This note describes the formation, tributaries and major site for the portocaval anastomosis (also called portosystemic anastomosis or portal-systemic anastomosis).

Portal Vein
The portal vein is the vein of the gut that drains blood from the abdominal part of the gastrointestinal tract from the lower third of esophagus to halfway down the anal canal including spleen, pancreas and gall bladder.

It is about 2 inches long and formed by the union of superior mesenteric vein and splenic vein behind the neck of the pancreas. It ascends to the right behind the first part of the duodenum and enters the free margin of the lesser omentum. Entering through the porta hepatis, it divides into right and left terminal branches which further break up into sinusoids. The blood from the sinusoids is collected by hepatic veins that join the inferior vena cava.

The tributaries of the portal vein are:
Splenic and superior mesenteric veins - the formative tributaries
Left gastric,
Rright gastric and
Cystic veins

Portocaval or Portosystemic anastomosis

Under normal conditions, the portal venous blood traverses the liver and drains into the inferior vena cava of the systemic venous circulation through the hepatic veins. This is the direct route. However, other, smaller communications exist between the portal and systemic systems, and they become important when the direct route becomes blocked.

These communications are as follows:

1.     At the lower third of the esophagus, the esophageal branches of the left gastric vein (portal tributary) anastomose with the esophageal veins draining the middle third of the esophagus into the azygos veins (systemic tributary).

2.     Halfway down the anal canal , the superior rectal veins (portal tributary) draining the upper half of the anal canal anastomose with the middle and inferior rectal veins (systemic tributaries), which are tributaries of the internal iliac and internal pudendal veins, respectively.

3.     The paraumbilical veins connect the left branch of the portal vein with the superficial veins of the anterior abdominal wall (systemic tributaries).

4.     The veins of the ascending colon, descending colon, duodenum, pancreas, and liver (portal tributary) anastomose with the renal, lumbar, and phrenic veins (systemic tributaries).

Following resources are used while preparing this post (readers are strongly recommended to go through them for more details):

R. Snell's Clinical Anatomy
K. L. Moore's Clinically Oriented Anatomy