Imaging- On CT scans, epidermoids lesions usually have the same attenuation as that of cerebrospinal fluid (CSF); this characteristic makes their differentiation from arachnoid cysts difficult. Enhancement is rare, but can sometimes be seen around the margin of the tumor. Calcification occurs in only 15-20% of cases.

MRI characteristics: On T1-weighted images these lesions are generally slightly hyperintense or isointense relative to gray matter. More specifically, the T1-weighted signal intensity tends to vary with the lipid content. The lesions are usually isointense relative to CSF on T2-weighted images, but they may be slightly hyperintense. There are central areas of heterogeneity.

Enhancement of portions of the rim may be seen after the administration of contrast material. The remainder of the lesion does not enhance. Proton density–weighted and then fluid-attenuated inversion recovery (FLAIR) images were first used to differentiate epidermoids from arachnoid cysts. These sequences demonstrate epidermoids as being hyperintense relative to CSF. Now,diffusion-weighted imaging can be used to differentiate these entities, because epidermoids have markedly restricted diffusion and, therefore, high signal intensity on the diffusion-weighted trace images. The free water in arachnoid cysts has low signal intensity. Diffusion-weighted images are helpful in assessing residual epidermoid tumors after surgical resection.
Introduction

Epidermoid cysts or tumors are benign congenital lesions of ectodermal origin.that arise from ectopic ectodermal cells retained within the neural groove at the time of closure (at 3-5 weeks' gestation).Due to their slow growth however
Age group -  presentation is by 20-40 years of age.

 The most common locations are within the cerebellopontine (CP) angle, parasellar region, and middle cranial fossa. The CP angle is the most common site for epidermoids.  meningiomas. Occurrences within the ventricular system, brain parenchyma, and even the spinal cord, . Although the vast majority of epidermoids are intradural, they can be extradural.