Subarachnoid haemorrhage


Subarachnoid haemorrhage


A subarachnoid haemorrhage is an uncommon type of stroke caused by bleeding on the surface of the brain. It is a very serious condition and can be fatal.

Subarachnoid haemorrhages account for around 1 in every 20 strokesin the UK.

The main symptom of a subarachnoid haemorrhage is a sudden and very severe headache that is often described as a blinding pain, unlike anything experienced before.

Other symptoms can include:

a stiff neck

being sick

sensitivity to light

blurred or double vision

seizures (fits) or loss of consciousness

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.

 How a subarachnoid haemorrhage is treated 

A person with a suspected subarachnoid haemorrhage will need to have a computerised tomography (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 are likely to be transferred to a specialist neurosciences unit.

Medication will usually be given to help prevent short-term complications (see below) and a procedure to repair the source of the bleeding may be carried out.

 What causes subarachnoid haemorrhages? 

The majority of subarachnoid haemorrhages are caused by a brain aneurysm bursting. A brain aneurysm is a bulge in a blood vessel, and is caused by a weakness in the blood vessel wall.

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:


high blood pressure

excessive alcohol consumption

Less common causes of subarachnoid haemorrhages include having abnormally developed blood vessels and inflammation of blood vessels in the brain.

Severe head injuries often cause subarachnoid bleeding, but this is a separate problem known as a "traumatic subarachnoid haemorrhage".

Who is affected

Between April 2012 and April 2013, over 11,000 people were admitted to hospitals in England with a subarachnoid haemorrhage.

Subarachnoid haemorrhages can happen at any age, even children, but they 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

Reducing your risk

It's not always possible to prevent a subarachnoid haemorrhage, but there are some things you can do to reduce your risk.

The three most effective steps you can take to reduce your chances of having a subarachnoid haemorrhage are:

stop smoking

moderate your alcohol consumption

take steps to keep your blood pressure at a healthy rate, such astaking regular exercise and losing weight if you are overweight

Possible complications

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:

epilepsy – where a person has repeated seizures (fits)

problems with certain mental functions, such as memory, planning and concentration

changes in mood, such as depression


Although the outlook for subarachnoid haemorrhage has improved in the last few decades, around half of all cases are 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 extreme tiredness, headaches and problems sleeping.

Symptoms of a subarachnoid haemorrhage 

A subarachnoid haemorrhage sometimes happens during physical effort or straining – such as coughing, going to the toilet, lifting something heavy or having sex.

There are usually no warning signs.

The main symptoms of a subarachnoid haemorrhage include:

a sudden agonising headache, which is often described as being similar to a sudden hit on the head, resulting in a blinding pain unlike anything experienced before

stiff neck

feeling and being sick

sensitivity to light (photophobia)

blurred or double vision


stroke-like symptoms, such as slurred speech and weakness on one side of the body

loss of consciousness or convulsions (uncontrollable shaking)

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.

Causes of subarachnoid haemorrhages 

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:


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.

Other causes

Less common causes of subarachnoid haemorrhages include:


arteriovenous malformations – where blood vessels develop abnormally

a brain tumour damaging the blood vessels (both cancerousand 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

Diagnosing a subarachnoid haemorrhage 

If it's thought that you have had a subarachnoid haemorrhage, you will need to have a brain scan in hospital as soon as possible.

A computerised tomography (CT) scan is used to check for signs of a brain haemorrhage. This involves taking a series of X-rays, which a computer then makes into a detailed 3D image.

In some cases, a subarachnoid haemorrhage is not picked up by a CT scan. If a CT scan is negative, but your symptoms strongly suggest you have had a haemorrhage, a test called a lumbar puncture will usually be carried out.

A lumbar puncture involves a needle being inserted into the lower part of the spine, so that a sample of the fluid that surrounds and supports the brain and spinal cord (cerebrospinal fluid) can be taken out. It will then be analysed for signs of bleeding.

Planning treatment

If the results of a CT scan or lumbar puncture confirm that you have had a subarachnoid haemorrhage, a test called an angiogram or arteriogram may be carried out to help plan treatment. This will usually be done in a specialist neuroscience unit.

An initial angiogram is usually done with a CT scan or an MRI scan, and this usually gives enough information to plan treatment. Occasionally, an angiogram may need to be done, which involves inserting a thin tube called a catheter into one of your blood vessels (usually in the groin). Local anaesthetic is used where the catheter is inserted, so you won't feel any pain. 

