Radiology: Adenoma vs. FNH

Oftentimes we are confronted with the diagnostic dilemma: is this a hepatic adenoma or focal nodular hyperplasia (FNH)?  It is critical that the distinction is made properly, for adenomas have the potential to grow, rupture or turn into hepatocellular carcinoma.  Furthermore, discontinuation of oral contraceptive use can be recommended.  None of the above is the typical case of FNH.

So, how to make the distinction?  Since not all FNH have the classic, central stellate scar on imaging, a routine triple phase CT or MRI is inadequate.  The answer lies in the histology!  FNH contains bile ducts within the lesion, while adenomas do not.  Adenomas are comprised of sheets and sheets of redundant hepatocytes and are devoid of bile ducts.

This distinction can be exploited by our choice of MRI contrast; Eovist or Multihance contrast is excreted via the biliary system.  Therefore, on the late phases of study (ie. portal, or washout phase) the biliary uptake of contrast by a FNH will make the lesion either hyper or isoattenuating to the surrounding parenchyma, while no uptake by an adenoma equates to a hypoattenuating lesion, as seen in the image below.

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