The carotid arteries are the two major arteries supplying blood to the head and brain. Two smaller arteries, the vertebral arteries, also supply blood to the brain.

The disease that affects the carotid arteries is atherosclerosis, also called arteriosclerosis. It can affect any artery in the body. Its plain English name is hardening of the arteries. In arteriosclerosis, a layer of cholesterol (a natural fat) builds up inside the artery.

As it grows thicker, this layer (a plaque) makes the inside of the artery narrower. This reduces the amount of blood that can flow along the artery. If the surface of a plaque splits, the blood reacts with it to form a clot on the surface (Thrombosis).

This clot may grow. If parts of it break off, they are carried upwards into the brain by the blood flow. These clots may be very small and dissolve rapidly, or be larger and more permanent. If a clot lodges in the brain, it blocks the blood supply beyond it.

If the clot dissolves and blood supply is restored quickly, the brain may not be permanently damaged. This temporary blockage is called a transient ischaemic attack (TIA).

Otherwise, permanent damage will be done, and the blockage is called a stroke.

Causes

The causes of carotid artery disease are the same as those of arteriosclerosis. They are really risk factors. Some or all can be present in one person. They include:

• Being male
• Old age
• Smoking cigarettes
• High blood pressure
• Diabetes mellitus
• A previous TIA
• Thickened blood (for example, in severe dehydration) or an increased tendency for your blood to clot
• Raised blood cholesterol
• Drinking too much alcohol over a long period.

Any underlying cause must be treated straight away.

In a stroke or TIA, aspirin reduces the thickness of the blood. It should be given as soon as possible to help prevent further strokes or TIAs.

If a stroke is still developing, anticoagulants (blood-thinning drugs given in hospital) may help prevent things getting worse.

An exciting development is the use of clot-busting drugs (streptokinase or tissue plasminogen activator), within 3 hours of the start of a stroke caused by thrombosis. If successful, these can restore blood supply and reverse symptoms completely.

If the carotid arteries are more than 70% blocked in someone who has been getting TIAs, surgery to unblock the arteries (endarterectomy) is recommended. This operation carries a 1%–2 % risk of causing a stroke itself, so the benefits must be weighed carefully against the risks for each person.