Cytologic diagnosis of pancreatic cystic lesions. A prospective study of 28 percutaneous aspirates.

To prospectively evaluate fine needle aspiration biopsy (FNAB) of pancreatic cystic lesions. We performed a blind, prospective study on percutaneous aspirates from 28 radiographically identified cysts, including 6 inflammatory cysts (5 pseudocysts and 1 abscess), 4 serous cystadenomas, 1 cystic islet cell tumor, 5 mucinous cystic neoplasms, 6 mucinous cystadenocarcinomas and 6 nonpancreatic cysts. Four of six (67%) cystadenocarcinomas were identified as malignant, and the other two, which lacked sufficient morphologic criteria for malignancy, as consistent with mucinous cystic neoplasm. Two of five mucinous cystic neoplasms were correctly classified. One, which contained atypical cells, did not appear to be mucinous on the ThinPrep, and one, which lacked an epithelial component, was suggested because of the presence of mucin in the background. The fifth one contained inflammatory cells only. One of four serous cystadenomas produced a diagnostic specimen. FNAB of the cystic islet cell tumor was nondiagnostic. Five of six inflammatory cysts (83%) were correctly diagnosed, whereas one case produced an acellular, nondiagnostic specimen. Six of 28 (23%) cases were nonpancreatic cysts, aspirated under the presumption that they were pancreatic cysts based on radiologic studies: only one case, a papillary cystadenocarcinoma of the stomach, was correctly diagnosed; the other five cases were nondiagnostic, and in two of these the assumption that the cysts were pancreatic in origin precluded an accurate classification. FNAB of pancreatic cystic lesions can differentiate mucinous from nonmucinous pancreatic cysts and provide definitive evidence of malignancy. In some cases, serous cystadenomas can be diagnosed. Pseudocysts can be suspected on the basis of an inflammatory smear lacking both epithelial cells and background mucin, but this finding is not specific. Nonpancreatic lesions constitute a significant percentage of cases aspirated as pancreatic cysts and present a major pitfall in cytologic interpretation.