Newly Developed Hydronephrosis in Patients Following Ureteroscopy: Who Is at Risk?

<b><i>Introduction and Objective:</i></b> Imaging rates are low after ureteroscopy in the United States. Detecting postoperative hydronephrosis is important to minimize patient morbidity, and predicting patients at greatest risk for new postoperative hydronephrosis could inform imaging guidelines. We used data from a clinical registry to understand new-onset postoperative hydronephrosis and associated risk factors after ureteroscopy and stone intervention. <b><i>Methods:</i></b> Using the Michigan Urological Surgery Improvement Collaborative registry, we retrospectively identified all ureteroscopy for urolithiasis between July 2020 and June 2023. We included patients without hydronephrosis on preoperative CT or ultrasound. New postoperative hydronephrosis was defined as hydronephrosis seen between postoperative days 29 and 60 following ureteroscopy. We compared demographic and clinical variables from patients with new postoperative hydronephrosis with patients who did not develop hydronephrosis. Logistic regression was performed to evaluate risk factors for new postoperative hydronephrosis. <b><i>Results:</i></b> Preoperative imaging was available for 4742 patients across 31 urology practices, of which 1066 also had postoperative imaging within 29 to 60 days of surgery. New postoperative hydronephrosis was seen in 87 (8.2%) patients. Among them, 51 patients (58.6%) had transient hydronephrosis, 6 (6.9%) strictures, 5 (5.7%) residual stones, 2 (2.3%) hematomas, and 23 (26.4%) did not have information available. Silent hydronephrosis was present in seven patients (0.66%). Factors associated with new postoperative hydronephrosis included location of the stone (kidney <i>vs</i> ureter), greater stone size, use of ureteral access sheath, ureteral stent placement after surgery, longer stent dwell time, and the presence of residual stones. After adjustment, renal location of the largest stone was found to be an independent predictor of developing postoperative hydronephrosis. <b><i>Conclusions:</i></b> Postoperative hydronephrosis in patients without preoperative hydronephrosis occurs 1 in 13 patients who had both pre and postoperative studies after ureteroscopy. More than half of these cases are transient, and silent postoperative hydronephrosis is rare. These data support a goal-directed approach to imaging rather than routine imaging for all patients.