Is subependymoma (subependymal glomerate astrocytoma) an astrocytoma or ependymoma?: A comparative ultrastructural and tissue culture study

A fourth ventricle lesion containing both areas of typical ependymoma and subependymoma has been studied with the electron microscope. Both foci show ependymal and astrocytic elements. In the subependymoma, a larger number of astrocytes, more frequent cytoplasmic degeneration, and increased glial filaments in the ependymal cells are found. These cellular changes in the subependymoma yield a distinctive light microscopic appearance. However, at the ultrastructural level, the similarity of cellular components, i.e. ependymal and astrocytic cells, makes us believe that subependymoma is a variant of ependymoma and not pure astrocytoma. Tissue culture study and further electron microscopic observation of these in vitro cells have also confirmed the presence of both ependymal and astrocytic cells. Like in vivo ependymal cells, these in vitro ependymal cells form not only glial filaments but also rosettes with specialized cell junctions, microvilli, and cilia. Perivascular pseudorosette formation is also described in detail.