.48C–F) [65,68,71]. Depending on their location, these tumors can prolapse into the left or RV in diastole. Myxoma can be confused with thrombus (Figs. 23.50 and 23.51) and the common distinguishing features are listed in Table 23.8.

FIGURE 23.50 RA thrombus. A well-defined filling defect is seen in the right atrium (arrows) on contrast enhanced CT (A) and four-chamber view of echocardiogram (B). The mass was isointense to myocardium on T1-weighted images (C) and there was no vascularity seen during postcontrast first pass images (D) and no delayed enhancement seen on short-axis atrial view of CMR (E). Patient was anticoagulated and the mass decreased significantly in 2 months on follow-up CT (F). LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

FIGURE 23.51 (A) Left atrial eccentric filling defect (arrows) due to thrombus in this patient after Maze procedure. (B) LV apical thrombus with calcification (red arrows) in patient with prior LAD territory MI as shown by thinned and hypodense distal interventricular septum and apical walls (white arrows). Ao, aorta; LA, left atrium; LV, left ventricle; RA, right atrium; RVOT, right ventricle outflow tract.

Table 23.8 Differentiating Features of Myxoma and Thrombus Feature Myoma Thrombus Location

LA>RA>Ventricles, along IAS in LA

LA, LAA>LV Apex>RA>RV

Clinical information

Asymptomatic or SOB, mitral stenosis features in LA myxoma

H/O atrial fibrillation, prior MI, indwelling central line

Mobility

Often mobile, can be sessile

Often immobile, can be mobile

Calcification

May be present, more common in RA myxoma

Rare, can be seen in chromic organized thrombus

Feature Postcontrast enhancement (MR, CT)

Myoma Variable; slight to moderate

Thrombus None except in chronic vascularized thrombi

Complete surgical resection has best long-term outcome with very low operative mortality [72]. After resection, annual follow-up with TTE is often recommended for at least 4 years since these tumors can reoccur, often at the site of original primary tumor.

Lipoma Second most common primary benign tumor of the heart, occurs commonly in middle aged and older patients [61]. Fifty percent of lipomas originate from the subendocardial layer and the rest from subepicardial or myocardial tissue. The majority of these patients are asymptomatic but can present with arrhythmia or less commonly valvular dysfunction. Very rarely the subepicardial lipomas can cause extrinsic mass effect on the coronary arteries leading to myocardial ischemia. Lipomas are well-circumscribed immobile homogeneously hyperechoic intracavitary masses without any calcification as seen on echo (Fig. 23.52B). On CT they are nonenhancing homogeneous masses with fat CT attenuation within the cardiac chamber, myocardium, or pericardium (Fig. 23.52) [70]. On MR, lipomas have homogeneous high signal intensity on T1- and T2-weighted images with marked suppression on fat saturation sequences and demonstrate no postcontrast enhancement (Fig. 23.52) [65,68]. The majority of the patients do not require any surgical removal except in rare severely symptomatic scenarios.

FIGURE 23.52 Right atrial lipoma. (A–C) Contrast-enhanced CT axial images (A) show a well-circumscribed noncalcified low-density mass in the right atrium (star) with CT attenuation values of fat. (B) Lipomas are hyperechoic heterogenous masses on echo. (C) They are hyperintense on T1 MR images (star). These can be associated with interatrial septal fatty hypertrophy. The majority of these lesions are benign and do not need resection. Ao, aorta; LA, left atrium; LV, left ventricle; RA, right atrium.

Fibroelastoma Papillary fibroelastomas account for 10% of cardiac tumors and 75% of all valvular neoplasms [68,73]. Their appearance resembles sea anemones with fronds around a central core. These cardiac tumors are often found on the valvular endocardium of the aortic and mitral valve, followed by tricuspid valve. They often are found on the downstream side of the valve, for example, LV side of the mitral valve or aortic side of the aortic valve. Patients often are middle age and present with embolic cerebral complications leading to imaging evaluation. Fibroelastoma is composed of collagen and elastic fibers with endothelial covering and a short connective tissue pedicle. Thrombus may form on their surface and can embolize. On echo they are small in size, echogenic tumors attached on the endothelial surface with slightly stippled margins due to fingerlike projections causing vibration at the tumor blood interface. Due to its small size, TEE is more sensitive than TTE (Fig. 23.53B–C). On cardiac CT, they could be difficult to see due to their small size. When seen they appear as focal low attenuating nodules attached to the valve and often better appreciated on a retrospective-gated study (Fig. 23.53A, D). These tumors are isointense on T1weighted and hypointense on T2-weighted images due to high fibrous content, although rarely they can have hyperintense signal (Fig. 23.54) [65,68].

FIGURE 23.53 Fibroelastoma. (A–D) A small nodular lesion is seen attached to the noncoronary aortic valve cusp (white arrow, A, D) in aortic valve shortaxis and LVOT 3D images. It is seen as echogenic nodule attached to aortic leaflet on echo (B, C white arrow). Fibroelastomas are attached along the aortic side of the valve and have tendency to form thrombus and embolize; therefore, they are resected as surgical cure. Ao, Aorta; L, left; LA, left atrium; LV, left ventricle; NC, noncoronary; R, right.

FIGURE 23.54 Pulmonary valve fibroelastomas are rare as seen in this patient. (A) On axial contrast-enhanced CT, there is a small slightly irregular filling defect in the main pulmonary artery near the pulmonary valve (arrow). (B) On oblique sagittal T1-weighted image, the nodule is isointense to the myocardium and is slightly hyperintense on balanced turbo field echo (bTFE) sequence (C) and hyperintense on triple inversion fat suppressed sequence (D). The lesion was very mobile on cine images. There is contrast enhancement seen on delayed postcontrast images (E, arrow). Better seen in transesophageal echocardiogram (F) as pedunculated mobile nodule (white arrow) attached to the pulmonary valves (small blue arrows). Ao, aorta; AV, aortic valve; RV, right ventricle; RVOT, right ventricular outflow tract.

Surgical excision is often reserved for large mobile left-sided fibroelastomas. The right-sided papillary fibroelastomas are usually managed medically unless there is risk of paradoxical embolism due to intracardiac shunts or significant hemodynamically obstructing lesions.

Fibroma More common in infants, often located in the ventricles and composed of fibroblasts and collagen fibers with variable calcification. They are most commonly located in the left ventricle myocardium or interventricular septum and can mimic hypertrophic cardiomyopathy. These patients can present with ventricular arrhythmia and sudden death due to conduction disturbances. Larger tumor can also produce shortness of breath from obstruction to blood flow

[74,75]. These tumors can be associated with familial adenomatous polyposis and Gorlin syndrome and in these scenarios, the fibromas are often located in the atria. On echo they are well demarcated solid echogenic masses within the myocardium ranging in size from 1 to 10 cm with central calcifications. Cardiac CT clearly shows their intramyocardial location with homogeneously low attenuation and often with central calcification (Fig. 23.55) [70]. There is often minimal or no contrast enhancement. Fibromas are isointense compared to the myocardium on T1-weighted images and are also homogeneous and hypo intense on T2-weighted images with minimal to no postcontrast enhancement [65,68,71,75]. Since these tumors do not regress spontaneously and there is increased risk of arrhythmia and sudden death, surgical resection is recommended regardless of the symptoms.

FIGURE 23.55 LV fibroma. (A–B) In contrast-enhanced axial and coronal reformat CT, a well-defined homogenous hypodense mass is seen in the left ventricle lateral wall myocardium (arrows) with focal calcification. Most commonly seen in infants or young children and resection is recommended as these tumors do not spontaneously regress unlike rhabdomyomas. LV, left ventricle; RV, right ventricle.

Rhabdomyoma Most common primary cardiac tumor in first year of life [75]. Often they are multiple and involve apical ventricles. They can cause arrhythmias and rarely flow obstruction leading to heart failure symptoms. Their association is well known in patients with tuberous sclerosis [68,76–78]. On echo they are small well circumscribed multiple nodules or one large pedunculated mass in the cardiac cavity. Occasionally, they appear as lobulated homogeneous and hyperechogenic

masses within the myocardium due to myocardial embedding. Cardiac CT shows intramural location with homogeneous low attenuation and variable intracavitary extension. Presence of multiple masses and association with tuberous sclerosis distinguish rhabdomyomas from myomas. These tumors are isointense on T1weighted images and hyperintense compared to the myocardium on T2-weighted images without any postcontrast delayed enhancement (Figs. 23.56A, B) [65,76– 78]. Tuberous sclerosis has high association with renal angiomyolipomas, fat containing hepatic angiomyolipomas, cystic lesions in lungs, subependymal calcified tubers seen on head CT, subcortical hyperintensities and subependymal giant cell astrocytoma as seen on brain MRI (Figs. 23.56C–G). In comparison to fibromas, rhabdomyomas are known for undergoing spontaneous regression. Therefore, usually patients are followed with serial echocardiography and surgery is only reserved for patients with arrhythmia or heart failure.

FIGURE 23.56 Tuberous sclerosis. (A) On CT, the hamartomatous lesions are low or fat density intramyocardial areas lesions of variable sizes in LV myocardium (red arrows). (B) On T2-weighted MR, these lesions are hyperintense (red arrows). There is high association of renal angiomyolipomas (C, stars), liver fat containing angiomyolipomas (D), lung cysts (E), subependymal calcified tubers on brain CT (F), subcortical hyperintense signal (red arrows) and subependymal giant cell astrocytoma (yellow arrow) on FLAIR brain MR (G). LA, left atrium; LV, left ventricle; RV, right ventricle.

Cardiac Paraganglioma

Rare neuroendocrine tumor originates from the paragangliomic cells located in relation to the atria, great arteries, as well as coronary arteries. They most often arise in the visceral paraganglia of the left atrium in its posterior wall or roof and less commonly in the interatrial septum, coronary arteries, or aortic root [68,79]. Secretory paragangliomas lead to excessive sympathetic discharge causing Cushing-like symptoms such as palpitations, flushing, and tremors. A large size of the tumor can cause dyspnea and angina due to compression of the cardiac chamber or coronary artery. On echo, paragangliomas are usually broad-based hyperechoic masses. On cardiac CT, they are heterogeneous masses with low attenuation and often marked enhancement on contrast-enhanced imaging due to high vascularity [70,79]. On MR, these tumors show high signal intensity on T2weighted images and often demonstrate FDG uptake on PET imaging (Fig. 23.57) [65,71,79]. Surgical resection is difficult but is recommended if possible with preoperative medical optimization to prevent catecholamine surges. Preoperative transcatheter embolization can also be helpful in highly vascular tumors.

FIGURE 23.57 Cardiac pheochromocytoma. Axial (A) and coronal (B) CT images demonstrate heterogeneously enhancing noncalcified soft tissue middle mediastinal mass (M) located posterosuperior to the left atrium (LA). The mass is displacing and indenting the posterior wall and roof of the left atrium (red arrow). These tumors often are hypervascular and therefore are difficult to resect surgically. T1 (C), T2 (D) and triple inversion recovery (E) axial MR images demonstrate a slightly hyperintense middle mediastinal mass (stars) in comparison to myocardium. The mass shows intense contrast uptake as seen on postcontrast T1 sagittal oblique images (F). Ao, aorta; LA, left atrium; M, mass.

Malignant Secondary Cardiac Tumors Cardiac metastases are 20–40 times more common than primary cardiac tumors [59–61,63]. Pericardial involvement is more common than myocardial metastasis (Fig. 23.61). Melanoma has the greatest propensity for cardiac involvement; however, cancer of the lung, breast, kidney, and esophagus are the most common carcinomas that metastasize to the heart. Cardiac metastases can occur either hematogeneously, via lymphatics, transvenous spread via IVC, or direct invasion (Figs. 23.58–23.61).

FIGURE 23.58 Cardiac metastasis. Two different patients (A) with renal cell cancer metastatic to LV myocardium and (B) with colon cancer and RV myocardium metastasis. In a patient with known malignancy, any focal nodular myocardial abnormality should be suspected for metastasis. LV, left ventricle; RV, right ventricle.

FIGURE 23.59 Direct invasion from left upper lobe bronchogenic carcinoma. (A–B) There is lobular soft tissue mass (red arrows) seen in the left atrium (LA) which extended via left upper lobe pulmonary vein. LA, left atrium.

FIGURE 23.60 A 59-year-old female with right renal cell carcinoma. (A–D) Nongated chest and abdomen CT. A large mass is present in the right atrium (black arrow) which is contiguous with mass in the IVC (white arrow and yellow arrow) and right renal vein (red arrow) (B–D). There is increased vascularity with the IVC thrombus best seen in arterial phase axial and coronal CT images (B, C) suggesting it to be tumor thrombus. Patient underwent open right radical nephrectomy, caval thrombectomy, and right atrial thrombectomy. LV, left ventricle; RA, right atrium; RV, right ventricle.

FIGURE 23.61 Pericardial metastasis. Much more common than myocardial metastasis. (A) There is nodular enhancing thickening of the pericardium (yellow arrows) with moderate complex pericardial effusion in this patient with known lung cancer. (B) There are much larger solid enhancing masses (arrows) in the pericardium associated with pericardial effusion in this patient with metastatic synovial sarcoma. Rarely such patients present with large pericardial effusion or tamponade.

Clinically, myocardial metastases can present with conduction disturbances or rarely from coronary artery obstruction leading to ischemia. Other presentations include heart failure, valvular dysfunction, or symptoms from pericardial effusion and tamponade (Fig. 23.61). Echocardiography is often the initial technique. On MR most cardiac metastasis are low signal intensity on T1 weighted and high signal intensity on T2 weighted except for metastatic melanoma, which is hyperintense on T1 imaging due to the paramagnetic T1 shortening effects of melanin. Heterogeneous enhancement distinguishes tumoral thrombus from bland thrombus (Figs. 23.60A–C) [68,71,80]. Primary Cardiac Malignant Tumors Extremely rare, represent only 5–6% of all primary cardiac tumors [59–61,80,81]. Most common tumors are sarcomas, followed by primary cardiac lymphoma, and mesothelioma. Their clinical presentations can be variable but typically are according to the location of the tumor. Features suggestive of malignancy include rapid growth, local invasion, hemorrhage, or necrosis within the mass, involvement of more than one cardiac chamber, extension into the pericardium with pericardial effusion (Box 23.21).

Box 23.21

Features Suggesting Malignant Nature of Tumor ■ Rapid growth ■ Large size with necrosis and hemorrhage ■ Involvement of multiple cardiac chambers ■ Evidence of local invasion ■ Presence of pericardial effusion

Primary Cardiac Sarcoma: Primary cardiac sarcomas represent two third of all malignant primary cardiac tumors [59,60,81]. Often seen in younger patients in their 40s and carry worst prognosis in comparison to extracardiac soft tissue sarcomas. Histologically, sarcomas include angiosarcoma, leiomyosarcoma, liposarcoma, rhabdomyosarcoma, synovial sarcoma, myofibrosarcoma, and undifferentiated pleomorphic sarcoma [82].

Angiosarcoma: The most common type of cardiac sarcomas, composed of malignant cells that form vascular channels, usually very aggressive, often originate in the right atrium and extend into RV, right AV groove often encasing the RCA and pericardium (Fig.  23.62). There is often evidence of metastasis to lungs at the time of presentation. Men in their 40s are affected more than females [81,82]. Presenting symptoms are due to right heart failure, arrhythmia, or shortness of breath due to pericardial involvement. On echo these tumors are echogenic lobular or nodular masses in the right atrium often with pericardial effusion due to direct pericardial extension (Fig. 23.62A). On CT these tumors are highly vascular and demonstrate gross hemorrhagic and heterogeneous appearance with evidence of invasion into adjacent structure commonly present (Figs. 23.62B, C and 23.63) [82]. Pericardial effusion and thickening is common. On T1-weighted images on MR, these tumors are often isointense to hyperintense multiple nodules on which demonstrate LGE surrounding a large central necrosis (Figs. 23.62D–F) [71,80]. Cardiac angiosarcomas carry a poor prognosis without surgical resection. Neoadjuvant chemotherapy in conjunction with surgical debulking offers the best survival.

FIGURE 23.62 Metastatic right atrial angiosarcoma. A 35-year-old female presented with SOB and transthoracic echo (A) showed large pericardial effusion causing tamponade along with large right atrial mass (arrows). Pericardial effusion was tapped and was bloody but negative cytology. Contrast-enhanced chest CT (B, C) showed a large heterogenous vascular right atrial mass (white arrows) extending into the right atrioventricular groove with suspected pericardial extension. The mass was isointense to slightly hyperintense on T1 imaging and showed increased peripheral vascularity on postcontrast first pass images along with delayed enhancement (white arrows) on MR (D, E). The mass was resected and proved to be high-grade angiosarcoma. At 4-month follow-up, patient developed a right lower lobe nodule (white arrows) which showed FDG uptake (G, H). She was given chemotherapy, but unfortunately she developed hepatic (white arrow on I) and bone metastasis along with local recurrence. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle; RVOT, right ventricle outflow tract.

FIGURE 23.63 Primary cardiac sarcoma. (A–B) A lobulated soft tissue mass (red arrows) is seen in the right ventricle along the interventricular septum and extends into the right atrium. Multiple chamber involvement is one of the features for malignant mass. Ao, aorta; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Leiomyosarcoma: Highly aggressive and second most common sarcomas following angiosarcomas. These tumors are usually present in the posterior left atrium though can also involve other cardiac chambers. Clinical presentation depends on the size and location of the tumor. Tumors infiltrating the myocardium are frequently associated with arrhythmias with less common presentation include venous and intra-arterial thrombosis. On CT leiomyosarcomas are lobulated with irregular low attenuating masses usually associated with pericardial effusion. Rarely dystrophic calcification can be seen. When pulmonary veins are invaded, they are often seen as filling defects in the pulmonary veins. These tumors also have poor prognosis with high incidence of distant metastasis. Surgical resection offers palliation with the relief of obstructive symptoms.

Rhabdomyosarcoma: Most common pediatric malignant primary cardiac tumors and involve striated muscle. These tumors arise from the myocardium and have a tendency toward valvular involvement with no chamber predilection. Often these are large bulky and invasive tumors, more than 10 cm in size, presenting typically with symptoms relating to cardiac invasion or obstruction. On CT they are seen as irregular or smooth low attenuating mass within the cardiac chamber. They are isointense on

T1-weighted and hypointense on T2-weighted images with moderate homogeneous postcontrast enhancement. Both CT and MR can detect extra cardiac extension including pulmonary artery metastasis [68,70,71,80,82]. Combination of surgery, chemotherapy, and radiation therapy are often the standard treatment for rhabdomyosarcoma. Despite treatment, prognosis is dismal with survival less than 1 year in most cases.

Primary Cardiac Lymphoma: Primary cardiac lymphoma is much less common than secondary cardiac involvement (approximately 30% of patients with lymphoma have cardiac involvement) [83]. Majority are aggressive B-cell lymphomas, most commonly seen in immunocompromised patients with increasing incidence due to lymphoproliferative disorder from Epstein–Barr virus in patients with AIDS and those who received transplant. They most commonly involve the right side of the heart, particularly the right atrium although any chamber can be involved. Often there are multiple lesions and the mean age of diagnosis is often 60 years of age. Primary cardiac lymphoma symptoms may include arrhythmias including heart block, syncope, or even restrictive cardiomyopathy. Patients can have fever, chills, sweats, and weight loss along with chest pain and dyspnea and rarely acute heart failure could be the presentation (Box 23.22). Box 23.22

Primary Cardiac Lymphomas: Poor Outcome Predictors ■ Immune status ■ Left ventricular involvement ■ Presence of dyspnea ■ Presence of extracardiac disease

On echo they are homogeneous infiltrative masses causing wall thickening or nodular masses protruding into the cardiac chamber (Fig. 23.64D). The coronary artery can be encased due to involvement of the adjacent atrial ventricular groove (Fig. 23.64B). Similarly, pericardium involvement leads to effusion or rarely tamponade. On cardiac CT, they appear as focal or diffuse soft tissue masses or infiltrating multiple nodules demonstrating heterogeneous postcontrast

enhancement (Figs.  23.64A–B) [68,70]. Often there is associated mediastinal adenopathy. On T1-weighted images, tumors are isointense and usually show mild hyperintensity due to edema on T2-weighted images [71,83]. FDG PET can show uptake, degree of which is directly proportional to degree of the malignancy of the lesion (Fig. 23.64). Diagnosis often involves evaluation of pericardial fluid and/or endomyocardial biopsy. These tumors do respond to chemotherapy although recurrence rate is very high. Recurrence often develops at extra cardiac extra nodal sites.

FIGURE 23.64 B-cell lymphoma involves pericardium and coronary arteries. (A, B) Contrast-enhanced CT shows a large heterogeneous necrotic soft tissue mass in the anterior and middle mediastinum (M) inseparable from the LV anterolateral myocardium and encases the left anterior descending (white arrows) and circumflex (not shown) coronary artery as well as all three neck vessels. There is complex pericardial effusion and thickening. (C) The mass shows peripheral nodular uptake (white arrows) on PET scan. (D) Transthoracic echo also shows mass infiltrating the LV myocardium and pericardium (white arrows). (E) On postcontrast MR, there was transmural delayed enhancement of the anterior and anterolateral LV wall in the LAD and Cx territory (white arrows). Ao, aorta; LV, left ventricle; M, mass; RV, right ventricle.

Mesothelioma:

These tumors are derived from the pericardial mesothelial cell layer. By definition, these tumors must be localized within pericardial space without any pleural involvement. Association with asbestos exposure as cause relationship is unclear. These tumors often present with pericardial effusions with or without tamponade and have male sex predominance with most patients in their fifth or sixth decades. Echo often shows pericardial effusion and echogenic tumor mass encasing the heart. Both cardiac MR and CT can show multiple enhancing pericardial nodular masses with associated effusion [68,70,71,80,83]. These tumors demonstrate FDG uptake, therefore PET CT is very useful in staging and monitoring the disease during treatment. Primary pericardial mesotheliomas are highly aggressive tumors with extremely poor prognosis and median after diagnosis survival of only 6 months. Poor prognosis is due to late presentation, diagnostic difficulties, difficult for complete resection, and poor response to therapies.

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• P Rajiah, JP Kanne, V Kalahasti, P Schoenhagen, Computed tomography of cardiac and pericardiac masses, JCCT 5 (1) (2011) 16–29. • PJ Sparrow, JB Kurian, TR Jones, MU Sivananthan, MR imaging of cardiac tumors, Radiographics 25 (5) (2005) 1255–1276. • TY Tao, N Yahyavi-Firouz-Abadi, GK Singh, S Bhalla, Pediatric cardiac tumors: clinical and imaging features, Radiographics 34 (4) (2014) 1031–46. • J Jeudy, J Kirsch, F Tavora, AP Burke, TJ Franks, TL Mohammed, et al., From the radiologic pathology archives: cardiac lymphoma: radiologic-pathologic correlation, Radiographics 32 (5) (2012) 1369–1380.

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24

Pericardium Jena N. Depetris, Udo Hoffmann, Sandeep Hedgire

Introduction The pericardium is a fibrous structure that surrounds both the cardiac chambers and the origins of the great vessels. Composed of two layers, visceral and parietal, normally separated by a small amount of fluid [1], the pericardium plays several important roles in normal physiology, including decreasing the friction between the beating heart and surrounding structures, preventing excessive dilatation of the cardiac chambers, and limiting the spread of infection or inflammation from the adjacent mediastinum or lungs [2,3]. Numerous pathologies can affect the pericardium, including infectious, inflammatory, traumatic, acquired, congenital, and neoplastic processes. This chapter will discuss the characteristic imaging

features of both the normal and diseased pericardium with an emphasis on cross-sectional imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI), and review the advantages and limitations of various imaging techniques for assessment of the pericardium.

Imaging Techniques Transthoracic Echocardiography Transthoracic echocardiography is the standard initial noninvasive imaging technique used for the evaluation of pericardial disease [4]. Although this technique has the advantages of easy accessibility and real-time imaging without the use of ionizing radiation, pericardial assessment is frequently limited by the available acoustic window and image quality can be easily degraded, particularly in the setting of a hemorrhagic pericardial effusion or gas within the intervening soft tissues. Although transesophageal echocardiography can be an alternative approach, it is a more invasive imaging technique with many of the same limitations, which may still preclude full evaluation of the pericardium. In settings where

echocardiography is nondiagnostic or challenging to interpret, cross-sectional imaging with either CT or MRI can be advantageous for further characterization of the pericardium. In fact, the American College of Radiology 2020 appropriateness criteria considers both cardiac CT and cardiac MRI more appropriate diagnostic tests in the evaluation of dyspnea due to suspected pericardial disease compared with transesophageal echocardiography and invasive angiography with ventriculography [5].

Advanced Cross-Sectional Imaging By comparison, cross-sectional imaging techniques, including CT and MRI, are valuable adjuncts to echocardiography and offer unique advantages in assessing the pericardium, including a larger field of view with superior soft tissue contrast for anatomic assessment. These techniques are particularly useful to characterize loculated or complex pericardial effusions, constrictive pericarditis, and pericardial masses. In addition, given that both CT and MRI are performed in standard imaging planes, these techniques are less operator dependent compared with echocardiography. Given the numerous potential

applications of these techniques in the workup of pericardial disease, familiarity with these imaging techniques is important for all radiologists. Computed Tomography Cardiac CT, with the implementation of cardiac gating and increase in both spatial coverage and temporal resolution, now allows for motion-free imaging of the pericardium. These features, combined with multiphase, multiplanar reformatting capabilities allow for precise anatomic visualization of the normal pericardium and detailed assessment of anatomic variations or other pericardial abnormalities [3]. Additionally, CT allows for reasonable tissue characterization including the detection of pericardial calcifications, differentiation of simple and complex pericardial fluids, and characterization of certain pericardial masses. The obvious disadvantages of CT include the use of intravenous iodinated contrast and ionizing radiation, especially in patients with impaired renal function and young patients, respectively. Magnetic Resonance Imaging

By comparison, cardiac MRI can provide a comprehensive assessment of the pericardium utilizing a variety of sequences tailored for morphologic and functional assessment without the use of iodinated contrast media or ionizing radiation. Similar to CT, MRI has a wider field of view and multiplanar reformatting capabilities with excellent spatiotemporal resolution [3]. Evaluation of the pericardium by MRI involves the use of numerous cardiac- and respiratory-gated sequences (summarized in Table 24.1), including steady-state free precession or gradient-recalled echo cine sequences, real-time cine imaging of the interventricular septum during respiration, double and triple inversion recovery black-blood sequences, myocardial tagging, phase contrast or velocity encoded sequences, and late gadolinium-enhanced sequences, among others. T1and T2-weighted sequences allow for superior fluid and soft tissue characterization compared with echocardiography or CT, while cine sequences and myocardial tagging sequences enable dynamic assessment of the pericardium during cardiac motion, enhancing sensitivity for pericardial adhesions, and constrictive physiology. Despite its unique strengths, there are several disadvantages of MRI including far

more limited availability, the use of intravenous gadolinium, and long image acquisition times requiring a great deal of patient focus and cooperation. Furthermore, cardiac rhythm abnormalities, which are frequently associated with pericardial pathologies, can make cardiac gating difficult to achieve and produce profound artifacts that significantly degrade image quality. Table 24.2 provides a summary of the strengths and weaknesses of the imaging techniques discussed in this section. Table 24.1 MRI Techniques Commonly Used for Assessment of the Pericardium Clinical Utility for MR Technique Pericardium Steady-state free Assess myocardial precession (SSFP) (septal) wall motion Assess for the presence of pericardial effusion

MR Technique Double/triple inversion recovery fast spin echo (FSE) black-blood

Clinical Utility for Pericardium Assess pericardial thickness Assess for the presence of pericardial effusion

T1-weighted gradient Assess for pericardial echo myocardial tagged adhesions cine Real-time GRE cine during dynamic respiration

Assess for ventricular interdependence

T2-weighted fast spin echo (FSE) T1 and T2 fat saturation Assess tissue characteristics (e.g., pericarditis or pericardial neoplasm) Postcontrast (gadolinium) Adapted from Czum et al. [2].

Table 24.2 Summary of the Strengths and Limitations of Various Imaging Techniques in the Evaluation of Pericardial Disorders Technique Strengths Weaknesses Transthoracic First-line Operatorechocardiograp technique in dependent hy (TTE) suspected image quality pericardial Diagnostic disease utility limited Widely by available available at low acoustic cost window

◾ ◾

◾ ◾

◾ ◾ Narrow Portable/availabl field of view e at bedside ◾ Low signal◾ Functional to-noise ratio hemodynamic assessment

(SNR) of pericardium

◾

Technique

◾ Respirometry Strengths

available for respirophasic assessment

◾ Limited Weaknesses capacity for tissue characterization

◾ TEE as adjunct ◾ Can be performed in the acute setting and in hemodynamicall y unstable patients Cardiac CT

◾ Excellent ◾ Ionizing assessment of radiation pericardial ◾ Iodinated calcifications contrast ◾ Detailed relatively anatomic contraindicated

Technique

Strengths assessment of pericardium and extracardiac structures

◾ Simultaneous

Weaknesses in patients with poor renal function

◾ Functional assessment

available at preoperative relatively planning/clearan higher radiation ce doses

◾ Functional ◾ Image assessment quality available

susceptible to arrhythmias

◾ Requirement

for breath hold

◾ Patients must be

hemodynamical ly stable

Technique

Cardiac MRI

Strengths

◾

Weaknesses Modality not portable

◾ Second◾ Limited choice technique availability at for pericardial assessment (excluding calcifications)

◾ Detailed adjunctive

anatomic assessment of pericardium

◾ Superior tissue

characterization

◾ Ability to assess for

pericardial inflammation

high cost

◾ Limited assessment of pericardial calcifications

◾ Gadolinium relatively contraindicated in patients with poor renal function

◾ Image quality

susceptible to arrhythmias

Technique

Strengths (edema and late gadolinium enhancement)

◾ Requirement

available

hemodynamical ly stable

Weaknesses

for breath hold

◾ Functional ◾ Patients assessment must be

◾ Modality not portable Adapted from Xu et al. [4].

Normal Pericardial Anatomy The normal pericardium is a uniformly thin fibrous structure, typically measuring less than 2 mm in thickness, with any measurement of 4 mm or greater being considered abnormally thickened [2,3,6]. Although the pericardium is typically indistinguishable from the adjacent myocardium by chest radiography, cross-sectional imaging with CT or

MRI provides excellent delineation of the pericardium in a majority of patients. Clear discrimination of the pericardium from the adjacent myocardium by crosssectional imaging requires the presence of at least a thin layer of epicardial fat or pericardial fluid, and the pericardium is often most clearly seen over the rightsided cardiac chambers (Fig. 24.1).

Figure 24.1 Axial contrast-enhanced EKG-gated cardiac CT demonstrating the normal (4 mm) with or without a concurrent effusion (Fig. 24.21) [6,11]. Contrast-enhanced CT may additionally demonstrate dilatation and contrast reflux into the inferior vena cava, hepatic veins, and azygos vein, suggesting elevated right heart pressures due to constriction.

Figure 24.21 (A) Four-chamber contrastenhanced cardiac CT demonstrates pericardial calcifications, particularly along the right ventricular free wall with a tubular ventricular configuration and biatrial enlargement. (B) A corresponding short-axis late gadolinium enhancement sequence of the same patient demonstrates marked circumferential pericardial thickening and enhancement (arrows), particularly adjacent to the right ventricle in the region of calcification. (C) A tagged cine sequence demonstrates bending of the tag lines along the right ventricular free wall during systole (circled), a finding that is compatible with pericardial adhesions in the setting of constrictive pericarditis. MRI techniques in particular have evolved significantly and now have greater diagnostic capacities than both echocardiography and CT in detecting constriction, most notably with the use of tagged cine sequences aimed at assessing for regions of pericardial adhesion. The absence of normal pericardial slippage manifests as tag lines which bend but do not break as expected with ventricular

contraction (Fig. 24.21). MRI is also especially useful in assessing for the characteristic respirophasic variation of abnormal septal motion with respiratorygated steady-state free precession cine sequences (Fig. 24.22). The combination of pericardial adhesions with an exaggerated inspiratory septal bounce is suggestive of constrictive physiology.

Figure 24.22 Respirophasic dynamic SSFP cine imaging during (A) inspiration and (B) expiration demonstrates early diastolic septal flattening during inspiration (arrows) compatible a septal bounce. This finding confirms ventricular interdependence with respirophasic variation and is considered to be pathognomonic of constrictive physiology.

Cardiac Tamponade

Pathophysiology Cardiac tamponade describes the physiologic result of large or rapid accumulations of fluid/air/material in the pericardial space wherein diastolic function becomes impaired to the point of failure. As mentioned in an earlier section, the absolute volume of material within the pericardial cavity is somewhat less important than the rate of accumulation, because over short periods of time the pericardium is unable to remodel and adjust to the rising intrapericardial pressure. The result is progressive extrinsic compression of the ventricular chambers resulting in an emergent impairment of cardiac output [2]. Clinical Features Presenting symptoms of cardiac tamponade often include the so-called Beck triad of muffled heart sounds, hypotension, and jugular venous distension, along with pulsus paradoxus. Tamponade is frequently considered a life-threatening emergency and typically warrants immediate intervention in the form of ultrasound-guided pericardiocentesis.

Imaging Features The imaging features of cardiac tamponade are uncommonly encountered in clinical practice, but it is crucial for radiologists to recognize them when present and make a timely diagnosis and prompt appropriate therapy. Echocardiography is a quick and affordable first-line technique that can be utilized at the bedside when suspicion of cardiac tamponade is raised. Echocardiography may demonstrate abnormal motion of the interventricular septum in the form of a septal bounce suggestive of ventricular interdependence (also seen in constrictive pericarditis) with concurrent visualization of a large collection of fluid, blood, or other material within the pericardial space. Doppler evaluation of the tricuspid and mitral valve inflow can also assist in the diagnosis of tamponade, which will demonstrate exaggeration of the normal inspiratory increase in tricuspid inflow as well as the normal inspiratory decrease in mitral flow velocity. Cross-sectional imaging with CT can provide additional diagnostic information on a relatively quick

time course, and should be considered in the case of equivocal echocardiography findings. Pericardial collections of fluid, blood, or even air can be easily identified by CT, especially if loculated or in locations not well visualized by ultrasound, and contrast may be seen refluxing into dilated inferior vena cava, hepatic veins, or azygos vein due to impaired diastolic right ventricular filling. The most specific sign for tamponade physiology by CT is deformation or inversion of a ventricular free wall in diastole (Fig. 24.23). Unsurprisingly, due to the acute and emergent nature of cardiac tamponade, MRI remains impractical as a diagnostic technique.

Figure 24.23 Axial (A) and short-axis (B) contrast-enhanced cardiac CT demonstrate a large pericardial effusion resulting in inversion of the right ventricular free wall (arrows), consistent with cardiac tamponade physiology.

Pericardial Cyst Epidemiology Pericardial cyst is the most common benign pericardial mass and represents a congenital abnormality typically resulting from an excluded portion of a pericardial recess [1,3]. These masses are frequently asymptomatic and often are discovered incidentally by imaging, although larger cysts can rarely exert mass effect on the heart and adjacent structures. The most common location for a pericardial cyst is the right anterior cardiophrenic angle [1–3,11], although they can be seen in any location attached to the pericardium, directly or through a short pedicle, and they may grow slowly over time, sometimes measuring up to 8 cm or larger. Clinical Features The majority of pericardial cysts are asymptomatic and require no therapeutic intervention. Complications including cardiac compression, superimposed infection, and cyst rupture are exceedingly rare. In the unusual setting of large,

symptomatic, or infected cysts, percutaneous aspiration or surgical resection may be considered. Imaging Features Small pericardial cysts are likely to be radiographically occult on plain film, although larger cysts may distort or enlarge the cardiomediastinal silhouette. CT often demonstrates a wellcircumscribed hypodense rounded or ovoid lesion adjacent to the heart with a smooth, nonenhancing wall and no internal septations. Although the majority of pericardial cysts will measure water attenuation (between 10 and 30 HU), they may rarely contain internal debris, which may cause them to appear more hyperdense on CT. Occasionally pericardial cysts contain calcification and differentiation from other mediastinal masses can be difficult. MRI can be a valuable diagnostic tool in differentiating pericardial cysts from other more concerning lesions. MR features of simple pericardial cysts include T1 hypointensity, homogeneous T2 hyperintensity, lack of enhancement with intravenous gadolinium administration, and lack of restricted

diffusion on DWI sequences (Fig. 24.24). Pericardial cysts containing internal debris may demonstrate altered T1 and T2 characteristics; however, the lack of enhancement and lack of restricted diffusion should help clarify the diagnosis in this rare situation. The differential diagnosis for a pericardial cyst is summarized in Table 24.10.

Figure 24.24 Frontal chest radiograph (A) demonstrates an abnormal contour at the right cardiophrenic angle (arrow) partially obscuring the right heart border, which corresponds with coronal chest CT; (B) findings of a well-

circumscribed, low-density ovoid lesion near the right anterior costophrenic angle (asterisk). Axial T1 with fat saturation (C) and T2 (B) sequences demonstrate T1 hypointensity and T2 hyperintensity, of the same lesion which are characteristics of a simple pericardial cyst (asterisks). Table 24.10 Differential Diagnosis of a Pericardial Cyst [2] Pericardial cyst Foregut duplication cysts (bronchogenic, neurenteric, etc.) Pericardial diverticulum Thymic cyst Pericardial hydatid disease Diaphragmatic eventration or Morgagni hernia Thoracic pancreatic pseudocyst Cystic neoplasm

Pericardial Neoplasms

Epidemiology Pericardial neoplasms, both benign and malignant, are rare entities. Metastatic disease is far more common than primary pericardial neoplasms, with pericardial metastases most often originating from lung cancer, breast cancer, melanoma, or lymphoma primaries [1,6]. Metastatic involvement of the pericardium may occur as a result of direct extension/invasion from adjacent structures, lymphatic spread, or hematogenous spread, and autopsy studies have suggested that pericardial metastatic disease can be detected in up to ∼20% of patients with known malignancy [2]. If diagnosed before death, pericardial metastases are an indicator of poor prognosis, regardless of the underlying primary malignancy. Primary pericardial neoplasms include a heterogenous group of both benign and malignant masses, and accordingly they will present with a variety of imaging features. Benign pericardial masses include pericardial fibromas, teratomas, hemangiomas, or lipomas (Fig. 24.25), whereas malignant pericardial masses include pericardial mesothelioma, sarcomas, lymphomas, and other neuroectodermal tumors (Fig.

24.26) [2]. The most common primary pericardial malignancy (50% of primary pericardial tumors) is pericardial mesothelioma [3,6,9], although this represents less than 1% of all malignant mesotheliomas. Importantly, irrespective of the imaging features of any given pericardial neoplasm, biopsy is frequently required for definitive diagnosis, particularly if an underlying primary malignancy elsewhere in the body is not already known.

Figure 24.25 Axial (A) and oblique coronal (B) contrast-enhanced cardiac CT images demonstrate a low-density lesion in the pericardial space (asterisks), compatible with a pericardial lipoma.

Figure 24.26 Short-axis contrast-enhanced chest CT demonstrates a large heterogeneously enhancing masses arising from the pericardium, which represents a biopsy-proved pericardial synovial cell sarcoma. Clinical Features Clinically, pericardial neoplasms may have variable presenting symptoms, ranging from mild shortness of breath to constrictive or tamponade physiology.

Compression or invasion of the systemic or pulmonary vasculature may also contribute to physiologic alterations, such as decreased preload or increased afterload [2]. Most patients with pericardial metastases will die from their disease before experiencing symptoms related to pericardial involvement. Treatment for neoplastic pericardial disease is commonly palliative, in the form of a pericardial window or drainage catheter. Intrapericardial instillation of a sclerosing agent may also be considered, with the goal of generating intrapericardial scarring to prevent fluid reaccumulation. Imaging Features Several key imaging features are commonly seen in the setting of neoplastic pericardial disease, including a thickened, irregular, or nodular enhancing pericardium often with an associated pericardial effusion and loss of normal fat planes, all of which are particularly well demonstrated on cross-sectional techniques such as CT or MRI (Fig. 24.17). Individual

masses may demonstrate unique imaging features, such as internal fat and calcium within a teratoma or hemorrhagic pericardial effusion in the setting of a pericardial sarcoma or lymphoma. Nuclear medicine studies may demonstrate focal or diffuse pericardial FDG uptake depending on the extent of disease and the underlying primary malignancy. For example, pericardial lymphoma may demonstrate intense FDG uptake within the pericardium as it does when found elsewhere in the body. It is important to be able to distinguish pericardial FDG uptake from myocardial FDG uptake, as pericardial metastases may have different clinical and therapeutic implications compared with myocardial metastases. This is typically accomplished by co-localizing the areas of uptake with areas of nodularity or enhancement on the chest CT portion of a PET/CT. Cardiac MRI may be particularly useful in detecting or confirming neoplastic pericardial disease and providing additional information for tissue characterization (T1/T2 characteristics, enhancement patterns, etc.). MRI is very sensitive at detecting pericardial invasion, particularly when a STIR

sequence is used. This sequence, while lacking the resolution of other sequences, will demonstrate high signal associated with infiltration. Often infiltration through the pericardium produces a hemorrhagic pericardial effusion and this can be detected, with high signal on T1 weighted sequences. Despite its diagnostic utility, biopsy is still almost always needed for definitive diagnosis.

Other Rare/Unusual Pericardial Diseases Although this chapter focuses on the most common, high-yield pathologies affecting the pericardium, there are several additional unusual disease pathologies worth mentioning briefly, should they be encountered in clinical practice. Pericardial/epipericardial fat necrosis: A rare, benign, and self-limited inflammatory/reactive process of the pericardial or epipericardial fat. The etiology is commonly unknown, and patients should be managed conservatively with anti-inflammatory medications. Imaging findings on CT will demonstrate a region of epipericardial fat stranding, similar to what might be seen in a case of omental fat

necrosis in the abdomen, with possible adjacent pericardial thickening and occasional ipsilateral pleural effusion (Fig. 24.27) [1].

Figure 24.27 Axial (A) and oblique coronal (B) contrast-enhanced cardiac CT images demonstrate a region of focal fat stranding of the epipericardial fat (arrows), consistent with benign fat necrosis. Pericardial hydatid disease: An exceedingly rare disease wherein the characteristic hydatid cysts of echinococcus involve the pericardium, most commonly as a result of rupture of a cardiac hydatid cyst into the pericardial space [1]. Although the imaging appearance of this disease may vary depending on the stage of the cysts, the presence of daughter cysts on cross-sectional imaging techniques

most strongly suggests this unusual diagnosis (Fig. 24.28) [7]. Cyst rupture within the pericardium can result in reactive pericarditis and even cardiac tamponade [1].

Figure 24.28 Four-chamber SSFP image (A) demonstrates a multicystic structure within the pericardial space in the region of the left ventricular apex. The dominant cyst is surrounded by multiple satellite (“daughter”)

cysts (asterisks), all of which demonstrate T2 hyperintensity (B) and signal void on a PSIR image (C) confirming that these are fluidcontaining structures. An axial postcontrast image (D) demonstrates cyst wall enhancement (arrows), which is a common finding of hydatid disease.

(Courtesy: Dr. Ashita Barthur, Sri Jayadeva Institute of Cardiovascular Sciences & Research, Bangalore, India.) Erdheim–Chester disease: A rare non-Langerhans cell histiocytosis characterized by multisystem xanthogranulomatous infiltration [1]. The most common cardiac manifestation of Erdheim–Chester disease is diffuse pericardial infiltration and will manifest on imaging as pericardial thickening with or without an associated pericardial effusion.

Medical Devices in the Pericardium Every radiologist should be aware of the various medical devices that may be placed within or involve the pericardium. As discussed in the preceding

sections, pericardial fluid collections are commonly treated with the use of percutaneous pericardial drainage catheters, which will appear on radiographs and CT as linear radiodense/hyperdense catheters entering and terminating within the pericardium, often surrounding a portion of the heart (Fig. 24.29).

Figure 24.29 Maximal intensity projection sagittal reformat of a contrast-enhanced chest CT demonstrates a radiodense percutaneous catheter

(arrow) entering the anterior pericardial space and traveling superiorly. An additional portion of the catheter can be seen posteriorly behind the left atrium (circled). Another occasionally encountered device is the epicardial pacemaker. Although much less commonly used compared with the traditional transvenous or transcutaneous pacemakers, epicardial pacemakers are an alternative device treatment of arrhythmias in certain patients. Their appearance on lateral chest radiograph is distinct from a transvenous pacemaker device because the leads will follow the epicardial contour, rather than entering the cardiac chambers as in transvenous leads (Fig. 24.30). Similarly epicardial pacing wires can be encountered on imaging postcardiac surgery.

Figure 24.30 Lateral chest radiograph demonstrates an epicardial pacemaker device in the soft tissues of the upper abdomen with multiple leads terminating in the inferior pericardial space. Finally, it is important to be aware of the appearance of surgical material that may be used for repair or reconstruction of the pericardium in cases of trauma

or extensive pericardial surgery. Various patches and meshes may be used for pericardial reconstruction, mostly to prevent the dreaded and potentially fatal complication of cardiac herniation. On noncontrastenhanced chest CT, pericardial patch material is likely to appear hyperdense in a contour surrounding the heart (Fig. 24.31).

Figure 24.31 Axial noncontrast chest CT demonstrates postoperative changes of a right extrapleural pneumonectomy with right pericardial reconstruction using hyperdense surgical mesh material (arrows).

Overall Approach to the Pericardium/Take Home Points

◾ Echocardiography is considered the first-line imaging tool for assessment of suspected pericardial pathology ◾ CT and MRI are useful adjuncts in evaluating pericardial disease, particularly in the characterization of loculated or complex pericardial effusions, constrictive pericarditis, and pericardial masses Detailed functional/physiologic assessment can be performed using CT or MRI and is extremely important for diagnosing many pericardial diseases, including pericardial adhesions, constrictive pericarditis, cardiac tamponade in the appropriate clinical settings

◾

Suggested Readings • E Ünal, M Karcaaltincaba, E Akpinar, OM Ariyurek, The imaging appearances of various pericardial disorders, Insights Imaging 10 (1) (2019) 42.

• J Bogaert, M Francone, Pericardial disease: value of CT and MR imaging, Radiology 267 (2) (2013) 340–356. • SM O’Leary, PL Williams, MP Williams, AJ Edwards, CA Roobottom, GJ Morgan-Hughes, et al., Imaging the pericardium: appearances on ECGgated 64-detector row cardiac computed tomography, Br J Radiol 83 (987) (2010) 194–205. • N Oyama, N Oyama, K Komuro, T Nambu, WJ Manning, K. Miyasaka, Computed tomography and magnetic resonance imaging of the pericardium: anatomy and pathology, Magn Reson Med Sci 3 (3) (2004) 145–152. • LS Broderick, GN Brooks, JE Kuhlman, Anatomic pitfalls of the heart and pericardium, Radiographics 25 (2) (2005) 441–453.

References [1] E Ünal, M Karcaaltincaba, E Akpinar, OM Ariyurek, The imaging appearances of various pericardial disorders, Insights Imaging 10 (1) (2019) 42.

[2] Czum JM, Silas AM, Althoen MC. Evaluation of the pericardium with CT and MR. ISRN Cardiol. 2014;2014:174908. [3] Rajiah P, Cardiac MRI: part 2, pericardial diseases. Am J Roentgenol. 2011;197(4):W621–34. [4] B Xu, SC Harb, AL Klein, Utility of multimodality cardiac imaging in disorders of the pericardium, Echo Res Pract 5 (2) (2018) R37–R48. doi:10.1530/ERP-18-0019. [5] J Vogel-Claussen, ASM Elshafee, J Kirsch, et al., ACR Appropriateness Criteria® dyspnea: suspected cardiac origin, J Am Coll Radiol 14 (5S) (2017 May) S127–S137. Available at: https://acsearch.acr.org/docs/69407/Narrative/ [accessed 30.05.20]. [6] Bogaert J, Francone M. Pericardial disease: value of CT and MR imaging. Radiology. 2013;267(2):340– 56. [7] Peebles CR, Shambrook JS, Harden SP. Pericardial disease-–anatomy and function. Br J Radiol. 2011;84 Spec No 3:S324-337.

[8] O'Leary SM, Williams PL, Williams MP, Edwards AJ, Roobottom CA, Morgan-Hughes GJ, et al. Imaging the pericardium: appearances on ECG-gated 64-detector row cardiac computed tomography. Br J Radiol. 2010;83(987):194–205. [9] Rajiah P. Cardiac MRI: part 2, pericardial diseases. Am J Roentgenol. 2011;197(4):W621–34. [10] Oyama N, Oyama N, Komuro K, Nambu T, Manning WJ, Miyasaka K. Computed tomography and magnetic resonance imaging of the pericardium: anatomy and pathology. Magn Reson Med Sci. 2004;3(3):145–52. [11] Broderick LS, Brooks GN, Kuhlman JE. Anatomic pitfalls of the heart and pericardium. Radiographics. 2005;25(2):441–53.

25

Diseases of Arteries Viky S. Loescher, Michael Steigner

General Concepts The introduction of helical computed tomography with its capability of single breath-hold rapid acquisitions has led to the development of computed tomography angiography (CTA). This produces even higher quality images with better contrast enhancement than conventional CT and has the added advantage of being able to reformat oblique and curved multiplanar reconstructed (MPR) images, maximum intensity projection images, as well as three-dimensional (3D) images. Automated tube current modulation, a technique that now is widely available in all new scanners, should be used in conjunction with automatic tube potential selection. Vascular imaging uses a threshold-based test bolus or bolus-tracking algorithm using a region of interest typically placed in the ascending, proximal descending thoracic aorta or proximal abdominal aorta [1–3]. CTA is a noninvasive method of imaging used to assess any vasculature. When used to assess the aorta and arteries, it is generally performed before and after intravenous injection of iodinated contrast medium. Unenhanced images show calcification in the wall of arterial vessels, depict features of an intramural hematoma (IMH), helps differentiating high density surgical material such as pledgets from pseudoaneurysms, or identifies postoperative hematomas; whereas contrast-enhanced images show flowing blood, degree of stenosis, thrombus, or atheroma within the vessel lumen. Delayed phase images can be obtained to assess for endoleaks, iodine contrast extravasation such as in gastrointestinal bleeding or in post-traumatic or postprocedural settings, or to fully assess for mesenteric ischemia with venous etiology. The use of ECG-gated CTA significantly decreases the effect of cardiac motion in the evaluation of the aortic root and allows for accurate measurements and assessment of the thoracic aorta. The design of vascular imaging protocols is particularly challenging due to the nonuniform velocity of blood, differences

in cardiac outputs, and different effects of underlying conditions on blood flow that many times cannot be predicted before the scan [3]. CTA is commonly used in vascular imaging for the assessment of thoracic and abdominal aortic aneurysms (AAAs) to see if they are suitable for endovascular repair, and in the diagnosis of acute aortic syndrome [3]. CTA is also used-in the investigation of carotid and renal vascular disease. MR angiography (MRA) is also a noninvasive method of imaging the aorta and arteries which can be performed with or without the intravenous injection of a paramagnetic intravascular gadolinium-based contrast agent (GBCA). GBCA shortens blood longitudinal relaxation (T1). 3D spoiled gradient echo (GRE) pulse sequences with a short repetition time and a short echo time are ideal for MRA. 3D GRE T1 pulse sequence provides images with high signal-to-noise ratio and good spatial resolution. Time-resolved MRA is an acquisition mode of postcontrast images over successive time points and has specific vendor acronyms such as TWIST (Siemens, Germany), TRICKS (General Electric, USA), 4-D TRACK (Phillips, Netherlands), or TRAQ (Hitachi, Japan). This sequence is particularly helpful in small arteries such as run offs of feet and hands, as well as the arteries below the knee, or in cases of arteriovenous shunts. The core of this time-resolved sequence is also a 3D-spoiled GRE [3]. A typical MRA protocol includes localizers, coronal, and axial T2-weighted single-shot fast spin echo sequences, which allow a general assessment and planning of the 3D-MRA. The 3D-MRA noncontrast (mask) is acquired followed by two successive arterial phase acquisitions, as well as a delayed T1-weighted 3D spoiled GRE sequence with fat saturation. GBCA is administered to all patients with GFR >30 mL/min, followed by saline chaser. The decision to administer GBCA in patients with a lower GFR should be made on a caseby-case basis. For patients who cannot receive GBCA, a balanced steadystate free precession (SSFP) sequence is used because it provides bright blood imaging without gadolinium. It has been shown that MRA without contrast can detect aortic dissection with high accuracy when compared to MRA with contrast [4]. The associated off-resonance artifact seen on SSFP sequences can be decreased using lower strength magnetic fields (1.5 T). Doppler imaging is one of the principal diagnostic tools for the assessment of arterial diseases. The term Doppler is an eponym after Christian Johann Doppler (1803–1853), the Austrian physicist who first described the Doppler effect. Arterial ultrasound has three basic components, the first component is the standard brightness mode (B-mode) grayscale assessment. The second component uses color Doppler interrogation, allowing assessment of luminal narrowing severity. The third component uses interrogation of a small segment of an arterial vessel, producing the spectral Doppler waveform. Duplex Doppler refers to an ultrasound using the two first components, grayscale and color Doppler. Technically, the use of the three components

should be denominated as “triplex,” however, the inclusion of spectral analysis is also commonly referred as duplex Doppler imaging [5]. Spectral analysis interrogates usually a small 2–4 mm segment of a vessel of interest, ideally the midportion of the lumen, rather than the periphery, for optimal assessment of the laminar flow. The degree of stenosis is obtained by measuring peak systolic velocity (PSV) using spectral analysis. The Doppler angle is the angle between actual Doppler beam and the Doppler interrogation vessel sample, and it should always be less than 60° [5]. Doppler angles greater than 60° affect the accuracy of PSVs, and it could underestimate or overestimate the level of stenosis. There is an inverse relationship between stenosis and velocity, so decrease in sectional area increases velocity of flow if there are no branches. Resistive index is defined as the ratio between the difference of systolic and diastolic velocities and the systolic velocity [6].

Aorta Normal Anatomy of the Aorta Thoracic Aorta The aortic root involves the annulus, sinuses of Valsalva, and the sinotubular junction. The ascending thoracic aorta extends from the sinotubular junction to the origin of the brachiocephalic trunk, and the aortic arch extends from the origin of the brachiocephalic trunk to the ligamentum arteriosum. The aortic isthmus is between the distal aortic arch and the descending thoracic aorta. The proximal descending thoracic aorta always appears more dilated and it is known as the aortic spindle [7,8] (Fig. 25.1).

FIGURE 25.1 Normal anatomy of the thoracic aorta. The aortic root is composed of the annulus, sinuses of Valsalva (SV) and sinotubular junction (STJ). The ascending aorta extends from the level of the STJ to the origin of the brachiocephalic trunk. The aortic arch extends from right after the origin of the brachiocephalic trunk to the last aortic arch branch (between dashed lines). The descending thoracic aorta extends from right after the takeoff of the last branch of the aortic arch to the level of the diaphragmatic hiatus. The aortic spindle is a normal bulge of the proximal descending thoracic aorta.

The three-vessel aortic arch consists of the brachiocephalic trunk (innominate artery), the left common carotid artery, and left subclavian artery; this is the most common branching pattern of the aortic arch and is seen in about 70% of patients. The combined origin of the brachiocephalic trunk and the left common carotid artery is seen in about 20–30% of patients. This is the so-called “bovine” aortic arch, a misnomer since the bovine aortic arch shows a single trunk with common origin of the great vessels. The vertebral arteries usually arise from the subclavian arteries.

When the left vertebral artery instead arises directly from the aortic arch, it is called a four-vessel aortic arch and it is seen in about 5–10% of patients [9]. The most common aortic arch anomaly is a left aortic arch with aberrant right subclavian artery arising directly from the aortic arch. The aberrant right subclavian is the last vessel arising from the arch and shows a retroesophageal course, but not forming a vascular ring (Fig. 25.2). Another variant of the aortic arch is the ductus diverticulum, a small bulging along the inner aspect of the aortic isthmus representing an embryological remnant of the ductus arteriosum and should not be mistaken with an aneurysm or pseudoaneurysm [8] (Fig. 25.3).

FIGURE 25.2 Left aortic arch and aberrant right subclavian artery. The right subclavian artery (red arrow) arises directly from the aortic arch and courses posteriorly to the esophagus and is associated with dysphagia lusoria.

FIGURE 25.3 Aortic diverticulum. (A and B) CTA three-dimensional (3D) and oblique multiplanar reconstructed (MPR) images show a protrusion along the inner aspect of the isthmus with smooth contours (black arrows).

(Courtesy: Sandeep Hedgire, MD from Massachusetts General Hospital, Boston, USA.)

There are four major aortic arch types; left aortic arch, right aortic arch, double aortic arch, and cervical aortic arch [9,10]. With a right aortic arch, the most common anomalies include: 1. Retroesophageal aberrant left subclavian artery with diverticulum of Kommerell, which is associated with the presence of a left ductus or ligamentum forming the second most common vascular ring [9]. 2. Mirror image right aortic arch, which refers to the fact that the origin of the great vessels follows the opposite order of the left aortic arch. This type of aortic arch is also associated with other cardiac congenital abnormalities. 3. Double aortic arch refers to the persistence of both the left and right embryologic fourth arches forming the most common vascular ring. In the majority of cases, the right arch is superior and larger than the left (dominant right arch). The role of vascular imaging is to identify which arch is nondominant so it can be surgically ligated to relieve the vascular ring [9]. 4. The cervical aortic arch is a rare anomaly characterized by a high-lying aortic arch extending above the level of the clavicles [11] (Fig. 25.4).

FIGURE 25.4 Cervical aortic arch. CTA sagittal oblique multiplanar reconstructed (MPR) image shows the aortic arch (red arrow) extending above the head of the clavicle (yellow arrow).

The Abdominal Aorta The proximal abdominal aorta extends from the crura to the origin of the celiac artery. The renal arteries are used as a landmark to help recognize the suprarenal, juxtarenal, and infrarenal abdominal aorta. The infrarenal abdominal aorta extends to the level of the L4 vertebral body where it bifurcates into the bilateral common iliac arteries [2].

Aortic Diseases Aortic disease presentation ranges from asymptomatic (aneurysms or penetrating atherosclerotic ulcers [PAUs] incidentally detected on MDCT) to acute chest pain (IMHs, dissections, trauma, ruptures, etc.), as well as inflammatory and traumatic disorders [7]. Currently, there are 64-detector row and newer generation CT scanners that can evaluate the entire aorta in a single short breath hold. MDCT permits the evaluation of the entire aorta with 3D reconstructions in any orientation using MPR. Moreover, when compared with regular invasive angiography, MDCT allows the evaluation of extravascular structures using less radiation, as well as decreasing the

radiation exposure of the patient and the operator. The use of ECG gating should also be encouraged for the evaluation of the aortic root and ascending thoracic aorta, as cardiac motion could result in significant artifact decreasing the accuracy of aortic dimensions or mimicking dissections or pseudoaneurysms.

Aneurysms The normal dimensions of the thoracic and abdominal aorta have been established based on large population studies [7–10]. An aneurysm is defined as a dimension exceeding the normal measurement by more than 2 SDs, or greater than the 95% confidence interval (Table 25.1). Table 25.1 Maximum Normal Dimensions for the Aorta and Aneurysmal Size by Segments [2,8] Maximum Normal Dimensionsof the Aneurysmal Dimensions of the Aorta Aorta Segment

Size (mm)

Size (mm)

Sinuses of Valsalva

36.9 ± 3.8 (2 SD)

≥40

Sinotubular junction

29.7 ± 3.4 (2 SD)

≥35

Ascending thoracic aorta

32.7 ± 3.8 (2 SD)

≥40

Aortic arch Descending thoracic aorta

≥35 17–26 (95% CI)

≥35

Proximal abdominal aorta

≥30

Infrarenal abdominal aorta

≥30

CI, confidence of interval; SD, standard deviation. These are reference maximum dimensions that are used in common imaging practice. A new more individual approach is currently recommended, and maximum dimensions that trigger treatment currently vary according to the age, gender, body surface area, and other risk factors, as recently reviewed by the last

American Association of Thoracic Surgery consensus guidelines [66]. These thresholds may vary across institutions.

The prevalence of thoracic aneurysms increases with age, with an incidence of approximately 450 per 100,000 and a 3:1 male predominance. In aneurysms, all three layers of the vessel wall (intima, media, and adventitia) are involved. Aneurysms can be fusiform involving all of the circumference of the vessel (Fig. 25.5) or saccular with a narrow neck. Overall, atherosclerosis is the most common cause of aneurysms of the aorta. While cystic medial necrosis (e.g., Marfan, Ehler–Danlos, and Loeys– Dietz syndromes) is the major cause of aortic aneurysms involving the aortic root and the ascending aorta, causing effacement of the sinotubular junction and resulting in a classic tulip bulb appearance (Fig. 25.6). Aortic root aneurysms are also associated with bicuspid aortic valves and familial thoracic aortic aneurysm syndrome.

FIGURE 25.5 Fusiform aneurysmal dilation of the ascending thoracic aorta. (A) Three-dimensional (3D) and (B) oblique multiplanar reconstructed (MPR) images depicting fusiform aneurysmal dilation of the ascending thoracic aorta. Pink line shows level of the measurement, orthogonal to the aorta at the level of maximum dimension.

FIGURE 25.6 Classic tulip bulb aortic root appearance. MRA 3D of the thoracic aorta on a patient with Marfan’s syndrome shows aneurysmal dilation at the level of the sinuses of Valsalva with effacement of the sinotubular junction.

When a saccular aneurysm shows a wide neck and is present in the aortic root or ascending thoracic aorta, it is suggestive of a mycotic aneurysm due to the proximity to regions affected by endocarditis. Common associated factors are intravascular intervention, intravenous drug abuse, Staphylococcus, and Salmonella infections. Syphilitic aortitis shows a characteristic increased wall thickness thought to be related to neutrophilic infiltration of the arterial wall, which at the same time triggers enzyme pathways leading to the breakdown of the saccular dilation (Fig. 25.7). Paradoxically, this leads to very large aneurysms that typically do not rupture but can have mass effect on adjacent structures.

FIGURE 25.7 Syphilitic aortitis. (A and B) Oblique multiplanar reconstructed (MPR) and three-dimensional (3D) images show tertiary syphilis in a patient from a developing country who had never sought medical care in his entire life who presented with dyspnea on exertion. The cause is compression of the main pulmonary artery from the massive aortic aneurysm (blue arrow). (A and C) Oblique MPR and axial images depict the wall thickening as a hallmark of the disease (blue arrow).

AAA is rare before the age of 50 years old, can be seen in about 3.5% of European men population older than 65 years old, and most commonly involves the infrarenal abdominal aorta. The current prevalence in the United States is unclear due to the low rate of AAA screening. Nevertheless, the prevalence of AAA has decreased over the last two decades and this is believed to be related to the overall decreased of associated smoking. AAA can be assessed with ultrasound (Fig. 25.8), CTA, or MRA. The 2019 update of US Preventive Services Task Force (USPSTF) recommends:

◾(BOnerecommendation) time ultrasound screening for AAA in men aged 65–75 years who have ever smoked ◾screening For men aged 55–75 years who have never smoked, the USPSTF recommends selective in a case-by-case basis with relevant medical or family history, other risk factors, and personal values (C recommendation) ◾smoked The USPSTF also recommends against routine screening in women who have never and no family history of AAA (D recommendation) ◾women Also concludes that the evidence is insufficient to assess the benefits of screening in aged 65–75 years who have ever smoked or have a family history of AAA (I recommendation) [12]

FIGURE 25.8 Fusiform aneurysmal dilation of an infrarenal abdominal aorta. (A) Grayscale ultrasound and (B) color Doppler imaging, and (C) axial CTA show a 5.0 × 4.8 cm infrarenal abdominal aortic aneurysm, associated with a near circumferential intraluminal thrombus.

Crawford and DeNatale classified thoracoabdominal aneurysm in four types:

◾ Type I involves from the proximal descending thoracic aorta to the hiatus ◾ Type II involves the descending thoracic aorta and most of the abdominal aorta ◾ III only the distal descending thoracic aorta ◾ Type Type IV the majority of the abdominal aorta from the hiatus to its bifurcation

Another definition to indicate aneurysmal arterial dilation below the abdominal aorta is greater than half of the aneurysmal dilation on the level above. For example, an aneurysmal dilation of the common iliac arteries will be greater than 15 mm, given that the level above maximum dimension is 30 mm for the infrarenal abdominal aorta.

Pseudoaneurysm Pseudoaneurysms usually show disruption of one (intima) or two (intima and media) of the three layers of the vessel, while the blood is contained by the adventitia and periadventitial tissues. In situations of trauma such as motor vehicle accidents, the most common location for a pseudoaneurysm in the isthmus, given that it is the location with most survival after deceleration accidents. In the postoperative setting, pseudoaneurysms are seen at the level of the graft anastomosis with the native aorta (Fig. 25.9). Features that can help differentiate a pseudoaneurysm from a true aneurysm are depicted in Table 25.2.

FIGURE 25.9 Pseudoaneurysm. A saccular pseudoaneurysm at the proximal anastomotic site between an aortic graft and the native thoracic aorta. Patient had a repair of a type A IMH 5 years before this CT. (A-C) These images depict a fluid collection (green arrows) surrounding the graft with hyperdense components on the noncontrast CT (left). There is an associated pseudoaneurysm (red arrows) adjacent to the surgical material (yellow arrows) of the proximal anastomosis.

Table 25.2 Pseudoaneurysm Versus Aneurysm [8] Pseudoaneurysm

Aneurysm

Vessel wall layer

One or two layers involved

Three layers are intact

Etiology

Trauma, infection

Intrinsic

Shape

Saccular

Fusiform

Margins

Lobulated

Smooth

Rupture

Higher risk of rupture than aneurysms

Risk increases with size

Aortoenteric and Aortocaval Fistulas Aortoenteric fistulas can occur in patients that present with hematemesis, melena, sepsis, and pain, but sometimes patients can also be asymptomatic. Aortoenteric fistulas maybe primary or secondary. Primary fistulas are rare and almost always occur in the setting of a pre-existing aortic disease such as a PAU or aneurysm with different etiologies including syphilis, tuberculosis, mycotic infections, or connective tissue disease. Secondary fistulas are also rare and are related to early or late postprocedural complications with or without a stent graft. About 80% of this complication

occur at the third or fourth portion of the duodenum, followed by the esophagus, gastroesophageal junction. Secondary fistulas could be related to the combination of chronic low-grade infection of the aortic graft and repetitive pressure on the bowel from aortic pulsations [13]. The presence of soft tissue edema, fluid and ectopic gas adjacent to or within the aorta, is also expected findings in the immediate postoperative setting, but abnormal 3–4 weeks after. Any ectopic gas 2 or 3 months after the procedure, should raise the suspicion of infection with or without a fistula. CTA plays an important role identifying this entity [14], and the key finding is either extravasation of contrast from the aorta to the bowel lumen, or leakage of oral contrast from the bowel lumen to the aortic wall or para-prosthetic space [13]. Aortocaval fistula is a very rare complications of AAA and it is associated with a high mortality rate. It can present with abdominal pain, bilateral pedal edema, renal insufficiency, heart failure when it is a chronic fistula, and hemodynamically instability. It consists of an abnormal communication between an aortic aneurysm and the inferior vena cava (left to right arteriovenous shunt), most commonly between the posterolateral aortic wall and the adjacent IVC. CTA shows an early filling of a dilated inferior vena cava during arterial phase imaging. Aortocaval fistulas have to be treated emergently with open surgical repair and patch angioplasty of the inferior vena cava and endovascular repair of the aorta [15,16].

Acute Aortic Syndrome Acute aortic syndrome is a spectrum of emergencies that include PAUs, IMH, dissection, aneurysm rupture, and traumatic transection. The imaging features of aortic disease spectrum are depicted in Table 25.3 and Graph 25.1. Table 25.3 Imaging Features of Acute Aortic Disease [8,18] Disease Noncontrast Imaging Penetrati ng atheroscl erotic ulcer

Atheromatous plaque ulcerates the deepest layer of the intima known as the internal elastic lamina and displaces calcified plaque forming an outpouching beyond the contours of the aorta

Postcontrast CTA Localized outpouching beyond the contours of the aorta with intraluminal enhancement

Disease

Noncontrast Imaging

Postcontrast CTA

Intramur al hemato ma

Hyperdense crescent-shaped due to rupture of the vasa vasorum that feeds the media

Smooth crescentic thickening along its course without enhancement or identifiable flap Intramural blood pool (IBP) and ulcer like projections (ULP) are associated findings. ULP is a high-risk feature

Dissecti on

Central displacement of intimal calcification

Intimomedial flap which separates the true and false lumen

Impendi ng rupture

Periaortic fat stranding Displaced peripheral calcifications of the aortic wall Draped aorta sign

Irregular aortic lumen with disruption of the aortic wall Draped aorta sign Displacement of mural calcifications Surrounding fat stranding

Transecti on

Hemopericardium, hemothorax, mediastinal hematomas in 75% of cases. Retroperitoneal hematoma

Extraluminal contrast It happens most commonly at three locations, aortic root, isthmus, and diaphragmatic hiatus

Disease Rupture

Noncontrast Imaging Hemopericardium, hemothorax, mediastinal hematomas in 75% of cases. Retroperitoneal hematoma

Postcontrast CTA Irregular aortic wall, active extravasation of contrast Contained ruptures will not show active extravasation

GRAPH 25.1 Spectrum of arterial disease. Aggressive PAU can progress to IMH or dissections. F, false lumen; gray, adventitia layer; IMH, intramural hematoma; PAU, penetrating atherosclerotic ulcer; pink, blood pool; red, medial layer; red with white dots, vasa vasorum; T, true lumen; yellow, intimal layer.

Aortic Dissection The incidence of acute aortic dissection is 2.9 per 100,000 persons per year. The risk factors include pre-existing aneurysm, hypertension, bicuspid aortic valve, Marfan syndrome, and prior cardiovascular rupture. A typical dissection will show an entrance and exit tear between the intima and the inner layer of the media, forming the intimomedial flap which separates the true and false lumen. The blood in the false lumen is usually lateral, larger, may be free flowing or thrombosed, and usually feeds the left renal artery (Table 25.4). There are different types of complex dissection flaps; for example, when there is diffuse involvement of the entire intima, there will be a circumferential intimal flap with a narrow and filiform circumferential true

lumen that can result in intimointimal intussusception and a “windsock” appearance. There is also a three channel dissection flap that is known as the Mercedes-Benz sign, which occurs when there is a secondary dissection within one of the lumens resulting in a three channel appearance [17]. Table 25.4 Typical Features of True Versus False Lumen in Aortic Dissection [7,17] True Lumen False Lumen Medial lumen

Lateral lumen

Smaller size

Larger size

Better opacified on early arterial phase with washout on delayed phases

Poor opacification on early arterial phase or thrombosed with persistent enhancement on delayed phases

It may collapse

It often dilates

Usually, supplies flow to the coronaries, celiac trunk, superior mesenteric artery, and right renal artery

Usually, supplies the left renal artery

“Cobweb sign” is described as slender linear areas that represent strands of media that have incompletely sheared away during when the dissection occurred “Beak sign” is described as a wedge of hematoma and it is thought to create space for the propagation of the false lumen

The classification of aortic dissections is based on the location of the aortic dissection, and the most common systems are DeBakey and Stanford.

◾ Type I DeBakey, the dissection involves the ascending and descending thoracic aorta ◾ II DeBakey, the dissection involves the ascending aorta only ◾ Type Type III DeBakey, the dissection is limited to the descending thoracic aorta

In Stanford type A, the aortic dissections involve the ascending thoracic aorta with or without extension to the descending thoracic aorta (Fig. 25.10);

in Stanford type B, the dissection involves the descending thoracic aorta only (Fig. 25.11) [18].

FIGURE 25.10 Type A Stanford aortic dissection. (A–C) CTA axial views show a dissection flap originating at the level of the sinuses of Valsalva and extending to the descending thoracic aorta (center), consistent with type A dissection. There is sparing of the origin of the coronary arteries (left main not shown but also spared). asterisk, true lumen; double asterisk, false lumen.

FIGURE 25.11 Type B Stanford aortic dissection. CTA multiplanar reconstructed (MPR) images show a dissection flap extending from the proximal descending thoracic aorta until just above the level of the origin of the celiac trunk. There is an associated aneurysmal dilation of the proximal descending thoracic aorta measuring up to 5.5 cm. Red line depicts the area of maximum dimension of the aneurysm, asterisk shows the true lumen and double asterisk shows the false lumen.

A complicated thoracic aortic dissection can be lethal due to acute aortic regurgitation, major aortic branch obstruction, pericardial tamponade, or aortic rupture. Approximately 75% of aortic ruptures result in hemopericardium, hemothorax, and mediastinal hematomas. A case of aortic rupture also shows irregular aortic wall accompanied by active extravasation of contrast (Fig. 25.12). Contained ruptures do not show active contrast extravasation [17].

FIGURE 25.12 Aortic rupture. Axial CT noncontrast images show rupture of the descending thoracic aorta. There is marked aneurysmal dilation of the descending thoracic aorta with discontinuation of the peripheral calcifications (bidirectional yellow arrow) and periaortic hematoma (red asterisk). There is also associated mediastinal hematoma (red arrows) and hemothorax (curved yellow arrow).

Whereas impending rupture signs include irregular aortic lumen with disruption of the aortic wall and displaced peripheral calcifications, periaortic fat stranding changes, and draped aorta sign. The draped aorta sign is the disruption of the posterior aortic wall following the contours of an adjacent vertebral body (Fig. 25.13).

FIGURE 25.13 Progression of impending rupture of the aorta. CTA axial shows (A) an infrarenal abdominal aortic aneurysm (AAA) associated with near circumferential intraluminal thrombus (asterisk), which is known to increase the risk of aortic rupture due to wall destabilization. Short-term CTA follow-up shows (B) interval development of surrounding moderate fat stranding changes (red arrows) consistent with impending AAA rupture.

Penetrating Aortic Ulcer Penetrating atherosclerotic ulcer or penetrating aortic ulcer (PAU) are two terms that are interchangeable. In PAU, an atheromatous plaque ulcerates the deepest layer of the intima, known as the internal elastic lamina, and displaces calcified plaque forming an outpouching, or also known as a collar-button, beyond the contours of the aorta. A PAU also shows a variable extension to the media. When an atherosclerotic plaque penetrates into the media, the hemorrhage of the media will lead to either an IMH, localized aortic dissection, saccular pseudoaneurysm, or mediastinal hematoma. PAUs are often multifocal and most common in the descending thoracic aorta. It can be distinguished from an atheromatous plaque by the presence of a focal, contrast filled outpouching surrounded by an IMH, which is also consistent with aggressive behavior of a PAU. A PAU can be differentiated from a pseudoaneurysm by its more frequent association with atherosclerotic plaque, its more common location in the descending thoracic aorta, involvement of the internal elastica media and its more frequent association with IMH (Table 25.5). Table 25.5

Differences Between PAU and Pseudoaneurysm [7,8] PAU Pseudoaneurysm Atheroscl erosis

Very common

Incidental

Location

Most common in the descending thoracic aorta

Most common in the arch, then descending, ascending, and abdominal aorta

Penetrate s

Internal elastic lamina (deepest layer) of the media layer

External elastic media of the media layer

Neck

Variable

Narrow

IMH

Aggressive PAU are associated with IMH

Less common

IMH, intramural hematoma; PAU, penetrating atherosclerotic ulcer.

Intramural Hematoma An IMH is related to the spontaneous rupture of the aortic vasa vasorum of the medial aortic layer, and it is also understood as a hemorrhage localized to the aortic media in the absence of an intimal tear. A typical IMH is identified with a hyperdense crescentic thickening seen better in an unenhanced CT. IMH is differentiated from a thrombosed false lumen, because it does not enhance, lacks an intimal tear, as well as its constant shape along its course; whereas the false lumen of a dissection has a longitudinal spiral configuration; however, these two can be challenging to distinguish. Intramural blood pool is described as a benign finding that can regress overtime in the setting of underlying IMH; it shows a small pool of contrast within the IMH that communicates with the aortic lumen through a tiny intimal orifice, and also connects to an intercostal or lumbar arterial branch [19]. The more appropriate term is branch artery pseudoaneurysm, which refers to the dilation of the origin of the injured branch artery. When an IMH occurs, and the origin of the branch artery is sheared off. A hole is left between the aortic lumen and the thrombosed IMH, so blood flows into the pseudoaneurysm and finally into the branch artery [20]. On some occasions, there can be progressive branch artery tears accompanied by hemodynamic instability. The appearance of multiple branch artery pseudoaneurysm has been described as the Chinese sword sign, because of the resemblance of the pooling of contrast and branch artery pseudoaneurysms with the rings of this sword [21] (Fig. 25.14).

FIGURE 25.14 Chinese ring sword sign. (A) 3D CTA shows multilevel branch artery pseudoaneurysms of the intercostal arteries (depicted in red) in a patient with known intramural hematoma (IMH). This appearance is known as the Chinese sword sign due to the resemblance of the branch artery pseudoaneurysms with the rings of this sword. (B) The blade of the sword represents the thoracic aorta.

An ulcer like projection is morphologically distinct from an intramural blood pool and it has been associated with poor prognosis. An ulcer like projection is a pool of contrast protruding into the IMH and with a wider intimal disruption and no connection with any arterial branch [19] (Fig. 25.15).

FIGURE 25.15 Associated findings of intramural hematomas (IMH). CTA of the aorta showing associated findings in intramural hematomas. (A) Intramural blood pool (IBP), a benign finding that communicates with the aortic lumen through a tiny intimal orifice (blue arrow) and is accompanied by a branch artery (intercostal artery depicted by red arrow). (B) Noncontrast image showing the crescentic rim of hyperdensity (red arrow). (C) Ulcer like projection (ULP) shows a wide intimal disruption adjacent to the aortic lumen (yellow arrow) and no communication with adjacent arteries. ULP indicates a high risk feature when measured more than 10 mm.

Minimal aortic injury (MAI) is defined as a subcentimeter intimomedial abnormality, which could be a tear or a thrombus, and without any wall contour deformity. This usually involves the isthmus (60–72%), aortic root (3–14%), ascending aorta (8–27%), aortic arch (8–18%), distal descending thoracic aorta (11–21%), and abdominal aorta (7–22%). The most common imaging findings of MAI includes a subcentimeter rounded or triangular intraluminal filling defect, or a thin focal intimal flap. A subcentimeter IMH is also included as part of a MAI. The importance of recognizing the imaging features of MAI is based on the conservative approach of these aortic injuries, with the majority of them resolving in a period of 4–8 weeks short-term imaging follow-up [22]. On the other hand, a significant aortic injury is defined as the presence of aortic contour abnormality and includes an IMH with contour alteration, pseudoaneurysms, and aortic rupture [22]. Traumatic significant aortic injury can also occur at the aortic root, isthmus, and hiatus (Figs. 25.16–25.18).

FIGURE 25.16 Traumatic significant aortic injury at the aortic annulus after a motor vehicle accident. (A) Digital subtraction angiogram (DSA) shows significant aortic injury (SAI) associated with extravasation of contrast (black arrows) consistent with rupture at the level of the aortic annulus. (B and C) CTA shows extension of SAI throughout the ascending (red arrow) and descending thoracic aorta (yellow arrow), and associated hemopericardium (asterisk) and hemothorax (double asterisk) with mixed hyperdense products.

FIGURE 25.17 Traumatic significant aortic injury at the isthmus. (A) CTA shows intimal flap greater than 1 cm associated with contour disruption of the isthmus. (B) 3D reconstructions showing interval repair with placement of a stent graft extending from the distal aortic arch to the proximal descending thoracic aorta.

FIGURE 25.18 Traumatic significant aortic injury at the hiatus. (A) 3D global illumination rendering (GIR) and (B and C) CTA multiplanar reformats (MPR) show significant aortic injury with an intimal flap greater than 1 cm associated with contour abnormality.

Important pseudoaneurysm-mimics to recognize in the isthmus are the aortic diverticulum, spindle, and branch vascular infundibulum. The aortic diverticulum has smooth contours and is present in the inner contour of the isthmus and may or may not show associated calcifications, depicting the embryological remnant at the point of the ligamentum arteriosum. The aortic spindle is the normal mild “dilation” of the proximal descending thoracic aorta. The aortic infundibulum refers to the area of origin of the branches of the thoracic aorta (e.g., intercostal, bronchial, or spinal arteries), which could look more prominent and be mistaken for a small pseudoaneurysm [7,22]. Traumatic Aortic Transection A traumatic aortic transection is a tear involving the three layers of the aortic wall, usually by rapid deceleration and osseous pinching at the aortic root (4%), the arch or isthmus (95%), and the diaphragmatic hiatus (1%). The mortality rate of aortic transections is very high and most of the time, only patients with injury at the isthmus make it to the hospital [8]. Of the 10–20% of patients who arrive to the hospital, most will survive (60–80%). Management Criteria for management of the thoracic and abdominal aorta are depicted in Table 25.6. Table 25.6 Intervention Criteria for Aortic Aneurysms [2,7,8]

Aortic Segment

Aneurysm Intervention Criteria al Size

Aortic root or ascendi ng thoracic aorta

>4.0 cm

Aortic arch or descend ing thoracic aorta

>3.5 cm

Infraren al abdomi nal aorta

>3.0 cm

≥5.5 cm, symptomaticor growing >0.5 cm/yearConnective tissue disorders: ≥4.0–5.0 cm, symptomaticor growing >0.3 cm/yearBicuspid aortic valve: ≥ 5.0 cmor growing >0.5 cm/year

≥5.5 cm, symptomatic or growing >1.0 cm/year

Management of aneurysmal dilation of the ascending thoracic aorta or acute aortic syndrome (e.g., dissection or IMH) most commonly involves open surgical repair. Intervention of the aortic aneurysm depends on its size and risk of rupture, given that an aneurysmal size of the thoracic aorta greater than 6.0 cm is associated with up to 15% per year increased risk of dissection, rupture, or death. A size of 6.0 cm for the abdomen is associated with risk of rupture of up 20% and a size equal or greater than 8.0 cm is associated with a risk of rupture of 30–50% [1,23,24]. Generally, elective surgery is performed with a diameter equal to or greater than 5.5 cm [25]. Earlier surgical repair can be performed in patients with connective tissue disorders with maximum dimension in the 4–5 cm range or bicuspid aortic valves with a maximum dimension of 5.0 cm. Aneurysms that grow in a rate of greater than 0.5 cm per year or symptomatic patients, also merit earlier intervention. Most common surgical techniques to repair the ascending thoracic aorta include placement of a supracoronary ascending aortic graft, which could be done with aortic valve replacement (Wheat procedure), or without it (David valve-sparing procedure). The ascending aortic graft could be synthetic (Bentall and Cabrol procedures) or biologic (Ross procedure which uses pulmonary valve homograft, or cadaveric grafts). The surgical intervention can also include repair of the aortic arch (elephant trunk and arch first procedures). In general, the diseased native aorta is excised, and a

synthetic or biologic graft is placed. The graft is then reanastomosed with the native structures using felt pledgets, which are hyperattenuating, and in postcontrast images could be mistaken for a pseudoaneurysm. The addition of noncontrast phase images help identify the synthetic grafts and felt pledgets and becomes crucial in the assessment of postoperative changes [3,23,24] (Fig. 25.19).

FIGURE 25.19 Mimic of pseudoaneurysm in the postoperative setting. (A) The felt material used for the aortic graft mimics a pseudoaneurysm (red arrow) in the postcontrast axial images. (B) The noncontrast axial images help identifying the felt material.

Management of aneurysmal dilation of the descending thoracic aorta without complications mainly involves medical therapy with the main objective to control high blood pressure [8,26]. Endoluminal stent graft placement is preferred over surgical repair of the descending thoracic aorta and is generally indicated in complicated type B aortic dissection with progression of the dissection flap or associated aneurysmal dilation, intractable pain, and failure to control hypertension [8,26]. Endoluminal stent graft is also the main treatment for enlarging PAUs in the descending thoracic aorta (Fig. 25.20), and aneurysmal dilations of the abdominal aorta [27]. There are different types of abdominal aortic stent grafts; some of the approved and commonly used devices are depicted by Eliason and Upchurch [27] (Fig. 25.21).

FIGURE 25.20 Penetrating atherosclerotic ulcer repair. Penetrating atherosclerotic ulcer before (A & C) and after (B & D) repair. CTA oblique multiplanar reconstructed (MPR) and contrast-enhanced CTA images show a penetrating atherosclerotic ulcer (PAU) in the descending thoracic aorta (red arrows) measuring approximately 2.4 cm in length, and changes after endovascular repair with interval placement of a stent graft (B & D).

FIGURE 25.21 Types of abdominal aortic stent grafts. FDA-approved and currently marketed stent graft devices including (A) Medtronic, (B) Gore, (C) Cook, and (D) Endologix. An endologic stent graft has the metallic cover inside, which is important to recognize given that the normal blood flowing between the metallic and nonmetallic components can mimic an endoleak.

(Reprinted with permission from: JL Eliason, GR Upchurch Jr, Endovascular abdominal aortic aneurysm repair, Circulation 117 (13) (2008) 1738–1744.)

Endoleak is defined as persistent blood flow within the excluded aneurysm sac following endovascular aneurysm repair with placement of an endoluminal stent graft. Endoleaks are seen in 20–40% of the cases, and some of them are expected due to the presence of pre-existing branch vessels such as bronchial, thoracic, lumbar branches, or inferior mesenteric artery (IMA). There are five types of endoleaks:

◾ Type I at the proximal (Ia) or distal (Ib) graft attachment site (Fig. 25.22) ◾ Type II is an enlarging aneurysmal sac associated with a collateral vessel (Fig. 25.23) ◾ Type III is an endoleak through a defect in the graft or the graft components (Fig. 25.24) ◾ IV endoleak through the graft porosity ◾ Type Type V endotension endoleak refers to the continued expansion of the aneurysm without an identifiable endoleak

FIGURE 25.22 Type 1a endoleak. CTA oblique axial MPR images in this patient with history of prior stent graft placement for thoracic aortic aneurysm show a large amount of contrast within the aneurysmal sac which is not excluded by the proximal aspect of the stent-graft (red arrows) consistent with a type 1a endoleak.

FIGURE 25.23 Type 2 endoleak. CTA axial maximum intensity projection (MIP) images in this patient with history of prior stent graft placement for abdominal aortic aneurysm show a moderate amount of contrast within the excluded aneurysmal sac extending from the lumbar artery (red arrow), consistent with a type 2 endoleak.

FIGURE 25.24 Type 3 endoleak. CTA axial images in this patient with history of prior stent graft placement for abdominal aortic aneurysm show a large amount of contrast within the excluded aneurysmal sac extending from the graft defect (red arrow) consistent with a type 3 endoleak.

Type I and III endoleaks are considered emergent and usually treated with the addition of endovascular grafts or balloon re-expansion, while type II endoleaks are usually followed with imaging to ensure no continuous expansion of the excluded aneurysmal sac, but if found, then treated via percutaneously embolization techniques (Table 25.7). Table 25.7 Endoleak Types [2,7] Typ Inadequate sealing at the proximal (type 1a) or distal (type 1b) seal of e 1* the graft

Typ Inadequate sealing at the proximal (type 1a) or distal (type 1b) seal of e 1* the graft T y p e 2 * *

Associated with a collateral feeding and outflow artery, typically lumbar arteries, IMA, or bronchial arteries

T y p e 3 *

Inadequate seal of the graft components, it is a mechanical failure of the graft

T y p e 4

Leak through graft porosity

T y p e 5

Idiopathic, described as endotension because excluded sac continues to enlarge without identifiable source for the leak

IMA, inferior mesenteric artery; *, considered emergencies and grant a call to the surgical team; **, most common Endoleak type treated conservatively and it usually resolves spontaneously.

