Aneurysm is the word used to describe a swelling that occurs in an artery or vein when its wall is weakened. This happens to blood vessels in the same way that the tyre of a motor car may show a bulge at a weak point.

Aneurysms can form in the blood vessels in almost any part of the body and they can have serious consequences. Aneurysms that affect blood vessels in or around the brain are called intracerebral or intracranial aneurysms.

The greatest danger from an aneurysm is that it may rupture (burst). This may happen after many years of increasing pressure and thinning of the wall of the affected blood vessel, rather like a balloon that is over-inflated. When a brain aneurysm ruptures and bleeds (haemorrhages), it can cause a stroke.


Brain aneurysms that have not ruptured generally do not cause any symptoms, and may only be noticed when brain scans are done for other conditions. However, sometimes a growing aneurysm can put pressure on the surrounding brain tissue and nerves. This may cause symptoms such as:

  • weakness or numbness affecting one side of the face;
  • vision problems such as double vision; or
  • pain behind or around one eye.

A ruptured aneurysm can cause a subarachnoid haemorrhage (when blood collects between the brain and the membranes that surround it) or, less often, an intracerebral haemorrhage (bleeding within the brain).

The first symptom of a haemorrhage is usually a headache. The headache comes on suddenly, and is severe – many people have described this type of headache as ‘the worst headache they have ever had’. It is also described as a ‘thunderclap’ headache.

Sometimes a brain aneurysm will leak a small amount of blood, causing a sudden headache. It is almost always followed by a more severe bleed several weeks later.

In addition to a sudden, severe headache, other symptoms of a brain haemorrhage include:

  • nausea and vomiting;
  • stiff neck;
  • photophobia (dislike or extreme sensitivity to lights);
  • weakness of arms or legs, or one side of the face;
  • problems with eyesight (such as double vision or blurry vision);
  • confusion;
  • seizures; and
  • loss of consciousness.

If you or someone you are with has any of these symptoms, call 000 for an ambulance. A brain haemorrhage is a medical emergency and needs urgent medical attention.

Who gets brain aneurysms?

Brain aneurysms can affect Australians of any age, however they are most commonly found in people aged 40 to 60 years. Women tend to be affected slightly more often than men.

Overall, aneurysms are found in up to 5 per cent of people, but many of these people will not have a ruptured aneurysm.


There are several reasons why some people develop aneurysms. They may be present at birth (congenital aneurysm). Other causes include:

  • smoking;
  • high blood pressure;
  • atherosclerosis (a condition that affects blood vessels and results in a build-up of fatty deposits and reduced elasticity of arteries);
  • family history of aneurysms;
  • connective tissue conditions that can weaken the walls of blood vessels (including Ehlers-Danlos syndrome or Marfan syndrome);
  • polycystic kidney disease (an inherited condition that is associated with an increased risk of brain aneurysm); and
  • drug abuse (especially ongoing cocaine abuse, which can cause inflammation of blood vessels).

Rarely, a previous head injury can lead to the development of a brain aneurysm.

Risk factors for aneurysm rupture

The risk of an aneurysm bursting is increased if you:

  • have untreated high blood pressure;
  • have a sudden rise in blood pressure due to straining or heavy lifting, or stress or other strong emotions;
  • drink alcohol in excess;
  • are a smoker; or
  • abuse illicit drugs such as cocaine.

The size of the aneurysm also affects whether it is more likely to rupture, with very small aneurysms having a low risk of rupture.

Tests and diagnosis

Your doctor will ask about your symptoms and perform a physical examination.

Imaging tests

If an enlarging aneurysm is causing symptoms, testing with CT or MRI scans may be recommended. Sometimes a contrast material is injected into a vein before a CT scan to highlight blood flow in the brain – this type of scan is called CT angiography. Magnetic resonance angiography (MRA) is another type of scan that can give more detailed images of blood vessels.

In many cases, an aneurysm will not have any symptoms until it ruptures, causing a brain haemorrhage. A brain haemorrhage is an emergency that needs immediate medical attention in hospital. A brain scan (an MRI or CT scan of the brain) will most likely be done to confirm the diagnosis and show the extent of the bleeding.

