An aneurysm is an abnormal dilation or widening of a portion of an artery, due to a weakness of the blood vessel wall. An aneurysm of the thoracic aorta occurs in the part of the largest artery in the body (the aorta) that passes through the thorax. The most common cause of thoracic aortic aneurysm is hardening of the arteries. The condition is more common in people with high cholesterol, prolonged high blood pressure or who smoke.
Other risk factors for a thoracic aneurysm include:           
– Changes caused by age
– Connective tissue disorders such as Marfan syndrome or Ehlers syndrome – Danlos          
– Inflammation of the aorta           
– Injury from falls or car accidents           
– Syphilis