Imaging of the Scalp and Calvarium [1st ed. 2023] 3031496256, 9783031496257

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Philippe Demaerel

Imaging of the Scalp and Calvarium

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Imaging of the Scalp and Calvarium

Philippe Demaerel

Imaging of the Scalp and Calvarium

Philippe Demaerel Department of Radiology University Hospital Leuven Leuven, Belgium

ISBN 978-3-031-49625-7    ISBN 978-3-031-49626-4 (eBook) https://doi.org/10.1007/978-3-031-49626-4 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed 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 Paper in this product is recyclable

Introduction

The scalp and calvarium are next to each other, and therefore it makes sense to deal with them in one book. In brain imaging, often less attention is being paid to the scalp and the calvarium with the result that lesions are easily overlooked or remain unreported. The aim of this book is to provide an overview of the normal anatomy and variants of the scalp and the calvarium and to review the pathology involving these structures. Intentionally, plenty of figures are offered along with a description of the key findings. The calvarium is bordered by the dura on the inside and the scalp on the outside. Both scalp lesions and intracranial lesions can invade the calvarium, but calvarial lesions can also extend into the intracranial cavity and/or the scalp. For the sake of clarity, scalp and calvarial lesions will be reviewed in two separate sections. Although scalp lesions and calvarial lesions are often asymptomatic and incidental findings, the patient may also present with a bump on the head. There might be aesthetic reasons or local pain and occasionally neurological signs. Imaging plays a role in assessing the extent and the depth of invasion of a scalp lesion or the degree of extension and involvement of a calvarial lesion. Ultrasound plays a role in the first screening of scalp lesions, particularly in young children but often it will be necessary to obtain a CT and/or MR examination. Nowadays, plain X-ray is only used in specific circumstances such as the confirmation of valve settings of a ventricular drainage device after an MRI procedure. Plain X-ray is also part of the skeletal survey which is obtained for various indications such as suspected child abuse, skeletal dysplasia, m. Kahler and Paget disease. Digital subtraction angiography is occasionally indicated in the diagnostic workup of vascular malformations or in the preoperative embolization of large dural and/or calvarial meningiomas. Bone scintigraphy has a considerably high sensitivity but low specificity in detecting and assessing bone lesions. The imaging features can often help in narrowing the differential diagnosis. The high spatial resolution of CT is used to assess bone involvement, expansion, destruction or remodelling. The lesion margins, the bone matrix and calcification provide additional information on the nature of the lesion. In the evaluation of calvarial lesions, the CT findings can often significantly shorten the differential diagnosis list and can even be pathognomonic. CT features like regular cortical expansion with bone remodelling are in favour of benign pathology. Permeative and destructive changes strongly support the presence of a rapidly progressing process such as aggressive inflammation or malignancy. Some entities have characteristic CT features, for example, fibrous dysplasia, a venous malformation, Paget disease. Multidetector computed tomography (MDCT) allows rapid volumetric image data acquisition and with the use of sub-millimetric slice thickness, multiplanar reformations (MPR) and 3-dimensional (3D) reconstructions can be obtained. CT is the ideal method to assess the internal and external table of the calvarium, detecting bone lysis or sclerosis and visualizing the mineralized part(s) of the lesion. Cinematic rendering is a post-processing technique for 3D visualization of image data (CT, MRI). Compared to 3D volume rendering, 3D cinematic rendering results in a more photo-realistic representation of the anatomy and pathology.

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The advantage of MRI with its high contrast resolution is the assessment of the bone marrow in the diploic space and the evaluation of the intracranial and soft tissue involvement. Bone marrow involvement can be detected at an early stage, when changes in the bone architecture are still lacking on CT. Non-contrast T1-weighted images without fat saturation remain helpful in evaluating possible marrow replacement by a tumour or oedema. Fat-saturated contrast-­enhanced T1-weighted sequences are recommended because of the considerably high adipose tissue content of the scalp. T2-weighted and diffusion-weighted sequences may contribute to the characterization of the lesion. The definitive diagnosis of a calvarial lesion usually requires histopathological evaluation, but CT and MRI play an important role in limiting the differential diagnosis and in establishing the management plan. Often it will be possible to differentiate between a benign and a malignant bone lesion on imaging. Clinical factors such as the patient’s age, gender and medical history should always be taken into account when assessing a scalp or calvarial lesion.

Introduction

Contents

1 Scalp�����������������������������������������������������������������������������������������������������������������������������   1 1.1 Anatomy���������������������������������������������������������������������������������������������������������������   1 1.2 Trauma�����������������������������������������������������������������������������������������������������������������   3 1.2.1 Subcutaneous and Subgaleal Haematoma�����������������������������������������������   3 1.2.2 Thermal Burns�����������������������������������������������������������������������������������������   3 1.2.3 Cephalohaematoma and Caput Succedaneum�����������������������������������������   4 1.3 Infection���������������������������������������������������������������������������������������������������������������   6 1.3.1 Pott’s Puffy Tumour���������������������������������������������������������������������������������   6 1.3.2 Necrotizing Fasciitis �������������������������������������������������������������������������������   6 1.4 Vascular���������������������������������������������������������������������������������������������������������������   8 1.4.1 Sinus Pericranii ���������������������������������������������������������������������������������������   8 1.4.2 Vascular Malformation����������������������������������������������������������������������������  10 1.4.3 Sturge-Weber Syndrome �������������������������������������������������������������������������  10 1.5 Cysts���������������������������������������������������������������������������������������������������������������������  13 1.5.1 Trichilemmal Cyst�����������������������������������������������������������������������������������  13 1.5.2 Epidermoid Cyst �������������������������������������������������������������������������������������  13 1.5.3 Dermoid Cyst�������������������������������������������������������������������������������������������  15 1.6 Tumours���������������������������������������������������������������������������������������������������������������  18 1.6.1 Pilomatricoma �����������������������������������������������������������������������������������������  18 1.6.2 Lipoma�����������������������������������������������������������������������������������������������������  18 1.6.3 Miliary Osteoma Cutis�����������������������������������������������������������������������������  18 1.6.4 Fibroma and Granuloma �������������������������������������������������������������������������  18 1.6.5 Carcinoma �����������������������������������������������������������������������������������������������  20 1.6.6 Sarcoma���������������������������������������������������������������������������������������������������  28 1.6.7 Melanoma �����������������������������������������������������������������������������������������������  28 1.6.8 Metastasis�������������������������������������������������������������������������������������������������  28 1.6.9 Myeloma �������������������������������������������������������������������������������������������������  31 1.6.10 Haematolymphoid Tumours��������������������������������������������������������������������  34 1.7 Dermal Hypertrophy and Atrophy�����������������������������������������������������������������������  37 1.7.1 Dermal Hypertrophy �������������������������������������������������������������������������������  37 1.7.2 Dermal Atrophy���������������������������������������������������������������������������������������  37 2 Calvarium �������������������������������������������������������������������������������������������������������������������  43 2.1 Anatomy and Variants �����������������������������������������������������������������������������������������  43 2.1.1 Anatomy���������������������������������������������������������������������������������������������������  43 2.1.2 Emissary Veins, Parietal Foramina and Venous Lakes�����������������������������  47 2.1.3 Arachnoid Granulations���������������������������������������������������������������������������  50 2.2 Congenital �����������������������������������������������������������������������������������������������������������  53 2.2.1 Craniosynostosis �������������������������������������������������������������������������������������  53 2.2.2 Cephalocele���������������������������������������������������������������������������������������������  54 2.2.3 Dermoid Cyst�������������������������������������������������������������������������������������������  60 2.2.4 Epidermoid Cyst �������������������������������������������������������������������������������������  60 2.2.5 Lipoma�����������������������������������������������������������������������������������������������������  60 vii

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Contents

2.3 Trauma�����������������������������������������������������������������������������������������������������������������  68 2.4 Infection���������������������������������������������������������������������������������������������������������������  73 2.4.1 Osteomyelitis�������������������������������������������������������������������������������������������  73 2.4.2 Bartonella�������������������������������������������������������������������������������������������������  73 2.5 Vascular���������������������������������������������������������������������������������������������������������������  75 2.5.1 Venous Vascular Malformation���������������������������������������������������������������  75 2.6 Tumour�����������������������������������������������������������������������������������������������������������������  79 2.6.1 Osteoma���������������������������������������������������������������������������������������������������  80 2.6.2 Meningioma���������������������������������������������������������������������������������������������  83 2.6.3 Eosinophilic Granuloma �������������������������������������������������������������������������  84 2.6.4 Sarcoma and Fibroma �����������������������������������������������������������������������������  86 2.6.5 Haematolymphoid Tumours��������������������������������������������������������������������  90 2.6.6 Myeloma: Plasmacytoma�������������������������������������������������������������������������  92 2.6.7 Metastasis�������������������������������������������������������������������������������������������������  94 2.7 Systemic Diseases����������������������������������������������������������������������������������������������� 109 2.7.1 Osteopenia and Osteoporosis������������������������������������������������������������������� 109 2.7.2 Bone Thinning and Bone Thickening ����������������������������������������������������� 109 2.7.3 Haematological Diseases������������������������������������������������������������������������� 111 2.7.4 Hyperparathyroidism and Renal Osteodystrophy����������������������������������� 112 2.7.5 Fibrous Dysplasia������������������������������������������������������������������������������������ 113 2.7.6 Paget’s Disease����������������������������������������������������������������������������������������� 116 2.7.7 Skeletal Dysplasia����������������������������������������������������������������������������������� 116 2.8 Treatment-Related Pathology������������������������������������������������������������������������������ 134 2.8.1 Burr Hole and Craniectomy��������������������������������������������������������������������� 134 2.8.2 Radiotherapy and Drug-Related Bone Abnormalities����������������������������� 140 References �������������������������������������������������������������������������������������������������������������������������  143

1

Scalp

1.1 Anatomy The scalp covers the calvarium and reaches from the external occipital protuberance and superior nuchal line to the margins of the orbit and to the ears on both sides [1–3]. The scalp consists of five layers (Fig. 1.1): • The skin or cutis consists of the epidermis (approx. 0.2 mm) and the dermis (between 2 and 8 mm). The epidermis can be identified on MRI as a thin superficial line. The dermis contains sebaceous glands, hair follicles and apocrine glands and has a low signal. The dermis can be subdivided into a superficial layer with higher-signal intensity and a deeper layer of lower signal, reflecting the papillary and the reticular dermis. Pilosebaceous follicles appear as fine lines coming from the subcutis, passing through the dermis. • The subcutis or hypodermis is approximately 5–7  mm thick. This superficial fascia is a fibrofatty layer that provides a passage for blood vessels, nerves and lymphatic

tissue. The thickness may increase up to 20 mm in obese individuals. The subcutis mainly consists of fat. Within the subcutis, low-signal vertical lines correspond to interlobar septa, connecting the dermis to the galea aponeurotica. • The galea aponeurotica or deep fascia (approx. 1.5 mm) is a strong tendinous sheath in continuity with the scalp muscles (m. orbicularis oculi, m. frontalis and m. occipitalis). The galea cannot always be identified on MRI. • The subgaleal fibroareolar tissue consists of a dense collagenous layer surrounded by vascularized areolar tissue. • The periosteum/pericranium, a fibrous membrane that covers the external table of the skull, is not visible on MRI. On MRI, three of the five layers can usually be demonstrated: the cutis, the subcutis and the subgaleal tissue. Within the cutis, the epidermis and dermis can be seen as separate layers.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. Demaerel, Imaging of the Scalp and Calvarium, https://doi.org/10.1007/978-3-031-49626-4_1

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1 Scalp

a

b

c

Fig. 1.1  MR anatomy of the scalp. Axial T1-weighted images before (a) and after (b) intravenous gadolinium with fat saturation and T2-weighted (c) image. The epidermis and superficial dermis (1), the deep dermis (2), the hypodermis (3), the external table (4), the diploic space (5), the internal table (6) and the dura mater (7) are shown. More details of the scalp are seen in (b) with the epidermis (1), separated from the dermis (3) by a thin layer (2), the hypodermis (4), the galea aponeurotica and subgaleal layer (5), the calvarium (6) and the dura

mater (7). Vertically oriented septa connect the dermis (3) to the galea aponeurotica (5). In (c), the epidermis (1) and hypodermis (2) are shown. Vessels can be seen in the hypodermis (3). The dermis is visible between the epidermis and the hypodermis (white bar). Note the different signals of the layers within the dermis. Note the continuity between the dermis and the hypodermis where pilosebaceous follicles cross the border between both layers (4)

1.2 Trauma

3

1.2 Trauma

In case of rupture of the galea aponeurotica, the haemorrhage can extend into the subcutis resulting in a subcutaneous haematoma. Occasionally, this may be associated with a cutaneous laceration that can be identified by the loss of continuity of the epidermis and dermis (Fig. 1.3).

1.2.1 Subcutaneous and Subgaleal Haematoma Traumatic scalp haematomas can be located in the subcutis and/or in the subgaleal space. A subcutaneous haematoma usually resolves within a few days. The subgaleal haematoma is the most common traumatic scalp lesion and occurs secondary to radial forces to the blood vessels in the subgaleal space (Fig. 1.2). Vertically oriented septations in the subcutis connect the dermis to the galea aponeurotica and will move together upon traction. The subgaleal fibroareolar tissue is only loosely attached to the periosteum, and as a consequence, this layer can glide over the calvarium. Most subgaleal haematomas regress over 2–3 weeks.

a

1.2.2 Thermal Burns It is important to recognize burn injuries in patients with polytrauma. Burns can be identified on imaging when there is a third-degree destruction of the epidermis and dermis with necrosis extending into the subcutis (Fig.  1.4). Full-­ thickness burn injuries are recognized as an irregular thickening of the epidermis and dermis with stranding in the subcutis. The burn-related stranding regresses in the weeks after the acute event.

b

c

Fig. 1.2  Subgaleal haematoma. Sagittal FLAIR (a) and T1-weighted images before (b) and after (c) intravenous gadolinium with fat saturation demonstrate the subgaleal haematoma (arrows). Note the enhance-

ment of the galea aponeurotica (c, arrows). Note the subdural haematoma, clearly delineated on the FLAIR images (a)

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1 Scalp

a

b

Fig. 1.3  Subgaleal haematoma with extension into the subcutis. Axial CT demonstrates the subgaleal (black arrow) and the subcutaneous (white arrow) haematoma (a). Note the extension of a subgaleal haema-

Fig. 1.4  Skin burns. Sagittal CT shows irregular wavy thickening of the skin with some infiltration and stranding of the subcutis. Note the presence of a small subgaleal haematoma at the vertex

1.2.3 Cephalohaematoma and Caput Succedaneum Cephalohaematoma and caput succedaneum typically occur in neonates [4].

toma in the subcutis with a cutaneous laceration visible as a loss of the continuity of the epidermis and dermis (b)

Cephalohaematoma can be seen in relation to a birth trauma following a prolonged labour or instrumental delivery. It is a ‘crescent-shaped’ subperiosteal blood collection, often in the parietal region and without extension across the midline. A fracture can be associated. Calcification can be seen in the healing stage. On MRI, the cephalohaematoma often is T1 and T2 hyperintense, but other signal intensities can be seen depending on the degradation of the blood products (Fig.  1.5). Spontaneous regression occurs over 3–4 weeks, and no treatment is required. Rarely, superinfection can delay the healing (Fig. 1.6). A caput succedaneum refers to a bilateral subcutaneous fluid collection at the vertex. It is almost always associated with a long and difficult delivery, requiring vacuum extraction or forceps delivery. The collection typically crosses the midline, and this is the most important difference compared with the cephalohaematoma (Fig. 1.7). Caput succedaneum regresses without treatment in a few hours or days.

1.2 Trauma

a

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Fig. 1.5  Cephalohaematoma. Axial T2-weighted (a) and coronal T1-weighted (b) images show a left-sided cephalohaematoma with high signal on both sequences

a

Fig. 1.6 Cephalohaematoma with infection. Sagittal T1-weighted images before (a) and after (b) intravenous gadolinium with fat saturation demonstrate the subgaleal haematoma. The acute haematoma has a

b

low T1 signal. Note the enhancement of the subcutis and dermis overlying the haematoma and the enhancement anteriorly in the subgaleal space (b)

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1 Scalp

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Fig. 1.7  Caput succedaneum. Axial T2-weighted (a) and sagittal T1-weighted (b) images show a caput succedaneum extending from left to right, crossing the midline (a, arrows)

1.3 Infection

1.3.2 Necrotizing Fasciitis

1.3.1 Pott’s Puffy Tumour

Necrotizing fasciitis is a rapidly progressive necrosis of the subcutis and galea aponeurotica, which can be lifethreatening if not rapidly recognized. The overlying skin may appear normal. It can occur anywhere in the body and is rare in the scalp. The two scalp locations are the periorbital and the neck region. The periorbital involvement is often caused by group A Streptococcus pyogenes and usually has a rather benign course [6]. Although the infection can be seen in healthy individuals, usually there is evidence of impaired immunity. In adults, trauma and surgery can trigger an infection. Imaging may help in delineating the extent of the infection (Fig.  1.9). The epidermis usually appears intact. Thickening and enhancement of the subgaleal tissues are observed. Both the galea aponeurotica and the periosteum are affected.

