Predicting gallstone composition with CT: in vivo and in vitro analysis.

Chemical composition of gallstones is of major importance in selecting patients for nonsurgical therapy. In a combined in vivo and in vitro study of predictive potential, 50 patients undergoing cholecystectomy were evaluated with computed tomography (CT) and either plain abdominal radiography or oral cholecystography (OCG). The largest stone surgically removed from each patient was subjected to in vitro CT and chemical analysis. The authors found an inverse relationship between CT attenuation numbers and cholesterol content and a good positive correlation between CT attenuation numbers and calcium content. In vivo CT analysis improved sensitivity, specificity, accuracy, and positive and negative predictive values compared to plain abdominal radiography and OCG in detection of cholesterol stones. Using their prediction rule (a CT number smaller than 140 HU indicates a pure cholesterol gallstone), the authors correctly classified gallstones in 17 (84%) of another 20 patients. In vivo CT analysis can enable reliable prediction of gallstone composition and should play an important role in the selection of patients for nonsurgical treatment.