Regarding the anatomical segments of the liver and their blood supply, all of the following statements are correct EXCEPT:

Explanation

## Hepatic Segmentation and Vascular Supply ### Couinaud Classification Overview The liver is divided into 8 functional segments based on the hepatic vascular inflow (portal vein and hepatic artery branches) and outflow (hepatic veins). Understanding segment-specific vascular anatomy is critical for surgical planning and imaging interpretation. ### Analysis of Each Statement **Statement 1 (Correct): Segment I (Caudate Lobe)** - The caudate lobe has a unique independent blood supply from small branches of both the right and left hepatic arteries and portal vein branches - Critically, it drains directly into the IVC via small hepatic veins that bypass the main hepatic venous system - This anatomical independence makes it spared in Budd-Chiari syndrome (thrombosis of main hepatic veins) **Statement 2 (Correct): Segments II and III** - Left lateral segments (II = left posterolateral, III = left anterolateral) - Supplied by left branch of hepatic artery and left branch of portal vein - Drain via left hepatic vein **Statement 3 (Correct): Segment IV (Quadrate Lobe)** - Left medial segment, located between the falciform ligament and middle hepatic vein - Receives blood from BOTH right and left branches of portal vein and hepatic artery - Drains via middle hepatic vein (shared with right anterior segments) **Statement 4 (INCORRECT): Right Lobe Drainage** - Segments V, VI, VII, VIII are in the right lobe - However, they do NOT all drain via the right hepatic vein alone - Segments V and VIII (anterior) drain via the **middle hepatic vein** - Segments VI and VII (posterior) drain via the **right hepatic vein** - This is a critical distinction for hepatic resection planning ### Key Point: **The middle hepatic vein drains segments IV, V, and VIII (not just right lobe segments).** Segment IV is part of the left lobe but drains via the middle hepatic vein, which it shares with right anterior segments. ### High-Yield: **Mnemonic for hepatic vein drainage:** - **Left hepatic vein:** Segments II, III - **Middle hepatic vein:** Segments IV, V, VIII (the "middle" segments) - **Right hepatic vein:** Segments VI, VII - **Segment I:** Direct to IVC (independent) ### Clinical Pearl: In living donor liver transplantation, the middle hepatic vein is often the most challenging to manage because it drains segments from both the right and left lobes, requiring careful surgical planning to avoid devascularization. [cite:Robbins 10e Ch 18]