Beyond the Skull: CT and MRI Findings in Lesions of the Scalp in Adults - A Pictorial Review. Poster No.:

C-2579

Congress:

ECR 2012

Type:

Educational Exhibit

Authors:

L. P. PEREIRA , F. Clarencon , D. Leclercq , B. Jean , A. Drier ,

1

1

1

1

2

1 1

3

1

2

D. Galanaud , D. Dormont , J. Chiras ; Paris/FR, PARIS/FR, 3

Clermont-Ferrand/FR

Keywords:

Tissue characterisation, Education, MR, CT, Neuroradiology brain

DOI:

10.1594/ecr2012/C-2579

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Learning objectives To present the different lesions that may involve the scalp and their associated patterns in both CT and MRI.

Background There is a wide variety of scalp lesions that are identified as palpable masses or as incidental findings in radiographic studies. The radiologist must be familiar with the anatomy of the scalp and the most frequent lesions in this region in order to reach a positive diagnosis. ANATOMY OF THE SCALP The scalp consists of skin, fibrous and fatty tissue, galea aponeurotica, its connective tissue and pericranium: LAYERS OF THE SCALP (Fig. 1) Mnemonics S = Skin C = Connective tissue A = Aponevrotic layer (Galea Aponeurotica) L = Loose connective tissue P = Pericranium ARTERIAL SUPPLY (Fig. 2) The scalp has a rich vascular supply. The blood vessels cross the connective tissue layer, which receives vascular contribution from the internal and external carotid arteries. The

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blood vessels anastomose freely in the scalp. From the midline anteriorly, the arteries present as follows: • • • •

Supratrochlear artery and supraorbital artery (branches of the ophthalmic artery): supply the anterior scalp Superficial temporal artery: supplies the lateral scalp Posterior auricular artery: supplies the scalp above and posterior to the ear Occipital artery: supplies the posterior scalp

VENOUS DRAINAGE (Fig. 2 and 3) The veins of the scalp freely anastomose with one another and are connected to the diploic veins of the skull bones and the intracranial dural sinuses through several emissary veins (Fig. 3). The emissary veins are valveless. The scalp veins accompany the arteries and have similar names. IMAGING ANATOMY The different layers are presented on CT and MRI as shows in Fig. 4 and 5.

Images for this section:

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Fig. 1

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Fig. 2

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Fig. 3

Fig. 4

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Fig. 5

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Imaging findings OR Procedure details Scalp lesions should be divided into lesions involving only the scalp and those developing from the calvarium and presenting an extension to the scalp (Fig. 6). LESIONS INVOLVING ONLY THE SCALP: Sebaceous Cyst (also called epidermal cysts) (Fig. 7) • • •

•

The most common incidental finding Result from the proliferation of epidermal cells within a circumscribed dermal space. Probably formed by several mechanisms-remnant ectodermal tissues misplaced during embryogenesis, occlusion of the pilosebaceous unit, or traumatic or surgical implantation of epithelial elements. Usually a well-defined oval-shaped lesion, hypodense on CT with or without calcifications, and with characteristic MRI findings including a high-signalintensity with variable low-signal components on T2-weighted images, some bright foci on T1-weighted images, and peripheral thin rim enhancement.

Lipoma (Fig. 8) • • •

Can occur anywhere in the head and neck. Imaging: encapsulated mass with very low density on CT and typical fatty tissue MR signal intensity. If there are thick septations or areas of soft tissue density, exclusion of liposarcoma is necessary.

Neurofibroma •

• • •

• •

May occur as solitary lesion or multiple as a component of neurofibromatosis (more than 80% of patients older than 20 yo with neurofibromatosis type 1NF1). Consist of several nerve sheath cells, including Schwann cells, perinerium cells and fibroblasts. Etiology is unknown; affects young adults age 20-30. Classic peripheral nerve sheath tumors have a signal that is isointense to that of skeletal muscle on T1-weighted MR images and hyperintense to that of skeletal muscle on T2-weighted images, with variable degrees of inhomogeneity and enhancement. T2 finding of periperal hyperintensity is a common feature (target sign) (Fig. 9). May have malignant tranformation (up to 5% in NF1).

