Posterior fossa tumors.

Cerebellar and fourth ventricle tumors are usually associated with hydrocephalus, which is now treated with ventriculostomy and tumor removal so that permanent shunts are needed in only one third of children. Complete removals decrease the recurrence rate of cerebellar astrocytomas and ependymomas. Postoperative staging with spinal magnetic resonance imaging has decreased the need for myelography. Adjuvant chemotherapy improves the survival of children with high-stage medulloblastomas.