davidson's principles and practices of medicine 22nd edition. *85% of SAH are caused by saccular or berry aneurysm arise from bifurcation of cerebral aeries *SAH typically presented with a sudden ,severe ,thunderclap headache (often occipital) , which lasts for hours or even days,often accompanied by vomitting , raised blood pressure and neck stiffness or pain. *there may be loos of consciousness at the onset ,so SAHshould be consider if patient is comatose *focal neurological signs like hemiparesis,aphasia may be present at onset if there is an associated intracerebral hematoma *a third nerve palsy present due to local pressure from an aneurysm of posterior communicating aery. Ref Harrison20th edition pg 2456