The portal vein divides into right and left branches at the porta hepatis. Which anatomical structure marks the boundary between the right and left portal vein territories?

Explanation

## Main Portal Scissura (Cantlie's Line) — Functional Boundary **Key Point:** The main portal scissura (also called Cantlie's line) is an imaginary plane that marks the boundary between the right and left portal vein territories and defines the true anatomical midline of the liver. ### Definition and Course **High-Yield:** The main portal scissura: - Runs from the **gallbladder fossa anteriorly** to the **inferior vena cava posteriorly** - Divides the liver into true right and left halves based on **portal venous supply** - Is NOT the same as the morphological division (which follows the falciform ligament) - Separates segments IV and V (left and right, respectively) ### Anatomical Landmarks | Feature | Location | Significance | | --- | --- | --- | | **Anterior boundary** | Gallbladder fossa | Visible on visceral surface | | **Posterior boundary** | Inferior vena cava | Marks hepatic hilum | | **Functional significance** | Portal venous territory boundary | Defines true anatomical midline | | **Embryological basis** | Plane of hepatic vein confluence | Right and left hepatic veins drain on either side | ### Clinical Significance **Clinical Pearl:** Cantlie's line is crucial for: - **Hepatic resection planning:** Surgeons use this line to determine which segments to remove while preserving vascular inflow - **Hemi-hepatectomy:** Right hemi-hepatectomy removes segments V, VI, VII, VIII; left hemi-hepatectomy removes segments II, III, IV - **Living donor transplantation:** The graft division follows Cantlie's line to ensure adequate portal venous supply ### Distinction from Other Boundaries **Warning:** Do NOT confuse these: - **Falciform ligament:** Marks the morphological (anatomical) division between right and left lobes — NOT the functional portal venous boundary - **Gallbladder fossa:** Marks the anterior end of Cantlie's line but is not the entire boundary itself - **Hepatic hilum:** The porta hepatis is where vessels enter; it is not the scissura itself **Mnemonic:** **CANTLIE = Correct Anatomical Nidus for True Liver Ischemic Evaluation** — the plane that surgeons use to predict which segments will be ischemic if portal branches are ligated. [cite:Standring Anatomy 42e Ch 62]