A particular phenotype of ascending aorta aneurysm as precursor of type A Dissection

Background: It sought to identify a phenotype of ascending thoracic aortic aneurysm than more than the others evolving to dissection. Methods: Aortic specimens were obtained from patients (97 men and 37 women, whose median age 62,95± 11,44 years) undergoing surgical repair of an ascending aortic aneurysm (n=108) and type A dissection (n=26). Multiple histologic sections from each specimen were prepared and stained with hematoxylin-eosin, Weighert-van Gieson, Alcian-PAS. Features evaluated and graded included fragmentation of elastic fibers, cystic medial change, smooth muscle cell necrosis, medial fibrosis, atherosclerosis. Immunohistochimical staining was performed to evaluate the presence of lymphocyte and macrophages and the markers of medial apoptosis and metalloproteinases (MMPs). Results: Among degenerative thoracic aortic aneurysms, 35 (32,4%) aneurysms were non-atherosclerotic aneurysms (NADA) and 73 (67,6%) aneurysms were atherosclerotic aneurysms (ADA). In the context of NADA, we identified three phenotype: - phenotype I: cystic medial degeneration balanced by a substitutive fibrosis, in absence of medial apoptosis, and with a faint collagenases concentration. - phenotype II: cystic medial degeneration higher grade respectively than substitutive fibrosis, with focal medial apoptosis, and moderate collagenases concentration. - phenotype III: elevated cystic medial degeneration, without substitutive fibrosis, with plurifocal medial apoptosis and severe collagenases concentration. Conclusion: Morphologic identity of medial lesions observed in the phenotype III of NADA and in the aortic dissection permit to suppose that in the NADA the phenotype III represent the precursor of dissection independently of aneurysm diameter and or valvular disorder.