Formation and main roots of the portal vein
The anatomical formation of the portal vein trunk occurs in a strictly defined zone — behind the head of the pancreas. It is in this area that two large venous vessels, referred to in topographic anatomy as the roots of the portal vein, merge. These main roots include:
- Superior mesenteric vein (v. mesenterica superior).
- Splenic vein (v. lienalis).
During the formation of this extensive venous system, special attention is paid to the inferior mesenteric vein (v. mesenterica inferior). Its topography of termination shows high variability. In the majority of clinical cases, the inferior mesenteric vein empties directly into the splenic vein. However, anatomical variants are often encountered where this vessel flows into the superior mesenteric vein or takes a direct part in the formation of the main portal vein trunk by emptying right at the junction of the two main roots.
Direct tributaries to the main trunk
In addition to the main roots that form the vessel, a number of additional vessels empty into the already formed trunk of the portal vein on its path to the liver. The direct tributaries of the portal vein include:
- Superior pancreaticoduodenal vein (v. pancreaticoduodenalis superior).
- Prepyloric vein (v. prepylorica).
- Right and left gastric veins (vv. gastricae dextra et sinistra).
An important anatomical feature should be noted: the left gastric vein does not always empty directly into the trunk. Quite often, this vessel flows into the splenic vein, which surgeons must consider during surgical interventions on abdominal organs, particularly the stomach and spleen themselves.
Topography, syntopy, and clinical significance
The topography of the portal vein is characterized by a close relationship with surrounding structures. As noted earlier, the vein is located behind the head of the pancreas, although in some cases the vessel may pass directly within the parenchyma of this gland. This spatial relationship is of great clinical significance: when tumors of the head of the pancreas develop, mechanical compression of the venous trunk occurs. This inevitably leads to impaired normal blood flow and the rapid development of portal hypertension.
The further course of the portal vein trunk (total length ranging from 2 to 8 cm) runs behind the duodenum. Having passed the duodenum, the vessel enters the thickness of the hepatoduodenal ligament. Within this important surgical ligament, the elements are arranged in a strict sequence: the portal vein is located posterior to the hepatic artery and common bile duct.
Approaching the liver, at a distance of approximately 1.0–1.5 centimeters from the porta hepatis, the main venous trunk bifurcates. It divides into two large branches: the right and left lobar portal veins (vv. portae lobares dextra et sinistra).
Role of the umbilical vein in the system
When studying the portal vein system in detail, special attention is deserved by the anatomy of the umbilical vein (v. umbilicalis). In the process of human development, this vessel completely obliterates (i.e., becomes overgrown with connective tissue) only in the immediate vicinity of the umbilical ring. Along the rest of its length, the umbilical vein, which runs within the round ligament of the liver, maintains its natural lumen.
This lumen extends up to the site of confluence with the left lobar portal vein. The patency of this segment is of colossal clinical and practical significance. Specialists actively use the patent segment of the umbilical vein for X-ray vasography (portography) — a special contrast study of the portal vein system, as well as for targeted intravascular administration of medications directly into the hepatic vascular bed.
Briefly: answers to topical questions
What are the length and diameter of the portal vein trunk?
The length of the portal vein trunk ranges from 2 to 8 cm. The trunk is formed behind the head of the pancreas and heads into the thickness of the hepatoduodenal ligament. At a distance of 1.0–1.5 cm from the porta hepatis, the vein bifurcates into the right and left lobar branches.
From which specific abdominal organs does the portal vein collect blood?
The portal vein collects venous blood from all unpaired abdominal organs. Through its roots and tributaries, it drains the following structures:
- Small intestine — along with the cecum, appendix, ascending colon, and 2/3 of the transverse colon (via the superior mesenteric vein, v. mesenterica superior).
- Large intestine — descending colon, sigmoid colon, and upper rectum (via the inferior mesenteric vein, v. mesenterica inferior).
- Stomach — via the left and right gastric veins.
- Spleen — via the splenic vein (v. lienalis).
Where are portosystemic anastomoses located?
Portosystemic anastomoses are located in four main areas, ensuring collateral blood outflow from the portal vein system. The following localizations are distinguished:
- Umbilical anastomosis — on the anterior abdominal wall in the umbilicus region.
- Esophageal anastomosis — in the cardiac part of the stomach and the lower third of the esophagus.
- Rectal anastomosis — in the rectal venous plexus (plexus venosus rectalis).
- Retroperitoneal anastomoses (Retzius system) — in the retroperitoneal space on the posterior abdominal wall.
What methods and accesses exist for performing portography?
To perform portography (X-ray vasography), access through the umbilical vein (v. umbilicalis) is used. This vein obliterates only near the umbilical ring, while along the rest of its course it runs in the round ligament of the liver, preserving its lumen. The umbilical vein empties directly into the left lobar portal vein, making it a convenient anatomical access for administering contrast agents during X-ray examination of the portal vascular system, as well as for targeted drug administration.
Class and exam questions
What is the main function of the portal vein in the body?
The main function of this large vessel is that it collects and brings venous blood from all unpaired abdominal organs, delivering it to the liver.
Where exactly does the anatomical formation of the portal vein trunk take place?
The formation of the venous trunk occurs behind the head of the pancreas as a result of the fusion of its two main roots: the superior mesenteric and splenic veins.
What are the variants of termination of the inferior mesenteric vein?
Most often it empties into the splenic vein, but in some cases it may flow into the superior mesenteric vein or directly participate in the formation of the portal vein trunk.
How is the anatomy of the umbilical vein used by surgeons?
Since the umbilical vein maintains its lumen in the round ligament of the liver, it is used in clinical practice for portography and drug administration.
What else to study on this topic
- Variants of the anatomical termination of the inferior mesenteric vein and their frequency.
- Mechanism of portal hypertension development in pancreatic tumor lesions.
- Detailed syntopy of the portal vein, common bile duct, and hepatic artery.
- Features of the confluence of gastric veins and their clinical significance.
- Technique of using the umbilical vein for X-ray vasography.
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