Coloured computed tomography (CT) angiogram scan of the chest of a 61 year old male patient with an aneurysm (swelling, upper centre right) in the aortic spindle, which is at the top of the descending aorta. An aneurysm is a blood-filled dilation in a blood vessel wall. If left untreated, the blood vessel can rupture. Risk factors for aneurysm include smoking, high blood pressure, infection and atherosclerosis (hardening of the arteries).