The natural history of renal stone fragments following ureteroscopy.

OBJECTIVES: To describe the natural history of postureteroscopic renal stone fragments ≤4 mm based on computed tomography (CT) follow-up. The goal of ureteroscopy is to fragment stones, actively basket and remove fragments larger than 1 mm, and allow the remaining fragments to pass spontaneously. The reality is that smaller fragments may be difficult to extract or may be missed.
METHODS: Patients treated with ureteroscopy and holmium laser lithotripsy for urolithiasis by a single surgeon from May 2001 to July 2008 at a tertiary referral center were identified. Patients with residual renal fragments measuring ≤4 mm on initial postoperative CT and at least one additional follow-up CT were included. Outcomes measured were fragment growth and location, stone event (emergency department visit, hospitalization, or additional intervention), and spontaneous fragment passage.
RESULTS: Of 330 ureteroscopies, 51 met inclusion criteria. For these patients, the mean follow-up duration was 18.9 months (1.6 years). Among 46 ureteroscopies for calcium-based stones, 9 patients (19.6%) experienced a stone event, 10 patients (21.7%) spontaneously passed their fragments, and the remaining 27 patients (58.7%) retained asymptomatic residual fragments. Among this asymptomatic group, mean fragment sizes were similar at 2.7, 3.3, 3.5, and 3.0 mm at mean follow-up durations of 2.8, 10.2, 16.8, and 33.0 months, respectively.
CONCLUSIONS: This study suggests that among patients with postureteroscopic renal stone fragments ≤4 mm, approximately one in five (or 19.6%) will experience a stone event over the following 1.6 years. The remaining patients will either become stone-free via spontaneous passage or retain asymptomatic stable-sized fragments.