Subarachnoid hemorrhage : incidence, risk factors and sex differences

Abstract

Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space surrounding the brain. SAH may occur spontaneously, or following traumatic brain injury. Spontaneous SAH is in 85% of cases caused by rupture of an outpouching (aneurysm) of an intracranial artery. This is called an aneurysmal SAH (aSAH). The main findings of the present thesis concerned the incidence of aSAH in Norway, and sex differences in the risk factors for aSAH. The data source was the Norwegian Patient Register, and a combined cohort of the Tromsø study and the Nord-Trøndelag Health Study. The crude incidence of aSAH in Norway decreased from 11.1 per 100,000 person-years (95% confidence interval, CI: 10.5–11.6) in the period 1999–2001 to 8.9 per 100,000 person-years (95% CI: 8.4–9.4) in the period 2005–2007. Significant regional variations were observed, indicating an increasing gradient from south to north. Daily cigarette smoking was approximately twice as hazardous in women as in men (Hazard ratio, HR 6.5, 95% CI 3.56-11.9 vs HR 3.5, 95% CI 1.6-7.4). After adjusting for age, hypertension, and alcohol consumption, current cigarette smoking was 3.4 times more hazardous in female than male participants (HR 9.8, 95% CI 5.1-18.7 vs HR 2.9, 95% CI 1.3-6.3).