Classic Imaging Signs: A Guide to the Whole Body [1st ed.] 3030563472, 9783030563479, 9783030563486

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Classic Imaging Signs A Guide to the Whole Body Bo Gao Alexander M. McKinney Editors

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Classic Imaging Signs

Bo Gao  •  Alexander M. McKinney Editors Shi Zhou  •  Shi Zuo Associate Editors

Classic Imaging Signs A Guide to the Whole Body

Editors Bo Gao Department of Radiology Affiliated Hospital of Guizhou Medical University Guiyang China

Alexander M. McKinney Department of Radiology University of Miami Miller School of Medicine Miami, FL USA

ISBN 978-3-030-56347-9    ISBN 978-3-030-56348-6 (eBook) https://doi.org/10.1007/978-3-030-56348-6 © Springer Nature Switzerland AG 2021 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Foreword: Imaging Signs

Radiologic and radiographic “imaging signs” are critical to our quick recognition of disease states and instituting therapy. They are also perhaps even more vital to the teaching element for trainees, since such prompt recognition of an abnormal imaging pattern cements the appearance in the memory of the learner for future recognition. The goal of proposing such “signs” is that eventually a particular disease state’s radiologic appearance ultimately becomes accepted as a classic “imaging sign,” and thus gains recognition among radiologists and other subspecialists for general use. While it is acknowledged that a disease state does not absolutely have to exhibit the classic imaging sign (e.g., the “Rigler sign” of pneumoperitoneum), it is quite important to note such a sign, when present, as early as possible, in order to alert the ordering provider to a preventable complications of the disease state. The editors, Drs. Gao and McKinney et al., organized this text in a very practical fashion that can serve as a quick reference to enhance the reader’s understanding of each imaging sign, regardless of their level of training or experience. While there are many other texts and websites that address imaging signs by subspecialty (e.g., cardiothoracic or neuroradiology), body part (e.g., lung or renal), or particular disease state (e.g., pneumoperitoneum or meningioma), this text distinguishes itself as a compendium of each subspecialty/organ system. The text is organized by each body part/organ system (e.g., brain, spine, chest, etc.), with Individual topics for each sign. Another distinguishing factor is that this text also provides the proven or presumed pathophysiologic reasoning for that imaging appearance, as well as variants or alternative names for each sign. Finally, I note that the editors incorporated newer signs (e.g., the “swallowtail sign” on susceptibility-weighted MRI) along with the classic imaging signs and attempted to provide the reliability or sensitivity/specificity of these signs when such data were available. Hence, this text on “Imaging Signs” will likely serve to augment both the educational and clinical aspects for trainees and staff physicians, and enable prompt recognition of particular disease states. This is becoming increasingly

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vital in this era of remote education, diagnosis, and therapy. Further editions and versions will presumably expand upon this novel work and continue to enlighten our trainees and provide a useful resource to practicing physicians. Jafar Golzarian, MD Professor of Radiology and Surgery Vice Chair, Faculty Affairs Medical School Director, Division of Interventional Radiology University of Minnesota Medical Center Minneapolis, MN, USA

Foreword: Classic Imaging Signs: A Guide to the Whole Body

Medical imaging/radiology has developed tremendously in the last decades with the emergence of novel imaging techniques, especially the flourishing of advanced CT and MRI. In recent years, even with the rapid evolution of modern imaging modalities, radiology still has an irreplaceable role in diagnosis within standard clinical practice. The field of medical image analysis has grown exponentially, with an increased number of pattern recognition tools and an increase in data set sizes. Competent imaging acquisition often entails referring to other realms of knowledge to acquire insights with the aid of metaphors. Problems with timing, efficiency, and missed diagnoses may occur at all stages of the imaging chain. This book Classic Imaging Signs: A Guide to the Whole Body is written by leading experts with irrespective imaging specialty backgrounds. The editors, Drs. Gao and McKinney et al., organized this text in a very practical fashion that can serve as a quick reference to enhance the reader’s understanding of each imaging sign. This book is intended to help radiologists and students accomplish this task. It provides practicing radiologists and radiology residents or fellows with the level of knowledge necessary to avoid misinterpretation and help make precise diagnoses in the presence of certain classic pathognomonic features. Judgment of image sign, as one of the core principles of radiology, relies on the integration of multilayered data with distinctive decision-making. If we are to use terms with full understanding, we should be capable to visualize the object depicted by that term, imagine its radiologic appearance, and transfer that picture to the radiologic image before us. This book serves to augment both the educational and clinical aspects for trainees and staff physicians, and enable prompt recognition of particular disease states. This is becoming increasingly vital in this era of remote education, diagnosis, and therapy. The editors of this book have provided thorough and illustrative reviews of these emerging and controversial topics. I congratulate the editors on their accomplishment of this work, and I look forward to future editions since we seemingly encounter new diseases and signs every year. I am pretty glad to introduce this book to those who are addicted to the clinical practice and research of clinical radiology. Hai-yang Li, MD Professor of Surgery Chair, Clinical Medical School, Guizhou Medical University President, The Affiliated Hospital of Guizhou Medical University Guiyang, China vii

Preface

Image signs refer to the normal structures of the human body or imaging information or radiologic findings produced by pathology under any type of imaging modalities. An “iconographic” glossary of terms used for imaging is reproduced-placing side by side between radiological features and those may be associated with signs, symbols, or naturalistic images. Specifically, image signs refer to the metaphor of certain tissue, structure, or lesion. One way is by linking anatomic structures and pathologic conditions with objects, places, and concepts, and codifying these relationships as metaphoric signs. To describe an unnoticed finding specific to a particular entity has always been a challenge for the radiologists. Time will be needed on investigations before we can add the specific finding to the legions of “signs” in radiology. The “signs” may become part of our language of specialty after validating by different observers over time. The “classic signs” endorse us confidence in determining the diagnosis. Some imaging signs have been acknowledged, which are referred to as “Aunt Minnie.” When the sign is invoked, or an Aunt Minnie is recognized, it often brings an impression of the image to mind, and it may have specific diagnostic and pathologic significance. The advance of radiology, evolving with such signs, renders an otherwise difficult diagnosis easier, may help the radiologists appreciate the anatomy and pathology of an underlying abnormality, and may quickly direct the physicians to the proper diagnosis and timely intervention. This book systematically summarizes the imaging characteristics and theory of modern imaging, primarily summarizes the imaging signs characteristics and theory in the whole body, serving as a clinical guidance and having a practical significance for the understanding, prevention, and diagnosis of miscellaneous entities. This book consists of 10 chapters and covers over 300 classic radiologic signs with detailed discussion alongside illustrative photos for memory aids and clarification. The book is featured as follows: (1) covers hot topics including potential pitfalls of imaging and classic signs, (2) detailed discussions and case show highlighting clues and misinterpretation, (3) succinct content and bulleted text for quick and easy reference, and (4) detailed illustrations and annotated images. The materials included in the book were collected from various university hospitals and are well-organized, and all cases have been reviewed by subspecialty experts. Photos illustrate the etymology of each sign and enhance the learning experience. Accompanying text explains the history and meaning of the descriptive or metaphoric sign. Uniquely written from a practical point of view, each case leads you through a radiology ix

Preface

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expert’s thought process in analyzing imaging pitfalls and classic signs of different organs or systems. The cases highlight clinical presentation, relevant pathology, anatomy, physiology, and pertinent imaging features of common disease processes. Key information is distilled into succinct, bulleted with detailed illustrations and wonderful images. It is designed to enhance recognition of specific imaging patterns, enabling the image interpreter to confidently reach an accurate diagnosis. This book ought to be a valuable review for trainees preparing for boards licensing examinations and can become a trusted daily reference for practicing radiologists. We wish this book to become an irreplaceable reference for readers confronted with the challenges of imaging interpretation. We sincerely appreciate all the experts and contributors who engaged in this book. Guiyang, China Miami, FL, USA

Bo Gao Alexander M. McKinney

Contents

1 Introduction��������������������������������������������������������������������������������������   1 Bo Gao, Cong-jie Long, Li Zhang, and Chi Shing Zee 2 Brain��������������������������������������������������������������������������������������������������   9 Alexander M. McKinney, Yang Wang, and Ze Zhang 3 Head and Neck ��������������������������������������������������������������������������������  85 Zhongxiang Ding, Guoyu Chen, and Alexander M. McKinney 4 Chest�������������������������������������������������������������������������������������������������� 103 Tao Jiang, Yanling Zhang, Shanshan Wu, and Jujiang Mao 5 Solid Organs of Upper Abdomen���������������������������������������������������� 177 Xin Li, Chengkai Zhou, and Jie Zhou 6 Gastrointestinal Tract���������������������������������������������������������������������� 239 Jiani Chen, Hengtian Xu, and Gui Quan Shen 7 Peritoneum and Pelvis �������������������������������������������������������������������� 273 Pinggui Lei, Bin Huang, and Hui Yu 8 Signs in Musculoskeletal Radiology ���������������������������������������������� 291 Haitao Yang, Lingling Song, and Zhaoshu Huang 9 Spine�������������������������������������������������������������������������������������������������� 327 Lingling Song, Wen Wang, Muxi Wu, and Alexander M. McKinney 10 Vascular Imaging and Interventional Strategy ���������������������������� 349 Lei Xu, Xin Chen, and Shi Zhou Index���������������������������������������������������������������������������������������������������������� 369

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Contributors

Associate Editors Shi Zhou, MD  Department of Interventional Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, Guizhou, China Shi  Zuo, MD  Department of General Surgery, The Affiliated Hospital of Guizhou Medical University, Guiyang, China

Contributors Guoyu Chen, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Cong-jie  Long, MD Department of Radiology, GuiQian International General Hospital, Guiyang, China Jiani Chen, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Xin  Chen, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Zhongxiang Ding, MD, PhD  Department of Radiology, Affiliated Hangzhou First People’s Hospital, Zhejiang University School of Medicine, Hangzhou, China Bo Gao, MD, PhD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Bin Huang, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Zhaoshu  Huang, MD Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Tao  Jiang, MD Department of Radiology, Changhai Hospital, Shanghai, China

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Pinggui  Lei, MD, PhD Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Xin Li, MD, PhD  Department of Radiology Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China Jujiang Mao, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Alexander  M.  McKinney, MD Department of Radiology, University of Miami Miller School of Medicine, Miami, FL, USA Gui  Quan  Shen, MD Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Lingling Song, MD, PhD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Wen Wang, MD, PhD  Department of Radiology, Tangdu Hospital, Fourth Military Medial University, Xi’an, China Yang Wang, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Muxi  Wu, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Shanshan  Wu, MD Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Hengtian Xu, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Lei  Xu, MD, PhD Department of Radiology, Beijing Anzhen Hospital, Capital Medical University, Beijing, China Haitao  Yang, MD, PhD Department of Radiology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China Hui Yu, MD, PhD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Chi Shing Zee, MD  Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA Li  Zhang, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Yanling  Zhang, MD Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Ze  Zhang, MD  Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China

Contributors

Contributors

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Chengkai  Zhou, MD Department of Radiology Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China Jie  Zhou, MD Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China Shi Zhou, MD  Department of Interventional Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China

1

Introduction Bo Gao, Cong-jie Long, Li Zhang, and Chi Shing Zee

Contents 1.1 The Formation of Imaging Signs

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1.2 The Features of Imaging Signs

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1.3 Classification of Imaging Signs

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1.4 The Role of Imaging Signs in Diagnosis

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1.5 The Decision-Making of Imaging Signs

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1.6 Radiomics and AI

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References

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Medical imaging/radiology has evolved tremendously in the last decades with the emergence of novel imaging techniques, especially the flourishing of advanced CT and MRI. The field of medical image analysis has grown exponentially, with an increased number of pattern recognition tools and an increase in data set sizes [1]. The competent imaging acquisitions often entail referring to other realms of knowledge to acquire insights with aids of metaphor [2]. The

B. Gao (*) · L. Zhang Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China C-J. Long Department of Radiology, GuiQian International General Hospital, Guiyang, China C. S. Zee Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6_1

problems with timing, efficiency, and missed diagnoses may occur at all stages of imaging chain. Judgment of imaging sign, as one of the core principles of radiology, relies on the integration of multilayered data with distinctive decision-­making [3]. Imaging signs refer to the normal structures of the human body or imaging information or radiological findings produced by pathology under any type of imaging modalities [4]. An “iconographic” glossary of terms used for imaging is reproduced by placing them side by side between radiological features, and those may be associated with signs, symbols, or naturalistic images. Specifically, imaging signs refer to the metaphor of a certain tissue, structure, or lesion. One way is by linking anatomic structures and pathological conditions with objects, places, and concepts and codifying these relationships as metaphoric signs [5]. To describe an unnoticed finding specific to a par1

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ticular entity has always been a challenge for the radiologists. Time will be needed on investigations before we can add the specific finding to the legions of “signs” in radiology. The “signs” may become part of our language of specialty after validating by different observers over time. The “classic signs” endorse us confidence in determining the diagnosis. Some of imaging signs have been acknowledged, which are referred to as “Aunt Minnie.” When the sign is invoked, or an Aunt Minnie is recognized, it often brings an impression of the image to mind, and it may have specific diagnostic and pathological significance [6]. The advance of radiology evolves with such signs rendering an otherwise difficult diagnosis easier, which may help the radiologists appreciate the anatomy and pathology of an underlying abnormality and may quickly direct the physicians to the proper diagnosis and timely intervention.

1.1

 he Formation of Imaging T Signs

The language of radiology is rich with descriptions of imaging findings, often metaphorical, which have been commonly used in the daily radiology practice. The formulation of a medical terminology generally follows the nomenclatural rules such as customs, unity, science, and logistics. The naming of imaging signs usually depends on their cultural background or cognition of the founder or the author, linguistic traditions, or conventional principles as well [7]. For example, the scholars are accustomed to using familiar persons’ names, Greek letters and myths, English letters, foods, or animals and plants to name this metaphor. A collection of specialty-­specific signs can be obtained from general medical dictionaries or from encyclopedic texts in radiology and other specialties [2]. The signs can be separated into two categories: metaphoric and eponymous. About 66% of metaphoric signs (a total of 375) were collected from citations in the researches, and texts were radiological in reference [2]. The naming of metaphoric sign was reported frequently in the

radiological literature collection in the second half of last century, as a descriptive discipline for growth of radiology [4]. The evolution of radiology into a more analytic, data-driven pattern has resulted in its decline since then consequently. Eponyms usually recognize a person’s discovery and help remind us that the advancement of knowledge still depends on people, and that is important when our lives are so dominated by technology. However, eponymous signs were relatively infrequently seen in radiology specialty [2]. For example, most radiologists are quite familiar with the Rigler sign, which allows for the detection of pneumoperitoneum on supine radiographs of the abdomen [8]. The double-wall sign of free intraperitoneal air remains an important observation. Unfortunately, only a few eponyms are popularly used in radiological practice and research, unlike in the specialty of medicine or surgery. In every other specialty, the number of eponymous signs exceeds that of metaphoric signs [8]. This striking difference of percentages highlights the significance of metaphors for clinical diagnosis and educational instruction of radiology.

1.2

 he Features of Imaging T Signs

Imaging signs are often associated or analogous with certain objects or phenomena in nature, which are used to name imaging signs and to establish specific thinking connections with one or more diseases. Thus, imaging signs may present the following features: 1. Visualization: The inherent nature of radiological images as simulacra of both normal anatomy and disease entities makes imaging findings well suited to explanation by means of named patterns borrowed from other realms of knowledge [2]. A specific image sign is named after familiar things or phenomena in nature or life. The visualized composite is the common feature abstracted from many kinds of specific images.

1 Introduction

Therefore, the scholars take this specific metaphor as “Aunt Minnie.” 2. Characterization: The meaning of perceptual input is often recognized through associations with pictures encountered previously and understood both concretely and metaphorically in images interpretation [2]. A specific imaging sign often has its certain feature in the diagnosis of a disease. Mastering the main features of the metaphor may contribute to making a final diagnosis or differential diagnosis (DD). Pareidolias represent a quick and easy way of enhancing perception, improving the efficiency, and enhancing accuracy of image analysis. Pareidolic associations are commonly used in professional education to enhance perception of radiological abnormalities. For example, a couple of animal-inspired neuroradiological pareidolias specific to movement disorder diagnoses were defined [9]. 3. Practicality: Imaging sign is vivid and convenient to be recalled and is easy to be identified. The characterization also determines its clinical practicability. 4. Periodicity: Different imaging signs have been reported or found by radiologists at different stages of imaging technologies. Additionally, it should be a process to understand the diseases, and the understanding of imaging signs also has its period. 5. Hierarchy: Imaging signs are a combination of image information representing in different pathological stages of the disease, reflecting the unity of structure, function, tissue morphology, or biochemical changes.

1.3

Classification of Imaging Signs

There are many methods to classify imaging signs in clinical imaging interpretation: Based on whether the signs are the reflections of lesion itself, they can be divided into direct sign and indirect sign; based on the importance of the signs in imaging diagnosis and DD, they can be divided into primary sign and secondary sign;

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based on the specificity of the signs in imaging diagnosis and DD, they can be divided into typical sign and atypical sign: 1. Direct sign vs. indirect sign: Direct sign is the direct reflection of disease itself, is the main imaging feature of the disease, and is the key to imaging diagnosis. However, due to “Different diseases share the same image” and “One disease shows different images” or direct signs are unremarkable early on, indirect sign may sometimes become the main basis for diagnosis. In different situations, the status of direct and indirect signs can be exchanged from one to another, and sometimes, both may be equally important. 2. Typical sign vs. atypical sign: Typical sign refers to the standard morphology from complex imaging of general situation, which usually reflects the essentials of the lesion. Atypical sign is usually discrete and variant and lacks characteristic signs of the disease. Typical sign can only occur in some during the course of the disease, or the disease progresses to a specific stage; in the early stages of the disease, atypical sign prevails. The significance of typical sign and atypical sign is relative [10]. 3. Primary sign vs. secondary sign: Primary sign plays a major and decisive role in diagnosis of diseases among many of them; secondary sign plays a non-primary or subordinate role. Direct sign is usually regarded as primary sign, and indirect sign is regarded as secondary sign. The secondary sign of direct sign is predominant to indirect sign, and primary sign of indirect sign is secondary to direct sign. Generally, as a direct sign whether primary or secondary, it can clearly render diagnosis. 4. Sufficient sign vs. necessary sign: Sufficient sign means that once the sign appears, it must be a certain disease. Necessary signs refer to the percentage of the sign appearing in a disease that is 100%. Sufficient sign has strong specificity and must be direct signs; necessary sign has certain specificity and could be direct sign or indirect sign. Sufficient sign and nec-

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essary sign are typical, primary, and essential in imaging diagnosis. 5. Negative sign vs. possible sign: Negative sign may implicate that the metaphor is unlikely to occur in a disease; if it does, certain disease could be excluded; possible sign imply it may occur in a disease with low specificity, as an indirect sign which may provide reference for diagnosis.

1.4

 he Role of Imaging Signs T in Diagnosis

Specific images realize the effective connection between metaphor and diagnosis of disease. We should understand and master their features and pathogenesis of the metaphor; otherwise, there will be no way to use these imaging signs; in some cases, imaging signs may narrow the scope of DD. Most diseases are usually coexisting with varieties of imaging signs; a single sign could not indicate some disease. The more image signs appear, the more adequate and conducive to establish the diagnosis. Image diagnosis relies on the imaging signs of the disease. Some diseases could be shown as typical imaging signs, which makes it easier for radiologists to make a confident diagnosis. On the other side, imaging signs are the reflection of the comprehensive image information at different pathological stages of the disease, which may be affected by internal or external conditions, random factors, and other effects; thus, atypical appearances may present [11]. In clinical practice, we should not only focus on imaging signs, that is, its directed diseases and exclusive diagnosis, but also master the essentials of DD, relatively similarly featured appearances of different diseases.

1.5

The Decision-Making of Imaging Signs

The radiologists play a key role in the diagnosis and care of patients, and diagnostic errors may occur in interpreting hundreds of examinations

daily. The radiologists rely on heuristic principles to reduce complex tasks of assessing probabilities and predicting values into simpler judgmental operations. Heuristics in interpreting imaging studies are generally helpful but sometimes may result in cognitive biases or even significant errors [12]. Awareness of the cognitive process that the radiologists proceed in interpreting images would contribute to recognizing the inherent biases in decision-making. These mental shortcuts allow rapid problem-solving based on assumptions and prior expertise [13]. Medical errors are a leading cause of morbidity and mortality in the medical field and are substantial contributors to medical costs. Errors can be categorized as a “miss” when a primary or critical finding is not observed or as a “misinterpretation” when errors in interpretation lead to an incorrect diagnosis [14]. An understanding of the causes of cognitive biases can lead to the development of educational content and systematic improvements that mitigate errors and improve the quality of care provided by the radiologists [12]. Recognition of imaging sign is a good way to implement to minimize cognitive errors in daily practice, in which system-level processes that can be implemented can also minimize cognitive errors. In the daily reading practice, image analysis usually includes two basic steps: visualization and interpretation. Generally, we need to follow four steps: (1) perception – observing meaningful imaging signs; (2) recognition – deciding the pathological sign; (3) discrimination – characterizing the specific lesion type; and (4) determination  – making the final diagnosis. Perception is the basis of the diagnostic process. In the process of making the final diagnosis, typical manifestations of common diseases should be considered first, atypical manifestations of common diseases second, then typical manifestations of rare diseases, and lastly atypical manifestations of rare diseases, which are the basic thinking principles of imaging diagnosis. If only emphasize direct image sign, typical image sign, primary image sign, while ignoring indirect, atypical, secondary, rare, and possible image signs, which would fall into the situation of “put the cart before the horse.” If a radiologist misses an abnormality, it

1 Introduction

will lead to misdiagnosis and cause harm to the patient. In many cases, one or several signs cannot fulfill to make a diagnosis. Many common ethical dilemmas in radiology practices exist without an appropriate, objective, and unified approach to effectively guide the radiologist’s actions [15]. Medical ethics training should be highlighted during residency and more uniform recommendations to assist radiologists in addressing ethical issues in an appropriate manner [16]. A comprehensive analysis of clinical laboratory tests and therapeutic information would contribute to reach the final diagnosis. The Gestalt theory of modern psychology is grounded in the ideas that holistic rather than atomistic approaches are necessary to understand the mind and that the mental whole is greater than the sum of its component parts [17]. Although the Gestalt school fell out of favor due to its descriptive rather than explanatory nature, it permanently changed our understanding of perception. For the radiologist, such fundamental Gestalt concepts as figure-ground relationships and a variety of “grouping principles” (the laws of closure, proximity, similarity, common region, continuity, and symmetry) are ubiquitous in daily work, not to mention in art and personal life [17]. By considering the applications of these principles and the stereotypical ways in which humans perceive visual stimuli, a radiology learner may incur fewer errors of diagnosis. As used by radiologists, an Aunt Minnie or Aunt Minnie approach is a constellation of observations that the experienced reader finds virtually pathognomonic of an entity, usually an unusual or unexpected disease [18]. As a diagnosis based on having seen similar images many times, it is usually difficult to be explained systematically to a less experienced and sometimes incredulous colleague. This subliminal or subconscious pattern recognition resembles a person being able to recognize his or her Aunt Minnie among a large group of similar women, although it is difficult to analyze rationally or to explain verbally just how this process was accomplished. An Aunt Minnie is a diagnosis or recognition largely by Gestalt. With the increase of publications and the popu-

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larity of the Aunt Minnie, the original meaning of the term has been expanded and been applied to any classical constellation of findings. It may take a long time to validate and familiarize an imaging sign. Grasping the characteristics of an imaging sign is the key to find the question, and practice is the key of testing it. Accurate diagnosis depends on correct thinking and accurate understanding of the essence of the signs. The cognition of signs must be accurate; one-sided understanding of a certain sign will unfortunately lead to the deviation from right direction. Most studies on biases and heuristics in medical decision-making are based on hypothetical vignettes, raising concerns of applying the scientific findings to actual decision-making [19]. Radiologists motivate visual detection, pattern recognition, memory, and cognitive reasoning to develop the final diagnosis of radiological studies. This process is undergone in an unfavorable situation in which there are unpredictable distractors, increasing workloads and consequent fatigue. Given the ultimate human task of perception, some degree of error is likely inevitable. An understanding of the causes of interpretive errors can contribute to mitigating errors and improve quality of radiological interpretation [20]. In modern times, the fragmented information from the Internet can’t replace systematic knowledge learning and the organic combination of which is conductive to enhance verification and to deepen comprehension. Most importantly, building rigorous workstyle and scientific thinking habits is the unique road to improve our academic ability and diagnostic accuracy. Smartphones and tablets can be used by diagnostic imaging professionals, radiographers, and residents and to introduce relevant applications that are available for their field [21]. There is a long list of common radiology signs involving various body systems from head to toe. Identifying the signs and recalling their clinical relevance are crucial to not only radiologists but also general practitioners with access to clinical images. The apps can provide a ready-to-use and convenient reference list for radiologists via mobile phones [22].

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1.6

Radiomics and AI

Medical data is more and more likely to lead to major changes in modern imaging. In contrast to the traditional practice of treating medical images as pictures intended solely for visual interpretation, the advances of modern medical imaging have facilitated the development of high-­ throughput extraction of quantitative features in converting images into mineable data for subsequent analysis in decision-making, which is coined “radiomics” [3]. The models developed from combining imaging features, patient data, and bioinformatics may potentially improve diagnostic, prognostic, and predictive accuracy. Radiomics are intended to be conducted with standard data of images; the conversion of digital images into mineable data is conceivable to become practice. Radiomics exploits sophisticated image analysis and imagebased signatures for precision diagnosis and treatment. The standardized evaluation of the numerous publications of radiomics is still lacking currently [23]. Rigorous evaluation criteria and reporting g­ uidelines of imaging signs need to be established for investigations to meet urgent requirement in the field of radiomics. Imaging assessment of disease most commonly relies upon visual observations; advanced computational analyses may extend the scopes of interpretations [1]. Artificial intelligence (AI) has the potential to make great strides in the qualitative imaging interpretation by expert clinicians. AI may automatically process image interpretation and shift the clinical workflow of imaging detection, decision-making in intervention managing, or subsequent outcome observation [24]. The algorithms of AI for workflow improvement and outcome analyses are advancing. Using high-­ quality and high-quantity imaging data, AI can provide assistance to radiologists in imaging diagnosis and patient management [25]. AI may reduce cost and improve value at the stages of image acquisition, interpretation, and decision-­ making, but AI cannot yet be relied on or be responsible for physicians’ decisions-making that may affect survival. It is urgent for radiologists to receive the training and education of AI in daily clinical practice [26].

References 1. O’Connor JP. Rethinking the role of clinical imaging. elife. 2017;6:e30563. 2. Baker SR, Partyka L.  Relative importance of metaphor in radiology versus other medical specialties. Radiographics. 2012;32(1):235–40. 3. Gillies RJ, Kinahan PE, Hricak H. Radiomics: images are more than pictures, they are data. Radiology. 2016;278(2):563–77. 4. Baker SR, Noorelahi YM, Ghosh S, Yang LC, Kasper DJ.  History of metaphoric signs in radiology. Eur J Radiol. 2013;82(9):1584–7. 5. Gocmen R, Guler E, Kose IC, Oguz KK.  Power of the metaphor: forty signs on brain imaging. J Neuroimaging. 2015;25(1):14–30. 6. Dyer RB, Chen MY, Zagoria RJ. Classic signs in uroradiology. Radiographics. 2004;24(Suppl 1):S247–80. 7. Navarro-Sanchis EL, Sendra-Portero F.  Informatics in radiology (infoRAD): album of radiologic signs: a useful tool for training in radiologic semiology. Radiographics. 2005;25(1):257–62. 8. Lewicki AM.  The Rigler sign and Leo G.  Rigler. Radiology. 2004;233(1):7–12. 9. Mulroy E, Balint B, Adams ME, Campion T, Merello M, Bhatia KP. Animals in the brain. Mov Disord Clin Pract. 2019;6(3):189–98. 10. Koontz NA, Seltman TA, Kralik SF, Mosier KM, Harnsberger HR.  Classic signs in head and neck imaging. Clin Radiol. 2016;71(12):1211–22. 11. Raju S, Ghosh S, Mehta AC.  Chest CT signs in pulmonary disease: a pictorial review. Chest. 2017;151(6):1356–74. 12. Itri JN, Patel SH.  Heuristics and cognitive error in medical imaging. AJR Am J Roentgenol. 2018;210(5):1097–105. 13. Waite S, Grigorian A, Alexander RG, Macknik SL, Carrasco M, Heeger DJ, Martinez-Conde S. Analysis of perceptual expertise in radiology-current knowledge and a new perspective. Front Hum Neurosci. 2019;13:213. 14. Busby LP, Courtier JL, Glastonbury CM. Bias in radiology: the how and why of misses and misinterpretations. Radiographics. 2018;38(1):236–47. 15. Camargo A, Yousem K, Westling T, Carone M, Yousem DM. Ethical dilemmas in radiology: survey of opinions and experiences. AJR Am J Roentgenol. 2019;213(6):1274–83. 16. Camargo A, Liu L, Yousem DM. Radiology and ethics education. AJR Am J Roentgenol. 2017;209(3):640–2. 17. Koontz NA, Gunderman RB.  Gestalt theory: implications for radiology education [published correction appears in AJR Am J Roentgenol. 2008 Jun;190(6):1430]. AJR Am J Roentgenol. 2008;190(5):1156–60. 18. Hall FM, Griscom NT.  Gestalt: radiology’s aunt Minnie. AJR Am J Roentgenol. 2008;191(4):1272. 19. Blumenthal-Barby JS, Krieger H.  Cognitive biases and heuristics in medical decision making: a critical

1 Introduction review using a systematic search strategy. Med Decis Mak. 2015;35(4):539–57. 20. Waite S, Scott J, Gale B, Fuchs T, Kolla S, Reede D.  Interpretive error in radiology. AJR Am J Roentgenol. 2017;208(4):739–49. 21. Székely A, Talanow R, Bágyi P. Smartphones, tablets and mobile applications for radiology. Eur J Radiol. 2013;82(5):829–36. 22. Yeung AW. Review of radiology signs app for android. J Digit Imaging. 2016;29(5):523–5. 23. Lambin P, Leijenaar RTH, Deist TM, et  al. Radiomics: the bridge between medical imaging

7 and personalized medicine. Nat Rev Clin Oncol. 2017;14(12):749–62. 24. Bi WL, Hosny A, Schabath MB, et al. Artificial intelligence in cancer imaging: clinical challenges and applications. CA Cancer J Clin. 2019;69(2):127–57. 25. Dey D, Slomka PJ, Leeson P, et al. Artificial intelligence in cardiovascular imaging: JACC state-of-the-­ art review. J Am Coll Cardiol. 2019;73(11):1317–35. 26. Mendelson EB. Artificial intelligence in breast imaging: potentials and limitations. AJR Am J Roentgenol. 2019;212(2):293–9.

2

Brain Alexander M. McKinney, Yang Wang, and Ze Zhang

Contents 2.1 White Matter Buckling Sign

 10

2.2 CSF Cleft Sign

 12

2.3 Interhemispheric Fissure Sign

 13

2.4 Gyral Gathering Sign

 14

2.5 Lateral Ventricular Depressing Sign

 16

2.6 Little Ventricle

 17

2.7 The Swirl Sign

 18

2.8 Spot Sign

 19

2.9 Gray-White Matter Interface Displacement

 20

2.10 The Dense or Hyperdense Artery Sign

 21

2.11 The Middle Cerebral Artery Dot Sign

 23

2.12 Middle Cerebral Artery Susceptibility Sign

 24

2.13 The Cord Sign

 27

2.14 The Insular Ribbon Sign

 29

2.15 The Disappearing Basal Ganglia Sign

 30

2.16 The Obscured Lentiform Nucleus Sign

 32

2.17 Fogging Effect

 33

2.18 Coarse Flecks of Calcification

 35

A. M. McKinney (*) Miller School of Medicine, University of Miami, Miami, FL, USA e-mail: [email protected] Y. Wang · Z. Zhang Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6_2

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2.1

2.19 The Tram-Track Sign

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2.20 The Tuft Sign

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2.21 The Infundibulum Sign

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2.22 Target Sign

 41

2.23 Black Target Sign and White Target Sign

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2.24 Multilocular Ringlike Enhancement

 43

2.25 Hoop Sign and Popcorn Sign

 45

2.26 Ivy Sign

 47

2.27 Butterfly-Like Lesions

 47

2.28 The Mount Fuji Sign

 50

2.29 The Eye of the Tiger Sign

 51

2.30 Aura Sign

 52

2.31 Basilar Artery Encasement Sign

 53

2.32 The Tau Sign

 55

2.33 The Reversal Sign

 55

2.34 The False Falx Sign

 57

2.35 The Interpeduncular Fossa Sign

 59

2.36 The Empty Delta Sign

 60

2.37 The Parasagittal Sinus Sign

 61

2.38 The Pulvinar or Hockey Stick Sign

 62

2.39 The Radial Bands Sign

 64

2.40 The Triangular Pattern

 65

2.41 The Dural Tail Sign

 67

2.42 The Acute Angle Sign

 68

2.43 The Ependymal Dot-Dash Sign

 69

2.44 The Hummingbird Sign and the Swallowtail Sign

 71

2.45 The Hot Cross Bun Sign

 72

2.46 The Molar Tooth Sign

 74

2.47 The Caput Medusa Sign

 75

References

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White Matter Buckling Sign

Feature The white matter collapse sign refers to the extracranial occupying of growth under the inner plate of the skull that has embedded in the gray matter. It causes the white matter to become flat after compression subjacent to the gray matter. At the

same time, the distance increases between the compressed white matter and the inner plate of the skull. Explanation It is a reliable sign of extracerebral space-­ occupying lesions, especially meningiomas, that grow under the inner plate of the skull and embed

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a

Fig. 2.1  A mass with low T1WI, slightly high T2WI signal in the left frontal region on axial T1WI (a) and coronal T2WI (b), and the basal region is flat to the dural surface.

in the gray matter of the brain to flatten the white matter under the gray matter which protrudes into the brain like a finger and at the same time widens the distance between the compressed white matter and the inner plate of the skull [1] (Fig. 2.1).

11

b

It buckles (displaces) the gray matter-white matter interface inwards

CT and MRI signs of intracranial extra-cerebral occupying effects can be observed [2]: (1) white matter collapse sign and (2) displacement and compression of adjacent gyri. These refer to the gyral arcuate shift and compression change in contact with the extra-cerebral occupying lesions; Discussion this change forms a rim of increased attenuation The white matter collapse sign is a reliable fea- around the tumor on CT. The shape of the tumor ture of intracranial and extra-cerebral, extra-axial usually shows regular round or ovoid appearspace-occupying lesion (particularly in menin- ance, while peripheral edema is usually mild. This gioma). Gliomas, metastatic, and other intra-­ sign generally occurs in larger tumors and occurs cerebral tumors mostly have infiltrative growth, in meningioma where the brain appears convex where tumoral tissue is mixed with normal brain and adjacent to cerebral falx. Notably, this sign tissue; hence, with intra-axial lesions such as glio- is related to not only the tumor size, growth patmas, there is often no clear boundary, so we can’t tern, and speed but also its location. (3) Wide-base see this sign in intra-axial tumors. Meningioma is sign occurs when the wide base of the tumor is a common intracranial and extra-cerebral tumor closely connected with the skull and dura mater. that arises from the arachnoid cell and arach- The junction between the tumor and dura mater noid cap cell. The incidence of meningioma is an obtuse angle, so the typical contour of the (97.5/100,000 persons) is greater than glioma tumor is hemispherical, but it can be presented (4.7/100,000 persons). Meningiomas are typi- as round in some sections. (4) Pseudo-capsule cally relatively well-circumscribed extra-cerebral sign: the pseudo-capsule is a thin layer structure tumors with a hard texture and clear edge, being between the meningioma and adjacent brain tisslightly lobulated with a rich blood supply. sue on imaging. The pathological and anatomical Meningiomas occur outside the cerebrum, basis of pseudo-capsule is the CSF-perivascular and when the tumor grows into the brain, several space. In an extra-cerebral tumor, the incidence of

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the capsule is approximately 50%. The existence of a pseudo-capsule is a reliable sign for diagnosing an extra-cerebral tumor. (5) Skull changes in the attachment site: this is the site where the skull undergoes thinning after compression, hyperosteogeny, and sclerosis; bone destruction can be seen in some cases, or even extension through the skull, forming a soft tissue mass outside of the cranium in the deep scalp. Occasionally, the bony skull tissue can be mixed with hyperplasia and bone destruction. (6) Changes in the adjacent basal cistern and cerebral sulci: basal cistern and sulcal effacement in the tumor site and adjacent basal cistern and sulcal expansion. The origin of this sign is due to chronic and slow-growing meningioma that compresses adjacent brain tissue. In addition, meningioma can also exhibit a dural tail sign, which is the adjacent meningeal thickening and enhancement after contrast enhancement; however, the dural tail sign is not always characteristic of meningiomas, as acoustic neuromas, metastases. and chordomas also can appear as a dural tail. Even though the majority of meningiomas can be diagnosed easily with MRI, the diagnosis can be challenging when meningiomas show atypical imaging findings [1]. Diffusion-weighted imaging/diffusion tensor imaging (DWI/DTI), perfusion imaging, and magnetic resonance spectroscopy (MRS) can add value to help refine the diagnostic considerations of a dural-based mass and can also help further characterize the different subtypes of meningiomas [3].

2.2

CSF Cleft Sign

Feature On T2WI, the CSF cleft sign appears as a crescent of bright fluid (CSF) surrounding and separating the tumor margin from the cerebral or cerebellar cortex. Explanation The CSF cleft sign can be used to distinguish extra-axial lesion from intra-axial and is typically used in the description of meningioma. The cleft is regarded as representing a thin rim of CSF between tumor and brain parenchyma (Fig. 2.2).

Fig. 2.2  A 33-year-old woman with a right occipital space diagnosis of meningioma; a crescent of bright fluid (CSF) surrounds the tumor margin (white arrow) on T2WI

Discussion It is the most important factor for establishing an appropriate differential diagnosis by determining whether an intracranial mass is intraaxial or extra-axial. A majority of features differentiate extra-axial tumors from intra-axial tumors, such as the CSF cleft sign, intervening cortex between the white matter buckling sign and tumor, hyperostosis, and the dural tail sign. Especially, the CSF cleft sign is a common finding for meningiomas which makes it easier to distinguish meningiomas from intra-axial tumors. This sign is in conjunction with the aforementioned “white matter buckling sign.” On T2WI, where the CSF is depicted as bright, benign extra-axial/extra-cerebral lesions (most commonly meningiomas) may trap a crescent of bright CSF, confirming its extra-axial nature. The cleft can be confirmed as CSF by suppression (darkening) of the CSF signal on corresponding routine FLAIR images. However, in very large meningiomas causing severe amounts of mass effect or herniation, this sign is occasionally not present. The rim pattern of meningioma on nonenhanced 3D-FLAIR can predict surgical resectability and histological tumor grading [4].

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a

b

Fig. 2.3 (a, b) Axial FLAIR shows DCC, longitudinal Probst-Bündel (white arrow) and typical typical lateral ventricular straightening and culpcephaly (stars)

2.3

Interhemispheric Fissure Sign

Feature On axial CT, interhemispheric fissure and ventral/anterior portion of the third ventricle are abnormally close at the continuous level, which is called “interhemispheric fissure sign” of callosal dysgenesis. Explanation The interhemispheric fissure sign is a characteristic feature of dysgenesis of corpus callosum (DCC) on CT. During the embryonic period, the pseudocele between the bilateral lateral ventricle is pouch shaped and connected with the interhemispheric fissure. Later, it will be closed by the mouth of the developed corpus callosum. If the mouth of the corpus callosum is not developed, the interhemispheric fissure will connect with the pseudocele, direct or obviously close to the anterior part of the third ventricle (Fig. 2.3). Discussion DCC is a form of dysplasia of posterior midline structure in an embryonic period; it is one of the most common congenital malformations of the central nervous system, including hypo-

plasia or partial hypoplasia of the corpus callosum, which may exist alone or be accompanied by other craniocerebral deformities [5]. About 50% of the cases with DCC have been reported to be accompanied by other types of malformation, such as holoprosencephaly, hypoplasia of the septum, absence of the falx, gray matter heterotopia, schizencephaly, interhemispheric lipoma, interhemispheric arachnoid cyst, macrogyria, polymicrogyria, encephalomeningocele, microcephaly, Dandy-Walker syndrome, Chiari malformation, aqueduct stenosis, and other anomalies. CT features of DCC have been described: (1) Interhemispheric fissure widens and is situated abnormally close to the anterior part of the third ventricle; hence, “the interhemispheric fissure sign” is positive. Normally, the rostrum of the corpus callosum, septum pellucidum, fornix, and the anterior commissure separate the interhemispheric fissure from the third ventricle. When the corpus callosum and adjacent midline structures develop abnormally, the interhemispheric fissure and pericallosal artery will lie abnormally close to the anterior part of the third ventricle, and the hypoplasia of the adjacent white matter results in the expansion of the interhemispheric fissure. Because the rostrum of the corpus callo-

A. M. McKinney et al.

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sum develops later, whether the corpus callosum is dysplastic or partially hypoplastic, it is usually involved even in the mildest cases of callosal dysplasia. (2) There is lateral ventricle dilation, with bilateral lateral ventricular “inverted eight” or “crescent” shape. The anterior horn of the lateral ventricle is separated from the body, being straightened. In severe cases, the trigone and posterior horn of the lateral ventricle are irregular and asymmetrically enlarged, and the temporal horn can also be enlarged [6]. DCC is often accompanied with deep white matter dysplasia, so the lateral ventricle could also be enlarged. If the splenium of the corpus callosum is absent, the posterior horn will move up and enter dysplastic white matter, and occipital horn and trigone of lateral ventricular are asymmetrically enlarged, which is termed colpocephaly, i.e., lateral ventricular occipital horn enlargement. The parahippocampal gyrus and medial hippocampal formations are also often dysplastic, causing the temporal horn to expand. (3) There is enlargement and extension of the interventricular foramen. (4) The third ventricle can be enlarged, appearing raised, protruded, and to varying degrees protrude laterally, even forming interhemispheric fissure cysts. The diagnosis of DCC does not generally require advanced MRI or CT imaging, although noninvasive angiographic imaging can be helpful to observe occasional associated anomalies of the cerebral vessels. Severe DCC on CT is easy to diagnose, but mild callosal dysgenesis may be missed. Interestingly, in 39 cases of DCC reported by Sarwar, the positive predictive value of the interhemispheric fissure sign is 100%, and the other signs were relatively low [7]. It is suggested that some other signs may not be obvious in some cases due to the CT technique, while the interhemispheric fissure sign is a relatively reliable sign and can be important in diagnosing DCC.

2.4

Gyral Gathering Sign

Feature The sulci along the cerebral convexity narrow or disappear, and the distance between the gyri became smaller and close to each other.

Explanation A chronic subdural hematoma along the convex surface of the brain compresses the adjacent gyri, narrows, and obscures the subarachnoid space between the gyri, and the gyri become closer to each other. The gyral gathering sign is one of the important indirect signs of a chronic subdural hematoma on the convex surface of the brain (Fig. 2.4). Discussion The various components in chronic subdural hematoma can affect CT density, especially hemoglobin concentration. The speed of hematoma liquefaction is faster. After liquefaction, the CT image shows low density, and the lesion is clearly demarcated from brain parenchyma, which is compressed and moved inward. When there is fresh/hyperacute hemorrhage, particularly if actively bleeding, the hematoma can be iso-dense on CT due to the increase of protein content after hemolysis. The demarcation between lesion and brain parenchyma is not clear on CT, and the hematoma is not easy to identify. However, it can show indirect signs such as the convergence of cerebral gyri, displacement of gray-white matter interfaces, lateral ventricular deformation, and medial displacement of midline structures toward the opposite side [8]. Bilateral iso-dense chronic subdural hematomas (CSDH) may cause considerable difficulty in diagnosis on CT.  MRI can help in diagnosing such lesions. MRI is more sensitive than CT in determining the size and internal composition of CSDHs. Fresh bleeding, hemolysis, and hemoglobin changes can also be observed by MRI. Diffusion-tensor imaging (DTI) can examine anisotropic changes of the pyramidal tracts displaced by CSDH.  These anisotropic changes are caused by a reversible distortion of neuron and vasogenic edema by the hematoma. These changes in the affected pyramidal tract may correspond with motor weakness in CSDHs [9]. CSDHs are hyperintense on both T1- and T2-weighted images, in general. Notably, while there are some pitfalls (particularly in pediatric patients with abusive head trauma), in general, the age of subdural hematomas can be estimated using a combination of T1-, T2-, diffusion-­

2 Brain

a

Fig. 2.4  A 75-year-old male presented with recurrent headaches, accompanied by left eyelid droop. On MRI, arcuate areas of both hypo-intensity and iso-intensity, primarily with short T1 on T1WI (2.4a) and long T2 on T2WI

15

b

(2.4b), are shown in the right frontal lobe and left frontoparietal-occipital lobe. The brain parenchyma is shifted inwards, and the cerebral gyri converge

Table 2.1  The various phases of subdural and parenchymal hematomas can generally be classified based type of blood/hemoglobin and characterized by age on MRI, based on the sequences above Hemorrhage evolution on Tl, T2, DWI, SWI Type of blood Age Oxyhemoglobin (diamagnetic) Hyperacute Deoxyhemoglobin (paramagnetic) Acute Intracellular MetHgb (paramagnetic) Early subacute Extracellular MetHgb (paramagnetic) Late subacute Hemosiderin (paramagnetic) Chronic

T1 Isointense Isointense Bright Bright Dark

T2 Bright Dark Dark Bright Dark

DWI Bright Dark Dark Bright Dark

SWI Bright-ISO Dark Dark Dark Dark

Courtesy of Alexander M. McKinney, MD, University of Miami-Miller School of Medicine, Miami, FL

weighted imaging (DWI) and susceptibility-­ weighted imaging (SWI), as depicted in Table 2.1. A symptomatic CSDH tends to have a black band on the inner membrane of the CSDH on T2*WI or SWI.  The subdural “hyperintense bands” on DWI are intracellular and/or extracellular methemoglobin (i.e., subacute stages), based on T1- and T2-weighted imaging and based on intraoperative surgical findings. The subdural hyperintense band is an important finding indicating relatively fresh bleeding from the outer membrane [10]. Meanwhile, acute subdural hematomas are typically isointense on T1

and dark on T2, while hyperacute SDH may be isointense on T1WI and slightly bright on T2WI; however, note that hyperacute subdural hematomas are not dark on SWI. Hence, utilizing DWI and SWI may further help estimate the age of subdural hematomas. As the soft tissue resolution of MRI is high, the signal of chronic subdural hematoma is contrasted with that of brain parenchyma, and MRI also has advantages over CT in showing the convergence sign of cerebral gyri. Hence, MRI has more utility in the diagnosis of chronic subdural hematomas. Hemorrhage evolution on MRI is shown in Table 2.1.

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2.5

Lateral Ventricular Depressing Sign

Feature The outer sidewalls of the lateral ventricles on both sides move toward the midline, and the left and right widths of the bodies of the lateral ventricles become smaller. Explanation Subdural hemorrhage on both sides of the convex surface of the brain pushes parenchyma, indirectly compressing the lateral ventricle, resulting in a narrowing of the widths of the lateral ventricle (Fig. 2.5). Discussion Head trauma often leads to a subdural hematoma, which is caused by traumatic tearing across the cerebral arteriolar veins of the dura mater. An acute subdural hematoma is a serious condition and can progress rapidly and cause a worsening mass effect. The clinical symptoms such as increased intracranial pressure and neurologic deficits may appear earlier, but often, there is a lack of localizing signs. In patients with a traumatic acute subdural hematoma, there has been shown to be a strong correlation between the degree of midline shift and the thickness of subdural hematoma. Chronic subdural hematomas (CSDH) are more common in elderly patients, likely due to there being a more “brittle” blood vessel wall, where the dura mater is rich in blood a

b

supply, and the presence of slight trauma can lead to bleeding. CSDH composition and anatomy can be assessed using a modified Nakaguchi classification. Postoperative CSDH volume and the Nakaguchi classification subtypes may be the most powerful predictors of recurrence, cure, and the time to recurrence and cure [11]. Acute subdural hematoma on non-contrast CT appears as high attenuation with a typically crescentic shape. Subacute subdural hematoma density usually gradually decreases with time, due to the dissolution and absorption of hemoglobin. Hence, iso-attenuation hematoma may only exhibit indirect signs such as shift of the gray-­white matter interface, shallow sulcus, and narrowing of lateral ventricle. Contrast-enhanced CT demonstrate punctate or linear enhancement at the edge of the hematoma along the surface of the brain, making the edge of the hematoma appear more evident. CSDH is a mixture of hemoglobin breakdown products, CSF and fresh bleeding, which can exhibit low attenuation, iso-­ attenuation, high attenuation, or mixed attenuation. Regarding bilateral subdural hematomas, the thickness of bilateral subdural hematomas is usually the same, the degree of compression of the brain parenchyma is similar, and the degree of narrowing of the lateral ventricle is not much different relative to the presence of unilateral subdural hemorrhage. If the bleeding range is large, the width of the lateral ventricle can be slightly reduced. When the pressure is applied to both sides, the midline structure may not be displaced c

Fig. 2.5 (a) Acute right convexity subdural hematoma; (b) subacute left convexity subdural hematoma; (c) chronic left convexity subdural hematoma

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a

b

Fig. 2.6  A 5 year old male who suffered anoxic injury from forced submersion. On the initial non-contrast CT (a), there are small lateral ventricles, with early blunting of the gray-white matter differentiation. On brain MRI

with diffusion-weighted imaging the next day (b), there is diffuse brain swelling with cytotoxic edema, consisted with hypoxic-ischemic (anoxic) injury involving the cerebral parenhcyma and basal ganglia throughout

or the displacement may not be obvious. If the thickness of the subdural hematomas on both sides is more overt, the degree of narrowing of the lateral ventricles may differ, and the midline structures may be slightly deviated toward the smaller hematomas [12]. CSDH can be more extensive along the length of the cerebral convexities due to epidural hematoma, and the mass effect can be significant. If this occurs in combination with intracranial hemorrhage or diffuse brain swelling, the degree of compression of the lateral ventricle can be more obvious and can be prone to symptoms of increased intracranial pressure. Hence, bilateral subdural hematomas can have rapid clinical progression and poor prognosis and thus may have different degrees of clinical and radiologic sequelae after treatment. Urgent surgery for decompression of hematoma pressure may be recommended for bilateral CSDH [13].

Explanation If brain blood-CSF barrier is destroyed, the intravascular liquid diffuses and infiltrates into the extracellular space, the amount of water in the cerebral interstitium is increased, the intracranial pressure is increased, and the lateral ventricles pressures decrease (Fig. 2.6).

2.6

Little Ventricle

Feature Its features are diffuse swelling of brain tissue, decreased density, disappearance of the cerebral sulci, and smaller lateral ventricles.

Discussion Brain damage after head injury can be classified by its time course. Primary damage includes acute subdural hematoma (SDH), acute epidural hematoma (EDH), and such intra-axial lesions that include contusions, diffuse axonal injury (DAI), and intraparenchymal hemorrhage (IPH) which occur at the moments of impact and may be irreversible. Secondary damage includes herniations, diffuse cerebral swelling, and secondary infarction and hemorrhage; these evolve hours or days after injury as consequence of systemic or intracranial complications. The duration and severity of secondary damage can influence the clinical outcome [14]. Brain edema following traumatic brain injury (TBI) often increases the intracranial pressure and limits oxygen delivery. In severe brain edema, the cisterns will be compressed or absent; a decrease in density,

A. M. McKinney et al.

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as measured by Hounsfield Units (HU) of the brain, suggests edema. Diffuse cerebral swelling has a relatively high mortality rate, particularly if severe. In children with head injury, bilateral diffuse cerebral swelling is common; cerebral blood flow and CT density studies suggest that this is due to cerebral hyperemia. In comparison to adults, the clinical prognosis in these children is better if there are no secondary lesions on CT. Rotterdam score is an independent factor for predicting outcomes among patients with TBI and can predict outcomes [15]. The non-contrast CT findings in diffuse cerebral swelling include homogeneous decreased density, non-visualization of cortical sulcal spaces, loss of the gray-white matter interface, relative hyper-density of the cerebellum (white cerebellum sign), effacement of the basal cisterns, especially the peri-mesencephalic cisterns, and bilateral compression of the lateral ventricles. Cerebral swelling may sometimes be associated with fatal outcomes due to acute cerebral edema [16]. As traumatic brain injury patients typically have difficulty with daily tasks, physical and occupational therapy is highly recommended as patients attempt to regain a normal lifestyle.

2.7

The Swirl Sign

Feature The swirl sign is sometimes visible on nonenhanced brain CT.  It is recognized as an area of low attenuation within a larger high-density fluid collection in the cerebrum or cerebellum. Interpretation The swirl sign is an ominous sign of an actively bleeding epidural hematoma (extradural hemorrhage) that has two components: an actively bleeding/hyperacute component and an older one. The active component is usually a smaller, rounded lesion that is iso-dense to the brain parenchyma and likely represents actively extravasating (un-clotted) blood. The older (usually acute or subacute age) component is a h­ yperattenuating extra-axial collection, which usually measures 50–70 HU (Fig. 2.7).

Fig. 2.7  An internal focus of low attenuation within a high-density fluid collection along the left cerebral convexity on non-contrast CT, representing the swirl sign (arrow)

Discussion The “swirl sign” (SS) has been previously described as a tiny or smaller focus of hypo- or iso-density within a larger region of a hyper-­ density that has been shown to represent active hemorrhage on surgical evacuation [17]. The swirl sign can be a reproducible predictor of 1-month mortality and functional outcome, where it is first described in traumatic extraaxial hematomas; correspondingly, Greenberg et  al. and Al-Nakshabandi documented that following surgical exploration, the swirl sign correlates with areas of active hemorrhage in subdural hematomas [18–20]. An epidural hematoma usually appears as a lentiform or biconvex hyperattenuating collection along the cerebral or cerebellar convexity. Epidural hematomas may also occasionally present between the dural sinuses and the skull in the setting of skull fractures that cross the dural sinuses, and thus may simulate dural sinus venous thrombosis [20, 21]. An arterial epidural hematoma usually results from injury to the middle meningeal artery or its branches. An arterial epidural hematoma in the middle cranial fossa may compress the tempo-

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ral, frontal, or parietal lobes, depending on the size of the collection and the vessel injured. A venous epidural hematoma commonly occurs at the site of major dural sinuses (e.g., superior sagittal sinus, transverse sinus, or confluence of sinuses) [20, 21]. The black hole sign (BHS) also seems to be a good predictor for hematoma growth. The presence of the swirl sign on admission non-­contrast CT does not independently predict hematoma growth in patients with ICH. The black hole sign and the swirl sign are both imaging markers that reflect hemorrhage density heterogeneity. Hematoma growth may occur in a cascaded pattern, with initial bleeding causing secondary peripheral vessel rupture for ongoing bleeding. The CT attenuation of blood is dependent on the time course of the bleeding, so the heterogeneity of the hematoma represents blood of different ages. In addition, the hypoattenuation area may indicate fresh liquid blood bleeding. SS has a vague definition, and the evaluation of SS is more subjective. In BHS, a clear border and a delta of ≥28 HU between the two density regions can improve the reliability. Therefore, the inter-­rater reliability is higher than with SS. The rigorous definition of the BHS results in a high specificity of BHS (95.3%) but a low sensitivity (33.8%) [20].

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Fig. 2.8  Original CTA of head showing spot sign within hematoma high-density shadow in the shape of strip or dot (arrow)

A spot sign is actual spotlike change caused by contrast agent extravasation after enhancement. It is an independent enhancement focus and has no corresponding connection with blood vessels (Fig. 2.8).

Interpretation Hematoma evolution in IPH is a dynamic process that begins as a primary hemorrhagic insult, from various causes, most commonly from trauma 2.8 Spot Sign or infarct. Multiple studies have shown that a significant proportion of patients (~25–38%) Feature undergo hematoma expansion on repeat CT The spot sign is sometimes visible on dynamic imaging. The currently recognized clinical progcontrast-enhanced CT of the brain in the setting nostic factors (including initial hematoma volof intraparenchymal hemorrhage (IPH), typically ume, neurologic deficit at presentation, age, and in acute infarcts or IPHs of other causes, such infratentorial location) do not directly reflect as trauma. It is recognized as an area of higher the dynamic nature of hematoma evolution. attenuation within a larger high-density hemor- Hematoma growth is thought to be due to active rhage within the cerebrum or cerebellum. hemorrhage and rebleeding and has been shown to be a determinant of mortality and morbidity Explanation [22–25]. Early identification and limiting hemaThe contrast-enhanced focus on the original CTA toma expansion have become the primary treatimage of the head, i.e., spot sign, is caused by the ment goals; thus, identification of early signs of rupture of the arteriole in brain parenchyma. It is hematoma expansion can help determine patient defined as a single or multiple spotlike or line-­ prognosis. As such, the “spot sign” on dynamic like enhanced high-density lesion in the hem- contrast CT, such as CT angiography, has been orrhage substance on the original CTA image. shown to predict early/hyperacute IPH expan-

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sion with 89–91% sensitivity and specificity; the rate of IPH growth has also been identified as a significant predictor of the patient’s prognosis [25]. However, some patients may not undergo contrast-­enhanced CT, whether due to iodinated contrast allergy, intravenous access, renal failure, or for other reasons, and thus, the swirl sign on nonenhanced CT may be more universally applicable and not require the use of contrast. Hence, the usage of either the swirl sign and spot sign can predict patient’s likelihood of suffering hematoma expansion and can help determine patients’ prognoses. The nomogram model may accurately predict hematoma expansion of spontaneous intracerebral hemorrhage in the recent study [26].

2.9

 ray-White Matter Interface G Displacement

Fig. 2.9  A 68-year-old woman presented with a crescent-­ shaped high-density hemorrhage (subdural hematoma) overlying the left frontal and parietal lobes, with slight inward displacement of the brain parenchyma, and bluntFeature ing (or blurring) with straightening of the gray-white matWhen a subdural hematoma occurs, the gray-­ ter interface

white matter interface between the cortex and medulla of the hematoma side is displaced inward, and the distance between the hematoma side and the skull’s inner table increases, which is called gray-white matter interface displacement.

compression of the ipsilateral ventricle, dilatation of the contralateral ventricle, and effacement of the cortical sulci. Normally, the gray matter of both hemispheres is of equal thickness and, therefore, the gray-white matter interface Explanation (G-WMI) of each hemisphere is equidistant from Normally, the density of the gray-white matter the inner skull table. A small SDH with an atten(or “junction”) is readily visible. When an iso-­ uation value resembling gray matter will cause attenuating subdural hematoma of equal occurs, an apparent thickening of the gray matter. This the gray-white matter interface displacement is caused mainly by mechanical displacement often appears. The so-called gray-white matter of the G-WMI [27]. Extracerebral lesions, espeinterface sign refers to the change of the ipsilat- cially those with intact capsules, exert pressure eral gray-white matter interface when an extra- on the brain tissue without destroying it, causing cerebral space-occupying lesion is present. In the interface between gray matter and white matsuch a situation, the interface becomes nearly ter to move inward, which is called gray-white a straight line and becomes blunted, which is a matter interface (G-WMI). characteristic appearance caused by extracerebral This sign is better displayed by T1WI, proton-­ space-­occupying lesions (Fig. 2.9). weighted image (PDWI), and 3D T1WI used in recent years, as well as reversal sequences (such Discussion as inversion recovery), that reverse the gray The secondary signs of subdural hematomas and white matter signals. Subdural hematoma, (SDH) have previously been documented and epidural hematoma, and extracerebral tumors include midline displacement, small ventricles, such as meningiomas can affect the interface. It

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should be noted that this sign can be seen on both sides at the same time, especially in the setting of bilateral subdural hematomas or subdural effusions. It is easy to misdiagnose such bilateral extra-axial lesions when the degree of displacement is light [28]. SDH is a dynamic lesion, and its appearance on computed tomography is usually dependent on its age, as well as other underlying factors (including hemoglobin and hematocrit levels). Soon after a hemorrhage occurs (in the acute phase), the hematoma appears hyperdense when compared with the normal brain, due to the presence of fresh blood. During the next few weeks, (subacute phase) resolution occurs due to fibrinolysis, so the hematoma appears iso-dense. After approximately 4  weeks (chronic phase), it appears hypodense due to the resorption of fluid. However, repeated micro-hemorrhages into SDH can increase the density, giving rise to a heterogeneous and partially hyperdense picture [29]. Hence, a hyperdense hematoma can be readily recognized, but an iso-dense hematoma may be difficult to visualize on the computed tomogram. A specific finding is the displacement of the brain parenchyma away from the skull, and the usual convex border appears flattened or even concave. Also, several other indirect features may occur due to the displacement of the brain; for example, effacement of the sulci, compression of the ipsilateral ventricle leading to midline shift, and deformity of the normal ventricular anatomy could aid in the diagnosis of subdural hematoma.

2.10 T  he Dense or Hyperdense Artery Sign Feature The dense artery sign is characterized by an increase in the density of the first to second segments of the middle cerebral artery (MCA) or an increase in the density of other arteries in the brain compared to the contralateral side. This can be applicable to other major intracranial arteries, such as the anterior cerebral artery (ACA) or the posterior cerebral artery (PCA).

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Explanation The dense (or hyperdense) artery sign is an indirect sign of cerebral infarction caused by occlusion of a major cerebral artery (the MCA being most common). The high attenuation component represents a blood clot, thrombus, or emboli lodged in the cerebral artery’s lumen. The CT value of normal flowing blood is approximately 40  HU, whereas the CT value of a thrombus is approximately 80  HU, thus showing a higher attenuation than normal, un-clotted blood (Fig. 2.10). Discussion The dense arterial sign, or the hyperdense artery sign, which is believed to be caused by thrombus, has a density/attenuation (77–89 HU) that lies between normal arterial (35–60  HU) and calcified plaque (114–321  HU); it is common in cardiogenic cerebral infarction, for example. The M1 segment of MCA is located in the lateral cleft, and there are more chances of arterial obstruction, so there is a greater possibility of this sign being exhibited in the setting of acute ischemic stroke. Therefore, in this setting, it is also called the “hyperdense MCA sign (HMCA sign),” while ACA or PCA can less commonly have a similar appearance [30]. Non-­contrast CT is usually the first method of examination for acute cerebral infarction; however, in the first few hours after infarction, CT usually appears normal. When the image changes of early ischemic infarction occur, they are often concealed at first in the hyperacute phase but usually become obvious over time. Hence, recognizing certain signs of acute infarction can help to identify infarcts and lead to prompt therapy [31]. Thus, early signs of MCA occlusion include the HMCA sign, lenticular nucleus sign, insular ribbon sign, low-density focus, occupying effect, and the cortical effacement sign. These signs can become more apparent at approximately 6  hours after infarction. In theory, the HMCA sign can be seen on CT images when blood vessels are occluded and earlier than the other changes in acute stroke. In addition, as the HMCA sign is transient, most patients with acute cerebral infarction who have

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a

b

c

d

Fig. 2.10 An 81-year-old male patient. (a–c) Non-­ contrast CT shows increased attenuation of the left middle cerebral artery (i.e. a “hyperdense MCA sign”) and slightly low attenuation and blurred boundary in left frontal, temporal, and parietal lobes; A few days later, cranial

MRI follow-up, FLAIR (d) shows a large area of abnormal intensity in the left frontal, temporal, and parietal lobes, while DWI (e) shows obvious hyperintensity with restricted diffusion, indicating an acute cerebral infarction

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e

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2.11 T  he Middle Cerebral Artery Dot Sign Feature On non-contrast head CT, compared with the contralateral or even with other vessels on the same side, the hyperattenuating vascular shadow located in the Sylvian fissure is called middle cerebral artery dot sign.

Fig. 2.10 (continued)

the HMCA sign have that sign disappear within a few days post-infarct, or after thrombolytic therapy, which confirms the mobility of such blood clots within the hyperattenuating vessels. When HMCA sign is seen, it should be noted that it does not always represent vascular obstruction; for example, when the specific volume level of blood cells is high, the CT value of blood or calcification of blood vessel wall (often associated with diabetes and hypertension) will appear falsely positive for a thrombosed vessel, but will usually involve multiple vessels, and often appear bilaterally dense as regards the MCA [32]. Thus, the high density of a unilateral MCA is more reliable than bilaterally hyperdense MCAs. In one study, it is found that the sensitivity and specificity of the dense artery sign for arterial obstruction is approximately 52% and 95%, respectively, and the dense artery sign is more commonly identified in the larger proximal arteries, relative to the smaller distal arterial segments [33]. Although false positive, the dense artery sign has a higher diagnostic value in patients with cerebral infarction symptoms and is a relatively highly specific sign. When there are other early signs of early cerebral infarction, the reliability of the dense artery sign is even higher.

Explanation In non-contrast CT, normal vascular usually shows soft tissue attenuation; when thromboembolism and obstruction occur, the attenuation of blood vessels increased. The middle cerebral artery dot sign indicates thromboembolism in a branch of the middle cerebral artery (M2 or M3 segment) in the Sylvian fissure. In the axial plane, the M2 or M3 segments are perpendicular to the scanning plane; thus, these appear as a dot on non-contrast CT. MCA dot sign and the hyperdense MCA (HMCA) signs are CT findings of MCA occlusion occurring at different axial CT levels (Fig. 2.11). Discussion Non-contrast CT is utilized to exclude intracranial hemorrhage in an emergency setting and is an invaluable tool in the evaluation of suspected acute stroke. Beyond the detection of hemorrhage, early non-contrast CT can also be used to detect direct or indirect signs of acute ischemia or infarction itself. The MCA dot sign is an important indirect sign, which indicates a high attenuation thrombo-embolus or occlusion with an internal vascular shadow (appearing as a filling defect). It refers to the dot of high attenuation in the M2 or M3 segments of the MCA of the Sylvian fissure, especially in the annular sulcus [34]. It is generally believed that atherosclerosis mainly involves the internal carotid artery, MCA trunk (M1 segment), and basilar artery and less commonly involves the M2 segment of the MCA and smaller-diameter distant arteries. Therefore, the high attenuation shadows of M2 segment and distal artery are considered mainly thromboembolic rather than calcified atherosclerotic plaques. Some studies

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a

b

Fig. 2.11  An 81-year-old female with atrial fibrillation had a left-sided facial droop, with unclear speech and weakness of the left lower limb. (a) Non-contrast CT shows a focus of high attenuation in the right Sylvian fis-

sure, suggesting MCA dot sign. (b) Contrast-enhanced CT with 3D reconstructions shows occlusion of MCA M1 segment, with high-attenuation shadow thrombus extending into M2 segment

have found that in patients with MCA infarction in the region of blood supply, patients with the HMCA sign were found to have longer hospitalization times and worse short-­term prognosis, which is significantly worse than in patients with MCA dot sign alone or in those lacking the HMCA sign [34]. Although there is a report that the MCA dot sign can be falsely positive due to increased hematocrit, many scholars believed that the MCA dot sign was still a highly specific CT sign. According to Leary et  al. [35], MCA dot sign has a high specificity (100%) and a moderate sensitivity (38%) in the diagnosis of ischemic stroke in the blood supply area of MCA, with a positive predictive value of 100%, a negative predictive value of 68%, and an accuracy of 73%. Thus, the use of solely the MCA dot sign suggests M2 or M3 segment of the MCA is occluded, where the size of the injured brain tissue by the ischemic injury is small, and hence, there is a good short-term and long-term prognosis; in such patients, the effect of thrombolytic therapy is greater than that of the proximal MCA trunk (M1 segment) [35]. The use of the MCA dot sign can be very helpful in the diagnosis, treatment, and prognosis of MCA branch infarctions, and it has a better prognosis than the HMCA sign. Therefore,

recognition of the MCA dot sign is vital for the identification and quantification of the extent of those acute ischemic lesions that have a better prognosis. Incorporating multiplanar reconstruction may lead to a higher sensitivity of the middle cerebral artery “dot” sign [36].

2.12 M  iddle Cerebral Artery Susceptibility Sign Feature On susceptibility-based MR images such as susceptibility-­ weighted imaging (SWI), T2*weighted gradient echo (T2*WI), or MR perfusion imaging, the diameter of the apparently low-­ signal middle cerebral artery (MCA) or internal carotid artery (ICA) exceeds the diameter of the corresponding contralateral artery, which is called “middle cerebral artery susceptibility sign.” Explanation The middle cerebral artery susceptibility sign indicates acute thromboembolism in MCA or ICA. In acute thromboembolism, the concentration of deoxyhemoglobin is very high, the value of T2 in thrombus is shortened, and thus, the vis-

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ible signal is lost on the imaging sequence based on susceptibility, showing overtly low signal with a “blooming effect” of the dark signal beyond the expected MCA luminal diameter. This can occur a

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in other major intracranial arteries such as the anterior cerebral artery (ACA) or posterior cerebral artery (PCA) as well, albeit less common in those vessels (Fig. 2.12). b

c

Fig. 2.12  A 49-year-old male presented with the left middle cerebral artery susceptibility sign on SWI (arrow, a) and developed associated infarcts on DWI (b). On head

MRA (c) demonstrates distal occlusion (arrow) of M2 branch of the left middle cerebral artery (inferior division)

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Discussion In 2000, Flacke et  al. first reported that in MR perfusion imaging (PWI) of stroke patients with MCA occlusion within 6  hours after onset of symptoms, the signal of MCA in the occlusive segment is significantly reduced, and the diameter of MCA is larger than that of the corresponding contralateral artery, which is termed “middle cerebral artery susceptibility sign” [37]. This is related to the susceptibility effects from the paramagnetic effect of intraluminal thrombus, usually either in the acute phase of thrombus (deoxyhemoglobin) or subacute phase of thrombus (methemoglobin). The value of high attenuation sign of the middle cerebral artery on CT in the diagnosis and pre-thrombolysis evaluation of acute cerebral infarction has been recognized. However, its application is limited due to the application of a radiation dose, factors related to the possibility of there being a false positive (such as due to dehydrations or beam hardening artifacts), and difficulty in identifying lesions related to hyperacute cerebral infarction. Compared with the hyperdense middle cerebral artery sign, the middle cerebral artery susceptibility sign has the advantages of no radiation and strong repeatability/reliability, and is considered as good as or even a better predictor of vascular occlusion; Payabvash et  al. [38] found that there is greater than 90% specificity and positive predictive value on SWI MRI when this sign is demonstrated, while GRE T2*WI is less sensitive. Studies [39] have shown that the components of emboli include red blood cells, platelets, fibrin and nucleated cells (neutrophils, monocytes), etc., but the proportion of the manifold components of different emboli varies. Kimura et  al. [40] suggested that the middle cerebral artery susceptibility sign indicates that an embolus contains a higher concentration of red blood cells. White thrombi are typically rich in platelets and resist intravenous thrombolysis of recombinant tissue plasminogen activator (rt-PA), while red thrombi are rich in red blood cells and elicit a faster response to thrombolytics; hence, the nature of the embolus determines the therapeutic effect of revascularization. Therefore, the middle cerebral artery susceptibility sign may have the

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value of predicting vascular recanalization and clinical prognosis [41]. However, the middle cerebral artery susceptibility sign also has some false positives as well. Of note, SWI is an imaging technique developed on the basis of gradient-­ recalled echo (GRE), which can obtain both the amplitude and phase maps of patients’ MRI; ergo, SWI is more sensitive to the susceptibility effect induced by a substance, particularly metallic agents, gas/air, and other substances or agents that cause profound dephasing. With the aging of thrombus, the presence of susceptibility within the middle cerebral artery varies in patients with ischemic stroke at different stages. The order of degradation of oxyhemoglobin in erythrocyte, in approximate chronologic order (although the stages can overlap) is deoxyhemoglobin, methemoglobin, and finally hemosiderin formed by macrophage phagocytosis. The unpaired electrons of deoxyhemoglobin and hemosiderin have a significant paramagnetic effect (regardless of their bright or dark signal on T1WI and T2WI), resulting in inhomogeneous magnetic field and rapid proton spin dephasing near them, which cause significant signal loss on the SWI sequence. This “susceptibility effect” can appear even as a small “blooming” effect of the dark signal around the affected vessel and can create difficulty in accurately measuring the size of the vascular abnormality (such as with an aneurysm). Manipulation of the time to echo (TE) and time of repetition (TR) can also alter the degree of susceptibility effect on SWI and other GRE sequences. Thus, false positives can occur simulating intraluminal thrombus, due to susceptibility effects from artifacts (such as whether from the adjacent scalp to metals or foreign bodies or from the scalp or mastoid air cell gas, pulsation effects, or even motion), implants (e.g., adjacent clips or some stents), biologic deposits (e.g., calcium or iron), or even certain contrast agents (e.g., iron-containing). Therefore, it is necessary to accurately confirm that a middle cerebral artery susceptibility sign is a true positive by correlating both with other MRI sequences such as fast spin-echo T2WI, which is relatively insensitive to susceptibility artifacts), or FLAIR (which often has mildly

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hyperintense vascular signal in acute stroke, due to loss of the normal dark signal in normal moving arterial flow); alternatively, retrospectively correlating with the non-contrast CT can reveal a subtle hyperdense middle cerebral artery for confirmation. Less common signs such as the prominence of either cortical or medullary veins demarcating the territory of infarct on SWI (present in 10–20% of acute stroke patients, presumably due to venous stasis) and the presence of SWI-DWI mismatch (associated with lower infarct volumes and better outcomes) can help confirm and can help estimate the overall size of infarct, as such secondary signs have been shown to correlate with the eventual infarct size [42, 43]. At present, cases of the middle cerebral artery susceptibility sign are best visualized around 6  hours of stroke symptoms or later, while the signal evolution of thrombus on SWI in  vivo is not completely known, particularly with smaller thrombi approximately a millimeter in size or less. Therefore, while there is a lack of understanding of middle cerebral artery magnetic susceptibility within the first 3 hours of acute stroke symptoms, there is not enough data to determine the shortest time that MRI can depict acute thrombus on SWI. Therefore, the middle cerebral artery susceptibility sign cannot yet be reliably applied to patients with acute stroke within the first 3 hours of symptom onset.

2.13 The Cord Sign Feature The cord sign is a homogeneous, hyperattenuating, cord-like appearance on non-contrast axial CT of the brain. Explanation The cord sign appears as the result of increased attenuation within either the dural sinuses or a vein filled with thrombus. Thrombosis in veins can be visualized directly on unenhanced examinations as foci of increased attenuation within the distribution of the affected veins. For veins perpendicular to the transverse plane (including

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the cortical vein, the vein of Galen, and parts of the superior sagittal sinus), a round focus of increased attenuation may appear on the successive sections. In veins parallel to the scanning plane (including internal cerebral veins, medullary veins, and the straight sinus), the linear nature of the high attenuation may represent a thrombosed blood vessel or venous sinus. This appearance is termed the “cord sign” (Fig. 2.13). Discussion Cerebral venous thrombosis (CVT) is a type of stroke where the thrombosis occurs in the venous side of the brain’s circulation, leading to occlusion of one or more cerebral veins and potentially a dural venous sinus. CVT is more frequent in women. The age distribution of CVT is different from that of ischemic stroke, CVT being more frequent in children and young adults. CVT has a variable clinical presentation ranging from mild cases presenting only headache, headache plus papilledema or other signs of intracranial hypertension, focal deficits such as aphasia or paresis often combined with seizures, to severe cases presenting with encephalopathy, coma, or status epilepticus. The confirmation of the diagnosis of CVT by imaging requires the demonstration of thrombi in a dural sinus or cerebral vein [44]. The cord sign appears as the result of increased attenuation in either the dural sinuses or a vein filled with thrombus. Thrombosis in veins can be visualized directly on unenhanced examinations as foci of increased attenuation in the distribution of the affected veins. For veins perpendicular to the transverse plane (including the cortical vein, the vein of Galen, and parts of the superior sagittal sinus), a rounded focus of increased attenuation may appear on the successive sections. In veins parallel to the scanning plane (including the internal cerebral veins, medullary veins, and the straight sinus), the linear nature of the high attenuation may represent a thrombosed blood vessel or venous sinus [45]. On unenhanced CT, the most common cause of a false-positive case is a high hematocrit (e.g., in patients with polycythemia vera) causing a hyperdense sinus. However, the arteries of such patients also frequently have a hyperdense appearance, which is a clue to the correct diag-

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a

b

c

Fig. 2.13  In a 21-year-old male, axial unenhanced CT image (a) showed the cord sign (arrow) in the straight sinus. This was confirmed to be occlusive thrombus

(arrows) on postcontrast MR venography (b). Sagittal T1WI postcontrast (c) confirms the straight sinus thrombus as well (arrows)

nosis. The conundrum of a hyperdense appearance of normal dural sinuses is also frequently encountered in infants and young children, in whom the relative density of the dural sinus compared with brain tissue is typically high for two reasons: first, a usually higher hematocrit value than in adults and, second, a typically lower brain density than in adults [46, 47]. Thus, other conditions causing a hyper-dense appearance of the vascular, such as dehydration or polycythemia, can simulate a hyperdense venous sinus. The diagnosis of CVT is often made through analysis of source venographic and 3D images. The diagnosis is based on confirmation of thrombus

within the venous sinuses and identification of any secondary effects of thrombosis on brain parenchyma or CSF pathways. Unenhanced CT is typically the most common initial imaging modality for many of these clinical diagnostic considerations. Unfortunately, unenhanced CT examinations may often show only subtle findings or appear normal, which necessitates the use of 3D venographic images, if thrombosis is suspected. Before the advent of MRI, conventional CT is the best noninvasive method of diagnosing CVT.  The cord sign is originally found in only a minority of images of patients with cerebral venous thrombosis, and there were doubts

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approximately the sign’s value in routine diagnosis. With thinner CT sections, however, this sign is now detected more frequently with a higher sensitivity on non-contrast CT.  Since the cord sign demonstrates a newly formed thrombus, it will seldom be visualized in patients with subacute or chronic disease because the thrombus ages, usually becoming iso-attenuating and then hypoattenuating after the first 7–14 days. In other cases, the thrombosed veins are too small for the thrombi to be visualized, or the thrombi are obscured by artifacts from adjacent bone [45].

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ally slightly denser) and white matter (normally slightly less dense) at the outer edge of the insular lobe. Thus, in acute infarction, the insular ribbon becomes a blurred confluence of the gray matter-white matter junction in the middle cerebral artery distribution.

Feature One of the earliest non-contrast CT findings of cerebral infarction is the insular ribbon sign, which consists of the disappearance of the visible boundary between the gray matter (usu-

Explanation The claustral artery or insular artery from the branch of the middle cerebral artery M2 segment perfuses the insular ribbon area; alternatively, lateral lenticulostriate branches can uncommonly supply this region. When the M2 segment becomes occluded, this region is prone to infarction due to its being the furthest collateral circulation from the arteria cerebri posterior and arteria cerebri anterior. Hence, in the setting of an acute insular region infarction (supplied by a subdivision of an M2 segment), the loss of the insular ribbon is a reaction to acute edema caused by cerebral infarction (Fig. 2.14).

Fig. 2.14 On non-contrast CT (a) in a 38-year-old female, via bilateral comparison of the insular ribbon, there is a right insular ribbon sign on the right (arrow),

and the left side is normal. DWI (b) confirms an infarct subsequently occurred in the right MCA distribution in that location

2.14 The Insular Ribbon Sign

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Discussion In 1990, Truwit et al. reported an early CT manifestation of acute cerebral infarction caused by the disappearance of the insular zone from a middle cerebral artery (MCA) or internal carotid artery (ICA) acute occlusion [48]. Acute ischemic stroke due to arterial occlusion on non-­contrast head CT typically features the loss of gray-white matter differentiation, followed shortly thereafter by a confluent area of hypodense brain parenchyma representing the vascular territory of a subsidiary artery from the MCA. In the early phase of an MCA distribution infarct, this can usually be observed first at the level of the insula and is called the loss of the insular ribbon sign [49]. When the loss of the insular ribbon sign appears alone, it is caused by occlusion of the M2 segment (insular segment and/or claustral branches) of the MCA, and cortical infarction occurs. The claustrum, external capsule, and the extreme capsule together may be affected in this scenario, as they constitute the insular ribbon, for which the perfusion in this area is rich. However, when the distal M2 segment of the MCA is occluded, this area is prone to hemorrhage due to it having relatively distant collateral flow from the anterior and posterior cerebral arteries. As mentioned earlier in this section, the early CT signs of cerebral infarction (including both direct and indirect signs) include the following: (1) Hyperdense MCA sign: the blood clot can often be observed on non-contrast CT, while for other cerebral arteries or smaller vessels, the sign can be termed the dense artery sign [49]. (2) Obscured lentiform nucleus sign: after vasogenic edema occurs in acute cerebral infarction, the water in the blood vessel “leaks” into the extracellular space, the total water content in brain tissue increases, and thus, its CT value decreases, where obscuration sign of the lentiform nucleus hence appears in the early stage. (3) Loss of the insular ribbon sign: the gray matter-white matter boundary of the insular cortex becomes unclear in early infarction, showing a confluent area of hypoattenuation. (4) The boundary between the cortex and the medulla is blurred (“blurred cortex sign”): the CT Hounsfield units of the cortex are slightly reduced, and the boundary of white

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matter under the cortex along with the cortex is blurred, which can be visible within 2–3  hours of infarct onset; if the infarct size is large (often quoted as being >3 cm diameter), the prognosis is poor. After the lenticular nucleus is blurred, the gray matter-white matter junction of the infarct area may be slightly hypodense on CT and can be visible within 2–3  hours of onset. (5) Disappearance of the sulcus overlying the cortex of an infarct, occurring within 3 hours of onset, and being associated with larger areas of infarction; if appearing alone, this suggests that the infarct is irreversible and that thrombolytic therapy may not be efficacious. Therefore, insular involvement is a well-established early sign of ischemic MCA distribution infarct, whether detected by loss of gray-white matter differentiation on unenhanced CT, or restricted diffusion on DWI. Functional studies have also suggested that the insular ribbon has higher ischemic vulnerability relative to other cortical and deep gray matter brain structures [50].

2.15 T  he Disappearing Basal Ganglia Sign Feature On non-contrast CT of the brain, this sign showed that the normal basal ganglia disappeared, and the affected basal ganglia showed abnormal morphological features. Explanation The normal lenticular and caudate nuclei are slightly higher in attenuation than the surrounding white matter, and they exhibit lower attenuation on CT when ischemia occurs. The volume of a normal cell requires a normal electrolyte concentration and gradient inside and outside of the cell, and cell damage occurs when blood flow is interrupted. Such interruption causes damage to the internal environment, causing an influx of sodium ions, chloride ions, and calcium ions, and thereafter, moisture enters the cells to form metabolic acidosis. This net fluid flow into the cells causes cytotoxic edema and the focal edema noted on CT as hypoattenuation with loss

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Fig. 2.15  A 70-year-old male lacking clear speech for 3 hours. The normal left basal ganglia contour has disappeared on CT, indicating acute infarction

of the distinction of the basal ganglia, which normally are slightly more hyperdense on CT relative to the anterior and posterior limbs of the internal capsules (as the internal capsules normally have a higher concentration of myelin due to their white matter tracts); this cytotoxic edema usually later leads to cell lysis. On non-contrast CT, the low attenuation zone of the basal ganglia at this point is a sign of severe focal ischemia and subsequent infarction (irreversible insult) (Fig. 2.15). Discussion Non-contrast CT remains the primary initial imaging modality for acute stroke presentations because of its fast acquisition and widespread availability, as well as the need to immediately exclude intracranial hemorrhage. CT can quickly differentiate between ischemic and hemorrhagic stroke and can also be used to quantify the extent of early ischemic changes (EICs); DWI can later confirm the acute or early subacute infarct by having a bright appearance on DWI that is accompanied by a corresponding dark signal in that region on ADC maps. Non-contrast CT can be

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reliably used for rapid clinical decision-­making as well as prognostication given a standardized image quality, in order to detect EIC. The disappearing basal ganglia sign is a relatively common manifestation of acute cerebral infarction. This sign is often caused by incomplete or complete occlusion of the middle cerebral artery from vascular thromboembolic disease. Other differential diagnoses leading to such focal basal ganglial cytotoxic edema (also causing reduced diffusion on DWI) include vascular occlusion from arterial dissection, trauma, or rarely vasculitis, while uncommon nonvascular congenital or metabolic disorders can lead to basal ganglial cytotoxic edema, such as mitochondrial disease, encephalitis, or rarely hemolytic uremic syndrome [51]. It is important to detect early ischemic stroke on CT since the lack of early parenchymal hemorrhage or a larger (>3 cm size or 70 cc volume) hypodense region of infarct suggests that the patient may be amenable to thrombolytic therapy, where thrombolytic therapy can improve the patient’s prognosis [52]. Most ischemic cerebrovascular accidents occur in the area of blood supplied by the middle cerebral artery (MCA). The most common cause of cerebral infarction in industrialized countries is thromboembolism. The basal ganglia (of which the lentiform nuclei are part of) are very sensitive to ischemic injury as their blood supply is typically derived directly from small arteries, including the lenticulostriate arteries. The basal ganglia are the deep gray matter structure of the cerebral hemispheres and overall include the corpus striatum (itself composed of the nucleus accumbens of the basal forebrain plus the caudate plus the lentiform nuclei), along with the subthalamic nuclei and the substantia nigra of the midbrain. The lenticular nucleus (lentiform nuclei) includes the globus pallidus and the putamen. Additionally, part of the anterior limb of the internal capsule and the head of caudate are together supplied by the medial lenticulostriate artery, which originates from the A1 segment of the anterior cerebral artery. Notably, the recurrent artery of Huebner is the main branch of the medial lenticulostriate artery, which can be derived from the A1 or A2 segments of the anterior cerebral artery, but

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most often originates from the A2 segment in proximity to the anterior communicating artery. Meanwhile, the lateral lenticulostriate artery supplies the lenticular nucleus, part of the caudate nucleus, and the posterior limb of the internal capsule. The area supplied by these arteries varies in size and number, as there can be from 6–20 lenticulostriate arteries which may overlap in supply; these arteries are located along the upper contour of the M1 segment of the middle cerebral artery. Therefore, the early CT signs of the infarction of the territory supplied by the MCA include the high attenuation of the middle cerebral artery (hyperdense MCA sign), the disappearance of the lenticular nucleus’ border with the insula and Sylvian fissure (insular ribbon sign), a focal unclear margin of cortical gray matter at its junction with subjacent white matter (blurred cortex sign), and the complete disappearance of the outline of the basal ganglia or basal nuclei by the internal capsules (disappearing basal ganglia sign), as well as a lesser degree and more focal loss of the outline of the lentiform nuclei (obscured lentiform nucleus sign, described next).

2.16 T  he Obscured Lentiform Nucleus Sign

Fig. 2.16  On non-contrast CT 2 hours after the appearance of the clinical stroke symptoms, there is initially a normal appearance of the right basal ganglia (a: left image), which appeared resembling the normal left basal

ganglia. One day later (b: right image), the contour of the right lentiform nucleus disappeared. Note that this appears more focal than the disappearing basal ganglia sign, as the overlying right insular ribbon is intact

Feature Obscuration of the lentiform nucleus is a non-­ contrast CT finding of acute cerebral infarction. The attenuation of gray and white matter is decreased due to focal cytotoxic edema within the middle cerebral artery (MCA) distribution. The capsula interna and its inner and outer borders are vague. The most obvious finding is vague edges of the globus pallidus and putamen (which together comprise the lentiform nuclei) due to the decreased attenuation from acute ischemic infarct. Explanation When acute cerebral infarction leads to cytotoxic edema, intravascular water enters into the extracellular space, the total water content of the brain tissue is increased, and the density/attenuation (HU) is decreased on CT. At the same time, the obscured lentiform nucleus sign is seen due to the vessels supplying the lentiform nuclei being small terminal arteries, where the process of infarction accelerates quickly when ischemia occurs (Fig. 2.16).

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Discussion Obscured lentiform nucleus sign can be one of the earliest findings in patients with acute ischemic stroke within the MCA distribution. It occasionally occurs in some patients within the first hour of symptom onset, but mostly (73–92% of MCA distribution infarct patients), it is visible a bit later within the first 6 hours of onset [53]. This sign can be described as decreased attenuation involving the lentiform nucleus (comprises the globus pallidus and putamen) on CT, inducing loss of the precise delineation of this area. The lentiform nucleus is fed by the lenticulostriate arteries from M1 segment of MCA; thus, this sign is seen in patients with M1 segment or distal ICA distribution infarctions. Whether in hyperacute, acute, or subacute cerebral infarction, low attenuation of the affected cerebral parenchyma is one of the most important early changes of infarction. Within 6  hours of onset, the incidence of the obscured lentiform nucleus sign in MCA stroke patients is 92%. Besides this sign, other early non-contrast CT findings of cerebral infarction can be present, which include the following: (1) Hyperdense artery sign: an imaging sign suggesting occlusion of a major cerebral artery, usually the MCA, where the high-density components represent arterial blood clot, thrombus, and embolism. (2) Loss of the insular ribbon sign: the insular ribbon is perfused by the claustral/insular artery which separates the M2 segment of the MCA, and disappearance in graywhite matter boundary may occur early in acute MCA distribution infarction. Notably, the insular ribbon sign and the obscured lentiform nucleus sign have been reported to be relatively common. Both signs are produced by infarction in a specific vascular distribution, which is the middle cerebral artery and its subsidiary branches; thus, evaluating for the presence of either of these early signs can be helpful for the early diagnosis of this disease. Acute ischemic cerebral infarction has usually been defined as occurring within 72  hours of symptom onset. It is generally believed that cerebral infarctions that occur within hours are considered hyperacute cerebral infarctions. There is the need for early diagnosis and determination

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of ischemic penumbra in the pathophysiologic stage of acute cerebral infarction, as thrombolytic therapy for individuals in the effective reperfusion time window can rescue some of the impaired neurologic function from the ischemic penumbra. Non-contrast CT is still considered the preferred first-line imaging examination in stroke, as its purpose is to eliminate cerebral hemorrhage as well as to identify other CT signs of impending cerebral infarction that would preclude thrombolytic therapy [54]. Additionally, CT angiography (CTA) and CT perfusion (CTP) may play an important role in the early individualized assessment of the clinical outcome and can help to guide treatment decisions, via identifying the degree of occluded vasculature or even collateral circulation. Regarding CTP, various tissue perfusion parameters can be used to differentiate reversible from irreversible ischemic brain tissue and to assess tissue at risk. It was reported the measurement of maximum cerebral blood flow of collateral vessels within the Sylvian fissure is a feasible quantitative collateral assessment at perfusion CT.  Maximum cerebral blood flow of ­collateral vessels was associated with clinical outcomes in patients with acute ischemic stroke [55].

2.17 Fogging Effect Feature This sign can be seen on non-contrast CT and MRI but initially is described on CT.  Patients with cerebral infarction initially can have low attenuation on CT or long T1 and T2 signal on MRI; however, in the second and third weeks after infarction, the infarct can become iso-dense on CT or isointense on MRI (usually T1WI and T2WI) to other more normal cortical regions. Explanation Fogging effect is typically noted in the subacute phase of cerebral infarction. In the acute phase, cerebral infarction-related cytotoxic and angiogenic edema can lead to low attenuation on CT or high signal on T2WI.  However, at the beginning of the subacute phase of reabsorption and repair, the edema of the infarcted area decreases,

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the necrotic tissue is being cleared and replaced by macrophages, and astrocytes and endothelial cells proliferate to form new capillaries. Therefore, the water content and cell composition in the area of subacute cerebral infarction return to near-normal levels, so the subacute infarct can appear isodense on CT or isointense on MRI (usually T1WI and T2WI) to other cortical regions, thereby obscuring the region of the infarct. This can cause confusion as to the size of the infarct if the patient is not imaged earlier in the acute phase, particularly on MRI, since DWI can appear “pseudo-normal” at 7–10 days post-­ infarct onset (Fig. 2.17). a

b

d

e

Fig. 2.17 (a, b) A 64-year-old female is admitted to the hospital because of “sudden left limb weakness for over 1  day,” where a non-contrast CT demonstrated low-­ density infarction in the right temporal lobe, insula, and basal ganglia; (b) a non-contrast CT 11 days later in the same patient showed that the area of infarction became less clearly delineated. (c, d) In a 66-year-old female,

Discussion Cerebral infarction is a common clinical cerebrovascular disease. According to the onset time of cerebral infarction, it can be divided into the hyperacute stage (less than 6 hours), acute stage (2–7  days), subacute stage (1–4  weeks), and chronic stage (after 1  month). On non-contrast CT, images obtained at more than 24 hours post-­ onset depict a significant decrease in density of the region of cerebral infarction. Over time, the density will continue to decrease, and the fogging effect occurs at approximately 2–3  weeks. On MRI, low signal on T1WI, high signal on T2WI,

c

f

admitted to hospital because of “hypertension over 2 months, but increased dizziness for the past 3 days,” an MRI showed long T1 (hypo-intense) patches in the left cingulate and occipital lobes, with long T2 (hyper-intense) signal; (e, f) 10  days later, the infarct is not as clearly visible

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and fogging effect at 2–3 weeks were observed in acute cerebral infarction. Becker et al. [56] first described the increase of relative density on CT in the second and third weeks after cerebral infarction in 1979, which has been termed the fogging effect. This feature can be seen in the whole infarct distribution or part of the area; at the same time, it can be accompanied by the disappearance of the space-­ occupying effect. If CT is performed during this period, the diagnosis of cerebral infarction may be missed. At this time, if contrast-enhanced CT is performed, cerebral infarction with fogging effect often shows homogeneous and overt enhancement. Although the contrast resolution of MRI is higher than that of CT, this phenomenon can also be seen in conventional T1WI and T2WI. On MRI, the fogging effect is first reported in 1990 [57]. At present, it is believed that there are two reasons for the fogging effect of MRI: (1) after cerebral infarction, small vascular endothelial cells leak into the necrotic region following the onset of ischemia and hypoxia, and hemoglobin is oxidized to deoxyhemoglobin and methemoglobin; the latter two are paramagnetic substances, which can reduce the signal intensity of T2. (2) At 2–3 weeks after cerebral infarction (subacute phase), the water absorption of necrotic tissue decreases as large number of gitter cells enter the necrotic area, which can also reduce the signal of T2. Similarly, contrast-enhanced MRI in the subacute phase can prevent missed detection by exhibiting avid cortical or parenchymal enhancement. Recent studies have shown that after cerebral infarction, with the passage of time, through the space-specific regulation of neurovascular function by the body itself, the patient’s condition often shows some improvement, with some having even complete recovery, depending on the size and location of the infarct [58]. Therefore, the prompt and accurate diagnosis and treatment of subacute cerebral infarction patients are particularly important. Hence, identifying the fogging effect on CT and MRI, to exclude that a patient’s imaging exam is “normal” on CT and MRI in patients clinically having a cerebral infarction at 2 or 3 weeks. Also, identifying the fogging effect can prevent the underestimation

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of the size of the infarct. Hence, in such cases, attention should be paid to reexamination and the potential of a follow-up contrast-enhancement examination.

2.18 Coarse Flecks of Calcification Feature In the CT image, a curved strip of hyperdense calcification is noted within the tumor. Explanation Calcification begins with smaller blood vessels within the tumor, which create deposits along the tumoral vascular bundle and surrounding tumor tissue, forming a curved banded structure, which is a characteristic CT feature of oligodendroglioma (Fig. 2.18). Discussion Oligodendrogliomas are glial tumors, predominantly occurring in adults. Tumor growth is slow, and the tumor calcification rate is approximately 70–90%, being one of the most prone to calcification in the brain [59]. Notably, any glioma that grows slowly can calcify, where OGs are just one type that may exhibit slower growth; hence, it is understandable that calcification is quite common in these tumors. The calcification of tumors starts from small blood vessels, and the calcification of a certain number of tumor vascular bundles and surrounding tissues leads to the coarse flecks of calcification of the lesions on CT. On CT, many studies report coarse flecks of calcification within the lesion, and as such, coarse flecks of calcification can be a characteristic feature of oligodendroglioma. However, the calcified regions may not be clearly shown within smaller oligodendrogliomas on CT.  On MRI, the calcification may be less prominent or not at all visible and may have variable signal intensity adding to the heterogeneous appearance of the tumor. Also, it has been suggested that c­ alcification is less common in mixed oligoastrocytoma than in pure oligodendroglioma [59]. Their hallmark molecular feature is codeletion of the 1p/19q chromosome arms, which is

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a

b

c

Fig. 2.18 (a–c) Demonstrates a large area of low density, blurred edges, and uneven density in the right frontal lobe, with multiple curved strips of higher density

not only of diagnostic but also of prognostic and predictive relevance. Tumors with the 1p/19q codeletion more commonly show heterogeneous signal intensity, particularly on T2WI, calcifications, an indistinct margin, and mildly increased perfusion and metabolism than 1p/19q intact tumors [60]. Although multimodal MRI of oli-

godendroglial tumors has a lower contribution to 1p/19q genotyping compared with cMRI alone, it greatly improves the accuracy of grading of these neoplasms. Use of multimodal MRI could thus provide valuable information in preoperative management and treatment decisionmaking [61].

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2.19 The Tram-Track Sign Feature The tram-track sign is seen on skull radiographs as gyrus-like, curvilinear, and parallel calcifications. A similar appearance can be seen at CT. Explanation The tram-track sign is produced by cortical calcifications that result from vascular malformations of the leptomeninges, as found in patients with Sturge-Weber syndrome (SWS). The malformations consist of simple vasculature located in the interspace between the pia mater and the arachnoid. A simpler theory suggests that the primary defect in Sturge-Weber syndrome occurs at the early stage of formation of the venous vasculature, when there should normally be a persistent connection between the developing cortical veins (cerebral circulation) and the superior sagittal sinus (dura and calvarial circulation). If this connection does not exist during the differentiation and separation in these two areas of circulation, the venous outflow from the cerebral cortex will be impaired. Finally, the cerebral circulation in the affected areas will be deficient in metabolism, the cortex underlying the areas of leptomeningeal malformation usually becomes dysfunctional,

Fig. 2.19  In a 44-year-old female with Sturge-Weber syndrome (SWS), non-contrast CT (a) shows the typical tram-track calcifications throughout the leptomeninges. On MRI, non-contrast FLAIR (b) shows only focal right

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and thus, the affected parenchyma progressively atrophies and calcifies (Fig. 2.19). Discussion Sturge-Weber syndrome is a rare neurocutaneous syndrome (a phakomatosis) that includes a facial port-wine stain and associated leptomeningeal angiomatosis. Weber demonstrated the characteristic pyriform intracranial calcifications, indicative of the pial venous malformation, leading to the tram-track sign [62]. The diagnosis of Sturge-­Weber syndrome is based on typical clinical symptoms, facial appearance, and characteristic brain MRI findings. Gyriform calcifications can be seen on the skull radiographs and classically described as the “tram-track sign.” CT is the best modality to detect calcifications and show the other changes such as cortical atrophy and leptomeningeal enhancement on the postcontrast studies. However, CT uses ionizing radiation, and the routine use of CT in children is not recommended. Therefore, MRI of the brain with contrast is the recommended imaging modality of choice. The most common locations are occipital and posterior parietal/temporal lobes. The MRI findings depend on the stage of the disease and perhaps the patient’s age as well. In the early phase, there is transient hyper-perfusion

frontal-parietal atrophy, but post-contrast FLAIR (c) illustrates that the leptomeningeal and dural enhancement nearly follows the calcifications noted on CT

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with accelerated myelin maturation, leptomeningeal enhancement (seen as serpiginous enhancement along the sulci), and restricted diffusion (the latter finding if there is associated acute ischemic event). In the late phase, the increased T2 signal is visible in the region of gliosis with decreased pial enhancement and cortical atrophy. There is a lack of superficial cortical veins with prominent deep medullary/subependymal veins and at times an enlarged choroid plexus. Gyriform calcifications (having the “tram track” appearance) are best visualized on T2* or SWI, appearing as areas of signal loss along the gyri in a serpentine pattern. FDG-PET may be another useful modality to study the cerebral metabolism in patients with Sturge-Weber syndrome. The affected area is usually hypermetabolic in the early stages, with hypometabolism in the late stage. PET may be useful in the surgical planning when cortical resection is required for the treatment of intractable seizures. Given the high incidence of epilepsy in patients with SWS, presymptomatic prophylactic treatment has been proposed. A prospective study has shown possible improvement in the cognitive impairment in a group provided with prophylactic treatment, so the use of anti-­seizure drug therapy prior to seizure onset can modify the course of severe epilepsy in SWS patients [63].

