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A medulloblastoma is a fast-growing, very aggressive malignant brain tumor that usually forms in the cerebellum, an organ in the lower back part of the brain. (On the World Health Organization’s tumor grading system, a medulloblastoma is a Grade 4.) It’s the most common type of malignant brain tumor in children — 20 to 30 percent of pediatric brain tumors are medulloblastomas, and almost two-thirds of medulloblastomas develop in those under age 20. It is less common in adults, but about a third of all medulloblastomas occur in young adults, usually young men.  Medulloblastoma rarely occurs after age 45.

Medulloblastomas are a type of “embryonal tumor,” or “primitive neuroectodermal tumor” (PNET), meaning that they develop from immature cells left over as the central nervous system develops during pregnancy. They share many properties with other PNETs in other parts of the nervous system, including retinoblastoma and pineoblastoma. 

Medulloblastomas develop near the fourth ventricle, which is filled with the cerebrospinal fluid (CSF) that circulates throughout the brain and spine. This location allows medulloblastomas to spread quickly through the fluid surrounding the brain and spine, but it is relatively rare for them to spread beyond the central nervous system.

What Causes Medulloblastomas?
Researchers don’t know what causes a medulloblastoma to form — there are no known risk factors, and there is nothing that can be done to prevent them. In rare cases, the tumor can be associated with familial syndromes including Gorlin’s syndrome, Turcot’s syndrome, Li-Fraumeni, and Rubenstein-Taybi syndrome.

Medulloblastoma is a serious diagnosis, but when treated by experts at an advanced medical center the prognosis is good. With treatment, cure rates in the best circumstances reach 70 to 80 percent.  Read more about Doctors Who Treat Medulloblastoma in Children, or request an appointment using our online form.

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Reviewed by: Caitlin Hoffman, M.D.
Last reviewed/last updated: June 2017
Illustration by Thom Graves, CMI