The etiology of the majority of thoracic aneurysms (80%) is which of the following?

The majority of thoracic aneurysms, particularly around 80%, are attributed to degenerative changes in the arterial wall. These degenerative processes often involve age-related factors that lead to the weakening and dilation of the aorta over time. Conditions such as atherosclerosis, hypertension, and increased stress on the vessel wall are significant contributors to this degenerative process.

In individuals with degenerative aneurysms, the connective tissues that provide structural integrity to the aortic wall can become compromised. Factors such as inflammation, calcification, and loss of elasticity play critical roles in the development and progression of these conditions, ultimately resulting in the formation of thoracic aneurysms.

Other options represent considerable factors in specific cases but do not account for the majority of thoracic aneurysms. Genetic factors can contribute to syndromes that predispose individuals to aortic issues, but they are less common in the general population compared to degenerative changes. Chronic dissection and posttraumatic causes indeed occur but are recognized as less prevalent causes when evaluating the overall etiology of thoracic aneurysms.