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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.

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

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.

Given the importance of prompt and precise diagnosis, it is essential that physicians understand the myriad, atypical presentations of SAH, as well as the limitations of diagnostic tests, in order to avoid.

Cannot Miss Diagnoses Presenting as a Headache
Bacterial meningitis

Subarachnoid hemorrhage

Space-occupying lesion

Brain tumor

Brain abscess

Subdural and epidural hematoma

Others including other parameningeal infections

Pseudotumor cerebri

Hypertensive encephalopathy

Acute narrow angle glaucoma

Temporal arteritis

Cerebral venous and dural sinus thrombosis (including cavernous sinus)

Carbon monoxide poisoning


Bacterial sinusitis (can lead to complications on the list)

Defined as medical conditions that are simultaneously life, limb, or vision threatening and treatable

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

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

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 aneurysms accounts for the difference between the estimated 2 million Americans who

SAH can occur at any age, but it is rare in children and the mean age at the time of presentation is about 50 years. Overall, there is a female:male ratio of 3:2; however, below age 40, men are more

Natural History of Intracerebral Aneurysms

Prior to discussion of ruptured intracranial aneurysm, it is essential for the ED physician to understand the clinical manifestations and natural history of individuals who have intact cerebral aneurysms.

In one landmark study of 111 patients who had 132 unruptured aneurysms, patients were divided into three groups: Group 1 presented with acute symptoms; Group 2 presented with chronic (>2 weeks in

Ruptured Aneurysm. Once an aneurysm ruptures, patients may present with a wide range of signs and symptoms; they may be ambulatory and fully conscious or comatose. Several clinical grading systems are used for patients with SAH. The two most widely improved are the Hunt and Hess (H&H) and the World Federation of Neurologic Surgeons classifications, the latter of which is based on the Glasgow coma scale.