Pott’s puffy tumour was first reported as a subperiosteal abscess of the frontal bone with osteomyelitis and an epidural abscess by Sir Percivall Pott [5]. It is usually observed as a complication of rhinosinusitis but has also been reported following trauma. The patient typically presents with a ‘puffy’ tumour on the forehead, due to the underlying subperiosteal abscess. The mucosal venous drainage of the frontal sinus occurs through diploic veins that communicate with venous plexuses of the dura and periosteum, which explains the occurrence of epidural abscess in patients with intact frontal bone (Fig.  1.8). Occasionally, a subdural empyema can be observed, which is thought to result from septic thrombi in the veins that drain into the subdural space. Diffusion-weighted MRI can confirm the presence of subcutaneous and epidural pus formation. Surgical exploration or endoscopic sinus surgery and prolonged intravenous antibiotic treatment are indicated. Imaging may be indicated to monitor the treatment.

1.3 Infection

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Fig. 1.8  Pott’s puffy tumour. Sagittal contrast-enhanced CT (a) and T1-weighted images after intravenous gadolinium with fat saturation (b) demonstrate the subgaleal and the epidural abscess (a, arrows).

b

d

Axial diffusion-weighted images (c) and the ADC map (d) confirm the presence of pus in both abscesses (arrows)

1 Scalp

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a

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d

Fig. 1.9  Necrotizing fasciitis. Axial (a) and coronal (b) T1-weighted images after intravenous gadolinium with fat saturation show the extent of the subgaleal infection, involving the periosteum and the galea (b, arrows). The skin shows mild enhancement, and there is some infiltra-

tion in the subcutis (a, arrows). Axial diffusion-weighted images show a linear high signal (c, arrow) with evidence of restricted diffusion on the ADC map (d, arrow)

1.4 Vascular

usually less than 1.5 cm and increases in size upon Valsalva, coughing or sneezing. The anomaly is usually seen in newborns (association with dural sinus hypoplasia and developmental venous anomalies). Rare complications include thrombosis, infection and haemorrhage. Imaging is important to confirm the diagnosis but even more to exclude other bumps in children, e.g. eosinophilic granuloma, dermoid cyst, meningoencephalocele, growing fracture with leptomeningeal cyst, abscess and arteriovenous fistula.

1.4.1 Sinus Pericranii Sinus pericranii is a rare benign venous congenital low-flow malformation on or near the midline [7]. Trauma has also been reported to play a role in the development of sinus pericranii. The anomaly consists of one or several intradiploic veins connecting an intracranial venous sinus with a subgaleal varicose vein through a small bone defect. The lesion is

1.4 Vascular

The soft tissue component enhances on CT, and there may be some scalloping of the cortical tables, and a diploic channel can usually be demonstrated (Fig. 1.10). Both CT angi-

9

ography and MRI can be used in demonstrating the extent of the vascular malformation and the communication with the intracranial venous sinus.

a

c

Fig. 1.10  Sinus pericranii. Coronal native CT angiogram shows the connection between the dural sinus and the dilated subgaleal vein (a and b, arrows). Note the scalloping of parietal bone on CT (c, arrow). 3D CT with volume rendering shows the small bone defect (d, arrow). Coronal (e) and axial (f) T1-weighted images after intravenous gado-

b

d

linium with fat saturation (e) in another patient show the subgaleal varicose veins on the left side (e, arrow), communicating with the dural sinus. Note the presence of an associated complex developmental venous anomaly within the grey nuclei (f, arrow)

10

e

1 Scalp

f

Fig. 1.10 (continued)

Digital subtraction angiography (DSA) provides anatomical details and information on flow dynamics and used to be the gold standard, but non-invasive alternatives are available nowadays. However, in case of doubt on the subtype, one should always obtain DSA. Treatment depends on the subtype. In the dominant subtype, the sinus pericranii drains the brain, while in the accessory subtype, the role of the sinus pericranii is limited. As a consequence, a dominant sinus pericranii should not be treated. An accessory sinus pericranii has only limited contribution to the intracranial venous flow and can therefore easily be treated. Treatment consists of neurosurgical ligature or endovascular transvenous embolization taking into account the natural course (stable lesion or regression).

1.4.2 Vascular Malformation High-flow vascular lesions include arteriovenous malformation and fistula [8]. They can be congenital or posttraumatic, and the clinical presentation can be delayed until years after the trauma. A supplying artery and a draining vein can be identified with a nidus in an arteriovenous malformation on

MRI and/or DSA (Fig. 1.11). The AV malformation is usually located in the subgaleal space, and external carotid artery branches are usually the feeding arteries. The treatment options include excision, arterial ligation, embolization and sclerotherapy. Low-flow vascular lesions include venous, lymphatic or mixed malformations. They occur mainly in children and are characterized by progressive growth. They are characterized by a bunch of grapes configuration with septations and a variable degree of enhancement (Fig. 1.12). Sclerotherapy is usually the treatment of choice.

1.4.3 Sturge-Weber Syndrome Sturge-Weber syndrome is a neurocutaneous syndrome characterized by vascular malformations in the skin, eye and brain with the occurrence of angiomas of the face, choroid and leptomeninges. An associated calvarial enlargement can be seen with dilated intradiploic veins. The cutaneous haemangioma can best be identified on the T1-weighted images after intravenous gadolinium administration (Fig. 1.13).

1.4 Vascular

a

11

b

c

Fig. 1.11  Arteriovenous malformation. Axial T1-weighted image after intravenous gadolinium with fat saturation (a) and lateral digital subtraction angiogram (b) demonstrate the capillary nidus (a and b, arrow). The middle meningeal artery and the superficial temporal artery are

feeding the nidus (b). On an axial T2-weighted image (c) in a posttraumatic arteriovenous malformation, multiple flow voids are seen in the subgaleal space on both sides but more pronounced on the right side (arrows)

12

a

c

Fig. 1.12  Veno-lymphatic malformation. Axial T1-weighted image (a) and axial T1-weighted image (b) after intravenous gadolinium with fat saturation show the focal thickening of the subcutis and subgaleal tis-

1 Scalp

b

d

sues with strands of enhancement (b, arrow). The corresponding axial T2-weighted image is shown (c). Axial T2-weighted image 2 years later (d) shows the increased size of the vascular malformation

1.5 Cysts

a

13

b

Fig. 1.13  Sturge-Weber syndrome. Axial T1-weighted images before (a) and after (b) intravenous gadolinium. Note the enhancement of the cutaneous haemangioma (a and b, long arrow) and the enhancing thick-

ened calvarium on the left side (a and b, short arrows). Leptomeningeal angiomatosis is seen in the temporal and occipital lobe, and there is hypertrophy of the left choroid plexus

1.5 Cysts

Treatment is only considered in large TC or because of cosmetic reasons. A TC is a slowly growing benign lesion, but occasionally malignant degeneration occurs, leading to proliferating trichilemmal tumour (approx. 2%). This tumour is characterized by enhancement of the wall with variable thickness and mural nodules [9]. Enhancing soft tissue components, invasion in surrounding structures and adjacent bone erosion indicate malignant transformation. The lesions usually exceed 3–5 cm.

1.5.1 Trichilemmal Cyst The trichilemmal or pilar cyst (TC) is a benign cystic lesion in the dermis, originating from the outer root sheath of the hair follicle, with possible extension in the subcutis. The epidermis remains intact. It is the most common (sub)cutaneous lesion in the scalp, and multiple lesions can be observed [9]. More than 90% of all TC are found in the scalp. The TC is lined by squamous epithelium forming a thick capsule and contains a granular layer filled with keratin. It is more often seen in middle-aged women. On CT, the TC appears hypodense with some hyperdense components and calcification in up to 25% (Fig. 1.14). The low signal on T2-weighted images corresponds to the keratin and the calcification (Fig. 1.14). Occasionally, a fibrous capsule can be identified (Fig. 1.14). There is typically no contrast enhancement. The occurrence of multiple lesions, the absence of contrast enhancement and the low signal on T2-weighted images are useful to differentiate the TC from other scalp lesions.

1.5.2 Epidermoid Cyst An epidermoid or epidermal cyst is a dermal lesion lined by squamous epithelium in the dermis, filled with keratin and lipids [10]. Sometimes the lesion is falsely referred to as sebaceous cyst. True sebaceous cysts or steatocystomas contain sebum but are rare in the scalp. On clinical examination, the epidermoid cyst is difficult to differentiate from the TC. The lesion communicates with the skin surface and is more common in the face, neck and

14

1 Scalp

a

c

b

d

Fig. 1.14  Trichilemmal cyst. Axial CT (a, b) and axial T2-weighted images (c, d) show the calcification (a and b, arrow) and the low signal reflecting the keratin content (c, arrow) of the cyst in the dermis. The epidermis appears intact. The lesion has slowly grown over 14  years

(d). Coronal T1-weighted image (e) in another patient demonstrates a high signal in two trichilemmal cysts (arrows). Note the low-signal fibrous capsule

1.5 Cysts

e

15

Occasionally, there is a rim enhancement after intravenous gadolinium (Fig. 1.15). In ruptured cyst, enhancement of septa and enhancement of the adjacent subcutaneous tissue can be observed. The treatment consists of surgical excision.

1.5.3 Dermoid Cyst

Fig. 1.14 (continued)

trunk than in the scalp. It is more often seen in young to middle-aged adults with a male predominance. Epidermoid cysts can be seen in Gardner syndrome, one of the familial adenomatous polyposis syndromes. On CT, the lesion is non-specific. On MRI, the nodule is iso- to hyperintense on T1 and hyperintense with variable low-signal debris on T2 with diffusion restriction on the ADC map (Fig. 1.15).

A dermoid cyst develops from abnormal inclusion of ­ectoderm along the lines of skin fusion during ectodermal folding of the neural tube [11]. The cysts are often located in the midline at sites of sutures (e.g. anterior fontanelle or the occipital midline region) (Fig.  1.16). These congenital lesions present early after birth, but occasionally a delayed onset as late as the sixth or seventh decade of life is possible. They gradually enlarge due to the production of keratin, hair follicles and sebaceous material. Histologically, a sharply defined wall is observed, lined by stratified squamous epithelium. On CT, a dermoid cyst appears sharply defined with a density similar to soft tissue (Fig. 1.16). Erosion of the external table is possible. There are no calcification, no capsule and no internal reticulations. CT is very helpful in differentiating dermoid cyst from epidermoid cyst, encephalocele, lipoma, cephalohaematoma and sinus pericranii. On MRI, a low T1 and a high T2 signal are seen (Fig. 1.16). Surgical excision is the treatment of choice.

16

a

1 Scalp

b

c

Fig. 1.15  Epidermoid cyst. Axial T2-weighted (a) and axial diffusion-­ weighted image (b) and ADC map (c) show a dermal cyst with high signal on T2 and on diffusion-weighted images (a and b, arrow) and diffusion restriction on the ADC map (c, arrow). Coronal T1-weighted

d

image after intravenous gadolinium with fat saturation in another patient with an epidermoid cyst demonstrates the rim enhancement (d, arrow)

1.5 Cysts

17

a

c

b

d

e

Fig. 1.16  Dermoid cyst. Axial CT (a), sagittal (b) T1-weighted and axial (c) T2-weighted image in a neonate with a large midline dermoid cyst. Sagittal CT with bone window setting (d) and axial T2-weighted

image (e) in a 70-year-old woman with a large dermal mass with scattered calcification and intact epidermis (d, arrow)

18

1 Scalp

1.6 Tumours

1.6.3 Miliary Osteoma Cutis

Approximately 2% of all skin tumours are located on the scalp [12]. Only 1–2% of the scalp tumours are malignant, but they are often diagnosed at an advanced stage often because of late detection due to the hair and the lack of self-­ inspection. MRI is increasingly being used to assess the extension and the degree of infiltration of skin tumours [13].

Osteoma cutis is a common, idiopathic, benign and asymptomatic pathology in middle-aged and elderly men and women, predominantly seen in the frontal scalp and facial (maxillary) tissues [15]. The lesions can be recognized as firm skin-coloured papules. They are often observed in a setting of acne vulgaris and are then considered as secondary osteoma cutis. They may represent sebaceous inspissations. In a review of 1315 sinus CT examinations, the authors found evidence of primary (idiopathic) osteoma cutis in more than 40% of the cases, which are therefore considered as common benign age-related findings. Multiple millimetric (sub)dermal calcification, with a central lucency in the larger lesions, can be seen on CT (Fig. 1.19). If necessary, treatment consists of curettage, laser resurfacing or topical tretinoin gel application.

1.6.1 Pilomatricoma A pilomatricoma is a benign hair follicle-related tumour of the dermis with possible extension in the subcutis. The tumour originates from the cortex of a hair follicle and consists of epithelial cells surrounded by fibrous and oedematous stroma with a connective tissue capsule [13]. Pilomatrixoma and calcifying epithelioma of Malherbe are synonyms. It is a rare, slowly growing, mobile tumour, occurring more commonly in patients younger than 20 years but with a second peak in the elderly. The tumour is more frequently seen in the neck and in the extremities and is less common in the scalp. An association has been reported with Turner syndrome, Gardner syndrome and myotonic muscular dystrophy. On CT, there is a variable degree of (micro)calcification. There is no tissue plane between the skin and the lesion, and there is no infiltration of adjacent tissues. On MRI, an iso- to hyperintense lesion is seen with reticular hyperintensities on T2 and T1 representing the stroma. Peritumoral fat stranding on T2 can be observed, and a peripheral gadolinium enhancement can be seen (Fig. 1.17).

1.6.2 Lipoma The tumour is often located on the forehead and consists of encapsulated mature adipocytes in the subcutis. A subgaleal lipoma is located between the galea aponeurotica and the periosteum and is typically recognized as a semi-spherical mass [14]. The CT and MR appearances are identical to fat (Fig.  1.18). A larger size, enhancing thick septations and nonadipose tissue are considered signs of a possible liposarcoma.

1.6.4 Fibroma and Granuloma Nuchal-type fibroma is typically found in the neck region but can occur in the scalp. The extranuchal fibromas are clinically and histologically similar to those in the posterior neck. Histologically, this fibrous tumour consists of thick collagen fibres and fibroblasts. The lesion has been associated with trauma, diabetes and Gardner syndrome. On MRI, the subcutaneous unencapsulated lesion has a low T1 and T2 signal reflecting its histological features (Fig. 1.20). Surgery is the treatment of choice although complete excision can be difficult because of the unencapsulated nature of the tumour. A neurofibroma is an irregular benign tumour that can occur spontaneously or in association with neurofibromatosis type 1 [16]. The tumour is composed of Schwann cells, fibroblasts and vascular structures. Localized neurofibroma is the most common subtype (90%). On MRI, the T1 and T2 signal intensities are not specific, but a central low signal is a frequent observation on T2-weighted images (Fig.  1.21). This central low signal, sometimes called the ‘target sign’, corresponds to fibrous tissue. A low-signal rim can be identified on T1-weighted images, corresponding to the epineurium around the tumour (Fig. 1.21). There is no evidence of diffusion restriction on diffusion-weighted imaging.

1.6 Tumours

a

19

b

c

Fig. 1.17  Pilomatricoma. Sagittal T1-weighted before (a) and after (b) intravenous gadolinium and T2-weighted (c) image in an occipital pilomatricoma in the dermis and subcutis (a–c, arrow). The tumour is

sharply delineated. Note the contrast enhancement (b, arrow) and the reticular changes (c, arrow)

20

a

1 Scalp

b

c

Fig. 1.18  Subgaleal lipoma. Sagittal T1-weighted (a) and axial T1-weighted image without (b) and with (c) fat saturation in two different lipomas (a–c, arrows). Note the clear visualization of the galea aponeurotica (a, black arrow)

Diffuse neurofibroma is more often seen in children and adolescents and is usually associated with neurofibromatosis type 1 (Fig. 1.22). A plexiform neurofibroma is an extensive tumour often extending into the surrounding tissues (Fig. 1.22). Juvenile xanthogranuloma is a non-Langerhans histiocytic disorder, usually seen in children [17]. More than 90% of the lesions occur below 1  year of age. In most cases, a well-circumscribed dermal lesion can be delineated. Occasionally, extracutaneous locations can be observed including intracranial dural masses. It is a benign self-­ limiting condition, which does not require surgery. The CT findings are non-specific, and occasionally the external table can be eroded. On MRI, some features can help to suggest the diagnosis. These include a high T1 signal, low T2 signal, homogeneous enhancement and diffusion restriction (Fig. 1.23).

