Medulloblastoma or PNET

What is a medulloblastoma?

Medulloblastoma (also referred to as primitive neuroectodermal tumor or PNET) is a malignant tumor that originates in the cerebellum, the back part of the brain that controls motor movement coordination, balance, equilibrium and muscle tone. These tumors have the capacity to spread (metastasize) through the spinal fluid, occurring in approximately 30 percent of cases. They rarely spread to bone and bone marrow.

Medulloblastomas are categorized by their microscopic appearance, as defined by the World Health Organization (WHO) Classification System. All medulloblastomas are WHO IV tumors and are considered malignant. The WHO classification further subdivides medulloblastoma:

  • classic medulloblastoma
  • desmoplastic/nodular medulloblastoma
  • medulloblastoma with extensive nodularity
  • large-cell/anaplastic medulloblastoma

Medulloblastoma is the second most common pediatric brain tumor, following astrocytoma, and it is the most common malignant brain tumor in children. Medulloblastoma accounts for 20 percent of childhood brain tumors. Approximately 500 cases of childhood medulloblastoma are diagnosed in the United States each year. The peak incidence of medulloblastoma is 4 years of age, although 20 percent occur in individuals over 15 years of age.

What are the symptoms of a medulloblastoma?

The symptoms of medulloblastoma are related to its location within the cerebellum. The most common early symptoms of medulloblastoma are increased intracranial pressure resulting in headaches, vomiting, lethargy, papilledema (swelling of the optic nerve seen on ophthalmology exam), and poor balance. These symptoms are present in up to 90 percent of patients by the time of diagnosis. Poor balance, known as ataxia, and poor hand coordination, known as dysmetria are often present. Double vision and head tilt are often seen due to pressure on the brainstem. Symptoms in babies frequently include increasing head size (macrocephaly), failure to thrive, and increased irritability.

How is a medulloblastoma diagnosed?

Patients suspected of having a brain tumor will undergo a magnetic resonance imaging (MRI) scan of the brain and spine to further define the location of the tumor and to assess if there is any metastatic (spread) disease. A biopsy of the tumor is required to make the final diagnosis and staging of medulloblastoma. All patients require a spinal tap (lumbar puncture) to assess for microscopic spread of the tumor in the spinal fluid.

How is a medulloblastoma treated?

Medulloblastoma is treated based on a number of factors, including the age of the child, the extent of surgical resection, the presence or absence of metastatic disease and the presence or absence of large cell/anaplastic (LC/A) histology.

Surgery: The initial treatment for medulloblastoma involves surgery to remove as much of the tumor as possible. Typically a complete removal is accomplished, but sometimes residual tumor may be left behind because it may be growing within normal brain structures. Surgery alone will not cure medulloblastoma and chemotherapy and usually radiation therapy may also be necessary.

About treatment for Medulloblastoma at Children’s Hospitals and Clinics of Minnesota

Our cancer and blood disorders program consistently achieves excellent results ranking it in the top 10 programs in the United States. Children’s Hospitals and Clinics of Minnesota treats the majority of children with cancer and blood disorders in Minnesota and provides patients access to a variety of clinical trials using ground-breaking new treatments. Through our renowned program, patients experience unparalleled family support, a nationally recognized pain management team, and compassionate, coordinated care.

Contact us

If you are a family member looking for a Children’s neuro-oncologist, please call our clinic at (612) 813-5940.

If you are a health professional looking for consultation or referral information, please call Children's Physician Access at 1-866-755-2121 (toll-free) and ask for the on-call hematologist/oncologist.

Additional information on Medulloblastoma

For additional information, check out these web sites:

National Cancer Institute

American Brain Tumor Association


Pediatric Brain Tumor Foundation