Evidence of Cyclic Changes in the Metabolism of Abdominal Aortic Aneurysms During Growth Phases: 18F-FDG PET Sequential Observational Study

The rates of growth of medically treated abdominal aortic aneurysms (AAA) are difficult to determine, and relationships with parietal inflammation and with metabolic parameters from 18F-FDG PET remain unclear. This 18F-FDG PET sequential observational study was aimed at analyzing the metabolic changes accompanying the growth phases of medically treated AAA. Methods: Thirty-nine patients (37 men; age [mean ± SD], 71 ± 12 y) exhibiting small and medically treated AAA (maximal diameter, 46 ± 3 mm) underwent 18F-FDG PET and CT angiography at baseline and 9 mo later. Clinical and imaging parameter correlates of the 9-mo increase in maximal diameter were investigated; these included 18F-FDG maximal standardized uptake values (SUVmax) averaged for slices encompassing the AAA volume. Results: Of the 39 patients, 9 (23%) had a significant ($2.5 mm) increase in maximal diameter at 9 mo, whereas the remaining 30 did not. The patients with an increase in maximal diameter at 9 mo exhibited lower SUVmax within the AAA at baseline than patients who did not have such an increase (1.80 ± 0.45 vs. 2.21 ± 0.52; P 5 0.04); they also displayed a trend toward greater changes in SUVmax at 9 mo (difference between 9 mo and baseline: 10.40 ± 0.85 vs. �0.06 ± 0.57; P 5 0.07). Similar levels were ultimately reached in both groups at 9 mo (2.20 ± 0.83 and 2.15 ± 0.66). SUVmax was a significant, yet modest, baseline predictor of the absolute change in maximal diameter during follow-up (P 5 0.049). Conclusion: The enhancement in the maximal diameter of small AAA was preceded by a stage with a low level of 18 F-FDG uptake, but this low level of uptake was no longer docu