Which hepatic segment is located at the junction of the right and left lobes and receives dual blood supply from both right and left portal vein branches?

Explanation

## Segment I (Caudate Lobe): Dual Portal Blood Supply **Key Point:** Segment I (Caudate lobe) is the hepatic segment uniquely located **between the right and left lobes**, posterior to the porta hepatis, and is the **only segment that consistently receives dual blood supply from both right and left portal vein branches** as well as both right and left hepatic arteries. ### Anatomical Position and Boundaries | Feature | Detail | |---|---| | **Anatomical name** | Caudate lobe | | **Location** | Posterior surface of liver, between right and left lobes, posterior to porta hepatis | | **Boundaries** | IVC (posterior), porta hepatis (anterior), ligamentum venosum (left), right lobe (right) | | **Portal supply** | Both right AND left portal vein branches (dual supply) | | **Arterial supply** | Both right AND left hepatic arteries | | **Venous drainage** | Directly into IVC via short hepatic veins (independent of main hepatic veins) | | **Biliary drainage** | Both right and left hepatic ducts | ### Why Segment I is Unique Segment I (Caudate lobe) is anatomically positioned at the **junction of the right and left lobes**, straddling the plane between them. This unique position explains its dual vascular supply: - **Portal venous supply:** Receives branches from **both** the right and left portal veins - **Hepatic arterial supply:** Receives branches from **both** the right and left hepatic arteries - **Venous drainage:** Drains **directly into the IVC** via multiple short hepatic veins, bypassing the three main hepatic veins — this is why the caudate lobe is **spared in Budd-Chiari syndrome** (hepatic vein occlusion) ### Why Segment IV (Quadrate Lobe) is Incorrect Segment IV (Quadrate lobe) is the **left medial segment** and, while it may occasionally receive variable contributions from both portal pedicles, it is **not consistently described as having dual supply from both right and left portal vein branches** as a defining anatomical feature. Its primary supply is from the left portal pedicle. The **caudate lobe (Segment I)** is the textbook example of consistent dual portal supply. **High-Yield (Robbins / Gray's Anatomy):** Segment I is the only Couinaud segment with: 1. Dual portal venous input (right + left) 2. Direct IVC drainage (independent hepatic veins) 3. Sparing in Budd-Chiari syndrome **Clinical Pearl:** Because the caudate lobe drains directly into the IVC and receives dual portal supply, it undergoes **compensatory hypertrophy** in Budd-Chiari syndrome when the main hepatic veins are occluded — a classic radiological finding on CT/MRI. **Mnemonic:** **"Caudate = Caught between both sides"** — Segment I is caught between the right and left lobes, receiving blood from both sides and draining independently into the IVC.