Objectives: Several preoperative parameters have been studied to estimate stone-free rate (SFR) following RIRS procedures. The objective of this study was to evaluate the effects of stone density on surgical outcomes of RIRS. Methods: This retrospective study included 30 stone-free patients (Group SF) and 30 patients with residual fragments (Group RF). Patients’ age and gender, laterality, non-contrast computed tomography findings, including size and density of the kidney stones, infundibular pelvic angle (IPA), operational time, and postoperative pain were recorded and compared between the two groups. The stone density was measured by free hand region of interest (ROI) determination coincident with the stone borders and expressed as Hounsfield Units (HU). Results: The rate of single stones was significantly higher in Group SF compared to Group RF (p < 0.001). The mean stone size was found as 11.93 ± 7.81 mm in Group SF and 16.27 ± 7.29 mm in Group RF with the difference being statistically significant (p < 0.001). The mean infundibular pelvic angle (IPA) was 53.87 degrees in Group SF and 50.33 degrees in Group RF. The mean density was measured as 748.17 ± 318.14 HU in Group SF and 945.90 ± 345.30 HU in Group RF. The mean stone density was statistically significantly higher in patients with residual fragments compared to the stone-free patients (p < 0.001). Conclusions: This study revealed that stone density as measured as Hounsfield Units (HU) affects the treatment outcomes with retrograde intrarenal surgery (RIRS) procedure and the mean density is significantly higher in patients with residual stone fragments. Advances in knowledge: Studies about the effects of Hounsfield units on stone-free rate are limited in the literature. Stone density affects the treatment outcomes with retrograde intrarenal surgery (RIRS) procedure and the mean density is significantly higher in patients with residual stone fragments.
