Pseudolesions of the liver are non-neoplastic abnormalities and can be divided into parenchymal and vascular changes. Pesudolesions often occur due to blood flow abnormalities and can be found in both cirrhotic and non-cirrhotic livers.[1]
The liver has dual blood supply with the portal vein carrying 75% of blood and the hepatic artery with 25% of blood and a drainage route through the hepatic veins.
Fig. 1: Dual blood supply and third inflow
Both systems have communications between them that allow supporting mechanisms.[1]
Fig. 4: Arterio-portal shunts
There are anatomical variations of liver blood vessels of which only portal vein variants are important in pseudolesions pathogenesis. Portal vein variants form a
third inflow which is defined as aberrant veins supplying small areas of liver tissue independently that can cause hepatopetal portal flow in that region.[1]
Fig. 17: Third inflow
Third inflow frequently involves the cholecystic veins (drain into gallbladder bed), parabiliary venous system(
Fig. 29) (mainly drain into posterior aspect of segment IV) and epigastric-paraumbilical venous system(
Fig. 28) (mainly drain into anteromedial portion of the segment IV).
Fig. 3: Characteristic locations of FFC and focal sparing
Normally these veins would join the portal venous branches but in this case, they perfuse the liver directly.[2]
Thus parts of the liver may be perfused with:
- Portal blood
- Nonportal splanchnic and/or systemic blood
- Hepatic and/or extrahepatic artery blood[1]
Venous blood other than portal blood can be seen in imaging as perfusion defect, focal sparing, focal fatty change, hyperplastic area or transient hepatic attenuation/intensity differences. [3]
Pharmacodynamics of normal liver contrast enhancement:
- Arterial phase
o Arterial blood (contrast) is diluted 3:1 in the sinusoids by the unopacified portal blood so that parenchymal enhancement is minimal (25%)
- Portal phase:
o Contrast in both hepatic artery and portal vein thus liver parenchyma enhances maximally (25%+75%)[2]
Fig. 2: Pharmacodynamics of normal liver contrast enhancement(up) and of THAD (down)
Pseudolesions cand be divided into:
- Focal mass-like parenchymal change normal liver function
- Focal mass-like findings on imaging without parenchymal change[3]