Normal Diameters of the Hepatobiliary Tree
The normal common bile duct (CBD) diameter should be measured as less than 6mm in adults, with an acceptable upper limit of 8-10mm in elderly patients or those who have undergone cholecystectomy. 1
Normal Measurements of Bile Ducts
- The common bile duct should be measured in the transverse plane, using the intraluminal diameter (inside wall to inside wall) 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 (CHD) should normally measure less than 4mm in diameter 1
- In patients with primary sclerosing cholangitis (PSC), 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
Age-Related Changes in Bile Duct Diameter
- 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
Clinical Implications of Bile Duct Measurements
- An increased diameter of the common bile duct alone is not sufficient to identify patients with common bile duct stones (CBDS) and further diagnostic tests are needed 2, 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 2, 3
- Direct visualization of a stone in the common bile duct on ultrasound is a much stronger predictor of choledocholithiasis than bile duct diameter alone 4, 3
Measurement Technique
- The common bile duct is most accurately measured when imaged in a transverse plane on ultrasound 1
- The CBD can be located by identifying the portal vein, which, with the hepatic artery and CBD, comprise the porta hepatis 1
- In a transverse view of the porta hepatis, the CBD and hepatic artery are typically seen anterior to the portal vein 1
- Ultrasound demonstrates a sensitivity of 73% (44-90%) and specificity of 91% (84-95%) for detecting common bile duct stones 4, 3
Special Considerations
- In patients with suspected acute cholecystitis, additional findings such as gallbladder wall thickening greater than 3mm, pericholecystic fluid, and sonographic Murphy sign should be documented 1
- 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 4
- Relying solely on sonographic Murphy sign for the diagnosis of acute cholecystitis should be avoided due to its relatively low specificity 1
- Misinterpreting increased common bile duct diameter as definitive evidence of choledocholithiasis, especially in elderly patients, is a common pitfall 1