© Springer Science+Business Media Dordrecht 2016Lunan Yan (ed.)Operative Techniques in Liver Resection10.1007/978-94-017-7411-6_2
2. Anatomy in Liver Resection
Department of Surgery, Queen Elizabeth Hospital, Kowloon, Hong Kong, SAR, China
Department of Surgery, Pamela Youde Nethersole Eastern Hospital, Chai Wan, Hong Kong, SAR, China
Department of Surgery, Chinese Academy of Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, SAR, China
2.1 Surface Markings of the Liver
The position of the liver varies according to the posture of the body. In erect posture in adult male, the edge of the liver projects about 1 cm below the lower margin of the right costal cartilages, and its inferior margin can often be felt in this situation if the abdominal wall is thin. In supine position, the liver recedes above the margin of the ribs and it cannot be detected by palpation. Its position varies with respiratory movements; during deep inspiration, it descends below the ribs; in expiration it rises. In male, the liver weighs from 1.4 to 1.6 kg, while in female, the liver weighs from 1.2 to 1.4 kg.
The upper margin of the right liver, in the midline, is approximately level with the xiphisternal joint; on the right side, the margin arches slightly upward as far as the fifth costal cartilage in the mammary line and then curves down along the right border from ribs 7–11 in the midaxillary line. The upper limit of the left liver also arches slightly upward to the fifth intercostal space 7–8 cm from the midline. The inferior border lies along a line which joins the right lower and upper left extremities. On the right side, the inferior border lies approximately level with the right costal margin while centrally it crosses behind the right upper abdominal wall between the costal margins.
2.2 Surfaces of the Liver
The liver has three surfaces: diaphragmatic, visceral, and posterior surfaces.
2.2.1 Diaphragmatic Surface
The diaphragmatic surface is covered for the most part in peritoneum, which forms a sheath around the liver, except in places where the ligaments reflect to join the adjacent diaphragm. In the midline of the abdomen and over the anterior convexity of the liver, the falciform ligament is attached and divides the liver into the anatomical right “lobe” and left “lobe.” The ligamentum teres, a remnant of the left umbilical vein, runs from the umbilicus in between the two leaves of the falciform ligament to the visceral surface of the liver, where it disappears behind a bridge of either fibrous or liver tissue which connects the right “lobe” with the quadrate “lobe” to end in the left portal vein at the junction between the branches to liver segments 3 and 4. The fundus of the gallbladder peeps below the inferior border of the liver.
2.2.2 Visceral Surface
The sharp inferior border of the liver joins the diaphragmatic surface with the visceral surface which is the inferior surface of the liver. The main structures here are arranged in an H-shaped pattern. The cross-piece of the H is made by the porta hepatis (the hilum of the liver). The right limb of the H is made incompletely by the inferior vena cava posteriorly and the gallbladder anteriorly. The left limb of the H is made by the continuity of the fissures for the ligamentum teres anteriorly and the ligamentum venosum posteriorly. The vena cava lies in a deep groove. On its right side is the bare area and its left side the caudate “lobe.”
2.2.3 Posterior Surface
The inferior vena cava runs in the center of the posterior surface of the liver. A fibrous band called the ligamentum venae cavae (hepatocaval ligament) cover part of the inferior vena cava posteriorly. This fibrous band, sometimes replaced by a bridge of liver tissue, is attached to the bare area on the right side and the caudate “lobe” on the left side. The ligamentum venosum runs in a groove just to the left of the caudate “lobe.” The rest of the posterior surface of the liver is made up by the ligaments (the left triangular ligament, the coronary ligament, and the right triangular ligament) which attach the liver to the diaphragm.
2.3 Ligaments of the Liver
The liver is connected to the undersurface of the diaphragm and to the anterior wall of the abdomen by five ligaments; four of these—the falciform ligament, the coronary ligament, and the two triangular ligaments—have been described in the previous paragraph, and the fifth is the round ligament (or ligamentum teres).
2.3.1 Falciform Ligament and Ligamentum Teres
The falciform ligament is a sickle-shaped fold, consisting of two closely applied layers of peritoneum which connect the liver to the diaphragm and to the supraumbilical part of the anterior abdominal wall. At the upper end, the two layers of the falciform ligament separate from each other. The round ligament (its Latin equivalent ligamentum teres) is a fibrous cord resulting from the obliteration of the umbilical vein. It ascends from the umbilicus in the free margin of the falciform ligament to the umbilical notch of the liver, from which it may be traced in its fossa on the inferior surface of the liver to the porta hepatis, where the ligamentum venosum can be traced from the left portal vein in its fossa to the posterior surface of the junction of the trunk of the middle and left hepatic veins.
2.3.2 Coronary and Triangular Ligaments
At the upper end of the falciform ligament, its two layers separate from each other. On the right, the layer forms the upper layer of the coronary ligament, which continues inferiorly to form the right triangular ligament, then the lower layer of the coronary ligament. In between these ligaments is the bare area of the liver. At its left extremity, the lower layer of the coronary ligament passes in front of the lower end of the groove for the inferior vena cava and becomes continuous with the line of peritoneal reflection from the right border of the caudate lobe.
On the left, the other layer of the falciform ligament forms the anterior layer of the left triangular ligament, which turns backward to form the posterior layer. At the upper end of the fissure for the ligamentum venosum, it becomes the anterior layer of the lesser omentum. The posterior layer of the lesser omentum is the line of reflection of the peritoneum from the upper end of the right border of the caudate lobe. This layer then goes around the caudate lobe to join the lower layer of the coronary ligament.
