Walsh & Hoyt: Medulloblastoma

The term medulloblastoma is somewhat unfortunate because there is no such cell as a medulloblast. In fact, the cellular origin of these tumors, which usually develop in the cerebellum, is unclear. Some have postulated an origin in the fetal granular layer of the cerebellum. This subpial layer of small, primitive cells is present throughout the cerebellar cortex at birth, and gradually disappears during the first year of life as the cells migrate inward to augment the neurons of the definitive granular cell layer and differentiate into cortical neuroglia. An origin of medulloblastomas from these bipotential cells would explain the various microscopic appearances of these tumors in different patients, including the persistence of fetal granular layer tissue within medulloblastomas.