Using a series of X-rays displayed on a monitor, the catheter is guided into the blood vessels in the neck that supply blood to the brain. Once in place, special dye is injected through the catheter and into the arteries of the brain. This dye casts a shadow on an X-ray, so the outline of the blood vessels can be seen and the exact position of the aneurysm can be identified.

Treating subarachnoid haemorrhages 

If you are diagnosed as having had a subarachnoid haemorrhage, or a diagnosis is strongly suspected, you will probably be transferred to a neurosciences unit.

These units have a range of equipment and treatments that can be used to support many of the body's vital functions, such as breathing, blood pressure and circulation.

In more severe cases, you may be transferred to an intensive care unit (ICU).

The treatments you may have are described below.



One of the main complications of a subarachnoid haemorrhageis secondary cerebral ischaemia. This is where the supply of blood to the brain becomes dangerously reduced, disrupting the normal functions of the brain, causing brain damage.

You will usually be given a medication called nimodipine to reduce the chances of this happening. This is normally taken for three weeks, by which point the risk of secondary cerebral ischaemia has usually passed.

Side effects of nimodipine are uncommon, but can include flushing, feeling sick, increased heart rate, headaches and a rash.

Pain relief

Medication can be effective in relieving the severe headache pain associated with a subarachnoid haemorrhage.

Commonly used pain-relieving medications include morphine and a combination of codeine and paracetamol.

Other medications

Other medications that are sometimes used to treat people who have had a subarachnoid haemorrhage include:

anticonvulsants, such as phenytoin, which may be used to prevent seizures (fits)

antiemetics, such as promethazine, which can help stop you feeling sick and vomiting

Surgery and procedures

If scans have shown that the subarachnoid haemorrhage was caused by a brain aneurysm, a procedure to repair the affected blood vessel and prevent the aneurysm from bleeding again may be recommended.

This can be carried out using one of two main techniques. These are described below.

Neurosurgical clipping

Neurosurgical clipping is carried out under general anaesthetic, meaning you will be asleep throughout the operation. A cut is made in your scalp (or sometimes just above your eyebrow) and a small flap of bone removed, so the surgeon can access your brain.

When the aneurysm is located, the neurosurgeon (an expert in surgery of the brain and nervous system) will seal it shut using a tiny metal clip that stays permanently clamped on the aneurysm. After the bone flap has been replaced, the scalp is stitched together.

Over time, the blood vessel lining will heal along where the clip is placed, permanently sealing the aneurysm and preventing it from growing or rupturing again.

Endovascular coiling

Endovascular coiling is also usually carried out using general anaesthetic. The procedure involves inserting a thin tube called a catheter into an artery in your leg or groin. The tube is guided through the network of blood vessels into your head and into the aneurysm.

Tiny platinum coils are then passed through the tube and into the aneurysm. Once the aneurysm is full of coils, blood cannot enter it. This means the aneurysm is sealed off from the main artery, which prevents it from growing or rupturing again.

Coiling versus clipping

Whether clipping or coiling is used depends on things such as the size, location and shape of the aneurysm.

Coiling is often the preferred technique because it has a lower risk of short-term complications (such as seizures) than clipping, although the long-term benefits over clipping are uncertain.

People who have the coiling procedure usually leave hospital sooner than people who have the clipping procedure, and the overall recovery time can be shorter.

However, when these types of surgery are carried out as an emergency after a subarachnoid haemorrhage, your recovery time and hospital stay depend more on the rupture's severity than the type of surgery carried out.

Complications of a subarachnoid haemorrhage 

If you have a subarachnoid haemorrhage, there is also a risk of developing further problems.

Some of the main complications are described below.


A potentially serious early complication of a subarachnoid haemorrhage is that the brain aneurysm bursts again after it has sealed itself. This is known as rebleeding.

The risk of rebleeding is highest in the few days after the first haemorrhage, and rebleeding carries a high risk of permanent disability or death. Because of this, aneurysm repair is needed as soon as possible.

Delayed cerebral ischaemia

Delayed cerebral ischaemia, or vasospasm, is another serious and common complication of a subarachnoid haemorrhage. This is when the supply of blood to the brain becomes dangerously low, disrupting the normal functions of the brain and causing brain damage. It is most common a few days after the first haemorrhage.

The cause is uncertain, but vasospasm of the arteries inside the brain may be a factor. Vasospasm is when a blood vessel goes into a spasm, causing the vessel to narrow.

