The 30-day case fatality rate in patients with subarachnoid hemorrhage (SAH) from population-based studies since 1960 has ranged from 32% to 67%. Among the more recent studies, the case fatality rate is approximately 30%. If the patient is seen 24 hours after SAH, the mortality rate at 30 days is approximately 35%, at 48 hours about 30%, at 1 week about 25%, and at 2 weeks about 10%. Approximately 10% of patients die before they receive medical attention. Mortality after 30 days declines substantially, leveling off between 30 and 60 days. Significant predictors of outcome are the patient’s level of consciousness and clinical grade at admission. The probability of survival is better for patients with no neurologic deficit other than cranial nerve palsy (Hunt and Hess clinical grade 1 or 2) and worse for patients who present with coma, decerebrate rigidity, and moribund appearance (Hunt and Hess clinical grade 3, 4, or 5). The 30-day probability of survival is less than 20% for patients with clinical grades 4 and 5 and approximately 70% with grades 1 and 2. In addition, intracerebral hematoma or a history of hypertension increases the probability of death in patients with SAH.

One of the major causes of mortality after initial SAH is aneurysmal rebleeding. The rebleeding rate is approximately 2% per day during the first 10 days (total, ˜20%). The occurrence of rebleeding is a little less than 30% at 30 days and about 1.5% per year after 30 days. In patients with clinical grade 1, 2, or 3, the probability of having isolated cranial nerve palsies or an altered level of consciousness in the first 30 days after SAH is nearly 50%.

Among survivors of SAH, approximately one third remain dependent. Even physically independent survivors are likely to experience some change in their lives, such as ongoing cognitive deficits (especially memory problems in about 50% of survivors) and problems with mood (about 40%) and speech (about 15%). Only about one third of independent survivors report no reduction in quality of life at 18 months after SAH.

Patients who have SAH of unknown origin and in whom cerebral arteriography and other laboratory studies do not show an aneurysm or other cause of hemorrhage (such as vascular malformation or tumor) have a relatively good prognosis, with a rate of recurrent hemorrhage of approximately 2% to 10% within a follow-up period as long as 15 years.

Patients with SAH localized to the perimesencephalic region without extension into the Sylvian fissures or interhemispheric fissure (called pretruncal hemorrhage or perimesencephalic hemorrhage) have a very benign prognosis if their cerebral arteriograms are normal. The recovery period is very short, and patients are almost always able to return to work and other activities with no decrease in their quality of life. The risk for rebleed is extremely low, although some patients
may have early deterioration after presentation because of hydrocephalus. Delayed cerebral ischemia is also uncommon.

In general, SAH that is caused by an arteriovenous malformation (AVM) is associated with a much lower 30-day case fatality rate (10%-20%) than that caused by saccular aneurysm. Vasospasm and delayed ischemic neurologic deficit are also uncommon and contribute to a lower occurrence of long-term morbidity and mortality in the AVM subgroup.