Objective: To investigate changes in the differential renal function (DRF) before and after pyeloplasty in renal units with unilateral pelvi-ureteric junction obstruction (PUJO) with supranormal function, and to evaluate the clinical significance.
Patients and methods: We reviewed the medical and radiographic records of 29 children (26 boys and three girls) with unilateral PUJO with a DRF (estimated by (99m)Tc-mercaptoacetyltriglycine renal scintigraphy) of >/= 50% in the affected renal unit, who had pyeloplasty and were followed for >1 year after surgery. Patients were divided into two groups according to the degree of change in their DRF to compare the clinical variables, anteroposterior pelvic diameter and parenchymal thickness measured by renal ultrasonography. The mean (range) follow-up after pyeloplasty was 35 (12-89) months.
Results: After pyeloplasty, although the mean DRF reduced from 53.8% to 51.4%, in seven (24%) patients the DRF decreased significantly (>5%) while most (76%) showed a change of </= 5% of the preoperative function, or further improvement. In the seven patients with a DRF of >/= 55% before surgery, the DRF afterward was >55% in four and 50-55% in one. Between those with and with no significant reduction in DRF, only the preoperative renal parenchymal thickness differed significantly (2.78 vs 5.00 mm, P = 0.006).
Conclusion: Supranormal DRF exists and represents the true split function of the affected renal unit in patients with adequate renal parenchyma; these units maintained the supranormal function after pyeloplasty. Parenchymal thickness might be useful to differentiate between the true and false estimates and predict surgical outcome before surgery.