Surgical Techniques Illustrated Autumn 1976 [antikvár]

To make a rational decision concerning operation for an abdominal aortic aneurysm, one must have a reasonable idea of the patient's prognosis both with and without surgical intervention. The fact that patients with clinically detectable abdominal aortic aneurysms have a poor prognosis was brought home by the report of Estes [5] in 1950 of 102 patients followed without surgery. This study revealed a five-year survival of only 19 per cent for patients with abdominal aneurysm; 63 per cent of the patients died from aneurysm rupture. Following the advent of excisional aneurysm surgery in 1952, many reports [2, 6, 11, 12] have demonstrated a clear-cut relationship between aneurysm size and the danger of rupture. From these studies it seems likely that a diameter of 6 cm is the approximate dividing line between dangerous and less dangerous abdominal aortic aneurysms. In most series the risk of rupture of aneurysms less than 6 cm in diameter varies from 4 to 20 per cent, whereas for larger aneurysms the frequency of rupture ranges from 40 to 80 per cent within two to five years from the time the diagnosis is made. Although aneurysms under 6 cm in diameter cannot be considered completely benign since their incidence of rupture may be as high as 20 per cent in five years [11], patients with a small aneurysm clearly have a better prognosis than those who have a sizable lesion. In one large clinical study [12] the five-year survival for patients with aneurysms 6 cm or under was approximately 50 per cent, whereas it was about 5 per cent in those whose aneurysm was greater than 6 cm. Operative Mortality One major consideration in recommending surgery for abdominal aneurysm is the operative mortality rate itself, which is by no means inconsiderable even in the hands of experienced surgeons. An operative mortality of approximately 10 per cent for elective abdominal aneurysm resection was the norm in the United States five years ago [2, 4, 8, 9]. However, in the past five years sizable series of elective aneurysm resections have been reported with operative mortality rates of 3 to 5 per cent [1, 3, 7], suggesting a recent improvement in the survival of patients undergoing this operation, possibly resulting from better intraoperative and postoperative management. Decision to Resect Therefore, in the light of present knowledge, it seems logical to recommend elective aneurysm resection and graft replacement for patients whose lesion is 6 cm or larger in diameter and who are considered reasonable risks for major abdominal surgery. Obviously, this policy must be altered for extremely elderly patients depending upon the surgeon's estimate of their probable life expectancy. Moreover, in patients with severe coronary or cerebral arteriosclerosis, severe restrictive pulmonary disease, or significant renal disease, any blanket recommendation for elective aneurysm resection must be modified by the results of careful clinical evaluation on an individual basis. Some patients whose aneurysm is less than 6 cm in diameter should be treated conservatively, however, with repeated three-to six-month evaluations to determine whether there has been any increase in aneurysm size. Nonetheless, since the danger of rupture of a small aneurysm may ultimately be as high as 20 per cent [12], we recommend elective resection in good-risk individuals under the age of 65 years with aneurysms between 4 and 6 cm in diameter. This decision is also based upon the probability that the aneurysm in such patients will ultimately grow to dangerous size during their natural life span. These ground rules must be modified for abdominal aortic aneurysms that have become symptomatic. The early study of Gliedman and his associates [6] points out clearly that symptomatic abdominal aneurysms have a much worse prognosis than those which do not cause symptoms: at least 80 per cent of patients whose aneurysms have become symptomatic will probably be dead within one year unless the aneurysm is resected. A symptomatic aneurysm is therefore an urgent indication for surgery. Determination of Aneurysm Size Aneurysm size can be determined clinically in most patients by simple abdominal palpation. In obese people, roentgenograms may be needed to estimate the diameter of an abdominal aneurysm. For this purpose the best roentgenogram is usually a lateral film of the lumbosacral spine, which will reveal the calcified anterior and posterior walls of the aneurysm. Ultrasound has recently been used successfully to estimate aneurysm size [10]. Rarely, aortography may be necessary to gauge the extent of an abdominal aneurysm, though the information obtained may be misleading since contrast medium may not reach the aneurysm wall because of the presence of mural thrombus. However, aortography is performed routinely prior to aneurysm resection in many centers to give the surgeon information on the state of the vessels below the aneurysm, which may be used for distal anastomosis with the graft, and to demonstrate preoperative^ the degree of atherosclerotic involvement of the major visceral aortic branches. Preoperative aortography may be lifesaving in revealing the uncommon instance of the inferior mesenteric artery being the major source of intestinal blood supply. In this situation inferior mesenteric revascularization is necessary at the time of aneurysm resection, whereas the usual practice is simply to ligate this vessel at its origin.