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:
- Hereditary connective tissue disorders
- Septic emboli – rare – “mycotic aneurysm” – the name just means ‘caused by fungi’, although most are actually due to gram-negative bacteria
- 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.
- <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.