Radiological Imaging of Intra-Cranial Dermoid Tumors.

DR/ ABD ALLAH NAZEER. MD.

OverviewDermoid tumors are not true neoplasms but are inclusion cysts composed of ectodermal elements. They are uncommon, usually benign lesions, accounting for approximately 0.3% of all brain tumors and occur 4-10 times less frequently than do epidermoid tumors. Dermoid tumors are often discussed with epidermoid tumors because of their similar appearance and developmental origin.

Intracranial dermoid cysts are uncommon lesions with characteristic imaging appearances. They can be thought of as along the spectrum: from epidermoid cysts at one end (containing only desquamated squamous epithelium) and teratomas at the other (containing essentially any kind of tissue from all three embryonic tissue layers). On imaging, they are usually well-defined lobulated midline masses that have low attenuation (fat density) on CT and high signal intensity on T1-weighted MR images. Typically they do not enhance after contrast administration.

EpidemiologyDermoid cysts account for ~0.5% of all primary intracranial tumours and are slightly more common in females. Typically, dermoid cysts present in the first three decades of life. Clinical presentationMany intracranial dermoid cysts are asymptomatic and are only found incidentally. Often there is a long history of vague symptoms, with headache being a prominent feature. Symptomatic clinical presentation usually occurs in one of two ways: mass effect

compression of adjacent structures, e.g. optic chiasmrupture (spontaneous, traumatic, or iatrogenic (at resection))

leakage of sebum into the subarachnoid space results in aseptic chemical meningitisthe presentation is variable, ranging from a headache to seizures, vasospasm, and even death.

PathologyDermoid cysts are thought to occur as a developmental anomaly in which embryonic ectoderm is trapped in the closing neural tube between the 5th-6th weeks of gestation.Dermoid cysts, like epidermoid cysts, are lined by stratified squamous epithelium. Unlike epidermoid cysts, however, they contain epidermal appendages as well, such as hair follicles, sweat glands and sebaceous glands. The latter secrete the sebum that gives the characteristic appearance of these lesions on CT and MRI.A common misconception is that dermoid cysts contain adipose tissue. This is not the case, as lipocytes are mesodermal in origin, and dermoid cysts by definition are purely ectodermal. A dermoid cyst with adipose tissue would be a teratoma.

Radiographic featuresIntracranial dermoid cysts are typically located in the midline, although they can grow towards one side or the other. Locations include:posterior fossa / vermissuprasellar/sub-frontalIt is interesting to note that publications vary regarding the most common location of dermoid cysts.Plain radiograph: Historically, when skull x-rays were routinely used in the assessment of suspected intracranial pathology, a focal lucency dueto the low density of fatty sebum, would suggest the diagnosis. CT Typically dermoid cysts appear as well defined low attenuating (fat density) lobulated masses. Calcifications may be present in the wall. Enhancement is uncommon, and if present should at most be a thin peripheral rim.Very rarely they demonstrate hyperdensity, thought to be due to a combination of saponification, microcalcification and blood products. This most often occurs when present in the posterior fossa, although the reason is uncertain.

MRI Unlike intracranial lipomas that follow fat density on all sequences, intracranial dermoids have more variable signal characteristics:T1

typically hyperintense (due to cholesterol components)hyperintense droplets in the subarachnoid space may be visible if rupture has occurred

T1 C+ (Gd): generally do not enhanceextensive pial enhancement may be present in chemical meningitis caused by ruptured cysts

T2: variable signal ranging from hypo- to hyperintense

Intra-diploic epidermoid (a) X-ray skull AP view shows an expansile lesion in the right temporal bone. (b) X-ray skull lateral view shows the lesion is lytic. (c) X-ray skull Towne's view shows the lytic lesion in the temporal bone has sclerotic margins

Intra-diploic epidermoid, (a), Axial CT image, bone window, shows intradiploic lesion involving the right temporal and mastoid region of the skull. (b) Coronal CT images of the skull on bone window settings demonstrate erosion and involvement of the inner table of the skull in the vicinity of the lesion. (c) Axial CT image, soft tissue settings shows a hypodense lesion in the diploic space of temporal mastoid region of the skull. (d) Axial CT image shows the lesion is clear of middle ear cavity and normal ossicles seen in the middle ear, and is intradiploic in location

Intradiploic epidermoid, a) T1-Weighted MR image shows a hypointense well marginated lesion in right temporal diploic space, with few areas of high signal intensity within it. (b) The lesion on T2-Weighted MR image appears hyperintense. (c) Fat saturated MR image shows suppression of high intensity areas of the T1 image but the non fatty major component does not show signal suppression, Diffusion images show restricted diffusion and contrast study show thick rim enhancement, related to infected lesion.

