Subarachnoid haemorrhage

A subarachnoid haemorrhage occur when an artery near the brain ruptures spontaneously and leaks blood into the subarachnoid space, the erea between the middle and innermost of the three membranes that cover the brain. When this happens, the immediate symptom is an intensely painful headache.

Subarachnoid haemorrhage is rare, affecting only about 1 in 10,000 people in the UK each year. When the condition does occur, it is life-threatening and needs emergency medical attention.

What are the causes?

About 7 in 10 subarachnoid haemorrhages are caused by the rupture of a berry aneurysm, an abnormal swelling in an artery often found at a Y-shaped junction in the arteries that supply the brain. Berry aneurysms are thought to be present from birth, and there may be one or several. The aneurysms usually rupture between the ages of 40 and 60.

A further 1 in 10 subarachnoid haemorrhages are the result of a rupture of a knot of arteries and veins on the surface of the brain. The defect, known as an arteriovenous malformation, is present from birth, but haemorrhages do not occur until between the ages of 20 and 40. The cause of 2 in 10 subarachnoid haemorrhages s unknown.

In people who are at risk, subarachnoid haemorrhage may be triggered by intense exertion. The disorder is more common in people who have high blood pressure.

What are the symptoms?


The onset of symptoms is usually sudden and without warning. However, in a minority of cases, a headache comes on gradually a few hours before the haemorrhage occurs. Typical symptoms may include the following:

- Sudden, severe headache.
- Nausea and vomiting.
- Stiff neck.
- Dislike of bright light.
- Irritability.

In a few minutes, these may lead to:

- Confusion and drowsiness.
- Seizures.
- Loss of consciousness.

The body may react to the haemorrhage by constricting the arteries in the brain. As a result, the supply of oxygen to the brain is further reduced, and this may cause a stroke, possibly resulting in muscle weakness or paralysis.

What may be done?

If a subarachnoid haemorrhage is suspected, the affected person should be admitted to hospital immediately. CT scanning is usually carried out to identify the location and extent of bleeding. A lumbar puncture may need to be performed to look for signs of bleeding into the fluid surrounding the brain and spinal cord. MRI or cerebral angiography may also be performed to look at the blood vessels of the brain.

If a subarachnoid haemorrhage is confirmed, drugs called calcium channel blockers are usually given to reduce the risk of a stroke.

If cerebral angiography shows that one or more berry aneurysms are present, surgery will probably be required. During the operation, clips are applied to the affected arteries to prevent them from bleeding again at a later time. If surgery is carried out early, there is a good chance of recovery. Sometimes, knotted or distended vessels are blocked and made safe without the need for surgery by inserting coils or glue during angiography. If damage to the brain has caused persistent symptoms, such as muscle weakness as a result of a stroke, physiotherapy may be arranged.

What is the prognosis?

Nearly half of all people with a subarachnoid haemorrhage die before they reach hospital. Of those people admitted to hospital, about half are treated successfully, but the remainder have another subarachnoid haemorrhage. If there is no further haemorrhage within the next 6 months or if surgery is successful, further bleeding is unlikely.