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Common bile duct

The common bile duct (CBD) is the distal continuation of the extrahepatic biliary tree, formed by the union of the common hepatic duct and the cystic duct. It descends through the hepatoduodenal ligament, passes posterior to the duodenum and pancreas, and terminates in the second part of the duodenum at the major duodenal papilla (ampulla of Vater).

It plays a vital role in the delivery of bile from the liver and gallbladder into the duodenum, aiding digestion and fat absorption. Because of its location, it is a frequent site of obstruction, stones, and malignancy.

Synonyms

  • CBD

  • Ductus choledochus

  • Extrahepatic bile duct (distal portion)

Origin, Course, and Termination

  • Origin: Formed by the junction of the common hepatic duct and cystic duct

  • Course: Runs inferiorly within the hepatoduodenal ligament, anterior to the portal vein and right of the hepatic artery proper → passes posterior to the first part of the duodenum → traverses within the pancreatic head or groove → enters the second part of the duodenum

  • Termination: Opens at the major duodenal papilla (ampulla of Vater), usually joining the pancreatic duct (duct of Wirsung)

Relations

  • Anteriorly: First part of the duodenum, pancreas

  • Posteriorly: Portal vein, inferior vena cava

  • Medially: Pancreatic head and pancreatic duct

  • Laterally: Hepatic artery proper, duodenal wall

Function

  • Transports bile from liver and gallbladder to duodenum

  • Facilitates digestion and emulsification of fats

  • Regulated by the sphincter of Oddi at its distal end

  • Plays a role in biliary-pancreatic ductal convergence at the hepatopancreatic ampulla

Clinical Significance

  • Choledocholithiasis: Stones obstructing CBD → jaundice, cholangitis, pancreatitis

  • Strictures: Benign (post-surgical, inflammatory) or malignant (cholangiocarcinoma, pancreatic carcinoma)

  • Obstructive jaundice: Classic clinical presentation of CBD obstruction

  • Iatrogenic injury: During cholecystectomy, CBD injury is a serious complication

  • Imaging role: Evaluated by ultrasound, CT, MRCP, and ERCP

MRI Appearance

T1-weighted images:

  • Lumen: low signal (bile fluid)

  • Wall: thin, may enhance post-contrast

  • Pathology: stones appear as low signal filling defects

T2-weighted images:

  • Lumen: very bright (fluid signal)

  • Wall: thin hypointense rim

  • Dilatation: appears as tubular bright structure

STIR (Short Tau Inversion Recovery):

  • Lumen: bright hyperintense fluid

  • Wall: dark thin lining

  • Pathology: inflammation or edema → hyperintense periductal tissues

T1 Fat-Sat Post-Contrast:

  • Wall: minimal enhancement in normal state

  • Pathology: mural thickening, irregular enhancement in cholangitis or malignancy

  • Abscess or tumor: heterogeneous or rim enhancement

T2 Fat-Saturated HASTE (single-shot):

  • CBD lumen: uniformly bright

  • Stones: dark signal voids within bright lumen

  • Useful for rapid screening of obstruction

T2 TSE Fat-Saturated 3D (MRCP sequence):

  • CBD visualized as continuous bright tubular structure

  • Allows 3D reconstruction of entire biliary tree

  • Excellent for strictures, stones, or congenital anomalies

Thick-slab T2 Fat-Saturated HASTE:

  • Projectional bright image of CBD and biliary tree in a single thick slice

  • Stones or filling defects: appear dark against bright lumen

  • Excellent for quick overview in MRCP

CT Appearance

Non-Contrast CT:

  • CBD poorly seen unless dilated

  • Dilated CBD appears as hypoattenuating tubular structure anterior to portal vein

  • Stones: hyperdense if calcified, otherwise often isoattenuating and missed

Post-Contrast CT:

  • CBD lumen: low attenuation fluid

  • Wall: thin, minimally enhancing

  • Pathology: strictures, cholangiocarcinoma, or pancreatic head tumor show wall thickening, irregular enhancement, and abrupt narrowing

  • Dilatation upstream from obstruction is well demonstrated

MRI images

CT images

Common bile duct ct axial anatomy image-img-00000-00000

CT images

Common bile duct ct coronal anatomy image-img-00000-00000