RESIDUAL STONES AFTER PERCUTANEOUS NEPHROLITHOTOMY - SENSITIVITIES OFDIFFERENT IMAGING METHODS IN RENAL STONE DETECTION

Kidneys of 35 renal stone patients treated with percutaneous nephrolit hotomy (PNL) were examined at 12-36 months (mean 23 months) after the procedure by plain radiography (PR), conventional linear tomography (L T), computed tomography (CT), and ultrasonography (US) to find out the long-term stone-free rate as well as the accuracy of these imaging me thods to detect residual or recurrent renal stones. The present series included 36 kidneys with a 56% postoperative stone-free status examin ed by plain radiography and a 58% one examined by linear tomography at 12-36 months. CT showed 47% and US 72% of the kidneys to be stone-fre e, respectively. The sensitivity of CT was superior to plain radiograp hy (P < 0.05), linear tomography (P < 0.05) or US (P < 0.001) in the d etection of residual or recurrent stones after percutaneous nephrolith otomy analyzed statistically by McNemar's test. In the same group of 3 5 patients, which consisted of the above 36 postoperative kidneys toge ther with 19 contralateral kidneys, a total of 55 kidneys were evaluat ed by the above methods, revealing 56 stones in 31 kidneys. Of these s tones 95% were detected by CT, 70% by plain radiography, 68% by linear tomography, and 32% by renal US. Of the 55 kidneys, 14 contained 20 s tone fragments smaller than 3 mm, and 26 kidneys carried 43 concrement s smaller than 6 mm. The sensitivities of the four imaging methods in the detection of these small fragments were as follows: plain radiogra phy 60% and 60%, linear tomography 55% and 58%, CT 95% and 93%, and US 15% and 26%. The intermethod reliability, using CT as reference in th e stone detection, was measured by the percentage of agreement between the four imaging methods in the 55 kidneys. Thus, when other methods were compared to CT, the results were as follows: PR, LT, and US vs CT 75, 74, and 51%, respectively. The present results show that CT is th e most accurate imaging method in the evaluation of the stone-free sta tus after renal stone procedures and should therefore be used to disco ver the real stone burden of the kidney.