Common bile duct in children: sonographic dimensions.

PURPOSE: To determine the normal caliber and rate of growth of the extrahepatic biliary ducts in the pediatric population. MATERIALS AND METHODS: The diameter of the common bile duct was measured with sonography in 173 children aged 1 day to 13 years (mean, 6.0 years; median, 5.0 years) who were examined for reasons other than hepatic or biliary tract disease. Results were subjected to regression analysis and compared with similar measurements of the extrahepatic portal vein and hepatic artery. The size of the gallbladder was subjectively estimated as distended, moderately full, and contracted. Differences in the diameter of the common bile duct in these three groups were evaluated with the Mann-Whitney U test. RESULTS: The average diameter of the common bile duct in this population was 1.27 mm +/- 0.67 (<3.3 mm in all patients and <1.2 mm in children aged 3 months or less). The slope of the curve describing the growth of the common bile duct was relatively flat, similar to that of the hepatic artery and half that of the portal vein. There was a significant difference in the diameter of the common bile duct between patients with distended gallbladders and those with contracted gallbladder (P = .02). CONCLUSION: The pediatric common bile duct is significantly smaller than adult norms; it is a distensible structure responsive to fluctuations in prandial bile flow.