Chapter 160

Although nontraumatic subarachnoid and intracerebral hemorrhage account for a relatively small portion of ED visits, a missed diagnosis can produce devastating results. Early recognition and aggressive management may improve outcomes.

### Epidemiology

In the U.S., the annual incidence of subarachnoid hemorrhage is approximately 1 in 10,000 people.3 In contrast to intracerebral hemorrhage (ICH) and cerebellar infarction, the incidence of which has been declining since the 1950s, subarachnoid hemorrhage rates have remained steady. There is significant unexplained regional variation, with Finland and Japan having the highest reported incidence at approximately 2.1 per 10,000.4,5 Subarachnoid hemorrhage is slightly more common in women than in men. The median age at diagnosis is 50 years. Morbidity and mortality are very high. Approximately 12% of patients die before reaching medical care and 50% die within 6 months. More than one third of patients who survive have a major neurologic deficit.

### Pathophysiology

Subarachnoid hemorrhage is the leakage of blood into the subarachnoid space. Seventy-five percent of subarachnoid hemorrhages are caused by a ruptured aneurysm. Approximately 20% of patients with one aneurysm will have an additional aneurysm, which makes identification of the initial aneurysm more important. In 20% of subarachnoid hemorrhage cases, a cause is not identified.1 The remaining 5% are related to a variety of conditions, including arteriovenous malformations, cerebral artery dissection, coagulopathies, moyamoya syndrome, mycotic aneurysm, neoplasm, pituitary apoplexy, vasculopathy, brain tumor, and use of sympathomimetic drugs (particularly amphetamine, cocaine, phenylpropanolamine, and pseudoephedrine). The location of bleeding on CT can help identify the cause of the bleed.1

Hypertension more than doubles the risk of subarachnoid hemorrhage. Smoking increases the risk four to five times over that of matched controls.2 Additional risk factors are listed in Table 160-1. Two percent of family members of patients with subarachnoid hemorrhage will develop the same disease. This risk rises with increasing number of family members involved or with a family history of adult polycystic kidney disease.1 Use of medications containing caffeine, lower educational level, lower body mass index (<23), and use of nicotine medications are also noted to increase the risk of subarachnoid hemorrhage compared with that in the general population.6 Many of these causes are avoidable, which indicates that primary prevention with better physical health and avoidance of certain medications and recreational substances can help to prevent subarachnoid hemorrhage, especially in the young and middle-aged.6

Table 160-1 Risk Factors for Subarachnoid Hemorrhage

### Clinical Features

Patients with subarachnoid hemorrhage classically present to the ED with the so-called thunderclap headache or a severe headache of acute onset that reaches maximal intensity within minutes. Typically, the headache persists for several days, but may resolve in a shorter period.1 Subarachnoid hemorrhage is diagnosed in 11% to ...

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