[Invasive carcinoma derived from a branch-duct intraductal papillary mucinous neoplasm without mural nodules that developed after a long-term follow-up: a case report and review of literature].

A 71-year-old woman underwent semiannual imaging studies including endoscopic ultrasonography (EUS) for branch-duct intraductal papillary mucinous neoplasms (IPMNs) over approximately 11 years of follow-up after her first visit. EUS detected a hypoechoic region adjacent to a 25-mm diameter IPMN without mural nodules in the pancreatic body, and endoscopic ultrasound-guided tissue acquisition of the hypoechoic region confirmed adenocarcinoma. Distal pancreatectomy was performed, and histological examination of the resected specimens revealed invasive ductal adenocarcinoma adjacent to the cystic lesion lined by low papillary atypical epithelium. Despite the absence of mural nodules, this invasive carcinoma was considered to have originated from the adjacent IPMN.