Medulloblastoma arising from an immature teratoma of the posterior fossa. Case report.

Teratomas, a group of nongerminomatous germ cell tumors, account for 3% of all childhood tumors. These unusual lesions reproduce the cellular and structural phenotypic traits associated with the three classic germ layers in inappropriate places in the body and often retain an embryonal character. These immature cells can differentiate into more malignant neoplasms. An intracranial location for this lesion type is rare. The authors describe the case of a 2-year-old boy with a teratoma of the posterior fossa that had partially differentiated into a medulloblastoma.