Role of volume and attenuation value histogram of urinary stone on noncontrast helical computed tomography as predictor of fragility by extracorporeal shock wave lithotripsy.

OBJECTIVES

To test, for the first time, the predictive capability of the total stone volume (TSV) and the attenuation value histogram. Recently, the mean attenuation value (MAV) of urinary stones has been recognized as a predictor of fragility by extracorporeal shock wave lithotripsy. However, properties other than MAV, including the TSV and the heterogeneity of attenuation value histogram, may also be related to fragility.

METHODS

A total of 62 renal and proximal ureteral radiopaque stones treated with extracorporeal shock wave lithotripsy were included in this prospective study. Stones less than 5 mm or greater than 20 mm were excluded. Attenuation value histograms were graphed from the data from noncontrast helical computed tomography scans. The TSV, MAV, and hump existence (HE) on the histogram were also calculated. These parameters were compared between the treatment success and treatment failure groups.

RESULTS

Of the 62 stones, 6 were excluded, 39 were in the success group, and 17 in the failure group. Of the 56 stones, 16 had a hump and 40 did not on the attenuation value histograms. The TSV, MAV, and HE were significantly different statistically between the two groups (P <0.001), with an accuracy of 82.1%, 83.9%, and 91.1%, respectively. Also, HE was the only independent predictor of success or failure of extracorporeal shock wave lithotripsy on multivariate analysis (P = 0.0073).

CONCLUSIONS

Our results have suggested that TSV, MAV, and HE are good predictors of stone fragility. The treatment modality of the stone should be selected according to the HE, which is a practical, simple, and predictive index.