Medulloblastoma

Medulloblastoma

What is a medulloblastoma?

All the cells in our body including our brain normally divide in an ordered way. If something goes wrong with this process, the cells will start growing abnormally, and this forms a Tumor. Some of these tumors have the ability to shed cells which can then travel through the Cerebrospinal fluid (CSF) and can start growing in other areas of the Central Nervous System. Less commonly, these cells can also enter the blood stream and spread to other areas of the body. These are called Malignant (cancerous) tumors, and medulloblastoma is one of them.

Medulloblastomas form part of a group of tumors called primitive neuroectodermal tumors ( PNET). All PNET tumors are formed from undifferentiated cells at a very early stage of their lives. By definition, the primary tumor is always found in the Cerebellum in a part of the brain called the Posterior fossa. PNET tumors that are found in other areas are given other names. When they occur in the eye they are called Retinoblastomas, when they occur in the pineal region are they are called pineoblastomas. Other areas are simply called PNET.

Medulloblastomas can be divided into two categories: Classic and desmoplastic (or nodular). About 25% of cases are of the desmoplastic variant, and these have a slightly better Prognosis. The desmoplastic variant is more common in adults, and is a less aggressive tumor.

Who gets medulloblastoma?

Medulloblastoma can occur at any age, although they are more common in children. Three quarters of all cases occur in children, with a median age of 9 years. The tumor is more common in males than females with 60% of all cases being male. Medulloblastoma is the most common childhood brain tumor, making up about 20% of all childhood brain tumor cases.

What causes medulloblastoma?

  • Environmental: No environmental factors have been found to cause medulloblastoma.
  • Familial: Medulloblastoma is associated with recessively inherited Turcot and ataxia-telangiectasia syndromes. As many as 5% of patients with autosomal dominant nevoid basal cell carcinoma (Gorlin) syndrome develop medulloblastoma.
  • Other causes are not currently known.

Symptoms

Most patients present with a history of headaches, vomiting and fatigue. The headaches are usually worse worse in the morning, and worsen when coughing. These symptoms are due to increased pressure in the skull.

As the tumor progresses, cerebellar symptoms may occur. These include trouble with walking and coordination and speech problems.

Eye symptoms such as double vision, trouble focusing and nystagmus (jerky eye movements) can also occur.

Neck stiffness can be symptom of cerebellar tonsil herniation, and should be investigated before a lumbar puncture is performed. With tonsil herniation, a lumbar puncture can cause a change in pressure that can cause brain stem compression and sudden death - so insist on an MRI before this procedure is done.

Tests

The following are tests that your doctor may order.

Neurological examination

This is a physical exam performed by your doctor to check if the tumor has had any affect on your nervous system. They will check your reflexes, eye movements and coordination, and will look for any other signs they need to worry about.

CT scan

When you go for a CT scan, you lie on a table and get fed through a big donut like machine which takes x-rays of your brain and feeds it into a computer. The computer then builds up an image of your brain which the doctors can use to find the exact position and size of the tumor.

MRI scan

Quite similar to the CT scan, but is a lot more accurate, and is the preferred imaging study for medulloblastoma. An MRI is painless, but can be uncomfortable, as you have to lie perfectly still in a metal tube and the scan can take up to an hour to complete. If you are claustrophobic you should ask your doctor for a calming pill before this test.

Biopsy

A biopsy is usually done to find out what kind of tumor you have, and will probably only be done if the tumor can't be removed. It involves surgery where they take a small sample of the tumor to test it.

Lumbar puncture

A lumbar puncture is a procedure to get a sample of CSF to check if the Cancer cells have spread. It can be panful, as a needle is pushed between the bones of your spin to extract the fluid. This test is important for staging and will help your doctor determine what treatment you need, however if you are going for an aggressive treatment plan regardless of the outcome of the test, you might want to give this test a miss. Unless of course you want to know what your prognosis it.

Myelogram

This checks for any spread of the cancer cells to the spinal cord. A fluid that shows on x-ray is injected into the CSF to show an outline of the spinal cord.

Treatment

Your doctor will be able to determine the best treatment plan for you. These are some of the treatments you may encounter.

Surgery

If you have hydrocephalus, the pressure will need to be decreased before the tumor can be removed. There are two ways to do this. Either a shunt will be inserted to drain off excess fluid, or a procedure called an endoscopic third ventriculostomy may be performed. A shunt is a drainage tube which runs from the brain to another region of the body (usually the abdomen). In most cases the shunt can be removed once the tumor is removed and you have recovered from surgery. A third ventriculostomy involves drilling a hole in the skull and using an endoscope to make a hole in one of the ventricles, allowing the fluid to drain. This does not always work, in which case a shunt will need to be installed.

Most medulloblastoma patients have surgery to remove as much of the tumor as possible. If they remove the tumor completely it is called a 100% macroscopic resection. This means that they removed everything that they could see, but because medulloblastomas have the tendency to shed cells, there may be some cancer cells left. So even if they got it all, you will need follow up with radiation and/or Chemotherapy.

They may do an MRI scan following surgery to check how much of the tumor is left. This is usually done in the first 48 hours, as if is difficult to tell the difference between residual tumor and scar tissue.

Radiation

Radiation is used to destroy cancer cells. Fortunately medulloblastoma is highly sensitive to radiation, and this makes it a very effective treatment. Most medulloblastoma patients receive cranio-spinal radiation (radiation to the whole brain and spinal cord), with a boost to the tumor bed. This normally takes about 6 weeks. You will probably experience Nausea and vomiting, although your doctor can prescribe good anti-nausea medication. Many patients complain of gastric problems and sore throats. Towards the end of the treatment some patients get a condition called somnolence which is where you sleep all the time (about 23 hours of the day).

Radiation is not given to children under the age of three because of the effects of radiation of the developing brain. These children are usually given chemotherapy, and radiation is given when they are older. This is probably the main reason that infants have a worse prognosis than any other group.

Chemotherapy

Chemotherapy drugs are used to kill cancer cells. These drugs target fast dividing cells in the body, and unfortunately this includes normal cells like your hair, and your blood cells. Our normal cells are able to repair themselves faster than the cancer cells can, so chemotherapy is given in cycles. You get given a dose, and just enough time for your blood cells to recover. Once your blood cells have reached an acceptable level, they hit you again. Eventually the cancer cells are so badly damaged that they can't recover at all and die. In some cases marrow-ablative chemotherapy is given, which is where they don't give the blood cells time to recover. In this case you get high dose chemotherapy, followed by a bone marrow transplant or stem cell rescue. This has been shown to be very effective in recurrences, and many people have their stem cells harvested before beginning treatment in case of a recurrence.

Be careful of using alternative therapies with chemotherapy, as they may interfere with the chemo drugs ability to work. A good example is high doses of vitamins. Vitamins are good because they help your body repair cells, but they also help your body repair the cancer cells faster than was expected, in the effect of the chemo is useless. Speak to your doctor before taking any other drugs or supplements.

Each case is different and your Neuro-oncologist will work with you to put together your treatment plan.

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