Detection of residual stones after percutaneous nephrolithotomy: role of nonenhanced spiral computerized tomography.

PURPOSE: We addressed the impact of stone density and size on the role of computerized tomography for diagnosing residual stones after percutaneous nephrolithotomy.
MATERIALS AND METHODS: We prospectively evaluated 100 renal units that underwent percutaneous nephrolithotomy. The study included 55 opaque and 45 lucent or faint stones. Patients were examined after the procedure by plain x-ray of the kidneys, ureters and bladder, linear tomography, ultrasound and spiral computerized tomography. Minute residual stones were defined as 1 or 2 caliceal stones less than 5 mm, as measured by computerized tomography.
RESULTS: Stone-free status was achieved in 38 renal units. Minute and significant residual stones were detected in 26 and 36 renal units, respectively. For faint and lucent stones sensitivity for overall stone detection was 100% for computerized tomography, 11.1% for plain x-ray, 22.2% for linear tomography and 22.2% for ultrasound (p <0.05). Sensitivity for detecting significant residual stones was 100% for computerized tomography, 20% for plain x-ray, 33.3% for linear tomography and 20% for ultrasound (p <0.05). For opaque stones sensitivity for overall stone detection was 100% for computerized tomography, 62.9% for plain x-ray, 74.3% linear tomography and 48.6% for ultrasound (p <0.05). Sensitivity for detecting significant residual stones was 100% for computerized tomography, 85.7% for plain x-ray (p not significant), 95.2% for linear tomography (p not significant) and 57.1% for ultrasound (p <0.05).
CONCLUSIONS: Computerized tomography provides the most sensitive tool for detecting residual stones after percutaneous nephrolithotomy. Nevertheless, it should not be routinely performed in patients with opaque stones because it yields no statistically valuable increase in the diagnosis of significant residual stones compared with that of plain x-ray and linear tomography.