Histogenesis of sarcomatous component of the gliosarcoma: an ultrastructural study.

This report describes the ultrastructural findings of the sarcomatous component in five cases of gliosarcoma. The tumor contained a heterogenous population of cells with collagen scattered in the interstitium. Three main cell types were found: histiocyte-like cells, fibroblast-like cells and undifferentiated cells. The histiocyte-like cells had oval nuclei, short and flat rough endoplasmic reticulum, prominent Golgi apparatus, lysosomes, phagocytic vacuoles, ruffled cytoplasmic membrane with filopodia, segmental basal lamina and occasional intercellular junctions. The fibroblast-like cells had elongated nuclei, prominent cisterns of rough endoplasmic reticulum and microfilaments. The undifferentiated cell cytoplasmic processes suggesting differentiation toward histiocyte-like cell. In addition, intermediate cells, myofibroblasts, multinucleated giant cells and xanthomatous cells were also present. Occasional glial processes were interposed between tumor cells. Some were enclosed by cytoplasmic processes of histiocyte-like cells and others engulfed within the cytoplasm. Capillary showed surface infoldings, fenestrations of endothelial cells, thickened basal lamina, occasional pericytes and scattered collagen. Some capillaries were surrounded by aggregating histiocyte-like cells and undifferentiated cells. The present findings suggest that (a) the sarcomatous component in gliosarcoma is likely derived from undifferentiated cells with a broad differentiation into histiocytic, fibroblastic and other cell types, (b) endothelial cells and pericytes may not participate in sarcomatous development, (c) capillaries within the sarcomatous component are of non-gliomatous type, and (d) the histiocyte-like cells are capable of phagocytizing glial elements.