Rare pancreatic neoplasms and mimics of pancreatic cancer

Certain histologic types of pancreatic neoplasms are encountered uncommonly. Although these tumors can have characteristic imaging features, they often are non-specific in appearance. In addition, non-neoplastic abnormalities that affect the pancreas can simulate the appearance of a pancreatic neoplasm. This chapter reviews the clinical and imaging features of rare pancreatic neoplasms and the non-neoplastic processes that can mimic pancreatic cancer. Ductal adenocarcinoma of the pancreas is the most common type of cancer that originates from the pancreas. Other less common pancreatic cancers include acinar cell carcinoma, anaplastic carcinoma, osteoclast-like giant cell tumor, mucinous non-cystic carcinoma, adenosquamous carcinoma, signet-ring cell carcinoma and small cell carcinoma [1]. Acinar cell carcinoma is a rare pancreatic tumor comprising 1% of all exocrine neoplasms, despite the fact that acinar cells make up most of the pancreatic parenchyma [2]. Acinar cell carcinomas are less aggressive and have a better prognosis than the typical ductal carcinoma of the pancreas. This tumor may produce pancreatic enzymes and occasionally may cause polyarthritis and subcutaneous fat necrosis [2]. On computed tomography, acinar cell carcinoma typically is a well-circumscribed, exophytic, low-attenuation mass that may be partially cystic or contain calcifications (Figure 11.1) [3]. Anaplastic carcinoma comprises 2–7% of all pancreatic carcinomas. On CT, the tumor typically is large, partly necrotic, locally invasive, and invariably metastatic at the time of diagnosis [4]. Small cell carcinoma comprises 1% of all pancreatic carcinomas. Histologically, it is indistinguishable from small cell carcinoma of the lung.