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.
Keywords: <5 mm; asymptomatic renal stone; natural history.