Berry aneurysm Defect lies in

BERRY ANEURYSMS are saccular in appearance with rounded or lobulated bulge arising at the bifurcation of intracranial aeries. They are, therefore, not congenital anomalies but develop over the years from a developmental defect of the media of the aerial wall at the bifurcation of aeries forming thin-walled saccular bulges. There is an increased incidence of their presence in association with congenital polycystic kidney disease and coarctation of the aoa. In more than 85% cases of subarachnoid hemorrhage, the cause is massive and sudden bleeding from a berry aneurysm on or near the circle of Willis. The four most common sites are as under:- 1. In relation to the anterior communicating aery. 2. At the origin of the posterior communicating aery from the stem of the internal carotid aery. 3. At the first major bifurcation of the middle cerebral aery. 4. At the bifurcation of the internal carotid into the middle and anterior cerebral aeries. The remaining 15% of cases of subarachnoid hemorrhage are the result of a rupture in the posterior circulation, vascular malformations, and rupture of mycotic aneurysms that occur in the setting of bacterial endocarditis. Clinically, berry aneurysms remain asymptomatic prior to rupture. Ref: TEXTBOOK OF PATHOLOGY 6th EDITION - HARSH MOHAN PAGE NO:882