1.6.5 Carcinoma Non-melanoma skin cancer, predominantly basal cell carcinoma (approx. 40%) and squamous cell (spinocellular) carcinoma (approx. 20%), is the most common malignant skin cancer. Carcinoma occurs preferentially in >60-year-old patients, with a female predilection and usually related to chronic sun exposure. The tumour size, the poor delineation, the tumour recurrence and a history of immunosuppression or prior radiotherapy are poor prognostic factors. Although bone destruction is rare, it may occur in carcinoma, and CT is mandatory when invasion of the bone or dura is suspected (Fig. 1.24). Basal cell carcinoma and squamous cell carcinoma cannot be differentiated on imaging [18]. Non-specific low T1 and high T2 signal are usually seen with homogeneous

1.6 Tumours

21

a

b

Fig. 1.19  Benign miliary osteoma. Axial CT with bone window setting (a) and 3D CT with cinematic rendering of the scalp (b) demonstrate multiple calcified nodules in the dermis

a

b

c

Fig. 1.20  Nuchal-type fibroma. Sagittal T2-weighted (a) and axial T1-weighted images before (b) and after (c) intravenous gadolinium show a subcutaneous poorly defined lesion with low T2 and T1 signal (a and b, arrows) and moderate enhancement (c, arrows)

22

1 Scalp

a

c

b

d

e

Fig. 1.21  Neurofibroma. Axial T2-weighted (a) and T1-weighted before (b) and after intravenous gadolinium (c) and diffusion-weighted (d) images with ADC map (e). Note the central low T2 signal (a, arrow)

and the peripheral low signal rim on the T1-weighted image (c, arrow). There is no evidence of diffusion restriction (e)

1.6 Tumours

a

23

b

c

Fig. 1.22  Neurofibromatosis type 1. Coronal FLAIR (a) and coronal T2-weighted (b) images in neurofibromatosis type 1 show multiple subcutaneous neurofibromas. Axial T2-weighted image shows an extensive lobulated mass consistent with a large plexiform neurofibroma (c, arrows)

24

a

1 Scalp

c

b d

e

Fig. 1.23 Juvenile xanthogranuloma. Axial T2-weighted (a), T1-weighted before (b) and after (c) intravenous gadolinium, axial diffusion-­weighted image (d) and ADC map (e). Note the low T2 signal

(a, arrow), the high T1 signal (b, arrow), the homogeneous enhancement (c, arrow) and the diffusion restriction (d and e, arrow)

enhancement following intravenous gadolinium ­administration. Imaging can contribute in assessing the depth of invasion by the tumour. The imaging features include a thickened galea aponeurotica, subcutaneous fat tissue invasion, higher diameter-to-­ height ratio, frequent intratumoral hypointensity and mixed hyper- and hypointensity on T2, ‘fascial tail sign’ and thick

fascial enhancement extending from tumour margin (Fig. 1.25). Diffusion restriction is usually seen in the tumour (Fig. 1.26). Systemic treatment and radiotherapy can be initiated. Imaging is frequently used to monitor the tumour response (Fig. 1.26).

1.6 Tumours

25

a

c

b

d

Fig. 1.24  Basal cell carcinoma. Axial CT with soft tissue setting (a) and with bone window setting (b) and 3D CT with cinematic rendering of the bone (c) and scalp (d) show the extensive basal cell carcinoma with osteolytic bone destruction and dural invasion (a)

26

1 Scalp

a

c

b

d

e

Fig. 1.25  Squamous cell carcinoma. Axial diffusion-weighted image (a) and ADC map (b) and sagittal T2-weighted (c) and coronal T1-weighted (d, e) images after intravenous gadolinium. Note the diffusion restriction on the ADC map (b, arrow), the inhomogeneous predominantly low T2 signal (c, arrow) and the strong homogeneous

enhancement of the lesion (d, arrow) with superficial ulcerations and extending through all layers of the scalp reaching the galea aponeurotica with thickened fascial enhancement (d, short arrows). Note the ulceration in another squamous cell carcinoma (e, arrow)

1.6 Tumours

27

a

b

c

d

Fig. 1.26  Basal cell carcinoma. Axial diffusion-weighted image (a) and ADC map (b), axial CT with bone window setting prior to external radiotherapy with radiation mask in position (c) and axial T1-weighted image after intravenous gadolinium before (d) and after the treatment

(e). There is evidence of diffusion restriction in the tumour (a and b, arrow). Note the extension of the tumour through all layers of the scalp (d) and the response to treatment (e)

28

1 Scalp

e

complete resection, but local recurrence frequently occurs after incomplete resection. Other rare sarcomas are the fibromyxoid sarcoma, the fibrosarcoma and the leiomyosarcoma. Leiomyosarcomas are derived from either the arrector pili, cutaneously, or the smooth muscle wall of blood vessels, subcutaneously. There could be a potential link between the development of sarcoma and trauma due to the development of direct tissue damage and inflammation. The imaging findings are non-specific (Fig. 1.28). The infantile fibrosarcoma is a rapidly growing tumour, occasionally with bone involvement [21]. The tumour is highly vascular with visualization of vascular structures (Fig. 1.29). Histological similarities with haemangioma and haemangiopericytoma have been reported. The fibromyxoid sarcoma is a very rare tumour, characterized by an infiltrative extension along the fascia, resulting in its curvilinear shape (tail-like extension) (Fig. 1.30) [22]. The T1 and T2 signal remain non-specific.

1.6.7 Melanoma Fig. 1.26 (continued)

1.6.6 Sarcoma Many different sarcoma types occur in the scalp. From the imaging point of view, dermatofibrosarcoma protuberans (DFSP) appears to be the most relevant sarcoma. DFSP is usually seen in the third and fourth decade of life. It is a slowly growing, painless spindle cell tumour of the dermis. DFSP has been reported to occur in areas of repeated trauma or in tattoo sites. The tumour mainly occurs on the trunk and extremities, but approximately 10% are seen in the head and neck region. Multinodular protuberant growth and plaque formation occur. Local/distant metastases are absent. The tumour can extend into the subcutis and deeper, which is reflected in the tentacle-like tumour prolongations (Fig.  1.27). Intracranial extension has been reported but is extremely rare [19]. On MRI, non-specific low T1 and high T2 signal are seen with homogeneous enhancement (Fig.  1.27). Diffusion-­ weighted MRI is extremely useful in assessing the extension of the tumour and in detecting residual tumour after surgery [20]. There is no bone destruction but bone thinning may occur. Mohs micrographic surgery, with removal of one tissue layer at a time and on-site histological assessment, is the treatment of choice. DFSP has an excellent prognosis after

Melanoma occurs preferentially in >60-year-old patients, with a male predilection. Up to 7% of the melanomas occur in the scalp, with a less good prognosis because of the larger size (due to a later detection) and the associated higher risk of local and distant metastases. GNA11-mutated blue nevi and desmoplastic melanoma are more common subtypes in the scalp [23]. Imaging is only requested in the case of unusual presentation. CT shows a cutaneous soft tissue lesion (Fig. 1.31). On MRI, a high T1 signal and a low T2 signal are seen, except in amelanotic melanoma, which displays a low T1 signal and a high T2 signal (Fig. 1.32). Differential diagnosis includes cutaneous angiosarcoma, which may have similar signal characteristics on T1 and T2 but is almost always larger upon clinical presentation and usually consists of multiple (nodular) lesions.

1.6.8 Metastasis Scalp metastases from internal tumours are uncommon and account for approximately 4% of the cutaneous metastases [24]. Breast, lung, colorectal and liver are the most common primary tumours. Cutaneous metastases are a poor prognostic finding. There are no specific imaging features. In large metastases, CT can demonstrate bone involvement (Fig. 1.33).

1.6 Tumours

29

a

b

c

d

Fig. 1.27  Dermatofibrosarcoma protuberans. Axial diffusion-weighted image (a) and ADC map (b) and coronal T2-weighted (c) and axial T1-weighted images after intravenous gadolinium (d). Note the clear delineation of the tumour on the diffusion-weighted image with the

tentacle-like extension (a and b, arrows). The tumour involves all layers of the scalp, and a high T2 signal is seen with a strong homogeneous enhancement (c and d, arrows)

30

1 Scalp

a

b

Fig. 1.28  Leiomyosarcoma. Sagittal T2-weighted (a) and T1-weighted images after intravenous gadolinium (b) show a sharply delineated space-­ occupying lesion in the subcutis (a and b, arrows)

a

b

c

Fig. 1.29  Infantile fibrosarcoma. Axial CT with bone window setting (a) and axial T1-weighted images before (b) and after (c) intravenous gadolinium show a large strongly enhancing tumour with intratumoral vascular structures (b, c). Note the normal delineation of the bone (a)

1.6 Tumours

31

a

b

c

Fig. 1.30  Fibromyxoid sarcoma. Axial T2-weighted (a) and axial T1-weighted images before (b) and after (c) intravenous gadolinium. The subcutaneous tumour has a low signal and a curvilinear shape on T2-weighted images (a, arrow). Contrast enhancement is seen (c, arrow) Fig. 1.31 Amelanotic melanoma. Axial CT (a) and axial PET (b) demonstrate the small melanoma with central ulceration (a, arrows) and high metabolic activity (b, arrow)

a

1.6.9 Myeloma Multiple myeloma is a plasma cell malignancy. The minimal diagnostic criteria include the presence of at least 10% abnormal plasma cells in the bone marrow or histological proof of a bony or extramedullary plasmacytoma. The clinical presentation is usually a painless gradually enlarging scalp mass.

b

Scalp myeloma has been described as the sole presenting finding of multiple myeloma, but in most cases, extension into the bone and/or other distant signs of the disease are present too [25]. Imaging findings are atypical, and the lesion can be associated with osteolysis and intracranial extension. On MRI, diffusion restriction can be a helpful feature in the differential diagnosis (Fig. 1.34).

32

1 Scalp

a

b

Fig. 1.32  Amelanotic desmoplastic melanoma. Axial T2-weighted (a) and axial T1-weighted images after intravenous gadolinium (b). Note the high T2 signal corresponding to the absence of melanin (a, arrow). A homogeneous strong enhancement is seen (b, arrow)

a

b

c

Fig. 1.33  Metastasis of breast carcinoma. Axial CT images with soft tissue window setting (a, b) show the subcutaneous and subgaleal tumour. Two months later, the tumour appears larger. Note the dural

invasion and the erosion of the external table on the axial CT with bone window setting (c, arrow)

1.6 Tumours

33

a

c

b

d

Fig. 1.34  Myeloma. Axial T2-weighted (a) and axial T1-weighted smaller subcutaneous lesion on the right side (a, arrow) and the extenimages before (b) and after (c) intravenous gadolinium, diffusion-­ sion of the tumour into the galea aponeurotica (b and c, arrows). weighted (d) images and ADC map (e). Note the presence of a second Diffusion restriction is noted on the ADC map (d and e, arrows)

34

e

1 Scalp

1.6.10 Haematolymphoid Tumours Scalp lymphoma is relatively rare and usually presents as an extension from a calvarial lesion into the subcutaneous tissues. Lymphoma is more often seen in the fourth decade of life [26]. Typical B-cell scalp lymphomas are follicle centre lymphoma and marginal zone lymphoma, while the most common T-cell lymphoma is mycosis fungoides. MRI features consist of iso-T1 and iso-T2 signal with diffusion restriction on MRI (Fig.  1.35). Thorny tumour margins reflect lymphatic spread. Precursor B-ALL is very rare in the scalp. The imaging features are not specific, but diffusion restriction is often seen on MRI (Fig. 1.36).

Fig. 1.34 (continued)

1.6 Tumours

35

a

c

Fig. 1.35  Marginal zone lymphoma. Axial T2-weighted (a), coronal T1-weighted after intravenous gadolinium (b), axial diffusion-weighted (c) and axial PET image (d). Note the low T2 signal (a, arrow), the

b

d

caudal and cranial tumour extension (b, arrows), the high signal on diffusion (c, arrow) and the high metabolic activity on PET (d, arrow)

36

1 Scalp

a

b

L

c

d

Fig. 1.36  Precursor B-cell acute lymphoblastic leukaemia. Axial T2-weighted (a), axial T1-weighted after intravenous gadolinium (b) and diffusion-­weighted (c) image with ADC map (d). An extensive subgaleal lesion is seen with diffusion restriction (c and d, arrow)

1.7 Dermal Hypertrophy and Atrophy

1.7 Dermal Hypertrophy and Atrophy 1.7.1 Dermal Hypertrophy Primary cutis verticis gyrata is a hypertrophy of the skin, resembling the undulations (folds and furrows) of cerebral gyri (‘bulldog scalp’) [27]. It is more frequently seen in males, and the aetiology remains unknown. The skin folds are usually symmetrical and oriented in an anteroposterior direction (Fig. 1.37). Vertex and occiput are more frequently involved. Primary cutis verticis gyrata is subdivided into (1) isolated disease and (2) association with neurological (e.g. seizures) and/or ophthalmological (e.g. optic nerve atrophy) abnormalities. Secondary cutis verticis gyrata can be seen in association with acromegaly, Graves disease, tuberous sclerosis and several syndromes. The cutaneous changes are the result of an overexpression of growth hormone and insulin-like growth factor 1, acting on dermal fibroblasts. Dermal glycosaminoglycan accumulation and oedema cause skin thickening. In Prader-Willi syndrome, growth hormone therapy is able to reduce the number of thickened skin folds (Fig.  1.37). Growth hormone therapy is known to improve the body composition and physical strength. Other causes of secondary cutis verticis gyrata are pachydermoperiostosis or ‘primary hypertrophic osteoarthropathy and testosterone use’. In secondary cutis verticis gyrata, the skin folds tend to be more asymmetrical and not oriented in an anteroposterior direction. Generalized thickening of the skin is also observed in neurofibromatosis (Fig. 1.38). In patients with the Cushing syndrome, excessive subcutaneous fat accumulation can be seen in the neck, known as

37

lipodystrophy, with the characteristic appearance of a ‘buffalo hump’ (Fig. 1.38). This may occur following long-term use of steroids or in patients with an adrenal or pituitary tumour. Occasionally, thickened skin folds can be seen following asymmetrical positioning of the patient’s head in a CT scan and should certainly not be misinterpreted (Fig. 1.39).

1.7.2 Dermal Atrophy Parry-Romberg syndrome, a severe variant of linear morphea, is a craniofacial phakomatosis presenting in childhood [28]. It is a progressive hemifacial atrophy of the skin, subcutaneous tissue, muscles and bone, which ceases to progress at some stage. Rarely, inflammation and sclerosis may involve meninges and brain. The lesions extend unilaterally from the forehead into the frontal scalp (Fig. 1.40). Unilateral cerebral lesions can be observed too. Cutis marmorata telangiectatica congenita is a rare congenital vascular disorder characterized by discoloured patches of the skin caused by widened (dilated) surface blood vessels. More recently, the term macrocephaly-capillary malformation has been introduced [29]. The syndrome is characterized by megalencephaly, a variable asymmetry, cutaneous vascular anomalies and/or cutis marmorata and a variable wide range of vascular, neurological, ocular and musculoskeletal abnormalities. There is cutaneous atrophy with a purple or blue ‘marbled’ or ‘fishnet’ appearance (cutis marmorata) (Fig. 1.41). In some affected individuals, ulcerations or congenital skin defects (aplasia cutis) can be present.

38

a

c

1 Scalp

b

d

Fig. 1.37  Cutis verticis gyrata. Coronal T2-weighted images before (a) and after (b) growth hormone therapy show the decreased thickening of the skin folds. Anterior (c) and posterior (d) 3D CT with cinematic rendering of the skin show the anteroposterior orientation of the undulating skin

1.7 Dermal Hypertrophy and Atrophy

a

39

b

c

Fig. 1.38  Neurofibromatosis. Sagittal CT with soft tissue window setting (a) and 3D CT with cinematic rendering (b) show the thickened undulating skin folds. Axial T1-weighted image (c) shows the excessive

subcutaneous fat accumulation in a patient with Cushing disease with a so-called ‘buffalo hump’ appearance

40

a

Fig. 1.39  Position-related thickened skin folds. Axial CT with soft tissue setting (a) and with bone window setting (b) show the thickened skin folds on the right side due to asymmetrical positioning in the CT

a

1 Scalp

b

(a, arrows). The CT head support is shown compressing the skin on the right side (b, arrows)

b

Fig. 1.40  Parry-Romberg syndrome. Axial FLAIR (a) and T1-weighted images after intravenous gadolinium (b) demonstrate the thinning of the frontal scalp (a and b, arrow)

1.7 Dermal Hypertrophy and Atrophy

a

41

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Fig. 1.41  Cutis marmorata telangiectatica congenita. Axial T2-weighted (a) and FLAIR images (b) show the macrocephaly with thinning of the skin and the abundant dilated subcutaneous veins (a and b, arrows). 3D CT with cinematic rendering illustrates the dilated superficial veins (c)

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2.1 Anatomy and Variants The anatomy of the calvarium and the sutures will be briefly reviewed as well as the common anatomical variants sometimes called ‘pseudolesions’.

