Focal nodular hyperplasia

Focal nodular hyperplasia, abbreviated FNH, is a benign liver lesion, uncommonly seen by pathologists.

General

• Not commonly seen by pathologists, as these are usually distinctive on medical imaging.
• Benign lesions.
• May be seen in the context of hereditary hemorrhagic telangiectasia.

Note:

• Oral contraceptive pill (OCP) use does not appear to be a factor in the growth of these lesions; however, the study claims there is nothing on hepatocellular adenomas -- yet I found a JAMA paper by Rooks et al. on this topic.

Imaging

• FNH enhances on the arterial phase in triphasic imaging, i.e. triphasic CT or MRI.

Gross

Features:

• Well circumscribed, but no capsule.
• Lighter than surrounding parenchyma, may be yellow.
• +/-Stellate central scar with thick vessels.
  • Can be identified on medial imaging.

Note: Usually a solitary lesion.

Microscopic

Features:

• Classically a stellate scar that has large arteries with fibromuscular hyperplasia.
  • Thin fibrous septa radiate from the central scar - surrounded by lymphocytes & bile ductules.
    • Normal hepatocytes between fibrous septae.

Practical features:

1. Thick walled blood vessels.
   • Bile duct of same size not seen.
2. Bile ductular proliferation at the edge of the fibrosis tissue.
3. Clinical history: it is a focal lesion.

DDx:

• Hepatic adenoma - may be difficult to distinguish, if no scar and no ductal proliferation.
• Cirrhosis - complete nodules
  • FNH has incomplete nodules.

Memory device FNH = focal lesion, numerous bile ductules, hyperplasia of arteries.

Images

• 

  FNH - looks a bit like cirrhosis - low mag. (WC)

• 

  FNH - intermed. mag. (WC)

• 

  FNH - high mag. (WC)

www:

• FNH - several images (upmc.edu).

See also

• Medical liver disease.