Epidermoid cyst

Discussion:

This case illustrates a cystic extradural mass within the right middle cranial fossa are almost pathognomonic of an epidermoid cyst: high T2 signal partially suppressed on FLAIR, intermediate restricted diffusion on ADC and high DWI signal,  and no contrast enhancement. 

The intrinsic T1 and high signal along the medial border is unusual, but likely represents a component of what is referred to as "white epidermoid", recognized variant. The lack of central enhancement, and markedly increased DWI signal makes a chondroid lesion, or cavernous sinus hemangioma much less likely. The absence of a fatty component essentially excludes a dermoid/mature cystic teratoma.

The patient went on to have a resection, which not only confirmed the diagnosis but also confirmed that the lesion was extradural. 

Histology

MICROSCOPIC DESCRIPTION:  Paraffin sections show multiple fragments of laminated keratin consistent with the contents of an epidermal cyst. No hair remnants or mesenchymal elements are seen. No cyst lining is identified.

FINAL DIAGNOSIS: Contents of epidermal cyst.

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