2.1.1 Anatomy The cranium is formed by the viscerocranium and the neurocranium. The viscerocranium forms the facial skeleton. The neurocranium is a large neural cavity that covers and protects the brain and is formed by the tight engagement of the calvarium (membranous cranium, cranial/skull vault or skull) and the skull base (chondrocranium) [30]. The calvarium is formed by intramembranous ossification and consists of several flat bones: a large part of the frontal bone, the parietal bones, the squamous portion of the temporal bone and the interparietal part of the occipital bone. The calvarium is unilaminar at birth and becomes trilaminar around 4–6 years of age, when the diploic layer becomes apparent. The pericranium is the periosteal covering of the external table. Typically, the internal table of the calvarium is thinner than the external table although this may vary depending on the age (Fig. 2.1). The internal and external table return a very low signal on T1- and T2-weighted images with the diploic space between both tables. The diploic space consists of cancellous/spongy bone with trabeculae and contains red marrow and diploic veins (Fig. 2.1). In young patients, the hematopoietic bone marrow appears inhomogeneous, but, after 7 years of age, a high signal is often seen, reflecting the fatty marrow changes (Fig. 2.1). The diploic space is highly vascular and is connected with small arteries and veins in the scalp and meningeal layer. The calvarium should not be confused with the calvaria. The calvaria is the upper part of the neurocranium and consists of the upper portions of the frontal, occipital and parietal bones, corresponding to the roof of the skull or skull cap portion of the calvarium.

The sutures of the neurocranium connect the bones of the calvarium. Sutures can be considered as fibrous joints that are wide at birth and become rigid later in life. The sutures and synchondroses in a paediatric skull undergo changes in the first 4  years of life. Normal sutures in adults typically have a zigzag pattern with sclerotic borders (Fig. 2.1). It is important to be aware of the normal anatomy in order to distinguish sutures from fractures [31]. The total number of sutures still varies depending on the source, and it is beyond the scope of this section to review all sutures. The sagittal, coronal, lambdoid and squamosal sutures are open in all infants and close in early adulthood (Fig. 2.2). Closer to the mastoid part of the parietal bone, the squamous suture continues as the parietomastoid suture. At the most posterior parietal bone articulation, between the parietal and the temporal bone, the parietotemporal suture can be identified. Both parietomastoid and parietotemporal sutures are direct continuations of the squamous suture, and their exact borders are not always clearly defined. The metopic or interfrontal suture is present in the newborn and should be closed between 3 and 9 months of age. A persistent metopic suture is known as ‘metopism’ (Fig. 2.2). Several landmarks play a role in planning a neurosurgical approach, and these meeting points of sutures will be illustrated. The bregma (anterior fontanelle in the neonate) is the meeting point between the frontal bone and both parietal bones where the coronal and the sagittal sutures come together (Fig. 2.2). The lambda (posterior fontanelle in the neonate) is the meeting point between the sagittal and the lambdoid suture (Fig. 2.2). The vertex is the midpoint of the sagittal suture, between the bregma and the lambda (Fig. 2.2). The asterion is a meeting point between the lambdoid, parietomastoid (extension of the squamous suture) and occipitomastoid sutures where the occipital, parietal and mastoid portion of the temporal bone meet (approximately 4 cm behind and 1.2 cm above the centre of the ear canal).

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. Demaerel, Imaging of the Scalp and Calvarium, https://doi.org/10.1007/978-3-031-49626-4_2

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Fig. 2.1  Anatomy of the calvarium. Axial CT with bone setting (a–d, h), axial T1-weighted (e), T2-weighted (f) and T1-weighted image after intravenous administration of gadolinium with fat saturation (g). A thicker internal table (a, arrow) is seen in a 25-year-old woman, while both tables have approximately the same thickness in a 70-year-old man (b). Between both tables, the trabecular bone matrix in the diploic space can be seen (b, arrow). Depending on the degree of osteopenia, the trabecular bone of the diploe may appear differently (c, arrow). The fat

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in the diploic space is reflected by wider trabeculations on CT (d, arrows) and high signal on the spin-echo T1-weighted image (e, arrows). The internal and external tables have a low T2 and T1 signal on MRI.  The signal of the diploic space is higher on the T2-weighted image (f, arrow). There is no enhancement in the diploic space except from the diploic veins (g, arrows). The sutures in adults have a typical zigzag appearance (h)

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Fig. 2.2  Anatomy of the sutures. Different views from the 3D CT with cinematic rendering: posterior (a), posterior oblique (b), lateral (c), magnification of the lateral (d), top (e) and anterior view (f). The sagittal (a, 1) and lambdoid (a, 2 and c, 4) sutures are seen with their meeting point, the lambda (a, 3). The lambdoid (b, 1), occipitomastoid (b, 2) and parietomastoid (b, 3) sutures meet in the asterion (b, 4). The coronal (c, 1) and metopic (c, 2) sutures are seen with the anterior fonta-

nelle/bregma (c, 3). The magnified lateral view shows the coronal (d, 1), sphenoparietal (d, 2), squamosal (d, 3), sphenosquamosal (d, 4) and sphenofrontal (d, 5) sutures, defining the H-configuration of the pterion. The top view shows the lambda (e, 1) vertex (e, 2) and bregma (e, 3) along the sagittal suture. The coronal suture is also visible (e, 4). A persistent metopic suture is shown (f)

The pterion is a meeting point of five sutures: the coronal, squamous, sphenoparietal, sphenofrontal and sphenosquamous sutures. Four bones meet at this point: parietal, frontal, squamous part of the temporal and greater wing of the sphenoid. The pterion is known as the weakest part of the skull. The inion corresponds to the external occipital protuberance of the occipital bone. The basion and the opisthion are the anterior and posterior midpoint of the foramen magnum.

The obelion corresponds to a point on the sagittal suture where a line can be drawn between the parietal foramina and is thought to represent the starting point of the sagittal suture closure. Wormian bones are accessory bones that may occur within a suture, usually in the lambdoid suture (Fig.  2.3). They are considered as an anatomical variant but can occasionally be seen in osteogenesis imperfecta, hypothyroidism and cleidocranial dysplasia.

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2.1.2 Emissary Veins, Parietal Foramina and Venous Lakes

Fig. 2.3  Wormian bone. Lateral view of a 3D CT with volume rendering shows a Wormian bone (arrow)

The diploic space is highly vascular. Vascular channels or emissary veins are normal diploic connections between the dura and the scalp, but they can occasionally be large and may be confused with pathology (Fig. 2.4). Parietal foramina are a normal anatomical variant on each side in the parietal bone, through which emissary veins drain into the superior sagittal sinus (Fig. 2.5). Occasionally, they can be enlarged (e.g. in association with gene deletions in chromosome 11p) [32]. Venous lakes consist of enlarged venous spaces within the parasagittal dura, adjacent to the superior sagittal sinus (Fig. 2.6). Usually, three venous lakes are localized in each hemisphere, in the frontal, parietal (the most common location) and occipital bones. They receive blood from superficial cortical and meningeal veins and cerebrospinal fluid from arachnoid granulations. Some venous lakes can enlarge, extending from the internal table into the diploic space, resulting in an osteolytic area in the calvarium (Fig.  2.7). They behave as pure vascular entities, with contrast enhancement on both CT and MRI.

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Fig. 2.4  Emissary veins. Axial CT with bone setting shows normal emissary veins in the occipital bone (a, arrows) and an enlarged emissary vein in the parietal bone (b, arrow)

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Fig. 2.5  Parietal foramina. Coronal CT with bone setting (a) and 3D CT with volume rendering of the skull (b) and of the scalp (c) show bilateral parietal foramina in close relationship with veins in the scalp

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Fig. 2.6  Venous lakes. Axial CT with bone setting (a, b) shows large venous lakes in the left parietal bone (a) and in the frontal bones, more pronounced on the right side (b)

2.1.3 Arachnoid Granulations Arachnoid granulations of Pacchioni are very common and easily recognized. They consist of arachnoidal protrusions into the venous sinuses or diploe, often close to the transverse or superior sagittal sinus (Fig. 2.8). When they are larger than 1 cm, they are called ‘giant’ arachnoid granulation (Fig. 2.8).

They do not enhance and are recognized as well-defined indentations into the internal table, with a sclerotic rim. On MRI, they have the same signal as cerebrospinal fluid. Arachnoid granulations should not be confused with meningeal herniations. Meningeal herniations are common and are increasingly seen with age, due to weakening of the bone (Fig. 2.9).

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Fig. 2.7  Venous lake. Axial T2-weighted image (a, b) and axial CT with bone setting (c) show the growth of a venous lake with scalloping of the internal and external table (a–c, arrow)

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Fig. 2.8  Granulations of Pacchioni. Axial CT with bone setting (a, d), axial (b) and sagittal (c) T2-weighted image, sagittal post-contrast CT (e). The granulations of Pacchioni are seen in close relationship with

the transverse sinus (b and c, arrows). A giant granulation is shown in the superior sagittal sinus with scalloping of the bone (d and e, arrow)

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Fig. 2.9  Meningeal herniations. Axial CT with bone setting (a) and axial T1-weighted (b) and T2-weighted (c) images show the meningeal herniation with scalloping of the bone (a–c, arrows)

2.2 Congenital 2.2.1 Craniosynostosis Premature fusion of a suture will result in craniosynostosis (Fig.  2.10) [33, 34]. Advances in molecular biology and genetics have shown that molecular interactions are likely to play an important role in craniosynostosis [35]. In craniosynostosis, pulsatile pressure of the gyri on the internal table can result in a ‘copper beaten skull’ in neonates. This is due to an increased intracranial pressure and can also be seen in young children with hydrocephalus or in the presence of an intracranial tumour (Fig. 2.11). Thin-section volumetric CT with bone algorithm and 3D shaded-surface volume-rendered CT play a crucial role in the diagnostic workup of these children and in the follow-up after surgery. One should be aware of the radiation risk, and optimized low-dose CT protocols should be used. There have been attempts to use MR imaging for assessing craniosynostosis, but low-dose CT remains the gold standard today. Imaging is performed to confirm the diagnosis, to search for associated anomalies (e.g. Chiari 1 malformation, hydrocephalus and congenital abnormalities of the corpus callosum), to assist in surgical planning and to assess the postoperative status.

Fig. 2.10  Craniosynostosis. 3D CT with cinematic rendering (anterior top view of the frontal bone) shows premature fusion of the sagittal and coronal sutures

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Fig. 2.11  Copper beaten skull. Axial CT with bone setting (a) and inside view of the skull cap on 3D CT with volume rendering (b) demonstrate the prominent convolutional markings on the internal table due to gyral impressions

In synostosis of the sagittal suture, a thickened bony ridge is seen, resulting in an elongated shape of the head (dolichocephaly) and hypotelorism (Fig. 2.12). In synostosis of the coronal suture, the head appears short with occipital flattening, bilateral harlequin eye deformity and hypertelorism (Fig. 2.13). Early closure of the coronal sutures and a large anterior fontanelle are typically seen in the Apert syndrome, characterized by calvarial abnormalities and syndactyly (Fig.  2.14). Brachycephaly, hypertelorism and maxillary hypoplasia are observed. In Crouzon syndrome, one can see an abnormal shape of the calvarium due to premature craniosynostosis and in severe cases a so-called cloverleaf skull (premature closure of the coronal, sagittal and lambdoid sutures) (Fig. 2.15). In a unilateral coronal suture synostosis, there is flattening of the ipsilateral frontal bone. The ipsilateral orbit is hypoplastic with the ‘harlequin eye deformity’ (the elevation of the superolateral corner of the orbit) (Fig. 2.16). Synostosis of the metopic suture is characterized by a triangular thickened forehead and is associated with orbital hypoplasia (Fig. 2.17). Metopic ridge deformity is a normal anatomical variant of the closure of the metopic suture, without associated abnormalities. In a lambdoid suture synostosis, there is ipsilateral flattening and contralateral bossing of the occipital and parietal

bone. In unilateral coronal or lambdoid craniosynostosis, it can be difficult to differentiate a true craniosynostosis from a positional deformational plagiocephaly. Occasionally, CT can be necessary to differentiate between both clinical presentations (Fig. 2.18).

2.2.2 Cephalocele A cephalocele presents as a defect in the skull and dura and is most often seen in the occipital bone (Fig. 2.19) [36, 37]. Depending on the content of the cele, one may see a meningocele or a meningoencephalocele (Fig. 2.20). A third possible cele is the atretic cephalocele that contains dura and degenerated fibrous/nervous tissue (Fig. 2.20). The cranium bifidum occultum is a large parietal midline calvarial defect with normal scalp and dura (Fig. 2.21). There is no associated cephalocele, but the association between cranium bifidum occultum and cephalocele has been reported. A deficient ossification process is the underlying cause of the abnormality. Similar to the (enlarged) paired parietal foramina, there is a deficient ossification process around the parietal notch, most likely related to an ­interruption of the normal foetal growth. Associated facial and intracranial malformations frequently occur.

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Fig. 2.12  Scaphocephaly. Top (a) and anterior views of a 3D CT with cinematic rendering (b) show the premature fusion of the sagittal suture resulting in an elongated head and hypotelorism

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Fig. 2.13  Brachycephaly. Anterior top (a) and lateral view (b) of a 3D CT with cinematic rendering in a child with bilateral premature closure of the coronal sutures, with hypertelorism. Note the copper beaten skull in the parietal and occipital bones due to pressure-related gyral impressions

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Fig. 2.14  Apert syndrome. Anterior view of a 3D CT with volume rendering (a) and with cinematic rendering (b) after surgery in a child with premature closure of the left coronal suture, asymmetrical bony orbits and large anterior fontanelle

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Fig. 2.15  Cloverleaf skull. Lateral X-ray (a) and lateral view of a 3D CT with volume rendering after surgery (b) in a child with a tower-shaped head (turricephaly). Note the extensive ‘copper beaten skull’ appearance (a)

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Fig. 2.16  Craniosynostosis. Anterior view of a 3D CT with cinematic rendering (a, b) in a child with unilateral premature fusion of the left coronal suture with ipsilateral deformity of the bony orbit (‘harlequin

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eye deformity’) (a) and in a child with bilateral premature fusion of the coronal sutures with an orbital deformity (b)

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Fig. 2.17  Trigonocephaly. Axial CT with bone setting (a) and top view of 3D CT with volume rendering (b) show the triangular shape of the forehead due to premature fusion of the metopic suture

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Fig. 2.18  Positional plagiocephaly. Axial CT with bone setting (a) and 3D CT with volume rendering (b) show flattening of the right parietal bone (a and b, long arrow) with normal lambdoid suture (a, short arrow)

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Fig. 2.19  Cephalocele. Axial CT with bone setting (a) and posterior view of a 3D CT with volume rendering (b) show the occipital midline bone defect

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Fig. 2.20  Meningoencephalocele. Sagittal T1-weighted (a), sagittal T2-weighted (b, c), axial CT with bone setting (d) and coronal T2-weighed (e) image. A meningoencephalocele (a) and an atretic meningocele (b and c, arrows) are shown. Note the displaced and ele-

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vated sinus rectus (b, black arrow). The temporal bone defect is seen (d, arrow) with herniating material representing cerebrospinal fluid as well as degenerated brain tissue (e, arrow)

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(Fig. 2.24). Occasionally, an acquired dermoid cyst can be seen following trauma or following surgery. On MRI, a high T1 signal and a variable T2 signal are seen, occasionally with a peripheral rim enhancement.

2.2.4 Epidermoid Cyst Epidermoid cysts are due to inclusion of ectodermal remnants during the neural tube formation. The cyst has a squamous epithelial lining producing keratin and cholesterol, which explains its typical ‘pearly’ aspect. They usually present in the third to fourth decade of life. Epidermoid cysts can occur at any age and in all calvarial bones. Occasionally, an acquired epidermoid cyst can be seen following trauma or following surgery. When the lesion exceeds 5 cm, it is called a ‘giant’ epidermoid cyst [39]. They are characterized by a slow growth. On CT, a lytic lesion is seen with sharp and sclerotic margins. There is usually more erosion of the internal table (Fig. 2.25). The density is usually slightly higher than cerebrospinal fluid. An intralesional calcification can be present [40]. On MRI, there is a high/variable T1 and high T2 signal, restricted diffusion and no contrast enhancement (Fig. 2.26). Rarely, intraparenchymal extension of an intradiploic epidermoid cyst can be seen (Fig. 2.27). Fig. 2.20 (continued)

2.2.3 Dermoid Cyst Dermoid cysts are very common calvarial tumours and occur often in newborns, children up to 3 years of age and in the first and second decade of life. They represent slowly growing epidermal or dermal inclusions, often located ­ close to the sutures on the midline (Fig. 2.22). They may contain hair follicles, sweat glands and sebaceous glands. A dermal sinus can be associated. The density on CT depends on the content, and scalloping/remodelling of the bone is seen (Fig. 2.23) [38]. The presence of fat is useful to differentiate a dermoid cyst from an epidermoid cyst

2.2.5 Lipoma An intraosseous lipoma is a very rare benign tumour in the calvarium and has mainly been reported in the sphenoid bone [41]. On CT, one may see an area of fat attenuation and the ‘honeycomb’ appearance similar to the finding in cavernous haemangioma. This lesion may represent a haemangioma with extreme fatty degeneration. A periosteal or subgaleal lipoma may cause hyperostosis and bone erosion, while an intraosseous lipoma leads to expansion and deformation of the bone (Fig. 2.28) (see also Sect. 1.6.2). Treatment is only occasionally indicated because of cosmetic reasons.

