I have a thoracic anurism and an abdominal one.what causes this?could i prevent this?

Perhaps: Dear tiger, thoracic and abdominal aneurysms are caused by a variety of factors, including high blood pressure, high cholesterol, smoking, and genetic factors. Prevention focuses on eliminating and controlling as many of these risk factors as possible. Going forward, preventing and controlling these risk factors still apply, but it is unlikely the aneurysms will get smaller.

Arteriosclerosis: >90% are caused by arteriosclerosis. There are rare causes as well which likely don't apply to you. Prevention consists of: not smoking or stopping, keeping BP well controlled, eating a vegetarian or mediterranean diet, avoiding diabetes by maintaining normal weight and exercising regularly. Once established, aneurysms should be followed and, if enlarging, symptomatic, or very large, operated on.

Genetics and smoking: "true" aortic aneursyms (the most common type) are caused by degradation of elastin, a protein in the wall of your arteries. Elastin keeps your artery walls strong and healthy. How much elastin you have and the quality of it is determined by your genes. Smoking also destroys elastin. There are other kinds of aneurysms known as "false" and dissectin aneurysms, but these are less common.