The oxaloacetate/aspartate family of amino acids is composed of lysine , asparagine , methionine , threonine , and isoleucine . Aspartate can be converted into lysine, asparagine, methionine and threonine. Threonine also gives rise to isoleucine . All of these amino acids contain different mechanisms for their regulation, some being more complex than others. All the enzymes in this biosynthetic pathway are subject to regulation via feedback inhibition and/or repression at the genetic level. As is typical in highly branched metabolic pathways, there is additional regulation at each branch point of the pathway. This type of regulatory scheme allows control over the total flux of the aspartate pathway in addition to the total flux of individual amino acids. The aspartate pathway uses L-aspartic acid as the precursor for the biosynthesis of one fourth of the building block amino acids. Without this pathway, protein synthesis would not be possible.
The diagnosis of FNH is based on the demonstration of a central scar and a homogeneous enhancement.
However, a typical central scar may not be visible in as many as 20% of patients (figure).
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 (not shown).
This could also be an adenoma, but HCC would be unlikely because they show a fast wash out.