The brain

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 base of the brain and join together to make the spinal cord. This cord of nerve fibres runs down the middle of the spine. 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 for short. From the spinal cord the nerve fibres spread out to all areas of the body.

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. There is more about this in the page about types of brain tumours.

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. So, to understand why brain tumours cause the symptoms they do, it helps to know a little about the brain and how it works.

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 they 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 your 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 your body. So if you have a brain tumour causing weakness on the left side of your body, the tumour will be in the right side of your brain. Each hemisphere is divided into 4 areas called the

• Frontal lobe
• Temporal lobe
• Parietal lobe
• Occipital lobe

The frontal lobe contains areas that control your 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 your sight or sense of smell.

The temporal lobe helps to control behaviour, memory, hearing, sight and your emotions. Your emotional memory is in this area so a tumour here can cause strange 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 your 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

The tentorium is a flap of tissue that is part of the meninges. It separates the hindbrain and the brain stem from the rest of the brain. Doctors use the word supratentorial to mean 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 (cerebellum)

The hindbrain is also called the cerebellum. It controls balance and coordination. So cerebellar tumours can cause loss of balance or difficulty coordinating your movements. Even something as simple as walking needs a lot of coordination – you have to get your arms and legs doing the right thing at the right time. Normally, we don't even think about this – the cerebellum does it for us.

The brain stem

The brain stem controls body functions that we usually don't think about. Blood pressure, swallowing, breathing and 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. It is possible for cancers to start in the spinal cord, but this is rare. With some types of brain tumour, the cancer can spread down to the spinal cord unless it is treated with radiotherapy. A tumour growing in the spinal cord will press on the nerves in the cord and can cause many different symptoms depending on where it is.

The pituitary gland

This is a small gland right in the middle of the brain. It makes a lot of different hormones. And controls many different body functions. Pituitary hormones control

• Growth
• The speed of body processes (your metabolism)
• The production of natural steroids in the body
• Periods and egg production in women
• Sperm production in men
• Breast milk production after the birth of a baby

The ventricles

Ventricles 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 around the spinal cord. The fluid is mainly water with a little protein, sugar (glucose), some white blood cells and some hormones. A growing brain tumour can block the circulation of the fluid. The resulting increased pressure inside the skull from fluid build up is called hydrocephalus and can cause symptoms. With some types of brain tumours cancer cells can spread in the CSF, causing symptoms similar to meningitis – headaches, sickness, and problems with sight and movement.

In adults, most brain tumours grow in the

• Forebrain
• Thin layers of body tissue covering the brain (the meninges) or
• Nerves entering or leaving the brain

In children, the picture is slightly different. 6 out of 10 (60%) childhood brain tumours are in the hindbrain or brain stem. Only 4 out of 10 (40%) are in the forebrain.

In adults, most cancers found in the brain are not tumours that started in brain cells. They are other types of cancer that have spread to the brain. These are called secondary brain tumours.

If you or your relative have cancer in the brain, but have had another cancer diagnosed (for example in the lung, breast or bowel) then it is most likely that the cancer in your brain is a secondary cancer that has spread and not a primary brain tumour. Look at the section that is about your cancer type for more information about treatment.

In children, spread to the brain from another type of cancer is rare.

There is detailed information about primary and secondary brain tumours in this section of the website.