Number of Main Hepatic Veins
The liver typically has three main hepatic veins (right, middle, and left) that drain into the inferior vena cava, though anatomical variations exist in approximately 35% of cases. 1
Standard Anatomy
The most common configuration consists of three separate hepatic veins that drain into the IVC:
- Right hepatic vein (median diameter 1.5 cm, range 0.8-2.7 cm) 2
- Middle hepatic vein (median diameter 1.1 cm, range 0.5-1.5 cm when separate) 2
- Left hepatic vein (median diameter 1.2 cm, range 0.7-2.6 cm) 2
This three-vein pattern is found in approximately 33% of cases. 2
Common Anatomical Variations
Two-Vein Configuration
The most frequent variation involves two main hepatic veins (right and left-middle combined), occurring in 65% of cases. 2 In this pattern, the middle and left hepatic veins share a common trunk before entering the IVC.
Absent Middle Hepatic Vein
Complete absence of the middle hepatic vein has been documented, though it is rare. 3 In such cases, only the right and left hepatic veins are present.
Four-Vein Configuration
Rarely (approximately 2% of cases), four separate main hepatic veins may be present. 2
Additional Venous Drainage
Beyond the main hepatic veins, the liver has an inferior (minor) set of hepatic veins consisting of 2 to 16 veins (median 7 veins). 2 These accessory hepatic veins are particularly important:
- Accessory hepatic veins to segments VI and VII average 2.2 per liver and always drain the dorsal portions of these segments. 4
- The inferior right hepatic vein (IRHV) drains segment 6 in 18% of cases, with sizes ranging from 0.1-0.8 cm. 5
- The middle right hepatic vein (MRHV) drains segment 5 in 5.5% of cases, with sizes ranging from 0.1-0.9 cm. 5
Clinical Significance
Surgical Planning
Knowledge of hepatic vein anatomy is critical for:
- Liver transplantation using the piggy-back technique, which requires anastomosis of the donor's suprahepatic IVC to the recipient's three hepatic veins. 1
- Hepatic resections, where preoperative imaging must delineate the exact venous anatomy to avoid catastrophic hemorrhage. 6
- Right subtotal hepatectomy, where hypertrophic accessory veins (≥0.3 cm) may be larger than the main right hepatic vein in 12.6-18.1% of cases. 5
Diagnostic Imaging
In Budd-Chiari syndrome, the caudate lobe has separate venous drainage directly into the IVC through multiple short hepatic veins, allowing compensatory hypertrophy in 75% of patients when the main hepatic veins are obstructed. 1, 7
Key Pitfall
Never assume a standard three-vein anatomy without preoperative imaging confirmation, as the two-vein configuration (65% prevalence) is actually more common than the classic three-vein pattern (33% prevalence). 2 Failure to identify accessory hepatic veins preoperatively can lead to significant intraoperative bleeding or inadequate venous drainage after resection. 5