Pancreatic lipoma with a solid nodule mimicking invasion from adjoining intraductal papillary mucinous neoplasm.

A 74-year-old man was referred to our hospital for a mass in the pancreatic head found during screening chest computed tomography. Contrast computed tomography showed a 5-cm multicystic mass with an irregular border containing a solid component showing contrast enhancement. Caudal to this mass, a 5-cm solid mass of fat density with a nodular soft-tissue component was found. Cytology of the aspirated pancreatic fluid revealed malignant cells, and surgery was performed for suspected intraductal papillary mucinous carcinoma. Pathologic analysis of the resected specimen revealed a collision tumor of intraductal papillary mucinous neoplasm (IPMN) with high-grade dysplasia and pancreatic lipoma. The soft-tissue component within the lipoma was a nodule consisting of pancreatic tissue with inflammatory infiltration and hyalinization and was not associated with IPMN invasion.