Portacaval and cavacaval anastomoses

Why venous anastomoses are needed

The anatomy of the circulatory system provides for collateral pathways in case of impaired normal blood flow. The venous bed of the torso has three main basins: the superior vena cava (v. cava superior), the inferior vena cava (v. cava inferior), and the hepatic portal vein (v. portae hepatis).

Connections between these major pathways are called anastomoses. Normally, they are inconspicuous, but if outflow through the liver or toward the heart is hindered (e.g., in cirrhosis), blood rushes through these collaterals. Excessive pressure causes their pathological dilation and clinical complications.

Main portocaval anastomoses

These junctions connect the portal system with the tributaries of the venae cavae. According to anatomical nomenclature, there are four key zones of such contacts:

1. Esophageal anastomosis. Located in the cardiac part of the stomach and the lower third of the esophagus. Here, the left gastric vein and the right gastric vein (v. gastrica dextra, running along the lesser curvature) meet the esophageal veins. The latter carry blood into the azygos (v. azygos) and hemiazygos (v. hemiazygos) veins, which empty into the superior vena cava. Contact occurs via the well-developed esophageal venous plexus (plexus venosus oesophageus). When pressure increases, life-threatening esophageal varices develop here.

1. Rectal anastomosis. Localized in the wall of the rectum, forming the rectal venous plexus (plexus venosus rectalis). The superior rectal vein (v. rectalis superior), as the origin of the inferior mesenteric vein, drains blood into the portal system. The middle rectal vein (v. rectalis media) drains into the internal iliac vein, and the inferior one into the internal pudendal vein, directing blood into the inferior vena cava. The clinical manifestation of the dilation of this plexus is hemorrhoids.

1. Umbilical anastomosis. Formed on the anterior abdominal wall around the umbilicus. Paraumbilical veins (vv. paraumbilicales) run in the round ligament of the liver directly to the portal vein. They anastomose with tributaries of the superior vena cava (superior epigastric vein, v. epigastrica superior) and tributaries of the inferior vena cava (inferior and superficial epigastric veins, v. epigastrica inferior and v. epigastrica superficialis). Dilation of the subcutaneous abdominal vessels in this area is known as the «caput medusae» sign (caput medusae).

1. Retroperitoneal anastomoses (Retzius system). Located in the retroperitoneal space on the posterior abdominal wall. They provide a connection between the veins of the ascending and descending colon (portal basin) and the lumbar veins (vv. lumbales), which belong to the inferior vena cava system.

Cavacaval anastomoses

This type of junction ensures the redistribution of venous blood exclusively between the superior and inferior vena cava basins. There are several pathways for such collateral outflow:

• Via the azygos and hemiazygos vein system. Ascending lumbar veins (v. lumbalis ascendens) directly connect the iliac veins with the azygos and hemiazygos veins.
• Vertebral pathway. Implemented via the robust vertebral venous plexus (plexus venosus vertebralis).
• Deep pathway of the anterior abdominal wall. Achieved via the connection of the superior epigastric vein (tributary of v. thoracica interna) and the inferior epigastric vein.
• Superficial pathway of the torso. Subcutaneous vessels interconnect via the thoracoepigastric vein (v. thoracoepigastrica) and the superficial epigastric vein (v. epigastrica superficialis).

Class and exam questions

What else to study on this topic

• Topography and tributaries of the hepatic portal vein system
• Anatomy of the superior and inferior venae cavae
• Structure and functions of the vertebral venous plexus
• Veins of the retroperitoneal space and Retzius system
• Anatomical prerequisites for portal hypertension

Other topics in the "Angiology" section

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