Vasculitis Vasculitides can be primary (idiopathic) or secondary. Primary vasculitis includes large-vessel vasculitis such as giant cell arteritis (GCA) or Takayasu arteritis (TA), and medium sized vessels such as Kawasaki disease (KD), polyarteritis nodosa (PAN), primary CNS angiitis, and thromboangiitis obliterans (Buerger’s disease). Secondary vasculitis includes processes secondary to infections, inflammatory changes related to treatment response such as radiation, or other diseases like sarcoidosis, IgG4 vasculitis, Wegener’s granulomatosis, Behcet disease, rheumatoid arthritis,

ankylosing spondylitis, systemic lupus erythematosus, Cogan syndrome, or mimicking conditions such as neoplasias. Whereas GCA and TA have similar pathology mechanisms involving Tcells, macrophages and antigen-presenting cells; other vasculitides involve autoantibodies [28]. GCA and TA have imaging similarities, and some of the differences are depicted in Table 25.8. Table 25.8 Giant Cell Arteritis Versus Takayasu Arteritis [28,29] Giant Cell Arteritis Takayasu Arteritis Age

Elderly

Young ( Men

Women >>> Men

Vessels involved

Aorta (65%)

Aorta (95%)

Branches

Branches

Temporal arteries

Pulmonary artery (less common)

Giant Cell Arteritis GCA is characterized by granulomatous infiltration in the wall of large and medium size arteries. The classical presentation is a patient (F > M) older than 50 years old of Scandinavian decent, who presents with a headache, claudication of the tongue or jaw upon swallowing, abrupt visual disturbances, and/or claudication of the upper extremities, asymmetric blood pressures, elevated inflammatory markers and abnormal temporal artery pulsation. Sometimes, in the absence of all these features, only constitutional symptoms may be present. The gold standard diagnostic test is a temporal artery biopsy, although this can be falsely negative in a third of the patients. Color Doppler ultrasound is a noninvasive technique to assess the temporal artery, and it has been proposed by some to replace invasive biopsy. GCA is most of the time associated with long, skip areas of stenosis and dilation, segmented lesions with increased wall thickness. The increased edema and inflammatory extent can be assessed using MRA and 18F-FDG PET [29] (Fig. 25.25).

FIGURE 25.25 Giant cell arteritis. (A) Contrast-enhanced T1-GRE with fat saturation depicts diffuse transmural enhancement of the aortic wall. (B) Note correspondingly increased 18F-FDG uptake on threedimensional maximum intensity projection (3D MIP) image throughout the thoracic aorta (red arrow), abdominal aorta (yellow arrow), and bilateral subclavian arteries (blue arrows) with a standardized uptake value (SUV) of 6.5, which confirms long-segment inflammation of the aorta.

The most important sequence in the MRA protocol is the postcontrast T1weighted 3D spoiled GRE sequence with a fat saturation. This is acquired in a single breath hold with excellent spatial and contrast resolution. Traditionally, T1 double inversion recovery (DIR) has been used to image the aortic wall. DIR involves two successive 180 radiofrequency inversion pulses to null signal from moving blood and preserve the signal of nonmoving structures such as the aortic wall. DIR is excellent to depict aortic wall increased thickness and enhancement. Disadvantages of using DIR are incomplete nulling of the lumen, inconsistent tissue weighting, thick slices (8 mm), and excessive scan time since each slice requires a breath hold which adds considerable amount of time to the study, approximately 20–30 minutes. Takayasu Arteritis TA presents primarily in women between 10 and 40 years old with Asian background, low-grade fevers, fatigue, weight loss. TA progresses to a diverse variety of symptoms according to the arterial involvement, such as upper extremity claudication, decreased pulses and asymmetric blood pressures due to involvement of the subclavian arteries, secondary hypertension due to involvement of the renal arteries, gastrointestinal symptoms due to involvement of the mesenteric arteries, chest pain and dyspnea due to involvement of the pulmonary arteries, as well as neurologic symptoms due to involvement of the carotid and vertebral arteries. TA typically involves the left subclavian artery and progresses to involve the aorta in half of the patients (Fig. 25.26). The pulmonary artery can also be involved, but is less common than the aorta (Fig. 25.27).

FIGURE 25.26 Takayasu’s arteritis. Maximum intensity projection (MIP) image from an MRA showing long segment smooth stenosis of the juxtarenal abdominal aorta (red arrow) and both common iliac arteries (yellow arrows).

FIGURE 25.27 Takayasu’s arteritis. Axial CTA shows smooth circumferential thickening of the right pulmonary artery (yellow arrows).

Kawasaki Disease KD is a predominantly medium-vessel vasculitis of unknown etiology, which affects infants and children younger than 4 years. KD can occur in any artery but has a predilection for coronary vessels. Other common arteries include axillary, subclavian, brachial, femoral, iliac, splanchnic, and mesenteric arteries, usually near or at branching points [30]. This vasculitis is known to have at least two phases, the acute and the late phase. The acute phase is defined as the first 30 days of illness with development of coronary aneurysms in about 15–25% of untreated patients and only around 5–7% for patients treated with high-dose intravenous immunoglobulin [31]. The late phase is when small aneurysms can either regress completely within 2 years; or progress to occlusion or localized stenosis, even 10 or 20 years after the onset of the disease. A z-score of >2.5 to 3.5 meets RAS criteria), and (3) aliasing artifact which indicates turbulent flow. (C) Indirect signs of RAS with interrogation of the right kidney at the segmental arteries (distal to the arterial stenosis), it shows a decreased acceleration index of 298 cm/s2 (RAS criteria 70% in luminal diameter shows a PSV >200 cm/s. The Doppler waveform is still antegrade, low resistive, and monophasic. Median arcuate ligament syndrome, also known as celiac artery compression syndrome, is characterized by chronic upper abdominal pain in the setting of worsened compression during end-expiration by the diaphragmatic crurae. The typical imaging appearance is that of a hooked or “J” appearance of the celiac trunk. Imaging evaluation can be obtained during end-expiration and end-inspiration with arterial Doppler ultrasound or MRA, which show worsened stenosis during end-expiration and resulting increased mean PSV >350 cm/s during end-expiration (Figs. 25.37 and 25.38) [45]. CTA may be used but typically these patients are younger when the radiation exposure should be minimized, which is why MRA is preferred

(Fig. 25.39). Symptomatic patients are treated with surgical decompression, which is usually performed laparoscopically [46].

FIGURE 25.37 Median arcuate ligament syndrome (MALS). (A) CTA shows characteristic hooked appearance of the celiac trunk associated with median arcuate ligament compression on a patient with history of chronic abdominal pain. (B and C) Dynamic arterial Doppler images with spectral analysis at the celiac trunk, which shows a greater increased peak systolic velocity (PSV) during expiration (193 cm/s), than during inspiration (127 cm/s). Note aliasing artifact in the celiac trunk during expiration, indicating even a greater PSV during expiration.

FIGURE 25.38 Median arcuate ligament syndrome (MALS) involving the common hepatic artery. (A) CTA axial image shows a separate origin of the common hepatic artery arising directly from the aorta. There is a typical appearance of a band like hypoattenuation (black arrowhead) related to median arcuate ligament compression. (B and C) Dynamic arterial Doppler ultrasound with spectral analysis at the common hepatic artery, which shows a greater increased peak systolic velocity (PSV) during expiration (314 cm/s), than during inspiration (139 cm/s).

FIGURE 25.39 Median arcuate ligament syndrome (MALS). MRA shows (A) typical hooked appearance of the celiac trunk (red arrow) during inspiration due to median arcuate ligament compression, (B) and significant worsening of this morphology during expiration with resulting severe stenosis of the proximal celiac trunk (yellow arrow). Note the differences in positioning of the diaphragm between (A) inspiration and (B) expiration.

The normal SMA Doppler waveform changes during fasting and postprandial stages. During fasting it is antegrade, high resistive, and multiphasic with early diastolic flow reversal often apparent; and during a postprandial stage is antegrade, but waveform becomes low resistive and

monophasic (REF). A flow-limiting stenosis of the SMA with a reduction of >70% in luminal diameter shows a PSV >275 cm/s. The Doppler waveform is antegrade, low resistive and monophasic (REF). Superior mesenteric syndrome occurs when there is compression with or without obstruction at the level of the third portion of the duodenum between the aorta and the proximal SMA. The typical presentation is acute on chronic postprandial upper abdominal pain. There are factors that can precipitate these symptoms such as significant weight loss resulting in loss of the fat around the SMA. Imaging findings reveal decreased aortomesenteric angle to 6–22° (normal 28–65°), and decreased aortomesenteric distance to 2–8 mm (normal 10–34 mm) [2] (Fig. 25.40).

FIGURE 25.40 Superior mesenteric syndrome (SMA) and associated Nutcracker syndrome. Contrast-enhanced axial image shows decreased distance (2 but ≤3 ■ Severe stenosis = PSV ratio >3

HD access thrombosis occurs more commonly with AVGs than AVFs (Fig. 26.17). Commonly access thrombosis is most commonly associated with stenosis. However, other risk factors associated with access thrombosis include low flow, infection, systemic hypotension, and a hypercoagulable state. Multiple approaches toward declotting access have been described, which are detailed elsewhere. Although there are many approaches, must rely on pharmacomechanical means to physically break up the clot as well as dissolve it with a thrombolytic. Once patency is re-established the access has been declotted, the underlying cause (e.g., stenosis) needs to be addressed to prevent or delay recurrence [31].

FIGURE 26.17 Venographic images of a patient with a thrombosed AVG, (A) before and (B) after thrombolysis and thrombectomy.

Pelvic and Lower Extremity Venous System Anatomy and Variants Similar to the upper extremity, venous drainage of the lower limb can be divided into two separate systems, the deep veins and the superficial veins, which are also connected by the communicating veins or perforating veins (Figs. 26.18–26.19). The named deep veins include: ■ Common femoral ■ Femoral ■ Profunda femoris ■ Popliteal ■ Posterior tibial ■ Anterior tibial ■ Fibular ■ Calf muscle veins: soleus and gastrocnemius

FIGURE 26.18 Illustration of the normal lower extremity venous anatomy.

(Courtesy: Susanne Loomis.)

FIGURE 26.19 Contrast-enhanced CT coronal reconstructed image of the normal venous anatomy of the proximal veins of the bilateral lower extremities. CFV, common femoral vein; FV, femoral vein. The dashed arrows identify the profunda femoris.

The deep veins in the calf follow the same distribution as the main arteries but are usually double, forming the anterior tibial, posterior tibial, and peroneal veins. The calf veins, or sural veins, arise in calf muscles and emerge from them to join the peroneal, posterior tibial, or popliteal veins. The soleus usually drains into the posterior tibial or peroneal veins, while the gastrocnemius veins drain into the popliteal above the knee. Several variants exist for the deep system of the lower extremities. Some examples include congenital absence of the profunda femoris where there is a single drainage pathway of the lower limb and joining of the anterior tibial vein above the knee (Fig. 26.20). The named superficial veins include: ■ Great saphenous ■ Small saphenous

■ Accessory saphenous

FIGURE 26.20 Illustration of the variant anatomy of the anterior tibial vein.

(Courtesy: Susanne Loomis.)

The superficial leg veins drain into the saphenous veins. The small saphenous vein (SSV) passes up the lateral side of the leg to the knee, where it passes deeply to join the popliteal vein. The great saphenous vein (GSV) passes up the medial side of the calf and thigh and then joins the common femoral vein below the groin. In contrast to the upper extremities, the lower limbs are disproportionately drained by the deep system and have a higher endovascular pressure due to hydrostatic forces [12]. The communicating veins (also known as the perforators) are usually small and paired and connect the superficial and deep veins. Normally they are extremely narrow, but they can become quite large when hypertrophied. Similar to the upper

extremity veins, the lower extremity veins also harbor bicuspid valves, which serve to promote unidirectional blood flow and prevent reflux. The pelvic venous system includes a number of named vessels draining the pelvic organs and bilateral lower extremities (Figs. 26.21–26.22). The common femoral vein becomes the external iliac vein as it passes under the inguinal ligament and is located medial to the common femoral artery. The external iliac vein frequently drains the ipsilateral inferior epigastric, deep circumflex iliac, and pubic veins. The internal iliac vein drains the ipsilateral superior gluteal, inferior gluteal, internal pudendal, obturator, middle hemorrhoidal (and sometimes the inferior hemorrhoidal), vesical, lateral sacral and, in females, uterine veins. Within the posterior pelvis the internal and external iliac veins join to form the common iliac veins. The common iliac veins join at approximately the L5 vertebral body to form the IVC [12]. Variant anatomy where multiple internal iliac veins are present draining the ipsilateral and contralateral pelvis are also encountered [32].

FIGURE 26.21 Illustration of the normal pelvic venous anatomy.

(Courtesy: Susanne Loomis.)

FIGURE 26.22 Contrast-enhanced CT (A) 3D reconstructed, and multiplanar reconstructed images (B and C) demonstrating the normal venous anatomy of the pelvis. CIV, common iliac vein; EIV, external iliac vein; IIV, internal iliac vein.

Superficial and Deep Venous Thrombosis The incidence of DVT is estimated to be approximately 5 in 10,000/year [33] and occurs disproportionately in the lower extremities. Interestingly, the laterality of lower extremity DVT is not equal, with left-sided DVTs more common [34]. This may be related to May–Thurner anatomy, which is discussed in the next section. Pathophysiology Similar to the upper extremities, venous thrombosis is often multifactorial. Virchow's triad is helpful in categorizing or determining different factors promoting venous thrombosis in a patient: namely, hypercoagulability, venostasis, and endothelial injury. The well-known risk factors for venous thrombosis include recent surgery, immobility, cancer, oral contraceptives, obesity, and inherited or acquired thrombophilias [35,36]. Left untreated, a significant proportion of patients with above the knee DVT is at risk for developing a PE, which is associated with significant morbidity and mortality. Clinical Presentation Only about two-thirds of patients with a lower extremity DVT present with symptoms, which can lead to delayed or nondiagnosis in a substantial number of cases. Common symptoms include lower leg swelling, pain, and tenderness. DVT in the lower extremities frequently occurs distally and propagates proximally. Imaging Evaluation As most clinical scoring systems are suboptimal, imaging plays a critical role in diagnosis. Imaging is important for both determining the presence of

thrombosis, as well as the extent of disease. DVT location frequently influences management, as above the knee thrombosis carries an increased risk of PE and is often treated differently than below the knee DVT [37]. Duplex USG is the best first test for suspected lower extremity DVT [37]. Lower extremity DVT USG findings are the same as those for subacute or chronic upper extremity DVT, including, a non- or partially compressible vein with echogenic material filling the lumen (Fig. 26.23). Again, the indirect Duplex USG findings suggestive of a thrombus include abnormal flow patterns, loss of augmentation, and blunted or loss of the normal variation with respiration and the cardiac cycle. Additional imaging is necessary if a lesion is suspected proximal to the common femoral vein, as imaging of the iliac veins is suboptimal with USG. In specific clinical situations CTV or MRV may be helpful, such as in burn patients where sonographic evaluation is limited or where a more proximal lesion is suspected. Extrinsic venous compression within the abdomen or pelvis may lead to thrombus formation that extends distally. For CTV imaging, indirect CTV is the most commonly utilized. On CTV, a subacute or chronic thrombus will appear as a hypoattenuating filling defect within the vessel lumen (Fig. 26.24). If the involved vein is obstructed, it may appear enlarged and collateral vessels may be visualized. Indirect signs of venous thrombosis on CTV also include adjacent soft tissue stranding. Findings encountered with chronic thrombosis include calcification within the vein wall, small size of the vein, and intraluminal webs.

FIGURE 26.23 Grayscale compression ultrasound images of a patient with a popliteal vein DVT. (A) Echogenic material in the lumen (arrow) representing thrombus. (B) Partial compression.

FIGURE 26.24 Contrast-enhanced CT (A) axial and (B) coronal reconstructed images of a patient with a left common femoral vein DVT. Note the relative hypoattenuation compared to the contralateral vein.

Both contrast-enhanced and noncontrast MRV are useful techniques for evaluating for venous thrombosis, although contrast-enhanced studies are more reliable. Nonetheless, commonly used noncontrast MR sequences that permit thrombus visualization include TOF and SSFP. MRV findings are similar to those for CTV including a partial or complete filling defect, vessel enlargement in acute DVT, and the formation of collaterals. Venography, as in many other clinical circumstances, is reserved for cases where an intervention may be indicated. Venography findings for DVT include luminal filling defects, complete vessel occlusion, and collateral venous flow. Management Clinical management of lower extremity DVT is based on the extent of disease, the underlying etiologies, patient symptoms, and the risks associated with treatment. The reader is referred to the treatment strategies discussed in the section on upper extremity DVTs, as the treatment principles are applicable to lower extremity DVTs. Briefly, most stable patients with an isolated above the knee DVT are treated with anticoagulation. The recommended duration of anticoagulation treatment continues to evolve as new data emerge and is tailored toward the underlying cause or risk factors for the DVT [16]. Regarding catheter-directed therapies, treatment decisions are made on a case-by-case basis. A recent randomized clinical trial demonstrated no difference in post-thrombotic syndrome symptoms in patients treated with CDT for lower extremity and pelvic DVT, while demonstrating a higher risk of major bleeding [38].

May–Thurner Syndrome MTS represents one of the venous compression syndromes that can lead to unilateral left lower extremity swelling and DVT. Pathophysiology The condition arises from compression of the left common iliac vein as it crosses between the right common iliac artery and the spine, as well as the formation of internal webs or spurs within the left internal iliac vein that develop over time due to the chronic compression and arterial pulsations (Fig. 26.25). Variant forms of MTS include left common iliac vein compression by the ipsilateral common iliac artery, left common iliac vein compression by the ipsilateral left internal iliac artery, and compression of the IVC by the right common iliac artery or a tortuous left common iliac artery [39]. Interestingly, many individuals demonstrate extrinsic compression on cross-sectional imaging (sometimes referred to as May– Thurner anatomy), yet not all individuals develop symptoms or DVT. The prevalence of MTS is unknown, but the condition is most commonly seen in young and middle-aged women.

FIGURE 26.25 Illustration of the relevant anatomy in May–Thurner syndrome.

(Courtesy: Susanne Loomis.)

Clinical Presentation Patient presentation is variable ranging from unilateral left lower extremity swelling due to chronic venous insufficiency to left-sided DVT, PE, and phlegmasia cerulea dolens [40]. Phlegmasia cerulea dolens (inflammationblue-painful) is a rare complication of extensive lower extremity DVT characterized by edema, cyanosis, and arterial insufficiency. Imaging Evaluation Multiple imaging techniques are typically employed when considering MTS. Given the diagnosis of lower extremity DVT often precedes a suspicion for MTS, Duplex USG is typically the first best imaging study. Unfortunately, direct visualization of the iliac veins can be challenging to perform. Nonetheless, Duplex USG findings within the veins distal to the compression or obstruction suggestive of MTS include [41]: ■ Loss or blunting of respiratory variation

■ No response to Valsalva maneuver ■ Elevated common iliac vein velocities

However, diagnosis of MTS requires either venography or additional cross-sectional imaging. After USG, both MR and CTV are acceptable noninvasive imaging approaches that can identify the extrinsic venous compression that characterizes MTS [37]. CT and MRI demonstrate compression of left common iliac vein between the right common iliac artery and the spine, deep vein thrombosis if any of the ipsilateral iliac veins and development of retroperitoneal and pelvic venous collaterals (Fig. 26.26). The iliac vein compression is highly variable and is dependent on the blood volume; a physiological compression of the left common iliac vein of >50% luminal diameter is seen in normal adults. The presence of an enlarged left ascending lumbar vein, and pelvic varicosities on CT and MRI, and identification of retrograde flow in left internal iliac vein and left ascending lumbar vein on TOF MRI suggests a hemodynamically significant left common iliac vein compression. IVUSG is helpful in identifying mural spurs (the earliest sign of repetitive endothelial trauma), extent of venous compression, largest patent channel for recanalization and diameter of normal left common iliac vein. It also guides placement of an intravascular stent and detects in-stent stenosis.

FIGURE 26.26 Contrast-enhanced MR of a patient with May–Thurner syndrome. (A) Axial image demonstrating compression of the left common iliac vein (CIV) by the right common iliac artery (CIA). (B) Coronal reconstructed image of the same patient.

Management Clinical management of MTS depends on the presenting symptoms. Patients with May–Thurner anatomy but no symptoms are typically not treated prophylactically. Anticoagulation is universally used for patients with acute

or chronic thrombosis. For patients presenting with acute thrombosis, however, chemical and/or mechanical thrombolysis may be employed to recanalize the occlude vein(s). Moreover, given the condition arises secondary to an anatomic aberration, endovascular venous stenting is performed to maintain venous patency and prevent recurrent thrombosis (Fig. 26.27) [42]. Complications of left common iliac venous stenting include recurrent stent thrombosis, stent fracture, and thrombosis of right common iliac vein.

FIGURE 26.27 May–Thurner syndrome. (A) Fluoroscopy image demonstrating collateral flow (arrow). (B) Contrast-enhanced CT axial image of a patient with May–Thurner following thrombolysis/thrombectomy and left common iliac vein stenting (arrow).

Varicose Veins Varicose veins are the enlarged, tortuous superficial veins that develop, most often in the lower extremities, secondary to venous insufficiency where normal unidirectional flow of blood is disrupted. Pathophysiology Varicose veins are believed to represent one of several possible manifestations of chronic venous insufficiency. The underlying pathophysiology is posited to result from valvular incompetence and venous reflux enabling elevated venous pressures, engorgement, and stretching (Table 26.3).

Table 26.3 Risk Factors for Developing Varicose Veins [43] Patient specific factors

Age Gender Family history Pregnancy Obesity Lifestyle

Disease associated factors

Central venous hypertension Venous thrombosis

Within Western populations, varicose veins of the lower extremities are very common with an estimated prevalence of up to 25% in women and up to 15% in men [44]. Clinical Presentation The diagnosis of varicose veins is primarily clinical and patient presentation is varied. Indeed, some patients present with no symptoms seeking primarily cosmesis, for the associated undesired morphological and color changes. On the other hand, some patients present with chronic symptoms, most often including leg heaviness, swelling, pain, night cramps, itchy skin, or skin ulcerations [43]. Due to the spectrum of chronic venous disease, scoring systems have been devised to classify disease severity to help standardize evaluation and management. An important classification system is the Clinical Etiology Anatomy Pathophysiology (CEAP) scoring system. The CEAP integrates the clinical manifestations of disease, underlying etiology, vessels involved, and the suspected underlying cause. The updated 2020 CEAP classification system and reporting standards are listed in Tables 26.4A–26.4D [45]. Table 26.4A Clinical (C) Classification C Class Description C0

No visible or palpable signs of venous disease

C Class

Description

C1

Telangiectasias or reticular veins

C2

Varicose veins

C2r

Recurrent varicose veins

C3

Edema

C4a

Pigmentation or eczema

C4b

Lipodermatosclerosis or atrophie blanche

C4c

Corona phlebectatica

C5

Healed (venous ulcer)

C6

Active venous ulcer

C6r

Recurrent active venous ulcer

Table 26.4B Etiologic (E) Classification E Class Description Ep

Primary

Es

Secondary

Esi

Secondary—intravenous

Ese

Secondary—extravenous

Ec

Congenital

En

No cause identified

Table 26.4C Anatomic (A) Classification A Class Abbreviation Description A Superficial (vein) s

Tel

Telangiectasia

A Class

A Deep (vein)

Abbreviation Description Ret

Reticular veins

GSVa

Great saphenous vein above knee

GSVb

Great saphenous vein below knee

SSV

Small saphenous vein

AASV

Anterior accessory saphenous vein

NSV

Nonsaphenous vein

IVC

Inferior vena cava

CIV

Common iliac vein

IIV

Internal iliac vein

EIV

External iliac vein

PELV

Pelvic veins

CFV

Common femoral vein

DFV

Deep femoral vein

FV

Femoral vein

POPV

Popliteal vein

TIBV

Crural (tibial) vein

PRV

Peroneal vein

ATV

Anterior tibial vein

PTV

Posterior tibial vein

MUSV

Muscular veins

GAV

Gastrocnemius vein

SOV

Soleal vein

TPV

Thigh perforator vein

CPV

Calf perforator vein

–

No venous anatomic location identified

d

A Perforator p

A – n

Table 26.4D Pathophysiologic (P) Classification P Class Description Pr

Reflux

Po

Obstruction

Pr,o

Reflux and obstruction

Pn

No pathophysiology identified

The clinical manifestations, in order of increasing severity, include telangiectasias or reticular veins, varicose veins, edema, pigmentation or dermatitis, lipodermatosclerosis or atrophie blanche (white scar), healed venous ulcer or active venous ulcer [43]. An adjunctive scoring system, derived from the CEAP system, is the Venous Clinical Severity Score (VCSS), later revised in 2010, and was developed to better evaluate disease changes over time. VCSS is comprised of 10 categories that are scored from 0 to 3 based on severity (0, 1, 2, 3 representing none, mild, moderate, and severe, respectively). The VCSS categories are pain, varicose veins, edema, skin pigmentation, inflammation, induration, active number of ulcers, active ulcer duration, active ulcer size, and use of compression therapy [46]. Quality of life assessments are also typically used to effectively manage treatment and improve overall outcomes. Imaging Evaluation Despite being primarily a clinical diagnosis, imaging is very important in the management paradigm of varicose veins and chronic venous insufficiency. Indeed, USG is the primary technique utilized for evaluating uncomplicated cases of primary varicose veins, that is, varicose veins resulting from reflux and insufficiency, not secondary to thrombosis (Fig. 26.28). Duplex USG can identify the incompetent veins, document venous reflux, and map a patient's anatomy before treatment. USG examination should be performed standing while the patient distributes the majority of their weight toward the side opposite the leg being evaluated, enabling muscle relaxation in the queried leg. The great and small saphenous veins (GSV and SSV, respectively), as well as the deep veins, should be examined along their entire lengths, saving images, and diameters for abnormal segments. The GSV's normal diameter in a standing individual is ≤4 mm and the SSV is ≤3 mm. First, the GSV should be examined beginning from the saphenofemoral junction followed by the SSV. Duplex USG enables identification and quantification of reflux through segmental compression. Reflux, or reversal

of flow, is identified on probe relaxation by the operator. Duplex USG findings consistent with superficial vein incompetence include [43]: ■ GSV diameter >4 mm ■ SSV diameter > 3 mm ■ Reversal of flow lasting >0.5 seconds

FIGURE 26.28 Duplex and grayscale ultrasound images of a patient with right great saphenous varicose veins. The left image demonstrates abnormally long reflux time (7.6 seconds) indicating incompetence and the right image demonstrates one of several large varicosities in short axis.

Dedicated evaluation of perforating veins connecting the deep and superficial systems should be performed, as it is necessary to document incompetent perforators. Perforating veins in the lower extremities are more commonly seen posteriorly below the knee [12]. Normally perforators may be identified along the medial aspect of the lower extremity at the ankle, calf, above and below the knee, and in the mid-thigh (Fig. 26.29, from Kaufman and Lee. Vascular and Interventional Radiology: The Requisites, 2nd ed. Philadelphia: WB Saunders, 2014). Duplex USG findings consistent with incompetent perforators include [43]: ■ Diameter >3.5 mm ■ Reversal of flow lasting >0.5 seconds

FIGURE 26.29 (A-B) Illustration demonstrating the superficial veins of the lower extremity and common locations for perforators.

Additional cross-sectional (CTV or MRV) imaging is less commonly used and is typically reserved for more complex cases where proximal venous obstruction or insufficiency is suspected. Indeed, CTV and MRV are indicated when venous compression in the abdomen or pelvis is suspected, such as in MTS or NS, or gonadal vein insufficiency (GVI) and pelvic venous congestion syndrome (PVCS). Venography is often used in both diagnosis and treatment where characterization of the anatomy may be accomplished and subsequently treated. Management First-line therapy for symptomatic varicose veins is conservative, aimed at improving symptoms and promoting wound healing, if present. Conservative measures include lifestyle changes (e.g., increased leg elevation, exercise), compression therapy (e.g., compression stockings), and wound care, as needed. If conservative therapy fails, often after a 3-month trial period, more invasive, ablative approaches are considered. Historically, open surgery with vein ligation and stripping was the primary ablative treatment approach. However, open surgery is associated pain, increased recovery time and increased risk of infection. Minimally invasive, percutaneous ablative techniques have now been developed that have been shown to be effective and decrease recovery time. Contraindications to venous ablation for varicose vein management include [43]: ■ Pregnancy ■ Inability to ambulate

■ Presence of a DVT ■ Klippel–Trénaunay syndrome (or other congenital venous anomaly syndrome) ■ Arterial occlusive disease ■ Poor health

Percutaneous endovascular treatment approaches may be categorized as thermal and nonthermal techniques. The choice of ablation approach should be made based on a patient and provider level, as each has unique limitations and no one approach is superior. Endovascular thermal ablation involves heating the vessel wall leading to protein denaturation, structural damage, and the promotion of venous thrombosis. The two forms of thermal ablation are radiofrequency ablation and laser. The disadvantage of thermal approaches is associated pain, which varies by patient and extent of treatment. Endovascular nonthermal approaches include chemical and combined chemical and mechanical. Endovascular chemical ablation can be accomplished with the injection of a sclerosant, most commonly Sotradecol. Different forms of combined mechanical and chemical ablation exist. One commercial system involves both physical damage to the vessel wall with a rotating wire while simultaneously infusing a sclerosant to the traumatized vein to promote occlusion and fibrosis. Another novel system involves the direct injection of n-butyl-cyanoacrylate followed by extracorporeal physical compression of the vein to seal the vessel shut. Surgical approaches are typically used in patients not amenable to endovascular ablation. Surgical techniques include endoscopic vein surgery, phlebectomy, and vein stripping and ligation.

Inferior Vena Cava Anatomy and Variants In most individuals, the IVC is the largest venous structure within the abdomen located within the retroperitoneal space to the right of the thoracolumbar spine. The IVC serves as the predominant conduit for venous blood below the diaphragm returning to the right atrium. Inferiorly, the IVC is formed at the abdominopelvic junction at approximately the L5 vertebral body by the confluence of the common iliac veins. Superiorly, the IVC terminates at the inferior aspect of the right atrium (the inferior cavoatrial junction) after passing through caval hiatus of the diaphragm at approximately the T8 vertebral body. The IVC can be divided into four segments based on embryonic origin. From inferior to superior these segments include the infrarenal, renal, suprarenal, and hepatic. These segments arise during development from the anastomosis of the posterior cardinal veins, right supracardinal, right subcardinal, and vitelline veins.

Abnormalities in normal embryologic IVC development can give rise to several anatomic variants (Fig. 26.30). Often these anomalies are discovered incidentally on cross-sectional imaging, but it is important to be familiar with these variants as several IVC variants have clinical implications for IVC filter placement.

FIGURE 26.30 Illustration of the normal and variant IVC and left renal vein variants. (A) Normal anatomy. (B) Duplicated IVC. (C) Left-sided IVC. (D) Retroarotic left renal vein. (E) Circumaortic left renal vein.

(Courtesy: Susanne Loomis.)

IVC duplication results from the persistence of the bilateral supracardinal veins and has a prevalence of 0.2–0.3% (Fig. 26.31). A leftsided IVC has a prevalence of 0.2–0.5%, typically arising from the persistence of the left supracardinal vein and the regression of the right supracardinal vein (Fig. 26.32). Agenesis of the IVC is often seen with continuation of the azygos or hemiazygos veins [47]. Associated variants involving the left renal vein are also commonly encountered. A retroaortic left renal vein describes a left renal vein located posterior to the aorta, instead of in its normal anatomic location anterior to the aorta. A circumaortic left renal vein describes the variation where there are two left renal veins, one located in its expected anatomic location anterior to the aorta and there is a coincident retroarotic left renal vein. The estimated prevalence of a retroaortic and circumaortic left renal veins is 3% and 3.5%, respectively [48].

FIGURE 26.31 Contrast-enhanced CT (A) coronal and (B) axial reconstructed images of patient with a duplicated IVC. Solid arrows indicate the normal location of the IVC and the dashed arrows indicate the left IVC.

FIGURE 26.32 Contrast-enhanced CT (A) coronal and (B) axial reconstructed images of a patient with a left IVC (arrows).

Acute and Chronic IVC Thrombosis IVC thrombosis is an important cause of significant patient morbidity. The incidence of IVC thrombosis has been difficult to determine due to the associated nonspecific symptoms and sometimes insidious onset. However, it is estimated that up to 4% of patients with a lower extremity DVT have coincident IVC thrombosis [49]. Not surprisingly, IVC thrombosis is a risk factor for development of PE. IVC thrombosis is associated with congenital

IVC anomalies, DVT of the lower extremities, extrinsic IVC compression, Budd–Chiari syndrome (BCS), MTS, trauma, the presence of an indwelling IVC filter, and factors that promote a prothrombotic state (e.g., cancer, oral contraceptives, inherited/acquired thrombophilias, etc.). Patients with undiagnosed IVC thrombosis can present with variable, nonspecific symptoms including leg pain, swelling and cramping, back, abdominal or pelvic pain, and scrotal swelling [49]. The nonspecific presentation, possibility of isolated IVC thrombosis without lower extremity DVT and lack of disease familiarity by the referring physicians can lead to delay in diagnosis. As a result, diagnosis may occur after secondary complications develop, such as dyspnea in PE or oliguria with renal vein thrombosis [49]. Imaging evaluation of suspected IVC thrombosis should begin with a noninvasive technique such as a focused Duplex USG. However, patients newly post-op from abdominal surgery, obese patients or patients with excessive bowel gas may necessitate first-line cross-sectional imaging, such as CT or MR venography. On CTV, subacute-chronic bland IVC thrombus will appear as a hypoattenuating, persistent luminal filling defect (Fig. 26.33). In chronic cases, the IVC is small in caliber with or without intravascular enhancement and pericaval and periaortic collateral veins (Fig. 26.34) [50]. In cases of acute thrombus, noncontrast CT may demonstrate a hyperattenuating thrombus within the lumen. Differentiation between bland thrombus and tumor thrombus is most easily accomplished by looking for IVC expansion and contrast enhancement of the luminal filling defect. IVC luminal tumor, most often secondary to renal cell carcinoma (RCC), demonstrates contrast enhancement [47]. Invasive imaging, venography, is frequently reserved for certain circumstances where an intervention may be indicated, such as with acute/subacute thrombosis or with secondary thrombosis due to extrinsic IVC compression where an IVC stent may be beneficial.

FIGURE 26.33 Contrast-enhanced CT coronal reconstructed image of a patient with subacute IVC thrombosis (arrow).

FIGURE 26.34 Contrast-enhanced CT (A) coronal reconstructed and (B) axial images of a patient with chronic IVC thrombosis (arrow) and collateral flow manifesting through an enlarged left renal vein (dashed arrow).

Management of IVC thrombosis nearly always begins with anticoagulation. Additionally, symptomatic patients presenting with an acute or subacute IVC thrombus (28 days) are typically treated with percutaneous transluminal angioplasty and stenting [49].

Mechanical Interruption of the IVC (IVC Filters) A principle concern after diagnosing iliocaval thrombosis is the potential for life-threatening PE, or in unique cases where a right-to-left cardiac or pulmonary shunt is present resulting in paradoxical embolism to the arterial circulation. Therefore, in select cases, placement of a physical barrier within the IVC to prevent thrombus migration may be desired. Conventional mechanical interruption involves placement of an infrarenal IVC filter (Fig. 26.35). Consensus guidelines for IVC filter placement include [51–53]: 1. Patients with a proximal (above knee) deep vein thrombosis or PE and a contraindication to anticoagulation 2. Before pulmonary thromboendarterectomy in patients with chronic pulmonary thromboembolic pulmonary hypertension 3. High-risk PE in select groups (e.g., planned for regional thrombolysis/surgical embolectomy, presence of heart failure or older than 80 years)

FIGURE 26.35 Contrast-enhanced CT images of the abdomen. (A) Coronal reconstructed and (B) axial images with an IVC filter in situ (arrow).

An array of filters is commercially available, with selection often based on institutional vendor preference and pricing. No one filter has proven superior. Indeed, most filters have unique advantages and disadvantages. Filters may be chosen based on dwell time (permanent or temporary), IVC diameter, and desired venous access site for placement. Most filters are conical in shape designed to fit 28–30 mm IVC. Large filters can be used for IVC of up to 40 mm diameter. IVC filter placement is usually accomplished within a fluoroscopy suite with the objective of having the cranial most filter component below the lowest renal vein (Fig. 26.31). A suprarenal IVC filter may be indicated in the presence of intrinsic or extrinsic infrarenal IVC obstruction, renal, or gonadal vein thrombosis (GVT), presence of a circumaortic renal vein or a duplicated IVC and pregnancy. Before placement, IVC venography should be performed when cross-sectional imaging is unavailable to measure the IVC diameter, map the number and location of the renal veins, and determine if any variant anatomy or thrombus is present. Venography should ideally be performed with the catheter tip within the left common iliac vein, as it enables identification of a left or duplicated IVC. IVC filter utilization has declined since the early 2000s due to both the paucity of evidence supporting their use in various clinical circumstances, but also due to the recognition of their clinically significant complications. Complications vary and are often classified as early or late (Table 26.5).

Table 26.5 Complications Associated with IVC Filters [54] Access site related

Bleeding Venous thrombosis Arterial trauma, potentially leading to arteriovenous fistula

Early filter related

Tilt (>15° angulation relative to long axis of the IVC) Filter migration Incomplete filter opening Nontarget filter placement Incorrect filter orientation

Late filter related

Filter thrombosis Filter fracture (with or without embolization) IVC perforation

Thus, given the nontrivial nature of these devices, consensus guidelines recommend device removal as soon as they are no longer indicated and if reasonably safe to do so.

IVC Webs, Stenosis, and Extrinsic Compression Other acquired conditions can lead to clinically significant narrowing or obstruction of the IVC. IVC webs represent a rare disease where membranous webs and fibrotic tissue develop in the hepatic vena cava potentially leading to hepatic venous outflow obstruction. The condition is seen more commonly in developing countries [47]. Formerly thought to represent a congenital anomaly, the IVC membranous webs are believed to arise from localized bacterial-induced thrombophlebitis. In chronic disease, the condition may progress to hepatic vena cava syndrome where obstruction becomes clinically significant potentially leading to cirrhosis and hepatocellular carcinoma (HCC), which is why the condition has historically

been grouped under Budd–Chiari syndrome [55]. On CT, IVC webs often appear as a linear soft tissue attenuating abnormality within the lumen of the intrahepatic IVC. Similarly, on MRI, webs may appear as a focal luminal narrowing or wall irregularity in the intrahepatic or suprahepatic IVC (Fig. 26.36A). On venography IVC webs demonstrate focal narrowing (Figs. 26.36B–C). However, in more severe cases, there may be complete IVC obstruction with development of prominent intrahepatic and extrahepatic collateral flow [47].

FIGURE 26.36 IVC webs. (A) Axial MRI image demonstrating an IVC web involving the superior intrahepatic IVC. (B) and (C) show venographic images in another patient with focal IVC stenosis (arrow) secondary to a web before and after balloon dilation.

Retroperitoneal fibrosis (RPF) is a rare condition arising secondary to chronic inflammation of the retroperitoneal soft tissue that can lead to infrarenal compression of the great vessels, including the IVC [56,57]. RPF may be classified as idiopathic, comprising the majority of cases, or secondary with causes including malignancy, radiation, and certain medications. IVC stenosis or compression may also occur with a number of other conditions including pregnancy, in the presence of a large abdominal aortic aneurysm, after liver transplantation due to postoperative swelling, by retroperitoneal masses or secondary to trauma by retroperitoneal hematomas [47]. Duplex USG evaluation of the common femoral vein may suggest proximal IVC involvement by showing loss or blunting of the normal variation with respiration and the cardiac cycle. Direct sonographic visualization of the IVC is limited due to overlying bowel gas. On the other hand, CTV and MRV are the best noninvasive imaging techniques for evaluating IVC involvement in RPF (Fig. 26.37). Indeed, CT and MR often

demonstrate soft tissue encasing IVC and iliac vessels, occasionally with endoluminal thrombosis [58].

FIGURE 26.37 Retroperitoneal fibrosis. Contrast-enhanced CT (A) axial and (B) coronal images demonstrating IVC compression and stenosis (arrow) in a patient with retroperitoneal fibrosis.

Tumor Involvement of the IVC Malignant tumor involvement of the IVC may be primary or secondary, with primary IVC tumors considered very rare. IVC leiomyosarcoma is the most common type of primary IVC malignancy [47]. IVC leiomyosarcomas arise from the IVC wall smooth muscle and can demonstrate different growth patterns: intraluminal, extraluminal, or both. Intraluminal tumors can cause IVC obstruction and thrombosis, and extraluminal tumors can invade local structures. Interestingly, IVC leiomyosarcomas are disproportionately seen in middle-aged women [47]. Surgery represents the only potentially curative treatment option for patients with en bloc resection of the IVC with adjacent structures is sometimes required [59]. Secondary malignancies involving the IVC include: ■ Renal cell carcinoma ■ Adrenal cortical carcinoma ■ Hepatocellular carcinoma ■ Transitional cell carcinoma ■ Wilms tumor ■ Nonseminomatous testicular carcinoma

RCC represents the most common malignancy involving the IVC, seen in up to 10% of cases [47]. Similar to primary malignancies of the IVC, surgery

is centerpiece in management. CT and MR represent the most useful imaging techniques for evaluating tumor involvement of the IVC as they are best suited to help determine tissue origin and extent of invasion. On CECT, extraluminal tumors appear as exophytic, large heterogeneously enhancing lesions and may demonstrate areas of cystic necrosis. Intraluminal tumors usually result in focal IVC dilatation and obstruction, and display contrast enhancement (Fig. 26.38) [50]. On MR, tumors often appear as a hypointense and hyperintense mass on T1-weighted and T2-weighted images, respectively [60].

FIGURE 26.38 Contrast-enhanced CT images of the abdomen. Mixed growth IVC leiomyosarcoma manifesting as a mostly homogenous hypodense mass with luminal narrowing on (A) axial and (B) coronal reconstructed images.

Renal Veins Anatomy and Variants In most individuals, there is one main renal vein responsible for draining each kidney and are typically located anterior to their respective renal artery. The left renal vein is usually longer than the right, as the left renal vein must cross the aorta to join the IVC. Normally, the left renal vein courses between the aorta and the superior mesenteric artery (SMA). In approximately 3% of individuals, the left renal vein courses posterior to the aorta, termed a retroaortic left renal vein [61]. Supernumerary renal veins are not uncommon, seen in 15–30% of the population and occur more commonly on

the right [62]. Duplication of the left renal vein most commonly results in a circumaortic left renal vein configuration where there is a normal left renal vein found between aorta and SMA with the second seen retroaortic (Fig. 26.30). Rarely, the left renal vein may form a vascular network beyond the left renal hilum before converging into a single vein before joining the IVC, the so-called plexiform left renal vein [61]. In addition to draining the left kidney, the left renal vein often serves as the drainage conduit for the left adrenal and gonadal veins.

Renal Vein Thrombosis Renal vein thrombosis is a serious clinical condition that, if left undiagnosed, can be associated with considerable morbidity. Renal vein thrombosis is typically classified as either bland or tumor associated, as the underlying etiology significantly influences management. Risk factors include nephrotic syndrome, collagen vascular disease, diabetes, trauma, hypovolemia, inherited thrombophilias, renal vein compression, and malignancy. Thrombosis of the left renal vein is more common than the right, and rarely, arises as an extension of a left GVT [61]. Clinical presentation is variable, ranging from asymptomatic to complaints of flank pain, gross hematuria, or variable symptoms associated with acute renal injury. Some cases are discovered on imaging evaluation for PE where the thromboembolism is thought to arise from the renal vein(s). Renal vein thrombosis is diagnosed on imaging with USG representing the best first initial imaging technique. USG findings consistent with renal vein thrombosis include loss of corticomedullary differentiation, renal enlargement (due to decreased drainage), and absent or retrograde flow on Duplex USG (Fig. 26.39C). Renal arterial Duplex USG may show a high resistance flow pattern with reversal of flow during the diastole. CT findings include a dilated renal vein with hypoattenuating filling defect, delayed renal cortical enhancement, ipsilateral renal enlargement, and in cases of chronic thrombosis, the development of venous collaterals. Similar findings are observed on contrast-enhanced MRV.

FIGURE 26.39 Renal vein thrombosis. Contrast-enhanced CT (A) axial and (B) coronal images demonstrating a renal cell carcinoma tumor thrombus (arrow) in the left renal vein extending into the IVC (arrow). (C) Duplex USG demonstrating absent color flow in a patient with left renal vein thrombosis.

The most common malignancy causing renal vein tumor thrombus is RCC, as it has a tendency for vascular invasion (Figs. 26.39A–B). Indeed, tumor thrombus is associated with up to 35% of cases of RCC with the presence and extent of thrombus influencing the tumor stage, surgical management, and overall prognosis [42]. Less commonly, invasive adrenocortical carcinoma can lead to renal vein thrombosis [42]. Rarely, benign tumors such as an angiomyolipoma of the kidney may invade the renal vein or the IVC. The presence of fat attenuation within the tumor thrombus is the key in identifying vascular invasion by a renal angiomyolipoma. Management of malignant tumor thrombus usually involves resection of the tumor thrombus (and tumor), while bland renal vein thrombosis is managed with anticoagulation.

Nutcracker Syndrome (NS) NS refers to the clinical signs and symptoms associated with clinically significant left renal vein compression with left renal venous hypertension. Pathophysiology Most often, the left renal vein is compressed between the SMA and aorta (the aortomesenteric interval) as it courses toward the IVC, the so-called anterior NS. However, in a subset of cases, posterior compression may occur between the aorta and a vertebral body, where there is a retroaortic left renal vein [61], the so-called posterior NS. Clinical Presentation

NS is often seen in young females presenting with flank pain and hematuria. In some cases, left renal vein hypertension can lead to symptoms of pelvic venous congestion and/or a left varicocele in males, secondary to venous reflux in the ipsilateral gonadal vein. NS is a rare condition and the prevalence is unknown [63]. Diagnosis of NS should be considered after other more common conditions have been exonerated (acute cystitis, nephrolithiasis, nephritis, etc.). In other words, NS is considered a diagnosis of exclusion. Imaging Evaluation Diagnosis is confirmed with imaging. Duplex USG is the preferred first diagnostic imaging approach for evaluating NS, as it provides both static and dynamic information [61]. USG findings consistent with NS include elevated peak systolic velocities in the left renal vein at the aortomesenteric interval and a reduced inner diameter of the left renal vein at the interval relative to the renal vein diameter at the renal hilum (Fig. 26.40). More specifically, peak systolic velocities can exceed 200–300 cm/s. Proposed Duplex USG criteria consistent with NS include [64]: ■ Focal compression of the left renal vein near the origin of the SMA ■ Aortomesenteric interval to hilar vein segment peak systolic velocity ratio >5 ■ Aortic/SMA angle 3 mm

FIGURE 26.40 Grayscale ultrasound images of a patient with a reduced inner diameter of the left renal vein at the aortomesenteric interval, findings suggestive of Nutcracker syndrome.

When USG findings are ambiguous, cross-sectional imaging techniques, such as CT or MRI, may be useful. On sagittal cross-sectional images, CT or MRI, the normal angle at the aortomesenteric interval is >45°. However, in NS this angle is ≤35 (Fig. 26.41A) [61,65]. The most specific CT finding is a left renal hilar vein to aortomesenteric diameter ratio of ≥4.9 [65]. CT and MRI findings in NS demonstrate left renal vein compression with the most

specific finding being the beak sign (Fig. 26.41B). Additional findings include the presence of an enlarged ipsilateral gonadal vein and dilated pelvic veins in women and varicocele in men. The disadvantage of conventional cross-sectional imaging is that they provide only static information. For difficult cases where USG, CT and MRI do not provide a definitive diagnosis, venography with intravascular pressure measurements and with or without IVUS may be performed [65]. At venography, contrast material injection frequently demonstrates luminal narrowing and reflux of contrast material into the left gonadal vein (Fig. 26.41C). IVUS may also demonstrate luminal narrowing and extrinsic compression by the SMA. Pressure measurements proximal and distal to the compressed left renal vein will demonstrate a gradient >1 mm Hg [63].

FIGURE 26.41 Contrast-enhanced CT images demonstrating a patient with Nutcracker syndrome. (A) Sagittal image demonstrating left renal vein (LRV) compression (black arrow) between the aorta (A) and superior mesenteric artery (SMA). (B) Axial image demonstrating the “beak” sign (dashed black arrow) in a patient with Nutcracker syndrome. (C) DSA image of a patient with Nutcracker syndrome. Note the absence of contrast opacification at the aortomesenteric interval where there is left renal vein compression and reflux of contrast into the left gonadal vein (LGV). (D) DSA image of the same patient following left renal vein stenting (white arrow).

Management Optimal management of NS remains controversial, but historically involved open surgical treatment (e.g., left renal vein transposition or renal autotransplantation) for cases refractory to conservative therapy with the goal of surgery to reduce or relieve the venous compression. More recently, laparoscopic approaches and percutaneous endovascular interventions have gained traction, as they represent less invasive options. Percutaneous endovascular treatment involves stenting of the left renal vein for decompression (Fig. 26.41D) [65].

Hepatic Veins Anatomy and Variants After receiving blood from the portal venous and hepatic arterial systems, the liver returns blood to the heart by way of the IVC through the hepatic venous system, which normally comprises three hepatic veins: left, middle, and right. The hepatic veins are important anatomic landmarks for dividing the liver up into the Couinaud classification segments. The left hepatic vein drains segments II and III, the middle drains IV, V, and VIII and the largest, the right drains V–VII. Familiarity of the hepatic venous anatomy and possible variants is particularly important for preoperative planning for liver resections and in living donor liver transplantation [66]. In a majority of the population, the middle and left hepatic veins merge forming a common vessel before draining into the IVC. Hepatic venous variants are common, occurring in up to a third of the population, with accessory hepatic veins separately draining into the IVC being the most common variant [66].

Hepatic Vein Thrombosis and Budd–Chiari Syndrome Hepatic venous outflow obstruction is most often clinically seen in the setting of BCS. BCS is a severe form of hepatic vein thrombosis describing the clinical and laboratory abnormalities associated with hepatic venous outflow obstruction. BCS is most often associated with bland thrombosis and, overall, rare with an estimated incidence of 1 in 100,000 [67]. Pathophysiology Etiologies may be classified as primary or secondary (Table 26.6). Primary etiologies, conditions that promote thrombosis, comprise the majority of cases. Table 26.6 Causes of Hepatic Vein Thrombosis [67] Primary causes

Myeloproliferative disease Nocturnal paroxysmal hemoglobinuria Inherited thrombophilias Antiphospholipid antibody syndrome

Behçet's disease Celiac disease Sarcoidosis Pregnancy Estrogen containing contraceptives Secondary causes

Infection Malignancy

Myeloproliferative diseases are the most common cause of BCS, accounting for approximately 50% of cases [68]. Secondary causes of BCS are caused by vascular compression, as in cases of infection (e.g., amoebiasis, hydatid disease, or echinococcosis), or due to malignancy where there is vascular invasion (e.g., HCC, leiomyosarcoma of the IVC, or myosarcoma of the right atrium). Clinical Presentation Presentation of BCS is variable, dependent upon the stage of the disease and may be symptomatic or asymptomatic, with the chronic symptomatic form being the most prevalent [67]. Acute presentations may demonstrate ascites, upper abdominal pain, lower extremity edema, hepatomegaly, and encephalopathy [69]. Chronic presentations are characterized by portal hypertension typically with the development of collateral vessels circumventing the hepatic obstruction and ascites is variably present. Imaging Evaluation Imaging is critical for diagnosing, staging, and developing an effective treatment strategy for BCS. USG represents the best first test for suspected BCS cases, demonstrating characteristic static and dynamic imaging features (Table 26.7 and Fig. 26.42) [67]. Table 26.7 USG Findings Consistent With BCS Static USG features [67]

Hypoechoic endoluminal material (direct visualization of intraluminal thrombus) within the hepatic veins Hepatic venous stenosis or segmental occlusion with poststenotic dilatation

Hepatic vein replacement with a hyperechoic fibrous cord Intrahepatic venous collaterals Dynamic USG features [69]

Abnormal flow (e.g., absent, turbulent or reversed) in the hepatic veins

Loss or blunting of the normal hepatic venous flow variation with respiration and the cardiac cycle

FIGURE 26.42 Duplex ultrasound showing loss of flow in the middle hepatic (MHV) and right hepatic veins (RHV) in a patient with Budd– Chiari syndrome.

Overall imaging features vary based on the stage and extent of disease. Both CT and MR are very useful in diagnosis and management of BCS. CT and MR findings consistent with BCS include hepatomegaly and lack of hepatic venous contrast enhancement within the occluded vessels. The appearance of the hepatic veins varies based on the chronicity (Table 26.8). A “flip-flop” pattern may be seen in the portal venous phase of CECT, with low attenuation of the central part of the liver due to washout with increased attenuation in the peripheral part of the liver gradually due to contrast accumulation from capsular veins [69]. Lastly, venography is not used in diagnosis but is an important tool utilized during endovascular treatment [67]. Table 26.8 CT and MR Imaging Findings in BCS Based on Chronicity [69]

Acute features

Early homogenous enhancement of an enlarged caudate lobe at CT Hyperattenuating hepatic veins on noncontrast images at CT Hepatic vein hyperintensity on T2-weighted images at MR

Chronic features

Small, hypoattenuating hepatic veins at CT Hepatic vein hypointense signal on all sequences at MR Caudate hypertrophy Presence of regenerative liver nodules Development of intra- and extrahepatic collateral veins

Management Similar to other venous diseases, the treatment of BCS has evolved from a condition formerly managed primarily with surgery to one that is now primarily managed with percutaneous image-guided endovascular therapy. Specifically, percutaneous angioplasty and stenting of the IVC/hepatic veins are used as first-line treatment with the primary goal of restoring hepatic venous drainage, which has been shown to significantly improve patient outcomes. In patients who fail angioplasty and stenting, transjugular intrahepatic portosystemic shunt (TIPS) or direct intrahepatic portocaval shunt may be used for decompression of the portal system. In contrast to patients with cirrhosis, patients with BCS treated with TIPS demonstrate a relative low rate of hepatic encephalopathy [70].

Porto–Mesenteric–Splenic Venous System Anatomy and Variants The classic portal venous system is comprised of the main, right, and left portal veins. The main portal vein originates near the neck of the pancreas at the confluence of the superior mesenteric and splenic veins. As the main portal vein reaches the liver at the porta hepatis it divides into the right and left portal veins (Fig. 26.43). Portal venous variants include portal vein trifurcation, occurring in 10–16% of the population and dual venous supplies (both right and left) to segment VIII. Portal vein trifurcation describes the

presence of a right anterior portal vein, right posterior portal vein, and left portal vein [66]. Portal venous shunts, which are aberrant vascular communications between the portal and systemic venous circulations, are frequently observed. The most common form of shunt is the acquired, extrahepatic type that typically develops secondary to portal venous hypertension, discussed in the next section. Congenital extrahepatic venous shunts comprise the other form, which are relatively rare and organized by Abernethy types [71].

FIGURE 26.43 Illustration of the portosystemic collaterals. (Courtesy: Susanne Loomis.)

Noninvasive imaging evaluation of the portal venous system may be accomplished with USG, CT, and MRI. USG has the advantage of providing information about flow velocity and direction. MRI can provide some information about flow, but is inferior to US. CT is the best technique for the evaluation of portal venous gas and calcifications. Invasive imaging

approaches, such as direct and indirect portography, are frequently reserved for cases when a percutaneous intervention may be planned or when USG or cross-sectional approaches provide ambiguous findings. At most centers, however, CECT is the most commonly used technique for imaging evaluation of the portal venous system [71].

Portal Hypertension Portal hypertension is defined as elevated portal venous pressures above the normal range (7–12 mm Hg). Pathophysiology The most common cause of portal hypertension is cirrhosis from chronic liver disease [72]. Although, there are numerous potential causes and may be classified by their anatomic location: prehepatic, intrahepatic, and posthepatic. Prehepatic causes include portal vein thrombosis (PVT), splenic or mesenteric vein thrombosis, AVF, congenital stenosis of the portal vein, and extrinsic compression. The majority of causes of prehepatic portal hypertension are caused by PVT. Intrahepatic causes of portal hypertension may be further dichotomized into cirrhotic and noncirrhotic causes or idiopathic portal hypertension. Noncirrhotic causes are often associated with systemic diseases or conditions include, but are not limited to, HIV infection, recurrent gastrointestinal infections, immune disorders, and certain inherited conditions. Posthepatic causes result from hepatic venous obstruction, as in BCS [72]. The pathophysiology underlying the increased resistance within the portal system causing hypertension is hypothesized to result from both physical obstruction as well as dynamic changes in vascular tone. Clinical Presentation At presentation, patients often complain of abdominal distension from ascites, hemorrhoids, and unattractive veins about the umbilicus. These complaints arise from the complications of elevated portal venous pressures. Other findings include the develop-ment of multiple portosystemic collaterals, esophageal varices, hypertensive gastropathy, enteropathy, hepatic encephalopathy, and splenomegaly. One of the most important clinical consequences of untreated portal hypertension are esophageal varices, which can lead to life-threatening gastrointestinal hemorrhage. The diagnosis of portal hypertension is often inferred on imaging by observing the associated portal hypertension complications. Indeed, USG, CT, and MRI are useful techniques for evaluating sequela associated with portal hypertension as well as the underlying etiology. Imaging Evaluation

Imaging findings commonly seen with portal hypertension include an enlarged main portal vein (>12 mm in diameter, splenomegaly, a small nodular liver with or without left hepatic lobe enlargement, enlarged portosystemic shunts, and a patent umbilical vein). Duplex USG may demonstrate hepatofugal flow of blood within the portal or umbilical veins. Acquired portosystemic shunts, or collaterals, can be numerous in the setting of chronic portal hypertension and have the potential to cause significant morbidity and mortality. Table 26.9 lists the clinically important portosystemic collaterals. On cross-sectional imaging, shunts appear as enlarged, tortuous structures that demonstrate contrast enhancement. On Duplex USG, they typically demonstrate hepatofugal flow. The most common shunts include gastroesophageal, paraesophageal, paraumbilical, splenorenal, and inferior mesenteric venous collaterals [71]. Of these, the most important collateral pathway is within the distal esophagus and proximal stomach, the site of the gastroesophageal varices, where gastric variceal hemorrhage is fatal in up to 45% of patients [73]. Indeed, in certain cirrhotic patients meeting risk, esophagogastroduodenoscopy is recommended for variceal screening [74]. Esophageal varices develop in up to 70% of cirrhotic patients whereas gastric varices are present in up to a third [73]. Table 26.9 Portosystemic Collaterals Portal Venous Name Connection

Systemic Venous Connection

Esophageal varices

Left Gastric

Azygos

Gastric varices

Left Gastric Short Gastric Gastroepiploic

Azygos Phrenic/adrenal

Gastro-splenorenal shunt

Left Gastric Vein Short Gastric Gastroepiploic

Phrenic/adrenal and left renal

Caput medusa (enlarged paraumbilical vein)

Left portal vein

Femoral

Name

Portal Venous Connection

Systemic Venous Connection

Rectal varices

Superior hemorrhoidal (from inferior mesenteric vein)

Middle and inferior hemorrhoidal veins of internal iliac veins

Retroperitoneal varices

Branches of the superior and inferior mesenteric veins

Gonadal Lumbar

Patent ductus venosus

Left portal

Inferior vena cava

Stomal varices

Mesenteric

Epigastric

Since direct measurement of portal venous system pressure requires a fairly invasive approach, requiring direct cannulation of the portal vein, less invasive, indirect measures of portal hypertension are routinely used. Namely, the hepatic venous pressure gradient (HVPG) is the most commonly used metric for accurately diagnosing and staging portal hypertension. Indeed, the HVPG is viewed as the gold-standard method of assessing portal hypertension. Typically, performed by an interventional radiologist, the HVPG is determined through percutaneous endovascular placement of a pressure sensing balloon tipped catheter in a distal hepatic venule whereby occluding the vessel permits determination of the wedge pressure. The difference between the wedge hepatic venous pressure and the hepatic vein pressure represents the HVPG. HVPG values greater than 5 mm Hg defines portal hypertension and values greater than 10 mm Hg predict portal hypertensive complications [74]. In prehepatic portal hypertension, the HVPG is typically normal. Whereas, in intrahepatic portal hypertension, the HVPG is usually increased [72]. Management The management of clinically significant varices is dependent upon the stage of cirrhosis and degree of portal hypertension. For patients with compensated cirrhosis and documented varices (high-risk small or, medium or large varices), treatment begins with beta blocker therapy to prevent variceal hemorrhage. In patients presenting with an acute variceal hemorrhage, esophagogastroduodenoscopy with variceal ligation should be performed within the first 12 hours of admission, in addition to the other required standards of care, including blood product transfusion, antibiotic therapy, and administration of vasoactive agents [74]. TIPS represents an important treatment option for patients at high risk for variceal hemorrhage recurrence and is the best treatment for patients who fail

first-line variceal hemorrhage prophylaxis (beta blocker therapy plus variceal ligation). TIPS is also indicated for refractory ascites, hepatic hydrothorax, and symptomatic BCS [75]. Less common indications for TIPS include hepatorenal syndrome, portal hypertensive gastropathy, and ectopic varices. The TIPS procedure involves creating an artificial shunt through the hepatic parenchyma connecting a hepatic vein (usually the right or middle hepatic vein) with the portal venous system (usually the right portal vein). Preprocedural CECT or MRI is recommended for all patients to define the patient's portal and hepatic vascular anatomy (both venous and arterial), assess venous patency, evaluate the presence of underlying HCC and look for chronic hepatic parenchymal changes (e.g., atrophic right hepatic lobe and hypertrophied left). Conventionally, the tract is created under fluoroscopic guidance (Fig. 26.44). Additional image guidance like transabdominal US, IVUS improve the success rate close to 100%. The most common early clinically significant complications include intraperitoneal hemorrhage secondary to liver capsule puncture or extrahepatic portal vein puncture, renal failure, PVT, and worsening hepatic encephalopathy. An important late complication of TIPS is shunt stenosis or occlusion [75]. USG is the best imaging technique used to screen for TIPS stenosis or restenosis. Duplex USG findings suggestive of TIPS stenosis include [76]: ■ Abnormally low or high peak velocities within the shunt (190 cm/s) ■ Main portal vein velocity 5 mm) Multiple dilated para-uterine varices Retrograde flow in either gonadal vein Polycystic ovarian configuration

Contrastenhanced MRV features

Retrograde caudal flow of contrast material (best appreciated during the arterial phase) Dilated ovarian vein and para-uterine varices Slow flow (T2 hyperintensity) Presence of an arcuate vein crossing midline, vulvar, and/or other varices Polycystic ovarian configuration

CTV features

Single or bilateral dilated gonadal vein(s) (>8 mm) Four ipsilateral tortuous and dilated para-uterine veins

Following noninvasive imaging, venography is performed. Complete venographic evaluation should include imaging assessment of the IVC, left renal vein, bilateral gonadal veins, and bilateral common and internal iliac veins. Diagnostic criteria for GVI (and PVCS) include ectatic gonadal and uterine veins, contrast reflux with valvular incompetence and paradoxical cross pelvic flow of contrast through pelvic varicosities and collaterals [81]. Management The most effective treatment for PVCS is minimally invasive endovascular therapies. However, symptomatic patients are nearly always initially managed with conservative therapy. Conservative treatment involves lifestyle changes, nonsteroidal anti-inflammatory treatment, and in some cases pharmacologic ovarian suppression. Surgical management, involving laparoscopic venous ligation, hysterectomy, and/or salpinoophorectomy, is reserved for cases refractory to endovascular therapy [85]. Consensus guidelines recommend selective coil/sclerosant embolization of the gonadal vein with embolization or sclerotherapy of the ipsilateral internal iliac vein [82]. Lastly, embolization may also be used in males with symptomatic varicoceles.

Gonadal Vein Thrombosis GVT is rare. In females, it is mostly seen in the postpartum setting, whereas in men it can be seen in the postoperative setting or as a rare cause of spontaneous acute scrotal pain [86,87]. GVT can also occur secondary to thrombus extension arising in the IVC or left renal vein. Symptoms associated with GVT are nonspecific but can include flank or groin pain in females and flank, groin, or scrotal pain in males [88]. Gonadal venous thrombosis can be very difficult to identify using sonography. CTV and MRV are the most useful initial imaging techniques, which may demonstrate filling defects within the involved segments (Fig. 26.50). Consensus guidelines recommend anticoagulation for postpartum ovarian vein thrombosis [88].

FIGURE 26.50 Contrast-enhanced CT images of a patient with left ovarian vein thrombosis. (A) Axial and (B) sagittal reconstructed images demonstrating an enlarged left ovarian vein with a hypoattenuating filling defect within the lumen (arrow). The linear hyperattenuation adjacent to the left ovarian vein represents the left ureter with contrast filling the lumen (dashed arrow).

Adrenal Veins Anatomy and Variants In most individuals, there are single adrenal veins bilaterally with the right adrenal vein emptying directly into the IVC above the right renal vein and the left adrenal vein emptying into the left renal vein, often after receiving

blood from the inferior phrenic vein. Variant adrenal vein anatomy is infrequent. The most often encountered variant adrenal vein anatomy on the right includes a single main adrenal vein with multiple smaller veins draining into the IVC, two adrenal veins directly draining into the IVC and least commonly, drainage to the right hepatic vein with or without concurrent drainage to the IVC. On the left, variants include two adrenal veins draining into the left renal vein with or without shared drainage with the inferior phrenic vein. Variant anatomy appears to be more commonly encountered in patients with adrenal tumors [89]. Direct drainage of the left adrenal gland into the IVC is rare [90].

Adrenal Vein Imaging and Sampling CECT, MR, and venography are the most useful imaging techniques for evaluating the bilateral adrenal veins. Focused imaging evaluation of the adrenal veins is principally aimed at planning in preoperative adrenalectomy patients and preprocedural patients undergoing adrenal venous sampling for suspected functional adrenal adenoma(s). Preoperative knowledge of both the number and location of the adrenal vein(s) helps the surgeon perform a safe and efficient surgery. CECT appears to be the preferred technique, as it demonstrates better visualization compared to noncontrast-enhanced MR [91]. Thin slice CECT images acquired 60 seconds following injection with coronal reconstruction increase the likelihood of accurate identification [92]. Venography is reserved for cases where adrenal venous anatomy needs to be defined for accurate venous blood sampling to localize a functioning adrenal adenoma, predominately for cases of Conn syndrome (primary hyperaldosteronism) and less commonly in cases of suspected adrenal Cushing syndrome [92,93]. Patients diagnosed with hyperfunctioning adrenal adenomas are cured with surgical resection. For patients with laboratory evidence suggestive of primary hyperaldosteronism (elevated plasma aldosterone:plasma renin assay ratio), a CECT scan is routinely performed in the initial work up to look for CT evidence of one or more adrenal adenomas. Unfortunately, CT performs poorly at accurately identifying culprit hyperfunctioning adenomas. Venography with adrenal venous blood sampling is performed to determine lesion laterality and has an accuracy rate of up to 97% (Fig. 26.51) [93].

FIGURE 26.51 DSA images of a patient who underwent successful sampling of the (A) right adrenal and (B) left adrenal veins.

Central Thoracic Veins Anatomy and Variants The thoracic central venous anatomy is comprised of the bilateral subclavian, brachiocephalic, azygos, hemiazygos veins, and SVC. As each axillary vein passes under its respective clavicle, it continues medially as the subclavian vein eventually merging with the ipsilateral internal jugular vein forming the respective brachiocephalic veins. The SVC, the largest central vein in the mediastinum, is formed posterior to the manubrium within the superior mediastinum by the confluence of the brachiocephalic veins. Descending inferiorly within right aspect of the mediastinum toward the right atrium the distal SVC receives blood draining from the azygos vein. Noteworthy, congenital variant anatomy includes a double SVC (Fig. 26.52), occurring in 0.3% of individuals [12], a persistent left SVC (Fig. 26.53), occurring in less than 0.5% of patients and right upper lobe partial anomalous pulmonary venous return (PAPVR) occurring in 0.5–0.7% of the population (Fig. 26.54) [94]. A double SVC arises when the left anterior cardinal vein fails to regress, whereas a left SVC arises secondary to the abnormal regression of the right anterior cardinal vein instead of the left.

FIGURE 26.52 Noncontrast CT (A) axial and (B) coronal reconstructed images of a patient with a double SVC. The arrow denotes the aberrant left SVC.

FIGURE 26.53 Patient with persistent left SVC. (A) Chest radiograph illustrating the course of the persistent left SVC via the course of the patient's central catheter. (B) CT coronal reconstructed and (C) axial images of a left SVC (arrow).

FIGURE 26.54 Cardiac CT (A) axial and (B) multiplanar reconstructed images demonstrating a patient with a levoatriocardinal vein (connection of the left superior upper lobe pulmonary vein, left brachiocephalic vein, and left atrium). (C) Demonstrates the connection to the left brachiocephalic vein.

On cross-sectional imaging, a persistent left SVC is seen arising at the confluence of the left subclavian and jugular veins descending inferiorly where it drains into the right atrium via a dilated coronary sinus. It is seen lateral to the aorta and should be suspected if the coronary sinus appears dilated. This anomaly is important to recognize as the anatomy becomes important for patients requiring a left-sided CVC, pacemaker, or pulmonary artery catheter [94].

Superior Vena Cava Syndrome SVC syndrome refers to the constellation of clinical findings seen in patients with obstruction of the SVC. In the United States, each year approximately 15,000 patients present with SVC syndrome [95]. Obstruction of the SVC is frequently classified by etiology: benign or malignant. Benign etiologies comprise approximately 35% of cases [95] with examples including infection (tuberculosis and syphilitic aortic aneurysm), fibrosing mediastinitis, prior radiation therapy and iatrogenic SVC stenosis or thrombosis secondary to CVCs, pacemakers, and defibrillators [96]. Malignant SVC syndrome arises as a result of a cancer progressively compressing the SVC with the most common cancers including small cell and nonsmall cell lung cancer, lymphoma, and metastases. The most common cancer known to cause SVC syndrome is nonsmall cell lung cancer [95]. Patients present with variable symptoms on a spectrum of severity based on the degree of venous obstruction. Symptoms frequently include swelling of the head, neck, and arms with associated cyanosis, as well as, headaches, blurry vision, cough, hoarseness, stridor, dyspnea, and dysphagia [95]. Acute SVC syndrome is a vascular emergency. The best imaging technique for efficient evaluation of possible SVC syndrome is CECT of the chest. CT demonstrates variable loss of SVC

contrast-enhancement based on the degree of venous obstruction (Figs. 26.55–26.57). In cases of complete obstruction, there will be prominent collateral vessels demonstrating contrast enhancement. CT also has the advantage of helping to define the underlying cause as benign or malignant. When performing CECT, to minimize mixing artifact from peripheral intravenous contrast material injection, image acquisition may be performed after 60–75 seconds [94].

FIGURE 26.55 Contrast-enhanced CT showing (A) sagittal reconstructed and (B) axial images of a patient with benign SVC syndrome secondary to compression of the SVC (arrows) by a large partially thrombosed thoracic aortic aneurysm.

FIGURE 26.56 Contrast-enhanced CT showing (A) axial and (B) sagittal reconstructed images of a patient with malignant SVC syndrome secondary to compression of the SVC (arrows) by a large right upper lobe nonsmall cell lung cancer.

FIGURE 26.57 Contrast-enhanced CT coronal reconstructed imaging showing a patient with benign SVC syndrome secondary to a central line associated occlusive SVC thrombus (arrow).

Given lesions causing SVC syndrome are centrally located, Duplex USG is limited in evaluating SVC obstruction due to the lack of an adequate acoustic window. However, on Duplex USG of the upper extremity veins or the jugular veins, the indirect findings include a blunted or complete loss of normal waveform variability with respiration and the cardiac cycle. In patients where CECT is less desirable (such as in patients with an iodinated contrast allergy or in pediatric patients), gadolinium-enhanced MRV is equally sensitive and specific for evaluation of central venous obstruction. MRV will demonstrate similar findings of obstruction and development of collateral vessels. In patients with chronic renal insufficiency, noncontrast MR may be performed using SSFP sequences [94]. Venography provides the best overall imaging evaluation of the obstruction but is typically reserved for patients where endovascular treatment may be indicated, as this approach is more invasive. Depending on disease severity,

venography may demonstrate a luminal filling defect within the SVC or complete SVC obstruction with development of collateral vessels. A notable collateral pathway is through the left portal vein via the internal mammary and paraumbilical veins, where focal contrast enhancement may be seen in the quadrate lobe (Fig. 26.58). Historically, this has been referred to as the hot-quadrate sign due to the accumulation of radiopharmaceutical at this site due to SVC obstruction.

FIGURE 26.58 Contrast-enhanced CT showing focal contrast enhancement of the quadrate lobe (arrow) in a patient with benign SVC syndrome.

Treatment decisions for SVC syndrome are made at the individual level largely based on the severity of disease and toward addressing the underlying cause. In cases of malignant obstruction where disease severity is mild– moderate, chemotherapy, and radiation maybe used as first-line treatments, usually following pathologic tissue evaluation. Endovascular treatments with stenting of the SVC represent an important management strategy for cases of malignant obstruction in patients with severe symptoms, patients with persistent symptoms refractory to chemotherapy and in patients where chemoradiation are contraindicated. Endovascular angioplasty with stenting

may also be used as adjuncts to anticoagulation in cases of SVC obstruction secondary to thrombosis [97].

Pulmonary Veins Anatomy and Variants The pulmonary veins are responsible for returning oxygen replenished blood from the lung's capillary beds to the left atrium for systemic distribution. Within the population, there is considerable anatomic variation of the pulmonary veins. In most individuals, blood returns to the left atrium via four distinct openings, or ostia, within the left atrium. Common variant anatomy consists of a single left pulmonary vein, separate right middle lobe vein and a separate right top pulmonary vein draining the apical right upper lobe. Supernumerary pulmonary veins are usually seen on the right with the most common variant being a right middle lobe vein. In up to 20% of individuals, drainage of the left lung into the left atrium arises from a common ostium [98]. Anomalous anatomy primarily consists of PAPVR and total anomalous pulmonary venous return. Both scenarios result in pulmonary venous drainage in the systemic system resulting in a left-to-right shunting. In PAPVR seen on the left, usually one or more pulmonary veins drains into the left brachiocephalic vein through a cardinal vein. When PAPVR is detected it is important to carefully define the aberrant venous course, as in some cases a perceived PAPVR may actually represent a levoatriocardinal vein, which is another anomalous pulmonary vein connection to both a systemic vein and the left atrium (Fig. 26.54). A levoatriocardinal vein represents a possible route for a paradoxical embolus to travel from the venous system to the arterial system. The scimitar sign, a curvilinear right lower lung zone opacity on frontal chest radiograph, represents another form of PAPVR where there is drainage of the right lower lobe pulmonary veins into the IVC. The scimitar sign is often seen in patients with scimitar syndrome [98] (Fig. 26.59).

FIGURE 26.59 Aberrant pulmonary venous drainage. (A) Chest radiograph demonstrating the scimitar sign (black arrow). (B) Noncontrast-enhanced CT coronal reconstructed and (C) axial images showing the right lobe pulmonary venous drainage into the IVC.

Pulmonary Vein Imaging Both CT and MR are useful for evaluating the pulmonary venous anatomy (Fig. 26.60). Imaging evaluation of the pulmonary veins is important in cancer imaging, congenital heart disease, perioperatively for cardiac and thoracic surgery, and preprocedurally for pulmonary vein ablation planning (commonly referred to as pulmonary vein isolation) for management of selected patients with atrial fibrillation who are refractory to medical management. For pulmonary vein isolation planning, several important components should be present in the radiology report, including [98]: ■ Number, arrangement, and size of pulmonary veins ■ Ostial size and arrangement (independent or shared) ■ Size of fossa ovalis ■ Thickness and height of the ridge between the left superior pulmonary vein and the left atrial appendage ■ Relationship of left atrium and esophagus ■ When present: ○ PAPVR ○ Atrial septal defect ○ Left atrial anomalies ○ Anatomical variants of coronary arteries in close proximity to the pulmonary vein ostia such as S-shaped SA nodal artery

FIGURE 26.60 Cardiac CT for PVI. (A) Axial image of a normal appearing left atrium. (B) 3D reconstructed image of the left atrium. (C) Patient with left atrial appendage thrombus (arrow).

CECT is particularly advantageous as it can be performed quickly, it provides better special resolution and can be performed with electrocardiogram timed acquisition (ECG or cardiac gating). Indeed, cardiac-gated CT should be used when assessing pulmonary vein ostial sizes, as this approach can significantly limit cardiac motion artifact [98].

Part II: Diseases of Lymphatics and Vascular Malformations This section discusses the structure and function of the lymphatic system, as well as the common imaging techniques used to evaluate it. A brief summary of the most commonly encountered disorders affecting the lymphatic system is then discussed, with the exception of lymphoma which is reviewed elsewhere. The chapter ends with a discussion of vascular malformations.

Lymph System Anatomy and Variants The lymphatic system, sometimes referred to as the other circulatory system of the body, represents a complex network of vessels and secondary lymphoid organs that communicate with the circulatory system. Although the lymphatic system remains poorly studied compared to the circulatory system, it is indisputable that a functional lymphatic system is an important pillar of health. Analogous to the circulatory system, the lymphatic system is comprised of four parts: fluid (lymph), vessels (lymphatics), organs (lymph nodes), and cells (lymphocytes). Additionally, the lymphatic system can be organized into three distinct subsystems: the soft tissue lymphatics, intestinal lymphatics, and liver lymphatics [99]. The most important functions of the lymphatic system are to return interstitial fluid from the soft tissues back to

the circulatory system, facilitate absorption of dietary fats and fat-soluble nutrients, and support the adaptive immune system. The anatomy of the body's lymphatics is more variable and less predictable than the circulatory system. There are lymphatics within most body tissues except avascular tissues, such as articular cartilage. Additionally, lymphatics are not present in bone marrow and splenic pulp. Historically, the central nervous system was believed to also not have lymphatics, in the conventional sense, due to its lack of true lymphatic vessels. Recent research, however, has demonstrated that the CNS has its own pseudolymphatic network, termed the glymphatic system [100]. Within the peripheral tissues there are microscopic clefts that have a similar function to lymphatics but, in contrast to lymphatic capillaries, lack an endothelial lining. The characteristic endothelial wall seen in lymphatic capillaries is permeable to larger molecules that cannot pass through the endothelial lining of vascular capillaries. This allows the lymphatic system to absorb proteins and particulate matter, including cells and cell debris and microorganisms, as well as excess extracellular tissue fluid. The lymphatics draining the gut are also known as lacteals. Following a meal, the lymph (chyle) within these gut lymphatics appears milky white due to the presence of fat chylomicrons being transported away from the gut wall. In the body the larger lymphatic trunks accompany the arteries and veins. Similar to veins, lymphatics harbor valves which promote unidirectional flow of lymph. Lymph is driven through the lymphatics indirectly through skeletal muscle contractions and directly by the contraction of smooth muscle located in the larger lymphatic channels. In contrast to the circulatory system, movement of lymph is not driven by a central pump, leading to important differences in imaging and in disease. Most lymph in the body returns to the venous circulation by way of the main lymphovenous connection, the terminal thoracic duct, which is located at the junction between the left subclavian and jugular veins. The thoracic duct is the largest lymph channel in the body draining most of the body's lymph with the exception of the right arm, head, neck, and hemithorax which are drained by the right lymphatic duct [99]. The thoracic duct classically originates at the cisterna chyli, the central dilated retroperitoneal sac located anterior to the spine at approximately L1–L2 posterior to the abdominal aorta. The cisterna chyli is frequently seen on cross-sectional imaging appearance similar to as an enlarged retrocrural lymph node on CT or T1weighted images, but is very bright on T2-weighted image. As the thoracic duct courses toward its terminus in the left supraclavicular region, it receives lymph from the lower intercostal spaces and mediastinum. Typically, the thoracic duct consists of a single vessel, however, in up to 60% cases multiple channels exist. Variations from the classic single thoracic duct terminus also exist including a bifid termination, terminal branching with

reanastomosis, and a complicated trifurcation [99]. Approximately 80% of the lymph within the thoracic duct originates from the liver and intestinal lymphatic subsystems [101]. Lymph from almost all parts of the body traverses one or more lymph nodes before reaching the venous circulation. Lymph nodes are encapsulated aggregates of lymphatic tissue, normally small and bean shaped and situated in the path of the lymphatic vessels. A fibrous capsule covers the outer surface of the lymph node. Fibrous tissue extends into the lymph node in the form of trabeculae arising from the undersurface of this capsule, so that the lymphoid tissue within the lymph node is supported by a fine meshwork of fibrocellular elements. A slight depression on one side of the lymph node is termed the hilum, and it is through the hilum that blood vessels enter and leave the lymph node. A single efferent lymphatic also leaves from the hilum.

Lymphatic Imaging Historically, the development of lymphatic imaging techniques has lagged considerably behind the imaging techniques of the cardiovascular and circulatory systems, in large part due to the difficulty associated with delivery of lymphatic contrast agents. Nonetheless, several useful imaging approaches are available for evaluating normal and abnormal lymphatic function. Lymphangiography represents an indispensable, minimally invasive imaging tool for imaging the lymphatic system. Multiple forms of lymphangiography remain in use: interstitial, pedal, and intranodal. Interstitial lymphangiography involves injection of lipid soluble contrast material into the interstitial tissue, relying on the eventual contrast migration into the lymph vessels permitting radiographic visualization. With pedal lymphangiography direct lymph vessel cannulation with injection of contrast material (lipiodol) is performed. To identify the lymphatics, however, injection of a colored dye, such as isosulfan blue or methylene blue, typically is performed first. Lastly, with intranodal lymphangiography, USG-guided lymph node injection of contrast material (lipiodol) is performed (Fig. 26.61). This approach has proven itself as a superior alternative to pedal lymphangiography in many circumstances permitting injection of both oilbased iodinated and gadolinium contrast agents [101].

FIGURE 26.61 Fluoroscopy image of patient undergoing a bilateral inguinal intranodal lymphangiogram.

Lymphoscintigraphy is a nuclear medicine, minimally invasive imaging approach that is conceptually similar to lymphangiography. Lymphoscintigraphy was developed after lymphangiography as an alternative and has several unique advantages. The approach involves the subcutaneous injection of a small volume of gamma radiation emitting radionuclides (usually albumin bound 99mTc) that may be detected using a gamma camera. Similar to interstitial lymphangiography, the radioactive material is eventually taken up by the lymphatics permitting visualization. This approach represents a useful alternative in patients with an iodinated contrast allergy, in patients with pulmonary disease (it cannot cause PE, as

opposed to lipid soluble agents used in lymphangiography) and in intensive care patients. Lymphoscintigraphy is indicated for: ■ Lymphatic dysplasia ■ Primary and secondary lymphedema ■ Chylous leaks

Relative contraindications include pregnant patients, breast feeding, and patients unable to maintain a stationary position for a relatively short period of time [102]. More recently, developments in cross-sectional imaging, namely MRI, have led to improved evaluation of the central and peripheral lymphatics. Indeed, studies have shown contrast-enhanced MR lymphangiography demonstrates higher sensitivity for detecting lymph vessel abnormalities compared to lymphoscintigraphy [103]. MR lymphangiography is indicated for diagnosing lymphedema and in the preoperative planning (Fig. 26.62). Again, the approach relies on the initial injection of subcutaneous contrast agent before imaging (extracellular gadolinium-based contrast). Both spinecho and gradient-echo sequences with fat suppression over multiple time intervals are routinely used to provide adequate dynamic images [104].

FIGURE 26.62 MR lymphangiogram coronal image of a child with Milroy disease resulting in unilateral left lower extremity lymphedema. Note the dilated left hemipelvis lymphatics (arrows).

Lymphorrhea Lymphorrhea is defined as abnormal leakage or flow of lymph arising from lymph vessel disruption and can be observed anywhere in the lymphatic system. Disruption of the lymphatic channels in the abdomen or thorax can lead to chylous ascites (CA) or chylothorax, respectively. Chylothoraces represent an important disorder with the potential for considerable morbidity and mortality, and are frequently classified as traumatic or atraumatic [105]. Traumatic etiologies are believed to comprise a small majority of the total cases with prior thoracic surgery representing leading cause within this group [106]. The most commonly associated surgeries include esophagectomy, congenital heart disease, and lung resection. The most common causes of spontaneous chylothorax appear to be due to lymphoma and other malignancies [107]. Patients present with chest pain, fever, fatigue, and dyspnea, with the dyspnea being the most common presenting symptom.

Initial imaging evaluation during patient work up begins with a chest radiograph to confirm the presence of a pleural effusion and rule out other potential causes of dyspnea (Fig. 26.63A). Diagnosis is confirmed by laboratory analysis by sampling the fluid via thoracentesis and confirming the presence of chyle, with objective diagnostic criteria including a pleural fluid triglyceride level of >110 mg/dL and a ratio of pleural fluid to serum triglyceride level >1.0. Although imaging plays a minor role in the initial diagnosis, it often plays a much larger role in treatment planning in refractory cases [105].

FIGURE 26.63 Chylothorax. (A) Chest radiograph demonstrating a patient with a right hydropneumothorax that turned out to be a chylothorax following sampling by thoracentesis and laboratory analysis. (B) Lymphangiogram demonstrating mid-thoracic duct leak (arrow) leading to the right chylothorax. (C) Fluoroscopy image following successful lymphangiogram and coil embolization treatment.

Optimal management of a chylothorax typically depends on its recurrence following the initial thoracentesis used to diagnose the condition, as well as the patient's response to conservative therapy. Initial management includes addressing the underlying cause, if possible, palliative thoracentesis, dietary modification, and administration of certain medications, such as octreotide [105]. A trial of total parenteral nutrition while avoiding enteral nutrition is helpful in some cases. In refractory cases, thoracic duct embolization may provide a cure. Thoracic duct embolization describes a minimally invasive, percutaneous approach where first lymphangiography is performed to identify the thoracic duct, followed by its embolization, often using sclerosant or coils (Figs. 26.63B–C). TDE has become an increasingly popular approach as it avoids invasive surgery [106].

CA is another uncommon form of lymphorrhea that may occur following abdominal trauma or surgery. CA has been reported following gastrectomy, esophagectomy, pancreaticoduodenectomy, abdominal aortic surgery, IVC resection, and liver transplantation. Similar to chylothorax, CA is made on fluid analysis following sampling with percutaneous paracentesis. Laboratory criteria consistent with CA include a triglyceride >100 mg/dL and cholesterol >200 mg/dL. Even though the diagnosis is usually achieved via laboratory analysis, CT findings of a fat-fluid level within the abdomen is considered pathognomonic for CA [108]. Similar to management of chylothorax, conservative management is first-line therapy, involving exclusive total parenteral nutrition and octreotide administration. Patient's refractory to conservative measures may be considered for lymphangiography followed by percutaneous sclerotherapy or surgery. Patients with CA secondary to a large leak, defined as >1000 mL/day for 5 days, despite conservative measures are often take to surgery where ligation is performed [109].

Lymphedema Peripheral lymphedema describes the condition of progressive swelling, often involving the lower extremities, due to lymphatic dysfunction. Lymphedema may be categorized as primary, occurring as a result of abnormal lymph development, or secondary, due to disruption of the normally developed lymphatic system which may occur in trauma or following surgery. Over time, the inability to adequately clear fluid from the interstitial space leads to soft tissue changes characterized by fat deposition and fibrosis. Clinically, differentiating lymphedema from other causes of extremity swelling, such as DVT or syndromic causes of unilateral limb size discrepancy, is important for establishing an effective management approach [110]. On Duplex USG, lymphedema may manifest as increased extracellular fluid, appearing anechoic/hypoechoic. Also, the subcutaneous tissue may also appear hyperechoic secondary to increased fat deposition. Differentiating cellulitis from lymphedema is important for selecting appropriate therapy, but can be difficult to discern by imaging alone. Findings suggestive of cellulitis include warm, erythematous skin with apparent hypervascularity on Duplex USG. Limb swelling secondary to DVT is distinguished from lymphedema by identifying luminal thrombus: lack of venous compression with apparent filling defect.

Vascular Malformations

The International Society for the Study of Vascular Anomalies has classified the vascular anomalies into vascular tumors and vascular malformations [111]. Vascular malformations represent a large, diverse group of congenital anomalies that usually arise aberrantly during development and are classified based on their respective components (e.g., venous, arterial, or lymphatic), complexity, and affected structures [112]. Table 26.12 summarizes the current International Society for the Study of Vascular Anomalies classification system for vascular malformations. Table 26.12 Categorization of Vascular Malformations [112] Simple

Capillary malformations Lymphatic malformations Venous malformations Arteriovenous malformations Arteriovenous fistula

Combined

Various types defined as involving ≥2 types of vascular malformations in a single lesion (e.g., capillary + lymphatic)

Involving named vessels

Lymphatic, venous, and/or arterial

Associated with other anomalies

Syndromic forms (Table 26.13)

Capillary, lymphatic, and venous malformations (VMs) are considered low-flow lesions, whereas AV malformations and AVF are considered high flow.

Venous Malformations VMs are a very common type of vascular malformation with an estimated prevalence of 1% [25]. Most cases are thought to be sporadic, however certain syndromic forms exist demonstrating characteristic disease associations, some of which are listed in Table 26.13. Sporadic cases are frequently unifocal, whereas the syndromic VMs are frequently multifocal

[113]. When multiple lesions are detected in a single individual, additional work up should be pursued to identify a possible syndromic association that may require counseling and intervention. Table 26.13 Venous Malformations Associated With Other Anomalies Associated Syndrome Other Features Gene Mutation Klippe l– Trenau nay

Capillary malformations ± lymphatic malformations, + limb overgrowth

PIK3CA

Maffu cci

Venous malformations + enchondromas

IDH1/IDH2

CLOV ES*

Lymphatic + capillary ± arteriovenous malformations + lipomatous overgrowth

PIK3CA

*

CLOVES, congenital lipomatous overgrowth with vascular malformations, epidermal nevi, and skeletal anomalies.

