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Unruptured intracranial aneurysms

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


Most subarachnoid hemorrhages (SAH) are caused by ruptured intracranial saccular (berry) aneurysms. The epidemiology and pathogenesis of intracranial aneurysms and the management of unruptured aneurysms are discussed here. The epidemiology, etiology, clinical manifestations, diagnosis, and treatment of SAH, and issues related to screening for aneurysms are discussed separately. (See "Clinical manifestations and diagnosis of aneurysmal subarachnoid hemorrhage" and "Treatment of aneurysmal subarachnoid hemorrhage" and "Screening for intracranial aneurysm".)


The prevalence of intracranial saccular aneurysms by radiographic and autopsy series is estimated to be 3.2 percent in a population without comorbidity, a mean age of 50 years, and a 1:1 gender ratio [1,2],. Of patients with cerebral aneurysms, 20 to 30 percent have multiple aneurysms [3]. Aneurysmal SAH occurs at an estimated rate of 6 to 16 per 100,000 population [4]. In North America, this translates into approximately 30,000 affected persons per year. Thus, most aneurysms, particularly small aneurysms, do not rupture (see 'Risk of aneurysm rupture' below).

Rupture of an intracranial aneurysm is believed to account for 0.4 to 0.6 percent of all deaths. Approximately 10 percent of patients die prior to reaching the hospital, and only one-third has a "good result" after treatment. (See "Treatment of aneurysmal subarachnoid hemorrhage".)

Most intracranial aneurysms (approximately 85 percent) are located in the anterior circulation, predominantly on the circle of Willis. Common sites include the junction of the anterior communicating artery with the anterior cerebral artery, the junction of the posterior communicating artery with the internal carotid artery, and the bifurcation of the middle cerebral artery. Posterior circulation sites often include the top of the basilar artery, the junction of the basilar artery and the superior or anterior inferior cerebellar arteries, and the junction of the vertebral artery and the posterior inferior cerebellar artery [5].

There is a female preponderance for aneurysms ranging from 54 to 61 percent [2,4]. In populations older than 50 years, the increased prevalence in women may approach a 2 to 1 ratio or greater. (See 'Estrogen deficiency' below.)

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