Subarachnoid haemorrhage Dr Trisha Macnair This kind of bleed in the subarachnoid space lining the brain often occurs without warning, but that doesn't mean there's nothing you can do to reduce the risk.

In this article

What is it? What causes it?

Who's affected? What are the symptoms?

How's it diagnosed? What's the treatment?

At least one in 100 people go about their daily routine unaware that they have potentially deadly flaws in the blood vessels of their brain. These defects, known as berry aneurysms, are like tiny balloons where the wall of the artery has thinned and weakened. They're usually congenital - you're born with them - although they may be the consequence of ageing or high blood pressure.

Berry aneurysms may burst if put under extra stress. The end result is a brain haemorrhage or stroke.

The haemorrhage that occurs when a berry aneurysm bursts is known as a subarachnoid haemorrhage because the layer around the brain in which the bleeding occurs.

Fortunately, not every berry aneurysm ruptures - only about one in 7,000 people have a subarachnoid haemorrhage. And not every brain haemorrhage is due to a berry aneurysm. Although about 70 per cent of subarachnoid haemorrhages are caused this way, no defect can be found in at least ten per cent, and there are other types of brain haemorrhage. Also, not every stroke is due to a haemorrhage - the majority are caused by blockages of the blood supply by a clot or atherosclerosis.

The great tragedy of subarachnoid haemorrhage is that it frequently occurs in young adults

The great tragedy of subarachnoid haemorrhage is that it frequently occurs in young adults. Of course, a stroke at any age is a tragedy, but a subarachnoid haemorrhage is a particular disaster because it's often fatal - as many as 30 per cent die within hours, and a further 30 per cent die within the first month - or results in serious disability in people who have young dependents.

There's a slight tendency for the problem to run in families - if you're a blood relation of someone who's had a subarachnoid haemorrhage, you have a 14 per cent chance of having one, too. If you have two or more relatives affected, some experts recommend you have special screening tests of the blood vessels in your brain.

Women are more commonly affected than men, and people of African origin are also at increased risk, possibly because they're more likely to have high blood pressure.

Smoking and excessive alcohol intake are also linked to an increased risk that a berry aneurysm will rupture.

There's often little or no warning that a subarachnoid haemorrhage is about to occur. Typically, the person collapses with a sudden headache unlike any they've experienced before. They may vomit, develop signs of meningitis, such as neck stiffness and dislike of light, and may rapidly become drowsy, confused and unconscious.

In milder cases, the illness may appear like migraine or meningitis due to an infection, but in severe cases it's quickly apparent that something is seriously wrong.

Once a person reaches hospital, diagnosis is usually quickly confirmed with a CT scan of the brain.

Those who survive the initial episode are at great risk of another bleed unless action is taken. The standard treatment used to be surgery, which involves opening the skull and clipping off the faulty blood vessel. This operation, known as clipping, is usually done within days, but in severe cases and the elderly it may be delayed for a few weeks. However, although the operation puts an end to the risk, it carries a risk of damage (although this risk is far less than that of a second bleed.)

In recent years, a new technique has been developed as an alternative to clipping. In this technique, known as endovascular detachable-coil treatment or coiling, a detachable plantinum coil device is inserted into the blood vessels via a small cut in the skin (usually in the groin) and passed up into the brain under x-ray guidance to block off the faulty vessel.

In 2005, a long-term follow-up study of patients treated with coiling showed that it's as effective as surgery, has a lower risk of complications and offers a greater chance of survival without disability. It's now the standard treatment for most aneurysms in most areas of the UK.

Recovery from any type of stroke tends to be slow. Intensive rehabilitation therapy, including physiotherapy, speech therapy and occupational therapy, are usually needed.

Depression is a common problem after stroke, and good psychological and drug treatments are essential to help recovery.

After decades of being viewed as a fairly hopeless condition where only a little positive treatment could be done, new approaches are at last starting to make some impact on recovery rates from strokes. For example, researchers have shown for the first time in humans that rehabilitation therapy may help a stroke survivor's brain rewire itself, leading to regained use of a previously unused limb.

Children can have a stroke, especially a subarachnoid haemorrhage. Hemi-kids is a special site for children with stroke, and includes some valuable inspiration for parents.

This article was last medically reviewed by Dr Rob Hicks in July 2006.