Inflammatory
hepatocellular adenoma can show overlapping histological features with
focal nodular hyperplasia, including
inflammation, fibrous stroma, and ductular reaction. Expression of serum
amyloid-associated
protein in inflammatory
hepatocellular adenoma and map-like pattern of
glutamine synthetase in
focal nodular hyperplasia can be helpful in this distinction, but the pitfalls and limitations of these markers have not been established. Morphology and immunohistochemistry were analyzed in 54 inflammatory
hepatocellular adenomas, 40
focal nodular hyperplasia, and 3 indeterminate lesions. Morphological analysis demonstrated that nodularity, fibrous stroma, dystrophic blood vessels, and ductular reaction were more common in
focal nodular hyperplasia, while
telangiectasia,
hemorrhage, and steatosis were more common in inflammatory
hepatocellular adenoma, but there was frequent overlap of morphological features. The majority of inflammatory
hepatocellular adenomas demonstrated perivascular and/or patchy
glutamine synthetase staining (73.6%), while the remaining cases had diffuse (7.5%), negative (3.8%), or patchy pattern of staining (15%) that showed subtle differences from the classic map-like staining pattern and was designated as pseudo map-like staining. Positive staining for serum
amyloid-associated
protein was seen in the majority of inflammatory
hepatocellular adenomas (92.6%) and in the minority of
focal nodular hyperplasia (17.5%). The
glutamine synthetase staining pattern was map-like in 90% of
focal nodular hyperplasia cases, with the remaining 10% of cases showing pseudo map-like staining. Three cases were labeled as indeterminate and showed
focal nodular hyperplasia-like morphology but lacked map-like
glutamine synthetase staining pattern; these cases demonstrated a patchy pseudo map-like
glutamine synthetase pattern along with the expression of serum
amyloid-associated
protein. Our results highlight the diagnostic errors that can be caused by variant patterns of staining with
glutamine synthetase and serum
amyloid-associated
protein in inflammatory
hepatocellular adenoma and
focal nodular hyperplasia.