[PREOPERATIVE INTERNAL DRAINAGE FOR PEDIATRIC GIANT HYDRONEPHROSIS CROSSING THE MIDLINE: REPORT OF TWO CASES].

Giant hydronephrosis extending beyond the midline can cause marked dilatation of the renal pelvis and significant anatomical distortion. This distortion makes intraoperative visualization, identification of the ureteropelvic junction (UPJ), and planning of the anastomosis challenging. To address this issue, preoperative reduction of the renal pelvis can be achieved through either external or internal drainage, which may improve surgical feasibility in such cases. We report two pediatric cases of giant hydronephrosis crossing the midline (a 4-year-old girl and a 4-year-old boy), managed with a staged surgical approach. In the first case, the patient had intrinsic obstruction; hydronephrosis recurred after internal drainage, requiring placement of a urethral balloon catheter until definitive surgery. In the second case, the patient had extrinsic obstruction and did not require catheter placement after internal drainage. In both cases, internal drainage using a double-J stent was performed at least 1 month before pyeloplasty to reduce the size of the renal pelvis, followed by robot-assisted laparoscopic pyeloplasty after sufficient reduction was achieved. Both patients showed favorable postoperative outcomes. These findings suggest that preoperative internal drainage for giant hydronephrosis extending beyond the midline may facilitate identification of the UPJ and performance of the anastomosis by reducing renal pelvic size, thereby improving the safety and reliability of the surgical technique.