Splenic vein

The splenic vein (vena lienalis) is a major visceral tributary of the portal venous system, responsible for draining blood from the spleen and adjacent abdominal structures. It typically emerges from the hilus of the spleen and courses medially to join the portal vein, frequently after uniting with the cranial mesenteric vein and the caudal mesenteric vein, forming what is sometimes termed the portal confluence.

Origin and Course

In most domestic species, the splenic vein is formed by the convergence of trabecular veins within the splenic parenchyma. It exits the hilus of the spleen on the visceral surface and runs cranially or craniodorsally across the dorsal abdominal wall, lying dorsomedial to the left kidney and ventral to the left crus of the diaphragm, often in close proximity to the pancreas, particularly its left lobe.

As it courses medially, it may run within or adjacent to the greater omentum and passes dorsal to the stomach in ruminants, while in carnivores and pigs, it lies more distinctly in relation to the pancreas and gastrosplenic ligament.

Tributaries

The splenic vein receives several tributaries depending on the species and the development of the adjacent vascular networks. Common tributaries include:

• Short gastric veins: Drain the fundus and greater curvature of the stomach.

• Left gastroepiploic vein: Courses along the greater curvature of the stomach, draining into the splenic vein after receiving veins from the omentum and stomach.

• Pancreatic veins: These may drain directly into the splenic vein, particularly from the left lobe of the pancreas.

• Caudal mesenteric vein (in some species like the horse and pig): This may join the splenic vein or may independently merge with the portal trunk.

• Omental branches: Especially in ruminants, due to the extensive development of the omenta.

Termination

The splenic vein typically terminates by joining the portal vein, often at a point where the cranial mesenteric vein also enters. This union generally occurs near the portal fissure of the liver, caudal to the pancreas. In some species, the splenic and cranial mesenteric veins form a common trunk before entering the portal vein.

Species Variations

• Dog & Cat: The splenic vein courses dorsally from the spleen and joins the cranial mesenteric vein to form the portal vein near the pancreas.

• Ox & Sheep: It receives the left ruminal and reticular veins, reflecting the extensive venous drainage from the fore-stomachs.

• Horse: The caudal mesenteric vein usually joins the splenic vein; the splenic vein runs in the mesojejunum alongside the mesenteric veins.

• Pig: The splenic vein is particularly short, with the caudal mesenteric vein often joining it early before it merges with the cranial mesenteric vein.