Liver Anatomy

July 2, 2024

Key Points for Lobes and Surfaces

1. Liver Lobes and Their Separation

• The liver has two main lobes: a large right lobe and a smaller left lobe.
  • The line of fusion is along the falciform ligament on the upper surface.
  • The ligamentum teres enters the umbilical fissure at the inferior extent of the falciform ligament.

2. Inferior Surface of the Right Lobe

• When the liver is flipped upward, the inferior surface shows the transverse hilar fissure as the posterior limit of the right lobe.
  • Quadrate lobe: Located anterior to the fissure.
    • Boundaries:
      • Left: Umbilical fissure.
      • Right: Gallbladder fossa.
  • Caudate lobe: Located posterior to the hilar transverse fissure, hugging the IVC and extending upward on its left side.

3. Posterior Aspect of the Liver

• IVC (Inferior Vena Cava):
  • Lies snugly in a deep groove within the bare area of the liver.
  • Hepatic veins open directly into the IVC.
  • Right suprarenal gland is adjacent to the IVC, with the adrenal vein draining into the right of the IVC.
  • Bare area: Directly contacts the diaphragm.
• Caudate lobe:
  • Slopes upward from the inferior to the posterior surface.
  • Demarcated on the left by a fissure containing the ligamentum venosum.
  • Located within the lesser sac of the peritoneum, attached by the gastrohepatic omentum.
• Left lobe:
  • Situated anteriorly in the supracolic compartment of the peritoneal cavity.
  • Posterior surface is narrow with a very fine bare area.
• Fibrous tissue layer (sometimes called the ligament of the vena cava):
  • Shields the IVC on the right side.
  • Extends from the posterior edge of the liver backward towards the lumbar vertebrae.
  • Fibrous tissue fans out posteriorly, especially in the upper part.
  • Prolongation of this fibrous layer joins with a less marked fibrous extension from the lateral edge of the caudate lobe.
  • Occasionally, liver tissue embraces the IVC completely, forming a tunnel of parenchyma.

4. Surgical Considerations

• Ligament of the Vena Cava:
  • Must be divided on the right for surgical exposure of the IVC and the right hepatic vein.
  • Must be divided on the left to allow mobilization of the caudate lobe.

5. Major Hepatic Veins

• LHV: Left hepatic vein.
• MHV: Middle hepatic vein.
• RHV: Right hepatic vein.

Key points on Hepatic Veins

• RHV (Right Hepatic Vein)
  • Largest vein.
  • Has a short extrahepatic course.
• LHV (Left Hepatic Vein) & MHV (Middle Hepatic Vein)
  • Form a common channel.
• Umbilical Vein
  • Runs beneath the falciform ligament.
  • Empties into the terminal portion of the LHV.
• Umbilical Ligament
  • Obliterated left umbilical vein.
• Right Inferior Accessory Hepatic Vein
  • Present in 15% of cases.
  • If very large, during LDLT (Living Donor Liver Transplant) with right lobe resection, reimplant the RIHV to the IVC.
• Caudate Lobe
  • Drains directly to the IVC.

FUNCTIONAL SURGICAL ANATOMY

Liver Anatomy and Portal Triads

Internal Architecture of the Liver

• Symmetric Pedicular Pattern:
  • Despite the liver's asymmetric external appearance, the internal distribution of the portal vein, hepatic artery, and bile ducts is highly symmetric.
  • Each liver segment (I to VIII) receives blood supply from a branch of the portal vein and hepatic artery and is drained by a tributary of the right or left main hepatic ducts.

Portal Sectors (Sections)

• Main Hepatic Veins:
  • The liver is divided into four sectors (now called sections in Brisbane terminology) by the three main hepatic veins.
  • These sectors are independent units supplied by their own portal pedicles.
  • Hepatic veins run between these sectors in the portal scissurae.
• Portal Scissurae:
  • The scissurae that contain portal pedicles are called hepatic scissurae.
  • The umbilical fissure corresponds to one such hepatic scissura.

Right and Left Hemilivers

• Cantlie's Line:
  • The liver is composed of two hemilivers—the right and left—separated by the main portal scissura, also known as Cantlie's line.
  • It's preferable to refer to these as right and left livers rather than lobes, as there is no visible demarcation that distinctly separates the two on the liver’s external surface.

