A female presented with a severe headache of sudden onset. On CT scan a diagnosis of subarachnoid hemorrhage is made. The most common cause of subarachnoid hemorrhage is :

Ans. is 'b' ie. Berry Aneurysm (Ref. : Harrison, 17/e pl726 (16/e, p 2387, 15/e, p 238))" Excluding head trauma the most common cause of SAH is rupture of a saccular aneurysma (Berry aneurysm or congenital aneurysm). "Berry aneurysms - also k/a as congenital aneurysm although they are not present at birth. There is however a congenital defect of the media of the artery, which becomes the site of aneurysm in later life.Common sites :Junction of the anterior communicating artery with the anterior cerebral artery* (MC).Junction of the post communicating artery with the 1C A* (Internal carotid artery)The bifurcation of MCA* (Middle carotid artery)