Liver development is a complex process involving multiple interactions between the endoderm and the mesoderm. The hepatic bud derived from the foregut endoderm gives rise to hepatoblasts that will later differentiate into hepatocytes and cholangiocytes (bile duct cells). The mesoderm provides the structural framework, blood vessels, and hematopoietic elements [1].

Cells from the liver bud migrate and intermingle with the cells and connective tissue of the mesenchyme, which provides a scaffold for the nascent hepatocytes, bile ducts, and sinusoids. Concurrently, the developing liver accommodates hematopoietic stem cells, which participate in fetal hematopoiesis and later disappear. The extrahepatic ducts share a common developmental pathway with the pancreatic ducts. The mechanism through which the intra- and extrahepatic ducts anastomose remains to be elucidated [2].

Within the liver, the elements of the portal triad (portal vein, hepatic artery, and bile duct) travel together within a fibrous sheath, which is an invagination of Glisson’s capsule. This anatomical relationship forms the basis of the modern intraglissonian approach to liver resections. The embryological development of this pattern is not well understood.

Fetal circulation presents two main shunts that are absent in the adult. These shunts reflect the substitution of pulmonary and hepatic function by the placenta. The ductus venosus allows nutrient-rich blood returning from the placenta to bypass the liver and reach the systemic circulation by communicating the left branch of the portal vein with the inferior vena cava. In the adult, the obliterated ductus venosus becomes an important landmark to dissect the left hepatic vein. The second fetal shunt is the ductus arteriosus. It connects the pulmonary artery with the aorta, allowing the majority of the oxygen-rich blood from the right heart to bypass the non-ventilated lungs of the fetus to reach the systemic circulation [3, 4].

Riedel’s lobe was first described in 1888. It is a tonguelike projection of the right lobe of the liver that may present as a palpable right upper quadrant mass. It is present in approximately 3 % of the population as a normal anatomic variant. It is not an independent liver segment; instead, it shares its portal triad elements with the adjoining liver. Riedel’s lobe may harbor benign and malignant tumors and may be susceptible to torsion requiring surgical intervention [5–7] (Fig. 16.1).

The liver is divided into eight functional segments based on the branching pattern of the portal triad (portal vein, hepatic artery, and bile duct), in conjunction with planes established by the hepatic veins. While there is some correlation with superficial anatomical landmarks, the said divisions are not dependent on them.

The first functional division of the liver dates to 1888, when Rex showed that the falciform ligament was not a true landmark for the right and left lobe of the liver. Instead, he proposed that the liver was divided into two equal-sized lobes by a plane drawn from the left border of the gallbladder to the inferior vena cava. In 1897 Cantlie confirmed this finding, and the line marking this division bears his name.

In the 1950s, Couinaud, Healy, Schroy, Goldsmith, and Woodburne proposed further division of the liver into segments defined by the branching of the portal triad. In 1982 Bismuth integrated these systems into the classification we use today, which is echoed by the Brisbane Terminology of Hepatic Anatomy and Resection published in the year 2000.

In this system, the liver is progressively divided into lobes, sectors (or sections), and segments, with the caudate lobe being an independent segment based on its supply by both the right and left portal triad and its direct venous drainage into the vena cava (Fig. 16.2).

As illustrated below, the middle hepatic vein, which courses along Cantlie’s line, divides the liver into two lobes of similar mass. Each lobe is further divided by the right and left hepatic veins into sectors. On the left, there are a lateral and a medial sector. On the right side, there are anterior and posterior sectors. Finally, the transverse fissure, which is an imaginary line drawn along the right and left portal branches, divides the liver into superior and inferior segments [8–10] (Fig. 16.3).

As mentioned earlier, there is correlation between liver segmentation and superficial anatomical landmarks. The visceral surface of the liver presents an “H”-shaped indentation that outlines the porta hepatis (gateway to the liver).

To the right of the porta hepatis, we have a line coursing through the gallbladder fossa towards the inferior vena cava. This line is named Cantlie’s line and divides the liver into a right and left lobe. To the left of the porta hepatis, there is a line formed by the fissure for the round ligament anteriorly and the fissure for the ligamentum venosum posteriorly. The crossbar between these two lines is the porta hepatis itself. At this level, the hepatic artery, portal vein, and common hepatic duct have bifurcated into their right and left branches.

Anterior to the porta hepatis, between the lines described above lies the quadrate lobe (segment IV). Behind, we find the caudate lobe (segment I). Of note, the gallbladder belongs anatomically to segment 5.

The ligamentum venosum represents obliterated ductus venosus. In the adult, it helps identify the junction of the left hepatic vein to the vena cava. This anatomical landmark is helpful during left hepatic lobectomies [9, 10] (Fig. 16.4).