Small-Sized, Flat-Type Invasive Branch Duct Intraductal Papillary Mucinous Neoplasm: A Case Report
A 70-year-old man was referred to our hospital for evaluation of a small cystic lesion in the pancreas head detected by health screening ultrasonography. He had neither clinical symptoms nor abnormal physical findings. Routine laboratory data also showed no abnormalities. Serum levels of carcinoembryonic antigen and carbohydrate antigen 19-9 were within normal limits. Enhanced computed tomography (CT) revealed a 17-mm cystic lesion without a solid component in the pancreas head. The cystic lesion was connected to the MPD (fig. ). Magnetic resonance cholangiopancreatography revealed that the cystic lesion was multilocular and connected to the MPD, which was not dilated (fig. ). On endoscopic ultrasonography (EUS), neither mural nodules nor wall thickness within the cystic lesion were detected (fig. ). ERCP revealed a 15-mm cystic dilation of the branch ducts without dilation of the MPD (fig. ). The cystic lesion had no features suggesting malignancy such as a cyst size of >3 cm, dilation of the MPD or an enhancing solid component within the cyst. However, cytological examination of the pancreatic juice collected during ERCP showed atypical columnar cells with loss of polarity, enlarged and hyperchromatic irregular nuclei and partially intracytoplasmic mucin (fig. ). These results suggested atypical cells with high-grade dysplasia, and the cystic lesion was diagnosed as a malignant BD-IPMN.\nPylorus-preserving pancreatoduodenectomy was performed. Intraoperative lavage cytology of the MPD of the remnant pancreas revealed no atypical cells. Pathological examination of the resected specimen showed a multilocular cystic lesion (fig. ), 16 × 9 × 15 mm in size, composed of dilated pancreatic branch ducts lined by columnar epithelium with mostly low-grade to focally high-grade dysplasia showing micropapillary growth (fig. ). In addition, small nests of irregular glands with enlarged nuclei invading the pancreatic parenchyma were noted over a distance of 11 mm, surrounded by myxoid stroma (fig. ). These features were consistent with the histological diagnosis of IPMN with an associated invasive carcinoma. Immunohistochemically, the neoplastic cells were positive for MUC5AC and MUC6, but negative for MUC1, MUC2 and CDX2, suggesting gastric-type IPMN.