aortic aneurysm

Arch Aneurysms

Etiology and Pathology
Aneurysms can occur anywhere along the aorta, but isolated arch aneurysms are uncommon and are usually associated with ascending and/or descending aneurysms. Aortic aneurysms most commonly are due to medial degeneration with resulting loss of elastic fibers as in idiopathic cystic medial degeneration and in Marfan and Ehlers-Danlos syndromes. Other causes of arch aneurysms include atherosclerosis, infection, inflammation, trauma, chronic dissection, and poststenotic dilation.
Loss of elastic integrity causes weakening of the aortic wall. The weakened aortic wall dilates circumferentially, resulting in the more common fusiform aneurysm, or in a localized area that manifests as a saccular aneurysm. As the aorta dilates, wall tension increases according to LaPlace's formula (tension = pressure Ã— radius/twice the wall thickness). The increase in wall tension further dilates the vessel, leading to even greater wall tension and dilation in a progressive manner. The significance of progressive dilation is illustrated by the finding that the incidence of rupture is <10% for aneurysms 35 mm to 49 mm, 18% for those 50 mm to 59 mm, and >25% for aneurysms >60 mm.