Objective: To determine the clinical value of visually assessed renal tissue transit time (TTT) in 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) renography for patients undergoing pyeloplasty.
Materials and methods: Medical records of 164 patients who underwent dismembered pyeloplasty were retrospectively reviewed. Baseline and postoperative renal ultrasonography and 99mTc-MAG3 renography were performed. Two urologists blinded to clinical data evaluated the renography and classified TTT as timely or delayed based on visualization of the tracer in the kidney pelvis between 2 and 10 minutes. Renal functional change after pyeloplasty was compared between patients in the timely and delayed groups.
Results: A total of 126 patients (median age, 9 months) were evaluated after excluding patients with bilateral ureteropelvic junction obstruction, a single functioning kidney, duplicated ureter, or <3 months of follow-up. There were no differences between 89 patients with timely TTT and 37 patients with delayed TTT in mean preoperative hydronephrosis grade (3.7 vs 3.8) and pelvic diameter (3.1 cm vs 3.4 cm). Although the pre- and postoperative mean values of differential renal function (DRF) were significantly higher in the timely group than in the delayed group (47.2% vs 38.3% and 47.9% vs 44.6%), DRF change was greater in the delayed group (6.3% vs 0.6%). In multivariate analysis, delayed TTT was the only significant predictor of >5% improvement in renal function after pyeloplasty.
Conclusion: Delayed TTT in 99mTc-MAG3 renography was a significant predictor of renal functional improvement after pyeloplasty in ureteropelvic junction obstruction. Because substantial improvement of renal function is anticipated, we recommend immediate pyeloplasty in patients with delayed TTT and decreased DRF.
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