Liver Anatomy: Sectoral and Sectional Classifications

1. Sectoral Anatomy (by Couinaud)

• Based on: Portal Vein.
• Terminology: Portal Sectors.
• Portal Scissurae:
  • Contain Hepatic Veins.
  • Divide the liver into Right and Left sectors.
  • Further divided into:
    • Anterior Sector (Paramedian)
    • Posterior Sector (Lateral)
• Portal Pedicles:
  • Each sector is supplied by its own portal pedicle.
  • Right Anterior Sector: Supplied by the Right Anterior Portal Pedicle.
  • Left Posterior (Lateral) Sector: Segment 2; the only sector with a single segment.
  • Left Anterior Sector: Segments 3 and 4.
• Umbilical Fissure:
  • Also called Hepatic Scissure.
  • Contains the Left Portal Pedicle.

2. Sectional Anatomy (Brisbane Terminology)

• Based on: Hepatic Artery and Bile Duct.
• Terminology: Sections.
• Left Lateral Section: Segments 2 and 3.
• Left Medial Section: Segment 4.

Glissonian Approach

• by Takasaki
• Glissons Sheath was discovered by Johannis Walaeus
• Hepatic Artery, PV and BD is enclosed in Glissoneal Sheath and ligated enmasse (conventional = individual ligation of HA, PV, BD)

Plate System

• Hilar Plate = above the Confluence located at base of Segment IVb = below it we have Left Portal Pedicle
• Cystic. Plate = Separates Gall Bladder from Liver
• Umbilical plate = above umbilical portion of portal vein

Hepp Couinad Approach

Hepp-Couinaud Approach

• A. Relationship Between Segment IV and Biliary Confluence
  • The hilar plate (arrow) is formed by the fusion of the connective tissue enclosing the biliary and vascular elements with the Glisson capsule.
• B. Exposure of Biliary Confluence and Left Hepatic Duct
  • Segment IV is lifted upward after incision of the Glisson capsule at its base.
  • Lowering of the hilar plate technique is used to expose a dilated bile duct above an iatrogenic stricture or hilar cholangiocarcinoma.
• C. Extensive Mobilization of Segment IV
  • Line of incision (left) allows for extensive mobilization of Segment IV.
  • Particularly valuable for high bile duct strictures and in cases of liver atrophy or hypertrophy.
  • The procedure involves:
    • Lifting Segment IV upward (A and B).
    • Opening the umbilical fissure.
    • Incising the deepest portion of the gallbladder fossa.
  • Right: Incision of the Glisson capsule to access the biliary system (arrow).

Biliary & Vascular Anatomy of Left Liver

• Upper most = Bile Duct

• Lower = Portal Vein

  

• Note the location of the segment Ill duct above the corresponding vein.

• The anterior branch of the segment IV duct is not represented.

Caudate Lobe Anatomy and Relations

• Main Bulk of the Caudate Lobe (Segment I; dark area):
  • Lies to the left of the IVC (Inferior Vena Cava).
  • Left and inferior margins are free in the lesser omental bursa.
• Gastrohepatic (Lesser) Omentum:
  • Separates the left portion of the caudate from segments II and III of the liver.
  • Passes between them to attach to the ligamentum venosum.
• Left Portion of the Caudate Lobe:
  • Inferiorly traverses to the right between the LPV (Left Portal Vein) and IVC as the caudate process.
  • Fuses with the right lobe of the liver.
• Note the Position of the MHV (Middle Hepatic Vein):

• Lobes of Caudate and its Relations:
  • Large Left:
    • Posterior: IVC.
    • Superior: MHV/LHV (Left Hepatic Vein).
    • Inferior: Left Portal Triad.
    • Anterior: Segment IV.
  • Small Right:
    • Posterior: Segment VII.

Venous Drainage

• Drains into the IVC via short hepatic veins.

Blood Supply

• Left Side: Supplied by MPV/LPV (Main Portal Vein/Left Portal Vein).
• Right Side: Supplied by the Right Posterior Portal Pedicle.

Biliary Drainage

• Both Right & Left Ducts contribute to biliary drainage.

