Editing Liver (section)

== '''Vascular anatomy''' ==

=== '''Portal vein''' ===

** Provides about 75% of      hepatic inflow, and 50-70% of oxygen requirement. No valves, so      accommodates high flow at low pressure
** Embryology
*** Forms from right and left       vitelline veins
*** Left vitelline vein becomes       lower part of PV
*** Upper part of right       vitelline vein becomes upper part of PV
** Course
*** Forms behind the neck of       the pancreas from SMV and splenic vein. Also gets blood from left       gastric vein, with variable point of inflow.
*** Length 5.5-8cm, diameter       1cm
*** Runs behind D1 (with GDA       just anterior to it) and into the hepatoduodenal ligament, where it runs       along the right border of the lesser omentum (posterior to CBD and PHA)
*** Tributaries below duodenum       enter from the right, posteriorly and the left, but not anteriorly;       gentle blunt dissection anterior to PV can open up a plane behind the       neck of the pancreas
*** Does not tend to have tribs       above the duodenum, but some tributaries may be found lower down
**** Pancreaticoduodenal vein -        enters on the right side, behind or immediately above the duodenum
**** Right and sometimes left        gastric vein - if entering PV, do so on the left, usually behind the        duodenum
*** Divides into main right and       left branches at the hilum of the liver
** Branches
*** Right portal triad - short       extrahepatic course (1.5cm), which appears to be the continuation of the       main PV, before entering the liver and branching into anterior and       posterior sectoral branches. Division to right lateral sector describes       a gentle curve towards right posterior liver; right medial sector can       arise at an angle. These branches can sometimes be seen       extra-hepatically and can come off the main PV. Usually a small caudate       process branch off the main right PV.
*** Left portal triad - longer       extrahepatic course (4cm) and runs transversely along the base of       segment IV in a peritoneal sheath, which is the upper end of the lesser       omentum. Then runs anterior and caudally in the umbilical fissure,       giving branches to segments II and III on the left, branches to the left       side of the caudate lobe, and recurrent branches to segment IV on the       right. Ligamentum teres is attached to the vein in the umbilical       fissure.
** Tributaries
*** SMV and splenic vein
*** Right and left gastric       veins
*** Superior       pancreaticoduodenal veins
*** Cystic vein/s into the       right branch of the portal vein
*** Periumbilical veins running       with ligamentum teres
** Portosystemic shunts
*** Submucosal veins in upper       stomach and oesophagus - drain cephalad into azygos system - varices
*** Varices of the inferior       rectal (haemorrhoidal) veins in the wall of the rectum. Note that these       are different to haemorrhoids - these are true veins, occurring cephalad       to the haemorrhoidal venous plexuses.
*** Ligamentum teres -       occasionally the umbilical vein itself opens up, but more often small       para-umbilical veins which run with the ligamentum teres, enlarge and       allow dilatation of contiguous veins in the umbilicus and abdominal wall
*** Retroperitoneum - multiple,       usually small, veins from the splenic venous system can enlarge and       communicate with diaphragmatic, adrenal, or renal veins
** Variations
*** Standard anatomy seen in       70%
*** Most common variation is       the 'portal vein trifurcation': main PV divides into left, right       posterior and right anterior branches.
*** Other common variation is       the right posterior PV originating as the first branch of the PV, or the       right anterior PV arising from the left PV
*** Other very rare variations:
**** PV found anteriorly to        neck of pancreas and duodenum
**** Direct entry of PV to IVC
**** Pulmonary vein entering PV
**** Congenital absence of left        branch of PV (with right branch coursing peripherally through the liver        to supply the left liver)
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=== '''Hepatic artery''' ===

