almostadoctor app banner for android and iOS almostadoctor iPhone, iPad and android apps almostadoctor iOS app almostadoctor android app
This is localised dilation of an artery within the brain. They rarely occur in veins. They are a major risk factor for subarachnoid haemorrhage.

Epidemiology & Aetiology

Occur in 5% of the population
Risk factors include:



  • Most commonly occur at the circle of Willis, but do occur at other sites
  • They are not usually circular, but instead made up of many small sacs, hence the name berry aneurysms
  • Usually <2.5cm in diameter

Signs and Symptoms

  • Vast majority are asymptomatic
  • Occasionally might compress a local structures, typically the optic chiasm and the  III, IV, V and VI cranial nerves
  • Aneurysms themselves don’t cause headaches but they may cause subarachnoid haemorrhage, and in 6% of these cases, there may be a preceding headache, thought to be due to a small bleed of the aneurysm before rupture.


Is usually made with MR/CT angiography., and is often discovered incidentally.


  • <7mm risk of rupture is low, and these are not treated, unless causing a local compression problem
  • >7mm they should be treated, with surgical clipping, platinum coiling or less commonly, stenting and balloon treatments.
    • Clipping –  has a lower failure rate, but greater risk of intracranial bleed / mortality as well as post-operative epilepsy
    • Stenting – slightly higher failure rate but safer. A catheter is passed up through the femoral artery. A platinum coil (or several) is left in the aneurysm which causes thrombus of the aneurysm, eliminating it.
    • To coil or clip? – is a decision for the consultants and is usually considered on a case by case basis. Recurrences have better outcomes if clipped.


Read more about our sources

Related Articles