Renal Stone Features Are More Important Than Renal Anatomy to Predict Shock Wave Lithotripsy Outcomes: Results from a Prospective Study with CT Follow-Up

Abstract

Introduction: Lower pole kidney stones have been associated with poor shock wave lithotripsy (SWL) outcomes because of its location. However, the real impact of collecting system anatomy on stone clearance after SWL is uncertain. There is a lack of prospective well-controlled studies to determine whether lower pole kidney stones have inferior outcomes than nonlower pole kidney stones when treated with SWL. Methods: We prospectively evaluated patients with a single kidney stone of 5-15mm undergoing SWL from June 12 through January 19. All patients were subjected to computed tomography before and 3 months after the procedure. Demographic data (age, gender, and body mass index), stone features (stone size, stone area, stone density, and stone-skin distance-SSD), and collecting system anatomy (infundibular length and width, and infundibulopelvic angle) were recorded. Outcomes (fragmentation and stone clearance rates) were compared between lower pole and nonlower pole cases. Then, a multivariate analysis including all variables was performed to determinate which parameters significantly impact on SWL outcomes. Results: One hundred and twenty patients were included in the study. Mean stone size was 8.3mm and mean stone density was 805 Hounsfield units. Overall stone fragmentation, success, and stone-free rates were 84.1%, 64.1%, and 34.1%, respectively. There were no significant differences in stone fragmentation (76.0% vs 71.4%; p=0.624), success rate (57.6% vs 53.3%; p=0.435), and stone-free rate (40.2% vs 35.7%; p=0.422) in the lower vs nonlower pole groups, respectively. On multivariate analysis, only stone density (p<0.001) and SSD (p=0.006) significantly influenced fragmentation. Stone size (p=0.029), stone density (p=0.002), and SSD (p=0.049) significantly influenced kidney stone clearance. Conclusions: Stone size, stone density, and SSD impact on SWL outcomes. Lower pole kidney stones have similar fragmentation and stone clearance compared with nonlower pole kidney stones.