Effectiveness of noncontrast computed tomography in evaluation of residual stones after percutaneous nephrolithotomy

PURPOSE: We prospectively compared the sensitivity of antegrade pyelography (AGP), plain film radiography (KUB film), and noncontrast thin-slice abdominal CT for detecting residual stones after percutaneous nephrolithotomy (PCNL). PATIENTS AND METHODS: We prospectively evaluated 50 patients (53 renal units) who underwent PCNL for radiopaque renal pelvic stones with noncontrast abdominal CT 1 month postoperatively. We compared the number and size of residual fragments, as determined by immediate postoperative AGP and 1-month KUB film and CT scan. RESULTS: Stone-free rates according to AGP, KUB film, and noncontrast CT were 73.6% (39/53), 62.3% (33/53), and 20.8% (11/53), respectively. However, if clinically insignificant residual fragments are included in the success rates, these rates increased to 84.9% (45/53), 83.0% (44/53), and 41.5% (22/53), respectively. Of the 22 patients in whom residual stones were detected by CT but not by KUB film, 10 (45.5%) had stones >4 mm in diameter on CT, with a mean size of 7.4 mm. The sensitivity for the detection of residual fragments was 47.6% for KUB films as judged by noncontrast CT. After CT, seven patients received extracorporeal shockwave lithotripsy for residual stones. CONCLUSIONS: Noncontrast thin-slice abdominal CT was the most accurate imaging method to determine the stone-free rate after PCNL. Noncontrast abdominal CT gives accurate information for selecting patients who may benefit from additional treatment and for planning follow-up.