Radiological anatomy of the liver provides the structural foundation for accurate interpretation of cross-sectional imaging and image-guided interventions. Understanding the internal segmentation, vascular territories, and spatial relationships of liver segments enables radiologists and clinicians to localize lesions precisely and plan treatment.
This article outlines key morphological landmarks, segmental nomenclature, and practical imaging tips using a concise tabular summary, detailed sectional anatomy, and common clinical queries.
| Segment | Couinaud Number | Primary Blood Supply | Imaging Landmarks |
|---|---|---|---|
| Segment I | IV | Right and left portal branches | Posterior to portal confluence, between hepatic veins |
| Segment II | II | Left lateral sectional branch | Superior and lateral to left portal vein |
| Segment III | III | Left lateral sectional branch | Inferior and lateral to left portal vein |
| Segment IVa | IVa | Right and left portal branches | Anterior to middle hepatic vein |
| Segment IVb | IVb | Right and left portal branches | Posterior to middle hepatic vein |
| Segment V | V | Right anterior sectorial branch | Inferior to right hepatic vein |
| Segment VI | VI | Right posterior sectorial branch | Inferior to right hepatic vein, adjacent to IVC |
| Segment VII | VII | Right posterior sectorial branch | Superior to right hepatic vein |
| Segment VIII | VIII | Right anterior sectorial branch | Adjacent to right hepatic vein |
Couinaud Classification and Morphological Landmarks
Portal Vein Divisions and Hepatic Segments
The Couinaud classification links vascular anatomy to functional segments, using the portal vein bifurcation as the primary map. The right portal vein divides into anterior and posterior sectorial branches, while the left portal vein divides into medial and lateral branches. These divisions define the arterial and biliary territories that run within each segment, enabling precise radiological correlation.
Major Hepatic Vessels and Biliary Anatomy
The hepatic artery typically arises from the common hepatic artery, with segmental branches coursing alongside portal branches. The hepatic duct forms right and left main ducts that follow similar segmental planes. The middle hepatic vein drains segments IV and V, while the right hepatic vein courses between segments V and VI, and the left hepatic vein separates segments II and III from segment IV.
Portal System Anatomy and Segment Orientation
Portal Triads and Segmental Boundaries
Portal triads appear at the periphery of segments and contain portal vein, hepatic artery, and bile duct branches. Recognizing the spatial arrangement of these triads helps predict the course of vascular and biliary structures within each hepatic segment. Variations in branching patterns influence surgical resections and ablation strategies.
Relationship to the Inferior Vena Cava and Gallbladder Fossa
The inferior vena cava lies posterior to segments VI and VII, forming a key posterior boundary in axial imaging. The gallbladder fossa overlies the intersection of segments IVb and V, serving as an important surface landmark correlating with deep liver anatomy in cross-sectional images.
Hepatic Vein Anatomy and Segmental Orientation
Main Trunks and Their Spatial Relationships
The right hepatic vein typically runs along the plane between segments VI and VII, while the middle hepatic vein courses between segments IV and V. The left hepatic vein delineates the boundary between segments II and III and often marks the division between lateral and medial sections of the left lobe.
Imaging Planes and Artifact Considerations
Oblique coronal reconstructions aligned with hepatic vein courses improve visualization of segmental borders. Flow artifacts near large veins can mimic pathology, whereas contrast enhancement patterns help define segmental perfusion during the arterial and portal venous phases.
Clinical Applications and Imaging Modalities
Cross-Sectional Correlation and Resection Planning
Multidetector CT and MRI allow volumetric assessment of segmental anatomy, critical for surgical planning and tumor localization. Accurate labeling of segments on imaging facilitates communication among surgeons, oncologists, and interventional radiologists.
Interventional Radiology and Navigation
Knowledge of segmental vascular anatomy guides percutaneous ablations and targeted therapies, minimizing complications such as biliary injury or tumor seeding along needle tracks. Real-time imaging combined Couinaud-based mapping enhances procedural accuracy.
Key Takeaways for Radiological Anatomy of the Liver
- Master the Couinahd nomenclature and its correlation with portal vascular anatomy.
- Use hepatic vein orientation as a consistent reference for segmental localization.
- Apply segmental knowledge to optimize interpretation of cross-sectional imaging.
- Integrate vascular and biliary landmarks for precise intervention planning.
- Recognize normal variants to avoid mislabeling and ensure accurate reporting.
FAQ
Reader questions
How do I consistently identify segment I on contrast-enhanced CT or MRI?
Segment I is located posterior to the portal confluence and between the hepatic veins, often requiring multiplanar reformations for confident recognition.
What vascular landmarks distinguish segment II from segment III?
Segment II lies superior and lateral to the left portal vein, whereas segment III is inferior and lateral to the same vein, with the left hepatic vein forming their medial separation.
In axial images, how can I differentiate the anterior sector from the posterior sector on the right side?
The right hepatic vein separates the anterior sector (segments V and VIII) from the posterior sector (segments VI and VII), with the portal vein bifurcation providing additional orientation cues.
Why is the middle hepatic vein important when planning liver surgery or ablation?
The middle hepatic vein helps define the boundary between functionally independent sectors, guiding resection lines and minimizing postoperative necrosis or biliary complications.