Natural History of Residual Fragments Following Percutaneous Nephrostolithotomy

Purpose: We reviewed the natural history of residual fragments after percutaneous nephrostolithotomy. Materials and Methods: From April 1999 to January 2007 a total of 728 patients underwent percutaneous nephrostolithotomy at our medical center including 527 with a minimum documented radiographic followup of 6 months. Of these patients 42 (8%) with residual fragments on postoperative computerized tomography were observed rather than subjected to second look flexible nephroscopy. Computerized tomography was reviewed to define location, size and number of residual fragments. The primary study end point was a stone related event defined as growth of a residual fragment, or need for emergency room visit, hospitalization or additional intervention attributable to the residual fragment. Univariate and multivariate analyses were performed to determine predictors of a stone related event. Results: The median residual fragment size was 2 mm (range, 1 to 12). There were 18 patients (43%) who experienced a stone related event at a median of 32 months after percutaneous nephrostolithotomy (range 4 to 95). On univariate analysis residual fragment location in the renal pelvis or ureter (p = 0.02), maximum residual fragment size larger than 2 mm (p = 0.03) and cumulative residual fragment size (p = 0.03) predicted a stone related event. On multivariate analysis only maximum residual fragment size larger than 2 mm (HR 3.9, p = 0.01) and location in the renal pelvis or ureter (HR 4.4, p = 0.01) independently predicted a stone event. Conclusions: The size and location of post-percutaneous nephrostolithotomy residual fragments correlate with stone related events. Larger fragments are more likely to require secondary surgical intervention. Second look flexible nephroscopy may be of benefit in patients with residual fragments larger than 2 mm or in those with fragments located in the renal pelvis or ureter.