Predicting the fragility of renal calculi in response to shock wave lithotripsy through their radiographic appearance

Abstract

To evaluate the radiological characteristics of renal stones on plain X-ray film of the kidneys, ureters and bladder (KUB) area as predictors of stone fragility during shock wave lithotripsy (SWL). This prospective study included 336 patients who had a single renal pelvic stone ≤20 mm and were managed by SWL at 3 different centers. The patients were classified according to the radiological appearance of the stone on KUB film in terms of homogeneity, smoothness of the outline, and radiodensity in comparison to the last rib. The primary endpoint was the stone-free rate (SFR) within 3 months post-SWL. Multivariate regression analysis was used to compare the results. The overall SFR was 71.43%. SFR was significantly higher in heterogeneous compared with homogenous stones (86% vs. 53%; p<0.01) and in rough compared with smooth surface calculi (77% vs. 61%, p<0.01). SFRs for stones with density less than, similar to or higher than that of the last rib were 82%, 69% and 56%, respectively (p<0.01). Multivariate analysis showed a positive proportional relationship between stone fragility (SWL outcome) and one or more favorable radiological criteria. The radiological characteristics of renal calculi could predict their fragility after SWL. Stones which were heterogeneous, rough, or less dense than the last rib on KUB film were more likely to disintegrate during SWL.