Clinical Significance in Liver Failure/Cirrhosis

• Caudate Lobe Enlargement:
  • Occurs as it remains the only functioning lobe due to dual blood supply.
  • Results in fissural widening on CT
• Between the right portion and left portion of the caudate lobe is Segment IX.

Portal Vein

• Formation:
  • Formed behind the neck of the pancreas by the SMV (Superior Mesenteric Vein) and Splenic Vein.
• Division:
  • Divides into left and right branches (70% cases).
• Most Common Variant:
  • Trifurcation pattern.
• Second Most Common Variant:
  • Right Posterior originating as the first branch of the PV.
• Other Variants:
  • Pulmonary Vein may enter.
  • Absence of left portal vein.
  • Right Anterior arising from Left Portal Vein.
• Variant Anatomies in Liver Transplant which are doable ???:
  • Types 4b & 5 are significant in Hepatic Artery variations.

Hepatic Artery

• Mitchell Classification for Variations.
• Most Common Variation:
  • Replaced RHA (Right Hepatic Artery) in 10-15% of cases.
• Replaced/Accessory Arteries:
  • Right side: From SMA (Superior Mesenteric Artery).
  • Left side: From LGA (Left Gastric Artery).
• Most Common Location of Aberrant RHA:
  • Right posterolateral to the CBD (Common Bile Duct).
• CHA (Common Hepatic Artery) Pathway**:
  • CHA → GDA (Gastroduodenal Artery) → PHA (Proper Hepatic Artery) → RHA & LHA (Left Hepatic Artery, runs into Umbilical Fissure).

• Middle Hepatic Artery (supplying Segment IV):

  • Most commonly originates from the LHA.

  Hepatic Artery Overview

  • Function: Provides approximately 25% of hepatic blood flow and 30%-50% of its oxygenation.
  • Normal Distribution: The typical description of arterial supply occurs in only about 60% of individuals.

  Origin of Hepatic Artery

  • Celiac Trunk: Originates from the aorta below the diaphragmatic hiatus.
    • Branches:
      • Splenic artery
      • Left gastric artery
      • Common hepatic artery

  Path of the Common Hepatic Artery

  • Course:
    • Runs along the superior border of the pancreas.
    • Passes forward and to the right, along the right side of the lesser omentum.
    • Ascends toward the hepatic hilum.
    • Positioned anterior to the portal vein and to the left of the bile duct.

  Branches of the Common Hepatic Artery

  • Gastroduodenal artery: First branch as it heads superiorly.
  • Supraduodenal artery: Arises after the gastroduodenal artery.
  • Right gastric artery: Follows the supraduodenal artery.

  Proper Hepatic Artery

  • Origin: Beyond the takeoff of the gastroduodenal artery.
  • Division: Splits into right and left hepatic arteries at the hilum.

  Left Hepatic Artery

  • Course: Heads vertically toward the umbilical fissure.
  • Supplies: Segments II, III, and IV.
  • Middle Hepatic Artery: A branch supplying segment IV.

  Right Hepatic Artery

  • Course: Runs posterior to the common hepatic bile duct and enters Calot's triangle.
  • Branches:
    • Cystic artery: Supplies the gallbladder.
    • Continues into the right liver.

Portal Triad Anatomy

• Positioning:
  • Bile ducts are usually located above the portal branches, and arteries are located below the corresponding veins. (B - V - A: Bile duct - Vein - Artery). ??? QQQ
• Blood Supply to Bile Ducts:
  • Derived from arterial branches.

Bullet points for MCQ’s

1. Hepatic Veins and Segmentation

• RHV (Right Hepatic Vein) is the largest vein but not MHV (Middle Hepatic Vein).
  • RHV drains segments 5, 6, 7, 8.
  • MHV drains segment 4.

2. Cantlie's Line

• Cantlie's Line runs from the GB fossa to the LEFT of the IVC (Inferior Vena Cava).

3. Couinaud's Sectoral Anatomy

• Couinaud's sectoral anatomy is based on the PORTAL VEIN.

4. Ligaments

• Arantius (Ligamentum Venosum) = obliterated portion of ductus venosus.
  • MHV and LHV (Left Hepatic Vein) form a common trunk; this ligament is used to detect LHV during dissection.
• Makuchi = AKA IVC ligament.
• Round ligament = attached to LPV (Left Portal Vein).

