Gemistocytic astrocytes are essential components of malignant astrocytomas

Abstract

Malignant astrocytomas are characterised by the presence of a variety of cell types and according to the classification by Giangaspero & Burger, include small anaplastic cells, small fibrillated cells, fibrillated astrocytes, pleomorphic astrocytes, gemistocytic astrocytes, large bizarre cells and more recently, lipidized cells. Most classifications of central nervous system tumours retain gemistocytic astrocytoma as a distinct subgroup of low grade astrocytoma, but concede that, in a pure form, they rarely occur. In fact, there has been scanty information in recent literature concerning gemistocytic astrocytoma. We examined retrospectively 78 cases of glioblastoma multiforme and 33 cases of anaplastic astrocytoma, according to the diagnostic criteria of Burger & Vogel, and searched for geniistocyte-like cells, grading them +, ++, +++ when they were present focally, in small clusters and in sheets respectively. 51 glioblastoma multiforme (65%) and 21 anaplastic astrocytoma (54%) were found to contain gemistocytic foci. Overall, 44 cases (40%) contained ++ or +++ lesions, with areas that resemble a gemistocytic astrocytoma. However, careful examination invariably revealed a close intermingling with or transformation to small anaplastic cells, bizzare cells and lipidized cells and the occurrence of tumour necrosis and hyperplastic vascular elements in adjacent areas. Immunohistochemically, gemistocytes were mostly positive for GFAP and occasionally positive for cytokeratin. We conclude that gemistocytes are a carmon and essential cellular component of malignant astrocytomas. When gemistocytes <i>are</i> encountered in diagnostic neuropathology, deligent search for other histologic criteria for malignancy is warranted. A pure form of low grade gemistocytic astrocytoma is probably a pathologic curiosity.