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Hemorrhage within the intracranial or spinal subarachnoid space, most often resulting from INTRACRANIAL ANEURYSM rupture or CRANIOCEREBRAL TRAUMA (see also SUBARACHNOID HEMORRHAGE, TRAUMATIC). Clinical features include HEADACHE; NAUSEA; VOMITING, nuchal rigidity, variable neurologic deficits, intraocular subhyaloid hemorrhages, and a reduced level of consciousness which may progress to coma or death. Spasm of intracranial arteries (see VASOSPASM, INTRACRANIAL) frequently accompanies this condition and may lead to BRAIN ISCHEMIA or CEREBRAL INFARCTION. (From N Engl J Med 1997 Jan 2;336 (1):28-40)