Epidermoid cyst

Discussion:

Differential diagnosis includes arachnoid cyst. On MRI, both epidermoid and arachnoid cysts usually have the same signal intensity on T1 and T2 (low T1 and high T2). On FLAIR sequence, an arachnoid cyst tends to follow the signal intensity of the CSF, whereas an epidermoid shows a high signal. Sometimes an epidermoid cyst may demonstrate a low signal intensity on FLAIR sequences (as in this case). The use of DWI resolves this dilemma, on which an epidermoid remains bright (restricted diffusion) whereas an arachnoid cyst follows the CSF signal intensity.

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