Aortic dissection in the outer third of the media: what is the role of the vasa vasorum in the triggering process?

OBJECTIVES Extensive clinicopathological analyses of aortic dissection have implicated hypertension and genetic abnormalities as the major pathogenic mechanisms. However, previous findings from pathological examinations have often been inconsistent with these mechanisms. In this paper, we suggest a significant role for the vasa vasorum in the aetiology and pathogenesis of aortic dissection. METHODS We reviewed records of patients who underwent thoracic aortic dissection repair at our institution between June 2008 and August 2011. Twenty-one patients (10 men, 11 women; mean age, 65.0 ± 12.0 years) underwent surgery with subsequent histopathological examination of the aortic wall. We evaluated the history and histopathological findings of these patients. RESULTS Aortic medial changes were observed in all 21 patients. These changes included thinning and sometimes fragmentation of the elastic lamina, as well as atrophy of the smooth muscle cells, with surrounding accumulation of an Alcian blue-positive mucinous substance, mostly adjacent to the dissection. Importantly, the dissection was located in the outer third of the media in 20 of the 21 patients (95.2%). Of these 20, 18 showed histopathological evidence of sclerotic changes of the vasa vasorum, including muscular hyperplasia, elastosis, intimal fibrosis and/or luminal obstruction, and even rupture. These changes may have been secondary to hypertension or peri-aortic changes, leading to degenerative changes in the aortic media and even initiation of dissection. CONCLUSIONS Most aortic dissections initially developed in the outer third of the media alongside the vasa vasorum. In this type of aortic dissection, dysfunction of the vasa vasorum may play a key role in long-standing ischaemia or malnutrition of the aortic media.