2.20 The Tuft Sign

Fig. 2.20  Displacement or compression of the pituitary capillary bed to the left on dynamic post-contrast MRI in what is termed the “tuft sign.” After 30  seconds of gadolinium-­based contrast administration, dynamic coro-

nal T1WI demonstrates the tuft of incomplete enhancement of the pituitary on the right side of the gland (arrow, a), which is confirmed on several minutes delayed post-­ contrast T1WI (arrow, b)

Feature Pituitary dynamic post-contrast coronal CT can show a circular, punctate, or ribbon of intense/ hyperdense shadow in the center of the pituitary gland approximately 10  s after contrast agent reaching the supra-clinoid of carotid artery. When it is replaced or oppressed (the tuft sign), it can diagnose the tiny lesions within the pituitary. This can also be noted on MRI. Explanation Dynamic CT can demonstrate the pressure shift of the pituitary capillary bed (also called the secondary capillary bed), which is also called “the tuft sign,” is an important sign of the diagnosis of microadenoma. Histologically, vascular plexus is vascular sinus formed by many small branches of the hypophyseal-portal vascular system along the stalk at the distal side of the pituitary gland (Fig. 2.20). Discussion The two sides of the long and short portal veins of the pituitary gland are capillary networks. One side is called the primary capillary network, and the other side is called the secondary capillary network. The replacement and compression of

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the capillary bed by a tumor on dynamic CT is known as the tuft sign. This sign is an important feature in diagnosing pituitary microadenoma [64]. The superior hypophyseal arteries, of which the trabecular arteries are among the most important branches, arise from the supra-clinoid internal carotid and posterior cerebral arteries, while the inferior hypophyseal artery arises from the cavernous internal carotid artery and anastomoses with its counterpart on the opposite side to form a ring around the infundibular process of the neurohypophysis. Components of the inferior and superior hypophyseal arterial systems anastomose freely. While the epithelial tissue of the pars distalis receives no direct arterial blood, the superior hypophyseal arteries supply the median eminence and the infundibulum. The capillary bed extending through these two structures is drained by portal vessels of various lengths which open into vascular sinusoids lying within the anterior lobe of the pituitary gland. These sinusoids constitute the secondary plexus of the pituitary portal system. The portal system is of great functional importance, since it carries hormone-­ releasing factors that control the secretory cycles of the adenohypophysis. Displacement or compression of the pituitary capillary bed on dynamic CT or MRI is what we term the “tuft sign,” being an important feature in the diagnosis of pituitary microadenomas [65]. The secondary hypophyseal capillary bed becomes visible on dynamic CT and can begin to appear approximately 10 seconds after optimal opacification of the supra-clinoid carotid arteries, appearing as a rounded vascular tuft in the midline (just anterior to the pituitary stalk) and generally 3–4 mm in diameter, although occasionally smaller in caliber. Rarely, the capillary bed is spread along the upper surface of the gland, where it appears as a horizontal, band-like density/intensity. The density-intensity of this vascular structure is greatest approximately 20 seconds after optimal opacification of the carotid arteries or 40  seconds following the beginning of the contrast administration. Thereafter, the density-­ intensity of the vascular tuft progressively diminishes, while the pituitary gland enhances in a centrifugal fashion. Approximately 80  sec-

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onds after the beginning of the administration, pituitary enhancement is homogeneous, and the hypophyseal capillary bed is no longer visible [65]. Notably, the cavernous sinus enhancement on coronal MRI or CT occurs very soon (usually several seconds) of the cavernous internal carotid artery enhancement. MRI is the first choice for sellar and parasellar pathologies due to its ­superior soft tissue contrast, multiplanar capability, and lack of ionizing radiation. MRI also provides useful information approximately the relationship of the gland with adjacent anatomical structures and helps to plan medical or surgical strategy. Dynamic contrast MRI has been proven to be the best imaging tool in evaluating pituitary adenomas [66].

2.21 The Infundibulum Sign Feature On thin-section non-contrast or contrast-­ enhanced CT or MRI of the sella, the pituitary stalk is situated within the enlarged sella, being the infundibulum sign. Explanation The infundibulum sign is the manifestation of an empty sella, partially empty sella on coronal CT or MRI, where the sellar fossa is filled with CSF that has water-like attenuation on CT and CSF signal on MRI, while the pituitary stalk with soft tissue density/intensity can be displayed within the enlarged bony sellar fossa. Because of the enhancement of pituitary stalk after intravenous administration of contrast, the contrast between the pituitary stalk and surrounding CSF increases and becomes clearly displayed (Fig. 2.21). Discussion The term empty sella refers to the sella being occupied by the subarachnoid space. The pituitary tissue either atrophies or is displaced or compressed and flattened to the posterior and inferior part of the sellar base. This entity is present in about 5–10% of the population, may be associated with clinical symptoms in the minority (approximately 20–40%), and is thought to

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a

b

c

d

Fig. 2.21  In a patient with an empty sella, the pituitary stalk in an enlarged sella can be seen on coronal enhanced CT (a), suggesting that the infundibulum sign is positive. On 3.0  T MRI in another patient who is a 28-year-old

female (b–d), similar findings are noted on pre-contrast sagittal T1WI (b), T2WI (c), and FLAIR (d), where the signal surrounding the infundibulum follows CSF bright signal on T2WI and suppresses on FLAIR

have a higher incidence in obese patients, hypertensives, and in women, particularly those with multiple pregnancies [67]. An empty sella can be classified as primary and secondary according to the cause of disease. The former has no obvious etiology, which may be related to congenital sellar diaphragm development variation, CSF circulation disorder, and other factors. The latter is secondary to intrasellar or parasellar surgery, radiotherapy in sellar region, pituitary apoplexy, and intrasellar tumors [68]. Thus, an empty sella may or may not be symptomatic, which depends on the degree of sellar enlargement, pituitary displacement, and size of the pituitary gland. As such, the milder form, aka partially empty sella, is usually not symptomatic. In addition to empty sella, there can be solid or cystic masses that involve the sella, such as arachnoid cyst, cra-

niopharyngioma, Rathke cyst, pituitary adenoma, and third ventricular diverticulum in sella; the most common to be confused with the empty sella is the arachnoid cyst, since both have CSF signal. In addition to the diagnosis of a symptomatic empty sella, imaging of an empty sella is often more important to exclude occupying lesions in the sella, because the latter can cover the pituitary stalk, resulting in the infundibulum sign being negative [69]. Haughton et  al. have opined that if the infundibulum sign is positive, it strongly suggests an empty sella. At the same time, the negative infundibulum sign does not rule out the diagnosis of an empty sella or partially empty sella. As such, there are many possible reasons for a negative infundibulum sign occurring, including a slim pituitary stalk or pituitary hypoplasia, weak enhancement of the pituitary stalk,

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motion artifact, poor tissue contrast and spatial resolution, and too thick of a slice acquisition, or even the plane of imaging. In addition, the displacement of the pituitary stalk can also lead to a negative infundibulum sign [70]. MRI has the advantages of high resolution of soft tissue, no skeletal artifacts, and multidirectional, multiparameter imaging. It also has high accuracy in the diagnosis of an empty sella, particularly if utilizing isotropic imaging with 3D reconstructions. Generally, non-contrast MRI can make a definite diagnosis, and it has advantages in differentiating empty sella from space-­occupying lesions of the sella. If CT demonstrates an enlarged sella and a negative infundibulum sign, further examination by MRI should be performed.

2.22 Target Sign Feature On cerebral contrast-enhanced CT, there are central, punctate, calcified, or spotted intracerebral ring-enhancing lesions, being called “target signs.” Explanation Target sign is the feature of a mature tuberculoma on post-contrast brain CT, characteristically with focal punctate lesions in the center. Histologically, the circular zone of enhancement corresponds to the fibrous capsule containing inflammatory cells. The non-enhanced zone corresponds to caseous necrosis, where the mechanism of central spot enhancement is unclear (Fig. 2.22). Discussion Intracranial tuberculosis is caused by the spread of tuberculosis from other parts of the body via the blood. The primary TB lesions are more common in the lungs and may also be extrapulmonary tuberculosis such as lymph nodes, digestive tract, bones, and kidneys. The disease can also be secondary to remote primary infections that have not been noticed, as they occurred many years prior. The primary lesion in the lung may be small, the conventional X-ray finding may not be easy to show, and X-ray positive rate is only

Fig. 2.22  A 16-year-old female presented with a target sign in the right cerebellar hemisphere, later proven to be a tuberculoma

30%. It has been reported that approximately 10% of tuberculosis patients can be combined with central nervous system tuberculosis, and its incidence is directly proportional to the infection rate of tuberculosis. With the increase in human immunodeficiency virus (HIV) infection in recent years, central nervous system tuberculosis has gradually increased in prevalence in developed countries, and the central nervous system of HIVinfected people is more susceptible to infection by Mycobacterium tuberculosis. Brain tuberculosis is a rare form of intracranial tuberculosis. It refers to a tuberculous granulomatous lesion that induces mass effect within the brain parenchyma. Typically, M. tuberculosis spreads via the blood to the brain parenchyma or, alternatively, via the CSF along cortical veins and small penetrating arteries that penetrate the brain parenchyma. The diameter can be a few millimeters to 8 cm, round or ovoid, or lobulated, via the fusion of multiple smaller nodules. Cerebral tuberculosis can occur at all ages in developing countries, more commonly in children and younger people, while in developed countries, it occurs mainly in adults. Cerebral tuberculosis can have multiple or single/solitary lesions, with differing reports regarding the incidence of the multiplicity of lesions within the literature.

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The CT features of brain tuberculosis are varied, and non-contrast examinations can have iso-­density (to cerebral parenchyma), high attenuation, or low-mixed attenuation; can be single or multiple, round, or lobulated; can have mass effect; and are often with moderate to severe edema surrounding the lesion. On postcontrast-­ enhanced examinations, the lesions usually show ring enhancement, homogenous or inhomogenous nodular enhancement, and a minority of lesions do not enhance. The ring-enhancing lesions are mostly continuous, thick, and thin and have smooth or irregular edges. The tissues in the ring are close to the attenuation or low attenuation of brain tissue, and few of them are calcified. Among them, the small circular enhancement with the central point-like translucent area is called the micro-ring sign. In 1979, Welchman [71] first reported an enhancing CT examination of four cases of cerebral tuberculosis, including three cases of central point calcification with ring enhancement, and one case of central point enhancement with ring enhancement; thus, the target sign is considered characteristic of cerebral tuberculosis. The results of van Dyk’s [72] study supports this conclusion, where lesions having target signs occurred mainly in children, were less associated with tuberculous meningitis, and were more sensitive to drug treatment. On follow-­up CT, the lesions could disappear completely or significantly, and the mortality is low, with a good prognosis. The tuberculosis necrotic material in the tuberculoma center may appear calcified, forming a “target sign,” but the sign is not characteristic, as the same feature can also be seen in other granulomatous infectious diseases, such as cerebral cysticercosis and toxoplasmosis. Different degrees of vasogenic edema can also occur in tuberculomas, being caused by allergic reactions caused by tuberculosis, where the degree also reflects the activity of the lesion. The diagnosis and treatment of brain tuberculoma remain a big challenge even today. With the development of imaging technology, CT perfusion and MRS technology could be more helpful for the early diagnosis of intracranial tuberculomas [73].

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2.23 B  lack Target Sign and White Target Sign Feature MRI findings of neurocysticercosis (NCC) often show small round cystic lesions, having a size of 4–6 mm, with T1-dark signal that has a spotlike appearance of bright/enhancing T1-bright signal, which is the black target sign; on T2WI, the white target sign is the focally central T2-dark signal within the larger area of bright/white high signal on T2WI. Explanation The scolex of cysticercus cellulosae manifests punctate high signal on T1WI and lower signal than CSF on T2WI in the early vesicular stage and colloidal-vesicular stage (Fig. 2.23). Discussion Neurocysticercosis (NCC), the central nervous system form of cysticercosis, is caused by larvae of the tapeworm Taenia solium and is commonly associated with seizures, headache, and focal neurologic deficits. The MR imaging evolution of parenchymal NCC lesions recognizes four stages: vesicular, colloidal vesicular, granular nodular, and nodular calcified [74]. The imaging findings in neurocysticercosis vary with the stage of cyst development. The early vesicular stage is typified by a smooth thin-walled cyst that is CSFlike on MR image. Edema and contrast enhancement are rare. A mural nodule is often present that represents the viable larval scolex, the “cyst with a dot” appearance. When cyst degeneration begins (colloidal-vesicular stage) and the host inflammatory response ensues, pericystic edema and cyst wall enhancement are present. Cyst fluid appears hyperintense to CSF on MR images during this stage. In the healing, or granular nodular, stage, nonenhanced CT show an iso-attenuated cyst with a hyper-attenuated and calcified scolex. Surrounding edema is still present, and enhancement following contrast administration persists. The residual cyst is isointense to the brain on T1-weighted images and it is iso- to hypo-intense on T2-weighted images. A nodular or micro ring

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a

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b

Fig. 2.23  In this patient, there is high signal centrally within black/lower signal intensity on T1WI (a), which is the “black target sign”; the “white target sign” is shown as

the T2-darker focus within the larger area of bright/white hyperintense signal on T2WI (b)

of enhancement is common at this stage, suggesting granuloma. In the quiescent or residual stage, small calcified nodules without mass effect and usually without enhancement are seen. Notably, multifocal lesions and lesions in different stages of development are common [75]. The diagnosis of NCC is complicated, and neuroimaging is frequently required for a definitive diagnosis. Currently, there are no standard treatment guidelines for NCC, and treatment is tailored to individual cases, depending on factors such as the location and viability of the cysts. Therapeutic approaches might include symptomatic therapy, anthelmintic treatment, or surgery, and often more than one of these options is needed [76].

tiple lobulations/loculations; the rings can differ in size, while the angle of adjacent rings is sharp. Other names are large ring–small ring sign and multilocular sign.

2.24 Multilocular Ringlike Enhancement

Discussion The multilocular ringlike enhancement is seen during the formation of the brain abscess and is a specific sign of a brain abscess. The pathological basis is the collapse of the weaker area of the abscess wall, with the spread and limitation of inflammation leading to the formation of walls

Feature On post-contrast CT or MRI, the wall of a multilocular brain abscess is well circumscribed, with multiple circular or oval rings connected of mul-

Explanation Granulation tissue is formed around the lesion during the capsule stage of a brain abscess. If the wall/border is not complete, there will be a smaller subordinate lesion (sub-lesion) around the lesion, where a new abscess is eventually formed by the sub-lesion. In CT or MRI postcontrast examinations, the wall of the abscess significantly enhances, forming numbers of interconnected rings of the same size or different sizes (Fig. 2.24).

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a

b

c

d

e

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Fig. 2.24 (a, b) Post-contrast CT shows the lesion located in the left frontal lobe. Multiple elliptical rings were found to be connected to each other. (c, d) Post-­ contrast T1WI shows multiple ring-enhancing lesions in

the left cerebellar hemisphere, and the size of the rings varies, and they are interconnected. (e, f) Post-contrast T1WI shows multiple interconnected high signal rings of the left frontal lobe, where the size of the rings varies

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of sub-abscesses. According to the pathophysiology of the disease, the pathological changes can be divided into two periods: encephalitic period and capsular period. Acute encephalitis consists of inflammatory cell infiltration, with brain tissue softening, liquefaction, and necrosis that ultimately forms the abscess cavity. The development of the abscess typically occurs over 2 weeks to a few months. The surrounding abscess wall is a membrane formed by the proliferation of granulation tissue. It is sometimes accompanied by a wide surrounding rim of edema, causing significant mass effect [77]. The lesion is typically located at the deepest portions of gray-white matter junction. The brain abscess subring occurs mostly within the white matter side of the lesion, with the theoretical reason being that the blood flow on the white matter side is less than the cortical side, with the white matter’s granulation tissue being less, so the ring’s wall is relatively weak and thus is easier to break. Post-contrast in a multilocular abscess usually demonstrates a rim-enhancing collection connected with one or several small rings or several rings of similar sizes. The ring is usually round or oval in shape, and the angle with the adjacent ring is sharp, which is a distinguishing feature of multilocular brain abscesses. Ring enhancement of the wall of brain abscess represents granulation tissue; the formation of granulation tissue is related to the number of new blood vessels. The blood flow of cerebral cortex is three to four times more than white matter subjacent to the cortex, the terminal granulation tissue is thicker, and the deep portion is relatively thin, so the spread of inflammation is located in the deeper portion of an abscess and the formation of sub-lesion is also often located at that site. Thus, an abscess can extend deep into the brain and form a pocket-like structure. In the encapsulation period of a brain abscess, granulation tissue forms the wall. If the encapsulation is incomplete, the abscess may break through the defect area and form a sub-abscess beside it. In post-­contrast CT or MRI, the weak area of the abscess wall forms a localized defect, and the adjacent lesions communicate with each other via a gap, forming a sinus sign. When the

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abscess wall between the two connected rings is locally absorbed and the ring wall is incomplete, a deep ring wall incisural appearance is formed. The imaging features of brain abscesses are typical, but they still need to be differentiated from metastatic tumors or gliomas, which are also in the differential for rim-enhancing lesions of the brain [77]. Patterned-approach in the form of flowcharts for the purpose of quick reference is intended as a guide to radiologists for quickly narrowing the list of differentials when faced with a clinical challenge [78].

2.25 Hoop Sign and Popcorn Sign Feature On T2WI or SWI sequences, the low signal ring around the lesion in the brain parenchyma is termed a hoop sign, where the blooming effect of the hypo-intense ring widens gradually with the increase of time. The popcorn sign is similar, where the dark periphery is related to susceptibility/blooming effect on T2WI (sometimes T1WI) with a slightly brighter center of the lesion. Explanation The hoop sign is the MRI finding of a cavernous hemangioma in the brain parenchyma, where the low signal ring surrounding the lesion is caused by the accumulation of hemosiderin around the lesion, as a result of repeated, small amounts of chronic bleeding. The hemosiderin ring causes blooming effects from susceptibility, which are most prominent at the periphery of the cavernoma (Fig. 2.25). Discussion “Hoop sign” and “popcorn sign” are MRI manifestations of cavernous hemangiomas within the brain parenchyma, characterized by a low signal ring around the lesion, which gradually widens over time and can be seen in all sequences, but it is most apparent on T2WI, GRE T2*WI, and SWI.  The low signal ring around the lesion is caused by the accumulation of hemosiderin around the lesion, as a result of repeated and small amounts of chronic bleeding. The low signal may

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Fig. 2.25 (a–c) In a 43-year-old male, axial T2WI (a) showed a centrally hyperintense lesion in the right cerebellum with a hypo-intense, lower signal ring surrounding the lesion, measuring 10  mm transverse diameter (i.e., representing a “hoop sign” or “popcorn sign”). On MRI with coronal GRE T2*WI (b), the lesion has a greater degree of blooming (arrow), and measured 13 mm trans-

verse diameter; on SWI (c) the lesion measures 16  mm transverse diameter, demonstrating how susceptibility effects can change the apparent size of the lesion. Also, the presence of a large amount of susceptibility effect on B and C obscures the centrally hyperintense region, so the hoop and popcorn signs are not as evident

magnify, extend into the adjacent brain parenchyma when imaged with GRE and SWI due to the “blooming effect” of hemosiderin, effectively increasing the apparent size of the lesion [79], and make the signs more obvious. The presence of this susceptibility effect may make the lesion appear larger on T2WI, GRE T2*WI, and SWI, respectively (i.e., SWI may slightly overestimate the size of the lesion if there is a large amount of hemosiderin deposited). A cavernous angioma (aka cavernoma or cavernous hemangioma) is not a true tumor. It is one of the low-flow congenital vascular malformations and accounts for 5–13% of intracranial cerebrovascular malformations [80]. It can occur in any part of the brain, where a single focus is obviously more common than multiple. The imaging manifestations of cavernous angiomas are closely related to its pathological structure and evolution process. The main imaging basis of a cavernous angioma is caused by slow blood flow, deposition of hemorrhagic components in different stages following repeated hemorrhages, and secondary pathological changes such as thrombosis, calcification, and gliosis. The characteristics of the MRI

signal primarily depend on the timeline of intratumoral hemorrhage. Repeated small amounts of hemorrhage are the main factor for the formation of MRI features such as the “hoop sign” or the “popcorn sign.” When macrophages are dissolved and hemosiderin is deposited around the lesion, a ring-shaped low signal around the lesion can occur, which is an identifying characteristic. The typical MRI images of typical cavernous angioma are as follows: (1) lesions show different degrees of mixed-signal clusters; (2) hoop sign is a rounded low-signal ring in the outer circumference of the tumor, which is black in all imaging sequences, being most evident on T2WI and SWI; (3) reactive gliosis has long T1 and long T2 signal (i.e., dark on T1WI and bright on T2WI); (4) there is no brain tissue edema and no obvious space-­ occupying effect around the tumor; (5) the lesion enhances with intravenous contrast to varying degrees. MRI is the preferred method of examination for cavernomas, especially with GRE T2*WI and SWI sequences, where the SWI sequence is optimal, as it can detect likely double to triple the number of cavernomas, if multiple [80]. The use of high field MRI can further

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improve the detection of cavernomas by SWI. In addition, SWI is superior to GRE in the screening of multifocal familial cavernomatous malformations. Compared with GRE, SWI can also better delineate the lesion edge and improve the sensitivity in the setting of familial cavernous angiomas. SWI is especially useful in screening for suspected cavernous angiomas to help solidify the clinical diagnosis.

2.26 Ivy Sign Feature On T1WI post-contrast images and FLAIR images, the signs appear as linear high-signal shadows that are continuous or discontinuous along the sulci and subarachnoid space. Explanation The ivy sign is seen in Moya-moya disease, from diffusely prominent leptomeninges akin to ivy crawling along stones. This characteristic appearance of enhancement arises from the filling of the leptomeningeal reticular formation following chronic internal carotid artery (ICA) and/or anterior cerebral artery (ACA) and middle cerebral artery (MCA) occlusions; i.e., chronic anterior circulation occlusion near the ICA terminus. The reason for the high signal of the soft meninges on the FLAIR image is more complicated. It is probably due to the slow blood flow of the leptomeninges attempting collateral flow, and the hyperemia of the leptomeninges is also one of the reasons for the high signal on FLAIR images (Fig. 2.26). Discussion The “ivy sign” described in MDD is a finding on postcontrast MRI images. This finding is described in both post-contrast T1WI and FLAIR images. On post-contrast T1WI images, the ivy sign is prominently found along the cortical surfaces and potentially partially within the sulci, due to the development of leptomeningeal collaterals, via an increased number of leptomeningeal vascular network formations. The signal increase within or along the sulci may also be evident to

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a lesser degree on non-contrast FLAIR, which originates from the slow arterial flow of the leptomeningeal collateral vascular structures. This leptomeningeal formation is prominent along the cortical surface and resembles ivy growing on a rock and, thus, this appearance is termed the “ivy sign.” Moya-moya disease (MDD) is an idiopathic disease characterized by progressive stenosis and collateral development of the distal internal carotid arteries. It is observed as being 1.8–2.2 times more common in women than in men. Bimodal age in MDD has been reported to show high peaks at ages over 5 years’ and lower peaks at the age of 40  years. MDD shows different clinical features in children and adults. While it typically presents with subarachnoid and intraparenchymal bleeding in adults, in children, it presents with transient ischemic attacks with infarcts developing predominantly in the frontal lobe. The typical symptoms in children include monoparesis, hemiparesis, aphasia, and dysarthria. Studies evaluating the ivy sign on FLAIR MRI in pediatric patients with MMD showed a strong positive correlation between the hemispheric TIS and the severity of the clinical hemispheric symptoms. Also, a change in postoperative ivy sign appearance can be an indicator of effective cerebral reperfusion in MMD [81]. Hence, the prominence of leptomeningeal enhancement overall appears to relate to the degree of collateral perfusion, which is a current focus of research involving dynamic CT and MR perfusion and CT and MR angiography. The implementation of arterial spin labeling (ASL) in a clinical setting and the development of ASL can be considered to have become mature and ready for clinical prime time. Quantification of ASL as well as on new technological developments of ASL for perfusion imaging and flow territory mapping is the current focus [82].

2.27 Butterfly-Like Lesions Feature The white matter around the trigone of the lateral ventricle is symmetrical with a large area of

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a

b

c

Fig. 2.26 (a) Enhancement in an ivy-like fashion (arrows) along the leptomeninges of the frontal sulci on post-contrast T1WI, (b) FLAIR post-contrast images demonstrating a similar appearance as in a. (c) CTA of the head showed occlusion of the right internal carotid artery

and stenosis and occlusion of the lumen of bilateral anterior cerebral artery, proximal middle cerebral artery, and proximal posterior cerebral artery. Multiple hyperplastic vascular network formation can be seen around, typical of Moya-moya disease

reduced attenuation on CT. It has long T1 (dark) and T2 (bright) signal on MRI; the lesions on both sides are connected by the compression of the corpus callosum, with a “butterfly-like” distribution.

Discussion Adrenoleukodystrophy (ALD) is an X-linked recessive hereditary disease that mainly affects the white matter and adrenal glands and is the most common form of leukodystrophy. The disease is mainly seen in children, albeit occasionally in adults, where affected patients are almost all male and females are typically carriers (heterozygous). They may exhibit symptoms of neurologic deficits, mainly manifested by spinal

Explanation Butterfly-like lesions are typical signs of CT/ MRI in children type with adrenoleukodystrophy (Fig. 2.27).

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system tissues [85]. Most patients with cerebral adrenoleukodystrophy die within a decade after they receive the diagnosis if they are not treated with hematopoietic stem-cell transplantation. The children with ALD have characteristic MRI features, where MRI depicts lesions better than CT.  The lesions have low signal on T1WI and high signal on T2WI. The high signal pathologically represents the areas of myelin loss (demyelination) and vasogenic edema. The post-­contrast enhancing regions on MRI or CT correspond to the areas of active demyelination (so-called leading edge) and are characterized by peripheral enhancement. The “butterfly” lesions on MRI show a clearer distribution, best depicted on FLAIR or T2WI. The lesions are distributed along the nerve conduction bundle, and the lesions on both sides are connected by the corpus callosum; typically, involvement begins Fig. 2.27  A 8-year-old boy with bilateral temporal-pari- in the splenium of the corpus callosum. In the etal-occipital lobe adrenoleukodystrophy on FLAIR MRI majority of patients, as the disease progresses, has a symmetrical distribution of T2-hyperintensity postethe demyelinating lesions spread from posterior riorly in the cerebrum, resembling a “butterfly” shape to anterior, and the white matter region of the parietal lobes gradually migrates to the temporal cord involvement or mild pyramidal signs and lobes, basal nuclei, and frontal lobes and diffuses urinary disorders. ALD is usually divided into downward to affect the brain stem. The aforefour types: children, youth, adults, and adreno-­ mentioned appearance of posterior-predominant myeloneuropathy. Allogeneic transplantation is involvement is present in the majority (80–90%), the only effective therapy for cerebral adreno- whereas the minority (15–20%) have anterior leukodystrophy that has been identified to date, predominance affect the genu of the corpus caland it is more likely to be effective if it is per- losum and periventricular white matter and sparformed at an early stage of neurodegeneration. ing structures posteriorly in the early stages. In Gene therapy with autologous hematopoietic the advanced stage, the lesions have much lower stem cells has been investigated as an alternative T1WI signal and brighter T2WI signal, and at the to allogeneic hematopoietic stem-cell transplan- late stage do not enhance on postcontrast T1WI, tation [83]. Early results of this study suggest with resultant brain atrophy. Small calcifications that Lenti-D gene therapy may be a safe and may occur, which are not easy to visualize on effective alternative to allogeneic stem-cell trans- MRI.  Of note, recent research using advanced plantation in boys with early-stage cerebral adre- MR imaging, including MR perfusion, and difnoleukodystrophy [84]. Adrenoleukodystrophy fusion tensor imaging (DTI) have shown that is an X-linked genetic disease that is caused by the pretreatment (i.e., preceding transplantation) a defect in the gene ABCD1, which encodes the Loes score measured on FLAIR/T2WI, the MRP peroxisomal ABC half-transporter ALD protein. scores of the splenium, and certain DTI measures Mutations in ABCD1 result in abnormal break- may predict the eventual patient outcomes [86, down of very-long-chain fatty acids, a process 87]. In addition to adrenal leukodystrophy, butthat predominantly affects adrenal and nervous-­ terfly lesions can also occur when central nervous

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system lymphoma involving the corpus callosum and spreading to the bilateral hemispheres. Butterfly lesions can also occur when gliomas originating in the corpus callosum invade the cerebral hemispheres on both sides or when one side of the cerebral hemisphere glioma invades the contralateral cerebral hemisphere through the corpus. However, in the setting of such “butterfly” lesions of high-grade gliomas, or alternatively tumefactive demyelinating lesions (i.e. multiple sclerosis), the edema and accompanying enhancement is usually overt and pronounced, whereas edema and enhancement may be lacking in ALD, and the cerebrum may actually be significantly atrophied in cerebral ALD.

2.28 The Mount Fuji Sign Feature The mount Fuji sign is seen on CT scan as bilateral subdural low density cause compression and separation of the frontal lobes, the gaseous tension on both sides make the frontal lobes move back and the frontal lobes collapse and the ­interhemispheric space between frontal parietal lobe expand,which looks like the Fujiyama (in Japan). Explanation The low-density shadow is caused by the entry of air into the skull, the condition caused by the iatrogenic or non-iatrogenic disruption which makes the skull base or calvaria rupture. The tension pneumocephalus leads to increased air pressure within the subdural space. The increase of air pressure is resembling the principle of ball valve, air enters the subdural space through the skull base or cranial fissure, and the way out is blocked. Increased pressure leads to occupying effect and compression of the frontal lobes. The presence of air between the frontal-parietal lobe suggests that the pressure of the air is at least greater than that of the surface tension of cerebrospinal fluid between the frontal lobes (Fig. 2.28). Discussion The Mount Fuji sign on CT of the brain is useful indiscriminating tension pneumocephalus

Fig. 2.28  A 71-year-old-woman. Axial CT scan demonstrating a massive accumulation of air compressing the frontal lobes

from non-tension pneumocephalus. Tension ­pneumocephalus can be a neurosurgical emergency, unlike non-tension pneumocephalus. Tension pneumocephalus occurs most commonly after the neurosurgical evacuation of a subdural hematoma. The prevalence of tension pneumocephalus following the evacuation of chronic subdural hematomas has been reported from 2.5% to 16%. Tension pneumocephalus can also occur as a result of skull base surgery, paranasal sinus surgery, posterior fossa surgery in the sitting position, or head trauma. To diagnose tension pneumocephalus, the CT findings should correlate with clinical signs of deterioration [88]. Pneumocephalus is most easily diagnosed on CT, which can detect quantities of air as low as 0.5  ml. Air appears dark black (that is, darker than CSF) with attenuation values of −1000 Hounsfield units and will have a different distribution pattern depending on the localization. Depending on the underlying cause, the intracranial air can be distributed in the epidural space, subdural space or subarachnoid space, intraventricular or intracerebral, or a combination of these [89]. Tension pneumocephalus treatment includes a complex of manipulations directed to removing of intracranial air mass effect, adequate skull base defects closure, and

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secondary posttraumatic meningitis prophylaxis. Initial treatment is usually conservative, including bed rest in an upright position, high concentration oxygen, avoidance of maneuvers that might increase intra-sinus pressure (such as nose-blowing or valsalva maneuver), and antibiotics if there is evidence of meningism. Surgical treatment is indicated when there is recurrent pneumocephalus or signs of increasing ICP suggesting the development of tension pneumocephalus. Surgical options include direct insertion of a subdural drain connected to underwater seal or, indirectly, with the use of a salineprimed Camino bolt [90].

2.29 The Eye of the Tiger Sign Feature When the eye of the tiger sign is found on T2WI MRI, it shows significant hypo-intensity in the globus pallidus bilaterally. In the center of the hypo-intensity area, a hyperintensity area is visible on the anterio-medial side of the globus pallidus, which is a tiger-eye appearance.

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Explanation The eye of the tiger sign is most common in pantothenate kinase-associated neurodegeneration, or PKAN (formerly called Hallervorden-Spatz syndrome). The significant ring-shaped hypo-­ intensity on T2WI in the globus pallidus is due to excessive iron deposition (Fig. 2.29). Discussion PKAN involves extrapyramidal dysfunction and a pathological triad (i.e., iron deposition, axonal globules, and gliosis of the globus pallidus). PKAN is a familial (autosomal recessive) neurodegenerative disorder in children that is characterized by stiffness, dystonia, disruption of standard reflexes, and progressive dementia. Mutations in the pantothenate kinase gene (PANK2) have been reported to be the cause of the neurodegeneration, at the chromosomal locus 20p12.3-p13 [91]. The pantothenate kinase is quite metabolically active in the mitochondria, and this enzyme is also vital in producing the molecule coenzyme A. In patients with PKAN, the iron deposits increase pathologically and rapidly disproportionate to

Fig. 2.29  Axial T2WI (a) of a 49-year-old female with giving an eye-of-the-tiger sign (arrows). On SWI (b), worsening tremors showed bilateral symmetrical hypo-­ there is quite prominent iron deposition in that location intensity in the globi pallidi with central hyperintensity,

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the patient’s age, while iron levels in the blood adolescents, or young adults, such as with PKAN and CSF remain normal. Superparamagnetic or INAD, this distinction in the degree of iron iron materials (such as ferritin) have unpaired deposition for age should not be difficult, parelectrons, which can lead to increased mag- ticularly on SWI. netic sensitivity and hypo-intensity on T2WI. Thus, the central hyperintensity in the globus pallidus is caused by gliosis, increased water 2.30 Aura Sign content, and disintegration of neurons and formation of neurofibrous reticulum vacuoles, and Feature central T2-hyperintensity of gliosis/edema is The aura sign can be seen on T1WI or post-­ surrounded by the T2-dark signal of the acceler- contrast T1WI, showing a bright ringlike high ated iron deposition in the globi pallidi. The eye signal around the head of the patient. of the tiger sign is the most common manifestation of PKAN, but it can also be seen in other Explanation extrapyramidal Parkinson’s diseases and other When using clay or black beeswax to design disorders of neurodegeneration from brain iron curly hair or long hair strands, the iron oxide accumulation (NBIA’s), including cortico-basal content in clay or black beeswax can cause paraganglion degeneration, early-onset levodopa-­ magnetic effect. In MRI, T1WI or post-contrast susceptible Parkinson’s syndrome, Steele-­ T1WI shows a bright ring high signal. Therefore, Richardson Olszewski syndrome (progressive the aura sign is a kind of hair artifact in fact. supranuclear paralysis), multisystem atrophy, neuroferritinopathy, aceruloplasminemia, Discussion Kufor-­Rakeb syndrome, infantile neuroaxonal Duncan [94] first reported the aura sign of MRI dystrophy (INAD), and Woodhouse-Sakati syn- in 2001. He believed that this kind of hair artifact was related to national culture. It was mainly drome, to name a few. Before the appearance of MRI, the diagnosis seen in women of southern African tribes, especould only be suspected by clinical data, and the cially female healers, who often wove their hair final diagnosis is dependent on autopsy. CT can with a local brown-red fabric made of clay, only show nonspecific changes such as striatal because the ochre clay contained a large amount atrophy and globus pallidus mineralization [92]. of iron oxide. The obvious paramagnetic effect However, MRI with gradient-echo T2*WI or even was formed around the skull, which made the better, SWI, can demonstrate the findings well; T1-weighted image of the patient show a bright the eye of the tiger sign on MRI can solidify the ring around the skull. McKinstry et al. [95] had diagnosis of PKAN or other NBIAs. As a certain also seen similar artifacts of MRI caused by degree of normal iron deposition occurs with hair. Curly or long-haired hairstyles are popuincreasing patient age, one way to discriminate lar among black American groups. Hairstylists PKAN and other NBIAs from normal elderly use colorless beeswax or black beeswax colored patients is the degree and location: the globus with iron oxide, which can cause paramagnetic pallidus in adults and elderly should have more effects due to the iron oxide contained in black than the surrounding portions of the lentiform beeswax. Therefore, the curled hair of these nuclei and the caudate nucleus; if the caudate patients showed annular high signal artifacts nucleus and lateral lentiform nucleus (the puta- on MRI images. Most radiologists know that men) are darker than the globus pallidus, then iron-­containing pigments used in eye makeup NBIA is a consideration [93]. Note: the putamen can cause MRI artifacts, but they do not know and dentate nuclei can appear nearly as dark as much about the aura sign, because they have the globi pallidi in the elderly at 70-plus years’ certain characteristics of ethnic and geographiage, so clinical correlation may be necessary, to cal distribution, so radiologists should also know evaluate other structures. However, in children, something about it [96]. While the ferromag-

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netic properties of metallic objects, implantable medical devices, and cosmetics are well known, sand is not generally considered a consequential substance. Beaches in specific geographic regions have a propensity for ferromagnetic sand because of their geologic history. MRI facilities in areas where ferromagnetic sand is found consider educating technologists and screening patients for recent black sand exposure prior to scanning [97].

2.31 Basilar Artery Encasement Sign Feature Brain stem tumors can protrude forward into the prepontine region and encase basilar artery. When this occurs, it may have the shape of a circular or linear with low density or low signal shadow on transverse or sagittal sections of CT or MRI. Explanation Larger brain stem tumors or tumors originating from the anterior part of the brain stem protrude forward into the prepontine cistern, situated just dorsal to the clivus. The cistern becomes narrowed or occluded, and the basilar artery is pushed forward and enclosed, forming a basilar artery encasement sign (Fig. 2.30). Discussion Tumors originating in the pons, midbrain, and medulla oblongata are collectively referred to as brain stem tumors. The most common brain stem tumor is astrocytoma, which is more common in children. Brain stem gliomas account for 10–25% of intracranial neoplasms in childhood [98]. The growth patterns of brain stem tumors are different, and Epstein et  al. have classified them into exogenous, disseminated, and endogenous types. Exogenous tumors mostly protrude from the brain stem. Disseminated tumors spread along the longitudinal axis of the brain stem, reaching up to the dorsal thalamus, the cerebellum, or the posterior part of the third ventricle, and can travel even down to the upper thoracic segment of the spinal cord. The

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endogenous type is more common, in which the tumor causes localized expansion of brain stem or diffuses infiltrative growth. According to the scope of its invasion, it can be divided into the: limited type, diffuse type, or extended neck type [99]. MRI has a unique value in the evaluation and diagnosis of brain stem glioma. Its advantages over other imaging modalities mainly include the following: (1) Demonstration of the degree of brain stem enlargement and swelling, which can be expressed as a symmetry increase in size with a round or fusiform configuration, which can also increase the degree of asymmetry, and the mass protrudes in all directions. (2) Signal changes usually occur relative to the rest of the brain stem, where gliomas on T1WI have slightly lower signal or isointense signal relative to the remainder of the brain stem, or occasionally have mixed signals, being a mixture of hyperand hypo-intense signal on T2WI.  For children with diffuse intrinsic pontine glioma, T2WI demonstrates the greatest signal intensity variance suggesting tumor heterogeneity, and within this heterogeneity, T2WI hypo-intensity is correlated with increased cellularity [100]. There may be mild-moderate vasogenic edema around the tumor, having T2- or FLAIR hyperintensity, where the T2-bright tumor signal may not be easy to distinguish from the vasogenic edema. Cystic regions are also sometimes present, which have lower T1WI signal and higher T2WI signal. (3) On post-contrast, the larger tumors are usually rounded with mass effect on adjacent structures if large enough, potentially with peripheral/annular enhancement that is caused by tumor liquefaction and necrosis (present in a minority, and usually in larger tumors). On postcontrast T1WI, if there is hypo-­intensity that is non-enhancing surrounding the annular areas of enhancement, this represents peritumoral edema. (4) Regarding peritumoral edema, larger tumors may induce disappearance of the posterior border of the pons, with deformation and displacement of the fourth ventricle, and effacement of the adjacent basal cisterns and quadrigeminal plate cistern. (5) Regarding basilar artery encasement sign, when the brain stem tumor advances

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a

b

c

Fig. 2.30  A 5-year-old boy with brain stem glioma with obstructive hydrocephalus. The pons is significantly enlarged and deformed, showing a nearly circular shape with uneven signal shadows of T1-dark signal on axial T1WI (a), and T2-bright signal on axial T2WI (b). The

fourth ventricle is compressed from mass effect, and the cerebral aqueduct and the surrounding cisterns were narrowed due to the compression, also depicted on sagittal T2WI (c)

anteriorly, the sign may occur (approximately 40–45%); some scholars believe that this sign is one of the characteristic manifestations of a larger brain stem tumor (such as those >2 cm in size). Therefore, increased signal on T2WI and marked enlargement of the pons with engulfment of the basilar artery are typical imaging findings of larger brain stem tumors. The pres-

ence of enhancement on post-contrast MRI is variable but, when present, is more concerning for a higher grade or infiltrative tumor, potentially with malignant degeneration, especially if there is peripheral enhancement with necrosis and/or reduced diffusion on DWI.  Tumor pseudo-­progression has been reported in brain stem gliomas, which is characterized by an

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increase in mass effect post-therapy, which usually occurs from 1.5  months to 2.5  years after radiation therapy (mean 6  months); notably, pseudo-­ progression is sometimes associated with new or worsening symptoms, being dependent on the location of their tumor [101].

2.32 The Tau Sign Feature The tau sign is noted on coronal or sagittal MRI images of the brain. The shape of the intracranial artery near the sella and sphenoid’s clinoid processes is similar to the Greek letter tau. Explanation In patients with persistent trigeminal arteries, a sagittal MRI can reveal abnormal flow voids that represent an abnormal carotid-basilar anastomosis of blood vessels between the cavernous segment of the internal carotid artery and the basilar artery. The tau sign refers to a rare phenomenon of a flow void formed by the saddle anterior internal carotid artery and persistent trigeminal artery on either paramedian sagittal MRI or on maximum intensity projections (MIP) reconstructions from MR angiography (MRA) (Fig. 2.31). Discussion Persistent trigeminal artery (PTA), also known as the persistent primitive trigeminal artery, is a relatively uncommon anomalous variant consisting of an anastomosis between the internal carotid artery (ICA) and basilar artery. PTA is the most common of the four primitive anastomoses that may exist between the carotid and vertebrobasilar system that can persist in adults, with an estimated angiographic incidence of 0.1–1.0%, and represent over 90% of persistent carotid-­ vertebrobasilar anastomoses. The other such anastomoses are the persistent otic, hypoglossal, and proatlantal intersegmental arteries [102–104]. PTA often begins in the anterior portion of the cavernous ICA, where the anastomotic vessel (the PTA) often joins the basilar at a point located between the superior cerebel-

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lar artery and the origin of the anterior inferior cerebellar artery. According to the characteristics of angiography, Saltzman classified PTA into three types. Type I: PTA supplies the entire distal vertebral-basilar system, where the proximal basilar is often dysplastic with a lack of a posterior communicating artery. Type II: PTA supplies the circulation of both sides of the superior cerebellar arteries, and the ipsilateral side of the posterior cerebral artery is supplied by the developed posterior ­communicating artery. Type III: PTA does not combine with the basilar artery, but rather merges with the persistent longitudinal neural arteries to supply the cerebellar artery on the same side [103]. The clinical significance of PTA remains controversial. Most cases have been found incidentally on MRI, angiography, or autopsy. But there are also reports that persistent trigeminal artery can occasionally cause trigeminal neuralgia and oculomotor paresis, even without a concomitant aneurysm being present. Thus, it is important to identify the presence of a PTA in the events that a neurovascular intervention is necessary. Of note, the persistent primitive trigeminal artery can also become the collateral circulation pathway for vascular obstructive disease.

2.33 The Reversal Sign Feature The CT sign of hypoxic-ischemic cerebral injury in children manifests the attenuation of cerebral cortex diffusely decreased and relatively high attenuation of the basal nucleus, dorsal thalamus, brain stem, and cerebellum. Explanation The reversal sign is a CT-based manifestation of hypoxic-ischemic injury (HII) to the cerebrum injury in children. There is a decrease in the attenuation of the cerebral cortex, caused by nerve cell degeneration, necrosis, and axonal degeneration following hypoxic-ischemic injury. There may be resultant hyper-attenuation of the basal nuclei, dorsal thalami, and the brain stem caused by a combination of many factors, perhaps related

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Fig. 2.31 (a, b) Coronal T2WI and MRA reformat (PA view) demonstrate an artery connecting basilar artery trunk below superior cerebellar artery origin, with hypoplasia of the vertebral-basilar junction below the site of

anastomosis in a patient with a left-sided persistent trigeminal artery. Hence, both the superior cerebellar arteries and posterior cerebral arteries originate from the distal basilar artery

to the contrast of these structures with the mild edema in the affected cortical regions, bleeding at sites of vascular stasis, selective necrosis of certain neural structures, or the existence of calcium-containing neurons (Fig. 2.32).

inflammation of the brain and its meninges, hypothermia, and other causes of global cerebral ischemia [106, 107]. The presence of a reversal sign indicates irreversible damaged neural tissue and is associated with poor prognosis. Children displaying reversal signs on CT have a high mortality rate (35%) [106], and there is an increased incidence of profound neurologic deficits with developmental delay in those who survive. The III and IV layers of nerve cells of the cerebral cortex are the most vulnerable following hypoxic-ischemic injury. Eosinophilic denaturation and coagulation necrosis occur in cerebral cortical nerve cells after more than 12 hours after ischemia, where axonal cells begin to undergo denaturation at 2–3 days, glioblasts, fat granules, and neovascularization occur at approximately 7 days, and the formation of cavities and softening occur at 2–4 weeks. Regarding the attenuation increase

Discussion Han et al. first defined “reversal sign” as diffuse loss of gray-white matter attenuation in children with an unclear or disappearing boundary between gray and white matter and a reversal of the attenuation in gray and white matter, with relative increasing attenuation of the dorsal thalami, brain stem, and cerebellum [105]. The reversal sign indicates diffuse cerebral injury in patients who have suffered an ischemic/ anoxic insult and can be seen on CT of patients with conditions such as birth asphyxia, head trauma, status epilepticus, drowning, strangulation, carbon monoxide poisoning, infection/

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caused by the damage of basal nuclei and dorsal thalami, the hyper-attenuation is associated with the increased neovascularization that occurs 1–2  weeks after severe ischemia or relates to the congestion of deep medullary veins in the white matter of the brain, or the attenuation is not actually increased, rather representing normal brain tissue attenuation. Nonetheless, regardless of etiology and pathophysiology, the “reversal sign” is usually associated with poor prognosis and irreversible brain injury. According to the onset time of the reversal sign, it is divided into two phases: acute and chronic. The acute phase refers to the reversal sign that occurs at the time of CT, while the chronic phase demonstrates diffuse brain atrophy or encephalomalacia, which represents the sequela of the reversal sign. Hence, the reversal sign is an important CT sign of severe hypoxic-­ ischemic cerebral injury in children or in adults, but it is not specific to an etiology. The cause can be determined by means of the clinical history,

a

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laboratory examination, and CT characteristics; especially, it is important to note the chronic imaging findings and sequelae of the reversal sign as complications of hypoxic-ischemic encephalopathy. The chronic reversal sign is characterized on NCCT by diffuse low attenuation of the hemispheres, where the attenuation of central regions such as basal ganglia and dorsal thalami are markedly increased. Of note, common complications of hypoxic ischemic ­encephalopathy are diffuse brain atrophy and occasionally hydrocephalus.

2.34 The False Falx Sign Feature Linear attenuation with an increased shadowing in the interhemispheric fissure with a clear boundary. The CT attenuation in this scenario of “pseudo-hemorrhage” is lower than that of actual hemorrhage.

b

Fig. 2.32  The reversal sign represents severe anoxic-­ on non-contrast CT (a) and relative preservation of norischemic brain injury and can include diffuse, symmetric mal to high attenuation of central structures, such as bilatbilateral reversal of gray-white matter density relationship eral thalami (b)

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Explanation In patients with cerebral edema, there may be hyperemia of falx cerebri and/or venous sinuses, which may appear as linear high-attenuation in interhemispheric fissure, which is false falx sign. It should not be mistaken for subarachnoid hemorrhage (SAH) (Fig. 2.33).

images (the slope of the falx being best visualized on coronal images) makes the falx cerebri and the straight sinus appear to form a Y-shaped structure; the upper slice sections include the entire falx cerebri. The appearance and visualization of the falx cerebri on CT depend on its attenuation difference from neighboring structures as well as its orientation to the section plane. Hence, if Discussion there are low attenuation tissue and fluid around “The false falx sign” manifests as linear high it, the un-enhancing falx cerebri can be identiattenuation shadow in the interhemispheric fis- fied and may even appear slightly hyperdense. sure cistern, which can be seen in patient with Notably, more than 50% of children aged 4 years anoxic brain injury and many other causes of dif- or younger have a complete or partial falx cerefuse cerebral edema [108]. In anoxic (hypoxic-­ bri that is visible on NCCT examinations. NCCT ischemic) brain injury, the high attenuation with is widely accepted as the imaging standard for adjacent shadowing appearance results from a the diagnosis of acute SAH, as it has a sensitivity combination of a loss of cerebral gray-white and specificity that are reported to be as high as differentiation, with narrowing and effacement 100% in the first 6 hours after a severe headache of the subarachnoid spaces, and correspond- of acute onset [110]. Hyperemia of the falx cereing engorgement of the superficial pial veins. It bri and venous sinus, especially in patients with should not be mistaken for subarachnoid hemor- cerebral edema, may show the linear high attenurhage. The CT attenuation values in pseudo-SAH ation shadow in the interhemispheric fissure, are generally 30–45  HU but are 60–70  in true representing the false falx sign, which should not SAH [109]. be mistaken for SAH. The differential diagnosis Non-contrast CT (NCCT) at the level of the top or possible causes of this finding on NCCT are of the tentorium cerebelli usually shows the pos- (1) a relative high attenuation boundary from the terior falx cerebri, where the sloping falx on axial hyperemia in falx cerebri and venous sinuses, (2)

a

Fig. 2.33  In the patient with ischemia and hypoxia, the brain tissue is obviously swollen on axial non-contrast CT (a, b), and the linear high-attenuation shadow appears in

b

cerebral hemispheric fissure (arrows), representing the false falx sign, and should not be mistaken as subarachnoid hemorrhage

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the CT attenuation values are also lower than that in other intracranial hemorrhage sites of SAH, (3) the hyperemia in a venous sinus can form a solid triangular sign, where the high-attenuation hemorrhage shadows on both sides of the triangle (the base of the hyper-­attenuation being the skull’s inner table) and presents as an empty (black) triangle sign. Additional differentiating features are a diffuse loss of gray-white differentiation and effaced basal cisterns, indicating diffuse cerebral edema [109]. MRI is a valuable tool in the diagnosis of SAH, and SWI or FLAIR sequence has higher sensitivity than CT in detecting SAH [110], especially in the subacute phase of SAH.

2.35 The Interpeduncular Fossa Sign Feature On non-contrast CT (NCCT) examination, there is a high attenuation shadow in interpeduncular fossa/cistern (IPF) in the form of an inverted triangle, which is called interpeduncular fossa sign.

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the most fatal form of acute stroke, thus accounting for 5% of the total number of strokes. Many survivors often later develop severe cognitive impairment; thus, it can difficult to determine the clinical prognosis immediately following acute SAH, but it is critical to immediately identify signs of SAH on neuroimaging. Clinically, the disease is generally divided into two types, spontaneous and traumatic. Spontaneous can be further divided into primary and secondary. When bleeding from vessels within the pia along the surface of the brain enters directly into the subarachnoid space, it is primary, whereas intraventricular hemorrhage, considered to be the hemorrhage from the brain tissue into the ventricular system (also part of the subarachnoid space), is considered secondary. The main causes of SAH include ruptured intracranial aneurysms, cerebrovascular malformations, followed by hypertension, atherosclerosis, Moyamoya disease, hematological diseases, and brain tumors. As mentioned above, aneurysmal SAH is the most devastating form of stroke. There are many pathological changes after aneurysm

Explanation The interpeduncular fossa sign suggests the presence of subarachnoid hemorrhage (SAH). The interpeduncular fossa is situated between the left and right cerebral peduncles, and the IPF appears as an inverted triangle; at the anterior edge of the IPF is the suprasellar cistern. The density of the CSF in the interpeduncular fossa under normal conditions is akin to that of water (−5 to 10 HU); in the setting of subarachnoid hemorrhage, with the NCCT obtained in the supine position, the hemorrhage tends to accumulate dependently in the IPF, resulting in interpeduncular fossa sign (Fig. 2.34). Discussion SAH is a clinical syndrome caused by the rupture of blood vessels in the brain or superficial parts of the brain, leading to direct hemorrhage into the subarachnoid space. It is an acute disease, with high morbidity and mortality, being

Fig. 2.34  A 38-year-old man involved in motor vehicle trauma. Cranial NCCT reveals midline hemorrhage in the interpeduncular cistern

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rupture, including hydrocephalus, endothelial cell and neuronal apoptosis, cerebral edema, and blood-brain barrier integrity loss with potential microthrombus formation, neuronal depolarization, and vasospasm (usually the latter in the late acute or early subacute phase) [111]. In SAH patients, the most common accumulation sites of hemorrhage on imaging are usually within lateral/Sylvian fissures, cortical sulci, and basal cisterns (including suprasellar cistern, ambient cistern, and quadrigeminal plate cisterns, to name a few); actually, the site of hemorrhage most likely depends on the site of vascular rupture (in the setting of aneurysmal-related SAH), trauma (in the setting of contusional injury or axonal injury) or the site of hemorrhagic stroke (in the setting of parenchymal hemorrhage from ischemic or non-thromboembolic hemorrhagic stroke). In many cases, a small amount of blood accumulation in interpeduncular fossa is the main or only evidence of SAH; notably, IPF is easily identified anatomically with either basilar artery or anterior ponto-mesencephalic vein (APMV) within interpeduncular fossa [112– 115]. Of note, a couple of scenarios can simulate SAH within IPF: first, as the basilar artery is rounded and surrounded by CSF, it can be separated from the wall of the interpeduncular fossa, but due to slice thickness or slice orientation, it can simulate SAH within the IPF, which can be resolved by multiplanar reformats or noninvasive contrast-enhanced CT or angiographic CT or MRI.  Regarding the normal variant APMV, it is a normal, vertically oriented venous structure presenting in about 5% of the population, which can simulate SAH on NCCT, particularly if there are thicker slices of CT acquisition or the venous structures are hyperdense (such as from dehydration or polycythemia); this can be discerned from true SAH using post-contrast CT such as CT angiography or via MR angiography [114, 115]. After injecting intravenously contrast medium (whether via CT or MRI), the diagnostic criteria for SAH in other parts become unreliable due to the degree of vascular enhancement (often with normal contrast-enhancing veins adjacent to arterial structures in some regions); however, focal high density of the IPF with its characteristic inverted triangular shape can be a

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reliable sign, being easily identified relative to surrounding enhancing vessels, even on postcontrast CT or MRI. It should be noted that when the cerebral herniation occurs, the IPF may be displaced, be distorted, be deformed, or even disappear in the most severe cases. Under such circumstances, the interpeduncular fossa sign becomes unreliable, but there are usually other overt signs of SAH or other severe intracranial injuries [113–115]. At the same time, due to the angle of the NCCT acquisition (“slice selection”), the IPF can appear deeply situated in the midbrain, for which multiplanar reformats can help discern the IPF and confirm whether there is actual hemorrhage.

2.36 The Empty Delta Sign Features On post-contrast CT or MRI T1WI, the empty delta sign is manifested as when the superior sagittal sinus has a triangular appearance of enhancement or relatively low density/intensity within the hyperdense region on multiple consecutive CT images (or on multiplanar post-contrast T1WI). Explanation There is no universally accepted pathophysiologic explanation for the appearance of the empty delta sign. However, potential hypotheses include (a) intraluminal thrombus (static) with dynamically flowing contrast surrounding a thrombus, (b) recanalization of the thrombus within the sinus, (c) organization of the clot/thrombus, (d) blood-brain barrier breakdown with surrounding enhancement, and (e) dilatation of collateral peridural and dural venous channels around thrombosed dural sinus (Fig. 2.35). Discussion The so-called empty delta sign, which usually appears following contrast-enhanced CT (CECT), is reliable in CT-based diagnosis of SSS thrombosis, but it may not appear in all cases in the hyperacute stage (25% is the strongest predictor of large mismatch loss in proximal middle cerebral artery stroke. Stroke. 2013;44(11):3084–9. 51. Md Noh MSF, Abdul Rashid AM. The disappearing basal ganglia sign. QJM. 2018;111(5):343. 52. Zerna C, Hegedus J, Hill MD.  Evolving treatments for acute ischemic stroke. Circ Res. 2016;118(9):1425–42. 53. Leiva-Salinas C, Jiang B, Wintermark M. Computed tomography, computed tomography angiography, and perfusion computed tomography evaluation of acute ischemic stroke. Neuroimaging Clin N Am. 2018;28(4):565–72. 54. van Seeters T, Biessels GJ, Kappelle LJ, et al. The prognostic value of CT angiography and CT perfusion in acute ischemic stroke. Cerebrovasc Dis. 2015;40(5–6):258–69. 55. Shi F, Gong X, Liu C, et al. Acute stroke: prognostic value of quantitative collateral assessment at perfusion CT. Radiology. 2019;290(3):760–8. 56. Becker H, Desch H, Hacker H, Pencz A.  CT fogging effect with ischemic cerebral infarcts. Neuroradiology. 1979;18(4):185–92. 57. Uchino A, Miyoshi T, Ohno M. Fogging effect and MR imaging: a case report of pontine infarction. Radiat Med. 1990;8(3):99–102. 58. Lake EMR, Bazzigaluppi P, Mester J, et  al. Neurovascular unit remodelling in the subacute stage of stroke recovery. NeuroImage. 2017;146:869–82.

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82 139. Doddamani RS, Meena RK, Sawarkar D. Ambiguity in the dural tail sign on MRI.  Surg Neurol Int. 2018;9:62. 140. Bonneville F, Savatovsky J, Chiras J.  Imaging of cerebellopontine angle lesions: an update. Part 1: enhancing extra-axial lesions. Eur Radiol. 2007;17(10):2472–82. 141. McKinney AM.  Chapter 26: Skull base foramina: normal variations and developmental defects. In: Atlas of normal imaging variations of the brain, skull, and craniocervical vasculature. Cham: Springer; 2017. p. 810. 142. Yamamoto H, Fujita A, Imahori T, et al. Focal hyperintensity in the dorsal brain stem of patients with cerebellopontine angle tumor: a high-resolution 3 T MRI study. Sci Rep. 2018;8(1):881. 143. Bonneville F, Sarrazin JL, Marsot-Dupuch K, et  al. Unusual lesions of the cerebellopontine angle: a segmental approach. Radiographics. 2001;21(2):419–38. 144. Filippi M, Rocca MA, Ciccarelli O, et  al. MRI criteria for the diagnosis of multiple sclerosis: MAGNIMS consensus guidelines. Lancet Neurol. 2016;15(3):292–303. 145. Lisanti CJ, Asbach P, Bradley WG Jr. The ependymal “dot-dash” sign: an MR imaging finding of early multiple sclerosis. AJNR Am J Neuroradiol. 2005;26(8):2033–6. 146. Palmer S, Bradley WG, Chen DY, Patel S.  Subcallosal striations: early findings of multiple sclerosis on sagittal, thin-section, fast FLAIR MR images. Radiology. 1999;210(1):149–53. 147. Thompson AJ, Banwell BL, Barkhof F, et  al. Diagnosis of multiple sclerosis: 2017 revisions of the McDonald criteria. Lancet Neurol. 2018;17(2):162–73. 148. Mulroy E, Balint B, Adams ME, Campion T, Merello M, Bhatia KP.  Animals in the brain. Mov Disord Clin Pract. 2019;6(3):189–98. 149. Kim BC, Choi SM, Choi KH, et  al. MRI measurements of brainstem structures in patients with vascular parkinsonism, progressive supranuclear palsy, and Parkinson’s disease. Neurol Sci. 2017;38(4):627–33. 150. Schwarz ST, Afzal M, Morgan PS, et al. The ‘swallow tail’ appearance of the healthy nigrosome - a new accurate test of Parkinson’s disease: a casecontrol and retrospective crosssectional MRI study at 3T. PLoS ONE. 2014;9(4):e93814. 151. Mostile G, Nicoletti A, Cicero CE, et al. Magnetic resonance parkinsonism index in progressive supranuclear palsy and vascular parkinsonism. Neurol Sci. 2016;37(4):591–5. 152. Mueller C, Hussl A, Krismer F, et al. The diagnostic accuracy of the hummingbird and morning glory sign in patients with neurodegenerative parkinsonism. Parkinsonism Relat Disord. 2018;54:90–4. 153. Gulati A, Virmani V, Singh P, Khandelwal N.  The hot cross bun sign. Neurol India. 2009;57(1):104–5.

A. M. McKinney et al. 154. Lee YC, Liu CS, Wu HM, Wang PS, Chang MH, Soong BW.  The ‘hot cross bun’ sign in the patients with spinocerebellar ataxia. Eur J Neurol. 2009;16(4):513–6. 155. Gan Y, Liang H, Li X, et al. The hot cross bun sign in a patient with encephalitis. Brain and Development. 2018;40(6):503–6. 156. Deguchi K, Ikeda K, Kume K, et  al. Significance of the hot-cross bun sign on T2*-weighted MRI for the diagnosis of multiple system atrophy. J Neurol. 2015;262(6):1433–9. 157. Horimoto Y, Aiba I, Yasuda T, et  al. Longitudinal MRI study of multiple system atrophy – when do the findings appear, and what is the course? J Neurol. 2002;249(7):847–54. 158. Wenning GK, Colosimo C, Geser F, Poewe W.  Multiple system atrophy [published correction appears in Lancet Neurol. 2004 Mar;3(3):137]. Lancet Neurol. 2004;3(2):93–103. 159. Zhu L, Xie L.  Prenatal diagnosis of Joubert syndrome: a case report and literature review. Medicine (Baltimore). 2017;96(51):e8626. 160. Poretti A, Huisman TA, Scheer I, Boltshauser E. Joubert syndrome and related disorders: spectrum of neuroimaging findings in 75 patients. AJNR Am J Neuroradiol. 2011;32(8):1459–63. 161. Kafle P, et al. Joubert syndrome: a case report. Nepal J Neurosci. 2018;15:23–6. 162. Lasjaunias P, Burrows P, Planet C.  Developmental venous anomalies (DVA): the so-called venous angioma. Neurosurg Rev. 1986;9(3):233–42. 163. Lee M, Kim MS. Image findings in brain developmental venous anomalies. J Cerebrovasc Endovasc Neurosurg. 2012;14(1):37–43. 164. Ruíz DS, Yilmaz H, Gailloud P.  Cerebral developmental venous anomalies: current concepts. Ann Neurol. 2009;66(3):271–83. 165. McKinney AM. Slow-Flow, Asymptomatic Vascular Malformations: Brain Capillary Telangiectasias and Developmental Venous Anomalies. In: Atlas of normal imaging variations of the brain, skull, and craniocervical vasculature. Cham: Springer; 2017. pp. 487–521. 166. Campeau NG, Lane JI.  De novo development of a lesion with the appearance of a cavernous malformation adjacent to an existing developmental venous anomaly. AJNR Am J Neuroradiol. 2005;26(1):156–9.

Suggested Readings for this Chapter de Oliveira AM, Paulino MV, Vieira APF, et al. Imaging patterns of toxic and metabolic brain disorders. Radiographics. 2019;39(6):1672–95. Fink JR, Muzi M, Peck M, Krohn KA.  Multimodality brain tumor imaging: MR imaging, PET, and PET/MR imaging. J Nucl Med. 2015;56(10):1554–61.

2 Brain Gao B, Li H, Law M. Imaging of CNS infections and neuroimmunology. Singapore: Springer; 2019, ISBN 978-­ 981-­13-6903-2, ISBN 978-981-13-6904-9 (eBook). George E, Guenette JP, Lee TC. Introduction to neuroimaging. Am J Med. 2018;131(4):346–56. Gocmen R, Guler E, Kose IC, Oguz KK. Power of the metaphor: forty signs on brain imaging. J Neuroimaging. 2015;25(1):14–30. Kim M, Kim HS.  Emerging techniques in brain tumor imaging: what radiologists need to know. Korean J Radiol. 2016;17(5):598–619. Kizilca Ö, Öztek A, Kesimal U, Şenol U.  Signs in neuroradiology: a pictorial review. Korean J Radiol. 2017;18(6):992–1004. Marinković S, Stošić-Opinćal T, Strbac M, Tomić I, Tomić O, Djordjević D.  Neuroradiology and art: a review and personal contribution. Tohoku J Exp Med. 2010;222(4):297–302.

83 McKinney AM. Atlas of normal imaging variations of the brain, skull, and craniocervical vasculature. Cham: Springer; 2017. Print ISBN 978-3-319-39789-4, Online ISBN 978-3-319-39790-0. Mulroy E, Balint B, Adams ME, Campion T, Merello M, Bhatia KP.  Animals in the brain. Mov Disord Clin Pract. 2019;6(3):189–98. Özütemiz C, Roshan SK, Kroll NJ, et al. Acute toxic leukoencephalopathy: etiologies, imaging findings, and outcomes in 101 patients. AJNR Am J Neuroradiol. 2019;40(2):267–75. Suh CH, Kim HS, Jung SC, Park JE, Choi CG, Kim SJ.  MRI as a diagnostic biomarker for differentiating primary central nervous system lymphoma from glioblastoma: a systematic review and meta-analysis. J Magn Reson Imaging. 2019;50(2):560–72.

3

Head and Neck Zhongxiang Ding, Guoyu Chen, and Alexander M. McKinney

Contents 3.1 Progressive Enhancement Sign

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3.2 Tendon Sign

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3.3 V-Shape Sign

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3.4 Teardrop Sign

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3.5 Tram-Track Sign

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3.6 Double-Ring Sign

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3.7 Salt-and-Pepper Sign

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3.8 Steeple Sign

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3.9 Bitten Cookie Sign

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3.10 Prominent Ear Sign

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3.11 Gas Bubble Sign

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References

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Z. Ding (*) Department of Radiology, Affiliated Hangzhou First People’s Hospital, Zhejiang University School of Medicine, Hangzhou, China G. Chen Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China A. M. McKinney Miller School of Medicine, University of Miami, Miami, FL, USA e-mail: [email protected] © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6_3

Progressive Enhancement Sign

Feature On dynamic contrast-enhanced CT or MRI, orbital cavernous hemangioma exhibits nodular and small, focal patchy enhancement, where the range of enhancement gradually spreads to the center of the tumor and then eventually expands to the entire tumor over time. Explanation The “progressive enhancement sign” is a specific CT or MRI sign in the diagnosis of cavernous 85

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hemangioma on postcontrast imaging. Cavernous hemangiomas are composed of vascular cavities and stroma of differing sizes, where fibrous tissue separation exists between the cavities. The contrast medium enters the tumor via the junction between blood vessels and the tumor and then gradually fills each vascular cavity through the fibrous tissue separation (Fig. 3.1). Discussion Cavernous hemangioma is the most common primary orbital tumor in adults. These tumors develop slowly and are more common in women than in men, with the highest incidence in the fourth and fifth decades of life. They may enlarge during pregnancy [1]. The main clinical manifestations are progressive, painless unilateral exophthalmos leading to different degrees of hyperopia, transient amaurosis, and other ocular symptoms. The involvement of orbital apex could cause compressive optic nerve neuropathy, albeit rare, occasionally resulting in monocular vision loss. Other less common symptoms include pain, swelling, diplopia, or a palpable lump [2]. Cavernous hemangiomas are usually solitary; rarely, they may be multiple. Pathologically, cavernous hemangiomas have a clear boundary with the fibrous capsule and do not invade the extraocular muscles. On non-contrast CT, most of these tumors appear round or elliptical. Also, some are lobulated with clear boundaries, having equal attenuation with the extraocular muscles; occasionally, these tumors have uneven attenuation and calcification. After contrast administration, the progressive enhancement sign can be seen within the lesion. On non-contrast MRI, the lesion is isointense or slightly hypointense on T1WI and ­hyperintense as compared with the extraocular muscles on T2WI; the lesion is also notably isointense to the vitreous body. This is mainly due to the slow blood flow and greater concentration of liquid materials in the interstitium. Progressive enhancement sign is specific for the diagnosis of a cavernous hemangioma. In the early phase of postcontrast dynamic MRI, the contrast enhancement is most likely to start from multiple points in patchy or geographical regions, with a wide-

spread pattern. In comparison, the starting points of enhancement on CT are likely to be one or more focal points situated along the periphery of the lesion [3]. The enhancement pattern help differentiate cavernous hemangiomas from other tumors that may occur in the orbit, such as schwannomas and meningiomas. Schwannomas typically occur in the extraconal space, while cavernous hemangiomas usually occur in the intraconal space; meningiomas are usually intraconal as well but typically abut or surround the optic nerve due to the typical origin from the optic nerve sheath. After contrast enhancement, schwannomas show obvious inhomogeneous enhancement with nonenhanced necrosis and cystic areas, while meningiomas vary in their degree of enhancement, as well as the degree of calcification.

3.2

Tendon Sign

Feature The typical CT findings of orbital myositis are thickening of the extraocular muscles, which extends forward to the attachment of the tendon to the globe. The attachment may be irregular or have nodular thickening, called the “tendon sign” or “muscle tendon sign.” Explanation Orbital myositis is a nonspecific orbital inflammation that causes irregular thickening of the extraocular muscles and the attachment of the tendon to the globe. Both non-contrast and post-­ contrast CT reveal irregular thickening of the extraocular muscles and the attachment of the tendon to the globe, which is called the tendon sign, because intra-orbital myositis involves the tendinous membrane of the tendon that attaches to the globe. The appearance of this sign can be considered as a specific diagnostic clue for orbital myositis (Fig. 3.2). Discussion The “tendon sign” is characterized by thickening of the extraocular muscles and at the site of attachment of the tendon to the globe on pre- or

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a

b

c

d

e

f

Fig. 3.1 (a, b) Axial and coronal T2WI demonstrates an oval, lobulated, and homogeneously hyperintense mass within the cone of left orbit’s extraocular musculature superomedially. (c, d) Post-contrast T1WI demonstrates

early punctate enhancement within the mass. (e, f) The entire lesion showed more homogeneously at a point 10 minutes after intravenous injection of contrast medium

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Fig. 3.2  In a patient with orbital myositis, non-contrast CT reveals the enlargement of the bilateral medial rectus and lateral rectus, like tubular configuration, with the thickened muscles at the site of attachment to the globes (arrows)

post-contrast CT. The attachment site of the tendon to the globe may be irregular or have nodular thickening, indicating the diagnosis of orbital myositis. Orbital myositis is a nonspecific orbital inflammatory disease that mainly affects the extraocular muscles. The pathological manifestation is the thickening of one or more extraocular muscles. The site of attachment of the tendon to the globe that may appear irregular or have nodular usually has extensive inflammatory cell infiltration (mainly lymphocytes) on histopathology. The typical clinical symptoms of orbital myositis are acute periorbital pain, diplopia, ocular protrusion, swelling of the orbits, conjunctival hyperemia, and conjunctival edema adjacent to the affected extraocular muscle. On both pre- and post-contrast CT, orbital myositis usually involves a unilateral extraocular muscle but sometimes with bilateral involvement with the spread of the lesion along the tendon. The hyperdense appearance can appear much more pronounced after intravenous contrast administration, which can even involve more of the extraocular muscles (sometimes all of them) than noted on non-contrast CT; such diffuse enhancement may be related to the vascular accumulation and inflammation throughout the affected musculature. However, MRI is the preferred method for the diagnosis of orbital myosi-

tis. Post-contrast T1WI combined with fat suppression can clearly depict the inflammation of the muscles, tendons, and orbital fat [4], which contributes to the diagnosis of the disease. The differential diagnosis of extraocular muscle thickening mainly includes thyroid dysfunction, internal carotid cavernous fistula, cavernous sinus dural arteriovenous malformation, and neoplasms [5]. Thyroid dysfunction myopathy is manifested as bilateral muscle involvement and typically as thickening of the extraocular muscles into a spindle shape, with tapering at the attachment site of the tendon to the globe [5], while orbital myositis manifests as the tendon sign. Irregular or nodular thickening of the extraocular muscles and localized enhancement contribute to the differentiation of intraocular myositis from thyroid dysfunction. Internal carotid cavernous fistula and cavernous sinus dural arteriovenous malformation are usually manifested as diffuse thickening of the unilateral orbital musculature. High-resolution CT shows that if the findings of superior orbital venous dilatation are combined with the expansion of the ipsilateral cavernous sinus, then the findings are highly suggestive of internal carotid cavernous fistula or cavernous sinus dural arteriovenous malformation. Finally, neoplastic lesions can directly invade or metastasize to the orbit, resulting in extraocular muscle thickening; the thickened muscles are usually a result of direct tumoral invasion.

3.3

V-Shape Sign

Feature The typical retinal detachment shows a “V” shape with its tip on the optic disk and the end point toward the ciliary body. A subretinal effusion typically has high attenuation on CT, while on MRI, T1WI and T2WI show hyperintensity, without overt enhancement after injecting contrast agents. Explanation Retinal detachment refers to the separation of the retinal neuroepithelial layer from the pigment epithelial layer. The liquid leaks into the potential gap between the two layers, forming subretinal effusion (Fig. 3.3).

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a

b

c

d

Fig. 3.3 (a, b) On MRI, a rounded lesion of abnormal signal intensity is noted of the right globe on T1WI (a) and on T2WI (b), where the vitreous body around the lesion was isointense-hypointense on both sequences, and the signal intensity internally within the lesion was a bit inhomogeneous on T2WI. (c, d) Following contrast administration,

on axial (c) and sagittal (d) postcontrast fat-suppressed T1WI, there was slightly inhomogeneous enhancement within the lesion, and the “V-shaped” hypo-­intensity was visible (arrows). The tip of the arrow points to the optic disc, while the opposite end points toward the ciliary body; the “V” sign was more clearly seen in the sagittal plane

Discussion Retinal detachment is a common manifestation of subretinal effusion or other disorders (such as inflammation, trauma, and vascular disease). It can be divided into two major categories based on its causes: primary retinal detachment and secondary retinal detachment. The former refers to the absence of other diseases in the eye and is solely due to the formation of holes in the retina. The latter is caused by other diseases of the eye, such as retinal exudative inflammation, trauma, tumor, and proliferative lesions; also, any choroidal lesion can lead to retinal detachment [6]. Because a subretinal effusion contains proteins, CT shows a crescent-shaped or curved, uniform, high-attenuation shadow in the globe (compared with the vitreous matter’s attenuation). Regarding MRI, the concentration of protein affects T1 and T2 values. Hence, MRI intensity of the subretinal effusion is varied and mostly exhibits hyperintensity on T1WI/ T2WI. The typical retinal detachment sign shows a “V” shape on CT or MRI with its tip at the optic disc and the end pointing toward the ciliary body. The detached retina is very thin and cannot be

completely displayed on CT or MRI, but the contour of the retina can be depicted between the subretinal fluid and the liquid in the vitreous cavity. Retinal detachment is thus manifested on CT or MRI as an increase in density or signal intensity, respectively, of the entire vitreous cavity. A small number of retinal detachments can be expressed as spheres, termed “spherical” retinal detachment. Following contrast administration, a subretinal effusion does not enhance. Secondary retinal detachment appears not only with the imaging findings described above of retinal detachment but also often with visible primary lesions on CT or MRI [7]. Hence, MRI showing a subretinal effusion can demonstrate the primary lesion of secondary retinal detachment. However, the primary lesion may not be well-visualized on CT, although the diagnosis of certain entities causing the retinal detachment and subretinal effusion, such as choroidal osteoma, can be apparent. Of note, a detached retina is not directly visible on CT/MRI images, but ultrasound can depict a detached retina. Ultrasonographic assessment of the vitreous body, retina, and subretinal space adds a significant dimension to the

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diagnosis of retinal detachment and the management of patients with vitreoretinal abnormalities [8]. The main differential diagnosis for retinal detachment includes choroidal detachment and choroidal tumors. Regarding choroidal detachment, due to the limitation of the short posterior ciliary short artery and vortex vein, a posterior choroidal detachment appears as one or several hemispheres, and the detachment cannot reach the optic disc area; hence, the vicinity of the optic disc is not affected. Regarding a choroidal tumor, it can be distinguished from subretinal effusion by the intensity of the tumor and the subretinal fluid on MRI, as well as the degree of contrast enhancement on post-contrast images.

3.4

Teardrop Sign

Feature When the inferior wall of the eyelid is fractured, the contents of the eyelid penetrate the maxillary sinus through the fracture, shaped like tears. Therefore, it is called a “teardrop sign,” which is a specific indirect sign for the diagnosis of inferior wall fracture. Explanation The wound is around the eyelids, causing the pressure of the eyelids to rise. This indirectly leads to a fracture of the inferior orbital wall, or alternatively, there is injury to the infraorbital margin directly, thus causing the inferior wall fracture. The soft tissue in the orbit is embedded in the fracture and falls into the sinus, forming a teardrop sign (Fig. 3.4).

Discussion Multi-slice CT (MSCT) is the most effective method of initial examination for ocular trauma. The horizontal axis image shows not only the location and displacement of the fracture but also changes in the optic nerve, eye muscles, and intra-orbital fat. Multiplanar reformat (MPR) image is an important supplement. Volume reconstruction images can also be utilized to visualize the periorbital fractures. It is an important reference value for clinically determining whether to develop and operate a reasonable surgical plan. When the globe and the surrounding soft tissues are subjected to a blunt trauma such as a direct blow, the pressure acting on it is converted into hydraulic pressure. This pressure may cause an increase in the internal pressure within the bony orbital socket, resulting in the breakage of the platelike bone wall of the middle one-third, especially the weaker inner and lower sidewalls, which are the walls most prone to fracture. Typical clinical manifestations and signs of orbital burst fractures are enophthalmos, diplopia, vision decrease and loss, infraorbital nerve sensory loss, supracondylar syndrome, and globe shift. The CT signs of orbital burst fractures include direct and indirect signs. Direct signs include the following: the continuity of the inferior orbital bone is interrupted and comminuted, with no fracture in the lower margin of orbit. The fracture ends are angled or curved into the maxillary sinus, typically resulting in a sinus effusion. Indirect signs include thickening, displacement, and incarceration of the extraocular muscles adjacent to the fracture. In such instances, the

Fig. 3.4  A 37-year-old female with a fracture of the left inferior orbital wall. The left orbital content herniated inferiorly through the fracture site (arrow) into the left maxillary sinus, resembling teardrops (the “teardrop sign”)

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orbital contents may prolapse through the fracture into the maxillary sinus, forming a teardrop sign, which is a specific, indirect sign for the diagnosis of inferior orbital wall fracture. The main purpose of orbital repair is to reconstruct the orbits, restore them to the pre-traumatic state, and repair the invaginated globes, particularly so vision with its required extraocular muscle motion is not impeded. CT scan demonstrates not only the extent of the fracture but also the extent of fracture displacement; it also shows the embedded soft tissue. These factors provide the basis for conservative clinical treatment or surgical treatment, as well as the choice of the surgical plan and implant size. If the burst fracture causes an increase in the volume of the orbit of >2.25  cm3, it can be assumed that the globe invagination is >2 mm after the orbital swelling subsides. Therefore, an increase in the orbital volume of >2.25 cm is a new standard for the surgical treatment of orbital fractures [9]. Another study aimed to find an accurate and reliable CT measurement that could be used to identify patients with orbital inferior wall fractures requiring surgery to prevent subsequent diplopia and/or globe retraction. The results showed that a cranial-­ caudal dimension greater than 0.8  cm could predict the development of diplopia and/or enophthalmos; such patients then require surgical correction [10].

3.5

Tram-Track Sign

Fig. 3.5  A 58-year-old man with a progressive decline in vision. MRI shows optic nerve of the right eye appearing as low signal in relation to the surrounding, circumferential enhancement (arrows) of the optic nerve sheath on

axial (left) and coronal (middle) fat-suppressed post-­ contrast T1WI.  This represents the “tram-track” sign of optic meningioma. On non-contrast FLAIR with fat suppression (right), a corresponding appearance is noted

Feature The “tram-track sign” is most pronounced on post-contrast CT or fat-suppressed T1WI of the orbit. The optic nerve appears as low density or low signal, in relation to the surrounding, parallel-­ appearing enhancing tumor of the optic nerve sheath. Explanation The “tram-track sign” is most commonly used to describe optic nerve sheath meningiomas. Meningiomas tend to cause segmental or diffuse circumferential thickening of the optic nerve sheath. Once intravenous contrast material is administered, the optic nerve can be seen on CT or MRI as an unenhanced central linear structure (negative defect) surrounded by enhancing meningioma. Transverse or sagittal images demonstrate that this defect produces a “tramtrack sign” consisting of two parallel enhanced regions of the tumor separated from each other by the negative contrast defect of the optic nerve. The corresponding finding on coronal images is a doughnut configuration. Though less common, when linear calcification occurs within the optic nerve sheath meningioma, the tram-track sign may be apparent on non-contrast CT (Fig. 3.5).

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Discussion The tram-track sign is described as a feature to help distinguish between optic glioma and optic nerve sheath meningioma. In optic nerve sheath meningiomas, the tumor sheath demonstrates increased attenuation compared with the optic nerve on post-contrast CT, and may not be readily visible on non-contrast CT.  Notably, optic gliomas are derived from glial cells within the optic nerve and closely related to the optic nerve, regardless of the pattern of growth. Hence, no clear separation is present between the tumor and the nerve on non-contrast CT images [11]. Optic nerve sheath meningiomas (ONSMs) arise from meningothelial cells of the arachnoid mater, being situated along the optic nerve sheath. Histologically, the cell of meningioma is usually of the meningotheliomatous type, but it may occasionally be of the transitional type. The early subdural growth causes the tumor to surround the nerve. Since the nerve is only surrounded, and not completely covered or invaded by the tumor, the optic nerve can usually be identified as a “negative defect” within the tumor [11]. Post-contrast CT also reveals the changes of optic canal area, such as bone destruction and bone hyperplasia in the case of expanding optic meningioma. Johns et al. described three distinct density changes in ONSMs on post-contrast CT [12]: (1) the low-density optic nerve (the “negative contrast” defect described above); (2) the denser meningiomatous tumor mass; and (3) the denser, parallel linear enhancing areas adjacent to the optic nerve. This linear enhancement is believed to be related to the linear spread of the tumor along the subarachnoid space. Other retrobulbar masses usually do not exhibit perineural dissemination along the dura and arachnoid in such a focal fashion. On non-contrast MRI, an ONSM is usually isointense or slightly hypointense on T1WI and isointense or slightly hyperintense on T2WI, relative to the optic nerve itself. On gadolinium-based postcontrast imaging, the contrast enhancement is obvious, especially on fat suppression sequences [13]. Other conditions that can theoretically exhibit a tram-track sign include sarcoidosis, optic neuritis, orbital pseudotumor, perioptic hemorrhage, metastases, leu-

kemia/lymphoma, and Erdheim-Chester disease (a form of non-Langerhans cell histiocytosis).

3.6

Double-Ring Sign

Feature Cochlear otosclerosis (also called oto-­spongiosis) appears as an inhomogeneous hypodense ring surrounding the bony labyrinth of the basal turn of the cochlea on high-resolution CT (HRCT), representing peri-cochlear erosions. Thus, the appearance of a typical double-ring shape of lucency on HRCT at the bottom of the cochlea is called the “double-ring sign.” Explanation The trabecular meshwork in the region of peri-­ cochlear lucency on HRCT is, on histopathology, sparse and irregular, with large numbers of blood vessels, osteoblasts, and osteoclasts, which is the basis of the double-ring sign (Fig. 3.6). Discussion Otosclerosis/oto-spongiosis is a chronic, progressive hearing loss originating from the unknown, originally reported by Valsalva in 1735. Otosclerosis is an osteodystrophic disorder of the otic capsule that results in abnormal resorption of the endochondral bone, with deposition of abnor-

Fig. 3.6  Cochlear otosclerosis presents as a rounded pericochlear lucency that parallels the basal turn of the cochlea on HRCT, forming the double-ring sign (Black arrow)

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mal vascular bone. Otosclerosis usually appears in the third to fifth decades of life, being more common in women. On HRCT of the temporal bone, otosclerosis/oto-spongiosis is typically considered of two types based on their anatomic/ topographic location and imaging appearance: fenestral (involving the fissula ante fenestram just anterior to the oval window, ultimately resulting in stapes fixation) and retrofenestral (hypodense bone within the otic capsule surrounding the cochlea); of note, the fenestral variant is often limited to the region anterior to the oval window. Typically, fenestral (i.e., stapedial) otosclerosis presents with conductive hearing loss (CHL), although it can also present as mixed or sensorineural hearing loss (SNHL) in the absence of CHL. It is often called “cochlear otosclerosis”; fenestral otosclerosis/oto-spongiosis is notably the more common type, representing about 75–80% of oto-spongiosis cases, and is not always detectable on imaging [14]. The fenestral lesion is located along the lateral wall of the otic capsule focally at the fissula ante fenestram (just anterior to the oval window) and the tympanic segment of the fallopian canal. The retrofenestral type is more diffuse, affecting the labyrinthine capsule and peri-cochlear regions, and is described in more detail in the following paragraph [15]. As described above, the retrofenestral type is less common (about 20–25% of otosclerosis) and more commonly presents as sensorineural hearing loss (although also can present as a mixed hearing loss). It nearly always involves fenestral otosclerosis as well and can be much more extensive and overt on HRCT. This subtype can potentially involve the semicircular canals, internal meatus, vestibule, and cochlear and vestibular aqueducts in more severe cases; in such severe cases, these can clinically present rarely as a “third window” phenomenon causing hearing loss or vestibular symptoms. HRCT abnormalities are usually evident, which are visualized as a disease within the peri-labyrinthine bone and particularly along the cochlea in the retrofenestral subgroup. HRCT highlights differences in the density of the capsule outline, called the double-­ring sign, which is a low-density, demin-

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eralized endochondral defect outlining the cochlea. Thus, this appearance on HRCT can be considered a “gold standard” in the diagnosis of otosclerosis, where active oto-spongiosis, as described above, is visualized on HRCT as reduced bone density/radiolucency throughout the otic capsule; this appearance is also known as the fourth ring of Valvassori). HRCT can also be used to distinguish between otosclerosis and other pathological conditions such as tympanosclerosis, cholesteatoma, ossicular fixation, and congenital malformations [15]. As above, temporal bone HRCT using 1  mm (or less) thickness sections is the modality of choice for assessing the labyrinthine and peri-cochlear regions. MRI is useful for assessing the cochlear lumen prior to cochlear implantation in patients with profound hearing loss, via assessing their patency on heavy T2WI, preferably using 3D isotropic reconstructions of the labyrinthine structures [16].

3.7

Salt-and-Pepper Sign

Feature The salt-and-pepper sign is a typical MRI sign of paraganglioma (“glomus tumor”). On non-­ contrast T2WI, there is high-signal tumor tissue and low-signal vascular flow void intertwined, showing a characteristic “salt-and-pepper sign.” This appearance may variably be present on T1WI and post-contrast imaging as well. Explanation The typical appearance of a salt-and-pepper sign is best shown on T2WI and also can be demonstrated on T1WI and even on post-contrast T1WI.  The “pepper” predominately represents the intratumoral vascular flow voids, and the “salt” is the hyperintensity of the lesion caused by slow-flowing blood vessels or intratumoral hemorrhage on T2WI, enhancing tumoral stroma on post-contrast T1WI (Fig. 3.7). Discussion The salt-and-pepper sign was first described by Olsen et  al. in 1987 [17]. On T2WI, the tumor exhibits high signal, with multiple spotted intra-

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Fig. 3.7  Paragangliomas in two different patients. (a–d) A 43-year-old male with a right skull base mass, showing dynamic enhancement on CE MRA (top left, a), a “salt-­ and-­pepper sign” on coronal postcontrast T1WI (top middle, b), and intermediate reduced diffusion on axial ADC (top right- top image, c) and DWI (top right-bottom image, d), consistent with a paraganglioma (glomus jugulare). (e–g) In a 46-year-old male with bilateral paragan-

gliomas (arrows in each image) splaying the carotid bifurcations (“carotid body tumors”), there is characteristic avid enhancement with a slight “salt-and-pepper sign” on axial postcontrast CT (bottom left, e), having avid metabolic uptake on 18F-FDG PET (bottom middle, f); several months after right paraganglioma resection, there was a “salt-and-pepper sign” of the residual left glomus tumor on axial non-contrast T2WI (bottom right, g)

tumoral vascular flow voids, which is manifested as the salt-and-pepper sign. The sign is considered a characteristic feature of paraganglioma. Those authors believed that the incidence of this sign was related to the size of the tumor; with a tumor diameter of >2  cm size, the overall incidence of this sign was reported to be 80%. Of note, this sign can also be visualized on non-­ contrast T1WI and contrast-enhanced T1WI scans. On histopathology, a paraganglioma is composed of type I chief cells and type II sup-

porting cells. The chief cell cluster is separated by a fibrous matrix rich in large numbers of vascular lumens; these blood vessels form many extremely small capillary-level arteriovenous fistulas. These histopathological features likely form the basis for the MRI signal changes with the salt-and-pepper signs in this type of tumor, which again is found in paragangliomas with a diameter of >2 cm. Similar appearances are also found in other blood-rich vascular tumoral lesions such as metastatic adrenal adenoma and

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metastatic thyroid carcinoma. Additionally, certain malignant tumors of the temporal bone, such as adenoid cystic carcinoma of the e­ ndolymphatic sac, may also have this sign. Also notable is that glomus tumors may be bilateral in 5–10% of patients, particularly in the region of the carotid bodies. Diffusion-weighted imaging (DWI), contrast-­ enhanced MR angiography (CE-MRA), and dynamic contrast-enhanced (DCE) MRI have shown great potential in oncologic applications for head-and-neck tumors and can at times be used to help distinguish paragangliomas from other tumors. For paraganglioma, a higher signal is often visible on DWI, with corresponding mildly lower values on the ADC maps as related to that expected for other benign tumors [18]. The mildly lower ADC values are not related to cellularity or malignant potential as might be inferred; rather, the bright DWI/low ADC signal has been attributed to the inner texture of the lesion, where benign solid tumors lacking necrosis can sometimes have higher DWI signal and lower ADC values [19]. Regarding CE-MRA, it has been utilized to distinguish paragangliomas from other benign head/neck tumors such as meningioma and schwannoma, with a sensitivity and specificity of 100% and 90–95%, respectively [20]. On CE-MRA, in over 90% of paragangliomas, there are both earlier dynamic enhancement and much more prominent intratumoral flow voids as compared to meningiomas and schwannomas [20]. Regarding DCE-MRI, it has been used for the detection and evaluation of paragangliomas, where malignant tumors tend to exhibit a strong initial signal increase followed by a washout effect, whereas benign lesions (such as paragangliomas) mostly demonstrate a slower initial signal increase combined with a continuous signal increase [18]. Also, at present, morphological and functional imaging has become an important step in the diagnosis and staging of paraganglioma in multidisciplinary applications. Somatostatin receptor imaging and positron emission tomography are the most reliable examinations currently approved for this disease, while 18F-FDG PET usually demonstrates elevated uptake in the large majority [21, 22]. These functional imaging methods use

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highly specific tracers (specificity close to 100%). The major advantage of metabolic imaging is that it allows whole-body examination, which is very useful for detecting multifocal forms of paraganglioma, which happen in a minority [21].

3.8

Steeple Sign

Feature X-ray plain films of the posterior and anterior soft tissues of the neck show that the normal convexity on both sides of the trachea in the subglottic region disappears, and the narrow subglottic cavity leads to an inverted V-shape appearance of this region. The apex of the inverted V-shape is located at the level of the lower edge of the true vocal cords. The narrow subglottic cavity changes the shape of the tracheal air column, which resembles a steep inclined roof or church spire, hence being called the “steeple sign” (Fig. 3.8). Explanation Regarding the steeple sign, the adjacent area affected by airway stenosis is 1 cm proximal to the trachea, between the elastic cone and the true vocal cord. At this level, the mucosal junction is loose. The steeple sign is caused by tracheal edema, which can elevate the tracheal mucosa, leading to the disappearance of the shoulder of the air column. Discussion Viral howling (also known as acute laryngotracheobronchitis) is often caused by parainfluenza or respiratory syncytial viruses. It is the most common cause of upper-respiratory distress in infants and young children, with a peak incidence at 6 months to 3 years. Typical clinical manifestations are inspiratory wheezing and barking cough. The diagnosis of the viral roar is usually made clinically rather than radiologically. The purpose of the radiological examination is to exclude other diseases causing wheezing, such as foreign body inhalation, esophageal foreign body, congenital subglottic stenosis, diphtheria, glottitis, or subglottic hemorrhage, which have clinical symptoms resembling those of viral wheezing. The viral roar can be manifested as a

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a

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Fig. 3.8  A 70-year-old male; there was a question of subglottic stenosis in two locations (upper stenosis = arrows, lower stenosis  =  dotted arrows), resembling a “steeple” sign on chest X-ray (left, b), CT scan coronal reformat (left middle, c), virtual airway 3D reconstruction AP plane

(middle, d), and descending “fly-through” images (right, e–f). Note the normal true vocal cords in each image (*) and that the more inferior subglottic stenosis is more severe (dotted arrows) relative to the more proximal stenosis (arrows)

steeple sign, which can also be seen in some other lesions. Differential diagnosis includes glottitis, scald, neurovascular edema, and bacterial tracheitis. In viral roar, the glottis is normal on the lateral X-ray of the upper respiratory tract and has a 1–1.5  cm long subglottic stenosis.

Whether lateral X-rays of the soft neck tissue should be included in evaluating viral roar is still controversial. If glottitis cannot be ruled out clinically, the absence of illumination to the lateral film may result in misdiagnosis. Therefore, if viral roar is suspected in a clinic, anterior and

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lateral radiographs of the trachea and chest radiographs should be performed at the same time. Usually, viral howling is a self-limiting disease with a good prognosis [23]. To improve the gas exchange function, nonsurgical treatment, such as aerosol inhalation of racemic adrenaline and corticosteroids, is usually used. Further imaging can be necessary in some cases, preferably utilizing low-dose, non-contrast CT. In questionable cases or in adults with more complex anatomy and post-surgery, non-contrast CT with thin-section (5 mm is called a cavity), and vacuole sign can be single or multiple. Explanation The pathological basis of vacuolar sign includes (1) gas-filled lung tissue that was not occupied by tumor tissue; (2) unclosed or dilated bronchioles; (3) gas-filled cavity between papillary carcinoma structures; (4) cancer tissue growing along the alveolar wall that does not close, dissolve, destroy, or enlarge the alveolar space; or (5) formation after small focal necrosis discharge in the tumor. This sign is more common in bronchioloalveolar carcinoma and adenocarcinoma, but is also seen in squamous cell carcinoma. In some cases, the presence of mucus causes exfoliated tumor cells in the vacuoles. The CT value can be increased and be similar to the attenuation of water. On the CT lung window, it appears as a small bubble-like fuzzy low-attenuation shadow, or a small bubble-like radiolucent shadow on the mediastinum window (Fig. 4.4).

b

Fig. 4.4 (a) A nodular increased attenuation shadow can be seen in the left lower lobe. (b) Vacuole sign is seen in the lesion and shallow lobulation and burr growth at the edge of the lesion

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Discussion According to the foregoing definition, it is necessary to pay attention to the air bronchogram. The air bronchogram can show a thin strip of air attenuation shadow and can also be a small-­ diameter, 1-mm bubble air attenuation shadow. It can be seen on several consecutive levels, so the two signs should not be confused. In the process of image analysis, if the low-attenuation shadows in the nodules are localized, located within the nodules, and do not reach the edge of the nodules, it should be considered as a vacuole sign. The vacuole sign is most common in bronchioloalveolar carcinoma, adenocarcinoma, and occasionally in other lung benign nodules such as tuberculosis and bronchiolar cysts [6]. There are differences in the location of vacuolar signs between pulmonary carcinoma and benign nodules. The vacuole sign of pulmonary carcinoma is mostly located in the middle two thirds and outer part of the nodule, and the vacuole sign of benign nodules is mostly located in the middle two thirds and inside part of the nodule. The vacuole sign is an important imaging sign in the differentiation of pulmonary carcinoma and other benign nodules and quite importantly in the differential diagnosis of early lung cancer. When seen in subsolid nodules, particularly part-solid nodules, it is likely to suggest to a malignancy [7, 8].

4.5

Coarse Spicules Sign

Feature The coarse spicules sign is a thin, short line of radial unbranched shadow that extends from the edge of the tumor to the surrounding lung parenchyma and is not connected to the pleura. Explanation The coarse spicules sign is more common in peripheral pulmonary carcinoma. The pathological basis is the infiltration of tumor cells into an adjacent bronchial sheath or local lymphatic vessels or fibrous band of the tumor that promotes connective tissue formation. Benign nodules, such as inflammatory pseudotumor and tuberculosis, can also be seen on the edges of coarse

spicules, but longer and softer, often formed by hyperplastic fibrous connective tissue (Fig. 4.5). Discussion The coarse spicules sign has high clinical value in the diagnosis and differential diagnosis of peripheral pulmonary carcinoma, especially for isolated lung nodules [9]. The pathological basis is (1) invasive growth of cancer tissue, peripheral exudation, fibrosis, and interstitial reaction; or (2) obstructive pneumonia or pulmonary infarction caused by cancer cells infiltrating small bronchi and small blood vessels. When analyzing the coarse spicules sign, it should be noted that (1) it is not connected with the pleura (otherwise it is defined as pleural indentation: pleural line shadow, rabbit ear sign); (2) it shows radial but no branch, thus can be distinguished from vascular shadow; and (3) the sharp, triangular, or serrated shadows at the edge of the lesion are called the spinous process sign. For the convenience of description, the coarse spicules with length less than 5 mm are called short coarse spicules, and coarse spicules with length more than 5 mm are called long coarse spicules. The coarse spicules sign can be displayed on both plain radiography and CT, but CT has a greater advantage in displaying fine coarse spicules. When there is a coarse spicule sign in the isolated nodules in the lung, the possibility of pulmonary carcinoma should be considered. Short coarse spicules are more useful, but the absence of coarse spicules cannot rule out the possibility of pulmonary carcinoma [10]. Numerous reports in the literature have shown the coarse spicules sign is not a specific sign of malignant lesions. Benign nodules can also have coarse spicules, but the benign nodules have fewer coarse spicules, and this sign is more commonly seen in malignant nodules. Moreover, the coarse spicules sign is more likely to appear in peripheral pulmonary carcinoma associated with interstitial pneumonia and chronic obstructive pulmonary disease. For some cases that are difficult to identify and show little change in ­short-­term follow-up observation, biopsy should be suggested to avoid the delay in optimal time of treatment.

