Editing Liver (section)

=== '''Segments''' ===

** ''The liver      is further divided into eight portal segments based on their supply by      independent portal pedicles (each containing a 'portal triad' of portal      vein, hepatic artery and bile duct)''
** ''Start at      the inferior part of the liver and go around the PV in an anticlockwise      direction to name the segments''
**
** Caudate lobe (segment I) is      the dorsal part segment of the liver, lying directly on the IVC and      aorta. The main bulk is to the left of the IVC, but a small 'caudate      process' intervenes between the IVC and left portal triad. Vascular      inflow and biliary drainage to the caudate lobe comes from both right and      left pedicles. A number of small posterior veins drain directly into the      IVC - usually 1-3, but 70% have only one, usually emerging from lower or      middle third of the caudate lobe. The caudate lobe may have a fibrous      component posteriorly that attaches to the diaphragm and completely      encircles the IVC - the caval ligament - important in mobilising the      right liver or caudate lobe off the IVC. Can continue to function well in      hepatic venous outflow obstruction due to preserved links to IVC. Many      high cholangiocarcinomas also involve the ducts of segment I.
**
** Segment II: left posterior      sector. Often small, and unusual to remove that sector alone. Only a      single Glissonian sheath to segment II.
**
** Segment III: Lies between      the base of the falciform ligament and umbilical fissure on the right,      and the left fissure and segment II on the left. Commonly joined to      segment IV by a bridge of liver tissue over the ligamentum teres in the      umbilical fissure, which is easily broken down. Predominantly drains to      left hepatic vein, but can occasionally drain via the vein of the      umbilical fissure.
**
** Segment IV: between the main      fissure on the right, and the umbilical fissure on the left. Separated      from segment I by the dorsal fissure. Some authors refer to the anterior      part of segment IV as the quadrate lobe, calling it segment IVb. Don't      necessarily need to remove IVa if IVb is being resected. Lots of      variation in portal pedicles - most variable area in the liver. Resection      requires careful dissection, and usually means dissecting outside the      Glissonian sheaths. Often start off 5mm within segment IV itself, then      dissecting outwards to find the external boundary, to be sure not to miss      any variations.
**
** Segment V: between the main      fissure and the right fissure, anterior and inferior to segment VIII.      Variable size, in accordance with the variable location of right fissure.
**
** Segment VI: forms the right      inferior extremity, to the right and behind the right fissure. Venous      drainage mainly to right hepatic vein, but can be to middle hepatic.
**
** Segment VII: forms the major      portion of the posterior part of the right liver.
**
** Segment VIII: mainly on the      superior aspect of the liver, with little to define its borders.
** Riedel lobe - rare      malformation in which a tongue of liver extends inferiorly off the right      liver.