Pseudocyst of the pancreas: the role of cytology and special stains for mucin.

BACKGROUND

Currently, the preoperative diagnosis of a pancreatic cyst is based on clinical and imaging findings, frequently in conjunction with chemical analysis of cyst fluid and cytologic evaluation. The purpose of these diagnostic tests is to distinguish benign from malignant cysts of the pancreas. Accordingly, it is imperative to distinguish pancreatic pseudocysts from their mimics. In this study, the authors explored the cytomorphologic features of pseudocyst of the pancreas and evaluated the role of Alcian blue and mucicarmine stains in the cytologic evaluation of pancreatic cysts.

METHODS

Forty-two patients were identified who had an eventual diagnosis of pancreatic pseudocyst and had an endoscopic ultrasound-guided fine-needle aspirate available. Clinical and imaging findings and chemical analyses of cyst fluid were recorded. The cytologic preparations were evaluated for gastrointestinal contamination, inflammatory cells, mucin, and pigmented material. The cytomorphologic features of 110 neoplastic mucinous cysts (intraductal papillary-mucinous neoplasms/mucinous cystic neoplasms of the pancreas) were evaluated and compared with the pseudocysts.

RESULTS

The majority of patients (95%) had a prior episode of pancreatitis. On imaging, the pseudocysts were unilocular (92%). In 69% of cases, the endosonographic diagnosis was that of a pseudocyst. The mean carcinoembryonic antigen level was 41 ng/mL. In contrast, the cytopathologist rendered a definitive diagnosis of pseudocyst in only 10% of cases. The majority of smears (75%) revealed neutrophils and/or histiocytes. Atypical epithelial clusters were identified in 3 cases, 1 of which was diagnosed as suspicious for carcinoma. Yellow pigmented material, which was identified in 13 pseudocysts (31%), was not observed in neoplastic mucinous cysts. Alcian blue- and mucicarmine-positive material was identified in 64% and 40% of pseudocysts, respectively, and in 57% and 38% of neoplastic mucinous cysts, respectively.

CONCLUSIONS

The diagnosis of a pseudocyst depended primarily on clinical and imaging findings and on chemical analysis of cyst fluid. The cytologic features frequently were nonspecific. The presence of yellow pigmented material served as a surrogate marker of a pseudocyst. Special stains for mucin did not distinguish pseudocysts from neoplastic mucinous cysts.