5. Embryology of the Liver

• Liver arises as a liver bud (endoderm) at 3-4 weeks of development.
• Hepatic veins arise from the cranial part of vitelline veins.
• Portal veins develop from the caudal part of vitelline veins.
• Arteries and bile ducts develop later.
• Biliary system is developed by the 10th week and bile production starts from the 12th week.
• Single plate configuration of hepatocytes by 5 years.
• Extrahepatic umbilical vein closes to form the ligamentum teres.

6. Relations of the Caudate Lobe

• Segments 4, 6, 7 are in contact with the caudate lobe.
• Segments 2, 3 are not in contact, separated by the lesser omentum.
• Vasculature: IVC, LPV, and MHV.
• Caudate lobe enlarges during cirrhosis and Budd-Chiari syndrome.
• Predominant blood supply from LPV.
• Segment 9 is towards the right side of the caudate lobe.

7. Couinaud Approaches to a Portal Pedicle

• Intrafascial: Dissection within the sheath, individual elements.
• Extrafascial: Dissection around the pedicle sheath.
• Extrafascial and Transfissural: Dissection of sheaths at their origin from the hilar and umbilical plates (considered safest, especially for 2nd and 3rd order branches).

8. Hepatic Artery

• Hepatic artery is rarely involved by severe atherosclerotic changes.

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Crash Course Notes

• Couinad segments of Liver based upon = Portal Vein = but division into sectors with portal scissurae which contains HEPATIC VEINS
  • Left posterior sector = seg 2 only
• Brisbane = Sections
  • anatomical landmark on left side = arbitrary = umbilical fissure (hepatic scissurae) = contains left poral vein = divides into left medial and lateral
  • Left lateral section = seg 2 & 3

• Functional Anatomy:

  • Eight segments = each supplied by portal triad = PV;HA;Bileduct
  • Four sectors = scissurae containing three main hepatic veins
  • Right and Left lobe = two sectors each
  • No external land mark for Right and Left lobe
  • Right portal triad
    • divides into right anterior and posterior branches.
    • short extrahepatic course
  • Left portal triad
    • Long extrahepatic course
    • Umbilical fissure
    • branches to segment 4 and 2,3

• Caudate Lobe

  

  • Drains directly into IVC via Short hepatic veins
  • Fuses with seg 6 and 7 posteriorly
  • biliary drainage
    • 78% of times it drains into both Right and left duct
    • 15% into Left duct & 7% into Right ??
  • this is why we do caudectomy in case of Hilar cholangio carcinoma d/t dual biliary drainage
  • Venous landmarks of caudate
    • bulk is more towards left lobe = seg 1
    • Right process of caudate = paracaval portion = Previously called Seg 9
  • Arterial Supply
    • Majority by Left part = Left HA and PPV
    • Right part = close to Right posterior segment = so by Right posterior Pedicle
  • Papillary process = misidentified as enlarged LN = extension of Left part
  • Relations:
    • Seg 2 and 3 are separated from CL by lesser omentum
    • Seg 4 , 7 are in close contact with caudate
    • MHV & LHV is just above(superior) the caudate lobe
    • LPV is below caudate
  • PORTAL VEIN:
  • 75% of hepatic Blood flow
  • 50-70% of livers oxygen requirement
    • Even if there is a HA aneurysm and removed = Liver parenchyma survives d/t Collateral system [BUT NOT IN TRANSPLANTATION]
      • Inferior Phrenic collaterals
      • Collaterals of Inferior mammary artery
  • Length is 5.5 - 8 cms
  • Diametre = 1cm
  • Portal pressure = 6-10mm hg
  • It has the least variation in anatomies compared to bile duct and HA

  • NAKAMURA CLASSIFICATION:

    

    • MC variant = Portal Trifurcation
    • 2nd MC = Right posterior as first branch of PV
    • HEPATIC ARTERY:
      • 25% of hepatic blood flow
      • 30-50% of oxygen requirement
      • Exclusive blood supply to Bile Duct
      • Variations:
    • Right side
      • Replaced / Accessory = 11-21%
      • SMA
      • Lateral border of HDL
      • Behind Portal vein and Bile Duct
    • Left side
      • LGA
      • Replaced/ accessory = 3.8-10%