An aneurysm is a small local bulge in the wall of a blood vessel, usually an artery. Normally, blood vessels operate like pipes, carrying blood throughout the body to cells which depend on this supply for oxygen and nutrients. Like water in pipes, the blood is forced through blood vessels by pumping which creates pressure on the walls of the blood vessels. If there is a weak spot in the blood vessel wall, the pressure will cause the wall to balloon outward. Since the pressure is greater in arteries, which carry blood from the heart, than in veins, which carry blood back to the heart, most aneurysms occur in arteries. Surgery can repair an aneurysm by replacing the weakened portion of the blood vessel with a healthy segment taken from somewhere else in the body or with a synthetic graft. It is also sometimes possible to install a plastic or metal clip at the base of the aneurysm "balloon" to prevent further expansion.

If the pressure building inside an aneurysm is great enough, the aneurysm may rupture. In this case, blood spills out of the aneurysm. This can cause damage to the surrounding tissue, and also reduces the flow of blood to structures downstream which are normally supplied by that blood vessel. Most aneurysms rupture if untreated. In this case, surgeons may try to clip off the aneurysm using an implanted metal or plastic clip to prevent further leakage of blood out of the vessel.

Aneurysms are sometimes caused by congenital or inherited defects. Aneurysms may also be caused by other conditions which weaken blood vessel walls or which increase blood pressure, such as hypertension, arteriosclerosis or various infections and injuries.

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Article : "VASCULAR DEMENTIA"