Liver Segments (Couinaud Classification)
The liver is divided into eight functionally independent segments (I–VIII) based on the distribution of the portal vein, hepatic artery, and bile duct branches, as well as the hepatic veins. This classification is essential for surgical planning (e.g., liver resection).
Key Anatomical Landmarks
- Segment I (Caudate Lobe): Situated posteriorly, it has an independent blood supply and drains directly into the IVC.
- The Remaining Segments (II–VIII) are numbered in a clockwise direction, starting from the left lateral lobe.
- Dividing Lines:
- Main Lobar Fissure (Cantlie’s Line): Divides the liver into functional right and left lobes; it runs from the IVC to the gallbladder fossa.
- Hepatic Veins: The right, middle, and left hepatic veins divide the liver longitudinally into functional sectors.
Summary Table
| Segment(s) | Location |
|---|---|
| I | Caudate lobe. |
| II, III, IV | Functional Left Lobe. |
| V, VI, VII, VIII | Functional Right Lobe. |
High-Yield Exam Pearl:
The middle hepatic vein lies exactly in the main lobar fissure (Cantlie’s line). Surgical removal of the right or left functional lobe requires careful identification of this vein to prevent injury and manage bleeding.