Central nervous system tumors with ependymal features: a broadened spectrum of primarily ependymal differentiation?

Ependymomas are well-characterized central nervous system (CNS) tumors that occur most often in children and young adults. Several other CNS tumor entities, including astroblastoma, chordoid glioma, papillary tumor of the pineal region, angiocentric glioma, and pilomyxoid astrocytoma, variably display histopathologic features of ependymal differentiation. The ependymal differentiation in some of these tumors is generally accepted, whereas in others, it is controversial. This article briefly reviews ependymal cell development and conventional ependymomas, the pathologic findings and clinical behavior of tumors with variable ependymal features, and the rationales for their inclusion with ependymomas or exclusion from a larger family of ependymal tumors. These issues are addressed in the context of early morphologic insights of Bailey and Cushing, Friede, and others; contemporary oncologic concepts; and recent relevant molecular and tumor stem cell studies.