Objectives: To clarify the natural history of asymptomatic renal stones £5 mm in comparison with stones ‡5 mm. Calculi £5 mm are considered insignificant stones, but to what extent stone-related events can occur is unclear.Patients and Methods: In this retrospective study, 207 patients with asymptomatic renal stones confirmed by both CT and ultrasonography performed on the same day were enrolled. A follow-up ultrasound was performed every 6 months. The active indications for surgical intervention included stone relocations into the ureter and stone-related symptoms. The primary endpoint was the rate of surgical intervention.Results: A total of 207 patients (71 cases with stones £5 mm and 136 cases with stones >5 mm) were included in this study. At a median follow-up of 3.3 years, 14 patients (20%) from the £5-mm group and 52 (38%) from the >5-mm group underwent surgical treatment ( p = 0.0067). Moreover, 11 patients (16%) from the £5-mm group and 27 (20%) from the >5-mm group received surgical intervention as they manifested active indications, showing no significant difference ( p = 0.44). As regards stone events, there were no significant differences in spontaneous stone passage, pain, hematuria, and stone growth. Multivariate analysis revealed that age £50 years and a history of stone surgery were significant factors, but stone size was not. Conclusion: About 20% of asymptomatic renal stones £5 mm require surgical treatment within 5 years.

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Introduction: Cystine stone development is relatively uncommon among patients with urolithiasis, and most studies have reported only on small sample sizes and short follow-up periods. We evaluated clinical courses and treatment outcomes of patients with cystine stones with long-term follow-up at our center. Methods: We retrospectively analyzed 22 patients diagnosed with cystine stones between January 1989 and May 2019. Results: The median follow-up was 160 (range 6–340) months, and the median patient age at diagnosis was 46 (range 12–82) years. All patients underwent surgical interventions at the first visit (4 extracorporeal shockwave lithotripsy, 5 ureteroscopy, and 13 percutaneous nephrolithotripsy). The median number of stone events and surgical interventions per year was 0.45 (range 0–2.6) and 0.19 (range 0–1.3) after initial surgical intervention. The median time to stone events and surgical intervention was 2 years and 3.25 years, respectively. There was a significant difference in time to stone events and second surgical intervention when patients were divided at 50 years of age at diagnosis (p = 0.02, 0.04, respectively). Conclusions: Only age at a diagnosis under 50 was significantly associated with recurrent stone events and intervention. Adequate follow-up and treatment are needed to manage patients with cystine stones safely.