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Vascular - Superficial Arteriovenous Malformation (AVM) (Fig. 10 and 11) •

AVM of the scalp are rare vascular lesions present as a pulsatile mass with a propensity to hemorrhage.

•

Situated within the subcutaneous fatty layer with the feeding arteries derived from the vessels supplying the scalp.

Metastatic disease •

Rarely metastatic disease can present as subcutaneous nodules (Fig. 12).

CALVARIAL LESIONS EXTENDING INTO THE SCALP: Fibrous Dysplasia (Fig. 13) • • • • •

• • • • •

Benign condition, commonly affects adolescents and young adults. Most frequently in fronto-orbital location. Bone marrow replacement by proliferative fibro-osseous tissue with varied quantities of stroma and bone. Monostotic and polyostotic forms. Three radiographic patterns: Predominately sclerotic (38%) Predominately lytic (22%) Mixed pattern (40%) Outer table tends to bulge more than the inner table. Risk of malign transformation to osteosarcoma, fibrosarcoma and chondrosarcoma (0.5%). Variable enhancement after contrast injection. A noncontrasted CT scan with bone windowing will show the classic "ground glass" appearance. MRI shows homogeneous low signal on T1WI and heteregenous T2WI signal. Signal on T2WI depends on the amount of fibro-osseous tissue, cellularity, cystic alterations, hemorrhage and cartilaginous tissue. The lesions usually have well defined borders. All the sequences show a hypointense halo that corresponds to sclerotic margins.

Paget's Disease • • •

Also known as osteitis deformans, is a disorder of abnormal and excessive bone remodeling which may affect one or more bones. Affects about 3% of individuals over the age of 40 and 10% of the population above 85 years. The vast majority of patients are asymptomatic in all stages, when they are present, most of the symptoms are related to weakened and thickened bones, pain and nerve compression.

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• •

•

•

Usually polystotic. Three stages of disease in the skull: 1. Vascular - enlargement of skul; 2. Advancing sclerosis - thickening of the cortex and 3. Complete diffuse sclerosis - loss of distinction between the diploic space and calvarium The most feared complication is malignant transformation, which occurs in about 1% of all patients and approximately 10% of those with extensive polyostotic disease. CT - diploic widening and thickened cortex (Fig. 14)

Langerhans cell histiocytosis (LCH) • • •

•

Multisystemic disease of unknown etiology, which consists of abnormal proliferation of histiocytes that may form focal or diffuse clusters. The clinical presentation and evolution vary according to its extension and to the organs that are involved, sometimes resembling a true neoplasia. LCH can arise nearly anywhere in the brain and skull. This diagnosis should always be considered when a mass arises from the bones of the face, skull base, or calvaria in children. The most common imaging finding of calvarial LCH is a well-defined mass involving the diploe. On CT, a sharply circumscribed skull lesion is identified with differential involvement of the inner and outer tables. MRI shows these bone lesions as sharply defined soft tissue masses, with signal intensity equivalent to that of skeletal muscle and marked enhance after intravenous contrast medium (Fig. 15).

Intraosseous hemangioma (Fig. 16) • • • • • • •

Benign vascular tumor, 2 women/man. 4th and 5th decade. More common in frontal and parietal bones - 2nd location after the vertebral bodies. CT: lytic diploic lesion with spiculated or radial pattern, thinning or rupture of the outer table, respect for the inner table. MRI: heterogeneous signal on T1 and intense contrast enhancement, inconstant presence of a fatty component, hyper intense on T2. Flow voids can be seen on both T1 and T2 sequences. Confrontation of CT and MRI is necessary to avoid an unnecessary and dangerous biopsy.