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a

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Fig. 4.5 (a) A 66-year-old woman: chest CT shows a nodular increased attenuation in the right upper lobe; multiple long and thin coarse spicules can be seen. (b) A

78-year-old woman: chest plain CT shows a nodular increased attenuation in the left upper lobe and multiple short coarse spicules

4.6

Discussion Pleural indentation (PI) is an imaging sign secondary to peripheral lung lesions. In the past this image was called the rabbit ear sign, or pleural tail sign, which some scholars described as characteristically V-shaped, X-shaped, or star-shaped. Currently, the appearance of adjacent pleural changes in these peripheral lung lesions is collectively referred to as the pleural indentation sign. The PI is an important imaging manifestation in the diagnosis and differential diagnosis of solitary pulmonary nodules. Although PI and intrapulmonary nodules occur simultaneously as a malignant phenomenon, PI is not unique to lung cancer. It is very easy to misdiagnose if the diagnosis and differential diagnosis are based on PI alone. Because inflammatory lesions and lung

Pleural Indentation Sign

Feature On CT, the pleural indentation sign shows more than one or two linear shadows on the edge of the pulmonary lesion, terminating in the pleura with small triangular or trumpet-shaped shadows. Explanation The main pathological basis of pleural depression is fibrous tissue hyperplasia, scar formation, and connective tissue septum thickening in lesions, without local pleural thickening or adhesion. Inflammatory lesions and tumors with such pathological basis may show the pleural indentation sign (Fig. 4.6).

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a

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Fig. 4.6 (a, b) Pleural indentation sign: lesion in left lower lobe terminates in pleura with a linear shadow and a trumpet shape. (c, d) Pleural indentation sign: right lower

lobe lesions terminate in pleura with multiple linear shadows that appear as a small triangle

cancer are very similar, it is difficult to distinguish them. For example, the linear shadow can be seen in tuberculoma, mycotic globules, silicosis fusion, and metastasis, so PI is limited in the diagnosis of lung cancer [11]. PI was previously used as one of the principal signs of malignant tumor diagnosis. Recently, the benign and malignant nodules of the lungs are said to cause PI, but the pathological basis is not completely the same, so the morphological manifestations on the multi-slice CT (MSCT) images are also different. The pathological basis of benign pulmonary nodules is the inflammatory cells in various inflammatory lesions, which are directly infiltrated into the pleural side along the interstitial space of the pulmonary lobule or the subpleural lymphatic vessels, involving the visceral pleura and even the parietal pleura to make the pleural reac-

tion. Sexual thickening, followed by cellulose exudation, and adhesion, cause lung tissue contraction, and finally lead to pleural thickening, traction, and adjacent subsegmental atelectasis. Concurrent pleural attachment and indentation are risk factors for visceral pleural invasion, and the odds increase with a larger solid portion in the subsolid nodules. Early surgical resection could be encouraged for these patients to decrease the risk of recurrence [12]. On MSCT are seen thickening and twisting pull lines near the pleura, thick basal thickening adjacent to the pleura, pleural fat depression, and pleural effusion. The pathological basis of PI in malignant pulmonary nodules may be the contractile force of some component of fibrous scar tissue in the mass. It is transmitted to the free visceral pleura through the elastic fibrous reticu-

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lar structure of the alveolar stent, which causes the visceral pleura to collapse without thickening and adhesion along the traction direction. On MSCT, one or more thin and rigid stretch lines were seen at the edge of the lesion and terminated in visceral pleura with a triangle-like or trumpet-­like shadow. A linear pleural tag with soft-tissue component at the pleural end on CT can increase the accuracy of early diagnosis of visceral pleural invasion by non-small cell lung cancer (NSCLC) that does not abut the pleura [13]. Pleural depression is considered as a nonspecific sign of malignant solitary pulmonary nodules on HRCT. Pleural thickening and adhesion in pleural depression are common in inflammatory lesions, resulting in uneven linear thickness, which is the key to differentiating PI from lung cancer. Comprehensive consideration of these factors of pleural indentation, sex, tumor density, and distance between the lesion and pleura might improve the diagnosis of pleural invasion [14].

4.7

Beaded Septum Sign

Feature On high-resolution computed tomography (HRCT), irregular and nodular thickening of interlobular septum is called beaded septum sign, mainly occurring in the periphery or in one third of the outer part of lung. Explanation Beaded septum sign is a feature of pulmonary metastases on HRCT. An irregular, nodular thickened interlobular septum represents the irregular expansion of tumor cells in capillaries and lymphatic vessels, as well as secondary perivascular and interstitial edema and fibrosis [15] (Fig. 4.7). Discussion The interlobular septa of peripheral pulmonary interstitial tissue are composed of pulmonary veins, lymphoid tissue, and interstitial tissue. The smallest anatomical unit displayed on HRCT is the secondary lobule. Metastatic tumor cells or tumor thrombi stay in the capillary and lymphatic vessels around the lung through hematogenous

Fig. 4.7  A 63-year-old woman presented with multiple metastatic tumors in both lungs. The beaded septum sign was seen in the left lung

dissemination, lymphatic dissemination, or retrograde lymphatic metastasis. There may be two major factors in the formation of this sign. (1) Metastatic foci should be located at the edge of the lung; if a metastatic focus is located in the middle of the lung, this focus is prone to subsegment or segmental lymph nodes to form a mass, and it cannot form the beaded septum sign. (2) Tumors with a high degree of malignancy, and rapid growth, present easy to early metastasis along the lymphatic system, so that lung metastases and lung and hilar lymph nodes can form nodules or masses at the same time [16]. The pathological mechanism is tumor cells spread along the lymphatic vessels of the lungs and diffusely in the lymphatic vessels. The lymphatic vessels are highly dilated, and the tumors are silted into a single embolus or cluster of tumor emboli with variable degrees of edema, fibrosis, and inflammation. The cells infiltrate, causing the bronchial vascular bundle to be irregularly nodularly thickened and showing beaded changes. The appearance of beaded septum is highly suggestive of pulmonary metastases and is considered as the most specific CT feature for this diagnosis. However, the beaded septum sign is occasionally seen in pulmonary sarcoidosis and should be differentiated from this [17]. The typical early stage of sarcoidosis is bilateral hilar lymphadenopathy, mostly accompanied by adenopathy in the right superior mediastinum; and metastatic tumors often have unilateral hilar and multiple lymph nodes involved in the mediastinum. In sarcoidosis, eggshell-like and spotted

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calcification are seen in lymph nodes, whereas metastatic lymph nodes are enlarged and fused into a mass, with necrosis and nonhomogeneous enhancement. The nodule boundary of sarcoidosis is unclear, and the lesion can occur in either lobe, although the upper lobe is more common. The lesions are distributed along the bronchial vascular bundle, which is characterized by thickening of this bundle, which is bead like with pleural thickening and a small amount of pleural effusion; the metastatic tumor has bead-like changes caused by irregular thickening of interlobular septa.

4.8

Honeycomb Sign

Feature The CT appearance of bronchioloalveolar carcinoma (BAC) is mainly characterized by light consolidation. On the mediastinum window or intermediate window, multiple vesicles are integrated into the honeycomb shadows or shown as grid patterns, which is called “ honeycomb sign.” Explanation The pathological basis is tumor cells taking the alveolar wall as the stromal scaffold and diffusing along the local peripheral air cavity; that is, incumbent growth. The pulmonary structure is not destroyed and the alveolar cavity still exists, because the bronchioles are infiltrated by the tumor to form valvular stenosis, which results in varying degrees of dilatation, and the remaining gas or mucus can be seen in the dilated alveolar cavity or bronchioles (Fig. 4.8). Discussion Honeycomb sign is usually seen in pulmonary adenocarcinoma with inflammatory consolidation. It is manifested as a bubble-like airy shadow in consolidation involving one or more lobes or segments of the lung. Many pathogenesis mechanisms result in the honeycomb sign. The mechanism of a check valve after airway stenosis is accepted by most scholars; that is, cancer cells grow along the alveolar wall or septum and spread to bronchioles, or cancer cells

Fig. 4.8  In an 83-year-old man, HRCT showed honeycomb shadows in upper lobe of the right lung

directly destroy the walls of bronchioles, thus forming a single bronchiole. Because of the valve, the pressure in the alveoli increases as the gas forms in the alveoli, which then break down and fuse into larger cavities. The remaining alveolar wall or septum forms the septum of the honeycomb. The findings suggest a common underlying mechanism that drives thin-wall cavity formation in p­ rimary lung cancer, particularly in adenocarcinoma containing mixed BAC.  Thin-wall cavitation is most common in adenocarcinoma containing mixed BAC.  The high incidence of cavity formation in this histological subtype further supports the notion that thin-wall cavity formation is directly related to the infiltration of tumor cells into a bronchiole, resulting in the establishment of a unidirectional check valve [18]. The ground-glass component of a tumor usually corresponds to a partially aerated lung that bears cells of BAC, whereas the solid component may correspond to other adenocarcinomas. The frequency of the nodule type may depend on the frequency of the histopathological subtype of carcinoma. The relatively lower frequency of ground-glass nodules may reflect the lower frequency of BAC [19]. Likely the most significant change is the discontinuation of the term “BAC” in the 2004 WHO Classification, which was previously used for at least five different entities with disparate clinical and molecular properties, leading to great confusion in routine clinical care and research [20].

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4.9

Withered Tree Sign

Feature There are inflatable bronchial images in the shadow of large patches; the larger bronchus can be seen and the smaller bronchi cannot. The bronchial wall is irregular, uneven, generally narrow, rigid, twisted, and takes the shape of withered arborization. Other name: withered tree sign. Explanation An air bronchogram as commonly seen in diffuse bronchiolar carcinoma differs from general inflammation. This sign is characterized by irregular thickening and rigidity of the bronchial wall. Other air bronchial signs are manifested as inflatable bronchial development in large consolidation shadows, and the wall of the bronchi is not rigid (Fig. 4.9). Discussion An air bronchogram is an important radiologic sign of air–space consolidation, in which the normally invisible bronchial air column becomes visible because of the contrast with surrounding tissues. Two situations may exist for an air bronchogram to be identified: the bronchus must contain air (it cannot be occluded completely at its origin) and the surrounding lung parenchyma must have reduced air content or be airless. Although most commonly seen in the presence of air–space consolidation, a severe degree of inter-

Fig. 4.9  A 55-year-old woman with no obvious discomfort. Chest CT shows patchy density enhancement shadow in the right lung, with “air bronchogram sign”

stitial lung disease can also present as an air bronchogram. Lung cancer of the bronchioloalveolar cell type may produce air bronchograms on radiographs or CT. It was suggested that the presence of pseudo-cavitation in small peripheral bronchioloalveolar cell carcinoma may represent air bronchograms in cross section. However, air bronchograms have been considered uncommon in other types of lung cancer [21]. Bronchioloalveolar carcinoma (BAC) is one of the few lung tumors known to demonstrate the air bronchogram sign. Production of this valuable radiologic sign by this tumor has been ascribed to an “alveolar” filling process in which the tumor grows along alveolar walls with preservation of the architecture and secretes copious amounts of mucus. Thus, aerated bronchi are surrounded by alveoli that are filled with mucus and tumor [22]. BAC accounts for about 4% of all primary lung malignancies; it is more common in females and never-smokers. The radiologic presentations of BAC are diverse and vary from solitary or multiple pulmonary nodules to cystic disease, cavitation, and consolidation. Most consolidations in BAC are peripheral in location, and can persist for a long duration, making it difficult to differentiate from consolidation of an infective origin [23].

4.10 CT Angiogram Sign Feature Enhanced CT shows hyperattenuation dendritic pulmonary vasculature in the area of uniform and consistent pulmonary consolidation, with the shape of branching or punctiform shadows. Explanation CT angiogram sign is mainly seen in bronchoalveolar carcinoma (BAC), followed by lung consolidation caused by diseases such as primary pulmonary lymphoma, obstructive pneumonitis, and infectious pneumonitis. The homogeneous and consistent consolidation lung tissue is the sac cavity filled with mucus, and the high-density dendritic angiography is the shadow of undamaged pulmonary vessels, which is the result of the difference between the two tissues (Fig. 4.10).

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Fig. 4.10  Enhanced chest CT shows pulmonary vascular shadows in uniform hypoattenuation area of lung parenchyma with the shape of branching or punctiform shadows

Discussion The CT angiogram sign was first proposed by Im et al. in 1990 and is considered as a characteristic manifestation of BAC [24]. According to the study of Im et al., “CT angiogram sign” is described as the enhancement of normal vascular trees in the uniformly low-density atelectasis (or consolidation) of the lung, during peripheral intravenous contrast agent and chest dynamic CT scans. The CT angiogram sign must meet three conditions: (1) uniform consolidation or atelectasis of the unit lung (segment, lobe, and whole lung); (2) normal vascular network in the lesion area; and (3) appropriate injection of contrast agent and CT scanning protocols. The CT angiogram sign consists of enhancing pulmonary vessels in a homogeneous low-attenuating consolidation of lung parenchyma relative to the chest wall musculature at the mediastinal window. This sign has been described in the lobar form of bronchoalveolar cell carcinoma. Pneumonia is another important cause of CT angiogram sign. The low-attenuating area has been considered as the result of mucus production by tumor cells. CT angiogram sign has also been reported in pulmonary edema, obstructive pneumonitis caused by central lung tumors, lymphoma, and metastasis from gastrointestinal carcinomas [25]. BAC represents a subgroup of adenocarcinoma and accounts for 5% of all bronchogenic carcinomas in most series. BAC can be separated into two basic morphological types: mucinous and Clara

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cell, and two spread pattern types: tumors with aerogenous spread and those without aerogenous spread. The mucinous tumors account for 20% to 30% of BAC and are characterized by tall, mucusfilled columnar cells. The mucinous tumors tend to spread aerogenously, infiltrating along the preexisting normal framework of the lung (i.e., lepidic growth). Four clinical manifestations are reported: (a) single nodule, (b) multiple nodules, (c) single consolidation, and (d) multiple lobar consolidations. Single and multiple lobar consolidations are more common in the mucinous tumors. BAC in a patient with alveolar consolidation remains difficult to diagnose clinically and radiologically. In cases of obstructive pneumonitis and primary pulmonary lymphoma, investigators have suggested that it is the relative difference between the attenuation of the pulmonary vessels and that of the consolidated lung parenchyma rather than an absolute low attenuation value of the consolidated lung that is responsible for the CT angiogram sign. Although CT angiogram sign is not specific for BAC, it still may be considered a useful sign in imaging. The sign is seen with a limited number of entities, all of which involve the enhancement of unaffected pulmonary vessels coursing through low-attenuating consolidated lung parenchyma. Correlation of the imaging findings with the clinical findings may help to further narrow the differential diagnosis to a specific entity [26].

4.11 Air Bronchiologram Sign Feature Air bronchiologram sign refers to the air density shadow (the inflatable bronchus , which is parallel to the CT scan plane of a small tubular or small strip (diameter 1 cm) are composed of numerous nodules on CT images. There are small satellites points around large nodules with rela-

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tively clear boundary. The characteristic pattern of large nodules in the pulmonary parenchyma resembles a galaxy consisting of millions or even billions of stars. Explanation The galaxy sign is the characteristic CT appearance of large nodules in the pulmonary parenchyma of sarcoidosis, which is standard for noncaseating granuloma lesions from the confluence of numerous nodules (Fig. 4.35). Discussion The galaxy sign, also called the sarcoid galaxy, is used to describe pulmonary parenchymal nodules seen in sarcoidosis that are composed of several smaller interstitial nodules. The appearance of a central dense mass with tiny peripheral satellite nodules is akin to a galaxy cluster [97]. It is most often between 1 and 2 cm in diameter but can be larger. The galaxy sign represents interstitial granulomas that have coalesced and become

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inseparable, simulating the appearance of a larger nodule [98]. The galaxy sign was initially described in sarcoidosis but is not specific for this condition. The galaxy sign may also be present in active tuberculosis (TB). Findings mimicking the galaxy sign may be present in progressive massive fibrosis (PMF) and neoplasm. The location and number of conglomerated nodules as well as the overall pattern of parenchymal disease and presence of associated findings such as lymphadenopathy must be taken into consideration when formulating a differential diagnosis. The presence or absence of lymphadenopathy can also be very helpful. Bilateral hilar lymphadenopathy is a hallmark of sarcoidosis and occurs either alone or with mediastinal lymphadenopathy in 95% of patients with sarcoidosis. Calcification within hilar and mediastinal lymphadenopathy is also helpful as it is common in sarcoidosis but rare in untreated malignancy. Active TB can also present with a conglomerate nodule surrounded by smaller nodules. The location and

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Fig. 4.35  CT plain scan shows small nodules around the large nodules, with typical sarcoid galaxy sign (a, b)

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number of the nodules as well as associated findings are useful in differentiation from sarcoidosis. The galaxy sign in active TB favors the upper lobes and the superior segments of the lower lobes, although it does not demonstrate a specific lobar distribution in sarcoidosis. Therefore, a single isolated focus of the galaxy sign favors TB. Lymphadenopathy is more common in sarcoidosis whereas tree-in-bud opacities are characteristic of TB. PMF in pneumoconiosis can loosely mimic the appearance of a galaxy sign, but distinguishing PMF from the galaxy sign in sarcoidosis is usually not difficult. PMF is characterized by extensive architectural distortion, traction bronchiectasis, paracicatricial emphysema, and nodules mixed with haphazardly arranged bands of fibrosis. In the galaxy sign, fine nodules emanate from a larger central nodule without these extensive fibrotic changes. The satellite nodules must be distinguished from the spiculated lung nodules typical of malignancy. Extensive mediastinal and bilateral hilar lymphadenopathy is rarely seen in non-­ small cell lung cancer, especially in lesions less than 3 cm [97]. Clinical history and demographics can be helpful in troublesome cases. Sarcoidosis can affect patients at any age but is commonly diagnosed before the age of 40 years, with the peak incidence in the third decade of life. Malignancy is more common in older patients; tuberculosis risk factors or occupational exposure can lead one to more strongly consider active TB or PMF, respectively. The galaxy sign favors a benign etiology and in the context of appropriate demographics, history, and associated findings can be quite helpful in establishing a specific diagnosis [98].

4.36 Diaphragm Sign; the Interface Sign; the Bare Area Sign; the Displaced Crus Sign Feature In conventional upper abdominal CT scans, free pleural effusion is sometimes difficult to distinguish from peritoneal effusion. Especially when

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the volume of effusion is small, the following four signs can be used to differentiate pleural and peritoneal effusion [99]. (1) The diaphragm sign means the pleural effusion and peritoneal effusion are located in different positions of the diaphragm. Pleural effusion is located around the diaphragm, whereas peritoneal effusion is located in the center of the diaphragm, surrounded by the diaphragm. (2) In the interface sign, the interface between pleural effusion and adjacent liver or spleen is blurred, and the interface between peritoneal effusion and adjacent liver or spleen is clear. (3) The bare area sign refers to the area near the posterior abdominal wall of the right lobe of the liver, which lacks peritoneal tissue, and the liver directly contacts the posterior abdominal wall, so there is no peritoneal effusion on the posterior edge. (4) The displaced crus sign refers to the pleural effusion located between the diaphragm angle and the spine, pushing the diaphragm angle forward, causing diaphragm angle displacement. This is not the case with peritoneal effusion. Explanation In conventional upper abdominal CT scans, free pleural effusion is sometimes difficult to distinguish from peritoneal effusion. Halvorsen et al. have summarized four signs for the differential diagnosis of pleural and peritoneal effusion. In peritoneal effusion patients, any patients lack adequate perihepatic fat to identify the diaphragm. Because the attenuation of ascites is less than that of the diaphragm and the liver, the diaphragm sign is visible in patients with peritoneal effusion, and because of the small effect of partial volume, the boundary between ascites and surrounding organs is clear. Not only that, peritoneal effusion is prevented from extending behind the liver at the level of the bare area. When pleural effusion occurs, the interface between pleural effusion and adjacent liver or spleen is blurred. This appearance is presumed to be caused by the diaphragm separating pleural effusion from the liver. Pleural effusion can extend behind the liver at this level because the posterior sulcus of the right pleural space extends behind the liver. Therefore, fluid behind the liver

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at the level of the bare area is in the pleural space, not intraperitoneal. In practical work, these four signs are inseparable. If only one of them is used, it will lead to difficulties in identification or misjudgment. Taking the four signs

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into consideration, the correct rate of diagnosis can be significantly increased. Usually these four signs are collectively referred to as pleural and peritoneal effusion differential quadruple sign (Fig. 4.36).

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Fig. 4.36  Diaphragm sign (a): the diaphragm is clearly visible between the pulmonary and peritoneal effusions. Interface sign (c, d): the interface between pleural effusion and liver is blurred. (e, f) The interface between peritoneal effusion and liver is clear. Bare area sign (g):

peritoneal effusion diffuses to the front and side edges of the liver but does not enter the bare area of the liver. (h, i) Pleural effusion can be seen into the bare area. Displaced crus sign (j): in the right pleural effusion, the diaphragm angle is displaced to the outside

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Fig. 4.36 (continued)

Discussion CT diagnosis of pleural and peritoneal effusion is generally clear, but sometimes it is difficult to differentiate a small amount of pleural and peritoneal effusion. The CT value of peritoneal effusion is lower than 0–15 HU, which often gathers around the liver and spleen and pushes the latter forward. However, when pleural effusion is in the lateral posterior recess of the pleural cavity, it can also be in the lateral posterior part of the liver and spleen and push the liver and spleen forward. Therefore, pleural effusion should be differentiated from peritoneal effusion in CT scan of the upper abdomen [100]. The location of the diaphragm is easy to observe when peritoneal effusion occurs. However, in many patients with pleural effusion, because the diaphragm is insep-

arable from the liver, it is difficult to see, so the diaphragm sign is more useful for identifying peritoneal effusion. The boundary between the pleural effusion and the liver or the spleen is blurred, possibly because of the insertion of the diaphragm between the effusion and the liver or the spleen. Because the diaphragm is obliquely transected during transverse scanning, a partial volume effect is inevitable, leading to blurring of the interface between the effusion and the liver or spleen [101]. The peritoneal effusion is generally at a low position, and there is no partial volume effect from diaphragmatic insertion between the peritoneal effusion and adjacent organs, so the interface is clear and well defined. If the thickness of the scanning layer is thinned, the interphase

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between pleural effusion and liver or spleen can be clearer, but it cannot achieve the interface clarity of the peritoneal effusion. The posterior of the liver is attached directly to the posterior abdominal wall. This part of the liver without peritoneal coverage is called the bare area. The upper and lower layers of the hepatic coronary ligament are attached to the posterior part of the liver and the lower part of the liver. They form the bare area of the liver, occupying the lower and posterior of the right lobe of the liver and to the last third of the liver. Although the abdominal cavity is blocked by the bare area, the peritoneal effusion cannot reach the side of the spine. However, it is worth noting that the blocking scope of the bare area of the liver is limited, and it can flow freely above and below the bare area.

4.37 Split Pleura Sign Feature The split pleura sign is seen on postcontrast chest CT images with enhancement of the thickened inner visceral and outer parietal pleura, separated by a collection of pleural fluid. Explanation Thoracic empyema is defined as purulent content in the pleural cavity. Empyema most commonly occurs in the setting of bacterial pneumonia. It typically develops from transformation of a parapneumonic effusion (not infected) into a complicated effusion (features of infection but not purulent) and then into empyema. In parapneumonic effusion, fluid moves in the interpleural space by the increased capillary vascular permeability. Proinflammatory cytokines facilitate the fluid entry into the pleural cavity and cause hyperemia. With increasing fluid accumulation and bacterial invasion through the damaged endothelium, transudative effusion progresses to empyema. As empyema progresses, a fibrin peel coats the surfaces of the visceral and parietal pleural layers with ingrowth of capillaries and fibroblasts and subsequent thickening, forming the basis of the split pleura sign: thickened visceral and parietal pleural layers separated by empyema (Fig. 4.37).

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Fig. 4.37 Postcontrast CT shows empyema between thickened parietal and visceral pleural layers

Discussion Normal visceral and parietal pleura are indistinguishable on CT images. In the presence of an exudative pleural effusion with loculation, inflammatory changes may thicken both the visceral and parietal pleura that surround the fluid collection and may become evident as the split pleura sign, suggesting the presence of empyema. A loculated effusion may have an atypical chest radiographic appearance when located within a fissure. The split pleura sign may be seen in combination with the air–fluid level sign when a bronchopleural fistula occurs within empyema. Empyema should be considered when a patient presents with fever, cough, and chest pain and CT shows split pleura sign [102]. The split pleura sign is not specific for empyema but rather indicates the presence of an exudative effusion. Other important causes of this sign include parapneumonic and malignant effusions, hemothorax, and sequelae of previous talc pleurodesis, lobectomy, or pneumonectomy. Hemothorax usually has associated heterogeneously high attenuation, and talc pleurodesis has attenuation resembling that of calcium and is often clumped [102]. About half of empyema are caused by gram-positive bacteria (Staphylococcus aureus, Streptococcus pneumoniae); the remainder are gram-negative organisms commonly growing together with other gram-negative organisms or anaerobes. In summary, the split pleura sign refers to thickening and increased contrast enhancement of the

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visceral and the parietal pleura separated by empyema or an exudative effusion [103]. Increased attenuation of extrapleural fat and thickening of the fat layer of 3  mm or more is seen in 60% of empyema. Pneumonia, lung abscess, or obstructing malignancy are readily evident on contrast-enhanced studies. In patients with fibrinopurulent pleural infections, the underlying lung often shows multiple alternating outpouchings and indentations from fibrin strands that produce intrapleural adhesions. Septations within an infected effusion are less readily imaged as compared with ultrasonography. Pleural-based lung abscesses may be difficult to distinguish from loculated empyema. On CT scan, lung abscesses tend to be round rather than lenticular in shape as are empyema, have thick, irregular walls, and do not displace adjacent lung. If ineffectively treated, empyema can progress to a fibrothorax that appear as uniform smooth thickenings of the pleurae with hypertrophy of the extrapleural fat and reduced volume of the affected empyema with narrowing of the intercostal spaces and shift of the mediastinum to the affected side. Chest CT scan cannot predict the likelihood that pleural thickening during the fibrinopurulent phase of pleural infections will progress to fibrothorax [104].

4.38 S  ubpleural Line; Subpleural Curvilinear Shadow Feature Subpleural line refers to the linear within 1  cm below the pleura on chest CT, and parallels the pleura with a length of 1–5 cm. Explanation Subpleural curvilinear shadow is one of the CT findings of interstitial lung disease, which is a manifestation of the flattening of alveoli and atelectasis caused by peribronchiolar interstitial hyperplasia and pulmonary fibrosis (Fig. 4.38). Discussion Subpleural curvilinear shadow (SCLS) is commonly seen in the posterior part of the lung on

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Fig. 4.38  In a 76-year-old woman, chest plain CT shows subpleural fibrous cords of inferior lobe of the right lung, the subpleural curvilinear shadow (arrow)

HRCT, but the shadow is more than one lung segment in scope and located in the non-pendent part of the lung. When the position changes, its shape does not change and will not disappear. Most of the SCLS have a smooth, continuous surface; a few are irregular and discontinuous. SCLS has originally been visible in the lower dorsal lung field on chest CT scan in patients with pulmonary fibrosis and asbestosis. Some scholars described that SCLS in the lower dorsal lung field might be chronic changes such as fibrosis, and it might somewhat be attributed to the effect of gravity. Arai et  al. [105] showed two cases of transient SCLS caused by pulmonary congestion, and they speculated that SCLS was not a specific finding in pulmonary fibrosis and asbestosis. SCLS in a patient was located lateral to anterior parts of both upper lobe of the lungs. Therefore, it might not be a gravity-related chronic parenchymal abnormality. Histopathological findings of SCLS in a patient were alveolar septal thickening and marked infiltration of eosinophils. There was no fibrosis or organizing change. In addition, the shadow responded dramatically and disappeared soon after corticosteroid therapy. This response implied that the shadow might be a transient change such as plate-like atelectasis or inadequate lymphatic flow from an exudative lesion [106]. In the past, some scholars thought that the subpleural curvilinear shadow was more common in asbestosis, or that this sign was the unique

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Discussion Signet ring sign is a finding seen on chest CT, which is characterized by small circular soft-­ tissue attenuation shadow connected with a large soft-tissue attenuation ring with circular hypoattenuation area and shaped like a signet ring [107]. In histopathology, the soft-tissue attenuation ring represents the dilated bronchial wall, the low attenuation of which is the air contained in the dilated bronchus, and the small circular soft-­tissue attenuation shadow represents the pulmonary artery associated with the dilated bronchus. Bronchiectasis refers to the unrecoverable abnormal expansion of the local bronchi caused by destruction of the elastic tissue and muscle tissue of the bronchial wall, often accompanied by thickening of the bronchial wall. Bronchiectasis is often divided into cystic, columnar, varicose, and mixed types. Columnar bronchiectasis is the lightest type, characterized by mild and consistent expansion; variceal bronchiectasis refers to moderate, irregular bead-like dilatation; cystic bronchiectasis is most severe; and bronchus is saclike. The clinical manifestations of bronchiectasis are nonspecific, manifested as chronic cough, massive purulent sputum, repeated lung infections, and hemoptysis. Chest X-ray scan is the first step in the diagnosis of bronchiectasis. X-ray findings in 80% to 90% of patients with bronchiectasis can occur with lung texture aggregation, unclear edges, cir4.39 Signet Ring Sign cular light transmission, and thickening of the Feature bronchial wall to form two parallel linear shadSignet ring sign is formed by a small circular ows, also called the track sign. Although the chest soft-tissue attenuation shadow and large soft-­ X-ray can detect lesions, suggesting the possibiltissue attenuation ring with circular low-­ ity of bronchiectasia, it cannot make the diagnoattenuation area shaped like a signet ring on chest sis of bronchiectasis. The manifestations of CT. bronchiectasis CT vary widely, depending on the type of bronchiectasis and the relationship Explanation between the direction of bronchial travel and the The soft-tissue attenuation ring represents the scan plane. Normally, the diameter of the pulmodilated bronchial wall, the low attenuation of nary artery is slightly larger than the bronchial which is the air contained in the dilated bronchus, tube of the same level. When the ratio of the and the small circular soft-tissue attenuation bronchial artery is increased, that is, when the shadow represents the pulmonary artery associ- diameter of the bronchial tube is larger than that ated with the dilated bronchus (Fig. 4.39). of the adjacent pulmonary artery, and the signet manifestation of asbestosis patients, but research now shows that the subpleural curvilinear shadow can be seen in a variety of pulmonary interstitial fibrosis diseases, such as chronic bronchitis with pulmonary interstitial fibrosis, coal worker pneumoconiosis, idiopathic pulmonary interstitial fibrosis, or collagen disease caused by interstitial lung pulmonary changes from fibrosis and sarcoidosis. In addition, the subpleural curvilinear shadow is also seen in inflammation, pulmonary congestion, and inspiratory conditions. In the case of pulmonary interstitial fibrosis, the subpleural curvilinear shadow represents an early change in pulmonary interstitial fibrosis. The length of the subpleural curvilinear shadow is associated with the severity of pulmonary interstitial fibrosis, and some are reversible. Current research shows that the total percentage of all the interstitial lung features was then determined by combining the reticular, centrilobular nodule, linear scar, nodular, subpleural line, ground glass and honeycombing subtype volumes and dividing by the total volume of all subtypes including normal, interstitial, and emphysematous. There was no significant difference in the morphology of subpleural curvilinear shadow in different diseases. However, the subpleural curvilinear shadow lacks the value of differential diagnosis for most diseases.

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Fig. 4.39 (a–d) A 72-year-old woman with bronchiectasis. Chest CT shows the bronchial wall of the left lower lung is thickened, cystic dilated, with signet ring sign

ring sign appears. Then, bronchiectasis is considered [108]. The diameter of a cystic dilated bronchial tube is generally greater than 1  cm. The relationship between the trachea and the scanning plane is different, resulting in different CT findings of bronchiectasis. Parallel to the direction of bronchial movement, it manifests as track sign, and if perpendicular to the direction of bronchial movement, it appears as the signet ring sign. The CT findings of bronchiectasis include the signet ring sign, track sign, clustered sac, beaded shadow, and branching shadows from mucous caulking. The first three diagnoses are most useful.

4.40 Fallen Lung Sign Feature On sitting or standing chest films, lung tissue is collapsed and droops in a mass in the cardiophrenic angles or retrocardiac region. Explanation X-ray findings of the fallen lung sign are specific for bronchial rupture. With bronchial rupture, lung displacement is posterior and lateral in a supine position and inferior in a standing position. Symptoms that progress within hours raise the index of suspicion; a pneumothorax that per-

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Fig. 4.40  A 24-year-old man had no improvement in pneumothorax after chest tube. A large amount of gas was seen in the right thoracic cavity; lung tissue was collapsed and drooped in a mass in the cardiophrenic angles

sists or progresses despite a correctly placed chest tube is a valuable sign in the diagnosis of bronchial rupture (Fig. 4.40). Discussion The fallen lung sign was first described by Oh et al. in 1969 [109], indicating complete rupture or transection of the main bronchi. The term “fallen lung” refers to the peripheral displacement rather than the usual central displacement of the collapsed lung, which is usually the result of complete rupture of a bronchus. X-ray findings of the fallen lung sign are specific for bronchial rupture [110]. However, later it was reported that incomplete rupture also may produce this sign on CT and that the collapsed lung is displaced toward the dependent portions, or posteriorly in a supine patient. Although pneumothorax, pneumomediastinum, and soft-tissue emphysema may indicate a bronchial rupture, these signs may not be observed in early examination of most patients presenting with pneumothorax and pneumomedi-

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astinum following blunt trauma. Such ruptures are difficult to diagnose in an emergency, and the diagnosis is often delayed. Although fallen lung sign is rarely seen, it is highly specific for bronchial rupture. The specific signs of tracheal injury include deformity of the tracheal outline, an out-­ of-­place endotracheal tube, and an endotracheal tube cuff protruding beyond the outline of the trachea. Fallen lung sign is considered pathognomic of mainstem bronchial injury, in which the detached lung tends to collapse laterally and posteriorly, inferior to its attachment at the hilum, instead of being collapsed inward as in other cases of pneumothorax. Even partial injuries of the bronchus can produce this sign, and the changing position of the lung on patient repositioning can confirm the detachment [111]. Bronchial wall irregularity and surrounding air leakage may be seen in partial ruptures. The diagnosis in the rarely seen tracheobronchial rupture is generally established with CT or bronchoscopy. However, when the typical fallen lung sign is present, the diagnosis of bronchial rupture may be established on radiograph [112].

4.41 Ring Around the Artery Sign Feature On the lateral chest X-ray film, a clear and transparent image along or around the right pulmonary artery is called the ring around the artery sign. Explanation Pneumomediastinum refers to the accumulation of abnormal gases in the mediastinum. A gas shadow can delineate the boundary of the normal structure. When the gas surrounds the mediastinum (outer pericardium) of the right pulmonary artery, the lateral chest X-ray shows a clear shadow around the right pulmonary artery, which is called ring around the artery sign (Fig. 4.41). Discussion The ring around the artery sign was first reported by Hammond et al. in 1984 [113]. This sign is the

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Fig. 4.41  In a 20-year-old man with spontaneous pneumomediastinum, lateral chest X-ray shows a clear and transparent area (arrow) along the right pulmonary artery, called the ring around the artery sign

characteristic feature of pneumomediastinum in a lateral chest X-ray film. Pneumomediastinum refers to the accumulation of gas in the mediastinum, which can have various causes, the most common of which is the Macklin effect. Alveolar rupture is caused by the increase of intrapulmonary pressure. Gas spills into the interstitium around the alveolar through the rupture mouth. Under the compression of respiratory movement, gas can continue to move along the interstitium to the hilum of the lung, and finally enters the mediastinum to form a pneumomediastinum; this is the Macklin effect. Gases in the mediastinum can delineate different anatomical structures and have different imaging features. In addition to the circumferential sign around the mediastinum of the right pulmonary artery, the gas can also surround the thymus and elevate its position as sail sign; it can surround the ascending aorta, aortic arch, and the main branches of the aorta, as artery cannula sign; it can surround the trachea and proximal bronchus, as double bronchial wall sign; it can also surround the diaphragm and the

cephalobrachial vein. The ring around the artery sign is only used to describe patients with secondary asthma, trauma, subclavian artery intubation, and cocaine use or no definite inducement [114]. This sign is usually accompanied by other signs of pneumomediastinum. When pneumatosis occurs in the mediastinum, gas travels along the fascial space and accumulates around the pulmonary artery. Because only a small segment of the right pulmonary artery is located in the pericardium, the peripheral ring sign on lateral radiograph is only the extrapericardial segment of the pulmonary artery. In the differential diagnosis of pneumomediastinum, traumatic pneumomediastinum should be distinguished from spontaneous pneumomediastinum [115]. The former has a clear history of trauma, whereas the latter has no history of trauma and often accompanies basic pulmonary diseases. Second, traumatic pneumomediastinum should be differentiated from traumatic rupture of trachea and esophagus, because the former usually needs no treatment, and the gas can be absorbed by itself. Traumatic tracheal rupture often occurs near the bronchial bulge, showing continuous interruption of the tracheal wall. Pneumatosis is mostly around the end of the rupture without interstitial pneumatosis. When esophageal rupture occurs, if esophagography shows spillover of contrast medium, the diagnosis can be prompted. In a word, pneumomediastinum is caused by various reasons, and X-ray can make a diagnosis. On the lateral radiograph, the ring around the artery sign of pneumomediastinum can be displayed, and other signs of pneumomediastinum can also be observed.

4.42 Deep Sulcus Sign Feature A deep sulcus sign is seen on chest radiographs obtained with the patient in the supine position. It represents lucency of the lateral costophrenic angle extending toward the hypochondrium. The abnormally deepened lateral costophrenic angle may have a sharp angular appearance.

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Explanation When the patient is in the supine position, air in the pleural space (pneumothorax) collects anteriorly and basally within the nondependent portions of the pleural space; when the patient is upright, the air collects in the apicolateral location. If air collects laterally rather than medially, it abnormally deepens the lateral costophrenic angle and produces the deep sulcus sign (Fig. 4.42). Discussion In a supine film, a deep sulcus sign may be the only indication of a pneumothorax because air collects anteriorly and basally within the nondependent portions of the pleural space, as opposed to the apex when the patient is upright. Air enters the pleural space by crossing any of its boundaries, such as the chest wall, mediastinum, lung, or diaphragm. Recognition of a pneumothorax depends on the volume of air in the pleural space and the position of the body. The visceral pleural line, which is visible as a thin curvilinear opacity along the lung and is separated from the chest wall by air in the apical pleural space in the upright patient, is commonly not identifiable on radiographs of supine patients unless there is a sizable pneumothorax. Approximately 30% of

Fig. 4.42  Chest X-ray image of a newborn in the supine position: the indicated narrow, sharp, and black air-line forward to the abdominal region at the left costophrenic angle represents the deep sulcus sign in pneumothorax

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pneumothoraces are undetected on supine radiographs. The deep sulcus sign of pneumothorax may be present following severe chest injury [116]. However, false-positive deep sulcus signs have been described in chest radiographs of patients with chronic obstructive pulmonary disease and those receiving mechanical ventilation with high tidal volumes [117]. In addition to the deep sulcus sign, other clues may suggest the presence of a pneumothorax on supine radiographs: (a) relative lucency in the hypochondrial region or the entire hemithorax; (b) depression of an ipsilateral hemidiaphragm; (c) double-­ diaphragm appearance caused by air outlining of the anterior costophrenic angle and aerated lung outlining the diaphragmatic dome; (d) improved sharpness of the cardiomediastinal border by anteromedial collection of air, which may appear as a lucency; (e) increased sharpness of the pericardial fat pads; (f) visible inferior edge of a collapsed lower lobe or of the undersurface of the heart from air in the pleural space; (g) band of air in the minor fissure bounded by two visceral pleural lines; or (h) visible lateral edge of the right middle lobe caused by medial retraction in the presence of anterior pneumothorax [116]. The deep sulcus sign is a useful clue in the diagnosis of pneumothorax in neonates or in critically ill patients such as those who have undergone major trauma or are in intensive care units. This finding is also important in the intensive care setting for procedures such as insertion of a subclavian central venous catheter and for the use of positive pressure ventilation [116]. Pneumothorax is a common and important clinic condition in polytraumatized or critically ill patients. It is important that the lateral costophrenic angles are included on the radiograph, as failure to diagnose pneumothorax may be life threatening because of the risk of tension. However, up to 76% of all pneumothoraces may be occult when interpreted by trauma teams at the time of admission. In a retrospective review of 44 severely injured patients identified with occult pneumothoraces, the deep sulcus sign is the most commonly ‘missed’ radiologic sign [118]. Thoracic ultrasonography, as a part of extended focused assessment with sonography for trauma, can be utilized

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promptly at the bedside for early detection. The CT scan is the gold standard for the diagnosis of occult pneumothorax [118]. Nonetheless, identification of the deep sulcus sign on chest X-ray images obtained in the supine position can be useful for early diagnosis of pneumothorax.

4.43 Scimitar Sign Feature Scimitar sign is seen on the posterior and anterior chest X-ray film. It is a curved vascular shadow

on the right side of the heart, moving downward toward the diaphragm. Explanation The curved knife sign is formed by an abnormal pulmonary vein draining the right lung, which resembles a short curved Turkish knife (Fig. 4.43). Discussion Congenital pulmonary vein syndrome (CPVS) includes a group of congenital abnormalities of the chest that often occur simultaneously. CPVS

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Fig. 4.43 (a) CT angiography shows right pulmonary vein (RPV, arrow) draining into right atrium (RA). Angiography shows scimitar sign (arrows) of RPV in (b)

and draining into the RA in (c) [119]. (d) Chest X-ray pulmonary artery (PA) view shows scimitar sign in right lung field

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consists of many different developmental abnormalities, each representing a different congenital malformation of the chest. The main malformations of CPVS include pulmonary hypoplasia, partial anomalous pulmonary venous reflux (PAPVR), absence of pulmonary artery, pulmonary sequestration, unsegregated pulmonary artery blood supply, absence of inferior vena cava, repetitive diaphragm (accessory diaphragm); the secondary malformations of CPVS include tracheal triple, diaphragm bulge, partial absence of diaphragm, diaphragmatic cyst, horseshoe lung, esophagogastric lung, abnormal superior vena cava, and absence of left pericardium. Abnormalities associated with the heart and spinal cord are more common. The deformities just mentioned can occur alone or in combination. However, the most common deformities of CPVS are pulmonary hypoplasia and PAPVR.  When pulmonary hypoplasia and PAPVR coexist, it is called scimitar syndrome. Its characteristic manifestation is that a curved knife vein drains into the inferior vena cava from the upper or lower right diaphragm [120]. The scimitar syndrome is more common in women (1.4:1.0). Most of the patients were asymptomatic; in adulthood, this syndrome is only found accidentally after taking posterior and anterior chest X-rays. The symptoms of childhood are recurrent chest infections or dyspnea. Symptomatic patients have obvious left-to-­ right shunts or severe congenital heart disease. In most cases, this vein drains the whole right lung. However, in some cases, this vein may drain only the lower or middle lobes, and the upper lung may drain normally into the left atrium. Almost all blood from abnormal pulmonary venous drainage flows back to the inferior vena cava under the right diaphragm, and some to the portal vein, hepatic vein, and even left atrium. Because this abnormal pulmonary vein often drains unquantified blood flow from the right lung to the inferior vena cava, a left-to-right shunt is formed. Usually, this shunt is asymptomatic, unless the shunt reaches 2:1 or higher, and the cardiac cavity is normal, but 25% of patients have congenital heart disease, the most common being atrial septal defect. Other com-

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mon types are patent ductus arteriosus, aortic stenosis, tetralogy of Fallot, and ventricular septal defect [121]. The X-ray signs of the scimitar syndrome have diagnostic significance. The scimitar sign is common on posterior and anterior chest radiographs, but this sign may sometimes be blurred by overlapping with the heart, especially when the right heart is visible. This vein can be bent like a knife, straightened or thinned, and sometimes multiple veins are seen. Most of these are accompanied by right lung dysplasia, and the severity of this dysplasia determines the extent of heart and mediastinal displacement. The right lung is not only small, but also usually has trachea, bronchus, lobe, and deformities of interlobar fissure. Therefore, the upper or middle lobes and transverse fissures may be absent, and the right main bronchus may be elevated. These abnormalities make the right lung similar to the left lung [122]. Traditionally, angiography has been the best choice for displaying vascular anomalies when scimitar syndrome or pulmonary sequestration is suspected. CT angiography (CTA) as a noninvasive angiography is increasingly used in CPVS.  The scimitar syndrome rarely requires surgical treatment. Surgery is mainly intended for patients with left-to-right shunt, which can be treated by reorienting the curved vein into the left atrium. Recurrent pulmonary infections can be treated by lobectomy or pneumonectomy.

4.44 Bulging Fissure Sign Feature Bulging fissure sign represents expansive lobar consolidation causing fissural bulging or displacement by copious amounts of inflammatory exudate within the affected parenchyma. Explanation Classically associated with right upper lobe consolidation caused by Klebsiella pneumoniae, any form of pneumonia can manifest the bulging fissure sign (Fig. 4.44).

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Fig. 4.44  Posteroanterior (left) and lateral (right) radiographs show right upper lobe consolidation causing inferior bulging of minor fissure (black arrows), posterior

bulging of major fissure (white arrow), and inferomedial displacement of bronchus intermedius (asterisk)

Discussion The sign is frequently seen in patients with pneumococcal pneumonia [123]. The prevalence of this sign is decreasing, likely because of prompt administration of antibiotic therapy to patients with suspected pneumonia [124]. The bulging fissure sign is also less commonly detected in patients with hospital-acquired Klebsiella pneumoniae than in those with community-acquired Klebsiella infection [125]. Other diseases that manifest a bulging fissure include any space-­ occupying process in the lung, such as pulmonary hemorrhage, lung abscess, and tumor.

Explanation Lung abscess is commonly associated with aspiration pneumonia and septic pulmonary emboli. Common causative organisms include anaerobes, Staphylococcus aureus, and Klebsiella pneumoniae. Lung abscess is associated with increased morbidity and mortality. Prompt detection at imaging studies may improve patient care, enabling clinicians to treat patients with an appropriate course of antibiotic therapy (Fig. 4.45).

4.45 Air–Fluid Level Sign Feature In a patient with pneumonia, detection of an air– fluid level on chest radiographs or CT images suggests the presence of a lung abscess or empyema with bronchopleural fistula. The former typically requires medical treatment with antibiotics and the latter usually requires insertion of a chest tube for drainage.

Discussion Detection of an air–fluid level at chest radiography should prompt evaluation of its location as being in the lung parenchyma or within the pleural space. A lung abscess with an air–fluid level can be differentiated from empyema with bronchopleural fistula by measurement and comparison of the lengths of the visualized air–fluid level on orthogonal chest radiographs [126]. Because of the characteristic spherical shape of a lung abscess, an associated air–fluid level typically has equal lengths on posteroanterior and lateral chest radiographs. By contrast, empyema typi-

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Fig. 4.45 (a) Posteroanterior (left) and lateral (right) radiographs show right lower lobe cavity with air–fluid level (arrows) of equal length on both orthogonal views. Thick, irregular wall typical of lung abscess is evident. (b)

Axial CT image shows parenchymal location of right lower lobe cavity with air–fluid level, irregular internal contours, and associated bronchus (arrow) coursing to lesion

cally forms lenticular collections of pleural fluid, and an associated air–fluid level (e.g., bronchopleural fistula) usually exhibits length disparity when compared on posteroanterior and lateral chest radiographs. In addition, both entities typically display a difference in the angle of their interface with an adjacent pleural surface. A lung abscess usually forms an acute angle when it intersects with an adjacent pleural surface, and its wall is often thick and irregular. By contrast, empyema typically forms obtuse angles along its interface with adjacent pleura and usually has smooth, thin, enhancing walls [127]. Other differential diagnostic considerations for an intrathoracic air–fluid level include hemorrhage into a cavity, lung cancer, and metastatic disease.

and blurred on the other side, and the border is submerged in the adjacent tissue shadow.

4.46 Incomplete Border Sign Feature The incomplete border sign is a manifestation of an abdominal X-ray film or chest X-ray positive film, which means that the overall contour of a soft-tissue mass is clear and sharp on one side

Explanation The sign is an X-ray sign of extraabdominal mass and extrapulmonary mass. The blurred, incomplete border of the mass is because the soft-tissue mass fixed to the abdominal wall (or chest wall) has little difference in attenuation from the adjacent abdominal wall (or chest wall). On the other hand, the X-ray tangential line passes through the other side of the soft-tissue mass (free from the abdominal wall or protruding into the lung field), which can form a clear, sharp border (Fig. 4.46). Discussion In 1964, Mendelson et  al. first studied the “the incomplete border sign” and later it was discussed in some foreign textbooks [128]. It is a manifestation of abdominal radiograph or chest X-ray positive film, which means the overall contour of a soft-tissue mass is clear and sharp on one side and blurred on the other side, and the border is submerged in the adjacent tissue shadow [129].This sign may indicate that the mass origi-

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Fig. 4.46 (a) Chest film in the left-upper lung field (clavicle and first rib overlap) showed circular nodular shadow; the inner and lower boundary of the lesion was clear, the

outer upper edge was blurred, and showed the “incomplete border sign”; (b) CT showed that the lesion was a node protruding from the posterior chest wall [131]

nates from an extraabdominal or extrapulmonary site and is important for identifying the origin of the mass. On radiograph the border of the lesion is clear and sharp, depending on (1) the difference in attenuation between the lesion and the adjacent structure; or (2) the edge tangent to the X-ray beam [130]. Intraabdominal or intrapulmonary lesions satisfy these two conditions, the tissue attenuation is much larger than the surrounding air, and the edge is tangent to the bundle in any projection; while the extraabdominal and extrapulmonary lesions do not meet these criteria, often causing partial border blurring, resulting in the “incomplete border sign.” It is well known that a mass originating from the abdominal wall is easy to palpate. An incomplete border on the supine abdomen radiograph on a plain radiograph suggests that the mass is located outside the abdominal cavity (including hernia and masses), and this sign is more helpful in diagnosis when there is no gas in the hernia. When the extrapulmonary mass forms an incomplete border sign, it usually appears as a partial border smoothing of the lung field, and the border of the part connected to the chest wall is unclear. The most common extrapulmonary lesions are localized pleural effusion, rib lesions (fractures, primary or metastatic tumors, plasmacytoma), interstitial tumors, neurological tumors, hematoma, and intradermal

lesions. Any extrapulmonary lesions can produce incomplete border signs, but the most common is rib metastases, and the mediastinal mass can also have incomplete border sign. Pulmonary nodules are sometimes confused with the nipples. In addition to the position, the nipple shadow usually showed a sharp outer border and the inner border is unclear. The reason is that the nipples protrude out due to the compression of the film box, which is consistent with the formation mechanism of incomplete border sign. In short, in actual work, lesion localization is the first step in clinical practice and an indispensable step. Incomplete border sign is an important feature of extraabdominal or extrapulmonary masses. Understanding this sign can help radiologists correctly locate lesions and guide subsequent diagnosis and treatment.

4.47 Grey Snow Sign Feature In a patient with COVID-19 (CoronaVirus Disease 2019), an area of ground-glass opacity (GGO) with interlobular septal thickening or reticulation is detected on chest CT images. The GGO was defined as a hazy increase in lung attenuation with no obscuration of the underlying vessels on chest CT images.

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Explanation The pathological basis of COVID-19 is exudative inflammation. Histology shows bilateral diffuse alveolar damage with cellular fibromyxoid exudates. Interstitial mononuclear inflammatory infiltrates are seen in both lungs dominated by lymphocytes [132]. CT imaging shows pulmonary parenchyma and interstitium changes simultaneously, which are consistent with pathological changes. In the early stage, the distribution of lesions is mostly located in the subpleural peripheral pulmonary cortex; then gradually develops from the parenchyma of the lower peripheral to the interstitial in the center, involving alveoli and pulmonary lobules (Fig. 4.47). Discussion COVID-19 is a new type of pneumonia caused by the SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) that broke out in December 2019 in Wuhan City, Hubei Province, China [133]. COVID-19 is highly contagious. Currently, the main source of infection is patients with COVID-19, and asymptomatic infected people may also become the source of infection. Respiratory droplets and contact transmission are the main way of transmission, and the population is generally susceptible. The 2019-nCoV infec-

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tion was of clustering onset, is more likely to affect older males with comorbidities, and can result in severe and even fatal respiratory diseases such as acute respiratory distress syndrome; it is associated with intensive care unit (ICU) admission and high mortality [134]. The nasopharyngeal swab test for the COVID-19 ­ nucleic acids had been positive. The diagnosis of COVID-­19 should be based on comprehensive analysis of epidemiological history, clinical manifestations, laboratory tests, and imaging characteristics. Radiologic examination and diagnosis are an important part of the diagnosis and treatment. The hallmarks of COVID-19 infection on imaging were bilateral and peripheral ground-­glass and consolidative pulmonary opacities. There were more consolidated lung lesions in patients 5 or more days from disease onset to CT scan versus 4 or fewer days. Patients more than 50  years old had more consolidated lung lesions than those 50  years or younger. Notably, 20/36 (56%) of early patients had a normal CT.  With a longer time after the onset of symptoms, CT findings were more frequent, including consolidation, bilateral and peripheral disease, greater total lung involvement, linear opacities, “crazy paving” pattern, and the “reverse halo” sign [135].

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Fig. 4.47 (a, b) Grey snow sign. HRCT images of two confirmed COVID-19 patients showed lesions distributed in the subpleural peripheral pulmonary cortex, with single

(a, black arrow) or multiple (b, black arrow) GGO accompanied by interlobular septal thickening (b, white arrow) and thickened bronchial vascular bundle (b, arrow)

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Grey snow sign is often observed in the mild cases on HRCT. It is observed in single or bilateral GGOs with interlobular septal thickening or reticulation and thickened bronchial vascular bundle. The lesions are distributed in the subpleural peripheral pulmonary cortex, looking like a wedge or trapezium. Because the coronavirus is inhaled through the respiratory tract, most cases first reach the region of subpleural lung periphery for gas exchange, which also explains the characteristic distribution of lesions. The presence of GGO on CT often indicates inflammatory exudation and edema, mainly in the lung interstitium. Meanwhile, the parenchyma can also be involved, and the alveolar cavity can contain half liquid and gas. In severe cases, gas exchange is affected, and the partial pressure of oxygen drops seriously. The majority of patients with mild cases tend to be stable and improve through isolation treatment, showing that the range of lesions is narrowed, the density is gradually reduced, the number of lesions is reduced, and the GGO can be fully absorbed. A small number of patients with basic underlying diseases or elderly patients can be more seriously affected. The COVID-19 still needs to be differentiated from viral pneumonia (influenza virus pneumonia, avian influenza

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pneumonia, SARS), mycoplasma pneumonia, bacterial pneumonia, and other viruses [136].

4.48 Ace-of-Spade Sign Feature The “spade-like” configuration of the left ventricle (LV) cavity at end-diastole on ventriculogram or cardiac MRI (CMRI) is a typical finding of apical hypertrophic cardiomyopathy (HCM) without left ventricular outflow tract (LVOT) obstruction. Explanation Differing from the hypertrophic obstructive counterpart, apical HCM does not have LVOT obstruction, and apical obliteration and proliferation are the characteristic pathological changes of this kind of myocardiopathy (Fig. 4.48). Discussion Apical HCM is an uncommon variant of nonobstructive HCM in which the hypertrophy is predominantly at the apex of the left ventricle. Sakamoto et al. initially described the electrocardiographic (ECG) pattern and echocardiographic characteristics in 1976 in Japan [137], but it was

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Fig. 4.48  Two-chamber (a) and three-chamber (b) long-axis cine-MRI can demonstrate apical hypertrophy. The narrowed portion of the ventricular cavity forms the cusp of the spade

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Yamaguchi who described the syndrome subsequently and demonstrated the typical “spade-­ like” appearance on ventriculogram, so apical HCM is also known as Yamaguchi syndrome [138]. The prevalence of apical HCM has been difficult to quantify, for the data vary with region and ethnicity. Some studies have suggested that apical HCM is particularly common in East Asian populations (41% of Chinese with HCM and 15% Japanese with HCM) [139, 140]. Recently, another study directly compared findings in Japanese and European centers showing that predominantly distal and apical hypertrophy is seen in almost similar percentages of Japanese (13%) and European (11%) patients, suggesting there may not be significant differences in prevalence of apical HCM between Asians and other racial groups [141]. Apical HCM is generally asymptomatic because of the lack of LVOT obstruction classically seen in HCM, although presentation with angina, heart failure, myocardial infarction, and atrial fibrillation has been reported [142]. Audible and palpable fourth heart sound can be heard reflecting impaired LV relaxation. Deep T-wave inversions are usually picked up on ECG, typically in the left precordial leads. Some ST-T abnormalities and atypical angina could be confused with coronary ischemia. “Giant” negative T-waves (defined as 10 mm deep) can be seen in half the patients with T-wave inversions on ECG [143]. Although echocardiography detects left ventricular hypertrophy and obstructive HCM well, it performs poorly in evaluating localized apical hypertrophy, apical pouches, or aneurysms, which are characteristics of apical HCM. Apex of the heart is often not well visualized, and the echo density of the hypertrophied apex may not be significantly different from the near ventricular cavity. Contrast echocardiography could be used to make the diagnosis but is not often performed [144]. Without noninvasive imaging modalities, apical HCM was once diagnosed based on left ventriculographic appearance of a “spade-like” ventricle, but it is no longer routinely performed in present clinical practice. Multislice CT (MSCT) evaluates the coronary

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artery when excluding coronary artery disease (CAD) if patients have atypical chest pain, showing the morphology of the LV wall and shape of the LV cavity. However, radiation and contrast exposure must be considered and the tissue fibrosis is not as well demonstrated as by CMRI. CMRI is the accurate imaging modality of choice to detect apical HCM. It provides good spatial resolution and can show the tight spade shape characteristic in cine-imaging. The quantitative diagnosis can be made when apical thickness is greater than 15 mm or a left ventricular apex to base wall thickness ratio of 1.3 or more is determined by CMRI. Late gadolinium enhancement (LGE) on CMRI confirms the existence of patchy fibrosis in the hypertrophied segment. LGE is associated with a higher risk of sudden cardiac events caused by fibrotic tissue, which can affect heart rhythm [145]. So, establishing the type of HCM and ruling out CAD is very important to the diagnosis and differential diagnosis, because apical HCM is generally benign and frequently asymptomatic [146]. The benign clinical course and long-term prognosis require us to make accurate diagnosis via the various imaging modalities and genetic markers available to offer credible guidance for follow-up management.

4.49 SAM Sign Feature Patients with hypertrophic cardiomyopathy (HCM) frequently have systolic anterior motion (SAM), which can be observed via transthoracic echocardiography (TTE) or cardiac MRI (CMRI) [147]. Explanation “SAM” means the position of mitral valve moves anteriorly into left ventricular outflow (LVOT) in systole, recognized as the main cause of LVOT obstruction. There is contact between the mitral valve and the septum in patients with obstructive HCM; the more prolonged the duration of mitral– septal contact, the higher the LVOT obstruction (Fig. 4.49).

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(ECG), cardiac imaging modalities to identify LV hypertrophy (LVH) should be performed in all patients to acquire evidence supporting the diagnosis. ECG should be checked in all patients with susceptible HCM. Although 90% of patients shows abnormalities such as prominent abnormal Q waves in inferior (II, III, aVF) and lateral (I, aVL, V4–V6) leads, the test is still specific enough for further diagnostic evaluation [147]. Two-dimensional echocardiography can be used to reliably diagnose patients with HCM. A clinical diagnosis of HCM is confirmed when unexplained increased LV wall thickness of 15  mm or more is imaged anywhere in the LV Fig. 4.49 Apical three-chamber long-axis cine-MRI wall [149]. A wall thickness of more than 13 mm shows minimal systolic anterior motion (SAM) of the may also be considered diagnostic of HCM, parmitral valve (black arrow) and LVOT obstruction ticularly for patients with a family history. The most common location for LVH is the basal anteDiscussion rior septum in continuity with the anterior free HCM is a genetic cardiomyopathy caused by wall, with the posterior septum the third most mutations of the cardiac sarcomere, leading to common location. When detecting the presence heterogeneous phenotypic expression with of LVH, among various of views, the parasternal respect to the extent, location, and distribution of short-axis plane is primarily used in diastole at left ventricle (LV) wall thickening. The clinical the level of the mitral valve and papillary muscle course may include sudden death (often younger [148]. Other echocardiographic findings suggesthan 30  years of age), heart failure (HF), or tive of HCM include increased LVOT gradient, stroke. The prevalence of HCM in the general SAM of mitral valve, and increased LA size assopopulation is 1  in 500. Patients may remain ciated with atrial fibrillation (AF) [150]. For the asymptomatic for a long time and then develop assessment of anatomic structures, CMRI may one or more atypical symptoms such as HF with provide additional information that is not availresultant dyspnea, fatigue, atypical chest pain, able from echocardiography [151, 152]. CMRI, syncope, and palpitation [148]. Physical exami- emerging as a modality particularly well suited nation in a patient with HCM may be normal or for characterizing the diverse subtype of HCM, reveal nonspecific abnormalities such as a fourth has higher spatial resolution and tomographic heart sound or systolic murmurs. Significantly, imaging capability without the burden of expoLVOT obstruction, often caused by a combina- sure to radiation and contrast [151]. Areas of segtion of SAM of mitral valve and LV upper septal mental LVH that are not reliably visualized by hypertrophy, results in a harsh systolic murmur echocardiography can be accurately identified beginning slightly after S1. The murmur may via CMRI.  In the study performed by Hindieh reflect both aortic outflow obstruction and mitral et al., 195 patients underwent both echocardiogregurgitation in patients with large ventricle-to-­ raphy and CMRI within a 6-month period, and in aorta gradients. A variety of tests have been used half the patients, maximal LV thickness was simin the evaluation of patients with possible ilar, whereas in the other 97 patients there was a HCM. By performing these tests, we can estab- discrepancy greater than 10% discrepancy in lish the diagnosis, identify the presence of sever- maximal LV thickness between the two imaging ity of LVOT obstruction or mitral regurgitation, modalities, for the majority of echocardiography and assess the overall LV function. Based on the overestimated the thickness. In instances where physical examination and electrocardiogram the determination of massive LVH thickness

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would impact the follow-up clinical management decisions, CMRI should be performed more reliably [153]. Structural abnormalities of the myocardium, mitral valve (i.e., elongation leaflets), and papillary muscles (i.e., accessory and apically displaced or anomalous insertion into the mitral valve leaflets) can be clearly demonstrated, meanwhile precisely identifying the mechanisms responsible for LVOT obstruction [151, 154– 156]. Because of the importance of mitral valve and papillary muscle anatomy in patients with LVOT obstruction who are being considered to undergo invasive septal myectomy, CMRI should be performed as a part of the evaluation [149]. Myocardial fibrosis can be shown with late gadolinium enhancement (LGE). In a prospective multicenter cohort of almost 1300 patients with HCM who underwent contrast CMRI, extensive LGE was an independent predictor of sudden death [157]. Once the diagnosis of HCM is established, based on clinical and echocardiographic modes or CMRI, ambulatory ECG monitoring should be performed for 24–48 h as a part of risk assessment for arrhythmias and other cardiovascular events [158]. Nowadays, the diagnosis of HCM can generally be made via noninvasive imaging modalities, and invasive diagnostic assessments have been rarely necessary. Cardiac catheterization is reservedly used for patients with suspected HCM to exclude coronary artery diseases and sometimes for the precardiac transplantation assessment.

4.50 Linguine Sign Feature The linguine sign can be seen on T2WI. Breast implants are characterized by multiple curvilinear low signal lines in hyperintense silica gel. Hypointense lines are often scattered, long-stripe low-signal lines, which are tortuous between each other looking like linguine. Explanation The linguine sign prompts the rupture of the breast implant envelope. The coating and filling of silica gel prosthesis consist of dimethyl sili-

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cone with different degrees of polymerization. The coating of a silica gel prosthesis adds some chemical bonds between methyl and silicone to form an elastic solid. The signal intensity of this polymer is lower than that of silica gel on MRI, with hypointensities on each sequence. On T2WI the elastic silica capsule showed a low signal and silica gel showed a high signal. Silica gel is released after the rupture of the silica gel capsule, forming a fibrous capsule (scar tissue) around the breast implant. Layers of coiled wire represent the elastic capsule floating in the silica gel (Fig. 4.50). Discussion The linguine sign was first put forward by Safvi in 2000 [159] and was named because it resembles Italy’s linguine. More and more women now have breast implants for cosmetic or reconstructive reasons, the most common of which is silica gel. Complications associated with silicone breast implants include cystic fibrosis or calcified contracture, rupture and leakage, local pain, deformation, and sensory abnormalities. Breast implant rupture is common. The rupture of the implant is mainly divided into two types: intracapsular and extracapsular. Intracapsular rupture refers to the destruction of the implant envelope, a small amount of silicone leakage but not beyond the fibrous capsule; extracapsular rupture refers to the implant envelope damage, amounts of silicone leakage beyond the fibrous capsule. On MRI, the surface of normal implants is smooth and the boundary clear. Silica gel is homogeneous in hypointensity on T1WI and hyperintensity on T2WI. Because of the cross-­ linkage of methyl, the envelope is low signal in all sequences. Radial folds are normal features of the capsule, usually with one end connected to the fibrous capsule. There are several types of breast prostheses, the most common of which is a single-lumen silicone implant wrapped in an elastic silicone film, with a smooth or woven surface. Silicone bleeding refers to a small leakage of silica gel through the capsule, which is common after surgery. In intracapsular rupture, fibrous capsules encapsulate silica gel, and in extracapsular rupture, silica gel leaks from the

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Fig. 4.50 (a–d) Line-like low-signal shadows can be seen on T2 (arrow)

ruptured fibrous capsule into breast tissue. The linguine sign often indicates intracystic rupture. This MRI sign is the most sensitive of all diagnostic modalities for fibrous capsule rupture, but sometimes needs to be differentiated from larger folds [160]. Folds can be extended to the edge of the implant. Extracapsular rupture of the prosthesis is often a further development of intracapsular rupture. All signs of intracapsular rupture can be seen, and free silica gel signals can be seen outside the fibrous capsule.

Explanation A malignant mass has a faster blood flow speed in the periphery, larger capillary diameter, more capillaries, and higher capillary permeability, making the flow of contrast medium in the periphery faster than in the center (Fig. 4.51).

Discussion The sensitivity of the peripheral washout sign to diagnosis malignancy is quite low, but the specificity is very high. Factors that determine this include capillary permeability, the number and size of capillaries in tumors, and the speed of 4.51 Peripheral Washout Sign blood flow. Some of these factors are directly related to tumor vascularity. Some studies have Feature shown that tumor cells release vascular growth The degree of enhancement around the lesion is factors, resulting in increased number and size of reduced relative to the central lesion on delay-­ capillaries and increased capillary permeability. phase dynamic contrast-enhanced MRI. Faster blood flow speed in the periphery, larger

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Fig. 4.51  Woman, 47 years old, with right breast cancer. (a–d) In the early and delayed phase of dynamic enhancement, a nodular abnormal enhancement was seen in the right breast. The edge is coarse and the shape is irregular [161]

capillary diameter, more capillaries, and higher capillary permeability mean the contrast medium of the periphery has a high turnover rate compared with the center; it can be transported rapidly from the blood vessels to the tissues. There is another mechanism for the flow of contrast medium in the tumor. If the transport occurs between parts of the tissue that have different hydrostatic force, the contrast agent will flow from the high-pressure area to the low-pressure area. Some studies suggest that the center of the malignant tumor is high pressure, and the peripheral area of the malignant tumor is low pressure. Between these two different pressure zones, there is a radial pressure gradient around the tumor. This gradient causes the flow of interstitial fluid. The flow of interstitial fluid pushes the contrast medium from the peripheral zone to the outside

of the tumor, whereas the contrast medium in the central of the tumor remains current from lack of a pressure gradient. On MRI most breast cancers have unclear margins, irregular shapes, and edges that are needle like or radial. Tumors showed hypointensity on T1WI, heterogeneous internal signal on T2WI, and mixed with hypointensity and hyperintensity. After contrast enhancement, the tumor shows moderate enhancement, the internal signal is still irregular, and there is no enhancement area. The lesions often present hyperintensity on DWI [162]. The structure of normal ductal tissue around the tumor is obviously disordered. After injecting the contrast medium, the peripheral and central features of malignant breast lesions showed different enhancement characteristics. In some malignant tumors, the peripheral enhance-

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ment was more obvious than the central enhancement at the first 2 min, and the two times intensity curves crossed at 8  min, then the peripheral enhancement curve continued to decrease while the central enhancement curve remained as the platform manifesting as a washout curve. In the dynamic MRI images, the filling phase of contrast medium reflects the transmission rate of contrast medium from endovascular to interstitial. On the clear phase of contrast medium, just the opposite occurred. The peripheral washout sign is a special indication for malignant lesions in delay-phase dynamic MRI enhancement. This sign also has potential value in the presence of tissue interstitial pressure in malignancy.

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on radiomics can improve the diagnosis of breast cancer and help to quantify the tumor [163]. According to the relationship between spicula and mass, it is divided into long spicula, short spicula, and star shadow. There is a significant difference in histological composition between the star shadow and the former two. The long and short spicula are mainly homogenous in pathological type, and the ratio of cancer cells to interstitial can be as follows: simple type (type Ib), even distribution of cancer nest and collagen fibers; medullary type (type II), with few collagen fibers in the cancer nest; and the sclerotic type (type III), mainly composed of collagen fibers and a few cancer cells. The star shadow is mainly heterogeneous, that is, there is a large collagen fiber (type Ia) between the cancer nests, 4.52 Spicular Sign and the attenuation inside the tumor is not inhomogeneous on the X-rays. The spicula at the edge Feature of the mass may be accompanied by calcification, A sharp-angled, whisker-like, slender or thin-­ on basis of cancer infiltration and diffusion, and short, flaming, or irregularly shaped shadow is of great significance for suggesting malignant extending from the breast mass to the s­ urrounding diagnosis. The incidence of spicular sign is glandular tissue with occasional calcification. affected by many factors, especially the type of mammary gland development. Other factors Explanation (such as radiographic conditions, technical equipSpicular sign is an imaging manifestation of ment) are also related to the detection rate of breast cancer infiltrating into surrounding glan- lesions, and the use of CT, MRI, and molybdedular tissue. According to the relationship num target enhancement is easier to show spicubetween spicula and mass, it can be divided into lar sign, and can eliminate the false spicula sign three types: (1) long spicula: from the edge of the caused by the overlap of mammary trabecula and mass, the length of the spicula exceeds one half mass. the maximum diameter of the mass; (2) short The breast mass with spicular sign is the spicula: from the edge of the mass, the length of highest diagnostic X-ray sign of breast cancer, the spicula is smaller than one half the maximum with an incidence of more than 60%. For the hisdiameter of the mass; (3) star shadow: spicula tological essence of the edge of the spicular sign from the center of the mass to surrounding diver- in the breast mass, most scholars formerly gence, radial or no clear mass, only radial spicula believed that it was mainly collagen fiber hyperfeature (Fig. 4.52). plasia, especially hard cancer. The reaction of peripheral fibrous hyperplasia was obvious, and Discussion most of them had marked spicular sign, which Spicular sign is an image finding of breast cancer was longer, and sometimes could even cover up infiltrating into surrounding glands. It is a sharp-­ the mass. Some investigators have found activity angled, whisker-like, slender or thin-short, flam- of collagen fibers around the breast mass was ing or irregularly shaped shadow extending from mainly moderate to low, indicating fibroprolifthe breast mass to the surrounding glandular tis- erative response is unremarkable, but the cancer sue with occasional calcification. Recently, it has infiltration is correspondingly significant. been reported that mammography analysis based Therefore, the histological essence of spicular

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Fig. 4.52  A 64-year-old breast cancer patient. (a, b) A nodular high-density shadow is seen in the central area of the right breast; the margin was rough and lobulated and spicular sign could be seen

sign is mainly cancer infiltration. Pathology showed the root of the spicula is a cancerous bed belt, the middle part is the inflammatory cell exudation zone, and the tip is the fibrous tissue hyperplasia zone. In addition, spicular sign may also be associated with lymphatic invasion of the tumor, catheter infiltration, abnormal vascularization, and tumor invasion of the suspensory ligament. In short, benign tumors generally do not have spicula, but spicula may also occur in tuberculosis and postsurgical scars. We should identify clinically relevant history to improve the accuracy of diagnosis.

4.53 Tiny Calcium Sign Feature Microcalcification is a mammography sign of breast cancer. It shows that many small calcification foci in the breast form calcification clusters, which are in small in size, of various shapes, and may be accompanied by masses. Explanation Calcification can occur in breast cancer cells, including living cancer cells and necrotic cancer cells. When the calcification point is more than

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Fig. 4.53  A right breast cancer patient has dense glands in the upper outer quadrant of the breast with multiple microcalcifications

100 μm, fine and dense calcification shadow can be displayed on mammography (Fig. 4.53). Discussion Microcalcifications are defined as localized calcium deposits in the breast tissue that represent an early diagnostic sign of breast cancer. The current strategy for evaluating and managing microcalcifications makes the important assumption that the microcalcifications are present within or are closely related to the most important underlying pathological change in the breast. Microcalcifications occur as a sequela of inflammation, progression of fibroadenoma, intraductal papilloma, and cystic and fibrotic changes, but may also be actively secreted, as is the case with malignant lesions. Microcalcifications are one of the main categories of abnormalities detectable by mammo-

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grams. Mammography has a sensitivity of 63–95%, and sensitivity increases with the presence of palpable lumps and is reduced in dense breasts [164]. The survival rates of breast cancer have risen significantly in recent decades from a combination of improved treatment options and early detection. Although some controversy exists, most studies have shown the adoption of mammography programming to confer a significant decrease in breast cancer mortality. Breast cancer can be detected by numberous mammographic features including density, architectural distortions, and the presence of microcalcifications. The clinical relevance of ­ microcalcifications was first identified in 1951 by Leborgne, who recognized they could constitute the sole mammographic indicator of carcinoma [165]. Microcalcifications also display a significant association with human epidermal growth factor receptor 2 (HER2) overexpression, although their relationship with hormone receptor (estrogen or progesterone) status is unclear as various studies have found both positive and negative associations or no association at all. Despite their significant contribution to the detection of breast tumors, the detailed mechanism by which microcalcifications form remains unknown [166]. Mammographic detection of microcalcifications has come to be regarded as a highly useful marker of breast cancer, with between 30% and 50% of nonpalpable tumors found in screening identified solely by the presence of microcalcifications. They are also present in the majority of ductal carcinoma in situ (DCIS) cases. Microcalcifications detected by mammography can be categorized based on their size, shape, chemical composition, and spatial distribution within the breast, allowing for assessment as a benign or suspicious finding. In addition to their utility as a detection marker, the presence of microcalcifications within a breast tumor may also be of prognostic significance, with many studies highlighting links between calcifications and poor prognosis, high tumor grade, and increased risk of recurrence.

4 Chest

4.54 Tattoo Sign Feature On mammography, the calcification is characterized by relative immobilization at different radiographs or at the same location. Explanation Intramammary calcifications lie within a volume of compressible fat and fibroglandular tissue. The precise relationship of the individual calcifications within the cluster can change as the tissue is compressed. Intramammary calcifications, therefore, do not maintain a fixed relationship to one another on mammograms obtained with the same view over time. In contrast, dermal calcifications are fixed within a thin plane of dermal tissue and do not change with relationship to one other during compression. Therefore, in the same way that pigments are fixed within the dermal layer in a tattoo, dermal calcifications maintain a fixed orientation to each other on mammograms obtained at different times (Fig. 4.54). Discussion In 1994, the tattoo sign regarding the orientation of dermal calcifications was recognized [167]. We call this the tattoo sign because it looks like the fixed pattern of a tattoo on the skin.

Fig. 4.54  The tattoo sign. Calcifications do not change orientation between the craniocaudal and the mediolateral oblique projections or from year to year. The tattoo sign is characteristic of benign skin calcifications [169]

169

Intramammary calcifications are contained within a volume of breast tissue, and their arrangement appears different in different projections. In contradistinction, dermal calcifications are oriented in a thin plane so that their arrangement should be similar, regardless of the projection used [167]. A cluster of microcalcifications observed on mammograms may be an early sign of breast cancer. Various characteristics, such as number, size, shape, and location, are used to judge whether the calcifications appear benign or malignant and whether further evaluation is warranted. Dermal calcifications are benign and require no further evaluation [168]. The pathognomonic mammographic feature of skin calcifications is conspicuous, round, solid, or lucent-centered calcifications, which frequently are grouped. They are commonly seen along the inframammary fold, cleavage area, overlying the axilla, and around the areola. If superficial in location, a tangential view is needed to confirm that they are dermal versus parenchymal [169]. Tattoo sign is important because it may be the only clue that suggests the dermal location of microcalcifications when other characteristics of dermal calcification are not present. In addition to the tattoo sign, another similar unnamed mammographic sign also indicates the presence of dermal calcifications, and it should be applied in all cases of peripheral calcifications. When mammograms are compared with prior mammograms obtained with the same projection and the tattoo sign or the afore-­ described unnamed sign is present, the suspected location of the microcalcifications should be the dermal layer [168]. Tattoo signs may even appear bilaterally and are most likely caused by a degenerative metaplastic process, including trauma or even sunburn. Dermal calcifications could suggest other skin-related diseases, including skin cancer, but dermal calcifications are unrelated to breast cancer. Breast calcifications are common findings on mammography, and their frequency increases with the age of the patient. Although the majority of microcalcifications that occur are benign, some specific grouped patterns can be caused by malignant disease or high-risk lesions. It is

170

important to differentiate the microcalcifications of benign origin from those that are suspicious, because 55% of nonpalpable cancers are diagnosed by the presence of microcalcifications, and because microcalcifications are the main form of manifestation of ductal carcinoma in situ (DCIS). Some of these calcifications correspond not only to pure DCIS but also to the intraductal portion of infiltrating carcinomas. The density difference between the benign and malignant calcifications is mainly given by the various chemical compounds prevailing in each one. Benign calcifications are composed mainly of calcium oxalate, but malignant calcifications are composed predominantly of calcium phosphate. The two types coexist, and their components cannot be determined via mammography, so chemical studies are required for these purposes [170]. Tomosynthesis still exhibits a debatable usefulness in the detection of microcalcifica­ tions. Some studies show detection rates similar to or somewhat lower for tomosynthesis compared with digital mammography. A recent meta-analysis evaluated the usefulness of this method for classifying microcalcifications according to the BI-RADS categories, demonstrating that tomosynthesis classified the findings similarly to digital mammography in most cases; however, it subclassified some malignant and premalignant lesions. Therefore, tomosynthesis should still be used with caution in evaluating microcalcifications, and it is possible that the incorporation of new or complementary descriptors to the BI-RADS lexicon will be required in the future [170].

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174 130. Hsu CC, Henry TS, Chung JH, Little BP.  The incomplete border sign. J Thorac Imaging. 2014;29(4):W48. 131. Huang KY, Shen TC, Tu CY. Incomplete border sign. QJM. 2013;106(9):871–2. 132. Xu Z, Shi L, Wang Y, Zhang J, Huang L, Zhang C, Liu S, Zhao P, Liu H, Zhu L, Tai Y, Bai C, Gao T, Song J, Xia P, Dong J, Zhao J, Wang FS. Pathological findings of COVID-19 associated with acute respiratory distress syndrome. Lancet Respir Med. 2020; 8(4):420–2. 133. Chen N, Zhou M, Dong X, Qu J, Gong F, Han Y, Qiu Y, Wang J, Liu Y, Wei Y, Xia J, Yu T, Zhang X, Zhang L. Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study. Lancet. 2020;395(10223):507–13. 134. Huang C, Wang Y, Li X, Ren L, Zhao J, Hu Y, Zhang L, Fan G, Xu J, Gu X, Cheng Z, Yu T, Xia J, Wei Y, Wu W, Xie X, Yin W, Li H, Liu M, Xiao Y, Gao H, Guo L, Xie J, Wang G, Jiang R, Gao Z, Jin Q, Wang J, Cao B. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet. 2020;395(10223):497–506. 135. Song F, Shi N, Shan F, Zhang Z, Shen J, Lu H, Ling Y, Jiang Y, Shi Y. Emerging Coronavirus 2019nCoV Pneumonia. Radiology. 2020;295(1):210–7. 136. Koo HJ, Lim S, Choe J, Choi SH, Sung H, Do KH. Radiographic and CT features of viral pneumonia. Radiographics. 2018;38(3):719–39. 137. Sakamoto T, Tei C, Murayama M, et al. Giant T wave inversion as a manifestation of asymmetrical apical hypertrophy (AAH) of the left ventricle: echocardiographic and ultrasonocardiotomographic study. Jpn Heart J. 1976;17(5):611–29. 138. Yamaguchi H, Ishimura T, Nishiyama S, et al. Hypertrophic nonobstructive cardiomyopathy with giant negative T waves (apical hypertrophy): ventriculographic and echocardiographic features in 30 patients. Am J Cardiol. 1979;44(3):401–12. 139. Ho HH, Lee KL, Lau CP, Tse HF. Clinical characteristics of and long-term outcome in Chinese patients with hypertrophic cardiomyopathy. Am J Cardiol. 2004;116(1):19–23. 140. Kitaoka H, Doi Y, Casey SA, Hitomi N, Furuno T, Maron BJ. Comparison of prevalence of apical hypertrophic cardiomyopathy in Japan and the United States. Am J Cardiol. 2003;92(10):1183–6. 141. Chikamori T, Doi YL, Akizawa M, et al. Comparison of clinical, morphological and prognostic features in hypertrophic cardiomyopathy between Japanese and western patients. Clin Cardiol. 1992;15:833–7. 142. Maron MS, Finley JJ, Bos JM, Hauser TH, et al. Prevalence, clinical significance, and natural history of left ventricular apical aneurysms in hypertrophic cardiomyopathy. Circulation. 2008;118(15):1541–9. 143. Eriksson MJ, Sonnenberg B, Woo A, et al. Long-term outcome in patients with apical hypertrophic cardiomyopathy. J Am Coll Cardiol. 2002;39:638–45.

T. Jiang et al. 144. Leaphart D, Waring A, Suranyi P, Fernandes V.  Call a spade a spade: missed diagnosis of apical hypertrophic cardiomyopathy. Am J Med Sci. 2019;358(4):299–303. 145. Yamada M, Teraoka K, Kawade M, et al. Frequency and distribution of late gadolinium enhancement in magnetic resonance imaging of patients with apical hypertrophic cardiomyopathy and patients with asymmetrical hypertrophic cardiomyopathy: a comparative study. Int J Cardiovasc Imaging. 2009;25(suppl 1):131–8. 146. Camelia CD, Nicoleta D, Ana GF, Smarandita L, Daniela B. Apical hypertrophic cardiomyopathy: the ace-of-spades as the disease card. Acta Cardiol Sin. 2015;31:83–6. 147. Veselka J, Anavekar NS, Charron P. Hypertrophic obstructive cardiomyopathy. Lancet. 2017; 389(10075):1253–67. 148. Wigle ED, Rakowski H, Kimball BP, Williams WG. Hypertrophic cardiomyopathy: clinical spectrum and treatment. Circulation. 1995;92(7):1680–92. 149. Gersh BJ, Maron BJ, Bonow RO, Dearani JA, et al. 2011 ACCF/AHA guideline for the diagnosis and treatment of hypertrophic cardiomyopathy: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation. 2011;124(24):2761–96. 150. Nistri S, Olivotto I, Betocchi S, Losi MA, et al. Prognostic significance of left atrial size in patients with hypertrophic cardiomyopathy (from the Italian Registry for Hypertrophic Cardiomyopathy). Am J Cardiol. 2006;98(7):960–5. 151. Bogaert J, Olivotto I. MR imaging in hypertrophic cardiomyopathy: from magnet to bedside. Radiology. 2014;273(2):329–48. 152. Maron MS, Maron BJ. Clinical impact of contemporary cardiovascular magnetic resonance imaging in hypertrophic cardiomyopathy. Circulation. 2015;132(4):292–8. 153. Hindieh W, Weissler Snir-A, Hammer H, Adler A, Rakowski H, Chan RH. Discrepant measurement of maximal left ventricular wall thickness between cardiac magnetic resonance imaging and echocardiography in patients with hypertrophic cardiomyopathy. Circ Cardiovasc Imaging. 2017;10(8):e006309. 154. Sherrid MV, Balaram S, Kim B, Axel L, Swistel DG.  The mitral valve in obstructive hypertrophic cardiomyopathy: a test in context. J Am Coll Cardiol. 2016;67(15):1846–58. 155. Maron MS, Olivotto I, Harrigan C, et al. Mitral valve abnormalities identified by cardiovascular magnetic resonance represent a primary phenotypic expression of hypertrophic cardiomyopathy. Circulation. 2011;124(1):40–7. 156. Harrigan CJ, Appelbaum E, Maron BJ, et al. Significance of papillary muscle abnormalities identified by cardiovascular magnetic resonance in hypertrophic cardiomyopathy. Am J Cardiol. 2008;101(5):668–73.

4 Chest 157. Chan RH, Maron BJ, Olivotto I, Pencina MJ, Assenza GE, et al. Prognostic value of quantitative contrast-enhanced cardiovascular magnetic resonance for the evaluation of sudden death risk in patients with hypertrophic cardiomyopathy. Circulation. 2014;130(6):484–95. 158. Weissler-Snir A, Chan RH, Adler A, Care M, et  al. Usefulness of 14-day Holter for detection of nonsustained ventricular tachycardia in patients with hypertrophic cardiomyopathy. Am J Cardiol. 2016;118(8):1258–63. 159. Safvi A.  Linguine sign. Radiology. 2000;216(3): 838–9. 160. Berg WA, Nguyen TK, Middleton MS, Soo MS, Pennello G, Brown SL. MR imaging of extracapsular silicone from breast implants: diagnostic pitfalls. AJR Am J Roentgenol. 2002;178(2):465–72. 161. Rahbar H, Partridge SC.  Multiparametric breast MRI of breast cancer. Magn Reson Imaging Clin N Am. 2016;24(1):223–38. 162. Pinker K, Helbich TH, Morris EA.  The potential of multiparametric MRI of the breast. Br J Radiol. 2017;90(1069):20160715. 163. Sapate SG, Mahajan A, Talbar SN, Sable N, Desai S, Thakur M. Radiomics based detection and characterization of suspicious lesions on full field digital mammograms. Comput Methods Prog Biomed. 2018;163:1–20. 164. Ouyang YL, Zhou ZH, Wu WW, Tian J, Xu F, Wu SC, Tsui PH. A review of ultrasound detection methods for breast microcalcification. Math Biosci Eng. 2019;16(4):1761–85. 165. Leborgne R.  Diagnosis of tumors of the breast by simple roentgenography; calcifications in carcinomas. Am J Roentgenol Radium Ther. 1951;65(1):1–11. 166. Wang Y, Wang J, Wang H, Yang X, Chang L, Li Q. Comparison of mammography and ultrasonography for tumor size of DCIS of breast cancer. Curr Med Imaging Rev. 2019;15(2):209–13. 167. Homer MJ, D’Orsi CJ, Sitzman SB.  Dermal calcifications in fixed orientation: the tattoo sign. Radiology. 1994;92(1):161–3.

175 168. Loffman Felman RL.  The tattoo sign. Radiology. 2002;223(2):481–2. 169. Ozturk E, Yucesoy C, Onal B, Han U, Seker G, Hekimoglu B. Mammographic and ultrasonographic findings of different breast adenosis lesions. J Belg Soc Radiol. 2015;99(1):21–7. 170. Park GE, Kim SH, Lee JM, Kang BJ, Chae BJ.  Comparison of positive predictive values of categorization of suspicious calcifications using the 4th and 5th editions of BI-RADS.  AJR Am J Roentgenol. 2019;213(3):710–5.

Suggested Reading for This Chapter Algın O, Gökalp G, Topal U.  Signs in chest imaging. Diagn Interv Radiol. 2011;17(1):18–29. Chiarenza A, Esposto Ultimo L, Falsaperla D, et al. Chest imaging using signs, symbols, and naturalistic images: a practical guide for radiologists and non-radiologists. Insights Imaging. 2019;10(1):114. Collins J. CT signs and patterns of lung disease. Radiol Clin N Am. 2001;39(6):1115–35. Franquet T, Müller NL, Giménez A, Guembe P, de La Torre J, Bagué S.  Spectrum of pulmonary aspergillosis: histologic, clinical, and radiologic findings. Radiographics. 2001;21(4):825–37. Hansell DM, Bankier AA, MacMahon H, McLoud TC, Müller NL, Remy J.  Fleischner Society: glossary of terms for thoracic imaging. Radiology. 2008;246(3):697–722. Okada F, Ando Y, Yoshitake S, et al. Clinical/pathologic correlations in 553 patients with primary centrilobular findings on high-resolution CT scan of the thorax. Chest. 2007;132(6):1939–48. Shimon G, Yonit WW, Gabriel I, Naama BR, Nissim A. The “tree-in-bud” pattern on chest CT: radiologic and microbiologic correlation. Lung. 2015;193(5):823–9. Zompatori M, Bnà C, Poletti V, et al. Diagnostic imaging of diffuse infiltrative disease of the lung. Respiration. 2004;71(1):4–19.

5

Solid Organs of Upper Abdomen Xin Li, Chengkai Zhou, and Jie Zhou

Contents 5.1 Light Bulb Sign

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5.2 Bright Dot Sign

 180

5.3 Mother-in-Law Sign

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5.4 Rapid Wash-in Followed by Washout

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5.5 Mosaic Pattern

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5.6 Bull’s Eye Sign

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5.7 Pupil-like Sign

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5.8 Lollipop Sign

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5.9 Target Sign

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5.10 Cluster Sign

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5.11 Peripheral Washout Sign

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5.12 Halo Sign

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5.13 Transparent Ring Sign

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5.14 Wedge-Shaped Sign

 193

5.15 Straight Line Sign

 194

5.16 Liver Capsule Depressed Sign

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X. Li (*) · C. Zhou Department of Radiology Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China J. Zhou Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6_5

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178 5.17 Straight Border Sign

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5.18 Target Sign and Crescent Sign

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5.19 Pearl Necklace Sign

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5.20 Garland Sign

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5.21 Tortoise Shell Sign

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5.22 Periportal Tracking Sign

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5.23 Periportal Halo Sign

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5.24 Focal Hepatic Hot Spot Sign

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5.25 Cyst-in-Cyst Sign

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5.26 Floating Membrane Sign

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5.27 Beaded Sign

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5.28 Soft Rattan Sign

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5.29 Double Duct Sign

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5.30 Teardrop Superior Mesenteric Vein Sign

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5.31 Duct-Penetrating Sign

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5.32 Central Dots Sign

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5.33 Central Arrowhead Sign

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5.34 Golf Ball-on-Tee Sign

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5.35 Calyceal Crescent Sign

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5.36 Cortical Rim Sign

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5.37 Renal Halo Sign

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5.38 Perirenal Halo Sign

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5.39 Perirenal Cobwebs Sign

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5.40 Pseudo-capsule Sign

 225

5.41 Spoke Wheel Sign

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5.42 Soft-Tissue Rim Sign

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5.43 Comet-tail Sign

 228

5.44 Faceless Kidney

 229

5.45 Goblet Sign

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5.46 Cobra Head Sign

 231

5.47 Drooping Lily Sign

 233

References

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Fig. 5.1  A 38-year-old man. (a) A nodule was detected with low signal intensity on T1WI, with homogeneous signal intensity on T2WI well defined; the high signal inten-

sity resembled cerebrospinal fluid (CSF), and thus is called the “bulb sign” (b)

5.1

is small, even slit like. However, the latter has only a small number of collagen fibers and fibroblasts in the wall and the vascular lacuna is larger. Hepatic hemangioma is mainly composed of blood pools or sinusoidal structures with low-­ speed blood flow. Hemangiomas on T2WI are usually homogeneously hyperintense. Because the blood contains about 81% water, the T2 signal intensity is longer, and the lesion is markedly hyperintense on T2WI. With the extension of echo time, the signal intensity of the lesion becomes higher and higher, forming a light bulb sign. The sensitivity, specificity, and accuracy of magnetic resonance imaging (MRI) for the diagnosis of HCH are 100%, 93%, and 95%, respectively. Most of the lesions were round or oval, with clear and sharp margins. On T1WI, HCH shows homogeneous hypointense signals, and some may show heterogeneous signals from hemorrhage, necrosis, calcification, fibrosis, and thrombosis. In multi-echo sequences, the signal intensity of the lesion increases with the extension of echo time, which is the characteristic MRI feature for hepatic hemangiomas [1]. The light bulb sign is also commonly seen in liver metastases with smooth, round, or oval image manifestations. On T2WI, the signal content of the neoplasm resembles that of the gallbladder, cerebrospinal fluid, cyst, and hemangioma. However, high signal intensity is detected in hepatic metastatic lesions because of

Light Bulb Sign

Feature Hepatic hemangioma presents homogeneous hyperintensity on T2WI, and its signal intensity increases with the extension of echo time in a multi-echo sequence, called the light bulb sign. Explanation Hepatic hemangioma is mainly composed of sinusoids or blood pools. The blood flow is slow. Because of large amount of water in the blood and long T2 signal, the signal intensity becomes higher and higher with the extension of echo time, forming the light bulb sign (Fig. 5.1). Discussion Hepatic hemangioma is one of the most common benign tumors in the liver. The incidence of hepatic hemangioma ranges from 0.14% to 7.3%. Pathologically, hepatic hemangioma can be divided into cavernous hemangioma, sclerosing hemangioma, hemangioendothelioma, and capillary hemangioma. Hepatic cavernous hemangioma (HCH) is the most common type of hepatic hemangioma in the liver, accounting for 95% to 98% of hemangioma. HCH can be classified into thick-walled hemangioma and thin-walled hemangioma; the wall of the former has more collagen fibers and fibroblast, and the vascular lacuna

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the complete necrosis of the tumor. Although both hepatic hemangioma and hepatic metastasis may show “light bulb” sign, the former is benign, whereas the latter is malignant [2]. Spectral computed tomography (CT) with fast switching tube voltage may increase the sensitivity of differentiating small hemangiomas from small hepatic carcinomas [3].

5.2

Bright Dot Sign

Feature In dynamic contrast-enhanced CT or MRI, hepatic hemangiomas in the hepatic arterial phase (HAP) or portal venous phase (PVP) are mainly low density or hypointensity; enhanced nodules are seen in the periphery of the lesion. Explanation Some atypical hepatic hemangiomas show low density in CT images or hypointensity in MRI without obvious enhancement in HAP and PVP. This pathology may be related to thicker vessel wall, smaller lumen, difficult access of contrast medium, thrombosis, or hyalinization. The lesions are gradually filled in contrast medium in the delayed phase. The bright spot is the small nodule that is enhanced in the lesion, representing a small blood sinus filled with contrast medium (Fig. 5.2). Discussion Hemangiomas are usually small and solitary hepatic lesions formed of multiple blood-filled vascular malformations. They are the most common benign hepatic tumor, with a prevalence of 0.4% to 20% and female preponderance of 3 to 6:1, typically diagnosed in patients between 30 and 50  years of age. Noncontrast CT shows hypoattenuation in comparison to the adjacent liver parenchyma. The most striking imaging feature of a hemangioma is that it always follows the blood pool. The classic appearance of hemangioma on contrast-enhanced CT is of peripheral nodular enhancement in the arterial phase with centripetal progression on the portal venous phase. Certain variants of this classic CT appearance include the flash-filling hemangioma, a less

Fig. 5.2  Postcontrast CT shows a mainly unenhanced nodule in the right lobe of the liver, with markedly dot-­ like enhancement peripherally in the arterial phase

common manifestation where the entire hemangioma opacifies in the arterial phase. In addition, the giant hemangioma may not demonstrate complete centripetal opacification because of the internal thrombosis and scarring as a complication of its size. On serial imaging, an interval increase in its size should raise suspicion of a metastatic lesion. MRI exploits the long T2 relaxation time of the blood-filled vascular malformation, yielding a hyperintense signal intensity on T2WI that is not as bright as that of a simple cyst or cerebrospinal fluid (CSF). T2WI alone has a sensitivity of 100% in differentiating hemangioma from a hepatic lesion of malignancy [4]. Small hemangiomas are detected more frequently with multi-slice CT.  However, they are easily overlooked on conventional CT because they tend to be iso-attenuating on late-phase enhanced images. Because of earlier scanning after administration of contrast medium, slowly enhancing hemangiomas have more chance to show persistent hypoattenuation, the incidence being as much as 8% to 16%. In clinical practice, the incidence of this enhanced pattern is even greater than previously reported for hemangioma, especially for small hemangiomas that may not show the classic rapid fill-in pattern. Small hypoattenuating hemangiomas are particularly problematic in patients with underlying malignancy. If present, the “bright-dot” sign, tiny enhancing dots in the hemangioma that do not progress to the classic globular enhancement because of the small size of the

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a

181

b

c

Fig. 5.3  A 42-year-old woman with hepatic hemangioma. Nodular enhancement at edge of the lesion in arterial phase (a) and the enhancement area enlarged in the portal vein phase (b) manifest as mother-in-law sign in the delay phase (c)

lesion and the propensity for very slow fill-in, is helpful in diagnosing this type of hemangioma. One pathological correlative study suggested that hemangiomas with a slow fill-in pattern have relatively large vascular spaces and that those with rapid enhancement have small vascular spaces and a large interstitium. Such a tendency has no relationship to the size of the tumor. Therefore, hemangioma should be included in the differential diagnoses of small hypoattenuating lesions as well as hypervascular lesions [5].

5.3

Mother-in-Law Sign

Feature In the delayed phase of enhancement CT, contrast agent fills the lesion and stagnates for a long time, resulting in a loss of attenuation difference between lesion and surrounding liver tissue.

Explanation Mother-in-law sign is a characteristic CT finding of hepatic cavernous hemangioma (HCH). HCH consists of a blood-filled vascular sinus cavity with fibrous tissue spacing between the sinus cavities. In enhancement CT, the early manifestations are nodular enhancement around the lesion, and gradually progress toward the center with time delay. Finally, the contrast agent fills the entire lesion and remains for a long time. In Eastern and Western cultures, there is a custom of the mother-in-law who likes her son-in-law. When the daughter brings the son-in-law to her family, the mother-in-law always persuades him to stay for a few more days. Therefore, some scholars have called this phenomenon of contrast agent filled with cavernous hemangioma that stays for a long time as the mother-in-law sign (Fig. 5.3).

