Does Fresh Clot Shrink Faster Than Preexistent Mural Thrombus after Endovascular AAA Repair?

Purpose: To correlate the amount of preexistent thrombus in abdominal aortic aneurysms (AAA) to sac shrinkage after endovascular repair. Methods: From January 1993 through April 2000, 76 patients underwent endovascular AAA repair and were examined at 12 months to identify aneurysms that had decreased in size by >10%. Volume measurements were performed using a standardized spiral computed tomographic angiography (CTA) protocol with 3-dimensional postprocessing. Volume measurements were unavailable or incomplete in 16 patients, and another 16 did not have sac shrinkage >10%, leaving 44 patients in the study group. The percentage of preexistent mural thrombus in shrinking sacs (OldThr%) was calculated by dividing the preoperative thrombus volume by the postoperative nonluminal thrombus volume. The 12-month volume change, expressed as a percentage of the postoperative thrombus volume and as an absolute value, was correlated with OldThr% using the Pearson product moment test. Results: The median proportional shrinkage at 12 months was 56% (range 15%–89%) and the absolute nonluminal thrombus volume shrinkage was 49 mL (range 6–186). The median OldThr% was 53% (range 6%–94%). The correlation coefficients of OldThr% were 0.130 (p=0.40) with the proportional shrinkage in thrombus volume and 0.235 (p=0.13) with the absolute volume change. Conclusions: The rate of shrinkage of successfully excluded aneurysm sacs after endovascular repair is independent of the preoperative mural thrombus volume in the aneurysm. Other factors are responsible for the large variation in shrinkage.