The reliability and clinical limitations of sonographic scanning of the biliary ducts.

Sonographic scanning of the biliary ducts has been successfully used as a screening test to distinguish between patients with surgical and medical jaundice, with an accuracy of 90%. However, there is no consensus in the literature on what numerically defines a dilated biliary duct. To clarify this problem a prospective study of 102 consecutive patients was initiated to determine the sonographic size range of bile ducts in patients with and without extrahepatic ductal obstruction. The ultrasonic measurements were compared with direct measurements of the common bile duct, at surgery. The extrahepatic ductal system was visualized sonographically in 62% of the patients, while the intrahepatic ducts were found in 81% of the population. Direct measurements at operation agreed with the ultrasonic measurements in 84% of the patients. Analysis of the size range of the biliary ducts in patients with and without extrahepatic obstruction, by chi square analysis and the Student's t-test, allowed the following guidelines to be established. Extrahepatic bile duct obstruction was present if the extrahepatic bile ducts was 1 cm or wider (p less than 0.001) or if the intrahepatic bile duct was in excess of 0.5 cm (p less than 0.001). Similarly if the extrahepatic bile duct measured less than 0.8 cm sonographically, and the intrahepatic bile duct was 0.4 cm or less than bile duct, obstruction was not present (p less than 0.001).