Role of variation coefficient of stone density in determining success of shock wave lithotripsy in urinary calculi

Abstract

BACKGROUND

Various stone factors can affect the net results of shock wave lithotripsy (SWL). Recently a new factor called variation coefficient of stone density (VCSD) is being considered to have an impact on stone free rates.

AIM

To assess the role of VCSD in determining success of SWL in urinary calculi.

METHODS

Charts review was utilized for collection of data variables. The patients were subjected to SWL, using an electromagnetic lithotripter. Mean stone density (MSD), stone heterogeneity index (SHI), and VCSD were calculated by generating regions of interest on computed tomography (CT) images. Role of these factors were determined by applying the relevant statistical tests for continuous and categorical variables and a P value of < 0.05 was gauged to be statistically significant.

RESULTS

There were a total of 407 patients included in the analysis. The mean age of the subjects in this study was 38.89 ± 14.61 years. In total, 165 out of the 407 patients could not achieve stone free status. The successful group had a significantly lower stone volume as compared to the unsuccessful group (P < 0.0001). Skin to stone distance was not dissimilar among the two groups (P = 0.47). MSD was significantly lower in the successful group (P < 0.0001). SHI and VCSD were both significantly higher in the successful group (P < 0.0001).

CONCLUSION

VCSD, a useful CT based parameter, can be utilized to gauge stone fragility and hence the prediction of SWL outcomes.

Keywords: Computed tomography; Shock wave lithotripsy; Stone heterogeneity; Variation coefficient of stone density; Kidney stones

Core Tip: In the recent literature various computed tomography (CT) based stone parameters have been studied regarding their role in success of shock wave lithotripsy. These non-contrast CT parameters include skin-stone distance, stone volume, and stone density, which might help in prediction of the success of shock wave lithotripsy (SWL). In recent guidelines, it has been agreed upon that successful outcomes become less likely for harder stones-stone density more than 900-1000 Hounsfield units. Recently, novel parameters such as stone heterogeneity index and variation coefficient of stone density can be representative of stone heterogeneity and can be of utility in prediction of SWL outcome. We, in this study, tried to ascertain their predictive role in shock wave lithotripsy outcomes.