Intraosseous meningioma (Fig. 17) • • •

Rare ( 50 years. Normally develops in a suture (inclusion of ectopic arachnoid cells in organogenesis, post traumatic inclusion). Thickening of the vault - expands the inner and outer tables - may present intra and extra cranial extension, lobulated and spiculated (characteristic) contours.

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• •

Meningeal contrast enhancement on the intra cranial side. There may be no dural component.

Epidermoid/dermoid cysts • • • • • • •

•

Benign cystic lesions due to the inclusion of epithelial cells within the diploe (dermoid cyst: contains more fat) Children and young adults Dermoid cyst: fronto-parietal vault, near the coronal suture Epidermoid cyst: 90% intradural, primarily in basal cisterns, 10% extradural, primarily in the skull (occipital arch) and spine. Congenital or acquired (mostly post traumatic). Slow growth. CT: Epidermoid cyst: encapsulated unilocular hypodense lesion with clear boundary surrounded by a continuous rim of sclerosis, diploic initially and then blows or destroys tables. Dermoid cyst: imaging characteristics close to epidermoid cyst but may contain central or parietal calcifications, often more important extension to the soft tissues. MRI: Epidermoid cyst: hypointense on T1WI and hyperintense on T2WI, bright on diffusion weighted images. No enhancement. (Fig. 18). Dermoid cyst: Hyperintense on T1WI because of the presence of macroscopic fat and possible hemorrhage alterations. They may have a thick capsule with contrast enhancement.

Multiple Myeloma (Fig. 19) • • •

Malignant disorder of the bone marrow in which there is monoclonal proliferation of plasma cells. Solitary lesions are known as plasmacytomas. th

Most common primary malignant bone lesion occurring between the 4 and th

• •

•

8 decade, with a slight male predominance. The most common symptom is bone pain. The axial skeleton is the predominant site of involvement and the most affected bones. CT and plain radiography: diploic rounded defects without marginal sclerosis, evenly distributed, with uniform size (3 to 15 mm). Extension to inner and outer tables. MRI: Non-specific. Variable signal on T1WI and hyperintense on T2WI with contrast enhancement. Extension into the soft tissues or epidural space may also be present.

Plasmacytoma: • •

Younger patient. Single lesion, occipital and parietal vault (Fig. 20).

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Metastatic Disease • • • •

th

Most frequent calvarial lesion from the 5 decade of age. Most commonly breast, prostate, lung, renal cell carcinoma, thyroid. Lytic lesions much more common than blastic. Initially diploic with secondary destruction of inner and outer tables with extension into soft tissue and epidural space (Fig. 21 and 22).

Mucocele (Fig. 23) • • • •

Occurs when there is obstruction of the sinus ostia. Frontal sinuses most commonly involved. Expands bone. On CT it presents as a nonenhancing, homogeneous, and hypodense mass that fills and expands the entire sinus cavity. Its appearance on MRI varies depending on the protein concentration, which changes over time. On contrast-enhanced MRI, the sinus mucosa enhances as a thin line surrounding the mucocele.

Post-Surgery Conditions • • •

Subcutaneous CSF retention after craniotomy. Minor postoperative complication induced by insufficient closure of the dura mater and increased CSF pressure. CSF leaks through a dural defect, a fistula, or a suture line and then pool in both the epidural and subcutaneous spaces (Fig. 24).

Infection Tuberculosis (Fig. 25) • • • • •

•

The most common intracranial forms are tuberculous meningitis and tuberculomas. Calvarial, cranial epidural and subdural tuberculosis are rare. It can develop at any bone on the skull. Mostly in the parietal and frontal areas besides occipital, sphenoid, and ethmoid bones and clivus. Rare as isolated forms. Normally associated with pulmonary tuberculosis and tuberculous osteomyelitis involving other bones. It spreads by hematogenous route, by direct extension from neighboring tissue, and through secondary infection in the operative wound by Mycobacterium tuberculosis. Imaging: subgaleal soft tissue swelling, extradural soft tissue, calvarial destruction and parenchymal involvement (up to 10%).

