Vessel wall morphology is equivalent for different artery types and localizations of advanced human aneurysms

Aneurysm formation occurs most frequently as abdominal aortic aneurysm (AAA), but is also seen in other localizations like thoracic or peripheral aneurysm. While initial mechanisms for aneurysm induction remain elusive, observations from AAA samples show transmural inflammation with proteolytic imbalance and repair mechanisms triggered by the innate immune system. However, limited knowledge exists about aneurysm pathology, especially for others than AAA. We compared 42 AAA, 15 popliteal, 3 ascending aortic, five iliac, two femoral, two brachial, one visceral and two secondary aneurysms to non-aneurysmatic controls by histologic analysis, immunohistochemistry and cytokine expression. Muscular and elastic type arteries show a uniform way of aneurysm formation. All samples show similar morphology. The changes compared to controls are distinct and include matrix remodeling with smooth muscle cell phenotype switch and angiogenesis, adventitial lymphoid cell accumulation and M1 macrophage homing together with neutrophil inflammation. Inflammatory cytokines are up-regulated accordingly. Comparative analysis of different disease entities can identify characteristic pathomechanisms. The phenotype of human advanced aneurysm disease is observed for elastic and muscular type arteries, does not differ between disease localizations and might, thus, be a unique response of the vasculature to the still unknown trigger of aneurysm formation.