The usefulness of stone density and patient stoutness in predicting extracorporeal shock wave efficiency: Results in a North African ethnic group

Introduction: We determine the role of stone density and skin-to-stone distance (SSD) by non-contrast computed tomography of the kidneys, ureters and bladder (CT-KUB) in predicting the success of extracorporeal shock wave lithotripsy (ESWL). Methods: We evaluated 89 patients who received ESWL for renal and upper ureteric calculi measuring 5 to 20 mm, over a 12-month period. The mean stone density in Hounsfield units (HU) and mean SSD in mm was determined on pre-treatment CT-KUB at the CT workstation. ESWL was successful if post-treatment residual stone fragments were <= 3 mm. Results: ESWL success was observed in 68.5% of patients. Mean stone densities were 505 +/- 153 and 803 +/- 93 HU in the ESWL successful and failure groups, respectively (p < 0.001, student's t-test). The mean SSD were 10.6 +/- 2.0 and 11.2 +/- 2.6 cm in ESWL successful and failure groups, respectively; this was not statistically significant. Conclusions: This study shows that stone density can help to predict the outcome of ESWL. We propose that stone density <500 HU are highly likely to result in successful ESWL. Conversely, stone densities >800 HU are less likely to be successful.