Presentation
Headaches.
Patient Data
A well-defined extra-axial ovoid lesion at the base of the right frontal lobe. It appears inhomogeneous and hypointense on T1 and FLAIR, and T2-hyperintense with no enhancement seen on post-contrast T1. The DWI shows restricted diffusion.
Case 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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