Hepatic Segments: What are they? Anatomy, Function, Falciform Ligament and Cantle Line

The liver, an organ only found in vertebrates, detoxifies several metabolites, synthesizes proteins, and produces biochemical compounds necessary for digestion.

Anatomy and function

In humans, it is found in the upper right quadrant of the abdomen, below the diaphragm. Its other roles in metabolism include regulating glycogen storage, the breakdown of red blood cells, and the production of hormones.

The liver is an accessory digestive gland that produces bile, an alkaline compound that helps break down fat. Bile helps digestion through the emulsification of lipids.

The gallbladder, a small pouch just below the liver, stores the bile produced by the liver.

The highly specialized tissue of the liver, composed mainly of hepatocytes, regulates a wide variety of large-volume biochemical reactions, including the synthesis and decomposition of small and complex molecules, many of which are necessary for everyday life functions.

Estimates about the total number of organ functions vary, but textbooks generally cite about 500.

Terminology related to the liver often begins in heat- ἡπατο-, the Greek word for liver.

 

There is no way to compensate for the lack of long-term liver function, although liver dialysis techniques can be used in the short term.

Artificial livers have not yet been developed to promote long-term replacement in the absence of the liver. As of 2017, liver transplantation is the only option for complete liver failure.

In the widely used Couinaud (or “French”) system of the anatomy of the liver, the functional lobes are divided into a total of eight available independent units (called segments) based on a transverse plane through the bifurcation of the central portal vein.

The system is named after Claude Couinaud; it extends from the middle of the anterior bladder fossa to the inferior vena cava posteriorly. This anatomical division was first described by the French surgeon Claude Couinaud in 1957.

The notion that the hepatic segments of Couinaud are based in the administrative districts of Paris is an urban radiological myth 4, but it is still brilliant.

Instead of relying on the traditional morphological description based on the external appearance of the liver. The segments are numbered in Roman numerals I to VIII.

Each segment can be visualized as a wedge with the apex directed towards the hepatic hilum (porta hepatis).

At the apex, a single segmental branch of the portal vein, the hepatic artery, and the bile duct enter; At the same time, along the boundaries of each segment, there is a venous flow through the hepatic veins so that one hepatic vein drains two adjacent parts (and each piece has multiple draining hepatic veins).

The liver is divided into two parts: a right lobe and a left lobe, seen from the frontal surface (diaphragmatic), but the lower part (the visceral feeling) shows that it divides into four lobes and includes the caudate and square lobes.

The falciform ligament, visible in the frontal part of the liver, divides the liver into a left and a much larger right lobe. The two additional lobes are located between the right and left lobes, facing each other from the visceral surface.

You can imagine a line that extends from the left vena cava and all the way forward to divide the liver and gallbladder into two halves. This line is called the ” Cantlie line. “

Other anatomical reference points, such as the ligamentum venosum and the round ligament of the liver (ligamentum teres), also divide the left side of the liver into two sections.

A crucial anatomical milestone, the hepatic portal, also known as the transverse fissure of the liver, divides this left portion into four segments, which can be numbered starting at the caudate lobe as counterclockwise.

Seven segments can be seen from this parietal view because the eighth segment is only visible in visceral opinion.

Segments

Each segment has its vascular flow, outflow, and biliary drainage. In the center of each piece, there is a branch of the portal vein, the hepatic artery, and the bile duct. There is a vascular outlet at the periphery of each segment through the hepatic veins.

The four lobes of the liver:

  • Left lobe of the liver.
  • The right lobe of the liver.
  • The square lobe of the liver.
  • The caudal lobe of the liver.

The division of the liver into separate units means that the segments can be resected without damaging the remaining parts. To preserve the viability of the liver after surgery, resections follow the vessels that define the peripheries of each segment.

The resection lines parallel the hepatic veins, leaving portal veins, bile ducts, and hepatic arteries intact.

