A case of β-catenin-activated hepatocellular adenoma with concurrent hepatocellular carcinoma

β-Catenin-activated hepatocellular adenoma (B-HCA), particularly the exon 3-mutated subtype, has a high risk of malignant transformation to hepatocellular carcinoma (HCC). Here, we report a rare case of a man in his 60s with B-HCA containing embedded HCC. On dynamic contrast-enhanced computed tomography (DCE-CT), a 6-cm poorly enhancing mass suggestive of HCC was identified in the enlarged lateral segment of the left hepatic lobe. A 9-cm region surrounding the poorly enhancing mass appeared similar to adjacent liver parenchyma on non-contrast CT, but showed mild arterial enhancement without washout on DCE-CT. In addition, abrupt displacement of the adjacent hepatic vessels at its margins suggested a tumor component rather than a pseudolesion. On gadolinium-ethoxybenzyl-diethylenetriamine-pentaacetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (EOB-MRI), the surrounding region exhibited mild arterial enhancement and mild hyperintensity in the hepatobiliary phase (HBP) relative to the background liver parenchyma. Pathological analysis confirmed the poorly enhancing mass as well- to moderately differentiated HCC and the surrounding region as exon 3-mutated B-HCA, showing diffuse strong glutamine synthetase positivity. This case demonstrates malignant transformation of B-HCA to HCC and highlights the importance of recognizing this entity in clinical practice.