A-Z of Types

Basic question – what is a brain tumour?

A brain tumour is a mass of abnormal cells growing in the brain. The cells can come from the brain itself or from its lining (primary brain tumours) or from other places in the body (secondary or metastatic brain tumours).

Primary brain tumours can be benign or malignant. Secondary brain tumours are always malignant.

Size doesn’t matter… this is true. The size of a brain tumour doesn’t matter nearly so much as where it is located.

A large, benign tumour may be easily accessible and therefore easy to remove. Or you can have a pea –sized tumour that is critically placed, and so makes treatment very difficult.

However, treatments options are developing all the time and one size doesn’t fit all. Some small tumours, in tricky locations, may be treated by radiosurgery and some large, diffuse tumours crossing the midline of the brain can be difficult to treat with radiation. So each case needs to be reviewed, discussed and options explored. It’s complex!

What causes them?

No one knows. If we did, then we would be able to treat them more effectively, or even prevent them occurring at all. Some genetic disorders may mean that some people are predisposed to getting a brain tumour and there is suggestion that some environmental factors may increase our risk. We do know that the incidence of brain tumours is increasing by about 2% a year – and this isn’t down to better diagnostic weaponry.

Brain tumour classification and grading.

All tumours in the brain can pose a threat to health.

Benign tumours grow slowly and do not invade tissue, but they may put pressure on areas of the brain and cause problems.

Malignant primary brain tumours spread into the healthy tissue and tend to grow more quickly than benign tumours.

The World Health Organisation has developed a classification system for brain tumours. Knowing the classification and grade of an individual tumour helps to predict its likely behaviour.


Grade I (low-grade) — the tumour grows slowly, has cells that look a lot like normal cells, and rarely spreads into nearby tissues. It may be possible to remove (resect) the entire tumour by surgery, but tumours in the brain stem cannot be completely resected safely.

Grade II — the tumour grows slowly, but may spread into nearby tissue and may recur (come back). Some tumours may become a higher-grade tumour.

Grade III — the tumour grows quickly, is likely to spread into nearby tissue, and the tumour cells look very different from normal cells.

Grade IV (high-grade) — the tumour grows and spreads very quickly and the cells do not look like normal cells. There may be areas of dead cells in the tumour. Grade IV brain tumours are harder to manage than lower-grade tumours.  High- grade tumours can be difficult to treat.

Depending on their make up, tumours can be a mix of grades, so they will be defined by the highest grade.


Primary brain tumours are named according to the type of cells or the part of the brain in which they begin.

Generally benign tumours

Pituitary adenoma
Acoustic neuroma
Pilocytic astrocytoma
Colloid cyst
Epidermoid cyst

Malignant tumours and tumours with uncertain behaviour

Astroglial neoplasm
Anaplastic astrocytoma
Anaplastic oligodendroglioma
Mixed gliomas
Germ cell tumour
Choroid-plexus carcinoma

Information courtesy of brainstrust