Blue rubber bleb nevus syndrome (BRBNS) describes the rare condition characterized by multifocal VMs involving the skin and visceral mucosa, including the gastrointestinal mucosa. Frequently patients with BRBNS develop gastrointestinal bleeding which can lead to anemia. Recent research suggests somatic mutations in TEK are associated with BRBNS [114]. VMs are seen throughout the body, superficially on the skin, involving joints and in the deeper soft tissues and organs [113]. VMs extending into the joint capsule are referred to as synovial VMs. When visible on the skin, VMs often appear as blue–purple colored. On exam, the lesions are isothermic to adjacent skin, are nonpulsatile, do not demonstrate a thrill on palpation and may enlarge with certain maneuvers (e.g., Valsalva or applying a tourniquet). All of these findings are consistent with low-flow nature. Although VMs are considered benign lesions without neoplastic potential, they may fluctuate in size throughout life secondary to certain physiologic states. For instance, VMs may enlarge during pregnancy, during puberty, cyclically with hormonal changes, or with oral contraceptive use. Their low-flow state predisposes them to thrombosis and associated post-thrombotic discomfort [115]. In fact, their predisposition to thrombosis leads to the formation of phleboliths (vein-stones), which are characteristic of VMs. Many of the imaging features of VMs are consistent with their low-flow state. For instance, fluid–fluid layering may be observed, which is thought to

be secondary to layering of blood. For superficial VMs, Duplex USG is usually the best first imaging technique for further evaluation following a detail history and physical examination. On USG examination, superficial VMs are usually easily compressible, demonstrate heterogenous echogenicity and, consistent with being low-flow lesions, demonstrate little to no flow on Duplex USG. Phleboliths will appear as well-defined hyperechoic foci often demonstrating twinkling artifact, which appears as focal color flow (mixture of red and blue) deep to a highly reflect focus, such as calcification [114]. Contrast-enhanced MR is very sensitive for detecting and evaluating VMs, where they often appear as enhancing, heterogenous, lobulated masses frequently with septations (Fig. 26.64). Phleboliths usually appear dark on all MR sequences due to the density of calcification. Venography is reserved for cases where a percutaneous intervention may be anticipated/indicated. Findings consistent with a VM on venography include a low flow, disorganized network of connecting veins. Treatment is reserved for patients with symptoms or lesions with the potential for complications (e.g., craniofacial involvement). Management involves percutaneous sclerotherapy and surgery, with sclerotherapy representing the preferred firstline treatment. Sclerotherapy involves percutaneous catheterization with injection of a sclerosant, such as sodium tetradecyl sulfate, polidocanol, or ethanol [25].

FIGURE 26.64 MRI neck with contrast. (A) Coronal and (B) axial T1 fat-saturated images following contrast administration in a 43-year-old man with a left submandibular venous malformation (arrow) that drains to a large left retromandibular vein and into the left anterior jugular vein.

Capillary Malformations Similar to VMs, capillary malformations (CMs) are very common and may be isolated or combined with other abnormalities. In contrast to VMs, however, simple CMs are imaged less frequently than VMs, as they are often detected as an isolated cutaneous lesion that may be confidently diagnosed on physical examination. Nonetheless, some characteristic locations warrant further investigation: over the spine (spinal anomalies) or in a unilateral trigeminal nerve (VI) distribution (Sturge–Weber syndrome). Table 26.14 lists some of the simple and complex, anomaly associated CMs distinct from those listed in Table 26.13. Hereditary hemorrhagic telangiectasia (HHT) manifests mucosal telangiectasias in addition to AV malformations and is discussed in the section on AV malformations. Table 26.14 Capillary Malformations Features Sim ple

Associated Gene Mutation

Cutaneous or mucosal (port-wine stain) CM

–

Nevus simplex/salmon patch (nonsyndromic)

–

Telangiectasias (nonsyndromic)

–

Stu rge – We ber

Facial, leptomeningeal CMs, eye anomalies, ± bone and/or soft tissue overgrowth

GNAQ

Par kes We ber

AV fistula and limb overgrowth

RASA1

MC AP

Macrocephaly + CMs + polymicrogyria

PIK3CA

MI CC AP

Microcephaly + CMs

STAMBP

Lymphatic Malformations Similar to the VMs, lymphatic malformations (LMs) represent congenital anomalies that usually arise aberrantly during development. LMs are slightly less common than VMs with an estimated incidence of 1 in 12,000 [116]. LMs are usually diagnosed clinically by history and exam, however imaging is often performed to confirm the diagnosis, evaluate the extent of a lesion and for treatment planning. Like VMs, LMs are low-flow vascular malformations composed of irregular, dilated cystic structures. Morphology is often categorized as microcystic, macrocytic or combined. Macrocystic LMs are defined as having locules >1 cm in size, whereas microcystic LMs composed of smaller cysts. Superficial LMs often appear as a prominent soft tissue mass. LMs typically do not obey tissue boundaries and are most commonly found in the subcutaneous soft tissue of the head and neck. Also similar to VMs, the lesions are isothermic to adjacent skin on examination, are nonpulsatile, do not demonstrate a thrill on palpation and may transilluminate when found superficially. Usually, LMs are not painful to palpation, however, if they become infected, they may become enlarged, indurated, erythematous, and painful. USG is the best first imaging technique for evaluating suspected LMs. On USG LMs appear as anechoic, avascular, multiloculated cystic lesions, often demonstrating posterior acoustic enhancement. Occasionally echogenic debris may be seen within the cysts. MRI is also useful for evaluating LMs in select patients. On MR, LMs appear as multiloculated, septated cystic lesions without evidence of flow voids, bright on fluid sensitive sequences (Fig. 26.65) [116]. Focal areas of T1-weighted image hyperintensity may be seen in the setting of intralesional hemorrhage. Treatment is based on symptoms and risk of complications based on location (e.g., airway associated or retro-orbital). Percutaneous sclerotherapy is often the preferred first initial treatment with surgery typically reserved for refractory cases. Commonly used sclerosing agents include doxycycline, bleomycin, sotradecol, and ethanol [117].

FIGURE 26.65 Axial MR short tau inversion recovery (STIR) image of a child with a large lymphatic malformation (arrow) centered in the left axilla.

Arteriovenous Malformations and Arteriovenous Fistula In contrast to other malformations discussed thus far, arteriovenous malformations (AVMs) and AVF are considered high-flow lesions that demonstrate distinct properties unique from VMs, CMs, and LMs. AVMs are characterized by a disorganized network of enlarged arteries and veins. Indeed, on clinical exam, when these lesions are near the skin, they may feel warm, pulsatile, and even demonstrate a palpable thrill. AVFs are defined as direct communication between an artery and vein. The most common type of AVF are by design (HD AVF) or iatrogenic, secondary to trauma during vascular access or during solid organ biopsy. Rarely, AVF may be congenital, as in vein of Galen malformations and hepatic arterioportal fistula [112]. Hereditary hemorrhagic telangiectasia (HHT), also known by the eponym Osler–Weber–Rendu syndrome, represents the most commonly known syndrome predisposing AVMs and AVF. Patients with HHT often develop AVMs and telangiectasis on the skin, nasal, oral, and gastrointestinal

mucosa, as well as brain, lungs, and visceral organs [112]. Complications associated with HHT are related to lesion locations and include mild– moderate epistaxis, stroke, brain abscess, gastrointestinal hemorrhage, cirrhosis, and heart failure. The clinical importance of HHT is manifest by the establishment of dedicated management HHT centers in some developed countries, such as the United States. Given the risk of complications, screening, counseling, and monitoring are performed. Table 26.15 lists the types of HHT and related disorders. Table 26.15 Types of HHT and Related Disorders Disorder

Associated Gene Mutation

HHT type 1

ENG

HHT type 2

ACVRL1

HHT type 5

GDF2

HHT with juvenile polyposis

SMAD4

HHT with capillary malformation

RASA1

On Duplex USG, AVM often demonstrates low resistance waveforms in the arterial segment and arterialized flow in the venous segment. Phleboliths are rarely seen in AVMs. On CECT or MR, AVMs are characterized by early contrast enhancement and washout. The management of AVM and AVF depends both on clinical symptoms and on the risk of future complications for particular lesions if left untreated. Both medical and semi-invasive management strategies exist, with endovascular embolization playing major role for CNS, pulmonary, and hepatic lesions. Table 26.16 summarizes many of the important MRI features characteristic of each type of vascular malformation. Table 26.16 Summary of Vascular Malformation Contrast-Enhanced MRI Features [118] Flo Fluid– Arterial Delayed Septatio Phlebolit w Type Fluid Enhanceme Enhanceme ns hs Voi Levels nt nt ds

Type

Fluid– Septatio Phlebolit Fluid ns hs Levels

Flo Arterial Delayed w Enhanceme Enhanceme Voi nt nt ds

Capillar y

–

–

–

–

–

–

Venous

+

+

+

–

+

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Suggested Readings • GY Karande, SS Hedgire, Y Sanchez, V Baliyan, V Mishra, S Ganguli, et al., Advanced imaging in acute and chronic deep vein thrombosis, Cardiovasc Diagn Ther 6 (6) (2016) 493–507. • E Depopas, M Brown, Varicose veins and lower extremity venous insufficiency, Semin Intervent Radiol 35 (1) (2018) 56–61. • RP Smillie, M Shetty, AC Boyer, B Madrazo, SZ Jafri, Imaging evaluation of the inferior vena cava, Radiographics 35 (2) (2015) 578–592. • MC Olson, MG Lubner, CO Menias, VM Mellnick, LM Gettle, DH Kim, et al., Venous thrombosis and hypercoagulability in the abdomen and pelvis: causes and imaging findings, Radiographics 40 (2020) 875–894. • SK Sonavane, DM Milner, SP Singh, AK Abdel Aal, KS Shahir, A Chaturvedi, Comprehensive imaging review of the superior vena cava, Radiographics. 35 (7) (2015) 1873–1892. • M Itkin, GJ Nadolski. Modern techniques of lymphangiography and interventions: current status and future development, Cardiovasc Interventradiol 41 (3) (2018) 366–376. • JJ Borsa, NH Patel, The venous system: Normal developmental anatomy and congenital anomalies, Semin Intervent Radiol 18 (2) (2001) 69–81. • R Lamba, DT Tanner, S Sekhon, JP McGahan, MT Corwin, CG Lall, Multidetector CT of vascular compression syndromes in the abdomen and pelvis, Radiographics 34 (1) (2014) 93–115. • F Lurie, M Passman, M Meisner, M Dalsing, E Masuda, H Welch, et al., The 2020 update of the CEAP classification system and reporting standards, J Vasc Surg Venous Lymphat Disord 8 (3) (2020) 342–352. • KM Elsayes, AM Shaaban, SM Rothan, S Javadi, BL Madrazo, RP Castillo, et al., A comprehensive approach to hepatic vascular disease, Radiographics 37 (3) (2017) 813–836. • C Hassani, F Saremi, Comprehensive cross-sectional imaging of the pulmonary veins, Radiographics 37 (7) (2017) 1928–1954. • AC Merrow, A Gupta, MN Patel, DM Adams, 2014 revised classification of vascular lesions from the international society for the study of vascular anomalies: Radiologic-pathologic update, Radiographics 36 (5) (2016) 1494–1516.

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SECTION D

Abdomen and Gastrointestinal Tract

27

Conventional Abdominal Radiology Sandhya Vinu-Nair

Introduction At least 4–10% of all patients presenting to the emergency department (ED) present with acute abdominal pain, making it one of the most encountered complaints. Abdominal radiography has been long used as the initial imaging technique in the investigation of these patients [1]. However, with the advent of CT, this practice is starting to fall out of favor [2–4]. Acute abdomen has a myriad of causes including those due to referred pain from the chest. Patients are first subjected to a thorough clinical examination before they are tied to the appropriate radiological examination. Although the use of CT has significantly increased in the recent years, conventional abdominal radiography is still used as an important tool in the initial work up of patients with acute abdominal pain because it is inexpensive, widely available, and provides quick results [5]. Plain films are likely to remain as one of the best methods of imaging to study the gas pattern and distribution within the dilated and nondilated bowel, and to quickly diagnose the presence of gas inside or outside the bowel lumen [6,7]. Interpretation of plain films in the acute abdomen may present a formidable challenge to the radiologist. Although a specific diagnosis can be made in many cases, not infrequently the appearances are nonspecific or even positively misleading and further investigations using contrast media, ultrasound, radionuclides, or CT may be required. Negative or equivocal radiology should be ignored if clinical signs indicate that surgery or other morbidity reducing procedures must be performed [3]. The radiologist plays a major role in helping the surgeon or emergency team deciding whether surgery must be performed immediately or whether time can be spent in resuscitating the patient and carrying out further investigations. Hence, it is imperative that the radiologist be aware of the clinical history before giving an opinion [8]. It may be useful to view the radiographs unbiased to the

clinical scenario initially and then tie the final radiological opinion with the clinical history. In most patients, further imaging is warranted after conventional radiography.

Imaging Techniques Traditionally, Standard Abdominal Radiography Consists of Three Views

◾ Supine abdominal view ◾ chest film ◾ Erect Upright abdominal view

Frequently, depending on institutional policies or at the request of the interpreting radiologist, an additional left lateral decubitus view maybe obtained to add more information and to demonstrate fluid levels in patients who are too ill to be moved [9,10]. Wherever possible, the bladder should be emptied before the supine radiograph is taken, and this should always include the area from the diaphragm to the hernial orifices.

Chest X-Ray The objectives of obtaining a chest radiograph in the acute abdomen are as follows: 1. Small pneumoperitoneum: The erect chest film is superior to the erect abdominal radiograph to detect the presence of even small amount of pneumoperitoneum, seen typically under the right hemidiaphragm. The x-ray beam in an erect abdominal radiograph penetrates the gas at the top of the diaphragm obliquely and this area is also relatively dark due to overexposure. On the contrary, in the erect chest film, the top of the diaphragm and the gas beneath are penetrated almost tangentially by the x-ray beam, and the exposure of the diaphragm is optimal to show small amounts of gas. 2. Acute chest conditions: Acute chest conditions may present as acute abdominal pain and mimic an acute abdomen exactly (Box 27.1). Up to 10% of patients with an acute abdomen may have acute unsuspected chest conditions, which will be diagnosed on the chest radiograph. 3. Acute abdominal conditions: Acute abdominal conditions may be complicated by chest pathology. For example, pleural effusions frequently complicate acute pancreatitis; aspiration pneumonia may complicate prolonged vomiting in patients with intestinal obstruction. 4. Normal chest radiograph: Normal chest radiograph acts as a valuable baseline. Comparison with a previously normal film may detect subtle new changes or to detect postoperative complications, to enable early diagnosis and treatment [11]. Box 27.1

Chest Conditions That May Mimic An Acute Abdomen Pneumonia—particularly lower lobe Myocardial infarction

Pulmonary infarction Congestive cardiac failure Pericarditis Leaking or dissecting thoracic aortic aneurysm Pneumothorax Pleurisy

Abdominal Radiographs There is inherent contrast provided by soft tissues, fat, and intraluminal gas within the abdomen, and abdominal radiographs make use of this subject contrast caused by the differential attenuation of the x-ray beam in the patient. Abdominal radiographs taken in the radiology department use regular equipment with low kilovoltage exposures ranging between 60 and 75 kV (adjusted depending on the size of the patient), and short exposure times to avoid unsharpness [12,13]. The image quality in extremely ill or hospitalized patients might be slightly degraded, given their inability to adequately hold breath [14]. This degradation is compounded by the use of portable x-rays units with fixed milliampere settings, requiring higher peak voltage, which in turn causes reduced tissue contrast. The anteroposterior view of the abdomen with the patient supine is obtained for maximum detail of the anatomy and pathology. It allows the distribution of gas showing the caliber of bowel, displacement of bowel by soft-tissue masses, and allows the visualization of obliteration of fat lines [15]. The view of abdomen with the patient standing erect is obtained to demonstrate (i) free air under the diaphragm, (ii) fluid levels, (iii) more detailed double-contrast view of the intestinal wall, (iv) possible separation of the bowel and thickness of bowel wall when one loop is layered upon the other, (v) change in position of the bowel loops or a particular region of interest in changing from supine to erect.

If gas shadows are demonstrated which are suspected as lying outside the bowel, then horizontal-ray films are often particularly helpful by demonstrating that air–fluid levels lie within a confined space and are thus likely to represent an abscess cavity. In patients who are unable to sit or stand for an erect film, left lateral decubitus abdominal radiograph is the projection of choice to show small pneumoperitoneum. Additionally, in this position, free air originating from a perforated duodenal or antral ulcer, or air from the lesser sac after posterior gastric ulcer perforation, enters the main abdominal cavity. With left lateral decubitus abdominal radiograph, there is better visualization of focal

duodenal ileus, which is one of the commonest signs of acute pancreatitis. In some instances oblique views of the abdomen are obtained, the patient lying 30 degrees on either side and are most often performed for localizing foreign bodies or lines within the abdomen [13]. These oblique views have now become rare and obsolete. There are numerous causes of small-bowel fluid levels and the number, distribution, and length will not usually help to distinguish between the two commonest causes, obstruction and paralytic ileus, or any of the other causes (Box 27.2). Although there is a very high interobserver variability in the interpretations of gas patterns, short air–fluid levels may be seen in the stomach, duodenal cap, and in the small bowel centrally. Three or more small-bowel fluid levels longer than 2.5 cm are abnormal, and indicate dilated small bowel, usually with stasis. Box 27.2

Causes of Abnormal Small-Bowel Fluid Levels Small-bowel obstruction Large-bowel obstruction Paralytic ileus Gastroenteritis Mesenteric thrombosis Diverticulosis Uremia Hypokalemia Osmotic enemas Congestive cardiac failure

Fluoroscopy There is significant decline in the use of contrast agents and fluoroscopy techniques in the imaging of the hollow viscera given the ease of use and availability of CT scanners, MR, and endoscopy [16]. There are many causes which resulted in the progressive decline of fluoroscopy studies. However, these are still performed due to the following advantages.

◾ Study gastrointestinal (GI) motility and function ◾leaks Important role in evaluating postoperative patients and postoperative complications like ◾method Esophagogram and double-contrast upper GI examinations are safe and cost effective for evaluation of the esophagus and stomach

Contrast Agents and Techniques Single- and double-contrast examinations continue to have a role in modern radiology. There are three techniques of imaging the GI tract.

◾lumen Mucosal relief views: Small volume of barium in collapsed or partially collapsed bowel to assess the mucosa ◾evaluate Single-contrast views: Large volume of low-density barium filling the bowel lumen to strictures and growths within the lumen ◾coating Double-contrast views: Large amount of air and small volume of high-density barium the mucosa of the bowel lumen, to assess malignancy/ulcerations and inflammatory bowel disease

Normal Anatomy on Abdominal Radiographs As mentioned previously, the abdominal soft tissues, and the presence of gas, fluid, or food residue within the bowel provide a natural contrast to delineate soft-tissue planes and visceral surfaces on abdominal radiographs [9]. The surfaces best visualized are the ones smoothly marginated and tangential to the x-ray beam. Localization of pathologic processes requires familiarity with the normal anatomy (Fig. 27.1). The duodenal cap is often gas-filled and frequently contains a fluid level on erect films.

FIGURE 27.1 (A) Normal supine abdominal radiograph. (B) Pictorial illustration of the normal anatomy of the abdomen as seen on radiographs. HA, hepatic angle; PF, properitoneal fat; PM, psoas muscle; R, renal shadow; I, Ilium; S, sacrum; SCG, sigmoid colonic gas.

Stomach The stomach usually contains large amounts of air and fluid, seen in the left upper quadrant with its characteristic rugal folds. In the supine position, the stomach gas rises to the anterior antrum and fluid settles in the fundus. The stomach gas serves as an important landmark for identifying space-

occupying lesions in the spleen laterally, liver medially, and pancreas and lesser sac posteriorly.

Small Bowel The radiographic appearance of the small bowel is extremely variable. The small bowel along with the mesentery occupies the central portion of the abdomen. The small bowel is smaller in caliber, with typical mucosal folds called valvulae conniventes; these folds are usually thin and extend across the entire lumen of the bowel. Small-bowel caliber exceeding 3.0 cm is abnormal and indicates dilatation. Scattered gas and fluid within normally dilated bowel is seen in aerophagia and in minimally dilated bowel seen in pathological conditions such as gastroenteritis, inflammatory or infectious bowel disease, and pancreatitis (Fig. 27.2). Adynamic ileus or prolonged bowel transit caused by mechanical obstruction results in multiple air–fluid levels in a dilated bowel [17].

FIGURE 27.2 Air swallowing. There is gaseous distension of both small and large bowel, but this extends down to the rectum. A 7-yearold girl admitted to hospital with abdominal pain and distension after a single episode of vomiting. At the time of admission, she was distressed and crying. Shortly after admission her bowels were opened normally, and the abdominal distension and pain disappeared.

Large Bowel The adult colon consists of gas and fecal material and frames the abdomen. The large bowel consists of haustrations which are more widely spaced and usually do not cross the entire lumen. The colon caliber varies from 3 to 8 cm, with the largest diameter seen in the cecum. Persistent cecal diameter of 9–10 cm or more may indicate a risk of impending perforation from mechanical obstruction or ileus. In inflammatory bowel disease, however, a transverse colonic diameter exceeding 5.5 cm has been suggested as the upper limit of normal, and above this megacolon should be diagnosed [18]. Colonic fluid levels are a normal finding, and some of which are several centimeters long may be seen. Eighteen percent of normal people also have a

cecal fluid level. In severe pain, or when respiration is labored, as in pneumonia or asthma, increased swallowing of air often results in a dramatic plain abdominal radiograph. The gas-filled, slightly dilated loops of bowel so produced contain relatively little fluid; the term “meteorism” is applied to this appearance. It is sometimes difficult to distinguish meteorism produced, for example, by renal colic, from intestinal obstruction. A clinical history and examination frequently enable the radiological findings to be correctly interpreted.

Muscles, Retroperitoneum, and Pelvis The posterior extraperitoneal fat pad, which completely surrounds the kidneys, psoas muscles, and the posterior borders of the liver and spleen, extends anteriorly and laterally to surround the parietal peritoneum and is also intimately related to intraperitoneal organs. The fat lines produced are responsible for the visualization of most of these intra-abdominal organs. These fat lines can be displaced if the organs are enlarged and may be blurred or effaced by inflammation or fluid [12]. However, the visualization of these structures by fat lines is not universal. In 19% of normal people the right psoas outline is blurred, and the lower border of the spleen can only be visualized in 58%. This is particularly important in children, where the psoas outlines are lost in 52% and the properitoneal fat line is lost in 18% of normals [9]. Delineation of the various muscles and visceral structures in the pelvis is also variable and depends on a variety of factors, including the amount of extraperitoneal pelvic fat, bowel contents, degree of bladder distention, position, and body habitus of patient.

Pathology on Abdominal Radiographs Pneumoperitoneum Pneumoperitoneum may indicate a life-threatening situation and will require emergency surgery in over 90% of the cases and exploratory laparotomy in the absence of other recognizable causes. By careful radiographic techniques, it is possible to demonstrate as little as 1 mL of free gas on erect chest or left lateral decubitus abdominal films [19]. However, radiographic technique and positioning are important and a patient should be in position for at least 10 minutes before the film is taken, for it takes this time for free gas to rise to the highest point in the abdomen (Fig. 27.3) [20].

FIGURE 27.3 Pneumoperitoneum. (A) Erect chest film. Free intraabdominal gas is clearly demonstrated under the right hemidiaphragm. Under the left hemidiaphragm a small triangular collection of free gas can be identified between loops of gas-filled bowel (arrow). (B) Portable supine chest film of an ICU patient. Free intra-abdominal gas is clearly demonstrated under the diaphragm as the “continuous diaphragm sign” (arrow). Large amounts of gas may accumulate underneath the central tendon of the diaphragm in the midline—the “cupola” sign.

A combination of an erect film and a left lateral decubitus projection increases the detection rate [19,21]. The low rates of detection are due to a number of causes, including technical imperfections, sealing of the perforation, lack of gas at the site of perforation, or adhesions around the site of the perforation. Inability of proper patient positioning is one of the most important causes for low detection rates—particularly in those patients after trauma, the elderly or the critically ill, and those who are unconscious. About 56% of patients with pneumoperitoneum may have free gas detectable on a supine radiograph [19]. The causes of pneumoperitoneum are varied (Box 27.3) and can be benign, spontaneous, iatrogenic/surgical, secondary to barotrauma or trauma, hollow visceral rupture, pneumatosis, or due to gynecological or pelvic pathology. It is essential to understand and recognize the signs and patterns of pneumoperitoneum on both supine and erect radiographs. Some radiographic signs commonly seen are as follows [22,23]:

◾space Collection of gas in the right upper quadrant adjacent to the liver, mainly in the subhepatic and the hepatorenal fossa (Morison’s pouch), visible as an oval or linear collection of gas—“Morison pouch” sign or “doge cap” sign (Fig. 27.4) ◾(Fig. The visualization of the outer as well as the inner wall of a loop of bowel—“Rigler’s” sign 27.5). This sign may be misleading if gas-distended loops of bowel are in contact, with

apparent visualization of outer and inner walls, when in fact the inner walls of two loops of bowel are seen Small triangular collections of gas between loops of bowel on supine radiographs—“telltale triangle” sign

◾

◾abdominal Reflections of the peritoneum normally present on the inner surface of the anterior wall are not usually identified, but may be visualized by large amounts of free gas when it lies on either side. Thus, the falciform ligament (Fig. 27.4), medial and lateral umbilical ligaments, and the urachus can occasionally be identified when relatively large amounts of gas are present Relatively large amounts of gas may accumulate underneath the central tendon of the diaphragm in the midline—the “cupola” sign or in the center of the abdomen over a fluid collection—the “football” sign Free gas in the fissure for the ligamentum teres

◾ ◾

Box 27.3

Causes of Pneumoperitoneum A Pneumoperitoneum with peritonitis (a) Perforated hollow viscera—traumatic and nontraumatic (b) Necrotizing enterocolitis (c) Bowel infarctions, infections, and inflammations (d) Penetrating abdominal injuries B Pneumoperitoneum without peritonitis Chest

(a) Intermittent positive pressure ventilation (b) Penetrating air from pneumomediastinum and pneumothorax (c) Chronic obstructive airway disease (d) Asthma (e) Pulmonary peritoneal fistula Abdomen

(a) Postoperative/laparotomy/laproscopy, endoscopy (b) Peritoneal dialysis (c) Perforated jejunal diverticulosis (d) Sealed perforations of hollow viscus (e) Pneumatosis cystoides coli/intestinalis (f) Iatrogenic—postparacentesis Female pelvis

(a) Iatrogenic or postinstrumentation such as hysterosalpingography (b) Postpartum pelvic examination or exercises (c) Vaginal douching

FIGURE 27.4 Pneumoperitoneum. Abdomen, supine. A triangular collection of free gas is demonstrated in the subhepatic region (arrows). The falciform ligament is also outlined (arrowheads).

FIGURE 27.5 (A) Pneumoperitoneum on the abdominal supine film. The visualization of both sides of the bowel wall “Rigler’s sign” (white arrow). Both the inside and outside wall of multiple loops of small bowel can be clearly identified. (B) Pneumoperitoneum on CT abdomen showing how the Rigler’s sign is depicted on the radiograph.

CT is the most sensitive and most accurate diagnostic technique for the detection of peritoneal free gas, with even tiny bubbles of gas being visible. CT also aids in identifying the cause of perforation without delay. The radiologist should review the images on wide window settings to appreciate small volumes of gas, as the gas adjacent to neighboring fat and bowel loops is otherwise easy to miss. Free gas tends to collect over the liver, anteriorly in the mid abdomen, and in the peritoneal recesses (Fig. 27.6). Some studies have shown the pararectal and mid-rectal recesses (Fig. 27.7) as preferential spaces for collections of free air among other more commonly known areas such as the midline/parahepatic region, pelvis, and mesenteric spaces.

FIGURE 27.6 Free intraperitoneal gas. (A) On abdominal windows the free gas is not well seen anteriorly. (B) On wide window settings, the free gas is much more obvious.

FIGURE 27.7 Pictorial illustrations of the mid-rectus and pararectus recesses. Preferential spaces for collections of free air within the peritoneum.

Pneumoperitoneum without Peritonitis Occasionally, asymptomatic patients or those with very minimal signs and symptoms are found to have pneumoperitoneum. Many of these patients will subsequently be found to have a perforated ulcer which has sealed itself, or to have not yet developed the signs of peritonitis. Numerous other conditions that may produce a spontaneous pneumoperitoneum without peritonitis have been described (Box 27.3). Postoperative Pneumoperitoneum About 60% of all postlaparotomy patients will have evidence of pneumoperitoneum. Although, in most patients, the air will have been absorbed within a few days, a delay of up to 24 days before all the air has disappeared has been reported. Any increase in the volume of gas postoperatively indicates an anastomotic leak or further perforation [11]. Pseudopneumoperitoneum A number of conditions have been described which simulate free air in the peritoneal cavity on the plain film (pseudopneumoperitoneum). One of the commonest of these conditions is distended bowel, usually hepatic flexure of the colon, interposed between the liver and the diaphragm—the Chilaiditi syndrome [24]. Subdiaphragmatic fat, an extension from the posterior pararenal fat, is a common normal finding and frequently can be identified as a lucent crescent under the diaphragm; this may simulate a pneumoperitoneum. Its constant position in decubitus views will enable the

correct diagnosis to be made. Sometimes curvilinear pulmonary collapse parallel to and just above the diaphragm may simulate a pneumoperitoneum (Fig. 27.8). An uneven diaphragm, omental fat between the liver and the diaphragm, subpulmonary pneumothorax may also simulate free gas on occasions [1].

FIGURE 27.8 Pseudopneumoperitoneum. A band of curvilinear pulmonary collapse (arrows) with a crescent of normal lung beneath it simulates a pneumoperitoneum almost exactly.

Intestinal Obstruction Conventional abdominal radiographs remain the first line of imaging for those patients presenting to the ED with clinical features of intestinal obstruction. Determination of the site of obstruction on abdominal radiograph requires adequate knowledge about normal anatomy, demonstration of dilated loops of bowel proximally and nondilated/collapsed bowel loops distally to the presumed point of obstruction, and familiarity of the distinguishing features of small and large bowel depending mainly on their size, mucosal appearance, and distribution. Dilatation of bowel occurs

in mechanical intestinal obstruction, pseudo-obstruction, paralytic ileus, air swallowing, and several other conditions [25,26].

Gastric Dilatation The “stomach bubble” on an upright abdominal radiograph is the most important anatomical radiographic landmark is formed by the gastric fundus —the part of the stomach above a line drawn tangential to the gastroesophageal junction. It is the most superior portion of the stomach when the patient is upright, and the most dependent portion in supine position. The pylorus is the narrowest part of the stomach and the commonest portion of the stomach involved in gastric outlet obstruction (GOO) [27]. A “normal” stomach bubble is seen in the left upper quadrant, with the distal end, if filled with air, seen just crossing the midline. Abnormal dilatation of the stomach can be caused by four main groups of conditions: paralytic ileus, mechanical GOO, gastric volvulus, and air swallowing [28,29]. Other causes include postintubation, secondary to intestinal obstruction, and some drugs. Paralytic Ileus Group of Conditions These are frequently referred to as “acute gastric dilatation,” often occurs in old people and is associated with considerable fluid and electrolyte imbalance; other causes include eating disorders, trauma, diabetes mellitus, or gastric dysmotility in critically ill patients. Delay in treatment can result in necrosis, as a result it carries a high mortality (Fig. 27.9).

FIGURE 27.9 Acute gastric dilatation. Abdomen, supine. A 38-year-old woman admitted in diabetic precoma.

Mechanical GOO This is usually caused by peptic ulceration or carcinoma of the pyloric antrum, often leads to a massive fluid-filled stomach which occupies most of the upper abdomen and is demonstrable as a large soft-tissue mass with little or no bowel gas beyond. Fortunately, a little gas is usually present within the stomach and this can be identified on horizontal-ray films, which allow the organ to be identified [27]. Gastric Volvulus Stomach is an uncommon site for volvulus, but when it does occur the patients present to the ED with acute epigastric pain, nausea, and vomiting. It can be identified by a useful clinical triad which consists of sudden epigastric pain, intractable retching, and inability to pass a nasogastric tube into the stomach, named the Borchardt triad. It is of two subtypes— organoaxial and mesenteroaxial (Fig. 27.10) [29,30]. The fluid- and air-filled stomach is identified as a spherical viscus, displaced upward and to the left, and is associated with elevation of the hemidiaphragm. It is usual for the small bowel to be collapsed and it is uncommon to see any gas shadows beyond the stomach. If contrast medium is given in a case of suspected

gastric volvulus, there may be complete obstruction at the lower end of the esophagus, or if contrast medium does enter the stomach it may not pass beyond the obstructed pylorus.

FIGURE 27.10 Pictorial illustrations of stomach volvulus. It is of two types: organoaxial (A) where the stomach rotates along its long axis and mesenteroaxial (B) where the stomach rotates along its short axis.

Miscellaneous Frequently after resuscitation and intubation large amounts of gas enter the stomach and may lead to massive dilatation. This may sometimes be seen just after air swallowing, for example, in hysteria or in near-drowning. It is very important to differentiate a distended stomach from a cecal volvulus, which may also be positioned beneath an elevated left hemidiaphragm. However, with cecal volvulus, one or two haustra can frequently be identified and the inferior part of the cecum usually points caudally, in contrast to the pyloric antrum which points cranially.

Distinction Between Small- and Large-Bowel Dilatation Conventional abdominal radiography is the preferred initial radiologic examination for patient with obstruction and it is important to try to determine whether it is small- or large-bowel dilatation, or both. Useful differentiating features depend on the size, distribution, and marking of the loops and are summarized in Table 27.1 [31]. Table 27.1 Differentiating Characteristics of the Small-and Large-Bowel Loops Small Bowel Stomach Large Bowel Number of loops

Many

Sac-like structure

Few

Position

Central abdomen

Left upper quadrant

Peripheral/frame the small bowel

Mucosal/w all pattern

Valvulae conniventes

Rugal folds

Haustral folds

Diameter

3–5 cm

Variable

5–6 cm, Caecum 9 cm

Contents

Variable, some air/fluid levels

Air and fluid

Faeces of variable consistency

The valvulae conniventes usually form thin complete lines across the dilated small bowel and are prominent in the jejunum, but become less marked and widely spaced in the ileum. If the small-bowel blood supply becomes compromised and the bowel becomes edematous or gangrenous, the valvulae conniventes may become greatly thickened and may then be extremely difficult to distinguish from colonic haustra [31–33]. Haustra usually form thick, incomplete bands across the colonic gas shadow, interspaced with plicae semilunaris; however, rarely they may form complete transverse bands. Haustra may be completely absent from the descending and sigmoid colon, although they can usually still be identified in other parts of the colon even when it is massively distended [9]. The causes and management of small-bowel obstruction (SBO) are very different from those of large-bowel obstruction (LBO) and so it is essential to differentiate between them wherever possible. In most patients, this is

relatively easy but some can present a major diagnostic problem, and further investigation may be needed.

Small-Bowel Obstruction

◾examination As discussed earlier conventional abdominal radiography is the preferred initial radiologic despite its low diagnostic accuracy and specificity. It is usually diagnostic in up to 50–60% of cases, equivocal in about 20–30%, and normal or nonspecific in 10–20% ◾number There are multiple causes for SBO, some of which are listed in Box 27.4. The greater the of dilated small-bowel loops that are visible on the abdominal radiograph, the more distal the obstruction. Plain film changes in complete SBO may appear after 3–5 hours, and such changes are usually marked after 12 hours The commonest appearance is the presence of multiple fluid levels (Fig. 27.11). However, the presence of fluid levels alone may not be indicative of obstruction, as there are many other causes for dilatation, the most common being ileus. Ileus can be generalized (postoperative) or localized (adjacent to inflammatory conditions—pancreatitis or appendicitis) [34–37] In dilated small bowel which is almost completely filled with fluid, small bubbles of gas may be trapped in rows between the valvulae conniventes on horizontal-ray films; this is known as the “string of beads” sign which is traditionally considered a pathognomic radiographic finding [38]. When little or no gas is present and the dilated loops are predominantly fluid-filled, the classic obstructive bowel sounds may be absent, and so it is even more important for the radiologist to consider fluid-filled loops in SBO If the initial radiographs are considered normal, CT scanning is used for further diagnosis because it demonstrates the presence of bowel caliber change, fluid-filled bowel loops, and most times, the cause and the level of obstruction. The CT sensitivity for adhesions is around 73% [31] Plain films are generally poor at detecting bowel strangulation and ischemia The cause of obstruction is occasionally evident on plain film, for instance, when there is a groin hernia, volvulus, or gallstone ileus; however, obstructing lesions are better identified by CT. CT should be performed whenever there is a history of previous abdominal malignancy, as extraluminal disease in the peritoneum, nodes, and liver will be demonstrated, and may change the management of the patient

◾ ◾ ◾ ◾ ◾

Box 27.4

Causes of Small-Bowel Obstruction Intrinsic: Infection, Inflammation (inflammatory bowel disease, tuberculosis) Midgut volvulus Enteric duplication or mesenteric cysts Jejunal, ileal atresias Diverticuli Intussusception Extrinsic: Adhesions Hernias (external, internal, and incisional) Masses (benign/malignant), metastasis Iatrogenic (radiation enteritis) Vascular compromise causing intestinal ischemia Intraluminal causes Foreign body Bezoar Gallstones

FIGURE 27.11 Small-bowel obstruction: (A) supine; (B) erect. Multiple dilated loops of both gas-filled and fluid-filled small bowel are readily identified. There is little or no gas in the large bowel. Multiple fluid levels are noted on erect film. Patient was a 77-year-old woman with past history of several abdominal surgeries. The small-bowel obstruction was presumed to be due to adhesions and resolved with conservative management.

FIGURE 27.12 (A) abdominal plain film shows air–fluid levels within the upper abdomen indicative of bowel obstruction. (B) Coronal image of the abdomen shows high-grade closed loop small-bowel obstruction from an internal hernia involving the mid and distal small-bowel loops. It is worth noting that this patient has a history of multiple complex abdominal surgeries in the past, predisposing the formation of adhesions and increased risk of bowel obstructions.

Closed loop obstruction: Closed loop obstruction (Fig. 27.12) means mechanical SBO caused when two limbs of a loop are incarcerated by a band or in a hernia, frequently compromising the blood supply due to compression of the mesenteric vessels, resulting in its “strangulation.” The closed loop may fill with fluid and be palpable, or it may be visible on the radiograph as a soft-tissue mass or “pseudotumor.” The strangulated loop uncommonly contains gas; the limbs of the loop, separated only by the thickened intestinal walls, may resemble a large coffee bean. If gangrene occurs, lines of gas may be seen in the wall of the small bowel. However, the appearance in strangulating obstruction, with all its lethal potential, may be indistinguishable from that of simple SBO [17]. CT is much more sensitive for bowel loop strangulation than plain films. Volvulus of the small intestine: Volvulus of the small bowel may present as intermittent or persistent obstruction. It may occur as an isolated lesion or be combined with obstruction due to adhesive bands. In children, incomplete rotation, malrotation, or nonrotation of the gut may be associated with a massive small-bowel volvulus which may occur in the neonatal period, or months or even years after birth [29]. There is frequently an impaired blood supply in the small bowel so that intramural gas or thumb-printing may be seen. However, it is not usually possible to distinguish simple obstruction, strangulating obstruction, or small-bowel volvulus on plain radiographs alone [29]. Strangulated external hernia: This is usually detected clinically. However, sometimes this is overlooked due to obesity, and so it is important to search the radiograph for evidence of a hernia (Fig. 27.13). Many strangulated hernias will be fluid-filled and not visible on a plain film; furthermore, the mere presence of a hernia does not mean this is the cause of obstruction. However, if dilated bowel is identified ending at a hernial orifice, then the hernia is probably the cause of obstruction.

FIGURE 27.13 Small-bowel obstruction due to an incisional hernia in an obese patient. CT scout image showing dilated small bowel and illustrating the degree of obesity.

CT is very effective at detecting hernias, not only at the groin, but also elsewhere in the abdominal wall and within the peritoneum. It will also help establish if the hernia is the cause of the obstruction. Appendix abscess: It may present as SBO due to small bowel becoming adherent to the wall of the abscess. The appendix abscess may be identified as a soft-tissue shadow which may contain gas and indent the cecum (Fig. 27.14) [35].

FIGURE 27.14 Appendicular abscess causing small-bowel obstruction. A small gas bubble which lies within the abscess (arrow) is seen in the right iliac fossa. Age 11 years, vomiting with diarrhea for 1 week.

Gallstone Ileus

◾patient, Gallstone ileus or biliary ileus is a rare mechanical cause of intestinal obstruction [39]. The most commonly a middle-aged or elderly woman, will often have had recurrent episodes of right hypochondrial pain characteristic of cholecystitis ◾obstruct The obstruction is caused by the impaction of one or more gallstones which pass into and the distal stomach or proximal duodenum (Bouveret’s syndrome) or the terminal ileum (classic gallstone ileus) by eroding through the inflamed gallbladder wall resulting in bilioenteric fistulas. The most common of bilioenteric fistulas is between the gallbladder and the duodenum, seen in approximately 85% cases The stones have to be typically 2–2.5 cm in diameter to cause obstruction. Smaller stones just pass through the lumen without causing obstruction The diagnosis relies heavily on imaging. Abdominal radiography is the ideal imaging technique of choice in the ED, with sensitivity for the diagnosis of gallstone between 40% and 70%. The Rigler’s triad describes the typical radiological signs in plain film: ○ Air within the biliary tree (pneumobilia) (Fig. 27.15) ○ Signs of SBO ○ Ectopic radio-opaque gallstones Often times only two signs out of the triad are present. Rigler defined his triad in 1941. Since then, two more radiological signs for gallstone ileus have been added—change in the

◾ ◾ ◾

location of a previously noted gallstone (Rigler’s tetrad), and a right upper quadrant double air bubble on supine radiograph (Rigler’s pentad) [40] Pneumobilia is recognized by its branching pattern in that it is classically seen in central biliary ducts and can be differentiated from gas in the portal vein which is more peripherally located in small veins around the edges of the liver. Causes of pneumobilia or gas in the biliary tree are listed in Box 27.5 The visualization of the obstructing gallstone on plain films is frequently difficult, because it is often composed almost entirely of cholesterol, with only a thin rim of calcium within it. Sometimes gas in the biliary tree may be identified in SBO which is not due to gallstone ileus. In these cases the gas is presumed to have entered through a physiologically lax sphincter The small-bowel dilatation, gas within the biliary tree, and the gallstone at the point of obstruction may all be demonstrated elegantly on CT

◾ ◾ ◾

Box 27.5

Causes of Gas in the Biliary Tree Incompetent sphincter of Oddi—sphincterotomy Biliary surgery or instrumentations Biliary stent placements Endoscopic retrograde cholangiopancreatography (ERCP) Biliary-enteric surgical anastomosis Fistulous communication of the biliary tree with GI tract—gallstone fistula, trauma, and perforated peptic ulcer Infections—emphysematous cholecystitis, cholangitis, and abscesses Malignancy causing fistula

FIGURE 27.15 Gallstone ileus. Supine film. Multiple dilated loops of small bowel are seen. A band of gas in the right hypochondrium (arrow) lies within the common bile duct. The obstructing gallstone cannot be identified.

Bezoars In recent times there is a small increase in these cases because of the increasing numbers of gastric outlet surgeries; these surgeries prevent digestion of fibers which become impacted, causing obstruction [41]. On radiographs and CT, bezoar is seen as an ovoid intraluminal mass with a mottled gas pattern (Fig. 27.16A).

FIGURE 27.16 (A) Gastric bezoar: supine abdominal radiograph shows a gastric bezoar as a mottled soft-tissue mass (arrows) floating in the stomach at the air–fluid interface. (B-C) Small-bowel obstruction due to an ileal fecolith. (B) Dilated small-bowel loops. The gallbladder appeared normal. (C) Image through the pelvis. At the transition from dilated to collapsed bowel is a large densely calcified intraluminal fecolith.

Enteroliths Enteroliths are usually seen as ovoid high-density calcified densities usually in a patient presenting with repeated attacks of obstruction. Tubercular strictures, closed loop obstructions, and adhesions are common causes of detecting enetroliths in patients with recurrent attacks of subacute or acute obstruction. Associated features of obstruction depend on the timing of obtaining the radiograph or CT (Fig. 27.16B and C).

Intussusception The incidence of intussusception varies considerably in different countries, but in general it is most frequently seen in children under 2 years of age [42,43]. In children it usually commences in the ileum as the result of inflammation of the lymphoid tissue and tends to be associated with mesenteric adenitis [44,45]. The enlarged lymphatic patches are forced into the ileum by peristaltic movement and, acting as a tumor, one part of the ileum is pulled into the other and finally pulled into the colon. Although the condition is usually recognized clinically by pain, vomiting, blood in the stool, and a palpable tumor, the diagnosis may not be apparent initially and further investigations may be needed. Plain films may show evidence of SBO, or the intussusception itself may be identified as a soft-tissue mass sometimes surrounded by a crescent of gas and most frequently identified in the right hypochondrium (Fig. 27.17). The “target sign” has been described, comprising two concentric circles of fat density lying to the right of the spine—often superimposed on the kidney. It is probably due to the layers of peritoneal fat surrounding and within the intussusceptum alternating with the layers of mucosa and muscle but seen

“end on” as it passes forward from the right paraspinal gutter in the transverse colon.

FIGURE 27.17 Intussusception. Supine film. There are multiple gasfilled loops of slightly dilated small bowel. In addition, there is a softtissue mass in the right iliac fossa (arrow). A 5-month-old child with mesenteric adenitis.

In adults, an intussusception is a rare condition responsible for less than 5% of SBO, with lead point intussusceptions resulting from tumors (classically lipoma of the terminal ileum, lymphoma, and metastases from melanoma), foreign bodies, and adhesions [46]. Transient intussusceptions do not cause SBO. Any part of the small bowel may be involved, although the terminal ileum is still the most common site for the underlying pathology. USG is the technique still widely used for the diagnosis of this condition and CT readily demonstrates intussusception.

Enema therapies are still popular in treating intussusceptions. These include:

◾ Barium enema ◾ Water-soluble contrast enema ◾ Air enema ◾ saline enema ◾ Ultrasound-guided Ultrasound-guided air enema

Air enema has become widely popular in the western world, as it is quick, clean, uses lesser radiation than barium and has high success rates [45]. However, there is an increased risk of perforation and it is advised that the increase in pressure must be slow and progressive. Ultrasound-guided saline enema is also popular as it does not use ionizing radiation and gives high success rates [45].

Mesenteric thrombosis—Small Intestinal Infarction Stenosis or thromboembolic occlusions of the mesenteric arteries and veins result in bowel ischemia and necrosis which leads to bowel wall thickening resulting in SBO. The clinical diagnosis is often uncertain, but the sudden onset of abdominal pain, often associated with bloody diarrhea, in an elderly person is very suggestive of this condition. CT findings are more specific and are covered in detail in the following chapters. Plain film findings are nonspecific, some of which are:

◾ Gas-filled or fluid-filled, slightly dilated small-bowel loops ◾ Thickened walls of the small bowel—secondary to submucosal hemorrhage and edema ◾ Linear gas streaks in the bowel wall (pneumatosis coli; Fig. 27.18), from possible infarction ◾ intraperitoneal air—from possible perforation ◾ Free Colonic distension—from generalized paralytic ileus

FIGURE 27.18 Small intestinal infarction. Supine radiograph shows dilated small-bowel loops with thickened walls and linear gas streaks in the wall (arrows).

Large-Bowel Obstruction LBO differs considerably from SBO in its clinical findings and pathophysiology. The marked distension of colon proximal to the level of obstruction leads to mucosal edema, bowel ischemia, and subsequently leads to bowel infarction and perforation. There are many causes for LBO, listed in Box 27.6; the commonest however is carcinoma (>60%) [32], with the two most frequent locations being the splenic flexure and sigmoid colon. Box 27.6

Causes of Large-Bowel Obstruction Neoplasm—adenocarcinoma of colon Volvulus—sigmoid, cecum, and transverse colon Intussusception

Hernias—external, internal, and incisional Infection, inflammation—diverticulitis and inflammatory bowel disease Intraluminal—foreign body, gallstone, and fecal impaction

The commonest site of perforation in LBO is the cecum. Diverticular disease as a cause of obstruction has decreased in frequency since the introduction of high-fiber diets. Acute colonic volvulus comprises about 10– 15% of LBO [32]. In volvulus, the colon twists upon itself and if the twist is greater than 360 degree, then surgical intervention is necessary. Sigmoid volvulus is 3–4 times more common than cecal volvulus while volvulus of transverse colon and splenic flexure are rare. The key to the radiological appearance of LBO depends on the state of competence of the ileocecal valve. Three patterns (Fig. 27.19) of obstruction have been described.

◾colon Type IA—Ileocecal valve is competent and the radiological appearance is one of dilated with a distended thin-walled cecum but no distension of small bowel (Fig. 27.20) ◾toType IB—Progression of type 1A resulting in small-bowel distension, probably secondary the tightly closed ileocecal valve opening up

FIGURE 27.19 Large-bowel obstruction: Type IA: Competent ileocecal valve. Distended large bowel, particularly ascending colon and cecum. No distension of small bowel. Type IB: Competent ileocecal valve. Cecal distension and small-bowel distension. Type II: Incompetent ileocecal valve. No distension of cecum and ascending colon but distension of small bowel. Cecal perforation is much more likely to occur in type I large-bowel obstruction.

FIGURE 27.20 Large-bowel obstruction type IA (competent ileocecal valve). Supine film. There is gaseous distension of the large bowel from the sigmoid backward, including the ascending colon and cecum. The dilated cecum lies in the pelvis. There is no visible small-bowel distension.

(Carcinoma of the sigmoid.)

Both type I obstructions can lead to massive cecal distension, which is then at risk of perforation secondary to ischemia. A transverse cecal diameter of 9 cm has been suggested as the critical point above which the danger of perforation exists.

◾distended, Type II—The ileocecal valve is incompetent, and the cecum and ascending colon are not but the back pressure from the colon extends into the small bowel and there are numerous dilated loops of small bowel which may simulate SBO

The obstructed colon almost invariably contains large amounts of air and can usually be identified by its haustral margin around the periphery of the abdomen. However, on occasions the right half of the colon may be filled with fluid and massive cecal distension may be overlooked. Even more rarely, the whole colon up to the point of obstruction may be filled with fluid and so the diagnosis may be overlooked initially. When both small- and large-bowel dilatation is present in LBO, the radiographic appearance may be identical to that of paralytic ileus. However, the clinical signs will usually help differentiate. Demonstration of air in the rectum may differentiate paralytic ileus from low LBO. There are numerous causes of colonic distension without obstruction. These include all forms of paralytic ileus and pseudo-obstruction. Pseudo-Obstruction Pseudo-obstruction is a disorder of bowel which symptomatically, clinically, and radiologically may mimic intestinal obstruction. It may be acute and self-limiting and associated with pneumonia, septicemia, or certain drugs; or chronic with acute flare-ups, as seen in diabetes mellitus, collagen disorders, neurological disorders, and amyloid disease. A large proportion of patients, however, have no associated medical condition and these cases are called “idiopathic intestinal pseudoobstruction” (Fig. 27.21). A large quantity of bowel gas is usually present and there may be gastric, small- or large-bowel distension with associated fluid levels just as great as in true obstruction. CT imaging can help avoid an unnecessary surgery.

FIGURE 27.21 Pseudo-obstruction: (A) supine abdomen; (B) barium enema. On the plain film, gas-filled loops of both small and large bowel can be identified, with gas extending down to the rectum. The barium examination demonstrates diverticular disease in the sigmoid, but this is not obstructing, and barium flows freely into the dilated descending colon. Conservative management, using a flatus tube, failed and a laparotomy had to be undertaken. Dilated small and large bowel were found but there was no obstructing lesion. A cecostomy was performed.

Large-Bowel Volvulus A prerequisite for the formation of a volvulus is that a long and freely mobile mesentery must be present. This occurs normally in the sigmoid, which is the commonest organ involved. Occasionally, the cecum and ascending colon are on a mesentery, which is often associated with a degree of malrotation, and they comprise the second most common organs involved. Cecal Volvulus (Right-Colon Volvulus) Cecal or right-colon volvulus can only occur when the cecum and ascending colon are on a mesentery, and this is often associated with a degree of malrotation (it has been estimated that this occurs in about 11% of the population) [32]. In half of the patients with cecal volvulus, the cecum twists in the axial plane, rotating on its long axis and in other half of patients, the cecum twists and inverts resulting in apex of the cecal twist in the left upper quadrant. It is usually found in a relatively young age group of about 30–60 years. Gangrene may occur early in the course of the condition, and it is therefore vital that an accurate diagnosis be made promptly. The diagnosis can be made from radiographs in about 75% cases [29]. Even though there is considerable distension of the volved cecum, one or

two haustral markings can usually be identified, unlike sigmoid volvulus where haustral markings are usually absent. The distended cecum can frequently be identified as a large gas- and fluid-filled viscus situated almost anywhere in the abdomen. Identification of an attached gas-filled appendix confirms the diagnosis. Moderate or severe small-bowel distension is present in about half the cases, but the remainder only show minimal small-bowel distension. The left half of the colon is usually collapsed (Fig. 27.22).

FIGURE 27.22 Cecal volvulus showing the apex of the dilated loop toward the left upper quadrant. There is associated small-bowel distension.

Sigmoid Volvulus This is the classic volvulus, occurring in old, mentally subnormal, or institutionalized population. The usual mechanism is twisting of the sigmoid loop around the mesenteric axis which leads to a closed loop obstruction.

Sigmoid volvulus is usually chronic, with intermittent acute attacks; less commonly, a true acute torsion occurs. Although plain film diagnosis is often easy with the diagnosis evident in about 57–90% of cases; up to one-third can present diagnostic difficulty with the main problem being able to differentiate the sigmoid volvulus from distended but nontwisted sigmoid, or distended transverse colon looping down into the pelvis (pseudovolvulus) [29,32].

◾loop The essential radiological feature for diagnosis is to identify the wall of the twisted sigmoid separate from the remaining distended colon. When a sigmoid volvulus occurs, the

inverted U-shaped loop is usually massively distended and it is commonly devoid of haustra (ahaustral). This is a most important diagnostic point. The ahaustral margin can often be identified overlapping the lower border of the liver shadow—the “liver overlap” sign. Where the ahaustral margin of the volvulus overlies the haustrated and dilated descending colon, the term “left flank overlap sign” has been used. The apex of the sigmoid volvulus usually lies high in the abdomen, under the left hemidiaphragm, with its apex at or above the level of T10 Inferiorly, where the two limbs of the loop converge, three white lines, representing the outer walls and the two adjacent inner walls of the volved loop, meet. This is called the inferior convergence; it is usually on the left side of the pelvis at the level of the upper sacral segments. Frequently, a huge amount of air is present in sigmoid volvulus and an air–fluid ratio greater than 2:1 is usual (Fig. 27.23). As sigmoid volvulus can be a closed loop obstruction, there may be good amount of air within the proximal colon and the small-bowel loops. Paucity of rectal gas is a common finding

◾

FIGURE 27.23 Sigmoid volvulus. Supine film. The hugely dilated ahaustral loop of sigmoid can be seen rising out of the pelvis in the shape of an inverted U. Haustrated ascending and descending colon can be identified separate from the volved sigmoid loop.

The initial treatment of a sigmoid volvulus frequently involves the insertion of a flatus tube per rectum. In chronic sigmoid volvulus, shouldering may be seen at the point of torsion, and this corresponds to the localized thickening which is frequently found in the wall of the sigmoid at the site of the chronic volvulus. CT is extremely helpful in the diagnosis of sigmoid volvulus and it is especially useful in looking for bowel ischemia and necrosis. Transverse Colon Volvulus This is a rare condition and is seen in about 1–4% of all colonic volvuli cases. The presence of a redundant transverse colon on a long mesentery and the inadequate fixation of the mesentery increases the mobility of the hepatic flexure and the ascending colon increasing the risk of transverse colon volvulus. The mortality rate is about 33% in these patients owing to delayed diagnosis and the twisting happening at the mesenteric root. The diagnosis

can be made on contrast enema, where we see the typical beak at the point of the obstruction. Volvulus of the splenic flexure is the least common and usually occurs due to adhesions or abnormal peritoneal attachments.

Adynamic or Paralytic Ileus Adynamic or paralytic ileus occurs when intestinal peristalsis is arrested and enteric contents fail to pass through the unobstructed bowel, resulting in the accumulation of fluid and gas within the dilated bowel. It is very common and most frequently occurs in peritonitis and in the postoperative period. When it is generalized, it results in both small- and large-bowel dilatation and, on horizontal-ray films, multiple fluid levels will be seen. Sometimes it can be very difficult to distinguish paralytic ileus from some types of LBO (Fig. 27.24). The postoperative ileus recovery periods usually lasts up to 72 hours after surgery. Recovery periods are also seen to vary depending on the bowel anatomy, with the small bowel taking the shortest time (10 cm) of the esophagus. This typically has smooth borders with gradual tapering and dilation, as opposed to other strictures that are generally shorter (mean length 90°) abutment of the aortic arch (white arrow). Postsurgical Esophagus

Description and Imaging Appearance Surgery remains the standard of care in patients with early stage esophageal cancer. One of the most commonly performed approaches for esophagectomy for treatment of mid to lower esophageal carcinomas is the Ivor Lewis procedure (Fig. 28.29A). In this surgery, there is an initial laparotomy to mobilize the stomach and esophagus at the diaphragmatic hiatus, followed by celiac trunk lymph node dissection and pyloromyotomy to prevent GOO due to postvagotomy pylorospasm. Then, the patient is positioned in the left lateral decubitus position and a posterolateral thoracotomy is performed to divide the azygos and en-bloc resect the esophagus, thoracic duct, and other adjacent structures. Periesophageal, aortopulmonary, and subcarinal nodes are often dissected. Finally, the gastric conduit is pulled into the chest and anastomosed above the level of the azygos vein. Higher anastomoses are preferred to achieve adequate surgical margins and reduce gastroesophageal reflux [44].

Figure 28.29 Chest radiograph (A) of a patient who has undergone Ivor-Lewis esophagectomy for adenocarcinoma showing normal appearance of contrast within the intrathoracic stomach (black arrow) and a nasogastric tube (white arrow) terminating in the thoracic stomach. Esophogram (B) in a patient who has undergone esophageal bypass for a long segment esophageal stricture due to Lysol ingestion shows interposition of the transverse colon (arrow) in this case. CT (C) further demonstrates transposition of the transverse colon (arrow) within the anterior mediastinum. A rarer major esophageal surgery is the esophageal bypass surgery (Fig. 28.29B and C). This provides an

alternative passageway for food in the setting of esophageal obstruction, whether it be due to malignancy, strictures, or motility issues. Options for bypass conduits include the stomach, jejunum, and colon. There are multiple routes including most commonly the substernal and less commonly posterior mediastinal or subcutaneous approaches. One important benefit of the substernal approach is anatomical separation from tumor when bypass is performed in the setting of malignancy [44]. Much of the postoperative appearance for esophagectomy (Fig. 28.29) depends on both the choice of conduit (stomach, small bowel, or colon) and the location (most commonly in the posterior mediastinum for Ivor Lewis esophagectomy and substernal for bypass surgeries). It is important to interrogate the site of anastomoses if performed for malignancy to evaluate for recurrence (Fig. 28.30).

Figure 28.30 Normal postoperative appearance of the esophagogastric anastomosis following Ivor-Lewis esophagectomy (A). In this same patient, follow-up CT 2 years later (B) demonstrates ill defined, enhancing soft tissue at the anastomosis (white arrow) due to local recurrence of squamous cell carcinoma.

Stomach—Inflammatory Conditions Gastritis Pathophysiology and Clinical Presentation

Gastritis is focal, segmental, or diffuse mucosal inflammation of the stomach, which can present with loss of appetite, nausea, vomiting, and epigastric pain. The most common cause is nonsteroid antiinflammatory drugs, Helicobacter pylori infection or severe systemic illnesses. The gastric mucosa is protected by mucus production, bicarbonate secretion, and ion exchange at the cell surface. NSAIDS disrupt prostaglandin synthesis, which decreases gastric blood flow reducing bicarbonate and mucin secretion. Similarly, systemic processes, such as traumatic brain injuries, systemic shock, and burn injuries, result in mucosal ischemia and stressinduced hemorrhage. H. pylori is a helical gram-negative bacterium that colonizes the gastric mucosa (most frequently the gastric antrum) and can penetrate into the intercellular spaces. It is found in more than 50% of adults greater than the age of 60. Chronic colonization leads to prolonged antigen exposure, which in turn can lead to the development of lowgrade gastric mucosal associated lymphoid tissue lymphomas [45].

Imaging Features

◾ On upper gastrointestinal series, manifestations of gastritis include mucosal erosions and gastric fold thickening. Erosions are 1–5 mm punctate, linear, or stellate collections of barium due to a focal area of mucosal necrosis, which histologically does not extend through the muscularis mucosae [45] CT is often the first test performed in patients who present with nonspecific abdominal symptoms and can be the first study to suggest gastritis. The most common finding on CT is gastric fold thickening. Generally speaking, greater than 5 mm of thickness is suggestive of gastric pathology, however this can vary with the degree of luminal distension. The gastric antrum can measure up to 12 mm in normal patients. With severe gastritis there can be stratification of the bowel layers with hyperenhancing mucosa and muscularis with intervening hypoattenuating submucosal edema (Fig. 28.31) [46,47]

◾

Figure 28.31 Severe gastritis in a patient with gastroparesis and superimposed gastric outlet obstruction. Axial CT of the abdomen with contrast shows irregular antral thickening due to malignancy. There is gastric wall thickening with a striated pattern with enhancing mucosa and muscularis propria (arrows) with an intervening layer of hypoenhancing submucosa due to edema (*).

Gastric Ulcers Pathophysiology and Clinical Presentation

Unlike erosions, gastric ulcers are mucosal defects which penetrate through the muscularis mucosa. Most commonly, these are due to Helicobacter pylori and NSAID usage. With the advent of H2 receptor antagonists, PPIs and H. pylori treatment, peptic ulcer disease incidence has decreased but still affects approximately 10% of the world’s population [47]. Symptoms include dyspepsia, episodic epigastric discomfort, early satiety, and nausea. Complications of gastric ulcers include bleeding, perforation, GOO, or fistulization with the adjacent biliary tree, pancreas, or bowel. Imaging Features Gastric ulcers occur primarily on the posterior wall of the stomach. They can be round and symmetric or have a linear appearance. On double contrast upper gastrointestinal series there is a smooth central pit or depression with smooth radiating folds or retraction of the surrounding gastric wall (Fig. 28.32) [9].

Figure 28.32 (A) Benign gastric ulcer (*) arising from the posterior wall of the stomach with thin radiating folds emanating from the ulcer. (B) Benign gastric ulcer with crater projecting outside the lumen of the stomach. Axial CT of the abdomen with contrast shows mucosal outpouching at the gastric antrum (C, arrow) with surrounding antral wall thickening. Endoscopy (D) and biopsy confirmed an ulcer due to H. pylori (arrow). Axial CT of the abdomen with contrast (E) in a different patient

with gastric ulcer (arrow) complicated by perforation with pneumoperitoneum (*) anterior to the liver. Often gastric ulcers are isolated to the mucosa and not visualized on CT. Deep and penetrating ulcers will have direct findings of gastritis with associated luminal outpouching or mucosal discontinuity. Outpouchings correspond to the extent of the ulcer crater, which extends beyond the gastric wall (Fig. 28.32). An indirect sign of a gastric ulcer on CT is perigastric fat stranding [32]. In a patient with hematemesis, high attenuating fluid can represent hemorrhage complicating a gastric ulcer. The highest attenuating component (45–70 HU) is generally found near the source of bleeding (sentinel clot). However, high attenuating ingested material or residual oral contrast can confound the assessment. Multiphase CT including arterial and portal venous phase increases the sensitivity in identify active bleeding, which can be a subtle finding [48].

GOO occurs when gastric contents are blocked from entering the duodenum. Historically, peptic ulcer disease leading to gastroduodenitis was a leading cause of GOO, however that is no longer the case as the prevalence has decreased. GOO occurs in only 2% of cases of PUD. Acutely, it occurs secondary to gastric wall edema while in the chronic setting it is due to fibrosis and strictures where the gastric lumen is thickened and narrowed with upstream gastric distension. Endoscopy and biopsy is needed due to overlap in the imaging appearance with malignancy [48]. Presence of free intraperitoneal gas and fluid indicates ulcer perforation (Fig. 28.32). Ulcers along the posterior wall of the stomach can perforate into the lesser sac and can be contained, while ulcers along the curvatures or anterior stomach perforate into the peritoneal space and present with signs of peritonitis [49].

Zollinger–Ellison Syndrome Pathophysiology and Clinical Presentation

Zollinger–Ellison syndrome occurs due to hypersecretion of the peptide hormone gastrin from autonomously functioning islet cell tumors termed gastrinomas. About 85–90% of gastrinomas arise within the gastrinoma triangle, which is bordered by the porta hepatis, duodenal sweep, and the pancreatic head. An estimated 60% of gastrinomas are malignant, with metastases in nearly one-third patients at the time of presentation [50,51]. Gastrin results in hypersecretion of gastric acid from the gastric parietal cells, which leads to an increased incidence of ulcers in which are often postbulbar in location involving the duodenum and jejunum. Symptoms overlap with those of ulcer disease. Diarrhea can be present due to volume overload from acid hypersecretion. While most gastrinomas are sporadic, approximately 25% are associated with multiple endocrine neoplasia type 1 [50]. Imaging Features

◾ Marked gastric mucosal fold thickening with gastritis present. Distal esophagitis, duodenitis, and proximal jejunitis can also be seen. Gastric

mucosal outpouchings representing ulcers are often multiple. Presence of postbulbar ulcers should raise suspicion for a gastrin secreting tumor. The primary tumor itself will manifest as a hyperenhancing lesion, most commonly situated in the gastrinoma triangle (Fig. 28.33) [52]. The triangle is lined by the confluence of the cystic duct and common bile duct superiorly, junction of the second and third portions of the duodenum inferiorly, and junction of the neck and body of the pancreas medially Nuclear medicine can be used to evaluate neuroendocrine tumors and their metastasis, which can be underestimated with ultrasound, CT, and MRI. About 80% of gastrinomas express somatostatin receptors. SPECT/CT with In-111 octreotide can be employed to detect occult primary tumors and metastases with a sensitivity ranging between 65 and 100%. Ga-68-Dotatate PET/CT is also increasingly being used to evaluate primary neuroendocrine tumors and their metastasis as it is thought to have the highest sensitivity [51,53]

◾

Figure 28.33 Axial CT of the abdomen with contrast (A) shows diffuse rugal fold thickening of the gastric body and antrum (*). Coronal CT of the abdomen with contrast (B) shows diffuse postbulbar enteritis (arrow) within the distal duodenum and proximal jejunum. There is a hyperenhancing nodule (black arrow) within the gastrinoma triangle (dotted black lines) representing a gastrinoma. Constellation of findings is compatible with Zollinger–Ellison syndrome.

Menetrier’s Disease Pathophysiology and Clinical Presentation

Menetrier’s disease is a rare protein losing enteropathy with a prevalence of less than 1 in 200,000 people [54]. Patients most often present with epigastric pain, hypoalbuminemia, weight loss, diarrhea, and vomiting. There is a bimodal distribution. The childhood form occurs in children less than 10 years, is associated with CMV infection, and resolves spontaneously. In adults, the average age of diagnosis is 55 years and symptoms progress over time [54]. Imaging Features The hallmark of Menetrier’s disease is massive foveolar hyperplasia with relative sparing of the antrum. On fluoroscopy, there are giant and tortuous rugal folds in a pattern described similar to the convolutions of the brain. Linear strands of barium contrast can become trapped between the enlarged folds [54,55]. Similarly, on CT, the thickened gastric rugae protrude into the gastric lumen, with relative sparing of the antrum (Fig. 28.34). The stomach is often distended due to increased gastric secretions.

Figure 28.34 A 52-year-old man with hypoalbunemia. Axial CT of the abdomen with contrast shows marked rugal fold thickening involving fundus and body (arrow) with relative sparing of the antrum (*) compatible with Menetrier’s disease.

Crohn’s Disease

Pathophysiology and Clinical Presentation Crohn’s disease is a granulomatous process with transmural involvement. Although the small bowel and colon are the most common sites of disease, there is an estimated 0.5–4% prevalence of gastroduodenal involvement. Most patients with Crohn’s disease of the stomach are asymptomatic. Symptoms include epigastric pain, anorexia, weight loss, nausea, and vomiting. Given overlap with symptoms of small and large bowel Crohn’s (covered in detail in another chapter), as well as misattribution of symptoms to medication side effect, a high clinical suspicion along with radiographic and endoscopic findings is required to diagnose gastric involvement [56,57]. Complications of gastric Crohn’s include GOO due to strictures and fistulization between the stomach and duodenum or colon. About 30% of patients with gastrocolic fistulas report with a triad of diarrhea, feculent vomiting, and weight loss [56]. Imaging Features

◾ Features of gastric Crohn’s on fluoroscopy include thickening or cobblestoning of the gastric

mucosa, apthoid ulcers, strictures, and fistula formation most commonly with the duodenum and transverse colon [56] Apthous ulcers can appear slit-like and punctate, mimicking erosive gastritis Chronic inflammation leads to nondistension and smooth appearance of the antrum, widened pylorus, and narrowed bulb, also known as the rams horn sign on upper GI examination [58,59]

◾ ◾

Vascular Gastric Varices Pathophysiology and Clinical Presentation Gastric varices occur due to reversal of flow in the gastric fundal venous plexus, which is most commonly due to portal hypertension in the setting of cirrhosis or splenic vein thrombosis from pancreatitis. The short gastric veins drain the fundus into the splenic vein, the gastric veins drain directly into the portal vein along the lesser curvature, while the right and left gastroepiploic veins drain into the

superior mesenteric and splenic veins, respectively [60]. Gastric varices are present in 5–33% of patients with portal hypertension, the most common cause of which is hepatic cirrhosis [61]. Gastric varices bleed less commonly than esophageal varices, 25% versus 64%; however, given the large size and greater flow, gastric variceal bleeding carries higher morbidity with a mortality rate of approximately 45% [61]. Two distinct forms of gastric fundal varices are seen: submucosal and perigastric (adventitial). Almost all cases of fundal variceal bleeding are due to the submucosal variant [62]. Imaging Features

◾ On upper gastrointestinal series, gastric varices appear as thickened, tortuous folds, most commonly within the gastric fundus. A conglomeration of varices can produce lobulated submucosal mass-like appearance that can be mistaken for polypoid gastric malignancy [62]. With CT, one can not only detect submucosal varices but also evaluate for the underlying cause

◾

such as changes of pancreatitis and splenic vein thrombosis or findings of cirrhosis. Additionally, CT aids in evaluating afferent and efferent venous vasculature which can be useful in the setting of any planned intervention (e.g., balloon occluded retrograde transvenous obliteration). On contrastenhanced CT, gastric varices appear as multiple enhancing tubular vessels conforming to the contour of the stomach (Fig. 28.35) [63].

Figure 28.35 Axial CT of the abdomen with contrast in a patient with chronic pancreatitis

and splenic vein thrombosis. Multiple dilated, serpiginous structures are seen along the gastric submucosa and perigastric region (arrow) compatible with gastric varices.

Arteriovenous Malformation Pathophysiology and Clinical Presentation Gastric arteriovenous malformation (AVM) is an uncommon source of upper gastrointestinal bleeding, representing 1.4% of all intestinal AVMs [64]. They are often confused with gastrointestinal ectasias which occur in elderly patients. AVMs are congenital lesions present from birth with persistent direct connections between arteries and veins. They are more commonly seen in patients with Osler–Weber– Rendu syndrome (hereditary hemorrhagic telangiectasia). Imaging Features AVMs result in dilated submucosal arteries and veins which can simulate variceal disease. On multiphase

CTA, there will be early venous opacification with contrast seen on the arterial phase of the examination due to the direct arteriovenous connection (Fig. 28.36). CT can define extramural extent of the malformation that will not be appreciated on endoscopy and therefore very useful in surgical or pre-embolization planning [65,66].

Figure 28.36 Axial CT of the abdomen with contrast shows enhancing serpiginous tangle of vessels (arrow) representing a gastric arteriovenous malformation in this patient with Osler–Weber–Rendu syndrome.

Gastric Artery Aneurysm Pathophysiology and Clinical Presentation Gastric and gastroepiploic artery aneurysms are rare comprising 4% of all abdominal visceral aneurysms. Spontaneous rupture can lead to massive hemorrhage, with a mortality estimated to be greater than 70% [67]. Patients can have chronic unexplained left upper quadrant pain or be asymptomatic with incidental detection. Etiologies include atherosclerotic disease, trauma, vasculitis, infection, or adjacent to inflammatory processes such as pancreatitis or peptic ulcer disease [68]. While a true vascular aneurysm contains all three layers of the vessel wall (intima, media, and adventitia), a pseudoaneurysm contains only the adventitial layer with weak integrity and increased risk of rupture. The majority of gastric artery aneurysms are along the lesser curvature involving left or right gastric arteries, as opposed to the epiploic vessels along the greater curvature with a reported 10:1 ratio [69].

Imaging Features

◾ On a noncontrast CT, aneurysms will be a rounded soft tissue structure of varying attenuation depending on their degree of thrombosis. Thrombosed segments will be higher attenuation on noncontrast imaging. With injection of contrast, the nonthrombosed aspects of the aneurysm will follow the attenuation of the aorta on multiphase examinations (Fig. 28.37)

Figure 28.37 Axial CT of the abdomen with contrast in a patient with acute alcohol-induced pancreatitis and hematemesis shows an enhancing round lesion (arrow) along the lesser curvature of the stomach representing a left gastric artery aneurysm.

Gastric Antral Vascular Ectasia Pathophysiology and Clinical Presentation Gastric antral vascular ectasia (GAVE) is a rare and often underdiagnosed vascular condition involving the gastric antrum that may lead to chronic occult bleeding or acute hemorrhage in older patients. The cause is unknown, but one proposed theory is that gastric peristalsis results in prolapse of the loose antral mucosa resulting in elongation and ectasia of vessels [70]. GAVE is most commonly seen in middle aged or older women. There is an association with CREST syndrome, atrophic gastritis, autoimmune, and connective tissue disorders. About 40% of reported cases of GAVE are associated with portal hypertension or cirrhosis [70].

Imaging Features Tortuous, dilated submucosal vessels radiating from the pylorus lead to alternating bands of hyperemic and normal mucosa on endoscopy, akin to the stripes on the surface of a watermelon, hence referred to as “watermelon stomach.” On upper gastrointestinal series and CT there are thickened, scalloped mucosal folds extending from the gastric antrum to the pylorus (Fig. 28.38) [71,72].

Figure 28.38 Axial CT of the abdomen with contrast of a 79-year-old woman with melena.

There is antral thickening (arrow) with alternating bands of attenuation that was proven as gastric antral vascular ectasia on endoscopy.

Emphysematous Gastritis and Gastric Emphysema Pathophysiology and Clinical Presentation Emphysematous gastritis (EG) is an infection of the gastric wall due to gas-forming organisms with high mortality and often requiring emergent surgical management with partial or total gastrectomy. Many organisms have been associated with EG, including gram positive, gram negative, anaerobic, and fungal. There are associations with diabetes mellitus, corrosive ingestion, vasoocclusive disease resulting in ischemia or acute gastroenteritis [73]. In benign gastric emphysema (interstitial gastric emphysema) air is introduced into the gastric wall following trauma to the gastric mucosa or due to air entering via mucosal defects in the setting of GOO. It can also be seen with patients undergoing chemo- or immunotherapy [74]. Gastric emphysema is a benign

and self-limiting process that resolves with conservative management. On the other hand, EG presents with shock, severe abdominal pain, fever, and hematemesis [73]. Imaging Features It is difficult to differentiate the two entities with imaging alone. In both conditions, there will be focal or diffuse intramural gas which outlines the contour of the stomach. This can be seen on radiographs and CT. Gastric distension is often associated with both entities, however ancillary features such as rugal fold thickening, portal venous gas, fluid collections, or surrounding perigastric fat stranding should prompt consideration of EG especially in patients with a toxic clinical picture (Fig. 28.39A). If the patient is clinically well, gastric emphysema should be the primary consideration (Fig. 28.39B). Serial radiographs can be obtained that will show a gradual decrease and eventual resolution of intramural gas.

Figure 28.39 Axial CT of the abdomen with contrast in a patient with septic shock (A) shows a markedly distended stomach (*) with diffuse foci of intramural gas (white arrow) representing EG. Gas is also seen in the superior mesenteric vein (black arrow). A partial gastrectomy revealed transmural necrosis of the fundus and lesser curvature. Axial CT of the abdomen without intravenous contrast (B) in a patient with gastric outlet obstruction. There is gas within the wall of the stomach (arrow) without evidence of portal venous gas or pneumoperitoneum. Increased pressure due to gastric outlet obstruction resulted in benign gastric emphysema that resolved once obstruction was relieved.

Gastric Ischemia

Pathophysiology and Clinical Presentation Ischemia of the stomach is uncommon given its rich collateral blood supply discussed in the anatomy section. Gastric ischemia can result from diffuse or local vascular insufficiency. Causes include systemic hypotension, vasculitis, thromboembolism or vascular stenosis, vasoconstriction, or volvulus. It can manifest with acute abdominal pain or chronic abdominal angina [75]. Imaging Features

◾ The most common finding is gastric wall thickening. With contrast administration, the target sign may be seen as alternating high and low attenuation layers resulting from submucosal edema. Findings seen later in the course of ischemia include diminished gastric wall enhancement, pneumatosis, portal venous gas, and gastric distension with thinning of the gastric wall (Fig. 28.40). Free intraperitoneal air is indicative of transmural perforation [75] With vascular etiologies, one may see arterial occlusion in the setting of chronic atherosclerotic

◾

arterial insufficiency, thromboembolism, or dissection. Alternatively, venous thrombosis or volvulus will show significant mesenteric edema and mesenteric venous engorgement due to outflow obstruction [75]

Figure 28.40 Axial CT of abdomen with contrast (A) of a 40-year-old man who is recently status post-Whipple surgery. There is loss of normal gastric rugal fold pattern and hypoenhancement of the wall at the fundus (arrow) with surrounding fat stranding. CT performed 3 days later (B) shows a nonenhancing transmural defect (arrow) with

extraluminal fluid consistent with perforation form gastric ischemia.

Mechanical Gastric Disease Foreign Bodies and Bezoars Pathophysiology and Clinical Presentation While uncommon, foreign bodies are an important and often challenging diagnosis to make. Populations at risk include children, psychiatric or mentally handicapped patients, adults with unusual sexual or criminal behavior, trauma patients, and those with accidental ingestions. It is important to note that sharp and elongated objects can predispose to bowel wall injury and perforation. Objects such as magnets can result in bowel wall necrosis and erosion if they are in adjacent loops of bowel. Batteries can lead to corrosive mucosal bowel injury with bowel wall necrosis and perforation [76]. Bezoars are an accumulation of ingested foreign or undigested food material within the gastrointestinal

tract named by the materials that form them. The most common include: trichobezoars which are formed of hair and seen in patients with trichotillomania, and phytobezoars which are composed of poorly digested fruit and vegetable fibers in patients with gastroparesis. The most common presentation in these cases is bowel obstruction [77]. A body packer is a drug courier who conceals packages of illicit drugs within their alimentary tract. Increased sophistication of drug traffickers and variety of packaging materials can make diagnosis difficult. In the setting of package perforation, patients can present with florid overdose of the illicit drug [78]. Imaging Features

◾ Radiographs are initial imaging technique to diagnose and follow-up ingested foreign bodies. Visibility on radiographs is incumbent both on the attenuation characteristics of the foreign body, surrounding structures, and the overlying soft tissues

◾

◾ An object that is less radio dense will be easily visualized in an air filled and distended stomach; however, if the stomach were collapsed it would be obscured by the surrounding gastric wall and overlying soft tissue. Metal and ingested bones are the most radiodense objects. Glass can have a varying radiodensity. Wood and other organic foreign bodies are radiolucent and often radiographically occult (Fig. 28.41) [79] CT can be used to diagnose foreign bodies and delineate exact anatomical location with increased sensitivity to diagnose complications such as bowel perforation A gastric bezoar appears as a mottled, intraluminal soft tissue mass often simulating the appearance of stool (Fig. 28.42). When large, there is less diagnostic dilemma. In contrast to retained food within the stomach, small bezoars are rounded or ovoid, have a lower density than food (Hounsfield units of −150 to 50) and they tend to float on the water–air interface [77] With the appropriate clinical history, multiple well-defined small rounded or oval-shaped radiodense objects on abdominal radiographs should raise suspicion of drug packing. Parallelism

◾ ◾

◾

of the small packages within the bowel or the “condom” sign in which there is a clear crescent of air surrounding an ovoid object are described findings. Often, these patients are aware that attempts to degrade image quality such as motion will decrease diagnostic accuracy [78]

Figure 28.41 Abdominal radiograph (A) shows no radiopaque foreign bodies in a suspected case. Axial CT of the abdomen without contrast (B) confirms multiple linear foreign bodies of fat density (arrows), which were confirmed to be crayons on endoscopy (C).

Figure 28.42 Coronal CT of the abdomen with contrast of a 17-year-old psychiatric patient shows distended stomach with mixed attenuation material in the lumen composed of soft tissue density and gas compatible with an obstructing trichobezoar (arrow).

Bouveret Syndrome Pathophysiology and Clinical Presentation Bouveret syndrome is a complication of cholelithiasis where a cholecystoduodenal fistula results in GOO due to an impacted gallstone within the distal stomach or proximal duodenum. Gallstone ileus with

GOO is rare accounting for 1–3% cases. It occurs most commonly in elderly woman with a mean age of approximately 69 years [80,81]. Patients will present with nausea, vomiting, epigastric pain, and rarely hematemesis if there is gastric wall ulceration. Imaging Features

◾ On radiographs, an ectopic gallstone, pneumobilia, and gastric distension is specific for gallstone ileus, but has a low sensitivity only seen in 30–35% of cases [81] CT is the most often used technique for diagnosis, effectively confirming the presence of GOO, pneumobilia, an impacted ectopic gallstone and a biliary-enteric fistula (Fig. 28.43). One drawback is that 15–25% of gallstones can be isoattenuating to the bile or fluid and can be difficult to identify on CT. Oral contrast will surround the stone and can help confirm diagnosis [80] In cases when gallstones are not visualized on radiographs or CT, MRCP can help distinguish between bile and the stone. Additionally, the site of the cholecystoduodenal fistula can be better

◾

◾

delineated on MRCP if there is enough fluid present within the fistulous tract [81]

Figure 28.43 Axial CT of the abdomen without intravenous contrast shows a large impacted gallstone in the pylorus (arrow) with upstream gastric distension compatible with outlet obstruction in the setting of Bouveret syndrome. There is gallbladder wall thickening and intraluminal gas (*) secondary to a cholecystoduodenal fistula (not shown).

Gastric Volvulus Pathophysiology and Clinical Presentation

Gastric volvulus is twisting of the stomach resulting in GOO. Patients present with the Borchardt triad of intractable vomiting, sudden epigastric abdominal pain, and inability to pass a nasogastric tube into the stomach [49,82]. Depending on the axis of rotation, gastric volvulus is divided into organoaxial and mesenteroaxial subtypes. In some cases, there will a complex mixed volvulus with both organoaxial and mesenteroaxial components. Imaging Features

◾ With organoaxial volvulus, the antrum rotates anterosuperiorly and fundus rotates posteroinferiorly, resulting in the greater curvature lying superior to the lesser curvature (Fig. 28.44). Some patients will have less than 180° of rotation, with incomplete or partial volvulus in which there is not complete obstruction. Patients with paraesophageal hernias are predisposed to developing abnormal orientation of the stomach. When there is lack of clinical symptoms and outlet obstruction, it is more appropriate to use the terminology organoaxial orientation as opposed to volvulus [49,82]

◾

◾ Mesenteroaxial volvulus is much less common and occurs when the stomach twists about its short axis/mesentery in which the antrum is displaced above the gastroesophageal junction (Fig. 28.44) Upper gastrointestinal series will delineate the anatomy and rotation of the stomach, as well as assess for passage of contrast into the duodenum that is useful in cases of partial volvulus The appearance of volvulus is often confusing to unexperienced viewers on CT. Coronal reformatting often aids in delineating the anatomy and demarcating the anatomic relationships. Imaging findings include GOO, gastric wall thickening. It is important to evaluate for complications of gastric ischemia or perforation [49]

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Figure 28.44 Organoaxial gastric volvulus in an 85-year-old woman with vomiting and epigastric pain. Coronal CT of the abdomen without contrast (A) shows that the stomach is almost entirely intrathoracic with an upside down orientation (*). Follow-up radiograph after drinking oral contrast (B) shows no passage of contrast into the duodenum compatible with complete obstruction. Mesenteroaxial volvulus with rotation about the short axis of the stomach along its mesentery (C).

Gastric Diverticulum

Pathophysiology and Clinical Presentation Gastric diverticula are the rarest types of gastrointestinal diverticula with a reported incidence of 0.02% on autopsy studies [83]. They are true congenital diverticula containing all layers of the gastric tissue, and commonly located on the posterior wall of the gastric cardia. Most are asymptomatic and incidentally found on endoscopy, upper gastrointestinal fluoroscopy, or cross-sectional imaging. Rarely, they can present with vague symptoms of fullness or upper abdominal discomfort. Imaging Features

◾ On upper gastrointestinal series, gastric diverticula can be mistaken for hiatal hernias or hypertrophic gastric folds. They can range in size from 1 to 11 cm [84] CT can confirm an outpouching arising from the gastric cardia. Inexperienced observers can mistake these diverticula for an adrenal mass. Presence of intraluminal fluid and gas is diagnostic (Fig. 28.45)

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Figure 28.45 Axial CT of the abdomen without contrast shows a gas-filled outpouching from the posterior aspect of the gastric fundus (arrow) representing a gastric diverticulum.

Gastric Trauma Blunt and Penetrating Trauma Pathophysiology and Clinical Presentation

Penetrating trauma is the most common cause of gastric injury, with an incidence of approximately 20% cases of gunshot wounds and 10% cases of stab wounds. A single site of gastric injury is seen in nearly 50% of stab wounds to the left thoracoabdominal region, while gunshot wounds often result in two or more foci of injury in 90% of cases [85]. High velocity blunt trauma to the epigastric region can result in gastric injury. There is positive correlation between injury and degree of intraluminal pressure. As such, the risk of injury increases in the postprandial state [86]. Imaging Features

◾ The manifestations of gastric injury include traumatic gastrostomy, devascularization, intramural hematoma/contusions, or lacerations ◾ Intramural hematomas present as high attenuating material within the gastric wall. Devascularization is seen as hypoenhancement of the gastric wall In the setting of penetrating trauma, it is useful to pay particular attenuation to areas of the stomach along the penetrating wound trajectory.

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Gastrostomy sites reflect areas of gastric wall discontinuity and can be difficult to visualize if the stomach is decompressed and have to be inferred in some cases when tracing the missile tract [86]. In some cases, giving oral contrast may delineate the area of injury with leakage of contrast (Fig. 28.46)

Figure 28.46 Axial CT of the abdomen with oral contrast (A) shows moderate volume perigastric hemorrhage and extraluminal leakage of contrast (arrow) representing gastric perforation in this patient with gunshot injury to the abdomen. Upper gastrointestinal examination with water-soluble contrast (B) shows a large

area of extraluminal leakage (*) due to iatrogenic perforation from endoscopic biopsy.

Iatrogenic Gastric Injury Pathophysiology and Clinical Presentation Iatrogenic gastric injuries are rare and include lacerations, hemorrhage, and perforation. Reported rates of injury with diagnostic endoscopy are between 0.01% and 0.03% [87]. Therapeutic endoscopic procedures such endoscopic mucosal resections, polypectomy, and dilation or stent placement for malignant or inflammatory strictures have higher rates of complication depending on the procedure. For example, the American Society of Gastrointestinal Endoscopy reports that balloon dilation for benign GOO has perforations rates as high as 7.4% [88,89]. Imaging Features Injuries can manifest as perigastric fat stranding, focal areas of gastric wall thickening or extraluminal

fluid collection, and free intraperitoneal air in the setting of perforation. On upper gastrointestinal studies, there is either contained or free leakage of contrast (Fig. 28.46B).

