Cyst fluid cytologic analysis in the differential diagnosis of pancreatic cystic lesions

Pancreatic cystic lesions include inflammatory pseudocysts, benign serous cystadenomas, and mucinous neoplasms, some of which are malignant. Cytologic analysis of cyst fluid has been proposed to diagnose pancreatic cysts before definitive therapy. The authors report an analysis of 31 pancreatic cyst aspirates: 9 pseudocysts, 5 serous cystadenomas, 8 mucinous cystic neoplasms, 4 mucinous cystadenocarcinomas, 2 papillary cystadenocarcinomas, 1 mucinous ductal adenocarcinoma with cystic degeneration, and 2 cystic islet cell tumors. All pseudocysts were correctly classified as probable inflammatory lesions, because of the presence of abundant acute inflammation and histiocytes and the absence of glandular epithelium. Three of five serous cystadenomas were correctly classified, based on the presence of small cuboidal cells in clusters with microvesicular cytoplasm containing glycogen. Eleven of 12 mucinous tumors contained round cells with large cytoplasmic mucin vacuoles or columnar cells containing cytoplasmic mucin. Malignancy was diagnosed in 5 of 7 carcinomas, 1 case was classified as suspicious for malignancy, and 1 case was nondiagnostic because of the absence of a cellular component. The authors concluded that pancreatic cyst fluid cytologic analysis is useful in differentiating mucinous from nonmucinous pancreatic cysts and may provide definitive evidence of malignancy. In some cases, serous cystadenoma can be diagnosed based on cytologic analysis. An inflammatory smear without epithelial cells suggests a pseudocyst, but these findings are nonspecific, as a similar pattern may occur when a cystic neoplasm undergoes degenerative changes. Therefore, pseudocyst remains a diagnosis of exclusion.