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Imaging of focal calvarial lesions
Clinical Radiology xxx (2015) 1e10
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Imaging of focal calvarial lesions I. Mitra*, M. Duraiswamy, J. Benning, H.M. Joy Department of Radiology, University Hospital Southampton, Tremona Road, Southampton S016 6YD, UK
art icl e i nformat ion Article history: Received 27 May 2015 Received in revised form 8 December 2015 Accepted 15 December 2015
Focal calvarial lesions may present as a visible, palpable, or symptomatic lump; however, with increasing use of cross-sectional imaging they are often encountered as an incidental finding. Knowledge of the possible disease entities along with a structured approach to imaging is required to suggest an appropriate diagnosis and assist in management planning. Abnormalities range from common neoplastic lesions to rarer congenital conditions, benign pathologies, and calvarial defects that can mimic lesions. The aim of this article is to demonstrate the salient imaging features that may help to limit the differential diagnosis of a focal calvarial lesion. Ó 2016 Published by Elsevier Ltd on behalf of The Royal College of Radiologists.
Introduction The calvarium is composed of eight flat bones: the frontal and occipital bones, the parietal bones, the squamous and zygomatic portions of the temporal bones, and the tip of the greater wing of the sphenoid bones bilaterally.1 These originate from cranial neural crest cells and undergo intramembranous ossification in a radial pattern. By the sixth year of development there is complete formation of a middle intradiploic layer composed of cancellous bone and bone marrow, resulting in inner and outer tables of cortical bone2 which appear dense on computed tomography (CT). On magnetic resonance imaging (MRI) the cortical tables demonstrate marked low signal on all sequences, whereas signal intensity of the diploic space varies with age and is dependent on the degree of fatty change within the marrow.3 Although histological confirmation is often required for definitive diagnosis of a focal calvarial lesion, imaging appearances can help limit the differential diagnosis and
* Guarantor and correspondent: I. Mitra, Department of Radiology, University Hospital Southampton, Tremona Road, Southampton S016 6YD, UK. Tel.: þ44 07970 096120; fax: þ44 01753 653442. E-mail address: [email protected] (I. Mitra).
guide subsequent management. This may involve biopsy or definitive surgery, but some lesions may be treated with chemotherapy and others may only require surveillance or patient reassurance. CT and MRI are complementary in demonstrating the characteristics of a focal calvarial abnormality.3,4 MRI can show a lesion within the diploic space before it alters the bony architecture and can give greater detail about its internal content. Many lesions are T1 hypointense, T2 hyperintense and enhance to some degree,5 but some nuances may assist in determining the diagnosis. Scalp involvement and intracranial extension is also better delineated on MRI.6 However, CT is superior in defining bony architectural change and evaluating the lesion margin and cortical involvement.7 Imaging findings should always be considered with relevant clinical information, particularly the patient’s age and any history of trauma or primary disease. Table 1 highlights features that should be considered when reviewing a calvarial lesion. Table 2 outlines typical imaging features of some lesions which might suggest a definitive diagnosis. Focal calvarial abnormalities may be divided into aggressive and non-aggressive or benign and malignant lesions or classified according to biological activity; however, a radiological classification based on bony
http://dx.doi.org/10.1016/j.crad.2015.12.010 0009-9260/Ó 2016 Published by Elsevier Ltd on behalf of The Royal College of Radiologists.
Please cite this article in press as: Mitra I, et al., Imaging of focal calvarial lesions, Clinical Radiology (2015), http://dx.doi.org/10.1016/ j.crad.2015.12.010
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Table 1 Radiological features to consider when reviewing a calvarial lesion.
Location Solitary or multiple Lucent or sclerotic Expansile þ/- bony remodelling or destruction Type of margin: smooth, well-defined, sclerotic, ill-defined, permeative Bone remnants in the lesion Attenuation/signal characteristics indicating the presence of fat, blood or calcification Associated soft tissue involvement or vascularity
architectural change and the number of lesions (Table 3) can be useful in limiting the differential diagnosis.
Table 3 Classification of calvarial lesions based on radiological features. Multiple lucent Solitary lucent Metastases Multiple myeloma Langerhans cell histiocytosis Paget’s disease
Sclerotic
Cavernous haemangioma Fibrous dysplasia Eosinophilic granuloma Intraosseous meningioma (osteoblastic subtype) Epidermoid/dermoid Osteoma Lipoma Metastasis Lymphoma Plasmacytoma
Metastasis Paget’s disease Osteosarcoma Eosinophilic granuloma (healing phase)
Intraosseous meningioma (osteolytic subtype) Osteomyelitis Congenital Traumatic
Lucent lesions Cavernous haemangioma These are benign incidental lesions that develop in the diploic space and consist of multiple engorged vascular Table 2 Typical appearances and characteristics which found together may support a definitive diagnosis. Lesion type Lucent lesions Cavernous haemangioma Eosinophillic granuloma Epidermoid cyst Aneurysmal bone cyst Lipoma Metastases (osteolytic) Myeloma Lymphoma
Paget’s disease (osteolytic phase) Sclerotic lesions Osteoma Fibrous dysplasia
Intraosseous meningioma (osteoblastic) Metastases (osteoblastic) Osteosarcoma Paget’s disease (osteoblastic phase)
Characteristic appearance Honeycomb/sunburst trabecular arrangement Sparing of inner table Young age/adolescent Well-defined bevelled edge Button sequestrum Cystic, expansile Thinning þ/- breach of skull tables Fluidefluid levels Soap-bubble appearance Central calcification Older age Multiple lesions Permeative/irregular destruction Multiple punched-out lesions Soft tissue masses with minimal intervening bone involvement on CT Homogeneous Isointense to grey matter Lucent foci crossing sutures
Involvement of one cortical table only No involvement of the diploic space Ground-glass texture Outward bowing of outer cortical table No effect on inner cortical table Lack of associated soft tissue abnormality Inner cortical table involved with irregular margin Associated enhancing soft tissue Focal sclerosis without notable expansion Focal sclerosis and bone destruction Bone expansion with cortical thickening Coarsened trabeculae
elements interspersed among trabecular bone.8 A frontal or parietal location is common. They occur more frequently in middle-aged women9 and are usually solitary, although cases of multiple lesions have been reported.10 They have been thought to occur following trauma, with report of a “de novo” lesion arising at the site of previously documented injury,11 but a preceding incident is not often elucidated in the clinical history. Typically, a mildly expansile, well-defined lucent lesion often with a fine sclerotic border is seen on CT (Fig 1). The outer table is usually involved. The inner table may be spared.5 Involvement of adjacent soft tissue may be seen.9 The coarsened internal trabeculae may show a honeycomb or sunburst arrangement; however, a pattern of internal striations may also be seen with meningioma, metastasis, or osteogenic sarcoma.5 Cavernous haemangiomata can show a gradual increase in size with proposed mechanisms for this including pressure of blood in
Figure 1 Cavernous haemangioma. Axial CT image on bone window settings from a 45-year-old man showing a mildly expansile lucent lesion with coarse trabeculation in the left parietal bone. The inner table is relatively spared while fine spiculations of bone project from the outer table.
