Aortic aneurysms. Coloured computed tomography (CT) scan of the chest of a 26 year old with two aneurysms (indicated by arrows) in the descending aorta. The aorta is the body's main artery it carries blood from the heart to the rest of the body. An aneurysm is a blood-filled dilation in a blood vessel caused by a weakened vessel wall. These aneurysms are a result of Behcet's disease, a rare autoimmune disease that causes inflammation of the blood vessels. If left untreated aneurysms rupture and are often fatal. Treatment is with repair or replacement of the vessel.