Objectives: Although previous studies have indicated that stone heterogeneity can affect extracorporeal shockwave lithotripsy (SWL) outcomes, there is no established measurement of stone heterogeneity on CT imagery. We investigated whether variation coefficient of stone density (VCSD) can predict shockwave success. Materials and Methods: We conducted a retrospective review of 245 patients with urinary calculi who had undergone SWL. We compared the predictive powers of treatment success between VCSD and other parameters associated with CT attenuation. In addition, we performed logistic regression analysis to identify the factors contributing to treatment success. Treatment success was determined within 3 months after first treatment using noncontrast CT. Results: The treatment success rate was 47.8% (117/245 cases). From receiver operating characteristic curves for treatment success, area under curve of VCSD (0.7181) was larger than that of mean stone density (MSD) (0.6384, p = 0.09) and standard deviation of stone density (0.5412, p < 0.01). Multivariate analysis revealed that MSD (p = 0.028) and VCSD (p < 0.001) independently predicted the outcome. Categorized by stone location, VCSD was the independent significant predictor for SWL outcomes in both kidney (p = 0.047) and ureteral calculi (p < 0.001). Conclusions: We found that VCSD can be a novel predictor of SWL success. The development of nomograms or scoring systems, including VCSD, can assist in the decision process for patients and minimize unnecessary delay in treatment of urolithiasis.

Kidney stones are a major public health concern with continuously increasing worldwide prevalence. Shock wave lithotripsy (SWL) is the first line treatment choice for upper urinary tract calculi with ureteroscopy and has advantages of safety and noninvasiveness, but the treatment success rate of SWL is lower than that of other therapies. It is therefore important to identify predictive factors for SWL outcome and select a suitable treatment choice for patients with upper urinary tract calculi. In recent years, computed tomography (CT) has become the gold standard for diagnosis of upper urinary tract calculi. Several factors based on CT images, including skin-to-stone distance, mean stone density, stone heterogeneity index, and variation coefficient of stone density, have been reported to be useful for predicting SWL outcome. In addition, a new method of analysis, CT texture analysis, is reportedly useful for predicting SWL outcomes. This review aims to summarize CT parameters for predicting the outcome of shock wave lithotripsy in stone cases in the upper urinary tract.