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Fig. 2.21  Cranium bifidum occultum. Axial (a) and sagittal (b) CT with bone setting and posterior view of the 3D CT with volume rendering (c) show the large parietal midline bone defect

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Fig. 2.22  Dermoid cyst. Top view of a 3D CT with volume rendering (a) shows the midline sharply defined lytic bone defect at the junction of the sagittal and the coronal sutures (a). Axial CT with bone setting

(b) and axial diffusion-weighted image (c) in another patient demonstrate the lytic lesion with scalloping of both the internal and external tables (b) and high signal on the diffusion-weighted image (c)

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Fig. 2.23  Dermoid cyst. Lateral skull X-ray (a) and axial T2-weighted (b) images demonstrate a sharply defined osteolytic lesion with sclerotic borders (a) and a high signal on the T2-weighted image (b)

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Fig. 2.24  Dermoid cyst. Axial CT with bone setting (a) and coronal T1-weighted image (b) show the sharply defined lytic bone lesion, close to the coronal suture, with more extensive scalloping of the exter-

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nal table (a, arrow) and high signal on the T1-weighted image representing the fatty content (b, arrow)

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Fig. 2.25  Epidermoid cyst. Axial CT with bone setting in different epidermoid cysts (a–c). Typically, the internal table appears more eroded than the external table (a, b), but this is not always the case (c). Note the presence of free intracranial air secondary to ruptured mastoid cells (b)

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Fig. 2.26  Epidermoid cyst. Axial T1-weighted (a, b), T2-weighted (c, d), diffusion-weighted (e, f) images and ADC map (g, h) in two epidermoid cysts. Note the inhomogeneous predominantly low T1 signal with

areas of high signal (a, b) and the predominantly high T2 signal with areas of low signal (c, d). On the diffusion-weighted image and ADC map, diffusion restriction is observed (e–h)

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Fig. 2.27  Epidermoid cyst. Axial T2-weighted (a), T1-weighted after intravenous administration of gadolinium (b) and diffusion-weighted (c) image of an intradiploic epidermoid cyst with a small parenchymal extension (a–c, arrow)

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Fig. 2.28  Lipoma. Axial CT with brain (a) and bone (b) setting and axial T1-weighted image (c) show an intradiploic lipoma in the left frontal bone

2.3 Trauma Calvarial fractures are common in head trauma. Fractures can be linear but can also be complex with overriding or compressed fragments (Fig. 2.29). Linear fractures are more often associated with an epidural or subdural hematoma than compressed fractures (Fig. 2.30). Fractures are sharply delineated without sclerotic borders. They can cross sutures (often become somewhat larger in size when approaching the suture), and they can cause diastasis of sutures. There is often an associated subgaleal or subcutaneous hematoma (see also Sect. 1.2.1). 3D CT contributes to the overall assessment of fractures and should always be obtained because sometimes subtle fractures will be more easily depicted on a 3D image (Fig. 2.31). The association between fracture and intracranial traumatic injury has been studied [42]. A fracture can occur without intracranial haemorrhage, and it is well known that in young children with non-accidental cranial trauma, severe intracranial injuries can be seen in the absence of a fracture.

In a large study of 1383 patients with acute head injury, a fracture was seen in 61%, and there was evidence of intracranial injury in 71% of them. In the group without a fracture, intracranial injury was seen in 46%. In 13% of the patients, there was no fracture and no intracranial traumatic lesion. There was no intracranial injury in 31% of the patients. There is still controversy on the need to obtain a CT in mild head trauma, and there have been attempts to define possible indicators of intracranial haemorrhage. Not surprisingly, open skull or skull base fracture and a Glasgow Coma Scale of 13 or 14 after 2 h were the strongest predictors of haemorrhage [43]. The presence of a fracture contralateral to the side of an intracranial injury is an important finding because these patients are at risk of developing a delayed epidural hematoma following decompressive hemicraniectomy [44]. A leptomeningeal cyst or ‘growing skull fracture’ is a rare (0.6% of the fractures) and late complication of a fracture in children, below 3 years of age. Usually, the fracture involves the internal and external table and is associated with a dural

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Fig. 2.29  Complex and compressed fracture. Anterior view of a 3D CT with volume rendering demonstrates complex fracture in the frontal and maxillofacial bones (a). Axial CT with bone setting shows a compressed fracture on the left side with overriding fragments (b). Note the

diastasis of the lambdoid suture on the contralateral side (b, arrow). Sagittal 3D CT with volume rendering after the reconstruction of the compressed fracture (c)

laceration. Pulsatile CSF pressure widens the fracture line (being >4  mm), and erosion of the internal table can be observed (Fig.  2.32). Osteoblastic migration and healing does not occur. Surgery is often indicated to close the defect in the calvarium. A large defect remains visible in untreated patients (Fig. 2.33).

When there is only a fracture of the internal table with a dural tear, an intradiploic leptomeningeal cyst can develop (Fig.  2.34). Usually, there is a remote history of trauma. While growing skull fracture is typically seen in young children, the intradiploic cyst is seen at an older age, usually many years after the cranial trauma [45].

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Fig. 2.30  Linear fracture. Oblique top view of a 3D CT with volume rendering (a), coronal CT with bone setting (b, c) and coronal CT with brain tissue setting (d). A linear fracture is seen on the midline in conti-

nuity with the sutures (a). Note the sharp borders of the fracture (b, arrow) compared to the zigzag appearance of the sagittal suture (c, arrows). An associated subdural and subgaleal hematoma are seen (d)

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Fig. 2.31  Linear fracture. Lateral view of a 3D CT with volume rendering shows a fracture in the parietal bone extending into the squamosal suture (arrow) and a fracture extending in the squamosal part of the temporal bone (arrow)

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Fig. 2.32  Growing skull fracture. Axial CT with brain tissue setting (a) and with bone setting (b). A widening of the fracture is seen with a dilated subarachnoid space and a leptomeningeal cyst resulting in a

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Fig. 2.33  Growing skull fracture. Axial CT with bone setting (a), lateral view of a 3D CT with volume rendering (b) and axial T2-weighted image (c) in a 6-year-old child who had a linear fracture at the age of

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2.4 Infection

2.4.2 Bartonella

2.4.1 Osteomyelitis

Bartonella henselae are Gram-negative bacteria that can be transmitted from the cat to humans by the cat flea. Cat scratch disease is a common childhood infection [47]. The infection is caused by a bite or scratch from an infected cat. An erythematous papule usually becomes visible approximately 1 week after the bite. Typically enlarged painful lymph nodes with central necrosis can be demonstrated by ultrasound 1 to 3  weeks after the cutaneous infection. Pathology of the soft tissue lesion shows an epithelioid granulomatous inflammation. Calvarial osteomyelitis is extremely rare and can be limited to the cortex or extend into the diploic space. Erosion of the bone or lytic/destructive lesions can be demonstrated on CT (Fig. 2.36). MRI will better delineate involvement of the soft tissues.

Compared to skull base osteomyelitis, calvarial osteomyelitis is relatively rare and often involves the frontal bone, secondary to frontal rhinosinusitis, surgery or trauma [46]. The changes can remain limited to the frontal bone itself or extend into the periosteum, into the scalp and occasionally into the intracranial compartment. Most cases of frontal sinusitis resolve spontaneously, but persistent bacterial growth may lead to the so-called Pott’s puffy tumour (see Sect. 1.3.1). Osteomyelitis is then associated with subperiosteal abscess formation. Extension into the orbit through the lamina papyracea and intracranial complications have been reported, including epidural abscess, subdural empyema and brain abscess. CT shows lytic/destructive bone changes, while MRI better delineates the intrinsic changes in the diploic space, in the scalp and in the intracranial compartment (Fig. 2.35). Treatment with antibiotics is essential but a surgical intervention is often necessary too.

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Fig. 2.35  Osteomyelitis. Axial CT with bone setting (a, e), radionuclide scan with 99mTc-MDP tracer (b), axial T1-weighted image with intravenous administration of gadolinium (c) and sagittal T2-weighted image (d). Extensive destruction of the frontal bone is seen with osteolysis and more extensive involvement of the internal table (a). There is evidence of osteoblastic activity (b). A subgaleal abscess is seen (c,

black arrow), and there is pathological enhancement of the diploic space (c, white arrows). The continuity between the subgaleal collection and the diploic space with destruction of the external table is visible (d, white arrow). Follow-up shows diffuse sclerosis and a deformity of the frontal bone (e)

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Fig. 2.36  Bartonella infection. Axial CT with bone setting (a), coronal T2-weighted (b) and T1-weighted image before (c) and after intravenous administration of gadolinium (d). A scalp mass is seen with ero-

2.5 Vascular 2.5.1 Venous Vascular Malformation Cavernous haemangioma or venous vascular malformation is common in middle-aged females and is found more often in the frontal and parietal bone. Trauma is possibly a predisposing factor. A venous vascular malformation grows slowly and represents approximately 10% of all benign calvarial tumours. Treatment is only indicated in case of haemorrhage.

sion of the outer table (a). A cystic subcutaneous and subgaleal mass is seen with septations. There is enhancement of the eroded bone and of the diploic space (d)

The lesion consists of blood-filled sinusoidal spaces within the trabeculation reflecting osteoclastic activity following the vascular neoplasia and the osteoblastic remodelling. Some haemangiomas extend longitudinally in the diploic space (‘sessile’), and other haemangiomas tend to be more focal and expansile (‘globular’) (Fig. 2.37). They are usually supplied by branches of the external carotid artery. On CT, an osteolytic lesion is seen with spoke-wheel appearance (fibrous septa radiating from a common centre, separating the vascular lacunes) (Fig.  2.37) [48, 49]. The honeycomb (axial) and sunburst (sagittal) pattern have been

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Fig. 2.37  Venous vascular malformation. Axial (a–d) and coronal (e– g) CT with bone setting show different features of cavernous haemangioma. Examples are shown of an expansile (a–c) and of a sessile osteolytic lesion (d). Note the bony septations with the typical ‘honey-

comb’ pattern (a, b) and the ‘sunburst’ pattern (c). The trabecular changes can sometimes be very subtle (g, arrow). Although the internal table is relatively more spared (e), it is also possible to see sparing of the external table (a, f)

2.5 Vascular Fig. 2.37 (continued)

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reported corresponding to trabecular matrix radiating from the centre to the periphery. There is often relative sparing of the internal table. The margins are usually not sclerotic (but present in up to 30% of the cases), and a periosteal reaction can be observed. Sometimes the trabeculae may grow beyond the external table resulting in a hair-on-end-like periosteal reaction. Homogeneous contrast enhancement is seen.

Although a ‘sunburst’ pattern is considered fairly characteristic for a haemangioma, this can occasionally also be seen in meningioma, osteosarcoma and osteoblastic metastasis. On MRI, the signal depends on the proportion of fat and iron degradation products, usually T1 iso- to hypointense and T2 heterogeneous hyperintense with hypointense borders (possible fibrous tissue and/or calcification) (Fig. 2.38). Vascular channels can sometimes be observed as flow voids (‘bunch of grapes’). The trabecular thickening returns a low signal on all sequences. A strong enhancement is observed. Preoperative embolization of the vascular supply is recommended in large lesions. Cystic angiomatosis is a rare disorder with multiple haemangiomatous lesions in the bones [50]. Similar to cavernous haemangioma, a honeycomb pattern can be recognized (Fig. 2.39). The absence of soft tissue involvement is a helpful finding to differentiate the lytic lesions from malignancy. Contrast enhancement of the diploic space, ipsilateral to the port-wine stain, has been described in children with Sturge-Weber syndrome (see also Sect. 1.4.3) [51]. It has been suggested that this finding may appear before the leptomeningeal angiomatosis. The enhancement remains incompletely understood but may reflect venous dysplasia, vascular-induced osseous changes and/or venous engorgement [48].

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Fig. 2.38  Venous vascular malformation. Axial T2-weighted (a, b), T1-weighted before (c) and after intravenous administration of gadolinium (d), diffusion-weighted (e) image and ADC map (f). An inhomo-

geneous high T2 signal is seen with low-signal areas representing fibrous septa and trabecular matrix (a, b). There is strong contrast enhancement (d), and there is no evidence of diffusion restriction (e, f)

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Fig. 2.39  Cystic angiomatosis. Axial CT with bone setting (a), axial (b) and sagittal (c) T2-weighted and T1-weighted image after intravenous administration of gadolinium (d). The honeycomb pattern is seen in the extensive occipital lytic lesion. The lesion appears strongly

2.6 Tumour Calvarial bone tumours account for 0.8% of all bone tumours. Mineralization of the tumour matrix and zone of transition are two important imaging features in bone tumours. A wide zone of transition between the malignant osteolytic lesion and the normal bone is typically associated with an ill-defined tumour delineation. Sclerotic bone tumours typically have a narrow zone of transition.

hyperintense on T2-weighted images (b). There are additional lesions in the parietal bone and in the clivus (c, arrows) as well as in the vertebrae (not shown). Note the absence of enhancement after intravenous gadolinium administration (d, arrows)

The bone matrix is the substance produced by mesenchymal cells. Three different tumour matrices can be seen. In osteosarcoma, osteoblasts produce an osteoid matrix consisting of immature bone. On CT, this is recognized as ill-defined clouds of increased density centrally in the tumour. On the other hand, slowly growing osteoid-producing tumours will be characterized by a well-defined mineralized mass. In chondrosarcoma, chondroblasts produce a chondroid (calcified) matrix. On CT, a more lobulated configuration is seen with dots, arcs and rings. A third bone matrix is the so-called

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Fig. 2.40  Button osteoma/hamartoma. Sagittal CT with bone setting (a) and 3D CT with volume rendering (b). A button hamartoma is seen in the frontal bone. Note the satellite lesions in the left parietal bone (b, arrows)

woven bone or ground glass matrix, typically seen in fibrous dysplasia (see Sect. 2.7.5). The myxoid and collagen fibres are produced by fibroblasts that have converted into functional osteoblasts. A reactive bone mineralization results in a modulation of normal marrow to osteoblastic activity or a periosteal reaction at the margins. This will result in a coarsened or mottled trabecular pattern of combined osteoblastic and osteolytic changes. This can be observed in tumours (e.g. Ewing sarcoma, lymphoma) and in osteomyelitis. A lamellated or spiculated periosteal reaction is a feature of aggressive tumours. The process of intramembranous ossification explains the formation of calcified bony spicules.

2.6.1 Osteoma There is still some controversy regarding the terminology of the so-called calvarial button osteoma [52]. A button osteoma is a misnomer because it does not consist of osteoid-forming osteoblastic tissue, and therefore, a button hamartoma would be a more accurate name [53]. A hamartoma is an abnormality that resembles a tumour but results from maldevelopment. A button hamartoma is a very common benign primary bone lesion in the calvarium usually less than 1 cm in diameter. A button hamartoma contains intramembranous bone and is formed in the periosteum. Although an exostosis is sometimes considered to be different from an osteoma, it appears difficult to separate both entities, even histologically.

A sinonasal osteoma is a true osteoma because it may contain various bone types and not just only dense compact lamellar bone. CT shows a well-defined lesion with homogeneous bone density. The composition may vary from the compact ‘ivory’ osteoma (external table, exostotic), consisting of mature lamellar bone, to the spongiosa ‘mature’ osteoma (internal table, enostotic), containing trabeculous bone and fibroadipose marrow. On MRI, the lesions display a low T1 and T2 signal. The typical sessile/nodular or dome-shaped lesion is often asymptomatic and up to nine times more common in female patients. Occasionally, one may encounter a so-called satellite hamartoma, consisting of a button hamartoma surrounded by smaller less pronounced hamartomas (Fig. 2.40). Some lesions are more conspicuous and may display a wave-­ like bony growth (Fig. 2.41). Multiple hamartoma is associated with the Gardner syndrome (association with colonic polyposis, sebaceous cysts, lipomas and fibromas) and tuberous sclerosis. A ballooned osteoma is a very rare, solitary frontal bone lesion (Fig. 2.42) [53]. The lesion is larger than a button osteoma and has an irregular delineation. The roof consists of cortical bone with underlying trabeculous bone and diploic involvement [52]. Accelerated tumour growth may occur during puberty. The internal table osteoma is much less common (Fig. 2.43) [54]. The absence of contrast enhancement, vasogenic oedema and a soft tissue mass in osteoma/hamartoma usually easily allows the differential diagnosis with an intraosseous meningioma.

