ABSTRACT
The first reported case of successful replacement of an abdominal aortic aneurysm (AAA), performed by Charles Dubost in 1951, ushered in the era of the current standard of endoaneurysmorrhaphy and intraluminal graft insertion.[1]
The impetus for continuing to advance our knowledge regarding the natural history of abdominal aortic aneurysms is the serious risk of rupture. As recently reported in two institutional studies, the overall 30-day mortality rate for patients presenting to hospital with rupture was between 50 and 70%.[2,3] However, these studies derived their mortality rates by including only those patients who arrived at the emergency department after rupture in time for a diagnosis to be made. Undoubtedly, the true mortality for all ruptured aneurysms is higher, potentially reaching 90-95%. The prevalence of both small and large abdominal aneurysms appears to be increasing, which may be the result of improved imaging techniques and increased physician awareness,[4] but a consensus has yet to be reached regarding the natural history and indications for elective surgery.[5]
According to suggested standards, the definition of a true arterial aneurysm is a permanent, localized (i.e., focal) dilation of an artery with at least a 50% increase in diameter compared with the normal. The most common site for a true arterial aneurysm is the infrarenal abdominal aorta. Arteriomegaly is a diffuse arterial enlargement (i.e., nonfocal) with an increase in diameter of greater than 50% by comparison with the normal diameter. Ectasia is characterized by dilation less than 50% of the normal arterial diameter.[6]
Abdominal aneurysms are fusiform dilations that most commonly begin distal to the renal arteries and are either confined to the aorta or extend to involve the iliac arteries. The average age at the time of surgical repair is 69-70 years, with women accounting for 15-20% of all patients undergoing both elective and emergency aneurysm repair as
reported in the surgical literature.[7] As with cardiac disease, it has been suggested that perhaps gender bias exists in patient selection. However, the observed gender difference is not significantly different when a family history for abdominal aortic aneurysms is present.[8]
The landmark study in 1966 by Szilagyi et al. reported observations in a large cohort of patients with asymptomatic abdominal aneurysms and concluded that late survival as well as the 5-year risk of rupture were related to aneurysm size.[9]
For aneurysms 6 cm or smaller in diameter, the 5-year survival was 48% and risk of rupture was 20%, compared with the 5-year survival of 6% and a rupture incidence of 43% for aneurysms greater than 6 cm in diameter.[9] This report had huge impact on decision making for several years and was the basis for the 6 cm cut-off as the indication for elective repair. This conclusion was made despite the extreme variability by which aneurysms were measured in this study (physical examination, plain x-ray at laparotomy, or autopsy). The next report that affected surgical decision making was by Darling et al. in 1977,[10] when 24,000 consecutive autopsies at the Massachusetts General Hospital were reviewed over a 23-year period. This study supported the theory that aneurysm rupture was related to size, but it was noteworthy that rupture was also found in aneurysms less than 4 cm in diameter. On the basis of these observations, the authors recommended that even small aneurysms should be repaired because they are all potentially lethal. The critical limitation of this and other autopsy studies for the purpose of defining natural history is the inaccuracy of size determination when the aneurysm is not measured under conditions of physiologic blood pressure. This would result in underestimating the actual size of the aneurysm and therefore overestimating the risk at a given size.
