An aneurysm is the ballooning out of one part of an artery (or the heart), at a point where the artery becomes weakened. There may be a slight bump on the side of an artery, a quite large bubble or a long sausage-shaped extension along an artery. Any artery may be affected, but the most serious ones involve the aorta (the main artery down the back of the chest and abdomen – aortic aneurysm) and arteries in the brain (cerebral aneurysm).
Different types of aneurysm are categorised by their shape. The most common are saccular or berry aneurysms that are direct balloonings on the side of an artery. The most sinister are the dissecting aneurysms, where only part of the artery wall is damaged (often by cholesterol plaques – arteriosclerosis) and the blood penetrates in between the layers of the artery wall, slowly splitting them apart, and extending along the artery.
The weakness in arteries may be caused by plaques of cholesterol, high blood pressure, injury to the artery or a congenital (present since birth) weakness in the wall of an artery. The heart wall may be damaged by a heart attack, and the weakened area can bulge out as an aneurysm. There is a slight hereditary tendency.