Ependymoblastoma. A reappraisal of a rare embryonal tumor

This article reviews the clinicopathologic features of 12 ependymoblastomas, including those of 7 previously unreported cases. The histologic charateristics included a high density of small to mediumsized neuroepithelial cells with a uniform cytologic appearance, frequent mitotic figures, and numerous diagnostic ependymal rosettes and tubules. Differentiation was restricted to glil precursor cells and to cells with the differentiating features of ependymal cells. Cytogenetically, the tumor cells with the differentiating hallmarks of ependymal cells but which have retained their mitotic activity were considered to be ependymoblasts. Many of the rosettes in the tumors were of the ependymoblastic type, but ependymal rosettes were also present. The absence of pleomorphism, giant cells, multinucleation and pseudopalisades, and the scanty proliferation of vascular endothelial cells are additional features that delineate this tumor from an anaplastic (malignant) ependymoma. The median age of the patients was 2 years. After surgical treatment the median survival time was 12 months. Because of the frequency of leptomeningeal involvement, whole neuraxis radiation should be considered. Cuncer 55:1536-1542, 1985. HE EPENDYMOBLASTOMA has been defined as a T special type of embryonal central nervous system (CNS) neoplasm arising in young subjects and in which the cytologic features of a primitive, highly cellular neuroepithelial tumor are associated with the presence of numerous ependymal rosettes.' Since the earlier description by one of us (L.J.R.) of two such tumors, the existence of this exceptional entity has been confirmed in three further report^.^-^ Although the morphologic features of these examples clearly separate them from those malignant ependymomas in which cellular anaplasia has supervened upon a more differentiated neoplasm, confusion is still apparent on this distinction in a recent histologic classification of CNS t~mors,~ as well as on the definition of the ependymobla~toma.~