The effect of skin-to-stone distance on success in renal pelvis stones treated with ESWL

Our study aimed to investigate the effect of stone load, skin-to-stone distance, and stone density Hounsfield Unit (HU) measured in unenhanced computed tomography on the success of ESWL in patients with renal pelvis stones. The data of 136 patients, who were admitted to the Urology Polyclinic of Malatya Training and Research Hospital between January 2016 and 31 December 2018 due to side pain and who underwent ESWL in the Urology Clinic after renal pelvis stone was detected as a result of radiological evaluation, were evaluated. In unenhanced abdominal CT performed on patients before ESWL, skin-to-stone distance and Hounsfield unit measurements of the stone were performed. In CT, the size of the stone was calculated by the product of its width and length in the sections where the stone appeared the largest. Hounsfield Unit was evaluated. In the post-ESWL follow-ups, stone-free rates were examined, and whether the skin-to-stone distance and HU were determinant factors were evaluated. For each ESWL session of the patients, the shock number was planned as 1500-2500 (mean=2123) and shock intensity as 14-20 (mean=17) kV. There were at least 7 days between two ESWL sessions. The mean age of the patients was calculated as 42.4±12.3 years and the mean BMI as 26.2±2.8 kg/m2. The mean stone size was 118.4±62.3 mm2, skin-to-stone distance was 10.2±1.6 cm, and stone density HU was 886.4±372.2. In 92 patients with a mean skin-to-stone distance below 9.2±0.9 cm and a mean stone density below 689±78.2 HU, stone-free success was achieved. In 44 patients who had residual stones following ESWL, the mean skin-to-stone distance was 11.6±1.6 cm and the stone density was 1217±218.4 HU. While 52.9% of the patients were male, 47.1% were female. BMI, stone diameter, skin-to-stone distance, and stone density were determined as parameters affecting treatment success in the treatment of renal pelvic stones with ESWL. A positive correlation was determined between skin-to-stone distance and BMI (r=0.44, p<0.001). Mean stone density HU was found to be a strong predictive value in stone treatment, and stone densities of the patients with residual stones following ESWL treatment were found to be statistically higher (p<0.001). The success of ESWL depends on stone density, skin-to-stone distance, BMI, and stone size. It is seen that rate of success is lower in cases with high stone density, long skin-to-stone distance, high BMI, and large stone size. Multicenter studies involving larger numbers of patients will contribute to the inclusion of these predictive values in guidelines.