Atypical Intracranial Epidermoid Cysts: Rare Anomalies with Unique Radiological Features

Figure 2

(a) Plain CT brain (left) and magnified bone window (right) show an irregular, infiltrative mass in the left posterior cranial fossa with invasion into the cerebellum, calvarium (black arrow), and mastoid antrum (white arrow). The transverse sinus (white arrowhead) has also been invaded (compared to the normal transverse sinus on the right). No appreciable contrast enhancement is identified after IV contrast (not shown). Note the lack of perifocal oedema despite the aforementioned aggressive features. (b) T1-weighted (left) and T2-weighted (right) MRI images of the epidermoid cyst show the typical T1-hypo- and T2-hyperintense signal of an epidermoid cyst in the more anterior component. Heterogeneous signal intensity is noted in the most posterolateral component (black arrow). There is no perilesional oedema or appreciable contrast enhancement after IV gadolinium (not shown). (c) DWI with factor 1000 (left panel), masked ADC (right upper), and unmasked ADC (right lower image) demonstrate no significant restricted diffusion, as evident by the grossly isointense signal seen in the DWI and raw unmasked ADC map. (d) H&E section (×100 magnification) of the postsurgical specimen shows thick cyst wall of keratinizing squamous epithelium and amorphous keratin. Findings are compatible with an epidermoid cyst.

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