Summary

• Acquired focal abnormal dilation of the wall of an artery in the brain.
• Typically asymptomatic until ruptured, resulting in a subarachnoid haemorrhage.
• Head CT usually confirms the diagnosis, but lumbar puncture is indicated if CT is negative and suspicion persists.
• Cerebral angiogram is the definitive investigation. CT angiography or magnetic resonance angiography may also be used.
• Definitive treatment aims to obliterate the aneurysm from the cerebral circulation. Options include endovascular coiling or open surgical clipping.
• Screening with non-invasive neuroangiography is recommended for at-risk populations.