The ill-defined, subtle mass with heterogenous density and irregular margins in the superior aspect of the right lobe of the liver in this abdominal CT scan is a cholangiocarcioma, a primary liver cancer that occurs less frequently than hepatocellular carcinoma, and none of the same risk factors apply. In parts of the world where parasitic infestations by liver flukes (such as the trematode Clonorchis sinensis) occur, cholangiocarcinoma is more common.