Pathobiology of Aortic Aneurysms and Dissections

The pathobiology of aortic disease is linked to aortic region: atherosclerosis for abdominal aorta, primary medial degeneration or aortitis for ascending thoracic aorta, and all causes for descending thoracic aorta and thoracoabdominal lesions. The pathogenesis of aortic dissection involves damage of the outer media from impaired perfusion from dysfunctional vasa vasorum, formation of discrete foci of disrupted vascular smooth muscle cell-elastic fiber extension-contractile units, and imbalance of radial sheer stress across the aortic wall, thereby creating an intimal tear and linear dissection. Thoracic aortic aneurysms develop from the chronic progression of medial degeneration coupled with the weakening of the remodeled adventitia, allowing for aortic dilatation. Precipitating factors include hypertension and mutations of genes regulating the vascular smooth muscle cell-elastic fiber extension-contractile units. Criteria are presented for distinguishing genetic from acquired causes of thoracic aortic aneurysms and dissections, with important implications for therapeutic and surgical decisions in the care of these patients.