PART 1: ANATOMO-PHYSIOLOGIC CONCEPT: OVERVIEW
The liver parenchyma is subdivided into segments and sectors that share common arterial, portal venous, hepatic venous, and biliary flow.
As Molmenti described, the understanding of liver anatomy has shifted from the classic, purely topographic, outside-in depiction (Figures 3-1 and 3-2) into a dynamic inside-out anato-physiologic concept with fluid boundaries.
Classic depiction of liver anatomy. (From Bourgery JM, Jacob NH. Traité Complet de L’anatomie de L’homme. In CA Delaunay, ed. Tome Cinquième. Paris, France: 1839. [Private collection of Ernesto P. Molmenti, MD, PhD, MBA.])
Classic depiction of liver anatomy. (From Bourgery JM, Jacob NH. Traité Complet de L’anatomie de L’homme. In CA, Delaunay, ed. Tome Cinquième. Paris, France: 1839. [Private collection of Ernesto P. Molmenti, MD, PhD, MBA.])
The diverticulum hepatis (liver bud) arises from the endoderm in weeks 3 to 4.
The developing liver receives blood from both portal and umbilical veins, which are connected by the left portal vein.
The veins develop first, followed by the arteries and bile ducts.
There are 3 embryologic hepatic arteries:
Left hepatic artery – originating from the left gastric artery
Middle hepatic artery – originating from the celiac trunk
Right hepatic artery – originating from the superior mesenteric artery
Usually only the middle hepatic artery persists.
Other regression patterns account for the encountered variation in arterial configurations.
The ductal system is present by the tenth week of development.
The liver produces bile by week 12.
The falciform ligament arises from the septum (mesoderm) connecting the liver and abdominal wall.
The bare surface of the liver (surface not covered by peritoneum) represents the surface of the liver that arose in contact with the diaphragm.
The following events take place at birth:
The ductus venosus closes, interrupting flow between the left umbilical and common hepatic veins. Eventually it will become the ligamentum venosus.
The extrahepatic umbilical vein closes. It will eventually become the ligamentum teres.
The liver reaches a single cell plate configuration of hepatocytes by 5 years of age.
Hepatic tissue prolongations arising from the right (Riedel lobe) or left hemilivers can present as abdominal masses.
HEPATIC DIVISIONS (FIGURES 3-3 AND 3-4)
Eight hepatic segments (although segment 9 has also been described)
Hemilivers (2 hemilivers, right and left) – supplied by first-order branches
Sectors (4 sectors, 2 on each hemiliver) – supplied by second-order branches
Segments (8 segments, ...