A case of intrahepatic cholangiocarcinoma arising from a simple hepatic cyst via dysplasia and carcinomatous transformation.

We report a rare case of intrahepatic cholangiocarcinoma (iCCA) that arose from a simple hepatic cyst. A 72-year-old man was transferred to our hospital for treatment of a liver tumor. Dynamic contrast-enhanced computed tomography (CT) detected a small tumor surrounding a hepatic cyst in segment 8 that showed low attenuation on a pre-contrast CT, rim-like enhancement in the arterial dominant phase, and delayed enhancement in the delayed phase. On gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid-enhanced dynamic magnetic resonance imaging (MRI), the hepatic tumor had hypointensity on T1-weighted images, hyperintensity on T2-weighted images, hyperintensity on diffusion-weighted images, and hypointensity on the hepatobiliary phase. The tumor increased in size after 6 months, and partial hepatectomy was performed. Histopathologically, the tumor was consistent with moderately to poorly differentiated adenocarcinoma with the microscopic lymphatic, portal, and hepatic venous invasion. The epithelium of the cystic region largely comprised carcinoma in situ, with dysplastic biliary epithelial cells and a small portion of normal biliary epithelial cells. The transition from carcinoma in situ to invasive carcinoma was confirmed, and the patient was diagnosed with iCCA arising from a hepatic cyst via dysplasia and carcinomatous transformation.