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Fig. 2.41  Osteoma/hamartoma. Axial CT with bone setting (a), axial T2-weighted image (b) and 3D CT with volume rendering (c). A broad-­ based compact bone lesion is seen with a wave-like shape on top (a). The typical very low ‘absent’ signal is seen on MRI (b). Note the pres-

ence of satellite hamartomas in the left occipital and frontal bones and in the right parietal bone at the vertex, in the vicinity of the sutures (c, arrows)

A bone island, previously known as enostosis, is a common benign intradiploic sclerotic lesion usually with a size less than 1 cm (Fig. 2.43). Metaplastic dural ossification represents a degenerative finding in the elderly patient (Fig. 2.43) [55]. The plaque-like

nodular depositions are usually multicentric and have been reported in association with hyperparathyroidism. A focal dural ossification is also known as ‘brain stone’ or ‘dural osteoma’.

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Fig. 2.42  Ballooned osteoma. Sagittal CT with bone setting (a) and 3D CT with volume rendering (b) show a midline frontal exostosis. Note the different bone aspect compared with the button hamartoma

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Fig. 2.43  Internal table osteoma/hamartoma, bone island and metaplastic dural ossification. Axial CT with bone setting (a–c). Note the mushroom shape of an inner table hamartoma (a, arrow) and an intradi-

ploic bone island (b, arrow). Multiple metaplastic dural ossifications are shown (c, arrows)

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Fig. 2.44  Dural-based meningioma with hyperostosis. Axial CT with soft tissue (a) and with bone setting (b). A dural-based meningioma is seen in the right frontal lobe (a, arrows). Note the hyperostosis of the internal table (b, arrows)

2.6.2 Meningioma

The extradural meningiomas form the second group but represent only 2% of all meningiomas. There is no Meningioma is usually encountered between 40 and 60 years female predominance, and there is a peak in the third of age, predominantly in women. decade. They include the intraosseous meningiomas Several classifications have been proposed for calvarial (approximately 2/3) and the soft tissue meningiomas meningioma, but the terminology still remains, to some (approximately 1/3) (Fig. 2.47). The intraosseous meninextent, ambiguous [56–59]. Here we will attempt to give gioma is typically a bone-based lesion (approximately clarity to this issue. 30% osteolytic, 60% osteoblastic and 10% mixed lytic/ The meningiomas can be divided into two groups. The blastic) without dural involvement. There is typically first group includes the meningiomas that find their origin in bone expansion with an irregular external and internal the dura and typically have a large dural base. They can table lining, sometimes with radial bone spiculation. The become apparent as a mass (‘en masse’) or as a plate (‘en hyperostosis can be a mere eburnation or may present as plaque’). bone thickening with an irregular external table and someA dural meningioma may be associated with (tumour-­ times radial bone spiculation. The pathogenesis of intraosinduced) hyperostosis in up to 50%. It remains unsolved seous meningioma remains unsolved but is likely the whether the hyperostosis is due to tumour-induced changes result of trapped meningiomatous cells, stimulating an or to tumour infiltration (Fig. 2.44). It is known that menin- osteoblastic activity. They present with bone expansion giomatous cells can invade the Haversian canals, stimulating and irregular lining. Approximately 60% of the intraossean osteoblastic activity, and therefore, hyperostosis should ous meningioma will invade the dura [63]. On the other preferentially be considered as tumour infiltration. hand, intraosseous meningiomas may also extend into the A dural-based meningioma can invade the bone, and the soft tissues. differential diagnosis with an intraosseous meningioma that The lytic subtype with thinning of both the internal and invades the dura can be difficult. We suggest to consider the external tables and with well-defined non-sclerotic margins broadest base as the primary site of origin (Fig. 2.45). is seen in 20% (Fig.  2.48) [64]. Within the lytic tumoural An ‘en plaque’ meningioma is a moderate to extensive bone changes, enhancement can be seen on gadolinium-­ plate-like dural lesion with hyperostosis [60, 61]. The amount enhanced MR images. of hyperostosis is disproportionate to the volume of the Occasionally, transdiploic connections can be seen dural-based tumour (Fig. 2.46). The lesion is associated with between the intradural and the extracalvarial tumour composubdural calcification/ossification (containing tumour cells) nent. These are thought to represent routes of tumour extenand more frequently seen in the sphenoid bone than in the sion (Fig. 2.49). calvarium. It is known that the inner layer of the dura may Moth-eaten/permeative and aggressive periosteal reaction undergo metaplastic transformation with bone formation. can sometimes be observed resulting in a potential misleadThe lucent area between the hyperostosis and the dural ossi- ing diagnosis of a malignant bone lesion, e.g. lymphoma or fication corresponds to the dura (Fig. 2.46) [62]. osteosarcoma.

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Fig. 2.45  Bone-based and dural-based meningioma. Coronal (a), sagittal (c) and axial (e) CT with bone setting. Coronal (b), sagittal (d) and axial (f) T1-weighted image after intravenous administration of gadolinium. A bone-based meningioma (a, b) is shown with dural invasion. Note the bone expansion (a). There is continuity between the intraosseous tumour and the dural component (b, arrow). A dural-based meningioma with bone exten-

sion is shown (c, d). Note the mixed lytic/sclerotic bone expansion with erosion of the internal table and the bony spiculations both in the dural mass and in the intraosseous mass (c). A dural-based meningioma (e, f) with bone invasion and lytic changes is demonstrated. Note the irregular ‘periosteal’ bone spiculations on the external table (e, arrow). Diploic enhancement (f, black arrow) and a soft tissue component are seen (f, white arrow)

On MRI, a homogeneous tumour with a low T1 signal and a high T2 signal is seen, with strong homogeneous enhancement of the soft tissue component.

[65]. It corresponds to a monostotic Langerhans cell histiocytosis, is limited to the bone or lung and is more frequently seen in children below 15  years of age [66]. Pain is a frequent symptom. New osteolytic lesions can be seen within 1 or 2 years. Hand-Schüller-Christian disease is another clinical manifestation of LCH with skull lesions, exophthalmos and diabetes insipidus. Letterer-Siwe disease is the third LCH syndrome with disseminated disease in multiple organs.

2.6.3 Eosinophilic Granuloma An eosinophilic granuloma, also called histiocytosis X, is a benign manifestation of Langerhans cell histiocytosis (LCH)

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Fig. 2.46  ‘En plaque’ meningioma. Axial CT with bone setting (a, c) and axial T1-weighted image before (b) and after (d, e) intravenous administration of gadolinium. An extensive bone expansion and hyperostosis in the left frontal bone is seen (a). Another ‘en plaque’ menin-

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gioma is shown with a dural calcification (c). The space between the dural calcification and the hyperostosis is known as ‘the lucent line’ (c). On MRI, there is some enhancement of this subdural calcification (d and e, arrow)

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Fig. 2.47  Soft tissue meningioma. Coronal T1-weighted image after intravenous administration of gadolinium in a patient who had undergone surgery for an intraosseous meningioma in the past presents with a recurrent meningioma in the soft tissues (long arrow). A residual postoperative epidural collection is seen (short arrow)

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On CT, an eosinophilic granuloma appears as a well-­ defined lytic ‘punched-out’ lesion, without sclerotic margins or periosteal reactions, and more often in the temporal and parietal bone (Fig. 2.50). Endosteal scalloping and irregular erosions can be demonstrated. The lesion may contain a bone (button) sequestrum, representing intact bone (Fig. 2.50). The more extensive involvement of the external table compared with the internal table can result in a double contour (‘hole within a hole’ sign) (Fig. 2.51). This gives rise to the so-called bevelled edges, a typical finding on skull X-rays. Following treatment, centripetal bone formation can be observed leading to a disappearance of the lesion and sclerosis (Fig. 2.52). On MRI, an eosinophilic granuloma is iso- to hypointense on T1- and hyperintense on T2-weighted images (Fig. 2.53). Usually extensive bone marrow oedema is present. There is strong enhancement after gadolinium administration in the epidural and subgaleal component. A low ADC can be observed reflecting the high cellularity (Fig. 2.54).

2.6.4 Sarcoma and Fibroma Malignant calvarial tumours are very rare and the role of imaging in calvarial sarcoma is limited. It is important to suggest the possibility of a sarcoma and to describe the extent of the lesion. It is not possible to differentiate the different types of sarcoma. A primary osteosarcoma is rare (1–2% of all calvarial tumours) and tends to present at 30–40  years of age. Secondary osteosarcoma can be seen after Paget disease, radiotherapy, Li-Fraumeni, and retinoblastoma. Fibrous ­dysplasia, chronic osteomyelitis and trauma are possible risk factors. An osteosarcoma consists of excessive immature bone tissue, and the common histologic subtypes are osteoblastic, fibroblastic and telangiectatic. Tumour cells produce osteoid or immature bone in a lace-like pattern. Depending on the cellular characteristics, low-, intermediate- and high-grade osteosarcoma can be seen. The treatment consists of surgery, aiming for a total resection, followed by chemotherapy or radiotherapy. On CT, a poorly circumscribed expansile lesion is seen with osteolytic (and osteoblastic) areas and periosteal reaction, representing bone matrix mineralization [67]. A permeative growth pattern is observed at the periphery. A ‘sunburst’ matrix mineralization pattern is seen in up to 30% of the patients. MRI is superior for assessing the soft tissue involvement. The tumour appears isointense on T1 and hypointense on T2 with homogeneous enhancement. The mixed low and high signal on T1- and T2-weighted images corresponds to a ‘cloud-like’ osteoid matrix mineralization and haemor-

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Fig. 2.48  Osteolytic meningioma. Axial CT with bone setting (a) and sagittal T1-weighted image after intravenous administration of gadolinium (b) show an osteolytic bone lesion with more extensive erosion

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of the internal table and bony dots in the soft tissues (a). MRI more accurately demonstrates the dural mass with dural tail and the intraosseous extension as well as the extension in the subgaleal space (b)

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Fig. 2.49  Extension through diploic channels. Coronal CT with bone setting (a) and coronal T1-weighted image after intravenous administration of gadolinium. The internal and external table can still be delineated with some evidence of hyperostosis in the diploic space and

extensive periosteal bone spiculation along the internal table and in the soft tissue (a). Note the extensions along diploic channels from the dura towards the soft tissues (b, arrow)

rhage. The direct production (without normal osteogenic process through fibrous and cartilage way) of malignant osteoid is the characteristic histological finding in osteosarcoma. An osteoblastoma is an osteoid-forming tumour and is mainly seen in the second decade. The tumour is rare in the calvarium. The tumour has also been reported as osteoid osteoma, ossifying giant cell tumour and osteogenic fibroma.

A well-defined mixed lytic/sclerotic lesion is seen in the enlarged diploe with thinning of the internal and external table and with the presence of calcification. On MRI, the lesion appears hypo- to isointense on T1-weighted images with a variable signal on T2-weighted images and with enhancement after intravenous administration of contrast. High T2 signal corresponds to areas of osteoid production.

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Fig. 2.50  Eosinophilic granuloma. Axial CT with bone setting (a–c) show three examples of an eosinophilic granuloma. Note the sharply defined osteolytic lesion without sclerotic borders (a), the more extensive involvement of the internal table (b) and the button sequestrum (c, arrow)

Fig. 2.51  Eosinophilic granuloma. Cranial oblique view of a 3D CT with volume rendering shows the ‘hole within a hole’ sign and the bevelled edges in the frontal bone, due to the irregular and unequal erosion of the internal and external table (arrows)

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Fig. 2.52  Eosinophilic granuloma. Axial CT with bone setting (a, c) and axial T2-weighted images (b, d) show an eosinophilic granuloma in the right frontal bone (b, arrow). Note that on follow-up, a few months

later, there is new bone formation (c), and on the T2-weighted image, the signal in the diploic space has almost normalized (d, arrow)

Mesenchymal (intracranial extraskeletal) chondrosarcoma cannot be differentiated from an osteosarcoma. These rare osteolytic tumours have a dural connection and often contain calcifications [68]. They are thought to originate from mesenchymal cells in the dura or arachnoid and usually present as a large epidural and/or subdural mass (Fig. 2.55). The peak incidence of Ewing sarcoma is between 5 and 13 years of age. Ewing sarcoma commonly presents with a large epidural mass out of proportion to the amount of osseous vault bony erosion [69]. Ewing sarcoma has the ability to extend via the Haversian canals without causing macroscopic bony destruction (Fig.  2.56). The outer periosteum

and cortex is affected first, unlike most other malignant bony lesions, which typically affect the endosteum first. This gives rise to an appearance termed cortical saucerization. Ewing sarcoma does not produce osteoid tissue; hence, soft tissue calcification usually represents debris from periosteal new bone formation. Ossifying fibromyxoid sarcoma and sclerosing epithelioid fibrosarcoma are two examples of rare calvarial sarcoma. An ossifying fibromyxoid sarcoma is a mesenchymal tumour. An osteolytic lesion is seen with histological evidence of dense fibrous tissue (Fig.  2.57). On CT, an incomplete ­ossifying rim can be seen in 2/3 of the cases [70]. A sclerosing epithelioid fibrosarcoma is now considered a high-grade

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Fig. 2.53  Eosinophilic granuloma. Axial T2-weighted (a) and coronal T1-weighted MR images after intravenous administration of gadolinium (b). Note the inhomogeneous and central low signal on the

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Fig. 2.54  Eosinophilic granuloma. Axial diffusion-weighted image (a) and ADC map (b) show the restricted diffusion in an eosinophilic granuloma

sarcoma [71]. An osteolytic lesion is seen with sharp borders. The low-signal areas on MRI are thought to reflect areas of decreased cellularity and dense fibrous tissue or collagen deposition (Fig. 2.58). Infantile myofibromatosis is a tumour of the fibrous connective tissue and is usually seen before the age of 2 years. It can present as a solitary subcutaneous nodule, sometimes mimicking a haemangioma. The calvarium is often affected as well as the long bones. In generalized infantile myofibromatosis, there is diffuse visceral involvement. Spontaneous regression has been reported, but chemotherapy is indicated for aggressive lesions [72]. Imaging findings are non-­

specific, but multiple lytic calvarial lesions with peripheral enhancement should raise the suspicion of this fibrous infantile tumour (Fig. 2.59).

2.6.5 Haematolymphoid Tumours A calvarial non-Hodgkin diffuse large B-cell lymphoma is very rare. A lymphoma will often affect the bone and the soft tissues (both scalp and dura) (Fig. 2.60). A variable presentation is seen on CT, ranging from almost normal bone (approx. 17%) to extensive osteolysis (75%).

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Fig. 2.55  Mesenchymal chondrosarcoma. Axial CT with bone setting (a), axial T2-weighted (b), T1-weighted after intravenous administration of gadolinium (c) and diffusion-weighted (d) image. On CT, the erosion of the internal table (a, small arrow) and the intralesional calcifications (a, long

arrow) are seen. On the T2-weighted image, there is a large intracranial tumour with cysts, necrosis and vascular structures and with surrounding vasogenic oedema (b). There is a strong but inhomogeneous enhancement (c). A low signal is noted on the diffusion-weighted image (d)

The permeating transdiploic growth pattern with almost normal bone on CT (and fatty bone marrow replacement on T1-weighted images) and adjacent soft tissue mass could be characteristic of lymphoma [73, 74]. Hyperostosis is rare (approx. 5%), and in these cases, a lymphoma may mimic a meningioma.

On MRI, non-specific low T1 and T2 signal are seen. The T2 signal will be lower in the presence of fibrosis. Diffusion restriction is typically seen reflecting the hypercellularity (Fig.  2.60) [75]. Subcortical oedema and no clear border between the dura and the brain suggest brain invasion.

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Fig. 2.56  Ewing sarcoma. Axial CT with bone setting (a) and axial T2-weighted (b), T1-weighted after intravenous administration of gadolinium (c), diffusion-weighted (d) and ADC (e) image. An osteolytic lesion is seen with involvement of both the internal and external tables and with a large soft tissue mass. The tumour has a high T2 signal with

an epidural tumour component and a subperiosteal component (b). There is a strong enhancement with a central less enhancing area, most likely representing fibrous tissue (c). There is evidence of diffusion restriction (d, e)

Acute lymphocytic leukaemia is the most common leukaemia subtype in children. Diffuse bone marrow infiltration is often seen on MRI.  A high signal is seen on T2-weighted and FLAIR images. A mild diffuse diploic enhancement can be observed (Fig. 2.61). Granulocytic sarcomas are more common in the skull base and orbit than in the calvarium.

2.6.6 Myeloma: Plasmacytoma Multiple myeloma is a malignant bone marrow disorder with a monoclonal proliferation of malignant plasma cells, which release immunoglobulins and infiltrate hematopoietic structures. There is a slight male predominance. The solitary lesion is usually called a plasmacytoma.

