Atypical Intracranial Epidermoid Cysts: Rare Anomalies with Unique Radiological Features

Figure 1

(a) Plain CT brain shows a lobulated, uniform hyperdense cystic lesion in right cerebellar hemisphere with coarse calcifications (black arrows) and no appreciable contrast enhancement (not shown). Note the acute angle the lesion makes with the calvarium and lobulated contour suggestive of its intraparenchymal location. Hydrocephalus involves the third ventricle and temporal horns of both lateral ventricles (white arrowheads) are due to the mass effect on the fourth ventricle. Histology confirmed the lesion as an epidermoid cyst. (b) T1-weighted (left) and T2-weighted (right) MRI images of the epidermoid cyst show mild T1 hyperintense and dramatic T2 hypointense signal (white arrows). The signal combination is completely opposite to the typical epidermoid cyst. There is no appreciable contrast enhancement after IV gadolinium (not shown). Note the lack of significant perilesional oedema in the cerebellum (arrowhead), a cardinal characteristic of an epidermoid cyst. (c) Diffusion weighted image (DWI) with factor 1000 (left panel), magnified masked apparent diffusion coefficient (ADC) (right upper), and unmasked ADC (right lower) images demonstrate no appreciable restricted diffusion with marked hypointensity on the DWI. While the hypointense signal in the masked ADC map may suggest restricted diffusion, this was a result of postimage processing of ignoring low intensity voxels of bones or air. Raw unmasked ADC map (right lower panel) confirms the lack of restricted diffusion, as evident by its isointense signal. (d) H&E section (×100 magnification) of the postsurgical specimen shows thin cyst wall (black arrows) with keratinizing squamous epithelium; features are compatible with an epidermoid cyst.

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