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but hyperintensity on T1-weighted images due to blood or fat content with a stippled appearance due to the central bony trabeculae is characteristic.3,8 Enhancement is usually avid due to the vascular nature of the lesion.12
Eosinophilic granuloma (Langerhans cell histiocytosis)
Figure 2 EG. Axial CT image on bone window settings showing a lucent lesion in the right parietal bone of a middle-aged female patient with differential involvement of the cortical tables and a central remnant of bone, a “button sequestrum”. No additional lesions were found on systemic investigation.
the malformed vessels causing tortuous enlargement and/ or repeated intralesional haemorrhage.9 Regeneration and repair following haemorrhage may result in fat within the lesion. Therefore signal characteristics on MRI are variable,
Langerhans cell histiocytosis (LCH) is a systemic disease of unknown aetiology, of which eosinophilic granuloma (EG) is the commonest and mildest form.3 Most EGs occur in patients between 5e15 years of age, affecting males more than females.13 They usually present with local pain, often with an associated palpable mass.14 They may be solitary or multiple and spontaneous regression often begins after a few months but complete resolution may take as long as 2 years.3,15 The lesions begin in the diploic space and invade the inner and outer tables, a parietal location reported as the most frequent.5,14 Characteristically these are sharply circumscribed lucent lesions, often with a bevelled edge due to unequal involvement of the cortical tables16 (Figs. 2 and 3a). Sometimes a remnant of bone is seen centrally, known as a button sequestrum (Fig 2), but this is not specific and reported in other conditions including osteomyelitis, epidermoid cysts, and metastases from breast cancer.17 Marginal sclerosis is not usually a feature unless the lesion is healing.3,7 Cross-sectional imaging shows a soft tissue mass located in the diploe which is of higher attenuation than brain
Figure 3 LCH. Images of a 5-year-old female patient with multiple calvarial lesions. (a) The initial plain film shows a lucent lesion in the right parietal bone with differential involvement of the inner and outer tables. (b) Axial CT image on soft tissue window settings showing the tissue within the lucent lesion is of higher attenuation than adjacent brain parenchyma. (c) Gadolinium-enhanced coronal T1 image showing homogeneous enhancement, subcutaneous tissue extension, and adjacent dural enhancement of right squamous temporal and parietal lesions. Please cite this article in press as: Mitra I, et al., Imaging of focal calvarial lesions, Clinical Radiology (2015), http://dx.doi.org/10.1016/ j.crad.2015.12.010
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Figure 4 Epidermoid cyst. (a) Axial CT image on bone window settings and (b) axial T2-weighted image showing a large right temporo-parietal lucent lesion in a 70-year-old man with bony remodelling, thinning and breach of the cortical tables and marked internal expansion. The slow growth rate has allowed considerable mass effect on the underlying right cerebral hemisphere with little clinical effect. Some internal calcification is present but the contents are predominantly high signal on T2. (c) DWI and (d) corresponding ADC map from a different patient showing intense high signal on DWI in a right occipital lesion with the ADC similar to brain parenchyma.
parenchyma on CT18 (Fig 3b). On MRI, they appear T1 hypointense and T2 hyperintense.5 Decreased signal intensity on T2-weighted images is suggestive of a healing lesion.19 The soft tissue mass shows homogeneous enhancement with enhancement of adjacent dura often present20,21 (Fig 3c). Oedema and inflammation may be seen in the adjacent scalp.3 Once diagnosed, systemic imaging is required to exclude multifocal disease.
Dermoid and epidermoid cysts Both lesions are thought to arise due to inclusion of ectodermal remnants within the diploic space, but whereas epidermoid cysts only contain squamous epithelium, dermoid cysts contain other skin elements. Although the
distinction may only be made histologically,22 there are some distinguishing features. Dermoid cysts are more typically found in childhood and are located in the midline or related to sutures. Epidermoid cysts are usually located laterally, most often in the temporal and parietal bones and are commonly found in the third to sixth decade. Progressive accumulation of desquamating cells from the stratified squamous epithelial lining, cellular debris and keratin causes expansion of the diploic space with pressure erosion causing remodelling of the bone, affecting both the inner and outer tables of the skull4,23 (Fig 4a). The typical appearance on CT is of a well-defined lucent lesion, often with a sclerotic margin. On MRI, they usually exhibit low signal on T1 and high signal on T2 with little enhancement (Fig 4b), although signal characteristics vary according to
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Figure 7 Neuroblastoma metastasis. Axial CT image on bone window settings from a 5-year-old girl shows marked expansion of the left frontal bone. “Thickened bone” is a recognised pattern of metastatic bone involvement in neuroblastoma. On systemic investigation an adrenal mass was identified and shown histologically to be a neuroblastoma.
Figure 5 Sclerotic metastases. Axial CT image on bone window settings from a 41-year-old woman with metastatic breast cancer, which shows focal areas of dense sclerosis in the diploic space.
the protein and lipid content or rarely due to haemorrhage into the lesion.22 As with intracranial epidermoid cysts, marked hyperintensity on diffusion weighted imaging (DWI) is seen in intradiploic lesions also24,25 (Fig 4c); however, the apparent diffusion coefficient (ADC) within the cyst is no lower than is found in brain parenchyma, suggesting the increased signal on DWI to be due to T2 shine-through effect rather than true diffusion restriction (Fig 4d).
