The natural history of asymptomatic renal stones ≤ 5 mm: comparison with > 5 mm.

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 computed tomography 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.