Ultrastructure of ependymoma.

Twenty-six ependymomas were studied by light and electron microscopy. By electron microscopy, the acellular zones around small vessels in light microscopic sections were seen to be composed of large numbers of closely packed, filament-rich, cytoplasmic processes ringing small vessels. Lumina were consistently present but many of them were too small to be seen by light microscopy. The lumina contained slender, curving microvilli and variable numbers of cilia. Their bordering cells were connected by unusually long tight junctions. Electron microscopy can be useful to establish or confirm a diagnosis of ependymoma when the light microscopic appearance is atypical, or when the tumor arises in an unusual location. The clinical data on the 26 cases has been reviewed; follow-up information was available on 23 patients.