Couinaud classification of hepatic segments

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The Couinaud classification (pronounced kwee-NO) is used to describe functional liver anatomy. It is the preferred over morphological liver anatomy sinceclassification system as it allows the divisiondivides of the liver into eight independent functional units (segments) rather than relying on the traditional morphological description based on the external appearance of the organliver. The segments are numbered I to VIII.

The separation of the unitssegments is based on the fact that each has its own dual vascular inflow, outflowbiliary drainage and biliary as well as lymphatic drainage. In general each segment is wedged shaped with the centreapex directed towards the hepatic hilum (porta hepatis). At the apex of each segment there is aa single segmental branch of the portal vein, hepatic artery and bile duct enter; in the periphery of each segment there is vascularvenous outflow through the hepatic veins.

The classification system uses the vascular supply, which run in the liver to3 vertical planes that separate the functional units (numbered I to VIII)segments:

  • right hepatic vein located in the right intersegmental fissure, divides the right lobe (cephalic aspect) into anterior and posterior segmentsparts
  • middle hepatic vein lies in the main lobar fissure, divides the liver into right and left lobes (or right and left hemiliver): this vertical plane runs from the inferior vena cava to the gallbladder fossa alsoand is known as Cantlie's line
  • left hepatic vein located in the left intersegmental fissure, divides the left lobe (cephalic aspect) into a medial and lateral partparts

A fourth horizontal plane further divides the liver, known as the portal plane where the portal vein dividesbifurcates and becomes horizontal, dividing the liver into uppersuperior and lower segments: the left and right portal veins branch superiorly and inferiorly to project into the centre of each segment

The division of the liver into self-contained

inferior units means that each segment can be resected without damaging those remaining. For the liver to remain viable, resections must proceed along the vessels that define the peripheries of these segments. This means, that resection-lines parallel the hepatic veins and there is preservation of the centrally located portal veins, bile ducts, and hepatic arteries.

Segments

  • unitsegment I is the caudate lobe and is situated posteriorlposteriorly around the IVC and itdifferent to the other 7 segments. It may receive its supply from both the right and the left branches of portal vent. It containsvein and is drained directly into the IVC by one or more small hepatic veins which drain directly into the IVC

The remainder of the unitssegments (II to VIII) are numbered in a clockwise fashion starting superiorly in the left hemiliver :

  • unitssegments II and III lieare lateral to the left hepatic vein and falciform ligamentwith II superior and III inferior to the portal venous supply and III inferiorplane
  • unitsegment IV lies medial to the falciform ligament, between the left and middle hepatic veins. It is subdivided into IVa (superior) and IVb (inferior) subsegments. Easy tip: IVa above and IVb below the portal plane. Segment IV includes the quadrate lobe.

UnitsSegment V to VIII make up the right hemiliver and are easier to describe:

  • unitsegment V is located below the most medialportal plane between the middle and inferiorright hepatic veins
  • unitsegment VI is located more posteriorly, withbelow the portal plane lateral to the right hepatic vein
  • unitsegment VII is located above itthe portal plane lateral to the right hepatic vein
  • unitsegment VIII sitsis located above unit Vthe portal plane between the middle and right hepatic veins

Each hepatic vein therefore drains multiple adjacent segments, those that are bounded by the hepatic vein.

The division of the liver into self-contained units allows the surgical resection of individual segments and sections (two or more adjacent segments) without damaging those segments remaining. Hence for the liver to remain viable, resections occur along the hepatic veins and portal veins in the superio-medial positionplanes that define the boundaries of these segments.

History and etymology

It was first described by C Couinaud in 1957. The notion of the Couinaud liver segments being based on the arrondissements (administrative districts) of Paris is a radiological urban myth 4.

