Berry aneurysm - Defect lies in (AIIMS May 2011)
|A||Degeneration of internal elastic lamina|
|B||Deposition of mucoid material in media|
|C||Defect in muscular layer|
|D||Disturbance in vessel wall|
Degeneration of internal elastic lamina
1). Saccular (Berry) aneurysms occur at the bifurcations of the large to medium-sized intracranial arteries; rupture is into the subarachnoid space in the basal cisterns and often into the parenchyma of the adjacent brain.
2. Approximately 85% of aneurysms occur in the anterior circulation, mostly on the circle of Willis.
3. As an aneurysm develops, it typically forms a neck with a dome. The length of the neck and the size of the dome vary greatly and are factors that are important in planning neurosurgical obliteration or endovascular embolization.
4). The arterial internal elastic lamina disappears at the base of the neck. (Ref: Harrison, 18th edition, page 2262)
5). The media thins, and connective tissue replaces smooth-muscle cells. At the site of rupture (most often the dome) the wall thins, and the tear that allows bleeding is often ≤ 0.5 mm long.
6. Aneurysm size and site are important in predicting risk of rupture.
7). Those >7 mm in diameter and those at the top of the basilar artery and at the origin of the posterior communicating artery are at greater risk of rupture.