Hepatic veins

Hepatic veins originate from the central veins of liver lobules, converging into progressively larger sublobular veins and ultimately into several main hepatic veins that drain into the caudal vena cava. They lack valves and follow an interlobar and intersegmental course, helping delineate liver segments.

• Number and Drainage Pattern: Typically, 2 to 5 main hepatic veins (often grouped as right, middle, and left) enter the caudal vena cava just caudal to the diaphragm.

• No Accompanying Arteries: Unlike portal triads, hepatic veins travel without accompanying arteries or bile ducts.

The standard terminology from the Nomina Anatomica Veterinaria only describe the 3 main hepatic veins (left, middle and high hepatic veins). An ad hoc nomenclature was then developed by some authors to clearly identify and describe all other vessels :

• Lobar hepatic vein: A vein draining a single hepatic lobe. There may be one, two or more lobar hepatic veins draining a single lobe;

• Main lobar hepatic vein: The biggest hepatic vein draining a lobe;

• Minor lobar hepatic vein: Any smaller lobar hepatic vein with the same drainage (hepatic veins) as the main lobar vein;

• Accessory lobar hepatic vein: A lobar hepatic vein having a different drainage than the main lobar hepatic vein;

• Secondary lobar hepatic vein: Any further ramification of a lobar hepatic vein.

Species-Specific Descriptions

Dog and Cat

• Three main hepatic veins are identified:

  • Right Hepatic Vein: Drains the right lateral and caudate lobes.

  • Middle Hepatic Vein: Drains the quadrate lobe and medial part of the left and right lobes.

  • Left Hepatic Vein: Drains the left medial and lateral lobes.

• The caudate process of the caudate lobe may drain directly into the caudal vena cava.

• These veins open into the vena cava in close proximity near the liver hilum (porta hepatis).

Horse

• Has a large, well-developed liver despite being a hindgut fermenter.

• Hepatic veins drain similarly to carnivores, but with more anatomical variation due to the asymmetrical liver (larger right lobe).

• The vena cava groove is prominent, and the hepatic veins often open into it directly.

Ox (Cattle)

• The liver is located entirely on the right side; hence, the major hepatic veins are asymmetrically oriented.

• Two main hepatic trunks:

  • Left Trunk: Drains the left lobe and quadrate lobe.

  • Right Trunk: Drains the right lobe and caudate process.

• The caudate process vein often enters the caudal vena cava independently.

Pig

• The liver has a more horizontal orientation, facilitating lobular identification.

• Hepatic veins show a more radiating pattern from the center of the liver.

• Drainage is generally segmental and may involve more than three veins converging on the vena cava.

Sheep and Goat

• Similar hepatic venous architecture to that of cattle.

• The caudate process vein frequently drains independently into the caudal vena cava.

• The left and right hepatic veins are often distinguishable and conform to lobar anatomy.