eMedicine Specialties > Neurology > Neurological Emergencies

Subarachnoid Hemorrhage

Author: George I Jallo, MD, Associate Professor of Neurosurgery, Pediatrics and Oncology, Director, Clinical Pediatric Neurosurgery, Department of Neurosurgery, Johns Hopkins University School of Medicine
Coauthor(s): Tibor Becske, MD, Assistant Professor, Department of Neurology, New York University Medical Center
Contributor Information and Disclosures

Updated: Dec 4, 2008

Introduction

Background

Intracranial saccular aneurysms represent the most common etiology of nontraumatic subarachnoid hemorrhage (SAH), with about 80% of SAH resulting from ruptured aneurysms. SAH is responsible for the death and/or disability of 18,000 persons each year in North America alone. Unfortunately, the difficulties in detecting unruptured aneurysms in asymptomatic patients practically preclude the possibility of preventing most SAH.

About 6-8% of all strokes are caused by SAH from ruptured berry aneurysms. Over the past several decades, the incidence of other types of strokes has decreased; however, the incidence of SAH has not decreased.

Pathophysiology

Aneurysms are acquired lesions related to hemodynamic stress on the arterial walls at bifurcation points and bends. Saccular or berry aneurysms are specific to the intracranial arteries because their walls lack an external elastic lamina and contain a very thin adventitia—factors that may predispose to the formation of aneurysms. An additional feature is that they lie unsupported in the subarachnoid space.

Aneurysms mostly arise from the terminal portion of the internal carotid artery (ICA) and from the major branches of the anterior portion of the circle of Willis. In a 25-year autopsy study of 125 patients with ruptured or unruptured aneurysms conducted at Johns Hopkins, hypertension, cerebral atherosclerosis, vascular asymmetry in the circle of Willis, persistent headache, pregnancy-induced hypertension, long-term analgesic use, and family history of stroke all were correlated positively with the formation of saccular aneurysms.

The occurrence of aneurysms in children indicates the role of intrinsic vascular factors. A number of disease states resulting in weakness of the arterial wall are associated with an increased incidence of berry aneurysms.

Hypertension (previously documented acute severe hypertension with diastolic value over 110 mm Hg), smoking, alcohol, multiple aneurysms, increasing aneurysm size, fatty metamorphosis of the liver, long-term analgesic use, and oral contraceptives have been linked to aneurysmal subarachnoid hemorrhage.

Disease states associated with higher incidence of berry aneurysms include the following:

• Increased blood pressure - Fibromuscular dysplasia, polycystic kidney disease, and aortic coarctation
• Increased blood flow - Cerebral arteriovenous malformation (AVM); persistent carotid-basilar anastomosis; ligated, aplastic, or hypoplastic contralateral vessel
• Blood vessel disorders – Systemic lupus erythematosus (SLE), Moyamoya disease, and granulomatous angiitis
• Genetic - Marfan syndrome, Ehlers-Danlos syndrome, Osler-Weber-Rendu syndrome, pseudoxanthoma elasticum, and Klippel-Trenaunay-Weber syndrome
• Congenital - Persistent fetal circulation and hypoplastic/absent arterial circulation
• Metastatic tumors to cerebral arteries - Atrial myxoma, choriocarcinoma, and undifferentiated carcinoma
• Infectious - Bacterial, fungal

Frequency

United States

The frequency of ruptured and unruptured aneurysms has been estimated at 1-9% in different autopsy series, with a prevalence (of unruptured aneurysms) of 0.3-5%. Generally, the older age group is more likely to be hospitalized; therefore, these studies may not be representative of the general population.

Retrospective arteriographic studies show a prevalence of less than 1% with the limitation that some cases did not receive adequate evaluation and thus some aneurysms may have been missed. Overall estimated prevalence of unruptured aneurysms in the general population is around 1%.

The incidence of subarachnoid hemorrhage from ruptured saccular aneurysms in North America is approximately 12 cases per 100,000 population. Approximately 28,000 people experience aneurysmal SAH each year.

International

The reported incidence of subarachnoid hemorrhage is high in the United States, Finland, and Japan, while it is low in New Zealand and the Middle East. In Finland, the estimated incidence based on different studies is 14.4-19.6 cases per 100,000 population, although numbers as high as 29.7 have been reported. In Japan, the reported rates vary between 11 and 18.3 cases per 100,000 population, with one study showing an incidence of 96.1 cases per 100,000 population (this study included only patients aged 40 and older in the data collection, and results were not adjusted for sex and age to the same reference population). In New Zealand, age-adjusted incidence was reported as 14.3 cases per 100,000 population.

