Pancreatic acinar cell carcinoma with characteristic imaging due to extension into the main pancreatic duct and heterogeneity of its internal properties.

A 59-year-old man underwent computed tomography (CT) for evaluation of abdominal pain, which revealed a pancreatic tumor. The patient was subsequently referred to our hospital for further evaluation. Contrast-enhanced CT revealed a 22-mm lesion in the pancreatic tail with a contrast effect extending from the arterial phase. In addition, a 20-mm lesion with slightly less contrast enhancement was observed on the head side of the lesion. Endoscopic ultrasound-guided fine-needle tissue acquisition was performed on the lesion in the pancreatic tail, leading to the diagnosis of pancreatic acinar cell carcinoma, and distal pancreatectomy was performed. Preoperative imaging suggested the presence of two separate lesions; however, the resected specimen showed that the lesions had formed a single mass owing to their extension into the main pancreatic duct. The poorly enhanced region on the head side was primarily composed of edema and inflammatory changes with few tumor cells, whereas the enhanced region on the tail side consisted mostly of tumor cells. This difference in composition was thought to account for the variation in contrast enhancement. Awareness of imaging differences combined with histopathological correlations may aid in biopsy site selection and provide value in routine clinical practice.