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 5–20mm, 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 ≤3mm.

Results

ESWL success was observed in 68.5% of the patients. Mean stone densities were 505±153 and 803±93HU 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±2.6cm 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 <500HU are highly likely to result in successful ESWL. Conversely, stone densities ≥800HU are less likely to do so. This should be accounted for when considering ESWL.

Abbreviations: CT-KUB, non-contrast computer tomography of kidney, ureter and bladder, HU, Hounsfield units, ESWL, extracorporeal shock wave lithotripsy, SSD, skin-to-stone distance

Keywords: Hounsfield units, ESWL, Renal calculi, Stone density