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Discussion The mother-in-law sign is a characteristic CT finding of hepatic cavernous hemangioma. It is manifested as the contrast agent fills the lesion and stagnates for a long time, resulting in a loss of attenuation difference between the lesion and the surrounding liver tissue in the delayed phase of liver CT enhancement scan. Hepatic hemangioma is the most common benign tumor in the liver, accounting for 84% of these, and is more common in older women. Pathological classification includes cavernous hemangioma, capillary hemangioma, and hemangioendothelioma, which is more common in the former. The lesion can be single or multiple, and the site of the lesion is commonly in the right lobe. In most cases, there was no obvious clinical manifestation. Larger lesions could cause upper abdominal discomfort, and the mass was palpated. Pathologically, the tumor is covered with a layer of connective tissue membrane, which is composed of a blood-filled vascular cyst, with fibrous tissue partitions between the capsules, and the cyst wall is lined with flat endothelial cells. Tumors can undergo fibrosis, calcification, and thrombosis. Slowly growing hemangiomas in liver tissue can produce a mass effect, resembling a tumor. However, the microscopic histopathology is composed of abnormal sinusoids with different sizes of expansion, and there is no abnormal proliferation of sinusoidal endothelial cells. This finding indicates that the hemangioma is the result of poor blood flow and expansion of the sinus cavity caused by abnormal development of the sinusoidal embryo. It is a congenital malformation of the portal vein rather than a tumor. Noncontrast CT shows a low-attenuation lesion in the liver, with clear outline and uniform attenuation. Lower-attenuation areas in the central area are detected in a few lesions, which represent pathological changes of thrombotic or fibrous scar tissue. Further, some lesions may show calcification. Enhanced scanning is more characteristic or helpful to evaluate the hemangioma; one specific sign is that the early margin of typical lesions is significantly nodular or patchy. The attenuation resembles that of arteries. Over time, the enhanced area gradually expands and advances toward the center of the lesion. The

attenuation of this specific sign is of equal attenuation or slightly higher attenuation in the delay phase of enhanced examination. Hypoattenuation in the center of the lesion can never be enhanced [6]. Not all cavernous hemangiomas have the aforementioned classic CT features: some lesions may not be enhanced, or are not enhanced obviously, because the sinus wall of the hemangioma is thick and the cavity is too small. Therefore, the contrast agent does not enter easily or less may enter. Dynamic contrast-enhanced CT is an important method for diagnosing HCH. The diagnostic accuracy of hepatic hemangioma is as great as 90%. MRI T1WI shows low signal intensity, and T2WI signal is increased abnormally, expressed as “light bulb sign.” Cavernous hemangioma should be differentiated from the following diseases. (1) Hepatocellular carcinoma (HCC): CT enhancement of HCC lacks the mother-in-law sign; the specific sign of HCC is characterized as contrast medium wash-in in arterial phase, and washout in portal venous phase or delay phase [7]. (2) Liver metastasis: early enhancement of marginal enhancement may occur in some intrahepatic metastases, resembling hemangioma, but can be identified by low-attenuation performance in delayed scan. (3) Liver abscess: low-attenuation halo can be seen around the abscess, and the typical lesion shows ring-shaped enhancement.

5.4

 apid Wash-in Followed by R Washout

Feature In the three-phase enhanced CT scan of primary hepatocellular carcinoma (HCC), the carcinoma is in hyperattenuation in the arterial phase and hypoattenuation in the portal vein phase or delayed phase. The enhancement pattern of HCC is that the contrast agent shows the characteristics of rapid wash-in followed by washout. Explanation In three-phase enhanced CT scan of primary HCC, within 20–30 s after injection the contrast agent is in the arterial phase. The blood supply of the parenchyma is mainly supplied by the portal

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a

183

b

c

Fig. 5.4  Hepatic arterial phase (a) shows patchy enhancement fully occupying the right lobe of the liver; visible traversing vessels are detected in the tumor. In the portal

venous phase (b) and delayed phase (c), the enhancement pattern shows rapid wash-in followed by washout

vein (75%) whereas HCC is mainly supplied by the hepatic artery. In the arterial phase, CT value quickly reaches the peak. In 50–60 s after injection of contrast agent in the portal vein phase, the attenuation of the mass decreased rapidly. Delaying to the equilibrium phase of a 110–120 s scan, as the attenuation of hepatic parenchyma continues to rise and the contrast attenuation of HCC continues to decrease, attenuation in the tumor returns to the original state of low attenuation. If the CT value is measured on a dynamic CT and the time-attenuation curve is plotted, the curve of HCC is rapidly increasing in arterial phase and decreasing in portal venous phase: this reflects the characteristics of rapid wash-in followed by washout in tumors (Fig. 5.4).

or triple-phase enhanced scans are important in the diagnosis of hepatic space-occupying lesions. Not only can this improve the detection rate of tumors, but it also shows the blood supply characteristics of tumors to some extent, effectively carrying out differential diagnosis and guiding the treatment options. Postcontrast CT scans can more clearly show the features of tumors. (1) Abnormal blood vessels in the HCC lesion are found in the hepatic arterial phase with higher attenuation. During the subsequent portal and equilibrium phase scans, these abnormal blood vessels and tumor areas are rapidly changing, with the characteristics of contrast agent rapid wash-in followed by washout, which are different from hepatic cavernous hemangioma, hepatic metastases, and intrahepatic cholangiocarcinoma. (2) The margin of most tumors not only are enhanced in the hepatic artery phase, but also persist in the portal vein phase, indicating that there is a double blood supply from the hepatic

Discussion “Rapid wash-in followed by washout” is a characteristic sign of the CT three-phase enhanced scan of primary HCC. Liver spiral CT dual-phase

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artery and portal vein at the margin of such HCC, which indicates the marginal part grows vigorously. Single hepatic artery embolization ­ does not completely block tumor blood supply, which is a very important reference for selecting a reasonable intervention or other treatment options [7]. (3) The majority of intrahepatic metastatic foci showed significant enhancement of hepatic artery phase and rapid increasing and decreasing. The use of MR liver tissue-specific contrast agents can selectively target hepatocytes in the hepatobiliary phase, while maintaining good dynamic enhancement during the arterial phase, further improving the diagnostic accuracy of HCC [8].

5.5

Mosaic Pattern

Feature Heterogeneous signal intensity or linear low signal intensity structure appeared in the main hepatocellular carcinoma (HCC). The enhanced inhomogeneity is also known as the mosaic sign. Explanation The mosaic appearance is caused by an intratumoral septum or histological diversity. The mosaic pattern is defined as several areas or compartments with various intensities, shapes, enhancements, and sizes. Most overt HCCs present with a mosaic pattern. This feature is specific for HCC and often considered to be a major ancillary sign (Fig. 5.5). Discussion HCC is the most common tumor in the liver. It is composed of tumor cells with hepatocellular differentiation, arranged in a trabecular, acinar, or compact pattern. HCC often grows in a mosaic pattern with different cell types arranged in different architectural patterns in a large tumor. HCC can be occasionally combined with other cell types with nonhepatocellular differentiation. Combined hepatocellular-cholangiocarcinoma is the most common combination [9]. This feature is specific for HCC and is often considered to be a major ancillary sign. At the same time, the

Fig. 5.5  A 64-year-old man presented with a mass in the right lobe of the liver with uneven enhancement and enhancement of the intratumoral septum

mosaic pattern is mainly found in large HCCs, which are easier to diagnose [10]. HCC has a wide spectrum of radiologic characteristics depending on its size and degree of histological differentiation. HCC can be classified as early or progressed HCC.  Progressed HCCs are malignant lesions with the ability to invade vascular planes and metastasize. The radiologic pattern is variable, but frequently a mosaic pattern is exhibited because nodular areas are interspersed by areas of hemorrhage, arteriovenous shunting, fibrosis, and necrosis. The main findings are (1) high signal intensity on T2-weighted imaging; (2) hyperenhancement on arterial phase, and washout appearance on delayed phase; and (3) nodules surrounded by a capsule/pseudo-capsule (more evident in the delayed phase) [11].

5.6

Bull’s Eye Sign

Feature Hepatic metastases show low density in the center of lesion, annular enhancement zone around lesion, low-density zone with no obvious enhancement at the outermost layer on enhanced CT. Explanation The pathological basis is that necrosis or cystic degeneration in the center of the tumor is low density without enhancement after injection of

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Fig. 5.6  A 66-year-old woman presented with an annular enhancement lesion in the upper right lobe of the liver. Low-density necrosis was detected in the center of the lesion, and a low-density zone with no obvious enhancement at the outermost layer

contrast medium, the middle high density is tumor tissue, and the outer low density is the compression change of normal liver tissue and blood vessels (Fig. 5.6). Discussion The term bull’s-eye is used in archery and target shooting to denote the center of the target. The origin of the word is unclear. However, one theory is that English archers would often practice using the skull of a bull, with the most difficult shot being one that entered an eye socket. Multiple radiologic signs characterized by concentric circles are named after this [12]. Most hepatic metastases are hypovascular lesions. Because of the strong metabolism, insufficient blood supply, and lack of feeding conditions, necrotic cystic degeneration can easily occur, and central necrosis can also occur in small lesions. CT manifestations of liver metastases are complex and varied, with multiple diffuse distributions being common. Most metastases are revealed as low- or iso-attenuating masses on CT. Depending on lesion size, the margins tend to be irregular, and necrosis may be present in the tumor. Central low attenuation may be the result of necrosis or cystic change. Calcification may be present with metastases from mucinous gastrointestinal tract tumors, and primary ovarian, breast, lung, renal, and thyroid cancer [13]. Enhanced scan showed continuous annular enhancement at the edge of the lesion in

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the arteriovenous phase, with more obvious annular enhancement at the edge of the lesion in portal venous phase than that in arterial phase. The bull’s eye sign could also be seen in the portal venous phase. This sign is a more common sign among the special signs of hepatic metastases, showing no enhancement in the central low-density area, high-density shadows with circumferential enhancement, and low-density shadows in the outer layer. The bull’s eye sign is a classic imaging manifestation of hepatic metastases. However, we should know that this bull’s eye sign can also occur in other diseases, such as hepatic tuberculosis and metastasis.

5.7

Pupil-like Sign

Feature The CT signs of hepatic metastasis usually have multiple circular or quasi-circular shadows of low density. The lower-density region with clear boundaries is found in the center of the lesion. The diameter of the lower lesion is significantly smaller than that of the surrounding low-density area formed by tumor tissue, which resembles the shape of a pupil. The other name for this CT sign is thick rim sign. Explanation Most hepatic metastases are poorly supplied tumors, characterized by low density, with mild enhancement. For example, the necrosis in the center of a tumor shows a lower-density area without enhancement, forming a pupil-like sign (Fig. 5.7). Discussion When the density in the center of the tumor is lower during enhanced scanning, the area with a clear boundary is small and circular, and its diameter is significantly smaller than the surrounding low-density area formed by tumor tissue. The liver is the largest substantial organ in the human body, which has the dual blood supply of hepatic artery and portal vein. Therefore, many malignant tumors of organs are prone to liver metastasis, especially malignant tumors of the gastrointestinal tract.

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Fig. 5.7 Postcontrast CT reveals lesions with ring enhancement; the center is without enhancement, which is the pupil-like sign

Because a liver metastatic tumor is mainly supplied by the portal vein in the early stage and by the hepatic artery in the middle and late stages, the nature and type of tumor can be estimated according to the degree of enhancement of the tumor and the change of degree with time [14]. Multiple low-density nodules are common in liver metastatic tumors, and arterial blood supply is more common in enhanced scanning, presenting as peripheral ring enhancement or uniform and nonuniform enhancement of the full tumor. Among these, peripheral ring or low-density enhancement is typical, whereas the low-density nonenhancement area is in the tumor, namely, the bull’s eye sign. This difference is an important indication that metastatic liver tumors are different from primary liver cancer, and pathological studies have confirmed that the low-density unreinforced area is composed of compressed liver cells or fibrous tissue. The outer layer is a high-­ density enhancement zone, with the main pathological manifestations being compression of liver parenchyma, hyperemia of liver sinus, hyperplasia of connective tissue, infiltration of inflammatory cells, and hyperplasia of blood vessels. The clinical diagnosis of metastatic liver cancer is not difficult, but partial metastatic liver cancer is not easy to identify with liver abscess, especially cystic metastatic liver cancer. The pathological basis of the formation of cystic metastatic hepatocellular carcinoma is the severe liquefactive necrosis of the tumor lesions. The typical CT findings of

hepatic abscess are that the density of the lesion is lower than that of surrounding hepatic parenchyma in plain scanning; partial lesions have a gas body, and the circle-target sign, separation, and enhancement can be seen in enhanced scanning. MRI and CT are comparable in their ability to detect metastases, which generally appear hypointense compared with normal liver parenchyma on T1-weighted MR images and hyperintense on T2WI. CT remains the preferred screening test for hepatic metastases, and MRI is a useful tool to generally define lesions more clearly than CT, as well as to detect hepatic lesions in the liver parenchyma [15].

5.8

Lollipop Sign

Feature The lollipop sign, which is seen on postcontrast CT or MRI, manifests as multiple large unenhanced or nodular edge-enhanced masses. The hepatic vein or portal vein tapers toward these lesions and terminates at the edge of the lesions, forming a lollipop-like appearance. Explanation The lollipop sign is considered a typical manifestation of hepatic epithelioid hemangioendothelioma (HEH). This sign can better identify HEH in cross-sectional images. The lollipop sign consists mainly of two structures: (1) a clear mass with a low-attenuation border on the enhanced image, representing the candy in the lollipop; and (2) a histologically occluded vein, including the hepatic vein and the portal vein, representing the stick in the lollipop. Masses with unclear boundaries, gasfilled cavities, or outward-growth masses do not meet the characteristics of the lollipop sign. If there is a scar-like enhancement in the center of the lesion or a significant or irregular enhancement of the mass, it cannot be judged as the lollipop sign. The enhanced vein should terminate at the edge of the lesion or only extend into the enhancement ring of the lesion. If the blood vessel passes through the lesion or is moved by the mass, and the collateral vessels are formed, the lollipop sign cannot be considered (Fig. 5.8.)

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Fig. 5.8 Postcontrast CT shows multiple hypodense large parenchymal nodules in both liver lobes and the nodule in Couinaud’s segment VII, showing a lollipop sign (arrow)

Discussion The lollipop sign is a sign of postcontrast CT or MRI, manifested as multiple large unenhanced or nodular edge-enhanced masses. The hepatic vein or portal vein tapers toward these lesions and terminates at the edge of these lesions, forming a lollipop-like appearance [16]. The lollipop sign is considered a typical manifestation of HEH. HEH is a rare vascular endothelium tumor with mild to moderate malignancy, usually occurring in adults, in significantly more women than men. The cause is not known, but may be related to oral contraceptives, exposure to polyethylene, trauma, or viral hepatitis [17]. HEH is mostly asymptomatic. Occasional symptoms are mainly characterized by frequent episodes of upper right abdominal pain and weight loss, and some patients show liver failure, Budd–Chiari syndrome, or portal hypertension. The histological feature of HEH is the infiltration of the hepatic sinus and intrahepatic venous system, which surrounds the hepatic vein, portal vein, or venule and causes stenosis or occlusion. There are two manifestations of the affected vein. One is that the affected hepatic vein or portal vein is tapered around the tumor, and the edge is smooth. Second, the vein is completely occluded or cut off when it reaches the edge of the tumor. CT findings of HEH mainly include multifocal low-attenuation nodules of varying sizes. These nodules can grow and fuse into large masses, mostly distributed at the edge of the liver. Enhanced scans show that these nodules are cir-

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cumferentially enhanced, usually with calcification, central low density, and envelope invagination. Some patients were observed to have metastases, usually in the lungs, lymph nodes, spleen, bones, and other substantial organs. On MRI T1WI, the nodules show a low signal, and postcontrast T1WI shows marginal enhancement. The normal liver parenchyma enhancement is more obvious than enhancement of the tumor. The central part of the tumor shows a low signal resembling the findings on CT. The tumor shows an inhomogeneous high signal on T2WI. The signal component in the tumor is more complicated than CT. The decrease of the central part signal may be related to intratumoral hemorrhage, coagulative necrosis, and calcification. Differential diagnosis of HEH includes hepatic metastases, intrahepatic cholangiocarcinoma, and other intrahepatic vascular tumors [18]. The presentation of lollipop sign raises the specificity of diagnosing HEH, combined with other imaging findings, which can help differentiate the disease from other liver tumors.

5.9

Target Sign

Feature The typical finding of postcontrast CT for hepatic abscess is named target ring. It is characterized by a cystic-like low-attenuation mass in the liver; the margins are mostly vague, and a ring belt of different attenuations often appears around the abscess. In contrast-enhanced CT, the wall of the abscess shows different degree of ring enhancement, single ring or double ring or tricyclic. Explanation Target sign is a typical sign of hepatic abscess. The abscess liquefaction and necrosis in the formation of abscess cause the wall to be single ring, double ring, or tricyclic. The appearance of the target sign in hepatic abscess represents the pathological process of a certain stage of the disease, which is a characteristic finding of hepatic abscess and has great value for diagnosis (Fig. 5.9).

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Fig. 5.9  Patient with hepatic abscess. On postcontrast CT, the lesion shows target sign

Discussion Hepatic abscess is a common inflammatory disease in the liver. The clinical manifestations are acute and rapid, often accompanied by symptoms of inflammatory poisoning, such as high fever, chills, liver pain, or multiple organ failure. In a blood test, white blood cell count is significantly increased. The formation of hepatic abscess can be divided into suppurative inflammatory, early abscess formation, and abscess formation stage. The pathological changes in the stage of suppurative inflammatory stage are local inflammation, congestion, and edema of hepatic tissue. In the early abscess formation stage, hepatic tissue begins to show necrosis and partial liquefaction. During the abscess formation stage, the cavity of the abscess has complete necrosis and liquefaction, and the wall of the abscess is formed by fibrous granulation tissue or an inflammatory congestive zone. The liver tissue around the abscess is often accompanied by congestion and edema. Liver abscess occurs mostly within the right lobe, can be single or multiple, and varies in size. The boundaries of lesion are unclear and the abscesses are thicker. The more complete the necrosis of the diseased tissue, the lower the attenuation and the more uniform [19]. Such as in chronic hepatic abscess, the edge is clear, the CT value is close to the attenuation of edema, and sometimes a circle of low-attenuation edema ring is visible around, so it is easy to diagnose. If there is a gas–liquid level in the

abscess, it means that the liquefaction is relatively complete and accompanied by gas-borne infection, which is generally considered to be a specific sign for the diagnosis of hepatic abscess. After contrast-enhanced scan, the lesion revealed the relationship between the internal structure of the lesion, the margin of the lesion, and the normal liver tissue is clearer. The portal venous phase can show typical CT signs of hepatic abscess, which is the CT finding after the enhancement of typical three-layer pathological changes. The central necrosis area is not enhanced, and the middle layer is the low-density band between the liquefaction necrosis area and the normal liver tissue. The boundary of peripheral layer and normal tissue is vague [20]. Three rings correspond to different pathological structures for the wall of the abscess: edema, fibrous granulation tissue, and inflammatory necrosis tissue, respectively. It is worth noting target sign is not unique to hepatic abscess, but it is still important for this diagnosis.

5.10 Cluster Sign Feature In precontrast or postcontrast CT, focal or multiple smaller circular enhancements can be seen in the liver, stacked close to each other into the shape of clusters or honeycombs. Explanation This sign is more common at the early stage of bacterial liver abscess formation. The lesions are usually less than 2 cm in diameter, and connected to each other; the smaller low-density lesions are clustered together. Infecting bacteria are mostly Escherichia coli. Fungi or Mycobacterium spp. are rare in this sign (Fig. 5.10). Discussion The presence of the cluster sign usually suggests that the lesions are pyogenic abscesses [21]. With the necrosis liquefaction of the liver tissue in the lesion area, the cluster sign is the multifocal necrotic areas and the residual normal liver tissue that coexisted first. “Cluster sign” is only a phase of the pathogenesis of liver abscess, which can be

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Fig. 5.10  On postcontrast CT, arterial phase (a) and portal venous phase (b) solitary or multiple smaller circular enhancements can be seen in the liver, stacked close to each other into the shape of clusters

dissipated and absorbed with effective treatment and progression. In the period of inflammation, lesions do not present necrosis and liquefaction, and the performance is solid sign. In the early abscess formation stage, multiple scattered small abscess cavities begin to form, which then gather and merge, and dynamic enhanced scan shows “honey sign,” “cluster sign,” or “petal sign.” In the abscess formation stage, complete necrosis and liquefaction of the lesion are observed, the abscess wall is mature, and enhanced scan shows typical “ring target sign”; some lesions show small bubbles or gas level. In the fibrous granulomatous stage, the lesions show small petal sign, or single- or double ring sign. Pyogenic micro-abscesses may appear as multiple widely scattered lesions being resembling the distribution of fungal micro-abscesses in immunosuppressed patients, or as a cluster of micro-abscesses that appear to coalesce focally. The diffuse miliary pattern of pyogenic micro-­ abscesses is caused by staphylococcal infection in patients with generalized septicemia and usually involves both liver and spleen. The cluster pattern is associated with coliform bacteria and enteric organisms. It is likely that clustering of pyogenic micro-abscesses represents an early stage in the evolution of a large pyogenic abscess cavity. At postcontrast CT, large abscesses are generally well defined and hypoattenuating; They may be unilocular with smooth margins or complex with internal septa and an irregular contour. Rim

enhancement is relatively uncommon, as it is in the presence of gas. Pyogenic abscesses have variable signal intensity on T1WI and T2WI, depending on their protein content. Perilesional edema, characterized by subtly increased signal intensity, can be seen on T2WI [22]. On CT, the small abscesses showed a miliary pattern characterized by widely disseminated, hypodense lesions scattered throughout the liver. Probably the cluster pattern represents an early stage of abscess evolution. If left untreated, many of these small pyogenic abscesses might have coalesced into a larger abscess cavity with a multiseptated appearance. In some instances, abscesses could possibly coalesce into a relatively unilocular-­ appearing cavity. The diagnosis for liver abscess is that the appropriate imaging modalities and culture of causative organisms should be performed.

5.11 Peripheral Washout Sign Feature In dynamic postcontrast liver MRI, the signal intensities of lesions in the peripheral area is lower than that in central area during delayed contrast-enhanced phase, forming a low-signal ring. Explanation This sign is mainly caused by the difference of blood supply between the center and the periph-

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Fig. 5.11  A 55-year-old woman with right lobe hepatocellular carcinoma. (a) T1WI enhancement in the arterial phase. (b) Portal venous phase. (c) Delay phase. Peripheral washout sign shown by arrow

ery of lesion. The center represents the denatured and necrotic area with relative ischemia, and the periphery is the edge of the growing tumors. The edge with abundant peripheral blood supply in the delayed phase can be quickly cleared by contrast medium (Fig. 5.11). Discussion The peripheral washout sign was first reported by Mahfouz et al. in 1994 [23]. It was considered to reflect rapid perfusion and clearance of the margin of malignant liver lesions. The peripheral washout sign is associated with metastasis, hepatocellular carcinoma, and cholangiocarcinoma in most cases. In previous studies, this sign was considered always associated with malignant lesions, with a specificity of 100%. The dynamic manifestation of margin enhancement of malignant tumors is rapid enhancement in the early stage and then continuous decline. In contrast,

the enhancement of central region of malignant tumors shows a continuous increase, which may be related to a different proportion of vascular components and interstitial components between the two regions. Vascular components in the marginal region are more numerous than those in the interstitial region, and the qualitative components in the central region are more than those in the vessels, or to the different vascular structures between the two regions. The structure of blood vessels in the central area is relatively complete, and the blood flow is cleared quickly, while the structure of the central area is incomplete, and the blood enters and flows slowly. Alessandrino et al. [24] reported peripheral washout sign in a rare benign lesion of the liver, namely, hepatic epithelioid angiomyolipoma (HEA). Therefore, it is crucial to differentiate benign from malignant lesions that may have peripheral washout sign. Generally speaking, patients with HCC are more

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Fig. 5.12  A 64-year-old patient with chronic hepatitis and cirrhosis. On enhanced arterial phase (a), the lesions show obvious enhancement. Contrast agents were rapidly introduced in contrast-enhanced delayed lesions (b).

Thin-walled circular enhancement around the lesion could be seen in delayed phase, which was a pseudo-capsule of the tumor

common among middle-aged and elderly men with a history of hepatitis B and cirrhosis, often accompanied by elevated alpha-fetoprotein (AFP); HEA is more common in middle-aged women, with no history of hepatitis B or cirrhosis, and AFP is normal [25]. For HEA lesions, the surrounding and central veins are enlarged and convoluted. Drainage veins are visualized in the early stage. Peripheral and central veins of portal and delayed lesions are continuously enhanced, and the enhancement degree of arterial lesions is lower than that of HCC.  Fatty degeneration in HCC lesions is intracellular fat showing low signal T1 out of phase; the fat in HEA is mature fat, and the signal of fat suppression is decreased. The abundant blood supply of active and proliferative tumor margin tissue seems to be important in the performance of peripheral washout sign, which has high specificity for the diagnosis of malignant lesions, but cannot be used as the only feature to distinguish malignant from benign. In judging benign and malignant lesions, it should be considered in combination with other imaging modalities.

of translucent band on the edge of the mass in precontrast or postcontrast, which can separate the tumor from the liver tissue.

5.12 Halo Sign Feature The halo sign is a CT or MRI sign of hepatocellular carcinoma (HCH), which refers to a circle

Explanation Tumors with swelling growth are slower, compressing liver tissue or causing fibrosis of liver tissue, forming a thicker pseudo-capsule. Both the precontrast or postcontrast scan show a lower attenuation (or low signal) ring shadow or translucent band around the tumor, which is the halo sign (Fig. 5.12). Discussion The pseudo-capsule of HCC is a sign of qualitative value. The biological characteristics of tumors determine the performance and development of imaging, and the results of imaging examination are objective reflections of tumor pathology. If the tumor shows an equal attenuation, this sign is often the only finding to detect the lesion. A pseudo-capsule can be formed when the lesion is more than 1.5 cm; the tumors compress noncancerous liver tissue, with fibrous tissue components occupying the main body. Inflammatory cell infiltration and neovascularization can be seen around the capsule and around the compressed liver tissue. Because the contrast medium flows in and out slowly in the fibrous tissue, the tumor pseudo-capsule is enhanced during portal phase and delay phase.

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Some studies have suggested that HCC with no halo sign are poorly differentiated and grow faster. Kadoya et  al. [26] believed the pseudocapsule of small HCC is formed by the compression of tumor expansion, and the reticular fibers around the liver plate and the liver plate are formed by a radial arrangement and a parallel arrangement. The pseudo-capsule consists of two layers: the inner layer is thicker and composed of rich fibrous tissue, and the outer layer consists of extruded water-rich small blood vessels and new bile ducts; 78% of tumors are reported to have the pseudo-capsule [27]. As for MRI finding, the pseudo-capsule shows as a single-layer hypointensity ring around the tumor on T1WI and double-­ layered ring on T2WI (hypointensity in inner layer and hyperintensity in outer layer).

5.13 Transparent Ring Sign Feature The low attenuation ring around hepatocellular adenoma (HCA) appears on precontrast or postcontrast CT of the arterial phase; it can be complete or incomplete and located between tumor and normal liver parenchyma. The attenuation of this sign is lower than that of the tumor and the normal liver parenchyma. Other name: low-­ density peripheral ring. Explanation Transparent ring sign is a characteristic CT finding of HCA. It may be associated with hepatocellular fat vacuolation caused by tumor expansive growth and compression of surrounding liver parenchyma (Fig. 5.13).

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Fig. 5.13  Physical examination of a 23-year-old woman revealed decreased attenuation shadow on liver. (a) Abdominal plain CT scan: round low-attenuation shadow appears in the right lobe of the liver with unclear boundary is unclear. (b) Arterial phase: lesion shows inhomoge-

neous enhancement with low-attenuation ring seen around the lesion. (c) Portal phase: lesion is in equal attenuation with the liver, and circular-like high attenuation is seen around it. (d) Delay phase: lesion is in equal attenuation with the liver

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Discussion Transparent ring sign was first described by Angres in 1980 [28]. On plain CT, tumor shows slightly low attenuation, and the peritumoral area was surrounded by a lower-attenuation shadow (3–4  mm thick; CT value 18 HU). On enhanced CT scan, the tumor show slight enhancement; the low-attenuation ring between the tumor and the normal hepatic parenchyma shows no obvious enhancement, and is called a low-attenuation peripheral ring. Surgical pathology revealed that the peritumoral liver was surrounded by a yellow margin band, which contained numbers of compressed hepatocytes with fat vacuoles. It was speculated that the fatty degeneration of peritumoral hepatocytes might be the basis of the formation of low-attenuation rings. HCA was considered the most rare benign tumor of the liver. Since the 1970s, with the development of imaging technology, more and more studies have been reported for this tumor. The disease may be single or multiple; single cases often occur in women of childbearing age with a history of oral contraceptives; and 50% to 80% of children with type 1 or type 3 glycogen storage disorder can have multiple HCA. HCA is prone to bleeding and carcinogenesis. Imaging is of great value in the early diagnosis and differential diagnosis of HCA [29]. On plain CT, most show iso- or slightly low attenuation; the attenuation is homogeneous. On postcontrast CT, arterial phase can be enhanced to different degrees; portal vein phase and delayed phase can show equal or slightly high attenuation, or low attenuation. On MRI, it can show iso-intensity or hypointensity and hyperintensity on T2WI. Differentiation from HCC or focal nodular hyperplasia (FNH) is sometimes difficult because the attenuation or signal changes of tumors are not characteristic. The application of hepatobiliary specific contrast agent Gd-BOPTA or Gd-EOB-DTPA is valuable for differential diagnosis. The hypointensity of HCA in parenchymal phase results from the lack of bile duct structure in HCA, which may lead to change in intracellular transport of contrast agents in HCA [30].

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5.14 Wedge-Shaped Sign Feature The wedge-shaped area with increased hyperintensity on T1WI accompanying hepatic tumors is called wedge-shaped sign. Explanation Because of malignant hepatic tumor infiltrating along bile duct, wedge-shaped signal abnormalities are formed on MRI. The shortened T1 may be associated with atrophic hepatocyte lipofuscin deposition (Fig. 5.14). Discussion The wedge-shaped signs that appear as hyperintensity on T1WI are rare, which are excepted from focal fatty infiltration, infarction, and tumor hemorrhage. There are two types of wedge-shaped areas. One type was seen around the enlarged intrahepatic bile ducts with extension of tumor next to the lateral portion of the tumor mass. The configuration of this type of wedge-shaped area was variable because of tumor mass effect. The other type of wedge-shaped area was seen around the tumor

Fig. 5.14  Liver metastasis from colorectal cancer in a 65-year-old woman. MR T1 opposed-phase shows wedge-­ shaped area mild diffuse fatty infiltration with fatty sparing (arrow) around enlarged intrahepatic bile duct next to lateral portion of tumor [31]

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mass. The tip of the wedge-shaped area was separate from the tumor mass and located medially next to the enlarged intrahepatic bile duct; This configuration is useful for recognizing intraductal tumor spread toward the hepatic portal veins [31]. Lipofuscin consists of polymerized phospholipids and polymerized unsaturated fatty acids that are mixed with neutral lipids and protein. Some lipofuscins show positive fat-type reactions; others show positive reducing reactions [31]. Hepatic iron deposition is associated with iron overload disorders, such as primary hemochromatosis and hemosiderosis. However, iron deposition is commonly not segmental but diffuse [32]. Various factors may contribute to the formation of these wedge-shaped areas. The wedge-shaped areas of increased signal intensity are indicators of hepatic masses on liver MR images. In patients with hepatic neoplasms, these areas should be seen a possible predictive sign of disease progression. MRI studies have reported the high signal intensity of wedge-shaped areas that surround liver masses. These findings are seen mainly on T2WI and have been attributed to sinusoidal congestion and edema around tumors, bile stasis, parenchymal compression, and infiltrating tumor [31]. Hepatic infarction also appears as the wedge-shaped sign in CT, but there is little reference to MRI findings of hepatic infarction in the literature. In general, the infarcted foci are shaped by the partially obstructed vascular supply that is usually one- or two sided, resulting in irregular shapes such as a wedge or triangle [33].

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Fig. 5.15  CTAP demonstrates a peripheral perfusion defect (straight line sign) in the right hepatic lobe caused by compression of a portal vein branch [34]

portal vein branches by blood clots, especially hepatocellular carcinoma. The triangular or wedge-shaped low-density areas represent the distal low-perfusion areas of the involved portal vein branches, and the enhanced liver parenchyma represents the normal perfusion areas of the portal vein branches (Fig. 5.15).

Discussion Straight line sign was first described and formally named by Tyrrel et al. in 1989 [34]. CTAP is a sensitive and reliable technique for identifying defects in portal vein perfusion of the liver. Patients with squamous cell carcinoma (SCC) who are candidates for transarterial chemoembolization (TACE) often undergo CTAP before TACE to confirm the absence of HCC tumor thrombosis in the main portal vein, which helps prevent severe liver injury or liver failure associated with TACE. Portal vein 5.15 Straight Line Sign thrombosis involving the main trunk is usually a contraindication for TACE as a treatment for HCC Feature [35]. In most cases, the straight line sign at CTAP A triangular or wedge-shaped low-density area demarks a low-attenuation area of relative hypoappears in the hepatic parenchyma of computed perfusion distal to the obstructing tumor or vessel tomography arterial portography (CTAP), a line and may appear to resemble vascular infarction. of varying length dividing both contrast material-­ We believe it is primarily seen when the portal enhanced and less-enhanced liver, from the focal vein is obstructed by tumor or clot. Its recognition mass to the peripheral edge of the liver. We have is important when central primary hepatocellular named this the straight line sign. carcinomas are evaluated, because its appearance signifies that the tumor is inoperable. In patients Explanation with metastatic disease, it may not obviate surgery Straight line sign is a CTAP manifestation of but it does alert the surgeon to the proximity of the direct invasion of hepatic tumor or blockage of portal vein to the neoplasm [34]. Tyrrel et  al.

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described the straight line sign (a line dividing hepatic contrast material enhancement from less enhanced liver) at CTAP and discussed its appearance and significance. However, such line bordering had been reported earlier at unenhanced and enhanced CT. We use the term straight border sign to indicate hepatic attenuation differences bordered by straight lines on any type of CT scan, regardless of the use or technique of contrast enhancement [36].

5.16 Liver Capsule Depressed Sign Feature On abdominal CT scan, malignant tumors located on the surface of the liver leading to liver capsule invagination, loss of the original radian, and with its successive liver capsule to form a complete large radian, are known as the liver capsule depressed sign (LCD). Explanation During the development of hepatic malignant tumors, small blood vessels and small bile duct obstructions cause limited hepatic atrophy, central necrosis of tumors, proliferation of peritumoral fibrous tissue, and invasion of hepatic envelope and other factors, together leading to the liver capsule depressed sign (Fig. 5.16). a

Fig. 5.16 (a) Woman, 58  years old, with intrahepatic cholangiocarcinoma, low-density mass in left lobe of liver, and local hepatic capsule depression in portal phase enhanced by CT. (b) Man, 48 years old, with hepatocel-

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Discussion The liver capsule depressed sign, also known as retraction sign of hepatic capsule, refers to the flat or concave hepatic capsule, resembling the pleural indentation sign [37]. Previous studies have reported that the liver capsule depressed sign is a specific sign of hepatic malignant tumors. However, with the continuous updating of the examination equipment and the popularization of the examination, the liver capsule depressed sign can also be observed in benign liver lesions. The liver capsule depressed sign can be the result of focal and diffuse lesions, which are caused by tumors and nontumorous lesions [38]. Tumors include primary, secondary malignant tumors, and atypical hepatic hemangioma before and after treatment. Especially, some tumors contain or can induce large amount of fibrous tissue metastases, such as lung cancer, breast cancer, or colon cancer. Malignant tumors adjacent to the liver surface invade hepatic sinuses, small blood vessels, and small bile ducts, resulting in cholestatic cirrhosis and depression of the capsule after local hepatic atrophy. The center of the tumor necrosis, the proliferation of fibrous tissue traction near the liver envelope is flattened, retracted, even in the form of an anti-­arc or umbilical concave, invasion of the liver envelope when a serrated change. The retraction of hepatic capsule in cavernous hemangioma is related to fibrosis, thromboembolism, and ischemia. Nonneoplastic factors include cirb

lular carcinoma, heterogeneous enhancement mass in right lobe of liver, and hepatic capsule depression in portal phase enhanced by CT

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rhosis, fibrosis, cholangitis, bile duct necrosis, and liver injury. The depression of hepatic capsule caused by posthepatitis cirrhosis is caused by liver regeneration nodules and fibrous tissue proliferation, resulting in an uneven liver surface. With the progress of hepatic fibrosis, the degree of hepatic capsule depression is more obvious. The liver capsule depressed sign is related to the size of the tumors: the larger the tumors, the higher the probability of the hepatic capsule indentation sign. With increase of the tumors, width and depth continue to increase. The liver capsule depressed sign is common in malignant tumors, but it is not specific. Benign tumors and a variety of nonneoplastic lesions can also occur. There are differences between benign tumors and malignant tumors with different degrees of differentiation in the smooth or rough margin of retraction of the hepatic envelope. The rough margin of retraction of hepatic envelope of malignant tumors highly suggests that the tumors invade the envelope and tend to differentiate poorly. The width and depth of retraction of hepatic capsule vary with the amount of fibrous tissue proliferation. Therefore, careful observation of this manifestation can preliminarily determine the benign and malignant lesions, if the liver capsule is invaded, and the degree of liver fibrosis. It is very helpful to the clinical staging of tumors, the formulation of treatment plans, and prognosis evaluation. However, it is not enough to observe this manifestation alone, but also to make a complete diagnosis in combination with the overall imaging manifestations of the lesions.

5.17 Straight Border Sign Feature According to CT plain scan or dynamic enhancement, between different density areas in the liver, the edge of straight line appearance is called liver straight border sign. Explanation The straight border sign of liver is not a manifestation of liver mass, but is caused by vascular embolism, arterial–portal shunt, fat deposition,

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Fig. 5.17  Large patches of diffuse hypodensities are seen in the liver. Enhanced scan showed a straight border between a fatty liver lobe and normal liver lobe

aggregated fibrosis, radiation hepatitis, tumor, enhanced scanning factors, and artifacts (Fig. 5.17). Discussion Attenuation differences bordered by straight lines within the liver are occasionally encountered at unenhanced CT.  Entities have been reported to cause such attenuation differences, including fatty liver, radiation hepatitis, and vascular abnormalities. The prevalence of this finding increases with the use of contrast material, especially when administered via the superior mesenteric and hepatic arteries. Tyrrel et al. [39] described the straight border sign (a line dividing hepatic contrast material enhancement from less enhanced liver) at CT arterial portography (CTAP) and discussed its appearance and significance [36]. The liver is an unusual organ from the aspect of blood supply; it has dual blood supply through the hepatic artery and the portal vein. When vascular compromise occurs, this dual blood supply system can cause changes in the volume of blood flow in individual vessels or even in the direction of blood flow [40]. When portal venous blood supply is decreased or stopped by tumor thrombus, thrombo-embolus, or compression of the portal vein, the corresponding parenchyma appears as a hypoattenuating area with straight borders at CTAP. The concept of straight border sign of liver is different from that of linear sign. The common

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reasons are as follows. (1) Vascular anomalies are the common cause of this sign. (2) There are many types of fat infiltration in the liver, such as extensive, lobar, segmental, irregular, and focal. The anatomical division is determined by the blood supply, especially the portal vein. Even with extensive fat infiltration, it is usually distributed according to the anatomical region. The area affected by fat infiltration showed low density on CT plain scan and no enhancement on postcontrast CT images. There was no displacement of portal vein and hepatic vein during fat infiltration. (3) On plain CT, the aggregated fibrosis caused by liver cirrhosis presented as low density or peripheral low density, and isodense or slightly low density area on CT. In these areas, portal vein blood supply decreases while hepatic artery blood supply increases slightly, which can be detected on CTAP.  Aggregated fibrosis can show high density on delayed postcontrast scans, especially when a large amount of contrast media is injected. (4) Radioactive hepatitis showed low density on plain CT and high density on postcontrast CT. The density difference in the boundary area forms a straight border sign, but not all of these are distributed according to anatomical region. (5) Tumors generally do not have straight border sign unless secondary vascular abnormalities occur. (6) Artifacts in plain CT scan may also form a straight border sign [41].

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5.18 Target Sign and Crescent Sign Feature In the CT image, the stone in the center of the dilated common bile duct shows a dense or soft tissue shadow, surrounded by a water-like density of bile shadows, called the target sign. The common bile duct stones are incarcerated and close to a side wall, and the bile of the water sample density is crescent shaped on the opposite side, which is called the crescent sign. Explanation Target sign and crescent sign are direct CT signs of common bile duct stones. The stones showing the target sign and the crescent sign are mostly high density, soft tissue density, and mixed density. The density of the annular water around the stone is formed by surrounding bile and may also be related to the inflammatory edema of the internal wall of the common bile duct (Fig. 5.18). Discussion As a common disease, gallstones account for 60% of biliary diseases and have a high incidence. As an imaging method, the CT imaging principle is relatively simple, mainly depending on the absorption of material to X-ray. With image performance of hyperattenuation, isoattenuation, and hypoattenuation shadow, CT is the

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Fig. 5.18 (a, b) Two patients with choledocholithiasis: red arrow indicates the target sign, and yellow arrow the crescent sign

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most effective and sensitive imaging modality for evaluation of gallstones. (1) High-density stones are mainly bile pigment stones containing various calcium salts; CT value is more than 60 Hu and higher than surrounding soft tissue density. (2 Soft tissue density stones are cholesterol stones containing a small amount of calcium salts; CT value is 20–60 Hu with soft tissue density. (3) Low-density stones mainly contain cholesterol; CT value is less than 20 Hu with translucent shadow below the bile density. (4) CT images of mixed-density stones show inhomogeneous density of stones and are typically layered, a characteristic manifestation of bile duct stones. CT value is negatively correlated with cholesterol content and positively correlated with bile pigment and calcium content. Direct CT signs of common bile duct stones include these. (1) High-­ density stones in the common bile duct fill the entire lumen, with no surrounding low-density bile shadow. (2) The target sign was first proposed by Baron in 1987 and is considered a direct sign of common bile duct stones [42]. The stones showing the target signs are mostly high density, soft tissue density, or mixed density. The density of the annular water around the stone is formed by the surrounding bile and may also be related to the inflammatory edema of the internal wall of the common bile duct. A typical target sign can appear as a uniform ring or a wide upper and lower narrow, a left wide and a right narrow, or a left upper wide and a lower right narrow sign. (3) There are some common bile duct stones. The density of water samples around the stones does not constitute a complete ring shape, but a crescent shape, called the crescent sign. The crescent-­ shaped water sample density is mostly located at the upper left or left side of the stone, which may be related to the gravitational effect of the stone and the kinetic effect of bile flow from the upper left to the lower right at the lower end of the common bile duct. The target sign and the crescent sign are characteristic signs in the diagnosis of common bile duct stones, especially on enhanced images. The indirect CT findings of stones in the common bile duct follow. (1) Mild or moderate dilatation of the common bile duct above the obstructive

s­ egment. (2) High-density circular thickening of the wall of the common bile duct, the feature of choledocholithiasis and choledochitis. The diagnostic accuracy of CT in diagnosing common bile duct stones is 50% to 90%, depending on stone composition. CT is highly sensitive to pigment stones, that is, high-density stones and mixed-­density stones, and the diagnostic accuracy is more than 90%. In CT, it is difficult to diagnose cholesterol stones with approximate bile density. The combination of significant CT features, such as common bile duct (CBD) diameter of 8 mm or more, pericholecystic fat infiltration, and papillitis can be translated into a nomogram allowing a reliable estimation of CBD stone presence; this may serve as a decision support tool to determine whether to proceed to further diagnostic tests or treatment options [43]. Spectral CT has a high diagnostic value for negative gallstones or bile duct stones, and material decomposition CT images and spectral curves can make an accurate diagnosis [44]. The signal changes of gallstones on MRI are related to lipid and macromolecular proteins in gallstones, but not to the density of gallstones, which effectively complements the deficiency of CT in the diagnosis of gallstones. MR cholangiopancreatography (MRCP) can show three-dimensional images of the biliary tract system and has unique advantages in the diagnosis of gallstones.

5.19 Pearl Necklace Sign Feature On MRCP or T2WI, the thickened wall in gallbladder adenomyomatosis (GA) or diverticular disease shows multiple tiny, dotted high-signal cysts, 2–7  mm in size, generally 4  mm, resembling a pearl necklace. Identification of the pearl necklace sign is useful to distinguish GA from wall thickening secondary to gallbladder carcinoma (GC). Explanation The myometrium and epithelium of gallbladder proliferate and hypertrophy, and the mucosa valgus in the myometrium forms the Rokitansky–

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Fig. 5.19  A 49-year-old man. (a) Nodular thickening at the bottom of the gallbladder with cystic formation shown on postcontrast CT. (b–d) Fluid signals in the cystic cavity

were seen on T2WI, T1WI with fat-suppressed, linear enhancement of cystic septum on post-contrast T1WI

Aschoff sinus (RAS). RAS is filled with bile; significant high signal points can be seen in the thickened wall on MRCP or T2WI. MRCP depicts these closely located cystic spaces as tiny bright foci, all along the wall of gallbladder, resembling the metaphorical pearl necklace. MRCP is more useful than the other MRI sequences in identifying GA (Fig. 5.19).

cystography, and now is widely used to describe the MRI appearance of GA. The finding of GA is relatively common with a reported incidence of 2% to 5% of specimens at cholecystectomy [46]. The gallbladder wall is composed of four layers: mucosa, lamina propria, muscularis propria, and serosa. Adenomyomatosis or diverticular disease of the gallbladder is characterized by excessive proliferation of surface epithelium that results in multiple diverticula or out-pouches, termed RAS. These diverticula invaginate into the deep muscular layer and appear as cystic spaces in the wall, contiguous with the gallbladder lumen. These diverticula contain bile with cholesterol, which on precipitation results in cholesterol crystal formation. In the presence of fluid (bile), T2WI demonstrates the bright cystic spaces rep-

Discussion The pearl necklace sign indicates the presence of Rokitansky–Aschoff sinuses within the thickened gallbladder wall, specifically detected on MRCP for GA.  The sign was initially used in description of the characteristic appearance of GA on drip-infusion cholecystography [45]. This specific sign can also be seen on oral chole-

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resenting RAS.  MRCP depicts these closely located cystic spaces as tiny bright foci, all along the wall of the gallbladder, resembling the (metaphorical) pearl necklace. The pearl necklace sign is useful to distinguish GA from wall thickening secondary to GC [45, 46]. Focal adenomyomatosis may sometimes appear as a discrete mass and can be mistaken for GC.  Surgical resection is usually not indicated, except in symptomatic patients and in cases where GC cannot be completely excluded [47]. MRCP frequently depicted RAS within the thickened gallbladder wall (the pearl necklace sign) in the majority of patients with all morphological types of GA.  The pearl necklace sign of small connected sinuses on MRI, or the “rosary” sign on CT are additional characteristics that may assist in establishing a diagnosis of GA. MRCP is more useful than CT and arterial phase MR images in the differentiation between GC and GA [46]. A combination of arterial phase MRI T1WI and MRCP may be helpful for differentiation between GC and GA when the pearl necklace sign is not identified on MRCP images or GC coexists with GA, particularly the segmental type of adenomyomatosis [46]. A recent study reported the cotton ball sign was more sensitive than the pearl necklace sign for diagnosis of adenomyomatosis diagnosis and was also useful in differentiating GA from GC [48].

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5.20 Garland Sign Feature When CT cholecystography is performed with oral contrast medium, the thickened gallbladder wall is filled with small dots of contrast medium, which are connected with the gallbladder and resemble a garland, thus called the garland sign. Explanation The garland sign is a CT feature of adenomyomatosis of the gallbladder on oral contrast cholecystography. It is formed by the filling of contrast media in the thickened Rokitansky–Aschoff sinus of the gallbladder wall (Fig. 5.20). Discussion Adenomyomatosis of the gallbladder (GA) is a common benign disease characterized by asymptomatic gallbladder masses or thickening of the gallbladder wall [49]. The diagnostic rate in all cholecystectomies is from 2% to 9%. GA was proposed by Jutras in 1960 [50]. According to the range of lesions, GA can be divided into three types. (1) Diffuse type (extensive type): the entire gallbladder wall shows diffuse thickening and the thickened wall shows a diverticulum. (2) Segmental type (ring type) is characterized by ring-shaped thickening of the gallbladder wall, ring-shaped thickening of the typical part of the gallbladder body; the general specimen of the

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Fig. 5.20 (a) Localized gallbladder agenesis (GBA). (b) Diffuse GBA

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gallbladder showed hourglass-like changes, with the gallbladder divided into two interconnected small cavities. (3) The localized type (basal type), the most common, also known as adenomyoma, is characterized by a clear border at the bottom of the gallbladder mass, a semilunar or crescent (cap sign). The exposure of Rokitansky–Aschoff sinus (RAS) is the main basis for diagnosis of this disease by CT examination. CT shows mainly an enlarged gallbladder, diffuse or localized thickening of the gallbladder wall, and uneven distribution. The small cap sign appearing on the basal type is highly suggestive of this disease. Because Fig. 5.21  In a 26-year-old man, axial precontrast CT of the influence of partial volume effect, many shows manifestations characterized by interstitial striated calcification of the hepatic parenchyma, crisscrossing into small diverticula connected with a gallbladder the shape of a map cavity in the gallbladder wall cannot be displayed by precontrast CT, so are easy to confuse with ized by poor contractile function and no RAS. (3) gallbladder carcinoma. Dynamic contrast-­Xanthogranulomatous cholecystitis. Enhanced enhanced or multiphase spiral CT scan showed scan is typically characterized by “sandwich bisthe thickened gallbladder wall in arterial phase cuit sign,” that is, a thickened gallbladder wall was markedly enhanced in mucosa and submu- with enhanced inner and outer rings. cosa, the lesion was enhanced and expanded in portal vein phase, the gallbladder wall was enlarged in delayed phase, and the muscular layer 5.21 Tortoise Shell Sign of mucosa and submucosa was heterogeneously or homogeneously enhanced. This enhancement Feature is rare in other lesions of the gallbladder, reflect- CT of liver in schistosomiasis is characterized by ing the pathological hyperplasia and hypertrophy interstitial striated calcification of the hepatic of the gallbladder mucosa and muscular layer, parenchyma, crisscrossing into the shape of a which is the enhancement characteristic of gall- map or tortoise shell pattern. bladder adenomyosis. In addition, the interface between liver and gallbladder was clear, the inner Explanation and outer walls of gallbladder were smooth, and The eggs of schistosomes (trematodes), causing the boundary between the normal part of gallblad- schistosomiasis, stay in the small branch of the der and the involved part of gallbladder was clear. portal vein to form nodules of the eggs and a GA is often differentiated from other gallblad- fibrosis reaction, which leads to hyperplasia of a der diseases. (1) Gallbladder carcinoma shows large amount of fibrous tissues around the branch uneven thickening of the cystic wall with of the portal vein. Finally, linear calcification enhancement, uneven inner wall, unclear bound- forms. When linear calcification is very extenary between the outer wall and the surrounding, sive, the crisscross pattern will become the charwhich can directly invade the liver; the hepatobi- acteristic images of map-like or net-like liary interface disappears, and sometimes lymph morphology (Fig. 5.21). node metastasis can be seen surrounding. (2) In chronic cholecystitis, the fat meal test has differ- Discussion ential significance. Diffuse cystic adenoidopathy The German physician Theodor Bilharz first can be manifested as hyperactivity of the gall- described schistosomiasis after he performed an bladder. Chronic cholecystitis can be character- autopsy in 1851 in Egypt [51]. Schistosomiasis is

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a trematode infection endemic to various tropical and subtropical locations. Human infections with liver involvement are typically caused by the species Schistosoma mansoni and Schistosoma japonicum. After infection, schistosomes migrate into the mesenteric vasculature and release their eggs, which then travel to the liver via the portal circulation, inducing inflammation and sinusoidal hypertension. The smaller eggs of S. japonicum embed more peripherally within the liver. When the eggs die, they induce inflammation and fibrous septa formation with eventual calcification. The fibrotic septa, oriented perpendicular to the liver surface, surround normal liver parenchyma in a polygonal distribution to produce the classic “fish scale” appearance by ultrasound. On CT, the calcified fibrotic septa and thickened capsule result in the classic “tortoise shell” or “turtle back” appearance of chronic S. japonicum infection. On MRI, the fibrotic septa appear hypointense on T1WI and hyperintense on T2WI and enhance following intravenous contrast administration [52]. CT findings in patients with chronic schistosomiasis include target organ damage and the peculiar calcification pattern of eggs in the lesions. A peculiar type of septal calcification of eggs in Schistosoma japonica resembling a turtle shell also indicates the severity of hepatic fibrosis. This peculiar septal and capsular calcification results in a geographic or map-like appearance on CT [53]. Hepatocellular carcinoma (HCC) is associated with chronic hepatic schistosomiasis, a

and most of the nodules appear as masses of homogeneous low density surrounded by shell-­ ­ like calcification. CT evidence of septal enhancement in broad fibrous septa is suggestive of hepatic S. japonica infection. Other suggestive findings of schistosomiasis such as splenomegaly, ascites, and dilated collateral vessels are well demonstrated on CT. Both CT and US show characteristic features and are good modalities for evaluation of hepatic schistosomiasis. The MRI appearance is less characteristic. MRI has an inherent disadvantage in evaluation of schistosomiasis because it does not allow identification of the characteristic calcifications [53].

5.22 Periportal Tracking Sign Feature Postcontrast CT shows a tubular low-density shadow around the portal vein and its branches, with a dendritic orbital shadow on the long-axial section and a circular shadow on the cross section. Explanation Periportal tracking sign is an important sign of subtle liver injury. The pathological basis is rupture and hemorrhage of small blood vessels in the intrahepatic triangle area during hepatic blunt contusion, and the blood spreads along the connective tissue sheath with low resistance around portal veins (Fig. 5.22). b

Fig. 5.22  Periportal low attenuation. Postcontrast CT (Transverse view a and Sagittal view b) shows low-attenuation areas around portal vein and its branches (arrowheads). Note laceration in right lobe

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Discussion Macrander et  al. found the “periportal tracking sign” that may be an important sign of subtle liver injury in 1989. After blunt abdominal trauma, the periportal tracking sign (PPT), which may represent hemorrhage along the portal veins, has also been described. The periportal region describes the area around the portal vein and its branches. Hepatic artery branches, bile duct branches, autonomic nerves, lymphatics, and a potential space are found within. A variety of pathological manifestations can involve any of these structures with a characteristic finding in contrast-enhanced CT, best described as periportal low attenuation, which is called periportal tracking. The periportal lymphatics and nerves are not visible in the general population. These structures can be involved by various diffuse processes [54]. PPT has also been seen in patients with hepatitis, liver transplant, congestive heart failure, hepatic artery thrombosis, and lymphatic obstruction [55]. Vigorous intravenous fluid administration or elevated central venous pressure caused by tension pneumothorax or pericardial tamponade may be further reasons for PPT.  In inflammatory diseases, PPT seems to reflect altered hepatic lymphatic dynamics. However, the pathogenesis is uncertain. It is obvious from the foregoing that the differential diagnoses of PPT are numerous [56]. The other radiologic findings associated with hepatic periportal tracking include a thickened gallbladder wall, pleural effusion, and a dilated inferior vena cava. A multifactorial etiology for periportal edema in acute infectious disease has been suggested, including altered sodium reabsorption as a result of the infectious process involving the renal interstitium and increased vascular permeability secondary to systemic sepsis or hypoalbuminemia [56]. The PPT has been reported to be an extrarenal manifestation of acute pyelonephritis. The limited data suggest that PPT may be associated with a more severe course of acute pyelonephritis [54]. On occasion, this is the only sign of hepatic injury. The CT features of blunt liver trauma include lacerations, subcapsular or parenchymal hematomas, active hemorrhage,

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juxta-hepatic venous injuries, and periportal low attenuation. In addition, CT is a useful tool in the assessment of delayed complications in blunt liver trauma, including delayed hemorrhage, hepatic or perihepatic abscess, posttraumatic pseudoaneurysm and hemobilia, and biliary complications such as biloma and bile peritonitis. CT is also needed for follow-up in patients with high-grade liver injuries to identify potential complications that require early intervention in clinical practice [57].

5.23 Periportal Halo Sign Feature MRI T2WI and postcontrast T1WI show hypointensity surroundings around portal vein branches; CT enhanced scan showed a halo-like low-­ attenuation area around hepatic segments or peripheral portal vein branches; depending on the prognosis, development or disappearance of the disease follows. The branches of the portal vein in the left lobe of the liver run parallel to the transverse axis, so the low-attenuation area around the portal vein extends to a tram track line appearance; the branch of the portal vein in the right lobe of the liver runs in the coronal direction, so the low-attenuation area around the portal vein appears as a ring or circle. Explanation About 80% of the hepatic lymph drainage is to the hilar lymph nodes and into the small omental lymph nodes. The hilar mass and omental lymph node cause the intrahepatic lymphatic dilation to form lymphedema around portal vein. Heart failure and venule obstruction lead to excessive lymphatic production in the liver, lymphatic dilatation, and periportal edema, edema formed around the branches of the intrahepatic portal vein during trauma. All these changes increase the fluid around the portal vein branches, forming a halo sign around the portal vein. The low-­attenuation shadow around the portal vein caused by trauma is considered to be caused more by bleeding, and is called the periportal tracking sign (Fig. 5.23).

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Fig. 5.23 (a) CT postcontrast image shows halos of hypoattenuation around portal veins. (b) T2-weighted MRI also shows halos of high signal intensity around portal veins

Discussion Periportal halo sign is a valuable CT sign of occult liver disease. The pathophysiological basis of the periportal halo sign or tracking sign has not been confirmed. Periportal halo sign is likely to indicate fluid or dilated lymphatic system in the loose stroma around the portal vein and portal triple structure. The central hepatic vein of the hepatic lobule is closely connected with the adjacent hepatocytes, and there is no potential gap. The triple structure of porta hepatica located around the hepatic lobule includes not only the segment of portal vein, hepatic artery, and bile duct, but also lymphatic vessels. There is a potential space around the triple structure of the hilum of the liver, which is relatively loose connective tissue. The branches of lymphatic vessels are located around the portal vein: 80% of the lymphatic fluid is transported from the liver to the portal area, then drained to the adjacent lesser omental lymph nodes, and finally into the chylous cistern. A small portion (nearly 20%) of the hepatic lymphatic drainage system runs along the hepatic vein and enters the thoracic duct. Hilar masses can obstruct the lymphatic reflux of the liver. Lymphatic dilatation in the liver can lead to lymphedema around the portal vein. In some patients with severe hepatitis, congestive heart failure, or venule obstruction, the liver may become congested or develop edema, resulting in increased lymphatic production. Increased lymphatic volume overloads the lymphatic system

and consequently leads to lymphatic dilatation and edema around the portal vein. In patients with liver trauma, intrahepatic hemorrhage and edema occur in the area with the lowest tension, that is, the porous space around the portal vein. The similarity of these processes is the accumulation of fluid around the portal vein, which leads to the enlargement of the potential gap, which is manifested in the low-attenuation halo around the portal vein in enhanced CT scan [58]. Biliary dilatation, portal vein thrombosis, and normal fat around the main portal vein resemble the periportal halo sign. Periportal halo sign is common around the portal vein below the segment, away from the fat around the main portal vein. Unlike the low-attenuation shadow surrounding portal vein branches, the low-­attenuation areas of bile duct dilatation do not surround portal vein branches. In some patients, periportal halo and biliary dilatation may be associated. Portal vein thrombosis is characterized by focal low-attenuation areas around the hepatic artery after enhanced contrast. Understanding that complete or partial thrombosis is common in the main portal vein and understanding its anatomical relationship correctly usually leads to correct diagnosis. In conclusion, periportal halo sign and tracking sign may represent fluid accumulation, either hemorrhage or edema, or lymphatic dilatation around the portal vein and portal triple structure. The pathophysiological basis of this sign has not been confirmed. There is no specificity in this manifestation, but

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the hilar and lesser omentum areas should be carefully observed when this sign occurs. Periportal halo sign can occur in different diseases, including end-stage primary cholestasis cirrhosis, trauma, congestive heart failure, hepatitis, mass, lymph node enlargement in portal area, and hepatic vein obstruction, treated with liver transplantation and bone marrow transplantation [59].

5.24 Focal Hepatic Hot Spot Sign Feature The focal hepatic hot spot sign can be seen in 99m Tc-sulfur gel scanning of the liver and spleen; it can be shown as an increase in radiopharmaceutical intake of the liver. This sign can also be seen in postcontrast CT scanning [60]. Explanation When superior vena cava obstruction occurs, the left hepatic lobe on the radionuclide scan image occasionally shows an increase in localized blood flow in the collateral vein. The general collateral vein pathway includes an internal mammary vein that is drained through the paraumbilical vein to the left branch of the portal vein. Blood flow through the collateral vein can cause an increase in blood flow in the focal region of the liver. Especially when the superior vena cava (SVC) is obstructed, activity is increased in the fourth segment of the liver (Fig. 5.24). Discussion Other causes of the focal hepatic hot spot sign include Budd–Chiari syndrome, liver abscess, liver focal nodular hyperplasia, and hepatocellular carcinoma. Except for the hepatic hot spot sign caused by Budd–Chiari syndrome in the caudate lobe, the focal hepatic hot spot sign caused by all other diseases can be seen anywhere in the liver. Patients with SVC obstruction showed increased focal activity or hot spot in the fourth segment of the liver (S4) on 99mTc-sulfur gel scanning of liver and spleen. The hot spot is thought to be caused by the shunt of the superior vena cava and the portal vein, which leads to an increase in focal hepatic blood flow. SVC

Fig. 5.24 A 51-year-old male patient with systemic lupus erythematosus and SVC obstruction. Arterial phase postcontrast CT shows a patchy area with abnormal enhancement in S4. The boundary is clear, the shape irregular, and accompanied by formation of collateral veins (para-umbilical vein) [62]

obstruction is usually caused by extrinsic compression from malignant disease such as bronchogenic carcinoma, lymphoma, and metastatic lymph nodes; occasionally it may result from benign causes such as aortic aneurysms, chronic/ fibrosing mediastinitis, and retrosternal goiter [61]. There are many ways to form bypass of collateral vessels and central venous obstruction. There are three main collateral pathways in the chest: upper pathway, posterior pathway, and anterolateral pathway [62]. The upper pathway is seen in the distal central vein (subclavian) and includes the anterior jugular vein system that connects the subclavian and internal jugular vein system. The posterior pathway includes the venae azygos-venae azygos minor inferior and the paraspinal system. The presence of these collateral pathways on axial image strongly suggests superior vena cava obstruction. The anterolateral pathway system drains the anterior intercostal vein, internal mammary vein, and thoracic long vein to the inferior vena cava through the pericardial phrenic vein, diaphragmatic vein, lumbar vein, and hepatic vein. As with patients with SVC obstruction, patients with inferior vena cava obstruction can also have the focal hepatic hot spot sign if the 99mTc-sulfur gel is injected from the lower extremity. Collateral veins in patients with SVC obstruction send blood back to the left lobe of the liver

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Discussion Hepatic hydatidosis is divided into two types, echinococcosis caused by infection with Echinococcus granulosus eggs and echinococcosis caused by infection with Echinococcus multilocularis eggs. The cyst-in-cyst sign can be seen in echinococcosis granulosa. Echinococcosis granulosus is a parasitic disease caused by human infection with Echinococcus granulosus. The right lobe of the liver is the predisposing site of the disease. According to the literature, the proportion of liver, lung, and other locations is 75%, 15%, and 10%, respectively [63]. Hydatid cysts formed by Echinococcus granulosus mostly parasitized in the right lobe of the liver, often single, 5.25 Cyst-in-Cyst Sign a few multiple, with slowly expanding growth, gradually growing into giant cysts. During the Feature growth process, the inflammatory reaction around When hepatic echinococcosis is examined by CT, the hydatid cyst forms a thick fibrous capsule, there are different sizes and number of ascites in which constitutes the outer cyst of the hydatid the mother cyst, forming a multiple or honeycomb-­ cyst, and the hydatid cyst itself is the inner cyst. like, sometimes wheeled, appearance. There are abundant blood vessels between the external and internal cysts to ensure the blood Explanation supply of hydatid cysts. The inner capsule is thin The cyst-in-cyst sign is the characteristic mani- and consists of the outer corneal cortex and the festation of cystic hepatic hydatidosis. The inner germinal layer. The cortical cortex protects mother cyst is the hydatid cyst itself. The subcyst the germinal layer and absorbs nutrients; the geris the germinal cyst or ganglion produced by the minal layer has strong reproductive ability, and germinal layer of the mother cyst. The germinal can produce fine-pedicled germinal vesicles in cyst falls out into the cyst, forms the ascus, floats the cyst cavity, containing many cephalic nodes. in the mother cyst, and forms the characteristic The germinal sac falls off into the sac and forms cyst-in-cyst sign (Fig. 5.25). an ascus, which floats in the mother sac. The scolex also produces ascus. The ascus is the same as the maternal sac, and can continue to produce germinal or grandchild sacs, forming three generations coexisting in one sac. The rupture of cyst wall is a serious complication. The fluid containing toxic protein in the cyst can cause an allergic reaction or even anaphylactic shock. The ruptured scolex is planted in the abdominal cavity and a secondary hydatid cyst occurs. Calcification can occur in the cyst wall of long-term growth hydatid cysts. The CT features of echinococcosis granulosus are quite characteristic. CT is a major means of examination in the diagnosis of hepatic echinoFig. 5.25  A 48-year-old man. Intrahepatic space occupa- coccosis, the location of echinococcal cysts, and tion and cyst-in-cyst sign on postcontrast CT the number, size, shape and complications of through the internal mammary vein and the left umbilical vein, thereby forming a localized area of increased blood flow where the left umbilical vein and the left main branch of the portal vein are inserted. On arterial phase or early portal vein phase of postcontrast CT, focal high attenuation enhancement, or on the radionuclide scan the accumulation of focal radiopharmaceuticals, is manifested by an increase in blood flow from the collateral vessels of the liver, which is the focal hepatic hot spot sign. The focal hepatic hot spot sign strongly suggests SVC obstruction of the chest.

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cysts. Echinococcosis granulosus can be divided into four types [64]: (1) unilocular cystic type, single or multiple cystic low-density shadows, showing round or oval water samples of uniform density; (2) child–mother relation cystic type, in which the number and size of round, lower-­ density cysts filling can be seen, showing multichamber or honeycomb-like “cyst” changes, namely cyst-in-cyst sign; (3) calcific type, the wall of the cyst, that is, the contents of the cyst are calcified in large quantities; and (4) complicated type, manifested by cyst rupture, wherein the contents of the posterior capsule flow into the abdominal cavity, causing peritonitis. The cyst size of hepatic echinococcosis is related to the time of formation [65], which is generally larger, mainly because the onset of hepatic echinococcosis is concealed; the early clinical symptoms are mild, and the development is slow. Hepatic damage caused by hepatic echinococcosis is usually a single or multiple cyst in the liver. Its imaging classification is relative, and it is different from the same disease. Imaging examination can visually display various signs, such as cyst size, cyst wall shape, cyst wall thickness, cyst fluid density, combined with high calcification rate, cyst-in-cyst sign, and other characteristic imaging manifestations, and pay attention to a small number of cases may be accompanied by sensation. Complications such as dyeing and rupture can be used to diagnose hepatic echinococcosis.

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5.26 Floating Membrane Sign Feature This sign is one of characteristic CT signs of hepatic echinococcus cyst; the ascus appears in the mother cyst of hepatic echinococcosis, the ascus and the mother cyst are completely separated and detached, and the ascus floats in the mother cyst fluid, showing a floating membrane sign. Explanation Hepatic echinococcosis internal capsule separation is caused by infection or injury; if completely separated, then the falling internal capsule scatters in a floating membrane shadow (Fig. 5.26). Discussion Hydatidosis is a common zoonotic parasitic disease in livestock areas, and 70% of hydatidosis occurs in the liver. Generally, it is caused by accidental ingestion of tapeworm eggs; the larvae pass through the small intestine and invade the liver through the portal vein. There are two types of hepatic echinococcosis: one is hepatic cystic echinococcosis caused by Echinococcus granulosus infection, and the other is hepatic alveolar echinococcosis caused by Echinococcus multilocularis infection [66]. CT has obvious advantages in the diagnosis of hepatic echinococcosis, and its display of characteristic pathological manifestations is the key factor in this diagnosis

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Fig. 5.26  Postcontrast CT (a, b) shows floating ruptured ascus in the mother sac with floating membrane sign

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and activity judgment. According to the latest expert consensus, hepatic Echinococcus granulosus disease can be divided into single cyst type, multiple cyst type, internal cyst collapse type, consolidation type, and calcification type. The internal capsule collapse is caused by external forces, hydatid cyst degeneration, and infection. When the internal and external capsules are separated or ruptured fluid enters between internal and external capsules, “bilateral sign” is seen; when the internal capsule is completely separated, collapsed, or suspended from the cystic fluid, it is called “water lily sign”; when the internal capsule is completely exfoliated, it can show “floating membranes sign.” Calcification and polycystic and endocystic collapse have been identified as characteristic signs of hepatic hydatidosis. The floating membranes sign is one of the characteristic signs. Hepatic echinococcosis should be distinguished from simple hepatic cyst, liver abscess, hepatic hemangioma, and hepatocellular carcinoma [67]. The mechanism of hepatic alveolar echinococcosis is unknown and should be differentiated from multiple hepatic cysts. For exam-

ple, hepatic cystic type and hepatic alveolar type echinococcosis coexist. CT diagnosis is relatively easy. It is not difficult to differentiate and diagnose hepatic hydatidosis from hepatic hemangioma, hepatic abscess and hepatocellular carcinoma by comparing their CT features and clinical laboratory tests.

5.27 Beaded Sign Feature Endoscopic retrograde cholangiopancreatography (ERCP) and MR cholangiography (MRCP) in patients with primary sclerosing cholangitis (PSC) show stricture of intrahepatic and extrahepatic bile ducts with normal or mildly dilated bile ducts with beaded changes. Explanation In primary sclerosing cholangitis, short (1–2 cm) circumferential strictures of intrahepatic and extrahepatic bile ducts are accompanied by normal or mildly dilated bile ducts, which form the typical beaded change (Fig. 5.27).

Fig. 5.27  MRCP (a, b) in a 58-year-old woman presented with an uneven thickness of intrahepatic bile ducts of the liver and a slightly less smooth surface, showing the “string of beads” sign

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Discussion PSC, also known as stenotic cholangitis, closed cholangitis, or fibrotic cholangitis, is a rare disease caused by immune-mediated cholangiocyte injury through a complex interaction with environmental factors. Although the etiopathogenesis of PSC is still unclear, it is widely accepted that the interaction of different autoimmune, genetic, and environmental factors is responsible for the changes occurring in PSC [68]. PSC typically occurs in young and middle-aged men with an age of onset of 30 to 40 years. It is a chronic cholestatic liver disease characterized by intrahepatic or extrahepatic bile duct inflammation and fibrosis, and eventually develops into cirrhosis. The intrahepatic bile duct is almost always affected and tends to be more pronounced than in the extrahepatic bile duct. Moreover, the long-­ standing PSC is associated with serious complications such as hepatic osteodystrophy, development of dominant bile duct strictures, recurrent cholangitis, and disease-associated malignancies including cholangiocarcinoma. Most patients ultimately require liver transplantation, after which the disease may recur [69]. Liver histology changes in most patients are nonspecific, so liver biopsy has little value in the diagnosis of PSC, but may suggest PSC and histological staging. Histological changes in the disease include fibrosis around the bile duct, inflammation in the portal area, varying degrees of peripheral hepatitis in the portal area, and changes in liver parenchyma. As the disease progresses, fibrosis in the portal area increases, interlobular bile ducts decrease, and interlobular septal formation and eventually cholestatic cirrhosis appear. According to its abnormal degree, histology can be divided into stages I–IV. Phase IV is cholestatic cirrhosis. The characteristic radiologic features of PSC are irregular multiple local strictures and dilatations of intrahepatic and extrahepatic bile ducts, and typical beaded changes of stricture and normal dilated bile ducts. The branches of the intrahepatic bile duct are thinner and fewer. Stenosis of the intrahepatic bile duct is predominant. ERCP is the gold standard for diagnosing PSC, but it is an invasive examination and can cause

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many complications. According to the latest recommendations of the American Association for the Study of Liver Diseases (AASLD) and the European Association of the Study of the Liver (EASL) guidelines, MRCP is the first-line modality for investigating bile duct abnormalities in PSC patients. MRCP is a noninvasive examination. Moreover, MRCP allows for visualization of small ducts proximal to tight strictures, which are often not visualized during ERCP. Comparable to ERCP, sensitivity and specificity of MRCP are 88% and 99%, respectively [59]. However, when there is clinical suspicion with negative or nondiagnostic MRCP findings, ERCP should be performed. ERCP is also a therapeutic procedure with balloon dilatation or stenting possibilities, but with postprocedural complications ranging from 3% to 8%, and allows for histological sampling.

5.28 Soft Rattan Sign Feature Soft rattan sign refers to intrahepatic bile duct dilatation; as its course is gentle, on CT, MRI, MRCP, and ERCP like soft rattan, it is the so-­ called soft rattan sign. The incidence of malignant biliary obstruction is the highest. Explanation When a tumor causes complete obstruction of the bile duct in a short period of time, cholestasis may cause the bile duct above the obstruction to be uniformly expanded and may reach hepatic capsule. Because tube wall is still soft, it shows the soft rattan shape. The soft rattan sign suggests more acute obstruction. The cause is generally more common in fast-growing tumors, such as pancreatic carcinoma and cholangiocarcinoma, but other lesions can also cause similar changes (Fig. 5.28). Discussion The normal intrahepatic bile duct cannot be displayed. If it can be shown, its diameter is only 1–3  mm; when intrahepatic bile duct diameter reaches 5  mm, it is considered the bile duct is

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Fig. 5.28  In a 56-year-old woman with ampullary cancer, MRCP shows dilatation of the common bile duct, common hepatic duct, intrahepatic bile duct, and pancreatic duct

slightly dilated; 6–8 mm is moderate expansion; and up to 9 mm is severe expansion. The normal common hepatic duct and common bile duct are more than 1 cm in diameter. Clinically, the site of biliary obstruction is divided into four segments: (1) the hepatic portal segment refers to the hepatic left and right tube and common hepatic duct segment; (2) the upper pancreatic segment is the common bile duct before entering the pancreas; (3) the pancreatic segment is the common bile duct segment through the pancreatic tissue; and (4) ampulla segment refers to the bile duct segment below the pancreatic segment [70]. Common causes of biliary obstruction include bile duct tumors, stones, and inflammation. The former are mostly malignant lesions whereas the latter are benign lesions. With malignant obstruction in the upper pancreatic segment and the hepatic portal segment, first consider cholangiocarcinoma, followed by lymphatic metastasis; pancreatic carcinomas are common in the head of the pancreas, and ampullary carcinoma are common in the ampulla [71]. Malignant signs: (1) the soft rattan sign refers to the expansion of the intrahepatic bile duct, which is soft, shaped like soft rattan, with the highest incidence in malignant biliary obstruction; (2) the emptiness sign,

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originally proposed in ERCP, but also applying to MRCP images, is characterized by extreme dilatation of the bile duct above the lesion, soft rattan-­like dilatation of the intrahepatic bile duct, normal development of the bile duct below the lesion, and no development of the hepatic portal bile duct, which causes the hepatic portal bile duct filling defect to be emptied; and (3) the truncation sign is characterized by a sudden narrowing or disappearance of the dilated bile duct. When the hepatic portal biliary obstruction is present, in the higher position, the intrahepatic bile duct is dilated like arborization, also called the residual root sign. (4) The double duct sign: manifested as expansion of common bile duct and pancreatic duct at the same time, this indicates that the obstruction point is relatively low, which is more common in pancreatic head carcinoma, ampullary carcinoma, and duodenal papillary carcinoma; and (5) soft tissue mass shadow: most data suggest that soft tissue mass and sudden interruption of dilated common bile duct are the definite basis for the diagnosis of malignant biliary obstruction. Ultrasound, CT, or MRI are the main imaging modalities for biliary obstruction, but PTC and ERCP are still reliable methods. CT shows bile duct dilatation with accuracy of 98% to 100%. MRI shows intrahepatic, external bile duct diameter increased, with hypointensity on T1WI and hyperintensity on T2WI. MRCP can be seen from the hilar to the periphery of the liver from high to small hyperintensity dilatation of the bile duct, and can be observed from multiple aspects of the dilated biliary obstruction at the lower end of the biliary obstruction site [72]. The soft rattan sign is caused by obstruction in a short period of time of progressive aggravation, progressive increase in bile duct pressure, which leads to small bile duct cavity enlargement and small bile duct wall thinning. The bile duct wall is still soft and elastic, and the bile duct above the obstructive end is obviously dilated, with flexion and extension, showing a lotus-root shape. The appearance of the soft rattan sign highly suggests the existence of aa malignant tumor in the corresponding site of obstruction. Although soft rattan sign is an important sign of malignant obstruction, it is not

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a specific sign. A few benign obstructions can also appear as soft rattan sign.

5.29 Double Duct Sign Feature In MR cholangiopancreatography (MRCP), the common bile duct and pancreatic duct are simultaneously dilated, called the double duct sign. This sign can also be seen in endoscopic retrograde cholangiopancreatography (ERCP), CT with curved multiplanar reformats, and ultrasonography. Explanation This sign is usually caused by the pancreatic head tumor obstruction and embedding in common bile duct and main pancreatic duct. Double duct stenosis of the common bile duct and pancreatic duct causes simultaneous dilatation of the double duct (Fig. 5.29). Discussion “Double duct sign” was first reported by Freeny et al. in 1976 [73]. It was characterized by simultaneous dilatation of the common bile duct and pancreatic duct in ERCP. It is usually caused by the pancreatic head tumor obstruction and embedding the common bile duct and main pancreatic duct. The two most important causes of double duct sign are pancreatic head cancer and ampullary carcinoma. Other malignant lesions

Fig. 5.29  A 46-year-old woman with cholangiocarcinoma. MRCP shows dilatation of common bile duct and main pancreatic duct with double duct sign

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include cholangiocarcinoma, lymphoma, or metastases at the distal end of the common bile duct. Benign lesions include chronic pancreatitis and ampullary stenosis; primary retroperitoneal fibrosis and Kaposi sarcoma are rare causes, only reported in a few cases [74]. Because early symptoms of pancreatic head cancer are more insidious, early diagnosis of resectable lesions is more difficult. Its characteristic image manifestation is the double duct sign caused by the narrowing and obstruction of the pancreatic duct and common bile duct. Most pancreatic malignancies are adenocarcinomas and are intraductal growth, usually manifesting as a local mass of the head of the pancreas. In pancreatic head cancer, 62% to 77% of cases have double duct sign, but even though the pancreatic duct is not expanded, we cannot exclude the diagnosis of pancreatic head cancer, because the pancreatic duct diameter is normal in 20% of pancreatic malignant tumors. Smaller ampullary carcinoma can cause significant bile duct dilatation, and 52% of cases have double duct sign. Pancreatic cancer, ampullary carcinoma, and distal common bile duct cancer sometimes present difficulties in differential diagnosis. Tumors of ampullary carcinoma have different enhancement from pancreatic cancer in enhanced scans, whereas pancreatic head cancer has double duct sign and truncated changes. In addition, ampullary carcinoma rarely involves the postpancreatic fat gap and the fat layer between the superior mesenteric artery and the uncinate process. Pancreatic body atrophy is rare and can be differentiated from pancreatic cancer [75]. MRCP has a good shape and localization of pancreaticobiliary obstruction, and catheter morphology is useful in qualitative assessment. When obstruction or stenosis is suddenly interrupted, especially the irregular edge of the wall, 78% were malignant lesions [76]. Progressive interruption or stenosis, especially the smooth edge of the wall, is mostly a benign lesion. In short, the double duct sign is an important sign. In the clinical view, if there is a double duct sign, it can be highly suggestive of pancreatic malignant tumor, but it is not an absolute diagnosis. It is necessary to make a correct diagnosis by combining relevant medical history and other signs.

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5.30 Teardrop Superior Mesenteric Vein Sign Feature On postcontrast CT or MRI, the normal round superior mesenteric vein is compressed by tumor tissue and becomes teardrop, linear, or oval in shape. Explanation The portal vein is composed of the splenic vein and superior mesenteric vein, which converge behind the head of the pancreas. On axial CT, fatty tissue separation is seen between the normal pancreatic head or uncinate process and superior mesenteric vein. When pancreatic head cancer occurs, it can invade the surrounding area, break through the fatty layer, and infiltrate the surrounding blood vessels. When the superior mesenteric vein is directly infiltrated by cancer tissue or stretched by surrounding fibrous connective tissue, the circular section of the normal superior mesenteric vein can be changed into a teardrop, linear, or oval shape and the fat gap between tumor and superior mesenteric vein disappears. This sign is called the teardrop superior mesenteric vein sign (Fig. 5.30). Discussion Pancreatic cancer is a solid tumor with poor blood supply and no envelope. It is characterized by a

Fig. 5.30  A 67-year-old woman with pancreatic cancer. On postcontrast CT venous phase, a decreased attenuation mass was seen in the pancreatic head (a), with compres-

invasive growth, easily spreading and involving adjacent organs and blood vessels, with lymph node and distant organ metastasis. Surgical resection of pancreatic cancer is considered the only radical treatment. Before the superior mesenteric artery is involved, pancreatic head cancer invades the portal vein or superior mesenteric vein. The invasion of portal vein or superior mesenteric vein is a contraindication for pancreatoduodenectomy. The role of the invasive degree of the peripancreatic vein structure in evaluating the resectability of pancreatic head cancer has gradually attracted more and more attention. Invasion of the portal vein or superior mesenteric vein is no longer a contraindication. According to the recent radiology reporting guideline for pancreatic ductal adenocarcinoma, venous involvement should be described in terms of the tumor–vein interface (TVI); that is, values of 180° or less are defined as “abutment; resectable,” whereas those greater than 180° are referred to as “encasement; borderline or unresectable” [77]. A recent study showed that TVI and tumor size, determined using preoperative CT, were independently associated with histopathological portal vein–superior mesenteric vein (PV-SMV) invasion in patients with pancreatic head cancer. Histopathological PV-SMV invasion did not significantly affect overall survival after surgery [78]. When applying the teardrop superior mesenteric vein sign to evaluate the unresectability of b

sion of adjacent superior mesenteric vein and meeting with splenic vein, forming a teardrop superior mesenteric vein sign (b)

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pancreatic head cancer, the following points should be noted. (1) When advanced pancreatic head cancer has extruded into the superior mesenteric vein and presented annular stenosis or complete occlusion, it could present a false-­ negative, so it must be combined with other unresectable signs to improve sensitivity and accuracy. (2) The partial volume effect of CT is caused by vascular alignment for teardrop superior mesenteric vein sign, especially at the transition of superior mesenteric vein and portal vein, where the superior mesenteric vein transits from the XY plane to z-axis plane. Superior mesenteric vein deformation is best demonstrated on T1WI. Fig. 5.31  Duct-penetrating sign in pancreatic head mass Superior mesenteric vein deformation is consid- chronic pancreatitis ered as a useful sign of unresectable pancreatic head cancer. is also called mass chronic pancreatitis. It is an important imaging sign used to differentiate from 5.31 Duct-Penetrating Sign PC. Ichikawa et al. classified the pancreatic duct into four types according to the shape and dilaFeature tion of pancreatic duct on MRCP [80]: type I, On MRCP, there is a smooth perforation of the main pancreatic duct obstruction, with or without main pancreatic duct in the pancreatic mass, thickening of the upper main pancreatic duct; which is the duct-penetrating sign. type II a, narrowing of the main pancreatic duct tumor segment with irregular wall; type II b, narExplanation rowing of the main pancreatic duct tumor segThe duct-penetrating sign is a smooth stenosis or ment without irregular duct wall; type III, the no abnormality in the main pancreatic duct pass- whole main pancreatic duct is dilated without ing through the inflammatory mass (Fig. 5.31). clarity; and type IV, true stenosis, normal main pancreatic duct. Type II and type IV are generally Discussion positive for pancreatic duct penetration sign, sugDifferential diagnosis of pancreatic carcinoma gesting IPM, whereas type I and type III are (PC) and inflammatory pancreatic mass (IPM) mostly suggestive of pancreatic malignant has always been a tough clinical problem. tumors. Conventional CT, MRI, and ultrasonography Quantitative MRI is of great significance in have difficulty in distinguishing the two; some- differential diagnosis between IPM and choroid times diagnosis is difficult with surgical explora- plexus carcinoma. Niu et  al. found DWI had tion and even pathological biopsy. MRCP can important significance in differentiating PC from visually display the pancreaticobiliary tree, accu- IPM [81]. Cho et al. found lipid peaks on MRS of rately display the shape, extent, and extent of IPM patients decreased and other metabolites obstruction and dilation of pancreaticobiliary peaks increased [82]. MRI is of great value in the duct, and the shape of the obstruction end, thus diagnosis of IPM: it not only can assess physioproviding a powerful aid for the differential diag- logical and pathological changes of pancreatic nosis of pancreaticobiliary duct diseases [79]. It parenchyma, but also detects exocrine function is the characteristic manifestation of IPM, which and blood perfusion of the pancreas.

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5.32 Central Dots Sign Feature One CT sign of Caroli’s disease is a small round dot shadow in the cystic dilatation of the bile duct. Its density is less than or equal to the surrounding liver parenchyma, although higher than the surrounding liver parenchyma after enhancement; this is called the central dots sign. Explanation The pathological basis for the formation of the central dots sign is the axial projection of portal venous branch surrounded by dilated intrahepatic bile duct with congenital abnormal development, which is then involuted into dilated intrahepatic bile duct (Fig. 5.32).

Fig. 5.32 Longitudinal hepatic sonogram (a), axial contrast-­enhanced CT (b), axial contrast-enhanced T1WI (c), and T2WI reveal multifocal, segmental, cystic dilata-

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Discussion Central dot sign is suggested as a pathognomonic finding of Caroli disease (CD). Caroli disease is a rare, autosomal recessive disorder characterized by communicating cavernous biliary ectasia. It comprises two entities: the pure form, or Caroli disease, and a form associated with periportal fibrosis, also known as the Caroli syndrome. Caroli syndrome is a combination of Caroli disease with congenital hepatic fibrosis. The clinical course is usually asymptomatic for the first 5 to 20  years of life, and symptoms may seldomly occur throughout the patient’s life. Bile statis leads to recurrent episodes of cholangitis, stone formation, or liver abscesses, and biliary cirrhosis usually occurs years later [83]. Cases of this pure form of Caroli disease are uncom-

tion of the intrahepatic bile ducts with enhancing central dot sign (arrows) and multiple calculi (asterisks) [85]

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mon, and most patients have coexisting hepatic fibrosis [84]. On imaging, Caroli disease demonstrates multifocal, segmental, saccular or fusiform cystic intrahepatic biliary dilatation. These dilated bile ducts can contain calculi or biliary sludge. The central dot sign, representing a portal vein branch protruding into the lumen of a dilated bile duct, can be seen with ultrasound, CT, and MRI.  On CT scans, pontal radicles seem to be within the lumina of dilated bile ducts. However, they are not within the bile ducts but are surrounded by abnormally developed ectatic bile ducts. The central fibrovascular bundle enhances after contrast administration. Presence of the central dot sign is highly suggestive of Carolis disease, helping to differentiate it from other causes of intrahepatic biliary dilatation such as primary sclerosing ­ cholangitis and recurrent pyogenic cholangitis [85]. Treatment of CD depends on the clinical symptoms and location of the biliary abnormalities. Potential curative treatment of CD is surgical resection, such as segmentectomy, lobectomy, or hepaticojejunostomy, determined by the range of distribution [83].

5.33 Central Arrowhead Sign Feature Central arrowhead sign is a CT sign of suppurative cholangitis that shows dilatation of the first and second branches of the intrahepatic bile duct although the surrounding bile ducts are not dilated. The dilated intrahepatic bile ducts are aggregated and the endings can show an arrowhead shape. Explanation In suppurative cholangitis, asymmetrical or localized dilated bile ducts are often manifested in the first or second branches of intrahepatic bile ducts, with gas or pus in the bile ducts, whereas peripheral bile ducts lose the ability to dilate, presenting as a central arrowhead sign (Fig. 5.33).

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Fig. 5.33  Coronal reformatted CT demonstrates dilatation of first- and second-order ducts (arrows) with relative sparing of peripheral biliary tree. Multiple intraductal calculi are also seen (arrowhead) [86]

Discussion Suppurative cholangitis is often caused by bile duct obstruction and biliary tract infection. The most common obstruction is bile duct stones. Biliary inflammatory stenosis is also an important factor causing the disease. The main types of infecting bacteria are gram-negative bacilli, most commonly Escherichia coli, Proteus spp., and Pseudomonas aeruginosa. Most patients have a history of recurrent episodes. Acute episodes are characterized by epigastric pain, chills, fever, jaundice, and even coma and death [87]. Purulent cholangitis has relatively characteristic CT findings. CT is effective and ideal for purulent cholangitis. CT can show obstruction site, etiological lesion range, extent of bile duct dilatation, bile duct pneumatosis and/or p­ yogenia, and liver involvement. It can reflect various pathological indications of purulent cholangitis. Suppurative cholangitis has characteristic CT findings. (1) Hepatobiliary dilatation: intrahepatic bile duct dilatation often presents asymmetrical or localized distribution, with the left lobe obvious; dilated intrahepatic bile duct is aggregated, and bile duct dilatation often manifests in the first and second branches of intrahepatic bile duct, while peripheral biliary inflammatory fibers lose the ability to dilate, manifested as central arrowhead sign.

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Extrahepatic bile duct dilatation is also common and varied in degree. The postcontrast enhancement density of the intrahepatic bile duct wall is higher than that of hepatic parenchyma, which often indicates acute attack, and diffuse eccentric thickening of bile duct wall can be seen. (2) Liver abscess: because of infection of the bile duct, and infiltration of inflammatory cells around it, a large number of neutral polynuclear cells in the hepatic sinus, forming a small abscess, single or multiple, so single or multiple hepatic abscess is also one of the common manifestations. After enhancement, the abscess wall and its septa are enhanced. (3) Limited hepatic atrophy: as a result of repeated inflammatory obstruction and destruction, the volume of hepatic parenchyma is reduced and the liver segment atrophied locally, especially in the left liver. Limited hepatic parenchyma density decreased from fat infiltration in a small number of patients, such as homogeneous or heterogeneous hepatic parenchyma that enhanced significantly after enhancement, suggesting the development of acute suppurative inflammation. (4) Gas in the bile duct: diffuse or limited, more common in the left lobe of liver and associated with three factors, namely, a history of choledochojejunostomy, Odd’s sphincter insufficiency, and pneumonia infection. (5) Cholangiolithiasis: multiple, predisposing in the left lobe of the liver, especially the outer part. The stone is sandy or large pebble like. Most patients with suppurative cholangitis have intrahepatic bile duct stones, accompanied by or without extrahepatic bile duct stones, which indicates suppurative cholangitis and bile duct stones are causal and closely related [86].

5.34 Golf Ball-on-Tee Sign Feature Golf ball-on-tee sign is seen during excretory urography and appears as a contrast agent-filled cavity (the golf ball) that lies adjacent to a blunted calyx (the tee).

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Explanation Collecting tubules within the medullary pyramid come together to form papillary ducts that penetrate the papillary tip and drain into a calyx. In renal papillary necrosis, however, central necrosis and sloughing of papillae create a cavity, which is occasionally large, filling with contrast material and communicates with a calyceal concavity. Thus, golf ball-on-tee sign is created, indicating necrosis. The renal papillary tip is still within the sunken calyces. The calyx is filled with contrast agent to form a signet sign (Fig. 5.34). Discussion The “golf ball-on-tee” describes imaging findings that signify renal papillary necrosis. Once opacified with contrast material, the central calyceal cavity (the “golf ball”) appears to rest on the calyx (the “tee”). Although this sign originally was described at excretory urography, now the findings are most often seen on CT.  Other “classic” imaging patterns of papillary excavation seen in papillary necrosis include the “lobster claw” and “signet ring” appearance [88]. The lobster claw sign is seen in the papillary form of renal papillary necrosis on excretory urography or CT urography (CTU). Necrosis of the papilla causes the fornices of the minor calyx to elongate, creating the impression of a lobster claw. Eventually the fornices may even communicate all the way around the necrotic papilla, creating a signet ring [89]. The common etiology of papillary necrosis can be conveniently remembered with Dunnick’s mnemonic NSAID: nonsteroidal antiinflammatory medications, sickle cell hemoglobinopathies, analgesic nephropathy (specifically aspirin and phenacetin), infection (specifically tuberculosis), and diabetes. Some less common causes include renal vein t­ hrombosis, hypotension, and obstructive uropathy. The papillary necrosis seen in tuberculosis and severe pyelonephritis is a direct result of infection. The pathophysiology of papillary necrosis seen in other diverse group of

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Fig. 5.34 (a) Golf ball-on-tee sign. Axial CT image during excretory phase imaging shows a large lower pole papillary cavity in the left kidney with the golf balloon-tee appearance (arrow). (b) Coronally reconstructed image

during the excretory phase in the same patient shows the classic “golf ball-on-tee” appearance in multiple calyces (arrows) [88]

diseases appears to be ischemia to the papillae. The medullary papillae are especially susceptible to ischemic insult because of low oxygen tension, high blood osmolality, and relatively poor perfusion in the papillary tips [90] (Fig. 5.35). The radiologic appearance of papillary necrosis depends on the severity and chronicity of the necrosis [91]. The earliest and most subtle changes result in papillary swelling (necrosis in situ) that is often impossible to observe radiologically without serial urograms. These papillae often shrink over time and may calcify (as in medullary nephrocalcinosis); the calcification

may sometimes be detectable on a conventional radiograph. Progressive necrosis may result in interruption of the uroepithelial lining of the calyx. If the cavitation is central, as in the figure, the contrast agent will fill the medullary cavity adjacent to the calyceal concavity. As the necrotizing process proceeds (especially if the inciting factor is not removed), the cavity may enlarge, and create a radiographic appearance that resembles a golf ball on tee. Eccentric necrosis that originates at the margin of the papilla will cause irregular cavitation at the margin of the papilla and make the angle of the calyx appear elongated, which may result in a

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a

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c

Fig. 5.35  A 22-year-old woman with tuberculosis of the kidney. (a) The golf ball-on-tee sign is seen in the papillary form of renal papillary necrosis on excretory urography. Necrosis of the papilla causes the fornices of the

minor calyx to elongate, creating the sign. (b, c) Renal papillary necrosis on CT intravenous pyelogram with excavation of the calyces gives the appearance of a lobster claw [89]

“lobster claw” deformity. If the necrotic papilla is sloughed or resorbed, the resultant calyx will be blunted. The entire papilla or portions of it may be retained, in which case contrast material will surround the unextruded papillary tip, resulting in circular or irregular filling defects. The peripheral portions of these necrotic papillae may calcify. In conclusion, the golf ball-ontee sign is part of the spectrum of papillary necrosis and is distinguished by a papillary cavity that lies adjacent to a blunted calyx. Diagnosing papillary necrosis by recognizing the golf ball-on-tee sign is important for pre-

serving renal function because many of the causes of papillary necrosis are treatable.

5.35 Calyceal Crescent Sign Feature Calyceal crescent sign is seen in the early stages of intravenous pyelography (IVP). It appears as a crescent-shaped contrast agent density, gradually secretes into the renal pelvis system with the contrast agent, and disappears on subsequent contrast films.

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Explanation When chronic obstruction and hydronephrosis occur, the expansion of renal pelvis causes compression and deformation of papilla, and the nipple flattens and eventually turns over, resulting in a significant change in the direction of the col-

a

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lecting tube. An increase in intrarenal pressure increases the filtration time through tubules, resulting in an increase in urine content as it passes through the collection tube. These changes explain X-ray features of the calyceal crescent sign (Fig. 5.36).

b

c

Fig. 5.36 (a) IVP shows calyceal crescent sign (thin arrow) in the left kidney. (b) The calyceal crescent sign gradually disappeared at 2  min and the contrast agent

gradually secreted into the renal pelvis. (c) Contrast agent was excreted into the whole renal pelvic system at 90 min

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Discussion The calyceal crescent sign was proposed and systematically explained by Khanna in 2005 [92]. In mild hydronephrosis, the local development of the renal pelvis is visually called calyceal crescent sign. Its essence is caused by hydronephrosis, which causes the valgus of the renal pelvis to displace the collecting duct of the renal papilla, dilate and deform, and rearrange it parallelly around the valgus pelvis. It is the exact indication of hydronephrosis from the filling of contrast medium. It is also the exact indication of delayed development of urinary tract obstructive disease. The signs appeared earlier. Calyceal crescent sign can be seen in hydronephrosis caused by obstruction at the junction of the pelvis and ureter or at the end of the ureter. Many causes can cause obstruction of the pelvic–ureteral junction, such as an abnormal ureter itself, dilatation and abnormal peristalsis caused by defective muscles, obstruction of the lumen caused by ureteral valves, and polyps or abnormal renal vessels. X-ray radiography of hydronephrosis patients often shows various degrees of pyelomegaly, accompanied by poor emptying of the renal pelvic system. In more severe cases, thin renal parenchymal bands can be seen during renal imaging to delineate dilated undetected calyces. Contrast agents in dilated or rearranged collecting ducts can be distributed along the outer edge of the calyces and show calyceal crescent sign. The calyceal crescent sign needs to be differentiated from normal papillary staining of the normal collecting duct during IVU with hypoosmotic contrast agent [93]. As a common and frequently occurring disease of the urinary system, IVP is often used as the preferred choice for hydronephrosis in clinical practice. IVP has the advantages of simple, low price and many years of clinical practice. It is a mature examination method, but its false-positive rate and missed diagnosis rate are higher. With the development and application of imaging equipment in clinic, the advantages of CTU and magnetic resonance urography (MRU) in urinary hydronephrosis are becoming more and more obvious. The presence of calyceal crescent sign is considered a sign of increased intrapelvic pressure, suggesting that

delayed radiography should be performed and other imaging modalities are needed to better demonstrate the collective system and to determine the etiology of an obstruction [93].

5.36 Cortical Rim Sign Feature Renal infarction showing low density of infarct organs and linear high-density shadow around the cortical edge of infarcted kidney tissue on postcontrast CT. Explanation Cortical rim sign is a characteristic manifestation of renal infarction and represents the enhancement of the undamaged cortex under the capsule, which is the part of renal parenchyma that provides blood supply from perirenal capsule (Fig. 5.37). Discussion In 1974, Frank et al. [94] first described the cortical rim sign with a high-density ring around the infarcted kidney tissue on CT.  Postcontrast CT has a higher contrast resolution, and it is easier to see the cortical rim sign. It is characterized by a high-density margin 2–4  mm thick under the renal capsule with a smooth edge. The cortical rim sign may be continuous or discontinuous, and the discontinuous sign may be caused by a

Fig. 5.37 Postcontrast CT of a 35-year-old woman shows low density of the left renal infarction with linear high-density shadow, which is the cortical rim sign (arrow)

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discontinuous capsule plexus after trauma. The cortical rim sign, seen in about 50% of acute renal infarctions, is relatively specific to this condition and believed to result from intact renal collateral circulation following a vascular insult, such as renal artery thrombosis or embolization, renal artery dissection or renal trauma. Acute renal infarction can be cardiogenic or noncardiogenic in origin. In patients with noncardiogenic acute renal infarction who have no apparent risk factors (e.g., thromboembolism, coagulation dysfunction, hematological diseases), the cause often remains elusive [95]. Studies have shown that the cortical rim sign does not appear immediately after renal infarction, but the sign can appear about 1 week later, become most obvious at 2 weeks, and disappear after 8 weeks. Yoshiro et al. reported that the cortical rim sign appeared after 7  days of vascular occlusion, and the sign disappeared after the involvement of renal parenchyma began to significantly scar. The collateral circulation of the kidney is always present, and blood supply is provided by the renal capsule system, peripelvicular system, and the periureteral system. After acute renal artery occlusion, the collateral circulation responds immediately, increasing blood flow through vasodilation. No evidence of the cortical rim sign was found on CT after trauma and the infarction could not be ruled out, because it occurred 8  h to 1  week after trauma. Acute infarcts typically appear as wedge-shaped areas of decreased attenuation within an otherwise normal-­ appearing kidney. The parenchymal appearance depends on the size of the embolus, the location of the arterial occlusion, and its age. When large areas of the kidney are involved, an increase in the size of the kidney caused by edema can be seen. In global infarction, the entire kidney is enlarged and its reniform configuration remains preserved. The extent and degree of parenchymal loss reflect the distribution of the affected artery and revascularization from collateral circulation [96]. Differential diagnosis for the imaging appearance of renal infarction includes pyelonephritis. However, in kidney infection, neither the “cortical rim sign” nor “flip-flop enhancement” is found on CT [97].

