An aneurysm is an abnormal dilatation of a blood vessel which causes the tissue to become weak. When the aneurysm reaches a certain size it is more likely to rupture. The aorta is the main blood vessel of the body. The abdominal segment is that portion that travels in the abdominal cavity beneath the diaphragm. When an aneurysm develops here it becomes more likely to rupture when it reaches a size of 5 cm. To prevent complications of rupture the surgeon will open the abdominal cavity and replace the diseased segment of aorta with a synthetic graft.