The Stanford classification is divided into two groups; A and B depending on whether the ascending aorta is involved.
- A – Involves the ascending aorta and/or aortic arch, and possibly the descending aorta. The tear can originate in the ascending aorta, the aortic arch, or, more rarely, in the descending aorta. It includes DeBakey type I, II and retrograde type III (dissection originating in the descending aorta or aortic arch but extending into the ascending aorta).
- B – Involves the descending aorta or the arch (distal to right brachiocephalic artery origin), without involvement of the ascending aorta. It includes DeBakey type III without retrograde extension into the ascending aorta.
The Stanford classification is useful as it follows clinical practice, as type A ascending aortic dissections generally require primary surgical treatment whereas type B dissections generally are treated medically as initial treatment with surgery reserved for any complications. The reason for surgical repair of Type A dissections is that ascending aortic dissections often involve the aortic valve, which, having lost its suspensory support, telescopes down into the aortic root, resulting in aortic incompetence. This needs resuspending to reseat the valve and repair / prevent coronary artery injury. Also the area of dissection is removed and replaced with a Dacron graft to prevent further dissection from occurring. However type B dissections are not improved, from a mortality point of view, by operation, unless there is leaking, rupture or compromise to other organs, e.g. kidneys.