Fine structure of an intracerebral epithelial cyst

The wall of an intracerebral extraventricular cyst was studied with the electron microscope. The lining of the cyst consisted of a single layer of nonciliated, flattened or cuboidal epithelium similar to that in an ependyma. Unlike the ventricular ependyma, the lining cells of the cyst were bordered by a continuous basement membrane abutting on the leptomeninges or on the compressed brain tissue and thus shared some morphological similarities with the choroid plexus epithelium. Although pathogenesis of the cyst remains obscure, the fine structure of the lining cells is suggestive of their neuroepithelial origin. The occurrence of abundant pinocytotic vesicles in these cells further suggests the possibility of cellular transport of fluid to account for the continued expansion of the cyst.