Portal Vein Formation
The portal vein is formed by the confluence of the splenic vein and superior mesenteric vein (Answer A).
Anatomical Formation of Portal Vein
The portal venous system plays a crucial role in liver blood supply, providing approximately three-fourths of the liver's blood supply. Understanding its formation is essential for surgical and radiological interventions.
Normal Anatomy
- The portal vein is typically formed behind the neck of pancreas, at the level of the second lumbar vertebra by the convergence of the superior mesenteric vein and splenic vein 1
- This classical formation (superior mesenteric vein + splenic vein) is considered Type I pattern and represents the predominant anatomical arrangement, occurring in approximately 82.5-90% of cases 2, 1
Anatomical Variations
- Type II variation occurs when the portal vein is formed by the confluence of superior mesenteric, splenic, and inferior mesenteric veins, seen in approximately 7.5-12.5% of cases 1, 2
- Type III variation and other less common patterns account for the remaining cases 1, 3
Clinical Significance
Understanding portal vein anatomy is critical for several clinical scenarios:
Surgical Applications
- Knowledge of portal vein formation is essential for liver surgeries including transplantation and segmentectomy 1
- During pancreaticoduodenal surgeries, awareness of these variations helps prevent surgical adverse events 3
- When performing splenectomy, understanding portal venous anatomy is crucial as portal vein thrombosis can be a postoperative complication 4
Radiological Applications
- For interventional radiologists, knowledge of portal vein formation is important when performing catheter-based interventions 2
- When tracking the portal vein during ultrasound examination, following it from the confluence of the splenic and superior mesenteric veins is a standard technique 5
- In portal hypertension assessment, understanding normal portal venous anatomy helps in identifying pathological portosystemic collaterals 6
Portal Hypertension Management
- In portal vein thrombosis, the confluence of splenic and superior mesenteric veins is a critical anatomical landmark for potential recanalization procedures 5
- When performing TIPS (Transjugular Intrahepatic Portosystemic Shunt) with portal vein recanalization, understanding the normal confluence is essential 5
- For patients with gastric varices and portal vein occlusion, knowledge of the normal portal venous system helps in planning appropriate interventions 7
Key Measurements and Characteristics
- The average length of the portal vein is approximately 50.58mm 2
- The mean length of right portal vein differs between males (2.096±0.602 cm) and females (1.706±0.297 cm) 1
- The mean length of left portal vein also shows gender differences: males (3.450±0.661 cm) and females (3.075±0.632 cm) 1
In summary, the portal vein is formed by the confluence of the splenic vein and superior mesenteric vein, with variations occurring in approximately 10-18% of the population.