Elsevier

European Urology

Volume 51, Issue 6, June 2007, Pages 1688-1694
European Urology

Stone Disease
A Prospective Multivariate Analysis of Factors Predicting Stone Disintegration by Extracorporeal Shock Wave Lithotripsy: The Value of High-Resolution Noncontrast Computed Tomography

https://doi.org/10.1016/j.eururo.2006.11.048Get rights and content

Abstract

Objective

To assess the value of noncontrast computed tomography (NCCT) as a possible predictor of renal stone disintegration by shock wave lithotripsy (SWL).

Patients and methods

The study included 120 consecutive patients (71 males, 49 females; mean age: 42.6 yr) with a solitary renal stone of 0.5–2.5 cm in length. NCCT 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. The impact of patients’ sex, age, and body mass index (BMI) and the stones’ laterality, location, volume, mean attenuation value, and the skin-to-stone distance on disintegration were evaluated by univariate and multivariate analyses.

Results

Failure of disintegration was observed in 15 patients (12.5%). BMI and stone density >1000 HU were the significant independent predictors of failure (p = 0.04 and 0.02, respectively). The success rate of extracorporeal SWL at 3 mo was 87.5% (105 of 120 patients); 90 patients were stone free and 15 had residual fragments <4 mm. The only significant predictor of residual fragments was stone density (p < 0.001).

Conclusions

Obesity and increased stone density as detected by NCCT are significant predictors of failure to fragment renal stones by SWL. An alternative treatment should be devised for obese patients with stone density >1000 HU.

Introduction

Currently, extracorporeal shock wave lithotripsy (SWL) is the most common mode of therapy for small renal stones [1]. Stones are first disintegrated by shock waves, and then fragments are spontaneously cleared from the urinary tract. Failure of stone disintegration results in unnecessary exposure of the renal parenchyma to shock waves and the requirement of an alternative treatment procedure, which increases medical costs. Hence, it is important to identify patients who will benefit from SWL prior to treatment by examining stone fragility.

Many studies have attempted to correlate the radiographic findings of noncontrast computed tomography (NCCT) with SWL success [2], [3], [4], [5], [6], [7]. The main drawbacks of these studies were the use of low-resolution CT protocols in some [2], [3], [4], [5] or correlating NCCT stone characters with the stone-free rate [6], [7], which is influenced by other factors such as stone site and pelvicalyceal anatomy [8], [9].

In this study, we prospectively investigated the predictors of renal stone disintegration by SWL including the factors detected by high-resolution NCCT in a multivariate analysis.

Section snippets

Patients and methods

From 1 June 2004 through 31 May 2006, 120 consecutive patients agreed to participate in this prospective study. Our institution’s ethics committee approved the study, and a written informed consent was obtained from each subject. Patients were included in this study if they had a single renal stone of 0.5–2.5 cm in the longest dimension (as measured from excretory urography films) and had no contraindications to SWL.

The body mass index (BMI) was calculated by dividing the weight (kg) by the

Results

The 120 patients included 71 males and 49 females. Their mean age was 42.6 ± 11.4 yr, and their mean BMI was 28.6 ± 5.3 kg m−2. The mean stone volume was 1308.6 ± 943 mm3, and the mean stone density was 743 ± 181 HU. Failure of disintegration was observed in 15 patients (12.5%); 10 of these patients underwent percutaneous nephrolithotomy, and retrograde ureteroscopy and laser disintegration were performed on the other 5 patients. According to univariate analyses, higher BMI, female gender, stone density

Discussion

Because disintegration is the first step in treatment of renal stones by SWL, the magnitude of response of a calculus to disintegration (ie, stone fragility) should be considered before using SWL. It is often not possible to predict whether a given stone is amenable to fragmentation by shock waves before starting treatment, however, because there are many factors that affect stone fragility, such as size and composition [8], [10].

In general, stones composed of uric acid are broken up easily by

Conclusion

Based on this prospective study, we conclude that obesity and a high stone CT attenuation value are significant predictors of failure to fragment renal stones by SWL. Therefore, an alternative treatment should be devised for obese patients with stone density >1000 HU.

Conflicts of interest

The authors of the paper have no disclosure.

Editorial Comment

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Department of Urology, School of Medicine, University of Patras, GR 26500, Rion, Greece
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Department of Medical Physics, School of Medicine, University of Patras, GR 26500, Rion, Greece

Extracorporeal shock wave lithotripsy (ESWL) currently represents the most common approach for renal stone treatment [1], [2]. However, the influence of stone characteristics (size, shape, location, or

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