Aneurysmal bone cyst (ABC) This well-defined, expansile, lucent lesion is most frequently seen in children and adolescents.3 Only 3e6% of ABCs occur in the skull26 with reports of lesions in most of the calvarial bones.27 They are multiloculated with a low signal rim and internal low and high signal areas on MRI reflecting different stages of blood degradation.28 Fluidefluid levels in the locules and small cysts projecting into bigger cysts produce the characteristic soap bubble appearance28; however, fluidefluid levels have been reported in other conditions, including LCH and metastatic neuroblastoma.29 They can enlarge rapidly and may cause
Figure 6 Metastasis. CT images from a 48-year-old woman with breast cancer. (a) An axial image on bone window settings shows a poorly delineated permeative destructive lesion in the parieto-occipital region. (b) A sagittal reformat on soft tissue window setting shows the extent of intracranial and subcutaneous soft tissue masses. Please cite this article in press as: Mitra I, et al., Imaging of focal calvarial lesions, Clinical Radiology (2015), http://dx.doi.org/10.1016/ j.crad.2015.12.010
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Figure 8 Lymphoma: (a) Axial T2 and (b) pre and (c) post-gadolinium administration coronal T1 images from a 62-year-old woman demonstrate homogeneous, uniformly enhancing subcutaneous and intracranial masses centred around the left parietal bone. There is no detectable bone involvement on the T2 image, but marrow signal in the intervening bone is reduced compared to the contralateral normal parietal bone on the unenhanced T1 image. Histology following biopsy confirmed diffuse large B cell lymphoma.
symptoms due to pressure on intracranial structures.30,31 Like their skeletal counterparts, a preceding lesion may be present with calvarial ABCs also, such as fibrous dysplasia with those found in a frontal location.27
Lipoma Intraosseous lipomas are more frequently found in the appendicular skeleton with only a few cases of calvarial lesions reported in the literature.32,33 They appear as welldefined expansile lesions and may have a sclerotic margin.3 Fat necrosis can result in central calcification.34 Signal intensity on MRI is consistent with fat6 and therefore the more common differential diagnosis is a cavernous haemangioma.
Figure 9 Plasmacytoma. Coronal FLAIR image showing a sharply marginated, expansile lytic lesion in the left parietal bone of a 49year-old woman with known multiple myeloma. Histology following resection confirmed a plasmacytoma.
Metastases These are the commonest cause of a lucent calvarial lesion in middle-aged and older adults,19 with breast, lung, and prostate cancers the most frequent primary tumour. They are often small and multiple, but can be solitary and large,35 and depending on the primary tumour, can be lytic, sclerotic (Fig 5), or mixed.4 Radionuclide studies can be more sensitive than CT in detecting calvarial metastases.3 CT shows the extent of bone destruction usually with irregular margins and permeative erosion (Fig 6). MRI is better at demonstrating small lesions before overt bone destruction or involvement of the cortical tables, and in delineating an associated soft tissue mass. MRI signals can vary, but they are often seen as hypointense foci within the hyperintensity of fatty bone marrow on T1 weighted images and may be obscured following contrast medium administration if they enhance. In children, calvarial metastases occur with sarcomas and neuroblastoma.18 A variety of appearances have been reported with neuroblastoma metastases36 (Fig 7).
Figure 10 Arachnoid granulation. An axial CT image on bone window setting shows a well-circumscribed lobulate lesion in the occipital bone with involvement of the inner table.
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Lymphoma Although bone involvement is often seen in secondary non-Hodgkin lymphoma, primary malignant lymphoma of bone is rare.37 The imaging characteristics are non-specific, but on MRI the lesion is often homogeneous and isointense to grey matter on all sequences with avid enhancement38 (Fig 8). Bone destruction may be present, but more typically a permeative pattern of bone abnormality with a predominant intracranial and/or extracranial soft tissue component is seen.39 It may, therefore, be difficult to distinguish from a metastasis, but is an important differential diagnosis to consider as the treatment is usually nonsurgical.
Multiple myeloma and plasmacytoma
Figure 11 Osteoma. Axial CT image on bone window settings showing a smooth, well-defined sclerotic mass arising from the outer cortical table.
Multiple myeloma, which is due to the uncontrolled proliferation of monoclonal plasma cells in bone marrow, is the commonest primary bone malignancy in middle to old age. The solitary localised form is known as a plasmacytoma. On CT, the lucent lesions with sharply marginated, non-sclerotic borders affecting the inner and outer tables are said to resemble punch holes.3,5 However, the lesions can be expansile or resemble an angioma, or a more diffuse osteolytic process may be present. MRI is more sensitive in detecting the lesions, which are typically T1 hypointense, T2 hyperintense and enhance solidly3 (Fig 9). Positronemission tomography (PET) may provide prognostic information and can be used to evaluate response to treatment.40
Lucent bone defects A variety of developmental (cephalocoele, sinus pericranii, parietal foramina), traumatic (lepto-meningeal cyst) and iatrogenic (pseudomeningocoele) defects can occur in the skull. Limitation in the length of this article prevents further discussion but they should be remembered as they can mimic lucent bone lesions; however, arachnoid granulations deserve comment as they are frequently encountered. Arachnoid granulations are most commonly found in the occipital bone presenting as sharply marginated lucent lesions, often with a lobulated contour, with greater breach of the inner table than the outer (Fig 10). They may be more difficult to differentiate in other locations but cystic appearance of the contents on CT and MRI with low signal on fluid attenuated inversion recovery (FLAIR) along with lack of enhancement and no hyperintensity on DWI can help to differentiate them from solid lesions or epidermoid cysts.41
Sclerotic lesions Osteoma Figure 12 Fibrous dysplasia. Axial CT image on bone window settings showing a right parietal sclerotic lesion with central “ground-glass” texture, which expands the outer table but does not involve the inner table, maintaining the inner convexity.
Osteomas, the commonest benign calvarial tumour,19 are composed of mature dense bone and arise from the periosteum.6,18 On CT, a densely sclerotic mass, usually small,
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Figure 13 Intraosseous meningioma. (a) Axial CT on bone window settings demonstrating a sclerotic lesion in the left frontal and parietal bones involving the inner cortical table with an irregular margin. (b) A gadolinium-enhanced axial T1 image shows the adjacent enhancing mass.
with a smooth well-defined margin is typically seen arising from the outer table (Fig 11). They are less frequently found arising from the inner table and may be confused for a calcified meningioma. However, no associated soft tissue component or enhancement is seen with osteomas, which demonstrate markedly low T1 and T2 signal on MRI.42
Fibrous dysplasia
often it is hypointense on T1-weighted images but it demonstrates variable, often heterogeneous signal intensity on T2-weighted images related to the ratio of fibrous tissue to osseous matrix.45 Because of the fibrous element, they can enhance44 with variable patterns of enhancement reported.4 No associated soft tissue abnormality is seen, which may aid distinction from other sclerotic lesions. Malignant transformation to a sarcoma is rare but has been reported in up to 4% of cases.46
Fibrous dysplasia results from replacement of normal bone with fibro-osseous tissue and the calvarium may be involved in the monostotic and polyostotic forms.18 It usually presents in childhood or adolescence and is said not to progress once skeletal maturity is reached, although progression in adult cases has been reported.43 On CT, the typical appearances are a “ground-glass” texture of the diploic space with outward expansion of the outer table and no effect on the inner table, maintaining the convexity7 (Fig 12). However, some cases show a densely sclerotic appearance and around one fifth are lucent.44 On MRI, most
Figure 14 Malignant meningioma. Axial CT image on bone window settings showing a mixed lytic and sclerotic frontal lesion, which progressed rapidly, developing associated scalp thickening. Histology showed a poorly differentiated malignant tumour with immunochemistry favouring meningioma.