Miscellaneous Gastric Processes Ectopic Pancreatic Tissue Pathophysiology and Clinical Presentation Pancreatic heterotopia is when pancreatic elements are found outside of the pancreatic gland itself. There are two dominant theories as to their development. The migration theory suggests that fragments of pancreatic tissue separate from the developing pancreas during foregut rotation and deposit in aberrant locations. Another theory of origin involves pancreatic metaplasia of the endodermal tissue in the gastric mucosa. It is an uncommon condition, reported on 0.5–14% in autopsy series [90]. The stomach is the most common site of involvement with reported frequency of 24–38% [90]. Typically,

the ectopic tissue is located along the greater curvature within 3–6 cm of the pylorus. These are most commonly asymptomatic and found incidentally. Most common symptoms include abdominal pain, nausea, or vomiting if pancreatitis occurs within the heterotopic gland. Imaging Features

◾ On upper gastrointestinal series, heterotopic pancreatic tissue is usually a round or ovoid submucosal soft tissue mass that can be mistaken for a neoplasm (Fig. 28.47). A minority of cases will have a central umbilication corresponding to a rudimentary duct [90] The enhancement characteristics are similar to the pancreas on CT and MR. Signal intensity on additional sequences MRI also mirror the native gland. Superimposed pancreatitis leads to gastric wall thickening and inflammation with or without pseudocyst formation [90]

◾

Figure 28.47 Axial CT of the abdomen with contrast (A) of a patient with epigastric pain. There is an enhancing lesion within the gastric antrum (arrow). (B) Follow-up endoscopy confirmed a submucosal mass with a central umbilication that was biopsied confirming ectopic pancreatic rest.

Gastric Splenosis Pathophysiology and Clinical Presentation Autoimplantation of splenic tissue can occur on the gastric surface as a result of trauma or surgery [91]. Gastric splenosis is often detected incidentally and when present as a single lesion can be challenging to

distinguish on imaging from other gastric tumors such as GISTs. Multiplicity and correlation with patient history is helpful [92]. Imaging Features Ectopic splenic tissue will follow the enhancement pattern of spleen on contrast-enhanced CT and MRI. If large enough, characteristic tigroid pattern of arterial phase enhancement can be seen. The T1 and T2 signal is identical to that of the spleen with similar degree of diffusion restriction. In equivocal cases, heat-damaged Tc 99 red blood cell scan can help differentiate from other gastric neoplasms as native and ectopic splenic tissue demonstrate uptake of the radiotracer [93]. Changes of prior splenectomy and additional splenules over the left upper quadrant peritoneum and at times over the liver surface can be seen (Fig. 28.48).

Figure 28.48 Axial CT of the abdomen with contrast of a patient with prior history of gunshot wound and splenectomy shows an enhancing mass over the gastric fundus serosal surface (white arrow). Note additional enhancing nodules in the left upper quadrant and the left lung base (black arrows). Findings are consistent with post-traumatic splenosis.

Gastric Neoplasms Lipoma

Pathophysiology and Clinical Presentation Gastric lipomas are rare mesenchymal tumors of the stomach, accounting for only 1% of all gastric tumors [94]. They are almost always small asymptomatic lesions found incidentally on imaging. When lesions are larger, they can ulcerate with bleeding or present with obstructive symptoms. The lesions are composed of well-differentiated adipose tissue circumscribed by a fibrous capsule. Imaging Features

◾ On barium studies, they will appear as a smooth, sharply marginated, and compressible submucosal mass. Occasionally, lipomas can have a stalk and prolapse into the duodenal bulb when located in the antrum. With CT, they will appear as well circumscribed area of fat density, and attenuation ranging from −70 to −120 HU (Fig. 28.49). If there is ulceration, a portion of the lesion can present with soft tissue attenuation [95].

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Figure 28.49 Axial CT of the abdomen with intravenous contrast shows a fat attenuating well-circumscribed submucosal mass (arrow) in the gastric antrum consistent with a lipoma.

Leiomyoma Pathophysiology and Clinical Presentation Leiomyomas of the stomach are rare and almost always arise from the gastric cardia [96]. Leiomyomas are benign mesenchymal tumors

composed of smooth muscle that most commonly arise from the muscular propria. They are mostly asymptomatic; however, the most common symptom is bleeding due to ulceration. It is important to make a distinction between leiomyoma and GIST, because leiomyomas are benign and GISTs have variable risk of disease progression [95]. Imaging Features On CT, leiomyomas are well marginated and are homogenously hypoattenuating. Presence of intratumoral calcification and ulceration would suggest GIST over leiomyoma (Fig. 28.50). Involvement of the esophagogastric junction is another marker suggestive of leiomyoma as opposed to GIST. This may be explained by the fact that the most common mesenchymal tumors within the esophagus are leiomyomas while in the stomach GIST is predominate [97].

Figure 28.50 Coronal CT of the abdomen with intravenous contrast shows a well-marginated homogenously enhancing mass (arrow) at the gastroesophageal junction. Biopsy was performed showing leiomyoma.

Gastrointestinal Stromal Tumor Pathophysiology and Clinical Presentation GISTs are the most common mesenchymal soft tissue sarcoma of the gastrointestinal tract, graded by their rate of mitotic activity, size, and location [95]. The stomach is the most common site of involvement

representing 70% of cases in the general population [98]. GISTs originate from the interstitial cells of Cajal, which act as pacemaker cells for the smooth muscles. They stain positive for c-Kit (CD117) which is a stem cell growth factor receptor. Mutations of the c-KIT gene result in a gain of function in the enzymatic activity of the Kit tyrosine kinase [98]. They are often discovered incidentally when small. Larger tumors can present with abdominal pain and early satiety. Imaging Features

◾ They can be predominantly endophytic, exophytic, or dumb-bell-shaped masses. Smaller lesions (90%) being fundic gland polyps as opposed to adenomatous polyps. Fundic gland polyps have a low malignant potential and polypectomy is rarely performed, except with larger polyps typically greater than 1 cm in size in patients with FAP [96,100]. Hyperplastic polyps are the second most common gastric polyps that typically occur within the antrum and are less than 1 cm in diameter. They occur due to proliferation of the surface epithelium in the setting of chronic inflammation. While there is almost no malignant potential, there is an increased risk of synchronous cancer elsewhere within the stomach given they are found in the background of a chronic inflammatory process [100,101].

Adenomatous polyps (gastric adenomas) are true gastric neoplasms which can progress to gastric cancer. They can occur anywhere in the stomach; however, are most commonly found within the antrum. They represent approximately 6–10% of polyps within the western world. Histologic subtypes are similar to those of colonic polyps in order of increasing risk of malignancy: tubular, tubulovillous, and villous [100,101]. Imaging Features

◾ Fundic gland polyps are smooth sessile or hemispheric protrusions that are most commonly 1–8 mm in diameter. They can be single; however, are most commonly multiple with up to 50 polyps reported (Fig. 28.53). Classically, sporadic polyps are located within the fundus or body, while in FAP they can arise anywhere within the stomach [96,102] Hyperplastic polyps appear as single or multiple smooth sessile, round, or ovoid filling defects less than 1 cm in diameter [103]. They are most commonly found within the gastric body and fundus (Fig. 28.54)

◾ ◾

◾ Adenomatous polyps typically can be sessile or pedunculated. In contrast to hyperplastic polyps, they are more commonly lobulated and larger than 1 cm [98]. They are usually solitary and located within the antrum, however multiple polyps can be found in any location

Figure 28.53 Double contrast upper GI exam (A) shows multiple round filling defects at the gastric fundus (arrows) representing fundic gland polyps that were confirmed on endoscopy (B, arrow).

Figure 28.54 Axial CT of the abdomen with intravenous contrast (A) shows multiple enhancing filling defects (arrow) in the distal gastric body representing hyperplastic polyps as confirmed on follow-up endoscopy (B, arrow).

Gastric Adenocarcinoma Pathophysiology and Clinical Presentation Gastric adenocarcinoma represents 95% of the cases of malignant neoplasm of the stomach. The 5-year survival for patients with resectable disease is 10– 30% [98]. While screening is recommended in high incidence areas such as China or Japan, in the western world only high-risk patients (FAP,

Menetrier’s, etc.) are considered for endoscopic screening. Incidence peaks within the seventh decade of life [104]. In the absence of distant metastases or direct invasion of an adjacent organ, surgical resection is the treatment of choice. Risk factors for gastric adenocarcinoma include diets rich in salted or smoked foods, nitrites, and nitrates, as well as conditions such as chronic H. pylori gastritis, atrophic gastritis, Menetrier’s disease, adenomatous gastric polyps, and pernicious anemia [104]. Linitis plastica (Fig. 28.55) is a histological form of adenocarcinoma with mucinous features and “signet ring” cells that can infiltrate the gastric wall with loss of distensibility. It carries a worse prognosis than other forms of gastric cancer and often discovered late, at times requiring multiple biopsies to obtain a diagnosis [105].

Figure 28.55 Axial contrast-enhanced CT (A) demonstrates diffuse gastric wall thickening (*)

with heterogenous enhancement due to infiltrative signet ring variant gastric adenocarcinoma (linitis plastica). There is nodularity and stranding within the peritoneum (B, white arrow) and small volume ascites (C, *) which were findings compatible with peritoneal carcinomatosis. Staging of gastric cancer is via the TNM system. T1 lesions are confined to the muscularis, T2 lesions invade the muscularis and subserosa, T3 lesions invade the serosa, and T4 tumors invade the adjacent organs. Lymph node involvement is categorized by number of metastases within regional lymph nodes (N1: 1–6, N2: 7–15, N3 >15). Of note, the regional lymph nodes of the stomach are classified into four compartments using the Japanese Research Society of Gastric Cancer. They are subdivided by their anatomic location, including in the perigastric region, about the celiac axis, root of mesentery, splenic hilum, hepatoduodenal ligament, and paraaortic regions. M1 indicates distant metastases and/or spread to nonregional lymph nodes. Solid organ metastases are uncommon at time of diagnosis,

although very important for treatment planning [106,107]. Hematogenous metastases most commonly involve the liver given the stomach is drained by the portal vein. Less common sites include the adrenals, lungs, and bones. In reproductive age women, gastric cancer has a tendency to metastasize to the ovaries which when secondary to signet ring subtype are termed as Krukenberg tumors. At times, the patient can present with symptoms related to the ovarian metastases before the primary tumor is found [108]. Imaging Features

◾ On barium studies, early gastric adenocarcinomas can present as flat, depressed, or ulcerating lesions (Fig. 28.56). More advanced carcinomas are segmental or cause diffuse wall thickening. Table 28.1 gives the differentiating features to identify malignant from benign gastric ulcers. Barium studies are however almost never performed in the current day and age Like esophageal cancer, EUS has the highest accuracy (78–93%) in determining T staging for

◾

gastric cancer compared to CT (62% for T1/T2 tumors and 80% for T3/T4 tumors) [106,107]. However, CT can aid in further characterizing the extent of tumor involvement and locoregional/distant metastasis. The characteristic CT finding of gastric cancer is gastric wall thickening with disruption of the normal multilayered gastric enhancement pattern. If focal, enhancement of the involved gastric segment may be different than that of the normal adjacent gastric wall (Fig. 28.57). CT with neutral oral contrast agents (such as water) and/or with gastric distension via effervescent crystals can help detect subtle tumors and reduce false positives due to under distension of the stomach. Additional scanning with lateral decubitus or oblique CT can be pursued to adequately distend portions of the stomach depending on the location of the tumor On CT, T1 and T2 lesions are limited to the gastric wall. T3 lesions will have blurring of the serosal contour with stranding in the perigastric fat. T4 lesions will spread through the ligamentous and peritoneal reflections of the stomach and can extend to abut adjacent organs as follows: transverse colon by invasion through gastrocolic

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ligament, pancreas by invasion through the lesser sac, and liver by invasion through the gastrohepatic ligament (Fig. 28.57) [109] Metastatic sites include lymph nodes (Fig. 28.58) and peritoneal metastases. Peritoneal metastases can be subtle on CT and often, ascites may be the only indicator. Other CT findings of peritoneal disease include nodularity of the peritoneal fat, peritoneal surface nodularity of abnormal thickening of the serosal surface of intraabdominal organs such as the small bowel (Figs. 28.55B and C) Cross-sectional imaging is important in the diagnosis of gastric linitis because it can provide an earlier diagnosis compared to endoscopy. There is diffuse or segmental gastric wall thickening that appears regular, concentric, and symmetric. Homogenous wall enhancement is most pronounced in delayed phases of imaging [104]

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Figure 28.56 (A) Irregular gastric carcinoma (arrows) arising from the greater curvature of the stomach which ulcerates into the gastric lumen. (B) Separate patient with a malignant gastric ulcer along the lesser curvature with arrows pointing to contrast forming along the ulcer base that is convex toward the lumen (meniscus sign).

Figure 28.57 (A) Coronal CT of the abdomen with contrast shows marked asymmetric wall thickening and enhancement of the gastric antrum (arrow) resulting in gastric outlet obstruction proven to be secondary to gastric antral adenocarcinoma. (B) Axial contrastenhanced CT shows a hypoenhancing mass arising from the gastric body which extends to the splenic hilum (white arrow) and also abuts the pancreas (*) posteriorly. This was biopsied and found to be locally invasive gastric adenocarcinoma.

Figure 28.58 Axial contrast-enhanced CT of a patient with gastric adenocarcinoma (not shown) demonstrates locoregional metastatic lymphadenopathy involving the gastrohepatic ligament (A, white arrow) and left para-aortic chain (B, white arrow). Table 28.1 Differentiating Gastric Ulcers [110] Benign Malignant Round or ovoid Irregular shape shape Projects outside of the lumen margin

Remains inside the lumen margin

Benign Smooth ulcer mound

Malignant Irregular ulcer mound with rolled edge

Smooth, symmetric radiating folds extending to lip of ulcer

Nodular and fused radiating folds that do not extend to the lip of ulcer

Improves with conservative treatment

Fails to improve or worsens

Hampton’s line —thin line radiolucent line seen at the neck of benign gastric ulcers

Carman meniscus sign— lenticular shape of barium seen on compression views with contrast trapped between the margins of a large, flat ulcer

Gastric Lymphoma Pathophysiology and Clinical Presentation

About 5–20% of extra-nodal lymphomas involve the gastrointestinal tract, with the stomach being the most common site of involvement [111]. Lymphoma accounts for less than 5% of all gastric malignancies, with non-Hodgkin’s B cell lymphoma being the most common subtype [111]. Risk factors for gastric lymphoma include HIV or H. pylori infection, celiac disease, inflammatory bowel disease, and immunosuppression after solid organ transplantation [111]. Most low-grade gastric lymphomas arise from mucosal associated lymphoid tissue lymphoma in the setting of chronic H. pylori infection. There is normally no lymphoid tissue within the gastric mucosa, however chronic infection with H. pylori leads to development of lymphoid tissue within the lamina propria. This type of gastric lymphoma often regresses with treatment of the infection with antibiotics [111]. Imaging Features The most common CT finding is diffuse or segmental gastric wall thickening, often measuring 2–5 cm (Fig.

28.59) [111]. High-grade lymphoma may have greater thickening of the gastric wall and presence of extra-gastric lymphadenopathy. Lymphoma can less likely present as an ulcerative, polypoid, or infiltrative lesion, similar to that of gastric carcinoma. There is extensive gastric wall thickening without reduced distensibility of the stomach or obstruction, as opposed to linitis plastica which restricts the stomach (Table 28.2) [112]. When treated, there is increased risk of spontaneous gastric perforation.

Figure 28.59 Axial CT of the abdomen with contrast (A) shows marked thickening of the

gastric wall (arrow) without evidence of obstruction. There is extensive corresponding radiotracer uptake on the PET/CT (B) along with increased FDG avidity in the enlarged spleen (*) and bone marrow consistent with lymphoma. Table 28.2 Differentiating Gastric Adenocarcinoma and Lymphoma Gastric Gastric Adenocarcinoma Lymphoma More commonly associated Uncommon to with gastric outlet obstruction cause gastric outlet obstruction

Gastric Adenocarcinoma Nodal involvement can be present, but more commonly in the perigastric nodal stations including along the lesser and greater curvature, regional stations around the celiac artery branches or distantly to the diaphragmatic stations or paraaortic region

Can invade through serosa and into the surrounding perigastric fat

Gastric Lymphoma Nodal involvement common, often larger and beyond the normal gastric drainage pathways (above the diaphragm and below the renal veins) Predominately lateral/submucos al tumor extension without serosal invasion into the perigastric fat

Gastric Adenocarcinoma Focal, asymmetric gastric wall thickening, or diffuse gastric wall thickening in advanced disease

Gastric Lymphoma More commonly presents as marked (>2 cm) segmental or diffuse gastric wall thickening

Postsurgical Stomach Description and Complications Obesity is a chronic multifactorial illness affecting patients of all ages and with an increasing prevalence. Bariatric surgery is an increasingly popular form of treatment for patients with morbid obesity. The most common procedures include laparoscopic Roux-en-Y gastric bypass, laparoscopic gastric banding, and laparoscopic sleeve gastrectomy. Roux-en-Y gastric bypass is the most popular bariatric surgery performed because it has a higher long-term success rate compared to its counterparts.

It involves separating the stomach into a small fundal gastric pouch (approximately 15–30 mL in volume) and a larger excluded gastric component. The jejunum is divided 25–50 cm distal to the ligament of Treitz and the distal (Roux or efferent limb) is brought up and anastomosed in an end to end or side to side fashion with the gastric pouch (gastrojejunostomy). The distal jejunum limb can be brought up in anterior to the colon or posterior to the colon (ante- or retrocolic). The proximal jejunal limb (afferent, biliopancreatic limb) is anastomosed with the distal limb in a side-to-side fashion. Complications include leaks, marginal ulcers at the gastrojejunostomy secondary to chronic acidic exposure or obstruction. With regards to obstruction, adhesive disease is the most common cause in patients who undergo open Roux-en-Y gastric bypass. With laparoscopic technique the most common sites are usually internal hernias, either at the transverse mesocolon (for retrocolic approach), a defect in the jejunal mesentery (for creation of jejunojejunal anastomoses), or posterior to the Roux limb (Peterson’s defect) [113].

Sleeve gastrectomy involves dividing the stomach along its long axis with resection of the greater curvature removing approximately 75% of the stomach volume [114]. This creates a narrow gastric pouch along the lesser curvature of the stomach. This reduction in stomach volume creates early satiety. Although this technique has the longest staple line given the length of resection, postoperative leaks are reported in less than 1% of cases. Laparoscopic gastric banding is the least invasive surgical procedure performed for morbid obesity. It is a restrictive procedure in which a silicone band is placed around the proximal stomach to create a small pouch. The band is attached to a reservoir placed in the abdominal wall which can be used to inflate or deflate the cuff to adjust the stoma size. Complications include band slippage, erosion, and esophageal dilation if the band is too tight. Gastric band slippage can occur when the stomach herniates upward from below the band which can predispose to chronic stoma stenosis. Gastric band erosion results from overdistension of the band leading to ischemia and infection with a 0.3–14% prevalence [115,116].

Perforation is a rare complication occurring in 0.1– 0.8% of cases [115].

Imaging Features

◾ Upper gastrointestinal imaging via fluoroscopy is commonly performed both in the immediate postoperative setting and afterward to evaluate for complications. All procedures can be complicated by leaks at the staple lines or anastomoses Evaluation of Roux-en-Y patients will demonstrate a rounded gastric pouch which empties directly into the jejunum (Fig. 28.60). Gastric sleeve appears as a long, tubular gastric pouch with preservation of the gastric antrum, and eventual filling into the duodenum (Fig. 28.61). Gastric bands are radiodense rounded structures, which form an oblique orientation to the adjacent spine when reviewed on AP radiography (Fig. 28.62) Roux-en-Y gastric bypass can develop marginal ulcers, which manifest as discrete ulcers at either the gastrojejunal anastomosis or proximal Roux limb (Fig. 28.63). If there is a breakdown of the gastric staple line, a gastrogastric fistula can

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develop in which food is able to enter the excluded stomach (Fig. 28.64). This negates the restrictive effects of forming a small gastric pouch and can lead to recurrent weight gain. Small bowel obstructions may be due to adhesions, internal hernias from the defects created during surgery or strictures at the anastomoses (Fig. 28.65) On AP abdominal radiographs, the angle between longitudinal axis of the gastric band and spinal column, referred to as the (phi) angle, should be between 4 and 58 [115,116]. Malposition can suggest underlying issues such as gastric band slippage or erosion. In the case of slippage, a characteristic finding is the “O” sign when the band is viewed en-face. Gastric band erosion is manifested by the band surrounded by gastric wall on CT (Fig. 28.66). Perigastric stranding and fluid is often present due to leakage of gastric contents. On fluoroscopy, the band appears as a filling defect in the gastric lumen with extra luminal contrast seen with active leak. If the band is tightened too tightly patients can experience nausea and vomiting from a functional obstruction (Fig. 28.67). The band can be deflated

◾

by withdrawing saline from the reservoir that rests in the abdominal wall

Figure 28.60 Upper gastrointestinal series (A) demonstrates normal anatomy after Roux-en-Y with a proximal gastric pouch (black arrow) which directly communicates to the jejunum (*) via the gastrojejunostomy. Note the staple line more distally (B, black arrow) which demarcates the distal anastomoses of the jejunojejunostomy.

Figure 28.61 Upper gastrointestinal series (A) demonstrates normal anatomy after gastric sleeve in which there is long tubular remnant stomach (*) after resection along the greater curvature. Note the normal distal anatomy with the pylorus emptying into the duodenum (black arrow).

Figure 28.62 Normal gastric band anatomy with inflated band (black arrow) which has an acute angle (black lines) with the adjacent spine. There is long tubing (*) which connects the band to the reservoir (white arrow) in the abdominal wall.

Figure 28.63 Upper gastrointestinal series (A) demonstrates a focal outpouching from the proximal aspect of the jejunum (black arrow) just distal to the gastrojejunostomy. Endoscopy (B) confirmed the presence of a marginal ulcer which commonly occur either at or just distal to the gastrojejunostomy.

Figure 28.64 Upper gastrointestinal series (A) demonstrates contrast filling the gastric pouch and proximal jejunum (*), however note the faint opacification of the excluded stomach (black arrow) which was due to a gastrogastric fistula.

Figure 28.65 Coronal image of an abdominal CT with both oral and intravenous contrast (A) demonstrates a patient status post-Roux-en-Y gastric bypass with markedly dilated contrastfilled loops of small bowel. There is pseudofecalization and a transition point in the distal jejunal mesentery near the jejunojejunostomy staple line (white arrow). Upper gastrointestinal series (B) after decompression with nasogastric tube confirmed persistent high-grade obstruction. This patient was found to have an obstruction due to adhesive disease at time of operation.

Figure 28.66 Axial CT of the abdomen with intravenous contrast (A) shows the gastric band surrounded by gastric wall (arrow) along with fat stranding along the connecting tube (dashed arrow). Follow-up upper GI study (B) shows a round doughnut-shaped filling defect (arrow) within the gastric lumen representing the eroded band which was confirmed on endoscopy (C).

Figure 28.67 In this patient with a gastric band (black arrow) and significant nausea/vomiting postprocedurally, there is distension of the distal esophagus (*). This is compatible with functional obstruction due to a tight band. The band was deflated by withdrawing saline from the reservoir, at which time the patient’s symptoms improved.

Summary A wide variety of esophageal and gastric disease is encountered on imaging, the majority of which is benign. Barium swallow remains the preferred technique for initial evaluation of the esophagus while gastric disease and its complications may be better evaluated with CT especially in the emergent setting. Endoscopy remains the gold-standard for both in majority cases. A thorough knowledge regarding the imaging appearance of various entities is paramount for the radiologist to correctly diagnose the various non-neoplastic and neoplastic conditions and drive appropriate management.

Suggested Readings • CA Young, CO Menias, S Bhalla, SR Prasad, CT features of esophageal emergencies, Radiographics 28 (6) (2008) 1541–1553. • MS Levine, SE Rubesin, Diseases of the esophagus: diagnosis with esophagography, Radiology 237 (2) (2005) 414–427. • RB Lewis, AK Mehrotra, P Rodriguez, MS Levine, From the radiologic pathology archives: esophageal neoplasms: radiologic-pathologic correlation, Radiographics 33 (4) (2013) 1083– 1108. • RB Iyer, PM Silverman, EP Tamm, JS Dunnington, RA DuBrow, Diagnosis, staging, and follow-up of esophageal cancer, J Am Roentgenol 181 (3) (2003) 785–793. • P Guniganti, CH Bradenham, C Raptis, CO Menias, VM Mellnick, CT of gastric emergencies, Radiographics 35 (7) (2015) 1909–1921. • M Zulfiqar, A Shetty, V Shetty, C Menias, Computed tomography imaging of non-neoplastic and neoplastic benign gastric disease, Curr Probl Diagn Radiol 48 (1) (2019) 75–96.

• HC Kang, CO Menias, AH Gaballah, et al., Beyond the GIST: mesenchymal tumors of the stomach, Radiographics 33 (6) (2013) 1673–1690. • DM Richman, SH Tirumani, JL Hornick, et al., Beyond gastric adenocarcinoma: multimodality assessment of common and uncommon gastric neoplasms, Abdom Radiol 42 (1) (2017) 124–40. • MS Levine, LR Carucci, Imaging of bariatric surgery: normal anatomy and postoperative complications, Radiology 270 (2) (2014) 327–341.

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29

Imaging of Small and Large Bowel Priya Pathak, Puneet Bhargava

Anatomy The small bowel extends from the pyloric sphincter to the ileocecal valve with an average length up to 5–6 m. It consists of the duodenum, jejunum, and ileum; the duodenum measures approximately 20–25 cm in length, the jejunum 2.5 m, and the ileum approximately 3 m. The duodenum consists of four parts (first, superior; second, descending forming the C loop; third, horizontal; and fourth, ascending) and continues as jejunum at the ligament of Treitz in the left upper quadrant. Distinct mucosal folds of the small intestines, known as valvule conniventes, are well identified on imaging [1]. Small bowel layers (from outer to inner) consist of serosa encircling the jejunum and ileum and covering only the anterior portion of retroperitoneal duodenum; muscularis with outer longitudinal and inner circular layers of smooth muscles; submucosa containing blood vessels, nerves, and lymphatics; and mucosa covered with villi containing tall columnar cells. The crypts of Lieberkühn are the glands present in between the villi of the intestinal epithelium. The large bowel consists of cecum, ascending colon (right iliac fossa to hepatic flexure), transverse colon (hepatic to splenic flexure), descending colon, sigmoid colon, and rectum, with an average total length of approximately 1.5 m. Three outer longitudinal muscle layers called taenia coli give distinct sacculations, which are interrupted by incomplete rings called haustra. The cecum is the proximal pouch of ascending colon, containing appendix along the posteromedial wall. Ascending and descending colons are retroperitoneal organs [2]. Transverse colon is the longest and most mobile part of the large intestine. It is attached to the retroperitoneum by transverse mesocolon. Descending colon continues as the Sshaped sigmoid colon of variable length. The rectum starts at approximately S3 level and runs along the sacrococcygeal curvature to continue as anal canal at the anorectal angle formed by the puborectalis sling.

To briefly review the vascular anatomy:

◾level, The celiac artery originates from the aorta at T12 level, superior mesenteric artery (SMA) at L1 and inferior mesenteric artery (IMA) at L3 level. The celiac artery supply extends from the distal esophagus to the second portion of the duodenum. It trifurcates into the common hepatic artery (which further divides into gastroduodenal artery and proper hepatic artery [PHA]), splenic artery, and left gastric artery. The PHA further divides into the right and left hepatic arteries. Variant anatomy may be seen in the form of an accessory (if along with a corresponding PHA branch) or replaced (if without a corresponding PHA branch) left hepatic artery arising from the left gastric artery and an accessory or replaced right hepatic artery arising from the SMA The SMA supplies the third and fourth portions of the duodenum, jejunum, ileum, and colon up to the midtransverse colon. Branches of the SMA are; inferior pancreaticoduodenal artery; left-sided branches including the jejunal and ileal arteries; and right-sided branches including the ileocolic, right colic, and middle colic arteries (Fig. 29.1). Relatively common variant SMA branches include a replaced or accessory right hepatic artery (most common variant), common hepatic artery, splenic artery, celiac trunk, and gastroduodenal artery The IMA supplies the distal transverse colon up to the rectum and branches into the left colic artery, sigmoid arteries, and superior rectal artery

◾ ◾

FIGURE 29.1 (A) Coronal three-dimensional multidetector computed tomography scan demonstrates the normal superior mesenteric artery branches: the jejunal branches (black arrows), ileal branches (white arrows), ileocolic artery (white open arrow), and middle colic artery (black open arrow). (B) Image delineating the ileocolic artery (white arrow).

Terminal branches of SMA and IMA supplying the colon are linked together by an arterial arcade known as the marginal artery of Drummond, which provides collateral flow in the event of stenosis or occlusion (Fig. 29.2).

FIGURE 29.2 Illustration shows the marginal artery of Drummond.

The arcade of Riolan is an additional anastomotic arterial arcade between the SMA and IMA; however, it is inconsistently present. These arterial arcades can be small or underdeveloped, leading to formation of watershed area in the splenic flexure (Griffith point). The rectum is supplied by the inferior mesenteric and internal iliac arterial branches consisting of superior, middle, and inferior rectal arteries. The superior and inferior mesenteric veins run parallel to the respective arteries and drain into the portal vein [3–5].

Imaging Techniques Abdominal radiographs, fluoroscopic contrast studies with barium or water-soluble agents (small bowel follow-through, enema, enteroclysis), ultrasonography (USG), computed tomography (CT), magnetic resonance imaging (MRI), enterography, and CT colonography are the available imaging techniques for evaluation of the small and large bowel. Of these, multidetector CT has emerged as the imaging

technique of choice for primary evaluation and follow up of the majority of small and large bowel pathologies. The overall role of fluoroscopic contrast studies has markedly declined over the years; for example, in Crohn’s disease, contrast fluoroscopy may lead to obscuration of pathology because of overlapping bowel loops and is less accurate for evaluation of active disease than other techniques. Fluoroscopy may not be tolerated in acutely ill patients and is technically challenging. In addition, colonoscopy is superior to contrast enema for detection of early inflammatory changes [5]. Computed tomography enterography includes peroral (noninvasive, more common) and enteroclysis (requires placement of nasojejunal tube) techniques for enteric contrast administration. The major advantage of enteroclysis is superior distension of the jejunum, which imparts a specific role in elective evaluation of conditions such as Crohn’s disease, small bowel obstruction, and unexplained occult gastrointestinal (GI) bleed [7]. However, oral administration of contrast is more convenient and faster and demonstrates superior patient experience. Neutral oral contrast agents are more commonly used, such as Brezza (combination of sorbitol, mannitol, and xanthan gum), water, water with methylcellulose, polyethylene glycol, and low-density barium sulfate suspension (VoLumen). The major limitation of neutral oral contrast is suboptimal bowel distension because of rapid absorption [8]. Positive oral contrasts agents include dilute barium and water-soluble iodinated contrast. The predominant limitation of these agents is obscuration of mucosal enhancement pattern. Intravenous (IV) contrast with a single enteric phase at 60–70 seconds is usually adequate for small bowel imaging. Certain specific indications of CT enterography are provided in Box 29.1 [9]. BOX 29.1 Specific Indications for Computed Tomography Enterography

◾ Crohn’s disease ◾ Ulcerative colitis ◾ Small bowel tumors ◾ Occult gastrointestinal bleeding ◾ Partial small bowel obstruction ◾ Celiac disease

Similar to CT enterography, MR enterography involves administration of oral contrast agents (commonly Brezza or VoLumen) for adequate bowel distension. Antiperistaltic agents are crucial to minimize motion artifacts. Standard sequences include T2-weighted imaging with and without fat suppression, fat-suppressed T1weighted imaging with multiphase postcontrast acquisition including delayed

phase, and steady-state coherent sequences to evaluate for bowel peristalsis and fixed stenosis. Scanning with the patient in a prone position decreases scan time by minimizing the scan area and elevating and separating the small bowel loops; however, a supine position is usually more comfortable for the patients. MR and CT enterography demonstrate similar sensitivity for detecting small bowel inflammation; however, image quality is better with CT enterography. CT enterography has the advantages of superior assessment of perienteric abnormality, shorter scan time, lesser artifacts, and ability to scan uncooperative patients. Advantages of MRI enterography are elimination of ionizing radiation and the ability to image patients with impaired renal function [10]. CT colonography is a minimally invasive examination indicated for the screening of colorectal cancer, to evaluate colon after incomplete or unsuccessful colonoscopy, or to evaluate proximal to an obstructing neoplasm. The technique involves 1. Adequate bowel preparation with administration of laxatives because residual stool and fluid produce false-positive and false-negative results. Dilute barium is used for residual fecal tagging 2. Gaseous distension of colon with air or CO2 3. Administration of antispasmodic agents such as buscopan or glucagon

Scanning is performed with patient in both supine and prone positions. Two- and three-dimensional intraluminal reconstructions are used for image interpretation along with the raw images [11] (Fig. 29.3).

FIGURE 29.3 Computed tomography (CT) colonography three-dimensional endoluminal view shows a small polyp (benign on pathology) in the cecum (black arrow)(A), correlated as soft tissue nodule on axial CT (white arrow)(B).

General Causes of Non-neoplastic Bowel Wall Thickening Inflammatory Disorders Crohn’s Disease

Pathophysiology Crohn’s disease is a chronic inflammatory disease of the GI tract characterized by a relapsing–remitting course. It can occur from the mouth to the anus, with small bowel involvement present in 80% of cases. The terminal ileum is the most commonly affected site. The colon is involved with the small bowel in 50% of the cases. Several proposed causative factors are immune dysfunction, infections, genetic, familial, vascular, and dietary; however, the exact cause remains unclear [12]. On pathology, multiple discontinuous sites of bowel involvement or skip lesions are present. Active inflammation starts with neutrophilic infiltration into the mucosa with cryptitis, lymphoid hyperplasia, and aphthoid ulceration. Progression of inflammation causes transmural involvement with deeper ulceration, fistulation, sinus tract formation, and mesenteric involvement. Chronic inflammation leads to fibrosis with progressive increased extracellular matrix deposition by mesenchymal cells, which causes luminal narrowing and strictures. Long-standing disease causes progressive mucosal atrophy and submucosal fat deposition [13].

Clinical features Peak involvement occurs between 15 and 25 years of age with similar gender prevalence. The second peak is in the sixth and seventh decades of life [13]. Variable clinical features depend on the disease site and activity, which includes abdominal pain, diarrhea, fever, weight loss, perianal fissures, and anemia caused by chronic GI bleed. The condition is associated with myriad of extraintestinal manifestations such as dermatologic (erythema nodosum, aphthous ulcer, and pyoderma gangrenosum), musculoskeletal (ankylosing spondylitis, polymyositis), primary sclerosing cholangitis, and calcium oxalate stones [14]. Patients are at increased risk of colorectal cancer and lymphoma; increased risk of lymphoma is linked to immunomodulator therapies used in Crohn’s disease treatment [13].

Imaging features Features can be categorized into following subtypes: 1. Active inflammatory disease 2. Penetrating disease 3. Fibrostenotic disease 4. Reparative and regenerative disease Of note, there is extensive overlap between these subtypes without a stepwise progression [15]. Fluoroscopy Mucosal abnormalities on barium studies are thickened, nodular folds and a cobblestone pattern produced by a combination of longitudinal and transverse ulcers. Aphthous ulcers present as areas of barium collection within the mounds of mucosal edema (Fig. 29.4). Penetrating disease shows deep ulcers, fistula (enteroenteric, enterocolonic), and sinus tracts (Fig. 29.5). Strictures, stenosis, and wall sacculations are features of chronic stage (Fig. 29.6). The string sign of Kantor refers to a beaded stringlike appearance of the bowel caused by multifocal narrowing or strictures [16].

FIGURE 29.4 Double-contrast barium enema from a 34-year-old man with Crohn’s disease demonstrates numerous aphthous ulcers in the transverse and descending colon as tiny barium collection within mounds of mucosal edema (black arrow).

FIGURE 29.5 Small bowel follow-through in a 39-year-old man with penetrating Crohn’s disease demonstrates distortion of the mid sigmoid colon (arrow) and complex fistulation with the ileal loops (arrowhead).

FIGURE 29.6 Chronic Crohn’s disease with multifocal bowel strictures (black arrow) and sacculations (white arrows).

Ultrasonography Inflamed bowel segments show concentric mural thickening (Fig. 29.7), stratification, and hyperemia. Interbowel fluid and increased echogenicity of perienteric fat are seen.

FIGURE 29.7 Longitudinal grayscale ultrasound of a small bowel loop shows concentric hypoechoic bowel wall thickening due to Crohn’s disease.

CT and MRI enterography Imaging features can be divided according to the subtypes; however, patients usually present with varying combinations of active, fibrostenotic or chronic, penetrating, and reparative disease. On contrast-enhanced CT, active inflammatory disease presents with the following features:

◾hyperenhancement Mural thickening (commonly asymmetric), stratification, edema, and segmental mural (the term mucosal hyperenhancement is not preferred because bowel involved by Crohn’s disease may lack a mucosal layer secondary to inflammatory damage) (Fig. 29.8). Mural thickening is measured in a bowel segment adequately distended by enteric contrast and is graded into mild, 3–5 mm; moderate, 5–9 mm; and severe, 10 mm or greater Ulcerations are indicated by extension of air or contrast into the bowel wall Inflammatory strictures may be present Mesenteric changes include engorgement of the vasa recta (Comb sign), stranding, edema, and reactive adenopathy (see Fig. 29.8; Table 29.1)

◾ ◾ ◾

FIGURE 29.8 Contrast-enhanced coronal computed tomography of the abdomen and pelvis from a 26-year-old woman with Crohn’s disease demonstrates active terminal ileitis, with marked mural thickening, stratification and segmental mural hyperenhancement (black arrow), engorged vasa recta (Comb sign), and mesenteric adenopathy (black arrowhead).

Table 29.1 Pathology, Endoscopy, and Imaging Features of Active Crohn’s Disease, Penetrating Crohn’s Disease, and Fibrostenotic Crohn’s Disease

Pathology

Active Inflammatory Disease [13] Computed Endoscopy Tomography/Magnetic Resonance Imaging Features

◾ ◾ ◾

Early disease Neutrophil infiltration Lymphoid hyperplasia Noncaseating granuloma Progression of inflammation Transmural inflammation

◾

◾ Mural thickening, stratification, edema,

◾ ◾

Early disease Aphthous ulcer Mucosal fold abnormality Progression of inflammation Ulcers

ulceration, segmental mural hyperenhancement, inflammatory strictures Mesenteric change: engorgement of vasa recta (Comb sign), stranding, edema, and reactive adenopathy

◾

◾ ◾ Cobblestone mucosa

Penetrating Disease [13] Pathology

Endoscopy

Extension of inflammation through the serosa with fissuring ulcers, sinus, fistula, and abscess formation

Sinus and fistula identified as abnormal opening in the gastrointestinal tract

Computed Tomography/Magnetic Resonance Imaging Features

◾ Fistulous tracts, bowel tethering and angulations ◾ Abscess formation ◾ Perianal fistula

Fibrostenotic Disease [13] Pathology

Endoscopy

Computed Tomography/Magnetic Resonance Imaging Features

Pathology

Active Inflammatory Disease [13] Computed Endoscopy Tomography/Magnetic Resonance Imaging Features

Fibrosis with luminal narrowing and strictures

Luminal narrowing without actively inflamed mucosa

◾ Focal or long segment mural thickening ◾ Fixed angulated bowel loops. ◾ Strictures ◾ Sacculations

MRI demonstrates mural edema as T2 hyperintense signal, which is best appreciated on fat-saturated sequence (Fig. 29.9). An actively inflamed segment show diffusion restriction and arterial phase hyperenhancement that increases in all subsequent postcontrast phases [13,17].

FIGURE 29.9 Coronal fat-saturated T2-weighted magnetic resonance imaging of the abdomen and pelvis from a 26-year-old man with active on chronic Crohn’s disease demonstrates long segment distal ileal thickening, hyperintense submucosal edema (white arrowhead), prestenotic dilation(white arrow), engorged vasa recta, and mesenteric adenopathy. Note the skip bowel involvement in the upper abdomen (white open arrow).

Penetrating disease is characterized by formation complex fistulas between bowel loops (Fig. 29.10), bowel–mesentery, or bowel–skin. Involved bowel loops show tethering and angulations. Associated abscess presents as rim-enhancing collections. Simple and complex perianal fistulas are frequently associated (Table 29.1) [13].

FIGURE 29.10 Contrast-enhanced coronal computed tomography of the abdomen and pelvis from a 21-year-old man with active Crohn’s disease demonstrates tethering of ileal loops in the right lower quadrant with enteroenteric fistula (white arrow).

Fibrostenotic disease presents with focal or long segment T2 hypointense wall thickening without associated diffusion restriction. Fibrotic strictures demonstrate fixed luminal narrowing with upstream dilation. Sacculations are outpouching along the antimesenteric border of the bowel wall caused by asymmetric bowel shortening secondary to fibrosis (Fig. 29.11). Fibrosis also leads to diminished bowel motility and fixed stenosis detectable on MRI cine sequences (Table 29.1) [17].

FIGURE 29.11 Coronal fat-saturated T2-weighted magnetic resonance imaging of the abdomen shows distal ileal sacculations in chronic Crohn’s disease.

Affected bowel in the reparative stage shows submucosal fat deposition without signs of active inflammation or progressive fibrosis [13] (Fig. 29.12), although submucosal fat deposition in itself is a nonspecific finding and commonly incidental in normal adults.

FIGURE 29.12 Coronal contrast-enhanced computed tomography of the abdomen and pelvis from a 64-year-old woman shows submucosal fat deposition in the terminal ileum and ascending colon as a sequela of Crohn’s disease (white arrow).

Differential diagnosis The differential diagnosis includes ulcerative colitis, tuberculosis, ischemia, radiation enteritis, vasculitis, and graft-versus-host disease [17]. Ulcerative Colitis

Pathophysiology Ulcerative colitis is an idiopathic chronic inflammatory disease of the GI tract characterized by a relapsing–remitting course. The proposed pathogenesis involves a combination of environmental and genetic factors. There is involvement of the

colon in a continuous manner, with rectal disease present in up to 95% of the cases. Small bowel involvement is less commonly present [18]. On pathology, inflammation is limited to the mucosa and submucosa. The acute phase involves inflammatory infiltration into the crypts of Lieberkühn, causing cryptitis, crypt abscess, mucosal ulceration, and inflammatory pseudopolyps. Extension of inflammation to the terminal ileum is known as backwash ileitis [13]. Spread of inflammation in the deeper layers leads to nonobstructive bowel dilation with mural thinning and friability (known as toxic megacolon), a clinical emergency carrying a high risk of perforation. Long-standing inflammation leads to fibrosis with irreversible morphologic changes in the form of a featureless, shortened, and narrowed colon. Pseudopolyps are characteristic of ulcerative colitis. These are islands of normal colonic mucosa surrounded by denuded ulcerated mucosa. Inflammatory pseudopolyps are the areas of inflamed elevated mucosa. Postinflammatory pseudopolyps refers to regenerative hypertrophic mucosa.

Clinical features Peak involvement occurs between 15 and 40 years of age. Bimodal distribution is known with second peak between the seventh and eighth decades of life. The incidence is higher in men [13,18]. Clinical features include bloody diarrhea, tenesmus, urgency of defecation, fever, pain, and weight loss. Several associated extraintestinal manifestations include dermatologic (oral ulcers, pyoderma gangrenosum), musculoskeletal (arthritis), deep vein thrombosis, and primary sclerosing cholangitis [19]. Patients have an increased risk of colon cancer, with risk ranging from 0.5% to 1.0% per year after 10 years of disease [18].

Imaging Features Radiographs Upright and supine abdominal radiographs are helpful to screen for bowel perforation and toxic megacolon. Toxic megacolon is detected with more than 6 cm of distension of total or a segment of colon. It is best appreciated involving the transverse colon on supine radiographs (Fig. 29.13). Other findings include airfluid levels, loss of colonic haustrations, mucosal islands, and absence of formed stool [20].

FIGURE 29.13 Toxic megacolon.

Fluoroscopy Single- or double-contrast barium enema delineates mucosal abnormalities as granular and stippled mucosa, superficial erosions, and ulcers. Deeper ulcers or collar button ulcers are formed because of undermining submucosal extension limited by the muscle layer. Pseudopolyps are seen as nodular filling defects [20]. Barium enema is contraindicated in patients with acute severe inflammation because of the risk of perforation.

Chronic disease presents with luminal narrowing, strictures, and a featureless colon with loss of haustrations, also known as lead pipe colon (Fig. 29.14). A patulous Ileocecal vale (IC) valve with granular terminal ileum is indicative of backwash ileitis (Fig. 29.15). There is associated widening of the presacral space because of increased perirectal fat deposition (Fig. 29.16). Long-standing disease also leads to formation of dysplastic nodules manifesting as nodular filling defects indistinguishable from pseudopolyps. Colitis carcinomas usually present as annular narrowing and strictures [20].

FIGURE 29.14 Double-contrast barium enema in a 58-year-old man with chronic ulcerative colitis demonstrates diffusely irregular colonic mucosal pattern with a grainy appearance. There are narrowing and foreshortening of the descending colon with loss of haustration (lead pipe colon).

FIGURE 29.15 Double contrast barium enema shows patulous ileocecal valve with granular mucosa of the terminal ileum due to backwash ileitis.

FIGURE 29.16 Barium enema shows widening of the presacral space (asterisk) in chronic ulcerative colitis.

CT and MRI enterography Features are divided into active and chronic phase. The active phase is characterized by mural hyperenhancement, concentric mural thickening, and stratification (Fig. 29.17). On MRI, submucosal edema presents T2 hyperintensity, best appreciated on fat-saturated T2 sequences. Actively inflamed segments show diffusion restriction. Pseudopolyps demonstrate contrast enhancement (Table 29.2) [13].

FIGURE 29.17 Axial T1-weighted magnetic resonance imaging of the pelvis from a 36-year-old woman shows concentric mural thickening and enhancement of the rectosigmoid colon in active ulcerative colitis (white arrow).

Table 29.2 Histopathologic and CT/MRI Features of Active and Chronic Phases of Ulcerative Colitis Pathology CT/MRI Features Active Phase

Pathology

CT/MRI Features Active Phase

Inflammatory infiltration causing cryptitis, crypt abscess, mucosal ulceration, and inflammatory pseudopolyp.

Chronic Phase Fibrosis causing a featureless, thickened, and shortened colon with luminal narrowing

◾ Mural hyperenhancement ◾ Concentric mural thickening ◾ Submucosal edema. ◾ Mucosal ulceration and pseudopolyps ◾ Mural thickening with luminal narrowing ◾ Increased submucosal fat ◾ Increased perirectal fat deposition causing widening of presacral space Postinflammatory pseudopolyps

◾

The chronic phase leads to concentric mural thickening with luminal narrowing, strictures, a featureless lead pipe colon (Fig. 29.18), submucosal fat deposition, and widening of presacral space. Postinflammatory pseudopolyps may show contrast enhancement (Table 29.2) [13].

FIGURE 29.18 Coronal T1-weighted magnetic resonance imaging of the abdomen and pelvis from a 48-year-old man with chronic ulcerative colitis shows a featureless ascending colon and cecum demonstrating loss of haustration and mural thickening (white arrow).

Differential diagnosis The differential diagnosis includes Crohn’s disease and infective, ischemic, and radiation colitis. Certain differentiating imaging features between Crohn’s disease and ulcerative colitis are summarized in Table 29.3. Table 29.3

Differentiating Features Between Crohn’s Disease and Ulcerative Colitis Crohn’s Disease Ulcerative Colitis

◾ Skip lesions with predominant ◾ Continuous involvement of the involvement of the ileum and colon with rectal involvement in 95% caecum and relative sparing of the rectum Transmural inflammation leads to ulceration, fissure, and abscess formation Perianal disease present Marked bowel wall thickening Bowel wall may be affected asymmetrically with sacculations

◾ ◾ ◾ ◾

of cases; small bowel disease is not common Fissure and abscess are not common Perianal disease is not seen Bowel wall thickening is less compared with Crohn’s disease Circumferential bowel wall symmetry is usually maintained

◾ ◾ ◾ ◾

Mesenteric Ischemia Mesenteric ischemia can be into acute and chronic and is further subdivided into occlusive and nonocclusive types. Acute mesenteric ischemia is a life-threatening condition with a mortality rate of as high as 50–69%. Chronic mesenteric ischemia is relatively less common and is considered imminent acute mesenteric ischemia. Based on the cause, acute mesenteric ischemia is categorized into

◾ Mesenteric arterial embolism ◾ Mesenteric arterial thrombosis ◾ venous thrombosis ◾ Mesenteric Nonocclusive mesenteric ischemia [21,22]

Clinical Features Acute mesenteric ischemia presents with abdominal pain, classically described as out of proportion to the clinical examination; nausea; vomiting; diarrhea; and hematochezia. Severe ischemia and bowel necrosis manifest with signs of peritonitis. Chronic mesenteric ischemia has a more gradual course with chronic postprandial pain (described as abdominal angina), weight loss, and early satiety. The overall incidence is higher in the older adult population in the seventh decade of life [21]. Pathophysiology and General Imaging Features

The severity of ischemia damage depends on the degree and extent of flow reduction, duration of ischemia, and degree of collateralization. Early-phase ischemia is characterized by spastic bowel contraction, which proceeds to adynamic ileus caused by ischemia of the muscles and nerves. Complete occlusion of more than 6 hours leads to irreversible injury with mucosal and mural infarction, transmural infarction, and perforation. Beyond a critical level of ischemia, reperfusion also leads to damage because of mucosal barrier disruption, bacterial invasion, and septicemia [22]. Multidetector CT with acquisition of noncontrast and biphasic contrast-enhanced phases (arterial–venous) with maximum intensity projection (MIP) and volume rendering is the most sensitive and specific technique for evaluation. General imaging features of mesenteric ischemia are as follows (Figs. 29.19–29.21) [21,22]: 1. Bowel wall thickening: Occurs because of edema, hemorrhage, or superimposed infection. The target sign is produced by consecutive halos of hypo and hyperattenuation caused by submucosal edema and hemorrhage. Hemorrhage also imparts high attenuation to the bowel on unenhanced CT. 2. Abnormal wall enhancement: Mural hyperenhancement is produced by congestion or reperfusion injury. Mural hypoenhancement is more specific for cessation of arterial supply and implies severe or irreversible ischemia. 3. Bowel wall thinning: This may relate to adynamic ileus or loss of tissue in irreversible ischemia and infarction. 4. Bowel dilation: This indicates loss of muscle tone or adynamic ileus caused by ischemia of the muscles and nerves. 5. Pneumatosis, portal venous gas, and pneumoperitoneum: These are hallmarks of irreversible ischemia and bowel infarction. 6. Associated nonspecific mesenteric findings are engorgement of the vessels, interbowel fluid, fat stranding, and ascites.

FIGURE 29.19 An 85-year-old man with aortomesenteric stent graft complained of acute abdominal pain and vomiting. (A) Coronal contrastenhanced computed tomography of the abdomen and pelvis shows circumferential thickening of proximal jejunal loops with relative mural hypoenhancement and trace perienteric stranding indicating ischemia (ellipse). (B) A hypodense thrombus is identified within the superior mesenteric artery stent (black arrow).

FIGURE 29.20 Contrast-enhanced computed tomography axial and coronal images from a 39-year-old man with closed-loop obstruction demonstrates hypoenhancing, dilated small bowel loops in the pelvis, consistent with severe ischemia (A). There is extensive associated mesenteric air (white arrowhead) (B).

FIGURE 29.21 Contrast-enhanced coronal computed tomography of the abdomen and pelvis shows extensive small bowel pneumatosis (white arrow) from superior mesenteric artery thrombosis (white arrowhead). Note the associated extensive perienteric stranding.

Certain specific features of different types of acute mesenteric ischemia are further described. Mesenteric Arterial Embolism This group constitutes approximately 40–50% of cases and is associated with emboli of cardiac origin from conditions such as atrial fibrillation and myocardial infarction. The SMA is most commonly involved, with typically emboli lodging around 6–8 cm distal to the origin, near the branching of middle colic artery. Proposed factors for a higher incidence of SMA embolism are an inherent high flow rate and a narrow branching angle with the abdominal aorta. Emboli are identified as a hypoattenuating filling defect with associated vascular expansion on contrast-enhanced CT. Cessation of arterial flow leads to diminished or absent

contrast enhancement. Mural thickening is rarely present. Severe ischemia leads to wall thinning, pneumatosis, and perforation [22]. Mesenteric Arterial Thrombosis This accounts for about 25% of cases. This group demonstrates the worst prognosis because it is associated with a broader territory of bowel ischemia because of the presence of preexisting atherosclerosis and occlusion of SMA origin [21]. Major risk factors are atherosclerosis, antiphospholipid syndrome, and estrogen therapy. On CT, there is evidence of generalized atherosclerotic disease and vascular calcifications in the celiac trunk, SMA, and IMA with superimposed stenosis or occlusion. Dissection may be detected. Collateral vessels can be observed in long-standing ischemia [22]. Mesenteric Venous Thrombosis This group accounts for 5–15% of cases and is associated with hypercoagulable states such as oral contraceptive pills, pregnancy, sickle cell disease, and protein C/S deficiency. There is involvement of superior mesenteric vein (SMV) (70%– 95%), inferior mesenteric vein, and portal vein. On CT, thrombus is identified as intraluminal filling defects in the veins. Characteristic findings are prominent bowel wall thickening (with the halo or target sign), engorgement of the vessels, interbowel fluid, ascites, and mesenteric fat stranding (Fig. 29.22). Mesenteric findings are more pronounced in this group because of the higher hydrostatic pressure in the bowel wall produced by venous obstruction, although the degree of mesenteric abnormality does not correlate with the ischemia severity [3,21,22].

FIGURE 29.22 Contrast-enhanced coronal and axial computed tomography of the abdomen from a 54-year-old-man with superior mesenteric vein thrombosis (white arrowhead)(A) shows ischemic changes in the draining bowel loops, which demonstrate extensive circumferential wall thickening, submucosal edema, mesenteric standing, and interbowel fluid (black arrow)(B).

Nonocclusive Mesenteric Ischemia This refers to bowel ischemia caused by reflex mesenteric vasoconstriction occurring in the setting of decreased cardiac output states, such as hemorrhage or cardiogenic shock, myocardial infarction, and aortic insufficiency, which leads to shock bowel. Ischemic bowel lacks contrast enhancement and demonstrates a broader area of involvement of small and large bowel in a discontinuous manner. The typical finding on angiography is multifocal narrowing of the SMA branches with alternating dilation [22]. Characteristic findings of shock bowel are diffuse small bowel wall thickening and hyperenhancement with associated mesenteric fluid and relative sparing of the colon. It is commonly associated with additional signs of hypovolemia such as collapsed inferior vena cava (IVC) and hyperenhancing adrenal glands (Fig. 29.23) [3].

FIGURE 29.23 Coronal computed tomography angiography of the abdomen and pelvis from a 61-year-old man on Coumadin with history of fall demonstrate shock bowel with diffuse small bowel thickening (black arrow), hyperenhancement, and interbowel fluid (white arrow)(A). Associated signs of hypoperfusion include hyperenhancing adrenal glands (white arrow) and right renal infarct (black arrowhead)(B).

Chronic Mesenteric Ischemia Duplex USG is indicated to evaluate SMA stenosis in chronic ischemia, with a peak systolic velocity of 275 cm/sec or greater suggestive of more than 70% stenosis. However, there are several limitations to the examination such as operator dependance, overlying bowel gas, and body habitus. Multidetector CT angiography performs better in evaluation of vascular stenosis, collateral vessels, and associated changes of bowel ischemia [23]. Differential Diagnosis The differential diagnosis includes bowel wall thickening and mural hyperenhancement caused by infectious, inflammatory, and neoplastic processes; radiation injury; and graft-versus-host disease. Intramural bowel gas can be seen in benign pneumatosis [3].

Bowel Infections Pathophysiology and Clinical Features Infective enteritis and colitis are caused by bacterial, viral, fungal, and parasitic etiologies. Certain organisms have a predilection for specific bowel segments; for example, tuberculosis and amebiasis affect the distal ileum and cecum, Giardia

involves the proximal small bowel, and Salmonella and Shigella involve the distal small bowel. Gonorrhea, herpesvirus, and chlamydia predominately affect the rectum and sigmoid colon. Clostridium and cytomegalovirus (CMV) are associated with pancolitis [24,25]. Imaging Features On contrast-enhanced CT, general features of enterocolitis are circumferential bowel wall thickening and hyperenhancement, submucosal edema, perienteric and pericolonic fat stranding, lack of formed stool with air-fluid levels, interbowel fluid, and ascites. Characteristic features of certain common bowel infections are discussed next. Tuberculosis

Pathophysiology and clinical presentation Tubercular bacilli can enter the GI tract through ingestion of infected sputum or milk. The bacilli then invade the mucosa and submucosa with formation of epithelial tubercle in the submucosal lymphoid tissue followed by caseous necrosis and ulceration. The ileocecal region is the most common site of involvement because of abundant lymphoid tissues. Isolated colonic involvement is seen in approximately 10% of cases, which has increased incidence in immunocompromised patients. Tubercular lesions are morphologically classified into ulcerative, hypertrophied, and ulcer-hypertrophied subtypes. Spread of infection through direct, lymphatic, and hematogenous routes leads to multisystemic disease, with the lymph nodes and peritoneum being the most common sites of involvement in the abdominal cavity. Clinical manifestations of ileocecal tuberculosis include chronic abdominal pain, fever, weight loss, and altered bowel habits. The most common complications are bowel obstruction and perforations [26].

Imaging Features Radiographs These may depict enteroliths, bowel obstruction as air-fluid levels, and signs of pneumoperitoneum in perforation. Fluoroscopy On small bowel follow-through, acute to subacute disease presents as spasm and edema involving the ileocecal valve and terminal ileum, which eventually thickens

and ulcerates. The Stierlin sign refers to rapid emptying of barium in the inflamed segments of the ileum and cecum with the presence a normal column of barium in the adjacent uninvolved segments. There can be hypersegmentation of the barium column (chicken intestine), flocculation, and precipitation, with thickening of the mucosal folds. Progressive infection can lead to fistula (e.g., enteroenteric, enterocolonic), bowel matting, or localized mass formation. Chronic infection leads to fibrosis with distorted pulled-up cecum, a fixed gaping ileocecal valve, and annular stenosis of the terminal ileum leading to goose neck deformity. The Fleischner or inverted umbrella sign refers to gaping and thickened lips of the ileocecal vale with a narrowed terminal ileum (Figs. 29.24 and 29.25) [26–28]

FIGURE 29.24 Small bowel enteroclysis demonstrates nodular fold thickening and irregular narrowing of the terminal ileum, with loop separation and deep mucosal ulceration (black arrow) caused by tuberculosis. The cecum is pulled up contracted (black arrowhead) with a wide ileocecal valve (goose neck deformity).

FIGURE 29.25 Small bowel follow-through demonstrates irregular narrowing of the terminal ileum, contracted cecum with a wide ileocecal valve (white arrow) (Fleischner sign).

Contrast-enhanced CT CT demonstrates circumferential thickening of the terminal ileum and caecum with asymmetric thickening of the ileocecal valve. Associated mesenteric adenopathy is pathognomonic. Involved lymph nodes demonstrate characteristic central lowattenuation caused by caseous necrosis (Figs. 29.26 and 29.27). The chronic stage results in formation of multifocal short segment strictures superimposed on diffuse narrowing of the ileum.

FIGURE 29.26 Small bowel follow-through demonstrates irregular narrowing of the terminal ileum (black arrow) and cecum caused by tuberculosis (A). Contrast-enhanced coronal computed tomography of the abdomen and pelvis in another patient (B) shows multiple enlarged mesenteric nodes with central low attenuation (yellow arrow) and a stricture of the mid small bowel (white arrow).

FIGURE 29.27 Contrast-enhanced axial computed tomography of the abdomen and pelvis from a 28-year-old woman with ileocecal tuberculosis demonstrates masslike thickening of the ileocecal valve and terminal ileum (black arrow)(A). Associated enlarged mesenteric nodes show central low attenuation caused by caseous necrosis (black arrowhead)(B).

Differential diagnosis The differential diagnosis includes Crohn’s disease, lymphoma, amoebiasis, and cecal malignancy [26,27]. Amoebiasis This is a type of infectious colitis caused by protozoa Entamoeba histolytica. The infection is endemic in tropical and subtropical countries and is acquired through ingestion of contaminated food or water. However, symptomatic disease seen in only 10% of the infected population with clinical manifestations of fever, bloody diarrhea, abdominal pain, and weight loss. Spectrum of disease varies from acute proctocolitis or dysentery, fulminant colitis with bowel perforations, chronic colitis, and amoeboma formation. The most common extraintestinal manifestation is hepatic abscess secondary to the hematogenous spread of infection through the portal circulation. On CT, amoebic colitis presents as circumferential or asymmetric bowel thickening with a predilection for cecal and ascending colonic involvement (Fig. 29.28). Transmural extension of infection in fulminant colitis leads to deep mucosal ulceration causing intramural dissection of contrast, marked colonic distension, and perforations. Skip bowel involvement may be seen. Amoeboma involves formation of large tumefactive lesions simulating colon cancer. Differential diagnoses are tuberculosis, Crohn’s disease, ulcerative colitis, and colon cancer [29,30].

FIGURE 29.28 Contrast-enhanced axial computed tomography of the abdomen and pelvis from a patient with amoebic colitis demonstrates asymmetric thickening of the cecum (white arrow). There is an associated solitary amoebic liver abscess (white arrowhead).

Ascariasis Ascariasis involves intestinal infection with roundworm Ascariasis lumbricoides. Humans become infected after ingestion of embryonated eggs passed in the feces of infected individual. On small bowel series, worms are identified as tubular intraluminal filling defects associated with an internal linear collection of barium (Fig. 29.29). On real-time USG, adult worms are seen as mobile hypoechoic tubular structures with an echogenic wall. Major complications are mechanical bowel obstruction, volvulus, and intussusception [31].

FIGURE 29.29 Small bowel follow-through demonstrates an ascaris worm in the ileum as an intraluminal filling defect with an internal linear column of barium (black arrow).

Giardiasis Giardiasis is caused by water borne protozoan Giardia lamblia. The most common sites of involvement are the proximal jejunum and duodenum. The pathogenesis involves invasion of the bowel mucosa by the organism inciting acute and chronic inflammatory changes, crypt hyperplasia, and villous atrophy with resultant malabsorption. Spectrum of findings on small bowel follow-through are mucosal thickening, indistinctness of mucosal folds, flocculation, and rapid transit of barium caused by bowel irritation and spasm [32]. Whipple Disease Whipple disease is a multisystemic disease caused by infection with actinobacteria Tropheryma whipplei. GI manifestations are with symptoms of malabsorption such as weight loss, diarrhea, abdominal pain, and steatorrhea. The pathogenesis

involves macrophagic infiltration of lamina propria infected with T. whipplei, leading to swelling and thickening of the intestinal villi. On small bowel followthrough, there is nodular thickening of the valvulae conniventes with a normal small bowel caliber. There is a predilection for jejunal involvement. Mesenteric adenopathy is a predominant finding on CT, with involved lymph nodes demonstrating characteristic central low or fat attenuation [33]. Certain specific infections in immunocompromised hosts are as follows. Typhlitis Typhlitis, also known as neutropenic enterocolitis, most commonly occurs in patients undergoing treatment for malignancy. Summative effects of infection (particularly with CMV) and ischemia are proposed as the potential etiology. It is characterized by inflammation of the cecum, ascending the colon, and less commonly the terminal ileum. Severe cases demonstrate mucosal hemorrhage, transmural necrosis and perforation [28]. Contrast-enhanced CT demonstrates circumferential thickening involving the cecum and ascending colon with submucosal edema, pericolonic fluid, and stranding (Fig. 29.30). Pneumatosis and perforation are present in severe cases.

FIGURE 29.30 Contrast-enhanced coronal computed tomography of the abdomen and pelvis from a 64-year-old man with myeloid leukemia shows concentric ascending colonic thickening and mural enhancement secondary to typhlitis (black arrow).

HIV-related Enterocolitis Although opportunistic infections are the predominant cause of GI disease in HIV, primary HIV infection of the mucosa is known, particularly in the colon. Myriad of HIV-related opportunistic infections include CMV, cryptosporidiosis, Mycobacterium avium, Shigella spp., Salmonella spp., Campylobacter spp., Clostridium difficile, and Strongyloides spp. [34,35]. Cytomegalovirus GI disease develops in approximately 30% of patients with AIDS, particularly with a CD4 lymphocytes below 100/mm3. Presenting symptoms include persistent diarrhea, fever, weight loss, severe abdominal pain, and hematochezia. The infection leads to endothelial involvement with occlusive vasculitis, tissue edema, and necrosis. CT features of CMV colitis are colonic wall thickening, which is predominantly asymmetric with a mean mural thickness of 15 mm; mural edema; and deep ulcerations. There is a predilection for involvement of the rectum, descending colon, and cecum. The small bowel is involved in

approximately 42% of cases. Bowel involvement can be in a diffuse or segmental pattern. Lymphadenopathy is not common. A major complication is bowel perforation [36]. Clostridium Difficile–associated Pseudomembranous Colitis It usually follows administration of antibiotic and chemotherapy in hospitalized patients and carries significant morbidity. On CT, there is marked colonic wall thickening with characteristic accordion sign, which refers to trapping of enteric contrast between markedly thickened and edematous haustral folds resembling an accordion (Fig. 29.31) [24].

FIGURE 29.31 Contrast-enhanced axial computed tomography of the pelvis from a 56-year-old woman with Clostridium difficile colitis demonstrates marked thickening of rectosigmoid colon with the accordion sign (black arrow). Also seen are large-volume ascites and diffuse peritoneal thickening secondary to underlying peritoneal carcinomatosis from carcinoma of the ovary.

Radiation Injury Small bowel mucosa is the most radiosensitive tissue in the GI tract caused by rapid cell turnover. The rectum is the least radiosensitive part commonly affected by radiation damage because of the proximity to radiosensitive organs such as the prostate and cervix. Radiation injury has been divided into acute and chronic subtypes.

◾self-limited Acute radiation injury occurs within first few days or weeks of treatment, typically presenting with symptoms of malabsorption and short-term nonspecific CT findings such as focal circumferential bowel wall thickening, submucosal edema, and mucosal hyperenhancement (Fig. 29.32)

◾fibrosis Chronic radiation injury presents months to years after exposure because of progressive mural and microvascular damage. CT features of this stage are circumferential bowel thickening, strictures, adhesions, and fistulations [37]

FIGURE 29.32 Contrast-enhanced sagittal computed tomography of the pelvis from a 68-year-old woman with endometrial cancer and history of recent radiation to the pelvis demonstrates circumferential thickening, mucosal hyperenhancement, and trace interbowel fluid involving few small bowel loops in the pelvis indicative of radiation enteritis (circle)(A). Axial image delineates the submucosal edema in the affected loops (white arrow)(B).

Specific Small Bowel Abnormalities Small Bowel Obstruction Pathophysiology and Clinical Features Small bowel obstruction can be mechanical or functional, preventing normal transit of intraluminal contents. Causes of mechanical obstruction are divided into extrinsic, intrinsic, and intraluminal causes [38].

◾ Extrinsic: adhesions (most common), hernia, endometriosis, and vascular compressions ◾enteritis Intrinsic: Crohn’s disease, tuberculosis, neoplasm, intussusception, hematoma, and radiation ◾Distal Intraluminal: foreign body, gallstone ileus, bezoars, and distal intestinal obstruction syndrome. intestinal obstruction syndrome is a manifestation of cystic fibrosis involving intestinal

obstruction caused by inspissated feculent material and secretions in the distal ileum and right colon (Fig. 29.33)

FIGURE 29.33 Contrast-enhanced axial computed tomography of the abdomen and pelvis from a 31-year-old man with cystic fibrosis and distal intestinal obstruction syndrome demonstrates large obstructive stool ball in the distal ileum (black arrow).

Small bowel obstruction is further subclassified into high- and low-grade types, with high-grade obstruction indicating no passage of bowel contents beyond the point of obstruction. Clinical features are nausea, vomiting, colicky abdominal pain, distension, and high-pitched or absent bowel sounds. Associated leukocytosis and elevated lactate levels indicate strangulation or ischemia [39]. Management ranges from conservative with bowel decompression to surgery depending on the etiology and severity of obstruction. Imaging Features

Radiographs Supine and upright radiographs are the initial screening tests in symptomatic patients with overall low diagnostic accuracy (diagnostic in only 50–60% of cases). Detection sensitivity is relatively higher for high-grade obstruction.

Normal, equivocal, and findings of low-grade obstruction necessitate further evaluation with multidetector CT [38,40]. Small bowel loops are identified because of the presence of valvulae conniventes, with a normal diameter of less than 3 cm. Obstructed small bowel has a diameter exceeding 3 cm (Fig. 29.34). The differential diagnosis is ileus, which presents as generalized gaseous distension of small and large bowel loops without a distinct transition zone or as focally distended sentinel loop.

FIGURE 29.34 Supine abdominal radiograph from a 56 years-old-man with obstructive small bowel gas pattern. Small bowel loops are identified caused by valvulae conniventes (white arrowhead) and measure up to 3.5 cm in diameter.

Certain radiographic predictors of high-grade obstructions are

◾ Caliber of dilated small bowel loop more than 50% of caliber of largest visible colon ◾ levels with width greater than 2.5 cm ◾ Air-fluid Presence of air-fluid levels with height difference of more than 2 cm within the same loop [38,40]

The number of air-fluids levels proportionately increase with more distal obstruction (Fig. 29.35). Paucity of bowel gas or gasless abdomen occurs when bowel loops are predominately fluid filled, most commonly seen in the setting of high-grade or closed-loop obstruction. Upright abdomen radiographs in such cases can demonstrate the “string of beads sign” secondary to air trapping between the valvulae conniventes (Fig. 29.36) [39].

FIGURE 29.35 Erect abdominal radiograph shows obstructive small bowel gas pattern with numerous air-fluid levels. The presence of multiple air fluid levels with width greater than 25 mm (white arrowheads) and height difference exceeding 2 cm indicates high-grade obstruction.

FIGURE 29.36 Upright abdominal radiograph shows “string of bead signs” in high-grade small bowel obstruction (white arrows).

Ultrasonography It is not usually indicated because of inherent technical limitations in evaluating gas containing structures. Findings are dilated fluid and gas-filled bowel demonstrating increased whirling or to-and-fro peristalsis. The loops may show a thickened wall and valvulae conniventes. The presence of interbowel fluid, wall thickness exceeding 3 mm, and aperistalsis are indicative of ischemia [38].

Computed tomography It is the technique of choice to evaluate the presence, degree, transition point, etiology of obstruction, and complications. IV contrast is imperative to detect ischemia unless contraindicated. Although oral contrast was previously routinely administered to exclude high-grade obstruction, routine administration is debated in current clinical practice because of

1. Risk of aspiration in patients with vomiting 2. Retained intraluminal fluid serving as natural negative contrast 3. Contrast material rarely opacities bowel just proximal to transition point in high-grade obstruction 4. Elimination of the time delay in performing the CT examination [39]

Obstruction presents with dilated small bowel leading to a normal caliber or collapsed loop distally, with diameter exceeding 2.5 cm when measured from outer to outer wall [38]. To locate the transition point, we advocate tracking the bowel in a retrograde manner starting from the rectum to the point of obstruction, confirming with further anterograde tracking from the stomach down, and subsequent correlation on coronal and sagittal images. It is also helpful to locate any fecalized segment (small bowel feces sign), which is typically present immediately proximal or near the transition point (Fig. 29.37).

FIGURE 29.37 Contrast-enhanced axial computed tomography of the abdomen and pelvis from a 76-year-old man with small bowel obstruction caused by adhesions shows a fecalized small bowel (small bowel feces sign) at the transition point in left abdomen (white arrow).

Adhesions are bands of fibrous tissue formed secondary to inflammatory process. They are overall the most common cause of bowel obstruction in both early and late postoperative periods. Adhesions are not directly visualized on CT but manifest as abrupt transition or tapering between dilated and collapsed bowel (Fig. 29.38) [39].

FIGURE 29.38 Axial (A) and coronal (B) contrast-enhanced computed tomography of the abdomen and pelvis shows high-grade small bowel obstruction caused by adhesion, with transition point in the central abdomen (white arrow).

Gallstone ileus presents with an obstructing stone at or near the ileocecal junction (Fig. 29.39). Findings of strangulation are wall thickening, abnormal wall enhancement (hyperenhancement caused by slow perfusion and congestion, progressing to hypoenhancement in severe ischemia), interbowel fluid, mesenteric edema and hyperemia, pneumatosis, and mesenteric and portal venous air [38,39,41].

FIGURE 29.39 Coronal contrast-enhanced computed tomography of the abdomen and pelvis from a 44-year-old man with gallstones ileus demonstrates obstructive stone in the distal ileum (white arrow).

Closed-loop obstruction is a complex small bowel obstruction with a high risk of strangulations. It is characterized by obstruction of a segment of bowel at two points in a manner precluding any outlet for lumen decompression. Progressive buildup of secretions leads to increased intraluminal pressure and venous obstruction. Common causes are adhesive bands, internal hernias, umbilical hernia, and Roux-en-Y gastric bypass. It presents as U- or C-shaped, radially distributed small bowel loops, double beak sign caused by tapering of at least two loops at the transition point, and whirl sign secondary to mesenteric twisting (Fig. 29.40) [39,42]. Blood lactate levels can be normal with ischemia in closed loop because of simultaneous twisting and occlusion of both the supplying mesenteric artery and vein.

FIGURE 29.40 Coronal and axial contrast-enhanced computed tomography of the abdomen and pelvis from a 60-year-old man with closed-loop bowel obstruction caused by internal hernia. Small bowel loops are radially distributed in the central abdomen with beaking at the transition point (white arrowhead) and mesenteric vessel swirl (white arrow).

Certain reported imaging predictors of success of conservative treatment include the presence of the feces sign, anterior parietal adhesion (refers to close proximity of transition zone to the anterior peritoneum), and lack of the beak sign. The presence of two or more beak signs, whirl sign, and C- or U-shaped configuration of bowel loops are associated with failure of nonsurgical treatment [43].

Superior Mesenteric Artery Syndrome This is a rare acquired vascular compression disorder involving duodenal obstruction from compression of the third portion between the SMA and aorta. Normally, the third portion of the duodenum passes between the aorta and SMA at L3 level and is surrounded by retroperitoneal fat. Major causes include rapid and severe weight loss and wasting conditions such as immunodeficiency, cancer

cachexia, and malabsorption, which lead to loss of the retroperitoneal fat cushion. The incidence is higher in women presenting with symptoms such as postprandial epigastric pain, nausea, and vomiting. On barium studies, there is dilation of the stomach and proximal duodenum with a vertical extrinsic impression on the third portion of the duodenum. The obstruction decreases with postural change. Mesenteric angiography demonstrates acute angulation of the SMA and reduction in the aortomesenteric angle and distance, with reported aortomesenteric angle ranging from 6 to 22 degrees and aortomesenteric distance of 2–8 mm (normal aortomesenteric angle, 28–65 degree, aortomesenteric distance, 10–34 mm) (Fig. 29.41) [44].

FIGURE 29.41 Coronal contrast-enhanced computed tomography of the abdomen and pelvis from a 62-year-old woman with chronic abdominal pain shows massive distension of the stomach and proximal duodenum with narrowing of third portion of duodenum where it crosses between the aorta and superior mesenteric artery (SMA) (black arrow)(A). Sagittal image shows an abnormal aortomesenteric angle and distance (6 degrees, 3 mm), consistent with SMA syndrome (black arrowhead)(B).

Internal Hernias Pathophysiology and Clinical Features

Internal hernias are abnormal protrusion of abdominal viscera through the peritoneum or mesentery into a compartment of the abdominal cavity. The orifices of herniation can be congenital or acquired secondary to trauma, previous surgery, or inflammation. Internal hernias can be classified based on the hernial orifices, as shown in the Table 29.4 [45,46]. Table 29.4 Categories of Internal Hernia Hernial Orifice Hernia Type Normal foramen

Foramen of Winslow

Unusual peritoneal fossa or retroperitoneal recess

Paraduodenal, pericecal, and intersigmoid hernia

Abnormal opening in mesentery or peritoneal ligament

Hernia through mesentery, omentum, transverse mesocolon, sigmoid mesocolon, falciform ligament, or broad ligament and Roux-en-Y anastomosis–related hernia

The clinical presentation is with symptoms of bowel obstruction such as nausea, vomiting, abdominal pain, and distension. Intermittent abdominal pain and weight loss may accompany recurrent, spontaneously reducing internal hernias [45]. Imaging Features Multidetector CT is the technique of choice for evaluation. Multiplanar and 3D volume-rendered reconstructions increase the diagnostic accuracy and help in surgical planning. Use of IV contrast is essential to evaluate the vascular relationships and identify signs of ischemia [45]. Imaging features of the most common subtypes of internal hernia are described. Foramen of Winslow Hernia

Anatomy

The foramen of Winslow is an approximately 3-cm vertical slitlike communication between the lesser sac and peritoneal cavity. The foramen is located cephalad to the duodenal bulb, inferior to the caudate lobe, anterior to the IVC, and posterior to the hepatoduodenal ligament. These represent approximately 8% of internal hernias with hernia contents consisting of small bowel, cecum, ascending colon, transverse colon, and gallbladder [46].

Computed tomography features These include the presence of a herniated sac in the lesser sac with beak-shaped projection of the hernial sac pointing toward the foramen of Winslow, the presence of mesentery between the IVC and portal vein, absence of the ascending colon in the right paracolic space, and two or more bowel loops in the high subhepatic space (Fig. 29.42) [45,46].

FIGURE 29.42 Axial contrast-enhanced computed tomography of the abdomen and pelvis from a 79-year-old woman with acute abdominal pain shows herniation of the cecum and terminal ileum in the foramen of Winslow. Note the beaklike pointing of the hernia toward the foramen of Winslow (black arrow).

Paraduodenal Hernia These constitute approximately 53% of the internal hernia and are divided into left and right subtypes.

Left Paraduodenal Hernia Anatomy Hernia occurs through the fossa of Landzert, which is a congenital peritoneal recess formed by failure of fusion of the descending colon with the posterior parietal peritoneum. The inferior mesenteric vein and ascending left colic artery are situated at the anteromedial edge of this fossa [45,46]. Computed tomography features

These include saclike clustering of small bowel loops in the left anterior pararenal space with the inferior mesenteric vein located anterior and medial to the hernial sac (Fig. 29.43).

FIGURE 29.43 Axial (A) and sagittal (B) contrast-enhanced computed tomography of the abdomen and pelvis from a 61-year-old man demonstrates left paraduodenal hernia. Note the inferior mesenteric vein is located anterior and medial (white arrow) to the herniated bowel loops (black arrows in A).

Right Paraduodenal Hernia Anatomy Hernia occurs through the fossa of Waldeyer, located inferior to the third portion of the duodenum and just behind the root of the small bowel mesentery. The SMA and SMV are situated at the anteromedial edge of this fossa. The recess is formed by failure of fusion of part of the ascending colon with the posterior parietal peritoneum. The hernia most commonly occurs in the setting of small bowel nonrotation [45–47]. Computed tomography features The SMA and SMV are located anterior and medial to the hernial sac. As the fossa of Waldeyer extends to the right and downward into the ascending mesocolon, the right colic vein is displaced anteriorly by the hernial sac. In the setting of intestinal nonrotation, the SMV is more left and ventral relative to SMA with absence of normal horizontal duodenum (Fig. 29.44) [45–47].

FIGURE 29.44 Axial and coronal contrast-enhanced computed tomography of the abdomen and pelvis from a 54-year-old man demonstrates right paraduodenal hernia containing sigmoid colon (white arrowheads)(A and B). Note the superior mesenteric artery and vein are located anterior and medial to the hernia sac (white arrow in A).

Pericecal Hernia

Anatomy Unusual recesses around the caecum are superior ileocecal recess, inferior ileocecal recess, retrocecal recess, and paracolic sulci. Acquired adhesions may also cause these hernias [45]. Computed tomography features These include anterior or medial displacement of the cecum and ascending colon by the hernia sac. Sigmoid Mesocolon Hernia

Anatomy These account for approximately 6% of internal hernias and are classified into transmesosigmoid, intramesosigmoid, and intersigmoid subtypes. Transmesosigmoid and intramesosigmoid hernias occur through an abnormal defect within the sigmoid mesocolon, involving both peritoneal layers in the former and only one peritoneal layer in the latter. Intersigmoid hernia involve

herniation into a congenital retroperitoneal fossa (intersigmoid fossa) located just above and behind the root of sigmoid mesocolon [45]. Computed tomography features The hernia orifice is located between sigmoid colon and left psoas muscle in all the subtypes. Splaying of the sigmoid vessels is present in the intramesosigmoid hernia. There is characteristic absence of a distinct hernial sac in transmesosigmoid hernias [45]. Transmesenteric Hernia

Anatomy These account for approximately 8% of internal hernias. These are most commonly congenital with a higher incidence in the pediatric population. The mesenteric defect is typically 2–5  cm in size and is located near the ligament of Treitz or ileocecal valve. In adults, the hernia is mostly acquired from trauma, surgery, or inflammation [46]. Computed tomography features This presents with dilation of clustered small bowel loops with a transition zone of obstruction. There are engorgement, stretching, and crowding of the mesenteric vascular pedicle and displacement of the main mesenteric trunk with the mesenteric vessels converging at the hernia orifice [46]. Roux-en-Y Anastomosis–related Hernia

Anatomy These hernias are related to Roux-en-Y anastomosis with three subtypes: transmesocolic, jejunojejunostomy mesenteric, and Petersen hernias. Transmesocolic hernias occur through a surgical defect in the transverse mesocolon. Jejunojejunostomy mesenteric hernia occurs through a small bowel mesenteric defect at the jejunojejunostomy site (Fig. 29.45). Peterson hernia occurs through the Peterson defect, located between the jejunal mesentery of Roux limb and transverse mesocolon [45,48].

FIGURE 29.45 Coronal contrast-enhanced computed tomography of the abdomen and pelvis from a 46-year-old woman with Roux-en-Y gastric bypass demonstrates massive dilation of the excluded stomach and pancreaticobiliary limb secondary to internal hernia through the jejuno-jejunostomy mesenteric defect (A). On axial images, note the altered location of the jejuno-jejunostomy in midabdomen caused by internal hernia (white arrow)(B) compared with left hemiabdomen on the prior exam (white arrowhead)(C).

Computed tomography features The hernia is suggested by displacement of Roux limb, biliopancreatic limb, and transverse colon. Effects of herniation are mesenteric swirl, clustering of small bowel loops, and mesenteric edema. The mushroom sign (mushroom-shaped mesenteric root as it passes through a narrow opening between the vessels at the base of mesentery) and the hurricane eye sign (distal tubular mesentery fat surrounded by small bowel loops) have been described [45,49].

Small Bowel Neoplasms Benign Neoplasms

Hemangiomas These are rare congenital benign vascular malformations, classified into cavernous (most common), capillary, and mixed subtypes. The jejunum is the most common site of involvement. On contrast-enhanced CT, hemangiomas demonstrate nodular arterial phase and homogeneous delayed phase enhancement. Complications are GI bleed, obstruction, and intussusception, although the vast majority are detected incidentally [50].

Lipomas

These are incidental solitary tumors most commonly located in the duodenum and distal ileum. Complications are intussusception and GI bleed. On CT, lipomas are identified as circumscribed ovoid lesions with fat attenuation (Fig. 29.46). Larger tumors can present with necrosis, calcifications, and cystic degenerations [51].

FIGURE 29.46 Contrast-enhanced coronal computed tomography of the abdomen and pelvis shows an incidental lipoma in the second portion of duodenum (white arrow).

Leiomyomas These are usually solitary tumors with a predilection for the jejunum. The tumor originates from the muscle layer and can be submucosal, intramural, or subserosal. On CT, leiomyomas are circumscribed lesions with homogenous enhancement. Larger lesions may show calcifications [51]. Malignant Neoplasms

Adenocarcinoma Pathogenesis and clinical features Adenocarcinomas are rare tumors representing only about 1% of primary GI tract malignancies. The duodenum is the most common site of involvement followed by the proximal jejunum [51]. The incidence is higher in patients with Crohn’s disease, celiac disease, familial adenomatosis polyposis, Peutz-Jeghers syndrome, congenital bowel duplication, and neurofibromatosis [51,52]. General clinical features are abdominal pain, weight loss, and symptoms related to bowel obstruction. Imaging features On contrast-enhanced CT, adenocarcinomas characteristically demonstrate short segment bowel involvement as asymmetric wall thickening with enhancement. Other patterns include ulcerative growth, papillary, polypoidal, or large irregular mass [52]. Associated partial or high-grade bowel obstruction may be present. The tumor spreads by direct invasion into surrounding viscera, lymph nodal metastasis, and hematogenous spread to the liver. Contiguous tumor growth can be present in the mesenteric vasculature. Liver metastases are hypoattenuating on the portal venous phase (Fig. 29.47).

FIGURE 29.47 Contrast-enhanced axial (A) and coronal (B) computed tomography of the abdomen and pelvis from a 64-year-old man with duodenal adenocarcinoma shows large, exophytic, ulcerated distal duodenal tumor (white arrow), with contiguous tumor thrombus in the superior mesenteric vein (white arrowhead). Associated hypoattenuating liver metastasis are present (black arrow)(B). Incidental note of chronic right hydronephrosis from ureteropelvic junction obstruction.

Differential diagnosis The differential diagnosis includes lymphoma (adenopathy in adenocarcinoma is less bulky compared to lymphoma), periampullary carcinoma, gastrointestinal tumors (GISTs), leiomyosarcoma, and carcinoid [52].

Lymphoma Pathophysiology Lymphomas are the most common malignancy of the small bowel, classified into primary and more common secondary subtypes. Primary GI lymphomas accounts for approximately 5–20% of the extranodal lymphomas and are frequently associated with a single site of bowel involvement. The ileum (60–65%) and jejunum (20–25%) are the most common sites because of increased density of the lymphoid tissue in the lamina propria and submucosa [53,54]. On pathology, small bowel lymphomas are predominantly non-Hodgkin type (Bcell subtype > T-cell subtype); other less common types include Burkitt, mucosaassociated lymphoid tissue lymphoma, and Hodgkin lymphomas [53,54]. Peripheral T-cell subtype lymphoma affects the jejunum and duodenum in a multifocal pattern with a high incidence of perforation [53–55]. Clinical features

The variable clinical presentation is usually related to complications such as perforation, obstruction, fistula, or abscess formation. The incidence is higher in patients with HIV (B-cell type, high grade with poor prognosis), celiac disease (Tcell type), inflammatory bowel disease (IBD), and immunosuppression [53].

Imaging Features Ultrasonography There is marked circumferential, hypoechoic mural thickening with loss of stratification, giving a nonspecific pseudokidney appearance in the longitudinal view. Preserved peristalsis despite marked mural thickening, longer segment involvement, and mesenteric adenopathy favor lymphoma over adenocarcinoma [56]. Fluoroscopy Small bowel follow-through can demonstrate loss of mucosal pattern (Fig. 29.48), circumferential mass, ulcerated or cavitary lesion, diffuse or focal nodular lesions, or ulcerated constriction. Aneurysmal dilation can be depicted.

FIGURE 29.48 Small bowel follow-through from a 65-year-old woman with long-standing celiac disease demonstrates loss of mucosal pattern and small bowel thickening, predominantly involving the distal jejunum and early ileum (black arrowheads). Small bowel biopsy was positive for T-cell lymphoma. Incidental barium in the biliary tract is related to choledochoduodenostomy.

Computed tomography and MRI Small bowel lymphomas demonstrate relatively homogeneous bowel wall thickening, with wall thickness ranging from 1 to 7 cm. Reported patterns of primary tumors are polypoidal or nodular, infiltrative, aneurysmal, exophytic, and stenosing.

◾points The polypoidal pattern is predominately associated with follicular lymphomas and serves as lead for intussusceptions ◾ The aneurysmal pattern commonly coexists with the infiltrative form ◾ exophytic growth or mesenteric pattern forms bulky masses ◾ The The rare, stenosing form with concentric fibrosis is associated with classic Hodgkin lymphoma

Aneurysmal dilation of the bowel is a characteristic finding on imaging, caused secondary to destruction of the myenteric plexus in the muscularis propria (Fig.

