Microglioma, a histiocytic neoplasm of the central nervous system

Neuropathologists have long suspected the existence of a tumor derived from the microglia, which are the resident immunocompetent cells of the central nervous system. Previously, definitive characterization of this rare putative tumor was hampered by the lack of precise immunohistochemical reagents. We herein report on a patient with microglioma, and we define the immunohistochemical characteristics of the tumor. The patient was a 50-year-old white woman who presented with a 1-year history of progressive paresthesia, visual difficulties, and cranial nerve abnormalities. The patient died in June 1972. At autopsy, the brain weighed 1540 grams and was remarkable for a diffusely infiltrating periventricular tumor, which extended from the rostral tip of the lateral ventricles through the spinal cord. Microscopically, the tumor cells had extremely long, slender, twisted nuclei, and the cells diffusely infiltrated the brain parenchyma so that the extent of the tumor was difficult to determine. Formalin-fixed, paraffin-embedded tissue blocks from the neuropathology archives were studied. The neoplastic cells stained intensely with CD68 (KP1) and Ricinus communis agglutinin-120 markers for microglia and also with HAM-56, a marker for macrophages. The tumor cells stained negative for glial fibrillary acidic protein. The recent availability of precise immunohistochemical reagents has clearly defined this rare neoplasm and has facilitated reliable distinction from lymphoma and gliomatosis cerebri.