Simple and practical nomograms for predicting the stone-free rate after shock wave lithotripsy in patients with a solitary upper ureteral stone

Purpose: To develop practical nomograms for predicting the stone-free rate after shock wave lithotripsy (SWL) in patients with a solitary stone in the proximal ureter. Methods: Between July 2006 and June 2015, 319 patients with a proximal ureteral stone who underwent preoperative non-contrast enhanced computed tomography (NCCT) and subsequently received SWL were identified. Patients’ age, gender, laterality, stone size, mean and maximum Hounsfield Unit (HU) of the stone, and skin-to-stone distance (SSD) were assessed. The stone-free status was defined as no radiopacity detected on the 3-month follow-up plain radiography or NCCT. Results: Mean stone size was 10 mm (range 3–20 mm). Mean and maximum HU of the stone ranged from 115 to 1447 (mean 701) and from 265 to 1881 (mean 1062), respectively. The overall stone-free rate was 70%. Multivariate analyses identified stone size (p < 0.001), maximum HU (p < 0.001), and SSD at 90° (p = 0.038) as independent predictive factors for the stone-free status after SWL. Nomograms could be constructed for predicting the probability of stone-free status after SWL corresponding to SSD of 8, 10, and 12 cm using maximum HU and stone size. Conclusions: This study demonstrated that stone size, maximum HU of the stone, and SSD at 90° are significant predictors of successful SWL outcome in patients with a proximal ureteral stone. We have developed simple and practical nomograms corresponding to three different SSDs for predicting the stone-free rate after SWL.