Mondo Description A rare variant of diffuse astrocytoma. It is characterized by the presence of a conspicuous, though variable, fraction of gemistocytic neoplastic astrocytes. Gemistocytes are round to oval astrocytes with abundant, glassy, non-fibrillary cytoplasm which appears to displace the dark, angulated nucleus to the periphery of the cell. To make the diagnosis of gemistocytic astrocytoma, gemistocytes should amount to more than approximately 20% of all tumor cells. (Adapted from WHO)