Significance of computed tomography for shock-wave therapy of radiolucent gallbladder stones.

One hundred eleven symptomatic patients (91 women, 20 men) with solitary "radiolucent" stones (proved by a plain radiograph) underwent examination with computed tomography for stone analysis before extracorporeal shock-wave lithotripsy with a second-generation piezoelectric lithoptripter. The aim of the study was to assess the importance of computed tomography as a diagnostic pretreatment procedure compared with the plain abdominal radiograph: computed tomography density values greater than 50 Hounsfield units (HU) were found in 64 of 111 patients with radiolucent stones (58%). Of these 64, 50 patients even had values greater than 90 HU (50/111;45%). The majority of the stones with density values greater than 50 HU had a hyperdense rim (43 of 64) with a mean maximum attenuation of 134 +/- 68 HU. A significantly higher degree of stone disintegration was achieved with stones of group A (less than or equal to 50 HU) than with those in group B (greater than 50 HU and less than or equal to 90 HU) and group C (greater than 90 HU) with respect to the mean maximum fragment size after the first (P less than 0.001) and last (P less than 0.01) lithotripsy and with respect to the total number of shock waves applied (P less than 0.001) and the number of treatments (P less than 0.001). No difference was observed between groups B and C. After all follow-up periods, the rate of complete stone disappearance was higher in group A than in group B (NS for 1, 2, and 4 months of follow-up; P less than 0.01 for month 8; P less than 0.05 for month 12) and group C (P less than 0.05 for 1, 2, and 4 months of follow-up; P less than 0.001 for months 8 and 12). The authors conclude that computed tomographic analysis of gallstones before lithotripsy is more sensitive in detecting nonradiolucent stones than in the plain radiograph. Computed tomographic stone analysis seems to provide a better selection of patients suitable for biliary lithotripsy and could become a standard diagnostic pretreatment procedure to improve stone disintegration and complete stone disappearance after shock-wave lithotripsy and adjuvant chemolitholysis.