The fate of clinically insignificant residual fragments following retrograde intrarenal surgery and factors affecting spontaneous passage

The remaining stone fragments after retrograde intrarenal surgery (RIRS) can lead to stone recurrence/regrowth, or stone-related events (SRE). We aimed to delineate the clinical circumstances that are decisive for spontaneous passage of clinical insignificant residual fragments (CIRF) (primary outcome) and define risk factors for stone recurrence/regrowth and their clinical manifestation (secondary outcome). A total of 115 patients who had CIRF following RIRS were included in this study. Demographic, clinical data, stone, and anatomic characteristics including infundibulopelvic angle (IPA), infundibular length (IL) and follow-up data of patients were analyzed. The mean follow-up time was 27.5 ± 6.9 months. 31 (26.9%) patients passed the CIRF spontaneously. Patients were divided into two groups as spontaneous fragment passage group and fragment remaining group and compared with respect to demographic, clinical, stone-related, and anatomic characteristics. 61.2% of patients had lower pole CIRF in fragment remaining group and 83.3% of patients in spontaneous fragment passage group ( p = 0.031). In addition, IPA was wider in spontaneous fragment passage group (60.7° vs 51.4°, p = 0.001). A subanalysis was performed for fragment remaining group. In 84 patients, 44 (52.4%) patients were stable for their CIRF at their follow-up and included in stable group. 40 (47.6%) patients experienced stone re-growth (27 patients) or SRE (13 patients) at their follow up. Patients in re-growth/SRE group were older (49.1 vs 39.4 years, p = 0.047), had higher body mass index (28.2 vs 27 kg/m 2 , p = 0.03) and larger CIRF (2.8 vs 2.1 mm). CIRFs may be not expelled spontaneously and they may lead to additional morbidity and lithotripsy interventions.