29.49). Tumor extension into the mesentery leads to bulky mesenteric adenopathy. Larger tumors present with bowel perforation, enteric fistula, and abscess formation (Fig. 29.50). The incidence of bowel obstruction is rare despite marked mural thickening. An additional rare manifestation is peritoneal involvement with lymphomatosis, presenting with imaging features indistinguishable from peritoneal carcinomatosis [53,54]. On MRI, untreated tumor shows hypointense T2 signal with diffusion restriction and homogenous contrast enhancement.

FIGURE 29.49 Contrast-enhanced axial (A) and coronal (B) computed tomography of the abdomen and pelvis from a 56-years-old man with primary small bowel lymphoma, non-Hodgkin, B-cell type. Distal ileal tumor demonstrates marked mural thickening with homogeneous enhancement and associated aneurysmal dilation of the bowel (white arrow). Regional mesenteric adenopathy is present (white arrowhead)(B).

FIGURE 29.50 Single-contrast upper gastrointestinal imaging (A) from a 74year-old-man with duodenal lymphoma shows an ulcerated mass involving the third portion of duodenum (black arrow) with enteroenteric fistula (black arrowhead). Subsequent contrast-enhanced coronal computed tomography of the abdomen and pelvis shows the large exophytic, ulcerated duodenal mass invading into the jejunum (white arrow)(B).

Positron emission tomography (PET) 18-Fluorodeoxyglucose (FDG) PET is indicated for staging and posttreatment response assessment in combination with CT. Differential diagnosis This includes adenocarcinoma, leiomyosarcoma, metastasis, tuberculosis, and IBD [54]. Small Bowel Lymphoma: Pearls to Remember Aneurysmal dilation of bowel Associated with mesenteric adenopathy Pseudokidney appearance of bowel on USG Bowel obstruction is rare

Carcinoid Tumors Pathophysiology Carcinoids are neuroendocrine tumors (NETs) originating from endocrine amine precursor uptake and decarboxylation cells (APUDOMAS) found throughout the GI tract. There has been a substantial increase in the incidence of NETs in past decades worldwide, with carcinoid tumors now representing the second most common small bowel malignancy [57]. The distal ileum is the most common location (57% of small bowel carcinoids) [58,59]. Carcinoid tumors also represent approximately 80% of all appendiceal neoplasms and demonstrate certain unique features at this site such as increased incidence in young adults, an indolent clinical course (5-year survival rate >90%), and low risk of metastasis in tumors smaller than 2 cm. Tumors larger than 2 cm, however, have a higher risk of metastasis and require right hemicolectomy instead of an appendectomy [60]. On histology, ileum and jejunum tumors most commonly arise from argentaffinpositive Kulchitsky cell present in the crypts of Lieberkuhn. Overall, these tumors are more aggressive with a higher incidence of liver and nodal metastasis. Duodenal tumors commonly arise from gastrin-producing neuroendocrine cells with manifestation of Zollinger-Ellison syndrome; multiple endocrine neoplasia type 1 syndrome is a predisposing factor [61]. The 2010 World Health Organization classification divides gastroenteropancreatic NETs based on the mitotic count and Ki-67 proliferation index into NET grade I, NET grade II, and grade III neuroendocrine carcinoma (NEC) [62] (Table 29.5). Table 29.5 World Health Organization Grading of Gastroenteropancreatic Neuroendocrine Tumors Mitotic KI-67 2010 World Health Organization Classification Count Labeling NET grade 1

20

NET, neuroendocrine tumor: NEC, Neuroendocrine carcinoma.

Clinical features

The is a higher incidence in the sixth and seventh decades of life with similar gender prevalence. Patients can be asymptomatic or present with intermittent crampy abdominal pain, weight loss, fatigue, and vomiting. Metastasis to the liver presents with carcinoid syndrome, characterized by episodic cutaneous flushing, bronchospasm, abdominal cramps, and diarrhea [59,61].

Imaging Features Computed tomography Multidetector CT with dual-phase imaging (arterial and venous phase) is the technique of choice for evaluation. Neutral oral contrast is administered for adequate bowel distension and assessment of mucosal enhancement. The primary tumor can be difficult to detect because of small size or infiltrative growth, with detection sensitivity of as low as 60% [63]. The primary tumor can present as concentric or asymmetric bowel thickening, focal mucosal and submucosal infiltrative or plaquelike arterial hyperenhancement, or a nodular or polypoidal enhancing mass. Solitary or multifocal tumors can be present. There is extensive desmoplastic submucosal fibrosis caused by release of serotonin and vasoactive substance by the neuroendocrine cells, which causes bowel stiffening and wall curvatures (hairpin bends). The desmoplasia can also lead to bowel ischemia and obstruction [59,61] (Fig. 29.51).

FIGURE 29.51 Contrast-enhanced axial (A) and coronal (B) computed tomography of the abdomen and pelvis from a 45-year-old man with small bowel carcinoid tumor. The primary tumor in distal ileum shows focal plaquelike mucosal and submucosal enhancement and thickening (white arrow)(A), which is causing partial bowel obstruction. The larger spiculated mesenteric metastasis shows stippled internal calcifications with surrounding bowel angulation and tethering caused by desmoplasia (white arrowhead)(B).

The risk of metastasis increases with the size of the primary tumor, with a 20– 30% incidence of nodal and liver metastasis in tumors smaller than 1 cm. On the other hand, the incidence increases to 60–80% of nodal metastasis and 20% of liver metastasis when tumors are 1 to 2 cm and up to 80% nodal metastasis and 40–50% liver metastasis in tumors larger than 2 cm [59,61]. Mesenteric metastases are typically larger than the primary tumor. The mesenteric mass can be ill defined or spiculated and solid enhancing with areas of necrosis or cystic degeneration. Stippled, coarse, or diffuse calcifications are present in up to 70% of mesenteric masses (see Fig. 29.51). Hepatic metastases are usually multiple and hypervascular, but different lesions may demonstrate different enhancement characteristics. Because these are slow-growing tumors, diffuse liver involvement is often associated with hepatomegaly and normal liver function test results unlike in adenocarcinoma metastases. Magnetic resonance imaging MRI depicts the primary tumor as irregular bowel thickening or nodular mass that is iso- to hyperintense on T2-weighted imaging with intense arterial phase enhancement. Liver metastasis from carcinoids demonstrate T1 hypointensity, moderate to marked T2 hyperintensity, arterial phase hyperenhancement (Fig. 29.52), and diffusion restriction. Hepatobiliary phase imaging delineates the liver metastases as hypointense foci.

FIGURE 29.52 Multifocal hepatic metastases from ileal carcinoid. The dominant mass in segment 8 is heterogeneously enhancing on arterial phase axial T1-weighted magnetic resonance imaging (white arrow)(A) and is hyperintense on T2-weighted imaging (B)(white arrow).

Nuclear medicine Indium111 (111In)-octreotide scintigraphy detects NETs by binding to type II and V somatostatin receptors expressed by the tumor cells. (Type II receptors are present in up to 80% of enteropancreatic NETs.) However, octreotide scintigraphy and single-photon emission tomography has largely been replaced by gallium-68 (68Ga) DOTATE PET for initial staging and follow up because it provides significantly better sensitivity, specificity, and spatial resolution. FDG PET is the technique for assessment of high-grade or poorly differentiated NETs, which demonstrate loss of somatostatin receptors with lack of Dotatate uptake. A combination of 68Ga-DOTATE and FDG PET imaging helps in mapping out the sites of well and poorly differentiated tumors, with only the well differentiated components being the targets for Lutetium-based and peptide receptor radionuclide therapy (Fig. 29.53) [64,65].

FIGURE 29.53 Gallium-68 DOTATATE positron emission tomography (PET) shows intense avidity of well-differentiated neuroendocrine tumor with the primary mass in the pancreatic head (white arrow) and multiple osseous metastases in visualized ribs and spine (A). Compare with the low to absent avidity of all the lesions on subsequent fluorodeoxyglucose PET (B). DOTATATE avidity of the lesions made this patient suitable for peptide receptor radionuclide therapy.

Differential diagnosis This includes GIST, adenocarcinoma, metastasis, lymphoma, Crohn’s disease and sclerosing mesenteritis [61]. Small Bowel Carcinoids: Pearls to Remember Desmoplastic tumors cause stiffening and bowel kinking Mesenteric metastasis is typically larger than the primary tumor Calcifications are frequently present in mesenteric and nodal metastases 68Ga-DOTATE PET is more sensitive than 111In-octreotide scintigraphy and CT for detection of metastases

Gastrointestinal Stromal Tumors Pathophysiology GISTs are the most common mesenchymal tumors of the GI tract with variable malignant potential. After the stomach, the small bowel is the most common site of involvement [66]. Tumors originate from the muscularis propria. On pathology,

cellular morphology of the tumor cells is closely related to interstitial cells of Cajal (also known as pacemaker of GI smooth muscle), which are believed to be the cells of origin. Tumors cells are defined by expression of CD117, a tyrosine kinase growth factor receptor that is targeted by highly effective chemotherapeutic agent imatinib. Malignant GIST demonstrate high cell atypia and mitotic activity. Although the risk of malignancy increases with tumor size, a small bowel GIST is more aggressive than gastric GIST of the same size [66,67]. Clinical features The incidence is higher after the fifth decade of life. Associations are neurofibromatosis 1 (Fig. 29.54], Carney triad, and KIT germline mutations. Variable clinical manifestations range from asymptomatic to hematemesis, melena, and hematochezia related to GI bleed. Other symptoms include vomiting, weight loss, abdominal pain, obstructive jaundice, and symptoms related to bowel obstruction [66,67].

FIGURE 29.54 Coronal contrast-enhanced computed tomography of the abdomen and pelvis from a 42-year-old-man with neurofibromatosis demonstrates multiple gastrointestinal tumors of the jejunum (white arrows).

Imaging Features Fluoroscopy Small bowel follow-through depicts small tumors as well-marginated, smoothsurfaced filling defects. Large and aggressive GISTs can lead to displacement of bowel loops, ulceration, and fistulation. CT and MRI CT is the technique of choice to evaluate the local extent and distant metastasis.

◾ GISTs are variable sized tumors ranging from 2 to 20 cm [66,68] ◾ The mass can be intramural, intraluminal, or predominately extramural ◾enhancing Small tumors are well marginated with homogenous enhancement. Large tumors present as heterogenous masses with areas of hemorrhage, necrosis, cystic degenerations, and dystrophic calcifications [66,67] (Fig. 29.55) ◾interbowel Local spread leads to encasement of surrounding organs, vascular complications with bleeding, and ◾ The liver andfistulation peritoneum are the most common sites of metastasis

FIGURE 29.55 Axial contrast-enhanced computed tomography of the abdomen and pelvis from a 62-year-old woman with a large gastrointestinal tumor of the distal ileum (white arrow). The lobulated solid tumor demonstrates heterogeneous attenuation due to internal necrosis.

Treatment response to imatinib induces decreased enhancement in the primary tumor and liver metastasis, sometimes resembling simple cyst (Choi criteria) (Fig. 29.56). On MRI, the bowel mass is of variable signal intensity because of presence of hemorrhage and necrosis and demonstrates heterogenous enhancement.

FIGURE 29.56 Portal venous phase axial T1-weighted magnetic resonance imaging shows a rim-enhancing metastasis from gastrointestinal tumor in hepatic segment 8 (A)(white arrow). The lesions shows interval cystic change and lack of enhancement after treatment with imatinib (white arrow)(B).

Positron emission tomography 18-FDG PET may be used in patients on treatment to detect potential viable residual tumor (commonly located along the margins) in the hypoenhancing treated lesions [67,69]. Differential diagnosis This includes lymphoma, adenocarcinoma, carcinoid, desmoid, and metastasis.

Leiomyosarcoma These are malignant neoplasms arising from the smooth muscles of the bowel wall. They are predominately solitary and exophytic tumors with a predilection for the jejunum and ileum. Multifocal tumors are associated with neurofibromatosis [51]. On contrast-enhanced CT, leiomyosarcomas can be small, circumscribed, and homogenously enhancing lesions or large heterogenous masses with necrosis, cystic degeneration, or ulceration (Fig. 29.57). Cavitation or fistula may be present.

FIGURE 29.57 Contrast-enhanced axial computed tomography of the abdomen and pelvis from a 76-year-old woman with leiomyosarcoma of the ileum (white arrow) shows an exophytic, lobulated solid tumor with heterogeneous postcontrast enhancement.

Metastases Routes of bowel metastases are intraperitoneal seeding (e.g., in carcinoma of ovary and colon), direct extension, and hematogenous spread. Hematogenous spread is seen from melanoma and breast, renal cell, and lung cancers [51]. On CT, metastasis presents as asymmetric wall thickening, intraluminal masses, or serosal implants (Fig. 29.58).

FIGURE 29.58 Contrast-enhanced coronal computed tomography of the abdomen and pelvis from a 41-year-old woman shows terminal ileal metastasis from ocular melanoma (white arrow). The intraluminal mass is a lead point for associated ileocolic intussusception.

Miscellaneous Celiac Disease Celiac disease is a chronic autoimmune enteropathy characterized by intolerance to gluten. Gliadin fraction in food (predominantly in wheat) is responsible for T cell– mediated immune activation and production of antibodies such as antihuman tissue transglutaminase and antiendomysium antibodies, which causes damage to GI tract in genetically predisposed individuals [70]. The duodenum and proximal jejunum are the predominantly affected sites; however, the extent of bowel involvement is variable.

The pathogenesis involves initial lymphocyte infiltration in the bowel wall and crypt hyperplasia followed by progressive villous atrophy. The inflammatory damage leads to loss of jejunal folds with a compensatory increase in ileal folds (ileal jejunization) [70]. The most common clinical presentation is with symptoms of malabsorption such as abdominal pain, diarrhea, and weight loss.

◾(reversal On small bowel follow-through, there is loss of jejunal folds with increased, thickened ileal folds of jejunoileal fold pattern), small bowel dilation caused by increased intraluminal fluid, and flocculation (Fig. 29.59). The advanced stage presents with dilated jejunal loops demonstrating complete loss of folds (Moulage sign) (Fig. 29.60) [71] CT enteroclysis shows reversal of the jejunoileal folds, ileal fold thickening, and submucosal fat deposition in the bowel wall in chronic cases. Mesenteric adenopathy with occasional necrotic nodes and engorgement of mesenteric vessels may be present (Fig. 29.61) [70,72]

◾

FIGURE 29.59 Small bowel follow-through from a 36-year-old woman with celiac disease demonstrates increased jejunal and ileal caliber, with increased intraluminal fluid diluting the barium and producing poor coating (flocculation).

FIGURE 29.60 Small bowel follow-through from a 56-year-old man with celiac disease shows a mildly dilated jejunum with complete loss of the mucosal pattern (Moulage sign).

FIGURE 29.61 Contrast-enhanced coronal computed tomography from a 31year-old woman with celiac disease shows increased mucosal folds in the ileum (ileal jejunization) (black arrowheads), with associated extensive mesenteric adenopathy (black arrow)(B).

Complications are transient small bowel intussusceptions caused by uncoordinated peristalsis, multiple jejunal ulcerations, enteropathy-associated Tcell lymphoma, and small bowel adenocarcinoma [70]. Lymphangiectasia Lymphangiectasia is a rare disorder characterized by dilation of small bowel lymphatics secondary to lacteal blockage, with resultant loss of lymph in the lumen. It can be primary or congenital or caused secondary to inflammatory damage, trauma, or neoplastic process. The bowel can be involvement in a localized or generalized pattern. Clinical manifestations include protein-losing enteropathy, ascites, and pleural effusions. On CT, there is circumferential bowel wall thickening of varying degree with characteristic submucosal hypoattenuating halo caused by lymphatic congestion (halo sign). Broad differentials include bowel ischemia, inflammation, and neoplasms such as lymphoma [73]. Eosinophilic Enteritis This is a rare inflammatory disease involving focal or diffuse eosinophilic infiltration in the GI tract, with predilection for involvement of the proximal small bowel and distal gastric body. Allergic or immunologic dysfunctions are proposed as causative factors, although the exact cause is unclear. The imaging appearance varies with the predominance of mucosa, muscularis, or serosal infiltration. CT

features are mucosal fold thickening, intraluminal polyp, bowel wall thickening with layering or stratification, and luminal narrowing [74]. Small Bowel Diverticulosis Jejunoileal diverticulosis or jejunal diverticulosis is characterized by herniation of mucosa through the weakened bowel wall along the mesenteric border. The jejunum is more commonly affected than the ileum. It is an acquired condition with increased incidence beyond the fourth decade of life. On fluoroscopy, jejunal diverticulosis is recognized by multiple rounded, contrast-filled outpouchings along the bowel with a relatively narrow neck. On CT, these present as round or oval, air- or contrast-filled outpouchings along the bowel wall (Fig. 29.62). Airfluid levels or debris can be present. The diverticula have barely discernable wall and lack valvulae conniventes. Underlying communication with the adjacent bowel lumen is frequent delineated. Superimposed diverticulitis leads to bowel wall thickening, perienteric stranding and fluid, localized collections, or rarely free air. Other complications include stasis-related bacterial overgrowth causing diarrhea and malabsorption, hemorrhage, pseudo-obstruction, and less commonly perforation [75].

FIGURE 29.62 Contrast-enhanced coronal axial computed tomography of the abdomen shows jejunal diverticulosis (white arrowheads)(A and B). There is a larger diverticulum showing wall enhancement and subtle haziness of the surrounding fat indicating diverticulitis (white arrow in A).

The duodenum is the second most common site of diverticular disease after the colon. Its occurrence has no specific gender or age predilection. The condition can be congenital or acquired. The less common congenital type contains all the bowel layers and is subdivided into intraluminal and extraluminal subtypes. The acquired type is a pulsion diverticula formed by an outpouching of mucosa or submucosa

through foci of weakened duodenal wall, most commonly involving the second portion. On CT, duodenal diverticulum is recognized as a saccular outpouching containing air, air-fluid levels, debris, or contrast, frequently interposed between the duodenum and pancreas (Fig. 29.63). Compared with jejunoileal diverticulum, the incidence of complications such as inflammation and perforation is significantly less in duodenal diverticulum [76].

FIGURE 29.63 Contrast-enhanced coronal axial computed tomography of the abdomen shows a large duodenal diverticulum (white arrowhead).

Specific Large Bowel Abnormalities Large Bowel Obstruction

Pathophysiology and Clinical Features Acute large bowel obstruction carries high morbidity and mortality rate; however, the presentation is relatively gradual compared with small bowel obstruction. It commonly affects the older adult population [77]. Causes are colon cancer (most common), volvulus, diverticulitis, intussusception, intraluminal obstruction by foreign body, fecal impaction, hernias, and strictures in ischemic and IBD. Adhesions and extrinsic compression are rare causes [77]. Clinical features are abdominal pain, distension, constipation, and obstipation. Ischemia and perforation are the major complications, with higher risk associated with a combination of competent ileocecal valve and rapid obstruction leading to closed-loop physiology. Colonic pseudo-obstruction (Ogilvie syndrome) is characterized by diffuse colonic dilation without associated mechanical obstruction (Fig. 29.64). The incidence is relatively higher in male patients after the sixth decade of life. The proposed cause is autonomic system dysfunction causing impaired bowel motility and dilation; however, the exact etiopathogenesis is unclear. The condition is associated with myriad medical conditions such as metabolic (hypokalemia, hypocalcemia), cardiopulmonary disease (congestive heart failure, myocardial infarction, chronic obstructive pulmonary disease), systemic infection, malignancies, medications (anticholinergic, narcotics), and diabetes. Major complications are bowel ischemia and perforation [77,78].

FIGURE 29.64 Supine abdominal radiograph demonstrates diffuse gaseous distension of large bowel in Ogilvie syndrome.

Imaging Features

Radiographs Supine and upright abdomen radiographs demonstrate dilation of the colon up to the level of obstruction with a collapsed distal colon. Dilated segments show airfluid levels. Cut-off calibers are 9 cm for the cecum and 6 cm for the rest of the large bowel [77]. Sigmoid volvulus is characterized by coffee bean-shaped configuration of the dilated sigmoid colon (coffee bean sign) (Fig. 29.65), with cranial extension above the level of transverse colon (Northern exposure sign). The Frimann-Dahl sign refers to convergence of three dense white lines (representing

the wall of the sigmoid colon) to the site of obstruction combined with an absence of rectal air [79,80].

FIGURE 29.65 Supine abdominal radiograph shows coffee-bean sign in sigmoid volvulus.

Cecal volvulus presents with a gas-filled dilated cecum ectopically located in the left upper quadrant or midabdomen (Fig. 29.66). It can be confused with cecal bascule, which refers to a gas-filled, dilated cecum folded upward on itself without twisting, commonly located in the midabdomen [79].

FIGURE 29.66 Supine abdominal radiograph from a 54 year-old man shows a gas-filled, dilated cecum in the central abdomen, suggesting volvulus (A). Subsequent contrast-enhanced coronal computed tomography demonstrates dilated cecum in the central abdomen (white arrow) with beaking at the transition point caused by volvulus (white arrowhead)(B).

Computed tomography This is the technique of choice to evaluate the obstructive cause and complications and exclude pseudo-obstruction, which presents with lack of an abrupt transition point or mechanical cause. Large bowel obstruction presents with colonic dilation up to the transition point with collapsed distal bowel. Associated small bowel dilation is seen in patients with incompetent ileocecal valve or severe or longstanding obstruction. Mural thickening, abnormal wall enhancement, pneumatosis, and portal venous air indicate ischemia. In sigmoid volvulus, there is an abnormally positioned sigmoid colon with beaking of the bowel at the transition point and mesenteric swirl (whirl sign) (Fig. 29.67]. Cecal volvulus is recognized by an abnormally positioned cecum in the left upper or midabdomen, with associated swirling of the bowel and mesenteric vessels at the transition point (see Fig. 29.66) [79].

FIGURE 29.67 Contrast-enhanced coronal computed tomography from a 79year-old man with sigmoid volvulus shows massively dilated sigmoid colon (A) with beaking at the transition point (black arrowhead)(B) and mesenteric swirl (black arrow).

Differential Diagnosis This includes small bowel obstruction, pseudo-obstruction, and toxic megacolon.

Colorectal Cancer Pathophysiology Colorectal cancer is the most common cancer of the GI tract and the second most common cause of cancer-related deaths globally. Ninety percent of colorectal cancers are adenocarcinomas. Mucinous adenocarcinoma as a subtype is characterized by pools of extracellular mucin, a more aggressive clinical course, and certain distinct imaging features. Other rare types are neuroendocrine, squamous cell, spindle cell, and undifferentiated carcinomas [81]. Precursor lesions and risk factors are 1. Adenomas: Most colon cancers develop from adenoma (adenoma–carcinoma sequence). Subtypes include tubular, villous, and tubulovillous. Risk of malignant degeneration of an adenoma depends on following factors [82,83]: Duration: 2.5% cumulative risk at 5 years, 8% at 10 years, and 24% at 20 years Size: Polyps larger than 2 cm are at 40% risk of malignancy; those that are smaller than 0.5 cm have no risk Type: increased risk with villous architecture

◾ ◾ ◾

2. Hyperplastic or serrated polyps 3. Dysplasia in IBD 4. Lynch or hereditary nonpolyposis colorectal cancer syndrome: This is an autosomal dominant syndrome characterized by mutation in DNA mismatch repair genes, with increased risks of several GI and gynecologic malignancies; colorectal and endometrial cancers are the most common [81]. 5. Familial adenomatous polyposis: Autosomal dominant syndrome characterized by germline mutation in adenomatous polyposis gene, causing development of hundreds to thousands of adenomatous polyps in the colon and rectum. Imaging usually underestimates the disease burden because most polyps are subcentimeter in size. Polyps typically develop around puberty with nearly 100% of cases progressing to colon cancer in the third and fourth decades of life, necessitating total colectomy and ileoanal pouch creation as a prophylactic or definitive management (Fig. 29.68). Variants are Gardner syndrome characterized by development of desmoid tumors, epidermoid cyst, and osteomas and Turcot syndrome associated with medulloblastomas [81]. 6. Peutz-Jeghers syndrome: This is an autosomal dominant syndrome characterized by mutation in the LKB1/STK11 gene. It is characterized by multiple hamartomatous polyps in the GI tract (most commonly in the small bowel), colorectal cancers, and pigmented mucocutaneous lesions [81]. 7. Juvenile polyposis syndrome: This is an autosomal dominant syndrome associated with germline mutations in the SMAD4 or BMPR1A genes. It is characterized by formation of juvenile polyps throughout the GI tract with associated malignant transformation [81]. 8. Obesity and low-fiber and high-fat animal protein–based diets are additional risk factors.

FIGURE 29.68 Double-contrast barium enema from a 24-year-old woman with familial adenomatous polyposis (FAP) shows several polypoidal and sessile mucosal filling defects in the colon and rectum (A). Double-contrast upper gastrointestinal examination from a different patient with FAP shows numerous duodenal polyps (B).

Cancer frequency according to the location: sigmoid, 30%; rectum, 25%, cecum and ascending colon, 25%; and transverse and descending colon, 20% [83]. Clinical Features The incidence is higher in sixth and seventh decades of life. Clinical features are alteration in bowel habits, iron-deficiency anemia, weight loss, abdominal pain, hematochezia, and symptoms related to bowel obstruction. Imaging Features

Fluoroscopy Double-contrast barium enema has a higher sensitivity (48%) for detection of polyps more than 1 cm compared with single-contrast enema. Both examinations have low sensitivity for detection of smaller and early-stage lesions (35% detection sensitivity of double-contrast enema for lesions 10 cm) can present with abdominal pain. Hemangiomas are incidental findings requiring no further follow-up or treatment. When a finding classical for hemangioma is found on ultrasonography in a patient with no risk factors for primary or secondary hepatic neoplasm, no further follow-up is necessary. A follow-up ultrasonography in 6 months is recommended to confirm stability is recommended as an alternate option in doubtful cases. Further evaluation with a dedicated CT or MRI is recommended in indeterminate or doubtful cases. Nuclear medicine studies such as Tc-99m RBC labeled SPECT are now very rarely used for the diagnosis of hemangiomas. Surgical resection can be considered for patients with progressive abdominal pain, giant hemangiomas (>10 cm), or secondary complications (rupture, hemorrhage, or Kasabach Meritt syndrome). Percutaneous biopsy is rarely required for the diagnosis of hemangioma and should be avoided. Biopsy may be required in atypical hemangiomas (sclerosed or hyalinized hemangiomas),

particularly in patients with a history of malignancy, or primary liver disease predisposing to liver cancer.

Imaging Features Ultrasonography ■ Well-circumscribed, uniformly hyperechoic lesions with smooth, round, or lobular margins [30] (Fig. 31.15) ■ May appear hypoechoic in the background of hepatic steatosis ■ On color Doppler evaluation, typically, no vascular flow within the lesions

FIGURE 31.15 Hepatic hemangioma on ultrasonography. Hepatic hemangioma typically appears as a homogeneously hyperechoic mass (arrow in A) without internal vascularity on Doppler evaluation (A, B). Hemangiomas may appear hypoechoic to the background liver in the setting of hepatic steatosis (arrows in C).

CT ■ Hypoattenuating to the liver on unenhanced CT. Discontinuous, nodular, peripheral enhancement in the hepatic arterial phase with progressive centripetal fill-in on portal venous and delayed phase, following the “blood pool” in terms of attenuation [31] (Fig. 31.16) ■ Small hemangiomas often have significant surrounding perfusional abnormalities, with the lesion appearing as a “bright dot” within the region of perfusion abnormality in the arterial phase, with the persistence of the “bright dot” on the portal venous phase (bright dot sign) [31] (Fig. 31.17)

FIGURE 31.16 Classical cavernous hemangioma on CT. Axial contrast-enhanced CT images in the hepatic arterial phase (A), portal venous phase (B), and 3-minute delayed phase (C) demonstrate classical imaging features of a cavernous hemangioma with discontinuous peripheral nodular enhancement in the arterial phase and progressive centripetal enhancement in the venous and delayed phases (arrows in A, B, and C).

FIGURE 31.17 Small hepatic hemangioma (arrow in A) with significant surrounding perfusional abnormalities in the arterial phase (“bright dot” sign) (arrow in B).

MRI ■ Hyperintense on T2WI, hypointense on T1WI, with an enhancement pattern similar to that seen on dynamic, multiphase CT (Fig. 31.18) ■ Central cleft-like portion of increased T2 signal may sometimes be seen within large hemangiomas, reflecting cystic degeneration ■ On diffusion-WI and ADC maps, hemangiomas are often hyperintense secondary to the T2 shine-through effect. Occasionally, true restricted diffusion can be seen ■ “Flash-fill” hemangiomas refer to the rapid filling-in of smaller hemangiomas (5 mm Hg. In cirrhotic portal hypertension, this gradient is equivalent with the hepatic venous pressure gradient (HVPG) [17]. Clinically significant portal hypertension, which presages development of

decompensated cirrhosis with associated complications, is defined as a HVPG >10 mm Hg [18]. The HVPG is determined by obtaining the hepatic vein wedge pressure (approximating the hepatic sinusoidal pressure) and the free hepatic vein pressure through a transjugular catheter transducer. The wedge pressure is calculated by occluding the proximal hepatic vein with a balloon and then measuring the resulting pressure within the vein, which is equilibrated with the sinusoidal pressure. The balloon is then deflated and a second measurement is made of the free hepatic vein pressure. The difference between the two pressures is the gradient. In the setting of cirrhosis, the HVPG is the most accurate method for grading portal hypertension and for quantifying response of portal hypertension to treatment [19]. Given that this technique is invasive and relatively expensive, noninvasive imaging can be a helpful adjunct in the detection of clinically significant portal hypertension. The most specific finding of clinically significant portal hypertension on any noninvasive imaging technique is the identification of portosystemic collateral formation. This includes identification of esophageal varices or a recanalized umbilical vein, which should be sought on any imaging performed for a patient with suspected chronic liver disease or fibrosis (Figs. 33.5 and 33.6). The first-line examination for the detection of vascular manifestations of portal hypertension is Doppler USG of the liver. This can assess patency and direction of flow within the portal-venous system, and can detect collateral formation. The most common portosystemic collaterals detected by USG in the setting of portal hypertension are recanalized umbilical or paraumbilical veins, and the coronary vein (Figs. 33.7 and 33.8). Reversal of flow within the coronary vein, readily detected with Doppler USG, is another specific finding of clinically significant portal hypertension. Short of collateral formation, reversal, or sluggish within the portal vein is also highly suggestive of clinically significant portal hypertension [20]. Splenomegaly also often accompanies the development of portal hypertension, although the size of the spleen does not necessarily correlate with the severity of portal hypertension [21].

FIGURE 33.5 Diagram illustrating portosystemic collateral pathways, including esophageal varices, the coronary vein, and the umbilical vein. Although there are many sites of portosystemic collateralization, these are the most commonly identified ones at imaging, and are all identifiable with Doppler USG.

FIGURE 33.6 Examples of portosystemic collateral pathways. (A) Maximum intensity projection of a sagittal CT image shows a recanalized umbilical vein with dilated periumbilical and epigastric vein collaterals (arrows). The recanalized umbilical vein is identified at the terminus of the left portal vein umbilical segment at the base of the falciform ligament (asterisk). Postcontrast T1 sequences in a patient with cirrhosis and portal hypertension show tortuous and engorged esophageal varices (arrows, B and C) and marked splenomegaly (asterisk, C). Axial CT image with contrast shows a dilated, tortuous collateral vein extending from the splenic hilum to the left renal vein—a spontaneous splenorenal shunt (arrow, D).

FIGURE 33.7 Recanalized umbilical vein collateral in two different patients. Longitudinal grayscale (A) and power Doppler (B) views of the left hemiliver show an umbilical collateral (UMB. V. - arrow) seen as a small, 2.5-mm, central vessel in the ligamentum teres. Note that the umbilical vein collateral communicates with the umbilical segment of the left portal vein (U). (C) Transverse power Doppler view of the left hemiliver shows the umbilical collateral (arrow) in the middle of the echogenic ligamentum teres.

FIGURE 33.8 Normal coronary vein. (A) Transverse view shows the aorta (A) and the celiac axis. The coronary vein (CV) is seen immediately posterior to the splenic artery (SA). The hepatic artery (HA), portal vein (PV), and inferior vena cava (IVC) are also seen. (B) Longitudinal view shows the splenic vein (SV) immediately posterior to the body of the pancreas (P). The CV is seen arising from the SV and passing under the SA. (C) Longitudinal color Doppler view similar to B shows flow (arrow) in the coronary vein directed toward the splenic vein, as expected.

Liver stiffness values obtained by elastography have also shown value in the noninvasive prediction of clinically significant portal hypertension, with a transient elastography value greater than 15 kPa considered highly suggestive of compensated portal hypertension in an asymptomatic patient. Liver stiffness values greater than 20 kPa, and platelet counts of less than 150,000 mm−3 predict a high risk for clinically significant portal hypertension with the development of esophageal varices or other complications [22]. These patients require surveillance with endoscopy for the detection and treatment of varices in primary prevention of variceal bleeding. Patients with clinically significant portal hypertension can also develop refractory ascites or, as more spontaneous portosystemic shunts develop, hepatic encephalopathy.

Other Causes of Portal Hypertension (Noncirrhotic Portal Hypertension) The most common cause of portal hypertension is cirrhosis. However, there are other (noncirrhotic) etiologies of portal hypertension for which radiologists play an important role in the diagnosis and management. Budd–Chiari Syndrome Budd–Chiari syndrome encompasses a variety of conditions which result in obstruction of the large hepatic veins or of the IVC between the hepatic venous confluence and the right atrium. Obstruction of hepatic venous outflow at these levels results in congestion and venous stasis of the liver, ultimately causing progressive liver injury, fibrosis, portal hypertension, liver failure (which can be fulminant or chronic), and cirrhosis. The most common cause of large hepatic venous occlusion is an underlying hematologic disorder which results in hypercoagulopathy and spontaneous venous thrombosis. Any process obstructing

the hepatic veins or suprahepatic vena cava, including extrinsic compression by an adjacent mass, can also result in a secondary Budd–Chiari syndrome. It is important to recognize and distinguish the features of hepatic congestion, fibrosis, and portal hypertension associated with Budd–Chiari from those of cirrhotic portal hypertension, because the underlying etiologies and management differ substantially (Fig. 33.9). Apart from demonstrating occlusion or stenosis of the IVC or the hepatic veins, imaging often demonstrates the presence of venovenous collaterals in the liver, which can be distinguished from a normal hepatic vein or its tributary (which are straight) by their tortuous curvilinear appearance. Treatment involves identifying and correcting the underlying predisposition to thrombosis and relief of the venous outflow obstruction—with thrombectomy or angioplasty when possible, or with bypass of the obstruction with a portosystemic venous shunt, as discussed later [23].

FIGURE 33.9 A 42-year-old woman with JAK2 mutation and related hypercoagulopathy with recurrent, spontaneous thrombosis of the hepatic veins and features of chronic Budd–Chiari. Axial MRI T1 vibe postcontrast image at the level of the hepatic venous confluence (A) shows a narrowed, atretic IVC, and diminutive hepatic vein remnants (arrows). Another MR image inferior to this plane (B) shows a large, tortuous collateral vein (arrow) draining from the caudate lobe (arrowheads) into the IVC (asterisk). The liver is nodular, with relative hypertrophy of the central liver and caudate lobe (arrowhead). Color Doppler image (C) of the same collateral vein shows flow in the expected direction (arrows) toward the vena cava. (D) A 50-year-old woman with polycythemia vera and features of acute Budd–Chiari syndrome after liver transplantation for previous chronic Budd–Chiari and associated end stage liver failure. Axial CT image with contrast at the level of the hepatic vein confluence shows thrombosis of the left and middle hepatic veins (arrows) and a patent right hepatic vein (asterisk). Relative hypoenhancement is noted in the left and anterior right hemiliver, secondary to hypoperfusion, and edema (arrowheads). Superimposed liver infarction (“inf”) is seen in the periphery of the left lateral section. This patient went on to develop features of chronic Budd–Chiari and recurrent fibrosis within her transplant liver despite multiple interventions (not pictured).

Sinusoidal Obstruction Syndrome (Previously Veno-occlusive Disease) Previously known as “veno-occlusive disease,” sinusoidal obstruction syndrome (SOS) is distinguished from Budd–Chiari by venous outflow obstruction at the level of the hepatic sinusoids and venules, and is caused by toxic endothelial

injury of the sinusoids. The most common etiology is the conditioning phase of bone marrow transplantation, during which endothelial injury throughout the body is common and can produce a variety of organ-specific syndromes in addition to SOS. Another increasingly recognized etiology is oxaliplatin-based chemotherapy, such as in patients being treated for metastatic colorectal cancer. Most patients with sinusoidal endothelial injury do not progress to SOS—this occurs in a minority of patients, usually within 30 days after transplant. The diagnosis is primarily clinical, with liver failure and toxicity manifesting with fluid retention/ascites, tender hepatomegaly, and jaundice occurring within a suggestive time frame after bone marrow transplantation. Most of the imaging findings in SOS, as in other causes of acute liver failure, are nonspecific, but can suggest the correct diagnosis in the appropriate clinical context. Gadoxetate-enhanced MRI with delayed hepatobiliary phase imaging is relatively specific for SOS in the appropriate clinical setting, demonstrating a characteristic peripherally predominant, reticular pattern of hypoenhancement (Fig. 33.10) [24]. Treatment is primarily supportive, with cessation of any implicated therapy or exposures which might have triggered the toxic endothelial injury [25]. Prompt recognition and removal of the offending agent is crucial to avoiding irreversible liver damage, liver failure, and death.

FIGURE 33.10 Two different patients with sinusoidal obstruction syndrome (SOS). Imaging findings are generally nonspecific and may include heterogenous liver enhancement or edema, ascites, and splenomegaly. A reticular pattern of hypoenhancement on the delayed hepatobiliary phase of gadoxetate-enhanced MRI has been reported as a relatively specific finding of SOS. (A) T1 gadoxetate-enhanced axial MRI image of a 47-year-old woman with rectal cancer being treated with a oxaliplatin, which is known to cause hepatotoxicity and SOS. (B) Similar image in a 27-year-old man who recently underwent bone marrow transplant for leukemia.

Management of Portal Hypertension TIPS

Transjugular intrahepatic portosystemic shunt (TIPS) is a treatment for the complications of portal hypertension, which entails placement of a stent through the liver between a portal and hepatic vein, or the vena cava, allowing portalvenous inflow to bypass the liver into systemic circulation, thus lowering the portal and sinusoidal pressure and the likelihood of associated complications. Indications The primary indications for TIPS placement in the setting of cirrhosis are for secondary prevention of bleeding varices after failed first-line medical and endoscopic therapy, and for refractory large volume ascites. TIPS can also be used in the setting of life-threatening variceal bleeding if first-line therapy is unsuccessful (Fig. 33.11). TIPS can serve as a bridge to definitive management with liver transplant in any of these scenarios. TIPS is also indicated in the setting of Budd–Chiari syndrome, when direct relief of venous outflow obstruction (e.g., with thrombectomy or angioplasty) have failed or are impossible.

FIGURE 33.11 Flouroscopic digital subtraction angiography images obtained during placement of a TIPS device in a patient with cirrhosis, chronic portal-venous occlusion with cavernous transformation, and refractory bleeding of esophageal varices. Cavernous transformation necessitated cannulation of the portal system through transplenic puncture to access the splenic vein (arrowheads). (A) Initial contrast injection from the splenic vein shows the remnant portal vein (arrow) and multiple dilated, tortuous portal collaterals as well as dilated esophageal varices (asterisk). (B) Repeat injection after placement of the TIPS (arrows in B) from the right hepatic vein to the portosplenic confluence/portal vein remnant shows no filling of the varices.

TIPS has shown benefit in multiple randomized trials and meta-analyses, with overall reported success of portal decompression in over 95% of cases [26]. One of the main risks of TIPS placement is the development of hepatic encephalopathy, which occurs as ammonia and other toxins within the portal blood are shunted into systemic circulation. Other risks include heart failure from

increased preload from blood shunted into the systemic circulation, and progressive liver ischemia and failure if the liver's arterial supply is insufficient. Post-TIPS Imaging ■ Once a TIPS has been placed, it is commonly monitored for patency and evidence of failure—1 year patency rates for modern, covered stents range from 80% to 90%. USG with Doppler imaging is a noninvasive and relatively low-cost method for surveilling the TIPS device, although there is a lack of strong consensus on how it should be used [27]. At the author's institution, Doppler is performed at 24–48 hours for baseline assessment and followed up at 3 months, 6 months, and 12 months after placement, with annual follow-up thereafter ■ Doppler findings suggestive of TIPS malfunction can prompt transjugular venography and pressure gradient measurement for more precise assessment and treatment ■ The normal appearance of the TIPS on Doppler imaging includes detectable flow throughout the stent, the absence of focal aliasing artifact within the stent, flow velocities throughout the stent ranging from 90 cm/s to 190 cm/s, retrograde flow in the right and left portal veins toward the stent and flow velocity in the main portal vein >30 cm/s (Fig. 33.12) [28]. Conversely, findings at TIPS USG which are suggestive of a tips stenosis include focal aliasing within the stent, increased velocities (>190 cm/s) at the site of suspected stenosis, and reduced velocity ( 5 mm Hg; Clinically significant portal hypertension = HVPG > 10 mm Hg ■ Liver stiffness value >20 kPa and platelet count 190 cm/s at site of stenosis, velocities 40, Asian female >50, African or African-

American, family history of HCC, etc.) [57,58]. As mentioned earlier, cases of HCC have been seen in the setting of other disease process without cirrhosis, such as NAFLD; however at this time, incidence rates do not meet surveillance criteria. USG is a quick, cost-effective, and relatively harmless method for screening. Sensitivities for detecting HCC at any stage have been found to be in the low 90% range while sensitivity for early stage tumors is in the low 60% range. This increases to 70% when performing surveillance every 6 months as opposed to annually [58]. The addition of alpha-feto protein has been proposed; however, evidence supporting the benefit of AFP screening has been inconsistent as not all HCCs secrete AFP, and AFP can be elevated without HCC as well. It is recommended by the Asian professional liver societies in addition to USG, however, it is presented as an optional addition to USG by the AASLD. CT and MRI are not utilized currently in the surveillance setting given the paucity of data on their efficacy and cost-effectiveness, despite their high diagnostic performance. Abbreviated MRI examinations may play an important role in surveillance in the future as the cost and accessibility of these exams becomes more reasonable as a surveillance technique. This is especially true in situations where USG is difficult, such as truncal obesity or marked parenchymal heterogeneity. Ultrasound LI-RADS: The interpretation of surveillance US in high-risk patients can be guided by the US Liver Imaging-Reporting and Data System (LI-RADS) algorithm established in 2017. An “observation” is defined as any focal area distinct from background hepatic parenchyma and is preferred over the term “lesion,” as it does not imply a level of suspicion. There are three diagnostic categories which can be applied to each US screening examination, US-1 (negative), US-2 (subthreshold), and US-3 (positive). It is important to remember that the categorization is applied to the entire exam and not individual lesions. ■ If no observations are present, or the observation perceived is definitely benign, such as calcification, simple cyst, or previously identified hemangioma, then US-1 would be applied to this exam (Fig. 33.14) ■ If the observation detected is less than 10 mm in diameter, and not definitely benign, then US-2 would be utilized (Fig. 33.15) ■ Lastly, if the observation is larger than 10 mm in diameter and not definitely benign, or if there is a new thrombus identified in a vein, then exam would be categorized as US-3 (Fig. 33.16)

FIGURE 33.14 Ultrasound image from a patient with hepatitis B virus, who underwent HCC screening exam. There are no focal lesions in the liver, hence US-1.

FIGURE 33.15 Hyperechoic lesion identified in the posterior right hepatic lobe (segment 7) on HCC screening exam. The lesion measures up to 7 mm, consistent with US-2 lesion.

FIGURE 33.16 Slightly heterogenous, predominantly hyperechoic lesion identified on HCC screening ultrasound, measuring up to 21 mm, classified as US-3.

The threshold of 10 mm is applied between US-2 and US-3 because observations that are less than 10 mm are common, often benign, and difficult to characterize definitively on contrast-enhanced imaging. Therefore, observations resulting in US-2 categorization should be followed with a short interval US to determine if there is interval growth, especially to a degree greater than 10 mm in diameter, at which point it would warrant further evaluation with contrastenhanced imaging. If an observation is stable and smaller than 10 mm over 2 years, it can be considered benign [59]. Management for the three categories is as follows: ■ US-1 (negative): routine 6-month surveillance US ■ US-2 (subthreshold): short interval (3–6 months) surveillance US recommended ■ US-3 (positive): observation warrants multiphase contrast-enhanced exam (MR, CT, or USG)

In addition to a categorization, the exam will also receive a visualization score, ranging from A (no or minimal limitations) to C (severe limitations). With a score of A, limitations, if any are unlikely to meaningfully affect sensitivity. A score of B, moderate limitations, is applied when the limitation may obscure small masses. Finally, a score of C deems that the limitations significantly lower sensitivity for focal liver lesions. This is generally applied in situations when a majority of the liver or diaphragm is not visualized, or if there is severe heterogeneity of the liver, beam attenuation, or shadowing.

Key Pearls of Surveillance

■ Surveillance USG every 6 months recommended in anyone with cirrhosis or select noncirrhotic patients with chronic HBV infection. ■ Categories of US-1, US-2, and US-3 are given for all surveillance USG exams according to the LI-RADS criteria. ■ Visualization scores of A, B, and C are applied, depending on the amount of liver and diaphragm that is visualized and how limited the exam is in detecting liver lesions. ■ US-2 (observations 10 mm) should be further evaluated with multiphasic contrast-enhanced exam.

Diagnosis Background and Technical Considerations HCC is unique in that it is predominantly diagnosed by imaging features only, without the requirement of tissue sampling. Histopathologic confirmation of the diagnosis is avoided due to high specificity of the diagnosis through imaging and the risks and costs associated with biopsy. These include complications with the invasive procedure, as well as the low, but nonetheless concerning risk of biopsy tract seeding of approximately 2.7% [60]. First established in 2011, the LI-RADS aims to standardize imaging and reporting of studies used for the diagnosis of HCC in high-risk patients (namely, those with cirrhosis or chronic HBV, excluding a few select patients, for example, those under the age of 18 and patients with cirrhosis due to vascular causes). This classification system was initially established to be more specific in diagnosing HCC from imaging features alone and provide a high positive predictive value. A high specificity was desired because the definitive and preferred treatment in the United States for HCC is transplant, which is a great burden to undertake for the patients, providers, and healthcare system. Other countries, including Eastern countries, prefer early intervention over transplantation, likely related to the higher incidence of HBV-related HCC and better baseline liver function even in individuals presenting with HCC. Additionally, transplantation networks, resources, and coordination are often not as robust worldwide. For the early intervention treatment pathway, early detection is desired, thus exams with higher sensitivity are more prevalent often leading astray from the strict LI-RADS recommendations. Subsequent updates to LI-RADS have occurred in 2013, 2014, and 2017 with advances in knowledge and technology. In 2018, the AASLD adopted LI-RADS into their clinical practice patterns, after alterations to the system were made for it to be in line with AASLD and Organ Procurement and Transplantation Network definitions and criteria. As such, LI-RADS was updated again in 2018, with anticipated updates occurring every 3–4 years in the future.

After detection of a liver lesion on surveillance USG larger than 10 mm (US-3), or as an incidental finding on other imaging techniques, a diagnostic algorithm is initiated, resulting in a multiphase CT or MRI examination. In some cases, CT or MRI imaging examination may be used as an alternative to USG surveillance (such as difficulty with USG exams due to body habitus), in which case the screening and diagnostic exam is the same. Liver protocol multiphase contrastenhanced exams are performed with the following technical specifications guided by LI-RADS: ■ CT (eight rows of detectors or greater) ○ Required: Arterial phase (late-arterial phase preferred ∼35 seconds), portal-venous phase (∼75 seconds), and delayed phase (3–5 minutes) ○ Optional: Precontrast if patient had locoregional treatment previously, multiplanar reformats ■ MRI (1.5 or 3T with phased array torso coil) ○ Required: Unenhanced T1 in and out of phase imaging, T2-weighted imaging, T1-weighted arterial phase (late-arterial phase preferred), portal-venous phase, and delayed phase ○ Optional: Diffusion-weighted imaging, subtraction images, multiplanar acquisitions

The late-arterial phase is defined by the enhancement of the hepatic arteries and partial enhancement of the portal vein. Early arterial phase is when the hepatic arteries are the only vasculature opacified with contrast. The late-arterial phase is preferred to early arterial phase, as HCC enhances most avidly in the late-arterial phase where most of the contrast material has accumulated in the lesion. Subtraction imaging can help, especially with MRI, as intrinsic T1 signal can be separated from subtle enhancement within the lesion, which may be difficult on the raw images. Portal-venous phase subtraction can also be helpful in detecting subtle washout in the lesion, compared with background liver parenchyma, especially in lesions that have intrinsic T1 signal, perhaps from post-treatment change or internal hemorrhage. However, care must be taken when evaluating subtraction images to ensure that the lesions line up and there is no significant motion between the pre- and postcontrast images. Imaging Interpretation LI-RADS consists of several descriptive terms that an imaging abnormality in the liver can be defined with, as mentioned earlier. “Observation,” “lesion,” “mass,” and “nodule” are terms used hierarchically to describe these abnormalities. A nodule is a type of mass, a mass is a type of lesion, and a lesion is a type of observation. Thus, all nodules are observations; however, not all observations are nodules. For example, an artifact or perfusion defect in the liver would be categorized as an “observation” as there is an imaging abnormality. It would however not be further classified as a lesion, mass, or nodule as there is no pathologic abnormality appreciated. Lesions would be further categorized as mass lesions, or nonmass lesions, which include focal fat or iron deposition. Masses are space-occupying such as infiltrative cholangiocarcinoma. Nodules are masses that have spherical or ovoid margins, such as typical HCC, which would also classify as a “mass,” “lesion,” and “observation.” As a result, “observation” is used most often and is preferred to describe most imaging abnormalities in the liver [61]. Each observation is evaluated for the presence of certain features to determine the likelihood that the observation represents HCC. The major criteria (Figs. 33.17

and 33.18) that are used to favor HCC are as follows.

FIGURE 33.17 MRI of the abdomen with T1 precontrast (A), T1 arterial phase (B), T1 portal-venous phase (C), and T1 delayed phase images (D). Classic HCC near the dome of the liver with arterial phase hyperenhancement (arrow), washout on portal-venous phase (thick arrow), and enhancing pseudocapsule best seen on delayed phase (arrowhead). Note that the lesion is barely visible on the precontrast portion of the exam (circle). This lesion demonstrates the classic major features.

FIGURE 33.18 Late-arterial and delayed phase images demonstrate a segment III arterial hyperenhancing nodule (arrow in A) with washout and enhancing capsule (solid arrow in B), consistent with a LIRADS 5 lesion. Note an additional area of heterogeneity in segment IVb/V demonstrating washout on the delayed images (dashed arrow in B) without arterial hyperenhancement or enhancing capsule; LIRADS 4.

(Courtesy: Akshay Baheti, Department of Radiodiagnosis, Tata Memorial Hospital.)

Major criteria ■ Arterial phase hyperenhancement—Nonrim-like enhancement in arterial phase unequivocally greater in whole or in part than liver. The enhancing part must be higher in attenuation or intensity than background liver in arterial phase ■ Enhancing capsule—Smooth, uniform, sharp border around most or all of an observation, unequivocally thicker or more conspicuous than fibrotic tissue around background nodules, and visible as enhancing rim in portal-venous phase or delayed phase

■ Nonperipheral washout—Nonperipheral, visually assessed, temporal reduction in enhancement in whole or in part relative to composite liver tissue from earlier to later phases (with gadoxetic acid, hypointensity must be present in portal-venous phase) ○ If a nodule does not have APHE, but demonstrates reduced enhancement from earlier to later phases (i.e., on delayed phase), this would be deemed as “washout.” This feature in combination with APHE is much more specific for HCC rather than either feature alone ○ A nodule which enhances on arterial phase and has reduction in enhancement, but not below adjacent parenchyma would only be deemed as APHE, and have no “washout” ■ Threshold growth—Size increase of a mass by ≥50% in ≤6 months ○ Only applied if observation is a mass. Do not apply if lesion can be a pseudolesion such as a perfusion abnormality ○ Only applicable when comparing to a sufficient quality previous CT or MRI. Not applicable when comparing to previous contrast-enhanced ultrasound (CEUS) ○ Measure on same phase, sequence, and plane if possible

The observations are then classified into categories of LR-1 to LR-5, based on likelihood of it being HCC, with LR-1 being definite certainty of benignity and LR-5 being definite certainty of HCC (Fig. 33.19).

FIGURE 33.19 From the LI-RADS manual, this table is an easy reference to categorizes LR-3 to LR-5 observations based on the size and presence of certain imaging features [34]. In general, increase in the size and presence of major features results in a higher LR category. Note that LR-5 cannot be applied without APHE.

■ LR-1 (definite benign)—Definite cyst, hemangioma, vascular anomaly, perfusion alteration, focal scar, etc. ■ LR-2 (probably benign)—Similar to LR-1 but the appearance is highly suggestive instead of diagnostically certain. For example, atypical hemangioma. A distinctive nodule without malignant features (solid nodule 4 mm) ■ Small, contracted gallbladder ■ Cholelithiasis

Figure 35.24 Chronic cholecystitis. Sagittal view ultrasound of the gallbladder shows small, contracted gallbladder with wall thickening (between calipers), and intraluminal calculus (arrow).

MRCP shows small, contracted gallbladder and cholelithiasis. Pericholecystic edema is uncommon. MRCP is more commonly ordered to detect clinically silent concurrent CBD stones, which can be seen in 4–26% cases [45,46]. CT has no role. Differential Diagnosis Although the clinical differential diagnoses include peptic ulcer disease, irritable bowel syndrome, chronic pancreatitis, and gastroesophageal reflux disease; the imaging differential diagnosis includes causes of diffuse gallbladder wall thickening (Box 35.5). Box 35.5 Diffuse Gallbladder Wall Thickening: Differentials and Mimics Causes of the gallbladder wall thickening: ■ Acute and chronic cholecystitis ■ Ascites ■ Hypoproteinemia ■ Heart failure ■ Acute hepatitis Mimics of the gallbladder wall thickening: ■ Intraluminal sludge ■ Nonshadowing calculi Management

Medical methods aimed at dissolving the gallstones may be tried (ursodeoxycholic acid) but definitive management is elective laparoscopic or open cholecystectomy.

Xanthogranulomatous Cholecystitis Xanthogranulomatous cholecystitis (XGC) is commonly confused with the gallbladder carcinoma, both clinically and on imaging. Epidemiology XGC is uncommon but not rare, accounting for up to 1–5% of surgically resected gallbladder specimens. It is more commonly seen in women in their sixth and seventh decades, although some studies have shown male preponderance. About 80% cases are associated with gallstone, often impacted at the neck [47–49]. Pathogenesis Proposed pathogenesis of XGC involves extravasation of bile in the gallbladder wall resulting in a xanthogranulomatous response. Bile extravasation can be due to mucosal ulceration or rupture of Rokitansky–Aschoff sinus caused by calculous obstruction of the cystic duct. The mural nodules that are characteristic of XGC on imaging studies are probably lipid-containing xanthogranulomas or abscesses. Inflammation and fibrosis can involve surrounding structures which mimic gallbladder carcinoma. Carcinoma often coexist with XGC [50]. Clinical Features

Clinical features are similar to acute or chronic cholecystitis. Serum tumor marker carbohydrate antigen 19-9 (CA 19-9) can be elevated in up to 46% cases of XGC [51]. Imaging Features ■ One ultrasound, XGC shows segmental or diffuse wall thickening and hypoechoic or mixed echogenicity mural nodules are seen. Coexistent gallstones are usually seen ■ On CT, wall thickening and poorly enhancing mural nodules are seen. On contrast enhancement, the mucosa enhances and is seen as a thin, continuous layer with hypodense outer submucosal and subserosal layer. Stranding of pericholecystic fat and loss of fat plane with liver and other surrounding structures are common (Fig. 35.25) ■ On MRI, findings similar to CT are seen. Additionally MRI demonstrates the intraluminal calculus. As the mural nodules in XGC represent lipid, signal drop on opposed phase chemical shift T1-weighted images can be seen, however, this is not a common feature [52] ■ Differentiation from GBC is the biggest challenge and often the diagnosis is not made preoperatively [53]. A thick, interrupted layer of inner mucosal enhancement is more often noted in GBC. Diffuse wall thickening, presence of mural nodules and a thin, continuous mucosa is more common in XGC [52]. Image-guided fine needle aspiration may be helpful in the differentiation [50]

Figure 35.25 Xanthogranulomatous cholecystitis. (A) Oblique coronal view of upper abdomen shows thickened gallbladder wall. Note low-density areas within the gallbladder wall (arrows). (B) Axial contrast CT shows distended gallbladder with an impacted calculus at the neck and gross wall thickening. Small low attenuation areas are noted within the thickened walls (arrows).

(Courtesy: Dr. Akshay Baheti, Tata Memorial Hospital, India.) Management Laparoscopic cholecystectomy is difficult in cases of XGC and sometimes avoided because of suspicion of cancer. Open cholecystectomy can also be difficult due to dense adhesions and more extended resection of surrounding structures is often necessary. Since XGC is difficult to diagnose either preoperatively or intraoperatively, intraoperative frozen-section examination should be carried out to differentiate XGC from carcinoma of the

gallbladder. The plan of resection is decided based on the result of the frozen section.

Hyperplastic Cholecystosis Hyperplastic cholecystoses are noninflammatory pathologies of the gallbladder associated with hyperplastic thickening of the wall. It comprises cholesterolosis and adenomyomatosis of the gallbladder. Cholesterolosis Cholesterolosis is caused by diffuse deposition of cholesterol esters in macrophages of the lamina propria of the gallbladder wall that form yellowish excrescences. When it is associated with hyperemia, the mucosa resembles the skin of a strawberry (strawberry gallbladder). The diffuse form cannot be diagnosed on imaging. When cholesterol deposition forms focal polypoid lesions of size 2–10 mm, it gives rise to a cholesterol polyp and can be detected on imaging. Cholesterol polyps are the most common polypoid lesion of the gallbladder. These have no malignant potential. These polyps typically manifest as multiple small (usually 1–2 mm, always 4 mm ■ Gallbladder polyp >10 mm ■ Sessile polyp ■ Presence of irregular enlarged nodes in porta or close to celiac artery origin Box 35.7 Reporting a Gallbladder Cancer in Cross-Sectional Imaging: What the Referring Surgeon Wants to Know? (Fig. 35.29) ■ Primary gallbladder mass (size in at least two dimensions) ■ Liver invasion (segments involved, fissure for ligamentum teres involved or not) ■ Surrounding organ invasion (transverse colon, duodenum, antrum, and pancreas)

■ Biliary involvement (level of obstruction, patency of biliary confluences) ■ Vascular involvement (right and common hepatic artery, right and main portal vein) ■ Nodal involvement (operable: portal nodes, inoperable: retroperitoneal nodes) ■ Peritoneal metastases (omental nodule or caking, peritoneal nodule) ■ Other metastases (liver, adrenal, and lung) Management Definitive surgery is the only curative option, but only few patients present early enough to be operable. Radical cholecystectomy is necessary in all cancers involving muscularis propria. For tumors involving surrounding organs, liver resection and pancreaticoduodenectomy is often necessary as well. Inoperable cancers need to be palliated by biliary drainage and chemotherapy. Up to 47% patients are diagnosed with early GBC incidentally at or after gallbladder surgery for other indications [60]. Incidentally detected GBCs are often evaluated by CT to look for residual tumor, nodal involvement, and distant metastases before undergoing completion surgery. Nodes, liver, abdominal wall, and peritoneum (including ovaries) are common sites of metastatic disease. Radiologists need to be aware of this imaging indication beforehand as, in this case, the gallbladder itself will be absent.

Other Malignancies of the Gallbladder Metastases to the gallbladder most commonly result from malignant melanoma, gastric carcinoma, or renal cell carcinoma.

These are usually asymptomatic but may manifest with acute cholecystitis if the cystic duct is obstructed. Metastases from malignant melanoma, hepatocellular carcinoma, or renal cell carcinoma may manifest as polypoid lesions whereas that from gastrointestinal tract adenocarcinomas usually present as irregular gallbladder wall thickening [62]. Squamous cell carcinomas of the gallbladder are rare. Risk factors for these tumors are gallstones and parasitic infection. Biliary and bowel obstructions are common because of direct extension. Primary gallbladder melanoma is extremely rare, unlike metastatic melanoma. Primary or metastatic melanomas may show high-signal intensity on T1-weighted MR images because of the T1-shortening effect of melanin. Lymphoma of the gallbladder is also extremely rare. Low-grade lymphomas manifest as mild thickening of the gallbladder wall, and high-grade lymphomas manifest as a solid mass within the gallbladder or irregular wall thickening. A characteristic finding of lymphoma is the presence of intact mucosa with infiltration of the submucosal layer. It may be associated with periportal and para-aortic lesions [63].

Approach to a Case of Gallbladder Polyp A mass in the gallbladder wall that projects into the lumen is called a gallbladder polyp. The prevalence of gallbladder polyps detected at ultrasound of abdomen is approximately 0.3–9% [64]. Only 0.6% of these polyps turn out to be malignant [65]. A gallbladder polyp can be neoplastic in nature, or it can be a pseudotumor related to cholesterol deposition, adenomyomatosis, or inflammation (Box 35.8). A true polyp of the gallbladder is characterized by an intraluminal mass without any posterior acoustic shadowing or

comet-tail artifact in ultrasound. Presence of a comet-tail artifact indicates the diagnosis of adenomyomatosis. Box 35.8 Differential Diagnosis of a Gallbladder Polyp Common ■ Cholesterol polyps ■ Adenomyomatosis ■ Gallbladder adenocarcinoma Uncommon ■ Gallbladder adenoma ■ Metastases Mimics ■ Tumefactive sludge ■ Adherent gallstone The most important task of the radiologist is to assess the risk of malignancy of the polyp. A surgical consult for a potential cholecystectomy is recommended for polyps >1 cm in diameter, for polyps associated with symptoms of gallbladder disease, and for polyps between 6 and 9 mm if associated with other risk factors [66,67]. The high-risk factors for malignancy associated with a polyp is given in Box 35.9. Polyps between 6 and 9 mm without risk factors should be followed up with ultrasound at 6 months and then yearly up to 5 years. The American College of Radiology does not recommend follow up for asymptomatic polyps ≤6 mm [66].

However, according to the joint guidelines of European Society of Gastrointestinal and Abdominal Radiology, European Association for Endoscopic Surgery and other Interventional Techniques, and International Society of Digestive Surgery—European Federation, all polyps 1 cm) ■ Sessile polyp (including focal wall thickening >4 mm) ■ Presence of symptoms related to gallbladder ■ Age >50 years ■ Primary sclerosing cholangitis ■ Indian ethnicity (Modified from Wiles et al. [67].) Cholesterol polyps are the most common polypoid lesion of the gallbladder. Gallbladder adenomyomatosis accounts for approximately 25% of polypoid lesions of the gallbladder [54]. Gallbladder adenoma accounts for 3–7% of intraluminal polypoid lesions of the gallbladder and can display premalignant behavior [68]. Adenomas usually range in size from 5 to 20 mm. Internal vascularity at color Doppler imaging is reported. Differentiation of adenoma and adenocarcinoma is not possible with imaging studies alone.

Intracholecystic papillary neoplasms are premalignant lesions. These lesions are analogous to intraductal papillary mucinous neoplasm (IPMN) of the pancreas. It is rare with no strong association with gallstones. An associated invasive cancer is often present [69].

Bile Ducts Inflammatory Diseases of Bile Ducts Acute Bacterial Cholangitis and Cholangitic Abscess Pathophysiology:

Acute bacterial cholangitis occurs as a result of biliary obstruction and stasis, most commonly due to calculus, postoperative stricture, and malignancy. It is also called ascending cholangitis as the infecting organisms typically ascend from duodenum, most commonly E. coli, Klebsiella, and Enterococcus sp. Clinical Features:

The classic Charcot's triad (fever, abdominal pain, and jaundice) is not present in all patients. Only about 60–70% of patients have jaundice at presentation [70]. Laboratory features include leukocytosis, hyperbilirubinemia, and raised alkaline phosphatase. Most centers require imaging evidence of biliary obstruction for the diagnosis of acute cholangitis. Imaging Features

■ Ultrasound is the first and often the only imaging technique necessary for evaluation. Ultrasound shows biliary dilatation, circumferential thickening of the wall of the CBD along with the cause, and the level of obstruction. Ultrasound can also detect hepatic abscesses (cholangitic abscesses). These appear as grouped hypoechoic round lesions, often confined to a segment or a lobe of liver ■ CT is only necessary when ultrasound is unequivocal. CT shows dilated bile ducts with thickening and enhancement of the wall. Cholangitic abscesses appear as grouped centrally hypoattenuating lesions (“cluster sign”). The affected segment of liver may show perfusion abnormalities showing diffuse enhancement in arterial phase that becomes isoattenuating to the rest of the liver in portal venous phase. Individual lesions show a central low attenuation suppurative area which may contain gas, an inner enhancing hyperattenuating rim of granulation tissue, and an outer hypoattenuating rim of edema (“double rim sign”) (Fig. 35.30) [71]

Figure 35.30 Cholangitic abscess. Multiple rim-enhancing hypoattenuating rounded lesions are noted in liver (arrows). Note dilated left hepatic duct indicating biliary obstruction. Management:

Acute bacterial cholangitis is a medical emergency and requires immediate biliary drainage on antibiotic cover. In the presence of pancreaticobiliary malignancy with bile duct obstruction, abscesses can simulate metastases. Presence of fever, leukocytosis, and rim of edema surrounding the abscess on imaging are helpful features favoring an abscess.

Recurrent Pyogenic Cholangiohepatitis Recurrent pyogenic cholangiohepatitis (hepatolithiasis, oriental cholangiohepatitis) is characterized by chronic biliary obstruction, stasis, and pigment stone formation, leading to recurrent episodes of acute cholangitis. Chronic inflammation may lead to atrophy of the affected liver segment and multifocal biliary stricture. Its incidence is highest in Southeast and East Asia. The etiology is unclear. Left lateral segment of the liver is affected the most. Ultrasound shows dilated intrahepatic ducts filled with sludge and stones, confined to one or more segments of the liver. The CT scan localizes the disease better and shows dilated ducts as well as intrahepatic calculi, when they are radiodense. MRCP demonstrates the multifocal stricture involving the bile ducts and intraductal calculi with greater detail. Abrupt distal tapering of peripheral bile ducts with decreased arborization (“arrowhead sign”) and complete occlusion (“absent duct sign”) are seen in cholangiography (Fig. 35.31) [72,73].

Figure 35.31 Recurrent pyogenic cholangitis. (A) Axial T2weighted image of liver shows atrophy of left lobe of liver with focal dilatation of left hepatic duct with downstream

stricture (dotted arrow) and intraductal calculi (arrowhead). (B) Coronal T2-weighted image shows calculus within the common bile duct (arrow).

AIDS Cholangiopathy Opportunistic infection of the bile duct, with Cryptosporidium sp., Cytomegalovirus, or Pneumocystis jirovecii, results in an obliterative cholangiopathy with a picture similar to sclerosing cholangitis. Abdominal pain and cholangitis are the predominant presenting feature and endoscopic sphincterotomy may result in symptomatic and biochemical improvement.

Parasitic Infection Fasciola hepatica infection is caused by consumption of water or raw vegetables contaminated with the larva of the F. hepatica fluke. In the acute phase of the infection, the immature larvae migrate through the bowel wall into the peritoneal cavity and enter the liver through the liver capsule. Patients may present with acute abdominal pain, hepatomegaly, and prolonged fever. This migratory tract in the liver can be demonstrated in CT or MRI as a specific finding manifested by small cyst-like clusters (“cluster of grape” sign) or serpiginous tracks (“Fasciola tunnel” sign) in the peripheral subcapsular portion of the liver [74] (Fig. 35.32). In the chronic phase, the larva finally reaches the biliary tree. The mature Fasciola can be directly seen within the bile ducts on ultrasound. Living flukes can be shown within the gallbladder or bile ducts as moving structures [75].

Figure 35.32 Fasciola hepatica infection. Serpiginous tract (arrow) extending from the peripheral subcapsular portion of the liver to the central portal radicles. Clonorchis sinensis, Opisthorchis viverrini, and Opisthorchis felineus are endemic in East and Southeast Asia. The infection is acquired by ingestion of raw fish contaminated by the larvae that migrate up the bile duct, mature and live within the intrahepatic bile ducts. Ultrasound shows dilation of the peripheral portion of the intrahepatic bile ducts with normal appearing central and extrahepatic ducts. Other findings include periportal edema and sludge within the gallbladder. Chronic infection by these parasites is linked to CCA [76]. Ascaris lumbricoides infection is extremely common, predominantly involving the small bowel in children in developing countries. It may enter the biliary tree retrogradely through the

ampulla of Vater, causing acute biliary obstruction. Generally, infected patients are asymptomatic but may present with biliary colic, cholangitis, or acalculous cholecystitis. On ultrasound, most often a single worm is seen. It appears as a tube or as parallel echogenic lines within the bile ducts, simulating a biliary stent. On cross section, the worm gives a target appearance. With heavy infestation, multiple worms may be seen (Fig. 35.33).

Figure 35.33 Biliary ascariasis. (A) Percutaneous cholangiogram shows elongated filling defect suggestive of worm within the bile duct (arrow). (B) High-resolution ultrasound in a different case shows the worm in the common bile duct (between calipers) as a tubular structure simulating a tube or a stent (arrow). Hydatid cyst of liver is caused by the parasites Echinococcus granulosus and Echinococcus multilocularis. Humans are usually

infected by ingesting the ova of the parasite through contact with a dog or ingestion of food or water contaminated with a dog's feces. The ova releases the hexacanth embryo in the duodenum which is taken up by the portal circulation into the liver. On ultrasound, hydatid cysts appear as unilocular or multilocular cystic lesions with a characteristic double layer in the wall. The cyst may contain dependent and mobile amorphous echogenic foci (hydatid sand), detached endocyst (“floating membrane” sign), or several daughter cysts. The daughter cysts may give rise to a “honeycomb” or “wheel spoke” pattern on ultrasound. On CT, calcification of the cyst wall is commonly seen. Daughter cysts are seen on CT as relatively lower attenuation structures (compared with the fluid in the mother cyst) positioned peripherally within the mother cyst. Occasionally, hydatid cyst may rupture in the biliary tree. Patients may present with jaundice and fever with chills due to ensuing cholangitis. A cyst wall defect may be visible on ultrasound, CT, or MRI showing communication with a dilated bile duct (Fig. 35.34). Cyst material escaping into the bile ducts may be seen on ultrasound as echogenic linear structure without posterior acoustic shadowing.

Figure 35.34 Biliary rupture of hydatid cyst. Maximum intensity projection coronal MRCP image shows multilocular hydatid cyst with a large communication (dotted arrow) with a dilated bile duct (solid arrow).

Immunological Diseases of Bile Ducts Primary Biliary Cholangitis (Primary Biliary Cirrhosis) Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease of possible autoimmune etiology characterized by slow progression of cholestasis and the development of liver fibrosis,

eventually cirrhosis. It is commonly seen in females in their fifth to sixth decade. Patients usually present with fatigue and pruritus. On examination, jaundice and clubbing may be found. Laboratory investigations reflect cholestasis and chronic liver disease along with elevated serum antimitochondrial antibodies. The bile ducts involved in the disease are too small to be resolved by imaging and hence most findings in PBC are secondary to the development of liver fibrosis. Imaging shows changes of cirrhosis, periportal lymphadenopathy, splenomegaly, and portal hypertension. A sign described for PBC is the presence of a hypointense halo around a small portal venous branch in T1weighted, T2-weighted, and postcontrast T1-weighted images (“periportal halo sign”) [77]. However, this is not a very sensitive sign and it may also be seen in autoimmune hepatitis [78]. Primary Sclerosing Cholangitis Pathophysiology and Clinical Presentation:

PSC is a rare chronic progressive disorder characterized by inflammation and fibrotic stricture of medium and large caliber bile ducts ultimately resulting in cholestasis and liver failure. Most cases involve both intrahepatic and extrahepatic bile ducts. Up to 54% cases are associated with inflammatory bowel disease, most commonly ulcerative colitis [79]. Patients may be asymptomatic or present with altered liver function tests (elevated serum bilirubin and alkaline phosphatase). Some

cases may present with fatigue, pruritus, and jaundice. Serum pANCA is elevated in 30–80% cases [80]. Imaging Features ■ Ultrasound shows bile duct dilatation with focal areas of echogenic mural thickening, more easily seen in extrahepatic CBD. Choledocholithiasis may be present ■ MRCP is the imaging technique of choice [81]. Classic signs of PSC include short segment, band-like strictures with alternative areas of dilatation (“beaded” appearance), obliteration of the peripheral portions of the ducts (“pruned tree” appearance), and diverticular outpouching of bile ducts. Most strictures are located at ductal bifurcation (Fig. 35.35) ■ Note that due to multifocal nature of strictures, moderate to severe biliary dilatation is not commonly seen. Presence of marked biliary dilatation should make one suspicious of a developing CCA ■ Benign complications of PSC include choledocholithiasis, ascending cholangitis and cholangitic abscess. The lifetime risk of the development of CCA in PSC patients is about 10–15% [82,83]. The warning signs of the development of CCA are given in Box 35.10. Surveillance for CCA should be done imaging with either ultrasound, CT, or MRI with or without serum CA 19-9 measurement every 6–12 months. Any dominant stricture should be investigated with ERCP and brush cytology [84] ■ No definite medical management exists for PSC. Dominant symptomatic strictures can undergo endoscopic or percutaneous balloon dilatation and tissue sampling to rule out CCA. Liver

transplantation is the treatment of choice for patients with advanced liver disease

Figure 35.35 Primary sclerosing cholangitis. Endoscopic retrograde cholangiography shows characteristic multiple segmental strictures of PSC characteristically located at ductal bifurcation (arrow).

(Courtesy: Dr. Frank H. Miller, Northwestern University Feinberg School of Medicine, Chicago, USA.) Box 35.10 Warning Signs for the Development of CCA in PSC Patients

■ Rapid clinical deterioration (increasing jaundice and weight loss) ■ Dominant long segment stricture with progressive biliary dilatation ■ Obvious enhancing mass or duct wall thickening >5 mm IgG4-Associated Sclerosing Cholangitis IgG4-related disease is a rare systemic disorder characterized by tumor-like swelling of the affected organs, elevated serum IgG4 in up to two-thirds of the patients and excellent response to systemic corticosteroids [85]. Histopathological hallmarks of this entity are lymphoplasmacytic infiltrates, IgG4-positive plasma cells and varying degrees of storiform fibrosis. The biliary tract is the second most commonly involved structure after pancreas in IgG4-related disease. IgG4-associated cholangitis is predominantly seen in older men. Exact prevalence is not known. Autoimmune pancreatitis is frequently associated. Other common associations include lymphadenopathy, sialadenitis, autoimmune thyroiditis, and interstitial nephritis [86]. Obstructive jaundice is the most common presenting feature. About half of the cases have biliary stricture limited to the intrapancreatic portion of the CBD [86]. At MRCP or ERCP, long segment, continuous stricture of extrahepatic or intrahepatic bile duct associated with smooth rind of enhancing soft tissue and prestenotic dilatation is noted (Fig. 35.36). Major imaging differentials include PSC (Table 35.3) and CCA.

Figure 35.36 IgG4-associated cholangiopathy. (A) MRCP shows proximal common bile duct stricture (arrow). (B) T1weighted postcontrast axial MR, hepatic venous phase, shows subtle delayed enhancement of bile duct wall (arrow), likely representing fibrotic changes. Table 35.3 Differentiating Features of PSC and IgG4-RD Feature PSC IgG4-RD Common Ulcerative colitis Autoimmune association pancreatitis Cholangiograp hic features

Band-like strictures with beaded or “pruned tree” appearance and diverticulum formation

Long segment strictures with prestenotic dilatation

Lower CBD stricture

Less common

More common

Response to corticosteroid

No significant response

Dramatic response

From Nakazawa et al. [87,88].

Postoperative Bile Duct Injury Laparoscopic cholecystectomy is associated with more bile duct injury than open surgery [89]. Bile duct injury can present with a bile leak in the immediate postoperative period or as bile duct stricture after months to years after surgery. Bile leaks are more common [90]. The Strasberg classification classifies postlaparoscopy bile duct injury into five types based on involvement of major, minor or right aberrant bile duct and presence and level of bile duct stricture (Table 35.4, and Fig. 35.37) [91]. Table 35.4 Strasberg Classification of Bile Duct Injury (Fig. 35.37) Typ Subtyp Description e e A Bile leak from cystic duct stump or minor bile duct in GB fossa. Continuity of leakage site and main bile duct maintained. B

Ligation of aberrant right hepatic duct. No continuity with the main bile duct.

C

Leakage from aberrant right duct. No continuity with the main bile duct.

D

Lateral injury of main bile duct with bile leak.

E

Transection or stricture of the main bile duct E1

Transection or stricture >2 cm from the hilum.

E2

Transection or stricture 3 times the upper limit of normal), and ■ characteristic findings on diagnostic imaging [8].

Elevated serum amylase and lipase levels are 95% specific for the diagnosis of AP. Imaging is only required to establish the diagnosis if the first two criteria are not met and simultaneously to exclude alternative etiologies. Imaging plays a major role in the detecting late complications, helps guide treatment decisions, and elucidates the underlying cause. The two morphologic subtypes of AP include interstitial edematous pancreatitis (∼80–90%); and necrotizing pancreatitis that is characterized by pancreatic and/or peripancreatic necrosis [8].

The most common etiologies of AP are gallstones and alcohol consumption (∼80%); other causes include hypertriglyceridemia, hypercalcemia, post-ERCP, trauma, infection, toxins, medication, tumors, congenital anomalies (pancreas divisum), and idiopathic causes [9]. The underlying pathophysiology mechanisms consist of premature activation of pancreatic enzymes with associated inflammation and autodigestion of pancreatic tissue, disruption of small pancreatic ducts, and leakage of enzymes. The unencapsulated pancreas facilitates the spread of inflammation and enzyme-induced autodigestion in multiple anatomical compartments [10–12].

Imaging Classification of Acute Pancreatitis AP is divided into interstitial edematous and necrotizing morphologic subtypes based on imaging [8,13]. ■ In interstitial edematous pancreatitis, the pancreas is swollen, but the pancreatic microcirculation is intact with resultant homogenous contrast enhancement. Mild peripancreatic fat stranding and fluid are often seen. ■ Necrotizing pancreatitis is characterized by disruption of the microcirculation leading to nonenhancement of the necrotic pancreatic parenchyma. Pancreatic and peripancreatic inflammatory and necrotic changes are dependent on the severity of the episode; the imaging appearance is thus time-dependent. The degree of gland necrosis is predictive of the development of organ failure, superimposed infection, morbidity, and mortality.

Early CT within the first few days may fail to show morphological changes of necrosis and underestimate the severity of AP. Early heterogeneous pancreatic enhancement from edema may be difficult to distinguish from pancreatic necrosis, leading to the recommendation that CT should ideally be performed at least 72 hours after onset of pain [8]. In an attempt to eliminate ambiguity and improve communication between providers, the revised Atlanta classification was published to introduce a standard lexicon and terminology for AP imaging findings [8,12,14] (Table 36.1). Table 36.1 Revised Atlanta Classification of Morphologic Subtypes of Acute Pancreatitis Collection Collection After Morphologic Distribution Within the First the Fourth Subtypes 4 Weeks Week

Morphologic Subtypes

Distribution

Collection Collection After Within the First the Fourth 4 Weeks Week

Interstitial edematous pancreatitis

Necrotizin g pancreatitis

Combined pancreatic and peripancreatic necrosis (75%) Peripancreatic necrosis only (20%) Pancreatic necrosis only (5%)

Acute peripancreati c fluid collection (nonencapsu lated) (sterile or infected)

Pseudocyst (encapsulat ed) (sterile or infected)

Acute necrotic collections (nonencapsu lated) (sterile or infected)

Walled-off necrosis (encapsulat ed) (sterile or infected)

Based on the absence or presence of necrosis, acute collections in the first 4 weeks are called acute fluid collections or acute necrotic collections, respectively. The natural course of acute fluid collections varies; they can either be resorbed or persist/enlarge to become encapsulated typically over 4 weeks when fluid collections are referred to as pseudocysts, and necrotic collections are named as walled-off necrosis. All collections can be sterile or become infected, with the gas formation being the best imaging clue to suggest infection. Infected pancreatic necrosis is a severe condition that results when infection spreads from the pancreas to the peripancreatic tissues, retroperitoneum, and peritoneum in patients with acute necrotizing pancreatitis. Mimickers of an abscess include fistulization to the gastrointestinal tract and introduction of gas from previous interventions. In the absence of gas, differentiation of infected from noninfected collections is only possible by sampling. The revised Atlanta classification also advocates that ambiguous terms such as pancreatic abscess, acute pseudocyst, and intrapancreatic pseudocyst should be avoided; other authors have advocated for the use of a structured reporting template [12].

Imaging of Acute Pancreatitis Imaging is not required to make the diagnosis of AP. CECT is the first-line technique and considered the primary workhorse for comprehensive, initial assessment of AP [15]. Radiography

Radiographs play a limited role in the evaluation of AP. Abdominal radiographs may demonstrate a sentinel bowel loop due to localized small bowel ileus or the colon cut-off sign due to spasm of the left hemi-colon. Chest radiographs may demonstrate pleural effusions (typically on the left), elevation of the left hemidiaphragm, basal atelectasis, and in severe cases, noncardiogenic edema in the setting of acute respiratory distress syndrome. Ultrasonography Ultrasonography (USG) imaging of AP is of limited value. Imaging findings range from normal to focal or diffuse enlargement of the pancreas with hypoechoic changes because of edema or necrosis. USG allows for visualization of complications of AP such as peripancreatic fluid collections, ascites, and vascular thrombosis or pseudoaneurysm. However, the main role of USG is to evaluate for alternative etiologies of an acute abdomen in equivocal cases, and in the presence of AP, to identify gallstones as a possible etiology, and to evaluate for choledocholithiasis, which would prompt referral to ERCP. USG could be used to monitor peripancreatic fluid collections, differentiate fluid-filled collections, and could aid as guidance for diagnostic or therapeutic interventions [16]. Computed Tomography Interstitial edematous pancreatitis may demonstrate mildly heterogeneous enhancement of the pancreas, which should not be mistaken for pancreatic necrosis [12] (Fig. 36.20). In more severe cases, pancreatic necrosis develops in the form of distinctly hypoenhancing areas, often with surrounding acute necrotic fluid collections (Fig. 36.21). The fluid typically tracks along fascial planes and accumulates in the anterior and posterior pararenal space and in the lesser sac. CECT is the technique of choice for the evaluation of AP and its complications, which includes superinfection of collections, vascular complications, fistula formation, disconnected or disrupted duct secondary to necrosis, and additional extrapancreatic complications such as splenic and renal infarcts (Figs. 36.22–36.27) (Table 36.2). Hemosuccus pancreaticus is defined as bleeding from the pancreatic duct into the gastrointestinal tract through the ampulla of Vater and is commonly caused by the rupture of the pseudoaneurysm of a peripancreatic vessel into pancreatic duct or pancreatic pseudocyst in the context of pancreatitis or pancreatic tumors.

FIGURE 36.20 Acute interstitial edematous pancreatitis in three different patients. (A) Axial contrast-enhanced CT image of the pancreas shows mildly bulky pancreas with significant peripancreatic stranding (arrows). The pancreas is normally enhancing, and the splenic vein is patent. The modified CT severity index is 2, suggestive of mild pancreatitis. (B) Axial contrast-enhanced CT image 2 days after onset of symptoms demonstrates a heterogeneously enhancing pancreatic parenchyma with peripancreatic fluid collection (arrows). The modified CT severity index is 4 suggestive of moderate pancreatitis. The subsequent CT studies (not shown here) demonstrated normal enhancement of the pancreas with complete resolution of the peripancreatic fluid. These findings are consistent with acute peripancreatic fluid collection in a patient with interstitial edematous pancreatitis. (C) Axial contrast-enhanced CT image of the pancreas obtained 7 weeks after the symptom onset shows a well-defined peripancreatic fluid collection (arrow) consistent with a pseudocyst.

FIGURE 36.21 Necrotizing pancreatitis in four different patients. (A) Axial contrast-enhanced CT image 3 days after onset of symptoms demonstrates necrotizing pancreatitis with heterogenous appearance of the pancreas with predominant peripancreatic necrosis (arrow). (B) Axial contrast-enhanced CT image 10 days after onset of symptoms demonstrates a heterogeneously hypodense fluid collection in the body of the pancreas (arrow) in keeping with predominant pancreatic parenchymal necrosis resulting in an acute necrotic collection in the setting of necrotizing pancreatitis. (C and D) Necrotizing pancreatitis with combined pancreatic and peripancreatic necrosis. Axial (C) and coronal (D) CT images of the abdomen 20 days after onset of symptoms demonstrate combined pancreatic and peripancreatic necrosis with acute necrotic collections in the tail of the pancreas (arrow) and in the peripancreatic region (arrowheads). The modified CT severity index is 6 suggestive of moderate pancreatitis.

FIGURE 36.22 Pseudoaneurysm as a complication of necrotizing pancreatitis. Axial contrast-enhanced CT image of the pancreas shows an acute necrotic collection in the pancreatic uncinate process with a pseudoaneurysm arising from the gastroduodenal artery (arrow).

FIGURE 36.23 Splenic vein thrombosis as a complication of necrotizing pancreatitis. Axial contrast-enhanced CT image of the pancreas shows thrombosis of the splenic vein (arrow) secondary to extensive necrotizing pancreatitis and peripancreatic necrosis.

FIGURE 36.24 Colonic fistula as a complication of acute necrotizing pancreatitis (A and B). Axial (A) and coronal (B) contrast-enhanced MR images of the abdomen demonstrate necrotizing pancreatitis with walled-off necrosis in the tail (arrow) and fistulous communication with splenic flexure of the colon (arrowhead).

FIGURE 36.25 Infected pancreatic necrosis and emphysematous pancreatitis in two different patients. (A) Axial contrast-enhanced CT image of the abdomen shows significant pancreatic and peripancreatic necrosis with multiple air locules (arrow). Note that there is no fistulous communication with the bowel loops, which is the other possible differential for the presence of air. These findings are consistent with infected pancreatic/peripancreatic necrosis. (B) Coronal unenhanced CT image of the abdomen shows significant amount of air replacing the pancreatic parenchyma (arrowheads) consistent with emphysematous pancreatitis.

FIGURE 36.26 Pancreatic duct disruption in patient with acute necrotizing pancreatitis. (A) Axial contrast-enhanced CT image of the abdomen shows a large cystic lesion (arrow) in the body of the pancreas. (B) Coronal 3D MRCP images depict a large cystic lesion in the body of the pancreas (arrow) with associated dilated main pancreatic duct in the tail and body of the pancreas (arrowhead). These findings are consistent with duct disruption due to necrotizing pancreatitis.

FIGURE 36.27 Hemorrhagic pancreatic pseudocyst and hemorrhagic pancreatitis in two different patients. (A) Axial T1-weight MR image of the pancreas shows a T1 hyperintense cystic lesion in the pancreatic body (arrow) suggestive of hemorrhagic pancreatic pseudocyst. (B) Axial T1weight MR image of the pancreas shows diffusely T1 hypointense pancreas with heterogenous T1 hyperintense areas (arrowheads) suggestive of hemorrhagic acute pancreatitis.

