Medulloblastoma

Overview

Medulloblastoma is a malignant (cancerous) brain tumor that arises from the cerebellum, the part of the brain that controls balance, coordination and other complex functions. Most patients have symptoms of headache and vomiting, and can also have problems with balance and vision when they are diagnosed.

About 15 to 20 percent of all childhood brain tumors are medulloblastoma. It is diagnosed most commonly in children and adolescents. For most patients, the cause of medulloblastoma is unknown. However, there are a few rare, genetic syndromes that may increase a person's chance of developing medulloblastoma.

Medulloblastoma is a member of a larger group of tumors called primitive neuroectodermal tumors, or PNETs. PNETs typically look similar when observed under a microscope, but additional microscopic, biologic and clinical features help doctors distinguish the different types of PNET. Other PNETs that can occur in the brain include atypical teratoid/rhabdoid tumor (ATRT), pineoblastoma and supratentorial PNET. All PNETs, including medulloblastoma, have the ability to spread throughout the entire central nervous system.

While many patients can be cured, some forms of the disease are resistant to all treatments, at which point the disease becomes life-threatening. In addition, while conventional treatments can be effective for many patients, survivors are at risk for developing long-term side effects. These include possible learning problems, hearing problems, hormone and growth problems, fertility problems, and secondary cancers that can develop later in life.

Signs & symptoms

Because of their location, symptoms caused by the growth of medulloblastomas usually result from blockage of cerebrospinal fluid (CSF) flow, or from direct pressure on the brain and cranial nerves. The build-up of CSF in the brain is called hydrocephalus, and causes the common pattern of symptoms such as headaches, nausea, vomiting and difficulty walking. Direct pressure on cranial nerves adjacent to the tumor can also cause double vision and difficulty speaking or swallowing.

Diagnosis

When patients develop persistent headaches with vomiting, or symptoms caused by cranial nerve dysfunction, an imaging study is usually obtained. Although some patients will start with a CT scan of the head, an MRI is usually required to provide details of the tumor's location and its relationship to normal brain structures. Usually, additional images of the spine are also obtained to determine if the tumor has spread to the spinal cord.

Although there are several different kinds of tumors that can arise in the cerebellum, it is usually possible to narrow the diagnosis with advanced MRI scans.

Treatment

The most effective treatment for medulloblastoma is a combination of therapies that include surgery, radiation treatment and chemotherapy. Complete surgical removal of the tumor is important and is usually the first step in treatment. This is usually followed by radiation treatment to the entire brain and spine in older patients, followed by several months of chemotherapy.

Standard treatment for very young children — often defined as children less than 3 years old — includes surgical removal and chemotherapy. The use of radiation in this young age group is controversial, but some doctors are increasingly using radiation restricted to the area of the tumor. Because these young patients cannot tolerate whole brain and spine radiation, increasingly intensive doses of chemotherapy are being tested, including high-dose chemotherapy with autologous stem cell rescue, a form of bone marrow transplant.

With aggressive treatment, many medulloblastoma patients can be cured of the cancer. For patients 3 years or older, with "average risk" disease (defined as compete removal of the tumor and no signs of tumor spread to other parts of the central nervous system and body), who are treated with a combination of complete surgical removal of the tumor, radiation and chemotherapy, more than 80 percent can be cured.

Patients with "high risk" disease (the tumor has spread or cannot be completely removed with surgery) can still be cured, but the cure rates are lower. Treatment for younger patients, who are more prone to complications from extensive radiation treatment, is evolving. The goal is to identify effective strategies that will hopefully spare the patient the long-term complications of extensive radiation to the brain.