- Subarachnoid haemorrhage typically presents with a sudden, severe 'thunderclap' headache accompanied by vomiting that lasts for hours or days. It has an incidence of 6 per 100,000 people and only 1 in 8 with a sudden severe headache will have a SAH. - 85% of SAHs are caused by saccular aneurysms bulging from cerebral artery bifurcations, particularly in the circle of Willis. 10% are non-aneurysmal haemorrhages and 5% are caused by other rarities like arteriovenous malformations. - The immediate mortality of aneurysmal SAH is about 30%. Survivors have a 40% risk of re

1. SUBARACHNOID HAEMORRHAGE