Intraductal tubular neoplasm of the common bile duct.

Recently, biliary neoplasms resembling intraductal neoplasms of the pancreas have been documented. In this report, a rare case of intraductal tubular neoplasm (ITN) arising in the common bile duct is presented. A polypoid mass, 10 mm in diameter, was found in a 67-year-old woman in the intrapancreatic part of the common bile duct during the follow up to cholecystolithiasis and choledocholithiasis. Endoscopic polypectomy was performed for the lesion. Histology of the lesion revealed tubular neoplasm, composed of an admixture of tubular glands resembling pyloric gland adenoma with minimal atypia (low-grade tubular adenoma), and those resembling intestinal type tubular adenoma (high-grade tubular adenoma). There was no significant formation of papillae or oncocytic cytoplasm. Small foci of carcinoma in situ of the intestinal type were also observed. On immunostaining low-grade tubular adenoma was positive for MUC5AC and MUC6, and negative for MUC2 and cytokeratin (CK) 20, while high-grade tubular adenoma and carcinoma in situ were positive for MUC2 and CK20, and negative for MUC5AC. Although more case studies of ITN in the biliary tracts are required to clarify the tumorigenesis and pathological features, the lesion may be the biliary counterpart to pancreatic ITN.