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Bile duct serving liver segment III

The bile duct of liver segment III is a segmental intrahepatic bile duct draining bile from Couinaud segment III, which is the left lateral inferior segment of the liver. It represents one of the secondary biliary branches of the left hepatic duct.

This duct is clinically important because segment III is frequently targeted in percutaneous biliary interventions, segmental resections, and living donor left lateral liver transplantation (segments II and III). Precise understanding of its anatomy and imaging is essential for hepatobiliary surgeons and radiologists.

Synonyms

  • Segment III bile duct

  • Left lateral inferior segment bile duct

  • Intrahepatic bile duct of Couinaud segment III

Origin, Course, and Drainage

  • Origin: Arises from the biliary canaliculi of hepatocytes within segment III of the liver (left lateral inferior segment)

  • Course: Small intrahepatic radicles coalesce into a segmental duct running medially within the parenchyma of segment III

  • Drainage: Joins with the segment II duct to form the left lateral sectoral duct, which then drains into the left hepatic duct

Relations

  • Anteriorly: Left lobe hepatic parenchyma and visceral surface of liver

  • Posteriorly: Branches of the left portal vein and left hepatic artery

  • Medially: Converges toward the umbilical portion of the left portal vein

  • Inferiorly: Lies close to the visceral surface, related to stomach and left hepatic flexure (through liver surface)

Function

  • Drains bile from hepatocytes of segment III into the left biliary system

  • Contributes to bile transport for digestion and fat absorption

  • Serves as a critical anatomical landmark in left lateral segmentectomy and donor hepatectomy

Clinical Significance

  • Anatomic variants: Segment III duct may join directly with segment IV duct or have independent drainage, relevant in surgery and transplantation

  • Obstruction: Stones, strictures, or cholangiocarcinoma may cause localized dilation of the segment III duct

  • Interventions: Percutaneous drainage often targets segment III duct due to its superficial location

  • Transplantation: Segment II and III ducts must be identified and preserved in pediatric and living donor left lateral grafts

MRI Appearance

T1-weighted images:

  • Lumen: dark (low signal, fluid-filled)

  • Wall: very thin, usually not seen unless thickened or enhanced in pathology

T2-weighted images:

  • Lumen: bright (high signal, fluid)

  • Wall: hypointense rim, usually indistinct

STIR (Short Tau Inversion Recovery):

  • Fluid within duct: bright hyperintense

  • Fat suppressed, improving contrast with hepatic parenchyma

T1 Fat-Sat Post-Contrast:

  • Normal duct wall: minimal to no enhancement

  • Pathology (inflammation, cholangitis, tumor): irregular wall thickening and enhancement

T2 Fat-Saturated HASTE:

  • Segment III duct appears as a bright tubular structure

  • Excellent for quick visualization of dilated ducts or obstruction

T2 TSE Fat-Saturated 3D (MRCP):

  • Duct shows high-signal tubular branching pattern within segment III

  • Allows 3D reconstruction of intrahepatic biliary tree

  • Demonstrates variant anatomy or strictures

Thick-slab T2 Fat-Saturated HASTE:

  • Projects duct as bright linear/branching structure in a single image

  • Stones or filling defects appear as dark voids within bright bile

CT Appearance

Non-Contrast CT:

  • Normal nondilated ducts usually not visible

  • If dilated: appear as low-attenuation tubular channels within hepatic parenchyma

Post-Contrast CT:

  • Duct walls enhance faintly if inflamed or pathologic

  • Dilated ducts: visible as branching hypoattenuating structures radiating to segment III

  • Stones: hyperdense if calcified, otherwise isoattenuating to bile

MRI image

Bile duct serving liver segment III MRI axial anatomy image-img-00000-00000