We use strictly necessary cookies to make our site work. We would also like to set optional cookies (analytical, functional and YouTube) to enhance and improve our service. You can opt-out of these cookies. By clicking “Accept All Cookies” you can agree to the use of all cookies.

Cookies Statement and Privacy Statement

Bleeding in the brain

Page last reviewed: 13/07/2011

A subarachnoid haemorrhage is an uncommon cause of a stroke where blood leaks out of blood vessels over the surface of the brain. Like all strokes, a subarachnoid haemorrhage is a medical emergency that requires immediate treatment to prevent serious complications, brain damage and death.

It is known as a subarachnoid haemorrhage because the bleeding occurs in the arteries that run underneath a membrane in our brain called the arachnoid, which is just below the surface of the skull.

Three quarters of subarachnoid haemorrhages are caused when an aneurysm ruptures (burst). An aneurysm is a bulge in a blood vessel that is caused by a weakness in the blood vessel wall.

During a subarachnoid haemorrhage, the blood damages the brain tissue. The reduction of blood supply can also cause further brain damage, leading to disruption or loss of brain function and possibly death.

How common are subarachnoid haemorrhages?

Subarachnoid haemorrhages are uncommon, responsible for only 5% of all strokes. However, they are a leading cause of death, responsible for a quarter of all deaths related to strokes.

Every year around 500 people in Ireland have a subarachnoid haemorrhage. It is more common in middle-aged people, and women are more likely to be affected than men.


A subarachnoid haemorrhage is an extremely serious condition and for many people the outlook is poor. 10-15% of people with a subarachnoid haemorrhage will die before they can be admitted to hospital, and 50% will die within 30 days after the haemorrhage.

However, the prospects of recovery are good if the patient survives the initial bleeding and they are transferred quickly to a specialist neurosurgical unit (a medical unit that specialises in treating conditions of the brain and nervous system).

A number of surgical techniques have proved successful in treating subarachnoid haemorrhages. Following treatment, a long period of rehabilitation will be necessary.

If you have a subarachnoid haemorrhage, it may have implications for driving. See Subarachnoid haemorrhage -complications for more information and advice about driving following a subarachnoid haemorrhage.

To haemorrhage means to bleed or lose blood.
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Blood vessels
Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessels are veins, arteries and capillaries.
The brain controls thought, memory and emotion. It sends messages to the body controlling movement, speech and senses.
Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.

Page last reviewed: 13/07/2011

Symptoms of a subarachnoid haemorrhage include:

  • a sudden and severe headache - it has been described as a 'thunderclap headache', similar to a sudden hit on the head, resulting in a blinding pain unlike anything ever experienced before
  • stiff neck
  • sickness and vomiting
  • slurred speech
  • changes in personality and behaviour, such as depression, apathy or extreme mental confusion (delirium)

Around 30-40% of people who have a subarachnoid haemorrhage will also experience impaired or total loss of consciousness.

Sometimes, the symptoms of a subarachnoid haemorrhage can be similar to meningitis (an infection of the layers of the brain) because in both conditions people experience a severe headache and a stiff neck.

Unlike meningitis, people with a subarachnoid haemorrhage will not usually have a high fever or have a rash on their skin. However, both conditions are extremely serious and emergency medical treatment should be sought straightaway in either case.

Warning signs

Around 1 in 10 people will experience warning signs that they are going to have a subarachnoid haemorrhage, usually a few days or weeks beforehand.

The signs can take the form of:

  • a sudden and severe headache – which is the most common warning sign
  • dizziness
  • eye pain
  • double vision
  • loss of vision

If you experience any of these warning signs, it is recommended that you see your GP, especially if you have no previous history of having severe headaches. While the warning signs are unlikely to be caused by a subarachnoid haemorrhage, these type of symptoms require further investigation.

Page last reviewed: 13/07/2011

Blood circulation

Like all of the body's organs, the brain needs blood to provide it with oxygen and other essential nutrients.

Our circulation system is made up of arteries and veins. The blood is pumped from your heart through the aorta (the main artery leading from the heart), before travelling through smaller and smaller arteries that branch off from each other. The blood passes into tiny vessels known as capillaries, where the oxygen in the blood is transferred into the cells that make up our body's tissues and organs.

The capillaries then move the blood into our veins, which carry it back to the heart. The veins are weaker and smaller than the arteries, so the capillaries must also reduce the speed and pressure of the blood.

Subarachnoid haemorrhages are mainly caused by aneurysms and arteriovenous malformations, which are both defects or weaknesses in the blood vessels.