2.4 Functional Anatomy
2.4.1 Concept of Liver Sections, Liver Sectors, and Segments
The concept of functional liver anatomy based on the distribution of the portal pedicles and the hepatic veins is called Couinaud’s portal segmentation. This concept (portal segmentation) evolved from Couinaud’s study of vasculobiliary casts made by plastic injection of the hepatic and portal veins followed by corrosion of the surrounding liver parenchyma [1–3]. This concept is different from Healey’s arteriobiliary segmentation which is also based on corrosive studies of liver casts. However, Healey injected plastic materials into the branches of hepatic arteries and bile ducts. According to Couinaud, the liver is divided by the three hepatic veins into sectors (called suprahepatic segmentation by Couinaud). The middle hepatic vein runs in the main scissura (midplane of the liver) which divides the liver into the right and the left liver (or hemiliver). On the right side, the right hepatic vein runs in the right scissura (right fissure) which divides the right liver into the right anterior sector (right paramedian sector) and the right posterior sector (right lateral sector). It should be noted that in the right liver, Healey’s liver sections which he called segments are exactly the same as Couinaud’s sectors. On the left side, the left hepatic vein runs in the left scissura (left fissure) which divides the left liver into a left medial sector (left paramedian sector) and a left lateral sector (left posterior sector). However, in the left liver, Healey’s liver sections which he called segments are not the same as Couinaud’s sectors. Couinaud further subdivided the liver into eight segments (subhepatic segmentation) by using the branches of the portal vein.
In the right liver, as Healey’s sections are the same as Couinaud’s sectors, the right anterior section (sector) can be divided into segment 8 superiorly and segment 5 inferiorly. The right posterior Healey’s section (Couinaud’s sector) consists of segment 7 superiorly and segment 6 inferiorly. In the left liver, Healey’s sections are not the same as Couinaud’s sectors. The left medial Healey’s section lies between the main scissura (main fissure) and the falciform ligament, and it consists of only segment 4, while the left lateral Healey’s section consists of segments 2 and 3, being separated by the left hepatic vein which runs in the left scissura (left fissure). For the left medial Couinaud’s sector, it consists of segments 3 and 4, lying between the middle hepatic vein in the main scissura, and the left hepatic vein in the left scissura. The falciform ligament/umbilical fissure divides liver segment 4 from 3. The left lateral Couinaud’s sector, which lies on the left of the left hepatic vein, consists of liver segment 2 only. The liver segment 1 is the same as the caudate lobe in both the Healey’s arteriobiliary and the Couinaud’s portal segmentations.
The American surgeons commonly use the terminology proposed by Healey, while the European surgeons commonly use terminology proposed by Couinaud. It must be clearly pointed out that the original Healey’s segment is not the same as the Couinaud’s segment which is now commonly used throughout the world, and the term “section” used in Healey’s arteriobiliary segmentation can be the same, or different from the term “sector” used in Couinaud’s portal segmentation. To add things more confusing, there is the term “lobes” which may have different meanings to different people. On the other hand, there are many terms which have been used to mean one thing, e.g., the midplane of the liver which divides the liver into the right and the left hemilivers can also be called the Cantlie’s line, midline, principal plane, main scissura, main fissure, main sulcus, main portal scissura (Couinaud), and interlobar plane (American terminology). It is therefore desirable to have a uniform, internationally agreed upon terminology of liver anatomy and liver resections.
2.4.2 The Brisbane 2000 Terminology of Liver Anatomy and Resections
The Scientific Committee of the International Hepato-Pancreato-Biliary Association (IHPBA), at a meeting held in Berne, Switzerland, in December 1998, decided to create a Terminology Committee of international experts to deal with the confusion in nomenclature of hepatic anatomy and liver resections [4–7]. A terminology was sought which was anatomically correct in which anatomical and surgical terms agreed, and which was consistent, self-explanatory, linguistically correct, translatable, precise, and concise. After 18 months, the Committee presented a terminology which was endorsed by the IHPBA at the World Congress of the IHPBA held in Brisbane, Australia. To summarize this terminology, the liver is divided into two parts: the main liver and the caudate lobe (called dorsal sector by Couinaud). There are still some controversies on the terminology of the caudate lobe or the dorsal sector as called by Couinaud.
2.4.3 First-Order Division
The first-order division is based on the branching of the proper hepatic artery into the right and left hepatic arteries. This results in division of the liver into two parts or volumes referred to as right and left livers or hemilivers. The right hepatic artery supplies the right liver and the left hepatic artery supplies the left liver. The plane between these two zones of vascular supply is called a watershed. The first-order division which separates the right and the left liver is a plane that intersects the gallbladder fossa and the fossa for the inferior vena cava and is referred to as the midplane of the liver. Within this plane runs the middle hepatic vein.
2.4.4 Second-Order Division
The second-order division is based on the branching of either the right or the left hepatic arteries each divides into two sectional branches. Each of these sectional vessels supplies a defined volume referred to as a section and so in total there are four hepatic sections. On the right side, there is a right anterior section and a right posterior section. These sections are supplied by the right anterior sectional hepatic artery and the right posterior sectional hepatic artery. The sections are also drained by the right anterior sectional hepatic duct and the right posterior sectional hepatic duct. The plane between these sections is the right intersectional plane. Unlike the midplane and the left intersectional plane, the right intersectional plane has no markings on the hepatic surface. The left liver is divided into a left medial section and a left lateral section. These sections are supplied, respectively, by the left medial sectional hepatic artery and the left lateral sectional hepatic artery and drained by the left medial sectional hepatic duct and the left lateral sectional hepatic duct. The plane between these sections is referred to as the left intersectional plane, and it corresponds to the umbilical fissure and the line of attachment of the falciform ligament to the anterior surface of the liver.