Focal Nodular Hyperplasia : Glutamine Synthetase

Comments:
Focal nodular hyperplasia of liver shows a map-like staining pattern with glutamine synthetase (GS) - an important distinguishing feature from hepatocellular adenoma. There are broad, anastomosing areas of GS expression adjacent to hepatic veins. The map-like staining may be difficult to appreciate in small biopsies. GS staining is due to activation of β-catenin pathway without mutations in CTNNB1 or AXIN1 genes.

Image courtesy of: Dr. Matthew Gosse (@MattGosse); used with permission.