Residual fragments after percutaneous nephrolithotomy: is it mandatory to treat them all?

To investigate complication rates, stone growth and passage according to residual fragments (RFs) size in a cohort of patients treated with miniPCNL (mPCNL). We retrospectively analysed data from 572 patients who underwent mPCNL between 01/2018 and 11/2023. We identified 105 (19.4%) patients with RFs and at least 1-year follow up. Demographics and RFs passage, regrowth and complications were recorded by chart review and phone interviews. RFs were stratified into ≤ 5 mm; 6-9 mm and ≥ 10 mm groups. Descriptive statistics and logistic regression models were applied to test the association between RFs size and stone related events. Median number and diameter of RFs were 2 (1-3) and 8 (5-10) mm, respectively. RFs of ≤ 5 mm (Group 1), 6-9 mm (Group 2) and ≥ 10 mm (Group 3) were detected in 27 (25.7%), 47 (44.7%) and 31 (29.6%) cases, respectively, after mPCNL. Overall, 23 (21.9%), 20 (19%) and 9 (8.5%) patients had a stone related event [emergency room (ER) admission], stone growth and passage during follow up, respectively. Renal colic requiring ER admission were more frequent in Group 2 compared to the ≥ 10 and ≤ 5 mm one (36.1% vs. 9.6% vs. 11.1%, p = 0.01). Conversely, Group 1 showed higher rates of stone growth compared to the other groups (37.0% vs. 17.0% vs. 6.4%, p = 0.02). No difference in the rate of UTIs and stone passage was reported according to RFs size. Multivariable logistic regression analysis showed that RFs of 6-9 mm had higher risk of stone related events (OR 5.5, p = 0.04) compared to the other groups, even after adjusting for patients' BMI. Conversely, patients with RFs ≤ 5 mm had higher risk of stone growth (OR 9.6, p = 0.04), compared to the other RFs groups, after adjusting for patients' BMI. RFs after mPCNL have different impact on patient's clinical course, according to their size. Large RFs are less likely to grow or cause stone-related events. Conversely, RFs of medium size (6-9 mm) are associated with higher risk of ER admission and should be promptly treated. Small RFs can increase in size, but conservative management or delayed surgery may be considered, as they typically remain asymptomatic during follow-up.