Predicting the Success of Flexible Ureterorenoscopy for Kidney and Upper Ureter Stones

Urolithiasis remains one of the most common urological diseases globally, characterized by increasing incidence and recurrence rates. While flexible ureterorenoscopy (fURS) has become a preferred minimally invasive treatment for renal and upper ureteric stones due to its high efficacy and low morbidity, the stone-free rate (SFR) varies significantly among patients. To optimize patient counseling and treatment selection, predictive nomograms have emerged as practical tools that integrate multiple clinical and radiological variables into a single, individualized probability estimate for achieving stone clearance.

However, external validation is a critical prerequisite before adopting any predictive model into routine clinical practice. A nomogram developed in one population may exhibit different predictive accuracy in another due to variations in patient characteristics, stone burden, and local healthcare settings. Currently, there is limited evidence regarding the performance of published fURS predictive models in Middle Eastern and Egyptian populations. This study addresses this gap by conducting an independent external validation of a published nomogram at Assiut University Hospitals.

The study involves a comprehensive, multi-phase data collection process for all enrolled participants:

• Preoperative Assessment: Patients will undergo clinical, laboratory, and radiological evaluations. Baseline demographic data (age, sex, body mass index) and serum creatinine levels will be recorded. Stone characteristics will be evaluated using computed tomography (CT) to document stone size, volume, number, location, laterality, and the presence of hydronephrosis. CT findings specifically required to calculate the nomogram score will be systematically extracted.
• Intraoperative Parameters: During the fURS procedure, the surgical team will prospectively record the total operative time, utilization of a ureteral access sheath, specific laser lithotripsy settings utilized for fragmentation, the operating surgeon's experience level, and any intraoperative complications encountered.
• Postoperative Evaluation: Following the surgery, researchers will document the duration of the hospital stay, any postoperative complications, and the potential need for auxiliary procedures (such as repeat ureteroscopy, shock wave lithotripsy, or percutaneous interventions for residual stone burden).