Figure 15 Paget’s disease. Axial CT image on bone window settings from an elderly female patient shows bony expansion with focal sclerotic areas.
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Intraosseous meningioma Intradural meningiomas are common, accounting for 20% of intracranial (non-glial) tumours, and they typically induce local hyperostosis in adjacent bone. Primary extradural meningiomas (arising from any location outside of the dura) are rare, representing less than 2% of all meningiomas.47 Two thirds of these are primary intraosseous meningiomas,48 which are most commonly found in the fronto-parietal region or the orbit.49 Like their intradural counterpart, they usually present in middleage,45 but the female predominance is less strong.50 They are thought to arise from inclusions of arachnoid cells within the skull with proximity to a suture thought to indicate a developmental cause for some lesions and sequela of trauma suggested for others but their origins remain debated.49e51 Most lesions are osteoblastic and their appearances on CT of bone expansion and sclerosis, often with a groundglass texture, make fibrous dysplasia the most likely alternative diagnosis. However, unlike fibrous dysplasia, intraosseous meningiomas tend to involve the inner table, often demonstrating an irregular margin50,51 with associated enhancing soft tissue usually present (Fig 13). A sclerotic metastasis should also be considered, but these rarely show significant bone expansion.51 Osteolytic and mixed lesions are rarer. The osteolytic variety are often expansile, the thinned cortical tables maybe interrupted and tissue within the bony lucency is usually of higher density than brain parenchyma on CT and exhibits avid uniform enhancement.48,52 They can appear hypermetabolic on PET imaging53 and more frequently show malignant features than the osteoblastic variety48 (Fig 14).
Osteosarcoma Primary osteogenic sarcoma accounts for <2% of all skull tumours and usually occurs in children and young adults.54 In adults, sarcomas often occur secondary to Paget’s disease, fibrous dysplasia, chronic osteomyelitis, or radiotherapy.3,6,7 Several histological types are found and imaging appearances are varied. The most frequent type is osteoblastic, the lesion showing focal sclerosis and destruction.5 A sunburst pattern is associated with irregular destruction of both inner and outer cortical tables. CT best demonstrates mineralisation within osteoid of the tumour matrix, whereas heterogeneous signal intensity and enhancement characteristics are seen on MRI.
Paget’s disease This multifocal chronic skeletal disease is characterised by disordered, exaggerated bone remodelling. Three phases of the disease are recognised and can occur simultaneously in the same bone.55 Characteristic CT appearances are osseous expansion, trabecular coarsening, and cortical thickening7 (Fig 15). Lesions of the osteolytic phase involving the skull, known as “osteoporosis
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circumscripta”, are well-defined lucent foci that cross sutures and occur more frequently in the frontal and occipital bones. The intermediate mixed lytic-sclerotic phase produces a “cotton wool” appearance with associated skull thickening.
Conclusion Focal calvarial lesions may be increasingly identified with the continued increase in demand for cross-sectional imaging. CT and MRI are complementary in demonstrating pertinent features, which may assist in defining a limited differential diagnosis to guide appropriate management.
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24. Chen S, Ikawa F, Kurisu K, et al. Quantitative MRI evaluation of intracranial epidermoid tumours by fast fluid-attenuated inversion recovery imaging and echo-planar diffusion-weighted imaging. AJNR Am J Neuroradiol 2001;22:1089e96. 25. Juglard R, Elfikri A, Fesselet J, et al. Intradiploic epidermoid cyst: diagnosis by ultrasonography and MRI. J Radiol 2003;84:155e7. 26. Gan YC, Hockey AD. Aneurysmal bone cysts of the cranium in children. Report of 3 cases and brief review of the literature. J Neurosurg 2007;106(5 Suppl):401e6. 27. Sanghvi DA, Iyer VR, Chagla AS, et al. Intradiploic frontal bone aneurysmal bone cyst in a child: a case report. Dentomaxillofac Radiol 2010;39:252e5. 28. Senol U, Karaali K, Akyuz M, et al. Aneurysmal bone cyst of the orbit. AJNR Am J Neuroradiol 2002;23:319e21. 29. Nabavizadeh SA, Bilaniuk LT, Feygin T, et al. CT and MRI of pediatric skull lesions with fluid-fluid levels. AJNR Am J Neuroradiol 2014;35:604e8. 30. Curtis BR, Petteys RJ, Rossi CT, et al. Large occipital aneurysmal bone cyst causing obstructive hydrocephalus in a pediatric patient. J Neurosurg Pediatr 2012;10:482e5. 31. Genizi J, Srugo I, Attias D, et al. Giant pediatric aneurysmal bone cysts of the occipital bone: case report and review of the literature. Pediatr Neurol 2011;45:42e4. 32. Arslan G, Karaali K, Cubuk M, et al. Intra-osseous lipoma of the frontal bone. A case report. Acta Radiol 2000;41:320e1. 33. Tomabechi M, Sako K, Daita G, et al. Lipoma involving the skull. Case report. J Neurosurg 1992;76:312e4. 34. Campbell RSD, Grainger AJ, Mangham DC, et al. Intra-osseous lipoma: report of 35 new cases and review of the literature. Skeletal Radiol 2003;32:209e22. 35. Mitsuya K, Nakasu Y, Horiguchi S, et al. Metastatic skull tumours: MRI features and a new conventional classification. J Neurooncol 2011;104:239e45. 36. Egelhoff JC, Zalles C. Unusual CNS presentation of neuroblastoma. Pediatr Radiol 1996;26:51e4. 37. Duyndam DAC, Biesma DH, Van Heesewijk JPM. Primary non-Hodgkin lymphoma of the cranial vault: MRI features before and after treatment. Clin Radiol 2002;57:948e50. 38. Rezaei-Kalantari K, Samimi K, Jafari M, et al. Primary diffuse large B cell lymphoma of the cranial vault. Iran J Radiol 2012;9:88e92.
