about tumours

Medulloblastomas are the most common high grade childhood brain tumour, accounting for 15-20% of all childhood brain tumours. They are a central nervous system (CNS) embryonal tumour. They are:

• fast growing
• likely to spread to other areas of the brain or spinal cord.

Medulloblastomas usually develop in a part of the brain called the posterior fossa and are most commonly found in the cerebellum, an area of the posterior fossa that controls coordination and balance. They are commonly found in children between the ages of 3 and 8, with a higher occurrence in males.

In the past few years, research has significantly advanced the understanding of medulloblastomas and researchers have now been able to put them into 4 main groups based on demographic, clinical and genetic differences:

WNT medulloblastoma

• This is the best known subgroup of all the medulloblastomas and has been identified in 10-15% of patients. The average age of occurrence is ten years old and it is more commonly found in females. These tumours often occupy the fourth ventricle; the fluid filled space in the middle of the posterior fossa.

SHH medulloblastoma

• This type of medulloblastoma frequently occurs in both infants (under three) and adults (over sixteen), but are less frequent in children aged three to sixteen. SHH medulloblastoma is commonly associated with a condition known as Gorlin syndrome, due to a gene mutation that causes the over-activation of cells, leading to the formation of a tumour.

Group 3 medulloblastoma

• This type of medulloblastoma occurs more commonly in males than females, and are most common in young children ranging from one to ten years old. At diagnosis, these are often metastatic (already spread to other parts of the brain and spinal cord). Similar to the WNT medulloblastomas, the tumour is generally located within the fourth ventricle.

Group 4 medulloblastoma

• This is the most common subgroup of medulloblastoma, making up around 35-40% of all cases. These tumours can occur in all ages but are most prevalent in mid-childhood.

Unfortunately, a full genetic test to determine the type of medulloblastoma that a child may have is not yet routinely available on the NHS. However hospitals are developing the techniques to be able to do this in the near future.

How are medulloblastomas treated?

Treatment for medulloblastoma is likely to include a combination of surgery, radiotherapy and chemotherapy.

The first course of treatment is usually neurosurgery to remove the tumour. However, if your child’s tumour has caused a build-up of CSF, the surgeon may first need to perform an operation to reduce the pressure.

Following surgery, radiotherapy is often used to destroy any remaining tumour cells. It is normally given to the whole brain and spinal cord as medulloblastomas can travel through the CSF to the spinal cord.

If a child is aged under 3, whole brain radiotherapy is usually avoided and high-dose chemotherapy may be used to delay or eliminate the need for radiotherapy. In some cases, children older than 3 may be given several cycles of high-dose chemotherapy before or after radiotherapy.

What causes medulloblastomas?

It’s important to understand that there is nothing the patient or family have done or could have avoiding doing that would have prevented a brain tumour from developing.

As with all brain tumours, we don’t know for sure what causes medullblastomas to start growing, although we do understand some of the risk factors involved.

SHH medulloblastomas in particular are commonly associated with a condition known as Gorlin syndrome, due to a gene mutation that causes the over-activation of cells, leading to the formation of a tumour.