Fine-needle aspiration of pancreatic serous cystadenoma: cytologic features and diagnostic pitfalls

The preoperative diagnosis of pancreatic serous cystadenoma (SCA) is important because as a typically benign tumor it can be treated expectantly, whereas many other cystic tumors require excision. This study examines the cytology, clinical and radiologic features, diagnostic accuracy of fine-needle aspiration (FNA), and potential pitfalls associated with this rare tumor.

Cytomorphologic features were retrospectively reviewed from 28 FNAs of SCA from 21 patients. FNA biopsies were guided by percutaneous computed tomographic or ultrasonographic imaging in 10 cases and by endoscopic ultrasonographic imaging in 18 cases. Corresponding histology (14 tumors) and clinical/imaging findings were also evaluated.

Patients typically presented with upper abdominal discomfort or asymptomatically. Radiologically, a well-demarcated, multiloculated cystic mass involving the pancreatic head or uncinate process was common. Aspirates were sparsely cellular against a clean or granular, proteinaceous background. Tumor cells formed loose clusters or monolayered sheets composed of cuboidal cells with indistinct cell borders and granular or clear cytoplasm that was often stripped from the nucleus. Nuclei were small, round, with fine chromatin and indistinct nucleoli and devoid of mitotic activity. Seven (25%) of the aspirates were initially classified as "consistent with SCA," 6 (21%) as "no malignant cells," 3 (11%) as "nondiagnostic specimen," 3 (11%) as "suspicious for malignancy," 3 (11%) as "rare atypical cells," and 6 (21%) as "probably or consistent with mucinous cystic neoplasm." Features causing diagnostic difficulty were scant cellularity, papillary groups, nuclear atypia, and columnar cells mimicking those of mucinous neoplasms. Gastrointestinal (GI) epithelium and mucin also caused confusion. The detection of intracytoplasmic glycogen (3 of 6 cases) and cyst fluid analysis (2 of 2 cases) showing low viscosity and low or undetectable levels of carcinoembryonic antigen, CA 19.9, and amylase enhanced diagnostic confidence.

Diagnosing SCA by FNA is challenging. Familiarity with its morphologic spectrum, use of ancillary studies, and correlation with clinical/radiologic findings greatly improves diagnostic accuracy. Contaminating GI epithelium and mucin should be distinguished from components of a mucinous neoplasm.