Radiological Determination of Stone Density and Skin-to-Stone Distance—Can it Predict the Success of Extracorporeal Shock Wave Lithotripsy?

Abstract

Objectives:To 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 5–20 mm, over a 12 month period. Mean stone density in Hounsfield units (HU) and mean SSD in millimetres (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 the patients. Mean stone densities were 505 ± 153 and 803 ± 93 HU in ESWL successful and failure groups, respectively; this was statistically significant ( p < 0.001, student's t-test). 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 in predicting the outcome of ESWL. We propose that stone densities <500 HU are highly likely to result in successful ESWL. Conversely, stone densities ≥800 HU are less likely to do so. This should be accounted for when considering ESWL.