The natural history of aortic atherosclerosis: A systematic histopathological evaluation of the peri-renal region

BackgroundRisk factor profiles for the different vascular beds (i.e. coronary, carotid, peripheral and aortic) are remarkably different, suggesting that atherosclerosis is a heterogeneous disorder. Little is known about the morphologic progression of atherosclerosis in the peri-renal aorta, one of the primary predilection sites of atherosclerosis.MethodsA systematic analysis was performed in 260 consecutive peri-renal aortic patches (stained with Movat Pentachrome and H&E) collected during organ transplantation (mean donor age 46.5 (range 5-76) years; 54% ♂; mean BMI 24.9; 40% smokers; 20% hypertensive). Plaque morphology was classified according to the modified AHA classification scheme proposed by Virmani et al. [4]. Immunostaining against CD68 was used to identify the distribution of intimal macrophages and monocytes in several predefined locations among various plaque types and fibrous cap thickness.ResultsThere was significant intimal thickening (p < 0.013) and medial thinning (p < 0.032) with advancing age. The incidence of atherosclerotic plaques in the abdominal aorta correlated with age (r = 0.640, p = 0.01). During the first three decades of life adaptive intimal thickening and intimal xanthomas were the predominant lesions. In contrast, the fourth, fifth and sixth decades hallmarked more complicated plaques of pathological intimal thickening, early and late fibroatheromas (EFAs and LFAs), thin-cap FAs (TCFAs; cap thickness <155 μm), ruptured plaques (PRs), healed rupture and fibrotic calcified plaques. The mean percentage of lesional macrophages increased significantly from LFAs to TCFAs (5-17%; p < 0.001). Macrophage infiltration of the fibrous cap was negatively correlated with fibrous cap thickness (p < 0.0004); TCFAs and PRs (caps < 100 μm) contained significantly more macrophages (19%) compared with caps 101-300 μm (6%) and >300 μm (2%). Macrophages in shoulder regions were highest in early and late FAs (∼45%) followed by TCFAs (27%) and PR (20%). Further, intimal vasa vasorum were mostly seen adjacent to the necrotic core of advanced atherosclerotic plaques and remained confined to the intimo-medial border despite marked thickening of the intima.ConclusionThis study shows that peri-renal aortic atherosclerosis starts early in life. Gross plaque morphologies of the peri-renal abdominal aorta are similar to coronary atherosclerosis yet indications were found for site specific differences in macrophage content and neovascularization.