Area of hydronephrosis is a useful predictive factor of impacted ureteral stones.

Ureteroscopic lithotripsy for impacted stones is challenging, but it is important to predict impacted stones preoperatively. Hydronephrosis, which is evaluated by a grading system, is often apparent in impacted stones. However, the currently used grading system is a qualitative evaluation. We, therefore, focused on a quantitative evaluation: the area of hydronephrosis. The aim of this study was to investigate whether the area of hydronephrosis could predict impacted stones more accurately than Society for Fetal Urology grade. We retrospectively identified 160 patients who underwent ureteroscopic lithotripsy for ureteral stones at our hospital between January 2014 and April 2022. Impacted stones were defined as stones fixed to the ureteral wall that could not be moved by means of ureteroscopic manipulation or water pressure. Of the 160 patients, 54 (33.8%) had impacted stones. Comparing patient characteristics, there were significant differences in stone size, ureteral wall thickness, Society for Fetal Urology grade, renal pelvic width and area of hydronephrosis (all P < 0.01). Receiver operating characteristic analysis showed that area of hydronephrosis was the more significant predictive value (area under the curve 0.781) compared with Society for Fetal Urology grade (area under the curve 0.676, P < 0.01). Multivariate analysis revealed that significant independent predictive factors of impacted stones were thicker ureteral wall thickness and larger area of hydronephrosis (both P < 0.01). The area of hydronephrosis and ureteral wall thickness were significant predictors of impacted stones in patients undergoing ureteroscopic lithotripsy for ureteral stones. These factors may be useful for selecting the treatment and preoperative settings.