An aggressive malignant smooth muscle neoplasm, arising from an extrahepatic bile duct. It is characterized by a proliferation of neoplastic spindle cells. The disease is MONDO_0003377 (extrahepatic bile duct leiomyosarcoma). Also known as: bile duct leiomyosarcoma, leiomyosarcoma of bile duct, leiomyosarcoma of extrahepatic bile duct, leiomyosarcoma of the bile duct, leiomyosarcoma of the extrahepatic bile duct.