Contradictory supranormal function in hydronephrotic kidneys: Fact or artifact on pediatric MAG-3 renal scans?

Abstract

Objectives: Contradictory supranormal renal function (SRF) in unilateral hydronephrosis is a debatable subject resulting from the methodology of nuclear renography or the characteristics of the patient. In this study, we aimed to investigate the frequency and comparison of SRF with MAG-3 scans by 8 different technical analyses in pediatric hydronephrosis. Methods: We reviewed Tc-99m MAG-3 scans in 82 children with unilateral hydronephrosis (52 male, 30 female, mean age: 47.7 +/- 64.5 months). Of 82, 34 also had Tc-99m DMSA scans. Data were reprocessed with 4 different regions of background activity (subrenal, perirenal C-type, perirenal ring, and lateral) at 2 different time intervals (1-2 and 2-3 minute), and 8 different estimates of MAG-3 differential renal function (DRF) were obtained in 67 patients. SRF was defined as DRY greater than 55% in the hydronephrotic kidney. Results: The routine processing protocol showed only 3 renal units with SRF, and all were on the right side (3.6%). After reprocessing, a total of 10 dilated kidneys had SRF in I or more of DRF estimates (5.2% of all estimations). These cases were significantly younger (8.1 +/- 6.7 vs. 42.5 +/- 52.5, P < 0.05) and had a larger renal area ratio (1.25 +/- .24 vs. 1.07 +/- .2 1, P < 0.05). There was no SRF with DMSA. In comparison between MAG-3 and DMSA DRY in 20 children who underwent both tests within 3 months, the best correlation was obtained when C-type correction was used for both agents at 2 time intervals (r: .86 and .84 for early and late time intervals, P < 0.00001, respectively). Conclusions: SRF in unilateral hydronephrosis is, at least, in part, technical in origin in this particular pediatric patient population with tubular immaturity (ie, physiological high background activity) and asymmetric kidney size.