The study protocol was reviewed and approved by the Institutional Review Board at Ijinkai Takeda General Hospital (IRB no. 20200005). We retrospectively analyzed 865 patients who underwent fURS for renal or ureteral stones between October 2011 and December 2019 and were evaluated for hydronephrosis 3 months after surgery by ultrasonography. Exclusion criteria were patients who underwent only semirigid URS and could not be evaluated by imaging 3 months after surgery.
Patients’ baseline characteristics (age, gender, body mass index (BMI), performance status (PS), American Society of Anesthesiologists Score, preoperative ureteral stenting, stone location and diameter, and history of obstructive pyelonephritis) and operative parameters (operative time, use of ballistic or laser devices for ureteral stones, UAS diameter, intraoperative ureteral injury, and postoperative ureteral stent duration) were evaluated. Postoperative imaging at the 3-month follow-up was recorded by ultrasonography or computed tomography (CT) [11]. The clinical outcome was followed further for patients identified with an abnormal 3-month follow-up. The Society of Fetal Urology grading system was used to classify all patients [12], and a grade > 1 was considered as hydronephrosis. Grade 2 was defined as mild hydronephrosis, grade 3 as moderate hydronephrosis, and grade 4 as severe hydronephrosis.
The surgical procedure is described as follows. A 5- or 6-Fr polyolefin ureteral stent (double-J stent, Polaris™, Boston Scientific) was inserted 1–2 weeks before ureteroscopic lithotripsy when upper urinary tract stones other than the lower ureter were found.
In patients with obstructive pyelonephritis due to ureteral stones on admission, a 6- or 7-Fr polyether block amide stent (single-J stent, Porges stentR, Coloplast) was placed, and fURS was performed after general improvement.
A semirigid ureteroscope (8/9.8-Fr tapering shaft, Richard Wolf) was used for stones in the ureter. In contrast, a flexible ureteroscope (URF-V3, 8.4 Fr or URF-V, 9.9 Fr, Olympus) was used for stones in the renal collecting system or those in the ureter not accessible with the semirigid ureteroscope. During the use of a semirigid ureteroscope, a single 0.035-inch guidewire (Radifocus, Terumo Corporation) was used as a safety guidewire. If the stone was detected in the ureter, it was crushed using a ballistic lithotripter (Swiss LithoClastR, Boston Scientific). The crushed stone was extracted outside the body or bladder by using grasping forceps. After confirming that the stone was not present in the ureter, the UAS (12/14 Fr or 10/12 Fr, FlexorR, Cook, Proxis, Medicon) was inserted under fluoroscopy. The renal pelvis and calyces were examined by using a flexible ureteroscope, and a holmium laser was used to fragment the stone when deemed necessary. Fragments were retrieved with baskets (Urotech). After achieving laser lithotripsy and basket extraction of stones, the ureter was checked for ureteral injuries or residual stones as the UAS was withdrawn. A 6-Fr polyurethane ureteral stent (double-J stent, InLayR, Bard) was routinely placed in all patients postoperatively. After ureteral stent removal, upper tract imaging with ultrasonography was routinely obtained at a 3-month follow-up visit.
Ureteral injuries were graded using the Traxer ureteral injury scale (grade 0: no ureteral lesion or only mucosal petechiae; grade 1: ureteral mucosal erosion without smooth muscle injury; grade 2: ureteral wall injury, including the mucosa and smooth muscle, with adventitial preservation (periureteral fat not seen); grade 3: ureteral wall injury, including the mucosa and smooth muscle, with adventitial perforation (periureteral fat seen); and grade 4: total ureteral avulsion); a grade > 1 was defined as a ureteral injury [13].
All statistical analyses were performed with EZR [14]. Variables are shown as the median and interquartile range. The Wilcoxon signed-rank and Pearson chi-squared tests were used to check for statistical significance where appropriate. Logistic regression analysis was performed to evaluate the independent predictors of postoperative hydronephrosis. Statistical significance was defined as p < .05.