An aneurysm is a localized widening or sac-like dilation of a blood vessel caused by thinning of the vessel wall. A potentially fatal complication is rupture of the vessel, resulting in massive hemorrhage. Aneurysms usually occur in arteries but may also be seen in the heart.
There are many different types of aneurysms. Arterial aneurysms may be due to atherosclerotic degeneration, trauma, infectious injury, or a congenital defect. They occur most often in elderly persons. Aortic aneurysms usually occur in the abdominal portion of the aorta, generally below the arteries to the kidney. A relatively common type of sac aneurysm causes a hemorrhage in the brain. So-called "giant" aneurysms within the brain may cause increasingly prominent symptoms by compressing the neighboring brain tissue. Defects in eye arteries may result in multiple aneurysms of the retina. Dissecting aneurysm, also called aortic dissection, begins suddenly as a tear in the inner vessel lining followed by entry of blood and a stripping effect that rapidly spreads, perhaps like a tear in a nylon stocking. A ventricular aneurysm may occur following a heart attack. Scar tissue forms over the dead heart cells and creates a patch over the weakened area, which may bulge during ventricular contraction.
Treatment of an aneurysm may include surgical replacement of the weakened area by a graft or encasement in plastic or the mechanical stopping of blood flow to or through the aneurysm.