Intradiploic epidermoid inclusion cyst with classic radiologic features in a 1 9-year-old man. (a) Lateral skull radiograph shows a well-demarcated lyric defect with sclerotic and scalloped margins, suggestive of a slowly expanding mass. (b) Axial contrast material-enhanced CT scan shows an expansile, nonenhancing, intradipolic mass; its attenuation is low but higher than that of fat in the scalp. The inner margin of the mass is formed by a combination of the dura mater and the remodeled inner table of the skull and appears sclerotic and slightly nodular. (c) Axial Tl-weighted MR image shows the ovoid lesion within the diploic space. The mass is hyperintense relative to) cerebrospinal fluid. (d) On the gadolinium-enhanced Ti-weighted MR image, the lesion has signal intensity near that of water. (e) On the T2-weighted MR image, the mass becomes quite bright. Lateral intradipolic epidermoid lesions are usually not associated with any other malformations.

Dermoid and epidermoid tumors show peripheral stippled calcification, teratomas show internal calcification.

Pineal Teratoma.

Ruptured intracranial dermoid cyst.

Images of a ruptured pineal region dermoid.

Cerebello-pontine angle Epidermoid.

Cerebello-pontine angle Epidermoid.

left Cp angle Epidermoid cyst.

MRI of brain T1W images axial view. (a and b) pre-operative showing right cerebello-pontine angle and prepontine epidermoid. (c and d) Post operative, showing no residual tumor but there is residual dead space.

Intracranial epidermoid cyst.

Skull Vault Epidermoid.

Epidermoid cyst.

Two single axial CT images demonstrate a peripherally calcified, fat density mass in the middle cranial fossa. This is the superior extent of the dermoid cystic tumor (solid arrow). Additionally, there are multiple locules of fat (broken arrows) throughout the subarachnoid space and ventricular system at these levels.

(a) T1-weighted MRI, (b) T1 midline sagittal, and (c) T2-weighted MRI images demonstrate a hyperintense lesion in the middle cranial fossa corresponding to the dermoid tumor (solid arrows). Note scattered foci of hyperintensity throughout the subarachnoid space (broken arrows). The lesion was intimately associated with the left middle cerebral artery, which is apparent on the T2-weighted image (c).

Imaging study of the ruptured intracranial teratoma. A. Non-contrast CT, low density lesion in the fourth ventricle; B. Non-contrast CT, enlarged ventricles with hypodense lesions (arrows) in the lateral ventricles; C. Sagittal contrasted T1 MRI demonstrating fourth ventricular lesion; and D. Axial non-contrast T1 MRI demonstrating increased signal (arrows) in the lateral ventricles.

CT and MR Studies of Giant Dermoid Cyst Associated to Fat Dissemination at the Cortical and Cisternal Cerebral Spaces.

A 17-year-old girl was diagnosed at age 3 with a suprasellar dermoid cyst following complaints of headaches. At 15, headache worsened, with nausea, vomiting, and confusion. Headache was sudden,

severe, and pressure-like. Repeat brain MRI showed rupture of the dermoid cyst into the subarachnoid space

Dermoid / epidermoid cyst

A, CT scan revealed a hyperdense lesion containing irregular isodense area in the posterior fossa; The lesion presented hyper-intensity on T1WI (B), hypo-intensity on T2WI (C). D, macroscopic view of the removed lesion; E, interstitial hemorrhage within dermoid cyst; F, squamous epithelium, calcification, keratinous materials and cholesterol deposits. 

Coronal and Sagittal T1WI with a mild midline septal shift to the left is noted; this is due to compression of the right lateral ventricle by the dermoid tumor.

A large, well-circumscribed, low-attenuating, cystic lesion is present in the right temporal lobe, lateral to the cranial midline. Note the peripheral, marginal calcification in the lesion. No erosion is seen in the adjacent bone of the sella.

Rupture Intracranial dermoid cyst.

(a) MRI of brain TW1 image, sagittal view showing 4th ventricular epidermoid (Ep), (b) Per operative view showing 1-incised dural margins, 2-cerebellar tonsil, 3-Posterior inferior cerebellar artery, 4-floor of 4thventricle, and 5-epidermoid tumor

MRI of brainT1W images (a) sagittal view showing suprachiasmatic prelamina terminalis sub frontal epidermoid with hyper intense peripheral zone, (b) and (c) axial showing hyperintense epidermoid content in frontal and temporal horn (after rupturing into ventricle).

 Axial CT scan of the same patient of Figure 3. a, b, and c (pre-operative)- showing suprasellar epidermoid with calcified wall, d, e, and f (post-operative)-showing left sided fronto-temporal extradural collection with tumor dead space due to failure to collapse tumor wall (calcified).

MRI of brain T1W images sagittal views, (a) preoperative, showing pineal region epidermoid, (b) postoperative, showing no residual tumor

 MRI of brain showing pineal region epidermoid tumor, A-axial view and (b) sagittal view. (c) and (d) Post operative MRI axial and sagittal view respectively showing hyperintense residual tumor.

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