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Brain Tumour - Medulloblastomas

Medulloblastomas are the most common malignant (spreading) brain tumors in children. They account for as many as 30% of all solid brain tumors. Medulloblastomas are a type of primitive neuroectodermal tumor (PNET). They occur near the base of the skull and can spread to the spine or other parts of the body. They are thought to arise from primitive (undifferentiated) nerve cells left over from the gestational development of the nervous system. Because the tumors are malignant, they tend to spread easily through the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord. In rare cases, the tumors may spread beyond the central nervous system.

What are the symptoms of Medulloblastomas?

Medulloblastomas typically arise near the fourth ventricle, a chamber of the brain filled with cerebrospinal fluid. As a result, these tumors often result in a condition called hydrocephalus, in which the flow of CSF is disrupted and pressure inside the skull increases, resulting in symptoms, including:
  • irritability
  • nausea and vomiting
  • morning headache or headache that goes away after vomiting
  • weakness or change in sensation on one side of the body
  • seizures
  • unusual sleepiness or change in energy level
  • change in personality or behavior
  • unexplained weight loss or weight gain
More advanced symptoms associated with medulloblastomas include:
  • loss of coordination
  • problems with walking and balance
  • dizziness
  • double vision
How are Medulloblastomas diagnosed?

Diagnosis begins with a physical examination and history. As with other brain tumors, imaging studies are the key component in the diagnosis of medulloblastomas.

Magnetic resonance imaging (MRI) scans are used primarily. This imaging test can show the size and characteristics of the tumor, as well as the presence of Hydrocephalus.

Computed tomography (CT) scans also are used. For either study, an agent that provides contrast in the image is administered intravenously so neurological surgeons can visualize the tumor against the normal brain in the background.

Example of a Brain Tumour on MRI.

Treatment of Medulloblastomas

To determine and implement optimum therapy, treatment planning by a multidisciplinary team of cancer specialists who have experience treating childhood brain tumors is required. Treatment options depend on:
  • the age of the child, overall health and medical history when the tumor is found
  • the type, location and size of the tumor
  • the amount of tumor remaining after surgery
  • whether the cancer has spread to other parts of the central nervous system, such as the meninges (membranes covering the brain) or spinal cord
  • whether the cancer has spread to other parts of the body, such as the bone or lung
  • the child’s tolerance for specific medications, procedures, or therapies
  • how doctors expect the child’s disease to progress
Medulloblastomas may be treated with surgery, radiation therapy, chemotherapy and sometimes by implanting a ventriculoperitoneal shunt.

The primary goal of surgery for medulloblastomas is to remove as much tumor as possible and to restore the flow of CSF without producing neurological deficits. Surgery also provides tissue samples that can be used to obtain an accurate diagnosis. However, these tumors tend to spread, making total surgical removal of the tumor difficult. Follow-up treatment is necessary. Several studies have recommended aggressive surgical resection followed closely by both radiation therapy and chemotherapy.

Radiation therapy, using high-energy x-rays or other types of radiation to kill tumor cells is often used. Radiation therapy is not recommended for young developing brains and is avoided in children under the age of three. Radiation therapy, if needed, is technically very demanding and should be carried out in centers that have experience in that area to ensure optimal results.

Chemotherapy uses drugs to stop the growth of tumor cells, either by killing the cells or by stopping the cells from dividing. Chemotherapy is introduced to the bloodstream and travels throughout the body to kill tumor cells.

Chemotherapy can be given:
  • by mouth as a pill
  • by injection into muscle or fat tissue
  • intravenously (directly to the bloodstream)
  • intrathecally (injected by needle directly into the spinal column)
Clinical trials are studying ways of using chemotherapy to delay or reduce the need for radiation therapy in children younger than 2-3 years.

In approximately 30% of cases, the flow of CSF will not be returned to normal, and the child will require the implantation of a permanent shunt, called a ventriculoperitoneal shunt or VP shunt, after surgery. The shunt is a type of tube that maintains a normal level of pressure.