An intracranial epidermal cyst in a Sprague-Dawley rat.

An intracranial epidermal cyst was found incidentally in a 10-week-old female Sprague-Dawley rat. The cyst was located in the leptomeninx of the longitudinal cerebral fissure, ventral to the corpus callosum and dorsal to the third ventricle. It was approximately 0.7 mm in diameter, lined by stratified squamous epithelium and filled with concentric layers of desquamated keratin. The wall consisted of 2-4 layers of cells. Ultrastructurally, the sequence of epidermal differentiation was not normal in that the basal cell layer and was absent in certain areas. The adjacent brain tissues were slightly compressed but not otherwise damaged by the cyst.