The classification system uses the vascular supply in the liver to separate the functional units (numbered from I to VIII):

  • I am caudad.
  • II: upper subsegment of the side segment.
  • III: lower subsegment of the lateral segment.
  • IVa: subsegment superior to the medial segment.
  • IVb: lower subsegment of the medial segment.
  • V: bottom subsegment of the previous segment.
  • VI: lower subsegment of the back segment.
  • VII: Subsequent subset of the last segment.
  • VIII: superior subsegment of the anterior segment.

Left lobe

The left lobe is smaller and flatter than the right. It is located in the epigastric and left hypochondriac regions.

Its upper surface is slightly convex and is molded in the diaphragm; its inferior surface presents the gastric impression and the omental tuberosity.

The left hepatic vein divides the left lobe into lateral and medial segments.

Right lobe

The units V to VIII constitute the right part of the liver:

  • Unit V is the most medial and inferior.
  • Unit VI is later.
  • Unit VII is located above unit VI.
  • Unit VIII sits on unit V in the superior-medial position.

The right lobe is much larger than the left; their ratio is from six to one.

It occupies the right hypochondrium; on its posterior surface by the venous ligament for the cranial half (upper) and the round hepatic ligament (also known as the round ligament of the liver) for the caudal half (below).

The round hepatic ligament rotates around the inferior marking of the liver to exit ventrally in the falciform ligament.

The middle hepatic vein functionally separates the right lobe from the left lobe. A common misconception is that the falciform ligament separates the two lobes.

However, from a functional perspective (one that considers venous arterial, portal venous, and systemic venous), the falciform ligament separates the medial and lateral segments of the left hepatic lobe.

The right lobe is a somewhat quadrilateral shape. Three fossils mark its lower and posterior surfaces:

  • The fossa for the portal vein
  • The pit for the gallbladder
  • The graves for the inferior vena cava

These separate the right lobe into two smaller lobes on its left posterior part: the square and caudate.

Square lobe

The square lobe is an area of ​​the lever located on the lower surface of the left lobe of the medial segment (segment IV of Couinaud).

It is delimited ahead by the anterior margin of the liver; behind the hepatitis porta; to the right, through the pit for the gallbladder; and to the left, through the umbilical vein pit. It is oblong; its anteroposterior diameter is more significant than its transversal.

Caudate lobe

Unit I is the caudate lobe located further back and can receive its supply from the right and left branches of the portal vein. It contains one or more hepatic veins that drain directly into the inferior vena cava.

The rest of the units (II to VIII) are numbered in a clockwise direction:

  • Units II and III are medial to the falciform ligament, with II superior to the portal venous supply and lower III.
  • Unit IV lies lateral to the falciform ligament and is subdivided into IVa (excellent) and IVb (inferior).

The caudate lobe (posterior hepatic segment I, Spigelian lobe) is located on the posterosuperior surface of the liver in the right lobe of the liver, in front of the tenth and eleventh thoracic vertebrae.

The caudate lobe of the liver is delimited below by the hepatic portal; to the right, through the pit of the inferior vena cava; and, to the left, by the fossa for the venous ductus, the physiological division of the liver called ligamentum venosum.

It is located behind the porta and separates the pit for the gallbladder from the beginning of the fossa for the inferior vena cava.

The Budd-Chiari syndrome, caused by the occlusion of the hepatic venous flow, can lead to the hypertrophy of the caudate lobe due to its cava anastomosis that allows the continuous functioning of this hepatic lobe.

The caudate lobe is named after the hepatic caudate process of the liver tissue in tail cauda, ​​which provides superficial continuity between the caudate lobe and the visceral surface of the right lobe of the liver.

The caudate process is a slight elevation of the hepatic substance that extends obliquely and laterally from the lower extremity of the caudate lobe to the lower surface of the right lobe.

Sickle ligament

The left hepatic vein is slight to the left of the left hepatic vein; therefore, the falciform ligament roughly divides the liver into the right and left lobes.

Cantle line

It extends from the middle of the anterior bladder fossa to the inferior vena cava posteriorly.