39. Kantarci M, Erdem T, Alper F, et al. Imaging characteristics of diffuse primary cutaneous B-cell lymphoma of the cranial vault with orbital and brain invasion. AJNR Am J Neuroradiol 2003;24:1324e6. 40. Touzeau C, Moreau P. Multiple myeloma imaging. Diagn Interv Imaging 2013;94:190e2. 41. Esposito G, Della Pepa GM, Sturiale CL, et al. Hypertrophic arachnoid granulation of the occipital bone: neuroradiological differential diagnosis. Clin Neuroradiol 2011;21:239e43. 42. Avrahami I, Even I. Osteoma of the inner table of the skull. Clin Radiol 2000;55:435e8. 43. Davies ML, Macpherson P. Fibrous dysplasia of the skull: disease activity in relation to age. Br J Radiol 1991;64:576e9. 44. Chong VFH, Khoo JBK, Fan Y-F. Fibrous dysplasia involving the base of the skull. AJR Am J Roentgenol 2002;178:717e20. 45. Jee W-H, Choi K-H, Choe B-Y. Fibrous dysplasia: MRI imaging characteristics with radiopathologic correlation. AJR Am J Roentgenol 1996;167:1523e7. 46. DiCaprio MR, Enneking WF. Fibrous dysplasia. Pathophysiology, evaluation and treatment. J Bone Joint Surg Am 2005;87:1848e64. 47. Agrawal V, Ludwig N, Agrawal A, et al. Intra-osseous intracranial meningioma. AJNR Am J Neuroradiol 2007;29:314e5. 48. Elder JB, Atkinson R, Zee CS, et al. Primary intra-osseous meningioma. Neurosurg Focus 2007;23(4):E13. 49. Tokgoz N, Oner YA, Kaymaz M, et al. Primary intra-osseous meningioma: CT and MRI appearance. AJNR Am J Neuroradiol 2005;26:2053e6. 50. Daffner RH, Yakulis R, Maroon JC. Intra-osseous meningioma. Skeletal Radiol 1998;27:108e11. 51. Arana E, Diaz C, Latorre FF, et al. Primary intra-osseous meningiomas. Acta Radiol 1996;37:937e42. 52. Changhong L, Naiyin C, Yuehuan G, et al. Primary intra-osseous meningiomas of the skull. Clin Radiol 1997;52:546e9. 53. Yener U, Bayrakli F, Vardereli E, et al. Intradiploic meningioma mimicking calvarial metastasis: case report. Turk Neurosurg 2009;19:297e301. 54. Bose B. Primary osteogenic sarcoma of the skull. Sug Neurol 2002;58:234e40. 55. Cortis K, Micallef K, Mizzi A. Imaging Paget’s disease of bone d from head to toe. Clin Radiol 2011;66:662e72.
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Pictorial Review
Imaging of focal calvarial lesions I. Mitra*, M. Duraiswamy, J. Benning, H.M. Joy Department of Radiology, University Hospital Southampton, Tremona Road, Southampton S016 6YD, UK
art icl e i nformat ion Article history: Received 27 May 2015 Received in revised form 8 December 2015 Accepted 15 December 2015
Focal calvarial lesions may present as a visible, palpable, or symptomatic lump; however, with increasing use of cross-sectional imaging they are often encountered as an incidental finding. Knowledge of the possible disease entities along with a structured approach to imaging is required to suggest an appropriate diagnosis and assist in management planning. Abnormalities range from common neoplastic lesions to rarer congenital conditions, benign pathologies, and calvarial defects that can mimic lesions. The aim of this article is to demonstrate the salient imaging features that may help to limit the differential diagnosis of a focal calvarial lesion. Ó 2016 Published by Elsevier Ltd on behalf of The Royal College of Radiologists.
Introduction The calvarium is composed of eight flat bones: the frontal and occipital bones, the parietal bones, the squamous and zygomatic portions of the temporal bones, and the tip of the greater wing of the sphenoid bones bilaterally.1 These originate from cranial neural crest cells and undergo intramembranous ossification in a radial pattern. By the sixth year of development there is complete formation of a middle intradiploic layer composed of cancellous bone and bone marrow, resulting in inner and outer tables of cortical bone2 which appear dense on computed tomography (CT). On magnetic resonance imaging (MRI) the cortical tables demonstrate marked low signal on all sequences, whereas signal intensity of the diploic space varies with age and is dependent on the degree of fatty change within the marrow.3 Although histological confirmation is often required for definitive diagnosis of a focal calvarial lesion, imaging appearances can help limit the differential diagnosis and
* Guarantor and correspondent: I. Mitra, Department of Radiology, University Hospital Southampton, Tremona Road, Southampton S016 6YD, UK. Tel.: þ44 07970 096120; fax: þ44 01753 653442. E-mail address: [email protected] (I. Mitra).
guide subsequent management. This may involve biopsy or definitive surgery, but some lesions may be treated with chemotherapy and others may only require surveillance or patient reassurance. CT and MRI are complementary in demonstrating the characteristics of a focal calvarial abnormality.3,4 MRI can show a lesion within the diploic space before it alters the bony architecture and can give greater detail about its internal content. Many lesions are T1 hypointense, T2 hyperintense and enhance to some degree,5 but some nuances may assist in determining the diagnosis. Scalp involvement and intracranial extension is also better delineated on MRI.6 However, CT is superior in defining bony architectural change and evaluating the lesion margin and cortical involvement.7 Imaging findings should always be considered with relevant clinical information, particularly the patient’s age and any history of trauma or primary disease. Table 1 highlights features that should be considered when reviewing a calvarial lesion. Table 2 outlines typical imaging features of some lesions which might suggest a definitive diagnosis. Focal calvarial abnormalities may be divided into aggressive and non-aggressive or benign and malignant lesions or classified according to biological activity; however, a radiological classification based on bony
http://dx.doi.org/10.1016/j.crad.2015.12.010 0009-9260/Ó 2016 Published by Elsevier Ltd on behalf of The Royal College of Radiologists.
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Table 1 Radiological features to consider when reviewing a calvarial lesion.
Location Solitary or multiple Lucent or sclerotic Expansile þ/- bony remodelling or destruction Type of margin: smooth, well-defined, sclerotic, ill-defined, permeative Bone remnants in the lesion Attenuation/signal characteristics indicating the presence of fat, blood or calcification Associated soft tissue involvement or vascularity
architectural change and the number of lesions (Table 3) can be useful in limiting the differential diagnosis.
