A classic naneurysm of the ascending aorta is characterized by a 50% increase in its diameter with a risk of rupture. In comparison, an aortic dissection involves a spontaneous or traumatic splitting of the wall layers of the aorta with intramural bleeding, spreading, and accumulation of blood in the media. In the context of acute dissection, there is an acute increase in the overall vessel size (usually as a result of an acute increase in the false lumen, which is only limited by the weak tunica adventitia). Due to the increase in size, the dissected aorta is also commonly referred to as an aneurysma dissecans; however, compared to an aneurysma verum, it is a different pathology. A dissection can result from an aneurysm, but newer data increasingly indicate that the aorta is usually not dilated prior to an acute dissection. Rather, the elongation of the aorta seems to be a possible risk factor for the development of aortic dissection.