General characteristics of the portal vein
The portal vein (vena portae) is a large venous trunk that collects blood from the unpaired abdominal organs: the stomach, small and large intestines, spleen, and pancreas. Functionally, the portal venous system is the venous counterpart of the celiac trunk: just as the arterial blood supply to the digestive organs is provided by the celiac trunk and mesenteric arteries, venous drainage from these same organs occurs through the vena portae system.
The fundamental difference between the portal vein and other veins is that it does not drain directly into the inferior vena cava, but instead leads to the liver, where it divides into right and left branches and further into a capillary network of sinusoids. The liver acts as a biological filter where the blood undergoes detoxification. After passing through the liver parenchyma, the blood collects into 3–4 venae hepaticae that empty into the vena cava inferior.
Superior mesenteric vein
The superior mesenteric vein is one of the main roots of the portal vein. Its basin corresponds to the supply area of the artery of the same name and encompasses the jejunum and ileum, the ascending and transverse colon, part of the stomach, the greater omentum, and the pancreas.
Tributaries of the superior mesenteric vein:
- venae jejunales et ileales — jejunal and ileal veins, which form characteristic venous arcades;
- vena pancreaticoduodenalis — pancreaticoduodenal vein;
- vena pancreatica — pancreatic vein;
- venae colicae dextra et media — right and middle colic veins;
- vena ileocolica with vena appendicularis — ileocolic vein and appendicular vein;
- vena gastroomentalis dextra — right gastro-omental vein.
Splenic vein
The splenic vein (vena lienalis / splenica) accompanies the artery of the same name and empties into the portal vein by merging with the superior mesenteric vein posterior to the head of the pancreas. It has a relatively small number of tributaries, making them easier to memorize.
Main tributaries:
- venae pancreaticae — pancreatic veins;
- venae gastricae breves — short gastric veins;
- vena gastroomentalis sinistra — left gastro-omental vein, anastomosing with the right gastro-omental vein.
Inferior mesenteric vein
The inferior mesenteric vein collects blood from the descending colon, sigmoid colon, and upper rectum. Unlike the artery of the same name, which branches directly off the aorta, the inferior mesenteric vein has two termination variants: more commonly it empties into the splenic vein, and less frequently directly into the superior mesenteric vein or at their confluence angle.
Roots of the inferior mesenteric vein:
- vena rectalis superior — superior rectal vein;
- vena colica sinistra — left colic vein;
- venae sigmoideae — sigmoid veins.
Direct tributaries of the portal vein
In addition to the three large roots, the vena portae trunk receives direct tributaries:
- vena cystica — cystic vein;
- venae gastricae dextra et sinistra — right and left gastric veins, anastomosing with the esophageal veins;
- vena prepylorica — prepyloric vein;
- venae paraumbilicales — paraumbilical veins, running in the round ligament of the liver.
Portacaval anastomoses
Clinically significant portacaval anastomoses exist between the portal venous system and the superior and inferior vena cava systems. The main ones are:
- Esophageal anastomosis — between the left gastric vein (v. portae) and the esophageal veins draining into the azygos vein (v. cava superior);
- Rectal anastomosis — between the superior rectal vein (v. portae) and the middle/inferior rectal veins (v. cava inferior);
- Paraumbilical anastomosis — between the paraumbilical veins and the vv. epigastricae superior et inferior, forming a connection among all three venous systems (cava-cava-portal).
Clinical significance
In liver cirrhosis, the destruction of the parenchyma and restructuring of the vascular bed lead to increased pressure in the portal venous system, resulting in portal hypertension. As a result, blood is shunted through collateral pathways via portacaval anastomoses, which normally function very little.
Clinical manifestations:
- Esophageal varices resulting from blood shunting through the esophageal anastomosis; dangerous due to massive gastroesophageal bleeding with high mortality;
- Caput medusae (caput medusae) — dilation of the subcutaneous veins of the anterior abdominal wall due to the opening of the paraumbilical anastomosis;
- Hemorrhoidal dilation of the rectal veins during shunting through the rectal anastomosis.
Key points
- Vena portae is formed by the union of the superior mesenteric and splenic veins; the inferior mesenteric vein most commonly empties into the splenic vein.
- The portal vein collects blood from the unpaired abdominal organs and delivers it to the liver for detoxification.
- The tributaries of the superior mesenteric vein mirror the branching of the artery of the same name.
- The splenic vein has three main tributaries: pancreatic, short gastric, and left gastro-omental veins.
- The cystic, gastric, and paraumbilical veins drain directly into the portal vein trunk.
- There are three key portacaval anastomoses: esophageal, rectal, and paraumbilical.
- In portal hypertension, these anastomoses dilate, forming esophageal varices, caput medusae, and hemorrhoids.
- Knowledge of these anastomoses is of fundamental clinical importance and essential for understanding the complications of liver cirrhosis.