Intracranial aneurysms are a source of clinical concern because their rupture can cause subarachnoid haemorrhage, which is associated with high risk of death and disability. The prevalence of intracranial aneurysms has been difficult to assess but is estimated to be roughly 2% of the general population in North America. The size of an intracranial aneurysm is the greatest predictor of rupture. Other predictors of rupture include a prior history of subarachnoid haemorrhage and the location of the aneurysm. The majority of intracranial aneurysms discovered incidentally in the general population are smaller than 10 mm in diameter and pose little risk of rupture. Aneurysms requiring treatment can be treated with surgical clipping or endovascular coil embolisation. A large randomised study has shown that the functional outcome at 1 year is better after endovascular coiling than with surgical clipping in patients suitable for either therapy.

Key concepts:

• Intracranial aneurysms occur in an estimated 2% of the North American general population.
  
• Rupture of an intracranial aneurysm leads to a devastating type of stroke called subarachnoid haemorrhage.
  
• Size of an intracranial aneurysm is the greatest predictor of rupture.
  
• More than 90% of unruptured aneurysms are less than 10 mm in diameter and have a low yearly risk of rupture.
  
• Intracranial aneurysms at risk for rupture can be treated with surgical clipping or endovascular embolisation.
  
• Ruptured aneurysms require prompt treatment to prevent a catastrophic recurrent haemorrhage.