Medulloblastoma

Abstract

Twenty medulloblastomas were studied comparatively through clinical and light and electron microscopic observations. Electron microscopy (EM) seemed important and, at times, essential in the structural characterization of these tumors. By light microscopic criteria alone, there were 12 “classical” undifferentiated cases, 7 cases showing astrocytic differentiation, and 1 “differentiated” but unclassifiable case. After reclassification by EM criteria, there were 7 undifferentiated cases, 10 cases with astrocytic differentiation, and 2 cases with neuronal differentiation; 1 case remained unclassified. The astrocytic tumor cells, showing formation of bundles of 8- to 10-nm glial fibrils, were considered true tumor cells and not “reactive” cells, whereas the neuronal tumors contained cells showing axonal processes, dense core granules, and synaptic-like structures. The authors conclude that medulloblastomas are neoplasms of a neuroepithelial embryonic origin and as such they may remain undifferentiated or may differentiate in either an astrocytic or a neuronal direction. The glial route is common, whereas the neuronal route is rare. Medulloblastomas should be subclassified by EM criteria into three groups: I, undifferentiated; II, astrocytic; and III, neuronal. This subclassification will be of value in predicting the potential for short vs. long term survival of the patient. Patients with astrocytic tumors (Subgroup II) had a longer survival than those with undifferentiated tumors (Subgroup I): 4.6 vs. 3.5 years. The undifferentiated tumors were located predominantly in the midline, whereas tumors showing astrocytic differentiation were located equally in the midline or in the cerebellar hemisphere. (Neurosurgery, 6: 398-411, 1980)