Subarachnoid hemorrhage (SAH) is often a devastating event. Approximately 10 percent of patients die prior to reaching the hospital and, of those who make it in time, only one-third will have a "good result" after treatment .
Most SAHs are caused by ruptured saccular aneurysms. Recommendations for screening for aneurysms and methods of screening are discussed here. The epidemiology and pathogenesis of intracranial aneurysms and management of unruptured aneurysms, and screening for new aneurysms after treatment for SAH are discussed separately. (See "Unruptured intracranial aneurysms" and "Treatment of aneurysmal subarachnoid hemorrhage", section on 'Early rebleeding'.)
The prevalence of intracranial saccular aneurysms by radiographic and autopsy series is approximately 0.4 to 6.0 percent , or between 1 to 18 million people in the United States. In adult patients without risk factors, the best estimate is that approximately 2 percent harbor asymptomatic cerebral aneurysms . Of patients with cerebral aneurysms, 20 to 30 percent have multiple aneurysms . Aneurysmal SAH occurs at an estimated rate of 6 to 16 per 100,000 population . In North America, this translates into approximately 30,000 affected persons per year. Thus, most aneurysms do not rupture.
The probability of rupture is related to the size of the aneurysm. Small aneurysms (less than 6 mm in diameter) are most commonly identified with screening, and these are at low risk for rupture (figure 1) . In addition, patients with smaller aneurysms (<10 mm) that have ruptured have a better prognosis than larger aneurysm rupture .
Aneurysm surgery is associated with significant morbidity in mortality. In an international multicenter report of 1449 patients with unruptured intracranial aneurysms, the rate of surgery-related morbidity and mortality in those without a prior history of bleeding from a different aneurysm was 18 percent at 30 days and 16 percent at one year . The one-year rates were affected by age: 6.5 percent under age 45; 14 percent between the ages of 45 and 64; and 32 percent over the age of 64. (See "Treatment of aneurysmal subarachnoid hemorrhage".)