What is a brain aneurysm?

A brain aneurysm is a bulge on the wall of an artery that supplies the brain.  An aneurysm is an acquired lesion and not congenital (we are not born with an aneurysm). Aneurysms develop from wear and tear changes of the blood vessel wall. So, they occur with increasing frequency as we get older.

Risk factors for aneurysm development and rupture include:

  • a family history of aneurysms
  • smoking
  • high blood pressure

Occasionally, aneurysms are associated with connective tissue disorders such as Marfan’s syndrome, Ehlers-Danlos syndrome and with adult polycystic kidney disease.

Subarachnoid Haemorrhage – A Ruptured Brain Aneurysm

Most aneurysms do not cause any symptoms and patients are unaware of their existence. If an aneurysm ruptures, however, it causes a subarachnoid haemorrhage. This is bleeding around the surface of the brain and can be life-threatening. This is often associated with an abrupt onset of symptoms like:

  • severe headache
  • neck pain
  • nausea and vomiting
  • neck stiffness
  • photophobia (intolerance of bright light)
  • seizure
  • confusion or unconsciousness

Subarachnoid Haemorrhage Treatment

A ruptured aneurysm must be secured as soon as possible to prevent re-bleeding. This is done by endovascular coiling or by craniotomy and clipping.

Endovascular Coiling

Coiling is usually performed by an expert neuro-radiologist. They will pass a catheter through an artery in the groin and navigate through the arterial tree to reach the aneurysm and fill it with platinum coils.

Craniotomy and Clipping

Craniotomy involves an incision behind the hairline to open a small window on the skull to reach the outer membrane of the brain (dura). It is through this that a cerebrovascular neurosurgeon working under a microscope finds the aneurysm. They then apply a spring-loaded clip across its neck to stop it from filling.

Subarachnoid Haemorrhage Complications

After a subarachnoid haemorrhage, patients may develop other complications:


This is a build-up of fluid in the ventricles of the brain that may need drained. Find out more about hydrocephalus here.


A delayed stroke may occur from inadequate blood supply to parts of the brain. This problem often occurs several days after the initial haemorrhage. It is usually associated with the narrowing of cerebral blood vessels (vasospasm). Patients may need additional intensive treatments to prevent a permanent stroke.

Therefore, patients need to stay in hospital for one or two weeks or longer, for monitoring and treatment after a subarachnoid haemorrhage.

What are the risks of a brain aneurysm rupturing?

In many cases an aneurysm is discovered before it ruptures, often incidentally. In general, the risk of an aneurysm rupturing in the short term is small (usually less than 1% risk of rupture per year for an aneurysm less than 10mm).

This risk is higher with:

  • posterior circulation aneurysms
  • increasing aneurysm size
  • aneurysms that are seen to be growing on serial imaging

The risk of aneurysm rupture is also higher in patients who:

  • smoker
  • have high blood pressure that is not controlled with medication
  • have had a previous subarachnoid haemorrhage
  • have a first degree relative who had a subarachnoid haemorrhage

Even though the risk of rupture for most aneurysms is relatively small in the short term, this risk is cumulative. In the long term the risk of rupture adds up. For many patients it is safer to secure the aneurysm with either endovascular techniques or microsurgical clipping.

Click here to return to the cerebrovascular diseases page.

To make an appointment with one of our neurosurgeons, please call 03 9329 4761.

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