A patient presented with thunder clap headache followed by unconsciousness with pregressive III ranial nerve palsy. Likely diagnosis is

davidson's principles and practices of medicine 22nd edition. *85%of SAH caused by saccular aneurysm arise from bifurcation of cerebral aeries. *SAH present with sudden,severe,thunderclap headache (often occipital),which lasts for hours or even days ,often accompanied by vomiting,raised blood pressure and neck stiffness or pain *there may be loss of consciousness at the onset ,so SAH should be consider if patient found comatose *a third nerve palsy may be present due to local pressure from an aneurysm of posterior communicating aery. *focal hemispherical signs like hemiparesis or aphasia ,may be present at onset if there is associated intracerebral haematoma . Ref Harrison20th edition pg 2765