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Subarachnoid Hemorrhage

One of the primary goals of emergency medicine is prompt diagnosis and treatment of treatable, life-threatening conditions. Although emergency physicians are constantly on the alert for these so-called "cannot miss diagnoses, "clinical vigilance may be hindered by a variety of factors, among them, time constrains of a busy emergency department (ED), the financial pressures of managed care, the relative infrequency of these conditions, and variations in subarrachnoid hemorrhage, subarachnoid, hemorhage, aneurysm, anurism, anurysm.

Severe headache is among the most worrisome of symptoms suggesting catastrophic intracranial pathology. As far as headache, SAH is not the only "cannot miss diagnosis," and the physician is well-served to keep in mind the entire list of conditions that present with this chief complaint. (See Table 1.) In fact, studies show that about 3-5% of patients presenting to an ED with headache will harbor serious neurologic pathology, and about 1% will have SAH. Differentiating these patients from

Early diagnosis is essential in order to improve morbidity and mortality in subarachnoid hemorrhage (SAH). Overall 40-50% of patients with SAH die within one month of their hemorrhage, and

Clinical Anatomy and Epidemiology

SAH is defined as extravasation of blood into the subarachnoid space of the central nervous system (CNS). Excluding head trauma, which is the most common cause of SAH, ruptured intracerebral aneurysm accounts for about 80% of cases of SAH. Other causes include mycotic aneurysms, arteriovenous malformations (AMV), dissection of intracranial arteries, Moyamoya disease, and idiopathic cases. Aneurysms can also occur but as rare, late complication of head injury.

Unless otherwise specified, the term SAH, as it is used in this review, refers only to those cases caused by intracerebral aneurysm. Most of these aneurysms arise from arteries at the base of the

Aneurysms arising from the posterior circulation are most likely to occur at the bifurcation of the basilar artery and at the junctions of the basilar artery with the vertebral and the posterior inferior cerebellar vessels. At the time of initial presentation, about 25% of patients will have multiple aneurysms (usually 23), although as many as 13 aneurysms in the same patient have

Once an aneurysm develops, the rules of physics govern its subsequent behavior. LaPlace's law states that the tension on the wall of a chamber is a function of the radius of that chamber and the pressure

The reported incidence of saccular, intracranial aneurysms varies according to the epidemiological techniques used to identify this condition. For example, in autopsy series, they are found in up to 6% of the population, although many of these aneurysms are quite small. Based on cerebral angiographic studies, it is estimated that 0.5-1.0% of individuals have aneurysms. A recent expert panel sponsored by the American Heart Association estimated that approximately 2 million Americans harbor unruptured aneurysms.

In the United States, the annual incidence of SAH is about 30,000, or roughly 10 cases per 100,000 population. In Japan, the rate is about three times that number. The variable natural history of cerebral