Minigemistocytes and oligodendrocytic cells in mixed oligoastrocytomas: Immunohistochemical and Ultrastructural studies

In five mixed oligoastrocytomas, minigemistocytes and fibrous astrocytes showed similar immunoreactions to glial fibrillary acidic protein (GFAP), vimentin (VM) and cytokeratin. Some oligodendrocytic cells also exhibited immunoreactivities to these intermediate filaments. Intercellular myelin basic protein immunoreactive products were not associated with any tumor cell. Four recurrent tumors exhibiting GFAP and VM immunoreactions were found to consist of anaplastic astrocytes and irregular round cells with scanty cytoplasm rather than typical oligodendrocytic cells and minigemistocytes. Ultrastructurally, the three types of tumor cells showed cytoplasmic organelles in common, appearing light in electron density and exhibiting few characteristics of mature or immature oligodendrocytes. The number of intermediate filaments was the only significant ultrastructural difference among them; moderate to many in fibrous astrocytes and minigemistocytes, a few to moderate in some oligodendrocytic cells, and few in other oligodendrocytic cells. Immunohistochemically and ultrastructurally, minigemistocytes, GFAP‐positive oligodendrocytic cells, and possibly GFAP‐negative oligodendrocytic cells appeared to belong to an astrocytic lineage rather than transitional cells between oligodendrocytes and astrocytes.