Portal Venous System: Anatomy, Tributaries, and Portal Hypertension

Overview

The portal venous system is a unique venous network that carries nutrient-rich (but partially deoxygenated) blood from the gastrointestinal tract, spleen, and pancreas to the liver for processing. This is the only part of the systemic circulation that lies between two capillary beds — the gut capillaries and the hepatic sinusoids.

Formation of the Portal Vein

The portal vein is formed posterior to the neck of the pancreas by the union of:

1. Splenic vein (drains spleen, pancreas, stomach)
2. Superior mesenteric vein (SMV) (drains small intestine, cecum, ascending and transverse colon)

It ascends behind the pancreas, enters the lesser omentum, and reaches the porta hepatis, where it divides into right and left branches.

Length: ~8 cm

Tributaries of the Portal Vein

1. Splenic vein (often considered the main contributor to formation)
2. Superior mesenteric vein (SMV)
3. Inferior mesenteric vein (IMV): Usually drains into the splenic vein (most common pattern)
4. Left gastric (coronary) vein: Drains the lesser curvature of the stomach; anastomoses with esophageal veins
5. Right gastric vein: Drains the pyloric region
6. Cystic vein: From gallbladder
7. Para-umbilical veins: In the falciform ligament

Portocaval Anastomoses (Sites of Collateral Circulation)

In portal hypertension, blood is shunted around the liver through these anastomoses, causing varices:

Site	Portal Vein → Systemic Vein	Clinical Result
Lower esophagus	Left gastric → esophageal veins of azygos	Esophageal varices (hematemesis)
Rectum	Superior rectal → middle/inferior rectal	Hemorrhoids (rectal varices)
Umbilical region	Para-umbilical → epigastric veins of anterior abdominal wall	Caput medusae (radiating abdominal veins)
Retroperitoneal	Colic veins → renal/retroperitoneal veins	Usually asymptomatic