	the notorious "thunderclap"
Etiology	85% aneurysmal (van Gijn and Rinkel 2001), with highest risk of rebleed in first few days
Epidemiology	F>M 1.6:1. Peak age: 50-55. Risk factors: age, hypertension, smoking, ADPKD
Clinical presentation	maximal onset within seconds to minutes
Pathogenesis
Diagnostic investigations	CT within 6h - less useful after that LP - xanthochromia CT angiogram after 2/52 Ddx: reversible cerebral vasoconstriction syndrome - usually accompanied by trigger (Cittadini and Matharu 2009)
Management	A/B: does this patient need I+V (airway protection) C: Nimodipine - prevent vasospasm; BP control; Anticoagulant reversal if necessary D: Neurosurgical referral for clipping/coiling, ICP management Screening: only if >1 first-degree relative affected - only via specialty services to offer appropriate counselling

ottawa SAH rule: investigate further if any of the 6 rules are met

recent relevant research: SHED-CT