An Australian study reported an incidence of 26.4 cases per 100,000 population but only for patients older than 35 years, as age was not adjusted in the reference population. In the Netherlands, the age-specific incidence was reported as 7.8 cases per 100,000 population (this is believed to be an underestimate). Iceland reported 8 cases per 100,000 population, but a significant portion of the affected rural population was believed to be missed. Greenland Eskimos had 9.3 cases per 100,000 population, while ethnic Danes in the same country were found to have an incidence of 3.1 cases per 100,000 population. This latter figure is consistent with the figures in Denmark—marked differences are postulated to be related to genetic factors. On the Faeroe Islands (part of Denmark with an isolated population of the same genetic ancestry), the reported incidence is 7.4 cases per 100,000 population.

In China, the reported incidence is low but no good studies have been published to support this statement. Indians and Rhodesian Africans also have significantly lower incidence than those from European nations; this can be explained partly by the low incidence of atherosclerosis in these populations. In the Middle East, the numbers are very low as well; the best available estimate is 5.1 cases per 100,000 population in Qatar.

Mortality/Morbidity

• As many as 60% of patients die in the first 30 days as the result of subarachnoid hemorrhage. About 10% die immediately without any warning; an additional 25% die or become disabled as a result of the initial hemorrhage.
• Hospitalized patients have an average mortality rate of 40% in the first month. Rebleeding, a major complication, carries a mortality rate of 51-80%.
• Delayed cerebral ischemia due to vasospasm, the most deadly of all complications, affects 20% of angiographically visualized cases of vasospasm.

Race

North American blacks have been found to have a 2.1 times greater risk of subarachnoid hemorrhage than whites.

Sex

The incidence of subarachnoid hemorrhage is slightly higher in women than in men.

Age

The mean age for SAH is 50 years.

Clinical

History

• Aneurysmal subarachnoid hemorrhage presents with severe headache of sudden onset ("thunderclap headache") that can be accompanied by loss of consciousness at onset. The headache is frequently described as "worst headache of my life."
• Neck stiffness, photophobia, and low back pain are symptoms of meningeal irritation. Nausea and vomiting are due to increased intracranial pressure (ICP) and meningeal irritation.
• Focal neurological deficits may also occur.
• Approximately 10-25% of patients with SAH have a seizure, usually in the first few minutes after onset. This is due to the sudden rise in ICP or direct cortical irritation by blood.
• An estimated 10-15% of patients with ruptured aneurysms have symptoms related to their aneurysm prior to the rupture. The most common symptoms are headache (48%), dizziness (10%), orbital pain (7%), diplopia (4%), and visual loss (4%).
• Signs present before SAH include sensory or motor disturbance (6%), seizures (4%), ptosis (3%), bruits (3%), and dysphasia (2%). Some studies estimate an even higher incidence of premonitory symptoms—as many as 40-50%, with signs appearing 10-20 days prior to rupture.
• The premonitory symptoms may represent small leaks ("sentinel bleed") or expansion of the aneurysm.
• Approximately 30-40% of patients are at rest at the time of SAH. Physical or emotional strain, defecation, coitus, and head trauma contribute to varying degrees in the remaining 60-70% of cases.

Physical

• The physical examination findings may be normal.
• Global depression of neurological function may be noted, including altered level of consciousness and confusional state.
• Focal neurological findings may include the following:
  • Cranial nerve deficits: Oculomotor palsy (posterior communicating artery aneurysm) is most frequent. Abducens palsy is usually due to increased ICP rather than a true localizing sign. Monocular loss of vision can occur with ophthalmic artery aneurysms.
  • Hemiparesis: With or without aphasia, hemiparesis is due to middle cerebral artery (MCA) aneurysm, ischemia or hypoperfusion in the vascular territory, or intracerebral clot.
  • Leg monoparesis or paraparesis with or without akinetic mutism/abulia points to anterior communicating aneurysm rupture.
• Funduscopic findings include papilledema and subhyaloid retinal hemorrhages.

Causes

• Of nontraumatic subarachnoid hemorrhages, 80% are due to a ruptured berry aneurysm.
• Other vascular malformations such as AVMs and mycotic aneurysms cause most of the remaining 20%.

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