I attempted to review the medical literature but there is virtually no literature on this topic. I would get the MRI to see if this is truly a cyst. Sometimes people with a previous history of syphilis get aortic aneurysms or cysts. If that is not your case you may have cystic medial necrosis..I think the MRI will help clarify.
Thank you so much for your answer. I still haven't talked with my physician, but after reading up on this, I feel I am in a better position to understand the condition.
Again, thanks.
Maria