Common symptoms are increasing drowsiness, which can lead to a coma, with or without other stroke-like symptoms, such as weakness down one side of the body.


Hydrocephalus is a build-up of fluid on the brain, which increases pressure and can cause brain damage.

This can cause a wide range of symptoms, including:


being sick

blurred vision

difficulty walking

Hydrocephalus is common after subarachnoid haemorrhage, as the damage caused by a haemorrhage can disrupt the production and drainage of cerebrospinal fluid (CSF).This can lead to increased amounts of fluid around the brain.

CSF is a clear colourless fluid that supports and surrounds the brain and spinal cord. A constant supply of new CSF is produced inside the brain, while the old fluid is drained away into blood vessels.

Hydrocephalus may be treated with a lumbar puncture or a temporary tube that is surgically implanted into the brain to drain away the excess fluid.

Long-term complications

There are a number of long-term complications that can affect people after a subarachnoid haemorrhage. These are outlined below.


Around 1 in 20 of people who have a subarachnoid haemorrhage develop epilepsy.

This is a condition where the normal working of the brain is interrupted, causing a person to have repeated fits or seizures.

There are different types of seizure, and symptoms vary. You may lose consciousness, have muscle contractions (your arms and legs twitch and jerk) or your body may shake or become stiff. Seizures usually last between a few seconds and several minutes, before brain activity returns to normal.

In most cases of epilepsy following a subarachnoid haemorrhage, the first seizure occurs in the year after the haemorrhage.

Epilepsy can be treated using anti-epileptic medicines, such as phenytoin or carbamazepine. A specialist called a neurologist will help decide which treatment you need and how long you need to take it for. 

Cognitive dysfunction

Cognitive dysfunction is when a person experiences difficulties with one or more brain functions, such as memory.

Cognitive dysfunction is very common complication of a subarachnoid haemorrhage, affecting most people to a certain degree.

Cognitive dysfunction can take a number of forms, such as:

problems with memory – memories before the haemorrhage are normally not affected, but you may have problems remembering new information or facts

problems with tasks that require some degree of planning – you may find that even simple tasks, such as making a cup of tea, are difficult and frustrating

problems with concentration or attention

There are a number of self-care techniques you can use to compensate for any dysfunction. For example, breaking tasks down into smaller steps and using memory aids (such as notes or a diary) can help.

A specialist called an occupational therapist can also help make day-to-day activities easier, while a speech and language therapist can help with communication skills. The doctor in charge of your care can tell you how to access these types of services.

Most cognitive functions will improve with time, though problems with memory can be persistent.

Emotional problems

Emotional problems are another common, long-term complication of a subarachnoid haemorrhage.

These problems can take a number of forms, such as:

depression – feeling very down, hopeless and not getting any real enjoyment out of life

anxiety disorder – a constant sense of anxiety and dread that something terrible is going to happen

post-traumatic stress disorder (PTSD) – where a person often relives a previous traumatic event (in this case the haemorrhage) through nightmares and flashbacks, and they may experience feelings of isolation, irritability and guilt

These mood disorders can be treated using a combination of medication, such as antidepressants, and talking therapies, such ascognitive behavioural therapy (CBT).

Preventing subarachnoid haemorrhage 

It's not always possible to prevent a subarachnoid haemorrhage, but there are things you can do to reduce your risk of having one.

Most importantly, you should avoid two of the main things that increase your chances of developing a brain aneurysm – smoking and having high blood pressure.


Stopping smoking can significantly reduce your risk of developing a brain aneurysm.

If you decide to quit, your GP can refer you to an  Stop Smoking Service, which can give you help and advice. You can also call theSmoking Helpline on 0300 123 1044. The specially trained helpline staff can offer you free expert advice and encouragement.

If you're committed to giving up smoking but don't want to be referred to a stop-smoking service, your GP should be able to prescribe medical treatment to help with any withdrawal symptoms you may have after quitting.

High blood pressure

Having high blood pressure can also significantly increase your chance of developing a brain aneurysm.

You can help reduce high blood pressure by:

eating a healthy diet – in particular, cutting down on salt and eating plenty of fruit and vegetables

moderating your alcohol intake – it's recommended that men don't regularly drink more than 3 to 4 units a day; women shouldn't regularly drink more than 2 to 3 units a day

maintaining a healthy weight – if you are overweight, losing a few pounds will make a big difference to your blood pressure and overall health

exercising regularly – being active and taking regular exercise lowers blood pressure by keeping your heart and blood vessels in good condition