Granular cell neoplasm of the extrahepatic biliary tree: morphological, ultrastructural, and immunohistochemical study and review of the literature. A recent case of a biliary granular cell tumor of the cystic duct prompted a literature review and an extensive pathological examination of the tumor in question. A total of 44 cases have been described mostly in black females. Most cases present with biliary symptoms, and simple surgical resection allows complete control of this benign condition. Granular cell tumors are most likely derived from neural crest cells. 