Cerebellar primary germ-cell tumor in a young boy.

Germ cell tumors originating in the posterior fossa are very rare. Described herein is a case of primary germ cell tumor (yolk sac tumor) found in the cerebellar vermis. A 5-year-old boy who complained of headache was admitted. CT and MRI revealed a tumor with diffuse enhancement by contrast medium in the right cerebellar vermis. Total removal was performed and a diagnosis of medulloblastoma or ependymoma was suspected. However, the tumor proved to be a yolk sac tumor with embryonal carcinomatous components from histological findings. Abnormally high levels of alpha-fetoprotein were found in blood and cerebrospinal fluid. Extensive examination indicated that the intracranial lesion had not metastasized from a primary extracranial tumor.