What is medulloblastoma?

Medulloblastoma is the most common central nervous system (CNS) embryonal tumour and the most common high grade childhood tumour, accounting for 15-20% of all childhood brain tumours. They are commonly found in children between ages of three and eight, with a higher occurrence in males.

Medulloblastomas usually develop in a part of the brain called the posterior fossa, and may sometimes spread to other parts of the brain or spinal cord, through the cerebrospinal fluid (CSF) that surrounds the brain. They are most commonly found in the cerebellum, an area of the posterior fossa that controls coordination and balance.

Due to the location of these tumours, they may block the flow of CSF leading to a condition called hydrocephalus, which raises the pressure inside the skull.

Types of medulloblastoma

In the past few years, our understanding of medulloblastoma has advanced significantly by studying their genetic make-up and increasing our molecular understanding of this tumour type. Researchers have been able to identify that medulloblastoma can be subgrouped in to four main groups that have been defined by 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 10 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 16), 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.

What are the treatments for medulloblastoma?

The initial treatment for a child diagnosed with a medulloblastoma is surgery. However, if your child's tumour has caused a build-up of CSF, the surgeon may firstly need to perform an urgent operation to divert the flow of fluid to the abdomen, to reduce the pressure. There are different ways this can be done, from inserting a small, temporary drain, a more permanent shunt or a camera procedure to make a hole at the bottom of the brain (also known as a ventriculostomy). If a shunt is inserted, it may stay in place after surgery to prevent future fluid build-up.

If your child is treated for hydrocephalus, they will then require a second surgery to remove the tumour. To remove as much of your child's tumour as possible, the neurosurgeon needs to have greater access to your child's brain. During surgery a 'bone flap' will be removed from your child's skull. This type of operation is known as a 'craniotomy'.

Following surgery, radiotherapy is often used to destroy any remaining tumour cells. It is normally given to the whole brain and spinal cord as this tumour type may travel through the CSF to the spinal cord. However, if a child is aged under three, whole brain radiotherapy is avoided. As their brains are still developing, they are open to the long term side-effects of radiotherapy.

In children under three, high dose chemotherapy may be used to delay or eliminate the need for radiotherapy. In some cases, radiotherapy may be given just to the part of the brain where the tumour is located. In children older than 3, several cycles of high-dose chemotherapy may be given before or after radiotherapy.

Chemotherapy drugs destroy tumour cells by stopping their ability to grow and divide, hence reducing the risk of them spreading through the spinal fluid. A combination of chemotherapy drugs will be used to kill as many cells as possible. The choice of drugs and how and when they will be given will be discussed with you by your child's oncologist and will be based on your child's age.

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