For reasons largely unknown, around 1 in every 100 people are born with defects affecting the blood vessels in their brain. Some of the blood vessels have a thinned and weakened wall, which bulges outwards like a balloon when the blood runs through them. These are known as berry aneurysms.

If a berry aneurysm bursts, a subarachnoid haemorrhage will occur. Not everyone who has a berry aneurysm will experience a haemorrhage. In fact, haemorrhages among people with berry aneurysms are very rare, occurring in about 1 in 700 people.

However, you can increase the risk of aneurysm bursting by:

Around 70% of subarachnoid haemorrhages are caused by aneurysms. After it has burst, the aneurysm will often seal itself and the bleeding will stop. However, there is a high risk that without treatment, the aneurysm will burst again and cause more bleeding.

Arteriovenous malformations

Arteriovenous malformations occur when the blood vessels develop abnormally. They affect approximately 1 in every 100 people and, although the exact cause is unknown, they are thought to be the result of a problem that occurs during the development of the baby in the womb.

Arteriovenous malformations can occur anywhere in your body but they very rarely occur in the brain, with just 1 in every 10,000 people being affected. They can cause problems because they affect the way that blood is pumped around our body.

In people with arteriovenous malformations there can be a direct connection between the arteries and the veins, without the capillaries to reduce the speed and pressure of the blood. This can cause the veins to expand and, in the case of a subarachnoid haemorrhage, split and bleed.

Most people with an arteriovenous malformation in the brain experience no symptoms until a haemorrhage occurs. Arteriovenous malformations cause around one in ten subarachnoid haemorrhages.

Severe head injury

Bleeding inside the brain can also develop after a severe head injury.

Page last reviewed: 13/07/2011

The initial diagnosis of a subarachnoid haemorrhage can be made through the characteristic symptoms of the condition, such as a sudden onset of severe headache and a stiff neck.

Following an initial diagnosis it is likely that you will be referred to a specialist neurosurgical unit for further tests to confirm the diagnosis and, afterwards, to decide on the best course of treatment.
The most common tests that are used for investigating cases of subarachnoid haemorrhage are outlined below.

Computerised tomography (CT) scan

A computerised tomography (CT) scan is like an X-ray, but it uses multiple scans or images to build up a more detailed three-dimensional picture of your brain. The scan can be used to detect the presence and location of blood around your brain and any problems that it may be causing. Sometimes a coloured dye is injected into the blood to help pinpoint the source of the bleeding.

Lumbar puncture

The brain and spinal column are surrounded by a clear liquid called cerebrospinal fluid. If a subarachnoid haemorrhage has occurred, there will be blood in the fluid. To get a sample of cerebrospinal fluid, a needle is inserted into the lower end of your spine and a sample is drawn off. You may find the procedure a little uncomfortable but you will be given a local anaesthetic to numb the area.

MRI scan

A magnetic resonance imaging (MRI) scan uses strong magnetic fields and radio waves to produce a detailed image of the inside of the body. The scan can be used to detect problems in the blood vessels and, occasionally, detect the haemorrhage itself.

Doppler ultrasound

One of the most serious complications associated with subarachnoid haemorrhage is cerebral vasospasm. This is when the arteries in the brain go into spasm, leading to further loss of blood, brain damage and possibly death. Often, a cerebral vasospasm will cause no immediate symptoms so the condition can go unnoticed.

A Doppler ultrasound is a test that uses ultrasound to monitor the flow of blood in the brain. Sudden changes in the speed of blood flow would indicate that a cerebral vasospasm has occurred, so immediate treatment would then begin.

See Subarachnoid haemorrhage - complications for more information on cerebral vasospasm.

Page last reviewed: 13/07/2011


After a subarachnoid haemorrhage occurs, some of the blood vessels near the burst aneurysm can then go into spasm. This is known as cerebral vasospasm, and it can lead to a further loss of blood to the brain, causing brain damage.

To prevent this happening, you may be given a medication called nimodipine, which you will need to take for three weeks. Nimodipine was originally used to treat high blood pressure, but it was found to be more useful in preventing spasms. Side effects of nimodipine include:

  • sweating and flushing
  • nausea
  • swelling of the feet, ankles or legs
  • stomach upsets

The powerful painkiller morphine can be used to help relieve the symptoms of a severe headache. As your condition improves, less powerful painkillers such as paracetamol can be used as an alternative.

Neurosurgical clipping

Neurosurgical clipping is a procedure that is carried out under general anaesthetic (where you are put to sleep). During the procedure, an incision (cut) is made in your scalp and a small flap of bone is removed to reveal your brain below.

The neurosurgeon (an expert in surgery of the brain and nervous system) will carefully search for the aneurysm and, after locating it, seal it shut using a tiny metal clip. After the 'bone flap' has been replaced, the neurosurgeon will stitch the scalp together.

