medulloblastoma
A malignant, invasive embryonal neoplasm arising from the cerebellum. It occurs predominantly in children and has the tendency to metastasize via the cerebrospinal fluid pathways. Signs and symptoms include truncal ataxia, disturbed gait, lethargy, headache, and vomiting. There are four histologic variants: classic medulloblastoma, large cell/anaplastic medulloblastoma, desmoplastic/nodular medulloblastoma, and medulloblastoma with extensive nodularity.