PROSPECTIVE-STUDY OF THE NATURAL-HISTORY OF THORACIC AORTIC-ANEURYSMS

Background. The decision whether or not to recommend resection of mode rately large descending thoracic and thoracoabdominal aneurysms requir es weighing the relatively high mortality and significant risk of para plegia associated with operation against the likelihood that the aneur ysm will rupture spontaneously, with an almost invariably fatal outcom e. To better define the risk of aneurysm rupture, we undertook a prosp ective study of patients who had not had operation on their moderately large descending thoracic and thoracoabdominal aneurysms. Methods. Pa tients were enrolled at the time of their second computed tomographic scans: three-dimensional computer-generated reconstructions allowed de termination of several dimensional parameters for each study, includin g diameters and cross-sectional areas at the site of maximal dilatatio n in the descending aorta and in the abdomen as well as total thoracoa bdominal surface area. Comparisons of serial studies permitted calcula tion of yearly rates of change in these dimensions. Results. Of 114 pa tients, 8 died of causes unrelated to the aneurysm, 26 died of rupture , 20 met previously determined criteria for operation, and 60 survived without operation or rupture. Multivariate regression analysis identi fied maximal diameter in the descending and in the abdominal aorta as independent risk factors for rupture, as well as older age, the presen ce of even uncharacteristic pain, and a history of chronic obstructive pulmonary disease. A piecewise exponential model enabled construction of an equation allowing calculation of rate of rupture in patients in whom the values of the risk factors are known, and also of the probab ility of rupture in a given individual over a specified time interval. Conclusions. Because using this equation--based on easily determined risk factors (age, pain, chronic obstructive pulmonary disease, maxima l thoracic and maximal abdominal aortic diameter)--allows the risk of aneurysm rupture within a given interval to be estimated fairly accura tely for each individual patient, it is our current practice to recomm end operation when the calculated risk of rupture within 1 year exceed s the anticipated mortality of elective operation, rather than relying on general operative guidelines based almost exclusively on aneurysm size. (C) 1997 by The Society of Thoracic Surgeons.