How Do the Hepatic Veins Form?
The venous drainage system originates at the microscopic level within the hepatic lobule (lobulus hepaticus):
- Within the lobule, arterial and venous blood mix in hepatic sinusoids (vasa sinusoidea) located between plates of hepatocytes.
- The sinusoids drain into the central vein (v. centralis).
- Leaving the lobule, the central vein continues as the sublobular vein (v. sublobularis).
- Sublobular veins converge to form larger collecting veins.
- These collecting veins ultimately form 3–4 large trunks known as the hepatic veins (vv. hepaticae).
Main Trunks
The number of hepatic veins can vary, but anatomists typically distinguish three main trunks:
- Right hepatic vein (v. hepatica dextra) — drains the right lobe of the liver.
- Intermediate (middle) hepatic vein (v. hepatica intermedia) — drains the quadrate and caudate lobes.
- Left hepatic vein (v. hepatica sinistra) — drains the left lobe. Before termination, it connects with the ligamentum venosum (lig. venosum).
Topography and Drainage Site
The hepatic veins emerge from the liver parenchyma along its posterior border, within the groove for the inferior vena cava.
They empty into the inferior vena cava (v. cava inferior) immediately below the caval opening in the tendinous center of the diaphragm, just before the inferior vena cava enters the right atrium. The hepatic veins are the final tributaries of the inferior vena cava within the abdominal cavity.
The region where the inferior vena cava passes through the liver and receives the hepatic veins is referred to as the second (caval) hilum of the liver.
Clinical Significance
- Liver Surgery: The liver parenchyma is fragile and prone to tearing under tension; however, the vascular sheaths—particularly those of the portal and hepatic veins—hold sutures securely. The strength of these connective tissue sheaths allows surgeons to ligate the vessels during hepatic resections.
- Risk of Injury: Near the entry of the hepatic veins, the inferior vena cava forms an ampullary dilation, increasing the risk of iatrogenic injury during surgical mobilization.
- Oncology: In hepatocellular carcinoma, invasion of the major hepatic veins is a staging factor that categorizes the disease as advanced (e.g., BCLC stage C).
Fetal Circulation
During prenatal development, a portion of the blood passes through the portal system and hepatic sinusoids. This blood is collected by the hepatic veins (vv. hepaticae), which drain directly into the inferior vena cava.