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What is a stroke?

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A stroke means that the blood supply to a part of the brain is suddenly cut off. The brain cells need a constant supply of oxygen from the blood. Soon after the blood supply is cut off, the cells in the affected area of brain become damaged, or die. A stroke is sometimes called a 'brain attack'.

The blood supply to the brain comes mainly from four arteries - the right and left carotid arteries, and the right and left vertebrobasilar arteries. These branch into many smaller arteries which supply blood to all areas of the brain. The area of brain affected, and the extent of the damage, depends on which blood vessel is affected.

For example, if you lose the blood supply from a main carotid artery, then a large area of your brain is affected which can cause severe symptoms, or death. On the other hand, if a small 'branch' artery is affected, then only a small area of brain is damaged which may cause relatively minor symptoms.

What causes a stroke?

There are two main types of stroke - ischaemic and haemorrhagic.

Ischaemic stroke - occurs in about 7 in 10 cases

Ischaemic means a reduced blood and oxygen supply to a part of the body. This common form of stroke is usually caused by blood clot in an artery which blocks the flow of blood.

The blood clot often forms within the artery itself. This commonly occurs over a patch of fatty material called atheroma. (Atheroma is sometimes called 'furring' or 'hardening' of the arteries.) Small patches of atheroma form on the inside of arteries in most older people. If a patch of atheroma becomes thick, it can 'trigger' the blood to clot.
In some cases, the blood clot forms in another part of the body, and then travels in the bloodstream (this is called an embolus). The most common example is a blood clot which forms in a heart chamber as a result of abnormal turbulent blood flow. This may occur in a condition called atrial fibrillation. The blood clot is then carried in the bloodstream until it gets stuck in an artery in the brain.
There are other rare causes of ischaemic stroke.