Kidney Stone Size and Hounsfield Units Predict Successful Shockwave Lithotripsy in Children

OBJECTIVE To define the preoperative kidney and stones characteristics on noncontrast-enhanced computed tomography that affect the success of extracorporeal shockwave lithotripsy (SWL) for treatment of renal calculi in pediatric patients. MATERIALS AND METHODS From 2005 to 2011, 57 children (age <16 years) with documented preoperative noncontrast-enhanced computed tomography scans underwent SWL for treatment of renal stones and were included in the present study. Stone size, site, multiplicity, average skin-to-stone distance, stone attenuation value, and kidney morphology were determined from the preoperative noncontrast-enhanced computed tomography scans. Success was defined as radiographically stone-free status at the 3-month follow-up examination after a single lithotripsy session without the need for additional sessions or ancillary procedures. RESULTS After a single session of SWL, 24 children (42.1%) were stone free on the 3-month follow-up imaging study without the need for additional SWL sessions. Treatment failed in 33 patients (57.9), with residual fragments in 30 children, of whom 29 required repeat SWL, and 3 with stones that were considered unchanged and were finally treated with percutaneous nephrolithotomy. Logistic regression analysis revealed that stone attenuation in Hounsfield units (HU) and stone length were the only significant predictors of success. When the HU were stratified into 2 groups of <= 600 and >600 HU, the SWL success rate was 82.1% and 20%, respectively (P=.023). When length was stratified as <= 12 mm and >12 mm, the stone-free rate was 58.6% and 25.1%, respectively (P-.016). CONCLUSION Stone attenuation <= 600 HU and stone length <= 12 mm were significant independent predictors of SWL success in children. UROLOGY 81: 880-884, 2013. (C) 2013 Elsevier Inc.