Pathophysiology of aortic dissection and abdominal aortic aneurysm

The most common diseases seen in the aorta are aortic dissection and abdominal aortic aneurysm (AAA). Regarding the pathogenesis of the diseases, alteration of the medial structure is critical, as the media is the layer that integrates and stabilizes the aortic wall. The media is composed of a lamellar unit (an organized structure of smooth muscle cells, elastin, and collagen, among others) and elastin forms the framework structure consisting of elastic laminae and interlaminar elastin. Cystic medial necrosis is thought to be the pathogenetic change in the aortic dissection in Marfan syndrome, whereas in non-Marfan cases loss of interlaminar elastin appears to play a critical role in the initiation and propagation of the disease. Because of poor cohesiveness between each elastic lamina, the aortic wall may have poor resistance to shearing and the dissecting force in this condition. Laminar medial necrosis is frequently found in patients with aortic dissection, and it seems to be secondary to ischemic change. The pathogenesis of AAA is closely related to a reduction in the number of whole lamellar units and an overall reduction of elastin. Thus elastin appears to be a key component in both diseases.