The liver is situated in the right hypochondrium and epigastric region, reaching often the left hypochondrium , and is almost entirely protected by the ribcage. It is the largest internal organ in the human body. Its size when compared to the total body size is greater in the foetus than in the adult, constituting, in the former, about one eighteenth, and in the latter about one thirty-sixth of the entire body weight .

Classically, the liver is divided in to two large lobes (right and left) and two small central ones (quadrate and caudate lobes). Its external surfaces can be divided into superior, inferior and posterior. The superior surface lies under the diaphragm. The diaphragm separates it from the ribs and the costal cartilages on the lateral and posterior sides and the lungs with pleurae and the heart with the pericardium on the superior side. The superior and inferior surfaces are demarcated on the anterior side of the liver by a well-defined margin, the anterior border. This border is marked by two notches: the umbilical notch and the one where the gallbladder fundus lies. In children and women, this border projects below the ribs unlike in adult males where it generally corresponds with the lower margin of the thorax in the right mammillary line. Both intercostal and subcostal approaches for percutaneous liver biopsy are possible in children [14].

Most of the liver is covered by the visceral peritoneum, except for the ‘bare area’ on the posterior surface, which is in direct contact with the diaphragm and delimited by the coronary ligament. The porta hepatis is the entry point of the hepatic artery (to the left) and the portal vein (behind and between the duct and artery) and the exit point of the common hepatic duct (to the right). Nerves and lymphatic vessels can also be found in this region.

A few ligaments help keeping the liver in place or limit its lateral movements. The organ is connected to the diaphragm and to the anterior wall of the abdomen by five ligaments, four of which are peritoneal folds: the falciform, the coronary and two lateral (triangular) ligaments, the fifth being a fibrous cord (the round ligament) corresponding to the obliterated umbilical vein .

The subdivision of the liver into segments as proposed by Couinaud in 1957, is based on the intrahepatic distribution of the portal and hepatic veins, and is used in clinical practice, particularly in planning surgical resections. Couinaud divided the liver into two functional lobes of similar sizes, separated on the liver surface by an imaginary line going through the inferior vena cava sulcus and the middle of the gallbladder fossa. The right lobe is further divided into posterior and anterior sectors and the left lobe into medial and lateral part. Each of the two segments is separated into inferior and superior segments. Thus, eight total segments, with almost independent blood supply are formed, as follows: (I) caudate lobe, (II) superior subsegment of the left lateral segment, (III) inferior subsegment of the left lateral segment, (IV) left medial segment, (V) inferior subsegment of the right anterior segment, (VI) inferior subsegment of the right posterior segment, (VII) superior subsegment of the right posterior segment, (VIII) superior subsegment of the right anterior segment [15] .

The liver receives a dual blood supply through the portal vein and the hepatic artery. The hepatic artery in the foetal and early postnatal life is the largest branch of the celiac axis, its calibre decreasing with age to an intermediate size artery in adults. At the porta hepatis, it divides into a right and a left hepatic artery. They branch out progressively to terminal hepatic arterioles, which communicate with the hepatic sinusoids. The hepatic artery provides the blood supply to the biliary tree through a peribiliary plexus and forms a perivenous plexus around the portal vein branches. Hepatic artery thrombosis can cause ischemic necrosis of the biliary tree due to its dependence on the arterial supply. The portal vein drains the blood from most of the gut, and it is formed at the level of the second lumbar vertebra by the confluence of the superior mesenteric vein, inferior mesenteric vein and splenic vein. It enters the liver through the porta hepatis and subdivides into right and left branches and then progressively down to the terminal portal venules and inlet venules to open into the sinusoids. The sinusoidal blood drains into the centrilobular venules, and eventually through the hepatic veins into the inferior vena cava. Segments II, III and IV are drained by the left hepatic vein, the middle hepatic vein gathering blood from segments IV, V and VIII, while the right hepatic vein serves segments V–VIII. One small inferior hepatic vein drains the caudate lobe (segment I) directly into the inferior vena cava. Liver biopsy through the transjugular route is an established procedure to sample liver parenchyma via the hepatic veins [16].