Abstract
The patient was a 76-year-old man who was found to have a 2-cm sized cyst at the pancreas head which was diagnosed as an intraductal papillary mucinous neoplasm (IPMN) of mixed type in 2007. Thereafter he had been followed in the clinic, and the IPMN had not shown any apparent change for five years. In 2012, although an abdominal CT/MRI did not show apparent enlargement of the cyst and increase of the main pancreatic duct diameter, upper gastrointestinal endoscopy revealed the significantly opened orifice of the papilla of Vater. ERCP revealed a fistula from a multilocular cyst at the pancreas head to the duodenum, and a filling defect in the cyst. Intraductal US showed a solid nodule in the cyst. We performed pancreaticoduodenectomy under a diagnosis of mixed-type IPMN penetrating to the duodenum, suggesting that it was malignant change. The lesion was pathologically diagnosed as the non-invasive type of intraductal papillary mucinous carcinoma, based on the highest degree of epithelial atypia. However, the epithelium around the fistula was low-grade adenoma without a malignant component. This paper presents a case of malignant progression of mixed type IPMN which formed a duodenum fistula with little change of the main duct and cyst during long-term observation.
