Chronic thoracic aortitis versus primary medial degeneration in ascending aorta: a digital morphometric analysis of...

Chronic aortitis (CA) represents a diverse group of inflammatory conditions often diagnosed incidentally in ascending aorta biopsies. While the 2015 and 2016 Consensus Statements on the surgical pathology of the aorta provide standardised histological classifications, data quantifying structural remodelling within individual aortic layers remain limited. Furthermore, distinguishing CA from primary non-inflammatory medial degeneration (MD) can be challenging, particularly when inflammation is sparse or burnt out, and secondary degenerative changes predominate. We aimed to compare morphological changes in CA and MD aneurysms and apply digital image analysis to quantify aortic wall layers.

Retrospective histological analysis was performed on 63 ascending aortic specimens: CA (n=21), MD (n=21), and autopsy controls (n=21). Digitised elastic-stained sections were analysed using QuPath software to measure the thickness and cross-sectional area of the intima (I), media (M), and adventitia (A). Overall MD scores (i.e., summaries of each MD grade component) were evaluated. Diagnostic performance was assessed using receiver operating characteristic (ROC) curve analysis based on binary logistic regression models.

CA demonstrated a profound architectural shift, characterised by medial thinning alongside marked intimal and adventitial expansion, resulting in significantly lower M/(I+A) thickness and area ratios compared with MD and controls (p <0.001). CA specimens also exhibited the most severe secondary degenerative changes, with significantly higher overall MD scores (median: 15 vs. 8; p < 0.001). ROC curve analysis revealed diagnostic utility of both the M/(I+A) thickness ratio (AUC = 0.964) and the M/(I+A) area ratio (AUC = 0.955) for identifying CA. A multivariable model combining the overall MD score with the M/(I+A) thickness ratio achieved an AUC of 0.971 (accuracy 88.1%), whereas combining it with the M/(I+A) area ratio yielded an AUC of 0.968 (accuracy 90.5%).

Digital morphometric analysis provides a reproducible and feasible method for quantifying structural remodelling in chronic aortitis. Changes in the proportions of the aortic layers, specifically intimal and adventitial expansion combined with medial thinning and severe secondary medial degeneration, can facilitate accurate differentiation of aortic wall pathologies, particularly in cases with sparse inflammation.