Huge focal nodular hyperplasia difficult to distinguish from well-differentiated hepatocellular carcinoma

We present a 43-year-old man with huge focal nodular hyperplasia (FNH) that was difficult to distinguish from well-differentiated hepatocellular carcinoma (HCC). He previously had abnormal portal vein circulation due to hypoplasia of the intrahepatic portal vein, which was treated with a superior mesenteric vein-inferior vena cava shunt. Laboratory findings included predominantly indirect hyperbilirubinemia with concomitant elevation in aspartate aminotransferase (AST), alanine aminotransferase (ALT), and ammonia. Serum α-fetoprotein and des-γ-carboxy prothrombin were slightly elevated. Multidetector-row computed tomography detected the primary tumor in the left liver lobe, which partially showed a central stellate scar. Gd ethoxybenzyl diethylenetriamine pentaacetic acid-enhanced magnetic resonance imaging showed some low-intensity areas in the tumor in the hepatocyte phase. 99mTc-galactosyl human serum albumin scintigraphy showed normal intake of agent in the tumor. We could not rule out well-differentiated HCC. Extended left hepatectomy was performed. Final histopathological findings showed that most of the tumor was FNH against a background of portal vein hypoplasia with moderate atypia and hemorrhage. And immunohistochemical analysis revealed high expression of organic anion transporter (OATP) 1B3 and low expression of multidrug resistance-associated protein (MRP) 2 in a part of the tumor. The patient has remained alive with no hepatic lesion for 1 year after surgery. We describe a case of huge FNH that was difficult to distinguish from well-differentiated HCC even by current fully preoperative imaging technology and demonstrate the effectiveness of curative surgical resection.