FNH is the second most common tumor of the liver.
FNH is not a true neoplasm. It is believed to represent a hyperplastic response to increased blood flow in an intrahepatic arteriovenous malformation.
All the normal constituents of the liver are present but in an abnormally organized pattern.
US will show a FNH as a non specific ill-defined lesion.
The central scar may be detected as a hyperechoic area, but often cannot be differentiated.
With color doppler sometimes the vessels can be seen within the scar.
CT will show FNH as a vascular tumor, that will be hyperdens in the arterial phase, except for the central scar.
Above a typical FNH with a central scar that is hypodens in the portal venous phase .
Moreover a central scar may be found in some patients with fibrolamellar hepatocellular carcinoma, hepatic adenoma and intrahepatic cholangiocarcinoma.
The key to the diagnosis in the lesion on the left is the fact that it is isoattenuating to normal liver in the portal venous phase and stays that way without a wash out on the delayed phase