Liver Segments (Couinaud)

segmenta hepatis

The Couinaud system divides the liver into eight functionally independent segments, each with its own branch of the portal vein, hepatic artery and bile duct. The three hepatic veins run between segments and separate them into sections. Segment I is the caudate lobe, segments II-IV make up the functional left liver and segments V-VIII the functional right liver.

Anatomical Data

Structure & Supply

Location	Throughout the liver, numbered clockwise from the caudate lobe when viewed from the front
Parts	Segment I (caudate lobe) Segments II and III (left lateral section) Segment IV (IVa and IVb, left medial section) Segments V and VIII (right anterior section) Segments VI and VII (right posterior section)
Nerve Supply	Hepatic plexus from the coeliac plexus (sympathetic); Vagus nerve (parasympathetic)
Blood Supply	Segmental branches of the right and left hepatic arteries
Venous drainage	Segmental branches of the hepatic portal vein Right, middle and left hepatic veins (between segments)
Lymphatic drainage	Hepatic nodes

Biomechanics

Function & Actions

Provides a functional map of the liver based on blood supply and bile drainage, guiding surgery and imaging reports.

Clinical Relevance

Clinical Notes

Because each segment has its own blood supply and bile drainage, surgeons can remove one or more segments while preserving the rest, which is the basis of modern liver surgery and split-liver transplantation. Lesions on imaging are described by segment number to plan treatment. The middle hepatic vein marks the Cantlie line between the right and left liver.

Pathology

Common Injuries & Conditions

Colorectal Liver Metastases

Spread of bowel cancer to the liver, often treated by resecting the affected segments when enough healthy liver remains.

Hepatocellular Carcinoma

Primary liver cancer that may be treated by anatomical segmental resection in patients with adequate liver function.

Explore

More in Abdomen

Browse all of Abdomen →