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Calvarial plasmacytoma is rare and is usually seen between 50 and 70 years of age [76]. On CT, a well-defined osteolytic, the so-called punched-­ out, lesion without sclerotic borders is seen (Fig.  2.62). Sometimes residual bone fragments can be observed in the soft tissue mass. On MRI, the lesions appear iso- to hyperinD

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tense on T1 and iso- to hypointense on T2. There is strong contrast enhancement. The absence of adjacent bone sclerosis and the extension into the scalp leading to a biconvex mass are helpful signs to diagnose a plasmacytoma [77]. Diffuse osteolytic calvarial lesions will result in a so-­ called ‘raindrop’ skull (Fig. 2.63). E

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Fig. 2.57  Fibromyxoid sarcoma. Axial CT with soft tissue setting (a) and axial T2-weighted (b), T1-weighted after intravenous administration of gadolinium (c), diffusion-weighted image (d) and ADC map (e). A mixed osteolytic/osteoblastic tumour is seen in the left frontal bone

(a, arrow). The calcified components return a low signal on the T2-weighted image with lack of enhancement (b and c, arrow). There is no evidence of diffusion restriction (d, e)

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Focal circumscribed and sharply defined lesions can be seen (with a narrow zone of transition) as well as diffuse spreading lesions (Fig. 2.64). Permeative growth pattern can be observed (endosteal areas of bone resorption with cortical sparing) (Fig. 2.65). Osteolytic metastases are seen more frequently in renal cell carcinoma and thyroid carcinoma, the latter often with a ‘blowout’ pattern (Fig. 2.66). Osteoblastic metastases are more frequently seen in breast and prostate cancer (Fig. 2.67). Breast carcinoma was found to be the most frequent source of calvarial metastases although this might also be due to the more frequent screening for metastases from breast carcinoma compared with prostate cancer [79]. Metastases have a non-specific low T1 and high T2 signal with a variable degree of enhancement. MRI is superior for the assessment of scalp, dural and parenchymal invasion (Fig.  2.68). Subtle calvarial changes are often much more evident on MRI (Fig. 2.69). In children, metastases from neuroblastoma and sarcoma can be encountered in the calvarium. Neuroblastoma is the most common extracranial solid malignant childhood tumour, almost always occurring below 10 years of age. On CT, the metastases grow inward from the bone with centripetally oriented spicules of the bone (Fig. 2.70). A calvarial metastasis can sometimes present as a solitary lesion, and, in the absence of a known primary tumour, it may be difficult to differentiate a metastasis from osteomyelitis (Fig. 2.71). Calvarial metastases can undergo bone matrix changes in the follow-up after treatment (Fig. 2.72).

Fig. 2.57 (continued)

2.6.7 Metastasis Calvarial metastases can present as osteolytic and/or osteoblastic lesions. The additional finding of calvarial metastases usually does not have an impact on patient treatment [78]. Calvarial metastases are usually asymptomatic, but pain and cosmetic problems can occur.

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Fig. 2.58  Sclerosing epithelioid fibrosarcoma. Axial CT with bone setting (a) and axial T2-weighted (b), T1-weighted after intravenous administration of gadolinium (c), diffusion-weighted (d) image and ADC map (e). A large osteolytic lesion is seen in the occipital bone with

the presence of calcification (a). The lesion appears hyperintense on T2 with several areas of low signal (b). A heterogeneous contrast enhancement pattern is noted (c). There is no evidence of diffusion restriction (d, e)

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Fig. 2.59  Infantile myofibromatosis. Axial CT with bone setting (a) and T1-weighted image after intravenous administration of gadolinium (b) show multiple osteolytic lesions (a) with peripheral enhancement (b) and without extracranial extension

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Fig. 2.60  Non-Hodgkin lymphoma. Axial CT with bone setting (a) and axial T2-weighted (b), T1-weighted after intravenous administration of gadolinium (c), diffusion-weighted image (d) and ADC map (e). Note the permeative bone destruction pattern (a), the rather low T2 sig-

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nal (b) and the continuity between the epidural component, the bone invasion and the subgaleal component (c). Diffusion-weighted imaging and ADC map demonstrate diffusion restriction

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Fig. 2.61  Acute lymphocytic leukaemia. Axial FLAIR (a, d) and T1-weighted image before (b) and after (c) intravenous administration of gadolinium. Note the high signal of the diploic space on FLAIR

images (a, arrows) and the diffuse moderate enhancement (b and c, arrows). Following treatment, a normalization of the bone marrow signal is seen (d)

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Fig. 2.62  Multiple myeloma. Axial CT with bone setting (a, b). A large lytic lesion without sclerotic borders is seen in the occipital bone (a). Several sharply defined lytic lesions are seen in the calvarium (b, arrows)

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Fig. 2.63  Multiple myeloma. Plain X-ray (a) and axial CT with bone setting (b). A so-called ‘raindrop’ skull is shown (a) with multiple lytic lesions on CT (b)

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Fig. 2.64  Osteolytic metastasis. Axial (a) and coronal (b) CT with bone setting and coronal T1-weighted image after intravenous administration of gadolinium (c). Note the multiple lytic lesions with more

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Fig. 2.65  Permeative destruction in metastasis. Axial CT with bone setting (a) with follow-up 3 months later (b). Permeative bone destruction is seen with initially relative preservation of the bone matrix (a,

extensive erosion of the internal table (a and b, arrows). The T1-weighted image demonstrates the dural invasion (c, arrows)

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arrow). Follow-up shows more extensive lytic changes (b). There is a large subgaleal soft tissue mass

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Fig. 2.66  Follicular thyroid carcinoma, Hürthle cell variant. Axial T2-weighted (a), coronal T1-weighted after intravenous administration of gadolinium (b), axial diffusion-weighted image (c) and ADC map

(d). A large osteolytic, centrally necrotic, tumour is seen in the left frontal bone with dural invasion but without brain infiltration (a, b). Diffusion restriction is noted (c, d)

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Fig. 2.67  Osteoblastic metastases. Axial (a) and coronal (b) CT with bone setting. Multiple focal osteoblastic lesions are seen (a, b). Osteoblastic metastases from breast carcinoma are shown in a patient with hyperostosis frontalis interna (b, arrows)

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Fig. 2.68  Axial CT with bone setting (a) and axial diffusion-weighted (b), ADC map (c) and coronal T1-weighted image after intravenous administration of gadolinium (d). An osteoblastic lesion with irregular

delineation of the internal and external table is seen (a). Diffusion restriction is demonstrated (b and c, arrow). There is an extension into the soft tissues and dural invasion (d, arrows)

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Fig. 2.69  Osteoblastic metastasis. Sagittal CT with bone setting (a) and sagittal FLAIR (b) and axial T1-weighted image after intravenous administration of gadolinium (c). Only minimal bone changes are seen on CT (a, arrow), while the lesion is much more conspicuous on the

MR imaging where the dural and soft tissue involvement can be identified (b, arrows). There is almost no enhancement of the diploic lesion (c, arrow). There is some enhancement of the dura and the subgaleal space (c)

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Fig. 2.70  Metastasis of neuroblastoma. Axial CT with bone setting (a), axial diffusion-weighted image (b), ADC map (c), axial T2-weighted (d) and axial T1-weighted image after intravenous administration of gadolinium (e). Note the ‘typical’ centripetally oriented

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bone spicules (a, arrow). Diffusion restriction (b and c, arrow), a relatively low T2 signal (d, arrow) and enhancement of the soft tissue and dural extension (e, arrows) are seen

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Fig. 2.71  Osteolytic metastasis mimicking osteomyelitis. Axial CT with bone setting (a) and axial T1-weighted image after intravenous administration of gadolinium (b). In the absence of a known primary

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tumour, this osteolytic lesion was initially considered as possible osteomyelitis (a). There was extension in the soft tissues and dural invasion (b, arrows)

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Fig. 2.72  Treatment-related changes. Axial CT with bone setting (a–c). Note the progressive increase of the density of the bone matrix in the metastasis (a, arrow) with progressive smoother delineation on the follow-up scan 5 (b) and 10 (c) months after chemotherapy

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2.7.2 Bone Thinning and Bone Thickening

2.7.1 Osteopenia and Osteoporosis

Symmetrical thinning of the parietal bones is an uncommon finding (estimated prevalence 0.25–0.8%) and is more frequently seen in middle-aged women (Fig. 2.74). It is possibly associated with osteopenia [80]. Progression of thinning has been reported (Fig. 2.75). Because of the relative absence of osteoclasts, it appears more likely to reflect decreased bone formation rather than bone destruction. An idiopathic unilateral thinning of the bone has been reported (Fig. 2.74) [81]. Focal bone thinning or scalloping can be seen in association with an arachnoid cyst (Fig. 2.76). In patients with Parry-Romberg syndrome (see Sect. 1.7.2), a unilateral focal thinning of the bone can be demonstrated on the side of the hemiatrophy (Fig. 2.76). A focal thickening of the protuberantia occipitalis externa is known as ‘occipital spur’. Other terms are ‘inion hook’ or occipital knob. It can appear as a hook/spine or as a crest (Fig. 2.77). Acromegaly is typically seen in patient with growth hormone-­secreting pituitary adenoma. Typical findings on CT are thickening of the calvarium, thickening of the internal table, an enlarged frontal sinus (with frontal bossing) and an enlarged sella turcica (Fig. 2.78).

Osteopenia is the loss of bone mineral density. The typical bone structure resembles a honeycomb, and in osteopenia, the holes become larger, which results in weakening of the bones and risk of fractures (Fig. 2.73). If untreated, osteopenia may progress to osteoporosis. Osteoporosis is the most common metabolic disorder, affecting up to 20% of women and 5% of men older than 50 years. A bone marrow density more than 2.5 standard deviations below the normal value in a young healthy person is the definition of osteoporosis. Many factors, both genetic and environmental, play a role in the development of osteopenia. Several risk factors have been identified, e.g. insufficient intake of vitamin D and calcium, smoking, excessive alcohol intake, limited physical activity, low oestrogen levels and corticosteroid therapy. Several medical conditions increase the likelihood of osteoporosis, e.g. endocrinological disorders (hyperthyroidism, Cushing disease, etc.), diabetes mellitus, rheumatoid arthritis and inflammatory bowel diseases.

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Fig. 2.73  Osteopenia. Axial CT with bone setting (a) and axial T1-weighted image (b). Loss of bone density leads to an increased trabeculation of the diploic space (a). On a T1-weighted image, the high signal of the diploic space represents fatty bone marrow (b, arrow)

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Fig. 2.74  Parietal bone thinning. Axial (a, c) and coronal (d) CT with bone setting and top view of 3D CT with volume rendering (c). Bilateral parietal bone thinning (a, b) and unilateral left parietal bone thinning are demonstrated (c and d, arrow)

Secondary cutis verticis gyrata can be seen in association with acromegaly (see Sect. 1.7.1). Hyperostosis frontalis interna is characterized by irregular sharply defined progressive thickening of the internal table and diploic space of the frontal bones with midline sparing [82–84]. Other bones may also show increasing thickness. It is more common in older women and is associated with age, obesity, acromegaly and diabetes. Hyperostosis

frontalis interna can be symptomatic through progressive bone thickening with compression on the frontal lobes. Analysis of the expression of alpha-oestrogen receptors on dura supports a possible role of increased oestrogen stimulation during the reproductive years. The internal table appears thickened due to the formation of new cancellous bone, which may protrude into the diploic space and into the cranial cavity.

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Fig. 2.75  Parietal bone thinning. Axial CT with bone setting (a, b). Progression of bone thinning is shown with a fracture following a minor trauma 5 years later (b, arrow)

On CT, there is an expansion of the internal part of the diploic space with thicker and plate-like trabeculation. Research also demonstrated increased porosity of the internal table. Penetration of blood vessels from the dura may lead to the diploization of the internal table (Fig. 2.79). On MRI, the hyperostosis has the signal of fatty bone marrow (high on T1 and low on T2). Dyke-Davidoff-Masson syndrome consists of generalized cerebral hemiatrophy with unilateral calvarial thickening, most likely following an antenatal or early childhood insult (e.g. trauma, infection, ischaemia) although the aetiology remains uncertain (Fig. 2.80). Other imaging findings include an enlarged frontal sinus, hyperpneumatization of the mastoid cells and elevation of the petrous ridge. Seizures and hemiparesis are common symptoms [85].

2.7.3 Haematological Diseases Chronic iron deficiency anaemia leads to increased medullary erythropoiesis and marrow hyperplasia resulting in a widening of the diploic space, with loss of trabeculation, and thinning of the external table (Fig. 2.81). When perforation of the external table occurs, fine bony spicules can be seen, perpendicular to the external table (‘hair-on-end’ appearance) (Fig. 2.81). This phenomenon is due to the perforation

of the external table by the hyperplastic marrow with the formation of new subperiosteal bone spicules, perpendicular to the internal table. Similar imaging findings can also be seen in sickle cell disease, an inherited autosomal disease consisting of abnormal haemoglobin resulting in sickle cell-shaped red blood cells (Fig.  2.81). Pain, stroke and infection are common complications. Osteomyelitis and infarcts with subperiosteal haemorrhage can occur. Thalassemia is a congenital inherited dyserythropoietic anaemia and is characterized by a dysfunctional haemoglobin. Red blood cells are destroyed and compensatory red marrow hyperplasia is observed. Thickening of the frontal bones is seen. Perpendicular extension of trabeculae between the internal and external table, with cortical erosion, is seen, with preservation of non-­ hematopoietic occipital bone (Fig. 2.82) [86]. Patients with bleeding disorders, e.g. von Willebrand disease, have a low bone mineral density and are at an increased risk for osteoporosis and fractures (Fig. 2.83) [87]. Leukaemia is a malignant proliferation of myeloid or lymphoid cells, representing up to 1/3 of all childhood cancers. Diffuse or focal (‘granulocytic sarcoma’) bone marrow infiltration can be observed. The diffuse bone marrow involvement is subtle and is usually associated with osteopenia (see Sect. 2.6.5).

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Fig. 2.76  Bone thinning. Coronal CT with soft tissue (a) and bone (b) setting. Axial CT with bone setting (c) and 3D CT with volume rendering (d). An arachnoid cyst is seen with secondary dilatation of the lat-

eral ventricle and bone thinning (b, arrow). Unilateral thinning of the frontal bone is seen in a patient with Parry-Romberg syndrome (c and d, arrow)

2.7.4 Hyperparathyroidism and Renal Osteodystrophy

roidism) [86, 88]. Chronic overstimulation of the parathyroid glands in chronic renal insufficiency is known as tertiary hyperparathyroidism. Osteomalacia is an abnormal mineralization of the osteoid matrix in both cortical and trabecular bones. In the skull, a flat occiput, widened sutures and a squared skull appearance can be seen. Phosphate retention and decreased vitamin D conversion lead to hypocalcaemia. Hypocalcaemia stimulates the production of parathyroid hormone, causing bone resorption.

Primary hyperparathyroidism is most often caused by a parathyroid adenoma but is much less common than secondary hyperparathyroidism. The latter is often seen in patients with renal failure. Renal osteodystrophy refers to the bone changes in chronic renal insufficiency, haemodialysis, peritoneal dialysis and renal transplantation with an abnormal vitamin D metabolism (osteomalacia and secondary hyperparathy-

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Fig. 2.77  Occipital spur. Sagittal (a) and axial (b) CT with bone setting and 3D CT with volume rendering (c). The hook variant (a, arrow) and the crest variant (b and c, arrows) of an occipital spur are shown

There is diffuse calvarial thickening with loss of distinction between the internal and external table (remain preserved in osteopenia) (Fig. 2.84). Calvarial bone resorption is described as a pepper pot skull or the salt-and-pepper appearance (mixed osteolytic and sclerotic bone) representing lytic areas mixed to normal bone (Fig. 2.84). The internal and external table can no longer be defined, and there is a loss of trabeculation. Brown tumours, a form of osteitis fibrosa cystica, can occasionally be seen in the facial bones but not in the calvarium. Osteosclerosis can be observed in the healing phase. Fractures and partial skull defects can be seen in vitamin D deficiency rickets. In Noonan syndrome, an autosomal dominant disorder, a disruption of skeletal homeostasis due to an abnormal Ras-mitogen-activated protein kinase pathway, might be related to the bone

defects, in addition to vitamin D deficiency rickets (Fig. 2.84) [89].

