Editing Liver (section)

== '''Gross anatomy''' ==

=== '''General     description''' ===

** Solid organ weighing      1.2-1.6kg

=== '''Coverings''' ===

** Fibrous capsule of Glisson
** Capsule invaginated by each      portal triad at the hilum, forming a portal pedicle surrounded by a      fibrous sheath (sometimes called valoean sheath)
*** Within each sheath the PV       is surrounded by loose areolar tissue - dissection is relatively easy
*** Condensation of tissue       around artery and duct is denser and tougher
*** Within the sheath, the bile       duct tends to be elliptical rather than round, and inferior aspect       usually faces the corresponding artery, and is always close to it
*** PV tends to lie posterior       to the bile duct and hepatic artery
*** The sheath can be mobilised       and ligated as a whole from within the liver substance - often easier       and safer
** Visceral peritoneum (apart      from GB fossa, porta hepatis and two wedge-shaped areas on either side of      the IVC)
** Bare area - area between the      coronary ligaments/triangular ligaments which is not covered by      peritoneum. See below under 'coronary ligament'.

=== '''Divisions''' ===

** Historically, was divided      into (small) left lobe and (large) right lobe using the umbilical      fissure/falciform ligament, however this has been abandoned in favour of      functional anatomy
** Divisions now based on      functional anatomy - three hepatic veins that travel in three portal      scissurae (fissures/clefts), along with bile ducts and hepatic artery      branches
*** ''Right       liver/left liver is more correct than right lobe/left lobe, because       there are no external markings.''
*** Middle hepatic vein (in the       main fissure) divides liver into right and left hemilivers along       Cantlie's line
**** This plane is known as the        main fissure of the liver (see 'main fissure' below)
*** Right and left hepatic vein       scissura further divide the liver into '''four separate portal sectors''' (right anterior - V and       VIII; right posterior - VI and VII; left anterior - III and IV; left       posterior - II)

=== '''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.

=== '''Fissures''' ===

** The limit between the      territories supplied by two adjacent pedicles. The blood flow from one      pedicle cannot trespass the fissure, although continuity is secured by      the sinusoids. Therefore, very helpful in defining anatomical resections.
** ''The      important fissures do not exist as such, but have to be made by the      surgeon''
** ''Some      sources say 'scissura' can be used interchangeably, but 'fissure' is more      common''
** Main fissure
*** Separates the right side       from the left, with a constant vertical plane through Cantlie's line
**** Posteriorly: from        supra-hepatic IVC, through the middle of the cystic fossa, then passes        slightly to the left at the porta hepatis to pass in the middle of the        region where the portal structures bifurcate, and then across the        caudate process
**** Anteriorly: Cantlie's line        can be estimated from the middle of the gallbladder notch back to the        point where the falciform ligament disappears posteriorly
**** Runs between segments V        and VIII, and segment IV
*** Main trunk of middle       hepatic vein lies within this fissure
** Left fissure
*** Separates left lateral from       left medial
*** Runs between two points:
**** On superior liver edge,        halfway between falciform ligament and left edge of liver
**** Left side of base of        falciform ligament in front of IVC
*** Contains main trunk of left       hepatic vein
** Umbilical fissure
*** Lies deep to the falciform       ligament attachment
*** Contains the left portal       pedicle
*** Often also contains an       important vein - the vein of the umbilical fissure
*** Note that the umbilical       fissure is not a scissura because it does not contain a hepatic vein -       it just contains the left portal pedicle
** Fissure venosum
*** The continuation of the       umbilical fissure on the posterior surface of the liver
*** Lesser omentum passes in       here
*** Contains the obliterated       ductus venosum
*** Lies more or less in the       coronal plane, and is continued in the plane of the dorsal fissure -       with fingers placed in the fissure venosum, they point to the dorsal       fissure in front
** Dorsal fissure
*** The least definable fissure
*** Separates posterior segment       IV from segment I
** Right fissure
*** Between right anterior and       right posterior sectors
*** Contains right hepatic vein
*** Indicated by the point       midway between GB bed and right extremity of liver, but in about 40% of       cases lies much closer to the right margin of the GB bed, and can also       be found in the opposite direction sometimes
*** Can sometimes be seen on       the under surface of the liver as the fissure of Gans
** '''Porta      hepatis'''
*** The transverse fissure in       the liver between the quadrate lobe in front and the caudate process and       caudate lobe behind
*** Receives structures of the       hepatic pedicle at its left end, and GB neck at its right end
*** Note that the CBD tends to       be in the free edge of lesser omentum, while the artery lies in front of       the PV

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