Abstract: Objective To explore the etiology of hydronephrosis with urinary tract infection in children. Methods The clinical data of 98 children hospitalized with urinary tract infection who were found to have renal pelvis separation by urinary tract color Doppler ultrasonography from 2010 to 2020 were retrospectively analyzed. Results Based on the urinary tract dilation grading system, hydronephrosis was graded in 98 children with urinary tract infection: normal in 42 cases, grade 1 in 17 cases, grade 2 in 28 cases and grade 3 in 11 cases. Thirty-six children ( 64 . 3 %) with hydronephrosis grade 1 , 2 and 3 were complicated with urinary malformation, the incidence was higher than that in the normal group ( 18 cases, 42 . 9 %), and the difference was statistically significant (χ 2 =4.45, P= 0 . 035 ). The urinary malformations in hydronephrosis mainly included 16 cases of ureteropelvic junction obstruction, 16 cases of vesicoureteral reflux and 8 cases of vesicoureteral junction stricture. The ureteropelvic junction obstruction and vesicoureteral junction stricture were mainly on the left side, while vesicoureteral reflux was mainly bilateral, and the difference was statistically significant (P> 0 . 05 ). There was significant difference in operation rate among different grades of hydronephrosis (P< 0 . 05 ). Conclusion The common etiology of hydronephrosis is urinary malformation, among which the obstruction of the ureteropelvic junction and vesicoureteral reflux is the most common, followed by vesicoureteral junction stricture. The classification of hydronephrosis and urinary tract malformations can be considered as the basis for diagnosis and treatment.

Key words: hydronephrosis; urinary tract infection; urinary malformation