Variation Coefficient of Stone Density: A Novel Predictor of the Outcome of Extracorporeal Shockwave Lithotripsy.

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.