Medial Neovascularization: A Novel Mechanism of Aortic Dissection in a Hypertensive Population?

This study aimed to elucidate the impact of vasa vasorum on the natural progression of aortic dissection in patients with hypertension.

Full-thickness ascending aortic walls from 43 participants (median age, 53 years; 32.6% women) were analyzed using pathological observation and shear stress measurement. Comparisons among hypertensive dissection (AD, n=23), hypertensive control (n=12), and nonhypertensive dissection (non-HT-AD, n=8) groups were performed using Kruskal-Wallis and repeated-measures ANOVA tests.

Compared with the control group, a higher density of vasa vasorum was observed within the outer third of the tunica media (medial neovascularization [MN]) in the AD group (adjusted P=0.02). In the AD group, MN frequently coincided with the site of medial tearing, and the MN grade was higher than in the other 2 groups (overall: P=0.01; non-HT-AD versus AD group: adjusted P=0.05; control versus AD group: adjusted P=0.05). Medial degeneration was observed in all of the groups. Compared with the non-HT-AD group, the medial degeneration grade was even lower in the AD group (adjusted P=0.006). Multicenter fractures of elastic and collagen fibers were evident within the MN region in the AD group. Biomechanical testing revealed a significantly increasing translamellar discrepancy in stretch ranges inside the similar region (P<0.001 for interaction; P_{column factor}<0.001) in the AD group when compared with the control group.

MN and subsequent vasa vasorum rupture in the outer tunica media may represent an alternative initiating event in hypertension-related aortic dissection, distinct from the classical intimal tear. However, the cross-sectional nature of this study precludes definitive causal conclusions.