Fate of residual stones after percutaneous nephrolithotomy: a critical analysis.

PURPOSE: To analyze the fate of residual stones after percutaneous nephrolithotomy (PCNL) and identify the factors that predict spontaneous passage.

PATIENTS AND METHODS: We retrospectively analyzed the records of 2469 patients who underwent PCNL at our center between January 2000 to January 2008.

RESULTS: Residual fragments (RF) were identified in 187 (7.57%) patients. The most common site of RF was lower calix (57.7%), and the mean size of RF was 38.6 +/- 52 mm(2). Eighty-four stones passed spontaneously at a mean follow-up of 24 months (range 1-100 mos). Of the stones that passed spontaneously, 65.47% did so in 3 months. RF <25 mm(2) and those situated in the renal pelvis had the best chance of clearance. Stepwise multiple regression analysis showed that a history of intervention (P < 0.006), metabolic abnormalities such as hypercalcuria (P < 0.001) and hyperuraecemia (P < 0.03), preoperative nephrostomy drainage (P < 0.05), presence of a Double-J stent, (P < 0.001), time of presentation of residue (P < 0.08), size of residue (P < 0.007), and surgeon experience (P < 0.001) were significant factors in predicting the fate of RF after PCNL.

CONCLUSIONS: The most common site of post-PCNL RF was the lower calix. Renal pelvic RF <25 mm(2) have the best chance of spontaneous passage. Approximately half the RF will pass spontaneously, and the majority will clear in 3 months. The size of the residual stone, history of intervention, renal failure, and metabolic hyperactivity are predictors of persistence of RF.