A subarachnoid haemorrhage is an uncommon type of stroke caused by bleeding on the surface of the brain. It's a very serious condition and can be fatal.
There are usually no warning signs, but a subarachnoid haemorrhage sometimes happens during physical effort or straining, such as coughing, going to the toilet, lifting something heavy or having sex.
The main symptoms of a subarachnoid haemorrhage include:
A subarachnoid haemorrhage is a medical emergency. Dial 999 immediately and ask for an ambulance if you or someone in your care has these symptoms.
A person with a suspected subarachnoid haemorrhage needs a CT scan in hospital to check for signs of bleeding around the brain.
If a diagnosis of subarachnoid haemorrhage is confirmed or strongly suspected, you're likely to be transferred to a specialist neurosciences unit.
Medication will usually be given to help prevent short-term complications, and a procedure to repair the source of the bleeding may be carried out.
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Subarachnoid haemorrhages are often caused by a burst blood vessel in the brain (a ruptured brain aneurysm).
It's not known exactly why brain aneurysms develop in some people.
But certain risk factors have been identified, including:
Severe head injuries can cause subarachnoid bleeding, but this is a separate problem known as a traumatic subarachnoid haemorrhage.
Read more about the causes of subarachnoid haemorrhages.
Subarachnoid haemorrhages can happen at any age, but are most common in people aged between 45 and 70. Slightly more women are affected than men.
Subarachnoid haemorrhages are also more common in black people compared to other ethnic groups. This could be because black people are more likely to have high blood pressure.
There are some things you can do to reduce your risk of a subarachnoid haemorrhage.
The most effective steps you can take to reduce your chances of having a subarachnoid haemorrhage are:
A subarachnoid haemorrhage can cause both short and long-term complications.
Serious short-term complications can include further bleeding at the site of any aneurysm and brain damage caused by a reduction in blood supply to the brain.
Long-term complications include:
Read more about the complications of a subarachnoid haemorrhage.
Although the outlook for subarachnoid haemorrhage has improved in the last few decades, it can be fatal, and people who survive can be left with long-term problems.
Recovering after a subarachnoid haemorrhage can also be a slow and frustrating process, and it's common to have problems such as:
Read more about recovering from a subarachnoid haemorrhage.
Our guide to care and support explains your options and where you can get support.