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5.37 Renal Halo Sign Feature Normally, the internal boundary of perirenal fat is clearly shown on the abdominal X-ray, although the external boundary is not clear. On the abdominal X-ray, the inner and outer boundaries of the perirenal fat space can be clearly seen when effusion is accumulated in the anterior renal, so that the perirenal fat space appears as a ring-shaped low-density shadow, which resembles a halo. Explanation When the retroperitoneal disease causes inflammatory exudate to accumulate in the prerenal space, the external boundary of the perirenal fat gap can be clearly displayed by the obvious difference in the absorption rate of X-rays between inflammatory exudate and perirenal fat. At this time, the perirenal fat gap appears on the X-rays as a ring-shaped low-density shadow with a clear boundary, so it is called the renal halo sign. This sign is most common in acute pancreatitis (Fig. 5.38). Discussion The retroperitoneal space refers to the gap between the wall peritoneum and the transverse fascia and its anatomical structure. The prerenal fascia, the posterior fascia, and the lateral vertebral fascia divide the retroperitoneal space into three parts: the anterior renal space, the perirenal space, and the posterior renal space. The anterior renal space is located between the prerenal fascia and the posterior wall peritoneum, and the lateral side is located in the lateral vertebral fascia, which mainly contains the pancreas. The perirenal fascia is located between the prerenal fascia and the posterior fascia, which mainly contains the adrenal gland and the kidney. The posterior renal space is located between the posterior fascia and the transverse fascia, and contains only adipose tissue. Although the three posterior retroperitoneal spaces are anatomically intact, there is potential traffic between them, and one gap lesion can affect the others.

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Fig. 5.38  A plain radiograph of the abdomen (a) and corresponding radiograph from an excretory urogram (b) show a radiolucent halo about the left kidney. Contrast enhancement (b) of the perirenal (Gerota) fascia has

resulted from acute inflammation. The left psoas shadow is obliterated. An impression on the bladder from the left (b) is caused by extension of inflammatory process retroperitoneally into the pelvis

Normally, the internal boundaries of the perirenal fat spaces are clearly shown on the abdominal X-ray because of the different X-ray absorption rates of the parenchyma and perirenal fat. The external boundary of the perirenal fat space is not clearly shown on X-ray because of the lack of contrast between the perirenal fat and the pararenal retroperitoneal fat fusion. Inflammatory exudates caused by retroperitoneal disease accumulate in the prerenal space, because inflammatory exudates and perirenal fat absorb significantly different X-rays, so the perirenal fat space can be clearly shown outside; at this time perirenal fat space on the X-ray features of a clear border ring low-density shadow, known as the renal halo sign. Susman, through a series of abdominal X-ray and CT studies of acute pancreatitis, proposed a renal halo sign [98]. The appearance of the renal halo sign suggests that there is more fluid accumulation in the retroperitoneal space, especially in the prerenal space, thus indirectly suggesting the presence of acute pancreatitis. This sign is usually seen on the left

side, rarely on the right side [99]. However, the presence of renal halo sign is not a specific sign of pancreatitis; retroperitoneal bacterial inflammation, traumatic hematoma, and disseminated lymphoma completely invading the perirenal fascia can also occur with renal halo sign, so it also needs to be distinguished from acute pancreatitis. When the abdominal X-ray shows renal halo sign, combined with the typical clinical features, it should be initially diagnosed as acute pancreatitis. The renal halo sign is a sign on X-ray that is manifested as a perirenal halo sign on CT. Perirenal halo sign indicates that the extent of retroperitoneal inflammatory expansion has reached the perirenal adipose layer, and Balthazar grade can reach grade E [100]. It is a reliable diagnostic criterion for acute necrotizing pancreatitis, suggesting that the perirenal fascia has been broken through. The perirenal halo sign can also be seen in renal diseases such as renal lymphoma and abscess. Perirenal halo sign is one of the CT signs of complications of acute necrotizing pancreatitis (ANP).

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5.38 Perirenal Halo Sign Feature On CT, the anterior renal fascia thickened, the anterior pararenal space is exuded, and the perirenal space fat density is replaced by halo-like low-density shadows. The low-density shadows had a higher CT value, which could exceed 25 Hu. Explanation The perirenal halo sign is one of the CT signs of complications of acute necrotizing pancreatitis. In ANP, loose connective tissue inflammation is caused by extravasation of proteinase containing pancreatic fluid, often occurring in the tail of the pancreas, presenting as prerenal fascia thickening, penetrating renal fascia involving the perirenal fat layer, forming the perirenal halo sign (Fig. 5.39). Discussion CT findings of acute pancreatitis depend on the severity and extent of the inflammatory process. A CT scan that is performed within the first 48 h of the onset of symptoms may be completely normal. CT findings of acute pancreatitis include enlargement of the pancreas (localized or diffuse), poorly defined parenchymal contours, and decreased density and inhomogeneity of the pan-

Fig. 5.39  In a male patient with acute pancreatitis, the anterior renal fascia was thickened (left), and the anterior pararenal space exuded on abdominal CT

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creatic parenchyma and fluid collections in the peripancreatic region. The inflammatory reaction can produce increased attenuation of the peripancreatic fat tissue, commonly described as “stranding.” The inflammatory process is usually diffused and involves all the gland [101]. The inflammatory process in acute pancreatitis usually expands toward the left of the pancreatic tail and the left pararenal space. A relative decrease in the density of the perirenal fat tissue caused by an increase in the density of Gerota fascia and the pararenal space resulting from the inflammatory process leads to the “renal halo” sign [102]. The perirenal halo sign indicates that the retroperitoneal inflammatory extension has reached the perirenal adipose tissue; Balthazar grade can reach grade E. It is a reliable diagnostic and grading sign of acute necrotizing pancreatitis. Renal halo sign is a sign of abdominal plain film before perirenal fat; the adjacent inflammation exudation absorption rate is different, resulting in plain film that can clearly show the perirenal fat peripheral edge, the performance of abdominal plain film on the perirenal light, suggesting acute pancreatitis. The renal halo ring sign on CT is the loose connective tissue inflammation in the renal anterior space, presenting as effusion and exudation. The perirenal halo sign is loose connective tissue inflammation in the perirenal adipose tissue, suggesting that the perirenal fascia has broken through. The perirenal halo sign can also be seen in renal diseases, such as renal lymphoma and abscess. The imaging manifestations of renal lymphoma depend on the proliferation pattern of the tumor. Because malignant lymphocytes are easily disseminated through the bloodstream, they can proliferate in the interstitium and spread to the retroperitoneal cavity or other adjacent tissues after dissemination to the renal parenchyma. If the malignant lymphocytes grow or proliferate infiltratively along the normal interstitial tissue in the kidney, the normal shape of the kidney will not change; only the volume of the kidney will increase. If the malignant lymphocytes show focal proliferation, it would destroy the adjacent renal parenchyma to form swelling or nodular lesions, which could occur unilaterally or bilaterally. If a large number of

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small lesions of the tumor merge, it will destroy the kidney shape and cause the change of the wheel.

5.39 Perirenal Cobwebs Sign Feature The perirenal cobwebs sign refers to the fibrous curve high-density shadow of the medial perirenal interspace of Gerota’s fascia caused by various pathological conditions. Explanation The perirenal cobwebs sign originally referred to the collateral vessels in the perirenal space in patients with renal vein thrombosis. Perirenal fat contains peritoneal perforator arteries and veins, which anastomose with the branches of adrenal vessels, superior and inferior mesenteric vessels, and gonadal vessels. When these vessels do not dilate, they are hard to see on conventional CT scans; however, they clearly appear to show enhanced perirenal cobwebs sign (Fig. 5.40). Discussion In 1981, Winfield et al. coined the term “perirenal cobwebs” to describe vermiform curvilinear densities observed around the kidney on CT [103]. Perirenal cobwebs were initially attributed to collateral vessels seen in the perinephric

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space in patients with renal vein thrombosis. As our ­ability to image the perinephric space with CT improved, it became clear that numbers of disease processes were manifested by development of prominent perinephric structures [91]. The renal interspace is not a simple, undivided fat interspace, but is composed of multiple fibrous divisions. Tumors or inflammation within the anterior renal interspace often extend along and thicken Gerota’s fascia, and the dense renal capsule is similarly demarcated. Fluid, inflammatory tissue, and invasive neoplasms may all enter along the blood vessels through the weakness of the perirenal space, giving priority to dividing the loose lobules that support the perirenal vessels. The striated shadows in the spider web of perineal kidney represent pathological thickening of fibrous separations that can envelop or limit the diffusion of inflammatory exudation or effusion. There are several types of septa that compartmentalize the perirenal space and which may confine, or act as a conduit for, extension of a disease process [91]. Perirenal cobwebs (visualization of perirenal septa) are most frequently encountered during the CT evaluation of urinary tract obstruction from stone disease. Perirenal stranding, occurring in the setting of flank pain from ureteral colic, is an exaggeration of the visibility of these septations caused by edema and fluid extravasation, and is an important secondary sign of acute

Fig. 5.40 (a, b) In a 68-year-old man, noncontrast CT shows the fibrous curve high-density shadow of double kidneys, which is the perirenal cobwebs sign

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ureteral obstruction from stones. Perirenal stranding in the asymptomatic patient is often a nonspecific finding that may be seen in benign and malignant conditions [91]. Inflammatory and neoplastic processes, particularly those originating in the kidney, may produce similar appearances. If no cause for the cobwebs is found in the kidney, extrarenal pathology should be considered, acute pancreatitis or aortic aneurysm rupture particularly [103]. This appearance is nonspecific and often results from fluid within the septations existing in the perirenal space. The perirenal cobwebs sign is most common in urinary stones with infection, which also can be seen in a variety of lesions, including subcapsular hematoma, abdominal aortic aneurysm rupture, acute pancreatitis, and pyelonephritis [104].

5.40 Pseudo-capsule Sign Feature The pseudo-capsule of renal carcinoma appears as a complete or intermittent low-signal ring or band on the edge of the tumor on MRI, showing better on T2WI, that is, pseudo-capsule sign. Explanation The pathological basis of the pseudo-capsule sign is the peritumoral structure, which is composed of a fibrous capsule and a compacted renal parenchyma. The fibrous tissue is in close contact a

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with the tumor tissue of renal carcinoma, and the compacted renal parenchyma continues to the outside of the fibrous capsule. The tightly packed renal parenchyma is uneven in thickness, and coagulation necrosis, hyaline degeneration, and fibroblast proliferation can be seen. The appearance of the pseudo-capsule sign has a certain value for the MRI staging of the tumor. The occurrence of the pseudo-capsule sign allows considering that the perirenal fat sac has not been infiltrated, suggesting that the tumor can be partially removed by surgery (Fig. 5.41). Discussion The “pseudo-capsule sign” is an MRI finding of renal cell carcinoma (RCC) that appears as a complete or intermittent low-signal ring or band on the edge of the tumor and is better shown on T2WI. The appearance of the pseudo-capsule sign has a certain value for the MRI staging of the tumor. The occurrence of the pseudo-capsule sign may consider that the perirenal fat sac has not been infiltrated, suggesting that the tumor can be partially removed by surgery. RCC accounts for 1% to 3% of visceral tumors. Partial nephrectomy can only be performed if the tumor is confined within the renal parenchyma and there is a clear pseudo-capsule around it. RCC does not have a true histological capsule, but a surrounding pseudo-capsule that is composed of compressed renal parenchyma and fibrous tissue. The fibrous tissue can be connected to the fibers that b

Fig. 5.41  A 62-year-old female patient with renal cell carcinoma. Axial T1WI (a) false capsule sign was not obvious, and axial T2FS image (b) showed a regular pseudo-capsule surrounding high-signal tumor, the “pseudo-capsule sign”

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extend into the tumor. When the tumor grows, the fibrous tissue of the renal interstitial is stimulated to grow around the tumor, which has a certain limiting effect on the tumor growth. The thickness of the pseudo-capsule varies with different growth rates and where the tumor is located. Carcinoma tissues with a lower degree of malignancy grow more slowly. The interstitial fibers have a longer period of reactive hyperplasia and a thicker fiber component in the pseudo-capsule. Carcinoma tissues with a higher degree of malignancy grow faster. Interstitial fibers do not have enough reactive hyperplasia, and the fiber component in the pseudo-capsule is thinner. In 1985, Hricak et al. first discovered the existence of the pseudo-capsule with a low signal band in renal MRI [105]. Scholars have conducted much research. It was reported that T2WI has a sensitivity of 68%, and specificity up to 91%, for displaying pseudo-capsule; it is considered characteristic of MRI of renal cell carcinoma [106]. The pseudo-capsule appears in T1WI and T2WI as a low-signal ring surrounding the tumor, separating the tumor from normal renal parenchyma or peripheral fat, and interruptions of the pseudo-capsule are associated with perirenal fat infiltration and higher staging [107]. On T2WI, because the renal parenchymal signal is significantly increased, renal cell carcinoma is often equal or higher than the renal parenchyma; therefore, the low-signal pseudo-capsule sign is easily compared. Tumors with low signal on T2WI chemical shift artifacts are potential shortcomings in detecting the pseudo-capsule sign on MRI [107].

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area in the center and the spoke shadow of the wheel are not enhanced. Explanation Pathologically, renal oncocytoma originates from proximal convoluted tubules of the renal cortex. The cytoplasm of the tumor cells is filled with eosinophilic granules. The gross specimens are brown-red or brown-yellow, with complete capsule, rare hemorrhage, and necrosis. The center of the tumor is a colloidal viscous substance, which extends radially to the surrounding area. Radial septation is the essence of the tumor (Fig. 5.42). Discussion Renal oncocytoma (RO) is a benign tumor originating from distal convoluted tubules and collecting ducts, accounting for 3% to 9% of primary renal tumors [108]. Because of its low incidence, it is difficult to diagnose and identify, and is often misdiagnosed as clear cell renal cell carcinoma (CCRCC). CT scan showed homogeneous or low-density lesions with clear boundaries. Enhanced scan showed homogeneous enhancement, but it was still lower than the density of kidney. The low-density area without enhancement in the center showed a wheel-spoke distri-

5.41 Spoke Wheel Sign Feature On noncontrast CT, renal oncocytoma presents as a low-density mass with clear boundary. The center of the tumor is a lower-density area and extends radially into surrounding tumor parenchyma, resembling the spoke of a wheel. On postcontrast CT, the tumor parenchyma is homogeneous in enhancement, but the lower-density

Fig. 5.42  Postcontrast CT shows enhancement of parenchymal components, irregular center without enhancement of low-density area, and wheel-like radiation to the surrounding area

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bution to the surrounding tumor parenchyma. The spoke wheel sign was first proposed by Quinn in 1984 and is considered to be the characteristic feature of RO [109]. Stellate scar and segmental enhancement inversion are also considered to be characteristic features of RO, and are often used in the differential diagnosis of RO and CCRCC. Kim et al. [110] report that segmental enhancement inversion is helpful in differentiating RO and CCRCC less than 4 cm. Segmental inversion enhancement refers to the enhancement of cortical and medullary phases in CT enhanced scan, which shows two different degrees of enhancement in tumors. In the delayed phase, the enhancement degree of the two parts is reversed; that is, the obvious part of corticomedullary phase was weakened in the delayed phase, and the weak part of corticomedullary phase was strengthened obviously in the delayed phase. However, it should be noted that the spoke wheel sign, stellate scar, or segmental enhancement inversion can be reported in renal cell carcinoma, and the central stellate scar is sometimes difficult to distinguish from the central necrosis of renal cell carcinoma [111]. In summary, RO is a relatively rare benign tumor of kidney, and its imaging features have certain characteristics. However, preoperative CT enhanced examination did not completely distinguish between RO and CCRCC. For those cases difficult to differentiate, it is recommended that puncture biopsy or frozen section be performed to avoid unnecessary radical nephrectomy.

5.42 Soft-Tissue Rim Sign Feature The soft-tissue rim sign is described on CT obtained in patients suspected to have ureteral calculi, an area of soft-tissue attenuation surrounding a suspended ureteral calculus that appears calcified. Explanation The soft-tissue rim sign is caused by edema of the ureteral wall surrounding a stone at its site of impaction (Fig. 5.43).

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Fig. 5.43  CT plain scan shows calcified calculus on right side of the ureter with soft tissue around it, showing the soft-tissue rim sign

Discussion The soft-tissue rim sign has evolved as a useful sign in the diagnosis of urolithiasis in patients with renal colic. The sign usually develops within 4 to 24  h after obstruction. The soft-tissue rim sign has been found to have a sensitivity of 77% and a specificity reaching 92% [112]. Visualization of the soft-tissue rim sign is dependent on stone size; smaller ureteral calculi are more likely to exhibit this finding than are larger calculi. It has been postulated that larger calculi tend to thin the ureteral wall to a greater degree than do smaller stones, which makes detection of the ureteral wall more difficult. Heneghan et al. [113] determined that the rim sign tends to be present with smaller stones (mean size, 4.3 mm) rather than with larger stones (mean size, 6.3 mm). Most ureteral calculi are of sufficiently high attenuation to be readily apparent on noncontrast CT. Occasionally, it may be difficult to differentiate a ureteral calculus from a phlebolith. This problem typically occurs in patients who are elderly, who have minimal retroperitoneal fat, or who have nonobstructing calculi. CT evaluation of stones has given rise to new signs. The soft-tissue rim sign is caused by edema of the ureteral wall surrounding a stone at its site of impaction. The importance of the sign lies in the fact that it may help to distinguish a stone in the ureter from a phlebolith in an adjacent vein, because the occurrence of a soft-tissue rim around a phlebolith is uncommon [91]. If the

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soft-tissue rim sign is present, it is useful in differentiating ureteral calculi from pelvic phleboliths in patients suspected of having ureteral colic. The soft-tissue rim sign is visible for 76% of ureteric calculi but only 2% of phleboliths. Kawashima et  al. reported that 50% of stones manifested a rim sign, 34% of stones were indeterminate for a rim sign, and 16% of the stones did not manifest a rim sign [114]. The presence or absence of this soft-tissue rim sign correlates with the size of a calculus but not with the degree of urinary obstruction. When CT reveals an indeterminate soft-tissue rim sign, careful inspection for other findings, such as ipsilateral ureteral dilatation, perinephric edema, dilatation of the intrarenal collecting system, and renal swelling, is necessary [114]. In evaluation for ureteral stone, one should focus at the most common locations; narrowing of the ureter occurs naturally at the uretero-vesicular junction (UVJ), the pelvic brim as the ureter crosses iliac vessels, and at the uretero-pelvic junction (UPJ). Frequently, a transition point is visible, with urinary decompression more distally. Secondary CT findings in obstructive uropathy include hydroureter, hydronephrosis, perinephric stranding, and possible enlargement of the unilateral kidney. Periureteral wall thickening and perinephric/periureteral fat stranding reflect acute inflammation. A positive soft-tissue rim sign is specific for the diagnosis of ureterolithiasis. However, a negative soft-tissue rim sign does not preclude such a diagnosis.

5.43 Comet-tail Sign Feature Calcification in the abdominal cavity or pelvic cavity vein or venous plexus appears as a linear, curved, or crescent-shaped soft-tissue attenuation shadow of different length or width that is connected to calcification on CT, referred to as the comet-tail sign. It usually indicates the calcification of the abdominal cavity or pelvic cavity are phleboliths.

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Fig. 5.44  In 56-year-old man, on CT plain scan, a soft-­ tissue attenuation shadow in front of the high-attenuation shadow shows the comet-tail sign

Explanation After the vein wall thrombus is calcified, the phleboliths are formed. Because the phleboliths locate in the vein or venous plexus, a vein blood vessel adjacent to phleboliths appears as a linear, curved, or crescent-shaped soft-tissue attenuation shadow of different length or width and connected to the phleboliths, thus forming the comet-­ tail sign (Fig. 5.44). Discussion Phleboliths most often occur in the pelvic veins near the end of the ureter and in the venous plexus around the prostate or around the vagina. Phleboliths can be seen at any age, and the number of phleboliths tends to increase in middle-­ aged and elderly people. The main factors of phlebolith formation in adult pelvic vein traffic include venous hypertension caused by cough, venous deformation, and residual venous valve orifice caused by the absence of a normal venous double valve. In the case of venous blood flow

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stagnation, residual valve fragments cause thrombosis, and eventually after the thrombus is calcified, the phleboliths are formed [115]. The “comet tail sign” is thin soft tissue extending from a focus of calcification in the abdomen or pelvis; it can also be used to differentiate these two entities, and typically indicates a phlebolith. CT is the main method for diagnosing phleboliths. Because thrombosis and ureteral calculi are similar in location and performance on CT scan images, sometimes it is difficult to identify these, especially if there is no sign of secondary obstruction in ureteral calculi and the fat content in the retroperitoneal and pelvic cavity is very low [116]. Although intravenous urography, retrograde ureterography, and enhanced CT scan can show a clear separation of phleboliths from contrast medium-filled ureters, thereby distinguishing between phleboliths and ureteral calculi, however, if the CT scan can show comet tail sign, this can help identify ureter calculi and phleboliths. In addition, the curved unexpanded ureter connected to the ureteral calculi may resemble the soft-tissue image formed by the venous structure of the phleboliths on the CT plain scan. Called false tail sign, this is most often located in the pelvic ureteral bladder junction, where the ureter often travels in the axial direction. The existence of the false tail sign indicates that the diagnostic effect of the comet tail has certain limitations. However, it is possible to avoid mistakes by carefully observing the relationship between the tail and the ureter, the attenuation of the center of the tail, and the direction of the tail associated with suspected calcification. If the upper ureter and the lower tail traffic or the center of the tail is liquid attenuation, it is suggested to be a false tail sign. In many instances, observers did not agree about whether the rim and comet-­ tail signs were present. The rim sign was observed in the absence of any secondary signs of urinary tract obstruction in only 1 (1.5%) of 65 patients [117]. The comet-tail sign, when accompanied by secondary signs of obstruction, should indicate that an ipsilateral ureteral stone is present and not the reverse [117].

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5.44 Faceless Kidney Feature The faceless kidney refers to the renal parenchyma lacking vascular or collecting system elements, which is a characteristic CT sign for duplication of the renal pelvis and ureter. Explanation In kidneys with either bifid renal pelvis or complete duplication of the collecting system, a CT section obtained at the mid-pole or junction of the fused upper and lower pole cortical moieties may reveal a “faceless” renal appearance lacking vascular or collecting system elements. Recognition of this finding allows a correct diagnosis of partial or complete duplication of the collecting system and prevents a false impression of an intrarenal mass lesion (Fig. 5.45). Discussion Duplication of renal pelvis and ureter is the most common congenital disease of the upper urinary tract, with many complications. The incidence rate reported in the literature is high, about 0.7%. In 1986 Hulnick et al. first described the faceless kidney. This sign was originally reported on CT, as an indication of a renal duplication anomaly (either a bifid renal pelvis, or incomplete or complete ureteral duplication) [118]. The sign is most often seen on axial CT images obtained between the upper- and lower-pole duplicated collecting system elements of the kidney. The image obtained between the separate sinus elements shows normally enhancing renal parenchyma, without the anticipated renal sinus components, such as fat, blood vessels, and collecting system elements [119]. Recognizing a “faceless” kidney should then prompt a search for some form of collecting system duplication anomaly. It should be noted that the meaning of a faceless kidney has been expanded to include conditions that alter the appearance of the renal sinus, either from edema (pyelonephritis or contusion) or from neoplasia. Fetal genital anomalies are rare as well and among the most difficult

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Fig. 5.45  A 37-year-old woman with complete duplication of the collecting system. A CT section obtained at the mid-pole or junction of the fused upper and lower pole

cortical moieties shows a “faceless” renal appearance lacking vascular or collecting system elements

to diagnose. A combination and pattern of findings allows for specific diagnosis of renal tract abnormalities [91].

also be shown when the ureter is not completely occluded.

5.45 Goblet Sign Feature The goblet sign is a cup-shaped contrast agent at the distal end of the ureteral lumen defect, which is best seen in retrograde ureterography. Venous renal angiography and now CTU or MRU can

Explanation The goblet sign suggests that the filling defect in the ureter is caused by a lump rather than a stone. The slow growth of the intraluminal mass originating in the urothelium causes ureteral dilatation at the distal end of the mass and adjacent sites. The ureteral peristalsis pushes the distal end of the ureter to promote the expansion of the distal ureter of the mass, thus forming a cup-like struc-

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Fig. 5.46 Ureteral transitional cell carcinoma in a 65-year-old patient. On retrograde ureterography, arrow shows a goblet sign and a filling defect formed by the mass

ture of the contrast agent, and the mechanical obstruction caused by the stone is the stenosis caused by the edema of the ureter at the distal end of the ureter (Fig. 5.46). Discussion The goblet sign was first proposed and systematically described by Daniels in 1999 [120]. That is, in retrograde ureterography, because of the ureteral mass caused by nonmechanical obstruction of the ureter, the proximal end of the stenosis is a filling defect, and the distal end expansion is a goblet change. In the setting of acute obstruction such as ureterolithiasis, the ureter is unable to accommodate the obstructing process. Focal downstream ureteral dilatation does not occur, and a goblet sign will be absent. In fact, the distal ureter is often narrowed with an acute obstructive process by reactive edema and ureteral spasm [120]. The proximal ureter can be dilated to a variable degree in both the acute and chronic set-

231

ting, depending on the extent of obstruction, and therefore is not a helpful discriminator of chronicity [121]. Uroepithelial carcinomas usually occurs in elderly patients, including transitional epithelial cell carcinoma, squamous cell carcinoma, and adenocarcinoma [122]. Urinary tract carcinoma located in the ureter is relatively rare compared to other tumors located in the urinary tract. Transitional epithelial cell carcinoma is the most common tumor of the ureter, and tends to be low grade, with slow infiltration and late metastasis. Therefore, transitional epithelial cell carcinoma is most strongly associated with the goblet sign, which is caused by the slow growth of the ureteral mass. Intravenous urography has been the first choice of evaluating ureteral tumors. Once a lesion is found in the ureter, a complete ureteral examination is required because transitional epithelial cell carcinoma has a multi-lesion tendency. The nonmechanical obstruction caused by the ureteral mass is manifested by the expansion of the distal ureter of the mass, which is caused by ureteral peristalsis propelling to the distal end of the ureter. Mechanical obstruction caused by ureteral calculi is characterized by stenosis from edema of the ureter at its distal end. Intravenous urography shows a goblet sign of the ureter, mostly caused by the slow infiltration of transitional epithelial carcinoma. CT and MRI are the main imaging modalities for ureteral diseases, especially CTU and MRU, which can detect lesions early and aid in early treatment.

5.46 Cobra Head Sign Feature The cobra head sign was manifested by intravenous urography. In the bladder filled with contrast medium, spherical dilatation of the distal ureter and transparent halo around it were seen, which resembled a cobra head. Explanation Ureteral cysts are filled with contrast medium and surrounded by high-density urine in the bladder during intravenous urography because the

232

Fig. 5.47  Magnetic resonance urography (MRU) demonstrated the hydronephrotic upper pole collecting system and cobra head appearance of a right ureterocele in a 2-year-old child with duplicated renal collecting systems

bilayer mucosal wall of the ureter cyst forms a thin light or halo around it. The translucent band represents the thickness of the ureteral wall and the prolapsed bladder mucosa. It is supported by contrast medium in the bladder cavity. The translucent band is thin and smooth. It delineates the ureter cyst and forms the cobra head-like appearance [123] (Fig. 5.47). Discussion Ureteral cyst (ureterocele) refers to the balloon dilatation of the distal ureter. Distal ureteral dilatation reflects the obstruction of urine flow at the entrance of the ureter and bladder. The cobra head sign is common in ureteral orifice cysts in the bladder. Because it originates in the triangle of the ureter and bladder, it is also called orthotopic ureteral cyst. Ureteral cysts are classified as intravesical and ectopic [124]. The intravesical type is considered simple; the ureteral orifice and ureterocyst are both in the bladder. The ectopic type is located under the bladder mucosa and

X. Li et al.

may extend into the human bladder neck or urethra. Intravesical ureteroceles can be unilateral or bilateral. They are usually found in adulthood, so they are also called adult-type ureteroceles; these are more common in females than in males. The ureteral cyst is a congenital disease, and ureteral orifice stenosis is one of its causes. But there is reason to believe that not all unilateral ureteral cysts are congenital, because inflammation and trauma can lead to fibrosis and develop into ureteral cysts. Most intravesical ureterocysts are occasionally found in asymptomatic adult patients. When ureterocysts are large, they can cause bladder neck and unilateral ureteral obstruction, which leads to an increase in the incidence of stones and infections. With the occurrence of obstruction and delayed filling of the ureter, delayed imaging examination is required. Ectopic ureteral cysts are almost always associated with duplicate ureteral deformities and originate from the upper pole of the ureter. They are usually found in childhood and are characterized by filling defects in the bladder rather than typical cobra head signs [125]. The cobra head sign is a sign of simple ureteral cyst, but the snake-head dilatation of the distal ureter can also be caused by incomplete obstruction of the distal ureter caused by tumors and stones. This manifestation is called pseudo-­ ureterocele. The light transmission wall around the dilated distal ureter is an important distinguishing point between ureterocyst and pseudo-­ ureterocyst, pseudo-ureterocele. Swollen translucent walls or halos are thick and unclear. In tumors, they can be irregular and have filling defects in ureteral cysts. Although cobra head sign is a typical sign of ureteral cyst, about 50% of ureteral cysts show this sign [125]. Cystoscopy confirmed that the size and shape of ureteral cyst vary with the filling degree of contrast medium; this also explains why some ureteral cysts are invisible during IVU. Ultrasonography can show ureteral cysts protruding into the bladder cavity. In some questionable cases, cystoscopy may help to determine whether a pseudo-ureteral cyst is caused by a tumor if the cobra head sign is atypical.

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233

5.47 Drooping Lily Sign Feature The drooping lily sign can be identified at excretory urography in patients with duplicated renal collecting systems. The sign consists of inferolateral displacement of a functioning lower-pole moiety, usually by a nonopacified, hydronephrotic upper pole collecting system. The appearance of the lower-pole collecting system is reminiscent of a lily flower that is wilting or drooping. Explanation In intravenous pyelography, because of the severe accumulation of water in the upper pole with duplicated renal collecting systems, the displacement of the renal pelvis and renal calyces is suppressed, and the angle between the renal pelvis and the ureter becomes smaller (Fig. 5.48). Discussion The “drooping lily” has been used as a metaphor for the urographic appearance of the opacified, functioning lower-pole moiety in a completely duplicated collecting system. The mass effect of

a

the dilated and often nonopacified upper collecting system elements displaces the lower-pole collecting system inferolaterally, producing the appearance of a fading flower [126]. An obstructing ectopic ureterocele or ectopic insertion of the upper-pole ureter is the usual cause of hydronephrosis of the upper-pole collecting system in a duplex kidney. The enlarged, obstructed upper-­ pole moiety exerts a mass effect on the remaining lower portion of the kidney, which results in inferolateral displacement of the lower-pole moiety and lateral displacement of the most superior calyces of the lower-pole collecting system. During excretory urography, a normally functioning, nonobstructed, completely duplicated collecting system will demonstrate two separate renal pelvises and two separate ureters. However, in the setting of an obstructed upper-pole moiety, which is usually dysplastic and poorly functioning, there is often absent or severely delayed contrast material excretion into the upper-pole collecting system. This lack of upper-pole excretion, combined with visualization of ­ decreased numbers of calyces oriented in an abnormal axis, are the fundamental components of the drooping lily sign [127]. Albeit rare, the

b

Fig. 5.48 (a, b) A 31-year-old male patient with duplicated renal collecting systems. CTU VR and MPR image shows inferolateral displacement of lower pole moiety by

a non-opacified, hydronephrotic upper-pole collecting system, which is the drooping lily sign

234

drooping lily sign can also be identified in a nonduplicated collecting system in the presence of an upper-pole renal mass, such as a renal abscess or Wilms tumor. The drooping lily configuration would not be expected if the entire kidney is displaced by an extrarenal mass lesion; as such, displacement of only the lower-pole moiety, rather than displacement of the entire kidney, allows the radiologist to suggest an intrarenal rather than an extrarenal process [127]. The drooping lily sign is often seen in conjunction with an ectopic ureterocele, and manifests as an eccentrically placed round or ovoid filling defect within an opacified bladder. This filling defect is usually best seen with a small amount of contrast material in the bladder, as increasing bladder distention may efface or evert the ureterocele [127]. Duplex kidneys are a common abnormality of renal tract development, carrying an incidence of approximately 1%. This diagnosis is defined as a renal unit composed of two pelvicalyceal systems and is the most frequent congenital anomaly of the urinary tract [128]. The “drooping lily” sign is identified on intravenous urography or voiding cystourethrography in patients with a duplicated renal collecting system and refers to inferolateral displacement of a functioning lower-­pole moiety by an obstructed upper-pole collecting system [129]. A good rule of thumb is to consider the presence of an obstructed, upper-­pole duplicated system any time a cystic structure is seen in the upper pole of the kidney. The obstructed upper moiety and its draining ureter may also be recognized on ultrasound or MRI [126].

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237 106. Roy C Sr, El Ghali S, Buy X, et al. Significance of the pseudocapsule on MRI of renal neoplasms and its potential application for local staging: a retrospective study. AJR Am J Roentgenol. 2005;184(1):113–20. 107. Lopes Vendrami C, Parada Villavicencio C, DeJulio TJ, et al. Differentiation of solid renal tumors with multiparametric MR imaging. Radiographics. 2017;37(7):2026–42. 108. Moch H, Cubilla AL, Humphrey PA, Reuter VE, Ulbright TM.  The 2016 WHO classification of tumours of the urinary system and male genital organs-part a: renal, penile, and testicular tumours. Eur Urol. 2016;70(1):93–105. 109. Quinn MJ, Hartman DS, Friedman AC, et  al. Renal oncocytoma: new observations. Radiology. 1984;153(1):49–53. 110. Kim JI, Cho JY, Moon KC, Lee HJ, Kim SH.  Segmental enhancement inversion at biphasic multidetector CT: characteristic finding of small renal oncocytoma. Radiology. 2009;252(2):441–8. 111. O'Malley ME, Tran P, Hanbidge A, Rogalla P. Small renal oncocytomas: is segmental enhancement inversion a characteristic finding at biphasic MDCT? AJR Am J Roentgenol. 2012;199(6):1312–5. 112. Al-Nakshabandi NA.  The soft-tissue rim sign. Radiology. 2003;229(1):239–40. 113. Heneghan JP, Dalrymple NC, Verga M, Rosenfield AT, Smith RC. Soft-tissue "rim" sign in the diagnosis of ureteral calculi with use of unenhanced helical CT. Radiology. 1997;202(3):709–11. 114. Kawashima A, Sandler CM, Boridy IC, Takahashi N, Benson GS, Goldman SM.  Unenhanced helical CT of ureterolithiasis: value of the tissue rim sign. AJR Am J Roentgenol. 1997;168(4):997–1000. 115. Arac M, Celik H, Oner AY, Gultekin S, Gumus T, Kosar S.  Distinguishing pelvic phleboliths from distal ureteral calculi: thin-slice CT findings. Eur Radiol. 2005;15(1):65–70. 116. Tanidir Y, Sahan A, Asutay MK, et al. Differentiation of ureteral stones and phleboliths using Hounsfield units on computerized tomography: a new method without observer bias. Urolithiasis. 2017;45(3):323–8. 117. Guest AR, Cohan RH, Korobkin M, et al. Assessment of the clinical utility of the rim and comet-tail signs in differentiating ureteral stones from phleboliths. AJR Am J Roentgenol. 2001;177(6):1285–91. 118. Hulnick DH, Bosniak MA. "faceless kidney": CT sign of renal duplicity. J Comput Assist Tomogr. 1986;10(5):771–2. 119. Athanasatos G, Dyer RB.  The "faceless" kidney. Abdom Imaging. 2015;40(6):2051–3. 120. Daniels RE 3rd. The goblet sign. Radiology. 1999;210(3):737–8. 121. Morgan WJ, Dyer RB.  The goblet sign. Abdom Imaging. 2015;40(4):931–3. 122. Rouprêt M, Babjuk M, Compérat E, et al. European Association of Urology guidelines on upper urinary

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Dyer RB, Chen MY, Zagoria RJ. Classic signs in uroradiology. Radiographics. 2004;24(Suppl 1):S247–80. Grazioli L, Ambrosini R, Frittoli B, Grazioli M, Morone M.  Primary benign liver lesions. Eur J Radiol. 2017;95:378–98. Hoodeshenas S, Yin M, Venkatesh SK.  Magnetic resonance elastography of liver: current update. Top Magn Reson Imaging. 2018;27(5):319–33. Jiang HY, Chen J, Xia CC, Cao LK, Duan T, Song B. Noninvasive imaging of hepatocellular carcinoma: from diagnosis to prognosis. World J Gastroenterol. 2018;24(22):2348–62. Liu PS, Abramson RG.  Hepatobiliary imaging. Magn Reson Imaging Clin N Am. 2014;22(3):xv–xvi. Mamone G, Cortis K, Sarah A, Caruso S, Miraglia R. Hepatic morphology abnormalities: beyond cirrhosis. Abdom Radiol (NY). 2018;43(7):1612–26. O' Donoghue PM, McSweeney SE, Jhaveri K.  Genitourinary imaging: current and emerging applications. J Postgrad Med. 2010;56(2):131–9. Renjen P, Bellah R, Hellinger JC, Darge K. Advances in uroradiologic imaging in children. Radiol Clin North Suggested Readings for this Chapter Am. 2012;50(2):207–18. Santillan C, Fowler K, Kono Y, Chernyak V.  LI-RADS Boesch C.  Quantitative MR imaging is increasingly major features: CT, MRI with extracellular agents, and important in liver disease. Radiology. 2018;286(2):​ MRI with hepatobiliary agents. Abdom Radiol (NY). 557–9. 2018;43(1):75–81. Cerny M, Chernyak V, Olivié D, et al. LI-RADS Version Van Beers BE, Garteiser P, Leporq B, Rautou PE, Valla 2018 Ancillary Features at MRI.  Radiographics. D.  Quantitative imaging in diffuse liver diseases. 2018;38(7):1973–2001. Semin Liver Dis. 2017;37(3):243–58. Donato H, França M, Candelária I, Caseiro-Alves F. Liver Yu HS, Gupta A, Soto JA, LeBedis C.  Emergency MRI: From basic protocol to advanced techniques. abdominal MRI: current uses and trends. Br J Radiol. Eur J Radiol. 2017;93:30–9. 2016;89(1061):20150804.

tract Urothelial carcinoma: 2017 update. Eur Urol. 2018;73(1):111–22. 123. Chavhan GB.  The cobra head sign. Radiology. 2002;225(3):781–2. 124. Tirman PA, Dyer RB. The cobra head sign. Abdom Imaging. 2015;40(3):609–10. 125. Xiang H, Han J, Ridley WE, Ridley LJ. Cobra head sign: Ureterocele. J Med Imaging Radiat Oncol. 2018;62(Suppl 1):67. 126. McPherson AM, Dyer RB.  The drooping lily sign. Abdom Imaging. 2015;40(6):2056–7. 127. Callahan MJ.  The drooping lily sign. Radiology. 2001;219(1):226–8. 128. Doery AJ, Ang E, Ditchfield MR.  Duplex kidney: not just a drooping lily. J Med Imaging Radiat Oncol. 2015;59(2):149–53. 129. Sahakyan K, Spevak MR, Ziessman HA, Gorin MA, Rowe SP. The Scintigraphic drooping lily sign. Clin Nucl Med. 2018;43(5):352–3.

6

Gastrointestinal Tract Jiani Chen, Hengtian Xu, and Gui Quan Shen

Contents 6.1 Double Bubble Sign

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6.2 Small-Bowel Feces Sign

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6.3 Bird’s Beak Sign

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6.4 String of Pearls Sign

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6.5 Coffee Bean Sign

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6.6 Spoke Wheel Sign

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6.7 Whirl Sign

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6.8 Corkscrew Sign

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6.9 Target Sign

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6.10 Target Sign

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6.11 Double Halo Sign

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6.12 Comb Sign

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6.13 Gastrointestinal String Sign

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6.14 Bowel Wall Fat Halo Sign

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6.15 Disproportionate Fat Stranding Sign

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6.16 Misty Mesentery Sign

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6.17 Fat Ring Sign

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6.18 Hyperattenuating Ring Sign

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6.19 Arrowhead Sign

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6.20 Accordion Sign

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6.21 Apple Core Sign; Apple Core Lesion

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J. Chen (*) · H. Xu · G. Q. Shen Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6_6

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6.1

6.22 Duodenal Wind Sock Sign

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6.23 Rigler Sign

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6.24 Football Sign

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6.25 Dependent Viscera Sign

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6.26 Northern Exposure Sign

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References

 270

Double Bubble Sign

Therefore, the possibility of duodenal atresia should be considered in infants with biliary vomiting, and an imaging examination should be performed immediately. In addition to abdominal X-ray, prenatal diagnosis can now be made by ultrasound or fetal magnetic resonance imaging (MRI), both of which can observe fluid-filled dilated stomach and duodenum. Prenatal double bubble sign is a reliable predictor of duodenal atresia. In addition to trisomy 21, heterotaxy may be encountered [3]. Neonatal malrotation very seldom mimics duodenal atresia. The classic double bubble sign is

Feature On abdominal X-ray radiographs, there are two air-filled cystic structures in the upper abdomen, slightly below the left upper abdomen and the right midline. Gas–liquid level can be seen in the abdomen. There is no or only a small amount of gas in the distal intestinal canal. Explanation The double bubble sign is a specific manifestation of duodenal obstruction in neonates or infants. In duodenal obstruction, the proximal duodenum and stomach progressively accumulate gas, accumulate fluid, and expand, forming the so-called double bubble sign (Fig. 6.1). Discussion The double bubble sign was systematically described by Traubici in 2001 [1]. It is considered a classic imaging manifestation of duodenal atresia. Typical imaging findings are that larger gastric bubbles occupy the left upper abdomen on abdominal X-ray plain film, while smaller duodenal bubbles are locating in the right upper abdomen or the right middle abdomen. Double bubble dilation reflects postpartum gas swallowing, and atresia of the duodenal segment does not allow the swallowing gas to pass through the distal end. If newborns develop abdominal distension, vomiting, and other symptoms within the first 24  h after birth, the possibility of duodenal atresia should be considered [2]. Vomiting in duodenal atresia is often biliary, because the atresia is usually located at the distal end of the duodenum.

Fig. 6.1  A 1-year-old female infant. On neonatal abdominal radiograph, upper abdomen has two inflatable structures. Larger transparent structure of left upper abdomen (black arrow) is the dilated stomach. Smaller transparent structure in right mid-abdomen represents the gas that expands proximally to the duodenum. Note lack of distal intestinal gas, a typical manifestation of duodenal atresia

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the only true double bubble sign [1]. Over the years, the usage of this term has become altered so that it has become a little unclear. However, anything other than this sign should be treated with great suspicion for the presence of malrotation and midgut volvulus. Furthermore, if the patient has bilious vomiting, the diagnosis is basically secured [4]. Although double bubble sign is a classic sign of duodenal atresia, differential diagnosis includes duodenal stenosis, duodenal reticulum, annular pancreas, and malrotation with midgut volvulus. The degree of obstruction and the cause of obstruction can be generally judged according to the double vesicle sign and its accompanying signs. If the bilateral vesicles are large and the distal part is not inflated, this indicates complete duodenal obstruction (duodenal atresia); if the bilateral vesicles are small and the distal part has more or less inflatability, it is mostly incomplete obstruction (intestinal malrotation, duodenal stenosis, circular pancreas, etc.). Sometimes incomplete obstruction is absorbed by the intestinal wall because the gas does not enter the distal part of the obstruction or a small amount of air is absorbed by the distal part of the obstruction. It can also be manifested as a simple double vesicle sign. On the other hand, the possibility of complete obstruction cannot be ruled out when the distal intestinal tract of double vesicle sign is inflated, because when duodenal atresia combined with abnormal bile duct development, the proximal gas of obstruction can enter the distal part of the obstruction through an abnormal bile duct. Therefore, in judging the degree of duodenal obstruction and the cause of the obstruction, we should not depend on whether the distal part of the obstruction is inflated, but should observe and analyze comprehensively, with barium or ultrasonogram if necessary. It is important to keep in mind that there is only one true double bubble sign, which need not require immediate attention or intervention. Anything other than this sign requires immediate management if the diagnosis would be malrotation with possible midgut volvulus [4].

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6.2

Small-Bowel Feces Sign

Feature On computed tomography (CT) scans of the abdomen, colon-like feculent matter mingled with gas bubbles can be seen in the lumen of dilated loops of the small intestine. Explanation The contents of the dilated small intestine seen in the small-bowel feces sign are similar to colon-­ like feculent matter on CT scans. It is the result of delayed intestinal transit and is believed to be caused by incompletely digested food, bacterial overgrowth, or increased water absorption of the distal small-bowel contents because of obstruction (Fig. 6.2). Discussion The small-bowel feces sign was first described in 1995 by Mayo-Smith et al. [5]. The presence of the small-bowel feces sign indicates small-bowel obstruction or other acute small-bowel lesions (such as metabolic or infectious diseases). Bowel obstruction accounts for approximately 20% of acute abdominal surgical interventions in 60–80% of cases of intestinal obstruction. The clinical performance of small-bowel obstruction includes abdominal tenderness, distention, and increased high-pitched bowel sounds. However, in complete obstruction with predominantly fluid-filled bowel loops, there may be less distention and diminished sounds. Similar clinical presentations can be found in paralytic ileus, intraabdominal abscess, malignant tumor, pancreatitis, peptic ulcer disease, or gastroenteritis. Thus, an early and accurate radiologic diagnosis of small-bowel obstruction is very important clinically. The small-bowel feces sign is most often present in the distal small intestine at length of 4–200 cm. The reported prevalence of the sign is low (7–8%), but the diagnostic reliability is high. The small-bowel feces sign has shown a high specificity for subacute or low-grade small bowel obstruction [6], because in the process of progressive small intestinal obstruction, the intestinal contents pass slowly, resulting in increased water absorption and subsequent for-

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a

b

Fig. 6.2 A 59-year-old male patient with intestinal obstruction, on coronal and sagittal abdominal CT plain scan. Adhesions of small intestine on the abdominal wall

after operation. Narrowing of small bowel and feculent matter mingled with gas bubbles in the proximal dilated small bowel is called the small-bowel feces sign

mation of colon-like feculent matter. It is important to recognize the sign as early as possible in the clinic so that early surgical treatment can be carried out; as the sign often appears in the proximal part of the obstruction it may be helpful in recognition of the exact site and cause. The primary reason for this sign is classic mechanical small-bowel obstruction caused by adhesions, hernias, and tumors. Other causes are inflammatory stenoses and infectious, metabolic, and ischemic disorders [7]. Other conditions may include heterogeneous patchy substances with gas accumulation in the small intestinal cavity, such as cystic fibrosis, infectious or metabolic bowel disease, rapid jejunostomy tube feedings, or, rarely, bezoars. However, according to the definition of this sign, the diameter of intestinal dilatation more than 2.5 cm is also a necessary diagnostic criterion. In a few cases, fecal residues can be seen in normal nondilated distal ileum, presumably from fecal reflux in the cecum. The small-­ bowel feces sign is a useful auxiliary sign for the diagnosis of small-bowel obstruction based on other traditional obstructive signs, particularly in patients with low-grade or intermittent obstruction. Most patients with this sign need to be hospitalized and often require surgical treatment. Radiologists should master this sign to make an

accurate diagnosis of small-bowel obstruction as soon as possible.

6.3

Bird’s Beak Sign

Feature This is a CT sign of closed loop intestinal obstruction. The dilated intestinal loop gradually becomes sharp at the obstructive site, and the intestinal loop contracts, resembling slightly a bird’s mouth. Explanation When intestinal obstruction occurs, a transitional zone is formed between the atrophic bowel and the dilated bowel, and the dilated bowel extends to the protruding part of the atrophic bowel, which resembles the beak of a bird (Fig. 6.3). Discussion The causes of intestinal obstruction are complex and varied, including intestinal adhesion, primary or secondary tumors, Crohn’s disease, vascular lesions, parasites, gallstones, feces, abdominal hernia, chronic colonic diverticulitis, intussusception, and volvulus [8]. When intestinal obstruction occurs, the

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a

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b

Fig. 6.3  In a 19-year-old girl, multi-planner reformation (MPR) shows small intestinal obstruction and bird’s beak sign

intestinal cavity widens with the accumulation of fluid and gas. The lower the obstruction site and the longer the obstruction time, the more obvious the dilatation of the intestinal cavity. The intestinal cavity below the obstruction is atrophic, empty, or with only a small amount of feces. CT features are intestinal dilatation, significantly enlarged diameter, intestinal dilatation in general visible gas–liquid level, also filled with liquid, and intestinal wall thinning. Obstruction distal bowel collapse, with obstruction distal and proximal bowel diameter significantly different, is a very valuable sign to judge the location of intestinal obstruction [9]. Closed loop intestinal obstruction is mostly caused by intestinal volvulus resulting from the rotation of the loop along the long axis of mesentery. It can also be formed by the contraction and convergence of the two ends of a bowel by the adhesion of fibrous bands [10]. When the scan plane passes through the closed loop, there are two dilated intestinal rings, and the distance between the two adjacent intestinal rings is gradually closer as the plane approaches the root of the closed loop. When the scan plane passes through the root of the closed loop, the intestinal tube is deformed and the soft tissue density is triangular when the intestinal volvulus occurs. When the closed loop is parallel to the scanning plane, it appears as U-shaped closed loops. At the scanning level, the two adjacent collapsing intestinal rings are seen

through the input and output terminals of the closed loop. When the long axis of the input or output segment of the volvulus closure loop is parallel to the CT scan, the input segment becomes thinner and the output segment becomes thicker because of volvulus. On the CT image, the beak sign appears [11].

6.4

String of Pearls Sign

Feature The string of pearls sign can be seen on abdominal radiographs obtained with the patient in the upright position or on decubitus abdominal radiographs. The sign consists of a row or line of several small air bubbles obliquely or horizontally oriented in the abdomen. It is also commonly referred to as the “string of beads sign.” Other name: the string of beads sign. Explanation The obliquely oriented row of air bubbles represents small amounts of air trapped between the valvulae conniventes along the superior wall of predominantly fluid-filled, dilated small bowel loops. The meniscal effect of the surrounding fluid gives the trapped air an ovoid or rounded appearance. The appearance of the string of pearls sign depends on the combination of air, fluid-filled bowel loops, and peristaltic hyperactivity (Fig. 6.4).

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Fig. 6.4  In a 72-year-old woman, the string of pearls sign can be seen on abdominal radiographs obtained with the patient in the upright position. The sign consists of a row or line of several small air bubbles obliquely or horizontally oriented in the abdomen

Discussion The string of pearls sign metaphorically describes a radiographic finding highly suggestive of mechanical small bowel obstruction (SBO). SBO is a common clinical syndrome for which effective treatment depends on a rapid and accurate diagnosis. The importance of recognizing the string of pearls sign is often related to the clinical findings of SBO.  As the small bowel becomes distended, intraluminal fluid traps gas along the valvulae conniventes. Upright radiographs depict a row of elliptical lucency produced by the meniscal surface of fluid on one side and the bowel wall on the other, evocative of a string of pearls [11]. SBO typically produces gaseous distention of the bowel loops proximal to the obstructing lesion. The dilatation of the small bowel stimulates the mucosa to secrete fluid. Thus, the distended bowel contains varying amounts of air and fluid, which accounts for the air–fluid interfaces seen on horizontal beam radiographs. As the small bowel dilates, the valvulae conniventes widen, causing the small bubbles of air to become trapped [12]. Although the string of pearls sign is rarely seen in adynamic ileus, acute gastroenteri-

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tis, and saline catharsis, when present in the right clinical setting, it is considered to be virtually diagnostic of SBO.  The classic signs of SBO include abdominal tenderness, distention, and increased high-pitched bowel sounds. However, in cases of complete obstruction with predominantly fluid-filled loops of bowel, there may be much less distention, and the bowel sounds may be normal or diminished because there is little or no air to cause the typical high-pitched gurgling sounds. Knowledge of the radiographic findings of fluid-filled obstructions, including the string of pearls sign, can help diagnosis of SBO when the clinical picture is somewhat confusing [12]. SBO is often difficult to diagnose on the single conventional radiograph. Horizontal beam radiograph and radiographs obtained in the supine position are the second choice when SBO is suspected. Often, sequential views obtained within a 12–24  h timeframe help establish an evolving obstructive gas pattern. Successive abdominal radiographs obtained in 5-min intervals are a reliable tool for differentiating mechanical obstruction from a dynamic ileus [12]. When an SBO is accompanied by signs of strangulation, emergent surgical treatment is advised. If surgery cannot be performed immediately or if a partial obstruction is suspected, then a more detailed radiologic workup is needed. The imaging sign can also be observed on computed tomography. In the absence of indications for urgent operative intervention, a CT scan with and without IV contrast should be obtained in most patients to identify the location, grade, and etiology of the obstruction. The sensitivity and specificity of MRI to diagnose and characterize SBO resemble CT scanning; however, it is more expensive and less available. MRI is most appropriate for children, younger patients with multiple prior CT examinations, and pregnant women. Despite advances in imaging and a better understanding of small-bowel pathophysiology, SBO is often diagnosed late or is misdiagnosed, resulting in significant morbidity and mortality. If a low-grade partial obstruction is suspected, enteroclysis and CT enteroclysis are preferred. If a complete or high-grade obstruction is sus-

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pected, ultrasonography or CT are preferred to exclude strangulation. The imaging techniques used subsequently vary according to the initial findings. An algorithmic approach to imaging is proposed for the management of SBO to determine its severity, site, and cause and to assess the presence of strangulation. Radiologists have a pivotal role in clinical decision making in cases of SBO. A comprehensive approach that includes clinical findings, patient history, and triage examinations such as plain abdominal radiography will help the clinician develop an individualized treatment plan. Confounding conditions include age greater than 65 years, post Roux-en-Y gastric bypass, inflammatory bowel disease, malignancy, virgin abdomen, pregnancy, hernia, and early postoperative state [13].

6.5

Coffee Bean Sign

Feature The coffee bean sign is seen on abdominal radiographs obtained in a supine patient as an area of hyperlucency that resembles the shape of a coffee bean. Explanation The coffee bean sign is a classic conventional radiographic finding of sigmoid volvulus. As the closed loop of the sigmoid colon distends with gas, apposition of the medial walls of the dilated bowel form the cleft of the coffee bean, and the lateral walls of the dilated bowel form the outer walls of the bean (Fig. 6.5). Discussion The coffee bean sign has been described as an indication of a closed-loop obstruction of the small bowel but commonly applies to the appearance of a closed-loop obstruction of the sigmoid colon [14]. The coffee bean sign is a metaphor describing the classic radiographic appearance of a closed loop obstruction, most notably associated with sigmoid volvulus. Twisting of the sigmoid colon about its mesenteric axis creates an inverted, U-shaped, and gas-filled segment of dilated bowel originating in the pelvis and

245

Fig. 6.5  Abdominal radiographs of a patient with sigmoid volvulus show the “coffee bean sign”

extending cephalad. A central linear opacity bisects the dilated loop, mimicking the cleft of a coffee bean. Failure to recognize this finding may lead to delayed diagnosis with increased risk of ischemia, infarction, and perforation [15]. Routinely, the diagnosis of acute sigmoid volvulus is established by clinical and radiologic findings. From a clinical point of view, sudden abdominal pain, abdominal tenderness, asymmetrical abdominal distension, constipation, abdominal tympany, abnormal bowel sounds, and a palpable abdominal mass are among the most prevalent initial symptoms and signs. CT scans are often unnecessary because since a plain X-ray is diagnostic in 57–90% of patients. The classical sign of an acute sigmoid volvulus in plain X-rays is the coffee bean sign; in an abdominal CT scan, the characteristic “whirl sign” as well as dilated colon with air–fluid levels can be detected. Those radiologic findings are the result of the torsion of the often long and redundant sigmoid colon around its elongated mesenteric axis, which ultimately leads to intestinal obstruction [16]. In as many as 80% of the occurrences, sigmoid volvulus can be diagnosed only by supine abdominal radiograph. The absence of rectal gas may help with diagnosis. If the supine abdominal radiograph cannot be clearly diagnosed, a single-­ contrast barium enema examination should be

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performed. In the distorted position, the barium column will abruptly terminate at a point that typically has the appearance of a bird’s beak. Barium that is forced beyond the twist may result in perforation or convert a partial obstruction into a complete blockage. A barium enema examination should be avoided altogether, and if there is evidence of bowel ischemia or perforation, surgery should be performed immediately [17].

6.6

Spoke Wheel Sign

Feature During an abdominal CT plain scan, the mesenteric vessels are thickened, prolonged, and gathered. The fluid-filled enlarged intestinal loop is radially aligned along the mesenteric vessels. Explanation When small intestinal volvulus occurs, mesenteric root volvulus occurs correspondingly, the mesentery shortens and tightens, and a funnel shape is displayed along the axis of rotation, causing the intestinal tube connected with the mesentery to show a concentric circle around the mesenteric vessels. The distorted mesenteric vessels become thicker, occupying the center, and the intestines are dilated and filled with fluid. The vessels distributed on the mesentery are arranged in a radial direction from the intestinal wall to the reversed mesenteric root, forming plica of soft-­ tissue attenuation. The shape resembles connection of the spoked wheel to the central axle, and thus is called the spoke wheel sign (Fig. 6.6). Discussion Small intestinal volvulus is a rare but life-­ threatening surgical emergency. It has been reported that the incidence of intestinal ischemia is as high as 46%, and the total fatality rate is 9%. Intestinal volvulus combined with various factors makes the damage of the intestinal tube more serious than the simple mechanical intestinal obstruction. No matter in which segment of the intestine obstruction occurs, intestinal fluid accumulates rapidly, and the proliferation of bacteria will cause a large amount of gas to be produced;

intestinal pressure will increase, intestinal tube dilatation will be further aggravated, and the intestinal wall blood supply will be obstructed, eventually leading to hemorrhagic infarction, necrosis, and perforation [17]. The most common cause of small intestinal volvulus is intestinal adhesion and internal and external hernia. The squeezing effect caused by the adhesion of two adjacent intestinal tubes causes a long-moving obstructed intestinal tube to have only a relatively narrow base. This anatomical structure makes the closed loop rotate along its long axis and then forms an intestinal volvulus [18]. There are some signs on CT scans to diagnose simple or closed loop intestinal obstruction. (1) The two adjacent collapsed loops represent the intestinal tube adhesions with limited dilatation, and between them is a closed loop of obstruction. (2) The dilated fluid-filled small intestine has a U-shaped structure, resulting from the obstructed liquid-filled dilated intestinal loops that are arranged radially around the tightly twisted mesentery; the CT findings are seen after longitudinal section scanning. (3) The least common CT findings are triangle sign (or beak sign) and (4)

Fig. 6.6  On abdominal plain CT, the attenuation of mesentery increases and gathers around the mesenteric vessels, which show radial arrangement. The shape resembles the wheel of spokes connected to the central axle, called spoke wheel sign

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whirl sign. The triangle sign appears in the longitudinal section at the distorted collapse of the intestine, and the intestinal loop gradually thins into a sharp triangular shape. The whirl sign is formed by a twisted mesentery [19]. (5) Spoke wheel sign: in addition to diagnosing closed loop intestinal obstruction, the spoke wheel sign can also predict strangulated small intestinal obstruction, because it can evaluate the intestinal loop, mesentery, and mesenteric vessels, and the aforementioned structures can show characteristic changes during intestinal ischemia and necrosis. These signs have been suggested to help distinguish necrotic and nonnecrotic intestinal segments in closed loop intestinal obstruction. The CT findings of small intestinal obstruction vary. Despite the importance of diagnosing complex obstacles, there are still some difficulties. Experienced physicians can detect volvulus and ischemia caused by internal hernia in closed loop intestinal obstruction, but the detection rate is less than 50%. The appearance of spoke wheel sign strongly suggests small intestinal volvulus: it provides diagnostic information on both the mesentery and the intestine at the same time, thus helping to detect closed loop intestinal obstruction. Other signs of ischemia and necrosis should also be observed in the presence of this sign to further confirm the presence or absence of intestinal stenosis.

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Fig. 6.7  In 42-year-old woman with abdominal pain, visible twisted mesenteric vessels and collapsed intestinal canals form a whirl sign (arrow)

ribbon-shaped shadows of soft tissue density in the whirlpool sign. The background is a low-­ density shadow formed by mesenteric fat, thus forming a whirlpool image resembling a meteorological map. The appearance of the sample is called the whirl sign. When the CT scan axis is perpendicular to the torsional axis of the small intestine, the spiral sign is more clearly displayed (Fig. 6.7).

Discussion Intestinal volvulus has symptoms of intestinal obstruction and intestinal ischemia. It is an emergency surgical disease. Early detection and timely operation are of great value to the prognosis of patients. Intestinal volvulus can cause intestinal blood flow disorders, leading to intesti6.7 Whirl Sign nal wall ischemia, edema, and necrosis. The diameter of the mesenteric artery is small, and its Feature wall is relatively thick. The mesenteric vein is On CT, the whirl sign is a circular or quasi-­ large in diameter with a thin wall. It is easily circular soft tissue mass whose internal structure compressed, narrowed, and occluded under is formed by the spacing between the soft band external force. The pathological changes of small density shadow of the turbine ribbon and the fat intestinal volvulus are submucosal edema and density shadow. intestinal wall congestion. The location of the whirl sign may provide the cause of the whirl. If Explanation the upper abdomen shows swirling sign and the The whirl sign is a sign of volvulus. As the input intestinal tube is fixed in a fixed position, we and output loops of the twisted small intestine should consider whether it is complicated with rotate around the fixed obstruction point, the intraabdominal hernia, such as small omentum mesentery is twisted around the rotation axis and hernia or para-duodenal hernia. The whirl sign wraps tightly around the loops. These twisted that appears in mid-abdomen mostly suggests loops and branches of mesenteric vessels form small intestine volvulus, whereas a whirl sign

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appearing in lower abdomen may be related to sigmoid colon volvulus. The manifestations of whirl sign can be as follows: (1) intestinal swirl, often accompanied by edema of mesentery; (2) mesenteric swirl, often accompanied by expansion of mesenteric vessels between edema of mesentery, accompanied by formation of swirl; (3) swirl mainly composed of mesenteric vessels, mostly veins. The whirl sign has specific value for the diagnosis of small-bowel volvulus. The whirl sign is found on CT of volvulus and described as a rotational arrangement centered on the volvulus mesenteric artery [20]. In acute abdomen, bowel volvulus and intestinal adhesion occur simultaneously in the mesentery and are vascularly related in many cases. Whenever there is a whirl change in CT images, it can be called a whirl sign. Although the whirl sign as a specific sign of CT diagnosis of small intestinal volvulus, Yang et al. believe that the whirl sign is more sensitive to the diagnosis of small intestinal volvulus [21]. ­Blake  et  al. pointed out that this manifestation can also occur in patients with malrotation of the midgut, intestinal adhesion, intestinal tumors, and abdominal and pelvic surgery [22]. Gollub et al. also reported that whirl signs on CT did not always indicate small-bowel volvulus [23]. Whirl sign has important diagnostic value for CT diagnosis of small intestinal volvulus, but some non-­ small intestinal volvulus factors should be excluded. Close reference to other signs of intestinal obstruction, such as intestinal wall thickening, edema, enhancement weakening, ascites, and pneumatocele dilatation, especially to actively find the causes of obstruction, are helpful to the correct diagnosis of intestinal volvulus before operation.

6.8

Corkscrew Sign

Feature Upper gastrointestinal radiography of neonates with midgut volvulus revealed spiral movement of the ascending duodenum and adjacent jejunum on both lateral and positive radiographs. It resembles a corkscrew.

Explanation The mesentery is a large retrograde peritoneum attached to the posterior abdominal wall. The jejunum and ileum are connected by the mesentery to the posterior abdominal wall. Midgut volvulus mainly occurs in the neonatal period. Because mesentery is relatively free in neonatal period, especially in middle jejunum and upper ileum. During the neonatal period, the abdominal cavity volume is small. If intestinal malrotation occurs, sometimes it cannot be self-repositioned, thus aggravating the formation of intestinal volvulus. The horizontal part of the duodenum, the ascending part and the adjacent jejunum do not cross the midline, but go downward, resulting in the spiral of the intestinal loop, forming a corkscrew-­like appearance. Discussion In 2007, Ortizneira named and described the corkscrew sign; that is, when performing upper gastrointestinal radiography, the ascending part of the duodenum and its adjacent jejunum were spiral shaped, resembling the corkscrew [24]. The corkscrew sign often indicates that neonates have malrotation of intestine combined with midgut volvulus, which requires close clinical observation and active treatment. When the intestine rotates poorly, the mesenteric root becomes thinner, and the duodenal jejunal flexure (Treitz ligament) almost always is ectopic. The most typical part is that the duodenal jejunal flexure descends and is ectopic to the right front of the midline. The most serious complication of intestinal ­malrotation is volvulus. Because the mesentery is only narrowly attached to the root of superior mesenteric artery, midgut volvulus occurs when the mal-fixed duodenum and upper jejunum twist clockwise around the root of mesentery. Intestinal volvulus often occurs in newborns, infants, and children. The typical clinical manifestation of intestinal malrotation is biliary vomiting. Therefore, infants and young children with biliary vomiting should be considered for the possibility of intestinal malrotation, and should undergo immediate imaging examination. When neonatal intestinal malrotation is combined with midgut volvulus, the early manifestations of neo-

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natal intestinal malrotation are mainly biliary vomiting, oliguria, or incontinence, and even hematochezia in the late stage. The preferred method of examination for intestinal malrotation is usually abdominal X-ray plain film. Positive and lateral X-ray examination is the key to display the connection between duodenum and jejunum. Projection in the front and back direction is the clearest. Patients can use the supine left anterior oblique position to fill the stomach cavity with contrast agent. Then, patients rotate to prone right anterior oblique position to make the contrast agent flow into the duodenum. Lateral X-ray radiograph can accurately observe the direction of duodenum. When intestinal malrotation occurs, anterior and posterior X-ray radiograph can show that duodenal jejunal curvature descends to the right or midline of the spine while the lateral X-ray radiograph is anterior to the spine. If combined with midgut volvulus, the corkscrew sign may be shown; if there are peritoneal cords, the duodenum will expand. With the degree of proximal duodenal obstruction further aggravated, the corkscrew sign will disappear. The emergence of corkscrew sign requires long-­term observation, because in some cases of severe obstruction, the passage of barium is not smooth, and often requires continuous observation for several hours; if necessary, the patient takes the right lateral decubitus position until the upper jejunum shows. Doppler ultrasound has been more and more used in the diagnosis of intestinal malrotation. The “whirlpool sign” of color Doppler ultrasound is considered as the characteristic manifestation of intestinal malrotation [25]. In a word, the corkscrew sign often indicates midgut volvulus [26].

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names: concentric circle sign, layering target mass. Explanation Target sign is the most common characteristic CT sign of intussusception. It is the feature of intussusception when the long axis is perpendicular to the CT scan plane. It reflects the anatomical relationship among the intestinal wall, intestinal cavity, and mesentery of intussusception. Typically arranged from the outside to the inside are the sheath of the outer intestinal wall, sheath of the intestinal cavity contrast agent, sheath of the inner intestine, eccentric intussusception of the mesentery, intussusception of the intestinal wall, and intussusception of the intestinal cavity contrast agent (Fig. 6.8). Discussion Intussusception is the most common cause of intestinal obstruction in infancy and early childhood. Intussusception occurs when a more proximal portion of bowel invaginates into more distal bowel. These patients often present with a wide range of nonspecific symptoms. The classic presentations are intermittent abdominal pain, vomiting, and red currant jelly-like stool. The mechanism of intussusception is generally believed to be caused by intestinal peristalsis rhythm disorder, local circular muscle spasm, severe intestinal peristalsis with spastic bowel and its adjacent mesentery in the adjacent intestinal cavity and formed mostly in the direction of

Target Sign

Feature On a CT scan of the abdomen, this sign appears as a round or rounded mass, with the structure arranged in the target ring layers, from the inside to the outside density showing high–low–high layered changes, like the target ring name. Other

Fig. 6.8  An 11-year-old girl with right colon intussusception, showing visible target sign (arrow)

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intestinal peristalsis anterograde intussusception [27]. A high rate of bowel resection is a ­consequence of delayed presentation, and efforts should be made for an early diagnosis of intussusception and prompt referral to improve outcome [28]. The most common CT manifestation of intussusception is the target sign, which reflects the anatomical relationship among the intestinal wall, intestinal cavity, and mesentery of the various layers of the body of intussusception, and is the most common characteristic CT sign of intussusception [29]. The target blocks are circular or round, and can be in concentric circles. Because of intestinal fissure, irregular alignment and direction, when CT scan is parallel to the long axis of intussusception, the transverse section can show comet tail sign or renal sign, that is, mesenteric fat and vascular involvement. Comet tail sign is a sign of pull-up and coalescence of proximal mesenteric intussusception vessels, and its composition includes intussusception of the proximal mesenteric tube. Nephroid sign or renal mass is the oblique CT image of the free margin of the sheath and the proximal intestine and mesentery of the intussusception. Comet tail sign accompanied with renal sign is another common characteristic CT sign besides target sign in intussusception. Target sign can be seen in all types of intussusception. Comet tail sign and kidney sign are most common in small-bowel intussusception. CT features of intussusception have certain characteristics, the diagnosis is relatively easy, but the etiology is sometimes difficult to determine, and examination should focus on the head of intussusception, to find hidden primary lesions.

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Explanation Target sign is a variety of intestinal lesions that can cause intestinal edema, inflammation, or both. The inner layer represents the mucosa layer, the outer layer represents the muscular coat and serous layer, showing high attenuation after injecting contrast medium. The low attenuation in the middle layer is thought to be mainly caused by submucosa edema. The presence of target sign suggests congestion of the mucosa or muscular coat and serous layer with submucosa edema and inflammation (Fig. 6.9). Discussion On CT, a benign intestinal tube lesion usually manifest as a circular or homogeneous thickening of the intestinal wall, which usually does not exceed 1 cm from the mucosa layer to the serous layer. According to the etiology and severity of the disease, this thickening may be slightly more than 1  cm but is generally less than 2  cm. The target is caused by the circumferential thickening of the intestinal wall. The earliest report was in the CT finding of Crohn’s disease, but this sign can be found in a variety of benign intestinal tube lesions. These lesions include ischemic enteropathy (ischemic enterocolitis), small intestinal wall hemorrhage, idiopathic inflammatory intestinal disease (Crohn’s disease and colitis gravis), vascular diseases (Henoch–Schonlein purpura), infectious disease (infectious enteritis and pseudomembranous colitis), radiation injury, and intestinal edema from portal hypertension. The target sign is not a specific diagnosis, but because there is usually no target sign in a malignant

6.10 Target Sign Feature Target sign can be seen on postcontrast CT of the abdomen. The thickened intestinal wall shows three-layer structures; the inner and outer layers are high attenuation enhancement layers with a low attenuation middle layer between them.

Fig. 6.9  In patient with Crohn’s disease, CT shows thickened intestinal wall at the end of ileum with target sign

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lesion, the appearance of the target usually indicates that the thickening of the intestinal wall is caused by inflammatory disease rather than a tumor. One exception should be noted: infiltrating sclerosing carcinoma seen in the rectum can also appear as target sign [30]. Wall ischemia is thickening of the intestinal wall, sometimes with target sign. This sign is an early nonspecific sign of intestinal ischemia. Ischemic colitis is usually seen in the elderly and is a nonobstructive ischemic bowel disease with no gender differences. When thickening of the intestinal wall is observed on CT in patients receiving anticoagulant therapy or with a potential bleeding tendency, bleeding in the intestinal wall should be considered at this time [31]. The most common finding of Crohn’s disease and colitis gravis on CT is thickening of the intestinal wall. In the acute phase, the small intestine and colon of Crohn’s disease show mucosa stratification when no scar has been formed, which usually also appears as the target sign. When injecting contrast medium, the inflamed mucosa and serosa can be enhanced, and the degree of enhancement is related to the activity of the clinical disease. Intestinal fibrosis in patients with chronic Crohn’s disease does not show target sign [31]. The target sign can appear in postcontrast CT; although there is no specificity, it can be predicted that the thickened intestinal wall is generally caused by inflammatory enteropathy when the target sign is found [32].

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the inherent muscular layer of mucosa is not strengthened or weakened, there is no difference in density between the middle layer and the low-­ density submucosa caused by inflammation and edema. Some researchers believe that the weakness of the inner layer of the intestinal canal indicates that intestinal blood perfusion is poor and will soon develop into irreversible ischemic necrosis, suggesting that surgery is needed as soon as possible (Fig. 6.10). Discussion The double halo sign was first proposed on CT in Crohn’s disease of the small intestine. Pathologically, small-bowel ischemia may be divided into several types: mucosal necrosis in which the lesion is limited to the mucosa; mural necrosis in which the lesion extends to the submucosa or even into, but not through, the muscularis propria; and transmural necrosis in which the lesion extends through the muscularis propria [33]. It cannot solely attribute a high small-bowel necrosis or mortality rate to different enhancement patterns of bowel [34]. The mucosa is the most vascularized part of the intestines, followed by the submucosa and the muscularis propria. A normally perfused mucosa should be the most intensely, or at least iso-intensely, enhancing layer of a thickened small-bowel wall. The submucosa is composed of connective tissue with nerves, vessels, and lymphatics traversing it.

6.11 Double Halo Sign Feature Resembling the target sign, the thickened intestinal wall shows a double-layer structure; the outer layer is a high-density enhancement layer, and the inner layer is weaker or not as enhanced as the outer layer, showing soft-tissue density. Explanation The double halo sign is also seen in a variety of inflammatory bowel diseases. The meaning of each layer resembles the target sign, but because the inner layer represents the mucosal layer and

Fig. 6.10  A 61-year-old woman presented with abdominal pain for 1 month. Computed tomography angiography (CTA) showed the wall of the distal ascending colon was thickened, and the enhancement manifested as a double-­ layer structure

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However, its microvascular network is less abundant than that of the mucosa. The normal submucosa is uncommonly seen as a separate structure on CT scans unless it is edematous, hemorrhagic, or infiltrated by tumor, or has fat deposits. Contrast enhancement of the thickened ­submucosa rarely if ever approaches that of the normally perfused mucosa. Homogeneous ­ enhancement of a thickened wall might be attributed to a hyperemic mucosa. Although poor inner-layer enhancement does not necessarily mean the absence of perfusion, it may represent a severe compromise of the blood supply to the mucosa or sloughing of the mucosa [33]. The diagnostic value of CT in intestinal wall thickening diseases and differential diagnosis has been discussed widely [34]. The small bowel is associated with a group of acute disorders that are distinct from those that affect the colon, in part because of its unique vascular supply and physiological functions, which differ from those of the colon. Nonlocalized acute abdominal pain is often the first clinical presentation of disease, which leads to an initial imaging examination, usually performed with postcontrast CT in the emergency department. Diffuse or regional acute disorders of the small bowel often manifest with nonspecific findings on CT, most commonly mural stratification and circumferential bowel wall thickening. On postcontrast CT images of the abdomen and pelvis, the “target” or “double halo” sign represents mural stratification caused by hyperenhancement of both the inner mucosa and the outer muscularis propria/serosa, with a middle layer of low-attenuating submucosal edema. In the absence of contrast enhancement, stratified hyperenhancement is not depicted; the only indications of underlying disease may be bowel wall thickening (with or without associated edema), peri-enteric inflammatory change, or ascites [35].

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in a comb-like shape can be seen on the mesangial side of the ileum. Explanation The arteries supplying the small intestine are emitted from the superior and inferior mesenteric arteries, forming a series of small intestine arteries that are arched together in the mesentery. Its terminal branch (straight arteriole) is longer in the jejunum and greater in distance from each other, whereas it is shorter and relatively close in the ileum. Therefore, when the small arterioles in the ileum are enlarged, distorted, and expanded, and the distance between them increases, it appears as a comb-like shape in the CT enhanced scan, thus called the comb sign. This sign results from the increase of blood flow in the affected intestine when the inflammatory bowel disease occurs, and the corresponding mesentery is caused by the proliferation of fibrous fat, which is more common in Crohn’s disease (Fig. 6.11). Discussion Crohn’s disease is a chronic granulomatous inflammatory disease involving the entire layer of the intestinal wall [36]. The digestive tract can be affected throughout the course, but the terminal ileum and proximal colon are the most common. The earliest microscopic manifestations

6.12 Comb Sign Feature In the abdominal pelvic postcontrast CT, a number of straight tubular, twisted shadows arranged

Fig. 6.11  A 56-year-old woman with small intestinal lesions with “comb sign.” Crohn’s disease was considered

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were enlarged lymphoid follicles and small ulcers of thrush, which are often seen in double contrast barium angiography and are often difficult to resolve because of low spatial resolution. Thickening of the intestinal wall is the most common features of Crohn’s disease, seen in ­ more than 82% of patients. It is usually thickened by 5–10 mm or even 20 mm [37]. The thickened intestinal wall is more common in the terminal ileum and can also be seen in digestion. The clinical history, the distribution of the disease, and other related tests are helpful for differential diagnosis of the disease. In the acute phase, the intestinal wall is stratified, and there is a target or double halo on CT, which may be caused by submucosal edema or intestinal wall fat infiltration. Thickening of the intestinal wall is not a unique manifestation of Crohn’s disease. In fact, more than 60% of patients have inactive ulcerative colitis, and only about 8% of patients have Crohn’s disease [38]. It can also be found in radiation enteropathy, graft-­ versus-­host disease, and chronic ischemia of the intestinal wall. Inflamed mucosal and serosal layers can be intensified during postcontrast CT scanning, and the degree of enhancement is related to the clinical activity of the disease. In patients with longer course of disease, intestinal wall fibrosis, stratification loss, and intestinal wall density were uniform on CT [38]. In patients known to have Crohn’s disease, if the aforementioned mesenteric vascular proliferation, distortion, dilatation, and comb signs caused by protrusion of the small blood vessels occur, it indicates a tendency for the disease to deteriorate acutely. Patients with clinical symptoms for the first time can have a CT scan that reveals the possibility of Crohn’s disease diagnosis, but this is not an absolute specificity because it can also occur in patients with lupus mesangial vasculitis. Other diseases can develop vasodilatation during development, such as vasculitis (including nodular polyarteritis, Henoch–Schonlein syndrome, microscopic polyangiitis, Bechet’s syndrome), mesenteric thrombosis, strangulated intestinal obstruction, or ulcerative colitis. The appearance of comb signs is of great help in iden-

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tifying lymphomas and metastases, as these two diseases usually show less blood supply. About 28% of patients with Crohn’s disease can also show complications on CT, which is very helpful for the treatment of the disease. The main complications are abscess, fistula, sinus, or perianal disease, which can be well shown on CT. In addition, patients with Crohn’s disease should also be carefully examined for other signs of the disease on CT, including liver fatty infiltration, kidney stones, gallstones, ankle arthritis, and hydronephrosis [37].

6.13 Gastrointestinal String Sign Feature In small intestinal barium examination, fine barium lines resembling rough cotton threads are formed in the small intestine. Explanation The gastrointestinal tract is severely narrowed, leading to linear changes in the internal cavity. Gastrointestinal stricture is generally termed as endoluminal stenosis, but the term was originally used to describe reversible stenosis in Crohn’s disease. The cause of stenosis is incomplete obstruction from irritability and spasm caused by severe ulcer, and alternation of stenosis and dilation can be found. When stenosis is mainly caused by edema and spasm, the degree of stenosis is not the same. If the small intestinal wall is thickened by fibrosis, the internal diameter of the cavity will be narrowed uniformly. Mucosa is replaced with fibrous necrotic tissue; islands of mucosa can be found occasionally. Discussion The gastrointestinal string sign has been identified as a characteristic manifestation of Crohn’s disease, most commonly in the terminal ileum [39]. Intestinal abnormalities in stage Crohn’s disease include coarse villus sign, fold thickening, and aphthous ulcer. These signs are not specific and can be found in other diseases, but their presence provides solid evidence for Crohn’s disease. Linear ulcers along the mesenteric mar-

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gin are one of the most important diagnostic features of Crohn’s disease of the small intestine, parallel to shortened, concave, or rigid mesenteric margins. Adjacent mesentery thickens and retracts, especially at the junction with the invaded intestinal segment. The rigid mesenteric margin is caused by transmural inflammation that spreads from a linear ulcer into the mesentery. As the ulcer progresses, spasms and irritability increase, folds become coarser and thicker, and gastrointestinal strings can appear. According to the different stages of development of the lesion, the proximal intestinal tract may or may not be dilated. Spasms are often changeable. Repeated observation of photographs confirms that dilation sometimes occurs in the lesion intestinal segment. However, when the spasm persists, temporary proximal intestinal dilatation may occur with symptoms of intestinal obstruction. In the stenosis stage, spasms secondary to ulcers lead to sustained proximal dilation, although stenosis and complete intestinal obstruction are rare. Barium fluoroscopy remains a valuable diagnostic technique for evaluating structural and functional disorders of the small bowel in the sophisticated imaging modalities. Conventional small-bowel follow-through studies can be performed in most patients, in which periodic imaging of the entire small bowel is examined using fluoroscopic guidance. Some patients may benefit from enteroclysis, in which barium is instilled into the small bowel via a catheter placed in the proximal jejunum for optimal distention and better depiction of individual small-bowel loops. A pattern approach for the wide spectrum of abnormalities found on barium studies would contribute to the diagnostic clues [40]. In addition to Crohn’s disease, other diseases can also show similar signs. In cases of pyloric stenosis, the narrow elongated pyloric canal shows a single barium line. If the intestinal tract narrows and some obstructions occur, carcinoid tumors can also lead to radiologic manifestations of gastrointestinal linear signs. In conclusion, the presence of gastrointestinal string sign is highly suggestive of Crohn’s disease, but it can also occur in other diseases [41].

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6.14 Bowel Wall Fat Halo Sign Feature In the CT scan the thickened middle layer of the intestinal wall or the submucosa forms low density from fat infiltration, thereby forming a three-­ layer structure throughout the intestinal wall. Other names: fat halo sign. Explanation The appearance of the bowel wall fat halo sign on CT is usually seen in Crohn’s disease in the small intestine or idiopathic inflammatory bowel disease in the colon, and can also occur in normal people without inflammatory bowel disease. The black density formed by the infiltration of fat in the middle layer of the intestinal wall is different from the gray density formed by edema of the fat wall. The CT value of the infiltrated tissue of the annular fat is mostly less than 10 Hu, but its density is different from pure mesenteric fat or retroperitoneal fat, which may be caused by partial volume effect or simultaneous edema of the intestinal wall. The outer margin of the lamina propria of the mucosa may be more clearly visible or may be unclear from dispersion in the infiltrated fat (Fig. 6.12).

Fig. 6.12  A 43-year-old woman presented with bowel wall fat halo sign in the terminal ileum

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Discussion The presence of fat in the intestinal wall is usually considered to be the evidence of prior inflammatory bowel disease (IBD). Essentially, fat in the intestinal wall is a pathological change of chronic inflammation [42]. When fat halo sign is visible in the small intestine and colon, it is often considered as a specific sign of Crohn’s disease. Only when there is colon involvement are the extent of involvement and the extent and distribution of thickened intestinal wall the main basis for distinguishing between ulcerative colitis and Crohn’s disease. The fat halo sign of the intestinal wall is different from edema. The pathological basis of the fat halo sign is the accumulation of submucosal fat, and the edema is the increase of the water in the interstitial space of the intestinal wall. Therefore, edema is mainly caused by thickening of the intestinal wall, whereas fat halo sign is mainly separated by mucosa and intestinal wall. In addition, edema is often an acute reaction to a disease, and it generally has corresponding clinical symptoms, but patients with fat halo signs do not necessarily have gastrointestinal symptoms [43]. Some studies have found that scattered fat halos can be seen in the distal ileum or colon on CT in some patients with kidney stones. In the absence of a history of IBD or other supporting signs of IBD, intestinal fat halo is thought to be a normal feature, especially in obese patients [44]. Fat halo sign is best seen when the intestinal cavity is moderately dilated, but is less seen when the intestinal cavity is dilated significantly, presumably the result of intestinal wall tension and compression of the adipose layer when the intestinal cavity was dilated excessively. If the intestinal cavity is clean and full of gas, the mucosal layer between the intestinal cavity and the fat halo can be shown. If the intestinal cavity is unclean, the mucosal layer and intestinal contents may be mixed. In general, fat in normal intestinal wall is thinner than that seen in idiopathic IBD.  The mucosa propria muscle layer is also uniform in thickness structure; the thickness is generally less than 1 mm, the surrounding mesentery is rarely abnormal, and normal intestinal wall fat in the intestinal cavity generally is not

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dilated or is slightly dilated. It is difficult to distinguish between normal fat and Crohn’s disease when fat layers are found in the wall of the terminal ileum. Fat halo syndrome in Crohn’s disease is often accompanied by mucosal disorders, intestinal wall thickening, intestinal stenosis, and other changes, but the simple “fat halo syndrome” is not [44]. It is necessary to inquire about the detailed medical history and other tests for further diagnosis. In summary, intestinal fat halo is one of the manifestations of inflammatory bowel disease, but it can also occur in the absence of inflammatory bowel disease; the sign is normal or only represents obesity.

6.15 Disproportionate Fat Stranding Sign Feature The fat stranding adjacent to thickened bowel wall suggests the cause of abdominal pain coming from gastrointestinal tract on CT. It is a CT sign of abdominal inflammatory diseases. The key point of disproportionate fat stranding is the degree of fat stranding is significantly heavier than the degree of bowel wall thickened and out of proportion. Explanation In a few acute diseases of the gastrointestinal tract, the pathological process is c­ haracteristically centered in the mesentery adjacent to the bowel wall rather than in bowel wall itself. In these diseases, the fat stranding is often disproportionately greater than the degree of wall thickening. Because the duration of diseases typically manifesting disproportionate fat stranding is short, this sign may help narrow the scope of differential diagnosis (Fig. 6.13). Discussion The disproportionate fat stranding sign is a CT sign proposed by Pereira et  al. [45] that shows that the fat stranding adjacent to thickened bowel wall on CT scan and the degree of fat stranding is significantly heavier than the degree of bowel wall thickened and out of proportion. Most acute

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Diverticula are typically present. The inflammatory process can result in accumulation of fluid in the root of the sigmoid mesentery, and engorgement of the mesenteric vessels [46]. 2. Appendices epiploicae are pedunculated adipose structures protruding from the external surface of the colon into the peritoneal cavity, typically 1–2  cm thick and 2–5  cm long. Epiploic appendagitis often occurs in the left and right lower abdomen, because sigmoid colon and cecum have numbers of large appendices epiploicae. An epiploic appendagitis is a lesion caused by torsion of the omental fat sag or spontaneous venous embolization, resulting Fig. 6.13  Noncontrast CT of a male patient with right-­ sided diverticulitis shows severe peri-colonic fat in ischemia or embolism of intestinal lipids, stranding and concurrent infection. The patient’s clinical manifestations are sudden, with severe abdominflammatory diseases of the gastrointestinal inal pain resembling appendicitis. Generally, tract are centered in the bowel wall; the degree of only conservative treatment is needed. On CT, bowel wall thickening typically exceeds the the main manifestation is oval fat attenuation degree of associated fat stranding. In a few acute lesions of 1–4 cm, and the surrounding mesendiseases of the gastrointestinal tract, the pathotery may have an inflammatory exudation ring logical process is characteristically centered in surrounded by an obvious high-attenuating the mesentery adjacent to the bowel wall rather crescent sign [47]. A small number of patients than in the bowel wall itself. In these diseases, the have a point-like high attenuation (embolized fat stranding is often disproportionately greater blood vessels or bleeding) in the center of the than the degree of wall thickening, then the dislesion. Adjacent bowel walls may be thickened proportionate fat stranding sign are formed. On and compressed, with disproportionate fat CT this sign often suggests the cause of abdomistranding around them. nal pain coming from the gastrointestinal tract, 3. The omentum is formed by the overlapping of mainly including four diseases: diverticulitis, the peritoneum between the transverse colon epiploic appendagitis, omental infarction, and and the stomach, which contains a large appendicitis. amount of fat and hangs in front of the intestine. Omental infarction involves a segment of 1. Diverticulitis is a mucosal and submucosal the omentum that often occurs on the right capsular bag that passes through the muscular side. Because the blood supply route on the layer of the colon wall. The muscle layer right side is long and fragile, it easily caused between the colonic zone and the mesentery venous embolism, which eventually leads to undergoes perforation involving the nerves omental infarction. The specific CT signs of and blood vessels. Diverticula can be found omental infarction are a large pie-shaped anywhere in the colon, but they occur prehigh-attenuation fatty mass in the omentum, dominantly in the descending and sigmoid which can be adjacent to the colon or at a cercolon. The appearance of acute diverticulitis tain distance. The bowel wall can be thickened on CT scans parallels the pathological feanearby, but fat stranding is more pronounced. tures. The most common CT finding is paraOmental infarction and epiploic appendagitis colic fat stranding, which characteristically is are benign and self-limiting diseases. disproportionately more severe than the rela- 4. Appendicitis is the most common cause of tively mild, focal colonic wall thickening. acute abdominal pain that requires surgical

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intervention. The most characteristic CT manifestation of appendicitis is the direct ­ visualization of a dilated (>6 mm in diameter) and fluid-filled appendix. Other direct signs include an abnormally thickened appendix, increased attenuation of the appendix after contrast material administration, and peri-­ appendicular fat stranding. Secondary signs include the appearance of appendicolith or thickening of the cecal apex. Peri-­appendicular fat stranding is typically mild to moderate, but it can be severe. The diagnosis of appendicitis from CT findings is straightforward if the appendix is easily visualized. However, in cases of perforated appendicitis with peritonitis or abscess formation, the appendix may be difficult to see. The finding of severe fat stranding in the right lower quadrant without substantial cecal or ileal thickening may suggest the possibility of appendicitis. A careful search for a thickened or focally perforated appendix will yield the diagnosis. The disproportionate fat stranding sign suggests the causes of abdominal pain coming from the gastrointestinal tract, including diverticulitis, epiploic appendagitis, omental infarction, and appendicitis. It was reported that fat stranding sign is one of the most frequent findings in ischemic colitis regardless of severity of involvement [48]. It is necessary to make a correct diagnosis, as epiploic appendagitis and omental infarction are typically self-limited conditions, whereas appendicitis and many cases of diverticulitis require surgery or other intervention.

6.16 Misty Mesentery Sign Feature Abdominal CT scan shows an increase in mesenteric fat density, which may be homogeneous or heterogeneous, diffuse or focal, depending on the nature of the lesion. Explanation The term “misty mesentery” indicates a pathological increase in mesenteric fat attenuation on

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Fig. 6.14  A 64-year-old woman presented with upper abdominal pain for 1 day. Abdominal CT shows uneven increased attenuation of the mesenteric fat

CT. On abdominal CT scans, normal mesenteric fat showed uniform low density, similar in density to the fat in subcutaneous and retroperitoneal spaces. CT sensitively shows the changes of mesenteric fat density caused by abdominal lesions. Mindelzun et al. [49] used mesenteric turbidity to describe the infiltration of mesenteric fat by inflammatory cells, fluid (edema, lymph, blood), tumor, and the increase of mesenteric fat density during fibrosis. The main causes include edema, inflammation, hemorrhage, neoplasm, and mesenteritis (Fig. 6.14). Discussion A misty mesentery is a sign of mesenteric infiltration, showing increased attenuation of the mesenteric fat-called misty mesentery, with some soft tissue nodules on CT. It was first described by Mindelzun in 1996 [49]. This sign is seen in mesenteric panniculitis, a nonspecific inflammatory disorder of the mesenteric fat, which can be either acute or chronic. Mesenteric panniculitis can lead to fat necrosis, fibrosis, and retraction of the mesentery. The normal small bowel mesentery is rich in fat, which has the same attenuation as subcutaneous fat on CT (−100 to −160 HU). However, if there is cellular or acellular infiltration of the mesentery, the attenuation value increases (−40 to −60 HU). This increased attenuation of the fat is referred to as the misty mesentery sign. In such cases, the mesenteric vessels,

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which normally appear distinct from the fat, may sometimes become indistinct or effaced like a tree in the mist. The sign is nonspecific and has been ascribed to various factors such as edema, inflammation, malignancy, lymphatic obstruction, hemorrhage, or idiopathic (mesenteric panniculitis). There are no specific presenting complaints and it is usually diagnosed incidentally, with an incidence of about 0.6% [50]. The treatment usually involves treating the underlying condition. Atypically, mesenteric lymphoma can present with imaging findings that overlap with sclerosing mesenteritis. Calcification is not typically seen in lymphoma before treatment, and its presence in a mesenteric mass suggests an alternate etiology such as sclerosing mesenteritis or carcinoid tumor. In the absence of a known history of malignancy, the presence of a “misty mesentery” with small nodal masses incur diagnostic dilemma. More specifically, differentiating lymphoma from asymptomatic sclerosing mesenteritis can present a challenge [51]. A wide spectrum of diseases can result in the misty mesentery. Although on occasion the cause of this misty mesentery may prove elusive, in most situations the cause can be determined by analysis of the patient’s history and associated CT findings [52]. In patients suffering from acute abdominal disease, misty mesentery may be considered a feature of the underlying disease. Otherwise, it may represent an incidental finding

for other reasons [53]. The development of malignancy in patients with incidentally detected misty mesentery is reported to correlate with mesenteric lymph node size. Patients with misty mesentery and largest mesenteric lymph node less than 10 mm without lymphadenopathy in other areas demonstrate a benign course, and no further follow-­up may be necessary [54].

Fig. 6.15  Two cases with mesenteric panniculitis. (a) The fat density of the mesentery had increased unevenly, which appeared foggy or like ground glass, and surrounded the mesentery vessels on postcontrast

CT. Multiple lymph nodes at the root of mesentery with “fat ring sign.” (b) Postcontrast CT of another case indicated the pseudo-capsule of the mesenteric panniculitis

6.17 Fat Ring Sign Feature CT findings of mesenteric panniculitis. The density of mesenteric adipose tissue increased (−40 to −60 HU), showing a single or multiple soft tissue density masses with clear boundary and uneven density. The masses surround the mesenteric macrovascular but do not involve the vascular, and fat may exist around the mesenteric vascular, forming a fat ring sign. Explanation Mesenteric panniculitis is characterized by chronic inflammatory cell infiltration, fat necrosis, and fibrous tissue forming a “pseudo-tumor nodule.” It surrounds but does not invade mesenteric vessels. Mesenteric arteriovenous vessels are growing in the lesion and adjacent vessels have normal fat density (Fig. 6.15).

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Discussion Sclerosing mesenteritis (SM) is a rare idiopathic and complex inflammatory and fibrotic disorder primarily affecting the small-bowel mesentery. Its exact cause is unknown. The spectrum of this disease has included mesenteric lipodystrophy, mesenteric panniculitis, mesenteric sclerosis, and retractile mesenteritis [55]. The integrity of mesenteric vessels and gastrointestinal lumen is compromised by mass effect, leading to the clinical symptoms. The most common symptoms include abdominal pain, nausea, vomiting, diarrhea, weight loss, and rarely ascites and small-bowel obstruction. In physical examination, abdominal tenderness, palpable abdominal mass in the left upper quadrant or epigastrium, are noted. The mass is often deep and poorly defined. Surgical resection is sometimes attempted for definitive therapy, although the surgical approach is often limited by vascular involvement. The most common complications of SM include bowel obstruction, ileus or ischemia, and obstructive uropathy or renal failure; 85.7% of deaths are secondary to SM-related complications [56]. The CT appearance of SM may vary depending on the predominant tissue component (fat, inflammation, or fibrosis). CT has an important function in suggesting the diagnosis in the proper clinical setting and is useful in distinguishing SM from other mesenteric diseases with similar CT features such as carcinomatosis, carcinoid tumor, lymphoma, desmoid tumor, and mesenteric edema. The most common finding on CT is a soft-tissue mass within the small bowel mesentery. Two signs seen on CT, that is, “fat ring” and “tumor pseudo-capsule,” are considered somewhat specific for mesenteric panniculitis [57]. The fat ring sign is caused by preservation of the fat nearest the mesenteric vessels; the tumor pseudo-capsule represents separation of the uninvolved mesentery from the inflamed fat by a band of tissue [58]. The CT appearance of sclerosing mesenteritis can vary from subtle increased attenuation in the mesentery to a solid soft-tissue mass. Sclerosing mesenteritis most commonly appears as a soft-tissue mass in the small-bowel mesentery, although infiltration of the region of the pancreas or porta hepatis is also possible. The

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mass may envelop the mesenteric vessels, and, over time, collateral vessels may develop. Sclerosing mesenteritis is a benign chronic inflammatory condition often confused with neoplastic process. There may be preservation of fat around the mesenteric vessels, a phenomenon that is referred to as the “fat ring sign.” This finding may help distinguish sclerosing mesenteritis from other mesenteric processes such as lymphoma, carcinoid tumor, or carcinomatosis [59]. CT angiography is especially helpful in delineating the relationship of the mass to the mesenteric vasculature, significant involvement of which can compromise blood supply to the bowel and result in bowel wall ischemia.

6.18 Hyperattenuating Ring Sign Feature The hyperattenuating ring sign is found in abdominal CT scan, which consists of a thin circular or oval soft tissue high-density ring around the colon surrounding the low-density fat. Explanation The hyperattenuating ring sign is the characteristic finding of primary epiploic appendagitis (PEA). The hyperattenuating ring represents the thickened peritoneum, the fat density in it represents inflamed epiploic appendages. Histologically, white blood cells exudate around the inflammatory epiploic appendages [60] (Fig. 6.16). Discussion Primary epiploic appendagitis (PEA) is a rare cause of acute abdominal pain determined by a benign self-limiting inflammation of the epiploic appendages, and ischemia is the main pathophysiological mechanism [61]. The possible reasons are related to the spontaneous torsion of intestinal fat lobe and spontaneous venous thrombosis, which result in aseptic fat necrosis and aseptic inflammatory reaction. It may manifest with heterogeneous clinical presentations, mimicking other more severe entities responsible for acute abdominal pain, such as acute diverticulitis or

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Fig. 6.16  A 34-year-old woman presented with abdominal pain and visible paracolonic fat density lesions surrounded by hyperattenuating rings (arrows). Hyperattenuating rings represent the thickened peritoneum around the lesion

appendicitis. PEA is a benign self-limiting disease and spontaneously resolves without surgery within 5–7 days [62]. Imaging is crucial to avoid inaccurate diagnosis that may lead to appropriate therapy, and it is imperative that radiologists be familiar with this entity. The hyperattenuating ring sign is a characteristic manifestation of PEA, although the negative sign cannot exclude the diagnosis of PEA. CT is currently the most effective means to diagnose PEA. The CT findings of PEA change with time. The size, extent, size of high-density ring, and exudation around the lesion will change, but the change is irregular, and the lesion may persist for several months before disappearing. Correct understanding of the sign and definite imaging diagnosis of the disease can avoid unnecessary clinical ­ overtreatment. The imaging features of PEA have certain characteristics, most of which can provide a definite diagnosis. The most common CT findings of PEA are round-like fat-density lesions on the opposite side of the mesocolon adjacent to the colon. Soft tissue density rings (the hyperattenuating ring sign) can be seen around them, representing inflammatory reaction of the peritoneum covering the mesocolon. Punctate or small patches of high-density shadow can be seen in the center of the lesion, suggesting necrosis or thrombosis of the central vein of epiploic appendage [61], slight enhancement of the thin wall on

postcontrast CT scanning, high-density shadow of cords and strips in the fat space around the lesion, rare involvement of the adjacent intestinal wall, and no obvious signs of fluid accumulation around the lesion. CT represents the gold standard technique for the evaluation of patients with indeterminate acute abdominal pain [63]. Imaging findings include the presence of an oval lesion with fat-attenuation surrounded by a thin hyperdense rim on CT (“hyperattenuating ring sign”) abutting the large bowel, usually associated with inflammation of the mesentery. A central high-attenuation focus within the fatty lesion (“central dot sign”) can be observed and indicates a central thrombosed vein within the inflamed epiploic appendage. PEA may be located within a hernia sac or attached to the vermiform appendix. Chronically infarcted epiploic appendage may detach, appearing as an intraperitoneal loose calcified body in the abdominal cavity [63].

