Focal Nodular Hyperplasia : Differential

Comments:
Differential Diagnosis: The differential diagnosis of focal nodular hyperplasia (FNH) includes: hepatocellular adenoma, cirrhosis, and well-differentiated hepatocellular carcinoma. The distinction between FNH and hepatocellular adenoma may be extremely difficult in small biopsies.

Features favoring FNH: central stellate scar, nodularity, rare/no hemorrhage and necrosis, ductular reaction, large thick-walled vessels in fibrous septa, map-like positivity with glutamine synthetase (GS), intact reticulin network, and negative beta-catenin.

Hepatocellular adenoma is favored by features such as fat, isolated arteries, sinusoidal dilatation, and absence of map-like GS staining. There is considerable histologic overlap between the two in 20-30% of cases.

Hepatocellular carcinoma shows cytologic atypia and disruption of reticulin network. Mitotic activity is extremely rare in FNH. If present, the possibility of hepatocellular carcinoma should be excluded.

About this image: Low power view showing nodules of hepatocytes separated by fibrous stroma containing bile ductular proliferations. This nodular appearance may resemble cirrhosis or nodular regeneration. CK7 and CK19 immunostaining can be used to highlight bile ductular structures, which distinguish FNH from hepatocellular adenoma.