Gross Anatomy

The adult liver weighs from 1200 to 1800 g, dependent on the overall body size, takes up the majority of the right upper abdominal cavity beneath the rib cage, and extends from the right lateral aspect of the abdomen 15–20 cm transversely toward the xiphoid process. Although the weight of the adult liver constitutes about 1.8–3.1% of the total body weight, at birth the liver is larger compared with adjacent thoracic and abdominal viscera and constitutes about 5–6% of the body weight. Anatomically, the liver has four lobes: right, left, caudate, and quadrate. The right lobe accounts for one-half to two-thirds of the total liver volume and is divided from the left lobe by the falciform ligament on gross inspection; however, functionally the right and left lobes are of about equal size and are divided by a line extending from the inferior vena cava superiorly to the middle of the gallbladder fossa inferiorly. A total of eight functional segments are present, each having its own vascular supply and biliary drainage: the right posterolateral (VI and VII), right anterolateral (V and VIII), left anterior (IV), left posterior (II and III), and the caudate lobe (I), the latter being a watershed area of both the right and left lobes blood supply (Figure 1.2).

The portal vein, which is the main route of vascular drainage of the gastrointestinal tract, is formed by merger of the superior mesenteric and splenic veins, with additional blood supply from the coronary and cystic veins. The portal vein divides at the porta hepatis into the right and left main branches. The right branch divides early into anterior and posterior segments, while the left branch divides into the pars transversus, which extends to the left in the porta hepatis, and the pars umbilicus, which descends into the umbilical fossa. The caudate lobe veins arise from both the right and left main portal vein branches. The hepatic vein is composed of three major tributaries: right, middle, and left. The middle and left hepatic veins often converge to form a single outflow vessel before draining into the inferior vena cava, while the right hepatic vein opens through a separate ostium. The caudate lobe drains directly into the inferior vena cava. The hepatic artery is a branch of the celiac artery and ascends along the hepatoduodenal ligament, eventually dividing into the right and left main branches. The right hepatic artery, usually located behind the common hepatic duct after giving rise to the cystic artery, eventually divides into the anterior and posterior branches. The left hepatic artery passes obliquely upward and to the left in the porta hepatis, eventually dividing into the medial and lateral branches. The quadrate lobe is fed by a branch of the middle hepatic artery, while the caudate lobe is fed by both right and left hepatic artery branches. The biliary system originally arises from the bile canaliculi within the hepatic lobule and is first seen on gross inspection in the larger interlobular branches. The biliary drainage of the right lobe is derived from anterior and posterior segmental branches that merge to form the right hepatic duct, while the lateral and medial segmental branches merge to form the left hepatic duct that drains the left lobe. The caudate lobe is drained from three duct branches directly into the right and left hepatic ducts. The smaller interlobular bile ducts do not have a wall, but the larger septal branches have a thin wall of collagen fibers. The intra- and extrahepatic bile ducts are directly fed by the hepatic artery and its anastomosing branches, which parallel the ducts as they progress through the various hepatic divisions. The lymphatic channels are divided into deep and superficial branches. The deep branches parallel the portal and hepatic vein branches, while the superficial branches arise from Glisson capsule and drain through the adjacent falciform ligament, diaphragm, esophagus, and hilar lymph nodes. The nerve supply parallels the main hepatic artery and portal vein and is divided into parasympathetic and sympathetic fibers. The nerve supply enters the hepatic hilum through both anterior and posterior routes, feeds the arteries and bile ducts through sympathetic innervation, and branches through the main portal tracts, with smaller unmyelinated branches feeding the periportal hepatocytes. Many of the nerve fibers terminate on endothelial cells lining the smallest arterioles and along Kupffer cells, stellate (fat-storing) cells, and hepatocytes.