2.7.5 Fibrous Dysplasia Fibrous dysplasia (FD) is a benign non-neoplastic developmental bone marrow disorder, often seen below 30 years of age. Both monostotic (2/3) and polyostotic (1/3) variants can be seen (Fig. 2.85) [90]. Craniofacial bone involvement is seen in 10–20% of the monostotic forms and in up to 50% of the polyostotic forms. All craniofacial bones can be affected although FD is rarely seen in the temporal and occipital bone [91]. FD is caused by a sporadic mutation of the α-subunit of the Gs stimulatory protein and is associated with abnormal

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Fig. 2.78  Acromegaly. Sagittal CT with bone setting (a), 3D CT with volume rendering (b) and coronal T1-weighted image without fat saturation (c). An occipital spur (a, small arrow) and thickened frontal bone

with frontal bossing (a, long arrow, and b) are shown. On MRI, the enlarged pituitary gland (c, long arrow) and the thickened diploic space with fatty bone marrow replacement (c, short arrow) are seen

differentiation and maturation of osteoblasts resulting in replacement of normal cancellous bone into immature bone with irregular bone trabeculation and fibrosis (immature woven bone). Typically, on imaging, the so-called ‘ground glass’ matrix is seen in the affected bone. FD is a complex disease with age-related changes. Malignant degeneration into osteosarcoma, chondrosarcoma, malignant fibrous histiocytoma or fibrosarcoma is rare (0.5%). FD has been reported in association with McCune-­ Albright syndrome [92]. Typical features of this syndrome include precocious puberty, hyperthyroidism, café au lait spots and excessive growth hormone secretion. In the Mazabraud syndrome, FD is associated with soft tissue myxoma. Cherubism, formerly called hereditary FD, is not related to FD.  In this disease, there is symmetrical facial swelling with multiple lytic lesions and without ground glass appearance on CT (70–130 HU). In FD, sclerotic (ground glass appearance) (ca. 35%), cystic (lytic) (ca. 10%) or mixed sclerotic/lytic (>50%)

lesions can be seen on CT (Fig. 2.86). Lytic components are more frequently encountered in calvarial FD [93]. The lytic lesions are sharply defined with sclerotic margins. The mixed ­sclerotic/lytic form is sometimes referred to as the Pagetoid form (Fig.  2.86). There is expansion of the external table with a thin cortex (sclerotic margin) and sparing of the internal table. The separation from normal bone is not always clear. Occasionally, a thick layer of reactive sclerotic bone is seen (rind sign) (Fig. 2.85). Small focal calcifications can be seen within the lesion, representing ossified cartilage (Fig.  2.85). The mechanism of acute cystic changes in the Pagetoid or sclerotic form is unknown. Histologically, these cystic changes can be simple bone cysts, aneurysmal bone cysts or non-specific degeneration. Occasionally, an exophytic FD subtype, also called FD protuberance, can be encountered (Fig. 2.87) [94]. Intralesional haemorrhage, aneurysmal bone cyst or pathological fracture may complicate FD [95]. An aneurysmal bone cyst can be recognized on CT when a lytic lesion is seen with well-defined non-sclerotic margins

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Fig. 2.79  Hyperostosis frontalis interna. Sagittal CT with bone setting (a–c) and coronal T2-weighted (d) and sagittal T1-weighted images (e). A thickened sclerotic frontal bone is seen with a ballooned vascularized area and an internal cortical sclerotic bone layer (a). A more sclerotic variant is shown (b), and an example is shown with a clear demarcation

inside the diploic space demonstrating the thickening of the internal part of the diploic space (c, arrow). The corresponding MR images show the slightly different signal of the ‘normal’ diploe (d and e, long arrow) and the thickened internal part of the diploe (d and e, short arrow). Note the sparing of the midline (d) and fatty bone marrow content (e)

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gested. The disease affects approximately 10% of the population above 85 years of age. The disease, first described as ‘osteitis deformans’ by Sir Paget, is characterized by osteolysis followed by excessive bone formation, cortical thickening, coarsened bone trabeculation and diploic widening. Different phases can be distinguished in PD [96]. The early (vascular) stage is characterized by sharply defined osteolysis with an advancing edge and often a lucent rim surrounding the lesion (internal and external table) also called ‘osteoporosis circumscripta’, resulting in vascularized fibrous connective tissue (often in the frontal or occipital bone) (Fig.  2.90) [97]. This is followed by a mixed osteolytic/osteoblastic (advancing sclerosis) stage with irregular cortical and trabecular thickening (mosaic pattern) (Fig. 2.91) [98]. The internal table becomes thicker than the external table, and the latter is smooth but perforated by vascular defects (Fig. 2.91). Bone thickening is observed in the late (diffuse sclerosis) stage with ‘cotton wool’ appearance of sclerotic lesions, mimicking enostoses, within the osteolytic areas (Fig.  2.92). The enlarged skull with widened diploic space is sometimes called ‘Tam o’ shanter’ skull referring to the similarity in appearance with the Scottish cap (Fig. 2.92). On MRI, a dominant fat signal is seen in long-standing disFig. 2.80 Dyke-Davidoff-Masson syndrome. Axial T1-weighted ease, and in the late sclerotic stage, the predominant low sigimage shows the left hemiatrophy with compensatory thickening of the nal corresponds to dense bone (Fig. 2.93) [99]. In the active diploic space (arrows) phase, granulation tissue and increased vascularization present as speckled low T1 and high T2 signal (Fig. 2.93). In the third stage, a low T1 and T2 signal is seen when the bone (Fig.  2.88). The septations may enhance and typical fluid-­ replaces the fat cells. There is usually no enhancement of the fluid blood levels can be observed. pathological tissue. MRI is superior in assessing patients with symptoms in Rare cases of sarcomatous degeneration have been order to detect compression of vital vascular structures and reported in approximately 1% of all patients and in approxinerves. The low signal on T1-weighted images reflects the more mately 10% of the patients with polyostotic disease. mineralized matrix while the intermediate signal reflects the Both FD and PD are characterized by osteolytic and fibrous component of FD (Fig.  2.89). Occasionally, small osteoblastic changes with bone thickening [100]. The ground areas of high signal can be recognized, representing haemor- glass appearance is never seen in PD, and there is a more rhage. The T2 signal is heterogeneous low (more mineral- asymmetrical distribution of bone lesion in FD. The age of ized ‘osseous’ matrix) and high (more fibrous) compared to presentation in FD is usually below 30 years of age, while the signal of muscle (Fig. 2.89). The low ADC on diffusion- PD is typically seen in patients older than 40 years of age. weighted MRI corresponds to the collagen-producing fibroblastic cells and a dense network of collagen fibres. A variable degree of Gd enhancement is seen in the fibrous 2.7.7 Skeletal Dysplasia components of FD (Fig. 2.89). Surgery is the best treatment option, if there are neuro- Numerous disorders caused by genetic mutations may affect logical symptoms or for cosmetic purposes. the normal bone development. Craniofacial and skeletal In patients with bone pain, bisphosphonates have been bone abnormalities and oral abnormalities can be observed recommended because of the prevention of osteoclastic bone in cleidocranial dysplasia. Here, calvarial dysplasia will be resorption. illustrated in a few syndromes [101]. Hajdu-Cheney is an autosomal dominant connective tissue disorder with mutations in exon 34 of NOTCH2 [102]. 2.7.6 Paget’s Disease The disease is associated with neurological symptoms, cardiovascular abnormalities and polycystic kidneys. The The cause of Paget’s disease (PD) remains unknown, and patients have osteoporosis and craniofacial and dental abnorboth genetic factors and slow virus infection have been sug- malities. There is scaphocephaly and bathrocephaly, an out-

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Fig. 2.81  Sickle cell disease. Axial (a, b) and sagittal (c) CT with bone setting. The thickening of the diploic space is seen with loss of trabeculation and thinning of the internal and external table. Note the presence of several focal sclerotic nodules, most likely representing the healing

stage after a bone infarct (a, arrows). Perforation of the external table results in bony spicules perpendicular to the surface and the ‘hair-on-­ end’ appearance (b, c)

ward bulging of the occipital bones. Delayed closure of the sutures is observed, and Wormian bones are often seen in the lambdoid sutures (Fig. 2.94). Mucopolysaccharidoses are a group of inheritable lysosomal disorders caused by a deficiency in glycosaminoglycan-­ degrading enzymes. Brain abnormalities can be observed as well as extensive bone changes, known as dysostosis multi-

plex [103]. Dysostosis multiplex includes thickening of the calvarial bones (Fig. 2.95). Proteus syndrome is characterized by asymmetrical and disproportionate growth of the body, nevi, dysregulated ­adipose tissue and vascular malformations. It is caused by a somatic activating mutation in AKT1. This bony overgrowth can involve the calvarium and consists primarily of diploic

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Fig. 2.82 Thalassemia. Axial CT with bone setting (a), axial T2-weighted image (b) and sagittal CT with bone setting (c). Perforation of the external table by the trabeculae, with cortical erosion, is visible

(a). Bone marrow hyperplasia and bone thickening are noted with low signal on T2-weighted images (b) and sparing of the occipital bone (c, arrow)

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Fig. 2.83  von Willebrand disease. Axial CT with bone setting (a) and 3D CT with volume rendering (b) showing focal symmetrical thinning of the occipital bones (a and b, arrows)

expansion, preferentially involving the frontal bone (Fig. 2.96) [104]. Meningioma is the most common intracranial tumour and is associated with hyperostosis in Proteus syndrome. Osteopetrosis is an inherited disorder. Dense sclerosis and thickening of the bones are seen, and therefore, terms like ‘chalk bone disease’ and ‘marble bone disease’ have been used (Fig. 2.97). Osteopetrosis is a rather benign autosomal dominant disorder in adults. In adults with type 1 osteopetrosis, there is thickening of the calvarium with sparing of the temporal bone. In type 2, the skull base is involved but the calvarium is spared [105].

The more severe autosomal recessive type is seen in children. The bone changes are the result of decreased osteoclast function with impaired absorption of the spongiosa. In children, the autosomal recessive type will lead to foraminal narrowing of, e.g. the carotid canal, jugular foramen and foramen magnum. ‘Lückenschädel’ or lacunar skull is the result of abnormal collagen development and abnormal ossification of the ­membranous bone leading to the well-defined lucent lesions more pronounced in the internal table mainly along the sutures (Fig. 2.98). It is often seen in neonates with a Chiari 2 malformation and meningomyelocele and usually resolves by the age of 6 months.

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Fig. 2.84  Chronic renal insufficiency and vitamin D deficiency. Axial CT with bone setting (a–c), T1-weighted (d) and T2-weighted (e) image. The calvarial changes in chronic renal insufficiency are illustrated. A ‘salt and pepper’ appearance (a) and a thickened calvarial

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bone with sclerotic changes and thinning of the internal and external table are shown (b and c). On MRI, the signal of the diploic space is slightly hyperintense on T1- and T2-weighted images (d, e)

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Fig. 2.84 (continued)

Fig. 2.85  Fibrous dysplasia. Axial CT with bone setting shows a polyostotic form of fibrous dysplasia involving the occipital and sphenoid bones surrounded by a thick layer of reactive sclerotic bone (‘rind sign’) (arrows). Note the islands of ossified cartilage within the lesions

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Fig. 2.86  Fibrous dysplasia. Axial (a) and sagittal (b–d) CT with bone setting. A sclerotic form of fibrous dysplasia is shown (a). An extensive mixed lytic/sclerotic form of fibrous dysplasia is shown before surgery

(b), immediately after surgery (c) and 1 year after surgery (d). Note the lytic changes (b, arrows) and the progressive lytic transformation (d). Note the surgical clip on the early postoperative CT (c, arrow)

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Fig. 2.87  Fibrous dysplasia. Axial CT with bone setting (a) and axial T2-weighted image (b). A fibrous dysplasia protuberance is shown. Note the exophytic growth and the ground glass appearances with small

cystic components (a, arrow). On a T2-weighted image, a predominantly low signal is seen with minimally increased signal in the cystic components (b, arrow)

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Fig. 2.88  Fibrous dysplasia and aneurysmal bone cyst. Axial CT with bone setting (a, b) and axial FLAIR image (c). A mixed lytic/sclerotic fibrous dysplasia of the frontal bone is shown (a). Following a minor

trauma, there is a fracture of the external table with an associated subgaleal hematoma (b). On the FLAIR image, the typical blood fluid level of an aneurysmal bone cyst is recognized (c, arrow)

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Fig. 2.89  Fibrous dysplasia. Axial T2-weighted (a, b) and T1-weighted before (c) and after (d) intravenous administration of gadolinium. A predominantly low signal is seen on T2-weighted images reflecting the mineralized ‘osseous’ matrix (a, b). The high-signal areas represent

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fibrous components (a, arrow). A low signal is seen on T1-weighted images with some evidence of enhancement after intravenous administration of gadolinium (c, d)

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Fig. 2.90  Paget’s disease. Axial CT with bone setting (a, b). Early stage with sharp delineation of the osteolysis with an advancing edge and a lucent rim (a and b, arrows)

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Fig. 2.91  Paget’s disease. Axial (a, b) and sagittal (c) CT with bone setting show different examples of the mixed osteolytic/osteoblastic stage (mosaic pattern). There is more extensive thickening of the inter-

nal table. The external table is perforated by vascular defects (c, white arrow). Sclerotic (‘cotton wool’) lesions appear (c, black arrows)

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Fig. 2.92  Paget’s disease. Axial (a, b) and coronal (c) CT with bone setting show examples of the sclerotic stage with the appearance of multiple sclerotic lesions within the osteolytic bone (a, arrow, and b). Note the ‘Tam o’ shanter’ skull appearance (c)

2.7 Systemic Diseases Fig. 2.93  Paget’s disease. Axial T1-weighted (a) and T2-weighted (b) image. In long-standing disease, a predominant fat signal is seen in the thickened diploic space (a, arrows). In the active stage, a mixed high signal is seen on the T2-weighted image (b, arrow). Note the low signal of the sclerotic lesion (b, arrow)

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Fig. 2.94  Hajdu-Cheney. Sagittal CT with bone setting (a) and posterior view of a 3D CT with volume rendering (b). Note the protrusion of the occipital bone, known as bathrocephaly (a), and the multiple Wormian bones within the lambdoid sutures (b)

130 Fig. 2.95  Mucopolysaccharidosis. Axial CT with bone setting. Note the generalized increased bone density of the calvarium

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Fig. 2.96  Proteus syndrome. Axial CT with bone setting (a), axial T1-weighted image (b), lateral view of a 3D CT with cinematic rendering (c and d) and axial CT with soft tissue setting (e). Unilateral cal-

varial hypertrophy of the frontal bone is seen (a) with a fatty bone marrow content (b, arrow). 3D CT is shown before (c) and after surgery (d). The Xilloc implant is seen on the axial image (e)

132 Fig. 2.96 (continued)

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Fig. 2.97  Osteopetrosis. Axial CT with bone setting (a) and lateral X-ray before (b) and after (c) treatment. Note the very high attenuation of the calvarium (a). The lateral X-ray in another patient shows the

‘bone in bone’ appearance in the frontal bone and skull base (b) and the decreased bone sclerosis following bone marrow transplant (c)

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Fig. 2.98  Lückenschädel in Chiari 2 malformation. Lateral (a) and posterior oblique (b) view of 3D CT with volume rendering and axial CT with bone setting (c, d). Note the gaps in the parietal (a, b) and

occipital bone (b) due to abnormal ossification of the calvarium. The impressions on the internal table of the calvarium are seen (c and d, arrows)

2.8 Treatment-Related Pathology

hematoma can be seen. On MRI, enhancement of the burr hole is possible. The burr hole or a small craniectomy is sometimes packed with bone allograft dust or Spongostan, a haemostatic gelatin sponge (Fig.  2.99). The burr hole can also be used for the positioning of an Ommaya reservoir, an intraventricular catheter connected to a subcutaneous reservoir that can be used for cerebrospinal fluid aspiration or drug delivery (Fig. 2.99).

2.8.1 Burr Hole and Craniectomy A burr hole is created by a surgical drill. It concerns a focal sharply defined defect in the calvarium. Occasionally, a fluid-fluid level can be observed following the procedure, and a small adjacent subgaleal or subdural

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Fig. 2.99  Burr hole—craniotomy. Sagittal (a, b) and axial (c) CT with bone setting. A burr hole is shown with Spongostan packing (a, black arrows). An Ommaya reservoir is seen with a catheter in the ventricular

system (b, arrow). A small craniotomy after surgery for trigeminal neuralgia is packed with bone fragments/dust and Spongostan (c)

The repair of a small craniotomy can be carried out by using the bone fragments together with Spongostan and Tisseel, a fibrin sealant (Fig. 2.99). Occasionally, one can see a ‘sinking skin flap syndrome’ or ‘syndrome of the trephined’ following decompressive craniectomy [106]. When the atmospheric pressure exceeds the intracranial pressure, the skin flap is forced inward and depresses the underlying brain tissue, resulting in a paradoxical herniation (Fig. 2.100). The clinical deterioration can produce symptoms of headache, dysautonomia, chronic fatigue, seizures, impaired vigilance, motor deficits and visual symptoms. In order to raise the intracranial pressure, Trendelenburg position or clamping the cerebrospinal fluid drainage is recommended in anticipation of a cranioplasty. Cranioplasty corresponds to the surgical repair after craniectomy or craniotomy. Autologous cranioplasty has been the most used procedure. Autologous bone can be preserved by freezing or by placement in a subcutaneous abdominal pocket. Cryopreservation can induce matrix changes, which could then lead to bone flap resorption when osteoconduction is not possible anymore. Incidental bone flap resorption is fre-

quently seen but does not always need a neurosurgical intervention. It is more common in young patients. Thinning of the reimplanted autologous flap with normal internal and external tables is more common than the complete lysis of the skull flap (Fig. 2.101). The Oulu scoring system has been proposed to assess the bone flap status [107]. Remaining bone volume (extent), cortical perforations (severity) and integrity of the bone flap (focus) are scored. The extent (scores 0, 2 or 3) is scored 0 as long as 75% of the bone volume is present. When