Left Hepatic Duct

The left hepatic duct is one of the two major intrahepatic bile ducts that drain bile from the liver and contribute to the formation of the common hepatic duct. It collects bile from the left functional lobe of the liver, including segments II, III, and IV, and merges with the right hepatic duct at the liver hilum. Although typically slightly longer and more horizontal than its right-sided counterpart, the left hepatic duct holds equal clinical importance, especially in liver transplant surgery, segmental liver resections, and hilar cholangiocarcinoma. Anatomical variations of the left duct are also significant, as misidentification during procedures can lead to serious complications.

Structure

The left hepatic duct begins as a union of multiple intrahepatic ducts within the left lobe of the liver. These smaller ducts arise from distinct functional segments and converge near the left portal vein to form the left hepatic duct.

Segmental Contributions

Liver Segment	Duct Contribution
Segment II	Drained by the left lateral superior duct
Segment III	Drained by the left lateral inferior duct
Segment IV (a and b)	Drained by separate medial segmental ducts that often join near the umbilical portion of the left portal vein

These segmental ducts form a confluence near the transverse fissure of the liver and proceed medially to form the left hepatic duct, which then joins the right hepatic duct to become the common hepatic duct.

Length and Diameter

• Length: 2–3 cm, though variable depending on exact confluence point
• Diameter: Approximately 4–6 mm

Anatomical Variations

• Normal: Left hepatic duct joins the right duct to form the common hepatic duct
• Trifurcation: Segmental ducts from the left and right lobes form a three-way confluence with no dominant left duct
• Early confluence: Segment II and III ducts join very early and separately connect to the common hepatic duct

These variations have direct implications in surgical planning and intervention, especially in transplant and biliary reconstructions.

Location

The left hepatic duct lies in the liver’s transverse fissure (porta hepatis), slightly anterior and superior to the left portal vein. It follows a more horizontal and anterior course compared to the right hepatic duct and is often more superficial in radiologic imaging.

Topographic Relations

• Posterior: Left branch of the portal vein
• Inferior: Left hepatic artery
• Superior: Segment IV of the liver
• Anterior: Peritoneal surface of the left lobe

The duct runs along the umbilical portion of the portal vein, and in its medial course, it merges with the right hepatic duct anterior to the portal vein bifurcation. This region is also the typical site of involvement in hilar cholangiocarcinomas (Klatskin tumors).

Function

The left hepatic duct plays a fundamental role in collecting and channeling bile produced in the left lobe of the liver. It represents one half of the liver’s drainage system and integrates seamlessly into the larger biliary tree.

Bile Transport

• Upstream: Receives bile from segmental ducts of segments II–IV
• Midstream: Conducts bile toward the right hepatic duct for merger
• Downstream: Contributes to the formation of the common hepatic duct

Bile flow through the left hepatic duct is passive, driven by secretion pressure and ductal peristalsis. The flow can be redirected in pathologic conditions, such as obstruction or altered biliary tract anatomy following surgery.

Clinical Relevance

The left hepatic duct is clinically important in multiple contexts, including diagnostic imaging, surgical resections, transplantation, and interventional radiology.

1. Liver Transplantation

• Living donor transplants: Left lobe grafts require precise division and reconstruction of the left hepatic duct
• Biliary anastomosis: Duct-to-duct or Roux-en-Y hepaticojejunostomy techniques rely on accurate localization of the left duct

2. Segmental Resections

• Left hepatectomy: Removal of segments II–IV requires ligation or reconstruction of the left hepatic duct
• Segmental IVb resection: Must preserve lateral ducts (II and III) if only segment IV is targeted

3. Imaging Interpretation

On MRCP, CT cholangiography, or intraoperative cholangiograms:

• Normal duct: Seen as a tubular structure joining with the right duct
• Dilated left hepatic duct: Suggests distal obstruction, such as a stone or tumor
• High bifurcation: May be mistaken for a segmental duct if not carefully traced

4. Biliary Obstruction and Cholangiocarcinoma

Hilar cholangiocarcinoma (Klatskin tumor) frequently involves the confluence of the left and right hepatic ducts. When the tumor spreads proximally into the left duct:

• Surgical resectability decreases
• Bilateral drainage may be needed for palliation

5. Iatrogenic Injuries

• Left duct injuries may occur during left liver resections or hilar dissections
• Inadvertent ligation can cause segmental cholestasis and bile leaks
• Endoscopic and percutaneous interventions must recognize ductal anatomy to avoid misplacement of stents or drains