What is Medulloblastoma

Medulloblastoma is a brain tumour that is found in the cerebellum, the part of the brain that controls movement and balance. Medulloblastoma is the most common malignant central nervous system tumour of childhood. It accounts for 20 percent of paediatric brain tumours. Within the cerebellum, medulloblastoma are most often seen in the region of the fourth ventricle, between the brain stem and the cerebellum or the central part of the cerebellum, and less frequently they arise within the cerebella hemispheres. The cause of medulloblastoma is not yet known.

Common symptoms are unsteadiness, headaches, and vomiting due to hydrocephalus (from blockage of cerebrospinal fluid flow). Diagnosis is usually within one to three months of the onset of symptoms, it is a very aggressive (fast growing) tumour. It is unknown why this tumour has a tendency to spread outside of its primary site of origin, to the spine, meninges and rarely to other organs such as the bone marrow/bone and/or liver and other organs. Over the past 10-20 years, surgery for children with medulloblastoma has become safer, however some children will develop severe, sometimes irreversible, neurological problems afterwards, including loss of speech and severe balance difficulties e.g. right or left sided weakness.

Identifying the stage of the tumour may involve a biopsy but usually surgery to remove as much of the tumour as possible will take place and then analysis will be made from the tissue. However a cerebrospinal fluid analysis (spinal taps) can evaluate the presence of tumour cells within the spinal fluid. MRI scans (head and spine), performed with and without contrast agents will identify if the tumour has spread to the spine and will always be done after diagnosis of medulloblastoma as it often spreads due to the aggressiveness of this tumour. Radiation to the entire brain and spine with additional radiation (boost) to the tumour site has been a major treatment advance. With it, the overall five-year survival rate has risen from 20% to well over 50% in the last 10-20 years. Over the past ten years, there has been increasing evidence that chemotherapy improves survival for children whose tumours only partially removed, or have spread beyond the primary site (disseminated) at diagnosis.

For children who are very young or have disseminated disease at diagnosis, where the cancer has spread to the spine and/or surface of the brain (leptomeninegeal disease) survival is not as good. Research is being carried out to determine the biology of this tumour, its cell origin, and what controls its growth. By understanding the biology of this tumour, the goal of curing children with medulloblastoma may be achieved. Also research is trying to find ways to making treatment safer for children with this disease, so that they not only survive, but will allow them to experience a good quality of life.

To understand more about medulloblastoma it is important to understand the brain and how it works.

The brain is the control centre of the body. Everything we do, think or feel involves the brain. It controls the body by sending electrical messages along nerve fibres. The nerve fibres run out of the brain and join together to make the spinal cord. This cord of nerve fibres runs down the middle of the spine. And the nerve fibres then spread out to all areas of the body. Together, the brain and spinal cord form the central nervous system. A clear fluid circulates around the brain and spinal cord. It is called cerebrospinal fluid or (CSF).

6 out of 10 (60%) childhood brain tumours are in the cerebellum or brain stem. Only 4 out of 10 (40%) are in the forebrain.

The brain is made of nerve cells called neurones. There are billions of these neurones. Also in the brain are other types of cells that support the neurones. These are called glial cells. Glial cells can become cancerous and grow into a brain tumour. Different areas of the brain control different parts of the body as well as our thoughts, memories and feelings. There is a centre in the brain for speech, for example. And another for sight. Brain tumours can develop anywhere in the brain. They can develop from

• The cells that make up the brain tissue
• The nerves entering or leaving the brain
• The coverings of the brain (the meninges)

They will cause different symptoms depending on the part of the brain they are growing in. Therefore, to understand why brain tumours cause the symptoms they do, it is important to know a little about the brain and how it works.

The parts of the brain

The meninges

The skull protects the brain. Inside the skull, and covering the brain, are 3 thin sheets of body tissue. These are called the meninges and also help to protect the brain.

The forebrain

The forebrain is divided into 2 halves - the right and left cerebral hemispheres. The cerebral hemispheres control movement, thinking, memory, emotions, senses and speech. As the nerve fibres leave the brain, they cross over from one side to the other. This means that the nerves that come from the right side of your brain control the left side of the body. Each hemisphere is divided into 4 areas.

1. Frontal lobe
2. Temporal lobe
3. Parietal lobe
4. Occipital lobe

The Frontal lobe contains areas that control personality, thought, memory and behaviour. Towards the back of the Frontal lobe are areas that control movement and feeling. A tumour in this part of the brain may also affect sight or sense of smell.

The Temporal lobe helps to control behaviour, memory, hearing, sight and emotions. Feelings of having been somewhere or done something before (also called déjà vu).

The Parietal lobe is mainly to do with language. A tumour here can affect speech, reading, writing or understanding of words.

The Occipital lobe is the visual centre of the brain. A brain tumour in this area can cause sight problems.

The tentorium

This is a flap of tissue (part of the meninges that separates the hindbrain and the brain stem from the rest of the brain). Supratentorial means above the tentorium - or anywhere apart from the hindbrain (cerebellum) or brain stem. Infratentorial means below the tentorium - in the hindbrain (cerebellum) or brain stem.

The hindbrain

This area is also called the cerebellum. It controls balance and co-ordination. Cerebellar tumours can cause loss of balance or difficulty co-ordinating movements.

Medulloblastoma form in the cerebellum

The brain stem

The brain stem controls body functions that we usually don't think about. Blood pressure, swallowing, breathing, heartbeat are all managed by this area of the brain. The 2 main parts of the brain stem are called the pons and the medulla oblongata. The brain stem also includes a small area above the pons called the midbrain.

The brain stem is also the part of the brain that connects the forebrain (the cerebral hemispheres) and the cerebellum with the spinal cord. All the nerve fibres leaving the brain to go to the limbs and trunk of the body pass through here.

The spinal cord

The spinal cord is made of all the nerve fibres that pass down from the brain. There is a space in the middle of the spinal cord that is filled with fluid called cerebrospinal fluid. With medulloblastoma, the cancer can spread down to the spinal cord. A tumour growing in the spinal cord will press on the nerves in the cord and can cause many different symptoms including:

1. Pain
2. Numbness in part of the body
3. Weakness in the legs or arms
4. Loss of control of the bladder or bowel

The ventricles

These are spaces inside the brain, filled with the fluid called cerebrospinal fluid or CSF. The ventricles connect with the space in the centre of the spinal cord and with the membranes covering the brain (the meninges). So the fluid can circulate around and through the brain and down the spine. A growing brain tumour can block the circulation of the fluid. The resulting increased pressure inside the skull from fluid build up can cause symptoms. This may be called hydrocephalus. The fluid is mainly water with a little protein, sugar (glucose), some white blood cells and some hormones. With medulloblastoma cancer cells can spread in the CSF, causing symptoms similar to meningitis – headaches, sickness, problems with sight and movements.

Information from CancerHelp UK. www.cancerhelp.org.uk

The information provided is intended to give a general idea but is not a substitute for professional/medical advice.