Medulloblastoma is a type of aggressive brain tumor that primarily occurs in children, typically arising in the cerebellum, which is responsible for coordination and balance. It is classified as a primitive neuroectodermal tumor (PNET) and can spread to other parts of the central nervous system. Symptoms may include headaches, nausea, vomiting, and coordination difficulties. Treatment usually involves a combination of surgery, radiation therapy, and chemotherapy.