462 Computed tomography-based novel prediction model for the outcome of SWL in proximal ureteral stone

Abstract

INTRODUCTION AND OBJECTIVES: Variations in morphology and internal structure of urinary calculi may cause differences in stone fragility. Stone heterogeneity index (SHI), a proxy of such variations, was defined as the standard deviation of a Hounsfield unit (HU) on noncontrast computed tomography (NCCT). As shown in Fig. 1, because the composition of urinary stones can vary even though they have a similar MSD, we postulated that a heterogeneous stone may be more fragile than a homogeneous stone. Herein, we defined the stone heterogeneity index (SHI) as the standard deviation of stone density on NCCT, and investigated whether SHI can be a novel predictor for SWL outcomes in patients with ureteral stones. METHODS: Medical records were obtained from the consecutive database of 1,519 patients who underwent the first session of SWL for urinary stones between Nov 2005 and Dec 2013. Ultimately, 604 patients with radiopaque ureteral stones were eligible for this study. Stone related variables including stone size, mean stone density (MSD), skin-to-stone distance, and SHI were obtained on NCCT. Patients were classified into the low and high SHI groups using mean SHI and compared. RESULTS: One-session success rate in the high SHI group was better than in the low SHI group (74.3% vs. 63.9%, P1⁄40.008). Multivariate logistic regression analyses revealed that smaller stone size (Odds ratio [OR] 0.889, 95% Confidence Interval [CI]: 0.841-0.937, P<0.001), lower MSD (OR 0.995, 95% CI: 0.994-0.996, P<0.001), and higher SHI (OR 1.011, 95% CI: 1.008-1.014, P<0.001) were independent predictors of one-session success. Similarly, stone size, MSD, and SHI also had an independent impact on one-session stone-free status (Table 1). CONCLUSIONS: The radiologic heterogeneity of urinary stones or SHI was an independent predictor for SWL success in patients with ureteral calculi and a useful clinical parameter for stone fragility.