  • -<p>The <strong>Couinaud classification</strong> (pronounced kwee-NO) is used to describe functional <a href="/articles/liver">liver</a> anatomy. It is preferred over morphological liver anatomy since it allows the division of the liver into eight independent functional units rather than relying on the traditional morphological description based on the external appearance of the organ.</p><p>The separation of the units is based on the fact that each has its own vascular inflow, outflow and biliary as well as lymphatic drainage. In the centre of each segment there is a branch of the portal vein, hepatic artery and bile duct; in the periphery of each segment there is vascular outflow through the hepatic veins.</p><p>The classification system uses the vascular supply in the liver to separate the functional units (numbered I to VIII):</p><ul>
  • +<p>The <strong>Couinaud classification</strong> (pronounced kwee-NO) is used to describe functional <a href="/articles/liver">liver</a> anatomy. It is the preferred anatomy classification system as it divides of the liver into eight independent functional units (segments) rather than relying on the traditional morphological description based on the external appearance of the liver. The segments are numbered I to VIII.</p><p>The separation of the segments is based on the fact that each has its own dual vascular inflow, biliary drainage and lymphatic drainage. In general each segment is wedged shaped with the apex directed towards the hepatic hilum (<a href="/articles/porta-hepatis">porta hepatis</a>). At the apex of each segment a single segmental branch of the portal vein, hepatic artery and bile duct enter; in the periphery of each segment there is venous outflow through the hepatic veins, which run in 3 vertical planes that separate the segments:</p><ul>
  • -<a href="/articles/right-hepatic-vein">right </a><a href="/articles/hepatic-veins">hepatic vein</a> located in the right intersegmental fissure, divides the right lobe (cephalic aspect) into anterior and posterior segments</li>
  • +<a href="/articles/right-hepatic-vein">right </a><a href="/articles/hepatic-veins">hepatic vein</a> located in the right intersegmental fissure, divides the right lobe into anterior and posterior parts</li>
  • -<a href="/articles/middle-hepatic-vein">middle </a><a href="/articles/hepatic-veins">hepatic vein</a> lies in the main lobar fissure, divides the liver into right and left lobes (or right and left hemiliver): this plane runs from the inferior vena cava to the gallbladder fossa also known as <a href="/articles/cantlies-line">Cantlie's line</a>
  • +<a href="/articles/middle-hepatic-vein">middle </a><a href="/articles/hepatic-veins">hepatic vein</a> lies in the main lobar fissure, divides the liver into right and left lobes (or right and left hemiliver): this vertical plane runs from the <a href="/articles/inferior-vena-cava-1">inferior vena cava</a> to the gallbladder fossa and is known as <a href="/articles/cantlies-line">Cantlie's line</a>
  • -<a href="/articles/left-hepatic-vein">left </a><a href="/articles/hepatic-veins">hepatic vein</a> located in the left intersegmental fissure, divides the left lobe (cephalic aspect) into a medial and lateral part</li>
  • +<a href="/articles/left-hepatic-vein">left </a><a href="/articles/hepatic-veins">hepatic vein</a> located in the left intersegmental fissure, divides the left lobe into a medial and lateral parts</li>
  • +</ul><p>A fourth horizontal plane further divides the liver, known as the portal plane where the <a href="/articles/portal-vein">portal vein</a> bifurcates and becomes horizontal, dividing the liver into superior and inferior units.</p><h4>Segments</h4><ul><li>
  • +<strong>segment I</strong> is the caudate lobe situated posteriorly around the IVC and different to the other 7 segments. It may receive its supply from both the right and the left portal vein and is drained directly into the <a href="/articles/inferior-vena-cava-1">IVC </a>by one or more small hepatic veins</li></ul><p>The remainder of the segments (II to VIII) are numbered in a clockwise fashion starting superiorly in the left hemiliver :</p><ul>
  • -<a href="/articles/portal-vein">portal vein</a> divides the liver into upper and lower segments: the left and right portal veins branch superiorly and inferiorly to project into the centre of each segment</li>
  • -</ul><p>The division of the liver into self-contained units means that each segment can be resected without damaging those remaining. For the liver to remain viable, resections must proceed along the vessels that define the peripheries of these segments. This means, that resection-lines parallel the hepatic veins and there is preservation of the centrally located portal veins, bile ducts, and hepatic arteries.</p><ul><li>
  • -<strong>unit I</strong> is the caudate lobe and is situated posteriorl and it may receive its supply from both the right and the left branches of portal vent. It contains one or more hepatic veins which drain directly into the IVC</li></ul><p>The remainder of the units (II to VIII) are numbered in a clockwise fashion:</p><ul>
  • +<strong>segments II and III </strong>are lateral to the left hepatic vein and <a href="/articles/falciform-ligament">falciform ligament </a>with II superior and III inferior to the portal plane</li>
  • -<strong>units II and III </strong>lie lateral to the <a href="/articles/falciform-ligament">falciform ligament</a> with II superior to the portal venous supply and III inferior</li>
  • +<strong>segment IV</strong> lies medial to the falciform ligament, between the left and middle hepatic veins. It is subdivided into <strong>IVa</strong> (superior) and <strong>IVb</strong> (inferior) subsegments. Easy tip: IV<strong>a a</strong>bove and IV<strong>b b</strong>elow the portal plane. Segment IV includes the quadrate lobe.</li>
  • +</ul><p>Segment V to VIII make up the right hemiliver and are easier to describe:</p><ul>
  • -<strong>unit IV</strong> lies medial to the falciform ligament and is subdivided into <strong>IVa</strong> (superior) and <strong>IVb</strong> (inferior)</li>
  • -</ul><p>Units V to VIII make up the right hemiliver:</p><ul>
  • +<strong>segment V</strong> is located below the portal plane between the middle and right hepatic veins</li>
  • -<strong>unit V</strong> is the most medial and inferior</li>
  • +<strong>segment VI </strong>is located below the portal plane lateral to the right hepatic vein</li>
  • -<strong>unit VI </strong>is located more posteriorly, with</li>
  • +<strong>segment VII</strong> is located above the portal plane lateral to the right hepatic vein</li>
  • -<strong>unit VII</strong> above it</li>
  • -<li>
  • -<strong>unit VIII</strong> sits above unit V in the superio-medial position</li>
  • -</ul><h4>History and etymology</h4><p>It was first described by <strong>C Couinaud</strong> in 1957. The notion of the Couinaud liver segments being based on the arrondissements (administrative districts) of Paris is a radiological urban myth <sup>4</sup>.</p>
  • +<strong>segment VIII</strong> is located above the portal plane between the middle and right hepatic veins</li>
  • +</ul><p>Each hepatic vein therefore drains multiple adjacent segments, those that are bounded by the hepatic vein.</p><p>The division of the liver into self-contained units allows the surgical resection of individual segments and sections (two or more adjacent segments) without damaging those segments remaining. Hence for the liver to remain viable, resections occur along the hepatic veins and portal veins in the planes that define the boundaries of these segments.</p><h4>History and etymology</h4><p>It was first described by <strong>C Couinaud</strong> in 1957. The notion of the Couinaud liver segments being based on the arrondissements (administrative districts) of Paris is a radiological urban myth <sup>4</sup>.</p>

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