6.19 Arrowhead Sign Feature The arrowhead sign, which is obtained after the administration of oral or rectal contrast material, is seen on CT images as an arrowhead-shaped collection of contrast medium localized to the upper part of the cecum near the orifice of the appendix. An air-arrowhead sign has also been described, which refers to a collection of air rather than of contrast medium at the same location. Similar manifestations can also be seen in the diverticulum mouth of the colon, also known as arrow sign. Explanation Inflammatory changes associated with acute appendicitis can cause focal, symmetrical thickening and coaptation of the upper cecal wall, which allows contrast material to assume the configuration of an arrowhead as it funnels to the  level of the obstructed appendiceal orifice. The amount of contrast medium collected at the cecal–appendiceal junction can vary and depends on the presence or absence of cecal air, the degree of cecal distention, and the cecal wall swells in

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the particular manner. Hence, the resulting arrowhead sign also assumes a variety of appearances ranging from short and fat to long and thin. Although the arrowhead sign is generally most conspicuous on transverse CT images, it may occasionally be difficult to see. In these cases, additional images reformatted in the sagittal or coronal plane will occasionally show a more expected arrowhead shape. The arrowhead sign formed by inflammatory changes occurring in colonic diverticula resembles the arrowhead sign formation mechanism of acute appendicitis. The pathophysiology of diverticulitis mirrors that of appendicitis, with an obstructive fecalith initiating the inflammatory process. Discussion Appendicitis is the most common cause of acute abdominal pain that requires surgical intervention. Primary diagnostic criteria for acute appendicitis have been defined as visualization of an enlarged appendix greater than 6  mm in diameter. Secondary criteria were wall thickening and enhancement, appendicolith, periappendiceal fat stranding, free fluid in right lower quadrant or pelvis, peri-appendiceal abscess, small bowel obstruction, and mural thickening of cecum [64]. However, because the position of the appendix varies, the diagnosis of appendicitis in a patient with abdominal pain can be a challenge. It is reported that up to one third of patients with appendicitis have atypical findings at presentation. The use of clinical criteria alone to diagnose appendicitis results in removal of a normal appendix in approximately 20% of patients undergoing diagnostic laparotomy and causes approximately 20% of patients with appendicitis to be discharged without undergoing surgery. As a result, many imaging modalities, including CT examination of the abdomen or of the right lower quadrant, have been employed to balance the false-positive laparotomy rate with the rate of perforation and peritonitis at the time of surgery. When nonvisualization of the appendix is a problem, the radiologist must rely on the presence or absence of so-called secondary signs of appendicitis to help make or exclude the diagnosis [65].

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The CT arrowhead sign is another of these secondary signs of appendicitis. Rao et  al. [66] performed a study with 100 patients suspected of having appendicitis. The CT arrowhead sign was present in 17 of the 56 patients with appendicitis (sensitivity, 30%). The sign was absent in all 43 of the patients without appendicitis (specificity, 100%). This sign is, therefore, helpful in the evaluation of patients with appendicitis whose studies otherwise reveal (i.e., in addition to the arrowhead sign) only mild, nonspecific inflammatory findings in the right lower quadrant. Because the sign is formed by the extension of inflammation from the appendix to the cecum, the arrowhead sign may allow for placement of patients with appendicitis into two surgical groups: those who likely will do well with standard ligation (arrowhead sign not present) and those who may require partial cecectomy (arrowhead sign present) [65]. The pathophysiological process of colonic diverticulitis mirrors appendicitis; that is, a diverticulum is obstructed by a fecalith and becomes inflamed. Contiguous spread of inflammation at the site of diverticular perforation through the colonic wall results in focal inflammation of the colonic wall. On occasion, as the inflammation spreads through the colonic wall, an arrowhead-shaped collection of contrast material becomes evident in the adjacent colonic lumen. The appearance and frequency of occurrence of the arrowhead sign at CT are dependent on the degree of colonic luminal distention, the orientation of the affected bowel relative to the axial scanning plane, and the amount of potentially obscurant adjacent inflammation. In addition to contrast material, luminal air may also collect at the site of focal wall thickening, resulting in an “air-arrowhead” sign [67].

6.20 Accordion Sign Feature The accordion sign is a finding on CT scans in patients who have received oral contrast material. It constitutes alternating bands of lower soft tissue attenuation and higher contrast material attenuation within the large bowel.

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a

b

Fig. 6.17 (a, b) Accordion sign in a patient with pseudo-membranous colitis. Contiguous CT sections show marked wall thickening of the colon with contrast material (arrows) in crevices between the folds

Explanation A small amount of contrast agent that reaches the colon after oral contrast is filled in the fissure between the thickened colon folds. This low attenuation and high attenuation strip-like appearance is very similar to an accordion. The pattern varies depending on the degree of colonic edema and the amount of contrast agent deposited between the folds of the colon (Fig. 6.17). Discussion The low-attenuation soft tissue shadow of the accordion sign represents a significant thickening of the colon fold from edema of the intestinal wall. This sign is considered a characteristic CT manifestation of pseudo-membranous colitis (PMC) [68]. Pathologically, low-attenuation soft tissue shadow represents a markedly thickened colon fold caused by intestinal wall edema, and the high-attenuation shadow is a small amount of contrast agent that reaches the colon after oral contrast and is filled into the fissure between the thickened colon folds [69]. PMC is an intestinal disease caused by gram-positive anaerobic bacteria, primarily Clostridium difficile in the colon, also known as C. difficile overgrowth of intractable Clostridium spp. This reaction causes a decrease in the normal flora in the intestine from heavy use of antibiotics, and some oncology drugs can also produce the same effect. It is a series of diseases that are clinically capable of producing fulminant colitis from mild diarrhea to life-threatening colitis. The diagnosis of PMC

relied on the positive detection of toxins in the feces and the detection of pseudo-membranous plaques under colonoscopy. This pathological change can be manifested in imaging. Plain radiography, contrast enema studies, and CT are useful in the evaluation of PMC. Conventional radiography can show nonspecific changes such as thickening of colon folds, colon expansion, and peritoneal effusion. Plain film can demonstrate polypoid mucosal thickening, “thumb printing” (wide transverse bands associated with haustral fold thickening), or gaseous distention of the colon. Small nodular filling defects representing mucosal plaques is the primary finding in mild cases of PMC on contrast enema. Contrast enema study is contraindicated in patients with severe PMC by the potential danger of perforation. CT is mainly used in patients with advanced PMC who have no specific symptoms and are difficult to diagnose. Common CT findings include wall thickening, low-attenuation mural thickening corresponding to mucosal and submucosal edema, the accordion sign, the target sign (double halo sign), pericolonic stranding, and ascites [70]. Macari et  al. [71] believed that the accordion sign was a manifestation of a high degree of edema in the colon and was unspecific for the cause. Intestinal wall thickening and nodules can also be seen in other colitis, but mainly in patients with PMC. In general, except for Crohn’s disease, the degree of colon wall thickening of pseudo-membranous colitis is usually greater than other causes [69].

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Fishman et  al. reported that the accordion sign occurred in 5 of 26 patients with confirmed PMC [72]. Since then, there have been further reports that the positive rate of accordion signs in advanced PMC patients accounted for 51% to 67%. Familiarity with these imaging features may help make the diagnosis and prevent progression to deterioration.

6.21 A  pple Core Sign; Apple Core Lesion Feature The apple core sign refers to the local stenosis of the colorectal during the barium enema examination. This stenosis is characterized by the shape of the shoulder at both ends, and the central lumen is narrow, the mucosa is destroyed, and the edges are irregular, which shape resembles a leftover apple core. Explanation This sign is observed when the cancer infiltrates around the intestinal wall more than two thirds of a

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the circumference of the intestinal lumen. The two ends of the sign are the bulging boundary formed by the round mount, and the central narrow segment of the lumen is the cancer canal of ulcer (Fig. 6.18). Discussion An apple core lesion is the radiologic manifestation of a focal stricture of the bowel at a contrast material enema study [73]. The apple core sign was originally described on barium enemas as an abrupt, irregular, and segmental stenosis with “shouldered margins” in the colonic wall. This sign represents a nondistensible narrowing of the intestinal lumen by a stenosing circumferential colorectal mass that allows passage of only a small amount of contrast media. The appearance resembles an apple core, the remnant of a partially eaten apple. The apple core sign is also known as “napkin ring sign” [74]. From the pathological point of view, when the diameter of the cancer exceeds 4–5 cm, the incidence of “apple core sign” is significantly increased, indicating that as the volume of the cancer increases, infiltration along the circumference of the intestine b

Fig. 6.18  In this 66-year-old man, the apple core sign refers to the local stenosis of the sigmoid colon during barium enema study

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also increases. When the infiltration exceeds two thirds of the circumference of the lumen, it can cause narrowing of the lumen, which is manifested as apple core sign. When the cancer has infiltrated along the intestine, the two sides of the ring are merged and disappear, and a cancerous ulcer tunnel is formed in the center. The two ends of the mass retain the ring embankment, forming a bulge boundary at both ends of the lesion [75]. Imaging studies are a major component in the evaluation of patients for the screening, staging, and surveillance of colorectal cancer. CT colonography provides important information for the preoperative assessment of T stage as an option for colorectal cancer screening. Three-­ dimensional CT to image the vascular anatomy facilitates laparoscopic surgery. MRI is more accurate than CT in evaluating liver metastases. Positron emission tomography (PET)/CT is valuable in the evaluation of extracolonic and hepatic disease. The classic apple core sign is not specific for colorectal cancer and has also been described in other diseases of the colon, such as diverticulitis, inflammatory colitis, ischemic colitis, radiation-­induced colitis, including Crohn’s ­disease, and intestinal tuberculosis, and even in colonic amyloidosis [74].

6.22 Duodenal Wind Sock Sign Feature The duodenal wind sock sign is a finding that may be seen on an upper gastrointestinal series. This sign consists of a barium-filled sac that lies entirely within the duodenum and is surrounded by a narrow radiolucent line that is well demonstrated as the barium in the duodenum passes distal to the diverticulum. Explanation The duodenal wind sock sign has been described as a typical appearance of an intraluminal duodenal diverticulum. The narrow radiolucent line represents an intraluminal mucosal diaphragm or web caused by failure of normal recanalization of the duodenum after epithelial cell occlusion of the foregut lumen in the 7-week human embryo. Over time, the diaphragm passively elongates as

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Fig. 6.19 Upper gastrointestinal series shows orally administered barium filling a sac-like structure extending from the distal second to the proximal third portion of the duodenum, surrounded by a narrow radiolucent line [78]

a result of continual peristalsis to form the wind sock configuration of an intraluminal duodenal diverticulum. Because of the thin radiolucent stripe surrounding the diverticulum, the appearance on an upper gastrointestinal series has also been described as the halo sign (Fig. 6.19). Discussion  The “wind sock” sign refers to the pathognomonic appearance of an intraluminal duodenal diverticulum [76]. An intraluminal duodenal diverticulum is a rare developmental anomaly usually within the second portion of duodenum. Most cases originate near the ampulla of Vater and lie in an isoperistaltic direction. Attachment of the diverticulum to the duodenum usually involves less than one half of the wall circumference, although in a few cases to the entire circumference also has been reported. When the diverticulum is attached to the entire circumference of the duodenal wall, an aperture or fenestra located either centrally or peripherally may allow the distal passage of duodenal contents. It has a characteristic radiographic appearance on contrast studies, resembling a “wind sock web” or “thumb of a glove” [77]. Intraluminal duodenal diverticula are rare congenital abnormalities, thought to arise from improper recanalization of the foregut lumen during the seventh week of

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embryogenesis. This anomaly results in an intraluminal mucosal web which, with repetitive peristalsis, can elongate over time to form a featureless intraluminal cul de sac. These structures typically reach 2 to 4 cm in length and arise from the second portion of the duodenum near Vater’s ampulla. On upper gastrointestinal series, administered barium fills the sac-like diverticulum, which appears “blown” into the duodenal lumen, mimicking the configuration of a wind sock. A radiolucent stripe, representing the mucosal web, separates contrast within the diverticulum from contrast in the true duodenal lumen, an appearance described as the “halo” sign [78]. Although the “wind sock” description is derived from the findings on upper gastrointestinal series, intraluminal duodenal diverticula have also been diagnosed by ultrasound and CT. Findings similar to those observed on upper gastrointestinal series can be seen on CT with oral contrast material or when the diverticulum is distended with debris. A collapsed diverticulum on CT can mimic an intraluminal mass or appear as a subtle low-density flap [78]. Patients with an intraluminal duodenal diverticulum can present in childhood, but more typically in the ages of 30 to 40 years. There is wide variation in clinical presentation, ranging from dull postprandial epigastric pain to diverticular ulceration and hemorrhage. The close relationship of the diverticulum to the ampulla of Vater has been associated with an increased incidence of pancreatitis. Treatment traditionally consists of surgical excision, with endoscopic incision advocated by some. Given the nonspecific clinical presentation of this entity, radiologists should be familiar with the imaging appearance of this congenital abnormality, as they could be the first to suggest the diagnosis [78]. It is quite important to know the duodenal wind sock sign, the characteristic manifestation of intraluminal duodenal diverticulum.

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shows the inner wall, the pneumoperitoneum can display the outer wall of the gastrointestinal tract. The Rigler sign is an indication of free air enclosed within the peritoneal cavity (pneumoperitoneum), imprinting a visible pattern on abdominal plain radiograph in supine. Other name: double-wall sign. Explanation Gas normally outlines only the luminal surface of the bowel wall and not the serosal surface, which has a degree of opacity resembling that of adjacent peritoneal contents. However, when there is appropriate amount of free gas in the abdominal cavity, this free air is more likely to accumulate between bowel loops, thus permitting visualization of the outer walls of the bowel: this is the classic appearance of Rigler sign. When the intestinal cavity is filled with fluid, the inner wall is invisible, and only the lateral wall is visible, it shows an atypical double-wall sign (Fig. 6.20).

6.23 Rigler Sign Feature On the supine position abdominal radiography, although the gas in the gastrointestinal tract

Fig. 6.20  Abdominal supine radiograph shows air in both sides of the bowel wall (Rigler sign) (white arrows). Both sides of the bowel wall are visualized; the wall appears as a white linear stripe

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Discussion The double-wall sign was first proposed and described by Rigler in 1941 [79]. At present, most literature reports are named after the Rigler sign [80]. The emergence of pneumoperitoneum often indicates the severity of the lesion, which should be receive attention in emergency surgical observation. Therefore, it is very important to recognize its regular abdominal X-ray finding. There are four etiological categories of pneumoperitoneum: iatrogenic, spontaneous, traumatic, and miscellaneous, and these may also be female genital tract related (douching, sexual intercourse, insufflation). A wide range of clinical symptoms of pneumoperitoneum are possible, or there may be no symptoms at all, or there may be marked peritoneal signs. Often, a careful history can elucidate the cause [80]. This sign presents because of the separation between free air and intraluminal by the intestinal wall, marking the air radiolucency and radiopacity of the wall; both serosal and luminal surfaces of bowel are then visible [81]. Orthostatic chest radiography is the best choice to detect a small amount of free gas in peritoneal cavity, on which the free gas in the lower diaphragm can be shown. For patients who cannot stand, an alternative is to lie on the left side. The results showed that the free gas in peritoneal cavity less than 1 ml could be found in the quality lateral position radiography as the orthostatic chest radiography. CT can detect 1 ml free gas and help confirm suspicious pneumoperitoneum on plain film. However, infants or ICU patients often can only undergo supine position abdominal radiography. In this case, it is important to recognize the Rigler sign. It is not uncommon to have performance similar to the double-wall sign. It is necessary to distinguish the true positive Rigler sign from the false-­ positive Rigler sign without pneumoperitoneum sign. The double-wall sign can sometimes be disturbed by the adjacent intestinal loops. Therefore, the contour of adjacent intestinal loops can also appear inside the loops, leading to misdiagnosis as free gas. A few residual contrast media covering the inner surface of the intestinal cavity can also increase the density of the intestinal wall and

form false Rigler sign. Equivocal appearance of Rigler sign may be clarified using erect or lateral decubitus radiograph and CT [82]. In conclusion, pneumoperitoneum often indicates potential serious intraperitoneal diseases. Critical patients often only can take decubitus position abdominal radiography. Discovering free gas in decubitus position abdominal radiography can provide important treatment information by recognizing the Rigler sign [83].

6.24 Football Sign Feature On supine abdominal X-ray plain film, a large oval translucent image resembling a football can be seen. Other name: rugby sign. Explanation Football sign is more common in infants with pneumoperitoneum caused by spontaneous or iatrogenic gastrointestinal perforation. The long axis of the ball is from the head to the tail. The diaphragm and the bottom of the pelvis form two ends of the ball, which are obtuse and circular. The oval translucent shadow represents a large amount of gas in the peritoneal cavity, which expands and expands the peritoneal cavity. In supine position, these free gases accumulate between the front of the abdominal viscera and the peritoneum of the wall of the anterior abdominal wall, creating a football-like appearance. Some believed that the structure of the anterior abdominal wall is a necessary part of the football sign and have described it as the suture or ribbon of the football [84] (Fig. 6.21). Discussion Pneumoperitoneum is caused by the rupture of the hollow viscus including stomach, small bowel, and large bowel, except those portions that are retroperitoneal in the duodenum and colon. When enough free gas is gathered in the abdominal cavity, the football sign can appear on supine abdominal plain film. Pneumoperitoneum with enough free gas is more common in infants or newborns than in adults or adolescents, which

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Fig. 6.21  Anteroposterior radiograph of a neonate shows a large radiolucency resembling the shape of an American football. This sign represents an extensive pneumoperitoneum, which is demarcated by the parietal peritoneal reflections

may be caused by the timely and conscious ­consultation of adults with gastrointestinal perforation symptoms and early treatment. In adults, pneumoperitoneum may not be enough to show football sign sometimes, but the same amount of gas can be shown in infants. Only 2% of adult patients with pneumoperitoneum found by X-ray have football sign, but there are no exact statistics in the literature about football sign in infants. The causes of pneumoperitoneum are numerous, ranging from iatrogenic and benign causes to more life-threatening conditions [85]. Other causes include necrotizing enterocolitis, colonic obstruction (such as intestinal malrotation, meconium intestinal obstruction, digestive tract atresia, etc.), and inflammation caused by gastric and duodenal ulcers. In the absence of a benign cause of pneumoperitoneum, the identification of free intraperitoneal gas usually indicates the need for emergency surgery to repair a perforated bowel. The large oval translucent area seen on the supine abdominal X-ray film resembles rugby and represents a large amount of gas accumulated in the peritoneal cavity, which is called football sign. In most cases, infants with rugby syndrome

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can be diagnosed as gastrointestinal perforation without further imaging. In a few cases, when only a small amount of gas is located outside the intestinal cavity, there is no football sign. It may only be seen on both sides of the intestinal wall or in a local light transmission area. The lateral position or lateral projection is needed for further diagnosis. The appearance of falciform ligament sign may be delineated by the presence of these gases, which shows a long blurred linear shadow located longitudinally in the right upper abdomen [86]. Similarly, the shape of the umbilical ligament or lateral umbilical ligament can also be foiled by a large amount of gas, which shows a blurred longitudinal linear shadow in the mid- or mid-lower abdomen. The plain film is the primary diagnostic tool for detecting pneumoperitoneum: multiple signs of free intraperitoneal air can be found especially on supine abdominal radiographs. CT has been shown to be more sensitive than radiographs for the detection of free intraperitoneal air. It is quite important for the radiologist be familiar with the signs of pneumoperitoneum on radiographs and CT [87].

6.25 Dependent Viscera Sign Feature The dependent viscera sign is seen at supine CT in the thoracoabdominal area. The viscera (i.e., the bowel or solid organs) are positioned against the posterior ribs, with obliteration of the posterior costophrenic recess. Explanation The dependent viscera sign is seen with diaphragmatic rupture. The absence of posterior support by the diaphragm allows viscera to “fall” against the posterior ribs to a dependent position. On the right side, the upper one third of the liver typically does not abut the posterior chest wall (i.e., the right ribs) when the diaphragm is intact. On the left side, the stomach and bowel lie anterior to the spleen and generally do not abut the left ribs when the diaphragm is intact. Therefore, the dependent viscera sign is said to be present on the right side if the upper one third of the liver

J. Chen et al.

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a

b

c

Fig. 6.22 (a) Axial abdominal CT scan demonstrates dependent viscera sign in a patient with proven diaphragmatic rupture. (b, c) MPR demonstrates the collar sign (or hourglass sign)

abuts the posterior ribs and on the left side if the stomach or bowel abuts the posterior ribs or lies posterior to the spleen (Fig. 6.22). Discussion Bergin et  al. [88] first described the dependent viscera sign in diaphragmatic rupture in 2001. The dependent viscera sign on CT scan refers to hollow and solid organs lying in a dependent position against the posterior thoracic wall, with obliteration of the posterior costophrenic recess, in patients with diaphragmatic rupture. Blunt abdominal trauma usually is the cause, and it can involve either hemidiaphragm [89]. Most diaphragmatic ruptures are longer than 10  cm and occur in the posterolateral aspect of the hemidiaphragm; this site is structurally weak because of its embryologic origin from the pleuroperitoneal membrane. In healthy patients, CT images obtained at the level of the right hemidiaphragm show the liver suspended anteriorly in the right hemithorax. The position of the liver in the anterior hemithorax creates a deep posterior costophrenic sulcus, and the lung separates the upper one third or more of the liver from the posterior chest wall. In patients with right-sided diaphragmatic rupture, the deep posterior costophrenic sulcus is obliterated, and the upper one third or more of the liver lies dependent on the posterior chest wall. In patients with rupture of the left hemidiaphragm, the left costophrenic sulcus is obliterated, and the bowel, spleen, or kidneys lie dependent on the posterior ribs [88]. Although visceral herniation was detected at CT in 60% of patients with diaphragmatic rupture, the dependent viscera sign was observed on

the scans in 90% of patients. This result suggests that the dependent viscera sign may be an early indicator of diaphragmatic tear before visceral herniation can be confidently diagnosed using cross-sectional imaging, likely reflecting the fact that the sign is dependent on the absence of posterior diaphragmatic support rather than on frank visceral herniation [88]. CT often allows the direct depiction of diaphragmatic lesions as segmental defects; other direct signs of blunt diaphragmatic lesions (BDL) are diaphragm nonvisualization, dangling diaphragm sign, and diaphragm thickening. Many different indirect signs have also been associated with BDL, such as intrathoracic viscera herniation, dependent viscera sign, collar sign, and hump and band sign [90]. The dependent viscera sign is up to 100% sensitivity as a sign of diaphragmatic rupture and 83% sensitivity for right-sided injury. Intrathoracic herniation of the abdominal contents is 32–64% sensitive for diaphragmatic rupture and represents a late feature of this condition. Also, diaphragmatic discontinuity is 71–80% sensitive for rupture. In 6% of the general population, discontinuity is a normal variant and is seen more commonly in older patients, in women, and in those with emphysema. The collar sign is seen when the diaphragm constricts the herniated bowel or solid organs in a waist-like manner. The collar sign is 67% sensitivity for left-sided rupture and 50% sensitivity for right-sided rupture when sagittal and coronal reformats are used [91]. Various imaging modalities including chest radiograph, ultrasonography, CT, and MRI have been used in the diagnosis of diaphragmatic rupture. CT is the first-choice modality in detecting

6  Gastrointestinal Tract

diaphragmatic injury, as well as in detecting the associated injuries of chest, abdomen, ribs, and bones in these polytrauma patients [92].

6.26 Northern Exposure Sign Feature In supine position, the sigmoid colon, which was obviously dilated on abdominal X-ray, rose to the upper edge of the abdomen and was located above the transverse colon. Explanation When the patient is supine, intraluminal gas tends to accumulate in the transverse colon, the most ventral segment of the large intestine. The transverse colon crosses the midline, with its suspending mesentery separating the greater peritoneal cavity into supra- and infra-mesocolic hemispheres. Thus, the transverse colon may be considered the “equator” of the abdomen. Under normal circumstances, the sigmoid colon is normally confined to the “southern hemisphere,” caudad to the transverse colon (infra-mesocolic). When the apex of the sigmoid colon has migrated cephalad or “north” of the equator (supra-­ mesocolic), in cases of sigmoid volvulus, we term this sign the “northern exposure” sign [93] (Fig. 6.23). Discussion Javors et al. first described this finding in sigmoid volvulus in 1999, noting that this feature indicated sigmoid volvulus with 86% sensitivity and 100% specificity. Several reports have corroborated this hypothesis. Currently, suspected sigmoid volvulus often is evaluated with computed tomography (CT). The northern exposure sign is detectable on the CT scout view, also on CT coronal reformations [93]. Sigmoid volvulus, a form of closed-loop obstruction, results in dilatation of the involved colonic segment. In the occluded loop, the haustra are effaced as the sigmoid colon balloons upward and out from the pelvis. In doing so, the sigmoid colon ascends in the anterior abdomen to become situated ventral and rostral to the transverse colon. In either a dynamic dis-

269

tention (ileus) or simple obstruction of the left colon, the dilatation of the colon is more diffuse. In these circumstances, the pressure that develops within the sigmoid lumen is probably inadequate to force the sigmoid colon to relocate anterior to the less markedly distended transverse colon. Hence, there is an underlying anatomic and physiological basis for the northern exposure sign [94]. A small-bowel volvulus or other closed-loop obstruction of the small bowel can often be differentiated from a sigmoid volvulus by the large amounts of retained fluid within the involved jejunum or ileum. A cecal volvulus is distinguished by its origin and position outside the pelvis, the retention of one or two plicae in the distended lumen, and the usual absence of gaseous dilatation in both the small bowel proximal to the twist and the large bowel distal to the point of obstruction. In the absence of concomitant gas-filled dilatation of the small bowel, a diffuse dynamic distention of the colon (11  cm) can sometimes be mistaken for sigmoid volvulus.

Fig. 6.23  CT scout view of a patient with sigmoid volvulus shows the apex of the sigmoid colon (arrowheads) cephalad to the transverse colon (star) [93]

270

Atony of the sigmoid loop results in a wide tubular lucency emanating from the pelvis. Nevertheless, no matter how dilated the unobstructed sigmoid colon may become, it does not extend above the transverse colon. Therefore, the northern exposure sign would not be present in an atonic large bowel [94]. CT of patients with sigmoid volvulus shows a spectrum of findings that can be approached with the use of established and novel imaging signs but also shows that indeterminate features can be present in one fourth of patients. The need to assess for multiple imaging signs is supported by the relatively low sensitivity of several findings that have been generally assumed to be sensitive (e.g., the whirl sign and the northern exposure sign). CT signs are ineffective for prediction of the presence of pathologically proven ischemia until there is frank bowel necrosis [95].

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272 68. O'Sullivan SG.  The accordion sign. Radiology. 1998;206(1):177–8. 69. Singh D, Chawla A.  The "accordion sign". Abdom Radiol (NY). 2016;41(11):2285–6. 70. Kawamoto S, Horton KM, Fishman EK.  Pseudomembranous colitis: spectrum of imaging findings with clinical and pathologic correlation. Radiographics. 1999;19(4):887–97. 71. Macari M, Balthazar EJ, Megibow AJ.  The accordion sign at CT: a nonspecific finding in patients with colonic edema. Radiology. 1999;211(3):743–6. 72. Fishman EK, Kavuru M, Jones B, et  al. Pseudomembranous colitis: CT evaluation of 26 cases. Radiology. 1991;180(1):57–60. 73. Roche CJ, O'Keeffe DP, Lee WK, Duddalwar VA, Torreggiani WC, Curtis JM.  Selections from the buffet of food signs in radiology. Radiographics. 2002;22(6):1369–84. 74. Fonseca EKUN, Tridente CF, Ogawa RE, Yamauchi FI, Baroni RH. Apple core sign in colorectal cancer. Abdom Radiol (NY). 2017;42(7):2001–2. 75. Kajihara Y. The apple-core sign of an ileocecal carcinoma. QJM. 2019;112(3):229. 76. Materne R. The duodenal wind sock sign. Radiology. 2001;218(3):749–50. 77. Kapuria D, Jonnalagadda S.  The "windsock sign": intraluminal duodenal diverticulum. Clin Gastroenterol Hepatol. 2016;14(8):e93–4. 78. Pendergrast TE, Dyer RB.  The "windsock" sign. Abdom Radiol (NY). 2018;43(3):751–2. 79. Rigler LG.  Spontaneous pneumoperitoneum: a roentgenologic sign found in the supine position. Radiology. 1941;37(5):604–7. 80. Ly JQ.  The Rigler sign. Radiology. 2003;228(3):706–7. 81. Lewicki AM.  The Rigler sign and Leo G.  Rigler. Radiology. 2004;233(1):7–12. 82. Indiran V, Sivakumar V.  Rigler sign. Abdom Radiol (NY). 2017;42(10):2588. 83. Markogiannakis H, Fili K, Spaniolas K, Bizimi V, Katsiva V, Theodorou D.  Rigler sign: an underappreciated alert for pneumoperitoneum. Am J Surg. 2008;196(3):e5–6. 84. Alshahrani MA, Aloufi FF, Alabdulkarim FM, Nadrah AH. The football sign. Abdom Radiol (NY). 2017;42(11):2769–71. 85. Rampton JW.  The football sign. Radiology. 2004;231(1):81–2. 86. Chou PC, Su YJ. Falciform ligament sign. N Engl J Med. 2017;377(20):e28. 87. Pinto A, Miele V, Schillirò ML, et  al. Spectrum of signs of Pneumoperitoneum. Semin Ultrasound CT MR. 2016;37(1):3–9. 88. Bergin D, Ennis R, Keogh C, Fenlon HM, Murray JG.  The "dependent viscera" sign in CT diagnosis

J. Chen et al. of blunt traumatic diaphragmatic rupture. AJR Am J Roentgenol. 2001;177(5):1137–40. 89. Meuriot F, Badet N, Delabrousse E.  Classics in abdominal imaging: the dependent viscera sign. Abdom Radiol (NY). 2017;42(4):1285–6. 90. Bonatti M, Lombardo F, Vezzali N, Zamboni GA, Bonatti G.  Blunt diaphragmatic lesions: imaging findings and pitfalls. World J Radiol. 2016;8(10):819–28. 91. Cantwell CP. The dependent viscera sign. Radiology. 2006;238(2):752–3. 92. Panda A, Kumar A, Gamanagatti S, Patil A, Kumar S, Gupta A. Traumatic diaphragmatic injury: a review of CT signs and the difference between blunt and penetrating injury. Diagn Interv Radiol. 2014;20(2):121–8. 93. Lubrano J, Fohlen A, Delabrousse E.  The northern exposure sign. Abdom Radiol (NY). 2017;42(3):971–2. 94. Javors BR, Baker SR, Miller JA. The northern exposure sign: a newly described finding in sigmoid volvulus. AJR Am J Roentgenol. 1999;173(3):571–4. 95. Levsky JM, Den EI, DuBrow RA, Wolf EL, Rozenblit AM.  CT findings of sigmoid volvulus. AJR Am J Roentgenol. 2010;194(1):136–43.

Suggested Readings for this Chapter Erturk SM, Mortelé KJ, Oliva MR, Barish MA. State-of-­ the-art computed tomographic and magnetic resonance imaging of the gastrointestinal system. Gastrointest Endosc Clin N Am. 2005;15(3):581–x. McSweeney SE, O'Donoghue PM, Jhaveri K.  Current and emerging techniques in gastrointestinal imaging. J Postgrad Med. 2010;56(2):109–16. Pickhardt PJ.  Gastrointestinal Imaging: Rapid Advancements Leading to Improved Patient Care. Gastroenterol Clin North Am. 2018;47(3):xv–xvii. Robinson C, Punwani S, Taylor S.  Imaging the gastrointestinal tract in 2008. Clin Med (Lond). 2009;9(6):609–12. Romero M, Buxbaum JL, Palmer SL. Magnetic resonance imaging of the gut: a primer for the luminal gastroenterologist. Am J Gastroenterol. 2014;109(4):497–510. Schooler GR, Davis JT, Lee EY.  Gastrointestinal Tract Perforation in the Newborn and Child: Imaging Assessment. Semin Ultrasound CT MR. 2016;37(1):54–65. Shin D, Rahimi H, Haroon S, et  al. Imaging of Gastrointestinal Tract Perforation. Radiol Clin North Am. 2020;58(1):19–44. Tkacz JN, Anderson SA, Soto J.  MR imaging in gastrointestinal emergencies. Radiographics. 2009;29(6):1767–80.

7

Peritoneum and Pelvis Pinggui Lei, Bin Huang, and Hui Yu

Contents

7.1

7.1 Sentinel Clot Sign

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7.2 Concentric Ring Sign

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7.3 Onion Skin Appearance

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7.4 Hyperintense Rim Sign

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7.5 Floating Aorta Sign

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7.6 Sandwich Sign

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7.7 Spongiform Gas Bubbles

 280

7.8 Floating Ball Sign

 281

7.9 Shading Sign

 282

7.10 Ovarian Vascular Pedicle Sign

 283

7.11 Bridging Vascular Sign

 284

7.12 Double Peak Sign

 286

7.13 Spur Sign

 287

References

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Sentinel Clot Sign

Feature This sign is a computed tomography (CT) sign of acute injury from an abdominal organ, which manifests as a high-attenuation blood clot near

P. Lei (*) · B. Huang · H. Yu Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6_7

the abdominal organs such as liver, spleen, intestine, and mesentery with postcontrast CT value greater than 60 HU. Explanation In the early stage of injury, change of the solid organ attenuation may not be obvious. The sentinel clot sign is formed by the blood flowing into the subcapsular or extracapsular region through the site of the leakage. Intraabdominal 273

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a

b

Fig. 7.1 (a) Plain CT shows hyperattenuation surrounding the spleen, called the sentinel clot sign. (b) Another trauma patient with this sign on noncontrast CT

h­ emorrhage is more commonly detected in the adjacent region of the injured organ, which is related to local coagulation when the blood overflows the vessel (Fig. 7.1). Discussion Orwig et al. first reported the sentinel clot sign in 1989 [1]. On noncontrast CT, the high-­attenuation hematoma appears at the position closest to the bleeding organ, and the CT value is greater than 60 HU, which is a reliable sign of the adjacent organ injury. This sign suggests severe damage to the abdominal organs. In the early stage of the abdominal organ injury, the attenuation change of the solid organ usually is not obvious. It is only manifested as a hematoma formed by the blood flowing into the subcapsular or extracapsular region through the site of the breakage. The intraabdominal hemorrhage is more common in the adjacent part of the injured organ, as is related to local coagulation after the blood overflows the blood vessel. Hematoperitoneum often occurs in patients with severe abdominal injuries and is a common sign of abdominal visceral injury. There is a characteristic distribution of hemorrhage in the abdomen, depending on the amount of blood and the location and time of bleeding. Peritoneal hemorrhage is often located near the source of bleeding and flows into the pelvis along the common peritoneal effusion pathway. CT is widely accepted as the first-line choice for assessing visceral injuries and determining

treatment options, which has been approved to be most accurate for the diagnosis of abdominal visceral injuries. The value of CT attenuation helps for the identification of simple ascites, nonclotting blood, hematoma, bile, urine, chylorrhea, and active bleeding caused by recent bleeding. The sentinel clot sign is a reliable sign of adjacent organ damage. Especially for spleen, intestine, and mesentery damage, 9% of spleen injury, and 32% of intestinal and mesenteric injuries, the sentinel clot sign is the only positive sign. Because the direct CT signs of damage to the mesentery and hollow organs (intestines, bladder) are uncommon or are nonspecific, the sentinel clot sign is more valuable [2]. Spleen injury is the most common; the incidence of sentinel clots is 85.8%, and the incidence is relatively low in liver injury. For cases of spleen, intestine, and mesenteric injury, the sentinel clot sign can improve the diagnostic accuracy rate, and this sign is the only sign of diagnosis in 14 cases, accounting for 14.3% of the total number of cases. Sentinel clot sign is a reliable CT sign indicating the damage of adjacent abdominal organs and has important guiding significance for the clinic. However, not all patients with acute abdominal blunt trauma have sentinel clots. Because some of the damaged areas are small, the degree is light, no fluid or blood appeared in the liquid. Therefore, even if the sentinel clot sign is not observed, organ damage should not be ruled out.

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7.2

Concentric Ring Sign

Feature Abdominal hematoma with a period of more than 3 weeks can clearly show concentric ring sign on T1WI, showing iso-intensity in the center of the lesion and two concentric ring structures with distinct signal intensity around it. The inner ring is obviously the high signal and the outer ring is the low signal.

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effects of hemoglobin degradation to methemoglobin. The short T1-weighted image from cells can form a high signal loop, but macrophage cells around the hematoma devour the hemosiderin to cause the edge ring of the hematoma (Fig. 7.2).

Explanation Concentric ring sign can be seen in chronic hematoma of the abdomen caused by different causes. The center of the hematoma is a gelatinous blood clot surrounded by liquid, in which short T1 has been attributed to paramagnetic

Discussion Hahn et al. first proposed the concentric ring sign in 1986, in which two cases of duodenal chronic hematomas showing three concentric rings on T1WI, T2WI were described [3]. The outer layer is a regular and thin low signal ring, the middle layer is a very high signal ring, and the center is a relatively uniform equal signal region. CT has become the preferred imaging technique for evaluation of hemorrhage. The ring sign appears in abdominal hematomas at the time when the CT

Fig. 7.2  A 49-year-old man had history of left upper abdomen with an adrenal hematoma with partial rupture for more than 20 days. Iso-signal intensity was observed on T1WI, and concentric ring appearance with a dark

peripheral rim (a, white arrow) surrounding a bright ring (a, black arrow) was detected in the hematoma. The adrenal hematoma was without enhancement in arterial phase (b), portal venous phase (c), and delay phase (d)

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appearance often becomes nonspecific. Acutely hyperdense hematomas become iso-dense or hypodense as sedimented blood and fibrinous clot are reabsorbed; after 2 to 3 weeks a specific diagnosis of abdominal hematoma by CT may be impossible. In magnetic resonance imaging (MRI) diagnosis of hematoma, both the internal architecture and the temporal evolution of the lesion are important. Concentric ring sign is best recognized on T1WI. Surrounding a central core of intermediate signal are two discrete concentric rings. The inner ring is bright, indicating short T1 signal. The outer rim is dark on all pulse sequences, consistent with a short T2 signal. Our findings are consistent with studies of intracranial hematoma, in which the short T1 has been attributed to paramagnetic effects of hemoglobin degradation products such as methemoglobin. Hemosiderin digested by phagocytic cells surrounding the hematoma may account for the dark rim of short T2. The concentric ring sign in our series was a sensitive indicator of the maturing abdominal hematoma. The sign developed reliably about 3 weeks after hemorrhage and was not present earlier [3]. The ring sign on T1WI may prove to be a “tissue-specific” MR feature, arising in hematomas of more than 2 to 3 weeks of age. The ring sign may be valuable in distinguishing hematomas from other abdominal masses on fluid collections. The ring sign is common in abdominal hematomas of varying cause [4]. Some pitfalls and limitations exist in using MRI to detect and diagnose abdominal hematomas. Early in the acute period, hematomas may be iso-intense with adjacent tissue on T1WI. The differential diagnosis of abdominal chronic hematoma mainly includes a solid abdominal mass and a liquid accumulation area (e.g., pancreatic pseudocyst around); the latter two often have fat and a bag around, so that is characterized by a high signal on T1WI. But the high signal of the ring is the same in strength as the s­ ubcutaneous fat and the lack of peripheral low signal rings. Chronic abdominal hematoma on T1WI, like the bright high signal, is higher than fat tissue, which is formed more easily to identify with peripheral low signal loop. Hemorrhage in the tumor necro-

sis area and internal hemorrhage after tumor biopsy can also present as a bright spherical or strip-like high signal in a T1WI image. It is easy to distinguish that neither presents as ring sign. In the diagnosis of adrenal tumors, the concentric ring sign is an important differential finding to confirm adrenal hemorrhage or hematoma. One should be aware that short-term MRI follow-up is needed [5].

7.3

Onion Skin Appearance

Feature On abdomen CT scan, the spleen, kidney, and other visceral organs increased significantly. Under the subcapsular, there are slit-like highand low-density shadows, blurred interspaces with the surrounding tissues, with an onion skin appearance. Explanation Onion skin appearance is a CT sign of abdominal parenchymal organ contusion and subcapsular hemorrhage, which is generally chronic repeated hemorrhage after blunt contusion, resulting in blood deposition and stratification (Fig. 7.3). Discussion Spleen is the most common organ to be injured and the most common surgery performed is sple-

Fig. 7.3  A 53-year-old male patient underwent routine examination after an accident. Abdominal CT showed an enlarged spleen with uneven density and slit-like highand low-density shadows

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nectomy. The most common extraabdominal injury is rib fracture, with mortality rate of 4%. Wound sepsis was the most common complication [6]. Owing to the current trend toward a more conservative approach to injury, there has been an increased emphasis on identifying, staging, and follow-up in imaging of splenic trauma. Dynamic contrast-enhanced CT scanning is very sensitive (95%) for the detection of splenic injuries. The subcapsular hematoma is a peripheral, welldefined, lenticular, relatively low-­ attenuation mass that displaces the splenic parenchyma inwardly. Rarely, an intrasplenic contusion or hematoma can be a small, irregular, low-­ attenuation mass within the splenic parenchyma. The splenic laceration is seen as a cleft, usually with irregular borders, extending through the capsule into the parenchyma. It is associated with peri-splenic or intraabdominal fluid. The laceration traversing two capsular surfaces is designated a fracture. Repeated episodes of bleeding may lead to a peri-splenic clot with an onion-skin appearance [7]. In addition, the presence of active hemorrhage and/or contained vascular injuries (pseudoaneurysms and arteriovenous fistulae) increases the risk of failed nonsurgical management. Active hemorrhage is identified as a contrast material blush or focal area of hyperattenuation in or emanating from the injured splenic parenchyma. In contradistinction to a contained vascular injury in which the initially identified contrast material blush is seen to wash out on subsequent a

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delayed-phase images, the hyperattenuation of active hemorrhage persists and grows larger with time on a delayed-phase study. Thus, delayedphase image acquisition is useful for definitive characterization of vascular splenic injury as active hemorrhage or contained vascular injury. Recently, a CT-based scale system that includes vascular injuries and active bleeding as part of the grading criteria has been proposed to improve the accuracy of predicting the need for intervention, as compared with the traditional AAST scale. Not all vascular injuries of the spleen are identified on the combination of portal venous and delayedphase images; some advocate routine acquisition of an additional arterial phase series during abdominal CT. Arterial phase imaging in abdominal trauma warrants further study [8].

7.4

Hyperintense Rim Sign

Feature On fat suppression of MRI, ring-like hyperintensity appears at the edge of an adrenal mass. Explanation Hyperintense rim sign is a characteristic sign of adrenal adenoma. Hyperintense rim sign is helpful to distinguish adrenal adenoma from metastasis. This sign may be related to the envelope of the tumor or the squeezing of normal adrenal tissue (Fig. 7.4). b

Fig. 7.4 (a) T1WI shows left adrenal mass with signal intensity consistent with the liver. (b) Enhanced scan shows high signal edge sign

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Discussion An adrenal adenoma is the most common benign adrenal tumor. With the development of imaging technology, the detection rate of adrenal lesions is becoming higher and higher, but the qualitative diagnosis is still difficult. The adrenal gland itself is significantly contrasted with the surrounding high-signal fat capsule and is clearly visualized on MRI.  An adrenal adenoma is rich in lipids. The section of adrenal adenoma is golden yellow; it consists of clear cells and granular cells, mainly clear cells. Adrenal nodules or masses appear on MR images. The signal on T1WI is similar to that on the liver. Most of the signals on T2WI are equal to that of the liver, and a few are higher than that of liver or even high signal [9]. Chemical shift imaging is important in the diagnosis of adrenal adenoma. This difference increases with the increase of field strength. The in-phase image is normal T1WI, and the anti-phase image is characterized by obvious attenuation of tissue signals mixed with water and fat, whereas the signals of pure adipose tissue and pure water tissue are not attenuated significantly. An adrenal adenoma contains a certain amount of fat, and there is a characteristic signal reduction on the antiphase image. Hyperintense rim sign is a characteristic sign of adrenal adenoma. If this sign is found in adrenal lesions and the signal of tumors is decreased on out-of-phase images, the lesions are a

slightly and moderately enhanced in the early stage. Dynamic contrast enhancement is helpful in the diagnosis of adrenal adenomas. Most of the adenomas show early mild or moderate enhancement and rapid clearance, which has a certain significance in differentiating adenomas from nonadenomas. However, a recent meta-analysis demonstrated that, despite routine use of imaging assessment for adrenal masses, there was insufficient evidence of diagnostic value in distinguishing a benign mass from malignancy [10].

7.5

Floating Aorta Sign

Feature On abdominal CT, the abdominal aorta is embedded in the lymph nodes, which fuse together to form a mass that is better shown on contrast CT. When lymph nodes are enlarged to a considerable extent, the large vessels can move forward, and the large blood vessels are floating in the mass, which is called a floating aorta sign. Explanation The retroperitoneal enlarged lymph nodes often fuse into masses at a later stage. The abdominal aorta, celiac trunk, inferior vena cava, or superior mesenteric artery are obviously removed and embedded (Fig. 7.5). b

Fig. 7.5 (a) A 61-year-old female patient with non-­ aorta and involving the right renal and ureter, leading to Hodgkin’s lymphoma. On abdominal contrast CT, a soft hydronephrosis. (b) Another patient with malignancy attenuation mass is seen in the paraaortic space. The atten- shows floating aorta sign on postcontrast CT uation is homogeneous, slightly enhanced, enclosing the

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Discussion Retroperitoneal lymphoma is a rare retroperitoneal malignant tumor. It can be either primary or part of lymphoma disease. Histologically, it is divided into two categories: Hodgkin’s lymphoma and non-Hodgkin’s lymphoma. It is more common in young and middle-aged patients and more common in women. The Hodgkin’s lymphomas rarely occur in children younger than 5  years, but the non-Hodgkin’s lymphomas frequently affect children younger than 5  years. Patients may complain of abdominal discomfort, pain, palpable mass, and other symptoms [11]. Retroperitoneal lymphoma is most likely to invade the anterior aortic lymph node and left aortic lymph node, followed by right aortic lymph node and posterior aortic lymph node. Lymphomas rarely invade a single group of lymph nodes. CT findings. (1) Solitary enlarged lymph nodes can be seen beside the aorta. The plain scan can clearly show enlarged lymph nodes, which are nodular or irregular, with irregular edges and inhomogeneous attenuation. The diameter of lymph node larger than 1.5 cm indicates enlargement, and more than 2 cm can confirm enlargement. Lymphoma is characterized by huge masses, most lymphomas being larger than 5  cm. After contrast enhancement, the lesion shows mild to middle enhancement. (2) The lymph nodes fuse into a mass with a large soft tissue attenuation mass, with necrosis in the center, and the fat angle of the blood vessels disappears after the aorta and vena cava. The abdominal aorta, celiac trunk, inferior vena cava, or superior mesenteric artery are obviously removed and embedded. The enlarged lymph nodes cross the midline and fuse into a mass, showing a typical abdominal aortic inundation sign or vascular embedding sign [12]. When lymph nodes are enlarged to a considerable extent, the large vessels can move forward, and the floating aorta sign appears. (3) Adjacent organs such as liver and pancreas are displaced and metastasized. On magnetic resonance imaging (MRI), lymph nodes are typically iso-intense to muscle on T1WI, iso- or hyperintense on T2WI with moderately homogeneous or patchy enhancement [13].

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The floating aorta sign is an important sign for the identification of retroperitoneal lymphoma and other lymph node diseases.

7.6

Sandwich Sign

Feature On abdominal CT, mesenteric fat and blood vessels are the “sandwich filling.” The “bread” on the upper and lower sides is made up of a soft tissue shadow of homogeneous attenuation, which is shaped like a sandwich. Explanation On CT, mesenteric fat and blood vessels resemble fillings in the middle of a sandwich, and the enlargement of the mesenteric lymph nodes is similar to the two slices of bread. After injecting the contrast medium, the structure of mesenteric vessels is significantly enhanced more than the fat, thus making the “sandwich filling” more prominent (Fig. 7.6). Discussion Sandwich sign refers to a sandwich-like image of a giant hyperplastic mesenteric lymph node that surrounds the mesenteric fat and blood vessels [14]. There are many causes of mesenteric lymph node enlargement. In addition to lymphoma, cancer, sar-

Fig. 7.6  Patient with mesenteric lymphoma. On postcontrast CT, an oval and long strip increased attenuation shadow can be seen on the left side, but the boundary is not clear. Visible mesenteric vessels and fat were encapsulated in both lesions, forming the sandwich sign

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coma, carcinoid, acquired immunodeficiency-­ associated lymph node hyperplasia syndrome, tuberculosis, intestinal fat metabolism disorder (Whipple disease), and inflammatory bowel disease are also the most common causes. Carcinomas, sarcomas, and carcinoid can originate from the small intestine and then spread to the mesenteric lymph nodes. These tumors invade the intestinal wall and cause perforation, hemorrhage, and lesions that diffuse rapidly. Infectious and inflammatory lesions usually do not cause massive lymph node enlargement. It usually manifested as central necrosis, surrounded by ring enhancement, which is similar to tuberculosis. Therefore, these tumors, or infectious Fig. 7.7  CT imaging of gossypiboma misdiagnosed as and inflammatory lesions, do not present the sand- intraabdominal mass wich sign. The sandwich sign is more common in mesenteric lymphoma, because only in the mesen- Explanation teric lymphoma can the lymph nodes grow very The remaining intraperitoneal mass is covered large and surround the fat, intestines, and blood ves- and adhered by the omentum and adjacent intessels without any clinical symptoms [14]. The mes- tinal tubes. At the early stage, there were more enteric lymphoma occasionally invades the serous bubbles inside without the surrounding envelope. and muscle layer; sometimes it causes small intesti- With time, the bubbles inside the mass gradually nal bleeding but it rarely causes free perforation. decreased, then disappeared, and the surrounding The mesenteric lymphoma can also cause retroperi- envelope gradually changed from incomplete to toneal lymph node enlargement. Most mesenteric complete (Fig. 7.7). lymphomas are non-Hodgkin’s lymphoma (NHL), and approximately 30% to 50% of patients with Discussion NHL have the mesenteric nodal disease [15]. Numerous reports about gossypiboma have been Immune dysfunction is a risk factor for NHL. The published since it was described by Wilson in sandwich sign also can be seen in posttransplant 1884 [16]. The term gossypiboma is derived from lymphoproliferative disorders (PTLD). NHL can- the Latin word gossypium, meaning cotton, and not be distinguished from the PTLD on morpho- the Kiswahili word boma, meaning place of conlogical grounds, as both conditions are caused by cealment. Gossypiboma is an uncommon surgithe Epstein–Barr virus. For patients without a his- cal complication with an estimated incidence of tory of transplantation, NHL is the main cause of 1  in 1500. Gossypibomas are most frequently sandwich signs; in patients with a history of trans- discovered in the abdomen. However, occurplantation, the cause of the sandwich sign may be rences in the thorax, extremities, central nervous PTLD.  As an increasing number of patients are system, and breast have also been reported. undergoing transplantation, the sandwich sign may Pathologically, there are two types of foreign-­ become more common in clinical practice. body reactions in gossypibomas. One is an aseptic fibrous response resulting in adhesion, encapsulation, and granuloma, and the other is an 7.7 Spongiform Gas Bubbles exudative reaction leading to cyst or abscess formation [17]. Feature Imaging methods such as plain X-ray, mediThere are many different sizes of bubble gas density cal sonography (USG), CT, MRI, and endoscopy shadows in the abdominal gossypiboma on CT scans, are usually helpful in the diagnosis. Basically, a which show the modifications of honeycombs. “whorl-like” mass imaging on plain X-ray,

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imaging of a hyperechogenic mass with the hypoechoic rim on USG, or a rounded mass with a dense central part and enhancing wall on CT are the basic signs of gossypiboma. CT seems to be the first diagnostic modality to rule out other conditions. MRI can be confusing because the radiopaque marker is not magnetic or paramagnetic [16]. CT is the best method to detect gossypiboma and its complications. CT findings have certain features. (1) Morphology and size of lesions: almost all foci are round or oval, 3–20  cm in diameter; average diameter is approximately 9 cm. (2) Periphery: the envelope is complete, composed mostly of the thin walls and a few thick walls with regular boundary. The mass may adhere to the adjacent abdominal wall and surrounding intestinal tube. The envelope can be continuously strengthened by the contrast agent. (3) Internal density: multiple bubble gas density shadows of different sizes can be seen in the mass at the early stage of a case, showing modification of a honeycomb shape, and thus called spongiform gas bubbles. “Spongiform gas bubbles” are usually observed 3 years after surgery, the characteristic CT sign of early abdominal gossypiboma. Clinical symptoms may appear in the immediate postoperative period or even after weeks, months, or years. The interval of time from the causative operation to clinical presentation has been reported to range from the first postoperative day to 43  years. Clinical presentation is strongly associated with the type of foreign-body reaction, which may manifest in various clinical

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presentations ranging from mild abdominal pain to major surgical complications including bowel or visceral perforation, obstruction, fistula formation, or sepsis, although it may remain asymptomatic for many years [16].

7.8

Floating Ball Sign

Feature Mature teratoma of the ovary can be seen on CT images as many lipoid globules floating in the cyst fluid, forming the so-called floating ball sign. Explanation Mature cystic teratoma is characterized by a cystic or cystic solid mass. Cholesterol, fat, fatty acids, and other substances in the tumors may be liquid when they are above 34° C. Many movable lipid-like globules float in the cystic fluid, forming the so-called floating ball sign (Fig. 7.8). Discussion Ovarian teratoma is a common gynecological ovarian germ cell neoplasm that originates from abnormal proliferation of multifunctional embryonic cells. It consists of two or three embryonic layers of multiple mature tissues, including skin, sebaceous glands, hair, some teeth, and nerve tissues. Mesodermal tissues such as fat can also be seen. Fatty acids and cartilage rarely have endodermal tissue. The main incidence group is women of childbearing age, 20 to 40 years old [18].

b

Fig. 7.8 (a, b) A cystic mass with fat and calcification (arrow) in the right adnexal area of the uterus forms the so-called floating ball sign

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Most of the cases have some specificity on CT, so diagnosis is not difficult. On CT, mature teratomas are mostly cystic. Adipose-dense tissues are characteristic CT findings. Cholesterol, fat, fatty acids, and other substances in tumors form many movable lipid-like globules floating in the cystic fluid, forming the floating ball sign. On MRI most of the tumors were cystic or cystic solid masses with fat components. Both T1WI and T2WI showed high signal intensity, and the signal intensity of the fat suppression sequence decreased. The latter could be differentiated from hemorrhage but still showed high signal intensity in the fat suppression sequence. Teratomas should be differentiated from other fatty tumors. Uterine fatty leiomyoma, pelvic lipoma, and retroperitoneal teratoma, all containing fat components, need to be differentiated from ovarian teratoma. The former originates from the uterus; the latter two are rare and mostly located in the retroperitoneum. Careful observation of the location of the lesion and its relationship with the uterus and ovary can avoid misdiagnosis. CT is more sensitive than MRI in displaying microadipose tissue and calcification, especially in thin-slice CT and three-dimensional reconstruction. The possibility of ovarian teratoma should be considered first if the floating ball sign is found in the uterine appendage area on CT [19].

7.9

Shading Sign

Feature Shading sign is the MRI finding of T2 shortening in an adnexal cyst that is hyperintense on T1WI. The hypointensity was initially described as either focal or diffuse; however, the most common manifestation is a complete loss of signal intensity or dependent layering with a hypointense fluid level. Explanation The precise mechanism of the shading sign is complex. Endometriotic cysts are highly viscous and have a high concentration of protein and iron from recurrent hemorrhage. All these components can shorten T2 and may contribute to signal intensity loss, described as shading. In addition, intracellular and extracellular methemoglobin markedly shorten the T1 of fluids, resulting in hyperintensity on T1WI and hypointensity (shading) on T2WI (Fig. 7.9). Discussion Historically, shading sign has been considered a distinguishing feature of endometriomas on MR imaging. First described in 1987 by Nishimura and his team, the shading sign was confirmed to be associated with endometriomas by the work of Togashi et  al. in 1991, which evaluated 374

Fig. 7.9 (a) Axial T1WI demonstrates left adnexal endometriomas with high signal intensity (white arrows). (b) Axial T2WI with the “T2 shading sign” visible (white arrow)

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female patients and concluded that a definitive diagnosis of endometrioma could be made when a cyst that was hyperintense on T1WI exhibited hypointense signal on T2WI (shading), reporting a sensitivity of 90% and a specificity of 98% [20]. The shading sign has been considered a distinguishing feature of endometriomas on MRI. However, our daily practice showed us that the same signal loss is seen in other cysts and even in cystic portions of mixed masses. To the best of our knowledge, some studies have been published regarding the diagnostic accuracy of the shading sign for endometriomas, but data in the literature are scarce concerning its patterns and false positives. During this retrospective analysis, the authors found five different shading patterns: layering, liquid–liquid level, homogeneous, heterogeneous, and focal/multifocal shading within a complex mass. First, homogeneous shading was the most prevalent pattern in endometriomas, followed by heterogeneous, layering, and liquid–liquid level. Second, all lesions with heterogeneous shading sign were endometriomas, as well as most lesions with homogeneous shading and layering shading. Third, none of the endometriomas presented with focal/multifocal shading within a complex mass. Fourth, half the cases with focal/multifocal shading within a complex mass corresponded to endometrioid carcinomas [20]. Endometriosis is an important gynecological disorder that can impact significantly on an individual’s quality of life and has major implications for fertility. Deep infiltrating endometriosis is a severe form of endometriosis that can cause obliteration of anatomical compartments. Laparoscopy remains the gold standard for diagnosis of endometriosis, although it is an invasive procedure that has the potential to be hindered by obliterative disease. Ultrasound is often the first-­ line imaging modality when endometriosis is suspected; however, MRI is more accurate in the assessment of complex disease. Preoperative MRI is highly specific in the diagnosis of endometriosis and characterization of disease extent and has a key role in guiding surgical management [21]. Patients with endometriosis usually present with one of three com-

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plaints: pelvic pain, adnexal mass, or infertility. Because endometriosis is a benign process that becomes quiescent with pregnancy or menopause, consideration of the natural history and severity of the disease, as well as age and reproductive status, is necessary when deciding on treatment. There are many treatment options such as observation, hormonal therapy, and conservative or radical surgery. Relief of symptoms may be the goal of treatment in all the protean manifestations of endometriosis [22].

7.10 Ovarian Vascular Pedicle Sign Feature Ovarian vascular pedicle sign is the direct connection of ovarian vein and pelvic mass. It is the spiral CT sign of a pelvic mass originating from the ovary. Explanation The ovary is mainly supplied by the ovarian artery and drains to the ovarian vein, which forms a vascular plexus in the broad ligament of the uterus. The broad ligament of the uterus communicates with the uterine venous plexus through the double blood supply. The ovarian vascular pedicle anatomically includes blood vessels that enter and exit the ovary and communicate with the branches of the uterine blood vessels. When the ovary appears to be occupying space, the ipsilateral ovarian blood vessels may expand. Because the gonadal vein is always in front of the psoas muscle and the common iliac vessels, a spiral CT scan can show the reflux of the ovarian vein to the ovary (Fig. 7.10). Discussion Distinguishing the pelvic mass of ovarian and nonovarian origins may help to determine the relationship between the mass and the pelvic anatomy. The location of the uterus relative to the pelvic mass may be the most helpful clue to the origin of the ovarian mass. Tumors originating from ovaries are usually located in the ovarian bed, which is usually in the anterior or anterome-

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Fig. 7.10  A 56-year-old woman with right ovarian neoplasm. CT image shows a large solid mass in venous phase (a) and delay phase (b), which is located in the pel-

vis. (b) Right ovarian vein was observed in axial CT enhanced images (white arrow)

dial part of the uterus. When the mass is large, the uterus is pushed backward or posterolateral. However, if CT shows that the lumps originating from the ovary, uterus, intestines, and retroperitoneum are large, it may be difficult to distinguish the origin of the organ from the mass. Studies have shown that multidetector computed tomography (MDCT) is highly consistent with the display of gonadal veins, and MDCT can also provide important information for determining the origin of larger pelvic masses (>8  cm) in women [23]. The ovarian suspensory ligament is an inaccurate term; here a pelvic mass can be highly suggestive of ovarian origin. The suspensory ligament is not continuous with the ovarian large blood vessels, but it is also difficult to display as a separate structure on CT so that it can be distinguished from the ovarian blood vessels that drain into it. Therefore, the ovarian vein is traced down the ventral side of the psoas muscle to the pelvic cavity, and the suspensory ligament may be found attached to the ovary or an ovarian mass, or the ovarian vein may be draining directly to the ovary or ovarian mass without visualization of the ligament. The suspensory ligaments are difficult to identify, especially when there is a very large pelvic mass. Moreover, because the fallopian tube is close to the attach-

ment point of the ovary and ovarian ligament, a mass originating from the fallopian tube is difficult to distinguish from an ovarian mass [24]. If the uterine suspensory ligament cannot be distinguished, the pelvic mass that is directly connected to the ovarian vein is most likely to originate in the ovary, or in the f­ allopian tube, or uterus, or occasionally a nongynecological mass. It was found that separation of the mass from the ipsilateral ovary suggests a nonovarian origin, but often the ovary is unclear or inconspicuous. Ultrasound (US) is the preferred method for pelvic examination in women; it is also an alternative method of examination for the uterus and attachments that cannot be evaluated well in CT. It is especially helpful to find the ipsilateral ovaries that are distinct from the pelvic mass, showing morphological changes such as hydrosalpinx, and to further evaluate the internal composition of ovarian cystic masses.

7.11 Bridging Vascular Sign Feature On color and power Doppler ultrasound and MRI of the pelvic cavity, multiple blood vessels can be seen at the interface between the uterus and the peri-uterine mass. This finding is called the

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Fig. 7.11  MRI features of subserous leiomyoma: axial T2WI (a) and axial T1WI (b). The signal of the myoma was uneven and slightly heterogeneous. A curved vascular empty structure (white arrow), the “bridge vascular sign,” is seen

bridging vascular sign. On color and power Doppler ultrasound, blood vessels appear as flow signals. On MRI, blood vessels appear as curvilinear tortuous signal voids.

relationship. In addition, the mass associated with the uterine round ligament is likely to be a uterine myoma rather than an accessory tumor. Solid ovarian masses, such as fibroids, granulosa cell tumors, germ cell tumors, metastases, and Explanation lymphomas, are similar to subserosal uterine Bridging vascular sign suggests that the peri-­ myomas and are easily confused [27]. The presuterine mass, such as subserosal uterine myomas, ence of normal ovaries is usually a clue to the originates in the uterus. The bridging vascular evaluation of the source of pelvic masses, but in sign is formed by nourishing blood vessels that postmenopausal women, normal ovaries may not originate in the uterine arteries, which supply be seen. In addition, ovarian tumors can originate large exogenous myomas (>3  cm) through the in the periphery, and normal ovaries are observed muscular layer (Fig. 7.11). in the vicinity of the tumor, so the possibility that the tumor originates from the ovary cannot be Discussion completely ruled out. The “bridging vascular sign” is a finding of color The bridging vascular sign is very important and power Doppler ultrasound and MRI of the for the diagnosis of exogenous uterine myomas pelvic cavity, which shows that multiple blood and identification of the mass of the attachment. vessels can be seen at the interface between the The nourishing blood vessels originating from uterus and the peri-uterine mass. On color and the branch of the uterine artery are located at the power Doppler ultrasound, blood vessels appear junction of the uterus and subserosal myomas as flow signals. On MRI, blood vessels appear as and can be classified according to their morpholcurvilinear tortuous signal voids [25, 26], sug- ogy and the direction of the interface. A blood gesting that the peri-uterine mass originates in vessel parallel to the interface is defined as an the uterus. Pathologically, the bridging vascular inserted blood vessel, a blood vessel crossing the sign is formed by nourishing blood vessels that interface is referred to as a crossed blood vessel, originate in the uterine arteries, which supply and a blood vessel having both these expressions large exogenous myomas (>3  cm in diameter) is defined as a mixed-blood vessel. These vessels through the muscular layer. Peri-uterine masses are seen in subserosal uterine myomas more than include subserosal myomas, accessory masses, 3  cm in diameter. The ovarian mass is directly intestinal masses, and other pelvic lesions. In supplied by the ovarian artery or the ovarian imaging, differential diagnosis depends on under- branch of the uterine artery. Therefore, these standing of the characteristics of these tumors, interfacial blood vessels are also seen when ovarincluding content, structure, and uterine serosa ian malignant tumors invade the uterus.

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7.12 Double Peak Sign

tion, wrapping and squeezing the posterior urethra in the central and transitional areas [28]. The CT diagnosis of BPH is based on the diameter measurement. The standard for the maximum diameter of the upper and lower diameter, anteroposterior diameter, and left and right diameter of the prostate of men 60 to 70 years old is listed as 50 mm, 43 mm, and 48 mm, respectively, with the upper boundary not more than 10 mm of the upper edge of the pubic symphysis. Only when the prostate as seen in the upper edge of the pubic symphysis is 20–30  mm can it be diagnosed as enlarged. Because the hyperplasia of the central region of the prostate differs from the degree of atrophy in the peripheral region, prostate volume may or may not increase. Therefore, it is generally believed that the diameter measurements have limited diagnostic value for BPH, especially for older patients. BPH shows no density difference between the central zone and the peripheral zone during the CT scan, and sand-like or short curved calcification is observed at the junction of the two zones. The central area of the enhanced scan is strengthened around the urethra or slightly off the side, and the nonenhanced area with a crescent-shaped or eccentric ring surrounds the central area. The unreinforced area is thin or disappears, and the ratio of the diameter of the thickest part of the central area to the surrounding area is greater than 1. Prostate cancer or BPH can form a soft tissue mass that protrudes into the bladder cavity. Prostate cancer on CT is a mass mostly from the two sides of the posterior wall of the bladder that

Feature The enlarged prostate protrudes into the bladder, sometimes showing symmetrical, smooth-edged masses on both sides, called the double peak sign. Explanation Benign prostate hyperplasia originates from the middle lobe. When the hypertrophic middle lobe protrudes into the bladder cavity, because the central part of the prostate is restricted by  the urethra, it usually goes up or forward from the central part of the lower wall of the bladder, showing a bimodal shape with smooth edges (Fig. 7.12). Discussion The prostate is located below the bladder and behind the pubic symphysis. The parenchymal adnexal gland enclosing the root of the urethra, it is flat behind and has a longitudinal shallow sulcus in the middle. The main body of the prostate is divided into left and right lobes, through which the urethra passes. Benign prostate hyperplasia (BPH) begins in the glands surrounding the urethral seminal position, which are called transitional zones, accounting for about 5% of the prostate tissue. The remaining 95% of glands is composed of peripheral zones (three of four) and central zones (one in four). BPH is a typical clinical manifestation of glandular tissue, smooth muscle tissue, and connective tissue prolifera-

a

b

Fig. 7.12 (a) In a 61-year-old man, plain pelvic CT scan showed enlarged prostatic gland with bimodal protrusion into the back of the bladder to form a bimodal sign. (b) Another patient with double peak sign seen on noncontrast CT

7  Peritoneum and Pelvis

is spherical and protrudes into the bladder cavity; The change of bladder wall caused by BPH is mainly caused by the migration. When the hyperplastic nodule is larger, it can protrude into the bladder, and the edge is smoother. The prominent part is from the central area of the lower wall of the bladder upward or forward, showing a double peak protrusion. BPH needs to be differentiated from prostate cancer. The invasion of the bladder wall by prostate cancer and the change of BPH to the bladder wall reflect the pathological basis; 75% of prostate cancer originates from the posterior lobe envelope. In the lower area, BPH originates in the middle lobe, and the hypertrophic middle lobe protrudes into the bladder cavity, showed a double peak change because the central part is restricted by the urethra. It is generally believed that the morphology and location of the mass in the bladder are important for identification. Cone-beam CT may be a useful adjunctive technique to identify the anatomy of the prostatic arteries and ais treatment planning [29]. BPH should also be differentiated from bladder cancer. When BPH occurs, sometimes the mass shadow can be seen in the bladder, which is caused by partial volume effect. The upper and lower diameters of the mass shadow are smaller than the transverse diameters, indicating that the mass shadow is located outside the bladder, which is different from that of bladder cancer, which is manifested as a mass protruding into the bladder cavity.

7.13 Spur Sign Feature The spur sign is seen on transverse CT images or conventional obturator oblique (45° internal rotation and 15° cephalic tilt) radiographs of the pelvis. The fracture fragments that appear as triangles resemble a spur-like shape with the tipping point downward. Explanation The spur sign is produced by a triangular fragment of iliac bone that remains attached to the

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Fig. 7.13  Axial CT scan shows fracture fragments (white arrows) medially displaced

sacroiliac joint but is separated from the fractured acetabulum. The spur sign is indicative of fracture in both the anterior and posterior acetabular columns (both-column fracture). Not all acetabular double-column fractures have the spur sign; the spur sign is exposed when the fractured acetabular columns are medially displaced (Fig. 7.13). Discussion The acetabulum is composed of two columns and two walls. The columns represent a condensation of trabecular bone along lines of stress and transfer weight-bearing force from the hip joints to the axial skeleton. The effect of the walls is to stabilize the hip joint. The two columns are unequal in size and, together, form an inverted Y. The anterior column is composed of the anterior portion of the ilium, including the iliac crest; the anterior superior portion of the acetabular roof; and the pubic symphysis. The posterior column ­(squatting column) is shorter; it provides the major support for the hip joint and includes the weight-bearing dome of the acetabulum and posterior portion of the ischium [30]. The type of fracture is determined by the damage mechanism and force of fracture. Fractures of the anterior column are often the result of force applied in external rotation, whereas fractures of the posterior column are the result of force applied in internal rotation. Transverse fractures may occur as the result of force applied to the adducted (high transverse) or abducted (low transverse) hip [31]. The both-column and transverse fracture are among the more common acetabular

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fractures and account for 18.8–29.0% and 10.4– 11.3% of fractures, respectively. The spur sign seen on CT and conventional obturator oblique radiograph is encountered only in both-column fractures.

References 1. Orwig D, Federle MP. Localized clotted blood as evidence of visceral trauma on CT: the sentinel clot sign. AJR Am J Roentgenol. 1989;153(4):747–9. 2. Gudelj M, Giroul F, Dorthu L. Intraperitoneal bladder rupture revealed by the sentinel clot sign. J Belg Soc Radiol. 2018;102(1):33. 3. Hahn PF, Saini S, Stark DD, Papanicolaou N, Ferrucci JT Jr. Intraabdominal hematoma: the concentric-­ ring sign in MR imaging. AJR Am J Roentgenol. 1987;148(1):115–9. 4. Hahn PF, Stark DD, Vici LG, Ferrucci JT Jr. Duodenal hematoma: the ring sign in MR imaging. Radiology. 1986;159(2):379–82. 5. Taguchi T, Inoue K, Terada Y. Concentric-ring sign in adrenal hemorrhage. Endocrine. 2014;47(3):965–6. 6. Mehta N, Babu S, Venugopal K. An experience with blunt abdominal trauma: evaluation, management and outcome. Clin Pract. 2014;4(2):599. 7. Taylor AJ, Dodds WJ, Erickson SJ, Stewart ET.  CT of acquired abnormalities of the spleen. AJR Am J Roentgenol. 1991;157(6):1213–9. 8. Soto JA, Anderson SW.  Multidetector CT of blunt abdominal trauma. Radiology. 2012;265(3):678–93. 9. Boraschi P, Braccini G, Gigoni R, et  al. Diagnosis of adrenal adenoma: value of central spot of high-­ intensity hyperintense rim sign and homogeneous isointensity to liver on gadolinium-enhanced fat-­ suppressed spin-echo MR images. J Magn Reson Imaging. 1999;9(2):304–10. 10. Dinnes J, Bancos I, Ferrante di Ruffano L, et  al. Management of endocrine disease: imaging for the diagnosis of malignancy in incidentally discovered adrenal masses: a systematic review and meta-­ analysis. Eur J Endocrinol. 2016;175(2):R51–64. 11. Xu Y, Wang J, Peng Y, Zengb J. CT characteristics of primary retroperitoneal neoplasms in children. Eur J Radiol. 2010;75(3):321–8. 12. Nishino M, Hayakawa K, Minami M, Yamamoto A, Ueda H, Takasu K.  Primary retroperitoneal neoplasms: CT and MR imaging findings with anatomic and pathologic diagnostic clues. Radiographics. 2003;23(1):45–57. 13. Scali EP, Chandler TM, Heffernan EJ, Coyle J, Harris AC, Chang SD.  Primary retroperitoneal masses: what is the differential diagnosis? Abdom Imaging. 2015;40(6):1887–903. 14. Hardy SM.  The sandwich sign. Radiology. 2003;226(3):651–2.

P. Lei et al. 15. Theodorou SJ, Theodorou DJ, Briasoulis E, Kakitsubata Y.  The “Sandwich sign” in mesenteric lymphoma. Intern Med. 2015;54(22):2953. 16. Sozutek A, Colak T, Reyhan E, Turkmenoglu O, Akpınar E.  Intra-abdominal gossypiboma revisited: various clinical presentations and treatments of this potential complication. Indian J Surg. 2015;77(suppl 3):1295–300. 17. Lu YY, Cheung YC, Ko SF, Ng SH. Calcified reticulate rind sign: a characteristic feature of gossypiboma on computed tomography. World J Gastroenterol. 2005;11(31):4927–9. 18. Ozgur T, Atik E, Silfeler DB, Toprak S. Mature cystic teratomas in our series with review of the literature and retrospective analysis. Arch Gynecol Obstet. 2012;285(4):1099–101. 19. Outwater EK, Siegelman ES, Hunt JL.  Ovarian teratomas: tumor types and imaging characteristics. Radiographics. 2001;21(2):475–90. 20. Togashi K, Nishimura K, Kimura I, et al. Endometrial cysts: diagnosis with MR imaging. Radiology. 1991;180(1):73–8. 21. Dias JL, Veloso Gomes F, Lucas R, Cunha TM. The shading sign: is it exclusive of endometriomas? Abdom Imaging. 2015;40(7):2566–72. 22. Thalluri AL, Knox S, Nguyen T. MRI findings in deep infiltrating endometriosis: a pictorial essay. J Med Imaging Radiat Oncol. 2017;61(6):767–73. 23. Devrim K, Musturay K, Deniz K, Deniz A, Mustafa O.  MDCT of the ovarian vein: normal anatomy and pathology. AJR Am J Roentgenol. 2009;192(1):295–9. 24. Yoshiki A, Kengo Y, Hitoshi A, Akihiro N, Daisuke K, Hiroyuki I, et al. MDCT of the gonadal veins in females with large pelvic masses: value in differentiating ovarian versus uterine origin. AJR Am J Roentgenol. 2006;186(2):440–8. 25. Kim SH, Sim JS, Seong CK.  Interface vessels on color/power Doppler US and MRI: a clue to differentiate subserosal uterine myomas from extrauterine tumors. J Comput Assist Tomogr. 2001;25(1):36–42. 26. Kim JC, Kim SS, Park JY. Bridging vascular sign in the MR diagnosis of exophytic uterine leiomyoma. J Comput Assist Tomogr. 2000;24(1):57–60. 27. Madan R.  The bridging vascular sign. Radiology. 2006;238(1):371–2. 28. Thorpe A, Neal D.  Benign prostatic hyperpla sia [published correction appears in Lancet 2003;362(9382):496]. Lancet. 2003;361(9366): 1359–67. 29. Wang MQ, Duan F, Yuan K, Zhang GD, Yan J, Wang Y.  Benign prostatic hyperplasia: cone-beam CT in conjunction with DSA for identifying prostatic arterial anatomy. Radiology. 2017;282(1):271–80. 30. Johnson TS.  The spur sign. Radiology. 2005;235(3):1023–4. 31. Miller AN, Prasarn ML, Lorich DG, Helfet DL. The radiological evaluation of acetabular fractures in the elderly. J Bone Joint Surg Br. 2010;92(4):560–4.

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Suggested Readings for this Chapter Alapati S, Wadhwa V, Komarraju A, Guidry C, Pandey T.  Magnetic resonance imaging of nonneoplastic musculoskeletal pathologies in the pelvis. Semin Ultrasound CT MR. 2017;38(3):291–308. Arraiza M, Metser U, Vajpeyi R, et  al. Primary cystic peritoneal masses and mimickers: spectrum of diseases with pathologic correlation. Abdom Imaging. 2015;40(4):875–906. Dillman JR, Smith EA, Morani AC, Trout AT.  Imaging of the pediatric peritoneum, mesentery and omentum. Pediatr Radiol. 2017;47(8):987–1000. Gangadhar K, Mahajan A, Sable N, Bhargava P. Magnetic resonance imaging of pelvic masses: a compartmental approach. Semin Ultrasound CT MR. 2017;38(3):213–30. Sandstrom CK, Gross JA, Linnau KF.  Imaging of pelvic ring and acetabular trauma. Semin Roentgenol. 2016;51(3):256–67.

289 Skitch S, Engels PT.  Acute management of the traumatically injured pelvis. Emerg Med Clin N Am. 2018;36(1):161–79. Ssi-Yan-Kai G, Rivain AL, Trichot C, et  al. What every radiologist should know about adnexal torsion. Emerg Radiol. 2018;25(1):51–9. Tannus JF, Dagoglu G, Oto A.  Magnetic resonance imaging of maternal diseases of the abdomen and pelvis in the pregnant patient. Am J Perinatol. 2008;25(10):605–10. Wasnik AP, Maturen KE, Kaza RK, Al-Hawary MM, Francis IR. Primary and secondary disease of the peritoneum and mesentery: review of anatomy and imaging features. Abdom Imaging. 2015;40(3):626–42.

8

Signs in Musculoskeletal Radiology Haitao Yang, Lingling Song, and Zhaoshu Huang

Contents 8.1 Introduction

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8.2 Flipped Meniscus Sign

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8.3 Absent Bow Tie Sign

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8.4 Fragment-in-Notch Sign

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8.5 Cyclops Lesion

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8.6 Anterior Tibial Translocation Sign

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8.7 Celery Stalk Sign

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8.8 Double Posterior Cruciate Ligament Sign

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8.9 Double-Line Sign

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8.10 Crescent Sign

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8.11 Yo-Yo on String Sign

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8.12 Arcuate Sign

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8.13 Double Oreo Cookie Sign

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8.14 J Sign

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8.15 Secondary Cleft Sign

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8.16 Lateral Capsular Sign

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8.17 Fallen Fragment Sign

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8.18 Iliac Hyperdense Line

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H. Yang (*) Department of Radiology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China e-mail: [email protected] L. Song · Z. Huang Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6_8

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8.19 Terry Thomas Sign

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8.20 Lateral Femoral Notch Sign

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8.21 Elephant Trunk Sign

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8.22 Fat–Blood Interface Sign

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8.23 Elbow Fat Pad Sign

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8.24 C Sign

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8.25 Target Sign

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8.26 Swirl Sign

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8.27 Flow Void Sign

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8.28 Button Sequestrum Sign

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References

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Introduction

8.2

In this chapter we describe a number of easily recognizable signs in musculoskeletal radiology such as bone and joint trauma, sports medicine, bone and soft tissue tumors. These signs are demonstrated with imaging to help understand direct or indirect evidence of the pathology and mechanism of injury. Familiarity with these signs allows the radiologist and the clinician to toward an accurate diagnosis or make a brief differential diagnosis.

a

b

Fig. 8.1  A 40-year-old man with flipped-over lateral menisci of the left knee. (a) Coronal T2WI with fat-­ saturated MRI shows a main meniscus body located in the intercondylar notch (arrow) and absence of a lateral

Flipped Meniscus Sign

Feature On magnetic resonance imaging (MRI) in sagittal plane, the posterior horn of the meniscus is torn or has disappeared, and the maximum height of the anterior horn of ipsilateral meniscus reaches 6 mm or higher. It is also possible that a well-defined meniscus structure (double anterior horn sign) may appear behind the anterior horn of the meniscus, and the posterior horn may become shorter or even disappear, which is defined as the flipped meniscus sign.

c

meniscus structure in the expected location. (b, c) Sagittal T1WI and T2WI with fat-saturated MRI show a bizarre-­ shaped posterior horn (arrow) protruding relative to the edge of the tibial plateau and the small anterior horn

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Explanation Flipped meniscus sign may occur in a bucket-­ handle tear of the meniscus. The meniscus fragments are usually displaced to the intercondylar fossa under pressure. If the meniscus fragment does not move toward the intercondylar fossa but directly forward to the anterior horn of the ipsilateral meniscus, this is called flipped meniscus sign [1] (Fig. 8.1). Discussion The meniscus of the knee is a kind of fibrous cartilage. The common tears of the meniscus can be divided into four types: (1) the longitudinal tear is called a bucket-handle tear (BHT) when both ends are connected, and the cleft can catch the femoral condyle like a noose; (2) the transverse tear (radial tear) is rarely completely broken; (3) the horizontal tear is a tear parallel to the meniscus plane; and (4) a marginal tear is along the joint capsule attachment. BHT of the meniscus is a special type of meniscus injury, which refers to the displacement of the combined meniscus fragments to the central area of the joint in longitudinal and vertical tears or oblique tears, named after its bucket-handle shape [2]. It is important to determine whether there is BHT because this type of tear usually requires the removal of displaced fragments. BHT usually involves the medial meniscus. The torn meniscus fragments usually move to the intercondylar fossa and then forward to the patellar tendon. It has been reported that the transposed bucket-­handle fragments in the intercondylar fossa are often located in front of the posterior cruciate ligament, which can result in false “double posterior cruciate ligament,” which is called the double posterior cruciate ligament sign. If the meniscus fragment does not move toward the intercondylar fossa but directly forward to the anterior horn of the ipsilateral meniscus, this is called flipped meniscus sign. The diagnostic criteria of flipped meniscus sign include (1) tear of posterior horn or not developed; (2) the maximum height of anterior horn in the same side meniscus reaches 6 mm or higher, and the torn meniscus fragments are reversed and superimposed with anterior horn of meniscus, resulting in abnormal hypertrophy of anterior

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horn; (3) a well-defined meniscus structure appears behind the anterior horn of meniscus, also called double anterior horn sign, which is caused by torn meniscus fragments displaced behind the anterior horn of the meniscus [3].

8.3

Absent Bow Tie Sign

Feature On sagittal MRI, anterior and posterior horns of the medial or lateral meniscus are connected through the body, and the cross section of the normal knee joint resembles a bow tie (the tie sign). On an MR image 4–5 mm thick, with 0–0.5 mm spacing, there are at least two bow ties connected by the body. When bucket-handle tear occurs, there is only one or no bow tie, called the absent bow tie sign. Explanation The average width of the normal meniscus body is 9–12  mm, and the body of the meniscus can appear as a bow tie on two consecutive sagittal MRI images with a thickness of 4–5  mm. The absent bow tie sign indicates a meniscus bucket-­ handle tear. The bucket-handle tear is a special longitudinal rupture of the meniscus; the medial segment is displaced, the displaced segment is similar to a bucket handle, and the nondisplaced lateral segment resembles a bucket, so it is called a bucket-handle tear (Fig. 8.2). Discussion Bucket-handle tear is a special type of longitudinal tear of meniscus, which occurs most frequently in the middle of the meniscus. Bucket-handle tear is common in young patients with severe trauma, often involving the entire meniscus, but may also involve the anterior, posterior, or body of the meniscus alone. Because the displaced segments are often located between the intercondylar fossa or parallel to the posterior cruciate ligament, or in the anterior or posterior part of the posterior cruciate ligament, bucket-­ handle tear often causes joint stiffness, limited extension, or joint instability. Therefore, it is very important to confirm the displaced fragments for arthroscopic segmentectomy or replacement [4].

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a

b

c

Fig. 8.2  A 71-year-old woman with knee trauma. Sagittal T1WI (a–c) shows absent bow tie sign (arrow); the normal tie-like meniscus body is not shown on consecutive slices

A normal meniscus shows hypointensity in each sequence of MRI.  On sagittal MR images with slice thickness of 5 mm, the anterior and posterior horns of the normal meniscus show a triangle uniform hypointensity at the level of the meniscus body. The two triangles are connected by the body to form two bow-shaped changes looking like a bow tie sign. When the bow-shaped meniscus cannot be seen on one or two consecutive layers of sagittal MRI images, it is called absent bow tie sign. However, bucket-handle tear may be difficult to diagnose on sagittal MRI, such as longitudinal tear without displacement and discoid meniscus with bucket handle tear. In discoid meniscus, part or all of the meniscus tissue can cover the tibial plateau, so the tie-like meniscus displayed can be seen in the upper two levels. At this time, it may not show the absent bow tie sign. Helms et al. described necktie disappearance as a sign of tearing of the barrel-­handle meniscus in 1998 [5]. Some normal structures of the knee joint, including transverse meniscal ligament, accessory meniscal ligament, and carmine tendon, can be similar to the displaced segments in meniscus bucket-handle tear, which can easily lead to misdiagnosis. In addition, in some cases, such as meniscal free margin resection, osteoarthritis with meniscal free margin softening, long-term wear of meniscal free margin in elderly patients, and narrow meniscus in children, because there are fewer than two layers of the tie-like meniscus on sagittal MRI, it may be mistaken for the absent bow tie sign and misdiagnosed as bucket-handle tear, which needs to be differentiated [6].

8.4

Fragment-in-Notch Sign

Feature Coronal MRI shows abnormal band- or clump-­ like hypointensity in intercondylar notch and around the cruciate ligament, which is similar to the signals of meniscus on T1WI and T2WI. Another name: internal displaced fragment sign. Explanation The free edge of a bucket-handle tear is shifted to the intercondylar notch and around the cruciate ligament, forming a bucket handle-like structure, and the low signal is the shape of a strip or mass on the coronal MRI image (Fig. 8.3). Discussion Fragment-in-notch sign appears to serve as a reliable indicator of the displaced bucket-handle component of medial meniscal tears. A bucket-­handle tear commences as a vertical or oblique tear at the posterior horn of the meniscus. Longitudinal extension toward the anterior horn often allows the inner segment to undergo varying degrees of displacement into the intercondylar notch. The term bucket handle is derived from the appearance of the tear in which the inner displaced fragment of the meniscus resembles a handle and the peripheral nondisplaced portion has the appearance of a bucket. The medial meniscus is usually involved [7]. Terezidis et al. [7] confirmed two thirds of isolated meniscal tears in young athletes ranging from 16 to 32 years of age (mean, 22 years) were in the medial meniscus, presumably related to its

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a

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b

c

Fig. 8.3 (a–c) A 42-year-old man with a bucket-handle tear in the posterior horn of the medial meniscus of the left knee. Coronal T1WI shows abnormal clump-like hypointensity in the intercondylar notch and around the posterior cruciate ligament. Sagittal fat-suppressed T1WI reveals an

enlarged appearance of the posterior horn (vertical solid arrow) and reduced appearance of the anterior horn (horizontal solid arrow); axial fat-suppressed T2WI shows a bucket handle-like structure (dashed arrow) that tore from the post horn of the meniscus

firm attachment to the tibia, especially posteriorly when compared to the more mobile lateral meniscus. Vertical tears, including bucket-handle tears, are more common than horizontal tears both in children with concomitant anterior cruciate ligament (ACL) tears and in young athletes with isolated tears; in adults, horizontal degenerative tears are frequently seen. Meniscal injuries in children younger than 10 years of age usually relate to an abnormal discoid morphology. According to the literature, there are five kinds of signs of bucket-handle tears: (1) internal displaced fragment sign: striated or clustered low-­ signal meniscal fragments of knee intercondylar notch is positive on coronal or sagittal images; (2) abnormal circumferential meniscus sign: the meniscus and joint capsule on coronal image are obviously smaller, in which the signal of abnormal or no abnormal is positive; (3) double posterior cruciate ligament sign (the sign of double PCL): on sagittal image, if there is a parallel low-­signal shadow in front of the posterior cruciate ligament, it is positive; (4) absent bow tie (ABT) sign: normal meniscus body can be seen in at least two consecutive layers on sagittal images, likely a bow tie. If the complete shape of the meniscus body is less than two layers or none, it is positive. (5) Double meniscus forefoot sign: if a clearly demarcated meniscus structure is seen behind the anterior horn of meniscus on sagittal image, the posterior horn becomes obviously smaller. Internal displaced fragment sign has the highest sensitivity, accuracy, and negative predictive value, whereas a double

PCL sign has the highest specificity and positive predictive value. The reported sensitivity of ABT sign is 88% in MRI when compared with arthroscopic findings. Similarly, the free fragment sign has a sensitivity of 90.7% with arthroscopic correlation [8]. The diagnosis of meniscal tears is usually based on MRI, which is now considered the gold standard for meniscal pathologies [9].

8.5

Cyclops Lesion

Feature On MRI, cyclops lesion manifests as a proliferative fibrous tissue nodule at the leading edge of the reconstructed anterior cruciate ligament. The pedicle is connected to the anterior cruciate ligament. In all sequences, it is usually equal signals, and sometimes low or high signal. Explanation Cyclops lesion is one of the major complications after anterior cruciate ligament reconstruction. Pathologically, it is mainly localized fibrous connective tissue hyperplasia, located at the leading edge of the reconstructed anterior cruciate ligament. The pedicle is connected to the anterior cruciate ligament. Because the lesion resembles an eyeball during arthroscopy, it is called cyclops lesion (Fig. 8.4). Discussion The cyclops lesion is mainly characterized by localized fibrous tissue nodules, located in front of

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a

b

c

d

e

f

Fig. 8.4  (a–c) A 26-year-old man at 6 months after ACL T1WI with fat-saturated MRI. (d–f) A 16-year-old boy at reconstruction. The cyclops lesion shows a circular iso-­ 3 months after ACL reconstruction for 3  months. The intensity nodule (arrow) in front of the reconstructed ACL cyclops lesion is also shown of the intercondylar fossa on sagittal, coronal, and axial

the anterior cruciate ligament of the intercondylar fossa. It is similar to an eyeball under arthroscopy. Because the lesion is located in the anterior part of the joint, it is also called localized anterior joint fibrosis. The cyclops lesion is one of the complications of anterior cruciate ligament reconstruction. The total incidence is 1–9.8% and the incidence of symptomatic cases is 0–2% [10]. The mechanism of formation of cyclops lesion is not yet clear, and there are currently two main explanations. First, the debris generated by the tibial borehole during the establishment of the anterior cruciate ligament graft tunnel causes fibrous tissue hyperplasia; second, the long-term impact damage of the intercondylar anterior cruciate ligament graft during joint movement leads to the formation of local fibroproliferative nodules [11]. The boundary between the cyclops lesion and the anterior cruciate ligament is unclear, and the pedicle is connected to it, which supports the latter theory. Once the cyclops lesion

is formed, the hyperplastic fibrous tissue nodules insert between the femur and the tibia during the movement of the knee joint, resulting in the knee joint not being fully extended. The cyclops lesion shows moderate signal on MRI. However, a few cases show high signals on PDWI and low or high signals on T1WI. The lesions are mostly in front of the anterior cruciate ligament, and a few are located inside or outside. The sensitivity of MRI in the diagnosis of cyclops lesion is 85%, the specificity is 84.6%, and the accuracy is 84.8%. In lesions with a diameter greater than 10 mm, the sensitivity, specificity, and accuracy of MRI diagnosis are higher [12]. When a cyclops lesion occurs, the probability of the graft appearing as hyperintensity on PDWI is increased, and it is often arched, presumably by the compression stimulation of the fibrous hyperplastic nodule. It is worth mentioning that not all cyclops lesions have clinical manifestations, and in a few cases,

8  Signs in Musculoskeletal Radiology

symptoms may appear and progressively worsen as the lesions gradually increase.

8.6

Anterior Tibial Translocation Sign

Feature The anterior tibial translocation sign is seen on sagittal images of the lateral femoral condyle. Parallel lines are drawn through the posterior cortex of femoral condyle and the posterior cortex of tibial plateau, and the vertical distance between the two is 7 mm or greater anterior translocation. Explanation An anterior cruciate ligament (ACL) tear causes the tibia to shift forward to different degrees relative to the femur, which is one of the indirect signs of the anterior cruciate ligament tear (Fig. 8.5). Discussion The primary role of the ACL is to provide stability to the knee joint. It resists anterior translocation and internal rotation of the tibia over the femur. The ACL also limits hyperextension and both valgus and varus forces on the knee. ACL injury is a

Fig. 8.5  Sagittal T1WI (a) and PDWI with fat saturated (b) MRI of the left knee in a 22-year-old male patient with anterior cruciate ligament (ACL) tear show abnormal

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associated with anterolateral instability of the knee. Deficiency of the ACL allows the tibia to undergo anterior subluxation relative to the femur, thus producing the anterior tibial translocation sign. The degree of anterior subluxation of the tibia can be measured directly at MRI; this is analogous to the anterior drawer test elicited during physical examination, in which the tibia moves anteriorly as the leg is pulled forward. Along the midsagittal plane of the lateral compartment of the knee, the distance between two lines drawn tangent to the posterior of the lateral femoral condyle and the proximal tibia indicates the degree of anterior tibial translocation. Two methods of drawing the tangent lines were described by Vahey et  al. [13]. In the first method, the tangents were drawn perpendicular to the tibial plateau. In the second method, the tangents were vertical and parallel to the image frame. The measured tibial displacement would be greater for the second method [14]. MRI studies of the sagittal section of the lateral femoral condyle are described as an indirect finding if there was an anterior translocation 7 mm or greater of the tibia relative to the femur. The mean anterior translocation amount in chronic ACL tears is 8.7 mm on average; in acute ACL tears, it is 5.4 mm on average. The anterior b

anterior tibial translocation of 7.5 mm. A kissing contusion in the lateral tibial and femoral subchondral bone and posterior horn tear of the lateral meniscus also can be seen

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a

b

Fig. 8.6 (a, b) In a 72-year-old man, the celery stalk sign can be seen on sagittal T1WI and PDWI with fat-saturated MRI, indicating ACL degeneration (arrow)

tibial translocation has been shown to increase with time. According to Vahey et  al. [13], the tibial anterior translocation was a specific finding for the ACL tear. It is accepted that subluxation of at least 5  mm has 58% sensitivity and 93% specificity for an ACL tear [15]. Exposure (or posterior displacement) of the posterior horn of the lateral meniscus has also been described as a sign of anterior tibial displacement; the tangent to the posterior edge of the lateral tibial plateau cuts the posterior horn of the lateral meniscus [16].

8.7

Celery Stalk Sign

Feature This sign is characterized by an enlarged anterior cruciate ligament (ACL) and unclear boundary. It shows high signal intensity on T2WI and there are strips of low-signal fibers in the ACL. It is named for its shape, similar to a celery stalk. Explanation Celery stalk sign is a characteristic feature of mucoid degeneration of the ACL. Under arthroscopy, mucoid degeneration is a pale yellow sclerosing substance. The enlargement and swelling of

ACL appear spherical with a certain degree of tension. MRI shows hyperintensity with blurred boundary; ACL fiber bundles are scattered in a hyperintensity area with hypointensity strips, forming the celery stalk-like appearance (Fig. 8.6). Discussion Celery stalk sign is a rare MRI sign of the knee joint. It shows enlargement of the ACL with an unclear boundary. It shows high signal on T2WI, with strips of low-signal fibers. It is named for its shape, resembling a celery stalk. Mcintyre et al. [17] first described this sign and considered it to be a characteristic sign of mucoid degeneration of ACL. The etiology and pathogenesis of ACL myxoid degeneration are not yet clear, but may be related to trauma, tenosynovial cyst, or degeneration, often occurring in middle-aged patients, without gender difference. The main clinical symptoms include knee pain, and inadequate knee extension or flexion; most patients have no definite history of trauma. The knee dyskinesia may be caused by the compression of the mass-­ like degeneration lesion in the ACL between femur and tibia. Therefore, even partial excision of the mucoid degeneration lesion can relieve or eliminate the clinical symptoms and signs.

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MRI is of great significance in the diagnosis and differential diagnosis of mucoid degeneration of ACL.  The normal ACL shows a regular low signal at the edge. When mucoid degeneration occurs, the ACL is enlarged locally and shows mass-like changes with unclear boundaries. On both T1WI and T2WI, a high signal is seen, and low signal fibers are visible, forming the so-­called celery stalk-like changes. Mucous degeneration of the ACL is often misdiagnosed by radiologists as partial or complete laceration of ACL [18]. Mcintyre et  al. [17] reported 10 cases of mucinous degeneration of ACL of which 6 cases were misdiagnosed as ACL laceration before arthroscopy. ACL mucinous degeneration often has no definite history of knee trauma. MRI shows diffuse thickening of ACL on the affected side, continuous and normal orientation of upper ligament bundles on T2WI, parallel to the high signal shadows of degenerated tissues, showing a typical celery stalk sign. The ACL laceration usually has a clear history of acute or chronic knee trauma. Most of the injuries are located in the middle part of the ligament, with a few located in the prone point of the femur or tibia. In addition, tenosynovial cysts and mucinous degeneration occurring in ACL have similar MRI findings, and sometimes they coexist. However, tenosynovial cysts are low and medium signal on T1WI and hyperintensity on T2WI [19]. The long axis of

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Fig. 8.7  A 19-year-old male patient with medial meniscus bucket-handle tear of the right knee. Sagittal T1WI (a), T2WI (b), and PDWI with fat saturated (c) MRI show a

tenosynovial cysts can be parallel to the ligament fibers, but the fibers bundles are arranged in an abnormal direction, so they can be differentiated.

