**1.1. Epidemiology & morbidity**

The clinical burden of aneurysmal SAH is immense. Case fatality approaches 50%, and approximately 1 in 8 patients die prior to reaching the hospital [2]. Of those that survive, nearly 50% will have significant functional impairment [3]. Aneurysmal SAH accounts for approximately 85% of all non-traumatic SAH. Approximately 30,000 Americans are affected annually [1]. The incidence of aneurysmal SAH ranges from 6-21/100,000 patient years [4].

#### **1.2. Risk factors**

Risk factors for development of aneurysmal SAH can be categorized as modifiable and nonmodifiable. Modifiable risk factors include cocaine abuse, hypertension, and cigarette smoking [4]. It is estimated that cigarette use increases the risk of aneurysmal SAH by a factor of 3.7-3.9 [5]. Non-modifiable risk factors include sex, ethnicity, family history, and collagen-vascular diseases. The female:male ratio for aneurysmal SAH is approximately 2:1 [6]. The incidence of aneurysmal SAH is higher amongst people of Finnish and Japanese descent; and the incidence of aneurysmal SAH is almost three times greater in Finland than other parts of the world [4]. The incidence of intracranial aneurysms is higher in patients

© 2012 Patel and Samuels, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

with collagen vascular diseases, such as Marfan's Syndrome, Ehlor's-Danlos Disease, Neurofibromatosis Type 1, and Autosomal dominant polycystic kidney disease [7].

Borrowed with permission: Ellegala D, Day A. (2005) Ruptured Cerebral Aneurysms. New England Journal of Medicine. 352: 121-124

**Figure 1.** The arterial blood supply to the brain is located primarily in the subarachnoid space (Panel B). Aneurysm formation occurs in the subarachnoid space (Panel C), which must be surgically accessed to provide definitive treatment of the aneurysm (Panel E).
