Usually when an ascending aorta has been measured to >4.0 cm it is medically referred to as an aneurysm and carefully watched to monitor any rapid growth, and if an when the size reaches 5.0 cm there begins to be concern that the vessel wall would be thin to the point where it could rupture. It is recommended to carefully control blood pressure.
Under some circumstance, there may be concern if the AA is 4.5 cm.