<prompt> Most common cause of subarachnoid hemorrhage: September 2011Aeriovenous malformationRupture of berry aneurysmVeebral aery dissectionNon-aneurysmal hemorrhage  <response>: Ans. B: Rupture of berry aneurysm Eighty-five percent of SAH are caused by saccular or berry aneurysms arising from the bifurcation of cerebral aeries, paicularly in the region of Circle of Willis SAH: Most aneurysm presents as sudden SAH Occipital and posterior cervical pain may signal a posterior inferior cerebellar aery or anterior inferior cerebellar aery aneurysm rare A classic presentation of SAH is the explosive onset of sever headache thunder clap type headache, or a sudden transient loss of consciousness followed by severe headache Nuchal rigidity and vomiting may be present simulating meningitis Rebleed and vasospasm are responsible for clinical deterioration in a week following CT scan is a sensitive indicator and usually allows for prompt diagnosis 