Ultrastructure of cerebellar hemangioblastoma. Some new observations on the stromal cells.

Five cases of hemangioblastoma were studied by electron microscopy with particular attention to the stromal cells and their surrounding structures. Most of the stromal cells of the tumor had abundant clear cytoplasm containing rough endoplasmic reticulum, mitochondria, scattered fibrils, and large lipid inclusions. They were usually aggregated without intervening cells. In the perivascular areas, their surfaces facing the perivascular collagen were surrounded by basal lamina. Their apposed cell membranes had occasional adhesive devices. Occasional, long, apparently cylindrical processes of the stromal cell cytoplasm were observed in some cases. These processes contained intermediate filaments of undetermined nature and microtubules. In the border zone between the tumor and the surrounding brain, the stromal cells were occasionally surrounded by narrow sheets of dark cell processes containing fibrils and glycogen granules, consistent with astrocytic processes. Altered neuronal elements were also observed in this area.