The fate of lower pole hydronephrosis after transurethral incision of upper pole ureteroceles in children with duplex systems.

PURPOSE: Duplex system is the most common upper urinary tract anomaly in childhood. The purpose of our study was to investigate the incidence, characteristics, and progression of lower pole hydronephrosis in children with duplex system who underwent transurethral incision (TUI) of upper pole ureterocele. MATERIALS AND METHODS: Among children who underwent transurethral incision of ureteroceles between 2006 and 2018, 69 renal units with duplex systems were included after exclusion of preoperative lower pole vesicoureteral reflux and follow up loss. We retrospectively analyzed the postoperative progression of lower pole hydronephrosis and compared patient characteristics between two groups according to the presence of lower pole hydronephrosis. RESULTS: The median age at operation and follow-up duration were 3.0 months (range 0-242 months) and 59 months, respectively. The median size of ureteroceles preoperatively was 14.5 mm. Thirty-five renal units (50.7%) demonstrated preoperative lower pole hydronephrosis of any grade (grade I in 13 [37.1%], II in 6 [17.1%], III in 10 [28.7%], and IV in 6 [17.1%]). In majority of cases, lower pole hydronephrosis drastically improved after transurethral incision, and 28 renal units (80%) demonstrated improvement of lower pole hydronephrosis to grade 0 or I. The preoperative diameter of upper pole ureter was significantly increased with lower pole hydronephrosis than without (11.30 ± 4.19 vs. 7.02 ± 4.94 mm, p < 0.01). Postoperative vesicoureteral reflux on upper pole was found in 16 (23%), five (7%) in lower pole. Eleven patients developed complications after TUI which required secondary surgeries. The differential renal function of affected renal units was decreased after TUI in group with preoperative lower pole hydronephrosis (46.77 ± 8.21 to 44.24 ± 8.55, p = 0.003), while it was maintained without significant difference in group without lower pole hydronephrosis (47.90 ± 6.39 to 46.24 ± 8.90, p = 0.091). CONCLUSIONS: Lower pole hydronephrosis was found in a considerable number of renal units (50.7%), and the occurrence was related with the diameter of upper pole ureter. Most of renal units demonstrated significant improvement of lower pole hydronephrosis after transurethral incision of ureterocele. Given that differential renal function may be decreased even after improvement of hydronephrosis with TUI, a more careful monitoring on renal function is required in patients with hydronephrosis on lower pole.