Table 3 Classification of calvarial lesions based on radiological features. Multiple lucent Solitary lucent Metastases Multiple myeloma Langerhans cell histiocytosis Paget’s disease
Sclerotic
Cavernous haemangioma Fibrous dysplasia Eosinophilic granuloma Intraosseous meningioma (osteoblastic subtype) Epidermoid/dermoid Osteoma Lipoma Metastasis Lymphoma Plasmacytoma
Metastasis Paget’s disease Osteosarcoma Eosinophilic granuloma (healing phase)
Intraosseous meningioma (osteolytic subtype) Osteomyelitis Congenital Traumatic
Lucent lesions Cavernous haemangioma These are benign incidental lesions that develop in the diploic space and consist of multiple engorged vascular Table 2 Typical appearances and characteristics which found together may support a definitive diagnosis. Lesion type Lucent lesions Cavernous haemangioma Eosinophillic granuloma Epidermoid cyst Aneurysmal bone cyst Lipoma Metastases (osteolytic) Myeloma Lymphoma
Paget’s disease (osteolytic phase) Sclerotic lesions Osteoma Fibrous dysplasia
Intraosseous meningioma (osteoblastic) Metastases (osteoblastic) Osteosarcoma Paget’s disease (osteoblastic phase)
Characteristic appearance Honeycomb/sunburst trabecular arrangement Sparing of inner table Young age/adolescent Well-defined bevelled edge Button sequestrum Cystic, expansile Thinning þ/- breach of skull tables Fluidefluid levels Soap-bubble appearance Central calcification Older age Multiple lesions Permeative/irregular destruction Multiple punched-out lesions Soft tissue masses with minimal intervening bone involvement on CT Homogeneous Isointense to grey matter Lucent foci crossing sutures
Involvement of one cortical table only No involvement of the diploic space Ground-glass texture Outward bowing of outer cortical table No effect on inner cortical table Lack of associated soft tissue abnormality Inner cortical table involved with irregular margin Associated enhancing soft tissue Focal sclerosis without notable expansion Focal sclerosis and bone destruction Bone expansion with cortical thickening Coarsened trabeculae
elements interspersed among trabecular bone.8 A frontal or parietal location is common. They occur more frequently in middle-aged women9 and are usually solitary, although cases of multiple lesions have been reported.10 They have been thought to occur following trauma, with report of a “de novo” lesion arising at the site of previously documented injury,11 but a preceding incident is not often elucidated in the clinical history. Typically, a mildly expansile, well-defined lucent lesion often with a fine sclerotic border is seen on CT (Fig 1). The outer table is usually involved. The inner table may be spared.5 Involvement of adjacent soft tissue may be seen.9 The coarsened internal trabeculae may show a honeycomb or sunburst arrangement; however, a pattern of internal striations may also be seen with meningioma, metastasis, or osteogenic sarcoma.5 Cavernous haemangiomata can show a gradual increase in size with proposed mechanisms for this including pressure of blood in
Figure 1 Cavernous haemangioma. Axial CT image on bone window settings from a 45-year-old man showing a mildly expansile lucent lesion with coarse trabeculation in the left parietal bone. The inner table is relatively spared while fine spiculations of bone project from the outer table.
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but hyperintensity on T1-weighted images due to blood or fat content with a stippled appearance due to the central bony trabeculae is characteristic.3,8 Enhancement is usually avid due to the vascular nature of the lesion.12
Eosinophilic granuloma (Langerhans cell histiocytosis)
Figure 2 EG. Axial CT image on bone window settings showing a lucent lesion in the right parietal bone of a middle-aged female patient with differential involvement of the cortical tables and a central remnant of bone, a “button sequestrum”. No additional lesions were found on systemic investigation.
the malformed vessels causing tortuous enlargement and/ or repeated intralesional haemorrhage.9 Regeneration and repair following haemorrhage may result in fat within the lesion. Therefore signal characteristics on MRI are variable,
Langerhans cell histiocytosis (LCH) is a systemic disease of unknown aetiology, of which eosinophilic granuloma (EG) is the commonest and mildest form.3 Most EGs occur in patients between 5e15 years of age, affecting males more than females.13 They usually present with local pain, often with an associated palpable mass.14 They may be solitary or multiple and spontaneous regression often begins after a few months but complete resolution may take as long as 2 years.3,15 The lesions begin in the diploic space and invade the inner and outer tables, a parietal location reported as the most frequent.5,14 Characteristically these are sharply circumscribed lucent lesions, often with a bevelled edge due to unequal involvement of the cortical tables16 (Figs. 2 and 3a). Sometimes a remnant of bone is seen centrally, known as a button sequestrum (Fig 2), but this is not specific and reported in other conditions including osteomyelitis, epidermoid cysts, and metastases from breast cancer.17 Marginal sclerosis is not usually a feature unless the lesion is healing.3,7 Cross-sectional imaging shows a soft tissue mass located in the diploe which is of higher attenuation than brain
Figure 3 LCH. Images of a 5-year-old female patient with multiple calvarial lesions. (a) The initial plain film shows a lucent lesion in the right parietal bone with differential involvement of the inner and outer tables. (b) Axial CT image on soft tissue window settings showing the tissue within the lucent lesion is of higher attenuation than adjacent brain parenchyma. (c) Gadolinium-enhanced coronal T1 image showing homogeneous enhancement, subcutaneous tissue extension, and adjacent dural enhancement of right squamous temporal and parietal lesions. Please cite this article in press as: Mitra I, et al., Imaging of focal calvarial lesions, Clinical Radiology (2015), http://dx.doi.org/10.1016/ j.crad.2015.12.010
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Figure 4 Epidermoid cyst. (a) Axial CT image on bone window settings and (b) axial T2-weighted image showing a large right temporo-parietal lucent lesion in a 70-year-old man with bony remodelling, thinning and breach of the cortical tables and marked internal expansion. The slow growth rate has allowed considerable mass effect on the underlying right cerebral hemisphere with little clinical effect. Some internal calcification is present but the contents are predominantly high signal on T2. (c) DWI and (d) corresponding ADC map from a different patient showing intense high signal on DWI in a right occipital lesion with the ADC similar to brain parenchyma.
parenchyma on CT18 (Fig 3b). On MRI, they appear T1 hypointense and T2 hyperintense.5 Decreased signal intensity on T2-weighted images is suggestive of a healing lesion.19 The soft tissue mass shows homogeneous enhancement with enhancement of adjacent dura often present20,21 (Fig 3c). Oedema and inflammation may be seen in the adjacent scalp.3 Once diagnosed, systemic imaging is required to exclude multifocal disease.
