QUIZ: No. 27, 20/09/2025

CT

MRI

ANS – White Epidermoid Cyst (Right Frontal Region)

Findings – Well-defined extra-axial lobulated lesion is seen in the right frontal region. On CT, the lesion appears hypodense with patchy areas of peripheral calcification. On MRI, the lesion is hyperintense on T1-weighted images, consistent with the “white” epidermoid variant. It demonstrates variable, heterogeneous signal on T2WI and FLAIR sequences. The lesion is hyperintense on DWI with corresponding hypointensity on the ADC map, confirming restricted diffusion. No significant perilesional edema or post-contrast enhancement (image not provided) is noted.

Both classical and white epidermoid cyst: Well-defined, lobulated, extra-axial lesion with restricted diffusion.

Classic epidermoid → T1 hypointense, T2 hyperintense (CSF-like).

White epidermoid → T1 hyperintense, T2 variable.

Differentials for T1 hyperintense lesions: Dermoid cyst, colloid cyst, subacute hematoma.

Clue: Only epidermoids (classic or white) show restricted diffusion consistently.

Take home points

·  T1 hyperintensity + restricted diffusion is diagnostic of White Epidermoid Cyst, differentiating it from other T1 bright lesions