Non-Neoplastic Lesions of the Ependyma: A Neuropathological Overview.

Non-neoplastic lesions of the ependyma have been neglected to date in comparison with neoplastic lesions derived from the ependyma, that is, ependymoma. The ependyma has a simple structure: mono-layered cuboidal cells covering the surface of the cerebral ventricles and the central canal of the spinal cord. In this review, the histopathological appearances of various non-neoplastic ependymal lesions are shown based on the author's personal experience, along with a review of the relevant literature. Following the introductory remarks about the normal histology and functions of ependymal cells including tanycytes, non-neoplastic lesions are then presented including, obliteration of the spinal central canal; the "ventriculus terminalis"; shedding of ependymal cells and "granular ependymitis"; "ependymal incorporation"; ependymal cells in hydrocephalus; ependymal reactions to various noxious stimuli; ependymal changes in cerebral dysgenesis; infections involving ependymal cells; glio-ependymal cyst; and finally, various intracellular inclusions in ependymal cells. Non-neoplastic ependymal lesions are intriguing and merit further investigations, which may provide deeper understanding of various brain lesions and of ependymal neoplasms.