Bile canaliculi-like lumina in fibrolamellar carcinoma of the liver: a light- and electron-microscopic study and three-dimensional examination of serial sections.

Fibrolamellar carcinoma (FLC) is a variant of hepatocellular carcinoma characterized by distinct pathological features. The presence of intracellular lumina resembling bile canaliculi was previously reported in tumor cells of FLC on electron microscopy. Using light microscopy, we describe the presence of intracellular lumina in FLC, which was resected from a 15-year-old Japanese girl, as round structures lined with a brush-like border. These lumina occasionally contained bile. Light microscopic examination of 1 micron thick serial sections of Epon-embedded tissue samples showed that the lumina were located in the intracellular space without any connection to the intercellular space. However, we also detected a small number of lumina that were lined by microvilli, which were present between adjacent tumor cells. Results suggest that the presence of the intracellular lumina in tumor cells probably represents a common histopathologic feature of FLC.