Abdominal aortic aneurysm. Oblique coloured computed tomography (CT) scan of a 58-year-old patient with an abdominal aortic aneurysm. An aneurysm is a blood-filled dilation caused by a weakening of the vessel wall. The liver is at upper left with one of the kidneys below it. Part of the aorta, the body's main artery is seen at centre, the widest part is the aneurysm. The patient has previously had a stent (white) placed in the aorta to treat a dissecting aneurysm. Aneurysms are most common in men over 65 years of age. If left untreated they rupture and are often fatal. Treatment is with repair or replacement of the blood vessel.