Non-Neoplastic and Neoplastic Cysts of the Pancreas.

Inflammatory, developmental, and neoplastic lesions may all present as cystic masses on imaging. Pseudocyst is the most common of these and presents in association with a history of pancreatitis. Pancreatic cystic neoplasms are uncommon compared to solid neoplasms. They often present incidentally; therefore, an incidentally discovered cyst in the pancreas should be assessed with a high index of suspicion for neoplasm. The most common and frequently encountered cystic neoplasms include serous cystadenoma, mucinous cystic neoplasm, and intraductal papillary mucinous neoplasm. Less common epithelial cystic neoplasms include acinar cell cystadenoma and cystadenocarcinoma. Any solid neoplasm occurring in the pancreas or vicinity of the pancreas that has undergone cystic degeneration may present as a cystic mass. Non-epithelial lesions, such as lymphangioma, are also included in the differential diagnosis. The work-up needs to begin with a review of the clinical and imaging findings to establish a differential diagnosis. The primary focus of the pathologist will be first on differentiating mucinous from non-mucinous entities, since this will determine if the mass is an intraductal papillary mucinous neoplasm or a mucinous cystic neoplasm. If it is mucinous, the next step is to determine if the cystic neoplasm contains cells with high-grade cytological features. If it is non-mucinous, the pathologist needs to assess for neoplastic cells that would indicate a different neoplastic process. The cytological features need to be integrated with cyst fluid carcinoembryonic antigen and amylase measurements. Currently, molecular pathology is being integrated into the analysis of pancreatic cyst fluids. Here we will cover the cytological features and ancillary findings in cystic masses of the pancreas.