Demonstration of the normal extrahepatic biliary tract with computed tomography

When optimum computed tomography (CT) technique and computed angiotomography are utilized, the normal extrahepatic biliary ducts (equal to or less than 6 mm in diameter in patients without cholecystectomy) can be demonstrated in approximately 30% of clinical scans. Measurement of the anteroposterior diameter of the bile duct is more accurate than recording the transverse diameter, since the apparent transverse dimension will vary depending on the orientation of the duct in the plane of section. Phantom studies indicate that the absolute error of measurement is approximately one pixel diameter irrespective of duct diameter. The normal and abnormally dilated extrahepatic biliary ducts should be distinguished with CT.