Three large intrahepatic veins drain the liver parenchyma, into the inferior vena cava (IVC), and are named the right hepatic vein, middle hepatic vein and left hepatic vein. The veins are important landmarks, running in between and defining the segments of the liver. There are separate smaller veins draining the caudate lobe of the liver. Hepatic venous anatomy demonstrates a broad spectrum of anatomic variance.
NB: the segments were originally numbered by Roman numerals I to VIII, but the Arabic numerals 1 to 8 are now preferred .
Right hepatic vein
The right hepatic vein (RHV) runs in the right hepatic fissure and drains segments 5, 6, 7 and 8. The vertical plane of the right hepatic vein separates the segments 6 and 7 (posterior to the plane) from segments 5 and 8 (anterior to this plane).
The right hepatic vein is a single dominant vein in ~70% (range 60-78%) of individuals. There may be an early bifurcation, early trifurcation or even multiple right hepatic veins entering the IVC. Hence this may make it difficult to accurately deduce segmental anatomy of the liver.
The commonest anatomical variant of the hepatic veins is an accessory right inferior hepatic vein.
Middle hepatic vein
The middle hepatic vein (MHV) runs at the middle hepatic fissure and drains segments 4a, 4b, 5 and 8. The vertical plane of the middle hepatic vein separates the segments 5 and 8 (posterolateral to this plane) from segments 4a and 4b (anteromedial to this plane).
Left hepatic vein
The left hepatic vein (LHV) runs partially in the fissure for the ligamentum teres and the left hepatic fissure. It drains segments 2, 3, 4a and 4b. It is always located anterior to the left portal vein. The vertical plane of the left hepatic vein separates the segments 4a and 4b from segments 2 and 3.
Caudate lobe veins
The highly variable caudate lobe veins (or a single vessel) drain directly into the inferior vena cava. These veins are occasionally referred to as the Spigelian veins and may become prominent in the setting of hepatic venous obstruction, as in Budd-Chiari syndrome. This finding may be considered analogous to the "bright caudate sign" seen on technetium-99m sulfur colloid liver spleen scans.