OBSERVATIONS ON THE NATURE OF SUBEPENDYMOMA: AN ELECTRON MICROSCOPIC STUDY

Abstract

Surgical biopsy material from 4 cases of symptomatic 4th ventricle subependymoma, all with typical light microscopic features, was studied by EM. The ultrastructural appearance of each case was similar with small groups of tumor cell perikarya widely separated by a meshwork of cell processes containing glial filaments. Large cells lacking specialized features were prominent in all cases and showed similarities with ependymoglial precursor cells described in the adult subependymal layer of animals. Other cells showed either astrocytic or poorly developed ependymal features, and transitional forms between these 2 appearances were common, suggesting the tumor to be of a single cell type. Pockets of microvilli were present, but they differed from ependymal-type microrosettes in lacking tight junctional complexes. Unlike low grade atrocytomas, the extracellular space was small and there was no close associaion of tumor cell processes with blood vessels. The subependymoma may be regarded as a separate entity from other 4th ventricle neoplasms and possibly takes origin from ependymoglial cells normally present in the adult subependymal layer.