Introduction. The combination duplication of upper urinary tract with ureteropelvic junction obstruction (UPJO) is a rather rare anomaly with a frequency of 2-7% among all UPJO. The rather low frequency of occurrence of UPJO in the duplex kidney and the variability of its anatomical variants determine the absence of standardized approaches to the choice of the method of plastic intervention. Materials and methods. The article presents the results of surgical treatment of 26 children with UPJO in the lower pole of a duplex kidney over the past 20 years in 7 clinics of the Russian Federation and the Republic of Belarus. Children are divided into 3 groups depending on the type of surgical technique. Group 1 – dismembered pyeloplasty of the lower pole with the formation of an end-to-end anastomosis between the pelvis and the ureter of the lower pole. Group 2 – ureteropyeloanastomosis side-to-side between the ureter of the upper pole and the pelvis of the lower pole. Group 3 – dismembered pyeloplasty of the lower pole end-to-end with a common ureter with simultaneous formation of a submerged ureteropyeloanastomosis end-to-side between the ureter of the upper pole and the pelvis of the lower pole. Results. Postoperative complications of varying severity according to Clavien-Dindo were observed in 4 (15.4%) children. 3 (11.5%) patients required repeated pyeloplasty. The immersive anastomosis in group 3 patients functioned satisfactorily in all cases. Conclusion. The experience of surgical treatment of UPJO in the lower pole of the duplex kidney demonstrates a higher recurrence rate compared to standard pyeloplasty. The variability of the anatomical features of the UPJO of the lower pole of the duplex kidney determines the need for a personalized approach to the choice of the UPJO reconstruction technique.

Presentation of a rare clinical case of hydronephrosis of the lower half of the kidney due to vasoureteral conflict against the background of the complete doubling of the upper urinary tract. The rarity of this anomaly is demonstrated by only a single mention of a similar case in an adult patient in the literature. The patient, three years old, had dilatation of the upper urinary tract that was detected antenatally. According to the postnatal ultrasound results at three months, the anterior-posterior size of the pelvis of the lower half of the left kidney was 13 mm, and the parenchyma of the left kidney was 11 mm. The child was followed up on an outpatient basis. There were no laboratory or clinical manifestations of urinary tract infection. Ultrasound monitoring revealed progression of dilatation of the pelvis of the lower half max up to 40 mm and thinning of the kidney parenchyma in the projection of the lower pole up to 7 mm, in connection with which the child successfully underwent antevasal ureteropyeloanastomosis of the lower half of a completely doubled kidney. The anterior-posterior size of the pelvis of the lower half after removal of the pyelostomy was 16 mm. The child did not have any clinical and laboratory disease manifestations in the postoperative period. The described clinical case expands our understanding of the anatomy of obstruction of the pyeloureteral segment and hydronephrosis of the lower half of the duplex kidney. It enables us to plan surgical tactics, considering the possible intraoperative detection of the described anatomical configuration.