Most common site for medulloblastoma is-

POORLY-DIFFERENTIATED AND EMBRYONAL TUMOURS CNS tumors composed of primitive undifferentiated cells include medulloblastoma and glioblastoma, and rarely, neuroblastoma and retinoblastoma. Medulloblastoma is the most common variety of primitive neuroectodermal tumor. The most common location is the cerebellum in the region of roof of the fouh ventricle, in the midline of the cerebellum, in the vermis, and in the cerebellar hemispheres. Medulloblastoma is a highly malignant tumor and spreads to local as well as to distant sites. It invades locally and by the CSF to meninges, ventricles and subarachnoid space and has a tendency for widespread metastases to extraneural sites such as to lungs, liver, veebrae, and pelvis. Microscopically, medulloblastoma is composed of small, poorly-differentiated cells with ill-defined cytoplasmic processes and a tendency to be arranged around blood vessels and occasionally forms pseudorosettes (Homer-Wright rosettes). Ref: TEXTBOOK OF PATHOLOGY 6th EDITION - HARSH MOHAN PAGE NO:889