Bleeding into the space between the two inner membranes covering the brain
- Most common between the ages of 40 and 60
- Sometimes runs in families
- Smoking and excessive alcohol consumption are risk factors
- Gender is not a significant factor
A subarachnoid haemorrhage occurs when an artery near the brain ruptures spontaneously and leaks blood into the subarachnoid space, the area 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 about 6–12 in 100,000 people in the UK each year. It sometimes runs in families, although no single causative gene has been identified, and is most common in middle-aged people. When the condition does occur, it is life-threatening and needs emergency medical attention.
What are the causes?
About 8 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 at birth, and there may be one or several. Some do not rupture. However, if rupture does occur, it is usually 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 1 in 10 subarachnoid haemorrhages is unknown.
In people who are at risk, subarachnoid haemorrhage may be triggered by intense exertion. The disorder is more likely to occur in people who have high blood pressure (see Hypertension), smoke, and drink excessive amounts of alcohol.
What are the symptoms?
The onset of symptoms is usually sudden and without warning. Typical symptoms may include the following:
Sudden, very severe headache.
Nausea and vomiting.
Dislike of bright light.
In a few minutes, these may lead to:
Confusion and drowsiness.
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 might be done?
If a subarachnoid haemorrhage is suspected, the affected person should be admitted to hospital immediately. CT scanning is carried out to identify the location and extent of bleeding. If the CT scan shows no bleeding, a lumbar puncture will be performed to look for signs of bleeding into the fluid surrounding the brain and spinal cord. If a subarachnoid haemorrhage is confirmed, MRI of cerebral angiography may also be performed to look at the blood vessels of the brain.
Once tests have confirmed a subarachnoid haemorrhage, drugs called calcium channel blockers are usually given to reduce the risk of a stroke.
If the tests have shown that one or more berry aneurysms are present, they may be treated by endovascular embolization or surgery. In endovascular embolization, a catheter (thin tube) is passed into an artery in the groin and up to the aneurysm. Special coils, glue, or plastic particles are then passed inside the catheter to seal off the aneurysm. Alternatively, conventional surgery may be used to apply clips to the affected artery to prevent it from bleeding again.
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 treatment is successful, further bleeding is unlikely. However, everybody who has had a subarachnoid haemorrhage should avoid smoking and excessive drinking and, if necessary, take measures to reduce high blood pressure.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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