Ultrastructure of botryoid sarcoma of the common bile duct.

A case of botryoid sarcoma of the common bile duct in a 4-year-old girl was reported. Electron microscopic examination disclosed that the neoplasm consisted of three types of cells: polygonal, elongated, and small cells. The former two contained moderate to large amounts of poorly developed myofibriles in the cytoplasm with occasional A, I and Z-bands. The small cells contained mitochondria and dilated rough endoplasmic reticulum but few myofilaments. Deposits of glycogen granules were constant components of the neoplastic cells. Mitosis was striking in the small cells. Abnormal multilaminar endoplasmic reticulum was observed in the small cells in the mitotic stage.