Role of stone density in predicting the outcome of extracorporeal shock wave lithotripsy (ESWL) for kidney stones

Abstract

Introduction. Since its introduction by Chaussy in 1980, ESWL, as minimally invasive procedure, is considered to be the best for the management of urolithiasis in most patients, especially when the stones are of < 2 cm in diameter. Computer tomography (CT) has long been used clinically to evaluate the calculi by using measurements of substance density in Hounsfield units (HU). Stone density on CT is reported to be a prognosis factor for ESWL. Aim of the study. To evaluate the usefulness of measuring stone density for predicting the outcome of treatment by ESWL and number of sessions. Materials and methods.. The study included 33 consecutive patients (21 males, 12 females; mean age: 47.7) with a solitary renal stone of 0.5–2.0 cm in length. The measurement of density was performed using a multidetector row CT scanner at 120 KV and 240 mA, with 1.25-mm collimation. A bone window was used to measure stone attenuation values. SWL was performed with an electromagnetic lithotripter. Failure of disintegration was defined as no fragmentation of the stone after three sessions. Results. Failure of disintegration was observed in 7 patients. Stone density >1200 HU were the significant independent predictors of failure. The success rate of ESWL was 87.5%. 26 patients were stone free and 7 had residual fragments <4 mm. The only significant predictor of residual fragments was stone density (p < 0.001).Conclusions. The use of CT to determine the density values of urinary stones before ESWL can help predict treatment outcome, and also in planning alternative treatment in patients with a likelihood of poor outcome from ESWL.