A dissecting aneurysm is a localized widening (dilatation) of an artery (an aneurysm) in which the wall of an artery rips (dissects) longitudinally. This occurs because bleeding into the weakened wall splits the wall. Dissecting aneurysms tend to affect the thoracic aorta. They are particularly a major danger in Marfan’s disease. Albert Einstein, for example, died ot a dissecting aneurysm.