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Introduction: Asymptomatic renal stones are identified in 10% of the population. Although many patients initially prefer watchful waiting, understanding the likelihood of eventual stone migration may better inform their treatment decision. Therefore, we evaluated the utility of stone location and other characteristics to predict stone migration.
Methods: With IRB approval, we retrospectively identified patients who opted to monitor asymptomatic renal calyceal stones. Patients were stratified based on those demonstrating stone migration [stone passage or development of hydronephrosis], and those who did not. Demographic data included gender and age. Stone location (upper pole/midrenal vs. lower pole), size (≤ 10mm or ≥ 10 mm), stone-growth greater than 50%, and reported renal colic were also compared between groups. Chi square analysis was used to determine differences in proportions between groups.
Results: A total of 135 stones from patients (42% female (57/135) with an average age of 56.1 (SD+/-13.2) and a mean follow up of 40.6+18.6 months were included. Overall, non-migratory stones comprised 77% (105/135) and migratory comprised 22% (30/135). The non-migratory group was more likely to have lower pole stones, 55.2% vs. 33.3% p=0.040 ) and were less likely to report renal colic (13.3% vs. 100% p-value <0.003). Although a greater proportion of the non-migratory group demonstrated stone growth greater than 50% (20% vs. 10%, p-value 0.206) this was not statistically significant. Specifically evaluating the utility of location for prediction of migration, lower pole stones were 2.5 times more likely to remain non-migratory (85% vs. 70%; OR 2.46 CI:1.05 to 5.9, p-value=0.040).
Conclusion: Lower pole renal stones are more likely to remain stable in position and less likely to pass or obstruct than upper pole or mid-renal calyceal stones. This information may be useful in advising management options, although further studies with extended follow up will better elucidate long-term outcomes.