Subarachnoid Haemorrhage: epidemiological studies on aetiology and outcome

Subarachnoid haemorrhage (SAH) is bleeding into the subarachnoid space ‒ the area between the arachnoid membrane and the pia mater surrounding the brain. SAH occurs spontaneously or can be caused by traumatic injury of the head. Spontaneous SAH is caused by rupture of an intracranial aneurysm in 85 percent of cases. In this thesis we consider both spontaneous SAH in general and in several studies aneurysmal SAH specifi cally. Reliable knowledge about the risks of (aneurysmal) SAH in diff erent populations will help in planning, screening and prevention strategies and in predicting the prognosis of individual patients. The overall incidence of SAH is in general between 5 and 10 per 100,000 person years. However, in Japan and Finland rates are as high as 20 per 100,000 person years. This can partly be explained by genetic and environmental diff erences between these and other countries. The incidence increases with age; and from midlife onwards incidence is higher in women than in men. The reasons for this higher incidence in women are not clear, but hormonal factors (including hormonal medication) have been suggested as a possible explanation.