Adenomyomatous hyperplasia, a common non-neoplastic lesion in the gallbladder, is rarely identified in the extrahepatic bile duct. Typically, these lesions appear as a nodule or mural thickening/elevation. However, in exceptional circumstances, pedunculated/polypoid adenomyomatous lesion occurs in the biliary tract; two cases in the gallbladder and only one case in the common bile duct have been reported. Despite their benign nature, adenomyomatous lesions, especially those with a polypoid appearance, are clinically difficult to exclude a possibility of malignant neoplasms. We describe a case of polypoid-type adenomyomatous lesion of the cystic duct in a 72-year-old man, which was considered as a cystic duct neoplasm preoperatively. Gross examination of the resected specimen revealed that the 9 mm-sized cystic duct polyp. Histologically, the polypoid lesion consisted of glands without atypia, fibrous stroma, smooth muscle bundles, and accompanying stromal inflammation, leading to the diagnosis of benign adenomyomatous lesion. The lesion might be considered as adenomyomatous hyperplasia arising in the valve of Heister, while true nature of the lesion is uncertain. Recognition and accumulating for this rare disease will contribute to better clinical management in the future.
Keywords: adenomyomatous hyperplasia; cystic duct; extrahepatic bile duct; mimic of malignancy; polyp.