RESUMEN
An electron microscopic study was carried out on eleven surgical liver biopsy specimens obtained from patients with cholangiocarcinoma associated with opisthorchiasis. The tumor cells of histologically well differentiated cholangiocarcinoma had few cytoplasmic organelles. They contained relatively large nuclei, abundant free ribosomes and numerous groups of fine fibrils. Each cell was surrounded by a basement membrane. Numerous long microvilli were seen projecting into the glandular lumen. The moderately differentiated cholangiocarcinomatous cells exhibited increased organelle content, marked variation in the shape of the nuclei with deep cytoplasmic invagination into the nuclear membrane; there were small intranuclear pseudoinclusions, and shorter microvilli. The tumor cells showed intracellular microvillus-lined spaces, abundant free ribosomes, many fine fibrils and their surrounding basement membranes were incomplete. The ultrastructure of the poorly differentiated cholangiocarcinoma was similar to that of the moderately differentiated tumor, except for fewer microvilli, abundant cytoplasmic organelles, and ill-defined or absent basement membrane.