Abdominal Aortic Aneurysm Repair

Published on 11/04/2015 by admin

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CHAPTER 25 Abdominal Aortic Aneurysm Repair

BACKGROUND

Abdominal aortic aneurysms, defined as focal dilations of the abdominal aorta to a 50% or greater increased diameter, are the most common true aneurysms. Mortality from AAAs results from aneurysm rupture; half of all patients with ruptured AAAs die before arrival at a hospital and those patients who do reach a hospital alive have a 50% in-hospital mortality rate. In the United States, ruptured AAAs are the 15th leading cause of death, accounting for 15,000 fatalities per year. In contrast, elective open (as opposed to endovascular) AAA repair has a surgical mortality rate of less than 5%. Most deaths from AAAs are, therefore, preventable with prophylactic surgery.

The majority of AAAs are infrarenal (i.e., they involve the aorta below the renal arteries). Approximately 5% of AAAs also involve the suprarenal aorta, and are termed suprarenal AAAs. A higher percentage of aneurysms are juxtarenal. Approximately 25% of AAAs also involve one or both iliac arteries (aortoiliac aneurysms). Aneurysm morphology may be described as fusiform (i.e., relatively symmetric and spindle-shaped) or saccular (i.e., focal asymmetric outpouching). Atherosclerotic ulcers or “blebs” sometimes involve the AAA, and this may increase the risk of rupture.

Most AAAs are degenerative (sometimes described as atherosclerotic). Other, much less common, etiologies are infection (mycotic aneurysms), arteritis, cystic medial necrosis (as in Marfan’s disease), trauma, and inherited connective tissue disorders. Risk factors for the development of degenerative AAAs include smoking history, male sex, age greater than 50 years, and family history of aneurysm disease.

Aneurysm size is the most significant determinant of the risk of aneurysm rupture. Aneurysms that are between 5 and 6 cm in diameter have a yearly rupture risk of approximately 10%. In addition, chronic obstructive pulmonary disease (COPD) and hypertension confer an increased rupture risk. Female sex is sometimes considered a risk factor for rupture as well, most likely because aneurysms of the same diameter are larger in comparison to the normal diameter of the abdominal aorta in women than in men.

PREOPERATIVE EVALUATION

Most AAAs are asymptomatic and are diagnosed on the basis of physical examination findings or, more often, are incidental findings on abdominal imaging performed for another reason. Patients with symptomatic but nonruptured aneurysms most often present with pain, suggesting expansion of the aneurysm. Patients with ruptured aneurysms present with some combination of abdominal or back pain, hypotension, syncope, or a pulsatile abdominal mass. Because morbidity and mortality rates after aneurysm surgery are significantly increased in patients with coronary artery disease and COPD, evaluation of patients before elective AAA repair commonly includes stress testing, echocardiography and, if pulmonary disease is suspected, pulmonary function testing. In addition, patients frequently undergo carotid ultrasound to exclude carotid stenoses, which would predispose to stroke in the perioperative period.

COMPONENTS OF THE PROCEDURE AND APPLIED ANATOMY

The standard treatment for patients with AAA is open endoaneurysmorrhaphy. This has traditionally been undertaken either through a transperitoneal (anterior) approach or a retroperitoneal approach. Since its introduction in 1991, endovascular AAA repair (EVAR) has largely supplanted open aneurysm repair for the treatment of infrarenal AAAs. These operative approaches, along with their attendant advantages, are addressed in the next section.