PNET (primitive neuroectodermal tumor) is a name used for tumors which appear identical under the microscope to medulloblastoma, but occur primarily in the cerebrum. PNET is used by some to refer to tumors such as the pineoblastoma, polar spongioblastoma, medulloblastoma, and medulloepithelioma. Except for medulloblastoma, these are all very rare tumors.
PNETs contain underdeveloped brain cells, are highly malignant, and tend to spread throughout the central nervous system. These tumors often contain areas of dead tumor cells (necrosis) and cysts. Fluid surrounding the tumor is not uncommon.
PNETs occur primarily in the cerebrum, but can spread to other parts of the brain and spine.
Because they tend to be large tumors, symptoms of increased pressure in the brain and mass effect are often present. Seizures are common.
Surgery is the standard initial treatment for these tumors. Because of their large size, tendency to spread, and extensive blood supply, total removal is rarely possible.
In children three years and older and in young adults, radiation therapy to the entire brain and spine usually follows surgery. Very young children are usually not treated with chemotherapy until they are older.
PNETs most often occur in very young children.