A β-catenin-activated hepatocellular adenoma with inflammatory features: diagnostic challenges of integrating imaging and biopsy findings.

Hepatocellular adenoma (HCA) is a rare, benign liver tumor classified into molecular subtypes based on immunohistochemical and genetic features, some of which are associated with an increased risk of malignant transformation. However, increasing evidence suggests an overlap among these subtypes, indicating that strict classification may not always reflect the biological complexity of these tumors. We report the case of a 75-year-old man with a slowly enlarging hepatic lesion identified during follow-up after treatment for diffuse large B-cell lymphoma. Magnetic resonance imaging showed low signal intensity on T1-weighted images, mildly hyperintense signal on T2-weighted images, persistent enhancement on dynamic phases, hypointensity on the hepatobiliary phase, and a relatively high apparent diffusion coefficient value. These findings suggested inflammatory HCA, although overlap with other hepatic tumors was considered. A percutaneous liver biopsy revealed hepatocellular proliferation with minimal atypia and inflammatory cell infiltration. Immunohistochemistry demonstrated diffuse glutamine synthetase positivity and nuclear β-catenin expression, consistent with β-catenin-activated HCA. In contrast, C-reactive protein and serum amyloid A expression were only focal. These findings suggest a phenotypic overlap between inflammatory and β-catenin-activated HCA. This case highlights the limitations of biopsy-based subtype classification and underscores the importance of integrating imaging, histopathological, immunohistochemical, and molecular findings.