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Images for this section:

Fig. 6

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Fig. 7: Sebaceous cysts. CT scan (A) and T2 (B), T1 (C) and T1 weighted images (WI) showing multiples oval-shaped lesions in the scalp, with some calcification and variable MR signal, in this case predominantly low signal on T2 and high signal on T1. Note the peripheral thin rim enhancement on T1 after gadolinium injection (arrow on D).

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Fig. 8: Soft tissue lipoma. CT scan (A), coronal T2 (B) and T1 WI (C) showing a typical soft tissue lipoma with fat density on CT and high T1 and T2 signal intensities.

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Fig. 9: Neurofibroma. CT scan (A), T1WI (B), T2WI (C) and T1WI after contrast injection (D) demonstrate a well-defined oval-shaped lesion in the connective tissue, isodense on CT and with the typical target sign on T2WI, hyper intense in the periphery and dark in the center (C), with heterogeneous enhancement, mostly peripheral (D).

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Fig. 10: AVM of the scalp. 35-year-old woman with a pulsatile and compressible mass in the frontal region and recent volume increase during pregnancy. Photograph of the scalp (A). Sagittal T1WI (B), coronal T2WI (C) and venous MR angiography (2D time-of-flight) showing the arteriovenous malformation nidus. The arrows demonstrate large draining veins (supraorbital and superficial temporal veins).

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Fig. 11: Superficial AVM of the scalp. Same patient as Fig. 10. CT angiography volume rendering technique (VRT) reconstruction (A), DSA: anteroposterior (AP) projection obtained from right ECA injection (B) and lateral projection from right ICA injection (C) demonstrating the main arterial feeder that is the supraorbital artery (white arrow), branch of the ophthalmic artery, the nidus (arrow heads) and the venous drainage of the AVM by means of superficial temporal and supraorbital veins (black arrows).

Fig. 12: Subcutaneous pulmonary carcinoma metastasis. PET-CT demonstrates FDG-18F uptake of the subcutaneous nodule in this patient with known pulmonary carcinoma confirmed by biopsy. A. CT acquisition, B. PET acquisition, C. Fusion of CT and PET acquisitions.

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Fig. 13: Fibrous Dysplasia with soft tissue component. Axial CT scan, bone window (A) showing the classic ground-glass appearance in fronto-parietal bones. Note the bulging of the outer table with cortical erosion with soft tissue component better depicted on MRI (B, C, D). Axial T1WI (B) and T2WI (C) demonstrate the homogeneous low signal on T1WI and heterogeneous T2WI signal, enhancing after contrast injection (D). The soft tissue component is seen as an isointense on T1WI and hyperintense on T2WI nodule in the scalp with contrast enhancement (arrows). There is also rim enhancement of the inner table (arrowhead in D).

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Fig. 14: Paget's disease. 80 year-old female hospitalized after trauma. Coronal (A) and axial (B) CT reconstructions, bone windowing, show expansion of the diploic space and multiple sclerotic areas with adjacent areas of lucency in the calvarium. Note the left inferior orbital fracture (arrow).

Fig. 15: Langerhans cell histiocytosis. CT scan (A) showing a well circumscribed lytic skull lesion, hypo intense on T1WI (B) and hyper intense on T2WI (C) with marked enhancement after contrast injection (D), with rupture of the outer table and extension into the scalp.

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Fig. 16: Intraosseous hemangioma. The CT scan, bone windowing (A) shows a typically located frontal lesion with sclerotic margins, spiculated pattern and loss of bone of the outer table. TIWI (B), T2WI (C) and T1WI after contrast injection (D) demonstrate a heterogeneous signal on T1 and T2, with some hyper signal on T1 and intense contrast enhancement (D). DSA (E) shows a high vascular lesion supplied from the external carotid artery branches.

