The ultrastructure of glial tumors of astrocytic lineage: a review.

In order to complete the classical descriptions of astrocytic tumors, I report here ultrastructural findings regarding this group of neoplasms. Fibrillary astrocytomas consisted of a mixture of cell bodies and their processes. Nuclei were indented and contained various types of nuclear bodies or filamentous paracrystalline inclusions. The cytoplasm with innumerable glial filaments was observed. Gemistocytic cells contained slightly more indented peripherally located nuclei while the whole cytoplasm was densely filled with glial filaments. The typical cells for the granular part of the astrocytic tumors and the granular tumors of astrocytic lineage contained the intracytoplasmic bundles of glial filaments and membrane-bound autophagic vacuoles. Pilocytic astrocytes were in the typical way elongated and contained many glial filaments in parallel bundles. Hirano bodies were rarely seen. Rosenthal fibers consisted of large electron-dense granular or amorphous masses merging at the periphery with glial filaments. In a case of the pleomorphic xanthoastrocytoma the electron microscopy showed numerous astrocytes connected by many long plaque-like junctions or hemidesmosomes with dense bundles of collagen fibrils. The majority of the astrocytes were covered with basal laminae, forming a complicated labyrinth-like pattern invaginated in astrocytic cytoplasm. Other astrocytes included also numerous vacuoles containing myelin figures and whorls. In a case of the subependymal giant cell astrocytoma, giant cells contained innumerable glial filaments, numerous ribosomes, distended endoplasmic reticulum, electron-dense bodies and peculiar crystalloids. Secondary glioblastomas retained clear stigmata of astrocytic tumor but the nuclei seemed to be more intended, cisterns of the endoplasmic reticulum appeared to be distended and frequently intranuclear pseudoinclusions were observed.