MEDULLOBLASTOMA (PNET) - CHILD

Medulloblastoma is a type of primary brain tumor that mainly affects children and young adults. It typically arises in the cerebellum, but can spread elsewhere in the brain or throughout the central nervous system. About 25 to 30 percent of medulloblastoma patients are found to have unsuspected dissemination (spread) of the disease at the time of diagnosis.

There are many different types of brain cancer and the categories by which they are classified tend to change or 'evolve' every few years. Brain tumors are mainly classified on the basis of what is called their histologic type. This term describes the appearance of the cancer cells found in specimens under the microscope. However, brain tumors may also be classified by where the initial tumor is found in the brain, or how far the tumor has spread to other portions of the brain or the central nervous system.

One term you are likely to hear in regard to medulloblastoma is "infratentorial." If we break the term down into its Latin roots, "infra" means "below," "underneath" or "within," while "tentorial" refers to the "tentorium," which is a fold of the tough, fibrous membrane or dura mater (one of the three meninges, or covering membranes of the brain and spinal cord) that forms the outer envelope of the brain. The English word "tent" is derived from the same Latin root, and you can think of the tentorium as a kind of "tent" that covers a portion of the brain.

About half of all brain tumors in children are infratentorial. Three quarters of these are located in the cerebellum or fourth ventricle. Some of the common infratentorial tumors include:

• medulloblastoma
• cerebellar astrocytoma
•  ependymoma
• brain stem glioma

The typical location for a medulloblastoma is in the cerebellum, mostly in the midline or the area known as the posterior vermis.

It is possible that you have been told that your child has "PNET," rather than medulloblastoma. The term PNET was introduced to encompass both medulloblastoma and other tumors that have a similar appearance under the microscope and similar clinical features. These include:

• Ependymoblastoma
• Pineoblastoma
• Cerebral neuroblastoma
• Multidifferentiated supratentorial PNET