* Provides 25% of the hepatic     blood flow and 30-50% of its oxygenation
* '''Embryology'''
** The embryo receives blood      from a right, middle and left hepatic artery
** Usually the right and left      arteries disappear
* '''Intra-hepatic'''
** Variations are relatively      common but most do not have significance
* '''Extra-hepatic'''
** Classic course (seen 60% of      the time - persistent of the middle primordial artery)
*** Classic anatomy is the CHA       arises from coeliac trunk, passes forward and to the right along the       superior border of the pancreas (behind the posterior wall of lesser       sac), then becomes hepatic artery proper after giving off GDA. There is       consistently a large flat ovoid lymph node just anterior to hepatic       artery at the point where it gives off GDA, and removal of this node is       the easiest way of accessing hepatic artery proper.
*** Hepatic artery proper runs       along the right side of the lesser omentum, ascending toward the hepatic       hilum, anterior to PV and to the left of the CBD
*** Hepatic artery proper       bifurcates into a left and right hepatic artery at the hepatic hilum
**** Variable point of        bifurcation - 20% have a low bifurcation, 5% have early division where        RHA arises first and crosses behind PV
****
*** RHA travels transversely,       posterior to CHD in 90-95% of patients, and eventually travels through       the triangle of Calot, at which point gives off the cystic artery. As       RHA enters the hilar plate, it often bifurcates into anterior and       posterior branches, with the latter entering the sulcus of Rouviere as       it joins the right posterior portal pedicle
*** LHA enters through the       umbilical fissure to supply segments II, III, and IV. LHA also usually       gives off a middle hepatic artery branch that supplies segment IV. LHA       is usually the most anterior and left-lying structure in porta hepatis.
** '''Variations''' - highly variable - below      are some of the variations, not exhaustive - there is a classification      system by Michel et al in 1955 types I-X
*** '''Classic       anatomy''' is       seen in about 60%
*** '''CHA'''
**** Origin:
***** Coeliac trunk >90%
***** Aorta 2%
***** SMA 2-4%
****** Hepatic          artery will then run behind portal vein
**** Division
***** Early division CHA - can         originate as far back as separate branches from SMA 5%
***** Low division CHA 15%
***** Trifurcation into RHA,         LHA and GDA
*** '''RHA'''
**** Origin (replaced RHA)
***** CHA 85%
***** SMA 12.5%
***** Coeliac trunk 2.5%
**** Path
***** Crossing anterior to CHD         instead of posterior - ''dangerous for lap         cholecystectomy''
***** Moynihan's         ('caterpillar') hump - makes a deviation into hepatocystic triangle         before giving off a short cystic artery then curling back towards         porta hepatis, often after passing anterior to CHD
*** '''LHA'''
**** Origin (replaced LHA)
***** CHA 85%
***** Left gastric artery 7.5%
*** '''Middle       hepatic artery'''
**** Origin
***** LHA
***** RHA (uncommon)
***** CHA (trifurcation)         uncommon
*** '''Accessory       vessels'''
**** RHA
***** Accessory RHA from SMA 4%
****** Usually          arises from SMA and ascends behind HOP and duodenum, passing behind          PV in the free edge of lesser omentum
****** Degree          of supply to liver varies from supplemental to sole segmental
***** Accessory RHA from aorta,         coeliac trunk, GDA - all rare
**** LHA
***** Accessory LHA from left         gastric artery 7.5%
****** Very          rare for this to be the ''sole'' blood supply to the          left liver
****** Runs in          lesser omentum, and enters liver through the fissure venosum
***** Accessory LHA from RHA
***** Accessory LHA from         coeliac, aorta, splenic, GDA - all rare
**** Accessory LHA and RHA: 1%
** Branches
*** Right gastric
**** See 'stomach'
*** GDA
**** Arises from CHA behind or        above duodenum
***** Can occasionally arise         from SMA
**** Just anterior to PV as it        initially descends, behind duodenum but in front of neck of pancreas,        in a groove on pancreatic capsule
**** Main trunk or        supraduodenal branch is commonly involved in bleeding ulcers
**** Terminates by dividing        into the right gastro-epiploic artery and two superior        pancreaticoduodenal arteries (those anterior and posterior branches        descend between duodenum and HOP, anastomosing with corresponding        branches of inferior pancreaticoduodenal arteries)

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=== '''Hepatic     veins''' ===

** Do not correspond with      portal segmentation
** Major hepatic veins lie      between the four main sectors
** There are only two major      hepatic veins entering the IVC
** Course
*** Right hepatic vein - runs       in the right scissura between the anterior and posterior sectors of the       right liver, and drains most of the right liver. Usually the largest,       but also the most variable. Enters IVC at about the upper pole of the       caudate lobe, a few mm lower than the left hepatic vein.
*** Left and middle hepatic       veins usually join intra-hepatically and enter the left side of the IVC       as a single vessel, but with the common trunk usually only 5mm in length       before reaching IVC.
**** Left hepatic vein runs in        the left scissura between segments II and III and drains those segments        only. Takes the ligamentum venosum. Situated in the posterior 2cm of        the left fissure, making up part of the posterior edge of liver, only        being covered by connective tissue of the left triangular ligament.
***** Also receives tributaries         from the vein of the umbilical fissure and a posterior branch from the         posterior part of the left liver, which can sometimes still allow         segment IV to drain after resection of middle hepatic vein
**** Middle hepatic vein runs        in the portal scissura between segment IV and the right anterior        sector, and drains segment IV and some of the right anterior sector
*** Umbilical vein, if patent,       usually empties into left hepatic vein, in umbilical fissure
*** Small inferior veins from       segment VIII and caudate lobe drain directly into IVC
**** In 15% of patients, there        is a moderately large right vein here, termed the accessory right        hepatic vein
**** Approach and ligate these        by mobilising the liver then exposing to the opposite side of the vein
*** Also common tributary from       caudate love into left hepatic vein
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