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 characteristics included a high density of small to medium-sized neuroepithelial cells with a uniform cytologic appearance, frequent mitotic figures, and numerous diagnostic ependymal rosettes and tubules. Differentiation was restricted to glial 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.