The typical patient who develops a subarachnoid hemorrhage frequently has a positive personal or family history for SAH, a history of polycystic kidney disease, hypertension, alcohol abuse, or cigarette smoking. In addition, the incidence is more common in patients with heritable connective-tissue disease, especially fibromuscular dysplasia. A ruptured saccular aneurysm is the most common etiology of subarachnoid hemorrhage, followed by trauma, arteriovenous malformations, illicit drug use (especially cocaine), and vasculitides.

The most common presenting symptom of subarachnoid hemorrhage is headache of unusual severity. Patients typically describe their pain as “the worst headache of my life.” Sometimes, the life-threatening bleed may be preceded by a small bleed and headache, which is called a sentinel headache. Other symptoms may include nuchal rigidity, diminished level of consciousness, aphasia, and bilateral weakness of the lower extremities. Signs that are apparent on physical examination include papilledema, third or sixth nerve palsy, nystagmus, left-side visual neglect, or retinal hemorrhage.

The most important study to obtain when suspecting a subarachnoid hemorrhage is a noncontrasted computed tomography (CT) scan of the head. Preferably, the study should be done with thin cuts about 3 mm in thickness in order to identify small collections of blood. The CT scan is most sensitive if obtained within 24 hours of the bleed. In one study, the percentage of positive scans went from 92% to 50% from day one to day seven. Of note is that if the underlying etiology of the subarachnoid bleed is a ruptured aneurysm, the location of blood on the CT scan does not accurately predict the location of the aneurysm. If the CT scan is negative but the clinical syndrome is still consistent with SAH, a lumbar puncture should be performed to identify blood in the cerebrospinal fluid.