8.8

 ouble Posterior Cruciate D Ligament Sign

Feature On sagittal MRI of the knee, arcuate hypointensity is seen anterior to the posterior cruciate ligament (PCL) and parallel to it, resembling a double PCL, and hence this is called the double posterior cruciate ligament sign. The appearance of this sign often suggests a bucket-handle tear (BHT) of the meniscus of the knee joint. Explanation In BHT of the meniscus, the avulsed portion is displaced anteriorly and inferiorly of PCL, both of which have hypointensities on all sequences; the avulsion-shifted fragments resemble a second PCL (Fig. 8.7). Discussion A double PCL is caused by an ACL located slightly outside the midline that prevents the torn fragments from continuing to shift outward. Therefore, the ACL is important in the formation of PCL sign

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parallel arc-shaped hypointensity in PCL (white solid arrow), with torn and displaced meniscus fragments (white hollow arrow)

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after BHT of the meniscus [20]. BHT of the meniscus is a common condition in the knee joint and is a common cause of knee pain and dysfunction. The clinical symptoms caused by BHT are more typical, such as joint lock or limited joint extension; the degree of meniscus tear is different, and the clinical symptoms are also different. If the torn fragments cannot be reset soon enough, the fragments will soften over time. MRI is an effective method to diagnose BHT of knee joint, and its sensitivity and specificity to BHT of the medial meniscus are higher than those of the lateral meniscus. BHT is a special form of longitudinal tear, a full-length longitudinal tear. Some of the fragments of a medial meniscus tear are connected to the meniscus. The stress can displace the torn part between the PCL and the medial intercondylar femoral and parallel to PCL. When the torn part of the meniscus is large, displacement may occur, forming more characteristic secondary signs, including double PCL sign, intercondylar debris sign, meniscus jump sign, and bow tie disappearance sign [21]. In the secondary signs of the meniscus BHT, the sensitivity of the bow tie disappearance sign is the highest, followed by intercondylar debris sign, meniscus jump sign, and double a

PCL sign. If combined with the coronal image, the sensitivity of secondary signs to the diagnosis of BHT can be further improved. Torn meniscus fragments can sometimes be confused with Humphry ligaments and oblique slab ligaments. ACL and PCL travel between each other. This movement can form an illusion resembling the double PCL. To avoid this illusion, the starting and ending points of the ligament should be found and differentiated [22].

8.9

Double-Line Sign

Feature The double-line sign is seen on T2WI of medullary bone as hyperintensity line within a parallel rim of decreased signal intensity surrounding osteonecrosis foci. Explanation Double-line sign is seen with avascular necrosis (AVN) on MRI.  The hyperintensity inner zone represents hyperemic granulation tissue, and the hypointensity outer zone represents adjacent sclerotic bone (Fig. 8.8). b

Fig. 8.8  A 75-year-old man with avascular necrosis of femoral head on both sides shows double-line sign on coronal (a, right femoral head) and axial (b, left femoral head) T2WI with fat-saturated MRI (arrow)

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Discussion This sign is considered pathognomonic for avascular necrosis (AVN) because the outer rim represents the reactive bone and the inner rim represents the vascular and repair tissue at the necrotic–viable osseous interface [23]. Trauma is the most common cause of AVN; other causes include hemoglobinopathies, Cushing syndrome, exogenous steroid use, alcoholism, pancreatitis, and human immunodeficiency virus. The epiphysis and metaphysis of long tubular bones are susceptible because of their limited arterial supply and limited venous drainage. Therefore, AVN may also be idiopathic. The hip is the most common site, but the knee, shoulder, and carpal and tarsal bones can also be affected. The location of AVN may be influenced by the underlying disease (e.g., the shoulder in sickle cell disease) [24]. AVN may be initiated by a traumatic disruption of a vessel or by other factors that cause ischemia, such as thromboembolism or venous stasis. After an initial traumatic insult, hematopoietic cells die within 6–12  h; fat marrow cells die in 2–5  days. Ischemic bone eventually undergoes repair from its periphery to its infarcted center. Healing begins with hyperemia at the ischemic periphery; the hyperemia is subsequently replaced by reactive tissue and sclerosis. Microfractures and bony collapse may occur as trabeculae are reabsorbed [24]. MRI has been reported to have a sensitivity of 97% and specificity of 98% in the diagnosis of AVN of the hip when a variety of findings are used to aid in the diagnosis. MRI is more sensitive than computed tomography (CT), scintigraphy, or conventional radiography [25]. MRI has become the first-choice imaging modality for AVN of the femoral head because of its high soft-­tissue resolution and multiplanar ability. T1WI show serpiginous band-like lesions with low signal intensity in the anterosuperior femoral head. The double-line sign is seen on T2WI and consists of a low signal intensity outer rim and a high signal intensity inner rim. With or without treatment, AVN may progress to cystic degeneration, intraarticular osseous bodies, and collapse of articular surfaces with subsequent secondary osteoarthritis. Patients may ultimately require joint replacement [25].

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8.10 Crescent Sign Feature Crescent sign is characterized by a subchondral arc-shaped transparent area, which can be seen on plain film and MRI showing arc-like hyperintensity on T2WI. It is common in the proximal anterolateral femoral head. Explanation Crescent sign is a sign of bone avascular necrosis. Poor perfusion at the articular end of bone leads to progressive necrosis and repair. When the repair reaction begins, a reaction band of fibrosis, congestion, inflammation, and bone resorption extends into the dead bone band, which is the interface. Repair occurs at the interface between dead bone and living bone. Reactive new bone grows on the necrotic bone trabecula and produces a sclerotic margin. The decrease of bone trabecular bearing capacity leads to progressive microfracture of subchondral bone trabecula and articular surface collapse, forming a translucent zone along the fracture line under the cartilage, that is, crescent sign (Fig. 8.9). Discussion AVN occurs most frequently in the proximal femur, followed by proximal humerus, distal femur, and talus, occasionally in lunate, metatarsal head, and tarsal scaphoid. Regardless of the location of avascular necrosis, the appearance of crescent sign is helpful for clinical staging and treatment options. In many cases, bone resorption causes destruction of the subchondral support structure, which leads to subchondral trabecular microfracture and joint collapse. At this time, articular cartilage can remain active because it absorbs nutrients from synovial fluid. As the disease progresses, articular cartilage is destroyed, joint space is narrowed, and then articular cartilage collapse occurs. Crescent sign is considered as an early indication of articular cartilage collapse. AVN is the most common type of osteonecrosis, which often leads to articular cartilage collapse of the femoral head and severe secondary osteoarthritis. The collapse of the

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Fig. 8.9  A 48-year-old woman with a year of pain in right hip joint. X-ray plain film (a), CT coronal reconstruction (b), and coronal T2WI (c) with fat saturated

show crescent-shaped transparent area/hyperintensity under right femoral head

articular cartilage of the femoral head is the result of the loss of mechanical support [26]. The appearance of crescent sign can help clinical staging. According to the findings of MRI, AVN can be divided into four stages [27]: stage I, complete femoral head, continuous articular cartilage and simple fat-like signal in necrotic area; stage II, complete femoral head, continuous articular cartilage and mixed signal of fat granulation tissue in necrotic area; stage III, collapse of femoral head, no fracture of articular cartilage of hip; stage IV, collapse of femoral head, fracture of articular cartilage of hip. Although crescent sign can also be seen occasionally in other osteopathy, such as osteochondral shear fracture of the femoral head, which can be easily identified by clinical history, it is most common in avascular necrosis of the femoral head and occurs at a later stage. The appearance of crescent sign indicates the collapse of the articular surface.

retracted ligament moves to the surface of the adductor aponeurosis, showing hypointense circular structure on all sequences. The adductor aponeurosis shows thin hypointensity line adjacent to folded UCL on coronal plane, and the shape resembles a yo-yo on a string.

8.11 Yo-Yo on String Sign Feature Coronal MRI shows rupture and retract of phalangeal ulnar collateral ligament (UCL). The

Explanation Yo-yo on a string sign is an MRI sign of a ulnar collateral ligament that is completely ruptured (Fig. 8.10). Discussion UCL injury is caused by external force in the radialis. Historically, such injuries have often occurred in Scottish gamekeepers and are now often associated with skiing and other sports, so it is also known as skier’s thumb [28]. Anatomically, the UCL is located deep in the adductor aponeurosis. The adductor aponeurosis consists of transverse fibers and oblique fibers from the adductor pollicis tendon and the extensor pollicis tendon [29]. UCL tear often occurs at the distal and near the junction of the phalanx. On MRI, the normal UCL shows a hypointensity band inside the metacarpophalangeal joint, and the adductor aponeurosis shows as a thin paper-­like hypo-intensity band

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Fig. 8.10  A 36-year-old male patient with right thumb trauma. MRI T2WI (a) and T1WI (b) show rupture and retraction of the UCL as a waved string appearance (white

hollow arrow); tear of the proximal radial collateral ligament is also seen (black arrow)

on the surface of the UCL, which covers from the distal half of the UCL to the base of the proximal phalanx. MRI can show UCL ruptures at the base of the proximal phalanx; the ligament retracts, and the retracted ligament moves to the surface of the adductor aponeurosis and shows a circular or a residual root-like structure with hypointensity in all sequences. The adductor aponeurosis shows a thin hypointense line adjacent to the folded UCL on the coronal MRI, which is called the yo-yo on a string sign. MRI is sensitive to a displaced UCL tear, with sensitivity of 100% and specificity of 94% [30].

8.12 Arcuate Sign Feature On X-ray the bone fragments avulsed from the fibula head moved upward. The size of bone ­fragments can range from blurred spots to centimeters in diameter, called arcuate sign. Explanation Avulsion fractures involving arcuate complex usually occur at the junction of the ligament and the fibula head. Arcuate sign indicates the rupture of the arcuate complex and the presence of acute posterolateral rotational instability of the knee joint (Fig. 8.11).

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Fig. 8.11  A 46-year-old male patient with right knee trauma. Radiography (a) shows an avulsion fracture of the fibular head (arrow). (b, c) Coronal T1WI and PDWI with fat saturation show avulsion fracture of fibular head with

edema near the attachment of the fibular collateral ligament combined with injuries of the posterolateral complex of the knee (arrow)

Discussion Arcuate sign was first described as an avulsion fracture of the fibula head indicating posterolateral knee instability. The arcuate sign is believed to be pathognomonic for an injury to one or more of the structures of the posterolateral structure of the knee, and an associated posterior cruciate ligament injury is frequently found. The posterolateral structure of the knee joint is a complex that includes the fibular collateral ligament, the ligament of sural head and fibula, the popliteal fibular ligament, the arcuate ligament, the popliteal tendon, and the tendon of the biceps femoris muscle [31]. The arcuate sign is described as a small bone fragment of the fibular head avulsion because of the trauma, and the bone fragments were torn off from the arcuate complex. However, the ligaments attached to the fibular head have different attachment points, so several different types of avulsion fractures may occur. Avulsion injuries of the popliteal fibular ligament, the arcuate ligament, and the ligament of sural head and fibula involve the tip of the fibular head (fibular styloid process) [32]. This avulsion injury is characterized by an oval bone fragment on X-ray radiography. On MRI, edema in the medullary cavity of the avulsed bone or fibular head can be observed. The avulsion fracture of the fibular head may be related to other ligament or tendon injuries in the posterolateral knee joint. In this case, the fibular

collateral ligament, the tendon of the biceps femoris muscle, and the popliteal tendon may be damaged. MRI can be used to evaluate the integrity of the posterolateral angle of the knee joint. The fibular collateral ligament, the tendon of the biceps femoris muscle, and the popliteal tendon are the larger structures; conventional MRI can accurately evaluate their injuries. However, the popliteal fibular ligament, the arcuate ligament, and the ligament of the sural head and fibula are the smaller structures, and they are oblique structures; it is difficult to identify and evaluate in conventional MRI.  An oblique coronal position is the best orientation to show these structures.

8.13 Double Oreo Cookie Sign Feature In coronal MRI arthrography, two hyperintensity lines appear on the superior labrum, which are sandwiched by three hypointensity lines, resembling a double Oreo cookie, and known as the double Oreo cookie sign. Explanation The contrast agent enters between the superior labrum and glenoid cartilage, indicating the rupture of the superior labrum. One of the two hyperintensity lines represents the lower crypt of the

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Fig. 8.12 A 36-year-old man with superior labrum anteroposterior (SLAP) tear. Oblique coronal T2WI with fat saturated shows two hyperintensity lines in the superior labrum, displaying the “double Oreo cookie sign”

labrum and one represents the rupture of the labrum. The three hypointensity lines represent the superior labrum and glenoid cartilage. The appearance of double Oreo cookie sign often suggests superior labrum anterior and posterior (SLAP) tear (Fig. 8.12). Discussion The appearance of double Oreo cookie sign often suggests superior labrum anterior and posterior (SLAP) tear, which is an important cause of shoulder pain and instability. Snyder et al. classified SLAP tears into four types under arthroscopy: type I is the wear and degeneration of the superior labrum, with no tear of the labrum, and the biceps tendon is normal; type II refers to the superior labrum peeling from the supracondylar nodules; type III is the superior labrum with a barrel-like tear that shifts into the joint, but the biceps tendon attachment is not involved. Type IV has the same handle-like tear as the type III and involves the biceps tendon. Type II lesions are the most common, and the incidence of types I–IV is 9.5–21%, 41–55%, 6–33%, and 3–15%, respectively [33]. The MRI coronal plane is most sensitive to superior labrum lesions. MRI diagnosis of SLAP

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tear is based on changes in signal and morphology. On MRI it manifests as an increase in the labrum signal, with or without the attachment of the biceps tendon to the tear of the superior labrum [34]. Several signs are useful for diagnosing SLAP tear: one is the upper one third of the superior labrum in the high signal and the other is the superior labrum is irregular or curved outward with high signal [35]. In addition, the normal lower labrum of the labial sac appears on the MRI as a high signal that curves inwardly. If it shows a hyperintensity that curves outward, it clearly indicates the tear of the superior labrum. MRI arthrography can better display the structure in the joint cavity and improve the accuracy of the diagnosis. In the MRI coronal position, if the contrast agent enters between the glenoid cartilage and the superior labrum, a hyperintensity band is formed, sandwiched by two hypointensity bands. That is a single Oreo cookie sign, which is common in the crypt under the labrums or type II lesions. The contrast agent enters between the superior labrum and the glenoid cartilage (the crypt of the labrum) and the cleft of the superior labrum. Two hyperintensity lines appear, one for the crypt of the labrum and one for the rupture of superior labrum. It is sandwiched by three hypointensity lines (representing the upper labrum and the glenoid cartilage), which resembles a double cookie sign, and known as the double Oreo cookie sign. A recent meta-analysis showed the sensitivity of MR arthrography in the diagnosis of labrum tear (80% vs. 63%) was superior to standard MRI with the similar specificity (91% vs. 87%) [36].

8.14 J Sign Feature On conventional MRI and MR arthrography, the continuous interruption of the right glenohumeral ligament, which looks like the shape of a “J,” and hyperintensity liquid accumulation can be seen around the broken structures. Explanation The J sign indicates humeral avulsion of the glenohumeral ligament (HAGL) lesion of the ­

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Fig. 8.13  A 23-year-old male patient with left shoulder trauma. Oblique coronal fat-saturated T2WI shows discontinuous inferior glenohumeral ligament (arrow) with surrounding edema and fluid

shoulder joint. The glenohumeral ligament originates from the anterior and posterior lip of the glenoid and ends around the anatomical neck of the humerus, located just at the edge of the humeral head and below the joint. The glenohumeral ligament is composed of anterior fascicle, posterior fascicle, and axillary sac. Shoulder effusion or MR arthrography may reveal a normal U-shaped glenohumeral ligament. The humerus anatomical neck attachment of the glenohumeral ligament was torn and the anterior or posterior fascicles were separated and pendulous, and the normal U shape was transformed into the J shape. The left shoulder joint HAGL lesion forms the reverse J sign. Continuous interruption of the glenohumeral ligament causes exudation around the free end of the isolated ligament and contrast agent accumulation after MRI arthrography (Fig. 8.13). Discussion HAGL is a rare but important cause of instability in the front of the shoulder joint. When the arm is abducted by 90°, the glenohumeral ligament lip complex is the main stable structure in front of

the shoulder joint [37]. It can prevent anterior dislocation of the shoulder joint with external rotation. The pathological mechanism of shoulder HAGL is traumatic excessive abduction and excessive external rotation of the arm. HAGL lesions are most common in anterior shoulder joint dislocation. HAGL lesions can occur in different sports, such as football, skiing or water skiing, surfing, football, basketball, volleyball, ice hockey, diving, wrestling, or boxing. Clinically, HAGL often occurs after reduction of acute anterior dislocation of shoulder or when traumatic dislocation occurs for the first time in patients with anterior unstable of shoulder joint. Then signs and symptoms include tenderness and pain in the front of the shoulder joint, fear of abduction and lateral rotation, external rotation, sensory loss of the shoulder joint, twisting pronunciation, and ligament relaxation [38]. MR arthrography and conventional MRI are effective in finding HAGL. Oblique coronal fat-­ saturated T2WI is the best method for showing HAGL [39]. MRI can also directly show discontinuity of the ligament and extravasation of contrast material in the region of capsular avulsion that results in an abnormal distribution of fluid within the articulation, the conversion of a U-shaped recess to a J-shaped recess, which can be used to diagnose HAGL.

8.15 Secondary Cleft Sign Feature The hyper-intensity along or below the median line of pubic symphysis joint and physiological cleft in the center of the pubic symphysis fibrocartilage disc, which is called secondary cleft sign, is best displayed on coronal T2WI or short-­ TI inversion recovery (STIR) images. Explanation There is a liquid cleft in the center of the pubic symphysis fibrocartilage disc, called the physiological cleft. On coronal T2WI and STIR images, the pubic symphysis fibrocartilage disc shows a linear hyperintensity in the center of the pubic symphysis fibrocartilage disc. The middle part of

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Fig. 8.14  A 32-year-old woman with chronic left groin pain. (a) Axial and (b) coronal T2WI with fat saturation MRI show significant marrow edema in the pubic bodies,

more marked on the left side. A subtle crescentric hyperintensity line along the anteroinferior margin of the left pubic body suggests a secondary cleft sign (arrow)

the pubis is the attachment of adductor ­aponeurosis, gracilis muscle, and inguinal falx. Injury of these ligaments can cause abnormal tension of pelvic ring and lead to rupture of the pubic symphysis fibrocartilage disc, forming a secondary cleft connecting with the physiological cleft or communicating with each other. This secondary cleft often extends beyond the edge of the fibrocartilage disc or between the adductor and gracilis muscle attachments. Therefore, the secondary cleft also shows linear hyperintensity with different lengths on coronal T2WI or STIR images (Fig. 8.14).

fests as a central focus of hyperintensity on fat-saturated T2WI or STIR [40]. The secondary cleft sign, which represents micro-tearing of the short adductor attachment, was described on MRI by Brennan et  al. [40]. A secondary cleft could develop as a result of chronic maceration of the central fibrocartilage by abnormal stress in the pelvic ring. Because secondary cleft is related to many factors, although some patients with pubic osteitis do not have secondary cleft sign on MRI, the display of secondary cleft sign on MRI can help explain the cause of inguinal pain, so other unnecessary examinations can be avoided [41].

Discussion Groin strain is more common in sports that expose the symphysis pubis to repeated shear and distraction, which is created by the pivoting and twisting that occurs when kicking, stretching a limb, or rapidly transferring weight from one limb to the other. Repeated shear and distraction occur in soccer, rugby, and Australian football players and have also been noted in professional football running backs. In maturity, the fibrocartilage of the symphysis pubis, which serves to buttress impaction and dissipate shear forces, develops a small central fluid-filled cavity or cleft. This cleft is identified clearly at symphyseal injection and mani-

8.16 Lateral Capsular Sign Feature X-ray of the knee joint shows a small bone shadow on the lateral side of the tibial plateau. Explanation Lateral capsular sign is a sign on knee X-ray suggesting Segond fracture. The small bone piece suggests a partial tear of the middle one third of the lateral capsular ligament, usually suggesting tearing of the lateral capsular ligament and anterior cruciate ligament (Fig. 8.15).

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Fig. 8.15  A 22-year-old woman presented with a free small bone patch on the lateral margin of the right tibial plateau on X-ray of the right knee joint (arrow)

Discussion Segond fracture refers to the avulsion fracture of the lateral edge of the tibial plateau, which occurs mainly in acute injury of the knee joint, and may be associated with structural damage of the joint [42]. The ACL is damaged after an internal rotation and varus force is applied to the knee flexion of 10° to 90°. Segond fractures occur after the violence continues to transmit to the outer joint capsule ligament. Therefore, Segond fractures are closely related to ACL injury. One study reported the incidence of Segond fracture combined with ACL rupture was 75% to 100%. ACL rupture is best developed in the middle part of the ligament, and second in the adjacent femoral attachment, at least in the tibia attachment [43]. ACL includes anterior internal bundle (AMB) and posterior external bundle (PLB). The adipose tissue inlay between the two bundles or the side, under the influence of volume effect, causes the MRI signal of ACL to be not uniform and higher than other ligaments. When ligament rupture occurs, the MRI manifestations include complete

discontinuity of ligament fibers, abnormal signal, and abnormal morphology. In acute injuries, the high signal line of T2WI crosses the ligament; blurred anterior cruciate ligament and abnormal tilt are observed. Acute ACL tear can also be accompanied by joint effusion and infrapatellar fat pad edema (especially infrapatellar fissure effusion). Because ACL rupture is often associated with rotational displacement injury, this type of injury usually occurs in the movement of sudden deceleration and simultaneous change of direction, which results in ACL stress and ligament tear. In the process of an ACL tear, tibial anterior movement and femoral condyle compression can cause meniscus degeneration or tear; the medial incidence is slightly higher than the lateral. Bone contusion and avulsion fracture (i.e., Segond fracture) are prone to occur at the attachment of the medial lateral capsular ligament of the tibial plateau, resulting in the formation of lateral capsular sign [44]. If radiography of the knee joint reveals free small bone patches on the lateral tibial plateau, Segond fracture is often suggested. If not handled in time, this will lead to instability of knee joint and osteoarthritis. Timely MRI can not only reduce missed diagnosis, but also aid treatment and patient rehabilitation.

8.17 Fallen Fragment Sign Feature This sign refers to the appearance of a patchy bone density shadow at the bottom of the bone cyst cavity on X-ray as it moves with the change of body position. Explanation Fallen fragment sign is an X-ray sign of bone cyst complicated with pathological fracture. The pathological fracture fragment falls into the cyst cavity, sinks to the lowest part of the cyst cavity, and can move with the change of body position (Fig. 8.16). Discussion Fallen fragment sign was first reported in simple bone cyst (SBC) with pathological fracture. The

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Fig. 8.16  A 12-year-old male patient with a simple bone cyst and pathological fracture of left humerus. X-ray plain film shows a cystic transparent shadow in the upper humerus and a patchy density fragment that has fallen within it (arrow)

fallen fragment sign has been demonstrated in 20% of cases of SBC. Minor trauma to the thin cortical wall results in a fracture that is bound by the outer intact periosteum and surrounding soft tissues. Complete detachment of the fragment from the periosteum allows it to sink to the bottom of the fluid contained within the cyst. Several authors have identified this sign in larger series of simple bone cyst, confirming the suggestion that it is a pathognomonic sign for SBC [45]; this occurs if the specific gravity of the fluid is less than that of the bony fragment. A variation of this sign occurs if the fragment fails to detach completely from the periosteum. Pathological fractures are reportedly present in approximately 65% of cases of simple bone cyst. Fragmentation of the inner bony wall of the cyst can occur after relatively minor trauma. Fragment migration cannot occur after the cortical fracture of a solid lesion such as fibrous dysplasia or nonossifying

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fibroma. Therefore, cystic bone lesions can be differentiated from solid bone lesions when the fallen fragment sign is present [46]. This sign can be demonstrated with radiographs or CT. Multiple views may be necessary to confirm the intramedullary location of the fragment, as a fracture through a solid lesion may produce a fragment that appears to be in the lesion but may actually be in the extraosseous soft tissues. Alternatively, CT may be helpful in identification of the intramedullary location of the bone fragment [46]. Some authors have suggested this sign does not occur in other benign lesions, but may be considered in the differential diagnosis of the later stages of eosinophilic granuloma (EG). One case of chondromyxoid fibroma has been reported as showing a pseudo-fallen fragment sign that is thought to be related to a fortuitous pattern of chondroid calcification [47]. Chondromyxoid fibroma typically causes cortical thinning but no periosteal breach. Theoretically, other focal fluid-containing lesions that cause expansion with cortical thinning and intact periosteum may predispose to fallen fragment sign after trauma. Although SBC is by far the most common cause for a central well-­ defined, lucent lesion with a fallen fragment, other lesions should be considered.

8.18 Iliac Hyperdense Line Feature On the radiography AP view of pelvis, the vertical hyperdense line shadow near the sacroiliac joint of the ilium wing is called the ilium hyperdense line. Explanation The iliac hyperdense sign is a relatively characteristic manifestation of gluteal muscle contracture (GMC) on X-ray plain film [48]. Normally, the outer cortex of the sacroiliac joint of the ilium is smooth and inclined from inside to outside. When the gluteus maximus muscle contracts, the muscles of the contraction and their fascia pull the posterior part of the femur. This long-term and  continuous pulling force leads to bone ­

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Fig. 8.17  A 16-year-old girl with right GMC. (a) Pelvic plain film shows a hyperdense line on the right ilium. The line runs roughly parallel to the sacroiliac joint (arrow). (b) Axial T1WI and (c) T2WI with fat saturation show con-

tracted right gluteal muscle with irregular margin (arrow) and deformity of the posterior ilium with part of the lateral cortex (arrow)

d­ eformation and thickening at the attachment of the gluteus maximus, and gradually changes the bone cortex of the external margin of the iliac sacroiliac joint into nearly forward and backward walking. The outer cortex of the iliac sacroiliac joint running forward and backward is consistent with the X-ray direction (Fig. 8.17).

involved piriformis muscle and hip joint capsule. The skeletal development of children has not yet been completed. After the formation of fibrous contracture bands, the balance of muscle strength attached to the pelvis and the upper femur is changed. The development of fibrotic muscle tissue is asymmetrical with the pelvis and femur attached to it, that is, the pelvis and femur develop rapidly, while the development of fibrotic gluteal muscle lags relatively slower, so it can gradually cause secondary changes of pelvis and hip joint. The slight cases only show hip joint abduction, external rotation, and pelvic rotation. The heavier cases may cause pelvic tilt, unequal length of lower limbs, even dislocation of hip joint, or compensatory scoliosis of lumbar spine [49]. Previous studies on X-ray manifestations of gluteal muscle contracture were mainly aimed at understanding the effects of gluteal muscle contracture on the growth and development of the pelvis in children, rather than as a means of diagnosing the disease. According to the literature, these studies included the increase of central margin angle (CE angle) and neck–shaft angle, the decrease of femoral head index, the decrease of iliac height–width ratio and acetabular angle, and pelvic tilt. The foregoing signs mainly reflect the morphological changes of the anterior external iliac bone and hip affected by gluteal muscle contracture, and to some extent reflect the extent of the disease. The study found that the occurrence rate of iliac hyperdense line in patients

Discussion Gluteal muscle contracture (GMC) is a clinical syndrome caused by degeneration and contracture of muscle and fascia fibers, which results in functional limitation of hip joint and shows special symptoms and signs. Its etiology is complex and varied, including intramuscular injection of gluteus, genetic factors, and scar constitution, gluteal muscle infection, gluteal compartment syndrome, and postoperative treatment of congenital dislocation of hip. At present, most scholars believe that repeated intramuscular injection is the main cause of gluteal muscle contracture, especially for benzyl alcohol solvent penicillin injection, and the younger the age at injection, the more injection times, and the greater the injection frequency, the more likely to cause disease. Because the opportunity of bilateral gluteal intramuscular injection is often equal, most of the cases are bilateral. However, the degree of bilateral contracture is different, and the scope also differs. Gluteus maximus was the most frequently involved, gluteus medius was the second, gluteus minimus was less involved, and severe cases

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more than 5  years old was significantly higher than that in patients under 5  years old, and the difference was significant. This conclusion indicates the appearance of iliac hyperdense line is directly related to the course of gluteal muscle contracture. The hyperdense line of iliac bone varies in length. The distances of the sacroiliac joint are different, which may be related to the degree, extent, and course of gluteal muscle ­contracture. The longer the course of disease, the wider the scope of contracture and the more severe the degree of contracture, and the more obvious, longer, and farther away from the sacroiliac joint of the iliac hyperdense line. On the contrary, the shorter the line of iliac hyperdense line is, the closer it is to the sacroiliac joint [50]. CT and MRI can directly display the shape of gluteal muscle, and determine the location, extent, and severity of the lesion, thus providing direct signs for the diagnosis of gluteal muscle contracture. CT has high-density resolution and can show the calcification of sand grains above and outside the gluteus maximus muscle, which is characteristic. MRI can clearly show morphological structure and signal changes of the muscles and fascia.

8.19 Terry Thomas Sign Feature  Positive X-ray plain film of wrist shows the space between scaphoid and lunate joint is more than 4 mm or twice as wide as that between the healthy side of (or around) joint. The midpoint of scaphoid and lunate relative to articular surface was taken as the measuring point. Explanation The carpal bone consists of eight bones, which have a certain range of motion and maintain a certain degree of stability. Terry Thomas sign is an X-ray manifestation of instability of the scaphoid and lunate joint, named for its resemblance to the characteristic anterior teeth of Terry Thomas, a famous British comedian. The common reason is that the gap between scaphoid and lunate is widened by a tear of the ligament connecting the scaphoid and lunate.

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Fig. 8.18  A 39-year-old man with chronic trauma of the right wrist. Radiograph shows scapholunate dissociation, with the space between the scaphoid and lunate widened (Terry Thomas sign) (arrow)

Untimely treatment often leads to chronic wrist pain and weakness (Fig. 8.18). Discussion Scapholunate dissociation results from a rupture of the scapholunate interosseous ligament following forceful extension of the wrist. The resulting instability allows widening of the scapholunate joint. Although scapholunate dissociation often occurs as part of a peri-lunate or lunate dislocation, it may occur as an isolated injury. Patients with scapholunate dissociation usually present with wrist swelling and pain, especially at extremes of motion. The resulting decreased strength and limitation of motion can significantly impair normal function. There is usually a history of a fall or force applied to the extended hand. Physical examination may reveal a palpable clunk in the wrist, in addition to mild swelling and tenderness over the dorsal wrist [51]. In scapholunate dissociation, the radiograph will reveal widening of the scapholunate joint.

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­   gap between the lunate and scaphoid greater A than 4 mm, which has been called “Terry Thomas sign,” is pathognomonic. The width of these gaps should not change significantly with radial or ulnar deviation. However, in dynamic scapholunate instability, the scapholunate interval may not appear widened on normal view. A clenched fist increases the force across the wrist because of the extrinsic ligaments, loading the capitate into the proximal carpal row and producing increased widening. Contralateral wrist radiographs may be necessary to detect or determine a significant amount of widening. Ulnar and radial deviation may also aid in diagnosis of dynamic scapholunate ligament injury, increasing gapping at the scapholunate or lunotriquetral joints, respectively. Physical examination and radiographs remain essential in the primary workup for carpal instability. Positive findings suggest the presence of carpal instability. However, in the diagnosing of scapholunate dissociation, because of the low sensitivity of the scaphoid shift test and radiographs, cine radiography is recommended in suspicion of carpal instability dissociation. ­ Cineradiography is a qualitative rather than a quantitative tool, so its exact role in diagnosing carpal instability is to be determined [52].

8.20 Lateral Femoral Notch Sign Feature An impaction fracture of the lateral femoral condyle with abnormal deepening could be apparent on the lateral radiograph of the knee as the lateral femoral notch sign, whose significance is that a sulcus is deeper than 1.5  mm. Another name: notch sign. Explanation Lateral condylopatellar sulcus, also known as lateral femoral notch (LFN), usually forms a shallow groove in the middle of the lateral femoral condyle. It represents the junction zone on the lateral femoral condyle where the tibiofemoral and patellofemoral radii of curvature meet. An abnormally deep lateral condylopatellar sulcus has been attributed to an impacted osteochondral

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fracture. A localized chondral or transchondral abnormality overlying the lateral condylopatellar sulcus has been observed with a torn ACL during surgical reconstruction. The most common mechanism of an ACL tear is rotation and valgus stress. Disruption of the ACL with valgus stress causes the posterior aspect of the lateral tibial plateau and the middle to anterior portion of the lateral femoral condyle to forcefully impact against one another. This stress causes a pattern of injuries known as “kissing contusions,” which are usually occult injuries to the cartilage and bone demonstrated as bone contusions On MRI study (Fig. 8.19). Discussion In 1992, Cobby et al. [53] sought to quantify and associate the depth of the condylopatellar sulcus with the likelihood of ACL tear. In normal subjects, the mean lateral sulcus depth was 0.45 mm, whereas 0.89  mm was found with confirmed ACL tears. No normal subjects had a sulcus depth greater than 1.2 mm, and 1.5 mm was suggested as a suitable cutoff for a reliable sign for an ACL tear [54]. The lateral femoral notch (LFN) signifies the junction zone where the tibiofemoral and patellofemoral radii of curvature meet. Normally, the lateral femoral notch represents a shallow groove in the middle of the lateral femoral epicondyle. An abnormally deep lateral condylopatellar sulcus has been associated with underlying pathologies, most notably an underlying ACL tear. Disruption of ACL may result in abnormal translation of the tibia onto the femur, causing forceful impaction onto one another. In some instances, such forceful impaction may lead to an osteochondral impaction fracture. Ultimately, an abnormally deep lateral notch sign may also be a harbinger for long-term pathology, including early-onset osteoarthritis. ACL is one of the most important stabilizers of the knee, providing primary restraint to anterior tibial translation and secondary stabilization in regard to rotational forces and varus or valgus stresses to the knee. There are few findings suggestive of an ACL tear on radiographs of the knee. Lateral femoral notch sign and posterior fracture of the lateral tibial plateau are infrequently seen

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Fig. 8.19 (a, b) A 26-year-old male patient with ACL tear of left knee. Lateral X-ray and sagittal PDWI show an impaction fracture of the lateral femoral condyle as the lateral femoral notch sign (arrow)

radiographic signs corresponding to the kissing contusions seen on MRI [54]. MRI is the imaging modality of choice to diagnose ACL injury, which can manifest as discontinuity, abnormal slope, or signal intensity of fibers. There is no statistically significant correlation between LFN depth on radiographs or MRI with preoperative lateral compartment translation or tibial acceleration during quantitative pivot shift analysis. LFN depth should not be used as an indicator of high-­ grade rotatory knee instability. A deepened LFN, either on imaging or during operation, however, may be used as an indicator in patients more likely to have a lateral meniscus tear [55].

8.21 Elephant Trunk Sign Feature This sign is a characteristic X-ray feature of calcaneonavicular coalition (CNC), and the conventional oblique position of the foot is the best observing position. Its appearance is that the anterior and superior processes of the calcaneus

protrude like a nose and form a pseudo-joint or bony fusion with the scaphoid bone of the foot. Some literature also refers to this feature of CNC as the anteater nose sign. Explanation Elephant nose sign is an X-ray feature of calcaneonavicular coalition (CNC), which is the most common type of syndesmosis. Radiograph shows abnormal connection between calcaneus and scaphoid bone, which is the clearest in 45° oblique positioning. Lateral radiographs show typical elephant nose (trunk) signs (Fig. 8.20). Discussion Elephant nose sign is an X-ray feature of calcaneonavicular coalition (CNC). The incidence of tarsal coalition is about 1% to 2%. CNC is the most common type of syndesmosis. The main clinical symptoms include pain, limited movement, and stiffness. Radiography shows abnormal connection between calcaneus and scaphoid bone, which is the clearest in the 45°oblique position. Lateral radiographs show typical elephant nose signs. Lysak systematically

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8.22 Fat–Blood Interface Sign Feature Fractures in the joint capsule can cause blood in the joint capsule. The fat in the bone marrow overflows into the joint capsule through the fracture. Because fat is relatively light, it floats on the blood level, forming a so-called fat–blood interface (FBI). X-ray, CT, and MRI can all show this sign.

Fig. 8.20  Lateral radiograph of the foot shows the union of calcaneus and scaphoid, presenting as elephant nose sign (arrow)

Explanation FBI sign has a certain significance in the interpretation of joint trauma. FBI sign is quite common in practice and its occurrence is related to the following factors: positioning of the patient, amount of bleeding, amount of fat spilled, and the restriction of the joint capsule (Figs. 8.21 and 8.22).

Discussion Fat–blood interface sign (FBI) is caused by an described the morphological changes of CNC intracapsular fracture resulting in articular capand divided the relationship between sule hemorrhage. Bone marrow fat spills into the ­calcaneoascaphoid syndesmosis into four types articular capsule through the fracture site. [56]: type 1 is a wide calcaneoascaphoid space Because the fat is relatively light, it floats on the with smooth and clear bones; type 2 is a narrow blood, forming the so-called fat–blood interface. calcaneoascaphoid space with flat and widened This sign is found in severe bone and joint injuanterior calcaneal space with smooth, regular, ries, especially in the major joints of the limbs, and clear bones; type 3 is a narrow calcaneo- especially in the knee joint. Most of the injuries ascaphoid space with a flat and widened ante- are accompanied by tibial plateau fractures, as rior calcaneal space with rough and irregular well as shoulder, elbow, ankle (talus and calf), and unclear bones; and type 4 is calcaneo- and hip joints; this will affect or delay the healing ascaphoid fusion. of trauma. Lipidemia of the joints is associated Radiography is currently the most com- with intraarticular fractures [58]. Therefore, monly used imaging method for the diagnosis accurate imaging diagnosis of traumatic arthroof the CNC. X-ray diagnosis of CNC relies on plasty is helpful to guide clinical treatment. The elephant nose sign, which shows that the abrupt pathological basis of this disease is generally increase of anterior and superior calcaneus is believed to be the compression of blood and adiblunt protrusion resembling the elephant nose. pose tissue into the articular capsule after intraCrim et  al. reported with simple training the capsular fracture. When joint trauma occurs, both sensitivity of diagnosis is 80–100% and the articular cartilage and synovium release enzymes specificity is 98% in diagnosing the X-ray that prevent blood coagulation. Blood is still in a signs of CNC [57]. CNC needs to be a differen- liquid state. Because of the low density of fat and tial diagnosis from degenerative joint disease. the high density of blood, a stratification of fat in CT and MRI are superior to X-ray in the diag- the upper and blood in the lower levels is formed, nosis of CNC and can detect abnormal fine that is, the lipid–liquid level. morphological changes in the calcaneal-­ X-ray radiography can show this sign, but navicular space. special positioning must be applied. It is possi-

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Fig. 8.21 (a–c) A 28-year-old male patient with left knee trauma caused by traffic accident. Sagittal T1WI, T2WI, and axial T2WI with fat-saturated MRI present the “fat– blood interface” sign in superior patellar bursa. Fat shows

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high signal on T1WI and T2WI, located above the interface, and low signal on T2WI with fat-saturated image; blood shows low signal on T1WI, located below the interface, and a high signal on T2WI

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Fig. 8.22 (a–c) A 23 year-old man with left knee trauma. “Fat–blood interface” sign is noted in the superior patellar bursa, fat showing hypointensities on fat-saturated T2WI

ble to observe this sign only in horizontal projection, whereas in shoulder joint projection, it can only be shown in anteroposterior or posteroanterior position. CT and MRI are sensitive to FBI signs. The knee joint has 5 ml fat and 15 ml blood, and both CT and MRI can show the levels of fat and liquid. The effusion signals of various components are obviously contrasted, which can better show this sign. Because of the different components of blood in different periods, the signal intensities are different, and there even may be multiple fluid levels, and different degrees of signal changes after the mixture of blood and intracapsular fluid, so the signal changes above and below the fluid level vary. However, the display of small fractures and a

nondisplaced fracture line on MRI are not so good as that on CT or X-ray, which requires comprehensive analysis. FBI sign is a characteristic imaging manifestation of traumatic lipohematosis of the joint and a reliable sign of intracapsular fracture of the joint [59].

8.23 Elbow Fat Pad Sign Feature Normally, on a lateral radiograph of the elbow held in 90° of flexion, lucency that represents fat is present along the anterior surface of the distal humerus, and no lucency is visualized along its posterior surface. An elevated anterior lucency or

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a visible posterior lucency on a true lateral radiograph of an elbow flexed at 90° is described as a positive fat pad sign. The presence of intracapsular fracture of the elbow is usually indicated. Explanation The synovium of the elbow joint is located in the deep part of the fibrous sac. Three small masses of fat rest in the radial, coronoid, and olecranon fossae and are separated by the fibrous sac and form fat pads. The anterior fat pad is a summation of radial and coronoid fat pads. The anterior part is strengthened by brachial muscle. On a lateral radiograph of the elbow, the anterior fat pad is usually seen as a faint line that is more radiolucent than adjacent muscle and is parallel to the anterior distal humerus. The posterior fat pad is strengthened by triceps brachii tendon and elbow muscle and is invisible under normal circumstances. When there is joint distention, the anterior fat pad is displaced further anteriorly and superiorly, and the posterior fat pad is displaced posteriorly and superiorly. The previously invisible posterior fat pad then becomes visible (Fig. 8.23).

Fig. 8.23  Lateral radiograph shows a positive fat pad sign in a 6-year-old girl. The anterior lucency (arrow) represents the elevated anterior fat pad, and the posterior lucency (arrowhead) represents the elevated posterior fat pad

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Discussion Elbow effusions are seen on lateral radiograph in the presence of fat pad sign. The elbow is frequently involved in trauma and is one of the most frequently radiographed joints in emergency departments. Although commonly emphasized as a sign of trauma, the fat pad sign frequently occurs in nontraumatic elbow disease. Fat pad displacement is a response to distention of the joint capsule and occurs irrespective of the cause. It has been described in a variety of disorders, such as hemophilia, rheumatoid arthritis, gout, osteoarthritis, and acute pyarthrosis, and can be expected to occur whenever there is distention of the joint capsule. It may be the manifestation of an occult fracture as a result of trauma, or may herald the onset of an inflammatory or other synovial process that occurs in a clinical setting. Elbow fat pads are best shown on lateral view radiography with the elbow in 90° of flexion, as any obliquity may obscure visualization. A false-­ negative fat pad sign may occur if there is poor positioning, extracapsular abnormality, or capsular rupture. Normal displacement of the posterior fat pad with the elbow in extension should not be mistaken for a sign of joint disease [60]. Rarely, properly performed conventional radiography may fail to demonstrate the fat pad sign in patients with joint effusion or capsular rupture (from severe trauma) or when there is massive soft-­ tissue swelling around the joint. Ultrasonography may be useful when conventional radiographs fail to show the fat pads or when spurious elevation of the fat pads is suspected. The value of the fat pad sign is greatest as a predictor of an intraarticular disease process at the elbow in the absence of any radiographically visible bone abnormality. Fat pad displacement is independent of fracture displacement and comminution, particularly in elbow examination in children, who often have very slight structural changes at presentation [61]. In properly performed radiography of the elbow, the fat pad sign is a highly sensitive indicator of disease processes involving the elbow joint. When present, the sign is easily demonstrable on conventional radiographs, which are often the first images obtained to study the elbow. Most important, being aware of the limitations of this sign and remembering that the sign is not specific

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to trauma alone will help provide more effective treatment for patients suspected of involvement of the elbow joint [62]. In short, when there is no sign of skeletal abnormality, the fat pad sign is of great value in indicating intraarticular lesions, especially in the diagnosis of occult elbow fracture in children.

8.24 C Sign Feature The talocalcaneal C sign is a continuous, C-shaped line that extends from the talus to the sustentaculum tali and can be seen on lateral radiographs of the ankle. Explanation The talocalcaneal C sign can be seen in patients with subtalar coalition on lateral ankle radiographs. The anatomic-pathological basis for a talocalcaneal C sign on lateral ankle radiographs is the bony bridge that extends from talar dome to sustentaculum tali, in combination with a prominent inferior outline of sustentaculum tali. The talocalcaneal C sign can also be seen in the absence of synostosis of the posterior subtalar joint in patients with a subtalar syndesmosis or synchondrosis, which lies in a plane that is not parallel with the X-ray beam. A posterior inter-

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ruption of the talocalcaneal C sign occurs in patients with radiolucent syndesmosis or synchondrosis of the medial part of the posterior subtalar joint that is parallel with the X-ray beam, or in patients with coalition of the middle subtalar joint without involvement of the posterior subtalar joint. The C sign may frequently be posteriorly interrupted in the absence of synostosis of the posterior facet; therefore, the sign has lower specificity. Subtalar coalition is frequently accompanied by a dysplastic sustentaculum tali, which may not cast a well-defined lower interface to contribute to the inferior aspect of the C sign (Fig. 8.24). Discussion Lateur and colleagues described the “C” sign on a lateral foot radiograph, which they believed was indicative of a talocalcaneal coalition [63]. Tarsal coalition is a common cause of rigid flatfoot deformity in adolescent patients. Patients with tarsal coalition may present with limited subtalar motion and pain in the area of the sinus tarsi or dorsum of the foot. Clinical diagnosis can be difficult, as most patients do not have peroneal spasm or flat feet. Numerous radiographic findings have been associated with talocalcaneal (TC) coalition, including talar beaking, a ball-­ and-­socket ankle joint, failure to see the “middle” subtalar joint, rounding of the lateral process of

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Fig. 8.24  In this 37-year-old man, ankle CT reconstruction images show the talocalcaneal C sign

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the talus, narrowing of the posterior subtalar joint space, and flattening or concavity of the undersurface of the talar neck. These observations have proven to be useful indicators of abnormal subtalar motion but are not specific for TC coalition. C sign noted on non-weight-bearing lateral ankle radiographs has been described as a feature of TC coalition. C sign is created by the medial outline of the talar dome and a bony bridge between the talar dome and the sustentaculum tali, in ­combination with a prominent inferior outline of the sustentaculum tali [64]. On standard radiographs, primary signs of subtalar coalition (i.e., narrowing and subchondral sclerosis of the posterior subtalar joint and absence of the middle subtalar joint and sinus tarsi) may be subtle or even absent in up to 50% of patients. Its secondary signs (e.g., talar beaking, ball-and-socket deformity of the tibiotalar joint, broadening of the talar lateral process, and concave undersurface of the talar neck), which are nonspecific, may be absent. Therefore, subtalar coalition can easily be missed on conventional radiographs. Lateur et al. [65] reported that in a study of 33 patients with subtalar coalition, only C sign was positive in 32 of 32 true-­ positive cases; the sensitivity and specificity were 86.6% and 93.3%, respectively, with 32 true-­ positive cases, 1 true-negative case, 0 false-­ positive cases, and 2 false-negative cases. The talocalcaneal C sign is subtle in cases of subtalar coalition with dysplastic or rounded sustentaculum tali, because the lower part of the talocalcaneal C is less prominent on lateral ankle radiographs as the X-ray beam strikes the inferior surface of the dysplastic or rounded sustentaculum tali tangentially over a shorter distance. Aplastic sustentaculum tali in patients with achondroplasia may render C sign absent. A positional artifact of the foot may cause a false-­ positive C sign in patients without subtalar coalition. The interrupted C sign may sometimes be seen with a valgus hindfoot or with inexact lateral X-ray beam angulation. CT is helpful in confirming subtalar coalition and establishing its extent, especially in patients with an interrupted C sign. MRI is ideally suited for differentiating syndesmosis and synchondrosis [66].

8.25 Target Sign Feature Target sign is a hypo-intensity area in the center surrounded by hyperintensity on T2WI. Target sign is seen in peripheral nerve sheath tumor (PNST), which is related to the composition of tumors. Explanation Pathologically, hypointensity in the central region of the tumor represents fibro-collagen tissue, whereas hyperintensity in the periphery corresponds to mucus-rich tissue. When target sign of peripheral schwannoma occurs, the central area is usually composed of an Antoni A region with richer cells, and the peripheral area is composed of an Antoni B region with poorer cells (Figs. 8.25 and 8.26). Discussion Target sign is the specific sign of PNST. The target signs were first proposed by Banks et al. [67]. PNST is a tumor originating from Schwann cells in the sheath of the nerve tract. PNST accounts for about 5% of benign soft tissue tumors. Most of the lesions are single, slow-growing painless masses with few symptoms, unless the lesions increase and cause compression symptoms [68]. Typical PNST is an isolated mass with clear margins and capsules. The general diameter is less than 5 cm. Tumor sections show various shapes, such as a solid gray-white homogeneous mass, beaded irregular nodules, multilocular cystic lesions of different sizes, or hemorrhagic and necrotic areas. MRI can clearly show the relationship between tumors and surrounding structures. Neurilemmomas are usually homogeneous or heterogeneous low and moderate signal intensity on T1WI, which is resembling adjacent muscle tissue, high signal intensity on T2WI, and most lesions showed heterogeneous high signal intensity. There is a low signal area in the center of the tumor and a high signal area around it. The target sign is the characteristic feature of extracranial neurogenic tumors. Target signs are correlated with histological features of the tumors; that is,

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Fig. 8.25 A 35-year-old man with peripheral nerve sheath tumor of the left forearm. Axial (a) and sagittal (b) T2WI with fat saturation show target sign (arrow), with

hypointensity in the center of the tumor and surrounding hyperintensity

Fig. 8.26 (a, b) A 64-year-old woman with multiple peripheral nerve sheath tumors on the ischiadic nerve of the right thigh. T2WI with fat saturation shows target sign

(arrow), with hypointensity in the center of the tumor and surrounding hyperintensity

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the low signal area in the center of the lesion is fibrous collagen tissue, and the high signal area around the lesion is myxoma-like tissue. Target signs are not unique to schwannomas, and neurofibromas have similar features. Neurilemmoma needs to be differentiated from neurofibroma and malignant neurilemmoma [69]. Typical MRI features of PNST are elliptical masses with clear boundaries consistent with nerve course. The target sign is helpful in the diagnosis of PNST.

The low density on CT and the high signal on MR T2WI are the result of the myxoid element and presence of water in the lesion (Fig. 8.27).

Discussion Aggressive angiomyxoma is relatively rare and has been sporadically reported. It most commonly occurs in the lower pelvis, perineum, or genital area of females, usually in the third to fifth decade; these are six times more common in females. The predominant location of the mass in the pelvis and the female predilection suggest 8.26 Swirl Sign that hormonal factors are important. It is not a malignant tumor, but it is locally aggressive and Feature tends to infiltrate adjacent structures [70]. Swirl sign is the CT or MRI feature of an aggresThe CT features are variable and include a sive angiomyxoma (AAM) manifested as soft-­ hypoattenuating or iso-attenuating mass tissue masses locating in pelvic cavity, perineum, involving the pelvis and perineum with and vulva. The signal or density of the lesion enhancement in the contrast-enhanced scan, resembles or is slightly lower than that of the which may show the classical swirled appearmuscle. There are strips of lower-density shadow ance. MRI is the modality of choice in charin the center of the lesion, with “swirled” or strat- acterization of the mass as well as for ified enhancement after enhancing. assessing the extent of the mass. The mass is usually iso-intense to muscle on T1WI and Explanation hyperintense on T2WI with “swirled” areas of The swirled appearance is likely caused by fibro- low signal areas within. This morphology is vascular stroma of AAM, which are stretched as characteristic of this tumor. The hyperintense they extend and involve the pelvic diaphragm. signal in T2WI is caused by the myxoid ele-

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Fig. 8.27 (a, b) A 42-year-old woman presented with lower abdominal and pelvis pain for more than 8 months. Sagittal and axial T2WI show a hyperintense well-defined

mass in the pelvic with “swirled” areas of low signal areas within (arrow)

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ment and presence of water. The swirled appearance is likely from the fibrovascular stroma, which are stretched as they extend and involve the pelvic diaphragm. On postcontrast T1WI, the mass shows significant enhancement from vascular component of the neoplasm. The characteristic swirled appearance can also be seen in postcontrast T1WI [71]. The distinctive imaging appearance is characterized by very high signal intensity on T2WI and swirled or layered internal architecture in most patients.

8.27 Flow Void Sign Feature On MRI T1WI, T2WI images, multiple punctate or tubular low-signal areas can be seen in or around the lesion, representing dilated vessels, called the flow void sign. Explanation Because there are multiple dilated and distorted blood vessels in or around the lesion, which manifest as multiple dots or tubular low-signal flow voids on MRI, the flow void sign is common in bone metastasis of renal cell carcinoma (Fig. 8.28).

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Discussion Flow void sign is a common sign on MRI in renal cell carcinoma with bone metastasis. It was first reported by Choi et  al. in 2003 [72]. Renal cell carcinoma (RCC) is a group of malignant tumors originating from renal tubular epithelial cells that must be considered in the differential diagnosis of any metastatic tumors. In patients with RCC, bone is the second most common site of metastasis after lung. A large number of low-signal punctate or tubular structures, namely flow void sign, are often observed on MRI of renal cell carcinoma bone metastases, which represent the dilated blood vessels that supply or drain the tumor [73, 74]. However, other musculoskeletal lesions with rich blood supply, such as arteriovenous malformation, hemangioma, synovial sarcoma, fibrosarcoma, osteochondroblastoma, giant cell tumor, osteoid osteoma, and aneurysmal bone cyst, may also show flow void sign on MRI. Although the specificity of flow void sign is not high, when metastatic lesions are confined to the skeletal system, it is still helpful to establish the diagnosis and treatment of RCC bone metastasis. Although the diagnostic sensitivity and specificity of flow void sign have yet to be determined, the significance of this sign lies in its correlation with

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Fig. 8.28  A 38-year-old male patient with spinal metastases from right renal cell carcinoma. Sagittal T1WI (a), T2WI (b), and STIR (c) show a mass with moderate signal intensity and hypointensity (arrow) at multiple points

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blood vessels, which is still helpful to the diagnosis and treatment, especially in patients with occult primary renal tumors.

8.28 Button Sequestrum Sign Feature Button sequestrum sign refers to a lesion locating in the bone and consists of bone opacity surrounded by a relatively well-defined lucent area. Initially described on radiographs, this sign can also be observed on CT scans. Explanation Button sequestrum sign is not specific for a single disease. A lucent area may result from numbers of processes. In cases of osteomyelitis, the lucent area is caused by infectious organisms that destroy the bone, which is then replaced by purulent material and granulation tissue. In cases of eosinophilic granuloma, the bone is replaced by an erosive accumulation of histiocytes that make

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the area appear lucent. The central opacity represents an island of dead bone (Fig. 8.29). Discussion This sign was first described as a radiologic manifestation of eosinophilic granuloma, a localized form of Langerhans cell histiocytosis [75]. Langerhans cell histiocytosis (LCH) is a systemic disease of unknown etiology, of which eosinophilic granuloma (EG) is the most common and mild form. Sometimes a remnant of bone is seen centrally, known as a button sequestrum [76]. The exact cause of EG has not yet been determined, although neoplastic, viral, and immunological origins have been implicated. The disease affects children and young adults and has a male predilection. Pain, tenderness, and soft-tissue swelling at the affected site are the most common symptoms. EG most commonly affects the skull, followed by the long bones, pelvis, ribs, spine, and mandible [77]. The button sequestrum sign is most often identified at radiography. In cases in which the

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Fig. 8.29 (a) A 22-year-old man. Lesion in lower segment of left femur consists of a lucent area with a central sclerotic focus, which is referred to as “button sequestrum sign” (arrow). (b) A 12-year-old boy with chronic pyo-

genic osteomyelitis of right tibia. The lesion in the upper part of the right tibia consists of a lucent area with a central sclerotic focus, which is referred to as the “button sequestrum sign” (arrow)

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presence of the sequestrum within a lytic lesion is questionable or not apparent, CT can help increase visualization of central density [77]. Studies reserve this appearance for four entities: osteomyelitis, eosinophilic granuloma, fibrosarcoma, and lymphoma. In osteomyelitis, an infectious organism destroys the bone, which is then replaced by purulent material and granulation tissue, thereby producing the lucent area. The central opacity represents an island of dead bone, and identification of such sequestrum can be an important indication for surgery in chronic osteomyelitis [78]. Other entities can demonstrate the button sequestrum sign on radiographs. Partially calcified intraosseous lipoma can also appear as a bone opacity surrounded by an area of relative lucency. Case reports of other conditions with a similar appearance include tuberculous osteitis, radiation necrosis, metastatic carcinoma, fibrous dysplasia, epidermoid and dermoid cyst, hemangioma, and meningioma. In most cases, lesions have only a lytic area without a bone opacity. It should be mentioned that the button sequestrum sign is an uncommon appearance of all these disorders, including EG. The absence of the sequestrum broadens the differential diagnoses even further.

References 1. Jin HA, Yim SJ, Yu SS, Ko TS, Lee JH. The double flipped meniscus sign: unusual MRI findings in bucket-handle tear of the lateral meniscus. Knee. 2014;21(1):129–32. 2. Haramati N, Staron RB, Rubin S, Shreck EH, Feldman F, Kiernan H.  The flipped meniscus sign. Skelet Radiol. 1993;22(4):273–7. 3. Fujikawa A, Amma H, Ukegawa Y, Tamura T, Naoi Y.  MR imaging of meniscal malformations of the knee mimicking displaced bucket-handle tear. Skelet Radiol. 2002;31(5):292–5. 4. Nguyen JC, De Smet AA, Graf BK, Rosas HG. MR imaging-based diagnosis and classification of meniscal tears. Radiographics. 2014;34(4):981–99. 5. Helms CA, Laorr A, Cannon WD. The absent bow tie sign in bucket-handle tears of the menisci in the knee. AJR Am J Roentgenol. 1998;170(1):57–61. 6. Fox MG. MR imaging of the meniscus: review, current trends, and clinical implications. Radiol Clin North Am. 2007;45(6):1033–vii. https://doi.org/10.1016/j. rcl.2007.08.009.

323 7. Terzidis IP, Christodoulou A, Ploumis A, Givissis P, Natsis K, Koimtzis M. Meniscal tear characteristics in young athletes with a stable knee: arthroscopic evaluation. Am J Sports Med. 2006;34(7):1170–5. 8. Dunoski B, Zbojniewicz AM, Laor T.  MRI of displaced meniscal fragments. Pediatr Radiol. 2012;42(1):104–12. 9. Vaishya R, Vijay V, Vaish A, Agarwal AK, Ghonge NP. Double posterior cruciate ligament sign on magnetic resonance imaging: imaging variants, mimics, and clinical implications. J Orthop Case Rep. 2017;7(6):76–9. 10. Facchetti L, Schwaiger BJ, Gersing AS, et  al. Cyclops lesions detected by MRI are frequent findings after ACL surgical reconstruction but do not impact clinical outcome over 2 years. Eur Radiol. 2017;27(8):3499–508. 11. Cha J, Choi SH, Kwon JW, et al. Analysis of cyclops lesions after different anterior cruciate ligament reconstructions: a comparison of the single-bundle and remnant bundle preservation techniques. Skelet Radiol. 2012;41(8):997–1002. 12. Bradley DM, Bergman AG, Dillingham MF.  MR imaging of cyclops lesions. AJR Am J Roentgenol. 2000;174(3):719–26. 13. Vahey TN, Hunt JE, Shelbourne KD. Anterior translocation of the tibia at MR imaging: a secondary sign of anterior cruciate ligament tear. Radiology. 1993;187(3):817–9. 14. Chiu SS.  The anterior tibial translocation sign. Radiology. 2006;239(3):914–5. 15. Kijowski R, Sanogo ML, Lee KS, et  al. Short-term clinical importance of osseous injuries diagnosed at MR imaging in patients with anterior cruciate ligament tear. Radiology. 2012;264(2):531–41. 16. Guenoun D, Le Corroller T, Amous Z, Pauly V, Sbihi A, Champsaur P. The contribution of MRI to the diagnosis of traumatic tears of the anterior cruciate ligament. Diagn Interv Imaging. 2012;93(5):331–41. 17. McIntyre J, Moelleken S, Tirman P.  Mucoid degeneration of the anterior cruciate ligament mistaken for ligamentous tears. Skelet Radiol. 2001;30(6):312–5. 18. Chudasama CH, Chudasama VC, Prabhakar MM.  Arthroscopic management of mucoid degeneration of anterior cruciate ligament. Indian J Orthop. 2012;46(5):561–5. 19. Mao Y, Dong Q, Wang Y. Ganglion cysts of the cruciate ligaments: a series of 31 cases and review of the literature. BMC Musculoskelet Disord. 2012;13:137. 20. Camacho MA. The double posterior cruciate ligament sign. Radiology. 2004;233(2):503–4. 21. Vaishya R, Vijay V, Vaish A, Agarwal AK, Ghonge NP. Double posterior cruciate ligament sign on magnetic resonance imaging: imaging variants, mimics, and clinical implications. J Orthop Case Rep. 2017;7(6):76–9. 22. Venkatanarasimha N, Kamath A, Mukherjee K, Kamath S.  Potential pitfalls of a double PCL sign. Skelet Radiol. 2009;38(8):735–9.

324 23. Kerimaa P, Väänänen M, Ojala R, et al. MRI-guidance in percutaneous core decompression of osteonecrosis of the femoral head. Eur Radiol. 2016;26(4):1180–5. 24. Manenti G, Altobelli S, Pugliese L, Tarantino U. The role of imaging in diagnosis and management of ­femoral head avascular necrosis. Clin Cases Miner Bone Metab. 2015;12(suppl 1):31–8. 25. Karantanas AH, Drakonaki EE. The role of MR imaging in avascular necrosis of the femoral head. Semin Musculoskelet Radiol. 2011;15(3):281–300. https:// doi.org/10.1055/s-0031-1278427. 26. Narayanan A, Khanchandani P, Borkar RM, et  al. Avascular necrosis of femoral head: a metabolomic, biophysical, biochemical, electron microscopic and histopathological characterization. Sci Rep. 2017;7(1):10721. 27. Gondim Teixeira PA, Savi de Tové KM, Abou Arab W, et  al. Subchondral linear hyperintensity of the femoral head: MR imaging findings and associations with femoro-acetabular joint pathology. Diagn Interv Imaging. 2017;98(3):245–52. 28. Spaeth HJ, Abrams RA, Bock GW, et al. Gamekeeper thumb: differentiation of nondisplaced and displaced tears of the ulnar collateral ligament with MR imaging. Radiology. 1993;188(2):553–6. 29. Clavero JA, Alomar X, Monill JM, et  al. MR imaging of ligament and tendon injuries of the fingers. Radiographics. 2002;22(2):237–56. 30. Simerjit Singh M, Pai DR, Avneet K, Ruchita D. Injury to ulnar collateral ligament of thumb. Orthop Surg. 2014;6(1):1–7. 31. Lee J, Papakonstantinou O, Brookenthal KR, Trudell D, Resnick DL.  Arcuate sign of posterolateral knee injuries: anatomic, radiographic, and MR imaging data related to patterns of injury. Skelet Radiol. 2003;32(11):619–27. 32. Yoo JH, Bo KY, Ryu HK. Lateral epicondylar femoral avulsion fracture combined with tibial fracture: a counterpart to the arcuate sign. Knee. 2008;15(1):71–4. 33. Snyder SJ, Karzel RP, Del Pizzo W, et al. SLAP lesions of the shoulder. Arthroscopy. 1990;6(4):274–9. 34. Tuite MJ, Cirillo RL, De Smet AA, et  al. Superior labrum anterior-posterior (SLAP) tears: evaluation of three MR signs on T2-weighted images. Radiology. 2000;215(3):841–5. 35. Boutin RD, Marder RA.  MR imaging of SLAP lesions. Open Orthop J. 2018;12:314–23. 36. Symanski JS, Subhas N, Babb J, et  al. Diagnosis of superior labrum anterior-to-posterior tears by using MR imaging and MR arthrography: a systematic review and meta-analysis. Radiology. 2017;285(1):101–13. 37. Fritz EM, Pogorzelski J, Hussain ZB, Godin JA, Millett PJ.  Arthroscopic repair of humeral avulsion of the glenohumeral ligament lesion. Arthrosc Tech. 2017;6(4):e1195–200. 38. Rebolledo BJ, Nwachukwu BU, Konin GP, Coleman SH, Potter HG, Warren RF.  Posterior humeral avulsion of the glenohumeral ligament and associated

H. Yang et al. injuries: assessment using magnetic resonance imaging. Am J Sports Med. 2015;43(12):2913–7. 39. Chung CB, Sorenson S, Dwek JR, Resnick D.  Humeral avulsion of the posterior band of the inferior glenohumeral ligament: MR arthrography and clinical correlation in 17 patients. AJR Am J Roentgenol. 2004;183(2):355–9. 40. Brennan D, O’Connell MJ, Ryan M, et al. Secondary cleft sign as a marker of injury in athletes with groin pain: MR image appearance and interpretation. Radiology. 2005;235(1):162–7. 41. Byrne CA, Bowden DJ, Alkhayat A, Kavanagh EC, Eustace SJ.  Sports-related groin pain secondary to symphysis pubis disorders: correlation between MRI findings and outcome after fluoroscopy-guided injection of steroid and local anesthetic. AJR Am J Roentgenol. 2017;209(2):380–8. 42. Woods GW, Stanley RF, Tullos HS. Lateral capsular sign: X-ray clue to a significant knee instability. Am J Sports Med. 1979;7(1):27–33. 43. Stallenberg B, Gevenois PA, Sintzoff SA Jr, Matos C, Andrianne Y, Struyven J.  Fracture of the posterior aspect of the lateral tibial plateau: radiographic sign of anterior cruciate ligament tear. Radiology. 1993;187(3):821–5. 44. Albtoush OM, Horger M, Springer F, Fritz J. Avulsion fracture of the medial collateral ligament association with Segond fracture. Clin Imaging. 2019;53:32–4. 45. Alyas F, Tirabosco R, Cannon S, Saifuddin A. “Fallen fragment sign” in Langerhans’ cell histiocytosis. Clin Radiol. 2008;63(1):92–6. 46. Killeen KL.  The fallen fragment sign. Radiology. 1998;207(1):261–2. 47. Park JS, Ryu KN.  Hemophilic pseudotumor involving the musculoskeletal system: spectrum of radiologic findings. AJR Am J Roentgenol. 2004;183(1):55–61. 48. Cai JH, Gan LF, Zheng HL, Li H.  Iliac hyperdense line: a new radiographic sign of gluteal muscle contracture. Pediatr Radiol. 2005;35(10):995–7. 49. Ni B, Li M.  The effect of children’s gluteal muscle contracture on skeleton development [article in Chinese]. Sichuan Da Xue Xue Bao Yi Xue Ban. 2007;38(4):657–77. 50. Rai S, Meng C, Wang X, et al. Gluteal muscle contracture: diagnosis and management options. SICOT J. 2017;3:1. 51. Meldon SW, Hargarten SW. Ligamentous injuries of the wrist. J Emerg Med. 1995;13(2):217–25. 52. Sulkers GSI, Strackee SD, Schep NWL, Maas M.  Wrist cineradiography: a protocol for diagnosing carpal instability. J Hand Surg Eur Vol. 2018;43(2):174–8. 53. Cobby MJ, Schweitzer ME, Resnick D. The deep lateral femoral notch: an indirect sign of a torn anterior cruciate ligament. Radiology. 1992;184(3):855–8. 54. Pao DG.  The lateral femoral notch sign. Radiology. 2001;219(3):800–1.

8 MSK 55. Kanakamedala AC, Burnham JM, Pfeiffer TR, et al. Lateral femoral notch depth is not associated with increased rotatory instability in ACL-injured knees: a quantitative pivot shift analysis. Knee Surg Sports Traumatol Arthrosc. 2018;26(5):1399–405. 56. Lysack JT, Fenton PV.  Variations in calcaneona vicular morphology demonstrated with radiography. Radiology. 2004;230(2):493–7. 57. Crim JR, Kjeldsberg KM.  Radiographic diagnosis of tarsal coalition. AJR Am J Roentgenol. 2004;182(2):323–8. 58. Czuczman GJ, Mandell JC, Khurana B.  Iliopsoas bursal extension of lipohemarthrosis: a novel imaging finding associated with hip fracture. Skelet Radiol. 2017;46(2):253–7. 59. Lugo-Olivieri CH, Scott WW Jr, Zerhouni EA. Fluid– fluid levels in injured knees: do they always represent lipohemarthrosis? Radiology. 1996;198(2):499–502. 60. Goswami GK. The fat pad sign. Radiology. 2002;222(2):419–20. 61. DeFroda SF, Hansen H, Gil JA, Hawari AH, Cruz AI Jr. Radiographic evaluation of common pediatric elbow injuries. Orthop Rev (Pavia). 2017;9(1):7030. 62. Blumberg SM, Kunkov S, Crain EF, Goldman HS.  The predictive value of a normal radiographic anterior fat pad sign following elbow trauma in children. Pediatr Emerg Care. 2011;27(7):596–600. 63. Murphy JS, Mubarak SJ.  Talocalcaneal coalitions. Foot Ankle Clin. 2015;20(4):681–91. 64. Brown RR, Rosenberg ZS, Thornhill BA. The C sign: more specific for flatfoot deformity than subtalar coalition. Skelet Radiol. 2001;30(2):84–7. 65. Lateur LM, Van Hoe LR, Van Ghillewe KV, Gryspeerdt SS, Baert AL, Dereymaeker GE. Subtalar coalition: diagnosis with the C sign on lateral radiographs of the ankle. Radiology. 1994;193(3):847–51. 66. Moraleda L, Gantsoudes GD, Mubarak SJ.  C sign: talocalcaneal coalition or flatfoot deformity? J Pediatr Orthop. 2014;34(8):814–9. 67. Banks KP.  The target sign: extremity. Radiology. 2005;234(3):899–900. 68. Jee WH, Oh SN, McCauley T, et al. Extraaxial neurofibromas versus neurilemmomas: discrimination with MRI. AJR Am J Roentgenol. 2004;183(3):629–33. 69. Wasa J, Nishida Y, Tsukushi S, et  al. MRI fea tures in the differentiation of malignant peripheral nerve sheath tumors and neurofibromas. AJR Am J Roentgenol. 2010;194(6):1568–74. 70. Srinivasan S, Krishnan V, Ali SZ, Chidambaranathan N. “Swirl sign” of aggressive angiomyxoma–

325 a lesser known diagnostic sign. Clin Imaging. 2014;38(5):751–4. 71. Benson JC, Gilles S, Sanghvi T, Boyum J, Niendorf E. Aggressive angiomyxoma: case report and review of the literature. Radiol Case Rep. 2016;11(4):332–5. 72. Choi JA, Lee KH, Jun WS, Yi MG, Lee S, Kang HS.  Osseous metastasis from renal cell carcinoma: “flow-void” sign at MR imaging. Radiology. 2003;228(3):629–34. 73. Chen SC, Kuo PL.  Bone metastasis from renal cell carcinoma. Int J Mol Sci. 2016;17(6):987. 74. Salapura V, Zupan I, Seruga B, Gasljevic G, Kavcic P. Osteoblastic bone metastases from renal cell carcinoma. Radiol Oncol. 2014;48(3):243–6. 75. Mitra I, Duraiswamy M, Benning J, Joy HM. Imaging of focal calvarial lesions. Clin Radiol. 2016;71(4):389–98. 76. Goosens V, Vanhoenacker FM, Samson I, Brys P.  Longitudinal cortical split sign as a potential diagnostic feature for cortical osteitis. JBR-BTR. 2010;93(2):77–80. 77. Krasnokutsky MV.  The button sequestrum sign. Radiology. 2005;236(3):1026–7. 78. Buckley B, Chan VO, Mitchell DP, et  al. The clothes maketh the sign. Insights Imaging. 2016;7(4):629–40.

Suggested Readings for this Chapter Guglielmi G, Nasuto M.  Emergency and trauma in MSK radiology. Semin Musculoskelet Radiol. 2017;21(3):165–6. Lefevre N, Naouri JF, Herman S, Gerometta A, Klouche S, Bohu Y. A current review of the meniscus imaging: proposition of a useful tool for its radiologic analysis. Radiol Res Pract. 2016;2016:8329296. Leggit JC, McLeod G.  MSK injury? Make splinting choices based on the evidence. J Fam Pract. 2018;67(11):678–83. Marinković S, Stošić-Opinćal T, Tomić O. Radiology and fine art. AJR Am J Roentgenol. 2012;199(1):W24–6. Math KR, Berkowitz JL, Paget SA, Endo Y. Imaging of musculoskeletal infection. Rheum Dis Clin N Am. 2016;42(4):769–84. Tagliafico AS, Isaac A, Bignotti B, Rossi F, Zaottini F, Martinoli C.  Nerve tumors: what the MSK radiologist should know. Semin Musculoskelet Radiol. 2019;23(1):76–84.

9

Spine Lingling Song, Wen Wang, Muxi Wu, and Alexander M. McKinney

Contents 9.1 Peripheral Spinal Cord Hypointensity Sign

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9.2 The Sugarcoating Sign

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9.3 The Polka-Dot Sign

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9.4 The Rugger Jersey Spine Sign

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9.5 The Ivory Vertebra Sign

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9.6 The Posterior Vertebral Scalloping Sign

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9.7 MRI Fluid Sign

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9.8 The Intravertebral Vacuum Cleft Sign

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9.9 The Inverted Napoleon’s Hat Sign

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9.10 The Scotty Dog Collar Sign

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9.11 The Incomplete Vertebral Ring Sign

 342

9.12 Wide Canal Sign

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9.13 The Naked Facet Sign

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9.14 The Fat C2 Sign

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References

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L. Song (*) · M. Wu Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China W. Wang Department of Radiology, Tangdu Hospital, Fourth Military Medial University, Xi’an, China A. M. McKinney Miller School of Medicine, University of Miami, Miami, FL, USA © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6_9

9.1

 eripheral Spinal Cord P Hypointensity Sign

Feature On T2WI in the setting of venous hypertensive myelopathy (VHM), hypointensity can be noted subjacent to the peripheral pia mater spinalis, which is particularly evident on gradient echo 327

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a

b

c

d

Fig. 9.1  The peripheral spinal cord hypointensity sign. (a) On sagittal postcontrast CT, there are many intensified and tortuous blood vessels surrounding the spinal cord. (b) On sagittal T2WI, there is abnormal spinal cord hypointensity, as well as serpentine and dilated perimed-

ullary venous plexi as flow voids. (c) Sagittal short TI inversion recovery (STIR) shows the same sign as in (b). (d) Postcontrast T1WI demonstrates gadolinium enhancement with tortuous and dilated perimedullary venous plexi

T2*WI and spin-echo T2WI sequences, without significant signal abnormality on the T1WI sequence. This manifestation is called the “peripheral spinal cord hypointensity sign.”

sure; as a consequence, the resulting impeded circulation damages spinal cord function. However, whether the finding of peripheral cord hypointensity represents a real pathological alteration or what this peripheral hypointensity represents is still undetermined [2]. Some investigators opined that the disease is related to the phenomenon of spinal canal veins with reversed flow with obstruction and caval reversed flow caused by vascular disease in the spinal canal (such as SDAVF, perimedullary arteriovenous fistula), dural arteriovenous fistula, vertebral arteriovenous fistula, or paravertebral venous system abnormalities (such as left renal vein, azygos vein, hemiazygos vein, accessory azygos vein). SDAVF, the most common cause for VHM, refers to the existence of a small arteriovenous shunt of blood from the radicular arteries, draining into the pial veins of the spinal cord. Because there is no venous valve in the spinal veins, when one or more supplying arteries direct flow into the spinal dural vein and through the dura mater, a special channel is formed. Under pathological conditions, once this channel is opened, it can become the fistula of a SDAVF. The arterial blood is drained through a normal vein on the surface of the spinal cord, leading to the arteriovenous

Explanation Peripheral spinal cord hypointensity sign is an MRI finding that is specific for VHM. It occurs most commonly in the setting of a spinal dural arteriovenous fistula (SDAVF). As blood flow is slow within the capillary and venous system, the deoxygenated hemoglobin leads to T2 shortening, thus causing hypointensity under the pia mater spinalis around the spinal cord (Fig. 9.1). Discussion Hurst and Grossman [1] first posited peripheral hypointensity of the spinal cord on T2WI, suggesting the presence of a venous hypertensive myelopathy (VHM). With this “sign” one should consider the possibility of an underlying spinal dural arteriovenous fistula (SDAVF). The VHM is a group of syndromes caused by a variety of vascular diseases in the spinal cord, spine, and surrounding structures. Obstruction of spinal cord venous drainage or accessory veins of the spinal canal leads to increased vein system pres-

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p­ ressure gradient disorder in the spinal cord, thus expanding the lumen, causing obstruction of the reverse flow of the spinal cord vein, edema of the cord, and subsequent stagnation of blood within capillaries; as a result, obstructions of the small arteries induce ischemia and interstitial edema within the cord, and ischemic necrosis may develop. The histopathological changes include pia mater spinal venous congestion, spinal parenchymal edema, and ischemia, as well as ultimately venous infarction of the spinal cord. The MRI findings of VHM related to the foregoing pathological changes mainly include spinal cord swelling and circuitous tubular vascular flow voids surrounding the spinal cord. T2WI depicts hyperintensity within the center of the cord, with parenchymal enhancement [3]. SDAVF have imaging features that are frequently missed or misinterpreted, which results in a significant delay to definitive diagnosis and therefore treatment [4]. Notably, the hyperintensity within the central cord is not specific for this diagnosis, as cord edema can also be seen in infectious, inflammatory, demyelinating, and vasculitic disorders of the spinal cord [3].

9.2

The Sugarcoating Sign

Feature The sugarcoating sign is a manifestation on postcontrast T1WI, with diffuse linear and nodular enhancements along the surface of the spinal cord or the nerve roots. Another name: the frosting sign. Explanation The blood–brain barrier (BBB) extends around the spinal cord and the intrathecal portion of the nerve roots. As a result, these structures usually do not enhance after the administration of contrast material. On the other hand, intradural (leptomeningeal) metastases, which adhere to the surface of the spinal cord and nerve roots, typically demonstrate enhancement on T1WI. Thus, there is a striking contrast between nonenhancing neural tissue, sheet-like enhancing tumor implants, and dark cerebrospinal fluid (CSF),

producing the sugarcoating sign in patients with leptomeningeal carcinomatosis (Fig. 9.2). Discussion Holz first reported the sugarcoating sign in 1998 [5]. This sugarcoating appearance is nonspecific on postcontrast T1WI, and may be noted with any process that affects the meninges and disrupts the BBB. A nodular enhancement pattern is said to be more specific for tumors than for infection, which usually demonstrates more linear enhancement. However, nonneoplastic conditions such as granulomatous disease (e.g., sarcoidosis), arachnoiditis, atypical infectious lesions (e.g., fungal or tuberculous), and neurofibromatosis also may occasionally produce nodular enhancement [5]. Leptomeningeal metastases of solid cancers usually result from hematogenous spreading to the subarachnoid space, direct infiltration from solid brain lesions, endoneural/perineural and perivascular spread, or iatrogenic spread following neurosurgery. Leptomeningeal metastases occur in approximately 5% to 10% of cancer patients, with breast cancer, lung cancer, and melanoma representing the three most common primary tumors. The diagnosis of leptomeningeal carcinomatosis is typically made in patients in advanced stages of cancer, where their prognosis remains poor, usually with only months of expected survival, even if multimodality treatment is promptly initiated [6]. Although postcontrast imaging is preferred, fluid-attenuated inversion recovery (FLAIR) images can be utilized to depict the presence of meningeal carcinomatosis without using gadolinium. When the sulci or cisterns show areas of hyperintensity on unenhanced FLAIR images in patients with cancer, meningeal carcinomatosis can be strongly suspected, and contrast-enhanced images should be obtained. In particular, postcontrast FLAIR has been shown to be as sensitive as, and perhaps even more sensitive than, postcontrast T1WI in detecting leptomeningeal disease. It is speculated that the appearance on noncontrast FLAIR is related to the fact that tumor cells in meningeal carcinomatosis induce an increase in CSF proteins, which is a typical laboratory finding; the increase in CSF proteins

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a

b

Fig. 9.2 (a, b) A patient with bronchogenic lung carcinoma. Sagittal T1-CE images of the cervical spine show linear, nodular, peri-medullar contrast enhancement, indicating the sugarcoating sign of leptomeningeal metastases

produces a change similar to that seen in subarachnoid hemorrhage on FLAIR images. Hence, unenhanced FLAIR images are more sensitive than T2WI in detecting this disorder. T2 elongation is difficult to discern on spin-echo T2WI as the CSF is normally hyperintense on that sequence [7]. Although the sugarcoating sign is highly suggestive of leptomeningeal tumor, its absence does not exclude neoplastic dissemination in the CSF.  Because of its microscopic nature, only approximately 20% to 25% of confirmed leptomeningeal carcinomatosis cases are positive for imaging findings. Thus, CSF cytological analysis is the most definitive test, sometimes necessitating flow cytometry via a higher-volume lumbar tap. CSF analyses yields positive results in approximately 45% to 55% of

leptomeningeal carcinomatosis cases. The yield may also be further increased using serial lumbar punctures [5].

9.3

The Polka-Dot Sign

Feature Parallel bands of osteosclerotic shadow can be seen in the longitudinal arrangement of the affected vertebral body contour when vertebral hemangioma (VH) involves vertebral bone, accompanied with strips of alternating increased and reduced density, which resemble a polka-dot sign (i.e., a defensive enclosure of vertical stakes). Other name: the corduroy sign [8].

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Fig. 9.3  A hemangioma of T9 vertebra in a 62-year-old woman. Sagittal (a) and coronal (b) nonenhanced computed tomography (NECT) reformats show the “palisades sign”; axial CT (c) shows the typical polka-dot sign

Explanation The polka-dot sign is a typical X-ray sign of VH.  The low-density area represents bone erosion and displacement by the vascular lesion, wherein most of the bone structure in these vertically hypodense regions is absorbed and the normal bone trabeculae disappear. The parallel strip-shaped bone hardening shadow is the tumor interspersed between the trabecular bone, and the residual trabecular bone is arranged in slightly more hyperdense longitudinal rows, thought to arise from compensation and adaptation, induced by weight on the vertebrae [9] (Fig. 9.3). Discussion X-ray radiography showed that the damaged vertebra usually exhibits the typical “palisade” or “corduroy” morphology in VH, including decreased bone mineral density, cortical thinning, and residual trabecular thickening [9]. VHs represent only 2% to 3% of all spinal tumors, with an incidence of 10% to 12% in the general population; only 0.9% to 1.2% of these are symptomatic, with the most common complaint (in the rare instance when they are symptomatic) of back pain. Asymptomatic patients with VHs are usually detected incidentally during imaging studies obtained for other diseases or symptoms. The physical examination shows pain in the spinous processes upon direct percussion [10]. Histologically, hemangiomas are divided into four categories: capillary, cavernous, arteriovenous, or venous, with the first two being the most prevalent. The pathological basis of the polka-dot sign is that the hemangioma parenchyma is com-

posed of pathological vessels with varied diameters, substituting for the normal parenchyma, and composed of fatty bone marrow. Most of the bone tissue at the lesion site is absorbed, thus exhibiting the stripe-shaped regions of reduced density. The interspersed stripes of thickened trabecular bone are caused by the residual compensatory reaction of the trabecular bone. When the remaining trabecular bones are arranged in longitudinal orientation, they form the palisade shape, or corduroy appearance. When they are irregularly intersected, they form the shape of trabeculae or mesh. Based on radiographic analysis, aggressive VH can be classified as typical or atypical. More than one third of aggressive VH lesions may have at least one atypical feature [11]. Another appearance is on CT images, where a typical sign of small punctate foci of high attenuation represents sparsely thickened hyperdense trabeculae, surrounded by hypodense stroma, thus forming the pathognomonic “spotted” or “polka-dot” appearance (polka-dot sign) as well; this mimics the polka dot clothing pattern [9]. Again, on the reconstructed sagittal and coronal CT images, such typical VHs demonstrate the classical vertically oriented thickened trabeculae that represent the “palisade” or “corduroy” sign [8]. MRI show high signals on both T1WI and T2WI. Intralesional fat causes the hyperintensity on T1WI whereas the hyperintensity on T2WI is the result of increased water content. Aggressive VHs contain less fat and more vascular stroma [11]. Such “atypical hemangiomas” may appear as bright on STIR or fat-suppressed FLAIR imaging, may have enhancement

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on post-contrast T1WI, and may even lose their T1 hyperintensity over time, thus simulating malignancy such as vertebral metastases. The polka-dot sign can be easily identified based on a single imaging modality. CT has a pivotal role in the workup of VHs with an atypical MRI appearance. When a VH is suspected to be aggressive based on one imaging technique, both CT and MRI (occasionally catheter angiography) can be performed to further delineate the lesion and etiology. CT-guided biopsies are indicated for these atypical cases [8, 11].

9.4

 he Rugger Jersey T Spine Sign

Feature On X-ray radiograph (AP or lateral views), the upper and lower edge endplates of the thoracolumbar vertebral body form a sclerotic zone, with a clear band in the center of each vertebral body. The combination of alternating parallel sclerotic zones and clear bands resemble the stripes on rugby sweaters; hence, most scholars refer to this as the “rugger jersey spine” appearance. This appearance of a clear band between two sclerotic zones also resembles that of a sandwich cake; thus, this is sometimes called the “sandwich cake sign.” Explanation The sclerotic zones at the lower and upper edges of the vertebral endplate represent excessive deposition of bone-like material, often caused by chronic renal failure. Although their ossification is insufficient for functional purposes, these bone-like tissues are denser than normal vertebrae, causing opacity of the sclerotic zones on X-ray radiograph [12] (Fig. 9.4). Discussion The “rugger jersey spine sign” is most common in secondary hyperparathyroidism associated with osteosclerosis and is caused by chronic renal failure (renal osteodystrophy). X-ray findings of renal osteodystrophy include osteomalacia, osteosclerosis, and soft-tissue calcifications; of note, osteosclerosis caused by renal ­osteodystrophy tends to

Fig. 9.4 A 50-year-old woman with chronic renal failure for 10  years. Reconstructed sagittal CT image shows increased opacity of the thoracic vertebral bodies, consistent with chronic osteosclerosis from renal osteodystrophy

occur in the axial skeleton, especially in the pelvis, ribs, and spine. About 20% of patients with chronic uremia and renal osteodystrophy develop osteosclerosis [13]. The mechanism in the setting of chronic renal failure is reduced intestinal absorption of calcium, calcium- and phosphorus-related metabolism disorders, changes in the metabolism of vitamin D, and serum calcium reduction; that reduction stimulates parathyroid hyperplasia, thereby resulting in secondary hyperparathyroidism. The increased activity of osteoclasts leads to

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increased release of calcium from bone and reactive osteogenesis resulting from the loss of bone minerals. The result is an overproduction of “bonelike tissue” (excluding hydroxyapatite), which appears hyperopaque on radiography, resulting in the appearance of the rugger jersey spine sign [14]. Other diseases can produce image features similar to the rugger jersey spine sign, such as Paget’s disease, osteoporosis, metastatic osteomas, or osteomalacia [14, 15]. The rugger jersey spine sign often affects multiple vertebral bodies, which are multi-segmental. The increased density along the upper and lower endplates of the vertebral body differs from Paget’s disease, bone metastasis, or lymphoma. The vertebral changes caused by bone metastases and lymphoma are also called the “ivory vertebral body” (see the following discussion), and these diseases usually invade only an individual vertebral body. Regarding Paget’s disease, which can have the appearance of a “picture frame” vertebra, the rugger jersey spine is significantly different; in Paget’s, the cortex of the vertebral body becomes thicker (result of excessive osteogenesis disrupting cortical formation), leading to the hyperdensity of bony cortex on radiography. Other systemic diseases can produce X-ray features resembling the rugger jersey spine sign, including skeletal fluorosis and myelofibrosis. Both diseases involve the axial bone, leading to increased bony

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Fig. 9.5 Lateral (a) and posteroanterior (PA) (b) plain film X-ray views of the thoracic spine. Note the multilevel sclerosis of at least four vertebral bodies (arrows) with the ivory vertebra sign, in the setting of metastasis from lung

density of the vertebrae, pelvis, and chest. Fluorosis can be distinguished from renal osteodystrophy by such conditions as extensive ligament calcification, periostitis, and vertebral osteophytes. Bone marrow fibrosis can be distinguished, as it produces megalosplenia and cortical thinning in the long bones. Hence, detailed clinical and laboratory data can help identify these disorders.

9.5

The Ivory Vertebra Sign

Feature On X-ray or axial CT, the vertebral body shows patchy or diffusely increased attenuation, but the structure of trabecular bone and cortical bone cannot be distinguished clearly, together causing an appearance of “ivory,” thus being called the ivory vertebra sign. Explanation Bony lesions may stimulate the mesenchymal cells of vertebrae to differentiate into osteoblasts. The ensuing osteogenesis of the trabecular and cortical bone results in thickening and fusion, creating either patchy increased attenuation, or alternatively increased attenuation of the entire vertebral body, resulting in the “ivory vertebra sign” (Fig. 9.5).

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cancer. (c) Another patient, a 75-year man with skeletal fluorosis. (d) Sagittal CT shows sclerosis of multiple vertebral bodies and appendices of a 79-year-old woman with bronchogenic carcinoma

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Discussion The ivory vertebra sign is found in different lesions in adults and children, being mainly observed in osteogenic metastasis, Paget’s disease, or lymphoma. In adults, osteogenic metastases are predominantly from prostate carcinoma and breast cancer [16]. The ivory vertebra sign is relatively rare in children, and is even less frequent in malignancies such as osteosarcoma, neuroblastoma, medulloblastoma, and osteoblastoma, which directly invade the vertebral body or cause osteogenic bone metastases in the vertebra. When osteogenic bone metastases occur in the vertebral body, mesenchymal cells in the bone tissue are transformed into osteoblasts, and bony proliferation occurs (tumoral bone). Thus, trabecular and cortical bone are simultaneously involved, leading to the blurred interface between these two types of bone. The resulting tumoral bone occupies part or the whole vertebral body, showing homogeneously increased ivory-like attenuation. Of note, osteogenic metastases of prostate carcinoma, being quite common in elderly male patients, involve multiple vertebral bodies, whereas those of breast cancer, being quite common in elderly women, usually involve a single vertebral body [17]. As just described, several types of lesions can cause an osteogenic appearance of a vertebra. Osteogenic lesions are characterized by osteoblast proliferation within the vertebral body. The cotton flocculent-like lesions occupy part of or the whole vertebral body with homogeneously high-attenuation shadow, forming the ivory vertebra sign. Osteolysis and osteogenesis may exist together, but osteogenesis can cover the osteolytic destruction to form this sign. Such osteolytic destruction leads to scallop-shaped changes in the vertebral body, which is the characteristic manifestation of lymphoma; of note, lymphoma can invade the vertebral body, producing osteolytic, osteogenic, or mixed lesions. Also, lymphoma can directly invade the vertebral body, more commonly via hematogenous pathways, rather than through proximate lymph nodes. Paget’s disease with vertebral involvement can also manifest as the ivory vertebra sign, which can involve single or multiple vertebral bodies, or

even all the vertebrae; in Paget’s, the lesion is initially dominated by osteoclast activity. As the osteoclastic activity gradually decreases, the osteoblastic activity gradually increases as the lesion becomes chronic. The osteogenic activity is more obvious within the periphery of the vertebral body than centrally, causing the thickened bony trabeculae to align in the vertical direction. On X-rays or axial CT images, this phenomenon can form the “picture frame vertebra,” which is characteristic of Paget’s disease [18].

9.6

The Posterior Vertebral Scalloping Sign

Feature The posterior vertebral scalloping sign is most evident on lateral spine radiographs. It is the enlargement of the concave shape of the normal cortices of the posterior edge of one or more vertebral bodies, similar to the edge of the scallop shell. This sign can also be seen in sagittal or axial images of CT or MRI. Explanation A slight depression of the posterior edge of the vertebral body is considered a variation of the normal body. If the depression of the posterior edge of the vertebral body increases to form single or multiple levels of scalloping, this pattern indicates pathological changes of the vertebral body (Fig. 9.6) Discussion The posterior vertebral scalloping sign was first proposed and described by Wakely et  al. [19] in 2006. It is characterized by the enlargement of the central depression on the posterior cortex of the vertebral body, which resembles the edge of a scallop shell. The posterior margin of the vertebral body can appear slightly depressed under normal conditions, but single or multiple scallop-­like depressions are mainly visualized with intraspinal lesions or abnormal vertebral bodies, whether from direct erosion or disorders of the spinal canal. The most common cause of a single scallop depression is

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Fig. 9.6 (a–c) CT shows the lumbar spinal canal expanded irregularly around the lumbar spine at L5 level. (d, e) On sagittal T1WI and STIR, hypointensity and

hyperintensity are found in the spinal canal at L5. (f) On axil T2WI, heterogenous high-signal intensity is found in the spinal canal at L5

increased intraspinal pressure caused by intraspinal tumors, with local forward indentation of the posterior edge of the vertebral body, such as from ependymoma or schwannoma. Causes of multi-level scalloped depressions include dural ectasia (e.g., from neurofibromatosis), increased intraspinal pressure caused by communicating hydrocephalus, achondroplasia, meningocele, and cartilage dysplasia, or hereditary connective tissue disorders (e.g., Marfan syndrome, Ehler–Danlos syndrome, Loeys–Dietz syndrome, or homocysteinuria). In the setting of posterior vertebral scalloping, the etiology of a single level of scalloped indentation is easy to diagnose, although multiple-level scalloping may lead to a differential diagnosis because of the varied mechanisms. However, the

specific cause is usually readily identified on physical or laboratory tests. The scallop-like depressions caused by neurofibromatosis (often having cutaneous skin lesions as well) often involve several vertebral bodies to varied extents, whereas those caused by communicating hydrocephalus and meningocele mostly involve the lumbar vertebral bodies [20, 21]. The typical stenosis of facet joints, pedicle shortening, and osseous spinal canal can be seen in patients with achondroplasia; the scallop-like depression on the posterior edge of the vertebral body is a compensatory change secondary to spinal canal stenosis. Hereditary connective tissue disorders usually have a clinically identifiable phenotype characteristic of the disorder, or are seen on dedicated labs in some cases. If the indentation of the

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posterior edge is at multiple levels with posterior vertebral scalloping, further diagnostic tests may be needed to identify the causes.

Discussion Baur et al. first proposed the “MRI fluid sign” in 2002, as an MRI sign indicating a benign osteoporotic vertebral compression/insufficiency frac-

ture [22]. On STIR sequence, the fluid sign appears as a focal, linear, or triangular high signal superimposed on the diffuse high-signal background of the collapsed vertebral body. The linear/triangular fluid signal is equivalent to that of the CSF, thus giving it the name MRI fluid sign. If a fluid signal is visible in the compressed vertebral body on the MRI examination, it suggests that there is vertebral body osteoporosis, and typically a benign, nonneoplastic lesion. Of note, vertebral compression fractures can be caused by trauma, osteoporosis, or tumoral invasion; in the elderly, osteoporosis and tumor-induced ­vertebral compression fractures are the most common causes. Thus, in routine, everyday imaging interpretation, the need to differentiate the cause of a collapsed vertebra from a benign nonneoplastic etiology (e.g., osteoporosis), or benign neoplastic etiology, versus a malignant neoplasm, is very important. As such, Baker et al. found that benign lesions causing vertebral body fractures are associated with an inhomogeneous MRI fluid sign, whereas vertebral body fractures caused by malignant etiologies are associated with a relatively homogeneous MRI fluid sign, indicating that the tumor cells have replaced the bone marrow throughout the vertebral body [23]. ­

Fig. 9.7 A 54-year-old woman with T12 vertebral compression fracture. (a) T1WI demonstrates that the T12 vertebral body has mostly lower signal within the midportion. (b) On T2WI, it is difficult to discern that there is high sig-

nal (edema) within the midportion. (c) STIR shows the vertebral body has a diffusely high signal, but the higher linear signal is observed within the midportion (arrows), typical of the linear signal from a benign insufficiency fracture

9.7

MRI Fluid Sign

Feature MRI fluid sign is a sign of vertebral compression fracture on MRI, which is characterized by a focal, linear, or triangular high signal superimposed on the diffusive high signal background of the collapsed vertebral body, best visualized on STIR MRI. The signal of the lesion is akin to that of CSF. Explanation If the MRI fluid sign is visible within the compressed vertebral body, it nearly always suggests that the vertebral body is showing insufficiency (osteoporosis), and typically represents a benign lesion (Figs. 9.7 and 9.8).

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Fig. 9.8  A 50-year-old man with L1 vertebral compression fracture and L2 linear fracture. (a) T1WI demonstrates L1 and L2 vertebral bodies. (b) On T2WI, it is difficult to discern that there is high signal (edema). (c)

STIR shows the vertebral body was diffusely high in signal, but low linear signal is observed within the upper portion, typical of linear signal from a benign insufficiency fracture

I­ n addition, this sign suggests a malignant lesion when a paravertebral soft-tissue mass is also observed. In the study by Baur et al., 23 (26%) of 87 vertebral compression fractures showed the fluid sign. Among them, 52 cases (40%) with fractures caused by osteoporosis had a fluid sign. In 35 cases of vertebral compression fractures caused by metastatic tumors, only 2 cases (6%) had a fluid sign. Of note, 16 fluid signs were located near the upper endplate, 5 were adjacent to the lower endplate, 20 were in the anterior vertebral body, and 2 were in the middle of the vertebral body. It is believed the MRI fluid sign is more common in acute vertebral fractures, and most of them are benign and nonneoplastic lesions. There is usually no or minimal liquid signal in the malignant lesions of the vertebral body. Histopathological examinations have confirmed that the liquid signal is caused by edema within the part of the vertebral body not invaded by tumor in those cases with neoplasms [24]. The appearance of the MRI fluid sign can help differentiate benign compression fractures from malignant lesions. Frederic et al. found that the mean T2* relaxation time constants of acute benign and malignant vertebral compression fractures were significantly different; the accuracy of differentiating acute benign from

­ alignant vertebral compression fractures was m 73% and 89%, respectively [25]. The MRI fluid sign can be an important sign for vertebral compression fracture. If MRI reveals linear or triangular fluid signal within the vertebral body, it usually indicates the acute/subacute vertebral body compression fracture is related to benign osteoporosis.

9.8

The Intravertebral Vacuum Cleft Sign

Feature An X-ray plain film shows a thin linear or semilunar clear area located in the center, or subjacent to, the endplate of the collapsed vertebral body. On noncontrast CT there is an irregular lucent (hypoattenuating) region, which is hypointense on all MRI sequences. Explanation A linear or semilunar translucent shadow represents the cleft formed by vertebral compression fractures, which is caused by a secondary compression fracture of the vertebral body with ischemic necrosis, resulting in the intervertebral cleft. The gas is released when the pressure within the

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Fig. 9.9  The intravertebral vacuum cleft sign of a fracture appears as a transverse, linear, or semilunar radiolucent shadow on plain radiographs and on coronal (a) and

sagittal (b) NECT reformats. The intravertebral vacuum cleft sign appears more heterogeneous and irregular on CT axial view (c)

cleft becomes negative, and the dissolved gas within the fluid within the vertebral body and serum escapes, ultimately forming a vacuum phenomenon with gas density within the vertebral body (Fig. 9.9).

natively arise from compression or embolization of the adjacent vertebral blood vessels, subsequently resulting in the decrease or even interruption of the vertebral blood supply. Ultimately, compression fractures occurring in vertebral bodies develop ischemic necrosis, resulting in the vertebral body cleft. The change to a negative pressure within the cleft subsequently forms a vacuum within the vertebral body. This sign can also occur in the setting of a vertebral body insufficiency osteoporotic fracture. Of note, the vertebral arteries of osteoporotic patients may be narrowed by atherosclerosis, fat embolism, prior/ chronic compression, or v­arious other causes, resulting in decreased vertebral blood supply. Osteoporosis can also lead to chronic vertebral fracture, vascular injury, and further reduction of the blood supply of a vertebra, making the osteoporotic vertebral body susceptible to ischemic necrosis [27]. On X-ray radiograph, the cleft is located in the central portion/midportion of the vertebral body, or alternatively inferior to the edge of the superior endplate, which is manifested as a thin linear

Discussion The intravertebral vacuum cleft sign, also known as a vacuum phenomenon in the vertebral body, was first proposed by Maldague in 1978 [26]. This sign refers to the presence of gas shadows within the vertebral body fracture. The majority of osteoporotic fractures occur within the vertebral body (including primary and secondary osteoporosis). A vacuum phenomenon within a vertebral body is most common in the thoracolumbar segments. A vertebral body with an obvious compression deformity, situated predominately near the endplate, is usually easy to recognize [27]. The vertebral body vacuum phenomenon is a characteristic manifestation of vertebral ischemic necrosis, also known as vertebral osteonecrosis, but the etiology is as yet unclear [28]. It may arise from the injury itself, or alter-

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or semilunar translucent shadow with a regular contour/shape, 1–3 mm thick, and usually having sclerotic edges; occasionally, the cleft may appear slightly rounded. When the vertebra is stretched or extended, the gas shadow increases in size or thickness. With flexion, the gas shadow/ cleft becomes smaller and even disappears; it may reappear when the vertebral body is extended or stretched. Both AP and lateral radiographs can depict this sign, but the lateral view may help determine the location of the vacuum cleft. Noncontrast CT can show an irregular translucent area within the vertebral body; on all MRI sequences, a vacuum cleft is hypointense from the gas signal with surrounding magnetic susceptibility artifact. Occasionally, the cleft can be confused with gas in the adjacent intervertebral space, such as most commonly from degenerative disease, which is more common than the intravertebral vacuum cleft that occurs within the vertebral body. The intravertebral vacuum cleft sign is highly suggestive of osteonecrosis, although not specific. Overall, most vertebral body vacuum phenomena occur following benign compression fractures, the majority of which are osteoporotic fractures, whereas this only rarely occurs within the vertebral bodies affected by malignant tumors. This sign signifies a benign lesion of the vertebral body, essentially excluding malignant tumors of the vertebral body, and avoiding further unnecessary imaging studies [29].

