Abdominal and thoracicaortic aneurysms are caused by a number of factors, including:

• Hardening of the arteries (atherosclerosis). Exactly how atherosclerosis leads to abdominal aortic aneurysms is unclear. It is thought that atherosclerosis causes changes in the lining of the artery wall that may affect oxygen and nutrient flow to the aortic wall tissues. The resulting tissue damage and breakdown may lead to the development of an aneurysm.
• Genetics. In some people who have Marfan's syndrome, Ehlers-Danlos syndrome, or other inherited conditions, the walls of the major arteries, including the aorta, are weakened. Aortic aneurysms run in families.
• Aging. The aorta naturally becomes less elastic and stiffer with age, increasing the risk of an abdominal aortic aneurysm.
• Infections. Infections such as syphilis and endocarditis, an infection of the lining of the heart, can cause aneurysms.
• Injury. A sudden, intense blow to the chest or abdomen, such as hitting the steering wheel in a car accident, can damage the aorta.
• Inflammation. Inflammation of the aorta can weaken the aortic wall. Although researchers have investigated several conditions, exactly what causes the aorta to become inflamed is not clear.

Thoracic aortic aneurysms are much less common than abdominal aortic aneurysms.¹ They are often caused by an abnormal breakdown of the elastic fibers in the aortic wall. Other causes of thoracic aneurysms include aortic coarctation (often resulting from a genetic disorder such as Turner's syndrome).