[Histological peculiarities of degenerative changes in the dilated ascending aorta]

Currently, an established indication for surgical repair of an ascending aortic aneurysm is the aortic diameter greater than 55 mm without hereditary connective tissue disorders and bicuspid aortic valve. The aortic size from 40 to 54 mm, regardless of the body surface area, is classified as aortic dilation. Histopathological changes in the dilated ascending aorta without genetic diseases still remain poorly investigated. There are no specific guidelines determining the surgical strategy in patients with the pathology concerned.

This study was undertaken to investigate histopathological alterations in the wall of the dilated ascending aorta.

A total of 25 gross specimens of the ascending aorta were obtained from corpses after sudden death. They were divided into two groups. The first group (n=5) included the samples of the dilated ascending aorta (diameter of 40 to 54 mm) and the second group (n=20) consisted of the samples of the ascending aorta of less than 40 mm in diameter. Three samples of the aortic wall were taken from each gross specimen at the level of the ascending aorta in the most dilated area. The obtained samples were fixed, stained with hematoxylin-eosin, Van Gieson, Weigert-Van Gieson stains and analyzed by means of light microscopy. Degenerative changes in the aortic wall were assessed according to the Consensus 'Noninflammatory degenerative diseases - nomenclature and diagnostic criteria' (2016). The groups were compared using the Student's t-test for the quantitative data and Chi-squared test and Fisher's exact test for categorical variables. The statistical significance threshold was set at p<0.05.

The obtained findings revealed a more severe grade of accumulation and distribution of the intralamellar mucoid extracellular matrix in the dilated ascending aorta (р=0.007; p=0.005, respectively), as well as a more pronounced grade and extent of elastic fiber degradation (р<0.001; p<0.001). Moreover, in the first group multifocal medial fibrosis was observed more frequently (p=0.027). The groups were not statistically different in the grade of translamellar mucoid extracellular matrix accumulation and distribution (p=0.103; p=0.504), the extent of smooth muscle cell alterations (p=0.179), and the grade of medial fibrosis (p=0.074).

Dilation of the ascending aorta is related with degenerative changes of the aortic wall. Mucoid extracellular matrix accumulation and elastic fiber alterations are the first degenerative manifestations. Thus, dilation of the ascending aorta is indicative of morphological alterations of the aortic wall and should be taken into consideration while determining the surgical strategy.