Natural history of cerebral saccular aneurysms.

Cerebral saccular aneurysms are relatively common, and are most commonly located at the branching points of large arteries of the circle of Willis. Many are asymptomatic and only discovered incidentally. Available evidence suggests that these aneurysms develop as a result of a combination of congenital or inherited defects weakening the arterial wall, and acquired degenerative vascular disease. It appears that most untreated cerebral aneurysms will get larger, and that all aneurysms have the potential to rupture. The only consistent significant predictor of aneurysmal rupture in most studies is the size of an aneurysm. Aneurysms less than 5mm have a very low rupture rate while those greater than 10mm have a significant risk of subsequent rupture. There is no consensus on the influence of the other reported risk factors such as hypertension, cigarette smoking and aneurysm location, on aneurysmal rupture. Those who have suffered a ruptured aneurysm are at a high risk for a recurrent haemorrhage shortly after the initial one.