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Aneurysmal subarachnoid hemorrhage: Epidemiology, risk factors, and pathogenesis

Robert J Singer, MD
Christopher S Ogilvy, MD
Guy Rordorf, MD
Section Editor
Jose Biller, MD, FACP, FAAN, FAHA
Deputy Editor
Janet L Wilterdink, MD


Twenty percent of strokes are hemorrhagic, with subarachnoid hemorrhage (SAH) and intracerebral hemorrhage, each accounting for 10 percent. Most SAHs are caused by ruptured saccular aneurysms. Other causes include trauma, arteriovenous malformations/fistulae, vasculitides, intracranial arterial dissections, amyloid angiopathy, bleeding diatheses, and illicit drug use (especially cocaine and amphetamines).  

The epidemiology and risk factors of aneurysmal SAH are reviewed here. The epidemiology and management of unruptured aneurysms and the clinical features, diagnosis and treatment of aneurysmal SAH, are discussed separately. Mycotic aneurysms and nonaneurysmal subarachnoid hemorrhage are also discussed separately. (See "Unruptured intracranial aneurysms" and "Clinical manifestations and diagnosis of aneurysmal subarachnoid hemorrhage" and "Treatment of aneurysmal subarachnoid hemorrhage" and "Overview of infected (mycotic) arterial aneurysm" and "Nonaneurysmal subarachnoid hemorrhage" and "Perimesencephalic nonaneurysmal subarachnoid hemorrhage".)


The incidence of aneurysmal SAH varies by geographic region. In the United States, the incidence is reportedly between 10 and 15 people per 100,000 population [1,2]. Much lower rates are reported in China (2 cases per 100,000) and in South and Central America (4 per 100,000), while higher rates are reported in Finland and Japan (19 to 23 per 100,000) [3,4].

The mean age at aneurysmal rupture is 55 years [5]. While most aneurysmal SAH occur between 40 and 60 years of age; however young children and the elderly can be affected [6,7]. African Americans appear to be at higher risk than Caucasian Americans [8]. There is a slightly higher incidence of aneurysmal SAH in women, which may relate to hormonal status (see 'Estrogen deficiency' below) [6,9].


Most SAHs are due to the rupture of intracranial aneurysms. Because of this, risk factors for aneurysm formation overlap with risk factors for SAH. Risk factors that are primarily associated with formation of intracranial aneurysms are discussed separately. (See "Unruptured intracranial aneurysms".)

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Literature review current through: Nov 2017. | This topic last updated: Sep 26, 2013.
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