Macrocystic serous adenoma of the pancreas.

Macrocystic serous adenoma of the pancreas (MSAP) is a rare neoplasm. Its preoperative diagnosis by physical examination and imaging studies is challenging, if not impossible. In recent years, a few cases of MSAP with correct cytodiagnosis by transabdominal fine-needle aspiration (TFNA) have been documented. This paper reports two cases of MSAP that were successfully diagnosed by TFNA cytology. Two adult women presented with epigastric discomfort. Abdominal imaging studies revealed a large pancreatic cystic lesion in both cases. TFNAs of the pancreatic lesions were subsequently performed and revealed a clear serous fluid containing small monolayered sheets of benign cuboidal epithelial cells with scant, clear or granular cytoplasm, vesicular nuclei and micronucleoli. The cell cytoplasm stained positively with periodic acid-Schiff (PAS) and negatively with PAS with prior digestion with diastase (PASD). The cytological findings in both cases were similar and suggested a serous cystadenoma. The two pancreatic lesions were removed by Whipple's operation. They showed features of a macrocystic serous adenoma of the pancreas that were characterized by a small number of large cystic cavities lined by a single layer of non-mucus secreting, PAS-positive and PASD-negative cuboidal epithelial cells. By electron microscopy, the epithelial lining cells showed short and aborted apical microvilli, well-formed desmosomes and a large amount of intracytoplasmic glycogen, suggesting a centroacinar ductal cell origin.