A dissecting thoracic aneurysm is caused by weakening of the wall of the aorta. The inner wall separates from the outer layers, and blood fills the space between them. Over time, the wall becomes too weak and can burst.

Causes include:

• Longstanding high blood pressure
• Atherosclerosis
• Abnormal development of the aorta:
• Coarctation of the aorta
• Syphilis infection
• Pregnancy
• Chest injury
• Cocaine use
• Heart surgery
• Marfan syndrome
• Ehlers-Danlos syndrome