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Fig. 17: Intraosseous meningiomas. CT scan (A) showing right frontal and left frontoparietal intraosseous lesions, expanding the inner and outer tables of the vault with slightly spiculated contours of the inner table. Axial and Coronal T1WI after contrast injection (B and C) depict the enhancement of the lesion and the dura. Note the predominant thickening of the outer table. Another patient (D-F) with a slowly enlarging frontal mass very hypo intense in T1WI (D) and T2WI (E) with less important intralesional and dural enhancement (F) than the previous patient.

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Fig. 18: Epidermoid Cyst. 50 year-old male with this incidental finding on a head MRI. Coronal T2WI (A) shows a high intensity signal lesion replacing the normal marrow and expanding the inner and outer tables. The lesion is heterogeneous on axial FLAIR (B) and T1WI (C) in which it has predominantly low signal intensity with iso and hyper intense spots. There is no contrast enhancement (D).

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Fig. 19: Multiple myeloma. CT scan (A, B) showing a large fronto-parietal lytic mass with aggressive pattern of bone destruction and soft tissue components (scalp and epidural) on both sides of the calvarium. Note the presence of other millimetric lytic lesions (arrows in B). Sagittal T1WI of the spine (C) of the same patient demonstrates the bone marrow replacement by MM lesions. Plain radiograph (D) of other patient shows the round lytic lesions without sclerotic margins of the calvarium.

Fig. 20: Plasmocytoma. Axial T2WI (A) and T1WI (B) showing the expansile lesion with heterogeneous signal slightly hyper intense on T2WI in the right parietal bone extending into the scalp and epidural space with homogenous enhancement on contrast enhanced T1WI (C). Plain radiograph shows the large lytic lesion with no sclerotic margins (arrow).

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Fig. 21: Metastatic disease. 58-year-old female with a history of breast carcinoma presenting with a palpable mass in the occipital region. Contrast enhanced CT scan (A, B) demonstrates a lytic mass in the occipital region with soft tissue components. MRI (C, D) shows the aggressive mass with intermediate signal on T1WI (C) and heterogeneous enhancement with a necrotic center.

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Fig. 22: Metastatic disease. Another patient with a lung cancer metastasis. Huge frontoparietal mass with soft tissue components, invasion of brain parenchyma and associated responsive edema. Coronal T2WI (A), sagittal T1WI (B) and T1WI after contrast injection (C).

Fig. 23: Mucocele. Patient with antecedents of trauma and recurrent frontal mucoceles. Axial T2WI (A) shows an expanded frontal sinus filled with iso to hypersignal intensity material. The lesion increases in signal intensity on T1WI (B) (high protein concentration). Note the bilateral frontal contusion sequelae.

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Fig. 24: Subcutaneous CSF retention after craniotomy for left MCA aneurysm clipping.

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Fig. 25: Tuberculous osteomyelitis. 35 year-old man with sphenoid tuberculosis and hematogenous spread to the skull. Axial CT scan, bone window (A) and soft tissue window (B) showing the osteosclerosis involving the entire thickness of the frontal and parietal bones with multiple lytic spots, rupture of the outer table (arrows in A) and soft tissue component (arrow in B). Sagittal T1 after contrast injection (C and D) demonstrate the epidural and subgaleal components with homogeneous enhancement, as well as the calvarial destruction of the outer table.

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Conclusion Being familiar with the anatomy of the scalp as well as the CT and MRI patterns of most common lesions involving the scalp are helpful to reach a positive diagnosis in the majority of cases.

Personal Information Licia Pereira, Frederic Clarençon, Delphine Leclercq, Betty Jean, Aurelie Drier, Damien Galanaud, Didier Dormont, Jacques Chiras. Service de Neuroradiologie, Professeur Chiras, Hopital Pitié-Salpetriere, Paris, France. E-mail: [email protected]

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