A brain tumour is a growth of cells in the brain which multiply in an abnormal, uncontrollable way.

There are different types of brain tumour, depending on the type of brain cells they have grown from. More than half of all brain tumours are gliomas (tumours of the glial tissue, the tissue that binds nerve cells and fibres together).

Brain tumours are also graded from 1 to 4 according to their behaviour, such as how fast they grow and how likely they are to spread.

An overview is provided below of:

Low-grade and mixed brain tumours and High-grade brain tumours

Links are also provided to more information on these conditions.

Low-grade and mixed brain tumours

Generally, low-grade brain tumours - grade 1 or 2 - are slow growing and unlikely to spread. They are usually benign (non-cancerous), which means they tend to stay in one place and do not invade other areas of the brain or spread to other parts of the body.

However, low-grade gliomas will frequently grow back after treatment. More seriously, they can also mutate (change) into high-grade tumours (grade 3 or 4), which are fast-growing cancerous tumours that are likely to spread. About half of all low-grade glioma tumours mutate in this way within five years of diagnosis.

If you have been diagnosed with a low-grade brain tumour, your treatment will depend on the type and location of the tumour and your outlook will depend on whether it grows back, and whether it mutates.

Mixed brain tumours are made up of two or more different types of tumours, sometimes of different grades.

For example, a mixed brain tumour may be a combination of a high-grade astrocytoma (a tumour of the cells thought to provide the brain's framework) and a low-grade or benign oligiodendroglioma (a tumour of the cells that produce the fatty covering of nerves).

If you have been diagnosed with a mixed-grade brain tumour, you will be treated for the most aggressive part of the tumour. Your outlook will depend on how much of the tumour is high-grade (malignant), the location of the tumour in your brain, and other factors such as your general health.

For more information, see the Health A-Z topic on low-grade/mixed brain tumours

High-grade brain tumours

High-grade brain tumours may be either:

• Primary tumours - these started in the brain and can spread to other parts of the brain or spine, but rarely to other areas of the body.
• Secondary tumours (the most common type) - these started as cancer in another part of the body and spread to the brain through the blood.

There are different types of primary high-grade brain tumour, depending on the type of brain cells they have grown from. The most common type is a glioma, which accounts for more than half of all primary brain tumours. About 300 new cases of high-grade glioma are currently recorded each year in Ireland

A primary high-grade brain tumour must be treated as soon as possible, because it can spread to and damage other parts of the brain and spinal cord.

Secondary brain tumours are as serious as primary tumours.

For more information, see the Health A-Z topic on high-grade brain tumours