Neurosurgery is an incredibly complex and difficult procedure and success can never be guaranteed.

However, neurosurgical clipping has a relatively good success rate, with 70% of people making a significant or even a full recovery after the operation.

Endovascular coiling

Endovascular coiling is a procedure that involves a tiny plastic tube or catheter being inserted into an artery in your leg or groin. The tube is then guided through the network of your blood vessels into your head and finally into the aneurysm.

Tiny platinum coils are then passed through the tube into the aneurysm. These coils block the flow of blood into the aneurysm and so prevent further haemorrhaging.

Endovascular coiling is an increasingly preferred treatment option as it has a higher success rate, with 77% of people making a significant improvement or a full recovery after the operation.

Also, due to the less invasive nature of endovascular coiling compared with neurosurgical clipping, recovery times are usually quicker.

Page last reviewed: 13/07/2011

Cerebral vasospasm

Cerebral vasospasm is the most serious complication of a subarachnoid haemorrhage and is common. It affects around half of people with a subarachnoid haemorrhage and is responsible for 20% of deaths or cases of serious brain damage associated with subarachnoid haemorrhage.

However, the number of cases of cerebral vasospasm is expected to fall due to the use of nimodipine as a preventative medication.

During a cerebral vasospasm the arteries in the brain go into spasm, interrupting the supply of blood to the brain. The reasons why cerebral vasospasm occurs is still uncertain.

Cerebral vasospasm usually develops three to four days after a subarachnoid haemorrhage.

The main symptom is increasing mental confusion. If left untreated, a person can then lapse into unconsciousness, then a coma, and then die.

Cerebral vasospasm can be treated with what is known as 'triple H therapy', where the 3 Hs stand for:

  • hypervolemia - which means pumping fluids into the blood
  • hypertension - using medication to raise blood pressure
  • haemodilution - where additional blood and plasma (the liquid that makes up most of your blood) is transfused into the body.

The goal of triple H therapy is to increase the flow of blood, so the supply of blood to the brain is restored.

If triple H therapy does not prove effective, surgery is usually required to prevent further damage to the brain. Surgery usually involves implanting a small balloon in an artery and then inflating it, to restore blood supply.


Around 5% of people who have had a subarachnoid haemorrhage develop epilepsy.

Epilepsy 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 can vary. You may lose consciousness, have muscle contractions (your arms and legs may twitch and jerk) or your body may shake or become stiff. Seizures usually last between a few seconds and several minutes. Brain activity then returns to normal.

In most cases of epilepsy following a subarachnoid haemorrhage, the first seizure occurs within the first year after the haemorrhage. If more than two years have passed since your haemorrhage and you have not had any seizures, it is extremely unlikely you will develop epilepsy.

Epilepsy can be treated using anti-epileptic medicines, such as phenytoin or carbamazepine. You may need to take these medicines for a few months or for the rest of your life.


Hydrocephalus is a condition that occurs when there is too much cerebrospinal fluid in the ventricles (cavities) of the brain. About one in ten people who experience a subarachnoid haemorrhage will develop hydrocephalus.

Cerebrospinal fluid (CSF) is produced in the brain and it protects the brain and spinal cord and carries away waste from brain cells. It flows continuously through the ventricles (cavities or chambers inside the brain) and over the surface of the brain and spinal cord. Any excess CSF usually drains away from the brain and is absorbed by the body.

The damage caused by a subarachnoid haemorrhage can stop the CSF from draining and an excess of fluid can build up. Symptoms include headaches, sickness and vomiting and a loss of balance. However, the condition can be treated by placing a tube into the brain to allow the fluid to drain properly.

Page last reviewed: 13/07/2011

The amount of time it will take you to recover from a subarachnoid haemorrhage will depend on the severity of the haemorrhage.

The location of the haemorrhage will also affect whether you have any associated neurological conditions, such as loss of feeling in your arms or legs or problems understanding speech.

Recovery can be a frustrating process. You may make a lot of progress and then suffer setbacks and it is likely you will have good days and bad days.

Feelings of anger, resentment and sadness are common. Talking to other people with similar conditions via support groups can help provide advice and reassurance. An assessment from a clinical psychologist or referral to a memory clinic can also be helpful.

The common effects of a subarachnoid haemorrhage are outlined below.

Extreme tiredness

During the first three months after your haemorrhage it is normal to feel extremely tired. Even simple tasks, such as going to the shops, can leave you feeling exhausted. Taking regular short breaks of about half-an-hour in a relaxing environment will help.


