Comparison of Rupture Risk Between Saccular and Fusiform Abdominal Aortic Aneurysms Using a National Clinical Database in Japan

Background Saccular AAAs are thought to pose an elevated risk of rupture, but not much is known about the extent of this risk. Therefore, we aimed to conduct a survey of saccular abdominal aortic aneurysms (AAAs) and to compare the risk of rupture between fusiform and saccular AAAs. Methods We performed a retrospective cohort study on patients who underwent primary endovascular repair for a degenerative AAA between 2016 and 2019, and who were registered in the National Clinical Database in Japan. Results A total of 27,290 patients were included in the study. Of these, 7.8 % (n=2142) had saccular AAAs and the remaining 92.2% (n = 25,148) were fusiform. In addition, 4.3% (n = 92) of saccular AAAs and 5.4% (n = 1351) of fusiform AAAs were ruptured. Saccular AAAs ruptured at smaller dimeters than fusiform AAAs (median, 55.6 mm vs 68.0 mm, p < 0.001), and were operated on at smaller diameters than fusiform AAAs in non-ruptured cases (median, 44.0 mm vs 51.0 mm, p < 0.001). The rupture rate was significantly higher in saccular AAAs than in fusiform AAAs in the 40-54 mm diameter range, in which saccular morphology was found to be an independent risk factor for rupture by adjusting for gender and aneurysm diameter (odds ratio, 2.54, 95% confidence interval, 1.75-3.69). In addition, receiver-operating characteristic analysis revealed that the cut-off diameter to predict rupture was smaller in saccular AAAs than in fusiform AAAs (50.5 mm and 59.5 mm, respectively). Conclusion Saccular AAAs are more prone to rupture than fusiform AAAs in the 40-54 mm diameter range, which supports the idea that saccular AAAs should be treated at smaller diameters. The 9.0 mm difference in the predicted diameters for the rupture between fusiform and saccular AAAs suggests that the threshold diameter for intervention of saccular AAAs can be set approximately 1 cm smaller than that of fusiform AAAs. Clinical Perspective What Is New? Saccular abdominal aortic aneurysms (AAAs) ruptured at smaller dimeters than fusiform AAAs (median, 55.6 mm vs 68.0 mm, p < 0.001), and receiver-operating characteristic analysis revealed that the cut-off diameter to predict rupture was smaller in saccular AAAs than in fusiform AAAs (50.5 mm and 59.5 mm, respectively). In AAAs with a dimeter of 40-54 mm, saccular morphology turned out to be an independent risk factor for rupture by adjusting for gender and aneurysm diameter (odds ratio, 2.54, 95% confidence interval, 1.75-3.69). What Are the Clinical Implications? Saccular AAAs are more prone to rupture than fusiform AAAs in the 40-54 mm diameter range, which supports the current idea that saccular AAAs should be treated at smaller diameters. The 9.0 mm difference in the predicted diameters for the rupture between fusiform and saccular AAAs suggests that the threshold diameter for intervention of saccular AAAs can be set approximately 1 cm smaller than that of fusiform AAAs.