Overview
This lecture explains how to identify different liver segments on CT scans using anatomical landmarks, including the hepatic and portal veins, and discusses the clinical significance of liver segmentation.
Liver Segmentation Principles
- The liver is divided into segments based on vascular (venous and portal) supply, not just morphology.
- Hepatic veins (left, middle, right) separate the liver into four main sections: left lateral, left medial, right medial (anterior), and right lateral (posterior).
- The portal vein divides these sections into superior and inferior segments.
- Each liver segment is a functional unit with independent blood, bile, and lymphatic drainage.
Segment Numbering and Anatomy
- Segment numbering follows a clockwise pattern from the left superior lateral section (segment 2) when viewed from the front.
- Segment 1 (caudate lobe) is functionally and anatomically separate, with its own venous drainage.
- Segment 4 is divided into 4a (above, superior) and 4b (below, inferior).
Identifying Segments on CT Scan
- The inferior vena cava (IVC) lies posterior to the liver and receives hepatic veins.
- Hepatic veins are used as landmarks to draw boundaries for the main liver sections.
- The portal vein, anterior to the IVC, creates a horizontal divide between superior and inferior segments.
- Segment 1 (caudate lobe) is medial to the IVC and should be checked for enlargement in cirrhosis.
- Segment 2 is left lateral and superior to the left hepatic vein; segment 3 is below segment 2.
- Segment 4a and 4b lie between left and middle hepatic veins.
- Segments 5, 6, 7, and 8 are on the right; 5 (anterior/inferior), 6 (posterior/inferior), 7 (posterior/superior), 8 (anterior/superior).
Clinical Importance
- Segmental liver anatomy helps guide surgical resections and assess liver function.
- Each segment can function independently if isolated or removed.
Key Terms & Definitions
- Hepatic veins — Vessels (left, middle, right) draining blood from the liver into the IVC.
- Portal vein — Vessel formed from the splenic and superior mesenteric veins, supplying blood to the liver.
- Caudate lobe (Segment 1) — Separate liver segment with its own venous drainage.
- IVC (Inferior vena cava) — Large vein returning blood from the body to the heart, located posterior to the liver.
Action Items / Next Steps
- Review color-coded liver segment diagrams.
- Practice identifying liver segments on multiple CT scans for repetition and mastery.