Liver segment: Difference between revisions

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The fissure for the [[round ligament of liver|round ligament of the liver]] (ligamentum teres) also separates the medial and lateral segments. The medial segment is also called the [[quadrate lobe]]. In the widely used [[Claude Couinaud|Couinaud]] (or "French") system, the functional lobes are further divided into a total of eight subsegments based on a transverse plane through the bifurcation of the main portal vein.<ref name="radiopaedia.org">{{cite web|url=http://radiopaedia.org/articles/couinaud-classification |title=Couinaud classification &#124; Radiology Reference Article |publisher=Radiopaedia.org |accessdate=2015-06-26}}</ref> The [[caudate lobe]] is a separate structure which receives blood flow from both the right- and left-sided vascular branches.<ref name="3d">{{cite web |url=http://dpi.radiology.uiowa.edu/nlm/app/livertoc/liver/liver.html |title=Three-dimensional Anatomy of the Couinaud Liver Segments |accessdate=2009-02-17}}</ref><ref name="strunk">{{cite journal |last1=Strunk |first1=H. |last2=Stuckmann |first2=G. |last3=Textor |first3=J. |last4=Willinek |first4=W. |title=Limitations and pitfalls of Couinaud's segmentation of the liver in transaxial Imaging |journal=European Radiology |volume=13 |issue=11 |pages=2472–82 |year=2003 |pmid=12728331 |doi=10.1007/s00330-003-1885-9 }}</ref> The Couinaud classification of liver anatomy divides the liver into eight functionally independent segments. Each segment has its own vascular inflow, outflow and biliary 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.<ref name="radiologyassistant.nl">{{cite web|url=http://www.radiologyassistant.nl/en/p4375bb8dc241d/anatomy-of-the-liver-segments.html |title=The Radiology Assistant : Anatomy of the liver segments |publisher=Radiologyassistant.nl |date=2006-05-07 |accessdate=2015-06-26}}</ref> The division of the liver into independent units means that segments can be resected without damaging the remaining segments.<ref>{{cite web|url=https://www.imaios.com/en/e-Cases/Channels/Radiology/Radiological-classifications-commonly-used-on-medical-imaging/Hepatic-segments-Couinaud-classification |title=Hepatic segments (Couinaud classification) / Radiological classifications commonly used on medical imaging / Radiology / Channels / e-Cases / |publisher=IMAIOS.com |accessdate=2015-06-26}}</ref> To preserve the viability of the liver following surgery, resections follow the vessels defining the peripheries of each segment. This means that resection lines parallel the hepatic veins, leaving the portal veins, bile ducts, and hepatic arteries intact.<ref name="radiopaedia.org"/>

The classification system uses the vascular supply in the liver to separate the functional unitssegments (numbered I to VIII):

*UnitSegment I is the caudate lobe and is situated posterior l and it may receive its supply from both the right and the left branches of portal vein. It contains one or more hepatic veins which drain directly into the [[Inferior vena cava|IVC]].<ref name="radiopaedia.org"/>

The remainder of the unitssegments (II to VIII) are numbered in a clockwise fashion:<ref name="radiologyassistant.nl"/>

*unitssegments II and III lie medial to the falciform ligament with II superior to the portal venous supply and III inferior

*unitsegment IV lies lateral to the falciform ligament and is subdivided into IVa (superior) and IVb (inferior)

UnitsSegments V to VIII make up the right part of the liver:<ref name="radiologyassistant.nl"/>

*unitsegment V is the most medial and inferior

*unitsegment VI is located more posteriorly

*unitsegment VII is located above unitsegment VI

*unitsegment VIII sits above unitsegment V in the superio-medial position

==References==