After having a subarachnoid haemorrhage, many people find they have insomnia (problems getting to sleep) or they can only sleep for short periods.

Having a set daily routine, where you try to get up and go to bed at the same time every day, can help. Also, set time aside for relaxation breaks. If you have returned to work, you could talk to your employer about having extra time for breaks.


Headaches are common after a haemorrhage but they tend to ease in time. They are not normally as severe as when you had your haemorrhage and you should be able to control them with over-the-counter painkillers such as paracetamol.

Drinking plenty of fluids (two to three litres of water a day) should also help reduce the severity and frequency of headaches.

Unusual sensations

After having a subarachnoid haemorrhage, some people have reported experiencing strange or unusual sensations in their brain. These sensations can be difficult to describe but some people have said that they feel ticklish or like somebody is pouring water across their brain.

Nobody is really sure exactly why these strange sensations occur, but they are common and you should not be concerned about them as they should pass in time.

Loss of feeling or movement

Following a subarachnoid haemorrhage, some people experience a loss of movement and/or feeling in their arms or legs. This can range from a slight weakness to a complete loss of power.

You may also have problems distinguishing between hot and cold, so you should be careful when taking a bath or showering. A training and exercise plan carried out under the supervision of a physiotherapist can often help restore feeling and movement to affected limbs.

Changes in senses

Many people experience changes to their sense of smell and taste after they have had a subarachnoid haemorrhage. The senses can be heightened or reduced.

You may find that your favourite food now tastes disgusting, while something you hated now tastes delicious. However, these changes in the senses are normally temporary and will resolve as the swelling on your brain goes down.


Following a brain injury, problems with your vision such as blurring, blind spots, black spots and double vision are common.

Your vision will be tested before you leave hospital and if necessary, you will be referred to an ophthalmologist (a doctor who specialises in the care of the eye). Improvement in your vision will usually happen gradually over a number of months.

Communication problems

Verbal and written communication is a complex neurological process involving many parts of the brain. These processes can often be disturbed by a haemorrhage. You may find it difficult to find the right words to express yourself or you may have problems understanding other people. Speech therapists can help you recover your communication skills.


Memory and concentration problems are common after a haemorrhage. You may find that even simple tasks, such as making a cup of tea, are difficult and frustrating.

Your memories before the haemorrhage are normally not affected, but you may have problems remembering new information or facts. Try breaking tasks down into smaller steps, and using memory aids such as notes or a diary.

Your memory and concentration will normally improve over time but it is unlikely they will return to their pre-haemorrhage levels.

Psychological effects

You may also experience a range of psychological effects, such as mood swings, stress, anxiety and depression. A clinical psychologist can assess you and help you with these.

Page last reviewed: 13/07/2011

Aneurysm screening

The risks of an aneurysm causing a haemorrhage in the general population is extremely low, so testing or screening for them is not routinely carried out.

However, two or more close blood relations who have experienced a subarachnoid haemorrhage increases the risk of you developing the condition.

A study carried out in Holland found that people with two (or more) close blood relations with a history of subarachnoid haemorrhage had a one in four chance of also having a subarachnoid haemorrhage.

It is recommended that you undergo screening every five years if you have two or more close (first-degree) blood relatives who have experienced a subarachnoid haemorrhage, such as your mother, father, brother, aunt or uncle (but not your grandmother or grandfather).

Your GP should be able to refer you to a neurologist for further assessment. If the neurologist finds that you have an aneurysm, it will be possible to strengthen it during surgery, reducing the risk of it bursting. See Aneurysm - treatment for more information.

Blood pressure

Taking steps to prevent high blood pressure (hypertension) will place less strain on any aneurysms that you have and will reduce the risk of them bursting.

You can help treat and reduce your risk of developing high blood pressure by making the following lifestyle changes:

  • Eat a healthy, well-balanced diet with less salt (the recommended level of salt is no more than 6g (0.2oz) a day; 6g of salt is about a teaspoonful).
  • Lose weight (if you are overweight) - you can use the Body Mass Index (BMI) calculator to find out whether you are a healthy weight.
  • Exercise regularly - 30 minutes of vigorous exercise a day, at least five times a week.
  • Stop smoking (if you smoke).
  • Reduce your alcohol and caffeine consumption to recommended levels. The recommended daily levels are between three to four units of alcohol for men, and between two to three units for women. One unit of alcohol is equal to about half a pint of normal-strength lager, a small glass of wine or a pub measure of spirit. The recommended daily level of caffeine is 300mg, which is roughly the equivalent of three cups of coffee.

See the Health A-Z topic about high blood pressure for more information and advice about how to control your blood pressure.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

Browse Health A-Z