Congenital medulloblastoma: an inquiry into origins.

An infant aged 8 h died from cardiorespiratory causes. At autopsy, a microscopic midline cerebellar medulloblastoma was found. Neoplastic cells occurred within the fetal external granular cell layers, with invasion of perivascular spaces as well as the molecular and internal granular cell layers. This extremely rare occurrence lends support to the hypothesis that cerebellar medulloblastoma occurring in older patients originates within retained rests of primitive cells in the fetal external granular cell layer.