Natural history of small asymptomatic kidney and residual stones over a long-term follow-up: systematic review over 25 years.

Introduction Incidental identification of small, asymptomatic renal calculi has risen with increasing high-resolution imaging. The natural history of such stones and small residual fragments remains unclear, however kidney stone disease (KSD) demands growing healthcare resource utilisation with wide-ranging costs of treatment and varying management recommendations. Materials and methods We systematically reviewed the natural history of small asymptomatic kidney and residual stones using the Cochrane and PRISMA methodology. We searched Medline, Scopus, Embase, EBSCO, Cochrane library and Clinicaltrials.gov using themes of "asymptomatic", "nephrolithiasis", "observation", "symptoms", "admission", "intervention" and similar allied terms for all English language articles from 1996-2020 (25 years). Inclusion criteria were studies of minimum 50 patients, stones ≤10mm, and mean follow-up of ≥24 months. Primary outcomes were occurrence of symptoms, emergency admission and intervention. Results Our literature search returned 2247 results of which 10 papers were included in the final review. Risk of symptomatic episodes ranged from 0-59.4%. Meta-analysis did not identify any significant difference in the likelihood of developing symptoms when comparing stones 5mm, nor those 10mm. Risk of admission varied from 14-19% and risk of intervention from 12-35%. Meta-analysis demonstrated significantly decreased likelihood of intervention for stones 5mm and 10mm. Studies had variable risk of bias due to heterogeneous reporting of outcome measures with significant likelihood that observed differences in results were compatible with chance alone (Symptoms: I2 =0%, Cochran's Q=3.09, P=0.69; Intervention: I2 =0%, Cochran's Q=1.76, P=0.88). Conclusions This systematic review indicates that stone size is not a reliable predictor of symptoms, however risk of intervention is greater for stones 5mm and 10mm. This review will inform urologists as they discuss management strategies with patients who have asymptomatic renal stones and offer insight to committees during the development of evidence-based guidelines.