Table 36.2 Complications of Acute Pancreatitis ■Superinfection of collections (typically in the setting of necrotic collections) ■Vascular complications ○ Hemorrhage ○ Pseudoaneurysm ○ Hemosuccus pancreaticus (wirsungorrhagia) ○ Splenic vein thrombosis and secondary perigastric varices ■Disconnected/disrupted duct secondary to necrosis ■Fistula formation ■Extrapancreatic infarcts and ischemia (spleen, kidneys, and bowel loops)

CT is also useful in monitoring peripancreatic collection and can guide intervention. Limitations of CT include limited ability to characterize internal content of peripancreatic collections, the ability to detect gallstones, and ionizing radiation. In an attempt to limit radiation exposure, CT should only be repeated in case a patient demonstrates pyrexia which may indicate superinfection of collections or bowel perforation, sudden clinical deterioration (in the setting of circulatory shock for example which may indicate hemorrhage), and when intervention is planned [17]. The CT severity index (CTSI) was developed to assess the severity of AP and is based on findings from a CECT by evaluating the Balthazar score (grading of pancreatitis) and the extent of pancreatic necrosis [18]. This has been updated to

the modified CT severity index (MCTSI) in 2004 to include pancreatic and peripancreatic inflammation, pancreatic necrosis as well as extrapancreatic complications, which includes one or more of the following: pleural effusion, ascites, vascular complications, and/or gastrointestinal involvement [19]. These indices are used to grade AP into mild, moderate, and severe forms and have been shown to correlate well with patients' clinical outcomes and can assist the clinician by providing valuable prognostic information (Table 36.3). Table 36.3 Modified CT Severity Index Prognostic Points Indicator Pancreatic inflammati on

Normal pancreas Intrinsic pancreatic abnormalities with or without inflammatory changes in peripancreatic fat Pancreatic or peripancreatic fluid collection or peripancreatic fat necrosis

0 2 4

Pancreatic necrosis

None Equal to less than 30% More than 30%

0 2 4

Extrapancr eas complicati ons

One or more of the following: pleural effusion, ascites, vascular complications, and/or gastrointestinal involvement

2

Modified CTSI 0-2: Mild pancreatitis. Modified CTSI 4-6: Moderate pancreatitis. Modified CTSI 8-10: Severe pancreatitis. Magnetic Resonance Imaging MRI can also be utilized to evaluate for the presence of pancreatic inflammation and/or necrosis, disease severity, the extent of retroperitoneal involvement as well as the underlying cause. MRI can detect more subtle cases of interstitial edematous pancreatitis as well as better characterize hemorrhage and necrosis due to its multiparametric nature compared with CT. Pancreatic edema and hemorrhage are best depicted on unenhanced T1-W images (Fig. 36.27) [20]. T2-W images are superior to CT in evaluating the internal content of peripancreatic fluid collections by demonstrating necrotic debris, which would typically necessitate necrosectomy at the time of the drainage procedure, possibly justifying an ancillary role for MRI to CT when intervention is contemplated (Fig. 36.28). Hemorrhage indicates a worse prognosis and is best

depicted as a high signal on T1 images (Fig.  36.27). Both MRI and CT are helpful in characterizing different fluid collections in AP. Both acute peripancreatic fluid collection and pseudocyst develop in peripancreatic region and contain homogenous fluid density, the former has no fully definable wall, and the latter contains a well-defined wall. In a similar fashion, acute necrotic collection, and walled-off necrosis both have heterogenous internal contents with hemorrhagic/necrotic debris; however, the former has no fully definable wall, and the latter has well-defined wall (Figs. 36.20, 36.21, 36.27, and 36.28). On MRCP, ductal disruption should be suspected when there is a discontinuity of the duct in an area of ≥2 cm pancreatic necrosis and viable upstream pancreatic tissue (Fig. 36.26) [21]. This can be confirmed with the extravasation of contrast on ERCP. MRI is particularly useful in pregnant and young patients as well as patients requiring multiple imaging studies. ACR appropriateness criteria discuss the role and timing of different imaging techniques in the evaluation of AP [22]. Although USG is usually appropriate as the initial examination in suspected AP with elevated lipase/amylase early on (less than 48–72 hours of symptom onset), CECT abdomen and pelvis or MRI abdomen with MRCP are useful in patients with equivocal symptoms/laboratory findings, more than 72 hours of symptoms onset and critically illpatients [22]. In addition, CECT/MRI is helpful for followup, assessing complications, and treatment response [22].

FIGURE 36.28 Role of MRI in differentiating pseudocyst from walled-off necrosis. (A) Pseudocyst: axial T2-weighted image of the pancreas shows a well-defined, uniformly T2 hyperintense cystic lesion in the peripancreatic region (arrow) without any identifiable T2 hypointensity. (B) Walled-off necrosis: axial T2-weighted MR image demonstrates T2 hypointense necrotic debris (arrow) with greater conspicuity in a postpancreatitis collection. The presence of necrotic debris may influence treatment decision-making (endoscopic cystogastrostomy with or without necrosectomy).

Prognosis and Management of Acute Pancreatitis

Predicting the severity of AP is critical for patient management. The two principal forms differ greatly in terms of mortality, being less than 1% in patients with interstitial edematous pancreatitis and range from 15% to 30% in patients with necrotizing pancreatitis, emphasizing the importance of early clinical identification of these subgroups to start an aggressive therapeutic approach to prevent mortality [23]. The therapy of interstitial edematous pancreatitis is mainly supportive with fluid resuscitation to maintain vital functions often being successful. The management of severe necrotizing pancreatitis is more complex requiring a multidisciplinary approach [23]. Prophylactic antibiotics are not indicated unless there are signs of infection. During the late phase, starting around days 7–10, patients with clinical suspicion of superinfection of peripancreatic collection should undergo percutaneous sampling to evaluate for infection [23]. Patients with infected necrosis require treatment with the appropriate antibiotics and debridement of infected necrosis. The timing of debridement is dependent on the clinical condition of the patient. There is a trend to delay debridement until it has been walled-off with debridement options including percutaneous and endoscopic techniques, minimally invasive and laparoscopic surgical techniques, and sometimes even traditional surgery to deal with the complications of the disease process. Lastly, it is recommended that patients with gallstones found on imaging undergo cholecystectomy before discharge [23].

Chronic Pancreatitis (CP) Pathophysiology and clinical presentation. CP is a progressive and prolonged inflammatory disease characterized by irreversible parenchymal fibrosis and atrophy, leading to endocrine and exocrine pancreatic dysfunction. The most common cause of CP is a long history of moderate to heavy alcohol consumption [9]. Additional causes include malnutrition, hyperparathyroidism, hyperlipidemia, trauma, cystic fibrosis, autoimmune diseases, smoking, pancreas divisum, and recurrent AP. In approximately a third of cases, no cause is identified, and CP is considered idiopathic [24]. The chronically inflamed pancreas becomes fibrotic and demonstrates loss of acinar tissue, which manifests over time in the form of morphologic changes such as ductal dilation, ductal irregularity, parenchymal atrophy, and intraductal stones and calcifications [25]. Clinical manifestations include chronic abdominal pain, weight loss, malabsorption (exocrine dysfunction), and type 3c diabetes mellitus (endocrine dysfunction). Tropical pancreatitis is a type of CP that usually occurs in young individuals in tropical countries and involves the main pancreatic duct resulting in multiple large ductal calculi. Although etiology is not well understood, environmental factors, and SPINK1 gene mutation [26]. Steatorrhea, abdominal pain, and diabetes are commonly seen, and malignant transformation is more frequent than in CP.

Imaging Features Radiography. Abdominal radiographs may reveal pancreatic calcifications projecting over the mid-abdomen at the L1-L2 level in the expected location of the pancreas (Fig. 36.2). Ultrasonography. USG may demonstrate parenchymal atrophy, hyperechoic changes indicating fibrosis, pancreatic calcifications, pancreatic ductal irregularity, and dilation (Fig. 36.29). Sequelae of CP such as pseudocysts, pseudoaneurysms, thrombosis as well as ascites may be seen with ultrasound.

FIGURE 36.29 USG appearance of chronic pancreatitis. (A) Transabdominal grayscale USG image of the abdomen shows atrophic pancreatitis with dilated main pancreatic duct (arrows) and a large intraductal stone (arrowhead). (B) Corresponding axial CT image shows severely atrophic pancreas with dilated main pancreatic duct (arrow). These findings are consistent with chronic pancreatitis. USG, ultrasonography.

Computed Tomography Although CT is limited in the early diagnosis of CP, it is useful to diagnose advanced disease and its complications. ■ CT findings of CP include changes in size, shape, contour, dilatation, and irregularity of the main pancreatic duct, pancreatic calcifications, and pseudocysts (Fig. 36.30) [27]. ■ Pancreatic calcifications develop due to calcium carbonate deposition in inspissated intraductal protein plugs predominantly located in peripheral side branches [28,29].

FIGURE 36.30 Chronic pancreatitis. Axial unenhanced CT demonstrates extensive coarse pancreatic calcifications (arrows) in an atrophic pancreas, typical of chronic pancreatitis.

Tumefactive CP (mass-forming CP) is reported in up to 30% of patients with CP and is most common in the head of the pancreas [30]. Features that favor an inflammatory process over cancer are evidence of CP (pancreatic calcifications and pseudocysts), lack of displacement of calcifications, and the absence of abrupt duct cutoff discussed under MRCP later [29]. As the incidence of pancreatic cancer is higher in CP, the differentiation between cancer and CP is even more difficult. FDG PET/CT may be helpful in select patients to identify pancreatic cancer in the background of CP [31]. Magnetic Resonance Imaging MRI exceeds other imaging techniques in its sensitivity of the diagnosis of early CP while accomplishing morphologic (parenchymal and ductal) and functional imaging [32]. Loss of acinar cells, which precede ductal changes in CP, is best seen as decreased T1 signal on T1-W fat-saturated precontrast images. Recently T1 mapping has been introduced as a quantitative technique for the evaluation of suspected mild CP, and it may be a more reliable method compared with conventional T1WI. Other advanced MRI techniques such as MR extracellular volume fraction calculation and MR elastography have also shown promising results in the early detection of CP. ■ MRCP allows for a detailed evaluation of the ductal manifestations of CP, including duct ectasia of side branches, main duct dilatation, strictures, and irregularities (chain-of-lake appearance), intraductal stones, and intraparenchymal cyst formation, which could be graded using the Cambridge classification (Figs. 36.31 and 36.32). This classification is used clinically in some

institutions and is based on abnormal side branches and main pancreatic duct and has five grades. Note that dilated main pancreatic duct indicates moderate to severe CP [29]. ■ The Consortium for the Study of CP, diabetes, and pancreatic cancer published a consensus document with new cross-sectional imaging feature definitions and standardized reporting recommendations for CP in an attempt to standardize the approach to diagnosis and disease severity assessment, which could also assist in longitudinal assessment in clinical trials [29,33]. ■ The important imaging findings to comment in CP patients include parenchymal thickening/contours, parenchymal calcifications, main pancreatic duct caliber/contour/strictures and intraductal calculi, side ductal morphology and dilatation, T1 signal intensity ratio, parenchymal enhancement ratio, and secretin enhanced MRCP observations [29].

FIGURE 36.31 Chronic pancreatitis. (A) Axial T1-weighted fat-saturated MR image demonstrates decreased intrinsic T1 signal of the pancreas in keeping with chronic pancreatitis (arrow). (B) Axial T1-weighted postcontrast fat-saturated MR image during delayed phase demonstrates increased enhancement (arrow) secondary to underlying fibrosis.

FIGURE 36.32 Chronic pancreatitis with intraductal calculi. Axial T2weighted MR image of the pancreas demonstrates changes of chronic pancreatitis with multiple T2 hypointense intraductal calculi (arrow).

Ductal changes could be augmented by hormonal stimulation of the pancreas by intravenous secretin administration [34]. Secretin stimulates the secretion of bicarbonate-rich fluid into the pancreatic ductal system and induces spasm of the sphincter of Oddi. Secretin simulation allows for the assessment of the exocrine function of the pancreas by evaluating duodenal filling by quantitative and semiquantitative methods (Fig. 36.33). Improved duct visualization with MRCP has led to the description of additional imaging features to assist in the previous conundrum of differentiating mass-forming CP from pancreatic cancer. ■ In addition to CT imaging features discussed earlier, the described MRCP features favoring massforming CP include the “duct penetrating sign” (referring to an unobstructed pancreatic duct penetrating a mass-like lesion; however, the duct often has mild smooth tapering) and the “attraction sign” (referring to the CBD being attracted or pulled into the inflammatory mass, if located in the pancreatic head). In contrast, the “corona sign” (referring to obstructed side branches being displaced by the pancreatic mass) and the well-known “double duct sign” (simultaneous dilation of the CBD and pancreatic duct) favor pancreatic cancer [35] (Fig. 36.34).

FIGURE 36.33 Role of secretin MRCP in the evaluation of chronic pancreatitis. (A) Presecretin MRCP image demonstrates mildly prominent main pancreatic duct with a few dilated side branches (arrow) which is equivocal for chronic pancreatitis. Also, note fluid is seen in the third part of the duodenum (arrowhead). (B) Delayed postsecretin MRCP 10 minutes after the secretin administration demonstrates the main pancreatic duct and the dilated side branches with more conspicuity (white arrows) and pancreatic secretions reach the fourth part of the duodenum and beyond (arrowheads) consistent with chronic pancreatitis with good pancreatic exocrine reserve.

FIGURE 36.34 Role of MRI and MRCP in differentiating chronic pancreatitis from pancreatic ductal adenocarcinoma (PDAC). (A) MRCP image demonstrates the “duct penetrating sign,” which refers to the pancreatic duct penetrating a mass-like lesion with smooth tapering (white arrow) with dilated main pancreatic duct with side branch ectasia (arrowheads) and the “attraction sign” which refers to the common bile duct being attracted or pulled into an inflammatory mass in the pancreatic head. These findings favor chronic pancreatitis. (B) MRCP image demonstrates the “double duct sign,” which refers to simultaneous dilation of the main pancreatic duct (arrowhead) and common bile duct due to a mass in the head of the pancreas (arrow). Other MRCP sign that favors malignancy is the “corona sign,” which refers to obstructed pancreatic side branches being displaced by the pancreatic mass (image not shown).

Variants of Chronic Pancreatitis Autoimmune Pancreatitis Pathophysiology and clinical presentation. Autoimmune pancreatitis (AIP) is characterized by chronic, relapsing, tumefactive, and steroid-responsive pancreatitis associated with immune dysregulation. AIP shows typical clinical, imaging, laboratory, and histopathology findings. Two subtypes have been described: type 1 AIP (lymphoplasmacytic sclerosing pancreatitis) and type 2 AIP (idiopathic duct-centric pancreatitis or granulocytic epithelial lesionpositive pancreatitis). These two subtypes are fundamentally two different diseases that display significant differences in demography, serology, multiorgan involvement, and disease relapse rates [36]. Type 1 AIP is a prototype IgG4related disease with elevated serum/tissue IgG4 levels, whereas type 2 AIP lack definitive serologic markers. Patients typically present with obstructive jaundice. Diagnostic criteria were proposed by the International Association of Pancreatology in 2010, which includes five cardinal features of AIP: imaging of the pancreatic parenchyma, serology, other organ involvement, pancreatic histology, and an optional criterion of response to corticosteroid therapy [37].

Imaging of Autoimmune Pancreatitis

■ On imaging, pancreatic involvement can be focal, multifocal, or diffuse (more common). A diffusely “swollen” pancreas resembling a “sausage” and associated peripancreatic fibroinflammatory “halo” are characteristic findings of AIP (Fig. 36.35). ■ AIP demonstrates progressive and delayed enhancement on CT and MRI as well as restricted diffusion on diffusion-weighted images [38]. ■ The focal form of AIP most commonly occurs in the head of the pancreas and may be difficult to distinguish from pancreatic cancer. ■ Imaging features favoring AIP over cancer include the “duct penetrating sign,” milder upstream main duct dilation, skipped duct strictures, delayed enhancement of pancreatic parenchyma, low ADC values on MRI, and presence of another organ involvement [38] (Fig. 36.36).

FIGURE 36.35 Autoimmune pancreatitis (IgG4-related disease) in two different patients. (A) Axial T2-weighted MR image demonstrates an edematous sausage-shaped pancreas with peripancreatic T2 hypointense rim and mildly dilated main pancreatic duct (arrow). These findings are diagnostic of autoimmune pancreatitis. (B) Axial contrast-enhanced CT image of the abdomen shows a diffusely hypodense, sausage-shaped edematous pancreas consistent with autoimmune pancreatitis.

FIGURE 36.36 Autoimmune pancreatitis (IgG4-related disease). (A) Axial T2-weighted MR image demonstrates mildly hyperintense appearance of the pancreas (arrow) and a stricture (arrowhead) in the pancreatic duct. (B) There is marked restricted diffusion restriction, predominantly in the pancreatic tail region on DWI (arrow). These findings are diagnostic of autoimmune pancreatitis.

Paraduodenal Pancreatitis Pathophysiology and clinical presentation. Previously known as groove pancreatitis and cystic dystrophy of the duodenal wall, paraduodenal pancreatitis is a distinct variant of CP that involves the groove between the head of the pancreas, the duodenum, and the common bile duct [39,40]. Presumed increased viscosity of pancreatic secretions caused by excessive alcohol consumption leads to stone formation and duct obstruction. Two forms of paraduodenal pancreatitis have been described: a “pure form” that exclusively involves the groove and a “segmental form” which involves the groove with spillage into the adjacent pancreatic head.

Imaging of Paraduodenal Pancreatitis ■ On CT/MRI, the most characteristic finding is a sheet-like, curvilinear soft-tissue mass centered in the pancreaticoduodenal groove, often with typical adjacent duodenal wall thickening and cystic change (Fig. 36.37) [39,40]. The soft tissue appears as a hypoenhancing mass on CT with occasional calcifications. ■ On MRI, the soft tissue centered in the groove is typically hyperintense on T2-WI in the acute or subacute phase due to edema and may become more hypointense on T2-WI as fibrosis sets in. Thickening of the duodenal wall with the associated cystic change, when present, is well depicted on T2-WI (Fig. 36.38) [39,40]. ■ On postcontrast imaging, the soft tissue demonstrates initial peripheral enhancement with gradual centripetal enhancement on more delayed imaging. There may be narrowing of the CBD and pancreatic duct with a widening of the space between the CBD and duodenal lumen best depicted on MRCP images. It is important to differentiate the segmental form of paraduodenal pancreatitis that involves the pancreatic head from pancreatic cancer, with abrupt CBD cutoff and vascular invasion favoring malignancy [39,40].

FIGURE 36.37 Paraduodenal (“Groove”) pancreatitis. Axial contrastenhanced CT image of the pancreas demonstrates sheet-like, curvilinear soft-tissue thickening in the pancreaticoduodenal groove (white arrow) consistent with paraduodenal or groove pancreatitis.

FIGURE 36.38 Paraduodenal (“Groove”) pancreatitis. (A–C) Axial T1weighted (A), T2-weighted (B), and contrast-enhanced T1-weighted (C) MR images of the pancreas demonstrate an ill-defined T1 hypointense and T2 hyperintense lesion with associated fat stranding in the pancreaticoduodenal groove (arrowheads) in between the duodenum (triangle) and head of the pancreas (arrows). These findings are consistent with paraduodenal or groove pancreatitis.

Hereditary Pancreatitis HP refers to genetic disorders that are characterized by mutations involving PRSS1 or SPINK1 genes that predispose patients to early onset (before 20 years

of age) and symptomatic pancreatitis [9]. PRSS-1-related disease typically presents with recurrent idiopathic AP in childhood with frequent progression to CP. The hallmark of the disease is large ductal calcifications with resultant ductal dilation seen in adolescent patients, often with a positive family history. There is an associated 50–70-fold increased risk of pancreatic adenocarcinoma; about 30–40% of patients with HP will develop cancer by the age of 70 years, particularly among smokers [9].

Pancreatic Neoplasms Pancreatic neoplasms can be subclassified into solid and cystic pancreatic tumors. Solid tumors can be further categorized into exocrine tumors, endocrine tumors, mesenchymal, and miscellaneous tumors (Fig. 36.39).

FIGURE 36.39 Classification of solid pancreatic neoplasms. SPT, solid pseudopapillary tumor.

Pancreatic Ductal Adenocarcinoma Pathophysiology and clinical presentation. Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer, a highly lethal malignancy with a 5-year survival rate of 4% [41]. Risk factors include hereditary syndromes (HP, Peutz–Jeghers syndrome, Familial atypical mole and

melanoma syndrome, Hereditary nonpolyposis colon cancer [Lynch syndrome], Hereditary breast and ovarian cancer syndromes, Ataxia-telangiectasia, Li– Fraumeni syndrome), smoking, CP, obesity, and long-standing diabetes mellitus. The high mortality rate of PDAC is attributed to the aggressive phenotype, combined with an indolent presentation. PDAC most commonly presents with nonspecific symptoms, including weight loss, abdominal pain, back pain, jaundice, and nausea; PDAC may also present with a new diagnosis or exacerbation of diabetes mellitus [42]. Over 90% of cases are diagnosed in stage III or stage IV with local invasion or distant metastases, limiting the treatment options [42]. The National Comprehensive Cancer Network (NCCN) classification into resectable, borderline resectable, and unresectable disease (Table 36.4) combined with the tumor/node/metastases staging system, determines the treatment options and prognosis. Surgical resection with negative margins is the only potentially curative treatment option [43]. The tumor marker CA19-9 (carbohydrate antigen 19.9) is frequently elevated in PDAC with a sensitivity of 80% and a specificity of 73%. The marker is used to assess treatment response in known cases and for surveillance, as opposed to as a screening tool. Table 36.4 National Comprehensive Cancer Network Criteria Defining Resectability Status of Pancreatic Adenocarcinoma [43] Arteri Veins es Resectable

No contact with the CA, SMA, or CHA

No contact with the SMV, PV, or venous abutment without contour irregularity

Borderline resectable

He ad or un cin ate pr oc ess

SMV/PV encasement or contour deformity (e.g., tear drop) or tumor thrombus, allowing for safe resection and reconstruction. IVC abutment

Abutment of the CHA without extension to the CA or HA. Abutment of SMA

Other

Arteri es Bo dy or tai l

Veins

Other

Abutment of CA

Encasement of CA without the involvement of aorta or GDA (permitting modified Appleby procedure) Unresectable/l ocally advanced

Encasement of SMA or CA

Tumor involvement or occlusion of SMV/PV that cannot be reconstructed

Dist ant meta stase s

Tumor contact with CA and aortic involvement CA, celiac axis; CHA, common hepatic artery; GDA, gastroduodenal artery. Abutment: tumor/vascular contact ≤180°, encasement: tumor/vascular contact >180° or vascular deformity; PV, portal vein; SMA, superior mesenteric artery; SMV, superior mesenteric vein.

Imaging Features ■ Pancreatic protocol CT is the primary technique for diagnosis and staging of PDAC. PDAC commonly appears as an infiltrative hypoattenuating mass with associated ductal obstruction and frequent stenosis/thrombosis of adjacent veins (Fig. 36.40) [44]. Extrapancreatic spread around the neighboring veins and arteries determines the feasibility of satisfactory surgical resection. ■ The remarkable proclivity of PDAC for perineural involvement and invasion of small veins are postulated to be a major determinant of advanced local disease, frequent liver metastases, and high rates of local disease recurrence. Delayed enhancement of the tumor is attributed to its characteristic dense desmoplastic stroma. ■ However, CT is inferior to multiphasic MRI in the evaluation of tumors that are “isodense” to the parenchyma as well as small (4 cm, MCNs with aggressive features on imaging studies, and in symptomatic patients. Long-term surveillance may be indicated in asymptomatic patients with smaller MCNs. Surveillance protocols vary from different institutions. However, annual imaging with either CT/MRI is commonly performed if the lesion is not resected. ■ EUS-guided biopsy is recommended in patients with suspicious findings and interval increase in size. Faster growth rates of MCNs have been observed in pregnant women that may prompt close monitoring in this patient cohort. ■ The prognosis of malignant MCNs is better than PDAC; 5-year survival rates vary from >60% in patients with invasive cystadenocarcinomas to 100% in patients with noninvasive tumors [55– 57].

FIGURE 36.55 Multimodality imaging findings of mucinous cystic neoplasms (MCNs) of the pancreas in different patients. (A) Color Doppler image of the pancreas in a 44-year-old woman shows a well-defined cystic lesion in the pancreas that demonstrates echogenic debris (arrow) and peripheral solid components with increased vascularity. (B) Axial CT image of the pancreas in a 39-year-old woman shows a pancreatic cystic lesion with multiple internal septations (arrow). (C and D) Axial T2-weighted (C) and contrast-enhanced T1-weighted MR images of the pancreas in a 49year-old woman show a cystic pancreatic lesion (arrow) with multiple septations (arrowheads) and a peripheral solid component (arrowheads). These features are somewhat characteristic of pancreatic MCN.

Solid Pseudopapillary Tumor of the Pancreas

Solid pseudopapillary tumor (SPT), also called solid pseudopapillary epithelial neoplasm, is an uncommon solid cystic neoplasm, accounting for 1–2% of all exocrine tumors [58]. Also referred to as the “daughter tumor,” it predominantly occurs in young women in the second and third decades of life [47], with a mean age of 25 years [56,59]. MCN (“mother tumor”) affects middle-aged women, and SCA (“grandmother tumor”) occurs in older women [59]. SPT shows a predilection for Asian and African-American women [58,60]. Clinically, SPT is often asymptomatic; nonspecific symptoms such as abdominal pain and mass may be seen [55,60]. Imaging Features ■ SPT typically presents as a large, well-encapsulated pancreatic mass, with an average diameter of 8 cm [58]. On CT, it manifests as a heterogeneous mass with solid and cystic components, frequently containing foci of hemorrhage and necrosis. The pancreatic duct is typically not dilated (Fig. 36.56) [56,58,61]. ■ Peripheral calcifications may be present. On MRI, signal intensity is variable; foci of hyperintensity on T1-W sequences suggest hemorrhage or high protein content. Fluid/fluid levels are identified in up to 18% of cases (Fig. 36.56) [57,59]. There is typically early heterogenous and slowly progressive enhancement with gadolinium contrast [61]. ■ SPT has a good prognosis, with low malignant potential. Surgical resection is curative in more than 80% of cases [58,59]. However, up to 15% of cases are malignant at presentation [55,58,60]. Malignant tumors are more likely to affect older and male patients.

FIGURE 36.56 Solid pseudopapillary tumor (SPT) of the pancreas in two different patients. (A) Coronal contrast-enhanced CT image of the pancreas in a 24-year-old woman shows a mixed solid cystic mass arising from the head/uncinate process of the pancreas (arrow) with peripheral calcifications (arrowhead). (B–D) Color Doppler image (B), axial T2-weighted (C), and T1-weighted (D) MR images of the pancreas in a 27-year-old woman show a predominantly solid, isoechoic mass with mixed signal intensities on T1and T2-weighted images (arrows). These findings are consistent with SPT of the pancreas.

Intraductal Papillary Mucinous Neoplasm Pathophysiology and clinical presentation. Intraductal papillary mucinous neoplasms (IPMNs) are characterized by intraductal papillary growth, abundant mucin production, and variable malignant potential [56–58]. IPMN is the most common macroscopic precursor for PDAC. IPMNs differ from MCNs on the following features: ■ Proclivity to involve the pancreatic head (two-thirds of tumors) ■ Origin within the larger ducts ■ Male preponderance ■ The absence of dense “ovarian” stroma at pathology [55–57] ■ Contradistinction to solitary MCNs, IPMNs are multifocal in 20–40% of cases

IPMNs may be broadly categorized based on anatomic distribution into the main duct, branch duct, or mixed types. IPMNs may also be classified based on the predominant epithelial cell type or histologic criteria. Gastric type IPMNs are

frequently multifocal that commonly involve branch ducts within the uncinate process and have a lower risk of malignancy [55–58]. Colloid carcinomas (intestinal type) and oncocytic subtype of malignant IPMNs demonstrate indolent behavior compared with tubular PDACs associated with pancreaticobiliary type IPMNs [56–58]. IPMNs comprise 25–50% of resected cystic tumors occurring mainly in men during the seventh decade (mean age: 65 years). Most patients are asymptomatic; symptomatic patients often present with nonspecific abdominal pain, jaundice, or diabetes mellitus. Imaging Features ■ MRI/MRCP exquisitely demonstrate cyst features such as septations, mural nodules, and wall thickening, as well as depict communication of the cysts with the ducts [56–58]. On CT/MRI, branch duct IPMNs manifest as unilocular or complex multilocular cystic lesions that communicate with the main pancreatic duct (Fig. 36.57). ■ Main duct IPMNs demonstrate cystic dilatation of the main duct, enhancing mural nodules, variable wall thickening, and thick/viscid mucus that obstructs the ducts (Fig. 36.58). Main duct IPMNs show a greater propensity for malignant change to invasive cancer than branch duct IPMNs (30–45% vs 3–15%) [56–58]. ■ Imaging features strongly suggesting malignancy include cysts bigger than 4 cm, main duct diameter (>1 cm), the cyst growth rate of >5 mm per year, and mural nodules (Fig. 36.59) (>5 mm at EUS) [55–57]. Imaging criteria for the imaging and follow-up of cystic pancreatic lesions will be discussed later.

FIGURE 36.57 Side duct IPMNs of the pancreas in two different patients. (A) Axial contrast-enhanced CT image of the pancreas shows a welldefined cystic lesion of the pancreas without any septations or solid components (arrow). (B) Coronal 2D MRCP image shows a few small cystic lesions in the uncinate process (arrow) that communicates with main pancreatic duct. IPMNs, intraductal papillary mucinous neoplasms.

FIGURE 36.58 Multimodality imaging findings of main duct IPMNs of the pancreas in three different patients. (A) Axial contrast-enhanced CT image of the pancreas shows diffusely dilated main pancreatic duct with a few septations (arrow). (B) Coronal 2D MRCP image shows a focal dilation of the main pancreatic duct in the tail region (arrow). (C) Axial contrastenhanced T1-weighted MR image of the pancreas shows diffusely dilated main pancreatic duct with parenchymal atrophy (arrow) and enhancing nodular component within the main pancreatic duct (arrowhead). These findings are consistent with main duct type IPMNs. IPMNs, intraductal papillary mucinous neoplasms.

FIGURE 36.59 Main duct IPMN of the pancreas with invasive adenocarcinoma. Axial contrast-enhanced CT image of the pancreas shows a solid mass involving the body and tail of the pancreas with scattered hypodensities (arrow). This was proved by a malignancy arising from main duct IPMN on pathology. IPMN, intraductal papillary mucinous neoplasm.

Cystic Pancreatic Neuroendocrine Tumors Cystic pancreatic neuroendocrine neoplasms constitute 10% of all neuroendocrine tumors. Cystic PanNETs tend to be larger and nonfunctional tumors compared with their solid counterparts [55,58]. Cystic PanNETs show intermediate to high T2 signal intensity and hypervascular wall enhancement (85% of tumors) on postcontrast images (Fig. 36.60) [56,57]. They are indistinguishable from other cystic tumors; definite diagnosis warrants pathological examination.

FIGURE 36.60 Cystic pancreatic neuroendocrine tumor (panNET) in MEN1 syndrome. Axial contrast-enhanced MR image of the pancreas demonstrates a cystic lesion with enhancing septations (arrow). This was proved to be a cystic panNET on pathology.

Incidentally Discovered Pancreatic Cyst There is an increasing incidence of incidentally identified pancreatic cysts in asymptomatic patients on cross-sectional imaging studies performed for unrelated conditions. Appropriate surveillance imaging and timely intervention play a pivotal role in the early detection of malignancies and improve patient outcomes. Multiple professional societies have proposed expert consensus

guidelines for the management of these incidental cysts; however, these guidelines are different from each other and are confusing [62–64]. The commonly used guidelines include the American College of Radiology White Paper on Incidental Pancreatic Cysts, Modified Fukuoka Guidelines for IPMN management, American Gastroenterology Association guidelines on asymptomatic PCNs, American College of Gastroenterology Clinical guideline on PCNs, and European study group on PCNs [62–64]. Recently, ACR appropriateness criteria for the management of incidental pancreatic cysts have been published in accordance with the ACR White paper that described five variants depending on size and imaging features (Table 36.5) [65]. Contrast-enhanced MRI with MRCP is the primary investigation of choice in all incidentally detected pancreatic cysts [65]. Based on the presence or absence of the “worrisome features” or “high-risk stigmata” on MRI, pancreatic cysts are categorized into two different groups. Worrisome features include cyst size greater than 3 cm, thickened/enhancing cyst wall, nonenhancing mural nodule, and main pancreatic duct diameter greater than 7 mm (Fig. 36.61) [62,65]. High-risk stigmata include head of the pancreas cysts causing obstructive jaundice, enhancing solid component/mural nodule within the cysts ≥5 mm, and main pancreatic duct diameter ≥10 mm without visualized obstruction (Fig. 36.62) [62,65]. The other features that are concerning in cystic lesions include abrupt change in the caliber of main pancreatic duct with distal pancreatic atrophy, developing/enlarging peripancreatic lymphadenopathy, increasing serum levels of CA-19.9, and cyst growth rate of greater than 5 mm per 2 years. Although cysts with high-risk stigmata are resected, cysts with worrisome features undergo EUS-guided fine needle aspiration with cyst fluid analysis for further characterization [65]. Although cyst fluid from SCAs is clear, nonmucinous and contain VEGF-A/VHL gene abnormalities, MCNs and IPMNs contain mucinous fluid with elevated CEA levels and abnormal KRAS. GNAS is elevated in IPMNs and CTNNB1 mutation is seen in SPTs. PIK3CA and MEN1 mutations are seen in cystic panNETs.

FIGURE 36.61 A side duct IPMN of the pancreas with worrisome features. Axial contrast-enhanced MR image of the pancreas demonstrates a cystic lesion with thick enhancing wall (arrow). IPMN, intraductal papillary mucinous neoplasm.

FIGURE 36.62 (A) A side duct IPMN of the pancreas with high-risk stigmata. Axial contrast-enhanced MR image of the pancreas demonstrates a cystic lesion with multiple enhancing solid components (arrow). (B) MRI appearance of main duct IPMN of the pancreas with high-risk stigmata. Axial T2-weighted MR image of the pancreas shows severely dilated main pancreatic duct (>10 mm) with significant parenchymal atrophy (arrow). IPMN, intraductal papillary mucinous neoplasm.

Table 36.5

Management of Incidentally Detected Pancreatic Cyst: ACR Appropriateness Criteria Appropriate Clinical/Imaging Variants Imaging Examination Variant 1: Incidentally identified pancreatic cyst, size less than 2.5 cm. Initial evaluation

Contrastenhanced MRI abdomen with MRCP

Variant 2: Incidentally identified pancreatic cyst, size greater than 2.5 cm. No worrisome features or high-risk stigmata. Initial evaluation

Contrastenhanced MRI abdomen with MRCP

Variant 3: Incidentally identified pancreatic cyst, size greater than 2.5 cm. Worrisome features or high-risk stigmata are present. Initial evaluation

Endoscopic ultrasound with cyst fluid analysis Contrastenhanced MRI abdomen with MRCP

Variant 4: Incidentally detected main pancreatic duct diameter greater than 7 mm. Suspected intraductal papillary mucinous neoplasm. Initial evaluation

Endoscopic ultrasound with cyst fluid analysis Contrastenhanced MRI abdomen with MRCP Unenhanced MRI abdomen with MRCP

Clinical/Imaging Variants Variant 5: Follow-up imaging of pancreatic cyst

Appropriate Imaging Examination CT pancreatic protocol Contrastenhanced MRI abdomen with MRCP Unenhanced MRI abdomen with MRCP

Cysts without worrisome features or high-risk stigmata are stratified based on the size and are followed-up on surveillance imaging. As per the ACR White Paper, the important points in managing incidental pancreatic cysts include management of cysts as mucinous unless proved otherwise, broad use of EUS and cyst fluid analysis for more refined characterization, specific definition of cyst measurement and growth criteria, follow-up periods of 9–10 years in most patients, and modified management for patients older than 80 years. The main reason for follow-up imaging is to identify PDAC when it is confined to the cyst or within the pancreas. The integration of biochemical/molecular profile of the cyst fluid, along with imaging features, risk of malignancy, comorbidities, and surgical candidacy, will ultimately govern the decision to operate on any incidental pancreatic cyst [62,65].

Suggested Readings • Pancreatitis Disease Focus Panel. Society of Abdominal Radiology. Teaching Series 2020: Atlas of Pancreatitis. Available from: https://cdn.ymaws.com/www.abdominalradiology.org/resource/resmgr/education_dfp/pancreatiti s/atlas/pancreatitis_dfp_atlas_2020-.pdf. • AK Shanbhogue, N Fasih, VR Surabhi, GP Doherty, DK Shanbhogue, SK Sethi, A clinical and radiologic review of uncommon types and causes of pancreatitis, Radiographics 29 (4) (2009) 1003–1026. • VS Katabathina, OY Rikhtehgar, AK Dasyam, et al., Genetics of pancreatic neoplasms and role of screening, Magn Reson Imaging Clin N Am 26 (3) (2018) 375–389. • NM Kulkarni, DM Hough, PP Tolat, EV Soloff, AR Kambadakone, Pancreatic adenocarcinoma: cross-sectional imaging techniques, Abdom Radiol (NY) 43 (2) (2018) 253–263. • L Khanna, SR Prasad, A Sunnapwar, et al., Pancreatic neuroendocrine neoplasms:2020 update on pathologic and imaging findings and classification, Radiographics 40 (5) (2020) 1240–1262. • DV Sahani, R Kadavigere, A Saokar, et al., Cystic pancreatic lesions: a simple imaging-based classification system for guiding management, Radiographics 25 (6) (2005) 1471–1484. • Expert Panel on Gastrointestinal I Gastrointestinal, K Fabrega-Foster, IR Kamel, JM Horowitz, et al., ACR appropriateness criteria(R) pancreatic cyst, J Am Coll Radiol 17 (5S) (2020) S198– S206.

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CHAPTER 37

Peritoneum, Retroperitoneum, and Abdominal Wall Priya Pathak, Puneet Bhargava

Anatomy of Peritoneum, Omentum, and Mesentery Peritoneum is a complex serous membrane consisting of parietal peritoneum lining the abdominal wall, and visceral peritoneum covering the viscus. It is lined by a single layer of mesothelial cells, and encloses the peritoneal cavity containing a thin film of serous fluid (approximately 50–100 mL). The cavity is a closed space in males. In females, the peritoneal cavity is open through the fallopian tubes [1]. To briefly review the peritoneal embryology, primitive gut is suspended by two primitive mesenteries in the abdominal cavity, which subsequently divide into dorsal and ventral portions. Development of various organs within these mesenteries leads to the creation of peritoneal ligaments. Anteriorly, development of liver within the ventral mesentery forms the gastrohepatic ligament (between liver and stomach), hepatoduodenal ligament (between liver and duodenum), and falciform ligament (between liver and abdominal wall). Posteriorly, development of spleen within the dorsal mesentery leads to the formation of the gastrosplenic ligament between stomach and spleen. Dorsal mesentery containing the pancreas fuses with subperitoneal tissues anterior to the kidney to form the splenorenal ligament (Fig. 37.1). Mid and hindgut develop within the dorsal mesentery to form the small bowel mesentery and mesocolon, respectively [2].

FIGURE 37.1 Illustration demonstrates the location of various peritoneal ligaments in the supramesocolic peritoneal compartment.

Peritoneal Ligaments Many infectious, inflammatory, neoplastic, and traumatic processes help delineate the peritoneal folds and ligaments that are normally not visible. These ligaments can be identified by recognizing the vessels traversing them (Table 37.1). Table 37.1 Attachments and Contents of the Peritoneal Ligaments Ligaments Organ Associated Vascular Contents Falciform ligament

Between liver and anterior abdominal wall

Obliterated left umbilical vein. Recanalized umbilical vein in portal hypertension

Gastrohep atic ligament

Between lesser gastric curvature and hepatic hilum

Coronary veins and left gastric artery. Replaced left hepatic artery

Ligaments

Organ Associated

Vascular Contents

Hepatodu odenal ligament

Between first portion of duodenum and hepatic hilum

Portal vein and common hepatic artery

Gastrosple nic ligament

Between greater gastric curvature and splenic hilum

Short gastric vessels. Venous collaterals in splenic vein thrombosis

Splenoren al ligament

Between splenic hilum and left kidney

Splenic artery and vein. Splenorenal shunts in portal hypertension

Small bowel mesentery

Between duodenojejunal junction and ileocecal valve

Superior mesenteric artery and vein

Transvers e mesocolon

Between transverse colon and posterior abdominal wall

Middle colic vessels

Sigmoid mesocolon

Between sigmoid colon and posterior abdominal wall

Sigmoid and superior rectal vessels

Peritoneal ligaments around the liver consist of the following: a. Right and left triangular ligaments formed by the fusion of superior and inferior coronary ligaments. Right triangular ligament is relatively long and separates the right subphrenic space from right subhepatic space. Left triangular ligament is shorter and poorly compartmentalizes the left subphrenic space. b. Falciform ligament, containing obliterated umbilical vein, partially separates right subphrenic from left subphrenic space (Fig. 37.2) [1].

FIGURE 37.2 (A) T2 W Coronal MR abdomen from a 58-year-old man with pancreatic cancer, multifocal hepatic metastasis, peritoneal carcinomatosis and large volume ascites delineates the thickened omentum (black arrowheads). Note the loculated fluid in the lesser sac causing mass effects on the stomach (white arrowhead). (B) T2 W axial image shows the involvement of the falciform ligament by the tumor implant (black arrow).

The greater and lesser omenta are double layers of visceral peritoneum attaching stomach and duodenum to the adjacent structures. Greater omentum hangs from the greater gastric curvature like an apron (Figs. 37.2 and 37.3). Gastrocolic ligament, as a component of the greater omentum, extends from the greater gastric curvature to the transverse colon and forms the anterior wall of the lesser sac. Lesser omentum consists of gastrohepatic ligament containing coronary veins and left gastric artery; and hepatoduodenal ligament containing portal vein, common hepatic artery, and common hepatic duct. Additional ligaments around stomach and spleen are gastrosplenic and splenorenal ligaments, the latter contains the tail of the pancreas [1,2].

FIGURE 37.3 Contrast-enhanced axial CT abdomen from a 52-yearold man with pancreatic cancer and peritoneal carcinomatosis shows reticulonodular tumor implants in the greater omentum (black arrowheads).

The peritoneal ligaments around the bowel are the small bowel mesentery, transverse colon, sigmoid mesocolon, and phrenicocolic ligament. Small bowel mesentery attaches the small bowel to the retroperitoneum and extends from ligament of Treitz to ileocecal valve; it contains the superior mesenteric vessels. Transverse and sigmoid mesocolon attach transverse colon and sigmoid colon to the posterior abdominal wall, respectively. The phrenicocolic ligament extends from splenic flexure of colon to the diaphragm, separating the left paracolic gutter from the left supramesocolic space (Figs. 37.4 and 37.5) [1].

FIGURE 37.4 Illustration demonstrates the compartments of peritoneal cavity and locations of the peritoneal ligaments.

FIGURE 37.5 T2 W Coronal MR abdomen and pelvis from a 50-yearold man with alcoholic cirrhosis delineates various peritoneal compartments and phrenicocolic ligament in the left upper abdomen (black arrow). RSP: Right subphrenic space, LSP: Left subphrenic space, SH: Subhepatic space, LPC: Left paracolic space.

The visceral peritoneum reflects over the bladder, uterus, and rectouterine spaces forming the folds of broad ligament, which further divides into mesometrium, mesosalpinx, and mesovarium [2].

Peritoneal Spaces The transvers mesocolon divides the peritoneal cavity into supra and larger inframesocolic spaces (Fig. 37.4) (Flowchart 37.1). Supramesocolic space is further divided into the right compartment containing right subphrenic, subhepatic spaces, and lesser sac; and left compartment containing the left subphrenic, perihepatic, and perisplenic spaces (Fig. 37.5). Of all the supramesocolic spaces, right subhepatic space (also known as Morrison's hepatorenal pouch) is the most gravity dependent in a supine position and serves as a site for early ascites and fluid collections resulting from the liver injury. Lesser sac is divided into the superior and inferior recesses by the peritoneal reflection of the left gastric artery (Fig. 37.6); the inferior recess communicates with the right subhepatic space through the foramen of Winslow. Inframesocolic space is divided into right and left inframesocolic, right and left paracolic and pelvic spaces. Smaller right inframesocolic space

is limited inferiorly due to the attachment of the small bowel mesentery to the caecum, whereas the larger inframesocolic space communicates freely with the pelvis (Fig. 37.7). Paracolic spaces are present lateral to the peritoneal reflections of the right and left colon, respectively (Figs. 37.5, 37.6, and 37.7). Pelvic space consists of the rectovesical space in males, and vesico-uterine and rectouterine spaces (also known as pouch of Douglas) in females; the latter is the most gravity-dependent site (Fig. 37.8) [1].

FLOWCHART 37.1 Compartments of the peritoneal cavity.

*Right inframesocolic space is closed by attachment of mesentery to caecum. Left inframesocolic space freely communicates with pelvis.

#Pelvic space is divided by medial umbilical ligament into medial and lateral compartments. Lateral compartment is further divided into medial and lateral inguinal fossa [1].

FIGURE 37.6 Contrast-enhanced coronal (A) and axial (B) CT abdomen and pelvis from a 62-year-old woman with ovarian cancer, peritoneal carcinomatosis, and moderate volume ascites demonstrate various peritoneal compartments. LS: Lesser sac, RPC: Right paracolic space, LPC: Left paracolic space, RIMC: Right inframesocolic space, LIMC: Left inframesocolic space. Note the thickened peritoneal reflection along the left gastric artery (black arrow) separating the superior (LSs) and inferior (LSi) lesser sac recesses (B).

FIGURE 37.7 Contrast-enhanced coronal (A) and sagittal (B) CT abdomen and pelvis from a 78-year-old woman with ovarian cancer, peritoneal carcinomatosis and large volume ascites demonstrate various peritoneal compartments and thickened mesentery due to tumor implants (M). RSP: Right subphrenic space, RPC: Right paracolic space, LPC: Left paracolic space, LIMC: Left inframesocolic space. Note the enhancing tumor implant in the right subphrenic space (black arrow) (A) and nodular thickening of the falciform ligament (white arrowhead) (B).

FIGURE 37.8 Longitudinal transvaginal USG from a 64-year-old woman with large volume ascites demonstrates fluid in the rectouterine pouch or pouch of Douglas (POD). Vesico-uterine pouch is present between the uterus (U) and bladder (B).

Role of peritoneal ligaments in tumor spread: The peritoneal ligaments can serve as both a barrier or as a conduit for spread of disease across the abdominal cavity. For example, the pancreas is situated in the anterior pararenal space but sits at the base of several mesenteries. The spread of pancreatic cancer occurs through the peritoneal ligaments along distinct pathways as follows (Flowchart 37.2) [2].

FLOWCHART 37.2 Routes of pancreatic cancer spread through the peritoneal ligaments.

Other examples are spread of gastric carcinoma to the liver through the gastrohepatic and hepatoduodenal ligaments. Liver and gall bladder tumors spread to the peripancreatic nodes via the hepatoduodenal ligament. Phrenicocolic ligament serves as a barrier to tumor spread between left paracolic space and left subphrenic space [2,3].

Pattern of Peritoneal Fluid Spread and Potential Areas of Stasis Flow of peritoneal fluid is described as circulatory and “preferential” (Fig. 37.9). Initially, fluid is present in the gravity-dependent areas with upward ascent in certain preferred pathways (Fig. 37.10) [1–3].

FIGURE 37.9 Illustration demonstrates the circulatory flow of peritoneal fluid in various peritoneal compartments. PC: Peritoneal Cavity, RS: Right subphrenic space, LS: Lesser sac, M: Morison's pouch, RP: Right paracolic space, LP: Left paracolic space, IC: Inframesocolic compartment, RV: Rectovesical space.

FIGURE 37.10 Preferential pathway for peritoneal fluid circulation.

Sites of peritoneal fluid stasis and hence hotspots for tumor seeding are rectouterine pouch, inframesocolic compartment, and paracolic spaces. Areas of peritoneal fluid reabsorption such as right subdiaphragmatic space and greater omentum serve as additional hot spots (Fig. 37.11) [4].

FIGURE 37.11 Contrast-enhanced axial CT abdomen and pelvis from a 68-year-old woman with metastatic ovarian cancer and peritoneal carcinomatosis. Although there is large burden peritoneal disease and ascites, tumor implants are most numerous at the site of peritoneal fluid stasis such as right paracolic space (white arrows) (A) and site of peritoneal fluid reabsorption at the right subphrenic space (black arrow) (B).

Imaging Techniques Ultrasonography (USG), CT, MRI, and PET are the technique for the assessment of peritoneal pathologies. USG is predominantly used in detection of ascites, differentiation of simple from complex ascites, and guided paracentesis. Although it is easily available and lacks ionizing radiation, it is limited in evaluation of peritoneal anatomy or detection of tumor implants, with added technical difficulties in obese patients. Contrastenhanced CT with a single venous phase (60–70 s) is the technique of choice to assess most peritoneal pathologies. Administration of neutral or positive oral contrast helps in better delineation of serosal implants [1]. Typical MRI protocol includes T1 and T2WI, DWI, and dynamic contrast sequences. Dynamic contrast sequences are essential as most peritoneal pathologies demonstrate slow enhancement with gadolinium. Antiperistalsis agents aid in decreasing motion artifacts. Although MRI provides better tissue characterization, its overall utility in peritoneal imaging is largely

limited due to motion artifacts, fat interface artifacts, dielectric artifacts produced by ascites, and increased scan time [1,5]. It is however evolving as a tool for the detection of subtle peritoneal disease and quantification of peritoneal carcinomatosis index.

Developmental Lesions Congenital Cysts Pathophysiology and clinical features: Congenital cysts include enteric duplication cysts, enteric cysts, and mesothelial cysts. These are most frequently present within the ileal mesentery [6]. Although a pediatric diagnosis, congenital cysts may remain undetected till adulthood. The cysts can be incidentally detected on imaging or present with complications secondary to infection, perforation, bowel obstruction, intussusception, or malignant degeneration [7]. On pathology, enteric duplication cysts are thick walled containing the entire gut lining from mucosa to muscularis layers. Enteric cysts are thin-walled cysts containing only the mucosal layer; these are formed secondary to migration of bowel diverticulum into the mesentery. Mesothelial cysts are thinned walled containing a single layer of mesothelial cells, and are formed secondary to incomplete fusion of mesothelial lined peritoneal surfaces [6,8]. Imaging Features USG: Enteric duplication cysts are thick-walled anechoic lesions with inner echogenic mucosal layer and outer hypoechoic muscle layer, and demonstrate the gut signature sign (Fig. 37.12). Complexities in the cyst result from calcification, hemorrhage, or fecolith formation. Enteric and mesothelial cysts are thin-walled unilocular lesions within the mesentery [8].

FIGURE 37.12 Transabdominal USG from a 1-year-old male shows an enteric duplication cyst associated with duodenum. No calcifications or solid components are present.

CT and MRI: Uncomplicated duplication cysts demonstrate simple fluid attenuation without solid components or enhancement on contrast-enhanced CT. On MRI, cysts follow fluid signal, that is low T1 and high T2 signal. Complex cysts demonstrate variable T1 and T2 signal secondary to calcifications and internal proteinaceous or hemorrhagic contents (Fig. 37.13).

FIGURE 37.13 (A) Contrast-enhanced axial CT abdomen from a 72year-old man with an incidental left enteric duplication cyst. The cyst demonstrates hyperdense internal contents (arrow). (B) On MR, the cyst shows hyperintense areas on single-shot FSE T2WI (arrow), (C) intrinsic T1 hyperintensities indicative of hemorrhagic/proteinaceous contents (arrowhead), and thin enhancing wall on venous phase T1WI (arrow in D). No discrete solid components are present.

Lymphatic Malformations Pathophysiology and clinical features: Previously known as lymphangioma, these are rare benign vascular malformations with lymphatic differentiation; typically described as slow-growing insinuating multicompartmental masses that do not respect fascial planes [9,10]. On histopathology, lymphatic malformations are thin-walled cystic masses with either large macroscopic interconnecting cysts or microscopic cysts containing dilated lymphatics lined by flattened endothelial cells [9]. Abdominal lymphatic malformations most commonly occur in mesentery, followed by omentum, mesocolon, and retroperitoneum; with retroperitoneal lymphatic malformation accounting for only 1% of cases [10]. The lesions can be asymptomatic or present with abdominal distention, palpable mass, or pain, often secondary to complications such as hemorrhage, infection, or rupture. Imaging Features

USG: Circumscribed multilocular cystic masses, anechoic or with layering internal debris. Avascular internal septae show variable thickness (Fig. 37.14) [11].

FIGURE 37.14 Longitudinal USG (A) with Doppler (B) of right lower quadrant shows a multiloculated multicystic lymphatic malformation. The mass shows no mural or septal vascularity or solid components.

CT and MRI: Contrast enhanced CT (CECT) demonstrates multilocular or multiseptated cystic mass with thin wall and septae showing mild or absent enhancement (Figs. 37.15 and 37.16). Areas of high attenuation could reflect hemorrhage or less commonly calcification [9]. On MRI, the mass follows fluid signal, that is, homogenously low T1 and high T2 signal, unless complicated by infection, hemorrhage or rare stromal myxoid degeneration and fibrosis, in which case it may present as a multilocular mass with solid components [12].

FIGURE 37.15 Contrast-enhanced axial CT abdomen shows left paraaortic lymphatic malformation (white arrow), which is insinuating between renal vasculature and extending into the renal hilum. The mass shows no enhancement.

FIGURE 37.16 CT abdomen shows a lymphatic malformation located in the porto-caval region, as a circumscribed hypoattenuating structure with lack of enhancement (white arrowhead). The mass is insulating between the involved structures without substantial mass effects.

Differential diagnosis: Cystic peritoneal and retroperitoneal lesions such as pseudocysts, lymphocele, hydatid cysts, cystic teratoma and peritoneal inclusion cysts [9,10].

Lymphatic Malformations: Pearls to Remember ■ Slow-growing insinuating multicompartmental masses that do not respect fascial planes. ■ Most commonly occur in mesentery, followed by omentum, mesocolon, and retroperitoneum. ■ On CECT, multilocular multiseptated cystic mass with thin enhancing wall and septae.

Nonpancreatic Pseudocysts

Pathophysiology and clinical features: These are rare, acquired and incidental mesenteric and retroperitoneal cysts unrelated to pancreatitis. Proposed etiologies are as a sequela of infection or unresolved hematoma. Retroperitoneal nonpancreatic pseudocysts arise from the fatty tissues of retroperitoneum. The cyst may have serous, purulent, hemorrhagic, or chylous internal contents [10,13]. Imaging features: On USG, these are unilocular or multilocular cysts, anechoic or with internal echogenic debris. CECT demonstrates well-defined cyst with internal fluid or fat attenuation, and a thin or thick enhancing wall (Fig. 37.17). Fluid-fluid or fat-fluid levels can be present. Calcification may be seen [10,13].

FIGURE 37.17 Contrast-enhanced axial CT abdomen from a 60-yearold man shows an incidental left mesenteric cyst with a thin nonenhancing wall and homogenous internal hypoattenuation (white arrow). Differential considerations are enteric cyst, mesothelial cyst, and nonpancreatic pseudocyst.

Infectious, Inflammatory, and Ischemic Disorders

Peritonitis Pathophysiology and Clinical Features Peritonitis is inflammation of the parietal and visceral peritoneum. It is classified into acute and chronic secondary to infectious and noninfectious etiologies. The vast majority of peritoneal infections are secondary to bacterial etiologies, with fungal, viral, and parasitic infections contributing to only small percentage of cases [14]. Bacterial Peritonitis It is further classified into primary (less common) and secondary types [14]. Causes of secondary bacterial peritonitis include bowel perforation, diverticulitis, Crohn's disease, appendicitis, and pelvic inflammatory disease. Small bowel and peptic ulcer perforation present with generalized acute peritonitis, whereas appendicitis, diverticulitis, and pelvic inflammatory disease usually cause localized peritonitis. Most common organisms involved are Gram-negative bacilli and anaerobes [5,14,15]. Tuberculous Peritonitis It can be secondary to reactivation of latent tuberculous foci or lymphohematogenous spread, with only 14% of the patients having associated radiological evidence of pulmonary tuberculosis [14]. It is classified into (1) wet type with ascites and loculated collections; (2) dry or plastic type characterized by mesenteric thickening, caseous nodules, and adhesions; and (3) Fibrotic type with formation of omental, mesenteric masses and matting of bowel loops [15,16]. Spontaneous Bacterial Peritonitis It is a subtype of primary infective peritonitis involving diffuse bacterial infection of the peritoneum in patients with cirrhosis or a nephrotic syndrome. Pathogenesis involves hematogenous spread of infection to peritoneum due to impaired filtration and neutrophil function. Typically, only one type of bacteria, most commonly Escherichia coli, is found in the ascitic fluid [14]. Less common noninfectious peritonitis includes chemical peritonitis (such as biliary peritonitis), granulomatous peritonitis (secondary to foreign body), and eosinophilic peritonitis [5]. Imaging Features Radiographs: These help in detection of free air under the diaphragm (pneumoperitoneum) due to bowel perforation. Large volume ascites can lead to centralization of the bowel loops.

USG: Bacterial peritonitis presents as particulate ascites or loculated intraperitoneal collection containing gas seen as posterior reverberation artifacts, echogenic debris, and septations associated with peritoneal thickening (Fig. 37.18) [14]. USG more accurately depicts ascites characteristics (simple vs complex) and guides diagnostic and therapeutic paracentesis.

FIGURE 37.18 Longitudinal USG abdomen (A) in a 64-year-old woman with bacterial peritonitis undergoing therapeutic paracentesis shows particulate ascites with internal septations. Contrast-enhanced coronal CT abdomen and pelvis (B) demonstrates large volume ascites, subtle diffuse peritoneal enhancement (arrow), and a loculated component in the mid abdomen (arrowheads).

Wet-type tuberculous peritonitis presents with simple or complex particulate ascites with loculations containing lattice-like floating internal septations composed of fibrin [14]. Dry and fixed types demonstrate irregular or nodular hypoechoic omental and mesenteric thickening and masses. Bowel and mesentery can be matted. Associated abdominal and retroperitoneal adenopathy is frequent [16,17]. CT and MRI: General features of both infective and noninfective peritonitis are smooth peritoneal enhancement (in contrast to carcinomatosis where peritoneal enhancement is nodular) (Fig. 37.18), ascites, and sometimes loculated intraperitoneal collections or abscess. Intraperitoneal free air is present in peritonitis secondary to bowel perforation. Wet-type tubercular peritonitis can present as high attenuation free ascites, loculated collections, or abscess (Figs. 37.19 and 37.20). Adhesions in drytype peritonitis can lead to clumping of bowel loops and cocoon formation (Fig. 37.21). Caseous nodules demonstrate soft tissue attenuation and contrast enhancement. Associated necrotic abdominal and retroperitoneal adenopathy is frequently seen. Involvement of ileocecal junction with

thickening commonly occurs in conjunction with peritonitis (Fig. 37.22). Dry and fibrotic type tubercular peritonitis shows extensive fibrous adhesions and cake-like omental thickening [15].

FIGURE 37.19 Contrast-enhanced axial CT abdomen shows wet-type tuberculous peritonitis with ascites and peritoneal thickening (white arrow).

FIGURE 37.20 Contrast-enhanced axial CT abdomen from a 44-yearold woman with tubercular peritonitis demonstrates a rim-enhancing perihepatic abscess (arrow).

FIGURE 37.21 Contrast-enhanced CT abdomen and pelvis from a 17year-old girl with abdominal pain and fever shows localized clumping of the bowel loops in the mid abdomen (abdominal cocoon formation) from tuberculous peritonitis (white arrow) (A and B).

FIGURE 37.22 Longitudinal USG abdomen of right lower quadrant (A) in a 31-year-old man with tubercular peritonitis shows large volume particulate ascites. Subsequent contrast-enhanced axial (B) and coronal CT abdomen and pelvis (C) demonstrates irregular mesenteric thickening (arrow) and enlarged necrotic retroperitoneal nodes (arrowhead). Thickening of terminal ileum and caecum indicates associated bowel involvement (ellipse) (C).

MRI has a limited role in routine evaluation. Dynamic enhanced MRI shows diffuse smooth peritoneal enhancement in both infective and noninfective peritonitis (Fig. 37.23).

FIGURE 37.23 Venous phase coronal T1WI MR abdomen and pelvis in a 62-year-old female with bacterial peritonitis shows large volume ascites and smooth diffuse peritoneal enhancement (white arrowheads).

Differential Diagnosis Peritoneal carcinomatosis is the major differential consideration, especially with dry and fibrotic types of tubercular peritonitis containing omental and mesenteric masses. Definitive diagnosis is such cases necessitates tissue sampling/omental biopsy, unless there is an active focus of tuberculosis elsewhere in the body as well to help clinch the diagnosis.

Sclerosing Mesenteritis Pathophysiology and Clinical Features

Sclerosing mesenteritis is a spectrum of idiopathic inflammatory disorder of the mesentery and peritoneum. Known associations are other idiopathic inflammatory conditions such as retroperitoneal fibrosis, sclerosing cholangitis, Riedel thyroiditis, and orbital pseudotumor [18]. It involves the mesenteric root (most common), mesocolon, omentum, and retroperitoneum. Proposed etiologies are autoimmune disorder, vasculitis, infection, trauma, and previous abdomen surgery. It is also associated with several malignancies such as lymphoma, melanoma, gastric, breast, lung and colon cancer [18,19]. Pathologically, three stages of sclerosing mesenteritis are described. ■ The first stage of mesenteric lipodystrophy involves replacement of mesenteric fat by foamy macrophages. ■ The second stage is mesenteric panniculitis consisting of infiltration of polymorphonuclear leukocytes, plasma cells, and foamy macrophages. ■ The third stage is retractile mesenteritis involving fat necrosis followed by fibrosis [20].

Misty mesentery is a nonspecific term for focal increase in mesenteric density in the setting of infiltrative processes such as panniculitis, hemorrhage, edema, and neoplasm, and is not specific for sclerosing mesenteritis (Fig. 37.24) [19].

FIGURE 37.24 Contrast-enhanced axial (A) and coronal CT (B) abdomen and pelvis from a 55-year-old man shows incidental mild midmesenteric stranding with prominent surrounding short-axis mesenteric nodes representing mesenteric panniculitis (white arrowhead, ellipse).

The condition is usually asymptomatic, but may present with nonspecific abdomen pain, elevated inflammatory blood marker, and anemia. Males have a higher incidence [18]. Imaging Features

USG: It has no added diagnostic value. USG may demonstrate altered mesenteric echogenicity with decreased compressibility, necessitating CT for further evaluation [21]. CT: Sclerosing mesenteritis presents with mass-like area of fat stranding, with preservation of fat around the mesenteric vessel or “Fat ring sign” and a pseudocapsule (Figs. 37.24 and 37.25) [18,22]. Incidentally detected mesenteric panniculitis does not warrant a follow up imaging, and is typically left untreated as it is expected to resolve spontaneously in most cases [23].

FIGURE 37.25 Contrast-enhanced coronal CT abdomen and pelvis shows halo of preserved fat around the mesenteric vessel or “Fat ring sign” in sclerosing mesenteritis (arrows).

Retractile mesenteritis demonstrates soft tissue masses, which can encase mesenteric vessels and bowel causing obstruction. Calcifications may be present and relate to the areas of steatonecrosis (Fig. 37.26) [19]. Concomitant enlarged mesenteric or retroperitoneal nodes may be present [22].

FIGURE 37.26 Contrast-enhanced coronal CT abdomen and pelvis shows an irregular soft tissue mass in the central mesentery with coarse internal calcifications in retractile mesenteritis (white arrow).

Differentials diagnosis: Carcinoid tumor, metastasis, lymphoma, desmoid tumor, and carcinomatosis [18,19].

Sclerosing Mesenteritis: Pearls to Remember ■ Spectrum of idiopathic inflammatory disorder most commonly involving the mesenteric root. ■ On CECT, mass-like area of fat stranding, fat ring sign, and a pseudocapsule. ■ Soft tissue masses present in retractile mesenteritis.

Encapsulating Peritoneal Sclerosis Pathophysiology and Clinical Features Also known as abdominal cocoon or sclerosing encapsulating peritonitis, it is a rare condition of bowel encapsulation by a fibro-collagenous peritoneal

membrane. Encapsulating peritoneal sclerosis is the preferred term indicating the morphologic abnormality as inflammation can be frequently absent [24,25]. The exact etiology is not known; however it is most commonly associated with continuous ambulatory peritoneal dialysis and tuberculosis. Contributing factors in peritoneal dialysis include a longer duration of dialysis, repeated episodes of bacterial peritonitis, certain compositions of the dialysate such as chlorhexidine, acetate, and glucose-based dialysate [24,26]. Clinical presentation is with nonspecific abdominal pain and distension, vomiting, and decreased peristalsis in the setting of obstruction. Imaging Features Radiographs: Peritoneal calcifications may be detected in extensive disease (Fig. 37.27). Air-fluid levels and dilated bowel are present with obstruction.

FIGURE 37.27 Calcifications in encapsulating peritoneal sclerosis. Abdomen radiograph (A) shows relative focal area of thin calcifications in the mid abdomen around the peritoneal dialysis catheter (black arrowheads) (A), which are delineated as curvilinear calcifications on the surface of the bowel on CT (black arrow) (B).

USG: It depicts an echogenic membrane along the bowel wall and loculated ascites. Bowel loops are tethered, clumped with fixed configuration, and trilaminar appearance comprising of outer echogenic membrane, middle hypoechoic muscle, layer and inner mucosa. Peristalsis is frequently altered [24]. CT: It shows centralization of bowel loops encased by a mantle of diffuse peritoneal thickening demonstrating continuous enhancement. Concomitant coarse peritoneal or serosal calcifications may be present (Fig. 37.27).

Adherent bowel loops show tethering, kinking, and angulation. Dysmotility is depicted as bowel dilation and air-fluid levels [24,26]. Differential Diagnosis Peritoneal carcinomatosis, mesothelioma, and bowel clumping due to internal hernias [24,26].

Epiploic Appendagitis Pathophysiology and Clinical Features Epiploic appendagitis is a benign, self-limiting condition involving inflammatory and/or ischemic damage to the epiploic appendages. Normal epiploic appendages are peritoneal outpouching from the serosal surface of the colon, consisting of adipose tissue and a vascular stalk. They range in size from 0.5 to 5 cm, and extend from caecum to the recto-sigmoid junction. The vascular supply consists of two feeding arteries with a single draining vein, which explains the increased susceptibility to venous ischemia from appendiceal torsion [27–29]. Incidence is higher between second to fifth decades with a male predominance. Nonspecific clinical features are abdominal pain, nausea, vomiting, diarrhea, mild fever, and leukocytosis; overall presentation is sometimes indistinguishable from acute appendicitis, diverticulitis, or omental infarction. Obesity and rapid weight loss are known risk factors [29]. Imaging Features USG: USG demonstrates epiploic appendagitis as an echogenic, noncompressible and avascular focus surrounded by a hyperechoic rim (Fig. 37.28).

FIGURE 37.28 Longitudinal grayscale (A) with color Doppler (B) USG images from a 36-year-old man with acute abdominal pain shows an ovoid, echogenic and avascular lesion in the left lower pelvic quadrant (white arrow) (A), representing an inflamed epiploic appendage.

CT: Presents as small (usually < 5 cm), oval area of fat attenuation with a hyperattenuating rim (hyperattenuating rim sign), surrounding fat stranding and absent contrast enhancement. A central dot in the lesion represents the thrombosed vein (Figs. 37.29 and 37.30). Spread of inflammation can lead to thickening of adjacent parietal peritoneum or less likely colon. It most commonly occurs along the sigmoid colon (50% of cases), followed by descending, ascending, and transverse colon. Chronically infarcted appendage usually transforms into fibrosed or calcified nodules attached to the colon or as loose bodies (Fig. 37.31); the latter tend to deposit in the dependent peritoneal recesses. A rare complication of epiploic appendagitis is peritoneal adhesion with resultant small bowel obstruction [27,29].

FIGURE 37.29 Contrast-enhanced axial CT abdomen from a 42-yearold man with abdominal pain demonstrates an ovoid, fat attenuating lesion with surrounding fat stranding in the right paracolic space representing epiploic appendagitis (black arrow). Note the central hyperattenuation due to the thrombosed vein in the lesion.

FIGURE 37.30 Contrast-enhanced axial CT abdomen and pelvis from a 39-year-old man with abdominal pain demonstrates epiploic appendagitis as a 2 cm fat attenuating lesion with surrounding mesenteric stranding along the sigmoid colon (white arrow).

FIGURE 37.31 Axial CT pelvis shows chronically calcified epiploic appendage in the left lower quadrant (white arrow) (A). Axial CT abdomen from a different patient shows rim calcification of previously inflamed epiploic appendage in the right mid abdomen (white arrowhead) (B).

Differential Diagnosis Omental infarction, acute appendicitis, acute diverticulitis, and mesenteric panniculitis. Inflamed appendages can rarely protrude in a hernial sac to simulate an irreducible hernia. Chronic calcified appendages can be confused with drop gallstones, calcified lymph nodes, or calcified uterine fibroids [29].

Omental Infarct Pathophysiology and Clinical Features Omental infarction is a relatively rare entity due to the presence of abundant collateral vascular supply in the greater omentum. Predisposing factors include trauma, hypercoagulable states, vasculitis, congestive heart failure, obesity, strenuous exercise, and abdominal surgery. Omental torsion with subsequent infarction can result from congenital anomalies such as bifid or accessory omentum or secondary to abdominal tumors, hernia, or surgical procedures such as Roux en Y reconstruction. Right lateral free edge of the omentum is believed to be most susceptible to ischemia due to sparse blood supply [27,28,30]. Clinical features are acute or subacute right upper or lower quadrant pain with mild elevation of white blood cell counts, and typically without associated nausea, vomiting, or fever. The condition affects approximately

15% of the pediatric population. No specific gender predominance is seen [28]. Imaging Features USG: USG demonstrates a focal noncompressible area of echogenic fat without vascularity, typically correlating to the site of pain (Fig. 37.32).

FIGURE 37.32 Longitudinal grayscale (A) with color Doppler (B) USG abdomen from a 24-year-old man with abdominal pain shows a large ill defined, heterogenous, incompressible and avascular lesion in the right upper quadrant representing omental infarction (calipers) (A).

CT: Presents as a large (> 5 cm), encapsulated, heterogeneous lesion with areas of fat and soft tissue attenuation and absent contrast enhancement (Fig. 37.33). Smaller infarct demonstrates central soft tissue attenuation with a peripheral halo. Early or developing infarction can manifest as an area of fat haziness or mild stranding (Fig. 37.34). Common location is anterior to the transverse colon or anteromedial to the ascending colon. There is swirling of the omental vasculature in omental torsion. Contiguous extension of inflammation may lead to focal colonic thickening. Rare instance of superimposed infection presents as rim enhancement, fat fluid, or air-fluid levels [27,28].

FIGURE 37.33 Contrast-enhanced axial CT abdomen shows an omental infarct abutting the distal gastric body. The lesion demonstrates heterogeneous attenuation with scattered fat and soft tissue densities and absent contrast enhancement (white arrow).

FIGURE 37.34 Contrast-enhanced axial CT abdomen from a 54-yearold man demonstrates early omental infarction as mild circumscribed stranding in the right upper abdomen (ellipse).

Differential Diagnosis Epiploic appendagitis, acute appendicitis, acute diverticulitis, and mesenteric panniculitis. Differentiation from epiploic appendagitis can be suggested by the size (epiploic appendagitis are usually less than 5 cm) and location (along the sigmoid colon in epiploic appendagitis and transverse or ascending colon in omental infarction). Infected omental infarction can mimic an abscess [28].

Intraperitoneal Collections Pneumoperitoneum Pathophysiology and Clinical Features Pneumoperitoneum is air within the peritoneal cavity. Etiologies are disruption of bowel secondary to peptic ulcer perforation, ischemia,

neoplasm, appendicitis, diverticulitis, trauma, foreign body, iatrogenic such as endoscopy, peritoneal dialysis, cardiopulmonary resuscitation, mechanical ventilation, vaginal aspiration, and insufflation and postoperative, peritoneal infection with gas-forming organism, and secondary to pneumomediastinum and pneumothorax with air dissecting into the peritoneal cavity [31,32]. Clinical symptoms are abdominal distention, tenderness, guarding, tachycardia, fever, and signs of shock. Imaging Features Radiograph: Pneumoperitoneum on upright chest and abdominal radiograph presents as subdiaphragmatic free air. Supine abdominal radiographs are less sensitive in detection unless there is large volume of air. Following radiographic signs are described [31,33]: a. Central abdomen: ■ Cupola, saddlebag, or mustache sign: Air collection below the central diaphragmatic tendon (Fig. 37.35). ■ Football sign: Massive pneumoperitoneum outlining the peritoneal cavity. b. Around the liver: ■ Falciform ligament sign: Air outlining the falciform ligament (Fig. 37.36). ■ Lucent liver sign: Lucent appearance of liver secondary to air anteriorly (Fig. 37.36). ■ Doge's cap sign: Triangular air collection in the Morrison pouch. c. Around the bowel: ■ Rigler's or double wall sign: Air outlining both sides of the bowel wall (Fig. 37.36). ■ Telltale triangle sign: Triangular air collection between three bowel loops. d. Pelvis: ■ Inverted V sign: Air along the lateral umbilical ligaments. ■ Urachus sign: Air along the median umbilical ligament.

FIGURE 37.35 Pneumoperitoneum from peptic ulcer perforation. Supine abdomen radiograph (A) shows free air under the diaphragm (black arrowhead) and cupola sign (black arrow). Subsequent noncontrast axial CT abdomen (B) demonstrates large volume pneumoperitoneum (white arrow).

FIGURE 37.36 Pneumoperitoneum from perforated sigmoid diverticulum. Supine abdomen radiograph shows Rigler's sign (black arrowhead), lucent liver sign (white polygon), and falciform ligament sign (black arrow).

USG: Sonographic detection is based on distortion of USG waves by air present in atypical location. A liner array transducer (10–12 MHz) is more sensitive than a curvilinear transducer. Reverberation of ultrasonic waves between transducer and air results in high amplitude linear echoes causing increased echogenicity of underlying peritoneum, known as peritoneal enhancement (Fig. 37.37). It is accompanied with posterior reverberation and ring down artifacts, best observed between liver and anterior abdominal wall where there is usually no intervening bowel. Extensive reverberation artifacts in large volume pneumoperitoneum can sometimes completely obscure the underlying viscera [32, 34]. A study conducted by Jones et al. showed sensitivity of plain radiographs at 79%, specificity at 64% and a positive predictive value at 96% for pneumoperitoneum detection.  USG demonstrated a higher sensitivity at 93%, specificity at 64%, and positive predictive value at 97% [35]. However, operator dependency limits the overall utility of USG in actual clinical practice as detection is technically challenging even for an experienced sonographer and in obese patients.

FIGURE 37.37 Linear array transducer USG image shows echogenic peritoneal stripe (white arrow) with reverberation artifacts in pneumoperitoneum.

(Courtesy of Dr Amit Sahu, Consultant, Max Hospital, Saket, India.)

CT and MRI: CT is the modality of choice to detect the presence, volume, location, and etiology of intraperitoneal free air. It helps in evaluation of complex postsurgical abdomen and patients with suspected anastomotic leak. MRI is rarely used for evaluation. Intraperitoneal air produces signal loss on T1 and T2WI with dephasing artifacts on gradient sequences [5]. Differential diagnosis: Chilaiditi Syndrome (Hepato-diagrammatic interposition of colon) (Fig. 37.38), linear basilar atelectasis, skin folds,

properitoneal fat stripe and subdiaphragmatic lipomatosis producing falsepositive lucencies on radiographs and pneumoretroperitoneum [31].

FIGURE 37.38 Upright chest radiograph shows hepato-diagrammatic interposition of colon in Chilaiditi syndrome (black arrowhead).

Pneumoretroperitoneum refers to the presence of air in the retroperitoneal space. The gas most often originates from perforation of retroperitoneal organs such as duodenum, ascending or descending colon, and rectum secondary to etiologies such as duodenal ulcer perforation, trauma, neoplasm, diverticulitis, endoscopy, and retroperitoneal surgeries. The extraluminal air is particularly high-volume post endoscopy due to large volume and pressure of the insufflated air. Cranial dissection of the air leads to accumulation in the upper abdominal quadrants, detected on radiographs as lucencies around the kidneys (Fig. 37.39). There can be obscuration of the normal psoas shadow. CT is the modality of choice in detection and differentiation from pneumoperitoneum. It may also demonstrate focal collection of extraluminal fecal matter or “dirty mass,” which is a specific indicator of colorectal perforations [36, 37]. The air is usually seen in multiple pockets in the extraperitoneal compartments, occasionally within the ligaments of the peritoneum and in the abdominal wall (Fig. 37.40).

FIGURE 37.39 (A) Upright abdomen radiograph from a patient with colonic perforation shows pneumoretroperitoneum as curvilinear air in the right renal fossa. (B) Subsequent noncontrast CT demonstrates retroperitoneal air around the kidneys, (C) retromesenteric (white arrow), and lateral conal planes.

FIGURE 37.40 Pneumoretroperitoneum. (A) CT abdomen from a patient with complicated sigmoid diverticulitis shows scattered air in the retroperitoneum including peripancreatic fat and greater omentum. (B) CT pelvis from a different patient with extra peritoneal bladder rupture shows scattered air in the pelvic retroperitoneum and presacral space (white arrow).

Hemoperitoneum Pathophysiology and Clinical Features Hemoperitoneum refers to the presence of blood within the peritoneal cavity. Etiologies are trauma (penetrating and blunt), neoplasm rupture (such as hepatic adenoma, hepatocellular carcinoma, ovarian cysts), rupture of vascular aneurysms, ruptured ectopic pregnancy, hemorrhagic pancreatitis, coagulopathy, and iatrogenic such as post biopsy and surgery [38].

Imaging Features USG: Sonographic appearance varies from hypoechoic to echogenic fluid in the peritoneal cavity with occasional blood-fluid levels [39]. CT and MRI: CT appearance depends on the age, extent, and location of hemorrhage with following attenuation values [38]:

a. Unclotted extravascular blood: 30–45 HU, except in patients with low hematocrit (attenuation usually less than 30 HU). b. Clotted blood: 45–70 HU. c. Bleed more than 48 h and old blood products: Usually less than 30 HU. Sentinel clot sign refers to higher attenuation of bleed near the organ of injury (Figs. 37.41 and 37.42) [40]. Blood in the peritoneal cavity produces hematocrit effects with layering densities and blood-fluid levels.

FIGURE 37.41 Contrast-enhanced axial CT abdomen and pelvis from a 35-year-old man involved in motor vehicular accident shows small volume free fluid in the right lower quadrant, with an associated hyperdense component along the caecum (white arrowhead) indicating the sentinel clot. Mesenteric hematoma was detected intraoperatively.

FIGURE 37.42 Contrast-enhanced axial CT pelvis from a 31-year-old woman with ruptured hemorrhagic ovarian cyst and free fluid in the pelvis. Focal hyperdensity in the rectouterine space indicates the sentinel clot (white arrowhead).

On MRI, signal intensity varies as bleed evolves with acute blood (deoxyhemoglobin) isointense on T1 and hyperintense on T2WI. Subacute bleed is T1 hyperintense and T2 hypointense (intracellular methemoglobin) and later T2 hyperintense (extracellular methemoglobin). Old hemorrhage is T1 and T2 hypointense (hemosiderin). Hemosiderin and deoxyhemoglobin demonstrate susceptibility dephasing on gradient echo sequences [5].

Neoplastic Disorders Mesothelioma Pathophysiology These are rare tumors derived from the mesothelial cells. Pathological subtypes are the aggressive malignant mesothelioma, and the lower-grade well-differentiated papillary mesothelioma and cystic mesothelioma. Debate and confusion persists about cystic mesothelioma and peritoneal inclusion cyst (described above) being the same entity due to similar reported imaging

features and common etiologies such as endometriosis, pelvic inflammatory disease, and prior surgery [41,42]. Asbestos exposure is the etiology in vast majority of malignant mesothelioma, with usually higher exposure level compared to pleural mesotheliomas. Papillary mesothelioma is not linked to asbestos exposure [41–43]. Clinical Features Malignant mesotheliomas are aggressive neoplasms occurring in older men in fifth to sixth decades. Papillary mesothelioma demonstrates low-grade malignant potential with higher incidence in women of reproductive age [41,42]. Patients present with nonspecific symptoms such as abdominal pain, weight loss, distention, or a palpable mass. Imaging Features CT: Malignant mesotheliomas present as dry versus wet types in a focal or diffuse pattern. Dry type demonstrates peritoneal plaques and enhancing masses without associated ascites (Fig. 37.43). Peritoneal plaques do not commonly show calcification unlike the pleural counterpart. Extensive disease presents with rinds of tumor encasing intraabdominal organs. Wet type demonstrates free or loculated ascites and enhancing peritoneal masses indistinguishable from peritoneal carcinomatosis (Fig. 37.44]. Scalloping of visceral organs may be seen. Nodal metastasis is uncommon [41–43].

FIGURE 37.43 Contrast-enhanced axial CT abdomen and pelvis from a 57-year-old woman with peritoneal mesothelioma shows irregular enhancing mass at the level of umbilicus infiltrating into the anterior abdominal wall and the underlying bowel (white arrow). Ascites is absent.

FIGURE 37.44 Contrast-enhanced coronal CT abdomen and pelvis from a 41-year-old man with peritoneal mesothelioma shows extensive peritoneal disease with multifocal peritoneal plaques, thickening and masses (white arrow). Note that only trace loculated ascites is present in the background of large burden peritoneal disease (white arrow).

Well-differentiated papillary mesothelioma demonstrates multifocal calcified peritoneal plaques without substantial associated soft tissue component. There is predilection for omental involvement with caking and extensive calcification. The absence of adnexal or ovarian mass helps to exclude metastasis from ovarian serous carcinoma [41,42]. Differential Diagnosis Peritoneal carcinomatosis, lymphomatosis, and tuberculosis [42].

Peritoneal Carcinomatosis Pathogenesis and Clinical Features Peritoneal carcinomatosis implies peritoneal metastasis from malignant tumors of the epithelial origin. Common primaries are carcinoma of the ovary, stomach, colon, appendix, pancreas, gallbladder, uterus, breast, and lung [3,4,44]. Metastasis occurs by direct extension or by hematogenous and lymphatic routes, by which tumor cells invade the peritoneal surfaces and

grow along the subperitoneal connective tissues. Histological characteristic vary with tumor type [3,45]. Patients can be initially asymptomatic but progressively develop abdomen pain and distention. Nausea, vomiting and constipation accompany bowel obstruction. Imaging Features USG: Ascites is the hallmark and is frequently complex with the presence of echoes indicating proteinaceous or hemorrhagic contents or septations. Peritoneal deposits present as hypoechoic nodules or irregular masses. Omental caking involves replacement of omental fat by malignant cells producing echogenic, free floating or fixed masses. Mesentery and small bowel loop are thickened, matted, and fixed with associated adenopathy in extensive disease. Ascites helps in better delineation these findings [14]. CT: It is the modality of choice for staging, restaging, and surveillance. It is imperative to pay dedicated attention to areas of peritoneal fluid stasis such as pouch of Douglas, right subhepatic, subphrenic, paracolic spaces, and right lower quadrant to detect early disease presenting as subtle abnormal peritoneal enhancement, thickening, or nodularity (Fig. 37.45). Patterns of carcinomatosis can be plaque-like, reticulonodular, formation of soft tissue nodules or large masses (Fig. 37.46) [4]. Soft tissue nodules may show calcification, particularly from serous carcinoma from ovary and mucinous carcinoma of the rectum. Mucinous deposits are typically low attenuating (Fig. 37.47) [46]. Infiltration of mesenteric fat leads to a pleated, radiating appearance of the mesentery [3]. Extent of secondary bowel involvement can vary from serosal thickening to endoluminal masses producing bowel obstruction.

FIGURE 37.45 Contrast-enhanced axial CT abdomen from a 57-yearold man with colorectal cancer shows early peritoneal carcinomatosis with subtle nodular peritoneal thickening in the right paracolic space (black arrow) (A) and tiny implants along the hepatic surface (white arrowhead) (B). Note the unremarkable appearance of upper right paracolic space in the same patient 1 year ago (C).

FIGURE 37.46 A 35-year-old woman with metastatic clear cell ovarian carcinoma. Contrast-enhanced axial and coronal CT abdomen and pelvis demonstrate large burden peritoneal carcinomatosis with numerous soft tissue nodules and omental caking (white arrow, black arrowhead) (A and B). On single-shot T2WI MR, the peritoneal masses show intermediate signal (black arrow) (C), with enhancement on delayed phase T1WI (white arrowheads) (D). The patient underwent subsequent USG-guided biopsy of the hypoechoic omental cake (O) (E).

FIGURE 37.47 A 62-year-old woman with mucinous ovarian cancer. Contrast-enhanced axial CT abdomen and pelvis demonstrate hypoattenuating implants in the right perihepatic space, left upper quadrants (white arrows) (A), and left pelvis (white arrow) (B). On single-shot T2WI MR, the peritoneal masses show high signal indicative of mucinous composition (black arrows) (C).

MRI: Peritoneal implants have low T1, mixed T2 signal with slow enhancement, increasing in conspicuity after about 5 min of gadolinium administration (Fig. 37.46) [44]. Implants demonstrate diffusion restriction (Fig. 37.48), with the exception of the mucinous variant due to low cellularity [46].

FIGURE 37.48 A 57-year-old woman with metastatic fallopian tube cancer. Axial diffusion MR abdomen at b = 800 (A, B) demonstrates high signal of small peritoneal implants in left paracolic (white arrow) (A) and right perihepatic spaces (white arrowhead) (B). Note that the implants are much less conspicuous on single-shot T2WI (white arrow) (C).

F18-Fluorodeoxy glucose PET: It can complement CT/MRI. Findings vary from focal increased F18-Fluorodeoxy glucose (FDG) uptake to diffuse uptake along the peritoneal and serosal surfaces. Limitations are nonvisualization of subcentimeter nodules, no uptake in mucinous tumor, physiological activity in the bowel obscuring serosal implants, and low spatial resolution [3,44,45]. Differential Diagnosis

Mesothelioma, tuberculosis, peritoneal lymphomatosis, and sarcomatosis [3]. Extensive peritoneal fat saponification and necrosis in pancreatitis can also mimic carcinomatosis (Fig. 37.49).

FIGURE 37.49 Contrast-enhanced coronal CT abdomen and pelvis from a 36-year-old man with necrotizing pancreatitis demonstrates widespread fat saponification mimicking peritoneal carcinomatosis (white arrowheads).

Peritoneal Carcinomatosis: Pearls to Remember ■ Metastasis occurs by direct extension, hematogenous, and lymphatic routes. ■ Sonographic findings are complex ascites, hypoechoic nodules, irregular masses, omental caking, mesenteric, and small bowel

matting. ■ Patterns of carcinomatosis on CECT are plaque-like, reticulonodular, formation of soft tissue nodules and large masses. ■ Mucinous deposits are typically low attenuating. ■ Peritoneal implants demonstrate slow enhancement with intravenous gadolinium.

Pseudomyxoma Peritonei Pathophysiology Pseudomyxoma is characterized by accumulation of copious mucinous or gelatinous material in the peritoneal cavity. Histological classification divides pseudomyxoma into low- and high-grade variants. Low-grade pseudomyxoma shows pools of mucin, sparse tumor cells with bland cytological features, and generally no invasion of subperitoneum or lymphatics. High-grade pseudomyxoma demonstrates high-grade malignant cells, invasion, and overall poorer prognosis [3,47]. The majority of lowgrade pseudomyxoma arises from low-grade mucinous tumor of the appendix, commonly secondary to appendiceal rupture. Occurrence with ovarian tumors is proposed secondary to be due to ovarian metastasis from an appendiceal primary rather than primary ovarian tumors [3,48]. Highgrade pseudomyxoma is associated with carcinoma of rectum, ovary, stomach, and urachus [47]. On pathology, there is jelly-like covering on the peritoneum with predilection for accumulation under the right diaphragm, right subhepatic spaces, paracolic and rectouterine spaces, with relative sparing of the bowel serosa due to constant displacement by peristalsis [3]. Clinical Features Incidence is higher in females, presenting with progressive abdominal distention and weight loss. Imaging Features Radiograph: Abdominal radiographs simulate the appearance of massive ascites in large volume pseudomyxoma, with centralization of bowel loops, diffuse ground glass opacification, and displacement of properitoneal fat. Faint curvilinear calcifications may be detected [3]. USG: It demonstrates echogenic ascites with nonmobile echoes and septations. Echogenic peritoneal and omental masses can be present [14].

CT and MRI: Mucinous ascites causes scalloping of visceral surfaces of intraperitoneal organs, a diagnostic finding on CT best appreciated along the hepatic and splenic surfaces. Low attenuating ascites may show septations, loculations, and occasionally solid elements. Curvilinear calcifications may be present (Fig. 37.50) [3].

FIGURE 37.50 (A) Contrast-enhanced axial CT abdomen shows widespread hypoattenuating implants causing scalloping of hepatic and splenic surfaces in pseudomyxoma peritonei (white arrows). Few areas of thin curvilinear calcifications are also noted. (B) CT image from a different patient with adenocarcinoma of the appendix with pseudomyxoma shows scalloping of the liver surface (white arrow).

Close inspection of appendix is warranted in all cases, which may demonstrate nodular or irregular wall thickening and periappendiceal soft tissues. High-grade pseudomyxoma demonstrates aggressive features such as abdominal and retroperitoneal adenopathy, omental caking, invasion of solid organs, and chest metastasis [3]. The peritoneal implants are hyperintense on T2WI due to mucin.

