Normal Diameters of the Hepatobiliary Tree

Normal Measurements of Bile Ducts

The common bile duct should be measured in the transverse plane, using the intraluminal diameter for accurate assessment 1
The normal upper limit of CBD diameter has traditionally been described as less than 6mm in adults 1
The common hepatic duct should normally measure less than 4mm in diameter 1
In patients with primary sclerosing cholangitis, a dominant stricture is defined as a stenosis with a diameter of 1.5mm or less in the common bile duct or 1.0mm or less in a hepatic duct within 2cm of the main hepatic confluence 2

The normal CBD diameter may increase by approximately 1mm for every decade of age 1
In elderly patients, CBD diameters up to 8-10mm can be considered normal in the absence of other pathological findings 1
Post-cholecystectomy patients may have CBD diameters up to 10mm without necessarily indicating pathology 1

An increased diameter of the common bile duct alone is not sufficient to identify patients with common bile duct stones and further diagnostic tests are needed 3, 1
A CBD diameter larger than 10mm is associated with a 39% incidence of common bile duct stones, while a diameter smaller than 9.9mm is associated with CBDS in only 14% of cases 3, 4
Direct visualization of a stone in the common bile duct on ultrasound is a much stronger predictor of choledocholithiasis than bile duct diameter alone 5, 4

The common bile duct is most accurately measured when imaged in a transverse plane on ultrasound 1
Ultrasound demonstrates a sensitivity of 73% and specificity of 91% for detecting common bile duct stones 5, 4

For suspected common bile duct stones with negative ultrasound findings but high clinical suspicion, additional imaging such as MRCP, EUS, or ERCP may be warranted 5
Relying solely on sonographic Murphy sign for the diagnosis of acute cholecystitis should be avoided due to its relatively low specificity 1