Anatomy Tutorial: Identifying Liver Segments on a CT Scan

Introduction

• Focus on identifying liver segments on a CT scan
• Use a diagram and axial CT slices for demonstration
• Goal: Understand liver segmentation for functional and clinical applications

Liver Segmentation Overview

Anatomical Orientation

• Patient viewed front on:
  • Patient's left on left side
  • Patient's right on right side
• Inferior Vena Cava (IVC) posterior to liver
• Superiorly, IVC receives blood from:
  • Left Hepatic Vein
  • Middle Hepatic Vein
  • Right Hepatic Vein

Sections

• Hepatic veins divide liver into four sections:
  • Left Lateral Section
  • Left Medial Section
  • Right Medial Section
  • Right Lateral Section
• Alternatively called:
  • Right Anterior Section
  • Right Posterior Section
• Sections further divided into superior and inferior segments
  • Divided by portal veins (Right and Left)

Liver Segments Numbering

• Clockwise fashion starting from left superior lateral section
• Segment Numbers:
  • 2: Left Superior Lateral
  • 3: Inferior to Segment 2
  • 4A & 4B: Left Medial (4A above 4B)
  • 5: Right Anterior Inferior
  • 6: Right Posterior Inferior
  • 7: Right Posterior Superior
  • 8: Right Anterior Superior
  • 1: Caudate Lobe (Independent functional unit)

CT Scan Identification

General Steps

• Use portal venous phase CT scan
• Identify liver on right side of patient
• Scroll through axial slices
• Identify IVC and hepatic veins
  • Posterior liver structure
  • Verify with renal veins and abdominal aorta

Identifying Segments

1. Segment 1 (Caudate Lobe):
   • Medial to IVC
   • Independent functional unit
   • Important in cirrhosis diagnosis
2. Segment 2:
   • Left Lateral Superior
   • Above left hepatic vein
3. Segment 3:
   • Inferior to Segment 2
   • Left Lateral Inferior
4. Segment 4 (4A & 4B):
   • Left Medial
   • 4A: Above left portal vein
   • 4B: Below left portal vein
5. Segment 5:
   • Right Anterior Inferior
   • Inferior to right portal vein
6. Segment 6:
   • Right Posterior Inferior
   • Inferior to right portal vein
   • Sometimes extends as Riedel’s lobe
7. Segment 7:
   • Right Posterior Superior
   • Superior to right portal vein
8. Segment 8:
   • Right Anterior Superior
   • Above right portal vein

Conclusion

• Liver segments are independent functional units
• Important for surgical planning and clinical evaluation
• Practice through repetition and reviewing multiple scans
• Additional resources available via linked playlists

Additional Notes

• Anatomy learning through repetition
• Importance of understanding subtle anatomical variations
• Encouragement to suggest future anatomy topics for discussion

---

Remember: Practice identifying liver segments on various CT scans to reinforce learning and improve anatomical comprehension.