A patient presented with thunder clap headache followed by unconsciousness with pregressive III ranial nerve palsy. Likely diagnosis is
Extradural hemorrhage
Aneurysmal subarachnoid hemorrhage
Basilar migraine
Cluster headache
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
C.N.S