Medulloblastoma and PNETs

What Is It?

Medulloblastoma is a brain tumor which occurs most frequently in children, accounting for about 30% of all pediatric brain tumors. It is named for its site of origin, in an area called the superior medullary velum, which is associated with the midline of the cerebellum, a large part of the brain that is important for motor coordination and balance. However, the tumor can spread from this origin to involve other parts of the central nervous system. Spread outside of the nervous system is also possible, but rare.

Most cases of medulloblastoma occur sporadically without a known cause. It is by far most common in young children, but can rarely occur in adults as well. However, a small number are associated with hereditary disorders such as Gorlin syndrome, blue rubber-bleb nevus syndrome, Turcot syndrome and Rubinstein-Taybi syndrome.

Medulloblastoma is in a family of related brain tumors called primitive neuroectodermal tumors (PNET). PNETs can occur throughout the brain but this location in the cerebellum is the most common. Other examples of tumors considered to be in this family of brain tumor include pineoblastoma, ependymoblastoma, retinoblastoma, central neuroblastoma, and peripheral neuroblastoma.


What Types of Symptoms Are Typical?

Because of its location in the cerebellum and near the 4th ventricle, a fluid-filled space in the brain, the most common presenting symptoms are cerebellar dysfunction and hydrocephalus.

Cerebellar dysfunction typically causes difficulty with motor coordination, particularly for gait and balance. Less commonly, poor coordination of the arms can occur.

Obstructive hydrocephalus, which results from the tumor blocking the normal flow of cerebrospinal fluid in the ventricles, leads to increased pressure in the ventricles which can lead to other neurological deterioration as well as headache, nausea and vomiting. In very young infants, the hydrocephalus can lead to enlargement of the head.

Later in the course of disease, if tumor spreads to other parts of the nervous system, neurological symptoms can occur, including cranial nerve dysfunction and spinal cord symptoms.


How Is The Diagnosis Typically Made?

After a neurological examination which suggests a tumor, a CT scan or MRI scan of the brain is generally performed. These imaging studies can help identify the tumor, its size and location. While the appearance and location of medulloblastoma typically clues doctors in to this diagnosis, any tumor needs tumor tissue examination to make the definitive diagnosis. Patients will often get imaging of the spine as well to determine if the tumor has spread elsewhere in the nervous system.


What Are Some Common Treatments?

Surgery is often recommended for medulloblastoma. The goal of surgery is to obtain tissue for diagnosis and usually to attempt to remove as much of the tumor as possible. Better long-term survival can occur with complete tumor removal but this is not always possible depending on the size of the tumor and other factors.

Other options which are considered in each case are radiation treatment, although this can be contraindicated in very young children due to the injury it can do to the developing nervous system, and chemotherapy. The specifics of the treatment for each case is variable and should be discussed with the patient with their own physician team.

Patients who present with hydrocephalus will sometimes require a separate procedure, such as a shunt or endoscopic third ventriculostomy, to treat the hydrocephalus. However, this condition will sometimes be cured simply by removal of the tumor itself.



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Important Note: This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.

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