Anatomy of the Liver

Topography of the Liver

The liver (Greek hepar ) is located in the upper part of the abdomen, where it occupies the right hypochondrium and the greater part of the epigastric regions ( Fig. 143.1 ). The left lobe of the liver extends into the left hypochondrium. The liver is the largest organ of the body and weighs an average of 1300 g (800–2400 g) in women and 1500 g (800–2600 g) in men. In healthy persons, the liver margin extending below the thoracic cage is smooth and offers little resistance to the palpating finger. Downward displacement, enlargement, hardening, and the formation of nodes or cysts produce impressive palpatory findings. Using percussion, the examiner must consider that the lungs overlie the upper portion of the liver and that the liver, in turn, overlies the intestines and the stomach.

The projections of the liver on the body surface have added significance with liver biopsy. The projections vary depending on patient position and body build, especially the configuration of the thorax. The liver lies close to the diaphragm, and the upper pole of the right lobe projects as far as the level of the fourth intercostal space or the fifth rib; the highest point is 1 cm below the nipple, near the lateral body line. The upper limit of the left lobe projects to the upper border of the sixth rib. Here, the left tip of the liver is close to the diaphragm.

The ribs cover the greater part of the liver's right lobe, whereas a small part of its anterior surface is in contact with the anterior abdominal wall. In the erect position, the liver extends downward to the 10th or 11th rib in the right midaxillary line. Here the pleura projects down to the 10th rib, and the lung projects down to the 8th rib. The anterior margin of the liver crosses the costal arch in the right lateral body line, approximately on the level of the pylorus (transpyloric line). In the epigastrium, the thoracic cage does not cover the liver. It extends approximately three fingers below the base of the xiphoid process in the midline. Part of the left lobe is covered again by the rib cage.

Over the upper third of the right half of the liver, percussion indicates a dull zone, because here the diaphragm, pleura, and lung overlie the liver. Over the middle portion, percussion results in a flat tone. Over the lowest third of the liver, a flat tone is usually heard as well except that sometimes intestinal resonance is produced by gas-filled intestinal loops. The border between dullness and flatness moves on respiration and is altered by enlargement or displacement of the liver and by conditions within the thoracic cage, which change the percussive qualities of the thoracic organs. In the horizontal position, the projection of the liver moves a little upward, and the area of flatness appears slightly enlarged. Measurement of the span of the flat sound, best percussed in the horizontal position, allows an assessment of the size of the liver.

Projections of the liver are altered in some liver diseases (e.g., tumor infiltration, cirrhosis, syphilitic hepar lobatum) by displacement of the liver or, more often, by thoracic conditions pushing the liver downward. Subphrenic abscesses, depending on their location and size, also displace the liver downward. Ascites, excessive dilatation of the colon, and abdominal tumors may push the liver upward, and retroperitoneal tumors may move it forward. Kyphoscoliosis or “barrel chest” alters the position of the liver. In some patients, the liver is abnormally movable (hepatoptosis), causing peculiar palpatory findings.

Surfaces and Bed of the Liver

The liver is pyramid shaped, and its apex is formed by the thin, flattened left extremity of the left lobe ( Fig. 143.2 ). Its base is seated on the right lateral surface, which rests on the diaphragm and on the right thoracic cage, producing the costal impressions on this surface. Its sides are formed by the anterior, posterior, and inferior surfaces. The border between the anterior and inferior surfaces is the anterior margin. The liver's consistency, sharpness of edge, smoothness of surface, and movement on respiration provide clinical information. On laparotomy, the anterior margin and anterior surface are first exposed. Otherwise the hepatic surfaces are not separated by distinct margins.

The liver is covered by peritoneum except for the gallbladder bed, the hilus, adjacent parts surrounding the inferior vena cava (IVC), and a space to the right of the IVC called the bare area, which is in contact with the right adrenal gland (adrenal impression) and the right kidney (renal impression). Peritoneal duplications, which extend from the anterior abdominal wall and the diaphragm to the organ, form the ligaments of the liver. Although the ligaments were previously believed to maintain the liver in its position, they probably add little to its fixation, as the liver is likely kept in place by intraabdominal pressure.

The horizontal peritoneal duplication is the coronary ligament, the upper layer of which is exposed if the liver is pulled away from the diaphragm. The free right lateral margin of the coronary ligaments forms the right triangular ligament, whereas the left triangular ligament surrounds and merges with the left tip of the liver, the appendix fibrosa hepatis (fibrous appendix of liver). Over the right lobe, the space between the upper and lower layers of the coronary ligament is filled with areolar connective tissue. Below the insertion of the lower layer of the right coronary ligament, the hepatorenal space extends behind the liver.

