A brain tumour is an abnormal mass of tissue inside the skull, which is caused by cells dividing at an increased speed.
There are two types of brain tumour: malignant and benign.
Malignant, or cancerous, tumours often invade surrounding tissue and can spread to other parts of the body through the blood stream or lymphatic system. They can also erode 'healthy' tissue, as the cells that make up a malignant tumour share very little in common with the healthy cells that surround them.
Because malignant tumours often grow and spread rapidly, early diagnosis can increase the chances of survival. If caught early, they will have had less chance to destroy healthy brain tissue, and are less likely to have spread to other parts of the body. Sometimes, brain tumours are the result of other malignant tumours in other parts of the body that have spread to the brain - these are known as 'metastases', or 'secondary tumours'. These are always malignant.
Benign, or non-cancerous, tumours tend to grow more slowly and do not spread, although people can have more than one benign tumour. A benign brain tumour can put pressure on the brain as it grows inside the enclosed space of the skull, and this may compress and damage healthy tissue.
Modern imaging techniques, such as MRI and CT scans, have made it possible for doctors to accurately judge the size and location of a tumour, making surgery possible where the growth is accessible, and allowing them to estimate how treatable it is. Surgery to remove all or part of a brain tumour is called a craniotomy, where the skull is opened. Where the entire tumour cannot be removed, radiotherapy or anti-cancer drugs may be tried to slow, limit or stop its spread.
The effects of a brain tumour are dependent on the size and location of the tumour and how much it has spread.
Headway UK Association of Brain Injury (2017) Brain Tumour.