Due to the high pressure of the arterial system, the aorta is susceptible to the development of aneurysms and dissection. An aortic aneurysm is a dilatation greater than 3 cm anywhere along the aorta, including the ascending, arch, thoracic, or abdominal portions. Aortic aneurysms are present in 1%–4% of the population over age 50. Aortic dissection occurs when a false lumen is created by blood flowing through a tear in the intimal layer. Dissections put the patient at risk for disruption of flow to the aortic branch arteries. Both aneurysm and dissection of the aorta have the potential for disastrous and possibly fatal aortic rupture if left untreated.
PATHOPHYSIOLOGY AND MANAGEMENT
The development of an aortic aneurysm is multifactorial. Both environment and genetics play a role. An aortic aneurysm is ultimately the result of atherosclerosis which results from a myriad of factors, including inflammation, infection, genetic defects in vessel wall components, mechanics, and arterial wall protease activity.
The specific risk factors associated with a higher incidence of aortic aneurysm are male gender, Caucasian, history of smoking, concurrent cardiac or vascular disease, and a family history of aortic aneurysms. In contrast, the risk factors for an aortic dissection include hypertension, connective tissue disease, blunt trauma, deceleration injury, cocaine use, pregnancy, and surgical trauma.
Aortic aneurysms are grouped into thoracic, abdominal, and thoracoabdominal types. A thoracoabdominal aortic aneurysm (TAAA) involves either the thoracic and abdominal aorta or the suprarenal segments of the abdominal aorta. TAAAs account for 10% of aneurysms of the aorta. TAAAs have a unique classification system which describes the aneurysm based on anatomic extent (Figure 78-1). Aneurysms may involve the descending thoracic aorta (left subclavian artery to celiac artery, Type I), most of descending thoracic and abdominal aorta (left subclavian artery to bifurcation, Type II), the lower thoracic and abdominal aorta (Type III), and the abdominal aorta including celiac artery (Type IV).
Crawford classification of thoracoabdominal aortic aneurysms. (Reproduced with permission from Edmunds LH. Cardiac Surgery in the Adult. New York: McGraw-Hill; 1997:1232.)
The indications for elective repair of a thoracic aneurysm are anatomic (diameter > 5 cm) or symptomatic (chest or back pain, cough, hoarseness). For asymptomatic abdominal aortic aneurysms, an elective repair is recommended when greater than 5.5 cm in diameter because of a 10% per year risk of rupture. If the rate of growth is more than 0.5 cm in a 6 month period or the patient is symptomatic, elective repair may also be recommended.
Thoracic aneurysms involving the ascending aorta or aortic arch usually require open surgery. Descending aortic aneurysms are routinely treated with endovascular grafting. Thoracoabdominal aortic aneurysms can be repaired open, endovascular, or with a hybrid technique. The patient’s comorbidities, physiologic reserve, anatomy, and experience of the treating ...