Functional Anatomy of the Liver

In this section, hepatic anatomy is briefly reviewed and the terminology adopted is clarified. A definition of anatomical and surgical terms is important since the nomenclature of hepatic surgical procedures and related anatomic terms is confusing. We adopted the terminology recently proposed by Strasberg &, based on the work of Healey and Schroy &, and Couinaud &.
The liver can be divided on the surface in the right and left lobes, that are defined by the umbilical fissure, the fissure for the ductus venosus, and the attachment of the falciform ligament $.
From the surgical point of view, the liver has two sides, that are called right and left hemilivers, and a separate small part known in surface anatomy as the caudate lobe. The two sides are divided by a plane, called the midplane of the liver, which on the surface of the liver passes through the gallbladder fossa and the fossa of the inferior vena cava $. The resection of an hemiliver is defined as right or left hemihapatectomy.
On the basis of the internal anatomy of the hepatic artery and bile duct, each hemiliver is further divided in two sections by the intersectional planes. The right intersectional plane, that contains the right hepatic vein and has no surface markings, divides the right hemiliver into the anterior and posterior sections. The left intersectional plane, that emerges from the liver at the umbilical fissure, the fissure for the ductus venosus, and the attachment of the falciform ligament, divides the left hemiliver into the medial and lateral sections $. The resection of a liver segment is defined as sectionectomy, while removal of a hemiliver with the adjacent medial section is called right or left triscetionectomy.
The liver may be further subdivided into segments, on the basis of the third-order division of the artery and bile duct. The right anterior and posterior sections, subdivides in two segments each: segments V and VI, and segments VIII and VII, respectively. The left medial section has no third-order division, and is therefore considered a single segment, segment IV. The caudate lobe is also considered as a single segment, segment I. Finally, the left lateral section divides into two segments II and III $.
While the artery and the bile duct divide inside the liver in a regular fashion, defining the liver surgical anatomy, the portal vein follows this rule only in the right hemiliver. The portal vein on the left runs outside the liver from the bifurcation to the left intersectional plane. Here, the vein enters the umbilical fissure, which is in the left intersectional plane, originating the umbilical portion of the left portal vein, that supplies both the medial and the lateral section of the left hemiliver $.
The three main hepatic veins are defined right, middle and left. The right and the middle hepatic veins lie in the midplane of the liver and in the right intersectional plane, respectively. On the contrary, only the terminal part of the left hepatic vein lies in the left intersectional plane, while the more peripheral portion of the vein runs between segments II and III. The left hepatic vein drains part of the left medial section of the liver by means of the umbilical vein, that enters the left hepatic vein in the left intersectional plane $.