Bleeding in the brain - Causes of subarachnoid haemorrhages
- Introduction
- Symptoms of a subarachnoid haemorrhage
- Causes of subarachnoid haemorrhages
- Diagnosing a subarachnoid haemorrhage
- Treating subarachnoid haemorrhages
- Complications of a subarachnoid haemorrhage
- Recovering from subarachnoid haemorrhage
- Preventing subarachnoid haemorrhage
- 'After my brain injury, there were suddenly men everywhere who I fancied'
In most cases, a subarachnoid haemorrhage is caused by an aneurysm in the brain.
Brain aneurysms
A brain aneurysm is a bulge in a blood vessel, caused by a weakness in the blood vessel wall, usually at a point where the vessel branches off. As blood passes through the weakened vessel, the pressure causes a small area to bulge outwards like a balloon.
Occasionally, this bulge can burst (rupture), causing bleeding around the brain. Around 8 out of every 10 subarachnoid haemorrhages happen in this way.
A brain aneurysm doesn't usually cause any symptoms unless it ruptures, although some people with unruptured aneurysms experience sight problems, pain on one side of the face or around the eye and persistent headaches.
It is not known exactly why brain aneurysms develop in some people, although certain factors that increase your risk of the condition have been identified. These include:
- smoking
- high blood pressure
- excessive alcohol consumption
- a family history of the condition
- some rarer conditions, such as autosomal dominant polycystic kidney disease (ADPKD)
Most brain aneurysms will not rupture, but a procedure to prevent subarachnoid haemorrhages is sometimes recommended if they are detected early.
Read more about diagnosing brain aneurysms and treating brain aneurysms.
Other causes
Less common causes of subarachnoid haemorrhages include:
- arteriovenous malformations – where blood vessels develop abnormally
- a brain tumour damaging the blood vessels (both cancerous and non-cancerous brain tumours can cause a subarachnoid haemorrhage)
- a brain infection, such as encephalitis
- fibromuscular dysplasia – a rare condition that can cause the arteries to narrow
- Moyamoya disease – a rare condition that causes blockages inside the brain's arteries
- vasculitis – where the blood vessels inside the brain become inflamed (swollen), which can be caused by a wide range of problems, such as infection or the immune system attacking healthy tissue
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