Stone-event-free survival after retrograde intrarenal surgery: is the stone-free-status so relevant for the future outcomes?

Introduction: The primary aim of stone treatment is to achieve stone-free status. Residual fragments can cause stone growth, recurrence, urinary tract infections, and ureteric obstruction. Our goal was to describe the natural history of stone burden after retrograde intrarenal surgery (RIRS) based on stone-free status (SFS), evaluating stone growth and stone-events.

Methods: We retrospectively reviewed data from patients who underwent RIRS at a tertiary care center between October 2014 and September 2019. The stone burden was assessed by measuring the maximum diameter (mm) and volume (mm). Patients were divided into four groups according to SFS-(A) absolute stone-free, no stones on non-contrast-enhanced computed tomography (NCCT); (B) relative stone-free with ≤ 2 mm fragments, (C) relative stone-free with 2.1-4 mm fragments, and (D) residual fragments > 4 mm. Our main outcomes were stone growth over time (defined as an increase in diameter compared to first postoperative measurement) and incidence of stone-related events (pain or additional intervention to treat symptoms, obstruction, or removing fragments).

Results: A total of 98 patients were included in the study-42 were classified as absolute stone-free (Group A), 20 were categorized as relatively stone-free (Groups B and C), and 36 had a residual stone burden with fragments larger than 4 mm (Group D) on postoperative NCCT. There was a significant difference in the number of stones among the groups (p < 0.001). The pre-operative stone volume differed significantly among the groups (p = 0.003). Group A had the lowest median total stone volume (551.3 mm). Twenty patients (20.4%) developed stone-events during a mean follow-up period of 62.3 months (± 26.0). Stone-event-free survival differed significantly between the groups (p = 0.028), with Group D demonstrating a higher incidence of stone-related events post-RIRS compared to the other groups. Sixteen patients (16.3%) had renal colic requiring a hospital visit across all groups. Thirteen patients (13.3%) required re-intervention (3 patients belonged to Group A, 1 to Group B, 2 to Group C, and 7 to Group D).

Conclusions: Group D shows a higher rate of stone-related events post-RIRS. Ensuring complete stone-free status after RIRS is crucial for treatment success. Other factors should be considered in the management, including ensuring compliance with general preventive measures and stone-specific pharmacological treatments to prevent recurrence.