9.9

 he Inverted Napoleon’s T Hat Sign

Feature The inverted Napoleon’s hat sign is visualized on the spine radiographs at the lumbosacral junction level, typically being L5–S1. The bone that overlaps the sacral vertebrae resembles the dome of an inverted “Napoleon’s cap,” where the transverse process of the superior vertebra (typically L5) forms the receding rim of a hat. Explanation In the standing position, gravity from the upper body passes through the lumbosacral joint, caus-

ing the vertebra to slide forward/anteriorly. Because of stable restriction from the anterior longitudinal ligament and the iliolumbar and posterior ligaments, the lumbosacral joint can resist anterior dislocation. Additionally, the lower joint surface of L5 can move forward and form a joint with the posterior joint surface of S1; the anatomy of the facet articulation is also usually helpful to prevent the lumbosacral joint from slipping forward and downward to the sacral promontory. The angle between the L5 and S1 axis is about 140°, whereas the angle between the S1 vertebral body and horizontal line is 40°; therefore, most of the external forces act on the superior articular process of S1. Any significant decrease of these stabilizing forces will lead to the “inverted Napoleon’s hat sign” (Fig. 9.10). Discussion Anterior displacement of the lumbosacral joint usually results from a lack of bone stability, which is most commonly secondary to either congenital defects of the L5 lamina, pedicle defects of the L5 inferior facet, or lamina defects of the superior sacral facet. According to the Newman classification system, a spondylolisthesis is classified into one of five categories: I: congenital or developmental abnormalities; II: spondylolysis; III: degenerative; IV: traumatic; V: pathology [30], with an addition to the original Newman classification of a sixth category, VI: post surgery. Overall, isthmus disconnection/disarticulation, degeneration, and postoperative causes are the most common types (of note, the interarticular region is often referred to as the isthmus or pars interarticularis). An isthmic fracture or excessive stretching/lengthening can cause subluxation of the vertebral body, such as nonunion of the isthmus and anterior displacement of the vertebral body. The spondylolysis had often been mistakenly referred as isthmic defects, particularly of the L5 vertebra. However, the term spondylolysis is now most commonly used to refer to degenerative diseases or partial incomplete development of vertebral joints [31]. Bilateral vertebral detachments lead to a greater degree of spondylolysis, and degenerative facet arthropathy often causes less displacement.

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Fig. 9.10 (a) Posteroanterior radiograph of the lumbosacral joint demonstrates the L5 vertebral body edge projects over the sacrum. The overlapped parts and the

transverse process form the inverted Napoleon’s hat sign. (b) A lateral lumbosacral joint radiograph shows grade 1 anteriolisthesis of the L5 vertebral body on the sacrum

Degenerative anterior displacement of the spine is most common at the L4–L5 level, usually accompanied by back pain or sciatica, indicating nerve root compression. The postoperative anterior displacement of the spine is usually secondary to joint instability caused by facet joint removal (more than 50%) or secondary to adjacent horizontal facet arthrodesis and ligamentum flavum hypertrophy several years post surgery [32]. In the setting of severe spondylolisthesis or severe lumbar lordosis, an inverted Napoleon’s hat sign can be quite evident, where, in general, spondylolisthesis is most easily assessed on lateral radiographs of the spine, and helps to quantify the extent of vertebral displacement. Hence, the presence of an inverted Napoleon’s hat sign can be quite helpful for radiologists when only a lumbar posteroanterior (PA) radiograph, or a PA abdominal or pelvic radiograph, is available as a starting point; subsequently, CT or MRI can help

further evaluate the lumbosacral joints in complex cases.

9.10 The Scotty Dog Collar Sign Feature This sign is a feature that is characteristic of lumbar spondylolysis on oblique plain film X-ray views, where the collar of the scotty appears as a translucent line shadow along the vertebral isthmus (pars interarticularis), which represents the spondylolytic defect. It passes through the isthmus from the back of the upper oblique downward, just like a scotty dog wearing a collar, giving it the name of the scotty dog collar sign. Explanation The projection of the normal vertebral arch is similar to the hunting dog on oblique plain film radiographs. The projection of the transverse pro-

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Fig. 9.11 (a, b) Bilateral pars interarticularis defect (arrows) of L5 on right and left oblique radiographs of the lumbar spine

cess represents the dog’s nose and mouth, the pedicle is projected as the dog’s eye, the superior articular process/facet represents the dog’s ear, the inferior articular process is the dog’s front leg, the isthmus/pars interarticularis is the dog’s neck, the lamina is the dog’s body, the contralateral inferior articular process is the dog’s hind leg, and the contralateral transverse process is the dog’s tail. When vertebral spondylolysis occurs, a transparent fissure is visible along the dog’s neck (the isthmus), which appears akin to a dog wearing a collar (Fig. 9.11). Discussion The scotty dog collar sign is a characteristic sign of lumbar spondylolysis in the oblique lumbar X-ray image, where the mostly linear defect appears as a transparent line/shadow through the vertebral isthmus [33]. On oblique lumbar X-ray images, the transparent line passes through the isthmus from superiorly to inferiorly, akin to a dog wearing a collar. With vertebral arch collapse, there is a lesion referred to as a vertebral arch isthmic defect, which is thought to lead to

the spondylolisthesis. The cause of the disease is unknown, but the mechanism is thought related to congenital defects and trauma, where congenital developmental defects or potentially weak areas make the vertebra susceptible to injury. Additionally, trauma itself can also induce isthmic defects. Overall, spondylolyses of L5 account for 90% of spondylolytic defects, followed by L4 and other segments for the remaining 10%. The spondylolysis can be unilateral or bilateral, and is more common in men aged 20–40  years. The typical clinical symptoms are lower back pain that radiates to the hip or lower limb. The lucent defect/crack in the vertebral isthmus is a direct X-ray sign of spondylolysis. On a posteroanterior (PA) film, the spondylolysis above L4 is often clearly depicted as a transparent crevice below the annular pedicular shadow (the isthmus). The following signs may indicate the presence of spondylolysis: (1) the lateral edge of the vertebral plate may have an irregular, broken border; (2) the lateral superior edge or the inferior edge of the vertebral plate may have a crescent-shaped depression; (3) attenuation of

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the pedicle area is uneven, suggesting disrupted bone structure [34]. On lateral films, especially on flexion lateral films, the defect from the break is often clearly indicated, with a positive detection rate of about 40%; however, it is difficult to tell whether the lesion is unilateral or bilateral. The defect extends between the posterior aspect of the pedicle and the articulation between superior and inferior articular processes, traveling obliquely anterior and inferior from the posterior aspect, often with a hardened edge. In the unilateral case, sometimes only an incomplete crack or no crack is visible. The width of the crack is related to the weight of the slip: the more overt the shift, the more evident the defect on PA images. The extent of L5 slippage is better determined on a lateral film [35]; an oblique film is the best projection position for diagnosing spondylolysis. The normal vertebral arches resemble scotty dogs (as mentioned previously on such oblique plain film images). When the pars is disrupted, a transparent band can be seen in the dog’s neck, like a dog wearing a neck collar (the scotty dog collar). If the vertebra has slipped forward (anterolisthesis), the dog’s head is slipped off because the transverse process and the upper articular process move forward. Of note, spondylolysis may be most clearly seen on CT images:

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irregular fissures can be seen within the isthmus of the vertebral arch with irregular, hardened edges, mostly bilateral, and occasionally being unilateral (a “cracked ring sign”). The scotty dog collar sign is a characteristic of spondylolysis. If the X-ray oblique film depicts a transparent, linear shadow through the vertebral isthmus/pars, this suggests that the vertebral isthmus is cracked, which can aid the clinical diagnosis.

9.11 The Incomplete Vertebral Ring Sign Feature On CT images through the isthmus of the vertebral arch, the integrity of the cortical ring of the osseous spinal canal is interrupted by unilateral or bilateral rupture of the isthmus, which is called incomplete ring sign [36]. Other name: annular fissure sign. Explanation Congenital dysplasia of, or stress on, the vertebral isthmus (i.e., the pars), causes the continuity of the isthmus to be interrupted. On a CT image of the isthmus, the integrity of the cortical ring around the spinal canal is interrupted (Fig. 9.12).

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Fig. 9.12 (a, b) A 67-year-old woman presented with defects within the bilateral isthmus/pars of the L5 vertebral body on lumbar spine CT. “Double joint sign” can be observed on axial imaging

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Discussion The isthmus of the vertebral arch (also called the “pars” or pars interarticularis) refers to the segment between the superior and inferior facets of the vertebral arch. The bony vertebral canal forms a complete circular structure (cortical ring), consisting of the posterior aspect of the vertebral body, the medial wall of the pedicle, the anterior surface of the isthmus, the lamina, and the anterior portion of the spinous process. A bilateral vertebral arch fracture is more likely to cause lumbar spondylolisthesis than a unilateral fracture. When a bilateral isthmic fissure/defect and the intervertebral joint appear at the same level, the “double joint sign” can be observed. In that situation, the “pseudo-joint” is located on the medial side, whereas the “true joint” is situated posterior to the lateral side. There are two major causes for a vertebral arch fracture: one is a congenital development abnormality and the other is stress-related injury. A fracture or crack of the vertebral arch can sometimes exist in tandem with other malformations, such as spina bifida (spinal dysraphism). Also, although the degree of lumbar spondylolisthesis is mild in adolescents, the degree of slippage gradually increases with increasing age. Most lesions can be clearly diagnosed on plain film X-ray images. On an oblique plain film, the normal appearance is that of a dog shape (the “scotty dog” discussed in the prior topic), where the isthmus/pars of the vertebral arch resembles a dog’s neck. When the isthmus is disrupted, the scotty dog’s neck can have a longitudinally strip-­ like translucent fracture; if accompanied by lumbar spondylolisthesis, the transverse process and the superior articular process move anteriorly, thus widening the gap of the fracture. Simultaneously, the step-like arrangement of the lumbar vertebral facets from inferior to superior disappears. On noncontrast CT the lumbar isthmus should appear continuous in the transverse plane, where the level of the isthmus of the vertebral arch is usually about 10–15  mm above the level of the corresponding intervertebral disc. On NECT displaying the isthmic fissures, the cortical ring of the osseous spinal canal appears interrupted, and the fissures appear low in attenuation,

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spanning the isthmus, with irregular serrated ends, bony sclerosis along the edges with fragmented bone, and narrowed caliber of the spinal canal, neural foramina, and corresponding lateral recesses. Such lesions can be unilateral, with unilateral isthmic rupture, and bilateral defects are characterized by bilateral isthmic rupture. If the scan level is limited to the intervertebral disc or facet joint level, the isthmic defect may not be visible, possibly leading to a missed diagnosis.

9.12 Wide Canal Sign Feature The sagittal canal ratio (SCR) is defined as the maximal anteroposterior diameter of the spinal canal, divided by the diameter of the canal at the isthmic–spondylolisthesis level of the L1 vertebra. The normal SCR has been determined to be less than approximately 1.25. Thus, “wide canal sign” refers to a SCR equal to or larger than 1.25, mainly in isthmic spondylolisthesis patients, caused by the increased anteroposterior diameter. Explanation When the anterior vertebral body segment becomes disconnected from the posterior segments by isthmic spondylolisthesis, this causes the vertebral body to slip forward, whereas the posterior segment either does not move or slips (is displaced) posteriorly. This change increases the anteroposterior diameter of the spinal canal, thus leading to an increased SCR. In general, the most common reasons for anterior slippage of a vertebral body are osteoarthritis, remodeling of the facet joints, disc degeneration, ligamentous laxity, prior trauma, sequelae of an indolent infection, etc.; however, the “degenerative disease” category is by far the most frequent cause overall (Fig. 9.13). Discussion As in the foregoing discussion, a sagittal canal ratio (SCR) of 1.25 or greater at the level of a spondylolisthesis is considered to represent an abnormally increased sagittal canal diameter

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Fig. 9.13 (a–c) An 80-year old woman presented with spondylolisthesis of the L5 vertebral body

(i.e., a “wide canal sign”), indicating the presence of bilateral pars interarticularis defects (isthmus defects). The wide canal sign on midline sagittal MR images (being >1.25) is a reliable predictor for pars interarticularis defects at the level of the spondylolisthesis. This sign can be useful for distinguishing degenerative disease from the causes of pars interarticularis defects that mimic spondylolysis [37]. Isthmic spondylolisthesis is the anterior translation of one lumbar vertebra relative to the next caudal segment as a result of an abnormality in the pars interarticularis; this causes a variable clinical syndrome of back and lower extremity pain, and may be accompanied by varying degrees of neurological deficits at or below the lesion level [38], the most common being the fourth lumbar vertebra (L4) slipping on the fifth (L5), and L5 on S1 (sacrum). Notably, the term spondylolysis has now been expanded to include a spectrum of the following pathological conditions, including (1) stress reaction: no obvious cortical or trabecular disruption but simply intraosseous edema with associated sclerosis of the pars interarticularis, lamina, or pedicle; (2) stress fracture: a disruption of the trabecular or cortical bone of the pars, but without separation of the fracture fragments; and (3) pars fracture: a separation of the pars interarticularis

fragments with associated displacement [39]. Degenerative spondylolisthesis is characterized by osteoarthritis and remodeling of the facet joints, disc degeneration, and ligamentous laxity, resulting in anterior slippage of a vertebral body along with an intact posterior arch. This closed-­ arch spondylolisthesis configuration is frequently accompanied by symptoms of spinal stenosis and nerve root compression. Surgical treatment may be necessary in such cases, which involves decompression of the spinal canal (and spinal fusion if postsurgical instability is suspected). In contrast to isthmic spondylolisthesis, which is more common in men at the L5–S1 level, degenerative spondylolisthesis is more common in women at the level of L4–L5 [37]. In adult patients with history and physical examination findings consistent with isthmic spondylolisthesis, standing plain film radiographs, with or without oblique views or dynamic radiographs, is considered as an appropriate, noninvasive test to confirm the presence of isthmic spondylolisthesis. CT is useful in detecting subtle but suspicious pars defects that are difficult to visualize on plain radiographs. Of note, even on CT, the spondylolytic defects may be missed if they are oriented in the axial plane; sagittal and coronal reconstructions should be ­

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routinely obtained and reviewed. Overall, the wide canal sign is highly reliable and effective in differentiating isthmic and degenerative spondylolisthesis on midline sagittal MRI images of patients referred with lower back pain or radicular symptoms; other signs and modalities may initially depict the abnormality to varying degrees [39].

9.13 The Naked Facet Sign Feature The naked facet sign refers to the appearance of uncovered articular processes on CT. The affected plane depicts the isolated facets without joint space. Explanation Normally, the facet joints are symmetrical and consistently overlap at each level, and remain in the fixed position (i.e., do not deviate or dislocate or change significantly on follow-up). CT can show the facet joints and their articular spaces as resembling hamburgers, where the upper facet process forms a semicircular bun, and the upper and lower articular processes form a small round slice of bread, called the “hamburger sign.” However, although they remain relatively fixed in positioning, there can be slight physiological movement in the flexion and extension positions. Under such normal physiological conditions, the supraspinal ligament, interspinous ligament, ligamentum flavum, and articular capsule maintain their anatomical relationship; the anterior longitudinal ligament and posterior longitudinal ligament predominately align with the vertebral bodies and have an indirect role in maintaining the stability of facet joints. In severe spinal flexion and separation injury, the rupture of these ligaments with (or without) fractures can lead to anterior subluxation of the vertebral body, thus widening the distance between the facet joints, and baring the upper and lower facets (i.e., making them appear naked) (Fig. 9.14). Discussion Routine radiography is still the primary initial method in examining spinal injury, so one should

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be familiar with the routine X-ray signs of spinal trauma. Green et al. present a list of conventional X-ray signs of spinal injury that include local kyphosis, anterior subluxation of the vertebral body, posterior vertebral space widening, anterior superior vertebral wedge fracture, and separation of vertebral facet joint or spinous processes. These features are critical for early diagnosis, as subsequent spinal instability is common (20%) [40]. CT as well as sagittal and coronal reconstructions can provide intuitive visualization of bony and soft-tissue injury, as well as accurately describe the anterior and posterior structures, vertebral alignment, and the integrity of the osseous spinal canal. Anterior subluxation of the vertebral body is usually the result of ligamentous complex ruptures. Subsequently, the upper vertebral body is dislocated anteriorly, and the corresponding inferior articular process is subluxated, resulting in the exposed facet. The extent of facet exposure can be partial or complete, and further flexion forces can cause facet locking. Cross-­sectional NECT can depict the inverted facets [41]. The naked facet sign was initially used for thoracolumbar trauma and dislocation of lower

Fig. 9.14  A 45-year-old man who was injured in a traffic accident. An axial NECT image through the cervical spine shows a vertebral facet (apophyseal) joint (arrows) with the “hamburger” appearance. The superior facet of the lower vertebra forms the top bun of the hamburger, the joint space is the meat patty, and the inferior facet of the upper vertebra forms the bun beneath the hamburger. On the patient’s left side, the facet joint is dislocated, and the hamburger sign is no longer present

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thoracic facets. Although normal thoracolumbar joints differ in configuration from the cervical spine, the mechanism is similar, and thus a similarly method of evaluation can be used. In conclusion, the naked facet sign is a characteristic CT finding of spinal flexion distraction injury, suggesting severe ligamentous injury, with ligamentous rupture and spinal instability.

9.14 The Fat C2 Sign Feature The fat C2 sign represents an apparently increased gap between the anterior and posterior margins of the C2 vertebra when compared with that of the C3 vertebra on a lateral plain film radiograph of the cervical spine. Explanation The fat C2 sign results from an oblique fracture, involving the C2 body, causing displacement of either one or both anterior and posterior margins, thus increasing the anteroposterior distance between the two surfaces. The degree between oblique fracture and the coronal plane determines whether the actual fracture can be visualized on

a

b

lateral plain radiograph. This injury may occur as a result of isolated hyperflexion or hyperextension forces, or from combined hyperflexion and hyperextension. There may also be some component of vertical loading or distraction in these injuries. The fracture plane is oblique when it undergoes some degree of rotational stress. The identification of a fat C2 sign implies a potentially unstable fracture with fragment displacement, which usually requires further imaging evaluation (Fig. 9.15). Discussion The “fat C2 sign” was first proposed by Smoker et al. in 1987 [42]. It was proposed that so long as a fat C2 sign appeared on plain radiographs, no matter whether the fracture line was clearly identified or not, a C2 fracture could be definitively diagnosed [42]. Complex fractures involving the body of the axis may result from a combinational injury force, such as rotationextension, rotation-­flexion, lateral subluxation, or a complex of these. These forces/planes of injury may lead to the separation of the axis body into two or more fragments. Disruption of the anterior longitudinal ligament line occurs when a fracture fragment is displaced

c

Fig. 9.15  (a–c) Both the anterior and posterior longitudinal ligament lines are interrupted. The anteroposterior dimension of C2 is much greater than that of C3

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anteriorly, whereas posterior fragment displacement will result in interruption of the posterior line. Also, a “burst” type of fracture, or a combined hyperflexion-hyperextension injury, may produce anterior shift of one fragment and posterior shift of the other fragment, resulting in simultaneous disruption of the longitudinal ligament lines. This pattern of line displacement is commonly encountered in the traumatic setting [43]. Similarly, Davis et al. found that the combined disruption of the anterior and posterior ligamentous lines is the most common form of such injury in an autopsy series [44]. In such conditions, the anteroposterior diameter of the axis vertebral body, as visualized on plain radiographs, will be larger than the anteroposterior diameter of the subjacent normal C3 vertebral body; hence, the fat C2 term suggests a complex fracture involving the axis. The horizontal fragment shift results in the increased anteroposterior diameter of the centrum axis on plain lateral radiographs [1]. The main implication of a fat C2, as identified on plain radiographs, is an unstable fracture with fragment displacement, and further imaging assessment is necessary to evaluate the effect of the fracture on the adjacent spinal cord and meningeal structures. Imaging is critically important in the appropriate management of patients presenting with spinal trauma. Plain radiographs have essentially been replaced by multi-slice CT (MSCT), the mainstream modality utilized most in the diagnosis of bony abnormalities in the acute setting. MSCT also offers information that is useful in determining spine stability. MRI is advantageous in the delineation of spinal cord and soft tissue/ligamentous injuries and also offers prognostic information following spinal cord injury. Newer studies utilizing advanced MRI techniques have shifted the focus from macroscopic to microscopic, with diffusionweighted techniques, such as diffusion tensor imaging (DTI), offering structural information on the integrity of white matter tracts in the spinal cord [45].

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References 1. Hurst RW, Grossman RI.  Peripheral spinal cord hypointensity on T2-weighted MR images: a reliable imaging sign of venous hypertensive myelopathy. AJNR Am J Neuroradiol. 2000;21(4):781–6. 2. Quencer RM. Is peripheral spinal cord hypointensity a sign of venous hypertensive myelopathy? AJNR Am J Neuroradiol. 2000;21(4):617. 3. Jeng Y, Chen DY, Hsu HL, Huang YL, Chen CJ, Tseng YC.  Spinal dural arteriovenous fistula: imaging features and its mimics. Korean J Radiol. 2015;16(5):1119–31. 4. Hunt R, Roberts RM, Mortimer AM.  Spinal dural arteriovenous fistula: delay to radiological diagnosis and sources of radiological error. Clin Radiol. 2018;73(9):835.e11–6. 5. Holz AJ.  The sugarcoating sign. Radiology. 1998;208(1):143–4. 6. Le Rhun E, Galanis E. Leptomeningeal metastases of solid cancer. Curr Opin Neurol. 2016;29(6): 797–805. 7. Tsuchiya K, Katase S, Yoshino A, Hachiya J. FLAIR MR imaging for diagnosing intracranial meningeal carcinomatosis. AJR Am J Roentgenol. 2001;176(6):1585–8. 8. Liu SZ, Zhou X, Song A, Wang YP, Liu Y. The corduroy appearance & the polka dot sign [published online ahead of print]. QJM. 2019;2019:hcz184. 9. Persaud T.  The polka-dot sign. Radiology. 2008;246(3):980–1. 10. Gaudino S, Martucci M, Colantonio R, et al. A systematic approach to vertebral hemangioma. Skelet Radiol. 2015;44(1):25–36. 11. Wang B, Zhang L, Yang S, et al. Atypical radiographic features of aggressive vertebral hemangiomas. J Bone Joint Surg Am. 2019;101(11):979–86. 12. Wittenberg A.  The rugger jersey spine sign. Radiology. 2004;230(2):491–2. 13. Guler I, Koplay M, Nayman A, Kivrak AS, Tolu I. The  rugger jersey spine sign. Spine J. 2015;15(8): 1903. 14. Appelman-Dijkstra NM, Navas Cañete A, Soonawala D. The rugger-jersey spine. Kidney Int. 2016;90(2):454. 15. Shigenobu K, Kobayashi Y, Tsuyuzaki J.  Rugger-­ jersey spine in osteopetrosis. BMJ Case Rep. 2017;2017:bcr2017220275. 16. Matthews G, Dyer RB.  The “ivory vertebra” sign. Abdom Radiol (NY). 2017;42(1):334–6. 17. Graham TS.  The ivory vertebra sign. Radiology. 2005;235(2):614–5. 18. Braun RA, Milito CF, Goldman SM, Fernandes Ede Á. Ivory vertebra: imaging findings in different diagnoses. Radiol Bras. 2016;49(2):117–21. 19. Wakely SL.  The posterior vertebral scalloping sign. Radiology. 2006;239(2):607–9.

348 20. Chou SC, Chen TF, Kuo MF, Tsai JC, Yang SH. Posterior vertebral scalloping of the lumbar spine due to a large cauda equina paraganglioma. Spine J. 2016;16(5):e327–8. 21. Tsirikos AI, Ramachandran M, Lee J, Saifuddin A. Assessment of vertebral scalloping in neurofibromatosis type 1 with plain radiography and MRI. Clin Radiol. 2004;59(11):1009–17. 22. Baur A, Stäbler A, Arbogast S, Duerr HR, Bartl R, Reiser M.  Acute osteoporotic and neoplastic vertebral compression fractures: fluid sign at MR imaging. Radiology. 2002;225(3):730–5. 23. Baker LL, Goodman SB, Perkash I, Lane B, Enzmann DR. Benign versus pathologic compression fractures of vertebral bodies: assessment with conventional spin-echo, chemical-shift, and STIR MR imaging. Radiology. 1990;174(2):495–502. 24. Lin CL, Lin RM, Huang KY, Yan JJ, Yan YS.  MRI fluid sign is reliable in correlation with osteonecrosis after vertebral fractures: a histopathologic study. Eur Spine J. 2013;22(7):1617–23. 25. Schmeel FC, Luetkens JA, Feißt A, et  al. Quantitative evaluation of T2* relaxation times for the differentiation of acute benign and malignant vertebral body fractures. Eur J Radiol. 2018;108:59–65. 26. Maldague BE, Noel HM, Malghem JJ. The intravertebral vacuum cleft: a sign of ischemic vertebral collapse. Radiology. 1978;129(1):23–9. 27. Wu AM, Chi YL, Ni WF. Vertebral compression fracture with intravertebral vacuum cleft sign: pathogenesis, image, and surgical intervention. Asian Spine J. 2013;7(2):148–55. 28. Libicher M, Appelt A, Berger I, et al. The intravertebral vacuum phenomenon as specific sign of osteonecrosis in vertebral compression fractures: results from a radiological and histological study. Eur Radiol. 2007;17(9):2248–52. 29. Sarli M, Pérez Manghi FC, Gallo R, Zanchetta JR. The vacuum cleft sign: an uncommon radiological sign. Osteoporos Int. 2005;16(10):1210–4. 30. Wiltse LL, Newman PH, Macnab I.  Classification of spondylolisis and spondylolisthesis. Clin Orthop Relat Res. 1976;117(117):23–9. 31. Ebraheim NEH, Gagnet P.  Spondylolysis and spondylolisthesis: a review of the literature. J Orthop. 2018;15(2):404–7. 32. Talangbayan LE.  The inverted Napoleon’s hat sign. Radiology. 2007;243(2):603–4. 33. Millard L. The Scotty dog and his collar. J Ark Med Soc. 1976;72(8):339–40.

L. Song et al. 34. Legaye J. Radiographic analysis of the listhesis associated with lumbar isthmic spondylolysis. Orthop Traumatol Surg Res. 2018;104(5):569–73. 35. Mushtaq R, Porrino J, Guzmán Pérez-Carrillo GJ. Imaging of spondylolysis: the evolving role of magnetic resonance imaging. PMR. 2018;10(6):675–80. 36. Langston JW, Gavant ML. “Incomplete ring” sign: a simple method for CT detection of spondylolysis. J Comput Assist Tomogr. 1985;9(4):728–9. 37. Ulmer JL, Elster AD, Mathews VP, King JC.  Distinction between degenerative and isthmic spondylolisthesis on sagittal MR images: importance of increased anteroposterior diameter of the spinal canal (“wide canal sign”). AJR Am J Roentgenol. 1994;163(2):411–6. 38. Kreiner DS, Baisden J, Mazanec DJ, et al. Guideline summary review: an evidence-based clinical guideline for the diagnosis and treatment of adult isthmic spondylolisthesis. Spine J. 2016;16(12):1478–85. 39. Daniels JM, Pontius G, El-Amin S, Gabriel K.  Evaluation of low back pain in athletes. Sports Health. 2011;3(4):336–45. 40. Lingawi SS.  The naked facet sign. Radiology. 2001;219(2):366–7. 41. Kuzhimattam MJ, Krishnakumar R. Naked facet sign in a case of traumatic injury to the thoracic vertebra. Spine J. 2016;16(2):e37–8. 42. Smoker WR, Dolan KD. The “fat” C2: a sign of fracture. AJR Am J Roentgenol. 1987;148(3):609–14. 43. Pellei DD.  The fat C2 sign. Radiology. 2000;217(2):359–60. 44. Davis GG, Glass JM.  Case report of sudden death after a blow to the back of the neck. Am J Forensic Med Pathol. 2001;22(1):13–8. 45. Shah LM, Ross JS.  Imaging of spine trauma. Neurosurgery. 2016;79(5):626–42.

Suggested Readings for this Chapter Baig MN, Byrne F, Devitt A, McCabe JP. Signs of nature in spine radiology. Cureus. 2018;10(4):e2456. Harrop JS, Hanna A, Silva MT, Sharan A.  Neurological manifestations of cervical spondylosis: an overview of signs, symptoms, and pathophysiology. Neurosurgery. 2007;60(1) suppl 1:S14–20. Kushchayev SV, Glushko T, Jarraya M, et  al. ABCs of the degenerative spine. Insights Imaging. 2018;9(2):253–74. Roche CJ, O’Keeffe DP, Lee WK, Duddalwar VA, Torreggiani WC, Curtis JM.  Selections from the buffet of food signs in radiology. Radiographics. 2002;22(6):1369–84.

Vascular Imaging and Interventional Strategy

10

Lei Xu, Xin Chen, and Shi Zhou

Contents 10.1

Flat Cava Sign

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10.2

String of Beads Sign

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10.3

Hyperattenuating Crescent Sign

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10.4

Yin-yang Sign

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10.5

Draped Aorta Sign

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10.6

Dog Leg Sign

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10.7

Double Lumen Sign

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10.8

Floating Viscera Sign

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10.9

Double Rail Sign

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10.10 Thread and Streak Sign

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10.11 Angiographic String Sign

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10.12 Snowman Sign

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10.13 Scimitar Sign

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10.14 Mistletoe Sign

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10.15 The “3” Sign

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References

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L. Xu (*) Department of Radiology, Beijing Anzhen Hospital, Capital Medical University, Beijing, China X. Chen Department of Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China S. Zhou Department of Interventional Radiology, Affiliated Hospital of Guizhou Medical University, Guiyang, China © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6_10

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10.1 Flat Cava Sign Feature The flat cava sign refers to the inferior vena cava (IVC) flattening on at least three consecutive slices. Explanation The collapse of the IVC at multiple slices of computed tomography (CT) in trauma patients may be an important sign of insufficient blood volume from massive hemorrhage. The collapse of the IVC in patients with insufficient blood volume is most likely caused by a decrease in venous blood flow. Some patients have a collapsed IVC after clinical signs of shock. Because the collapse of IVC is an important sign of insufficient blood volume, we must pay attention to identifying it at multiple levels (Fig. 10.1). Discussion In 1988 Jeffery and Federle first referred to the phenomenon of continuous IVC flattening in three 1-cm-thick adjacent layers as flat cava sign [1]. The relationship between the flat inferior vena cava (fIVC) and blood volume is complicated, and current opinion is not uniform. The wall of the IVC is weak, and its morphology often changes significantly after traumatic blood loss or rapid injection of contrast agent or diuretic. The intracavitary pressure of the IVC is closely related to its morphology. If the direct compression and indirect traction of the distorted blood vessels are removed, IVC morphology

depends mainly on the comparison of intraluminal pressure and abdominal pressure. CT is widely used in the examination of trauma patients. The morphology of the IVC is clear. After quickly eliminating the factors that cause flattening, such as direct compression and indirect traction, fIVC can indirectly assess the status of blood volume. Eisenstat et al. [2] retrospectively analyzed the abdominal CT of 500 nontraumatic patients and identified four planes of observation: adjacent to the underside of the liver, below the renal vein, above the bifurcation of the IVC, and at the midpoint of the renal vein and the bifurcation of IVC. If the R value (long– short-diameter ratio) of any one of the four planes is 3:1 or more, this is fIVC. Liao et al. [3] established three criteria for defining fIVC: (1) R >3:1; (2) maximum transverse diameter of IVC 5 cm, the risk of rupture within 5 years increases to 25–41%; if >7 cm, the possibility of rupture increases to 72–83%. The imaging features suggesting that the aneurysm is unstable or about to rupture include aneurysm enlargement, low thrombo-luminal ratio, and thrombus bleeding, which is the high-attenuating crescent sign [9]. Suspected AAA rupture should be preceded by plain CT to prevent masking of highattenuation crescents indicating acute or impending

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Fig. 10.4 (a) In this patient with aneurysm, enhanced CT scan shows abdominal aorta enlargement; partially enhanced and partially not enhanced areas are seen, the

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rupture. The high-attenuating crescent sign, which is a CT sign of unstable AAA [10], represents blood entering the wall thrombus or the aortic wall, thus weakening the support structure of the aneurysm, and increasing the likelihood of complete aortic rupture. Once this sign occurs, regardless of the patient’s hemodynamic changes and clinical manifestations, surgery is required; otherwise, the mortality rate of acute rupture of AAA is close to 100%.

10.4 Yin-yang Sign Feature Yin-yang sign is an enhanced CT finding of aneurysms, mainly in the abdomen or cerebral ­vessels. Half the round or oval shadow with clear boundaries is enhanced while the other half is not, which resembles the Taiji symbol of “Yin-­Yang and Five Elements” in China [11]. Explanation Yin-yang sign suggests partial embolization (eccentricity) of true aneurysms and pseudoaneurysms. On postcontrast CT, increased attenuation of the lumen is filled with contrast media whereas the attenuation of the part embolized by mural thrombosis is low. Yin-yang sign can also be seen in digital subtraction angiography (DSA) and ultrasonography [12] (Fig. 10.4).

b

yin-yang sign. (b) In another case, a round aneurysmal structure is protruding from the abdominal aorta, with a patchy nonenhanced area

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Discussion Aneurysms are local or diffuse dilatations of the artery with a diameter greater than 50% of normal size. True aneurysms are caused by acquired or congenital lesions of the vascular wall that cause vasodilation but remain intact; pseudoaneurysms are caused by defects in the wall of the artery, leading to the formation of localized hematoma. True aneurysms and pseudoaneurysms can grow rapidly without causing symptoms [13]. The pathophysiological mechanism of the yin-yang sign is an aneurysm wall thrombosis that partly blocks the lumen. The main causes of mural thrombosis are abnormal blood lipids, damage to the vascular intima, and slowed blood flow. Therefore, the mural thrombosis is often limited and is often attached to the wall of the atherosclerotic aorta wall or aneurysm lumen, the inner wall is irregular, and the calcified plaque is located outside the mural thrombosis. If intramural calcification displacement and intramural lesions are found, intramural hematoma should be considered. The presence of a yin-yang sign cannot be used as a basis for the diagnosis of aneurysms [14]. In intracranial cases, it is sometimes necessary to differentiate it from larger suprasellar cystic meningiomas, craniopharyngiomas, pituitary adenomas, and hemorrhagic metastases.

10.5 Draped Aorta Sign Feature In this sign, rupture of an aortic aneurysm on CT shows the posterior wall of aorta is close to the spine but the demarcation is not clear. Explanation During the development of aortic aneurysms, compression, displacement, or erosion of peripheral organs occur, which will produce the draped aorta sign on contrast enhancement CT. This sign strongly suggests aortic wall damage and encapsulated hemorrhage (Fig. 10.5). Discussion Aneurysm rupture is a fatal clinical emergency. If the diagnosis or treatment is not timely, the fatal-

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Fig. 10.5  A 78-year-old woman with a ruptured abdominal aortic aneurysm. Posterior wall of the aorta is close to the vertebral body edge, with unclear demarcation (arrow), the draped aorta sign

ity rate can reach 90% [15]. Its clinical manifestations include abdominal pain, pulsatile mass, hypotension, and shock, but nearly one third of the patients are misdiagnosed as urinary calculi, diverticulitis, appendicitis, pancreatitis, or intestinal obstruction because they did not have these typical clinical manifestations. The draped aorta sign is helpful in diagnosing aneurysm rupture. It refers to the posterior wall of the aorta or the wall of the aneurysm close to the vertebral body and psoas major muscle, resulting in the disappearance of the normal contour [16]. Studies have reported that this sign may also be associated with vertebral erosion, suggesting that rupture of aortic aneurysm is imminent [17]. Understanding and familiarization with the draped aorta sign are very important to reduce mortality caused by rupture of aortic aneurysms. CT is one of the most effective examinations for rupture of aortic aneurysm. The larger the diameter of the aortic aneurysm, the greater the possibility of its rupture. Aneurysms may occur at any segment of the artery, but most of them occur in the abdominal aorta below the renal artery [18]. The rupture of an abdominal aortic aneurysm often occurs in the lateral posterior wall, and blood then flows into the retroperitoneal space. Retroperitoneal hematoma is the most common imaging manifestation of rupture of abdominal aortic aneurysm. CT signs of ruptured aortic aneurysm include forward displace-

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ment of kidney, extravasation of contrast medium, fluid accumulation, hematoma in retronephric and perinephric space, intraperitoneal free blood, and perirenal spider web sign. Local calcification discontinuity and unclear arterial wall are unreliable signs if there are not previous CT images for comparison. Chronic aortic rupture and bleeding can result in stratified calcification of the aortic wall and a mixed soft tissue mass around the artery. An aortic hanging sign often indicates damage of the aortic wall and encapsulated hemorrhage. CT angiography, which can show the extravasation of active contrast media, has become a routine imaging method for ruptured abdominal aortic aneurysms. However, to avoid confusion with highdensity hematoma, oral contrast agent is not needed routinely; noncontrast CT should be performed first, because intravenous contrast agent is seldomly needed to detect definite bleeding. Severe rupture of an aortic aneurysm can cause massive hemorrhage and sudden death, and the onset of the disease is more rapid. Patients with ruptured aneurysms may experience hemodynamic instability without any warning; early diagnosis is the primary, and urgent, goal for these patients.

10.6 Dog Leg Sign Feature This sign, seen in lower-extremity popliteal artery angiograms, is characterized by acute curvature of the popliteal artery lumen, which may or may not be related to lumen expansion as shown on angiography. Explanation The normal popliteal artery passes through the popliteal fossa from medial to lateral, with a relatively straight course. When popliteal aneurysms are present, because of the wall-attached ­thrombus in the dilated lumen, the lumen is narrowed and the contrast agent cannot fill the entire dilated lumen. The contrast agent flow in angiography is then called to have a dog-legged appearance (Fig. 10.6).

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Fig. 10.6  In a 50-year-old woman, lower-extremity CTA shows acute curvature of the right popliteal artery lumen and a right popliteal artery aneurysm

Discussion Uppal et  al. first proposed the dog leg sign, which is a CT sign of popliteal aneurysm [19]. When popliteal aneurysms exist, because of the wall-­ attached thrombus in the dilated lumen, narrowing of the lumen means the contrast agent cannot fill the entire dilated lumen. Contrast agent flowing on the contrast image has a dog-leg-like appearance. This finding appears in lower-­extremity popliteal angiography, is characterized by acute bending of the popliteal artery lumen, and may or may not be related to the luminal dilation shown on angiography. The popliteal aneurysm is one of the most common peripheral aneurysms: 50% are bilateral, 40% have an abdominal aortic aneurysm, 34% have a femoral aneurysm, and 25% have iliac aneurysm [20]. The clinical symptoms are mostly related to the size of the tumors. The main manifestations are a pulsatile mass in the popliteal fossa. Some patients complain of ischemic symptoms of the distal limbs caused by thromboembolism in the tumors or pseudoaneurysms caused by rupture of the tumors, which are characterized by a giant mass in the popliteal fossa or peripheral compression symptoms. Arteriosclerosis, syphilis, and trauma are the main causes of popliteal aneurysms. Morbidity is more common in males, accounting for about 70%, which may be related to genetic factors [21].

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The diagnosis of popliteal aneurysms mainly depends on the finding of dilatation of the arterial lumen and wall calcification during angiography. Doppler ultrasonography, CTA, and digital subtraction angiography can provide a definite diagnosis. However, when thromboembolism occurs in the popliteal aneurysm lumen, CTA can only show popliteal artery interruption and occlusion but cannot show the body of the aneurysm. Doppler ultrasound can show thromboembolism in aneurysms and lumens at the same time, and its cost is low. It can be followed up regularly, and it can also dynamically observe the changes of the aneurysms, providing guidance for surgical planning. In ultrasound, popliteal aneurysms often present as cystic structures with blood flow, or as cystic structures with complex echoes of blood flow and thrombus. The differential diagnosis of the dog leg sign includes distorted atherosclerotic popliteal artery, popliteal artery entrapment syndrome, and adventitial cystic disease. These lesions can cause an abnormal course of the popliteal artery but rarely produce acute curvature of the lumen. The popliteal artery entrapment shows dorsal curvature stenosis during arteriography; atherosclerosis shows irregular stenosis, and cystic lesions show eccentric stenosis with external pressure changes. For patients with the dog leg sign, attention should be paid to looking for other aneurysms, including contralateral popliteal aneurysms and abdominal aortic aneurysms. This finding may lead to changes in surgical treatment: asymptomatic popliteal aneurysms usually have better clinical outcomes after surgery than distal embolization with clinical sequelae. This finding will significantly improve the treatment of popliteal aneurysms.

10.7 Double Lumen Sign Feature On contrast enhancement CT, the aorta manifests as both true and false lumen enhancement, or false lumen enhancement and slightly delayed emptying compared to the true lumen. The two lumens are separated by dissection, so this is called the double lumen sign.

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Explanation Aortic dissection is an intimal rupture of the aorta; blood enters the aortic tunica media to form an intercalated hematoma. The original lumen of the aorta is called the true lumen and the newly formed lumen is called the false lumen. The wall between the two lumens is called the dissection. Thrombus is more likely to form in the false lumen than in the true lumen. In a few cases, the false lumen is filled with thrombus and cannot be displayed, so only a single lumen (true lumen) is displayed; the true lumen is often increased by the compression of the false lumen (Fig. 10.7). Discussion The initiating event in aortic dissection is a tear in the aortic intima through which blood surges into the aortic media, separating the intima from the adventitia. Dissections usually propagate from the intimal tear distally in the aorta, although proximal extension can occur. The origin of any arterial trunk arising from the aorta may be compromised, and the aortic valve may be rendered incompetent. Blood in the false channel can reenter the true lumen anywhere along the course of the dissection. Rupture of the aorta, as one of the most common causes of death, occurs most frequently in the pericardial space and the left pleural cavity. Aortic dissection (AD) may manifest as chest pain, back pain, abdominal pain, neurological deficit, or syncope, as well as with evidence of end-organ ischemic and mechanical dysfunction. AD is rare, but carries a high risk of mortality. The age distribution is bimodal; the most common risk factor for elderly patients is hypertension, whereas younger patients typically have other risk factors, such as medial wall abnormality or sympathomimetic toxidrome [22]. The radiologic assessment of patients with suspected aortic dissection must be based on an understanding of the treatment options and how these are to be employed in any clinical setting. Accurate CT differentiation between the true and the false lumen has previously been relatively unimportant, because surgery has been the mainstay for therapy, and therapeutic decisions have

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b

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Fig. 10.7 (a) A patient with aortic dissection shows an obvious “double lumen sign” on enhanced CT scan. (b, c) In another patient, the double lumen sign is seen on axial and sagittal views of CTA

relied predominantly on the presence or absence of involvement of the ascending aorta [23]. However, at the present time, percutaneous treatment methods are maturing and have become more prevalent, partly fueled by advances in CT angiography. Reliable CT findings that differentiate the true and false lumen may become particularly important in planning endovascular treatment

of dissection. Beak sign and large cross-sectional area on contrast-enhanced CT are the most useful indicators of the false lumen in classical acute and chronic aortic dissection. The pattern of mural calcification, presence of intraluminal thrombus or cobwebs, and wraparound feature in the transverse arch are less common and less reliable identifiers of the true and false lumens [24]. The

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diagnosis and differential diagnosis of dissection must be quickly confirmed, and the type and extent of dissection must be established to aid in formulating an appropriate therapy plan.

10.8 Floating Viscera Sign Feature The floating viscera sign is the image of the visceral branches of the aorta when the catheter is located in the compressed aortic true lumen for angiographic examination. These vessels (including the celiac trunk, superior mesenteric artery, and renal artery) seem to have no origin, so the anterograde blood flow in the true aorta is slightly or not visualized. Explanation When aortic dissection occurs, there are two pathophysiological mechanisms of branch vessel compression. One is called stationary stenosis, which refers to the origin of the branching ­vessels involved by the intimal patches raised by the interlayer, so that the subintimal hematoma extends to the wall of the branching vessels, resulting in true lumen stenosis of the branching vessels. Another is called active

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Fig. 10.8  A 53-year-old man. (a) Cather angiography shows catheter located downstream of the obstructive branch of the aortic true lumen. Visceral vessels (celiac

stenosis, which means that the intima of the interlayer does not involve the opening of the branch vessels, but the raised intima sheet crosses the branch level like a curtain. Because of the impact of blood flow, the active intima sheet blocks the branch vessels like a towel at the drain of a bathtub. The two mechanisms may occur simultaneously in the same patient. Moreover, if the intimal dissection does not involve a branch, the diameter of the supply vessel (aortic true lumen) on the plane of the branch is larger than that of the branch. At this time, the true lumen of the aorta upstream of the branch is compressed by the enlarged pseudo-­lumen of the aorta, and blood flow in the true lumen of the aorta downstream and its branches is reduced or disappears accordingly. If contrast agent is injected into the downstream aortic true lumen during angiography, the visceral branch vessels will be visible, that is, will show the floating viscera sign. At this time, the visceral vascular branches originating from the aortic pseudo-lumen will not be visualized unless there is a re-entry at the corresponding branch level. When resting stenosis occurs, angiography does not show the floating viscera sign, but a fan-­shaped margin (no re-entry) or a linear filling defect can be seen in the branching vessel lumen (Fig. 10.8).

b

trunk, superior mesenteric artery, and left renal artery) are visible. (b) The catheter is located in the pseudo-lumen, and the main visceral branches are not visible

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Discussion Aortic dissection is caused by an intimal tear of aorta for various reasons. Blood in the aortic cavity enters the middle layer of the aortic wall through the intimal tear, forming two lumens, true and false [25]. Aortic dissection is a serious aortic disease with dangerous conditions, rapid development, and high mortality. In about 30% of patients the aortic dissection is accompanied by compression and ischemia of branches, which can lead to disappearance of pulse, poor renal or other visceral perfusion, stroke, and paraplegia. Branch vessel involvement often predicts a higher mortality rate, so the floating viscera sign is very important in judging prognosis. The floating viscera sign was first proposed by Switzer in 2004 [26]. Both dynamic stenosis and static stenosis can lead to damage of the branches of aortic dissection. In the dynamic stenosis of aortic dissection, the true lumen of the aorta upstream of the visceral branch is narrowed by the pressure of the dilated pseudo-lumen of the aorta, which reduces the anterograde blood flow in the true lumen of the aorta downstream and in the branches. Injecting contrast agent into the downstream aortic true lumen can develop the branching vessels and produce visceral vascular floating sign. Branches of the aortic pseudo-lumen will not be visible unless there is a reentrant tear. The floating viscera sign not only indicates the existence of aortic dissection but also demonstrates the dynamic damage of the aortic true lumen and related visceral branches. Conventional angiography is invasive and may not be effective in judging the extent of the pseudo-lumen. If a thrombus is formed in the pseudo-lumen and does not appear, the diagnosis may be missed. Noninvasive imaging including CT, magnetic resonance imaging (MRI), and transesophageal ultrasound has been widely used in the diagnosis of aortic dissection. Especially, multi-slice CT has become the preferred imaging examination for aortic dissection with nearly 100% sensitivity and specificity. However, no matter what kind of examination is used, the most important need is to identify the true and false lumen of aortic dissection. When aortic dissection occurs at the root of the aorta and involves

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the whole aorta, iliac artery, or even femoral artery and aortic root annular dissection, if the clinical symptoms are atypical and only abdominal or thoracic scans are performed, judgment of true lumen continuity is limited.

10.9 Double Rail Sign Feature Double rail sign refers to an embolus in the lumen of the pulmonary artery causing a central filling defect with contrast agent surrounding it; it forms a strip of low density in the center of the lumen, surrounding a high-density orbital image. Other name: railway track sign. Explanation The double rail sign is a feature of pulmonary artery thrombosis on postcontrast CT resulting from contrast between the embolus located in the center of the lumen and contrast agent surrounding it (Fig. 10.9). Discussion Pulmonary thromboembolism (PTE) is a disease caused by thrombosis from the venous system or right heart that blocks the pulmonary artery or its branches. Pulmonary circulation and respiratory dysfunction are the main clinical and ­pathophysiological characteristics. The thrombus that causes PTE comes mainly comes from deep vein thrombosis. It can be classified into four types according to the location and attachment site of the thrombus in the endovascular cavity [27]. (1) The partial filling defect shows filling defect in different degrees in the vascular cavity; it is irregular in shape and can be filled with contrast media. (2) The thrombus with a wall-filled defect is attached to the vessel wall, and the contrast agent is concave or convex, filling on the side of the vessel. (3) The thrombus of the central filling defect is filled in the center of the vascular lumen. If the scanning plane is perpendicular to the blood vessel, a central point-like filling defect is seen in a cross section of the blood vessel. The contrast agent is surrounded by a ring and is called a target. If the scanning plane is parallel to

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a

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Fig. 10.9 (a–c) Double rail sign in bilateral pulmonary arteries and branches. (d) In a 23-year-old man, axial reconstruction of lung CTA shows filling defects in the right middle lobe pulmonary artery

the blood vessel, the strip filling defect appears located in the middle of the longitudinal plane of the blood vessel, and the contrast agent on both sides is symmetrically distributed; this is called the railway track sign. (4) Completely obstructed blood vessels have a truncated obstruction with no contrast agent filling, and no contrast agent passes through the distal end of the blood vessel. The direct signs of PTE include filling defects of contrast agent in the pulmonary blood vessels, with or without blood flow blockage of orbital signs, and delayed venous return. However, because of the high technical requirements, about 6% of complications and a mortality rate of 0.5% occur. Multi-slice CT (MSCT) is a reliable, safe, and simple method for diagnosing a pulmonary embolism. Not only can the direct signs of pulmonary embolism be seen above the pulmonary segment,

but the pathological changes of pulmonary parenchyma can also be simultaneously evaluated. An embolus found in the pulmonary artery above the segment is one of the diagnostic methods of PTE. The direct sign of PTE is a low-­density filling defect in the pulmonary artery, partially or completely surrounded by opaque blood flow (railway track sign), or a complete filling defect, and the distal vessel is not developed (sensitivity, 53–89%; specificity, 78–100%). Indirect signs include highdensity wedges in the lobe, banded high-density areas or discoid atelectasis, central pulmonary artery dilatation, and reduced or absent branching of distal vessels. CT has limited diagnostic value for PTE in the ­subsegment, but it can simultaneously show other chest diseases of lung and extrapulmonary diseases. MRI has potential ability to identify new and old thrombi, which may provide a basis for future thrombolysis. On T1WI and T2WI,

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it can better show double rail sign according to the formation time of the thrombus. The double rail sign is a direct sign of diagnosis of pulmonary infarction; this sign is very helpful for radiologists and also nonradiologists to increase learning and assimilation of concepts [28]. Pulmonary embolism is treated by timely thrombolysis, and the embolus may be dissolved. Therefore, the double rail sign is of great significance for the diagnosis of emergency pulmonary infarction.

10.10 Thread and Streak Sign Feature “Thread and streak sign” is usually described as the thread and chain-like contrast agent filling in the portal vein, hepatic vein, renal vein, or inferior vena tumor thrombus at the early and middle stages of angiography, contrast CT, or MRI, forming continuous or discontinuous parallel arrangement lines with contrast agent filling or abnormal enhancement. Explanation The tumor invades venous blood vessels into an embolus, vessels of the tumor grow into a cancer suppository or the long narrow blood sinus formed in the emboli, in which the sign is formed by contrast agent filling. The sign reflects the growth of tumor, such as hepatocellular ­carcinoma growing into the portal or hepatic vein, kidney tumor into renal vein, and retroperitoneal osteosarcoma into inferior vena cava, often accompanied by arteriovenous malformations. Discussion The sign was initially described as indicating tumor vessels in portal thrombi seen on angiography. The sign represents blood spaces and vessels (both veins and arteries) located in and around a tumor cast that is growing in a large branch and trunk of the portal vein. The tumor cast contains many small, narrow blood spaces inside, as well as between, the tumor and vessel wall. The spaces are lined with a layer of endothelium and extend along the long axis of the vein. Arterial blood enters the tumor thrombus, flows through and

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around the thrombus longitudinally, and mixes with the portal vein blood near the portal hilum. The thread and streak sign therefore reflects the growth of tumor, such as hepatocellular carcinoma, into the portal vein. The thread and streak signs may be seen in other hypervascular tumors that grow into a large vein and demonstrate arteriovenous shunting. The sign has also been noted in patients with renal neoplasms, as well as in a case of retroperitoneal osteosarcoma growing into the inferior vena cava that had an appearance similar to malignant liver tumors [29]. In the hepatic artery, the clearest retrograde development of the portal vein can been seen after the contrast agent is injected within 3–4s, which can be mistaken for small arterial plexus. This sign is not associated with the injection pressure. The sign can be distinguished from the portal vein thrombosis. The thrombus appears as a filling defect in the portal vein or there is no contrast agent filling in the portal vein, and there is a lack of early linear enhancement of the artery. Portal vein thrombosis indicates the presence of a clot in the portal vein lumen or a permanent obliteration of the portal vein as a result of prior thrombosis with replacement by numerous tortuous venous channels (termed cavernomas) [30]. In patients with hepatocellular carcinoma, whether the sign is seen on angiography or postcontrast CT and MRI, it should be considered that the portal vein, hepatic vein, or inferior vena cava is invaded. Contrast-enhanced ultrasonography also demonstrates intratumoral blood flow in tumor thrombi. It converts adjacent spotty signals into a linear signal and enables vessel recognition. Tumor vessels are clearly demonstrated by the presence of the thread and streak sign [31].

10.11 Angiographic String Sign Feature Atherosclerosis leads to stenosis or occlusion of the initial lumen of the internal carotid artery. In the arterial angiography image, the former shows a long-distance narrower lumen behind the initial segment, which appears as a thin line or curved shape. The latter manifests as one or several

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c­ ollateral circulations around the occluded blood vessels, and the two ends of which coincide with the distal and proximal ends of the occluded blood vessels, respectively. These two signs are called angiographic string sign. Explanation Atherosclerotic plaque leads to stenosis or occlusion of initial segment of internal carotid artery. The former is caused by a decrease in vascular pressure in the distal part of the plaque, causing collapse of the lumen and stratification of contrast agent and blood. The lumen is narrowing with a thin line or curved. The latter is caused by atheromatous plaque that stimulates neovascularization and forms a collateral circulation. Discussion The “angiographic string sign” is common in the internal carotid artery, being caused by the stenosis from atherosclerosis. The initial atheromatous plaque can be recanalized after endarterectomy or arterial stenting; the collapsed vessels in the distal segment can return to normal. In the distal part of the plaque, intravascular contrast agent and blood can be stratified, and the thicker the tube diameter, the slower the blood flow, and the greater the difference in the specific gravity of contrast agent and blood flow, thus the more obvious the stratification phenomenon. Because the velocity of the contrast agent is less than that of blood flow, if a blood vessel moves in the direction of countergravity, the direction of contrast agent and blood flow may be opposite, forming a phenomenon in which contrast agent is poorly filled. Therefore, angiographic string sign is caused by the combination of vessel wall collapse caused by reduced intravascular pressure and contrast agent and blood flow stratification [32]. In selective carotid angiography, the blood vessels in the proximal segment of internal carotid artery are narrowed; the distal lumen is narrowed for a long distance, appearing linear or curved, and even becomes thinner or indistinguishable, forming the angiographic string sign [33]. The proliferation of neovascularization, increase in density of the vascular network

around the plaques, and communication between neovascularization and vascular wall-nourishing blood vessels and the formation of collateral circulation can also form the angiographic string sign. The angiographic string sign formed by this collateral circulation is phlegm and multiple, and some patients have larger collateral vessels, which is different from the sign formed by the collapse of the vessel wall [34]. Arteriography can show the degree of stenosis, partial or multiple, and the oblique image can also distinguish the illusion caused by the overlap of the external carotid artery. The branch of the latter does not enter the internal carotid artery of the pyramid, and the angiographic string sign is formed by the occlusion of the blood vessel; the contrast agent is in a thin bead shape along the internal carotid artery and finally enters the basilar artery ring.

10.12 Snowman Sign Feature Snowman sign is seen on radiography of the supracardiac total anomalous pulmonary venous connection (TAPVC), showing the quasi-circular contour of superior vena cava and vertical vein laid on the upper side of the cardiac border, which looks like a snowman. Explanation TAPVC refers to a cyanotic congenital defect in which all four pulmonary veins fail to make their normal connection to the left atrium. This defect results in drainage of all pulmonary venous return into the right-heart-systemic-venous circulation. The classic snowman sign is present in young children with supracardiac TAPVC (Fig. 10.10). Discussion Among all the four anatomical variants of TAPVC, supracardiac TAPVC is the most frequent type seen, according to the multicenter study. Supracardiac TAPVC is caused by retained pulmonary vein connections to the cardinal venous systems. In affected patients, the pulmonary veins from both lungs gather and form a common chamber from which blood can ascend

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ate pulmonary pathways and connections in great detail. As CTA better shows lung parenchyma, the bronchia, and pulmonary vasculature, exposure to radiation during the examination remains a problem to be solved [36, 37]. MRA requires a long scanning time, which may not be available to infants as they are not sedated enough to finish the examination. Snowman sign on radiography may hint to the existence of supracardiac TAPVC but cannot establish the diagnosis.

Fig. 10.10  Chest radiograph of an infant with supracardiac total anomalous pulmonary venous connection (TAPVC) shows dilation of the superior vena cava, innominate vein, and the silhouette produced by the vertical vein. Pulmonary vasculature is engorged; the cardiac silhouette is mildly enlarged

through a “vertical vein.” The vertical vein often connects to the innominate vein and then affluxes into the superior vena cava. The diagnosis of TAPVC can be made by various modalities, but the typical “snowman sign” is not always seen on chest radiography. Findings on X-ray are not specific and cannot be simply used to diagnose TAPVC. The clinical manifestation and imaging findings mainly depend on the presence and severity of the obstruction. Patients with unobstructed TAPVC may have a mildly enlarged heart size and the parenchyma of the lung may be normal. The classic snowman sign is present in young children with supracardiac TAPVC as there is no significant stenosis or compression affecting the pulmonary veins and the venous confluence. In patients with obstructed TAPVC, however, the size of heart may be normal and pulmonary congestion and parenchyma edema may exist, along with the dilation of the pulmonary artery. The typical snowman sign may not be found in these patients. Although the X-ray is not specific enough for the diagnosis of TAPVC, echocardiography serves as the most frequently modality to diagnose the underlying causes of such cyanotic congenital heart disease [35]. The gold standard for the diagnosis of TAPVC has been interventions such as cardiac catheterization. Both CTA and MRA can evalu-

10.13 Scimitar Sign Feature Scimitar sign refers to the abnormal connection from right lower pulmonary venous to hepatic vein, portal vein, or inferior vena cava (IVC). Chest radiography shows the tubular high-­density shadow extending from the right margin of heart to the diaphragm, which parallels the right heart border. The curved course of the right pulmonary vein shows the characteristic appearance of a Turkish sword, a scimitar, on radiography. Explanation The term “scimitar” was suggested to characterize the radiographic finding of a curvilinear, scimitar- or Middle Eastern sword-shaped density along the right cardiac border. The typical scimitar sign is usually seen in the partial anomalous pulmonary venous connection (PAPVC) with only a single pulmonary vein abnormally affluxing into the inferior vena cava, whereas the total anomalous pulmonary venous connection may not have this kind of sign (Fig. 10.11). Discussion A variety of congenital defects are commonly associated with this specific type of anomalous pulmonary venous connection. It is a rare autosomal dominant disorder with an incidence of 2 in 100,000, affecting more women than men [38]. The syndrome is characterized by the combination of hypoplasia of the right lung and right pulmonary artery, cardiac dextroposition, and extracardiac left-to-right shunting through the scimitar vein. Adults or elder children with

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drome [40]. The diagnosis could also be made by interventional modalities such as cardiac catheterization or pulmonary artery angiography. Interventional cardiology can also occlude small anomalous connections to refrain left-to-right shunting.

10.14 Mistletoe Sign Fig. 10.11  Scimitar vein on CTA. Curved density from scimitar-like right lower lobe vein is draining into inferior vena cava (IVC)

s­ cimitar syndrome may present with manifestations of fatigue, dyspnea, recurrent pneumonia, and some signs of right heart failure; symptoms of infantile scimitar syndrome include failure to thrive, cyanosis, and pulmonary artery hypertension. However, patients with a single anomalous pulmonary vein without associated defects are usually asymptomatic and have a good prognosis [39]. The scimitar sign on chest radiography may offer the first clue to find the defect, but other conditions may also produce the sign without the features of scimitar syndrome, which should draw our attention to differentiation. The term “meandering right pulmonary vein” was coined to describe the presence of the scimitar sign and an anomalous right pulmonary vein that drains normally and tortuously into the left atrium [40]. The initial diagnosis of scimitar syndrome is often made by echocardiography and confirmed by other imaging modalities such as CTA or MRA. CT can better demonstrate the anomalous pulmonary veins and other associated abnormalities; CTA especially is an invasive angiography intuitively showing the scimitar sign that the right pulmonary vein abnormally drains into IVC, portal vein hepatic vein, or the right atrium; also, it may show some cases with right lung hypoplasia and other malformations. Cardiac MRI can accurately assess the pulmonary venous anatomy, quantification of the ratio of pulmonary to systematic blood flow, the dilation of the right heart and pulmonary artery, and the left-to-right shunt. Thus, cardiac MRI also serves as a modality well suited to aid in the decision making of the syn-

Feature The perivascular masses around the coronary arteries on coronary CT angiography (CCTA) and cardiac magnetic resonance (CMR) resemble the shape of mistletoe. Explanation Mistletoe is a plant that attaches to the branches of other plants, which is like the perivascular soft tissue masses attached to the coronary tree. Also, the mass around the coronary artery may have some relationship with retroperitoneal fibrosis (RPF), according to some case reports, as a manifestation of the RPF cardiac involvement (Fig. 10.12). Discussion RPF is a perplexing disorder characterized by excessive tissue proliferation, consisting of chronic inflammation and marked fibrosis in periaortic or peri-iliac retroperitoneum that entraps the ureters or other abdominal organs [41]. RPF includes two kinds of forms, the idiopathic forms or Ormond disease, and secondary forms caused by malignancy or chronic inflammations and other conditions [42]. The clinical symptoms may conclude atypical chest or abdominal pain, weight loss, and fatigue. Maurovich-Horvat et al. reported a 69-year-old woman in whom was first found a confluent, irregularly shaped retroperitoneal tissue mass on CT growing around the aorta and trunk of the iliac artery, with the obstruction of both sides of the ureters. Follow-up biopsy and histological analysis confirmed the diagnosis of RPF. After 4 years of immunosuppressant therapy, there was no significant change of the retroperitoneal mass, and the same was seen on

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a

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b

Fig. 10.12 (a, b) Curved multiplanar reconstruction of coronary CT angiography (CCTA) shows the size of perivascular soft tissue (white arrow) around the middle seg-

ment of the left anterior descending artery (LAD). The lumen is moderately narrowed

the consequent ­biological therapy. Then, transthoracic echocardiography was performed, and no abnormality was found, although the cine CMR on transverse view demonstrated a softtissue mass around the proximal part of right coronary artery (RCA) and the left anterior descending (LAD), showing delayed material enhancement. Subsequently, CCTA was performed to assess whether there was obstruction or narrowing of the coronary lumen caused by the mass, and the finding showed mild to moderate stenosis to the proximal segment of RCA, LAD, and ramus intermedius (RI). From this case, a relationship between the peri-coronary mass and retroperitoneal fibrosis is likely [43]. In another, different, case reported by Xiao et al., RPF had an excess level of IgG4, but the imaging examination also showed soft-tissue masses growing around the left circumflex artery (LCX) and RCA with histological confirmation [44]. So, RPF can also be regarded as a kind of immunological disease, occurring independently but associated with other autoimmune disease. RPF can also demonstrate multifocal fibroinflammatory lesions, which belong to the range of immunoglobulin G4-related disease (IgG4-RD) [45]. The differential diagnosis for the described coronary pathological abnormality includes coronary arteritis, which is also a rare finding in

CCTA.  The imaging manifestations of systemic vasculitides, such as Takayasu disease, Kawasaki disease, and Behcet disease, include aneurysms, stenoses, mural thickening, and dissections. The presence of mistletoe sign on CMR and CCTA is probably rare, but it might be a characteristic manifestation of RPF. With the increasing number of noninvasive cardiac imaging tests performed worldwide, the recognition of the mistletoe sign could be helpful in diagnosing RPF [43].

10.15 The “3” Sign Feature The “3” sign (also called incisura of the aortic arch) is a characteristic imaging finding for diagnosing coarctation of the aorta (especially tubular hypoplasia) on X-ray radiography. Explanation On posteroanterior or left anterior oblique radiographs, the conjunction of the aortic arch (or dilated left subclavian artery, LSCA) and the descending aorta shows a double arch-like notch or defect that looks like the number “3.” Indentation of the aortic wall at the site of coarctation with pre- and postcoarctation dilatation can produce this sign (Fig. 10.13).

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Fig. 10.13 Chest radiography and CT angiography (CTA) show typical “3” sign consisting of the enlarged and distorted aortic knob and LSCA forming the upper

portion of the arch, the waist at the site of the coarctation, and the lower portion formed by the poststenotic proximal descending aorta

Discussion Coarctation of the aorta (CoA) is a narrowing of the aorta, usually located at the insertion of ductus arteriosus and distal to the left subclavian artery. This defect accounts for 4% to 6% of all congenital heart disease [46]. The precise pathogenesis is still unknown, and there may be a genetic predisposition and association with Turner syndrome (loss of an X chromosome) [47]. As mentioned previously, although most patients have a discrete narrowing of the descending aorta at the insertion of the ductus arteriosus, there is a spectrum of aortic narrowing that encompasses the usual discrete thoracic lesions, long segmental defects, and tubular hypoplasia. In a considerable proportion of patients, this defect is accompanied by complex cardiovascular abnormalities such as bicuspid aortic valve, ventricular septal defect (VSD), and transposition of the great artery and patent ductus arteriosus (PDA) [48]. The findings on chest radiograph vary with age and the severity of the coarctation. In infants with heart failure, the chest radiograph shows generalized heart size with increased pulmonary vascular markings caused by pulmonary congestion. A barium swallow radiograph, although not routinely performed nowadays, may demonstrate

a “reverse 3” or “E” sign. The diagnosis may be accurately confirmed by noninvasive imaging methods, particularly echocardiology. In most patients, high-quality transthoracic two-­ dimensional and Doppler echocardiography can make the diagnosis and detect an accompanying congenital heart defect, including infants with PDA [49]. Color and pulsed Doppler echocardiography can localize the area of coarctation by demonstrating increased velocities and turbulence, as well as forward diastolic flow. The severity of CoA can also be estimated by continuous wave Doppler and calculating the ratio of the maximal velocity across the narrow area [49]. Cardiovascular MRI (CMRI) or CTA clearly defines the location and severity of CoA, as well as collateral vessels [49]. Echocardiography often provides adequate anatomical and hemodynamic information, and CMRI or CTA serves as a complementary diagnostic tool providing important anatomical data before intervention or surgery. For adults or adolescent patients with CoA, CMRI or CTA is recommended for initial and follow-up diagnosis, and cranial MRA or CTA is also appropriate to search for underlying intracranial aneurysms [50]. CMRI is generally preferred over CTA to decrease the radiation and contrast burden. Given the accuracy of noninva-

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sive modalities for diagnosis and determination of severity, cardiac catheterization for CoA is generally performed in conjunction with a therapeutic intervention and evaluation of patients with complex congenital heart disease [51]. In adults, interventional methods are indicated when coronary artery disease is suspected. The clinical diagnosis of CoA can be made based upon the characteristic findings of systolic hypertension in the upper extremities, diminished or delayed femoral pulses, and low or unobtainable arterial pressure in the lower extremities. The 3 sign serves as a typical imaging finding on radiography, but further accurate diagnosis is expected to be made by echocardiology, with CMRI or CTA to provide complementary information.

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368 29. Raab BW.  The thread and streak sign. Radiology. 2005;236(1):284–5. 30. Berzigotti A, García-Criado A, Darnell A, García-­ Pagán JC.  Imaging in clinical decision-making for portal vein thrombosis. Nat Rev Gastroenterol Hepatol. 2014;11(5):308–16. 31. Matsumoto N, Ogawa M, Abe M, et  al. The thread and streaks sign. J Med Ultrason (2001). 2009;36(2):99–100. 32. Martin MA, Marotta TR. Vasa vasorum: another cause of the carotid string sign. AJNR Am J Neuroradiol. 1999;20(2):259–62. 33. Pappas JN. The angiographic string sign. Radiology. 2002;222(1):237–8. 34. Felbaum DR, Maxwell C, Naydin S, et  al. Carotid stenosis: utility of diagnostic angiography. World Neurosurg. 2019;121:e962–6. 35. van der Velde ME, Parness IA, Colan SD, et  al. Two-dimensional echocardiography in the pre- and postoperative management of totally anomalous pulmonary venous connection. J Am Coll Cardiol. 1991;18(7):1746–51. 36. Kim TH, Kim YM, Suh CH, et al. Helical CT angiography and three-dimensional reconstruction of total anomalous pulmonary venous connections in neonates and infants. AJR Am J Roentgenol. 2000;175(5):1381–6. 37. Shen Q, Pa M, Hu X, Wang J.  Role of plain radiography and CT angiography in the evaluation of obstructed total anomalous pulmonary venous connection. Pediatr Radiol. 2013;43(7):827–35. 38. Korkmaz AA, Yildiz CE, Onan B, Guden M, Cetin G, Babaoglu K. Scimitar syndrome: a complex form of anomalous pulmonary venous return. J Card Surg. 2011;26(5):529–34. 39. Osama E, Aiman S, Bradley DV, Gopi S.  Scimitar syndrome. J Gen Intern Med. 2016;31(2):253–4. 40. Seller N, Yoo SJ, Grant B, et  al. How many versus how much: comprehensive haemodynamic evaluation of partial anomalous pulmonary venous connection by cardiac MRI. Eur Radiol. 2018;28(11):4598–606. 41. Khosroshahi A, Carruthers MN, Stone JH, et  al. Rethinking Ormond’s disease: “idiopathic” retroperitoneal fibrosis in the era of IgG4-related disease. Medicine (Baltim). 2013;92(2):82–91. 42. Vaglio A, Maritati F. Idiopathic retroperitoneal fibrosis. J Am Soc Nephrol. 2016;27(7):1880–9. 43. Maurovich-Horvat P, Suhai FI, Czimbalmos C, et al. Coronary artery manifestation of Ormond disease: the “mistletoe sign.”. Radiology. 2017;282(2):356–60. 44. Xu X, Bai W, Ma H, Dong P, et  al. Remission of “mistletoe sign” after treatment. J Cardiovasc Comput Tomogr. 2019. S1934–5925(19)30354–5. 45. Vaglio A, Salvarani C, Buzio C. Retroperitoneal fibrosis. Lancet. 2006;367(9506):241–51.

L. Xu et al. 46. Reller MD, Strickland MJ, Riehle-Colarusso T, Mahle WT, Correa A. Prevalence of congenital heart defects in metropolitan Atlanta. J Pediatr. 2008;153(6):807–13. 47. Wong SC, Burgess T, Cheung M, Zacharin M.  The prevalence of Turner syndrome in girls presenting with coarctation of the aorta. J Pediatr. 2014;164(2):259–63. 48. Teo LL, Cannell T, Babu-Narayan SV, Hughes M, Mohiaddin RH.  Prevalence of associated cardiovascular abnormalities in 500 patients with aortic coarctation referred for cardiovascular magnetic resonance imaging to a tertiary center. Pediatr Cardiol. 2011;32(8):1120–7. 49. Teien DE, Wendel H, Björnebrink J, Ekelund L. Evaluation of anatomical obstruction by Doppler echocardiography and magnetic resonance imaging in patients with coarctation of aorta. Br Heart J. 1993;69(4):352–5. 50. Stout KK, Daniels CJ, Aboulhosn JA, et al. 2018 AHA/ ACC Guideline for the Management of Adults with Congenital Heart Disease: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. J Am Coll Cardiol. 2019;73(12):e81. 51. Marek J, Skovránek J, Hucín B, et al. Seven-year experience of noninvasive preoperative diagnostics in children with congenital heart defects: comprehensive analysis of 2,788 consecutive patients. Cardiology. 1995;86:488–95.

Suggested Readings for this Chapter Haage P, Krings T, Schmitz-Rode T.  Nontraumatic vascular emergencies: imaging and intervention in acute venous occlusion. Eur Radiol. 2002;12(11):2627–43. Kim G, Natcheva H. Imaging of cardiovascular thoracic emergencies: acute aortic syndrome and pulmonary embolism. Radiol Clin North Am. 2019;57(4):787–94. Oderich GS, Kärkkäinen JM, Reed NR, Tenorio ER, Sandri GA.  Penetrating aortic ulcer and intramural hematoma. Cardiovasc Interv Radiol. 2019;42(3):321–34. Partovi S, Ghoshhajra BB. Diagnostic work-up and endovascular treatment of traumatic and non-traumatic vascular emergencies. Vasa. 2019;48(1):5. Raptis CA, Fowler KJ, Narra VR, Menias CO, Bhalla S.  Emergency thoracic vascular magnetic resonance imaging: protocols and clinical considerations. Semin Roentgenol. 2014;49(2):157–68. Sriranjan RS, Tarkin JM, Evans NR, Chowdhury MM, Rudd JH. Imaging unstable plaque. Q J Nucl Med Mol Imaging. 2016;60(3):205–18.

Index

A Absent bow tie sign, 293–294 Accordion sign, 261–263 Ace-of-spade sign, 160–161 Acetabulum, 287 Acoustic neuromas (AN), 69 Acute angle sign, 68 Acute disseminated encephalomyelitis (ADEM), 71 Acute ischemic cerebral infarction, 33 Acute laryngotracheobronchitis, see Viral howling Acute subdural hematoma, 16 Adrenoleukodystrophy (ALD), 48, 49 Aggressive angiomyxoma (AAM), 320 Air bronchiologram sign, 115–116 Air bronchogram, 114, 116–117 Air crescent sign, 132–133 Air–fluid level sign, 156–157 Angiographic string sign, 361–362 Anterior cerebral artery (ACA), 21, 297 Anterior tibial translocation sign, 297–298 Appendices epiploicae, 256 Appendicitis, 256, 261 Apple core sign, 263–264 Arcuate sign, 303–304 Arrowhead sign, 260–261 Arterial epidural hematoma, 18 Artificial intelligence (AI), 6 Astrocytoma, 53 Atypical hepatic hemangiomas, 180 Atypical sign, 3 Aunt Minnie approach, 5 Aura sign, 52 Avulsion injury, 304 B Bare area sign, 144 Basal ganglia, 31 Basilar artery encasement sign, 53 Beaded septum sign, 112–113 Beaded sign, 208–209 Benign lobulation, 106 Bird's beak sign, 242–243 Bitten cookie sign, head-and-neck abnormalities, 97 © Springer Nature Switzerland AG 2021 B. Gao, A. M. McKinney (eds.), Classic Imaging Signs, https://doi.org/10.1007/978-3-030-56348-6

Black hole sign (BHS), 19 Black pleural line sign, 141–142 Black target sign, 42 Blood–brain barrier (BBB), 329 Blurred cortex sign, 30, 32 Bowel wall fat halo sign, 254–255 Brain acute angle sign, 68 aura sign, 52 basilar artery encasement sign, 53 black target sign, 42 butterfly-like lesions, 47 caput medusa sign, 75 coarse flecks of calcification, 35 cord sign, 27 CSF cleft sign, 12 dense artery sign, 21 disappearing basal ganglia sign, 30 dural tail sign, 67 empty delta sign, 60 ependymal dot-dash sign, 69 eye of the tiger sign, 51, 52 false falx sign, 57 fogging effect, 33 gyri gathering sign, 14 hoop sign, 45 hot cross bun sign, 72 hummingbird sign, 71 infundibulum sign, 39 insular ribbon sign, 29 interhemispheric fissure sign, 13 interpeduncular fossa sign, 59 ivy sign, 47 lateral ventricular depressing sign, 16 little ventriculus sign, 17 middle cerebral artery dot sign, 23 molar tooth sign, 74 mount Fuji sign, 50 multilocular ring-like enhancement, 43 obscured lentiform nucleus sign, 32 parasagittal sinus sign, 61 primary damage, 17 pulvinar sign, 62 radial bands sign, 64 369

Index

370 Brain (cont.) reversal sign, 55 secondary damage, 17 spot sign, 19 swirl sign, 18 target sign, 41 tau sign, 55 tram-track sign, 37 triangular pattern, 65 tuft sign, 38 white target sign, 42 Breast calcifications, 169 Bridging vascular sign, 284–285 Bright dot sign, 180–181 Bronchiectasis, 149 Bronchioloalveolar carcinoma (BAC), 113–115 Bronchogenic pulmonary carcinoma, 117 Bucket-handle tear (BHT), 294, 295, 299 Bulging fissure sign, 155–156 Bull’s eye sign, 184–185 Butterfly-like lesions, 47 Button sequestrum sign, 322–323 C Calyceal crescent sign, 218–220 Caput medusa sign, 75 Cavernous angioma, 46 Cavernous hemangioma, 86 Celery stalk sign, 298–299 Central arrowhead sign, 215–216 Central dots sign, 214–215 Cerebral infarction, 34 Cerebral tuberculosis, 41 Cerebral venous sinus thrombosis (CVST), 61 Cerebral venous thrombosis (CVT), 27 Chest ace-of-spade sign, 160–161 air bronchiologram sign, 115–116 air bronchogram, 116–117 air crescent sign, 132–133 air–fluid level sign, 156–157 beaded septum sign, 112–113 black pleural line sign, 141–142 bulging fissure sign, 155–156 coarse spicules sign, 109 comet tail sign, 129–130 crazy paving appearance, 140–141 CT angiogram sign, 114–115 deep sulcus sign, 152–154 double-wall sign, 139–140 fallen lung sign, 150–151 feeding vessel sign, 120–121 gloved finger sign, 119–120 Golden S sign, 124–125 grey snow sign, 158–160 ground-glass opacity, 136–138 halo sign, 131–132 hampton’s hump sign, 125–126 honeycomb sign, 113 incomplete border sign, 157–158

linguine sign, 163–164 lobulation sign, 106–107 luftsichel sign, 123–124 mosaic pattern, 135–136 mucous bronchogram, 118–119 multinodule accumulation sign, 105 peach-tip sign, 128–129 peripheral washout sign, 164–166 pleural indentation sign, 110–112 positive bronchus sign, 117–118 reversed halo sign, 130–131 ring around the artery sign, 151–152 SAM sign, 161–163 sarcoid galaxy sign, 142–144 scimitar sign, 154–155 silhouette sign, 122–123 spicular sign, 166–167 spinous protuberant sign, 107–108 split pleura sign, 147–148 square sign, 126–128 tattoo sign, 169–170 tiny calcium sign, 167–168 tree-in-bud sign, 138–139 vacuole sign, 108–109 vascular convergence sign, 108–109 water-lily sign, 133–134 withered tree sign, 114 Chest X-ray scan, 149 Chronic subdural hematomas (CSDH), 14, 16 CJD, see Creutzfeldt-Jakob disease Cluster sign, 188–189 Coarctation of the aorta (CoA), 366 Coarse flecks of calcification, 35 Coarse spicules sign, 109 Cobra head sign, 231–232 Cochlear otosclerosis, 92 Coffee bean sign, 245–246 Comb sign, 252–253 Comet tail sign, 129–130, 228–229 Concentric ring sign, 275–276 Congenital pulmonary vein syndrome (CPVS), 154 Contrast-enhanced CT (CECT), 60 Contrast-enhanced MR angiography (CE-MRA), 95 Cord sign, 27 Corkscrew sign, 248–249 Cortical rim sign, 220–221 COVID-19, 159 Crazy paving appearance, chest, 140–141 Crescent sign, 197–198, 301–302 Creutzfeldt-Jakob disease (vCJD), 63 Crohn’s disease, 252 CSF cleft sign, 12 C sign, 317–318 CT angiogram sign, 114–115 CT angiography (CTA), 33, 62 CT perfusion (CTP), 33 Curved knife sign, 154 CVT, see Cerebral venous thrombosis Cyclops lesion, 295–296 Cyst-in-cyst sign, 206–207

Index D Deep sulcus sign, 152–154 Dense artery sign, 21 Dense triangle sign, 61 Dependent viscera sign, 267–269 Developmental venous anomaly (DVA), 75 Diaphragm sign, 144 Diffuse cerebral swelling, 18 Diffusion-tensor imaging (DTI), 14 Diffusion-weighted imaging (DWI), 95 Direct sign, 3 Disappearance of the sulcus, 30 Disappearing basal ganglia sign, 30, 32 Displaced crus sign, 144 Disproportionate fat stranding sign, 255–257 Diverticulitis, 256 DNET, see Dys-embryoplastic neuroepithelial tumor Dog leg sign, 355–356 Double bubble sign, 240–241 Double duct sign, 211 Double halo sign, 251–252 Double lumen sign, 356–358 Double oreo cookie sign, 304–305 Double peak sign, 286–287 Double posterior cruciate ligament sign, 299–300 Double rail sign, 359–361 Double-line sign, 300–301 Double-ring sign, head-and-neck abnormalities, 92 Double-wall sign, 139–140 Draped aorta sign, 354–355 Drooping lily sign, 233–234 DTS, see Dural tail sign Duct-penetrating sign, 213 Duodenal wind sock sign, 264–265 Duplex kidneys, 234 Dural tail sign (DTS), 67 Dynamic contrast-enhanced (DCE), 95 Dys-embryoplastic neuroepithelial tumor (DNET), 65 Dysgenesis of corpus callosum (DCC), 13 E Echinococcosis granulosus, 206 Elbow fat pad sign, 315–317 Elephant trunk sign, 313–314 Empty delta sign, 60 Empty sella, 39 Endometriosis, 283 Endometriotic cysts, 282 Endoscopic retrograde cholangiopancreatography (ERCP), 208 Ependymal dot-dash sign, 69 Epidural hematoma, 18 Eponymous signs, 2 Eye of the tiger sign, 51 F Faceless kidney, 229–230 Fallen fragment sign, 308–309 Fallen lung sign, 150–151

371 False falx sign, 57 Fat–blood interface sign, 314–315 Fat C2 sign, 346–347 Fat halo sign, 255 Fat ring sign, 258–259 Feeding vessel sign, 120–121 Finger-in-glove sign, chest, 119 Flat cava sign, 350 Flipped meniscus sign, 292–293 Floating aorta sign, 278–279 Floating ball sign, 281–282 Floating membrane sign, 207–208 Floating viscera sign, 358–359 Flow void sign, 321–322 Focal cortical dysplasia, 65 Focal hepatic hot spot sign, 205–206 Fogging effect, 33 Football sign, 266–267 Fragment-in-notch sign, 294–295 G Gallbladder (GA), 200 Garland sign, 200–201 Gas bubble sign, head-and-neck abnormalities, 98 Gastrointestinal tracts accordion sign, 261–263 apple core sign, 263–264 arrowhead sign, 260–261 bird's beak sign, 242–243 bowel wall fat halo sign, 254–255 coffee bean sign, 245–246 comb sign, 252–253 corkscrew sign, 248–249 dependent viscera sign, 267–269 disproportionate fat stranding sign, 255–257 double bubble sign, 240–241 double halo sign, 251–252 duodenal wind sock sign, 264–265 fat ring sign, 258–259 football sign, 266–267 hyperattenuating ring sign, 259–260 misty mesentery sign, 257–258 northern exposure sign, 269–270 rigler sign, 265–266 small-bowel feces sign, 241–242 spoke wheel sign, 246–247 string of pearls sign, 243–245 string sign, 253–254 target sign, 249–251 whirl sign, 247–248 GBE, see Giant bullous emphysema Gestalt theory, 5 GGO, see Ground-glass opacity (GGO) Giant bullous emphysema (GBE), 140 Gloved finger sign, 119–120 Gluteal muscle contracture (GMC), 310 Golden S sign, 124–125 Golf ball-on-tee sign, 216–218 Granulation tissue, 43 Gray-white matter interface (G-WMI) displacement, 20

Index

372 Grey snow sign, 158–160 Ground glass opacity (GGO), 136–138 Gyriform calcifications, 37 Gyri gathering sign, 14 H Half delta sign, 62 Halo sign, 131–132, 191–192 Hampton’s hump sign, 125–126 Head-and-neck abnormalities bitten cookie sign, 97 double-ring sign, 92 gas bubble sign, 98 progressive enhancement sign, 85 prominent ear sign, 98 salt-and-pepper sign, 93 steeple sign, 95 teardrop sign, 90 tendon sign, 86 tram-track sign, 91 V-shape sign, 88 Hemangiomas, 180 Hepatic echinococcosis, 206, 208 Hepatic hemangioma, 179 Hepatic hydatidosis, 206 Hepatic metastases, 184 Heterogeneous signal intensity, 184 High-resolution CT (HRCT), 112 Hodgkin's lymphomas, 279 Honeycomb sign, 113 Hoop sign, 45 Horizontal tear, 293 Hot cross bun sign, 72 Hummingbird sign, 71 Hydatidosis, 207 Hyperattenuating crescent sign, 352–353 Hyperattenuating ring sign, 259–260 Hyperdense artery sign, 33 Hyperdense hematoma, 21 Hyperdense MCA sign (HMCA sign), 21, 30, 32 Hyperintense rim sign, 277–278 Hypoxic-ischemic injury (HII), 55 I Iliac hyperdense line, 309–311 Imaging signs, 1 classification, 3 decision-making, 4 features, 2 formation, 2 role, 4 Incomplete border sign, 157–158 Incomplete vertebral ring sign, 342–343 Indirect sign, 3 Inflammatory pseudotumor of the lung (IPL), 128 Infundibulum sign, 39 Insular ribbon sign, 29, 32 Interface sign, 144

Interhemispheric fissure sign, 13 Internal carotid artery (ICA), 30 Interpeduncular fossa sign, 59 Intracranial tuberculosis, 41 Intraparenchymal hemorrhage (IPH), 19 Intravenous urography, 231 Intravertebral vacuum cleft sign, 337–339 Intussusception, 249 Inverted Napoleon’s hat sign, 339–340 Iso-attenuation hematoma, 16 Ivory vertebra sign, 333–334 Ivy sign, 47 J Joubert’s syndrome (JS), 74 J sign, 305–306 L Late gadolinium enhancement (LGE), 161 Lateral capsular sign, 307–308 Lateral femoral notch sign, 312–313 Lateral ventricular depressing sign, 16 Lenticular nucleus, 31 Light bulb sign, 179–180 Linguine sign, 163–164 Little ventriculus sign, 17 Liver capsule depressed sign, 195–196 Lobulation sign, 106–107 Lollipop sign, 186–187 Loss of the insular ribbon sign, 30, 33 Luftsichel sign, 123–124 Lung abscess, 156 M Malignant mass, 164 Malignant tumor cells, 107 Marginal tear, 293 Mature cystic teratoma, 281 Medical imaging, 1 Meningiomas, 11 Meniscus of knee, 292 Metaphoric sign, 2 Microcalcification, 167, 168 Middle cerebral artery (MCA), 21, 30 Middle cerebral artery dot sign, 23 Middle cerebral artery susceptibility sign, 24 Minute gas, 99 Mistletoe sign, 364–365 Misty mesentery sign, 257–258 Molar tooth sign (MTS), 74 Mosaic pattern, 135–136, 184 Mother-in-law sign, 181–182 Mount Fuji sign, 50 Moya-moya disease (MDD), 47 MR cholangiopancreatography (MRCP), 211 MRI fluid sign, 336–337 MTS, see Molar tooth sign

Index Mucoid impaction, 119 Mucous bronchogram, 118–119 Multidetector computed tomography (MDCT), 284 Multilocular ring-like enhancement, 43 Multinodule accumulation sign, 105 Multi-planar reformat (MPR) image, 90 Multiple low-density nodules, 186 Multiple sclerosis (MS), 69 Multiple-vessel-oriented nodules, 122 Multi-slice CT (MSCT), 90, 161 Musculoskeletal absent bow tie sign, 293–294 anterior tibial translocation sign, 297–298 arcuate sign, 303–304 button sequestrum sign, 322–323 celery stalk sign, 298–299 crescent sign, 301–302 C sign, 317–318 cyclops lesion, 295–296 double-line sign, 300–301 double oreo cookie sign, 304–305 double posterior cruciate ligament sign, 299–300 elbow fat pad sign, 315–317 elephant trunk sign, 313–314 fallen fragment sign, 308–309 fat–blood interface sign, 314–315 flipped meniscus sign, 292–293 flow void sign, 321–322 fragment-in-notch sign, 294–295 iliac hyperdense line, 309–311 J sign, 305–306 lateral capsular sign, 307–308 lateral femoral notch sign, 312–313 secondary cleft sign, 306–307 swirl sign, 320–321 target sign, 318–320 Terry Thomas sign, 311–312 yo-yo on string sign, 302–303 Mycobacterium tuberculosis, 41 N Naked facet sign, 345–346 Nasopharyngeal swab test, 159 Necessary sign, 3 Negative sign, 4 Neurocysticercosis (NCC), 42 Northern exposure sign, 269–270 O Obscured lentiform nucleus sign, 30, 32 Oligodendroglioma, 35 Omentum, 256 Onion skin sign, 276–277 Optic nerve sheath meningiomas (ONSMs), 92 Orbital myositis, 86 Otosclerosis, 92 Oto-spongiosis, see Cochlear otosclerosis Ovarian suspensory ligament, 284

373 Ovarian teratoma, 281 Ovarian vascular pedicle sign, 283–284 P Pagoda-like multinodule accumulation sign, 105 Pancreatic cancer, 212 Pantothenate kinase-associated neurodegeneration (PKAN), 51 Parasagittal sinus sign, 61 Peach-tip sign, 128–129 Pearl necklace sign, 198–200 Peripheral spinal cord hypointensity sign, 327–329 Peripheral washout sign, 164–166, 189–191 Periportal halo sign, 203–205 Periportayl tracking sign, 202–203 Perirenal cobwebs sign, 224–225 Perirenal halo sign, 223–224 Peritoneum and pelvis bridging vascular sign, 284–285 concentric ring sign, 275–276 double peak sign, 286–287 floating aorta sign, 278–279 floating ball sign, 281–282 hyperintense rim sign, 277–278 onion skin sign, 276–277 ovarian vascular pedicle sign, 283–284 sandwich sign, 279–280 sentinel clot sign, 273–274 shading sign, 282–283 spongiform gas bubbles, 280–281 Persistent trigeminal artery (PTA), 55 Phleboliths, 228 Pleural indentation (PI) sign, 110–112 Pneumomediastinum, 151, 152 Pneumonia pseudotumor, 127 Pneumoperitoneum, 266 Polka-dot sign, 330–332 Popcorn sign, 45 Portal vein, 212 Positive bronchus sign, 117–118 Possible sign, 4 Posterior cerebral artery (PCA), 21 Posterior vertebral scalloping sign, 334–336 Primary capillary network, 38 Primary sclerosing cholangitis, 208 Primary sign, 3 Progressive enhancement sign, head and neck, 85 Progressive supranuclear palsy (PSP), 71 Prominent ear sign, head-and-neck abnormalities, 98 Pseudo-capsule sign, 225–226 Pseudo-delta sign, 61 PSP, see Progressive supranuclear palsy PTA, see Persistent trigeminal artery Pulmonary alveolar microlithiasis (PAM), 142 Pulmonary echinococcosis, 133, 134 Pulmonary hydatid disease, 133 Pulmonary thromboembolism (PTE), 359 Pulvinar sign, 62 Pupil-like sign, 185–186

374 Purulent cholangitis, 215 Pyogenic micro-abscesses, 189 R Radial bands sign, 64 Radiology, 1 Radiomics, 6 Rapid wash-in followed by washout, 182–184 Recurrent artery of Huebner, 31 Relapsing polychondritis (RP), 98 Renal halo sign, 221–222 Renal oncocytoma (RO), 226 Retinal detachment, 89 Retroperitoneal lymphoma, 279 Retroperitoneal space, 221 Reversal sign, 55 Reversed halo sign, 130–131 Rigler sign, 265–266 Ring around the artery sign, 151–152 Rokitansky-Aschoff sinus (RAS), 201 Rounded atelectasis, 129 Rugger jersey spine sign, 332–333 S Sagittal canal ratio (SCR), 343 SAH, see Subarachnoid hemorrhage Salt-and-pepper sign, head-and-neck abnormalities, 93 SAM sign, 161–163 Sandwich sign, 279–280 Sarcoid galaxy sign, 142–144 Schistosomiasis, 201 Scimitar sign, 154–155, 363–364 Scimitar syndrome, 155 Sclerosing mesenteritis (SM), 259 Scotty dog collar sign, 340–342 Secondary capillary bed, 38 Secondary capillary network, 38 Secondary cleft sign, 306–307 Secondary sign, 3 Sentinel clot sign, 273–274 Septic pulmonary embolus, 120 Shading sign, 282–283 Signet ring sign, 149–150 Silhouette sign, 122–123 Small cell lung cancer (SCLC), 121 Small-bowel feces sign, 241–242 Snowman sign, 362–363 Soft rattan sign, 209–210 Soft-tissue rim sign, 227–228 “Spherical” retinal detachment, 89 Spicular sign, 166–167 Spicule, 107 Spine fat C2 sign, 346–347 incomplete vertebral ring sign, 342–343 intravertebral vacuum cleft sign, 337–339 inverted Napoleon’s hat sign, 339–340 ivory vertebra sign, 333–334

Index MRI fluid sign, 336–337 naked facet sign, 345–346 peripheral spinal cord hypointensity sign, 327–329 polka-dot sign, 330–332 posterior vertebral scalloping sign, 334–336 rugger jersey spine sign, 332–333 scotty dog collar sign, 340–342 sugarcoating sign, 329–330 wide canal sign, 343–344 Spinous protuberant sign, 107–108 Split pleura sign, 147–148 Spoke wheel sign, 226–227, 246–247 Spongiform gas bubbles, 280–281 Spot sign, 19 Square sign, 126–128 Steeple sign, head-and-neck abnormalities, 95 Stenotic cholangitis, 209 Straight border sign, 196–197 Straight line sign, 194–195 String of beads sign, 350–352 String of pearls sign, 243–245 String sign, 253–254 Sturge-Weber syndrome (SWS), 37 Subacute subdural hematoma, 16 Subarachnoid hemorrhage (SAH), 59, 61 Subdural hematomas (SDH), 20 Subdural hemorrhage, 16 Subdural hyperintense band, 15 Subpleural curvilinear shadow (SCLS), 148 Subpleural line, 148–149 Sufficient sign, 3 Sugarcoating sign, 329–330 Superior labrum anterior and posterior (SLAP) tear, 305 Superior sagittal sinus thromboses, 61 Suppurative cholangitis, 215 Susceptibility effect, 26 Susceptibility-weighted imaging (SWI), 15 Swirl sign (SS), 18, 320–321 T Target sign, 41, 187–188, 197–198, 249–251, 318–320 Tattoo sign, 169–170 Tau sign, 55 Teardrop sign, head-and-neck abnormalities, 90 Teardrop superior mesenteric vein sign, 212–213 Tendon sign, in head and neck, 86 Tension pneumocephalus, 50 Terry Thomas sign, 311–312 Thoracic empyema, 147 Thread and streak sign, 361 “3” sign, 365–367 Thyroid dysfunction myopathy, 88 Tiny calcium sign, 167–168 Tortoise shell sign, 201–202 Total anomalous pulmonary venous connection (TAPVC), 362 Tram-track sign, 37, 91 Transparent ring sign, 192–193 Transverse tear, 293

Index

375

Traumatic brain injury (TBI), 18 Tree-in-bud sign, 138–139 Triangular pattern, 65 Tuft sign, 38 Typical sign, 3

teardrop superior mesenteric vein sign, 212–213 tortoise shell sign, 201–202 transparent ring sign, 192–193 wedge-shaped sign, 193–194 Ureteral cyst, 231, 232

U Upper abdomen beaded sign, 208–209 bright dot sign, 180–181 bull’s eye sign, 184–185 calyceal crescent sign, 218–220 central arrowhead sign, 215–216 central dots sign, 214–215 cluster sign, 188–189 cobra head sign, 231–232 comet-tail sign, 228–229 cortical rim sign, 220–221 crescent sign, 197–198 cyst-in-cyst sign, 206–207 double duct sign, 211 drooping lily sign, 233–234 duct-penetrating sign, 213 faceless kidney, 229–230 floating membrane sign, 207–208 focal hepatic hot spot sign, 205–206 garland sign, 200–201 goblet sign, 230–231 golf ball-on-tee sign, 216–218 halo sign, 191–192 light bulb sign, 179–180 liver capsule depressed sign, 195–196 lollipop sign, 186–187 mosaic pattern, 184 mother-in-law sign, 181–182 pearl necklace sign, 198–200 peripheral washout sign, 189–191 periportal halo sign, 203–205 periportal tracking sign, 202–203 perirenal cobwebs sign, 224–225 perirenal halo sign, 223–224 pseudo-capsule sign, 225–226 pupil-like sign, 185–186 rapid wash-in followed by washout, 182–184 renal halo sign, 221–222 soft rattan sign, 209–210 spoke wheel sign, 226–228 straight border sign, 196–197 straight line sign, 194–195 target sign, 187–188, 197–198

V Vacuole sign, 108–109 Vacuum phenomena, 99 Vanishing lung syndrome, 140 Variant Creutzfeldt-Jakob disease (vCJD), 63 Vascular and interventional angiographic string sign, 361–362 dog leg sign, 355–356 double lumen sign, 356–358 double rail sign, 359–361 draped aorta sign, 354–355 flat cava sign, 350 floating viscera sign, 358–359 hyperattenuating crescent sign, 352–353 mistletoe sign, 364–365 scimitar sign, 363–364 snowman sign, 362–363 string of beads sign, 350–352 thread and streak sign, 361 “3” sign, 365–367 yin-yang sign, 353–354 Vascular convergence sign, 108–109 Vasogenic edema, 42 vCJD, see Variant Creutzfeldt-Jakob disease Venous epidural hematoma, 19 Venous hypertensive myelopathy (VHM), 327 Viral howling, 95 V-shape sign, head and neck, 88 W Wall ischemia, 251 Water-lily sign, 133–134 Wedge-shaped sign, 193–194 Whirl sign, 247–248 White target sign, 42 Wide canal sign, 343–344 Withered tree sign, 114 Y Yin-yang sign, 353–354 Yo-yo on string sign, 302–303