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 > 50 Hounsfield units (HU) were found in 64 of 111 patients with radiolucent stones (58%). Of these 64, 50 patients even had values > 90 HU (50/111; 45%). The majority of the stones with density values > 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 (≤ 50 HU) than with those in group B (> 50 HU and ≤ 90 HU) and group C (> 90 HU) with respect to the mean maximum fragment size after the first (P < 0.001) and last (P < 0.01) lithotripsy and with respect to the total number of shock waves applied (P < 0.001) and the number of treatments (P < 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 < 0.01 for month 8; P < 0.05 for month 12) and group C (P < 0.05 for 1, 2, and 4 months of follow-up; P < 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.