Value of supranormal function on 99m Tc-mercaptoacetyltriglycine renal scan in paediatric patients with obstructive hydronephrosis

Abstract

Objectives: To study related factors and clinical significance of supranormal function in paediatric patients with pelvi-ureteric junction obstruction, and to predict which factors cause renal function overestimation.

Patients and methods: Patients who underwent pyeloplasty from 2012 to 2017 were prospectively collected. Variables were compared between patients with and without supranormal function on ^99m Tc-mercaptoacetyltriglycine renal scan (supranormal defined as differential renal function [DRF] ≥55%). Univariate, multivariate logistic and linear regressions analyses were performed.

Results: Of 100 patients, 18 were excluded because of comorbidities. Nine patients (11.5%) showed preoperative supranormal function. The preoperative anteroposterior pelvic diameter (APD; 24 mm vs 35 mm, P = 0.026) and the ratio between preoperative pelvic and kidney volumes (0.2 vs 0.6, P = 0.003) were higher in supranormal kidneys. For each unit increase in the preoperative ratio between pelvic and kidney volumes, the risk of supranormal function rose 3.23-times (95% confidence interval [CI] 1.051-9.955). A preoperative APD ≥30 mm was a reliable predictor of supranormal function (area under the curve 0.804, 95% CI 0.707-0.902), with 88.9% sensitivity. Patients with either preoperative supranormal function or preoperative APD ≥30 mm had a greater reduction in renal function after pyeloplasty.

Conclusion: Supranormal function is related to large hydronephrosis where geometrical features are modified. A preoperative APD ≥30 mm is a reliable predictive factor of supranormal function. Preoperative renal function is overestimated either in supranormal patients or severe hydronephrotic kidneys. DRF should be interpreted with caution in kidneys with large hydronephrosis with or without supranormal function. Surgical indication should not entirely rely upon DRF.

Keywords: MAG3; hydronephrosis; pelvic diameter; pyeloplasty; supranormal function.