Natural History and Reintervention After PCNL for Isolated Lower-Pole Stones with Residual Fragments > 4 mm: A Retrospective Cohort Study

Background: This study aimed to describe the long-term clinical trajectory, stone burden changes, and secondary endourological reintervention outcomes in patients presenting with residual stone fragments (RSFs) > 4.0 mm confined to the lower pole following percutaneous nephrolithotomy (PCNL). Methods: We retrospectively reviewed a single-center cohort of 29 consecutive patients who underwent index-PCNL for isolated lower pole calculi and presented with RSFs > 4.0 mm on routine non-contrast computed tomography (NCCT) at 3 months postoperatively (defined as study baseline and time zero), followed for a minimum of 12 months. Demographic data, baseline and terminal stone burden, stone-related clinical events, procedural complications, and secondary endourological interventions were analyzed. Results: Twenty-nine patients (20 males, 9 females; mean age: 50.1 ± 12.0 years) were analyzed. Preoperative median two-dimensional (2D) stone burden was 332.0 mm2 (IQR: 282.0–386.0 mm2). At the 3-month baseline NCCT, median residual 2D stone burden was 24.0 mm2 (IQR: 13.0–33.0 mm2). Over a median follow-up of 36.0 months (IQR: 18.0–48.0 months), four patients (13.8%, 95% CI: 3.9–31.7%) achieved spontaneous stone passage, 15 patients (51.7%, 95% CI: 32.5–70.6%) required secondary reintervention due to interval enlargement or symptoms, and 10 patients (34.5%, 95% CI: 17.9–54.3%) remained on active surveillance. Across the cohort, median stone burden on the last positive scan prior to clinical events or the final surveillance visit increased to 57.0 mm2 (IQR: 38.0–104.0 mm2). Conclusions: In this selected single-center cohort of 29 patients with lower-pole residual fragments > 4.0 mm at 3-month NCCT after PCNL, 15 patients underwent secondary intervention and four experienced documented spontaneous passage during variable follow-up. Because interval monitoring and intervention criteria were individualized, these findings are descriptive and do not establish the optimal timing of treatment. Larger prospective studies with standardized imaging protocols are required to better define management strategies.