Dermoid and epidermoid cysts Both lesions are thought to arise due to inclusion of ectodermal remnants within the diploic space, but whereas epidermoid cysts only contain squamous epithelium, dermoid cysts contain other skin elements. Although the
distinction may only be made histologically,22 there are some distinguishing features. Dermoid cysts are more typically found in childhood and are located in the midline or related to sutures. Epidermoid cysts are usually located laterally, most often in the temporal and parietal bones and are commonly found in the third to sixth decade. Progressive accumulation of desquamating cells from the stratified squamous epithelial lining, cellular debris and keratin causes expansion of the diploic space with pressure erosion causing remodelling of the bone, affecting both the inner and outer tables of the skull4,23 (Fig 4a). The typical appearance on CT is of a well-defined lucent lesion, often with a sclerotic margin. On MRI, they usually exhibit low signal on T1 and high signal on T2 with little enhancement (Fig 4b), although signal characteristics vary according to
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Figure 7 Neuroblastoma metastasis. Axial CT image on bone window settings from a 5-year-old girl shows marked expansion of the left frontal bone. “Thickened bone” is a recognised pattern of metastatic bone involvement in neuroblastoma. On systemic investigation an adrenal mass was identified and shown histologically to be a neuroblastoma.
Figure 5 Sclerotic metastases. Axial CT image on bone window settings from a 41-year-old woman with metastatic breast cancer, which shows focal areas of dense sclerosis in the diploic space.
the protein and lipid content or rarely due to haemorrhage into the lesion.22 As with intracranial epidermoid cysts, marked hyperintensity on diffusion weighted imaging (DWI) is seen in intradiploic lesions also24,25 (Fig 4c); however, the apparent diffusion coefficient (ADC) within the cyst is no lower than is found in brain parenchyma, suggesting the increased signal on DWI to be due to T2 shine-through effect rather than true diffusion restriction (Fig 4d).
Aneurysmal bone cyst (ABC) This well-defined, expansile, lucent lesion is most frequently seen in children and adolescents.3 Only 3e6% of ABCs occur in the skull26 with reports of lesions in most of the calvarial bones.27 They are multiloculated with a low signal rim and internal low and high signal areas on MRI reflecting different stages of blood degradation.28 Fluidefluid levels in the locules and small cysts projecting into bigger cysts produce the characteristic soap bubble appearance28; however, fluidefluid levels have been reported in other conditions, including LCH and metastatic neuroblastoma.29 They can enlarge rapidly and may cause
Figure 6 Metastasis. CT images from a 48-year-old woman with breast cancer. (a) An axial image on bone window settings shows a poorly delineated permeative destructive lesion in the parieto-occipital region. (b) A sagittal reformat on soft tissue window setting shows the extent of intracranial and subcutaneous soft tissue masses. Please cite this article in press as: Mitra I, et al., Imaging of focal calvarial lesions, Clinical Radiology (2015), http://dx.doi.org/10.1016/ j.crad.2015.12.010
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Figure 8 Lymphoma: (a) Axial T2 and (b) pre and (c) post-gadolinium administration coronal T1 images from a 62-year-old woman demonstrate homogeneous, uniformly enhancing subcutaneous and intracranial masses centred around the left parietal bone. There is no detectable bone involvement on the T2 image, but marrow signal in the intervening bone is reduced compared to the contralateral normal parietal bone on the unenhanced T1 image. Histology following biopsy confirmed diffuse large B cell lymphoma.
symptoms due to pressure on intracranial structures.30,31 Like their skeletal counterparts, a preceding lesion may be present with calvarial ABCs also, such as fibrous dysplasia with those found in a frontal location.27
Lipoma Intraosseous lipomas are more frequently found in the appendicular skeleton with only a few cases of calvarial lesions reported in the literature.32,33 They appear as welldefined expansile lesions and may have a sclerotic margin.3 Fat necrosis can result in central calcification.34 Signal intensity on MRI is consistent with fat6 and therefore the more common differential diagnosis is a cavernous haemangioma.
Figure 9 Plasmacytoma. Coronal FLAIR image showing a sharply marginated, expansile lytic lesion in the left parietal bone of a 49year-old woman with known multiple myeloma. Histology following resection confirmed a plasmacytoma.
Metastases These are the commonest cause of a lucent calvarial lesion in middle-aged and older adults,19 with breast, lung, and prostate cancers the most frequent primary tumour. They are often small and multiple, but can be solitary and large,35 and depending on the primary tumour, can be lytic, sclerotic (Fig 5), or mixed.4 Radionuclide studies can be more sensitive than CT in detecting calvarial metastases.3 CT shows the extent of bone destruction usually with irregular margins and permeative erosion (Fig 6). MRI is better at demonstrating small lesions before overt bone destruction or involvement of the cortical tables, and in delineating an associated soft tissue mass. MRI signals can vary, but they are often seen as hypointense foci within the hyperintensity of fatty bone marrow on T1 weighted images and may be obscured following contrast medium administration if they enhance. In children, calvarial metastases occur with sarcomas and neuroblastoma.18 A variety of appearances have been reported with neuroblastoma metastases36 (Fig 7).
Figure 10 Arachnoid granulation. An axial CT image on bone window setting shows a well-circumscribed lobulate lesion in the occipital bone with involvement of the inner table.
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Lymphoma Although bone involvement is often seen in secondary non-Hodgkin lymphoma, primary malignant lymphoma of bone is rare.37 The imaging characteristics are non-specific, but on MRI the lesion is often homogeneous and isointense to grey matter on all sequences with avid enhancement38 (Fig 8). Bone destruction may be present, but more typically a permeative pattern of bone abnormality with a predominant intracranial and/or extracranial soft tissue component is seen.39 It may, therefore, be difficult to distinguish from a metastasis, but is an important differential diagnosis to consider as the treatment is usually nonsurgical.
Multiple myeloma and plasmacytoma
Figure 11 Osteoma. Axial CT image on bone window settings showing a smooth, well-defined sclerotic mass arising from the outer cortical table.
