Aortic dissection Descending aortic dissection 2013-11-30T08:44:18Z Type B aortic dissection A separation of the layers within the wall of the descending aorta. Tears in the intimal layer result in the propagation of dissection (proximally or distally) secondary to blood entering the intima-media space. According to the Stanford classification, type B aortic dissection begins beyond brachiocephalic vessels (begins distal to the left subclavian artery). UMLS:C4022878 HP:0012499