Liver segment

File:Liver 04 Couinaud classification.svg

There are four lobes of the liver. The Couinaud classification of liver anatomy then further divides the liver into eight functionally independent segments. Each segment has its own vascular inflow, outflow and biliary drainage.{{cite web |last1=Kapoor |first1=Vinay Kumar |title=Liver Anatomy: Overview, Gross Anatomy, Microscopic Anatomy |url=https://emedicine.medscape.com/article/1900159-overview |website=Medscape |date=14 September 2017}} 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.{{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}} The division of the liver into independent units means that segments can be resected without damaging the remaining segments.{{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}} 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.

The classification system uses the vascular supply in the liver to separate the functional segments (numbered {{rn|I}} to {{rn|VIII}})

Segment {{rn|I}} is the caudate lobe and is situated posteriorly. 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).

The caudate lobe is a separate structure which receives blood flow from both the right- and left-sided vascular branches.{{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}}{{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 }}

The Caudate lobe includes: (1) the Spiegel lobe; (2) the paracaval portion; and (3) the caudate process portion. The Spiegel lobe has its portal venous and biliary branches ramified mainly from the left-side tract. The Paracaval portion has the portal venous branches ramified mainly from the left portal vein, while the biliary branches of this portion drained into the right and left biliary tracts at almost equal frequencies. The portal venous branches & Biliary branches of the caudate process portion has it ramified from the right-side tract.

Segments {{rn|II}} and {{rn|III}} lie medial to the falciform ligament with {{rn|II}} superior to the portal venous supply and {{rn|III}} inferior. Segment {{rn|IV}} lies lateral to the falciform ligament and is subdivided into {{rn|IVa}} (superior) and {{rn|IVb}} (inferior).{{cite journal |last1=Sibulesky |first1=Lena |title=Normal liver anatomy |journal=Clinical Liver Disease |date=March 2013 |volume=2 |issue=S1 |pages=S1–S3 |doi=10.1002/cld.124|doi-access=free|pmc=6448666}}

Segments {{rn|V}} to {{rn|VIII}} make up the right part of the liver:

• Segment {{rn|V}} is the most medial and inferior
• Segment {{rn|VI}} is located more posteriorly
• Segment {{rn|VII}} is located above segment {{rn|VI}}
• Segment {{rn|VIII}} sits above segment {{rn|V}} in the superior-medial position

The fissure for the round ligament of the liver (ligamentum teres) separates the medial and lateral parts of segment {{rn|IV}}. The inferior medial segment ({{rn|IVb}}) is also called the quadrate lobe.{{cite journal |last1=Germain |first1=T. |last2=Favelier |first2=S. |last3=Cercueil |first3=J.-P. |last4=Denys |first4=A. |last5=Krausé |first5=D. |last6=Guiu |first6=B. |title=Liver segmentation: Practical tips |journal=Diagnostic and Interventional Imaging |date=November 2014 |volume=95 |issue=11 |pages=1003–1016 |doi=10.1016/j.diii.2013.11.004|doi-access=|pmid= 24388431}}

The clockwise numbering of liver segments in Couinaud's classification is said to have been inspired by the numbering of arrondissements (administrative districts) of Paris.{{Cite journal |last=Majno |first=Pietro |last2=Mentha |first2=Gilles |last3=Toso |first3=Christian |last4=Morel |first4=Philippe |last5=Peitgen |first5=Heinz O. |last6=Fasel |first6=Jean H. D. |date=2014-03-01 |title=Anatomy of the liver: An outline with three levels of complexity – A further step towards tailored territorial liver resections |url=https://www.sciencedirect.com/science/article/pii/S0168827813007526 |journal=Journal of Hepatology |volume=60 |issue=3 |pages=654–662 |doi=10.1016/j.jhep.2013.10.026 |issn=0168-8278|doi-access=free }}

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Category:Liver anatomy