Predictive value of cortical transit time on MAG3 for surgery in antenatally detected unilateral hydronephrosis caused by ureteropelvic junction stenosis

Background In children with antenatally detected hydronephrosis caused by ureteropelvic junction (UPJ) stenosis, the main challenge is preserving renal function by identifying children who require early surgical intervention from those for whom watchful waiting may be appropriate because of the potential for spontaneous resolution without a significant loss of renal function. Objective To assess the impact of initial cortical transit time (CTT) on technetium-99m mercaptoacetyltriglycerine (MAG3) diuretic renogram on the need for surgery in children with antenatally detected unilateral hydronephrosis caused by UPJ stenosis. Study design We retrospectively reviewed the medical records of 33 patients with antenatally detected unilateral hydronephrosis caused by UPJ stenosis who were managed at our institution between 2006 and 2014. Delayed CTT was defined as the absence of activity in the subcortical structures within 3 min of tracer injection on a MAG3 scan. The surgical indication includes symptomatic UPJ stenosis, seriously deteriorating hydronephrosis with parenchymal thinning on serial USG, split renal function <40%, or progressive deterioration of split renal function (>5%) on a MAG3 scan. This study analyzed and compared the initial level of Society for Fetal Urology grade, anteroposterior diameter (APD), split renal function, drainage pattern on a diuretic renogram, and CTT with the need for surgery. Results Of the 33 children, 16 were classified into the delayed CTT group and 17 were placed in the normal CTT group. During the follow-up period (mean 31.8 months), surgery was needed in 75.0% (12/16) of patients in the delayed CTT group and in 5.9% (1/17) of those in the normal CTT group. Multivariate analysis showed that delayed CTT on initial MAG3 scan and APD on initial ultrasonography were independent predictive factors of the need for surgery. Discussion In this era of conservative management of antenatally detected hydronephrosis caused by UPJ stenosis, it is critical to identify which measurement on an image study is the most reliable for predicting the need for surgery by reflecting functional deterioration. In this study, multivariate analysis revealed that CTT on the initial MAG3 scan was an independent predictive factor of the need for surgery. In addition, CTT showed high negative predictive value for surgical need in children with antenatally detected unilateral hydronephrosis caused by UPJ stenosis. Conclusion CTT on an initial MAG3 scan may be a useful predictor of the need for surgery in children with antenatally detected unilateral hydronephrosis caused by UPJ stenosis.