medulloblastoma /mədul′ōblastō″mə/ [L, medulla + Gk, blastos, germ, oma, tumor] , a poorly differentiated malignant neoplasm composed of tightly packed cells of spongioblastic and neuroblastic lineage. The tumor usually arises in the cerebellum, occurs most frequently at 5 to 9 years of age, and affects more boys than girls. Medulloblastomas are extremely radiosensitive and grow rapidly. The prognosis is poor.