Multiple myeloma, which is due to the uncontrolled proliferation of monoclonal plasma cells in bone marrow, is the commonest primary bone malignancy in middle to old age. The solitary localised form is known as a plasmacytoma. On CT, the lucent lesions with sharply marginated, non-sclerotic borders affecting the inner and outer tables are said to resemble punch holes.3,5 However, the lesions can be expansile or resemble an angioma, or a more diffuse osteolytic process may be present. MRI is more sensitive in detecting the lesions, which are typically T1 hypointense, T2 hyperintense and enhance solidly3 (Fig 9). Positronemission tomography (PET) may provide prognostic information and can be used to evaluate response to treatment.40
Lucent bone defects A variety of developmental (cephalocoele, sinus pericranii, parietal foramina), traumatic (lepto-meningeal cyst) and iatrogenic (pseudomeningocoele) defects can occur in the skull. Limitation in the length of this article prevents further discussion but they should be remembered as they can mimic lucent bone lesions; however, arachnoid granulations deserve comment as they are frequently encountered. Arachnoid granulations are most commonly found in the occipital bone presenting as sharply marginated lucent lesions, often with a lobulated contour, with greater breach of the inner table than the outer (Fig 10). They may be more difficult to differentiate in other locations but cystic appearance of the contents on CT and MRI with low signal on fluid attenuated inversion recovery (FLAIR) along with lack of enhancement and no hyperintensity on DWI can help to differentiate them from solid lesions or epidermoid cysts.41
Sclerotic lesions Osteoma Figure 12 Fibrous dysplasia. Axial CT image on bone window settings showing a right parietal sclerotic lesion with central “ground-glass” texture, which expands the outer table but does not involve the inner table, maintaining the inner convexity.
Osteomas, the commonest benign calvarial tumour,19 are composed of mature dense bone and arise from the periosteum.6,18 On CT, a densely sclerotic mass, usually small,
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Figure 13 Intraosseous meningioma. (a) Axial CT on bone window settings demonstrating a sclerotic lesion in the left frontal and parietal bones involving the inner cortical table with an irregular margin. (b) A gadolinium-enhanced axial T1 image shows the adjacent enhancing mass.
with a smooth well-defined margin is typically seen arising from the outer table (Fig 11). They are less frequently found arising from the inner table and may be confused for a calcified meningioma. However, no associated soft tissue component or enhancement is seen with osteomas, which demonstrate markedly low T1 and T2 signal on MRI.42
Fibrous dysplasia
often it is hypointense on T1-weighted images but it demonstrates variable, often heterogeneous signal intensity on T2-weighted images related to the ratio of fibrous tissue to osseous matrix.45 Because of the fibrous element, they can enhance44 with variable patterns of enhancement reported.4 No associated soft tissue abnormality is seen, which may aid distinction from other sclerotic lesions. Malignant transformation to a sarcoma is rare but has been reported in up to 4% of cases.46
Fibrous dysplasia results from replacement of normal bone with fibro-osseous tissue and the calvarium may be involved in the monostotic and polyostotic forms.18 It usually presents in childhood or adolescence and is said not to progress once skeletal maturity is reached, although progression in adult cases has been reported.43 On CT, the typical appearances are a “ground-glass” texture of the diploic space with outward expansion of the outer table and no effect on the inner table, maintaining the convexity7 (Fig 12). However, some cases show a densely sclerotic appearance and around one fifth are lucent.44 On MRI, most
Figure 14 Malignant meningioma. Axial CT image on bone window settings showing a mixed lytic and sclerotic frontal lesion, which progressed rapidly, developing associated scalp thickening. Histology showed a poorly differentiated malignant tumour with immunochemistry favouring meningioma.
Figure 15 Paget’s disease. Axial CT image on bone window settings from an elderly female patient shows bony expansion with focal sclerotic areas.
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Intraosseous meningioma Intradural meningiomas are common, accounting for 20% of intracranial (non-glial) tumours, and they typically induce local hyperostosis in adjacent bone. Primary extradural meningiomas (arising from any location outside of the dura) are rare, representing less than 2% of all meningiomas.47 Two thirds of these are primary intraosseous meningiomas,48 which are most commonly found in the fronto-parietal region or the orbit.49 Like their intradural counterpart, they usually present in middleage,45 but the female predominance is less strong.50 They are thought to arise from inclusions of arachnoid cells within the skull with proximity to a suture thought to indicate a developmental cause for some lesions and sequela of trauma suggested for others but their origins remain debated.49e51 Most lesions are osteoblastic and their appearances on CT of bone expansion and sclerosis, often with a groundglass texture, make fibrous dysplasia the most likely alternative diagnosis. However, unlike fibrous dysplasia, intraosseous meningiomas tend to involve the inner table, often demonstrating an irregular margin50,51 with associated enhancing soft tissue usually present (Fig 13). A sclerotic metastasis should also be considered, but these rarely show significant bone expansion.51 Osteolytic and mixed lesions are rarer. The osteolytic variety are often expansile, the thinned cortical tables maybe interrupted and tissue within the bony lucency is usually of higher density than brain parenchyma on CT and exhibits avid uniform enhancement.48,52 They can appear hypermetabolic on PET imaging53 and more frequently show malignant features than the osteoblastic variety48 (Fig 14).
Osteosarcoma Primary osteogenic sarcoma accounts for <2% of all skull tumours and usually occurs in children and young adults.54 In adults, sarcomas often occur secondary to Paget’s disease, fibrous dysplasia, chronic osteomyelitis, or radiotherapy.3,6,7 Several histological types are found and imaging appearances are varied. The most frequent type is osteoblastic, the lesion showing focal sclerosis and destruction.5 A sunburst pattern is associated with irregular destruction of both inner and outer cortical tables. CT best demonstrates mineralisation within osteoid of the tumour matrix, whereas heterogeneous signal intensity and enhancement characteristics are seen on MRI.
Paget’s disease This multifocal chronic skeletal disease is characterised by disordered, exaggerated bone remodelling. Three phases of the disease are recognised and can occur simultaneously in the same bone.55 Characteristic CT appearances are osseous expansion, trabecular coarsening, and cortical thickening7 (Fig 15). Lesions of the osteolytic phase involving the skull, known as “osteoporosis
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circumscripta”, are well-defined lucent foci that cross sutures and occur more frequently in the frontal and occipital bones. The intermediate mixed lytic-sclerotic phase produces a “cotton wool” appearance with associated skull thickening.
Conclusion Focal calvarial lesions may be increasingly identified with the continued increase in demand for cross-sectional imaging. CT and MRI are complementary in demonstrating pertinent features, which may assist in defining a limited differential diagnosis to guide appropriate management.
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Please cite this article in press as: Mitra I, et al., Imaging of focal calvarial lesions, Clinical Radiology (2015), http://dx.doi.org/10.1016/ j.crad.2015.12.010