[Ependymoma: electron microscopic criteria and demonstration of GFAP]

We report on the ultrastructure of 21 ependymomas and propose the following diagnostic criteria: The presence of glycogen is the most constant phenomenon, followed by desmosomes, cilia, basal bodies and microvilli. Fifteen tumors had 3 or more of these criteria. The allegedly typical nuclear pattern was found in only 6 out of 21 cases. Special ultrastructural features of basement membranes were seen in a mid-thoracic spinal ependymoma, and two supratentorial tumors showed neurosecretory granules. Eleven cases were further studied with the PAP-method for demonstration of GFAP. All these cases were positive, GFAP was shown to be accumulated perivascularly. Positive cells were also found between the vessels. This distribution is characteristic for ependymomas.