What are the five most common causes of thoracic aortic aneurysm?

1. Atherosclerosis (75% of patients)
2. Trauma (pseudoaneurysm)
3. Infection
4. Cystic medial necrosis (connective tissue disease, hypertension, syphilis)
5. Aortitis (Takayasu's arteritis, giant cell arteritis, collagen vascular disease)