Nodular regenerative hyperplasia: The role of the CK7 immunohistochemistry pattern of expression in diagnosis.

Objectives: Nodular regenerative hyperplasia (NRH) is a rare vascular disorder of the liver. Clinically, patients present with portal hypertension with or without a cholestatic pattern of injury. Histologically, the liver parenchyma is composed of small nodules of hypertrophic hepatocytes surrounded by atrophic hepatocytes without significant fibrosis. Nodular regenerative hyperplasia is a difficult diagnosis on biopsy specimens, but biopsy remains the gold standard for diagnosis. In this retrospective review, cytokeratin 7 (CK7) immunohistochemistry (IHC) was used to aid in the diagnosis and further characterization of NRH and NRH-like changes.

Methods: The H&E-stained slides, reticulin, and CK IHC were reviewed for 22 cases. The percentage of hepatocytes staining for CK7 (0%-100%), the location of staining (centrilobular hepatic progenitor cells vs periportal/bile ductular reaction), and the pattern of staining distribution (patchy or diffuse) were recorded for comparison.

Results: Of the 22 cases, 9 were CK7 positive. Cases of NRH, however, expressed various degrees of CK7 positivity in centrilobular hepatic progenitor cells, unlike NRH-like changes, which were either CK7 negative or CK7 positive in periportal hepatocytes or in areas of bile ductular reaction.

Conclusions: In cases with the appropriate clinical history and histology, CK7 immunohistochemistry can be performed to distinguish nodular regenerative hyperplasia (primary) and NRH-like changes (secondary). In difficult cases, CK7 positivity in centrilobular hepatic progenitor cells can help confirm the diagnosis of NRH. These data support NRH as a true entity with a distinct pathophysiology from NRH-like changes.