Pseudomyxoma Peritonei: Pearls to Remember ■ Accumulation of copious mucinous or gelatinous material in the peritoneal cavity. ■ Divided into low- and high-grade variants. ■ Most commonly associated with low-grade mucinous tumor of the appendix. ■ Scalloping of hepatic and splenic surfaces on CT.

Desmoid Tumor Pathophysiology and Clinical Presentation Desmoids are locally aggressive tumors with a high rate of recurrence and no potential for distant metastasis. The most common location is rectus abdominis and internal oblique musculatures. Other locations include mesentery, extra-abdominal sites such as shoulder, extremities, and chest wall. Risk factors are trauma, prior surgery, pregnancy (pregnancyassociated desmoids almost always involve the abdominal wall), oral contraceptive pills, familial adenomatous polyposis, and Gardner syndromes [49,50]. On microscopy, the tumor contains fascicles of spindle cells and fibroblasts in a dense collagen stroma [49]. There is slightly higher incidence in females in third and fourth decades. Most common presentation is with a palpable mass. Imaging Features USG: Presents as a well-circumscribed or infiltrative hypoechoic mass with variable vascularity (Fig. 37.51).

FIGURE 37.51 (A) Transverse USG of left anterior abdominal wall desmoid shows a circumscribed hypoechoic mass with minimal vascularity. (B) Delayed phase T1WI coronal MRI demonstrates two lobulated anterior abdominal desmoids with heterogeneous enhancement (white arrows).

CT and MRI: CECT demonstrates a circumscribed or infiltrative soft tissue mass with variable attenuation and enhancement depending on the degree of necrosis and degeneration. On MRI, the tumor shows variable T2 signal

ranging from intermediate or high (due to increased cellularity) as seen in the active or growth phase of the disease (Fig. 37.51), and hypointense (indicating a high degree of collagen) seen in the later plateau or burnt-out phase of the disease, with heterogonous postcontrast enhancement [49,51]. The same tumor may demonstrate both components, which must be identified and reported accordingly. Differential diagnosis: Abdominal wall hematoma, abscess, hernia, sarcoma, and metastasis. When it occurs in the mesentery, carcinoid, lymphoma and sclerosing mesenteritis are in the differential consideration.

Miscellaneous Peritoneal Inclusion Cyst Pathogenesis and Clinical Features Also known as peritoneal pseudocyst or benign cystic mesothelioma, peritoneal inclusion cysts are slow-growing, nonneoplastic cystic pelvic masses occurring exclusively in the premenopausal women [52]. Pathogenesis involves initial peritoneal damage secondary to etiologies such as endometriosis, abdominal or pelvic surgery, trauma and pelvic inflammatory disease, with resultant defective absorption and adhesions. This leads to focal retention and gradual accumulation of ovarian secretion in the pelvis associated with reactive mesothelial proliferation [52,53]. The cyst can be incidental or present with pelvic pain and mass effects. Imaging Features USG: It is the mainstay diagnostic exam. Peritoneal inclusion cyst presents as a uni- or multilocular cystic adnexal mass of variable size, ranging from a few millimeters to several centimeters, occupying the entire pelvis or lower abdomen (Fig. 37.52]. The cyst can be anechoic or complex with internal debris. Complex cysts demonstrate internal septations with color flow. The lesion can be unilateral or bilateral [52,53]. Ovaries can be present within or along the wall of the cyst.

FIGURE 37.52 A 27-year-old female with a large peritoneal inclusion cyst in the left pelvis. Longitudinal pelvic USG shows multiloculated cystic left pelvic mass with thick internal septations (arrow) (A), left ovary is pushed medially (O). No significant color flow is present in the septa or cyst wall (B). Sagittal single-shot T2WI MR pelvis shows multiloculated multiseptated cystic mass (black arrow) surrounding the left ovary (black arrowhead) (C). The lesion demonstrates T1 hyperintense components indicative of hemorrhagic or proteinaceous contents (white arrow) (D), with thin septal (white arrow) enhancement on venous phase T1WI (E).

FIGURE 37.53 Illustration demonstrating the retroperitoneal anatomy. RMP: Retromesenteric plane, PS: Perirenal space, APS: Anterior pararenal space, LP: Lateral conal plane, RRP: Retrorenal plane, PPS: Posterior pararenal space.

CT and MRI: CT depicts a uni or multilocular cystic pelvic mass with fluid attenuation, thin enhancing wall, and with no solid components. Internal septations are often present. On MRI, hemorrhage may be present with variable signal intensities in the cyst components depending on the bleed chronicity (Fig. 37.52) [53]. Differential Diagnosis Hydrosalpinx, paraovarian cysts, cystic ovarian neoplasms, lymphatic malformations, and loculated ascites [52].

Peritoneal Inclusion Cyst: Pearls to Remember ■ Nonneoplastic cystic pelvic masses occurring exclusively in the premenopausal females. ■ Etiologies are endometriosis, abdominal or pelvic surgery, trauma and pelvic inflammatory disease. ■ Uni or multilocular cystic adnexal mass of variable size. ■ On CT, cysts have fluid attenuation, thin enhancing wall, internal septations, and no solid components.

Overall Clinical Approach for Diagnosis of Peritoneal Lesions A systematic approach for diagnosis of peritoneal masses requires categorization into cystic and solid lesions. Cystic lesions are further divided into simple cysts, complex cysts without solid elements, and lesions with solid elements. All the imaging features need correlation with clinical presentation. Cystic lesions: ■ Simple cystic lesions are enteric cysts, enteric duplication cysts, mesothelial cysts, seromas, and lymphoceles. ■ Complex cysts without solid elements include complex duplication cysts, nonpancreatic pseudocyst, lymphatic malformations, peritoneal inclusion cysts, abscess, and hydatid cysts. Peritoneum is an uncommon location for echinococcal cyst. Distinct imaging and clinical features of these lesions are summarized in Table 37.2. Cystic lesions with solid elements include pseudomyxoma and mucinous carcinomatosis. The differentiating feature of pseudomyxoma is scalloping of the liver and splenic surfaces.

Table 37.2 Imaging and Clinical Features of Complex Cystic Peritoneal Lesions Complex Lymphatic Nonpancreat Peritoneal Duplicatio Malformatio Abscess ic Pseudocyst Inclusion Cysts n Cyst n

Complex Lymphatic Nonpancreat Peritoneal Duplicatio Malformatio ic Pseudocyst Inclusion Cysts n Cyst n ■ Thick walle d, conta ining bowe l layer s on USG ■ Com monl y incid ental

■ Fatfluid levels ■ Commo nly incident al

■ Multilo cular multise ptated insinuat ing masses ■ Mesent ery is the most commo n location in the abdome n

■ Multilocul ar multiseptat ed masses in pelvis ■ Exclusivel y seen in premenopa usal females with history of endometrio sis, surgery, trauma and pelvic inflammato ry disease

Abscess ■ Rim enhancement, the presence of air ■ Usually associated with additional features of peritonitis and initiating etiology such as diverticulitis, appendicitis, pelvic inflammatory disease

Solid lesions: This includes tuberculosis, carcinomatosis, mesothelioma, sclerosing mesenteritis, carcinoid, desmoid and lymph nodal masses/lymphoma.

Retroperitoneum Anatomy The retroperitoneum is divided into three major compartments (Fig. 37.53): Perinephric space: It is a cone-shaped space containing kidneys and adrenal glands. It is bound anteriorly by anterior renal fascia (Gerota's fascia), and posteriorly by posterior renal fascia (fascia of Zuckerkandl). The posterior renal fascia consists of two layers; the anterior layer is continuous with anterior renal fascia. The posterior layer of posterior renal fascia forms the lateral conal fascia, which fuses with peritoneum anteriorly. The

perinephric space is usually closed inferiorly by fusion of anterior and posterior renal fascia [1,2]. Anterior pararenal space: It is present between the posterior surface of the parietal peritoneum and the anterior renal fascia. The space contains the pancreas, duodenum, ascending, and descending colon [2]. Posterior pararenal space: It is situated between posterior renal fascia and fascia transversalis. The space contains only fat and is continuous with the properitoneal fat [1,2]. ■ The small midline space between the perinephric spaces encloses the aorta and Inferior Vena Cava (IVC) and is contiguous superiorly with the posterior mediastinum. ■ The intervening spaces between the three compartments form the interfascial planes, consisting of retromesenteric plane, retrorenal plane, and lateral conal plane (Fig. 37.53). These expansile planes serve as additional routes of spread of pathologies such as tumor and infection [54]. ■ The retromesenteric and retrorenal planes communicate inferiorly with the pelvic retroperitoneum; pathological processes can also spread across the midline via retromesenteric space. Lateral conal plane is present between the layers of the lateral conal fascia. All three interfascial planes communicate at the fascial trifurcation [1]. ■ Grey turner sign in acute pancreatitis (manifesting as flank discoloration) is caused by spread of pancreatic enzymes from anterior pararenal to posterior pararenal space and then to lateral edge of the quadratus lumborum [55].

Nonneoplastic Disorder Retroperitoneal Fibrosis Pathophysiology: Retroperitoneal fibrosis is rare spectrum of disorders characterized by aberrant fibrotic reaction causing encasement of the retroperitoneal organs. It is classified into primary or idiopathic (two-third of cases) and secondary forms. It is also divided into benign and malignant subtypes depending on the prognosis, with malignant type commonly associated with retroperitoneal neoplasms [56]. Etiologies of secondary retroperitoneal fibrosis are drugs such as ergot, hydralazine, beta-blockers, methyldopa, and neoplasms such as lymphoma, sarcoma and carcinoid, infections (histoplasmosis, tuberculosis), Ig4 disease, radiation, and hemorrhage [56,57]. Perianeurysmal retroperitoneal fibrosis, as a subtype of retroperitoneal fibrosis spectrum, is associated with inflammatory aortic aneurysms (Fig. 37.54) [58].

FIGURE 37.54 Contrast-enhanced axial CT abdomen from a 65-yearold woman with abdominal aortic aneurysm shows perianeurysmal retroperitoneal fibrosis (white arrow).

Clinical features: Incidence is higher in males. Nonspecific presentation includes malaise, weight loss, pain, fevers, and features of renal failure secondary to obstructive uropathy [56,59]. Imaging Features USG: It has poor sensitivity to visualize retroperitoneal soft tissues, hence the utility is limited to detect and follow up hydronephrosis. CT: It is the modality of choice to evaluate the extent of disease and complications. Retroperitoneal fibrosis presents as ill-defined soft tissue encroaching and encasing retroperitoneal structures such as ureters, aorta, IVC and kidneys depending on the disease severity; with initial epicenter of the disease typically located near the distal aortic bifurcation or proximal iliac arteries (Fig. 37.55) [59]. The degree of enhancement varies with the stage, with avid enhancement seen in early disease and minimal to no enhancement in chronic fibrosis. The soft tissue is present anterior and lateral to the aorta, relatively sparing the posterior aspect and without associated aortic displacement; unlike lymphomas. Concomitant reactive retroperitoneal adenopathy can be present [56,59].

FIGURE 37.55 Contrast-enhanced axial CT abdomen from a 37-yearold man with idiopathic retroperitoneal fibrosis shows soft tissue encasing the common iliac arteries (white arrow).

MRI: It has better tissue characterization, with fibrosis demonstrating low signal on T1WI. On T2WI, signal intensity varies with the stage of fibrosis; early fibrosis shows high T2 signal due to edema and late fibrosis shows T2 dark signal. The degree of contrast enhancement usually parallels T2 signal, with avid enhancement in active inflammation (Fig. 37.56) [56,59].

FIGURE 37.56 Delayed phase axial and coronal T1WI MR abdomen and pelvis demonstrate ill-defined enhancing soft tissue encasing the distal abdominal aorta in active idiopathic retroperitoneal fibrosis (white arrow) (A and B).

Differential diagnosis: Lymphoma, retroperitoneal sarcoma, tuberculosis, and metastasis (Fig. 37.57).

FIGURE 37.57 Contrast-enhanced axial CT abdomen and pelvis from a 56-year-old woman with breast cancer demonstrates enhancing retroperitoneal soft tissue metastasis simulating retroperitoneal fibrosis (white arrow) (A and B). Note that the soft tissue encases both kidneys (white arrowhead), aorta, and extends into the pelvic retroperitoneum.

Retroperitoneal Fibrosis: Pearls to Remember

■ Spectrum of disorders characterized by aberrant fibrotic reaction causing encasement of the retroperitoneal organs. ■ On CECT, ill-defined soft tissue encroaching and encasing retroperitoneal structures such as ureters, aorta, IVC, and kidneys. ■ Avid enhancement in early disease and minimal to no enhancement in chronic fibrosis. ■ The soft tissue is present anterior and lateral to the aorta, relatively sparing the posterior aspect and without aortic displacement.

Retroperitoneal Bleed Etiologies of retroperitoneal bleed are trauma, blood dyscrasias, anticoagulation therapy, rupture of abdominal aortic aneurysm, and surgery. Appearance varies with the bleed chronicity, with acute and subacute blood hyperdense on CT (Fig. 37.58). Chronic hematoma has low attenuation. Major differential consideration is retroperitoneal sarcoma; with bleed characterized by temporal evolution/resolution time [60].

FIGURE 37.58 Noncontrast axial CT abdomen shows a large right retroperitoneal hematoma, with mixed densities, blood-fluid levels, and hyperdense components indicative of active bleed (white arrow).

Neoplastic Disorder Retroperitoneal Liposarcomas Pathophysiology and clinical features: These are the most common primary malignant retroperitoneal tumors of mesenchymal origin. Retroperitoneal liposarcomas are classified into (1) Well differentiated with or without dedifferentiation, (2) myxoid and round cell, and (3) pleomorphic subtypes. Well-differentiated liposarcomas are the most common subtypes [61]. Incidence is higher in fifth to sixth decades with no specific sex predilection. The tumor is frequently asymptomatic, often detected as a large mass [60,61]. Imaging Features CT and MRI: Well-differentiated liposarcomas present as lobulated fat– containing retroperitoneal masses, with typically large volume fat

composition (Fig. 37.59). The mass demonstrates septae and may have solid components 1 cm. Nonfatty areas are hypointense on T1WI and iso to hyperintense on T2WI. Myxoid liposarcoma is a more aggressive tumor presenting as a hypoattenuating mass due to its myxoid component. On MRI, the tumor shows high T2 signal with a variable degree of contrast enhancement (Fig. 37.60) [61]. Macroscopic fat forms a relatively small component of the tumor.

FIGURE 37.59 Contrast-enhanced axial and coronal CT abdomen shows a large, well-differentiated left retroperitoneal sarcoma displacing the small bowel loops and descending colon (A and B). The mass demonstrates fat attenuation without solid components or calcifications. On single-shot T2 W MR, the mass shows fat signal with thin internal septations (white arrowheads) (C). Note that the patient status is post left nephrectomy.

FIGURE 37.60 Contrast-enhanced axial CT pelvis (A) from a 42-yearold man with biopsy-proven left pelvic myxoid liposarcoma of the left gluteal region (white arrow) (A). The lobulated, hypoattenuating mass is extending into the greater sciatic foramen. On MR, the mass is T2 hyperintense (B), and shows heterogeneous enhancement on venous phase T1WI (C).

Pleomorphic liposarcoma is the most aggressive subtype presenting as a predominantly nonlipogenic mass with none or little fat. The tumor shows extensive necrosis and hemorrhage due to anaplasia [63]. Unlike the other subtypes that may be prospectively diagnosed on imaging, pleomorphic liposarcoma cannot be differentiated radiologically from other soft tissue sarcomas in most cases. Differential diagnosis: Fat containing retroperitoneal lesions such as lipoma, angiomyolipoma, teratoma, myelolipoma and sarcomas such as leiomyosarcoma [61,64]. Leiomyosarcoma Pathophysiology and clinical features: Retroperitoneal leiomyosarcoma is a malignant neoplasm with smooth muscle differentiation. The tumor originates from smooth muscle of the retroperitoneum or more commonly from the wall of large vasculature such as IVC and renal veins. On histology, the tumor is composed of fascicles of spindle cells with occasional fibrosis, myxoid change, or coagulative necrosis. Cellular atypia and mitotic figures are common. Most affected patients are in the fifth or sixth decades with a female predilection. The mass can be asymptomatic, which leads to the formation of large masses till diagnosis, or present with compressive symptoms due to pain. Intraluminal tumors tend to present early due to associated IVC obstruction and symptoms of the Budd Chiari syndrome such as hepatomegaly, jaundice, ascites, and leg edema [65]. Imaging Features USG: USG demonstrates lobulated, heterogeneous solid mass with scattered cystic areas and internal vascularity. Intravascular tumor shows expansile growth and best appreciated with color Doppler [65].

CT: The tumor is typically large lobulated solid mass with occasional scattered cystic components, areas of necrosis, and heterogeneous contrast enhancement (Fig. 37.61]. Calcifications are uncommon. Perirenal and posterior pararenal spaces are common locations for extravascular tumors. Intravascular tumors can be classified based on the location as present caudal to renal vein (segment 1), caudal to hepatic veins (segment 2, most common), and cranial to the hepatic veins (segment 3, least common). Bland thrombus can be present (Fig. 37.62]. The spread is by direct invasion to adjacent organs such as kidneys, adrenals, pancreas, or stomach or by distant metastasis. Sites of metastasis include the lungs (most common), peritoneum, liver, bones and lymph nodes, with overall higher incidence in intravascular tumors due to hematogenous dissemination [65–67].

FIGURE 37.61 Contrast-enhanced axial CT abdomen demonstrates retroperitoneal leiomyosarcoma as a large heterogeneous solid mass with scattered cystic areas (white arrow) (A). The mass is encasing the left renal vasculatures and extending along the right paraspinal musculature. On MRI, the mass shows hyperintense cystic areas on T2 WI (B), with heterogeneous post contrast enhancement (C).

FIGURE 37.62 (A) Contrast-enhanced coronal CT abdomen demonstrates IVC leiomyosarcoma as heterogeneously enhancing, expansile mass within the IVC (white arrow). (B) Axial CT image shows a bland thrombus present superior to the mass in the intrahepatic IVC segment (black arrowhead).

MRI: The solid tumor components demonstrate low to iso T1 and high T2 signal with heterogeneous contrast enhancement. Associated hemorrhage can impart high T1 signal to the tumor components. Black blood imaging helps in delineation of intravascular tumors, which are usually hyperintense, and to evaluate the tumor extent [66]. Differential diagnosis: Major differentials include other retroperitoneal neoplasms such as liposarcoma, lymphoma, metastasis, germ cell, and neurogenic tumors. Hematoma and retroperitoneal fibrosis are the most common nonneoplastic entities in the differential consideration [65]. Lymphomas Retroperitoneum is a common site of involvement by both Hodgkin and non-Hodgkin lymphomas. Findings on CECT are para-aortic lymphadenopathy and mass formation with mild homogenous enhancement. Calcification and necrosis are usually present posttreatment. Floating aorta sign refers to anterior displacement of aorta and IVC by extensive retroperitoneal adenopathy (Fig. 37.63). On MRI, lymphomatous masses are T1 isointense, iso to hyperintense on T2WI, with moderate homogenous or heterogeneous enhancement [60].

FIGURE 37.63 Contrast-enhanced axial CT abdomen from a 36-yearold man with non-Hodgkin's lymphoma shows bulky retroperitoneal adenopathy (white arrow). The adenopathy is lifting the abdominal aorta producing “floating aorta sign”.

Neurogenic Tumor These are tumors of variable malignant potential with higher incidence in younger age groups. The tumors can arise from nerve sheath (schwannoma, neurofibroma, malignant nerve sheath tumors), ganglionic (ganglioneuroma, neuroblastoma), and paraganglionic cells (paraganglioma, pheochromocytoma) [60]. Schwannomas represent 6% of retroperitoneal neoplasms. These are well-defined masses with homogenous (Fig. 37.64), or heterogeneous attenuation and variable enhancement. Internal calcifications and cystic changes may be present [60,68].

FIGURE 37.64 Contrast-enhanced axial CT abdomen from a 31-yearold-female with left retroperitoneal Schwannoma (white arrow). The circumscribed solid mass demonstrates mild homogenous enhancement.

Teratomas These are germ cell tumor with higher incidence in females and early adulthood. Classified into benign or malignant types; benign teratoma is further divided into mature and immature subtypes. Mature teratoma (also known as dermoid cyst) is predominately cystic and contains fat with sometimes fat-fluid level, cystic changes (Fig. 37.65), calcifications and occasional tooth formation. Differential diagnosis includes fetus in fetu, a rare anomaly occurring secondary to abnormal embryogenesis in diamniotic, monochorionic twins in which a vertebrate fetus is enclosed within the normally developing fetus (Fig. 37.66). It presents as a calcified mass with some identifiable fetal components such as vertebral column and limbs on CT. Retroperitoneum serves as the most common location for this anomaly [69]. Immature teratomas are commonly solid. Malignant transformation is associated with invasion of adjacent organs and vascular involvement; however, incidence is low in the retroperitoneum [60].

FIGURE 37.65 Contrast-enhanced axial CT abdomen from a 56-yearold woman with right retroperitoneal mature teratoma (white arrow). The lobulated mass demonstrates multifocal cystic areas, heterogeneous enhancement, and is inseparable from the aorta.

FIGURE 37.66 Patient with fetus in fetu. On abdominal radiograph, there is elevation of the right diaphragm with an ill-defined soft tissue density and coarse calcifications in right upper quadrant (A). Subsequent CT abdomen shows a large mass in the right retroperitoneum with internal coarse calcifications, tooth formation, and fat densities in fetus in fetu (white arrowhead) (B and C).

( Source: Chadha M, Aggarwal B. Foetus in Foetus: CT findings in two cases; Abdominal Imaging 27:595-599, September 2002.)

Abdominal Wall Anatomy: The layers of the abdominal wall (from superficial to deep) include the skin, subcutaneous fat, deep subcutaneous membranous tissue (also known as Scarpa fascia), muscle layer, extraperitoneal fat, and parietal peritoneum. The muscle layer can be further divided into anterior, lateral, and posterior compartments (Fig. 37.67). Anterior compartment includes two longitudinally oriented rectus abdominis muscles extending from the xiphisternum to pubis. Lateral compartment (from superficial to deep) consists of external oblique, internal oblique, and transverse abdominis muscles. Rectus abdominis is enclosed by a fascial sheath formed by aponeurosis of three lateral abdominis muscles; this fascial sheath is deficient posteriorly below the arcuate line. Curvilinear tendinous intersection at the junction of the anterior and lateral muscle groups forms the semilunar line. The posterior compartment includes the latissimus dorsi, quadratus lumborum, and erector spinae muscles; these muscle groups are lined by the thoracolumbar fascia. The major vascular supply of the anterior abdominal wall is through the superior and inferior epigastric vessels running along the posterior border of rectus abdominis [70].

FIGURE 37.67 Axial CT abdomen with colored illustration of the abdominal wall anatomy.

Abdominal Wall Hernia Pathophysiology and clinical features: Abdominal wall hernias (also known as external hernia) are abnormal protrusions of intrabdominal contents through the weakened musculofascial layers. They can be congenital or acquired. Their incidence is higher in males, with highest frequency being of inguinal hernias. Females have an increased tendency to develop femoral and umbilical hernias due to anatomic predispositions [71]. The diagnosis is made on clinical examination in patients presenting with abdominal bulge, mostly accompanied with pain and discomfort that increases with straining or cough. Clinical detection is limited in patients with obesity and in postoperative abdomen, warranting need for imaging. Imaging techniques USG: It is the modality of choice for detection, size measurement of the defect, delineation of the hernia contents, and real-time evaluation of reducibility and incarceration. Color Doppler helps in detection of flow abnormalities related to bowel ischemia [71].

CT: CT helps in preoperative planning, detection of hernia complications, in obese and postsurgical patients. Applications of maneuvers such as Valsalva or straining and scanning in decubitus positions aid in detection and evaluation of small hernias. CT also helps to distinguish hernia from other abdominal wall pathologies such neoplastic masses and hematomas. Classification of Abdominal Wall Hernias 1. Groin hernias: Inguinal (direct and indirect) and femoral hernia. a. Indirect inguinal hernia: Most common subtype involving herniation through the internal inguinal ring via a patent process vaginalis. The hernia sac is present lateral to the inferior epigastric vessels (Fig. 37.68). Inguinal hernia containing appendix is known as Amyand's hernia (Fig. 37.69). Littre hernia is inguinal hernia containing Meckel's diverticulum. Pantaloon hernia is a combination of adjacent hernia sacs of inguinal and femoral regions [72–74]. b. Direct inguinal hernia: Involves herniation through the posterior wall of inguinal canal due to acquired weakness in the transversalis fascia. The sac is present medial to the inferior epigastric vessels (Fig. 37.70) [71,72]. c. Femoral hernia: Involves herniation through the femoral ring into the femoral canal present posteroinferior to inguinal ligament and medial to femoral veins. It has increased incidence in females as broader pelvis predisposes herniation into the femoral canal. Narrow neck of the sac increases risk of complication such as obstruction and incarceration (Fig. 37.71). De Garengeot hernia is a femoral hernia containing appendix [71,75]. 2. Ventral hernias: Include hernia through the anterior, lateral, and posterior abdominal wall. Midline hernias include umbilical, paraumbilical, epigastric, and hypogastric. Spigelian hernia involves the lateral ventral wall. Lumbar hernia occurs through the posterior wall. a. Umbilical hernia: Most commonly acquired in adults. Predisposing factors are pregnancy, obesity, and ascites (Fig. 37.72) [72]. b. Paraumbilical hernia: Occurs through linea alba at the level of umbilicus secondary to rectus diastasis (Fig. 37.73) [72]. c. Epigastric and hypogastric hernia: Occurs along the linea alba above and below the level of umbilicus, respectively. Contents usually include properitoneal fat and rarely viscera. Obesity is a predisposing factor [76]. d. Spigelian hernia: Involves herniation along the linea semilunaris (fibrous union of rectus and oblique muscle aponeuroses) due to acquired weakness or prior surgery (Fig. 37.74) [71,72]. e. Lumbar hernia: Occurs through the defect in the musculature of superior (Grynfeltt– Lesshaft) or inferior lumbar triangles (Petit's) located between 12th rib and iliac crest. It can be posttraumatic, postsurgical (especially after renal surgeries), or spontaneous (Fig. 37.75) [72]. 3. Incisional hernia: These occur as a complication of abdominal surgeries, more commonly with vertical than transverse incisions. Parastomal and port site hernias are included in this subtype [72]. 4. Miscellaneous: Includes interparietal (between the fascial planes of abdominal muscles), Richter (herniation of partial circumference of the bowel wall), sciatic (through the sciatic foramen), obturator (through obturator canal), and perineal hernias (through the pelvic floor). All these are highly prone to incarceration [77].

FIGURE 37.68 Contrast-enhanced coronal (A) and axial (B) CT pelvis shows right indirect inguinal hernia containing small bowel and mesentery, occupying the scrotal sac (white arrow). No signs of obstruction or strangulation are present.

FIGURE 37.69 Contrast-enhanced coronal CT abdomen and pelvis shows Amyand's hernia containing appendix (white arrow).

FIGURE 37.70 Transverse USG of right groin shows a small fat containing direct inguinal hernia (white arrowheads). Note that the hernia sac is located medial to the inferior epigastric vessels (white arrow).

FIGURE 37.71 Contrast-enhanced axial and coronal CT pelvis shows an obstructed right femoral hernia containing small bowel (white arrow) (A and B). Note the upstream bowel obstruction (B). Note compression and flattening of the right femoral vein (arrowhead in A).

FIGURE 37.72 Contrast-enhanced sagittal CT abdomen and pelvis shows a moderate sized nonobstructed umbilical hernia containing fluid and mesenteric fat (white arrow) (A). Contrast-enhanced sagittal CT abdomen and pelvis from a different patient shows a moderate-sized small bowel containing umbilical hernia with closed-loop obstruction (white arrow) (B). The involved bowel shows dilatation and mural hyperenhancement. The presence of fluid and stranding in this hernial sac (with absent abdominal ascites) is related to strangulation.

FIGURE 37.73 (A) Transverse USG of umbilical region shows a nonreducible fat containing left paraumbilical hernia, with trace fluid in the hernia sac (white arrow). (B) Subsequent contrast-enhanced axial CT abdomen demonstrates left paraumbilical hernia with surrounding subcutaneous stranding related to underlying incarceration (white arrow).

FIGURE 37.74 Contrast-enhanced axial CT pelvis shows ascending colon containing right Spigelian hernia (white arrow). The presence of fluid and stranding in the hernia sac is related to underlying incarceration.

FIGURE 37.75 Contrast-enhanced axial CT abdomen shows a moderate-sized, nonobstructed left lumbar hernia containing descending colon (white arrow).

Table 37.3 summarizes the abdominal wall hernias with specific names. Complications are incarceration (implying nonreducibility), strangulation, and bowel obstruction. Strangulation refers to compromise of vascular supply, which presents as thickening of the hernia sac, fluid within the sac, mesenteric fat stranding, bowel wall edema, hypoenhancement or pneumatosis. Post hernia repair complications include recurrence, infections, fluid collections, and mesh related issues such as extrusion and infection [77]. Table 37.3

Hernias With Specific Names Amyand's hernia

Inguinal hernia containing appendix

Littre hernia

Inguinal hernia containing Meckel diverticulum

Pantaloon hernia

Combination of adjacent hernia sacs of inguinal and femoral regions

De Garengeot hernia

Femoral hernias containing appendix

Richter hernia

Herniation of partial circumference of the bowel wall

Differential diagnosis: Abdominal wall hematomas, abscess, lipoma, desmoid, hydrocele, and varicocele.

Neoplastic Disorder Desmoid tumors are the most common primary neoplasms of the anterior abdominal wall. These are discussed under the section on neoplastic disorders of the mesentery and peritoneum. Abdominal wall metastasis: These are the most common malignant lesions of the anterior abdominal wall. Abdominal wall metastases are usually associated with advanced stage malignancy with widespread metastasis, except in the instances of postsurgical, laparoscopic port site or needle tract seeding. Imaging features resembles the primary. Characteristic example is Sister Mary Joseph's nodule from cancers of the gastrointestinal tract and ovary [78]. This is an eponymous name given to a metastatic nodule at the umbilicus from these tumors. Gall bladder cancers and ovarian tumors in particular have a propensity for abdominal wall metastasis (Fig. 37.76).

FIGURE 37.76 Contrast-enhanced sagittal CT abdomen and pelvis from a 56-year-old man shows metastatic nodules at the umbilicus (Sister Mary joseph nodules; arrow) from carcinoma of GE junction (not shown).

Suggested Readings • R Diab, M Virarkar, M Saleh, et al., Imaging spectrum of mesenteric masses, Abdom Radiol 45 (2020) 3618–3636. • DMc Patrick, F Antonella, MM Michael, Neoplastic diseases of the peritoneum and mesentery, Am J Roentgenol 200 (5) (2013) W420–W430. • A Coffin, I Boulay-Coletta, D Sebbag-Sfez, M Zins, Radioanatomy of the retroperitoneal space, Diagn Interv Imaging 96 (2) (2015) 171–186. • Rajiah P, Sinha R, Cuevas C et al. Imaging of uncommon retroperitoneal masses, Radiographics 31 (4) (2012) 949–976. • HB David, M Parisa, CO Daniel, GL Meghan, OM Christine, JP Perry, DM William, M Vincent, Mellnick. Imaging of abdominal wall masses, masslike lesions, and diffuse processes, RadioGraphics 40 (3) (2020) 684–706.

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SECTION E

Genitourinary Tract

CHAPTER 38

Urinary Tract: Anatomy, Conventional Radiology, and Ultrasonography Smita Esther Raju, Shalini Govil

Introduction We begin the section on urinary tract imaging by focusing on the basics. We discuss the anatomy of the urinary tract viscera along with conventional imaging and ultrasonography (USG) techniques in the first half of the chapter. We subsequently focus on the basics of intravenous urography (IVU) interpretation, while advanced cross-sectional techniques and their interpretation are discussed in the chapters ahead.

Anatomy Kidneys and Ureters ■ The kidneys are bean-shaped organs with their concave edges pointing medially. The right kidney is placed lower than the left, owing to the presence of the liver above. In quiet respiration, the kidneys move up and down ∼2–3 cm but can move twice that distance on deep inspiration ■ The hilum of the kidney is a vertical opening on the medial aspect that contains the renal pelvis. The renal vein and one or two branches of the renal artery pass through the hilum to enter the kidney anterior to the renal pelvis, with a further branch of the renal artery passing through the hilum posterior to the renal pelvis. The hilum also contains fat, sympathetic nerve fibres, and lymphatic channels that drain into the para-aortic lymph nodes around the origins of the renal arteries from the aorta ■ Renal tissue is divided into a peripherally placed cortex and the central medulla. The cortex contains the glomeruli and the proximal and distal convoluted tubules. The medulla consists of 8–16 pyramids and contains the Loop of Henle and the collecting ducts. The apex of each pyramid projects into a calyx as a renal papilla. The medullary collecting ducts converge into central, papillary ducts (of Bellini) near the tip of each medullary pyramid and drain into a minor calyx through tiny orifices in the renal papillae (Fig. 38.1) ■ The superior end of the ureter expands to form the renal pelvis which divides into 2–4 major calyces, each of which divide into 2–4 minor calyces. Each calyx is indented by a papilla, which is the apex of a medullary pyramid. The calyces therefore have a characteristic shape with a well-defined extension around the convexity of the papilla (the fornices). The minor calyces drain into a major calyx via a neck (infundibulum). Often at the renal poles (especially the upper pole) several papillae drain into one large calyx. These are referred to as compound calyces and are particularly vulnerable to damage from reflux nephropathy ■ The ureter runs in the retroperitoneum along the anterior aspect of the psoas muscle, separated from it by the transversalis fascia. As it enters the pelvis, it crosses over the anterior aspect of the common iliac artery bifurcation immediately in front of the sacroiliac joint. It descends along the lateral pelvic wall, just medial to the obturator internus, to the level of the ischial spine, from where it runs anteromedially until it enters the superolateral angle of the bladder base. The vas deferens crosses over the ureter, separating it from the bladder just before the ureters enter the bladder wall (Fig. 38.2). The ureters run obliquely through the bladder wall for around 2 cm ■ A fibrous capsule is closely applied to the renal cortex over the entire kidney apart from the hilum. The kidney is surrounded by perinephric fat and lies within a space partly enclosed by layers of fascia: the perinephric space (Fig. 38.3) ■ During embryological development, as the kidneys ascend from the pelvis, the surrounding perinephric fascia forms a cone, with its apex inferiorly. The perinephric fascia anterior to the kidney is often referred to as Gerota's fascia, the posterior fascia as Zuckerkandl's fascia and the enclosed space as the perinephric space. It contains the kidney, the adrenal gland (anteromedial to the kidney on the left, superomedial to the kidney on the right), the upper ureter and the perinephric fat ■ The anterior interfascial or retromesenteric space is a potential space within the laminated anterior perinephric fascia that can eventually transmit disease processes across the midline. The posterior interfascial or retrorenal space is also laminated and contains a potential space. Fluid in either of these potential spaces may track to the other and also via the fascial trifurcation into the lateroconal fascia. Fibrous septae are found within the perinephric space running from the renal capsule to the perinephric fascia and act as potential conduits between the perinephric and interfascial potential spaces ■ Posteriorly, the kidneys lie over the psoas, paraspinal muscles, 12th rib on the right and 11th rib on the left. Anterosuperiorly, the kidneys are in contact with the adrenal glands and anteroinferiorly with the jejunum. Anterolaterally, the kidneys abut the liver and hepatic flexure on the right; the spleen and splenic flexure on the left. The right kidney is related anteromedially to the duodenum and the left kidney is related to the pancreas and stomach anteromedially (Fig. 38.4) ■ The arterial supply and venous drainage of the kidneys are both extremely variable. The renal arterial supply is most commonly provided by a single lateral branch of the aorta, the renal artery, originating at the level of the first lumbar disc. The right renal artery has the longer

course and runs posterior to the inferior vena cava. The renal arteries run posterior to their respective renal veins. The renal artery gives off the inferior adrenal and the renal capsular arteries and then classically divides into three branches as it enters the renal sinus, two running anterior to the renal pelvis, and one posterior. The main renal branches subsequently divide into the interlobar arteries, which run centrifugally within the cortical tissue between the medullary pyramids. At the level of the base of the pyramids the interlobar arteries give off the arcuate arteries, which run along the line of the corticomedullary junction ■ The venous drainage mirrors the arterial tree except that the kidneys are drained by five or six major venous branches, which most commonly combine to form a solitary renal vein that drains into the inferior vena cava, also around the level of the first lumbar disc. The lymphatic drainage of the kidneys is to the para-aortic lymph nodes around the origin of the renal arteries

FIGURE 38.1 Kidney: anatomy. Cortex (red asterisk) Medulla (white asterisk) Papilla (blue asterisk) Calyx (black asterisk) Bowman's capsule (brown) Proximal convoluted tubule (blue) Loop of Henle (black) Distal convoluted tubule (green) Collecting duct (yellow).

FIGURE 38.2 Urinary tract: anatomy. Adrenal gland (black arrow) Renal vein (blue arrow) Renal artery (red arrow) Kidney (black asterisk) Ureter (black dashed arrow) Gonadal vein (green arrow) Vas deferens (blue dashed arrow) Bladder (red asterisk)

(Courtesy: Dr. Karthikumar.)

FIGURE 38.3 Retroperitoneal fascial spaces. 1. Parietal peritoneum 2. Anterior pararenal space 3. Anterior perinephric (Gerota) fascia 4. Properitoneal fat line 5. Posterior pararenal space 6. Perinephric space 7. Posterior perinephric (Zuckerkandl) fascia 8. Transversalis fascia 9. Fascial trifurcation 10. Lateroconal fascia.

FIGURE 38.4 Anterior relations of (A) the right kidney and (B) the left kidney. 1. Hepatic flexure 2. Small intestine 3. Right adrenal gland 4. Liver 5. Duodenum 6. Left adrenal gland 7. Spleen 8. Stomach 9. Pancreas 10. Splenic flexure

Bladder and Pelvis ■ The urinary bladder lies immediately posterior to the pubic bones. When full, it is roughly spherical but when empty, it approximates to a pyramidal shape, having an apex and four roughly triangular surfaces: posterior (base), superior and two inferolateral. The apex lies immediately behind the upper margin of the symphysis pubis and gives rise to the urachus, which is the fibrous remnant of the allantois. The urachus runs superiorly in the extraperitoneal fat to the umbilicus as the median umbilical ligament ■ The superior surface of the bladder is covered by parietal peritoneum and loops of ileum and sigmoid colon. The inferolateral surfaces relate anteriorly to retropubic fat and pubic bones and posteriorly to the obturator internus (superiorly) and the levator ani (inferiorly). In males, the bladder base receives the ureters at its superolateral angles, gives rise to the urethra at its inferomedial angle and rests inferiorly on the prostate. Muscle fibres of the bladder wall run continuously into the prostate and are thickened around the origin of the urethra as the internal sphincter vesicae at the bladder neck ■ The bladder mucosa is thrown into folds when the bladder empties, except over the base where it is firmly adherent to the underlying muscle layers as the trigone. The superior border of the trigone is defined by a muscular ridge running between the ureteric orifices (the interureteric ridge). The upper part of the base is covered by peritoneum and lies anterior to the rectovesical pouch (uterovesical pouch in the female), the lower part is subperitoneal and separated from the rectum by the vasa deferentia and seminal vesicles (vagina in the female)

■ Lymphatic drainage of the bladder is into the internal and external iliac lymph nodes lying along the course of the respective arteries. These in turn drain into the common iliac nodes. The medial chains of the external iliac lymph nodes (obturator nodes) lie between the external and internal iliac vessels along the pelvic side wall. They are frequently involved early in metastatic spread of bladder or prostatic cancers and are therefore often referred to as sentinel nodes ■ The transversalis fascia that lines the inside of the abdominopelvic cavity extends from the inferior surface of the diaphragm, along the inner surface of the abdominal wall musculature to cover the superior surface of the pelvic diaphragm or levator ani. It then continues inferiorly as the pelvic fascia, lining the obturator internus laterally and the pelvic diaphragm inferiorly ■ The parietal peritoneum of the abdomen also continues inferiorly and is reflected over the pelvic viscera and fat-containing spaces of the pelvis, leaving most of the pelvic organs outside the peritoneal cavity ■ The umbilicovesical fascia is a large triangular fascia with its apex at the umbilicus that extends inferiorly, dividing the prevesical space anteriorly from the perivesical space posteriorly and centrally. The cave of Retzius is the part of the prevesical space immediately posterior to the pubis. The prevesical space continues posterolaterally into the paravesical spaces (Fig. 38.5). These spaces are continuous superiorly with the properitoneal fat stripes or lateral extraperitoneal spaces of the abdomen and the posterior pararenal spaces ■ The perivesical space contains the bladder, the urachus and the seminal vesicles and is limited posteriorly by the rectovesical septum in males and rectovaginal septum in females ■ The pelvic organs are supported by the pelvic floor, which is formed by the pelvic diaphragm that separates the pelvic cavity superiorly from the perineum inferiorly. The pelvic diaphragm consists of the large levator ani and the small coccygeus muscles and their covering fascia. The puborectalis sling is a prominent part of the levator ani which runs around the lateral and posterior aspects of the anorectal junction and sweeps forward along the lateral margins of the prostate and inserts into the posterior aspect of the body of the pubis

FIGURE 38.5 Extraperitoneal spaces of the pelvis. 1. Transversalis fascia 2. Prevesical space (cave of Retzius) 3. Perivesical space 4. Bladder 5. Prostate 6. Rectum 7. Seminal vesicles 8. Rectovesical septum 9. Paravesical space 10. Obturator internus.

Imaging Plain Radiography The standard plain radiographic imaging of the urinary tract is the “KUB” (kidneys, ureters, and bladder), a fulllength abdominal film extending down to the lower border of pubic symphysis to cover the bladder neck and urethra in the female/posterior urethra in the male. The image is obtained with the patient supine, using a low voltage technique (60–65 kV) to maximize soft-tissue contrast. The outline of several anatomical structures can be seen on the KUB, including kidneys, bladder, psoas muscles, lumbosacral spine, bony pelvis, bowel, and lung bases. Therefore, a wide range of pathology may be incidentally evident on a KUB radiograph taken for urinary calculi or as a 1st “scout”/precontrast image of an intravenous urography (IVU) (Fig. 38.6).

FIGURE 38.6 Normal KUB radiograph. (A) Supine x-ray AP view: kidney-ureter-bladder. (B) Color-key diagram: kidneys (brown line outline), psoas muscles (pink outline), the anticipated line of the ureters (yellow line), bladder (green outline) and anticipated line of the urethra (blue outline).

Sensitivity of KUB for ureteric calculi is dependent on many factors including stone location, size, composition, patient habitus and overlying bowel contents. Notably, the KUB is extremely limited in the detection of small calculi (1.5 cm 5. Chemical composition: COM and brushite stones 6. Higher stone-to-skin distance (obesity) 7. Stone location: narrow infundibulopelvic angle with a long, narrow infundibulum 8. High stone volume COM, calcium oxalate monohydrate; HU, Hounsfield units. Various treatment options are summarized in Table 39.12. Table 39.12 Treatment Strategies for Various Situations in Case of Ureteric Calculi Treatment When to Apply Strategy Observation As per the new AUA guidelines, uncomplicated calculi 40% (86% sensitivity, 95% specificity). In these calculations, placement of ROI when measuring the attenuation should ensure two-third coverage of adrenal surface area, while foci of necrosis should be excluded and image acquisition at a CT exposure parameter of 120 kVp, which is the best to estimate tissue density (Table 41.2) [6,7]. Table 41.2 Quantitative Imaging of Adrenal Cortical Adenoma Quantitative Imaging

Cutoff Thre shol d

CT dynamic delayed contrast

Absolute percentage washout (APW)

APW = attenuation in contrast-delayed scan/ attenuation in contrast–noncontrast × 100

>60 %

Relative percentage washout (RPW) RPW = attenuation in contrast-delayed/attenuation in contrast scan × 100 MRI chemical shift imaging

>40 %

Adrenal/splenic ratio (ASR)

ASR = (SI adrenal lesion out of phase/SI spleen out of phase)/(SI adrenal lesion in phase/SI spleen in phase) × 100

5 %

bowel peristalsis. MRI is therefore customarily reserved for use when CT is contraindicated and as second-line imaging. On T1 and T2, the normal adrenal gland is clearly delineated, hypointense to surrounding hyperintense retroperitoneal fat and isointense to muscle (Fig. 41.4). Most tumors are T2 hyperintense and T1 hypointense. CEMR enhancement patterns and washout kinetics are similar to that seen on CECT, and can help characterize adenomas, metastases, and pheochromocytomas. Additionally, MRI can provide a specific diagnosis when CT findings are equivocal, especially for lesions with macroscopic fat such as myelolipoma or microscopic, intracellular lipid found in adenomas. Chemical shift MRI (CS-MRI) is a noncontrast MRI technique that can detect both macroscopic and microscopic, intracellular fat and is based on the principle that the precession frequency of fat is lower than water when placed within a magnetic field. On T1 GRE, because of differing precession frequency, lipid and water signals are summated when in-phase but nulled when out-of-phase, resulting in a signal drop. Similar to CT densitometry, CS-MRI is both sensitive (81–100%) and specific (94–100%) in differentiating lipid-rich adenomas from other adrenal lesions and is invaluable in evaluating lesions with similar CT washout appearances. This CS-MRI advantage is however not available for lipid-poor adenomas where there is no out-of-phase signal drop. When signal drop is quantified as in the splenoadrenal ratio (ASR) and the signal intensity index (SII), the diagnostic accuracy for adenoma improves significantly at an ASR 5% (Table 41.2). When quantifying signal drop, same breath-hold for the in and out phases is important to ensure coregistration of data in the images of both sequences [8–10].

MRI Adrenal Protocol ■ T1 in-phase/out-phase chemical shift MRI (CS-MRI) ■ T2 ■ 3D GRE pre- and post gadolinium-based contrast ■ DWI (optional) ■ MRI (optional)

PET-CT PET-CT provides the dual advantage of NECT attenuation information as well as functional information. 18FDG-PET-CT is useful in detecting malignancies that have increased glucose metabolism as well as in functional, nonmalignant lesions like pheochromocytoma that also

demonstrate uptake of FDG radiotracer. Current technology provides resolution sufficient to detect 5-mm lesions and provide qualitative and quantitative information that can accurately differentiate benign and malignant lesions with 99% sensitivity and 96% specificity. Indications for FDG-PET include staging of ACC, neuroblastoma, search for the primary malignancy site in adrenal metastases and assessing response to treatment in lymphoma. FDG-PET can be false positive for malignancy because of uptake in benign functioning adenoma, sarcoidosis, TB, and adrenal cortical hyperplasia and false negative in low FDG-avid metastases from bronchioalveolar carcinoma and carcinoid tumors [1–3].

CT/MRI Mimics and Pitfalls[11] ■ Suboptimal timing of CT delayed phase is associated with a marked drop in sensitivity. ■ CT acquisition/reconstruction parameter differences between phases can alter attenuation values. ■ APW and RPW calculations apply only to CT adrenal protocols and not MRI. 8% adenomas >10 HU will not drop signal on CSMRI due to insufficient intracellular lipid. ■ ROI coverage 10 HU and portal venous enhancement with slower washout than adenomas: APW 60% and RPW >40%. Unfortunately, HCC and RCC metastases can drop signal on CS-MRI because of microscopic fat and mimic rapid washout because of hypervascularity (Fig. 41.15). In fact, most RCC and HCC adrenal metastases are misdiagnosed as adenoma at AWP >60% and RPW >40% [3]. In these situations, 18FDG-PET/CT can be of advantage since metastases are more likely to show evidence of hypermetabolism than adenomas. For

distinguishing between benign and malignant adrenal masses, 18FDGPET/CT has 97% sensitivity and 91% specificity because of the combined advantage of functional information from the adrenal: liver SUV ratio and morphological information from NECT attenuation. False negatives occur in 10 HU, portal venous enhancement, no local invasion ■ Slower washout: APW 60% ■ On MRI, the fatty component is T1 and T2 hyperintense, while the myeloid component is T1 hypointense and T2 hyperintense, with T1 hyperintensity suppressed on the fat suppression sequence (Fig. 41.20). Finding the India ink artifact on CS-MRI out-of-phase images at the myelolipoma-adrenal interface is virtually diagnostic of a myelolipoma. Signal drop is greater on the fat-suppressed sequences than on CS-MRI, because the fat is macroscopic within a myelolipoma. On CEMR, there is mild enhancement of the myeloid component [3,17,22]

FIGURE 41.19 Adrenal myelolipoma. (A) Ultrasonography and (B) CECT. Large right adrenal mass, well circumscribed, markedly hyperechoic on ultrasonography and fat density on CT.

FIGURE 41.20 Adrenal myelolipoma. MRI (A) axial T1 and (B) axial post-contrast T1 fat-saturation.

Ovoid, smooth, mixed signal left adrenal mass (white arrow) with dominant, central T1 hyperintense fatty component, suppressed on T1 fat-saturation surrounded by a small, solid, enhancing, irregular rim (myeloid component). (Courtesy: Dr. Mukesh Harisinghani.)

Teaching Points: Adrenal Myelolipoma ■ Findings dependent on fat-myeloid proportion of tumor components ■ Mixed fatty + solid myeloid components, well circumscribed

Adrenal Cysts

Overview Adrenal cysts range in size from 1 to 20 cm and are asymptomatic, incidentally detected benign lesions, three times more common in women (M:F = 1:3) and are classified as congenital endothelial or epithelial cysts, acquired posthemorrhagic pseudocysts, inflammatory cysts, parasitic cysts, or cystic neoplasms. Pseudocysts are clinically the most common, while endothelial cysts are more common at autopsy. Pseudocysts result from hemorrhage or necrosis and are seen in both normal glands and in large tumors that are either benign or malignant. Endothelial cysts are congenital cysts that are derived from congenital lymphangiomatous or hemangiomatous malformations and can contain lactescent fluid and a thin rim of calcification. Epithelial cysts are very rare since there are no acinar structures within the normal adrenal gland and are likely mesothelial in origin, incorporated within the adrenal during embryogenesis. Hydatid cysts are the main parasitic cysts involving the adrenal glands although they are rarely involved even where the disease is endemic. Adrenal hydatid cyst is usually asymptomatic, unilateral, and secondary to disseminated hydatid disease, being detected incidentally on imaging done for other reasons. Pseudocysts are thick-walled, contain debris, septations, fluid–fluid levels, blood products, and soft tissue related to previous hemorrhage, all easier to visualize on USG and MRI than CT. Imaging Investigations ■ On x-ray, dense, laminated, and porcelain-like calcification can be seen in calcified hydatid cysts (Fig. 41.21) ■ On USG, simple epithelial cysts are well defined, anechoic with an imperceptible wall (Fig. 41.22) ■ On CT, they are homogeneous, nonenhancing, and of water density (Fig. 41.22). Cysts can appear hyperdense and septated in the event of hemorrhage or infection and marginal curvilinear or egg-shell calcification may ensue in the wall in 20%. Cystic degeneration can also occur within pheochromocytoma (Fig. 41.23) and adrenal carcinoma ■ On MRI, hydatid cysts have characteristic cyst-in-cyst appearance, a low T2 intensity pericyst and rim-like or nodular calcification

FIGURE 41.21 Calcified hydatid cyst. (A) Axial CECT and (B) x-ray abdomen.

Large, peripherally calcified left adrenal mass with dense, whorled internal contents on CT and porcelain-like calcification in the left suprarenal region on x-ray, inferiorly displacing the left renal shadow.

FIGURE 41.22 Adrenal cyst. (A) Ultrasonography longitudinal left flank, (B) CECT coronal, and (C) CECT axial.

Anechoic, round, left suprarenal mass (asterisk) with posterior acoustic enhancement, confirmed on CT to be a homogeneous, water-density cyst (white arrows) arising from the left adrenal gland, inferiorly displacing the left kidney and contained by an imperceptible wall.

FIGURE 41.23 Cystic pheochromocytoma. (A) Axial venous phase CECT and (B) T2W MRI.

Large, multiloculated, thick-walled, septated right adrenal cyst with internal fluid–fluid levels related to cystic degeneration and hemorrhage within a pheochromocytoma.

(Courtesy: Dr. Mukesh Harisinghani.)

When cysts are very large, the organ of origin can be better defined in the coronal and sagittal planes on CT and MRI, while USG can show a lack of relative motion between the cyst and the organ of origin. Incidental, asymptomatic adrenal cysts with no apparent tumor can be treated conservatively. In doubtful cases, fine needle aspiration of the cyst may prove malignancy or confirm old hemorrhage [3,17].

Teaching Points: Adrenal Cyst ■ Simple adrenal cyst: scant septation, no enhancement, thin rim Ca+ ■ Benign endothelial cyst or pseudocyst ■ Coronal imaging: organ of origin ■ Complicated cyst: high density, thick-enhancing wall, septations ■ Complexity: underlying adrenal neoplasm (secondary pseudocyst)

Pheochromocytoma Overview Pheochromocytomas are rare tumors that arise from adrenal medulla chromaffin cells and produce norepinephrine and epinephrine, causing hypertension in 0.1–0.2%, often without the classic presentation of paroxysmal hypertension, headache, sweating, palpitations, anxiety, and tremor. About 20% of patients present with “silent pheochromocytoma,” with normal blood pressure and none of the classic symptoms, suggesting

that it would be prudent to screen all patients with adrenal incidentaloma for pheochromocytoma.

Pheochromocytoma “Rule of 10s”: ■ 10% bilateral ■ 10% extra-adrenal ■ 10% malignant ■ 10% pediatric

Extra-adrenal or ectopic pheochromocytomas are known as paragangliomas. They arise from sympathetic ganglia anywhere in the body, with 90% located below the diaphragm, mostly around or below the kidney, in the pelvis, urinary bladder wall, at the aortic bifurcation or the organ of Zuckerkandl ganglia at the inferior mesenteric artery (IMA) origin. Bladder pheochromocytomas can present with attacks of hypertension brought on by micturition (Fig. 41.24). Other extra-adrenal locations include sympathetic ganglia in the neck, mediastinum, and paravertebral region. Thoracic tumors are usually paravertebral or found in the mediastinum.

FIGURE 41.24 Malignant bladder paraganglioma. (A) Noncontrast, (B) arterial phase, and (C) venous phase. Lobulated bladder base mass (asterisk) containing punctate calcifications and demonstrating avid arterial enhancement, hypervascularity (white arrows), delayed washout, and seminal vesicle (SV) invasion.

(Courtesy Dr. Varun S.)

Malignant pheochromocytomas are locally infiltrative and metastasize to bone, liver, lymph nodes, lungs, and brain. Although 30% these tumors can be a part of syndromes: MEN-2A, MEN-2B, von Hippel–Lindau (Fig. 41.25), and NF-1, most are sporadic. The Carney triad is the combination of gastric GIST, pulmonary chondroma, and extra-adrenal paraganglioma that

can sometimes occur with an additional fourth component: adrenal adenoma (Fig. 41.26) [23].

FIGURE 41.25 Bilateral adrenal pheochromocytomas in von Hippel– Lindau syndrome.

CECT arterial phase at level of (A) adrenals and (B) pancreas.

Bilateral intensely enhancing adrenal pheochromocytomas (black arrows) and an intensely enhancing pancreatic neuroendocrine tumor (dashed black arrow).

FIGURE 41.26 Adrenal adenoma: fourth component of the Carney triad. CECT curved MPR reformat. Right adrenal adenoma (black arrow) seen with the Carney triad: gastric GIST (dashed black arrow), pulmonary chondroma (white arrow), and extra-adrenal paraganglioma (black arrowhead).

(Courtesy: Dr. Suma Jacob.)

Adrenal pheochromocytomas secrete catecholamines in 90% of cases, while only 50% of extra-adrenal tumors do so. Raised 24-hour urine vanillylmandelic acid or increased plasma catecholamine levels provide lab confirmation of the diagnosis. Plasma metanephrine test has 99% sensitivity and 89% specificity for levels greater than three to four times the upper limit of normal. Because the values may be affected by position, activity,

smoking, and stress, the blood sample is best collected from an indwelling IV cannula after the patient has been supine for 30 minutes and has avoided smoking for 4 hours. Normal plasma metanephrine almost always rules out pheochromocytoma. Imaging Investigations The tumor can vary in size from 2 to 20 cm, with a mean size of 5.5 cm and is heterogeneous with foci of necrosis, fibrosis, calcification, cystic and fatty change, mimicking other lesions, and earning the nickname “imaging chameleon.” This heterogeneity and hypervascularity is reflected on all imaging techniques. ■ On USG, pheochromocytomas are well defined, mixed echogenicity, solid masses with intralesional hypervascularity on color Doppler, and CEUS demonstrating arterial enhancement ■ On CT, small tumors are homogeneous while larger tumors are solid and heterogeneous, showing foci of hemorrhage, necrosis, and cystic change. CECT shows avid enhancement similar to HCC and RCC metastases with APW and RPW rapid washout similar to adenomas (Fig. 41.27). Calcifications and venous invasion occur more often in ACC and their presence favors the diagnosis of ACC over pheochromocytoma. There is no risk of hypertensive crisis with iodinated contrast and routine premedication (α and β blockade) is not recommended [24] ■ MRI in pheochromocytoma has a 98% sensitivity, being mildly T1 hypointense and T2 brightly hyperintense with no drop in signal on opposed-phase images and can therefore be differentiated from an adenoma, although foci of fatty degeneration can sometimes create a challenge on CS-MRI. DWI is useful in differentiating malignant and benign pheochromocytoma with lower ADC observed in malignant lesions, and is useful in detecting liver and nodal metastases

FIGURE 41.27 Bilateral pheochromocytoma. CECT arterial phase.

Bilateral, intensely enhancing, heterogeneous adrenal masses (black arrows).

CEMR shows a “salt and pepper” pattern due to tumor hypervascularity with “salt” enhancing parenchyma and “pepper” flow voids of vessels. Fluid–fluid levels related to hemorrhage from this hypervascularity are uncommon but well demonstrated on MRI (Fig. 41.23). Although pheochromocytomas show characteristic peaks on MRS due to catecholamines, this method is limited by the location of the adrenal gland near the diaphragm. Given the higher sensitivity and specificity of CT and MR in the diagnosis of pheochromocytoma, radionuclide imaging is limited mostly to locating elusive extra-adrenal tumors and screening the body for metastatic deposits. ■ 123I-mIBG scintigraphy is limited by false negatives related to low spatial resolution, lack of tracer uptake by necrotic and hemorrhagic tumors, and interaction with certain medicines with resulting low specificity and 80% sensitivity. 123I-mIBG uptake in an adrenal nodule is highly suggestive of pheochromocytoma (Fig. 41.28) but uptake outside the adrenal is not as specific since many neuroendocrine tumors also demonstrate uptake with mIBG

FIGURE 41.28 Right adrenal pheochromocytoma. (A) CECT arterial phase and (B) mIBG.

Well circumscribed, intensely enhancing right adrenal mass (white arrow) with increased mIBG tracer uptake.

Uptake of octreotide-labeled-111In-DTPA occurs in over 70% of tumors due to the expression of somatostatin receptors. Again, uptake by somatostatin receptors at other sites such as the kidney, breasts, liver, spleen, bowel, gallbladder, thyroid gland, salivary glands and within sites of inflammation, reduce the specificity ■ 68Ga-DOTANOC PET-CT imaging has been found to have a high accuracy of 92%, superior to mIBG imaging, because of greater lesion-to-background-tissue contrast and higher specificity for pheochromocytoma [1,20,25]

Teaching Points: Adrenal Pheochromocytoma ■ Heterogeneous, necrosis, cystic ■ Enhance avidly ■ T2 hyperintense ■ No signal loss out-of-phase

Bilateral Adrenal Disease Bilateral adrenal disease can be of a benign or malignant origin and can be due to metastases, lymphoma, hemorrhage, or infection from TB or fungal pathogens. Bilateral adrenal hemorrhage can be observed in the setting of trauma or coagulopathy when tumors like neuroblastoma or pheochromocytoma can sometimes bleed. Unfortunately, bilateral adrenal masses are likely to be due to metastases or lymphoma given that both these

malignancies tend to be bilateral in 40–50% of cases and tend to cause adrenal insufficiency. Restricted diffusion also favors malignancy while calcification favors granulomatous disease [3].

Adrenal Infection By usually causing bilateral adrenal disease, tuberculosis continues to be the main cause of adrenal insufficiency in the developing world. In the early stages, on CT and MRI, the adrenal is enlarged without loss of its adreniform shape, accompanied by peripheral enhancement around a central low density or hypointensity related to caseous necrosis. This progresses to bilateral atrophy with diffuse, focal, or scattered punctate calcifications. Caseous necrosis, when treated, heals by enhancing central fibrosis and calcification. Infections are markedly FDG-avid during the early, acute stage and can mimic metastases, although this does reduce with treatment. In disseminated histoplasmosis, CT can demonstrate hepatosplenomegaly, enlarged nodes, focal splenic lesions, adrenal enlargement with preserved adreniform shape or peripherally enhancing, centrally hypodense adrenal masses with foci of calcification. In the early stages especially, bilateral adrenal TB also closely resembles bilateral histoplasmosis (Fig. 41.29) and lymphoma, requiring guided needle biopsy for histopathological diagnosis [17].

FIGURE 41.29 Adrenal granuloma. CECT. (A) Histoplasmosis. Bilateral adrenal masses with heterogeneous enhancement and foci of necrosis (white arrows). (B) Tuberculosis.

Right adrenal mass with necrotic foci, periadrenal fat stranding, and fluid associated with a similar density lesion in the spleen.

Teaching Points: Adrenal Infection ■ Usually bilateral enlargement with preserved adreniform shape in acute infection

■ Adrenal calcification in chronic phase

Adrenal Lymphoma Overview Primary adrenal lymphoma (PAL) is rare and less commonly seen than secondary adrenal NHL. PAL incidence is 1–4% with 50% occurring bilaterally and associated with retroperitoneal lymphadenopathy. The adrenals can appear normal in the early stages, progressing to a subtle, nodular appearance, a diffusely infiltrated gland with a maintained adreniform shape and later an infiltrative soft-tissue mass replacing the adrenal gland. Large retroperitoneal nodal masses can encase the adrenal gland and be difficult to discern separately. Imaging Investigations ■ On USG, lymphoma is solid, homogeneous, and hypoechoic. On CT, lymphoma appears as a mildly enhancing, hypodense mass, without intralesional calcification (Fig. 41.30)

■ On MRI, lymphoma is T1 hypointense to isointense and mildly T2 hyperintense

FIGURE 41.30 Diffuse large B cell lymphoma. CECT (A) axial image and (B) coronal image.

Large, homogeneous, mildly enhancing, ill-defined adrenal masses (white and dashed white arrows).

Secondary adrenal lymphoma causes bilateral adrenal enlargement without alteration of the adreniform shape and is more homogeneous than PAL,

demonstrating mild enhancement and slow washout. As is true for lymphoma elsewhere, DWI shows restricted diffusion related to a high nuclear-to-cytoplasmic ratio and consequent reduced water diffusion and is FDG-avid on 18FDG PET-CT. Apart from these few distinctive appearances, adrenal lymphoma has a nonspecific appearance and cannot be easily differentiated from metastases. Secondary adrenal lymphoma may be suspected in patients with NHL but has to be definitively proved with guided needle biopsy. Lymphoma responds well to chemotherapy, unlike metastases, with decreased FDG uptake and resolution to normal. Immunotherapy-related adrenalitis is a rare complication of immunotherapy that may cause adrenal insufficiency. CT (Fig.  41.31) and MRI show bilateral adrenal enlargement with bilateral mild 18F-FDG-avidity on PET/CT [3,17].

FIGURE 41.31 Immunotherapy-induced adrenalitis. A 69-year old. CECT.

Diffuse bilateral adrenal thickening after immunotherapy.

Fine needle aspiration: chronic inflammation with immunotherapyinduced adrenalitis.

(Courtesy: Dr. Mukesh Harisinghani.)

Adrenal Hemorrhage Overview Adrenal hemorrhage can occur for a variety of reasons including trauma, anticoagulation, complex pregnancy, sepsis, surgery, or within most adrenal neoplasms other than lymphoma. Adrenal insufficiency occurs when >90% adrenal is destroyed. Post-traumatic hemorrhage is the most common cause, can be bilateral in 20% of cases, but is usually not accompanied by adrenal insufficiency. The right adrenal is more prone to hemorrhage during blunt abdominal trauma. Neonatal adrenal hemorrhage is the most common cause of an adrenal mass in an infant, in the first week of life within the large infantile adrenal (Fig. 41.32). Neonatal hemorrhage may present as an abdominal mass or as bilateral masses which can develop marginal calcification as they regress over several weeks. If clinically suspected, the diagnosis can best be confirmed by USG, which can differentiate hemorrhage from the more solid neuroblastoma.

FIGURE 41.32 Neonatal adrenal hemorrhage. Ultrasonography (A) initial presentation and (B) 2-month follow-up. Heterogeneous, echogenic right adrenal mass with cystic foci (dashed white arrow). Two-month follow-up scan shows marked reduction in size, indicating resolution of hemorrhage (white arrow).

Nontraumatic intratumoral adrenal hemorrhage occurs in 1% of autopsies, and usually occurs when the patient with underlying pheochromocytoma, myelolipoma, metastasis, or carcinoma is on anticoagulants. Findings that indicate hemorrhage have occurred within an underlying adrenal lesion

include the presence of enhancement, calcification, and increased metabolic activity on PET imaging. Imaging Investigations ■ USG is a good first-line imaging in children and the newborn: acute hemorrhage appears as a mixed, mostly echogenic blood clot that liquefies and turns hypoechoic, showing no vascularization ■ On CT, acute hemorrhage appears as a hyperdense enlarged gland, and in the setting of trauma, is associated with periadrenal and retroperitoneal hematoma (Fig. 41.33). Acute or subacute hematoma presents as a round or oval mass of high density (50–90 HU) in an asymmetrically enlarged gland, usually homogeneous and nonenhancing with inflammatory periadrenal fat stranding, thickening of diaphragmatic crura, with or without periadrenal hemorrhage. Additionally, traumatic pneumothorax, hydropneumothorax, rib fracture, and contusion of the lung, liver, spleen, or pancreas can be present

FIGURE 41.33 Traumatic adrenal hemorrhage. Blunt injury abdomen. CECT.

Right adrenal hemorrhage (white arrow) and liver laceration (dashed white arrow).

Chronic hematoma can liquefy into an adrenal pseudocyst or retract, with or without foci of calcification. Unilateral or bilateral adrenal hematomas may be associated with adrenal or renal vein thrombosis. Or, in the case of nontraumatic hemorrhage, an underlying large adrenal cyst or myelolipoma may be visualized. ■ On MRI, within the first week, acute hematoma is T1 isointense to mildly hypointense and T2 hypointense due to deoxyhemoglobin. Between 1 and 7 weeks, subacute hematoma

appears T1 and T2 hyperintense due to methemoglobin. After 7 weeks, chronic hematoma shows a hypointense rim on T1 and T2 due to hemosiderin and fibrosis [3,17]

Teaching Points: Adrenal Hemorrhage ■ Neonatal USG echogenic > liquefies > hypoechoic, no vascularization ■ CT ○ Round or oval, periadrenal fat stranding ○ Acute high density > decreased size, density > resolves ■ MRI ○ Acute: isointense T1, hypointense T2 (7w) ■ Organized adrenal hematoma > calcification/pseudocyst

Unusual Adrenal Tumors The following tumors are rare but of relevance when atypical features are encountered in an adrenal mass. Lipomas Lipomas are well-defined lobules of fat, which in contrast to myelolipomas, show no evidence of soft-tissue and may demonstrate foci of calcification. Hemangiomas Hemangiomas may be incidentally discovered in women 40–70 years and are capillary or cavernous in type. NECT may reveal calcified phleboliths or dystrophic calcification at the site of previous bleeds. On MRI, hemangioma T1 hypointense and markedly T2 hyperintense “lightbulb sign,” with T2 hypointense foci of calcification. On CECT and CEMR, hemangiomas may exhibit nodular peripheral enhancement, with or without centripetal delayed filling. Lymphangiomas Lymphangiomas are asymptomatic, incidental, benign lesions that can present at any age, appearing on CT as a well-defined hypodense, near-water density, septated, enhancing mass with scattered punctate or thick curvilinear calcification (Fig. 41.34). On MRI, lymphangiomas are nonspecific, appearing T1 hypointense and T2 hyperintense.

FIGURE 41.34 Adrenal lymphangioma. CECT.

Low-density mass (white arrow) in the left adrenal gland with a single punctate calcification (yellow arrow).

(Courtesy: Dr. Mukesh Harisinghani.)

Schwannoma Schwannoma is a benign tumor arising from nerve sheaths, usually asymptomatic although hemorrhage can cause abdominal pain. On CT, schwannomas are hypodense and heterogeneously enhancing with larger masses showing hemorrhage, calcification, and cystic areas, T1 isointense, and mildly T2 hyperintense on MRI. Adenomatoid Tumor Adenomatoid tumor is a benign, mesothelial, asymptomatic tumor, hypodense, and heterogeneously enhancing on CT with foci of calcification and septations. Oncocytoma Oncocytoma is an epithelial tumor, most often benign and nonfunctioning tumor that can be large and affect the left adrenal more often than the right. On CT and MRI, the mass is well defined, encapsulated, and heterogeneously enhancing. Differentiation from cortical carcinoma can be challenging [17].

Adrenal Incidentalomas Incidentaloma refers to unexpected pathology found in the course of an unrelated imaging investigation. The incidence of incidentalomas has increased with the widespread availability of CT and increases with age, but can present at any age. When there is a known malignancy, 27% of incidentalomas are metastases but in the absence of known malignancy, an incidentaloma is usually a benign nonfunctioning adenoma, while cysts, myelolipoma, and hemorrhage have characteristic imaging features.

“Rule of Four” in Adrenal Incidentalomas ■ 4% CTs across all age groups ■ 4% malignant etiology ■ 4 cm needs surgical removal ■ 4 years follow-up to prove stability

Incidentalomas >4 cm Size is a major predictor of malignancy in adrenal masses. If the lesion is indeterminate and ≥4 cm in diameter with no primary malignancy consider resection because of the possibility of an adrenocortical carcinoma without biopsy. If there is a malignancy history consider PET-CT or guided needle biopsy. Although adrenalectomy performed for incidentalomas >4 cm has a low specificity (42%), largely due to the low prevalence of ACC, this highly aggressive cancer still warrants the removal of  adrenal lesions >4 cm, especially in younger patients without comorbidities or evidence of extraadrenal malignancy. Indeterminate Incidentalomas 1–4 cm Of indeterminate 1–4 cm lesions, those measuring 1–2 cm in patients without history of malignancy are probably benign and require only a 12month follow-up. In those >2 cm indeterminate lesions that fit the criteria for a lipid-poor adenoma on CT, there is no need for follow-up. If the lesion is not a lipidpoor adenoma, and the patient has a malignancy history, consider PET-CT or guided needle biopsy. If there is no malignancy history, consider follow-up or resection.

ACR Guidelines for the Management of Incidentalomas [26] ■ 1 and 2 but 4 cm: if no known malignancy, proceed to surgical resection as for a presumed ACC

Many adrenal lesions can be categorized as typically benign and need no follow-up: ■ Lipid-rich adenoma (NECT 4 cm ■ Myelolipomas >4 cm and ■ Suspicion of malignancy (Fig. 41.35) [26–28]

FIGURE 41.35 Adrenal incidentaloma algorithm.

Guidelines for the management of an incidentally discovered adrenal mass.

Suggested Readings Mazzaglia, P.J., Varghese, J. & Habra, M.A. Evaluation and management of adrenal neoplasms: endocrinologist and endocrine surgeon perspectives. AbdomRadiol 45, 1001–1010 (2020). Taffel M, Haji-Momenian S, Nikolaidis P, Miller FH. Adrenal imaging: a comprehensive review. Radiol Clin North Am. 2012 Mar;50(2):219-43 Pamela T. Johnson, Karen M. Horton, and Elliot K. Fishman. Adrenal Mass Imaging with Multidetector CT: Pathologic Conditions, Pearls, and Pitfalls. RadioGraphics 2009 29:5, 1333-1351 Sharon Z. Adam, Paul Nikolaidis, Jeanne M. Horowitz, Helena Gabriel, Nancy A. Hammond, Tanvi Patel, Vahid Yaghmai, and Frank H. Miller.Chemical Shift MR Imaging of the Adrenal Gland: Principles, Pitfalls, and Applications. RadioGraphics 2016 36:2, 414-432 Albano D, Agnello F, Midiri F, Pecoraro G, Bruno A, Alongi P, Toia P, Di Buono G, Agrusa A, Sconfienza LM, Pardo S, La Grutta L, Midiri M, Galia M. Imaging features of adrenal masses. Insights Imaging. 2019 Jan 25;10(1):1

References [1] Mazzaglia, PJ, Varghese, J & Habra, MA Evaluation and management of adrenal neoplasms: endocrinologist and endocrine surgeon perspectives. Abdom Radiol 45, 1001–1010 (2020). [2] Panda A, Das CJ, Dhamija E, Kumar R, Gupta A K. Adrenal imaging (part 1): imaging techniques and primary cortical lesions. Indian J Endocr Metab 2015;19:8-15 [3] Dhamija E, Panda A, Das CJ, Gupta AK. Adrenal imaging (part 2): medullary and secondary adrenal lesions. Indian J Endocrinol Metab. 2015;19(1):16-24. [4] Michelle MA, Jensen CT, Habra MA, et al. Adrenal cortical hyperplasia: diagnostic workup, subtypes, imaging features and mimics. Br J Radiol. 2017;90(1079):20170330. [5] Taffel M, Haji-Momenian S, Nikolaidis P, Miller FH. Adrenal imaging: a comprehensive review. Radiol Clin North Am. 2012;50(2):219-243. [6] PT Johnson, KM Horton, and EK Fishman. Adrenal mass imaging with multidetector CT: pathologic conditions, pearls, and pitfalls. RadioGraphics 2009 29:5, 1333-1351 [7] Ng CS, Altinmakas E, Wei W et al. Utility of intermediate-delay washout CT images for differentiation of malignant and benign adrenal lesions: a multivariate analysis. AJR Am J Roentgenol 2018;211(2):109–115. [8] SZ. Adam, P Nikolaidis, JM Horowitz, H Gabriel, NA Hammond, T Patel, V Yaghmai, and FH Miller. Chemical shift MR imaging of the adrenal gland: principles, pitfalls, and applications. RadioGraphics 2016 36:2, 414-432 [9] BK Park, CK Kim, B Kim, and JH Lee. Comparison of delayed enhanced CT and chemical shift mr for evaluating hyperattenuating incidental adrenal masses. Radiology 2007 243:3, 760-765 [10] Freire, G, Ramalho, M Chemical-shift imaging: does it have a role in the management of adrenal masses? Abdom Radiol 45, 901–902 (2020). [11] Elsayes, KM, Elmohr, MM, Javadi, S et al. Mimics, pitfalls, and misdiagnoses of adrenal masses on CT and MRI. AbdomRadiol 45, 982–1000 (2020). [12] Sutton, D. Diagnosis of Conn's and other adrenal tumours by left adrenal phlebography. Lancet, 453–455(1968 ). [13] Dumba M, Jawad N, McHugh K. Neuroblastoma and nephroblastoma: a radiological review. Cancer Imaging. 2015;15(1):5.

[14] KM Sargar, G Khanna, R HulettBowling. Imaging of nonmalignant adrenal lesions in children. RadioGraphics 2017 37:6, 1648-1664. [15] YK Kim, BK Park, CK Kim, and SY Park. Adenoma characterization: adrenal protocol with dual-energy CT. Radiology 2013 267:1, 155-163. [16] Y Nagayama, T Inoue, S Oda, S Tanoue, T Nakaura, O Ikeda, and Y Yamashita. Adrenal adenomas versus metastases: diagnostic performance of dual-energy spectral CT virtual noncontrast imaging and iodine maps. Radiology 2020 296:2, 324-332. [17] Albano D, Agnello F, Midiri F, Pecoraro G, Bruno A, Alongi P, Toia P, Di Buono G, Agrusa A, Sconfienza LM, Pardo S, La Grutta L, Midiri M, Galia M. Imaging features of adrenal masses. Insights Imaging. 2019;10(1):1. [18] Elbanan MG, Javadi S, Ganeshan D. et al. Adrenal cortical adenoma: current update, imaging features, atypical findings, and mimics. AbdomRadiol (NY). 2020;45(4):905-909. [19] Morani, AC, Jensen, CT, Habra, MA et al. Adrenocortical hyperplasia: a review of clinical presentation and imaging. AbdomRadiol 45, 917–927 (2020). [20] Szolar DH, Korobkin M, Reittner P, et al. Adrenocortical carcinomas and adrenal pheochromocytomas: mass and enhancement loss evaluation at delayed contrast-enhanced CT. Radiology 2005;234:479–485. [21] Ahmed, AA, Thomas, AJ, Ganeshan, DM et al. Adrenal cortical carcinoma: pathology, genomics, prognosis, imaging features, and mimics with impact on management. AbdomRadiol 45, 945–963 (2020). [22] G Nandra, O Duxbury, P Patel, JH Patel, N Patel, and I Vlahos. Technical and interpretive pitfalls in adrenal imaging. RadioGraphics 2020 40:4, 1041-1060. [23] Carney JA, Stratakis CA, Young WF Jr. Adrenal cortical adenoma: the fourth component of the Carney triad and an association with subclinical Cushing syndrome. Am J SurgPathol. 2013;37(8):11401149. [24] Katabathina, VS, Rajebi, H, Chen, M, et al. Genetics and imaging of pheochromocytomas and paragangliomas: current update. AbdomRadiol 45, 928–944 (2020). [25] IoannisIlias, KP, Current approaches and recommended algorithm for the diagnostic localization of pheochromocytoma, J Clin Endocrinol Metab, 89(2) 2004, 479–491.

[26] Mayo-Smith WW, Song JH, Boland GL, Francis IR, Israel GM, Mazzaglia PJ, et al. Management of incidental adrenal masses: a white paper of the ACR incidental findings committee. J Am Coll Radiol. 2017;14(8):1038-1044. [27] BK Park, CK Kim, B Kim, JH Lee. Comparison of delayed enhanced CT and chemical shift MR for evaluating hyperattenuating incidental adrenal masses. Radiology 2007 243:3, 760-765. [28] Glazer, DI, Mayo-Smith, WW Management of incidental adrenal masses: an update. AbdomRadiol 45, 892–900 (2020).

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CHAPTER 42

Prostate Ciara O'Brien, Adriano Basso Dias, Sangeet Ghai

Introduction The prostate gland is a small organ resembling an inverted cone or walnut, it lies at the base of the urinary bladder anterior to the rectum and surrounding the urethra. During the third month of gestation, the prostate gland develops from epithelial invaginations at the posterior urogenital sinus [1]. The differing susceptibility of the prostate zones to developing cancer is due to the embryological origin of each zone. The peripheral and transition zones are derived from the urogenital sinus, whereas the central zone is derived from the Wolffian duct. Morphological prostate changes occur during puberty as the gland enlarges to weigh approximately 20 g by the age of 25– 30 years. The function of the prostate is to secrete alkaline fluid that is a component of seminal fluid. Despite the small size of the prostate it is associated with three major morbidities in men: benign prostatic hyperplasia (BPH), prostatitis, and prostate cancer. The anatomy of the prostate gland has been described in the literature since the mid-16th century [2]. Today prostate anatomy is described using zones to delineate the different anatomical areas of the prostate gland. Imaging of the prostate gland is performed using ultrasonography (USG) and magnetic resonance imaging (MRI).

Anatomy McNeal described the contemporary zonal anatomy of the prostate gland in 1981. The prostate is divided into four glandular zones surrounding the prostatic urethra: the peripheral zone, transition zone, central zone, and anterior fibromuscular zone (Figs. 42.1–42.3). Each prostate zone has a different embryological origin and therefore different susceptibility to

disease [3]. The gland has an anterior, posterior, and inferior-lateral surface, it is divided into regions called the apex, mid, and base of the prostate each accounting for approximately one-third of the prostate volume. Blood supply is from the prostaticovesical arteries that arise from the internal iliac arteries. Lymphatic drainage is through the internal iliac lymph nodes. Nerve supply is from the prostatic plexus, this is composed of parasympathetic supply from S2 to S4 sacral nerve roots and sympathetic supply through the hypogastric nerve [1]. The presence of a prostate capsule in contentious, the “real” prostate capsule at the outer layer of the gland is made of fibromuscular tissue composed of predominantly smooth muscle that can be separated from the prostate stroma. This lining surrounds the entire prostate gland and is the landmark for extraprostatic extension of cancer.

FIGURE 42.1 Main anatomic concepts of the prostate. The PI-RADS sector map (A) and the corresponding MRI images (T2WI), in the axial plane (B–E). The prostate is divided into three main regions: base (C), midgland (D), and apex (E). The gland is also divided into four zones: anterior fibromuscular stroma (AFMS), transition zone (TZ), central zone (CZ), and peripheral zone (PZ). The neurovascular bundles (NVB) course posterolateral to the prostate bilaterally, usually at the 5 o'clock and 7 o'clock positions. The rectoprostatic angles (RP angles) are depicted posteriorly to the prostate gland. The utricle (the

verumontanum) is a small indentation on the posterior wall of the mid prostatic urethra at the site of ejaculatory ducts opening into the prostatic urethra. AFMS, anterior fibromuscular stroma; CZ, central zone; NVB, neurovascular bundle; PZ, peripheral zone; RP, rectoprostatic; SV, seminal vesicles; TZ, transition zone. Note: The PIRADS sector map was adapted from the PI-RADS Version 2.1 document.

(Data from: https://www.acr.org/-/media/ACR/Files/RADS/PiRADS/PIRADS-V2-1.pdf ).

FIGURE 42.2 Correlation of axial MRI T2W images (A–C) and axial ultrasonography images of the prostate (D–F). The prostate is divided into four zones: anterior fibromuscular stroma (AFMS), transition zone (TZ), central zone (CZ), and peripheral zone (PZ). AFMS, anterior fibromuscular stroma; CZ, central zone; PZ, peripheral zone; SV, seminal vesicles; TZ, transition zone.

FIGURE 42.3 Correlation of sagittal MRI T2W image (A) and sagittal ultrasonography image of the prostate (B). Note that the surgical capsule (yellow dashed line) separates the transition zone from the peripheral zone. In this midsagittal view of the prostate, the prostatic urethra is entirely seen. PZ, peripheral zone; SV, seminal vesicle; TZ, transition zone.

The peripheral zone is the largest zone containing approximately 70% of the normal prostate tissue (Fig. 42.4). The peripheral zone surrounds the distal urethra and occupies the posterior, lateral, and apical regions of the gland [1,3]. The peripheral zone includes the area at the base of the urinary bladder where the ejaculatory ducts feed into the urethra, called the verumontanum. The verumontanum is a longitudinal mucosal fold that forms an elliptical segment of the prostatic urethra [1]. The preprostatic sphincter stretches from the base of the bladder to the verumontanum [2]. The peripheral zone is separated from the transition and central zones by a surgical capsule. The peripheral zone is composed of numerous ductal and acinar elements with sparsely interwoven smooth muscle; its composition makes it high signal intensity on T2-weighted MRI sequences. The peripheral zone is the site of approximately 70–75% of prostate cancer [1,3].

FIGURE 42.4 Histological concepts (A) and correlation with MRI prostate (T2WI, axial plane) (B). The peripheral zone is separated from the transition and central zones by a surgical capsule and it is composed of numerous ductal and acinar elements with sparsely interwoven smooth muscle, its composition makes it high signal intensity on T2WI (B). The transition zone is made up of two types of histologically different tissue: glandular and stromal tissue. Note that a nodule of benign prostatic hyperplasia, with predominant glandular component (yellow circle), is showed in the histology image (A). The central zone surrounds the ejaculatory ducts and narrows at the utricle (or the verumontanum). The utricle is a small indentation on the posterior wall of the mid prostatic urethra at the site of ejaculatory ducts opening into the prostatic urethra. The anterior fibromuscular stroma is a nonglandular thick sheath of the tissue that is continuous with the detrusor muscle of the urinary bladder neck.

The transition zone makes up 5% of the normal prostate and lies superior to the verumontanum. It is made of two small glandular areas straddling the proximal prostatic urethra. The normal transition zone is made up of two types of histologically different tissue: glandular and stromal tissue [4]. The glandular tissue is hyperintense and the stromal tissue is hypointense on T2weighted MRI sequences. The T2 hypointense appearance of the stromal tissue can mimic cancers making interpretation difficult. Approximately 20– 30% of prostate cancer occurs in the transition zone. BPH arises in the transition zone, this is a progressive disease related to age. It is estimated that BPH affects 50% of men over the age of 60 years and 90% of men over the age of 70 years. The transition zone progressively increases in size with age doubling in volume from the age of 40–80 years (5.5–11.1 mL) [5,6]. The central zone (Fig. 42.5) accounts for 25% of the glandular prostate tissue and lies between the peripheral and transition zones at the base of the prostate. The central zone surrounds the ejaculatory ducts and narrows at the verumontanum to form a wedge shape [3]. Prostate carcinoma of the central zone is rare accounting for only 5%. On MRI, the central zone is low signal intensity on T2-weighted sequences [7].

FIGURE 42.5 Anatomy of the central zone (CZ). Axial images of the prostate base show the normal CZ (yellow arrows) visible on T2WI (A) and ADC map (B) as bilaterally symmetric low signal intensity tissue encircling the ejaculatory ducts (arrowheads). Coronal image of the posterior prostate (C) illustrates the CZ (white arrows) and peripheral zone (PZ). Note that on the coronal plane, the CZ has the shape of an inverted cone with its base oriented toward the base of the gland and is homogeneously hypointense as it contains more stroma than the glandular tissue.

The anterior fibromuscular stroma (AFMS) is a nonglandular thick sheath of the tissue that is continuous with the detrusor muscle of the urinary bladder neck [3]. It forms an apron of the tissue forming the anterior surface of the prostate contacting the urethra at the apex of the gland and forms a crescent shape. The AFMS is low signal on T2-weighted MRI. Prostate cancer does not arise in the AFMS, but peripheral and transition zone cancer can extend into the AFMS and lead to loss of the normal symmetry. Anterior tumors in the prostate account for approximately 21% and are not palpable on digital rectal exam (DRE) [8,9]. The seminal vesicles are paired secretory glands that lie cephalad to the prostate gland. They are extraperitoneal and are located posterior to urinary bladder and anterior to the rectum. Their function is to produce seminal fluid that supports and maintains sperm. Seminal fluid makes up 80% of the ejaculate volume [10]. In the setting of prostate cancer, the seminal vesicles are a frequent site for extraprostatic disease.

Diseases Benign Prostate Cysts Benign prostate cysts are often identified on USG of the prostate gland; these include Mullerian duct cysts and prostatic utricle cysts. ■ Mullerian duct cysts arise from the embryological remnants of the Mullerian duct and can arise anywhere along the path of the Mullerian duct; however, they are commonly seen in the midline of the prostate gland. They range in size and can extend above the prostate gland

■ Utricle cysts (Fig. 42.6) arise secondary to dilatation of the prostatic utricle; they are also midline cysts and can be indistinguishable from Mullerian duct cysts on imaging. However, utricle cysts are typically smaller and do not extend beyond the prostate

FIGURE 42.6 Prostatic utricle cyst. Transrectal ultrasonography (axial: A; sagittal: B) and prostate MRI, T2WI (axial: C; sagittal D) show a midline cystic structure in the level of the verumontanum, compatible with a utricle cyst (arrows).

Although both cysts are benign, they can cause obstructive or irritative urinary tract symptoms. Rarely these cysts develop cancers including endometrial, clear cell, or squamous cell carcinoma. Ejaculatory duct cysts are extremely rare and typically asymptomatic [11]. Benign ductal ectasia is a condition of older men in the setting of prostatic atrophy and dilation of the peripheral prostatic ducts.

Benign Prostatic Hyperplasia BPH is a histological diagnosis showing glandular (Fig. 42.4A) and stromal hyperplasia within the transition zone of the prostate gland. BPH typically begins with enlargement of the subsphincteric periurethral glands. Glandular BPH enlargement causes enlargement of the prostate gland resulting in obstructive symptoms known as the static effect, while stromal BPH enlargement increases the resistance of the parenchyma, known as the dynamic effect. BPH is characterized by expansile nodules caused by proliferation of stroma, newly formed glandular structures, or a mixture of both. Hyperplasia of the periurethral glandular tissue results in a “median lobe” manifesting as a bulge into the urinary bladder. Symptoms of BPH usually occur after the age of 40, and its prevalence reaches 50–60% of men by the age of 60. Approximately 50% of men with BPH have lower urinary tract symptoms including urinary frequency, nocturia, hesitancy, slow or intermittent streams, incomplete emptying, and urgency. The international prostate symptom score is a questionnaire of eight questions to assess clinical severity and to monitor treatments. The etiology of BPH is thought to be due to aging and hormonal changes. BPH is diagnosed clinically, the first investigation is often a DRE performed by a urologist followed by imaging of the prostate with USG and MRI [6,12].

