INTRACRANIAL MALIGNANT FIBROUS HISTIOCYTOMA - CHARACTERIZATION OF GFAP-POSITIVE CELLS IN THE TUMOR

A case of malignant fibrous histiocytoma (MFH) arising in the cerebell opontine angle of a 57-year-old woman was reported. The immunohistoche mical and electron microscopic findings indicated distinct fibrohistio cytic nature and myofibastic differentiation of this peculiar tumor. I mmunohistochemistry disclosed that the tumor cells expressed monocyte/ macrophage markers including CD-68, MAC 387, and alpha-1-antichymotryp sin. In addition, the neoplasm contained scattered glial fibrillary ac idic protein (GFAP)-positive cells which made small nests in some area s. These GFAP-positive cells had bundles of densely packed intermediat e filaments and scanty organellae in the cytoplasm, as demonstrated by an immunostained-semithin and serial-ultrathin section method. By imm unostaining of MIB-1 and GFAP, and silver nucleolar organizer region ( AgNOR) impregnation on serial sections, the GFAP-positive cells were n ot labeled by MIB-1 and their AgNOR counts averaged 1.13/nucleus. Thus , these GFAP-positive cells seem to have lower proliferating activity than neoplastic astrocytes. It is concluded that they may be nonneopla stic astrocytic cells involved by MFH.