Lumbar puncture

Doctors sometimes recommend doing a test called a lumbar puncture to confirm a diagnosis of subarachnoid haemorrhage. This test involves taking a sample of cerebrospinal fluid (CSF) – the fluid that surrounds your brain and spinal cord – by inserting a small needle into the back (usually under local anaesthetic).


An angiogram may be recommended to detect a small aneurysm or if other scans have not provided detailed images of an aneurysm. An angiogram can provide more detailed information on the location and size of an aneurysm.

In an angiogram, a thin tube is inserted into an artery in the groin under local anaesthetic. The tube is gently threaded up to the arteries in the neck, where a special dye (called contrast) is injected to highlight blood vessels in the brain, and then scans are taken. This test is more invasive than the other imaging tests.


Treatment for a brain aneurysm will depend on its location and size and whether it has ruptured or is likely to rupture.

Monitoring and treating risk factors may be the only treatment needed for some people with small aneurysms that are considered to have a low risk of rupture. (Aneurysms less than 10 mm in size – which are often found incidentally during scans performed for other reasons – have a very small risk of rupture.) Regular scans to check the size of the aneurysm are usually recommended, as well as monitoring of blood pressure and other risk factors for rupture.

Treating aneurysms

Brain aneurysms can be treated to stop or prevent bleeding. Treatment may involve the following.

  • Surgically clipping the aneurysm. This is where a neurosurgeon puts a tiny metal clip around the aneurysm to prevent blood flow through it. This prevents the aneurysm from bursting and bleeding.
  • Endovascular coiling. This is a procedure where a thin tube is inserted into a blood vessel in your groin and then gently threaded through to the blood vessel in your head that has the aneurysm. Tiny, soft metal coils are inserted into the aneurysm, blocking blood flow and stimulating the formation of a blood clot in the aneurysm, stopping it from rupturing and bleeding. Endovascular coiling is less invasive than surgical clipping, but sometimes the procedure needs to be performed more than once.

These treatments are associated with some risks – your doctor can discuss the risks and benefits of treating an aneurysm to prevent bleeding. Your doctor will take into account your age, general health, family history and medical conditions that may increase the risk of rupture.

Treating brain haemorrhages

A ruptured brain aneurysm that causes a brain haemorrhage is a serious condition that needs immediate treatment in hospital.

Treatment will depend on:

  • the location of the bleeding;
  • the extent of possible damage to the brain; and
  • the general health of the person.

Treatment may include clipping or endovascular coiling of the aneurysm to prevent further bleeding.

Other treatments may be given to reduce brain swelling, optimise blood pressure and prevent complications. Rehabilitation may be needed to help recovery from a haemorrhagic stroke (brain damage resulting from the brain haemorrhage).

Treating complications

Common complications resulting from brain haemorrhages include the following.

  • Vasospasm of blood vessels in the brain. After a brain haemorrhage, the other blood vessels in the brain can suddenly contract (become narrower), affecting blood flow to the brain and causing further brain damage. Medicines are usually given to keep the brain’s blood vessels open.
  • Hydrocephalus is a build-up of cerebrospinal fluid (CSF) that leads to expansion of the spaces in the brain that contain CSF (the ventricles). This puts pressure on the brain tissue and can damage the brain. Treatment may include inserting a drain to relieve the pressure.


While it’s not possible to prevent a brain aneurysm from forming, you can help reduce the risk of an aneurysm rupturing by:

  • stopping smoking;
  • treating high blood pressure; and
  • avoiding stimulant drugs such as cocaine.

Last Reviewed: 05/07/2016



1. Mayo Clinic. Brain aneurysm (updated 1 Sep 2015). (accessed Jun 2016). 2. NHS Choices. Brain aneurysm (updated 14 Oct 2015). (accessed Jun 2016). 3. National Institute of Neurological Disorders and Stroke (NINDS). Cerebral aneurysms (updated 26 April 2016). (accessed Jun 2016). 4. Subarachnoid haemorrhage (published July 2011). In: eTG complete. Melbourne: Therapeutic Guidelines Limited; 2016 Mar. (accessed Jun 2016). 5. Intracerebral haemorrhage (published July 2011). In: eTG complete. Melbourne: Therapeutic Guidelines Limited; 2016 Mar. (accessed Jun 2016).