Imaging of Benign Prostatic Hyperplasia Transrectal USG is the gold standard test for imaging the prostate gland (Fig. 42.7). The prostate is measured in three orthogonal planes and the volume is calculated. Typically, the appearance of BPH is sonographic enlargement of the transition zone; homogeneously enlarged or with multiple nodules throughout. BPH nodules can be isoechoic, hypoechoic, or hyperechoic on USG and they have well-defined margins unlike prostate carcinoma. Calcifications are common in the setting of BPH causing twinkling artifact on USG, if there are numerous calcifications shadowing can limit transrectal ultrasonography (TRUS) assessment of the parenchyma. Degenerative or retention cysts can develop in the transition zone and appear as small hypoechoic areas on TRUS. BPH nodules sometimes arise in the peripheral zone causing bulging of the capsule, on palpation these are firm nodules that may mimic cancer. In this instance, a biopsy is often required to exclude prostate cancer [6]. USG is also used to assess the urinary bladder for sequalae of obstructive uropathy including bladder wall thickening and trabeculation, bladder calculi, and postmicturition volumes.

FIGURE 42.7 Benign prostatic hyperplasia (BPH). Transrectal ultrasonography image (7.5 MHz) of the prostate—axial view (A) and sagittal view (B) show an enlarged prostate due to benign hyperplasia (prostate volume of 70 mL). Note some nodules of hyperplasia in the transition zone (arrows). Transabdominal ultrasonography image (5.0 MHz). (C) A mildly thickened/trabeculated bladder wall and a small left bladder diverticulum (arrowhead), findings in keeping with chronic outlet obstruction.

On MRI, BPH (Fig. 42.8) manifests as an enlarged transition zone with varying signal intensities based on the ratio of glandular to stromal tissue.

FIGURE 42.8 Benign prostatic hyperplasia (BPH). A 65-year-old male presenting with a frequency of micturition and weak stream with hesitancy. Prostate MRI (axial: A; sagittal: B; coronal: C) reveals a gland markedly enlarged due to benign hyperplasia (prostate volume of 150 mL). Note that in BPH usually there is a mixture of stromal and glandular hyperplasia and it may appear as band-like areas and/or encapsulated round nodules with circumscribed or encapsulated margins. Predominantly glandular BPH nodules and cystic atrophy exhibit moderate-marked T2 hyperintensity (white arrows), whereas predominantly stromal nodules exhibit T2 hypointensity (yellow arrows). Hypertrophy of a median lobe of prostate, with mass effect or protrusion into the bladder is other common feature seen in BPH (arrowheads).

■ Glandular BPH nodules are more hyperintense on T2-weighted images (T2WI) ■ Stromal nodules are hypointense on T2WI

Treatment of Benign Prostatic Hyperplasia The treatment of BPH is primarily to alleviate the symptoms of lower urinary tract obstruction; more recently, treatment has also been focused on the elimination of disease progression and prevention of complications. The initial treatment of BPH is with lifestyle modification. Medications have been used since the 1980s with the use of two predominant classes of drugs: 5-alpha-reductase inhibitors and alpha-blockers. In cases of recurrent symptoms including acute/chronic renal insufficiency, refractory urinary retention, recurrent urinary tract infections, bladder stones, and gross hematuria, secondary intervention is necessary. Surgical management of BPH is with transurethral resection of the prostate (TURP) which involves removing the obstructing adenomatous tissue. In instances where the size of the prostate eliminates TURP, a prostatectomy may be performed [13]. In the past decades many minimally invasive techniques have been trialed to achieve similar outcomes as TURP with less side effects. Minimally invasive techniques that are currently on trial include: ■ Aquablation ■ Water vapor thermal therapy ■ Prostate artery embolization ■ Prostatic urethral lift

■ Nitinol butterfly-like stent (Table 42.1) [14]

Table 42.1 Procedures for the Treatment of Lower Urinary Tract Symptoms Associated With Benign Prostatic Hyperplasia (LUTS/BPH) 1. Standard Treatment Transuret hral resection of the prostate (TURP)

Mode of action: Surgical resection Guidance: Endoscopic Definition: Transurethral endoscopic resection of the obstructing adenomatous tissue

2. Novel Minimally Invasive Treatments 2.1 Transurethral procedures with immediate tissue ablation Aquablati on (AquaBe am®)a

Mode of action: High velocity water jet Guidance: Transrectal USG Definition: High velocity high-pressure saline jet stream (heat-free mechanism) to remove the adenomatous tissue

2.2 Procedures with delayed tissue ablation Water vapor thermal therapy (Rezu¯m ®)b

Mode of action: Water vapor thermal energy Guidance: Endoscopic Definition: Radiofrequency thermal therapy in the form of water vapor, to ablate the adenomatous tissue

Prostate artery embolizat ion (PAE)

Mode of action: Prostatic arteries embolization Guidance: Fluoroscopic Definition: Microspheres are injected into the prostatic arteries (embolization) to stop local blood circulation, which causes tissue infarction and necrosis of prostatic tissue, leading to secondary prostate shrinkage

2.3 Transurethral procedures without tissue ablation Prostatic urethral lift (PUL)

Mode of action: Implantation of permanent prostatic implants Guidance: Endoscopic

(UroLift ®)c

Definition: Placement of permanent implants that retract and lift the obstructing lateral lobes, allowing expansion of the urethral lumen

Nitinol butterflylike stent (iTIND®)

Mode of action: Implantation of temporary urethral stent Guidance: Endoscopic Definition: Transurethral implantation of temporary nitinol stent. During the period of 5–7 days, it expands within the prostatic urethra and bladder neck and exerts radial force on the tissue, causing ischemic incisions

d

Sources: aAquaBeam®:https://www.procept-biorobotics.com/aquabeam-surgical-robotic-system/ bRezu¯m®:https://www.rezum.com/home.html cUroLift®:https://www.urolift.com/ di-TIND®:https://www.olympus-europa.com/medical/en/Products-andSolutions/Products/Product/iTind.html

Prostatitis Prostatitis is an umbrella term for infection or inflammation of the prostate gland. The National Institute of Health classified prostatitis into the following four categories: 1. Acute bacterial prostatitis 2. Chronic bacterial prostatitis 3. Chronic prostatitis/chronic pelvic pain syndrome a. Inflammatory b. Noninflammatory 4. Asymptomatic inflammatory prostatitis.

The classification system is dependent on microscopic and culture evaluation of prostate-specific specimens including, prostatic fluid, ejaculate, urine, and/or prostate biopsy [15]. Acute bacterial prostatitis (Fig. 42.9) is commonly seen in young adults and if untreated may become chronic. Chronic prostatitis (Fig. 42.10) is seen in elderly males with lower urinary tract obstruction [16]. Granulomatous prostatitis (Fig. 42.11) is a unique inflammatory condition that may be idiopathic as a result of previous intravesical bacilli Calmette-Guerin therapy for bladder cancer, tuberculous prostatitis, and previous intervention. Granulomatous prostatitis presents clinically with an elevated prostate-specific antigen (PSA) and a firm nodule on DRE [17].

FIGURE 42.9 Acute prostatitis. A 77-year-old patient presenting with fever, dysuria, and abrupt elevation of the PSA. Prostate MRI shows an enlarged prostate, demonstrating a diffuse heterogeneous signal of the peripheral zone on T2WI (axial: A; sagittal: B) and diffusely enhancing on dynamic contrast-enhanced (DCE) imaging (C), in keeping with acute prostatitis (arrows), in this clinical scenario. In the left apex transition zone, also is noted a small collection with heterogeneous signal on T2WI (D), marked low signal on ADC map (E) (diffusion restriction), and peripheral enhancement on DCE (F), compatible with an associated prostatic abscess.

FIGURE 42.10 Chronic prostatitis. Prostate MRI shows bilateral linear hypointense abnormalities on T2WI (A) in the peripheral zone (arrows), in keeping with chronic inflammatory changes. Note that some of these abnormalities may enhance on DCE (D) (arrowhead) and usually there is no associated significant diffusion restriction (B and C).

FIGURE 42.11 Granulomatous prostatitis. Prostate MR T2WI shows a hypointense lesion in the left peripheral zone (arrow), biopsy-proved granulomatous prostatitis.

Imaging of Prostatitis Imaging has limited use in the diagnosis of prostatitis. On TRUS (Fig. 42.12) there may be a focal hypoechoic area in the peripheral zone. If the patient has developed a prostate abscess, a localized fluid collection with increased peripheral Doppler flow is seen.

FIGURE 42.12 Prostatic abscess. A 65-year-old patient presenting with fever and dysuria. Axial ultrasonography images show an anechoic/hypoechoic lesion (arrows) in the right posterolateral peripheral zone (A), with increased peripheral vascularity on Doppler (B). No internal vascularity seen.

Prostatitis has nonspecific MRI findings such as, wedge-shaped lesions in the peripheral zone, early nonfocal contrast enhancement, the absence of mass effect, and preservation of the capsule integrity. These findings are also true of peripheral zone prostate cancer; prostatitis is a pitfall for cancer diagnosis on MRI and can result in false-positive reports. Granulomatous prostatitis appears as a discrete mass with markedly abnormal T2-weighted signal intensity and apparent diffusion coefficient (ADC), this is more pronounced than other inflammatory conditions and is often deemed of extremely high suspicion for tumor. Granulomatous prostatitis is also associated with inflammatory infiltration of the periprostatic fat mimicking extraprostatic tumor extension. History of intravesical bacilli Calmette-Guerin therapy for bladder cancer will suggest a diagnosis of granulomatous prostatitis over prostate cancer. A repeat MRI in 6 months is recommended in uncertain cases of granulomatous prostatitis, if there is a high index of suspicion for tumor a targeted biopsy should be considered [8,17]. Treatment of Prostatitis The mainstay of treatment for bacterial prostatitis is with antibiotics. In the case of a prostate abscess or sepsis the patient will warrant admission to hospital for intravenous antibiotics. It is reported that 90% of prostatitis is nonbacterial, the treatment of this is challenging and often requires symptomatic support.

Hematospermia Hematospermia refers to blood in the semen or ejaculatory fluid which is usually self-limiting. The cause can often be unknown however, urogenital

infections including sexually transmitted infections, prostatitis, orchitis, and epididymitis can present with hematospermia. Other benign conditions such as trauma, recent instrumentation, calculi (Fig. 42.13), and BPH can also lead to hematospermia as well as some systemic disease such as uncontrolled hypertension, bleeding diathesis, or chronic infections. Malignant cause includes urogenital cancer, lymphoma, and leukemia. Men less than 40 years likely have a self-limiting condition. In cases of older patients or a protracted course, referral to urology and evaluation with USG is recommended [18]. TRUS is often requested in hematospermia to rule out an underlying cause.

FIGURE 42.13 Calculi within the ejaculatory duct as a cause of hematospermia. A 52-year-old patient with chronic recurrent blood in the semen (hematospermia). Prostate MRI (axial T1WI: A; multiplane T2WI: B, C, and D) demonstrates left ejaculatory duct dilation and obstruction due to calculi (arrows). The stones present as T2 hypointense structures within the ejaculatory duct. Note that there is also T1 hyperintense material (arrowhead) surrounding the calculi, representing hemorrhagic content inside the obstructed duct.

Prostate Malignancy Prostate cancer is the most common visceral cancer in men and has an incidence above 200 per 100,000 men per year. The high incidence is partly due to an aging population and factors such as metabolic syndrome. Recent improvements in the sensitivity of diagnostic techniques and screening have also led to an increase in the number of diagnoses [19]. It is worth noting that a high proportion of prostate cancers remain clinically insignificant, being demonstrable at the time of postmortem having failed to develop into significant disease during life. More than 95% of malignant prostate tumors

are adenocarcinoma that develops in the acini of the prostate ducts (Table 42.2) [20,21]. Table 42.2 Histological Classification of Prostatic Neoplasms Epithelial tumors

Glandular neoplasms ■ Acinar adenocarcinoma ■ Prostatic intraepithelial neoplasia ■ Intraductal carcinoma ■ Ductal adenocarcinoma ■ Urothelial carcinoma Squamous neoplasm ■ Adenosquamous carcinoma ■ Squamous carcinoma Basal cell carcinoma

Mesenchymal tumors

■ Stromal tumor of uncertain malignant potential ■ Stromal sarcoma ■ Leiomyosarcoma ■ Rhabdomyosarcoma ■ Leiomyoma ■ Angiosarcoma ■ Synovial sarcoma ■ Inflammatory myofibroblastic tumor ■ Osteosarcoma ■ Undifferentiated pleomorphic sarcoma ■ Solitary fibrous tumor ■ Solitary fibrous tumor, malignant ■ Hemangioma ■ Granular cell tumor

Hematolymphoid tumors

■ Diffuse large B-cell lymphoma ■ Chronic lymphocytic leukemia/small lymphocytic lymphoma ■ Follicular lymphoma ■ Mantle cell lymphoma ■ Acute myeloid leukemia ■ B lymphoblastic leukemia/lymphoma

Neuroendocrine tumors

■ Adenocarcinoma with neuroendocrine differentiation

■ Well-differentiated neuroendocrine tumor ■ Small cell neuroendocrine carcinoma ■ Large cell neuroendocrine carcinoma Miscellaneous tumors

■ Cystadenoma ■ Nephroblastoma ■ Rhabdoid tumor ■ Germ cell tumors ■ Clear cell adenocarcinoma ■ Melanoma ■ Paraganglioma ■ Neuroblastoma

In 1966 Donald F. Gleason created this unique grading system for prostate carcinoma which is based solely on the architectural pattern of the tumor. Histologically, prostate cancer is graded by the Gleason grading system which has a scale from 1 to 5. Score of ≥3 are considered cancer. The Gleason grade is assigned based on the two most common grade patterns seen in the specimen; these are summed together and reported as the Gleason grade [22]. Grade 6(3+3) is the least aggressive histological type of cancer, whereas grade 10 (5+5) is the most aggressive histological type. In 2014, the International Society of Urogenital Pathologists revised prostate cancer grading system [23] ■ Gleason 6(3+3) cancer is now classified as International Society of Urogenital Pathologists grade group (GG) 1 cancer (low-risk disease) ■ GG2(3+4) and GG3(4+3) constitute intermediate-risk cancer ■ GG4(4+4) and GG5 (4+5, 5+4, 5+5) constitute high-risk disease with increased risk of lymph node metastases (Fig. 42.14)

FIGURE 42.14 Chart categorizes prognostic groups in patients with prostate cancer according to ISUP-grading and Gleason score (pathologic classification). Five main prognostic groups according to Gleason score: prognostic group 1 (Gleason score 6, low risk), prognostic group 2 (Gleason score 7 = 3+4, low to intermediate risk or intermediate favorable), prognostic group 3 (Gleason score 7 = 4+3, high to intermediate risk or intermediate unfavorable), prognostic group 4 (Gleason score 8, high risk), and prognostic group 5 (Gleason score 9 or 10, high risk). ISUP, International Society of Urological Pathology.

Tumor size is an independent predictor of aggressive behavior such as metastases, seminal vesicle invasion being uncommon at a volume below 2.5 mL and lymph node or other distant metastases being uncommon at volumes below 4 mL. Tumor differentiation also tends to deteriorate with an increasing size. The TNM (Tumor [T], Node [N], Metastasis [M]) staging system is used for staging of prostate cancers. Prostate-Specific Antigen PSA is a glycoprotein produced exclusively by the glandular tissue of the prostate. It becomes elevated in the blood in prostatic disease, including BPH, inflammation, and cancer. The arbitrary upper limit of normal is often taken as 4 ng/mL; however, only 25% of patients with a value of 4–10 ng/mL are shown to have prostatic cancer. Above 10 ng/mL as many as 85% are shown to have cancer. A normal PSA value in the general population is usually associated with an absence of cancer but does not exclude it. A small proportion of extremely undifferentiated cancers will not produce a demonstrable rise in the PSA, and very small cancers may not produce enough of a rise for the value to fall outside the normal range. The use of PSA for screening of prostate cancer is controversial due to the lack of demonstrated impact on overall survival or cancer-specific survival. There is

also a reported risk of over diagnosis and over treatment. The recommendation for PSA screening is to target populations at high risk for prostate cancer or in males over 50 years old who desire screening after disclosure of the benefits and risks [19]. The classic diagnostic pathway for prostate cancer detection is initiated with a combination of the PSA level and DRE. If the PSA value is less than 10 ng/mL it is of limited sensitivity in discriminating between BPH and prostate cancer. ■ PSA density (PSAD) is used to enhance the specificity of PSA; it is calculated by dividing the serum PSA level by the prostate volume estimated on TRUS. A PSAD value of >0.15 is concerning for malignancy and should prompt a referral for prostate biopsy ■ PSA velocity (PSAV) is calculated when more than one PSA measurement is available to give the average PSAV. PSAV of >0.75 ng/mL/year is considered an indication for biopsy despite the PSA level. PSAV is an important parameter for predicting the behavior and prognosis of prostate cancer in men undergoing treatment [24–26]

In the setting of an elevated PSA/PSAD or an abnormal DRE the patient will proceed to TRUS and systematic TRUS-guided biopsies. The histopathological diagnosis is determined, and a Gleason score is assigned. Imaging of the prostate is typically performed by TRUS. However, in recent years, the role of multiparametric MRI (mp-MRI) has been extensively studied and demonstrated considerable promise in the detection, localization, risk stratification, and staging of prostate cancer [27]. Ultrasonography TRUS was implemented for routine assessment of the prostate to evaluate for benign and malignant conditions in the early 1980s. TRUS is utilized for cancer detection, screening, and biopsy in patients with or suspected to have prostate cancer. TRUS is typically performed with the patient in the left lateral decubitus position. The rectal probe is gently inserted into the rectum using lubrication after a DRE to ensure there are no rectal abnormalities. The prostate gland is imaged in a systematic method starting with grayscale and followed with Doppler flow USG. Both techniques begin in the transverse (TR) plane from the seminal vesicles to apex of the gland followed by the sagittal plane from right to left. The prostate is measured in three orthogonal planes and the volume of the gland is calculated using the “oblate spheroid” formula. Measurements are taken in TR, anteroposterior (AP), and craniocaudal dimensions. The seminal vesicles are two hypoechoic multiseptated structures lying at the base of the prostate gland; the vas deferens is adjacent smooth tubular structures that can be identified entering the prostate gland at the mid-base becoming the ejaculatory ducts.

The zonal anatomy of the prostate gland may be difficult to delineate on TRUS, the central gland incorporates the transition and central zones, while the peripheral zone is seen as a homogenous outer layer. The anterior aspect is often difficult to appreciate due to its location and the probe orientation. The transition zone is more echogenic than the peripheral zone; these are separated by a thin hypoechoic rim called the “surgical capsule.” The surgical capsule is a frequent site for calcific deposits called corpora amylacea. The surrounding periprostatic fat creates a plane allowing for delineation of the margins of the prostate gland. Approximately 40–60% of prostate cancers are not detected by grayscale TRUS, therefore a normal appearance on TRUS does not exclude prostate cancer and systematic biopsy of the prostate gland should be considered if there is clinical suspicion of cancer. When cancer is detected by TRUS in the peripheral zone prostate cancer it classically appears as a hypoechoic nodule (Fig. 42.15) because tumors replace the normal loose glandular tissue of the peripheral zone with a packed mass of tumor cells. Cancer in the peripheral zone may also appear as an ill-defined area of reduced echogenicity compared with the background parenchyma. Occasionally, prostate cancer can also appear hyperechoic on B-mode imaging secondary to a desmoplastic reaction of the tumor.

FIGURE 42.15 Transrectal ultrasonography (TRUS) images (7.5 MHz) of the prostate—axial plane (grayscale: A; color Doppler: B) demonstrating a hypoechoic lesion in the right peripheral zone (arrow in A), with increased vascularity on Doppler (arrow in B), suspicious for a malignant lesion.

Prostate cancer often demonstrates neovascularity and increased microvascular density. Color and power Doppler imaging can increase the detection of peripheral zone cancer which is isoechoic on grayscale imaging. When performing Doppler imaging, power Doppler mode is preferred

because it is more sensitive to flow, providing a more uniform display of vascular density within the lesion [6,28]. Cancers originating in the transition and central zones are less common and more difficult to detect with TRUS. This is particularly true in the setting of BPH where the background gland is heterogeneous with increased vascularity from the hyperplasia. Transition zone cancers may be detected as asymmetric hypoechoic areas relative to the background parenchyma, there may be asymmetric bulging of the surgical capsule or at the margin of the prostate gland. Tumors at the anterior midline of the prostate are typically not well visualized with TRUS due to their location in the fibromuscular area of the gland anterior to the urethra. It is also important to further emphasize the pitfalls of TRUS and Doppler imaging—not all cancers are vascular, and some benign inflammatory conditions can mimic hypoechoic tumor and demonstrate increased Doppler flow. ■ The initial prostate biopsy typically involves 10–12 samples obtained in a systematic fashion from the prostate gland (Fig. 42.16). If a suspicious area is identified on TRUS, additional samples are obtained from this area first ■ Follow-up or extended biopsy protocols are typically performed when the initial biopsy is negative and a high clinical suspicion for cancer remains. An extended biopsy consists of up to 17 systematic samples, which includes sampling of transition zones (two samples from either side) and from midline gland in addition to repeat extended sextant 12-core sampling ■ A saturation biopsy involves >20 core biopsies. These are again, obtained in a systemic fashion from the prostate gland; however, this biopsy is typically performed using a template transperineal approach and traditionally involves sedation or anesthesia for the procedure. The risk of complication from a saturation biopsy is about twice that of a standard 12 core TRUS biopsy [20]

FIGURE 42.16 Transrectal ultrasonography (TRUS)-guided prostate biopsy scheme. The standard systematic biopsy procedure consists of sampling randomly the parasagittal midline and lateral basal (A), medial (B), and apical (C) regions bilaterally for a total of 12 cores.

New advances in USG are emerging, which demonstrate greater sensitivity and specificity for the detection of prostate cancer. Nonlinear imaging (tissue harmonic imaging) allows improved contrast resolution and reduced clutter (noise) due to lower USG aberrations from the second harmonic. Spatial

compound imaging uses pulses that steer at different angles (typically 3–5 angles) improving structure delineation and identification. Improvements in the shape and frequency of transducers such as linear array transducers have resulted in improved spatial and contrast resolution, although may lead to increased attenuation of sound. Microconvex arrays require more interpolation to form images and typically provide reduced spatial resolution than linear arrays. The microconvex arrays are located at the tip of the transducer (end-fire probes) or proximal to the tip (biplane probes). There are ongoing trials examining the latest noninvasive USG techniques both as stand-alone techniques and in combination with other imaging techniques to evaluate their diagnostic accuracy. These techniques include: ■ Contrast-enhanced ultrasonography (CEUS) ■ Ultrasonography biomicroscopy ■ Elastography ■ Multiparametric ultrasonography

CEUS is a technique that exploits the increased microvascular density of prostate tumors. The contrast agent used is microbubbles that are blood pool agents and do not enter the interstitial space. They provide improved detection of low-volume blood flow by increasing the signal-to-noise ratio (SNR) and delineating the neovascular anatomy therefore enhancing the signal strength from small vessels. Contrast agents within the vascular lumen are more reflective than blood and improve flow detection with USG while the vibrations from the contrast agents generate higher harmonics in tumors compared with the surrounding tissue. Multiple studies have shown that CEUS provides greater sensitivity and specificity for the diagnosis of prostate cancer compared with conventional TRUS [19,29]. The limitations of CEUS are mainly linked to USG contrast agents and the enhancement pattern of prostate parenchyma/carcinoma. The resonant frequency of most USG contrast agents is close to 2 MHz. A TRUS transducer frequency ranges between 6 and 12 MHz therefore only a limited number of smaller size microbubbles administered intravenously provide the harmonic signals from the resonating microbubbles. Prostate cancer enhancement is transient during the arterial phase and can only be distinguished from surrounding parenchyma for 20 seconds after the bolus injection. It does not exhibit washout and therefore a short wash-in phase is useful in CEUS. BPH is also a limiting factor as the vascularity of the transition zone may overshadow the flow associated with malignancy. Finally, CEUS is dependent on identifying the target on B-mode imaging (single-level technique), having previously identified the target for biopsy on the reference diagnostic method [19]. Ultrasonography elastography is an emerging technique that is reported to improve both prostate cancer detection and characterization of the lesion.

This technique is based on the fact that prostate cancer tissue is stiffer than the surrounding normal tissue because it has increased cellular density with associated microvascularization with destruction of the normal glandular architecture. Two techniques have been developed and are utilized in clinical practice: strain elastography and shear-wave elastography. ■ Strain elastography assesses the difference in tissue strain produced by freehand manual compression and analyze the deformation generated by the compressive force. A speckle comparison before and after compression produces a color-coded map of local tissue deformation that is overlaid on a B-mode image from TRUS—this is called an elastogram. The limitations of strain elastography are like other techniques, small cancers can be missed, other inflammatory conditions such as prostatitis can produce greater tissue stiffness and the technique requires significant operator training [19,30] ■ Shear-wave elastography is a technique based on the measurement of shear-wave speed propagating through the tissues. This technique is impeded by compression on the prostate gland and also requires an experienced operator. This is a multiwave technique combining two different waves, the first is generated by the acoustic radiation force and the second is an ultrasonic wave that captures the propagation of the shear wave. The speed of the shear wave is linked to the stiffness of the analyzed tissue. The shear wave produces a dynamic quantitative map of soft-tissue stiffness in quasi-real-time which is derived from measuring the propagation speed and is color coded for each pixel overlaid on a B-mode TRUS image

Both elastography methods are limited by very large prostate glands, artifacts, and the limitation that not all cancers are stiff and not all stiff lesions are cancers [19,30]. Multiparametric ultrasonography is a concept derived from mp-MRI, it takes advantage of B-mode TRUS and combines it with newer techniques such as elastography and perfusion imaging to generate volumetric imaging of the prostate gland. This method is used in conjunction with mp-MRI to produce a map identifying potential targets for biopsy. Advances in USG technology have resulted in the development of new and promising high-frequency systems ranging between 14 and 29 MHz (microultrasound) compared with conventional TRUS frequencies between 7 and 9 MHz. Microultrasound allows for spatial resolution to 70 μ, three times higher than conventional platforms, and allows clearer and more defined anatomical evaluation. The resolution of 70 μ allows alterations in ductal anatomy and cellular density to be appreciated. A recent randomized multicenter trial comparing microultrasound to conventional USG showed a 19% improvement in the detection of clinically significant prostate cancer (csPCa) [31]. Subsequently the “prostate risk identification using microultrasound” (PRI-MUS) grading system (Fig. 42.17), analogous to prostate imaging reporting and data system (PI-RADS) (Fig. 42.18), was proposed to allow for more consistent interpretation of prostate images [32]. Multiple studies have also shown sensitivity of microultrasound comparable to that of mpMRI [33–35]; however it is a new technology and the data are preliminary. The studies are small and there is substantial heterogeneity between the

cohorts in the different studies. Therefore, microultrasound requires multicenter trials to establish and cement its role in prostate cancer detection [19,36]. Nonetheless, this technology has a number of potential benefits including lower relative technology costs compared with MRI, convenience for the patient (diagnostic test and biopsy performed in a single setting), ease of use and interpretation, and fewer contraindications.

FIGURE 42.17 Prostate risk identification using microultrasound (PRIMUS) grading system.

FIGURE 42.18 Comparative MRI (A, B, C) and microultrasound (D, E) images of index lesion. Axial T2WI (A) shows a hypointense focal abnormality with noncircumscribed margins in the right lateral midgland peripheral zone (white arrow in A), without evidence of extraprostatic extension (T2WI score: 3). High b value DWI (B) and ADC map (C) show a 1.3-cm lesion that is markedly hyperintense on the DWI (white arrow in B) and markedly hypointense on the ADC map (white arrow in C) (DWI-ADC score: 4). Therefore, this focal lesion was assigned a PIRADS assessment category of 4. Parasagittal microultrasound (D) of right lateral edge of prostate shows this hypoechoic index lesion with smudgy/mottled appearance consisted with PRI-MUS 4 score (white arrows). Microultrasound-guided biopsy (E) was performed, with pathological result compatible with Gleason 7 (3+4) involving 85% of the core.

Multiparametric Magnetic Resonance Imaging Over the past decade the use of mp-MRI for the diagnosis and staging of prostate cancer has exponentially increased (Fig. 42.19). Mp-MRI includes high-resolution T2-weighted imaging (T2WI) with functional MRI techniques including diffusion-weighted imaging (DWI), dynamic contrastenhanced (DCE) perfusion imaging, and spectroscopic imaging (MRSI). MRSI is an MRI technique that utilizes abnormalities of tissue metabolism. The metabolites produce photon peaks on the spectra derived from choline, creatinine, and citrate. In cancer, choline signals are elevated whereas the citrate signals decrease. There are high citrate levels in the peripheral zone which allows for interpretation of the choline plus creatinine-to-citrate ratios

as a biomarker for prostate cancer. T1-weighted imaging is of limited use except for ruling out postbiopsy hemorrhage.

FIGURE 42.19 Chart shows a proposal of sequences to be acquired in the performance of multiparametric MRI (adapted from PI-RADSv2.1). Chart also describes the clinical utility of these sequences and main radiological features that must be noted in each of them. ADC, apparent diffusion coefficient; DCE, dynamic contrast enhanced; DWI, diffusionweighted imaging; EPE, extraprostatic extension; FatSat, fat saturation; FOV, field of view; FSE, fast spin-echo; Gd+, gadolinium; mp-MRI, multiparametric magnetic resonance imaging; PI-RADS, prostate imaging reporting and data system; PZ, peripheral zone; T1WI, T1weighted imaging; T2WI, T2-weighted imaging; TZ, transition zone.

Patient Preparation and Clinical Considerations: There are clinical considerations to address before performing MRI including patient preparation and information (Fig. 42.20). Some institutions recommend that men refrain from ejaculation for 3 days before the exam to ensure maximum distention of the seminal vesicles. In institutions where an endorectal coil (ERC) is used stool in the rectum can interfere with coil placement. If an ERC is not used air/stool in the rectum may cause artifact, particularly for DWI. Therefore, patients are given a minimal preparation enema a couple of hours before the MRI. It is worth noting that the enema may promote peristalsis which can also cause artifacts. Antispasmodic agents may be administered to reduce bowel peristalsis; however this increases the cost of the study and can result in adverse drug reactions.

FIGURE 42.20 Chart categorizes prostate MRI protocol according to clinical considerations, patient preparation, and technical specifications that are recommended, those that are not recommended and some that are controversial practices, according to PI-RADS v2.1. 3-D, three dimensional; ADC, apparent diffusion coefficient; bpMRI, biparametric magnetic resonance imaging; DCE, dynamic contrast enhanced; DRE, digital rectal exam; DWI, diffusion-weighted imaging; FOV, field of view; FSE, fast spin-echo; GRE, gradient echo; mp-MRI, multiparametric magnetic resonance imaging; MR, magnetic resonance; PSA, prostatespecific antigen; T, Tesla; T1WI, T1-weighted imaging; T2WI, T2weighted imaging.*At least one pulse sequence should use a FOV that permits evaluation of pelvic lymph nodes to the level of the aortic bifurcation.

The timing of MRI postbiopsy is important to consider as hemorrhage is hyperintense on T1WI and may confound MRI assessment of the prostate gland and seminal vesicles. This is particularly important in the setting of MRI cancer staging and it is recommended that the study is postponed for 6 weeks or longer to allow the bleeding and inflammatory changes to settle. In instances of a recent negative TRUS biopsy, patients may proceed with MRI as the likelihood of a clinically significant cancer at the site of hemorrhage is exceptionally low. Technical Specifications: MRI is routinely performed at magnetic field strengths of 1.5T and 3T, both provide reliable diagnostic exams when the acquisition parameters are optimized (Fig. 42.20). Magnetic field strength of 3T is often preferred as it has a greater SNR than at 1.5T. The SNR can also be exploited to increase

spatial resolution and temporal resolution; however, 3T can be associated with signal heterogeneity and artifacts that are successfully addressed by the new state-of-the-art MRI scanners. Magnetic field strength of 1.5T imaging may be preferred if a patient has an implanted MRI compatible device that will cause artifact or if not rendered safe for 3T. ERCs are used in some institutions and have the advantage of increasing the SNR in the prostate at any magnetic field strength. The use of ERCs with a 1.5T system is valuable to ensure high spatial resolution providing diagnostic quality studies. Image quality with a 3T system is considered to be comparable to a 1.5T study with an ERC. ERCs are also valuable in larger patients where the SNR of the prostate may be reduced. The disadvantages of ERCs include patient discomfort, added cost, deformity of the prostate gland, and the introduction of artifacts. Adequate images can be obtained with and without ERCs; therefore radiologists are encouraged to use the MRI protocol that achieves the best image quality at their institution. Mp-MRI Sequences: T2WI is used to differentiate the zonal anatomy of the prostate, tumor detection, and local cancer staging (Fig. 42.19). The neurovascular bundles, ejaculatory ducts, seminal vesicles, and AFMS are all identified most clearly on T2WI. ■ The peripheral zone is high signal intensity and cancer is low signal on T2WI. However, other benign processes can also appear low signal on T2WI (prostatitis, fibrous scar tissue, postbiopsy hemorrhage, and postirradiation) ■ T2WI is considered the dominant sequence for the detection of transition zone cancers; these can be more difficult to differentiate in the setting of BPH. Transition zone cancer is typically ill-defined or lenticular in shape, it is low signal intensity and may extend into the peripheral zone or AFMS; the appearance is described as “erased charcoal” or “smudgy fingerprint” [27]. Stromal BPH nodules and transition zone tumors have some imaging overlap as both appear low signal on T2WI; however, stromal nodules are more encapsulated with heterogeneous low T2-weighted signal compared with homogeneously low signal, ill-defined, and lenticular-shaped transition zone cancers [8]

DWI is a functional imaging tool that measures the Brownian motion of water molecules in the tissue to produce image contrast. The ADC on MRI is calculated by acquiring at least two sets of images with differing magnetic field gradient duration and amplitude (b value). The degree of diffusion weighting is controlled by the amplitude, duration, and temporal spacing of gradient pulses and expressed in the diffusion b value unit (s/mm2). Higher b values allow better tumor detection by suppression of normal benign gland as well as to assess for treatment response. A “high b value” is defined between 1000 and 2000 s/mm2, and a high b value of ≥1600 s/mm2 is recommended (preferably ≥2000 s/mm2). High b values can be obtained by the following two methods: ■ the first method is by directly acquiring a high b value sequence which adds to scan time and

■ the second method is to calculate the b value by extrapolating it from the lower b value data acquired for the ADC map

The SNR decreases as the b value increases. At least two b values are required to generate an ADC map, low b value (50–100 s/mm2) and an intermediate b value (800–1000 s/mm2). The maximum recommended b value for ADC calculation is 1000 s/mm2 to avoid diffusion kurtosis effects described at higher b values [9,37,38]. The hallmark of prostate cancer is low signal intensity on ADC and iso to high signal intensity on the high b value (>1400 s/mm2) [27]. Studies have shown that DWI is the dominant MRI sequence for tumor detection, particularly in the peripheral zone [39]. DWI can also be used as a problemsolving tool to differentiate cancer from benign etiologies such as prostatitis, fibrosis, scar tissue, hemorrhage and postirradiation which will appear low signal on T2WI and ADC. DCE is a technique that exploits the dynamic uptake and rapid washout of gadolinium chelate. DCE consists of a series of fast T1-weighted (T1WI) sequences covering the entire prostate before and after rapid injection (2–4 mL/s) of a bolus of a low-molecular-weight gadolinium chelate [40]. During DCE-MRI, tumors demonstrate early and high amplitude enhancement followed by rapid washout in some cases compared with normal prostate tissue. DCE sequences should be inspected for focal early enhancement. PIRADS document describes a positive DCE as having focal, early, or contemporaneous with enhancement of adjacent normal prostate parenchyma corresponding to a finding on T2WI and DWI images. Visual assessment is improved with fat suppression and subtraction techniques. DCE is performed for 2 minutes to detect early enhancing lesions, the temporal resolution should be 0.5 cc, and/or extraprostatic extension (EPE).

FIGURE 42.25 Suggested measurements for ellipsoid formula when calculating prostate volume at MRI (T2WI) according to PI-RADS v2.1. Maximum transverse diameter (yellow line) should be measured on axial T2WI (A). Maximum longitudinal diameter (red line) and maximum anteroposterior diameter (blue line) should be measured on mid sagittal T2WI (B).

Prostate cancer can be multifocal; however, PI-RADS recommends that up to four most suspicious lesions should be reported. The minimum requirement for reporting suspicious lesions is to report the largest dimension on the axial image; however, if the largest dimension is on either the sagittal or coronal sequence this should be reported.

DWI is the dominant sequence for the assessment of the peripheral zone (Fig. 42.26); however, the score may be modified by the DCE sequence for lesions with a score of 3. Peripheral zone lesions should be measured on ADC with the image number and series included in the report.

FIGURE 42.26 Peripheral zone assessment according to PI-RADS v2.1. For peripheral zone lesions, the overall PI-RADS assessment usually follows the DWI score, but a score of 3 can be upgraded by the presence of dynamic contrast enhancement.

■ PI-RADS category 4 (Fig. 42.27) lesions in the peripheral zone are typically described as a well-circumscribed T2 (Table 42.3) hypointense mass measuring 50% intramural component Type 6: Subserosal fibroid with 20 cm3 is considered abnormal.

■ Prepubertal: 1–4 cm3. ■ Pubertal: 2–6 cm3. Volume >4 cm3 in prepuberty or ≥6 visible follicles indicate premature sexual development.

Physiology Before puberty, the ovaries are small, with few or no cysts or follicles. At puberty, several small cysts/follicles measuring 5–8 mm appear in the ovaries. This is associated with low levels of circulating estrogens and frequent anovulatory cycles typical of menarche. Once menstruation is established, regular cyclical changes occur in the appearance of the ovaries and uterus, reflecting the associated hormonal changes. ■ The follicular phase begins on day 1 of the menstrual cycle with the development of a small number of follicles. From days 8 to 10, one follicle

becomes dominant and continues growing at a rate of 2–3 mm/day, whereas the other follicles regress ■ Ovulation occurs about day 14, when the follicle measures 18–25 mm. Ovulation is indicated in 90% of cycles by disappearance of the follicle and escape of fluid around the ovary or into the pouch of Douglas. Other indicators of ovulation include a decrease in size, change in shape with thickening and crenulation of its wall, and the presence of internal echoes within the follicle ■ The luteal phase commences after ovulation and lasts 14 days, unless pregnancy supervenes Occasionally a well-defined luteal cyst develops and slowly increases in size to 3–5 cm. It usually resolves spontaneously over the next few months but can cause symptoms if large or undergoes a complication such as hemorrhage, torsion, or rupture. The identification and management of such physiological cysts are described in the sections ahead.

Imaging Techniques Radiography Plain radiographs have a very limited role in current gynecological practice. Pelvic calcifications due to gynecological causes may be visible on a plain abdominal radiograph. Differentials include: ■ Fibroids—typically coarse popcorn-type calcification ■ Dermoid cysts (teeth and/or a visible fat-fluid level would be pathognomonic (Fig. 45.2)) ■ Other ovarian masses—cystadenomas/carcinomas, fibromas ■ Peritoneal carcinomatosis, usually from metastatic serous cystadenocarcinoma ■ Fallopian tube calcification—rare, should suggest tuberculosis ■ Uterine, that is, endometrial calcification from chronic endometritis

Figure 45.2 Pelvic radiograph showing typical dermoid cyst calcifications.

Figure 45.3 Typical appearance of the ovaries in various age groups on USG (different patients), CT and T2W MRI, respectively (marked with solid arrows). (A–C) Prepubertal age group (11-year old in this case).

Note the presence of multiple follicles.

(D–F) Reproductive age group. Note the presence of multiple follicles at various stages of the development. CT also demonstrates right pelvic adenopathy (dashed arrow), which can be distinguished from the ovary which is intraperitoneal in location. (G–I) Postmenopausal age group. Follicles may or may not be visualized. In this case, USG shows few small peripherally located follicles, while it appears as a featureless (without any follicles) ovoid adnexal soft-tissue structure on CT. MRI shows small atrophic ovaries with the left ovary showing a follicle within.

Figure 45.4 Coronal postcontrast CT image in a prepubertal girl demonstrates the normal ovary (dashed arrow), identifiable as adjacent the gonadal vessels (solid arrow).

Ultrasonography (USG) Transabdominal or TVS is the mainstay of pelvic imaging. Transabdominal USG requires the patient to have a full bladder. The distended bladder displaces small bowel out of the pelvis, pushes the uterus posteriorly, and the ovaries laterally. If the bladder is inadequately distended, the pelvic structures may be obscured by bowel gas, but if over distended, the uterus becomes elongated, and the ovaries get displaced far too laterally. Longitudinal (sagittal) and transverse scans are performed using the bladder as an acoustic window. TVS is best performed with

an empty bladder and gives improved resolution of structures close to the probe but with a limited field of view. Doppler USG: The ovaries obtain blood supply through the uterine arteries and directly from the aorta. Flow in the uterine vessels can usually be seen in the broad ligament. Visualization of intraovarian vessels depends on ovarian activity. During menstruation and the early follicular phase, there is relatively high impedance flow in the ovary, that is, the resistive index is approximately 0.7. After ovulation and neovascularization of the corpus luteum, diastolic flow increases, leading to lower impedance flow and typical values of less than 0.6 for the resistive index. Doppler indices in the postmenopausal patient are those of an inactive ovary, that is, high impedance flow.

Computed Tomography Computed tomography (CT) has a limited role in adnexal lesion characterization as it has limited soft-tissue contrast and is mainly used in staging ovarian cancer. Oral contrast should be given for evaluating an adnexal pathology; it avoids confusing ovaries with collapsed loops and helps in identifying serosal deposits in patients with peritoneal disease (Fig. 45.5). Some institutes prefer distention of bowel loops with neutral oral contrast, as positive oral contrast may make identification of calcified serosal deposits suboptimal. A single portal venous phase contrast enhanced CT suffices for most indications.

Figure 45.5 Utility of oral contrast in assessing peritoneal disease in a patient of ovarian cancer. Baseline CT (A) demonstrated soft-tissue density nodular structures (white arrows); differentiating deposits from collapsed bowel loops were not possible. Follow-up CT after 3 months

(B) shows oral contrast distending the small bowel loop (dashed arrow), with overlying serosal deposits (arrowheads).

Magnetic Resonance Imaging MRI is the technique of choice for the characterization of sonographically indeterminate adnexal lesions, as it provides excellent soft-tissue differentiation and anatomical localization. An MRI is usually performed after 4 hours of fasting to mitigate artifacts of peristaltic movements, or after giving an antiperistaltic agent. A sample MRI protocol is given in Table 45.2. The protocol needs to be individualized based on the lesion characteristics. For example, a T1W fatsaturated image is obtained if the adnexal lesion has a T1 hyperintense component but may be skipped otherwise. The typical MR signal characteristics of various soft-tissue components of adnexal lesions and their differential diagnosis have been summarized in Fig. 45.6. Table 45.2 MRI Protocol for the Adnexal Lesion [4] Sequence Remarks Large FOV axial or coronal ■ Covering entire pelvis. SSFSE/HASTE without fat saturation. ■ Coronal sequence may also catch hydroureter. Sagittal T2W (FSE)* without fat saturation. Axial and coronal high-resolution T2W (FSE)* without fat saturation.

■ From one hip to another.

■ Orthogonal to lesion. ■ Provides anatomical detail and internal characteristics of lesion.

Sequence Axial or coronal high-resolution T1W (FSE) without fat saturation in same plane as the T2WI/

Remarks ■ Fat saturation sequence to be taken if T1 hyperintense component present.

DIXON GRE T1. ■ DIXON GRE T1 sequence is an alternative; it provides images with and without fat saturation simultaneously. DWI (b value of 1000) (bladder signal intensity should be suppressed).

Dynamic postcontrast 3D T1W GRE sequences with fat saturation (at least five contrast-enhanced sequences obtained at intervals of 20 seconds each).

■ Helps differentiate benign from malignant lesions in nonhemorrhagic nonfatty solid or solid-cystic masses. ■ Covering entire pelvis. ■ Precontrast sequence must be obtained, enabling subtraction and also to identify blood, fat or proteinaceous products. ■ Dynamic study also enables obtaining T1 kinetic curves.

Some centers obtain 3D T2W sequences and reformat in various planes instead. When unsure about site of origin (ovarian or uterine in nature) an oblique axial to ovaries in small FOV (20–25 cm), usually parallel to endometrial cavity obtained. *

Figure 45.6 MR characteristics of common adnexal lesions.

History, Clinical Examination, and Biomarkers History and gynecological examination are of utmost importance in evaluating gynecological lesions. Knowing the menstrual status of the patient and the last menstrual period is a must. Physiological and inflammatory or infectious findings are more common in younger age group (as also germ cell tumors [GCTs]), whereas the chances of malignancy increase with increasing age. It is important to note that more than half of the adnexal lesions in the elderly remain benign [5]. Certain biomarkers are useful in characterizing adnexal lesions and for assessing treatment response and in surveillance. CA-125 is raised in patients with epithelial ovarian malignancies; mild elevation can also be seen in benign pathologies like endometriosis or TB. Equally importantly, normal levels do not rule out a malignancy, as not all ovarian cancers cause increased levels. Thus, the main role of CA-125 is in assessing response to therapy and for surveillance of patients with ovarian cancer, rather than diagnosis. Various GCT markers, in contrast, are extremely useful for the diagnosis as well as in response assessment and surveillance (Table 45.3). Table 45.3 Tumor Markers in Adnexal Lesions [6]

Tumor Marker CA-125

Condition(s) Raised in ■ Epithelial tumors of the ovary ■ Endometriosis ■ Peritoneal disease (inflammation, carcinomatosis, etc.) ■ Adnexal tuberculosis ■ Pelvic inflammatory disease

Carcinoembryonic antigen (CEA)

■ Epithelial cancer ■ Peritoneal diseases

Alpha fetoprotein (AFP) Human chorionic gonadotropin (β hCG)

■ Germ cell tumors: immature teratoma, yolk sac tumor, embryonal carcinoma, ■ Germ cell tumors: choriocarcinoma, some dysgerminomas ■ Gestational trophoblastic neoplasia ■ Ectopic pregnancy

Estrogen

■ Granulosa cell tumor ■ Some thecomas/fibrothecomas ■ Stromal luteoma ■ Certain serous and mucinous tumors

Tumor Marker Inhibin A and B

Condition(s) Raised in ■ Granulosa cell tumor ■ Certain serous and mucinous tumors

Lactate dehydrogenase (LDH)

■ Dysgerminoma ■ Yolk sac tumor

Testosterone

■ Androgen producing tumors: stromal tumors, Sertoli–Leydig tumors ■ Polycystic ovarian disease ■ Brenner tumor ■ Stromal hyperthecosis

Lexicon for Reporting Adnexal Lesions A widespread variability in the morphologic description of various adnexal lesions exists internationally, nationally, locally, and often even within the same institute. For example, different radiologists use terms like “solid-cystic” or “complex” lesion in a variable manner. This makes standardized management and research difficult. The Europe-based International Tumor Analysis Group (IOTA) first proposed a standardized lexicon in 2000 [7], followed by prospectively validating “Simple Rules” (discussed later) and ADNEX model [8] to differentiate benign from malignant lesions. More recently (2018–2019), the American College of Radiology led Ovarian-Adnexal Reporting and Data System (O-RADS) [9] has adapted from the IOTA data and laid out standardized descriptors for reporting adnexal findings on ultrasound as well as MRI. They propose risk stratification

scores with associated management guidelines [10,11], enabling clear communication and helping improve patient management [7]. The relevant descriptors and reporting lexicon are discussed here, whereas risk stratification scores are discussed in more detail at the end of the chapter.

Ultrasound Descriptors Cyst Fluid containing structure, which may be anechoic or demonstrate echoes. It may also demonstrate solid component within. Solid or Solid Appearing Soft-tissue structures ≥3 mm in height. The presence of blood flow confirms solid nature, while its absence is less definitive, and such structures should be considered solid appearing. Normal ovarian stroma, avascular hyperechoic content of a dermoid, blood clot or mucin, septation(s), and an irregular cyst wall with focal thickening 3 mm); the thickness of the septation does not correlate with risk of malignancy. Thickness of the septum at its broadest point (except near its attachment with the wall) should be measured. Papillary Projection These are solid projections with height ≥3 mm arising from cyst wall or septation. If 10 cm or those with solid component ≥7 mm are at higher risk for malignancy, although very large simple cysts are usually benign cystadenomas. Overall, adnexal lesions can be categorized morphologically described in Fig. 45.7.

Figure 45.7 Graphical depiction of sonological classification of adnexal lesions.

Magnetic Resonance Imaging Descriptors [12] Purely cystic mass: A unilocular cyst (similar to USG) or hydrosalpinx. Follows typical fluid signal intensity (SI) and shows no contrast enhancement. Pure endometrioma: High SI on T1W (more than subcutaneous fat) does not get suppressed on fat-suppressed sequences and shows T2 “shading” without any postcontrast enhancement. Purely fatty mass: High SI on T1W (more than subcutaneous fat), suppressed completely on fat-suppressed sequences without any postcontrast enhancement or solid tissue. Grouped septa: Three or more septa present closely in a part of cyst. Thickened regular septum: Smooth septum ≥3 mm in thickness. Thickened irregular septum: Focal areas of thickened septum ≥3 mm in thickness. Bi or multilocularity: Cyst showing two or more septae.

Solid tissue: Enhancing component can include thickened irregular septae, papillary projections, or solid component. Vegetations/papillary projections: Solid papillary projections similar to its definition on USG (height ≥3 mm). Wall enhancement: Discernible enhancement along cyst wall. DWI high B value low signal: Signal similar to fluid (urine or CSF). DWI high B value high signal: Signal higher than fluid (urine or CSF). Solid component's T2 SI: Compared with outer myometrial SI. Accordingly labeled as high intensity or low intensity. T2 signal: An ovarian lesion is labeled hypointense when the SI is lower than that of the iliopsoas muscle and hyperintense when the SI is equal to or greater than that of CSF. All SIs which lie between these two spectra are labeled as T2 intermediate. Dynamic SI curves: These trace the intensity of lesion over short time intervals after administration of intravenous gadolinium. A curve is obtained with region of interest placed over the enhancing component of the lesion and another (of similar area) in adjacent normal outer uterine myometrium. The reference region of interest needs to be placed within the outer myometrium and the other, within the enhancing component of the lesion. ■ Type 1 time-SI curve on dynamic T1W imaging: Gradual increase in SI without plateauing or shouldering; also labeled as low-risk curve ■ Type 2 time–SI curve on dynamic T1W imaging: Moderate initial increase of SI relative to that of myometrium, with increase being less than that of myometrium; also labeled as intermediate-risk curve ■ Type 3 time–SI curve on dynamic T1W imaging: Initial increase in SI, steeper than that of myometrium; also labeled as high-risk curve

Specific Adnexal Lesions A myriad of adnexal lesions occur, and many cannot be diagnosed on imaging alone. As mentioned earlier, risk stratification of these lesions is important to

plan further management. Commonly occurring lesions involving the adnexa are tabulated in Table 45.4. Table 45.4 Differential Diagnosis of Adnexal Lesions—Morphology Based Benign Malignant Miscellaneou Non-Neoplastic Neoplasms Neoplasms s Cystic lesions Cystic lesions Cystic lesions Ovarian torsion Physiological cysts Mature cystic Borderline teratoma/derm tumors Ovarian Hydrosalpinx, oid cyst vein pyosalpinx, thrombosis hematosalpinx Cystadenomas Ruptured Polycystic ovarian ectopic syndrome pregnancy Ovarian hyper stimulation syndrome (OHSS) Peritoneal inclusion cyst Paraovarian cyst Obstructed uterine horn Appendiceal mucocele Bowel duplication cyst Lymphocele/lymphangio ma

Endometrio sis

Non-Neoplastic Solid and solid-cystic lesions Pelvic inflammatory disease Broad ligament leiomyoma (fibroid) Adenomyoma Fibromatosis/desmoid tumor Nerve sheath tumors— schwannoma/neurofibro ma

Benign Neoplasms Solid and solid-cystic lesions Fibroma, thecoma, and fibrothecoma Stromal tumors Brenner tumor/transitio nal cell carcinoma Cystadenofibro ma Struma ovarii

Malignant Neoplasms Solid and cystic lesions Serous cystadenocarcino ma Mucinous cystadenocarcino ma Clear cell carcinoma Endometroid carcinoma Carcinosarcoma Ovarian metastases Yolk sac tumors Embryonal carcinoma Granulosa cell tumors

Miscellaneou s

Non-Neoplastic

Benign Neoplasms

Malignant Neoplasms Solid lesions

Miscellaneou s

Dysgerminoma Ovarian metastases Primitive neuroectodermal tumor (PNET) Lymphoma Undifferentiated or unclassified

Non-Neoplastic Cystic Lesions Physiological Cysts Normal Findings

Physiological cysts are the most common lesions observed in premenopausal women. Note that follicles (simple cysts ≤3 cm) and corpus luteum ≤3 cm (Fig. 45.8) are considered normal findings. A corpus luteum is a regressing ruptured follicle after ovulation with diffusely thick wall, peripheral blood flow (“ring of fire” appearance on Doppler), with possible crenulated margins (can be confused with irregular walls) and internal echoes due to hemorrhage or proteinaceous contents. This peripheral vascularity is reflected on CT and MRI as smooth thick peripheral enhancement and must not be mistaken for malignancy. It is important to note that corpus luteum does not have solid component.

Figure 45.8 Typical appearance of corpus luteal cyst (A) as an irregular cyst with crenulated margins, internal echogenic content (proteinaceous or hemorrhagic), no solid component, with peripheral flow on Doppler —“ring of fire.” Corresponding findings are observed on grayscale (B) and Doppler ultrasound (C). Axial CT (D) shows this peripheral vascularity as thick peripheral enhancement, not to be confused for a more sinister pathology. Owing to cyclical changes, larger physiological (functional) cysts are also very commonly encountered in female pelvic imaging, and they may undergo hemorrhagic changes as well. It is important to confidently identify them and label them as such to avoid patient distress and unnecessary investigations. Simple Cysts

These are defined as round or oval anechoic structures on ultrasound with smooth thin walls, no solid component or septation, no internal color flow, and posterior acoustic enhancement. Extraovarian simple cysts also fall in this category. On CT/MRI, simple or “benign-appearing” cysts are defined as oval or round unilocular lesions with uniform fluid attenuation/signal, with a regular or imperceptible wall (Fig. 45.9), without solid component or mural nodule, and 20) evenly sized follicles in a peripheral distribution, none >9 mm. The stroma appears echogenic on left. On biochemical examination, there was a raised LH:FSH ratio, consistent with PCOS. The Rotterdam group does not mention the utility of MRI. Some studies have shown MRI to be superior to USG in the measurement of ovarian volumes (with USG underestimating the volume) and demonstrating a greater number of follicles compared with USG. MRI may be helpful in certain scenarios such as young patients where transvaginal USG is not feasible. MRI features are like that of USG: enlarged ovaries with multiple follicles within (Fig. 45.14).

Figure 45.14 Coronal T2W MRI shows bilateral enlarged ovaries with multiple peripherally arranged follicles. Thickening of central stroma present on the left (asterisk), which is intermediate to mildly hyperintense.

(Courtesy: Dr. Bharat Agarwal, Max Hospital, New Delhi, India. An imaging differential of PCOS is multifollicular ovaries [19] (Fig. 45.15), which represent a reversion to the ovarian morphology seen at the menarche. They are a feature of low levels of circulating estrogens and are seen in athletes and in association with weight loss and anorexia nervosa.

Figure 45.15 Ultrasound of a 10-year-old girl (A shows axial section and B shows longitudinal section) demonstrates centrally and peripherally located follicles. Total number of follicles was 5. Ovarian volume was 6 cc. USG features are suggestive of multifollicular ovary. Ovarian Hyper Stimulation Syndrome Pathophysiology and Clinical Presentation:

It is a serious and potentially life-threatening complication of assisted reproductive techniques. It can occur either in secretory phase of menstrual cycle or in early pregnancy. It is a result of administration of clomiphene citrate, luteinizing hormone, or HCG, which can cause release of vasoactive compounds which increase capillary permeability. Two distinct components are rapid enlargement of developing follicles in both ovaries and sudden movement of fluid from intravascular space into third spaces like pleural and peritoneal spaces, which can cause sudden abdominal distension (ascites) and breathlessness (pleural effusions). The rapid fluid movement also causes hemoconcentration (hypercoagulable state) and can result in acute thromboembolic episodes with pulmonary thromboembolism, stroke, hepatic failure, renal failure, etc. When severe, this may lead to hypovolemia, disseminated intravascular coagulation, venous thrombosis, and even death. Mild forms are common and usually self-limiting. Imaging Features ■ Rapid enlargement of follicles: diffusely bulky ovaries (as large as 10 cm) with multiple cysts within (Fig. 45.16) ■ Appearance of “spoke wheel” appearance, akin to that of theca lutein cysts ■ Ascites and pleural effusions

Figure 45.16 (A and B) Ovarian hyperstimulation syndrome in a patient who underwent in vitro fertilization. Ultrasound demonstrates bilateral enlarged ovaries containing multiple cysts of varying sizes, with echogenic debris within some of them. Peritoneal Inclusion Cyst These occur in patients with history of pelvic surgery (most common), endometriosis or infection, due to fluid getting entrapped around the ovary due to adhesions (also called peritoneal pseudocysts). They may be asymptomatic or cause cyclical pain (entrapped ovary syndrome). Peritoneal inclusion cysts have a pathognomonic appearance on ultrasound and MRI: ■ Conform to the shape of the pelvic peritoneal cavity or of adjacent pelvic organs ■ Do not cause mass effect (Fig. 45.17) ■ A morphologically normal ovary present either within the cyst or along its periphery (embedded ovary appearance) ■ Smooth internal septations may be seen owing to the underlying inflammatory/infective etiology

Figure 45.17 Peritoneal inclusion cyst in a 48-year-old lady with history of hysterectomy. Transvaginal ultrasound (A) shows left pelvic fluid collection after the contour of the pelvic cavity, with an ovary along its wall (arrow). Axial (B) T2W MRI shows the same (asterisk); note the embedded left ovary along its wall (dashed arrow). The right ovary is normal (solid arrow). The classic history and imaging appearance is sufficient for the diagnosis. These are benign and if not causing much distress, can be left alone with follow-up as per recommended guidelines. Large cysts which cause distress or pain can be removed surgically. Paraovarian Cyst These are developmental in origin and arise usually from mesonephric or paramesonephric duct remnants within the broad ligament. They present as simple cysts on imaging seen separately from an adjacent normal ovary (Fig. 45.18). They may reach a large size but can be separated from the ovary by gentle pressure with the ultrasound probe or external pressure by hands on the lower abdomen. Rare complications include torsion and development of a paraovarian cystadenoma.

Figure 45.18 Left paraovarian cyst on axial T2W MRI (short arrow). The left ovary is seen separately (long arrow). Arcuate uterus noted incidentally (curved arrow). (Reprinted with permission from: SK Thawait, K Batra, SI Johnson, DA Torigian, A Chhabra, A Zaheer, Magnetic resonance imaging evaluation of nonovarian adnexal lesions, Clin Imaging 40 (1) (2016) 33–45. doi:10.1016/j.clinimag.2015.07.031. Copyright (2016) by Elsevier.) Obstructed Uterine Horn This is with unicornuate uterus with a rudimentary horn. This rudimentary horn may get obstructed and result in an apparent cystic adnexal lesion, usually containing blood products. MRI is the investigation of choice. Lymphocele Lymphoceles are commonly seen in postoperative cases of pelvic nodal dissection, representing collections of lymphatic fluid. They have a fibrous wall

with no epithelization. These are seen as well-defined fluid collections with thin walls which usually do not show peripheral enhancement (Fig. 45.19). These can be easily diagnosed in the appropriate postsurgical setting.

Figure 45.19 Pelvic lymphocele in a postoperative case of carcinoma ovary. Sagittal view of left pelvis shows a large unilocular cystic lesion (asterisk) with dependent debris (solid arrow in A). This was aspirated (dashed arrow in B marks the needle tip), with no residual component postaspiration (C).

(Courtesy: Dr. Mukesh Harisinghani, Harvard Medical School, Boston, USA.) Other differentials of cystic adnexal lesions include appendicular mucocele, bowel duplication cyst, and a lymphangioma/venolymphatic malformation, discussed elsewhere in the textbook.

Pelvic Inflammatory Disease Pathophysiology and Clinical Features The term pelvic inflammatory disease all inflammatory processes involving the female genital tract: tubo-ovarian abscess, salpingo-oophoritis, endometritis, cervicitis, etc. Salpingitis is the most common form of acute pelvic inflammatory disease (PID). Salpingitis is essential to diagnose at its early stage due to long-term complications of infertility and ectopic pregnancy. In acute salpingitis, there is diffuse edematous thickening of fallopian tubes with pus-filled lumen, the spillage of which into peritoneal cavity causes peritonitis. This results in formation of peritubular adhesions, specifically adhesion of fimbriae to ovaries with loculated fluid collections surrounding the ovaries—the tubo-ovarian abscess. They can be easily confused with malignancy when presenting with

associated adenopathy and ascites. As the ovaries are nearly always involved in cases of salpingitis, the term salpingo-oophoritis is commonly used. The clinical features are mild and nonspecific, often resulting in delayed diagnosis [20]. Signs and symptoms include pelvic pain and mild fever, and subsequently vaginal discharge or dyspareunia. Route of spread is mostly through sexual/vaginal route with upward spread along the tract with possible involvement of pelvic peritoneum as well. Hematogenous mode of spread is less common. Causative agents include Chlamydia trachomatosis, Mycoplasma genitalium, common gram-negative bacteria, Neisseria gonorrhoeae, Mycobacterium tuberculosis, Actinomyces, etc. Many patients show infection with multiple organisms. In south Asia, tuberculosis is a common cause as well. Complications include infertility, ectopic pregnancy, peritonitis, ovarian vein thrombosis, and peritoneal adhesions (“frozen pelvis”). Imaging Findings Ultrasound is the preferred imaging method. However, owing to nonspecific symptoms, CT is often the most common first imaging performed [20]. ■ Ultrasound in acute infection may show free fluid in association with a complex adnexal mass (Fig. 45.20), which comprises the ovary and thickened surrounding tube ■ Fallopian tube widening/thickening is very specific (axial diameter is >5 mm). Ovaries can also be bulky due to inflammation (largest dimension >3 cm) and show increased vascularity of the ovarian stroma ■ In chronic disease, the ovary may be more easily identifiable with a thinwalled hydrosalpinx adjacent to the ovary ■ Salpingitis typically shows tubal tortuosity, hydrosalpinx and increased vascularity. The hydrosalpinx may contain internal echoes due to either blood or pus with fluid-debris level. Probe tenderness on transvaginal sonography should arouse a suspicion, although this can also be seen in endometriosis ■ Doppler shows low impedance flow due to a surrounding inflammatory reaction with increased vascularity

Figure 45.20 A 36-year-old lady with chronic pelvic pain. Axial ultrasound image shows a right adnexal complex cystic lesion, not seen separate from the ovary, along with a serpiginous tubular dilated fallopian tube with debris within (arrow). Probe tenderness was present. The patient had tubercular tubo-ovarian abscess.

(Courtesy: Dr. Mukesh Harisinghani, Harvard Medical School, Boston, USA.) CT usually shows: ■ Free fluid in rectouterine pouch ■ Thickening of pelvic soft tissue, particularly the uterosacral ligaments, along with reactive enlarged pelvic and para-aortic nodes ■ Fat stranding of pelvic peritoneum. This fat stranding usually renders the normally sharp lateral uterine margins hazy. This is specific for acute PID and seen in up to two-thirds of cases [21] ■ Fallopian tube thickening may be encountered ■ Rarely, air foci may be encountered in tubo-ovarian abscess Similar changes are demonstrated on MRI. It is more useful in distinguishing pyosalpinx from hematosalpinx.

Rarely patients present with right hypochondrial pain due to perihepatitis (Curtis–Fitz–Hugh syndrome). Adhesions around the liver have been described on ultrasound but are rare to see on imaging. A mention needs to be made about pelvic TB, which shows imaging features similar to chronic PID. In general, tubal involvement in TB is most common and is generally bilateral. Hysterosalpingogram findings of genital TB are described elsewhere in the book.

Neoplasms Epidemiology and Classification Primary ovarian tumors are classified into three main types, according to their cells of origin: epithelial, sex cord stromal, and Germ cell tumors (GCTs) (Fig. 45.21). In addition, approximately 10% of ovarian tumors are metastatic. The distribution of these tumors varies based on age and geographic distribution. However, broadly, epithelial neoplasms constitute the most common subtype followed by GCTs. As in other malignancies, ovarian neoplasms are broadly divided into benign and malignant variants. In addition, some ovarian tumors are classified as borderline, indicating that they have a better prognosis, with a lower risk of local recurrence and metastatic disease compared with malignant tumors.

Figure 45.21 Pathological classification of ovarian neoplasms.

Malignant ovarian tumors carry the highest mortality among gynecological malignancies in the West, whereas carcinoma cervix carries the highest mortality in south Asia [22]. Ovarian tumors are usually detected at an advanced stage, with extraovarian spread. The ovary does not have a true capsule and is only covered by visceral peritoneum, making peritoneal spread common. Lymphatic spread to the draining retroperitoneal nodes is also common. The role of imaging is to characterize an adnexal mass as benign or malignant, identify the tumor histology, if possible, help guide further management, give a roadmap for surgery, and to assess response to chemotherapy. Although ovarian neoplasms are managed based on histopathology, a morphological approach is necessary for preoperative imaging work-up and risk stratification. Risk factors for the development of ovarian carcinoma include: ■ Family history of ovarian, breast, endometrial, or colorectal carcinoma including syndromes such as Lynch and Peutz–Jeghers ■ BRCA1 or BRCA2 mutation—This confers a lifetime risk of 40% and 25%, respectively [23] ■ Increased number of episodes of ovulation, for example, nulliparous woman, after treatment with ovulation induction agents, and menopause at late age ■ Fertility treatments ■ Smoking (particularly for mucinous tumors) Some protection is conferred by: ■ Multiparity ■ Breast-feeding ■ Use of oral contraceptives ■ Tubal ligation ■ Posthysterectomy status Staging Gynecological tumors are usually surgically staged using the International Federation of Gynecology and Obstetrics (FIGO) staging system (Table 45.5) [24].

Table 45.5 FIGO Staging of Ovarian Cancer FIGO staging Stag e I

Definition IA

■ Confined to one ovary/fallopian tube ■ Intact capsule ■ No tumor on surface ■ No tumoral cells in ascites/peritoneal washing

IB

■ Involving both ovaries. ■ Rest all features of IA

IC One or more ovaries involved with peritoneal spread

I C 1

Tumor spillage intraoperatively

I Capsular rupture before surgery (e.g., tumor C biopsied), or tumor involving ovary/fallopian 2 tube surface I Ascites or peritoneal washing showing positive C cytology 3 II

IIA

Contiguous extension and/or implantation on uterus and/or fallopian tubes

IIB

Involvement of other pelvic intraperitoneal structures

FIGO staging Stag e III

Definition IIIA

I III I A1 (i) I A 1 III A1 (ii)

Metastatic retroperitoneal (RP) node, ≤10 mm

Metastatic RP node, >10 mm

I Microscopic involvement of extrapelvic I peritoneum (peritoneum above pelvic brim), I regardless of RP nodal status A 2

IV

IIIB

Macroscopic involvement of extrapelvic peritoneum (peritoneum above pelvic brim): ≤2 cm. Hepatic or splenic capsular involvement included

IIIC

Macroscopic involvement of extra-pelvic peritoneum (peritoneum above pelvic brim): >2 cm. Hepatic or splenic capsular involvement included

IVA

Malignant pleural effusion (positive pleural fluid cytology)

IVB

Distant parenchymal metastases to the liver, spleen, other abdominal organs, lungs, etc.

Epithelial Neoplasms Pathophysiology, Presentation, and Current Concepts Ovarian epithelial neoplasms originate from the surface covering (surface epithelium) of ovaries, which is similar to peritoneal cavity lining (mesothelium). These peak in the sixth to seventh decade. Majority are benign, very few are borderline (∼5%), and the rest malignant. Morphologically, most

epithelial tumors are cystic and malignant variants develop solid components, presenting as solid-cystic masses. Benign, Borderline, and Malignant Neoplasms On histopathology, epithelial neoplasms are broadly classified as benign, borderline, and malignant and this determines their biologic behavior. Broadly, nuclear atypia, number of mitoses and presence of infiltrative component determines the nature of these tumors. Radiologically, the differentiation between the three can be challenging. Borderline epithelial neoplasms are intermediate grade tumors between benign and malignant lesions and have also been described as “semimalignant,” “atypical proliferative tumors,” or “low malignant potential” tumors by some authors. On pathology, they show features of cellular atypia and high mitosis without infiltration of basement membrane/stromal invasion. These tumors occur at a younger age compared with their malignant counterparts (second to fourth decades) with some studies showing these to occur about 20 years earlier than invasive carcinomas [25]. These tumors may also have peritoneal disease in 10% of cases, and up to 25% may show associated regional adenopathy in advanced FIGO stages. Borderline tumors tend to have an indolent course and much better prognosis than malignant neoplasms. An important aspect on imaging is the presence of profuse solid papillary projections without any infiltrative or solid component, which can show mild to moderate contrast enhancement. Table 45.6 lists imaging features which can help differentiate benign and malignant epithelial neoplasms. Table 45.6 Imaging Differences of Benign and Malignant Epithelial Neoplasms Benign Epithelial Feature Malignant Epithelial Tumor Tumor

Feature Morphology

Cyst wall

Solid component/papilla ry projection Free fluid

Peritoneal implants Adenopathy

Benign Epithelial Tumor Cystic with thin septations: can be multilocular

Malignant Epithelial Tumor Cystic lesion with irregular thickened walls or septae, enhancing solid component or a large solid mass with cystic/necrotic areas within

Regular or thin. Smooth mild contrast enhancement may be present

Irregular thickened walls. Both cyst wall and septae may show perceptible enhancement

Absent

Present

Reactive mild free fluid may be present in the pouch of Douglas

Ascites usually present

Absent

Can be present

Absent

Metastatic adenopathy may be present

In 2014, WHO further classified the malignant tumors into two groups: Group I and group II [26]. These have different pathological, morphological, and molecular abnormalities and biologic behavior (Table 45.7). Table 45.7 Two Groups of Malignant Ovarian Epithelial Neoplasms Group I Group II

Group I Examples

Group II

■ Low-grade serous cystadenocarcinoma

■ High-grade serous cystadenocarcinoma

■ Low-grade endometroid carcinoma

■ High-grade endometroid carcinoma

■ Low-grade mucinous cystadenocarcinoma

■ High-grade mucinous cystadenocarcinoma

■ Low-grade clear cell carcinoma

■ Undifferentiated cancer ■ Carcinosarcoma

■ Malignant Brenner tumor Course Presentati on

Indolent tumors

Aggressive tumors

■ Detected early: Stage I or II

■ Detected late: Stage III or IV

■ Confined to ovaries

■ Usually have extraovarian spread at presentation

Group I Pathogen esis

■ 25% of all epithelial malignant neoplasms

■ 75% of all epithelial malignant neoplasms

■ Share molecular and morphological similarities with benign counterparts.

■ Do not share molecular and morphological similarities with benign counterparts

■ Likely develop from benign tumors through intermediate step of borderline tumor

Prognosis

Group II

Usually good

■ Likely develop from extraovarian sites (fallopian tubes most commonly) and probably involve the ovaries secondarily ■ Arise likely de novo rather than from benign counterparts Poor

Serous and Mucinous Neoplasms Pathophysiology and Clinical Presentation:

These tumors form a spectrum ranging from benign cystadenomas, borderline tumors to malignant cystadenocarcinomas, which can be low grade or high grade. ■ Serous tumors are the most common epithelial neoplasms and most common subtype of ovarian neoplasm overall. Among serous tumors, cystadenoma is the commonest variant (30%), whereas serous cystadenocarcinoma is the commonest malignant ovarian neoplasm ■ Mucinous neoplasms constitute 10–15% of all epithelial neoplasms with up to 90% being benign or borderline ■ Between 60–70% of serous tumors and 5–10% of mucinous tumors are bilateral ■ Cystadenomas (serous and mucinous) account for up to half the tumors in the reproductive age and 80% of benign tumors in postmenopausal women

■ Serous tumors contain serous or fluid-like contents and mucinous tumors contain mucin ■ Serous tumors' lining resembles those of fallopian tubes' internal lining. Serous cystadenocarcinomas can resemble primary peritoneal carcinomas on pathology ■ The lining of mucinous tumors can resemble that of intestinal mucosa (intestinal type) or lining of endocervix (endocervical type) ○ Endocervical variants are usually bilateral, can have coexisting endometriosis and closely resemble serous borderline neoplasms ○ Intestinal type is commonly associated with pseudomyxoma peritonei and may often actually be a metastasis from an appendicular primary ■ Borderline mucinous tumors tend to be larger in size compared with serous counterpart (nearly twice the size) Imaging Features Serous and Mucinous Cystadenomas ■ They have overlapping features on imaging (Figs. 45.22 and 45.23), and essentially present as thin-walled cystic lesions with or without internal septations and echogenic contents. They have no solid component or papillary projections ■ Even though they appear benign on imaging, at pathology, these may show small foci of borderline or malignant neoplasm. The imaging differences between serous and mucinous cystadenoma have been summarized in Table 45.8 but distinguishing between them on imaging is often challenging

Figure 45.22 Serous cystadenoma. Axial T2 (A) and coronal postcontrast T1WI (B) show a cystic abdominopelvic lesion without any septations or solid component. There is mild smooth wall enhancement, with enhancement of broad ligament structures (solid arrow) leading to the cystic lesion, suggestive of right ovarian origin. Note artifacts in A due to dielectric effect.

Figure 45.23 Mucinous cystadenoma. Ultrasound (A) shows a multilocular right adnexal cyst with no vascularity on Doppler (image not shown). Axial T2W (B) and postcontrast fat-saturated T1WI (C) show a smooth-walled right adnexal multilocular cystic lesion with multiple thin mildly enhancing internal septations. No solid component present. Table 45.8 Imaging Differences Between Serous and Mucinous Ovarian Tumors Feature Serous Tumor Mucinous Tumor Size Usually smaller Can be very large and present as than mucinous abdominopelvic cystic masses neoplasms Cyst wall and loculations

Wall: Regular or thin Septum: Absent or few thin internal septae Mostly unilocular

Wall: regular or thin Septum: Multiple thin internal septae Mostly multilocular

Feature Content

Serous Tumor Anechoic internal content to thin mobile internal echoes. Appears homogeneous and near fluid attenuation on CT and MRI

Mucinous Tumor Anechoic to coarse “jelly” like internal echoes, with varying attenuation/intensity locules on CT and MRI. Locules with thicker mucin are hyperdense on CT, hyperintense on T1, and hypointense on T2 compared with locules with thinner mucin (“stained-glass appearance”)

Solid component/Papill ary projection

Cystadenoma: None

Cystadenoma: None

Calcifications

Cystadenoma: Rare

Cystadenocarcino ma: Papillary projections often seen

Cystadenocarcino ma: Punctate or “psammomatous” calcifications may be seen Peritoneal carcinomatosis

Cystadenoma: Absent Cystadenocarcino ma: Very common

Laterality

More often bilateral (60–70%)

Cystadenocarcinoma: Papillary projections seldom seen

Cystadenoma and Cystadenocarcinoma: Rare in both, may be curvilinear, along the wall or septal

Cystadenoma: Absent, pseudomyxoma peritonei may occur due to rupture Cystadenocarcinoma: Uncommon but may be present due to rupture Less commonly bilateral (5–10%)

Malignant Cystadenocarcinomas ■ Usually present as cystic lesions with or without solid component with thick enhancing septations, papillary projection or large solid components (Fig. 45.24) ■ Features of extraovarian disease favor malignant and sometimes borderline neoplasms. The presence of peritoneal implants or clearly metastatic appearing adenopathy are the most specific signs of malignant epithelial neoplasms (Fig. 45.25) ■ Serous cystadenocarcinomas (Figs. 45.24 and 45.25) demonstrate papillary projections/solid components, which usually appear hypointense on T2W sequences. The cystic component follows typical fluid intensity (like urine or CSF). They may show amorphous/dystrophic calcifications within, better appreciated on CT, and correspond to psammoma bodies seen on histopathology ■ They usually present with extensive peritoneal disease, ascites, and metastatic appearing pelvic and retroperitoneal lymphadenopathy ■ Mucinous cystadenocarcinomas (Fig. 45.26) are usually large (10–15 cm) predominantly cystic masses. They tend to be multiloculated with multiple thick internal septations and diffuse internal echoes due to their high mucin content ■ The T1 and T2 intensities on MRI vary depending on mucin content. High mucin content can present as bright on T1 and low on T2. Intestinal variants can have pseudomyxoma peritonei (Fig. 45.27) ■ MRI is useful in defining and separating a uterine from an ovarian mass when ultrasound is equivocal. MRI is also useful in differentiating highgrade tumor from borderline tumors (Fig. 45.28) at times ■ Borderline tumors have overlapping features and can demonstrate intracystic solid components such as papillary projections and mural nodules as well

Figure 45.24 Serous cystadenocarcinoma. Axial and coronal CECT images demonstrate a solid right adnexal mass (solid arrow in A) with extensive peritoneal disease (B) involving bilateral subdiaphragmatic spaces (short arrows), falciform ligament (long arrow), hepatoduodenal ligament (curved arrow), and right paracolic gutter (dashed arrow). Note few punctate and stippled calcifications within the lesions; these were better appreciable on the noncontrast images (not shown).

Figure 45.25 Common sites of metastatic disease in carcinoma ovary.

(A and B) Bilateral pelvic side wall (arrows in A) and retroperitoneal (arrows in B) metastatic adenopathy in a patient with a large pelvic mass

(asterisk).

(C) Large volume ascites with peritoneal disease in the form of peritoneal nodularity along the posterior peritoneal lining (solid arrows) along with omental nodularity and mild caking (dashed arrows).

(D) Typical calcified metastatic disease along subdiaphragmatic and portocaval regions in serous neoplasms; low-grade serous cystadenocarcinoma in this case.

Figure 45.26 Bilateral ovarian mucinous adenocarcinoma. Axial CECT (A) shows a large right adnexal cystic mass with multiple locules showing varying densities within (arrowheads). A curvilinear area of calcification can be seen within (dashed arrow in A). Axial and sagittal T2WI (B and C) demonstrate multilocular large right adnexal mass, with variable intensity contents in the different locules (arrowheads). A focal area of capsular breach noted (arrow in C), consistent with malignant rather than benign etiology.

(Courtesy: Dr. Bharat Agarwal, Max Hospital, New Delhi, India.)

Figure 45.27 Pseudomyxoma peritonei. Right flank ultrasound image (A) shows large volume “ascites” which appears echogenic and “jelly”/“mucinous” like. Coronal CECT (B) shows multiple deposits (arrows) showing fluid-like attenuation, with characteristic scalloping of the liver (dashed arrows). Axial fat-saturated T2WI (C) shows these mucinous deposits (arrows) appearing fluid like. Scalloping of the liver (broken arrows) seen again. Coronal heavily T2W maximum intensity projection (MIP) (D) shows the extend of mucinous deposits in the abdominal cavity.

Figure 45.28 Borderline serous neoplasm. Ultrasound (A) shows a multilocular cyst with low level internal echoes (asterisk) and papillary projections (arrow). Axial T1W and T2W MRI (B and C) show multilocular cyst with areas of hemorrhage/proteinaceous content (dashed arrows). Dynamic postcontrast study (D) shows thick moderately enhancing septa (curved arrow) and enhancing papillary projections (dashed arrow) with a type II curve (E). No infiltrative component or peritoneal implants were seen. Brenner Tumor/Transitional Cell Carcinoma Pathophysiology and Clinical Presentation:

As the name suggests, these represent transitional cells of urinary bladder on pathology, likely due to differentiation into transitional cells of the ovarian epithelial cells. These are rare benign tumors (approximately 2% of ovarian tumors) in postmenopausal women (fifth and sixth decades of life) and are very rarely malignant or borderline. Most are detected incidentally on resected specimen. These may be associated with synchronous transitional tumor of urinary bladder or with another epithelial ovarian tumor in about 30% cases. Surgical resection is curative. Imaging Features

■ Usually predominantly solid and small but can present as a multilocular cystic lesion with solid component (Fig. 45.29) ■ Show amorphous calcifications in more than half the cases ■ T2 hypointense on MRI due to their fibrous component, with mild to moderate enhancement, mimicking a fibroma ■ Borderline Brenner tumors are usually solid cystic in nature with solid component occurring as polypoidal lesions or papillary projections [27]. These mostly have a biologically benign behavior. Malignant tumors show similar morphology as borderline tumors but may be bilateral ■ Ovary confined malignant Brenner tumors have a stage-by-stage better prognosis than malignant serous tumors

Figure 45.29 Brenner tumor. Axial T2 (A) and contrast-enhanced T1W fat-saturated (B) images show a large lobulated T2 hypointense right adnexal mass with minimal contrast enhancement. Endometroid Carcinoma Pathophysiology and Clinical Presentation:

As the name suggests, these epithelial tumors resemble uterine endometrium, and account for 10–15% of all epithelial tumors, with a peak in fifth to sixth decade of life. About half of these are bilateral and up to 30% are associated with endometrial thickening due to endometrial hyperplasia or carcinoma. These are also commonly associated with endometriosis. Although almost always malignant (without a benign or borderline counterpart), they usually present at an early stage (i.e., without peritoneal disease), and have better prognosis. Imaging Features:

Imaging findings are nonspecific (Fig. 45.30).

Figure 45.30 A 47-year-old female with known endometriosis presenting with hematuria. Axial noncontrast CT (A) shows classical hyperdense, bilateral ovarian endometriotic cysts, and a deposit along the uterosacral ligament (dashed arrow). Note the suspicious infiltration involving the posterior bladder wall (arrowhead), better seen on the sagittal postcontrast image (curved arrow in B—sagittal CECT image) along with right hydroureter (asterisk). A cystoscopic biopsy of the bladder component showed endometrioid carcinoma of the ovary. ■ They usually demonstrate both solid and cystic components; hemorrhagic contents may also be present ■ When arising from a pre-existing endometrioma, an enhancing mural nodule may be present in an otherwise classic endometrioma ■ Features of endometrial carcinoma or hyperplasia may be seen Clear Cell Carcinoma Pathophysiology and Clinical Presentation:

These are relatively rare epithelial ovarian neoplasms (5% of the total ovarian epithelial tumors) with a peak in the fifth decade of life. Nearly three-fourths of patients have pre-existing endometriosis. Majority of these present at stage I, with 20% having bilateral disease. They are named so because of characteristic histologic appearance comprising of clear cells (also known as hobnail cells). Benign and borderline variants of clear cell tumors are again rare. They may be associated with thromboembolic events, hypercalcemia (paraneoplastic

syndrome), and Lynch syndrome (which is also associated with endometroid carcinoma and endometrial carcinoma). Imaging Features:

They have a nonspecific imaging morphology (Fig. 45.31) ranging from completely solid to solid-cystic to a cystic mass with large internal polypoidal solid component. A typical endometrioma with enhancing solid component should raise suspicion of clear cell or endometroid carcinoma [28].

Figure 45.31 A 52-year-old female presenting with pelvic lump. Ultrasound (A) showed a large multilocular pelvic cystic mass with thick mobile internal echoes. CECT (B) showed multiple enhancing septations within (arrows) without peritoneal disease. MRI showed type III curve (C), indicating malignancy. Histopathology showed right ovarian clear cell carcinoma.

Germ Cell Tumors GCTs arise from germ cells within the substance of ovaries, likely from primordial germ cells. These are the female counterparts of testicular GCTs. They secrete various hormones and can be diagnosed based on the tumor markers. Mature Cystic Teratoma/Dermoid Cyst Pathophysiology and Clinical Presentation:

Dermoid cysts (mature cystic teratomas) are the most common benign neoplasm in women of reproductive age group, accounting for 20% of all ovarian tumors. Approximately 10–15% are bilateral. These arise from more than one of the

three embryonic layers (endoderm, mesoderm, and ectoderm). They can be both solid and cystic. If a teratoma contains components from predominantly one of the three layers, they may be referred to as specialized or monodermal (struma ovarii containing thyroid tissue being an example). Almost all dermoid cysts contain lipid material, either sebaceous or adipose tissue, which demonstrates a similar signal to subcutaneous fat. A focal internal protuberance (Rokitansky nodule) containing hair, teeth, muscle, bone, neural tissue, thyroid tissue, cartilage, etc. can be demonstrated. The cyst wall is most commonly lined by squamous epithelium. Malignant degeneration occurs in less than 2% [28]. Most common malignancies encountered are squamous cell carcinoma and papillary carcinoma of thyroid. Other related complications include rupture (which can lead to chemical peritonitis), ovarian torsion, autoimmune hemolytic anemia, secondary infections, and rarely, anti–N-methyl-D-aspartate receptor encephalitis, a paraneoplastic syndrome. Imaging Features These can be confidently diagnosed on imaging by identifying macroscopic fat within the lesion (Fig. 45.32).

Figure 45.32 Dermoid cyst. Axial CECT (A), axial T1W (B), and axial T1W fat-saturated postcontrast (C) images show a fat containing left adnexal lesion (solid arrow), with the fat getting completely suppressed in C. Note the adjacent normal ovarian follicles (dashed arrow in C). Ultrasound:

They typically present as a unilocular cystic mass with solid component, with a few showing septae within the cystic component. Majority are 5–15 cm in

diameter. The solid components are usually hyperechoic due to fat or calcification. The echogenic nature of the cyst can also make it difficult to differentiate from bowel; hence the size of a dermoid cyst may be underestimated with ultrasound. Calcification of Rokitansky nodule may demonstrate “twinkling” artifact on Doppler study. Various descriptors have been recommended to standardize reporting of dermoid cysts (Fig. 45.33). When confirmation or additional information is required, CT or MRI can be helpful.

Figure 45.33 Various O-RADS. Ultrasound descriptors of dermoid cyst.

(A and B) Hyperechoic lines and dots. Represent tufts of hair: lines on longitudinal and dots on transverse sections. Referred by many as “dermoid mesh” and “dot and dash.” Ultrasound image (B) with arrows marking the lines and dots.

(C and D) Acoustic shadowing from a hyperechoic component. Commonly referred as “Tip of the iceberg sign.” The hyperechoic component (arrow in D) is commonly referred as “Rokitansky Nodule.”

(E and F) Floating hyperechoic nondependent spherical structures. Very specific, rarely seen (arrows in F). Commonly referred as “dermoid balls.” CT/MRI:

CT shows typical fat containing areas, soft-tissue component, and presence of bone/coarse calcification/tooth within. These can be heterogeneous on MRI, but presence of macroscopic fat is diagnostic. Approximately 15% dermoids have none or very small foci of fat. Such fat-poor dermoids can be identified as chemical shift artifact at the fat-fluid interface and on fat-suppressed sequences [29]. Importantly, diffusion restriction may be present in solid component, even

in benign dermoids. Solid component enhancement with rarely type III curve may be encountered. These findings on DWI and DCE should not be confused with malignant transformation. Capsular penetration is the most important sign to indicate an underlying malignancy [29] (Fig. 45.34).

Figure 45.34 Malignant degeneration of dermoid. Axial images show a large pelvic soft-tissue mass with foci of fat (dashed arrow in A) and chunky calcification (solid arrow) in A, suggestive of teratoma. There is loss of fat plane with the adjacent bowel with air foci within (solid arrows in B), suggesting fistulous communication. Final diagnosis was malignant degeneration (to squamous cell carcinoma) in ovarian teratoma. Management:

Smaller dermoid cysts with typical features can be observed with serial ultrasounds. Larger dermoid cysts in postmenopausal women may be removed surgically. In premenopausal women, these may be followed up with annual ultrasounds if confident of diagnosis. If in doubt, a repeat USG in 8–12 weeks may be performed to confirm stability and then, annually thereafter. In postmenopausal women, when confident of diagnosis of dermoid cyst, these may be followed up with annual USG. If there is a change in size or morphology on follow-up, further evaluation with MRI and gynecological evaluation is warranted. Struma Ovarii

Struma ovarii is a specialized mature teratoma comprising entirely or predominantly of thyroid tissue (at least 50% of the total tumor volume should be thyroid tissue to label as struma ovarii on pathology) [30]. This can be a source of ectopic thyroid hormone production and can present with features of hyperthyroidism (