From the middle portion of the coronary ligament originates another peritoneal duplication, the falciform ligament, which extends from the liver to the anterior abdominal wall between the diaphragm and the umbilicus. Its insertion on the liver divides the organ into a right lobe and a left lobe. The inferior edge of the falciform ligament is enforced to form the round ligament (ligamentum teres), which extends to a point at which the longitudinal fissure of the liver crosses the inferior surface. With its anterior part, this fissure separates the quadrate lobe and the left lobe (tuber omentale) and forms a fossa for the umbilical vein or its remnant. The fissure proceeds toward the posterior surface, creating the fossa for the ductus venosus ( ligamentum venosum in adult life). The two fossae may be regarded as the right limb of an H -shaped pattern, characteristic of the inferior surface of the liver. The left limb is formed by the gallbladder bed and the fossa for the IVC. The horizontal limb is marked by the porta hepatis, which contains the common hepatic duct, hepatic artery, portal vein, lymphatics, and nerves.

The quadrate lobe, between the gallbladder and the fossa for the umbilical vein, is in contact with the pylorus and the first portion of the duodenum (duodenal impression). On the inferior and posterior surfaces lies the caudate lobe, between the fossa for the ligamentum venosum and the IVC; its anterior projection is the papillary process.

The inferior surface of the liver reveals further impressions of the organs it contacts, including the colon and right kidney (right lobe), and the esophagus and stomach (left lobe). The superior surface is related to the diaphragm and forms the domes of the liver.

Lesser Omentum and Variations in Form of the Liver

If the anterior margin of the liver is lifted, the lesser omentum is exposed. It represents a peritoneal fold that extends from the first portion of the duodenum, lesser curvature of the stomach, and diaphragm, to the liver, where the fold inserts at the fossa of the ligamentum venosum and continues to the porta hepatis ( Fig. 143.3 ). There, the layers are separated to accommodate the structures running to and from the hilus of the liver.

On the free right edge of the lesser omentum, the reunited peritoneal layers are enforced to form the hepatoduodenal ligament. The anterior boundary of the omental foramen (foramen of Winslow, epiploic foramen) is the entrance to the lesser abdominal cavity. The posterior wall of this cavity is formed by the IVC and the caudate lobe of the liver.

Near the right margin of the lesser omentum is the common bile duct (CBD), which divides into the cystic and common hepatic ducts. To the left of the CBD lies the hepatic artery, and behind both is the portal vein. The nerves and lymph vessels of the liver accompany these structures. The hilus of the liver is anteriorly limited by the quadrate lobe and posteriorly by the caudate lobe. On the right side of the hilus, the right and left hepatic ducts branch from the main hepatic duct and enter the liver. To the left of the ducts, the hepatic artery enters the liver behind the ductal branches. The forking portal vein enters posteriorly to the ductal and arterial ramifications.

The shape of the liver varies. Its great regenerative capacity and tissue plasticity permit a wide variety of forms, depending in part on pressure exerted by neighboring organs and on disease processes or vascular alterations. A greatly reduced left lobe is offset by an enlarged right lobe, which reveals conspicuous and deep costal impressions. Occasionally the left lobe is completely atrophic (see Fig. 143.3 ), with a wrinkled and thickened capsule and, microscopically, an impressive approximation of the portal triads, with almost no lobular parenchyma between them.

Vascular aberrations include partial obstruction of the lumen of the left branch of the portal vein by a dilated left hepatic duct or bile duct obstruction, considered the result of local nutritional deficiency, especially because the nutritional condition of the left lobe initially is poor. In other situations, associated with a transverse position of the liver, the left lobe is unduly large.

In previous centuries, the liver was frequently disfigured by laced corsets or tight belts or straps. Such physical forces may flatten and elongate the liver from above downward, with a reduction of the superior diaphragmatic surface and sometimes with tonguelike extension of the right lobe (see Fig. 143.3 ). In other cases, the corset liver is displaced and the renal impression is exaggerated. Clinical symptoms such as dyspepsia, cholelithiasis, and chlorosis have been ascribed to the corset liver, although these associations remain unproven.

Indentations on the liver produced by the ribs, diaphragmatic insertions, and costal arch are normal. In kyphoscoliosis, the rib insertions may be prominent. Parallel sagittal furrows on the hepatic convexity have been designated diaphragmatic grooves.

Functionally, none of these variations is currently considered significant.