Epidermoids can be differentiated from arachnoid cyst on MRI by:
C i.e. Restricted diffusion Epidermoids can be differentiated from arachnoid cyst characteristically by hyper-intense diffusion weighted images because of restricted diffusion of epidermoid cystQ. FLAIR and proton images are less specific than DWI.
Contrast enhancement
Smooth margins
Restricted diffusion
CSF signal on FLAIR