A medulloblastoma is a type of brain tumour that mainly affects children. These tumours can occur in adults but this is rare.
Medulloblastomas develop from poorly developed (primitive) cells and are sometimes also called primitive neuroectodermal tumours (PNET).
They occur in the cerebellum in a part of the brain called the posterior fossa (the area at the base of the skull attached to the spinal cord).
Medulloblastomas can spread to other parts of the brain or spinal cord, and occasionally to other parts of the body.