Squamoid cyst of pancreatic ducts: a case series describing novel immunohistochemistry, cytology, and quantitative cyst fluid chemistry.

Squamoid cyst of pancreatic ducts (SCPD) is a benign pancreatic cyst often misdiagnosed preoperatively as a mucinous cyst. The histopathologic features are well described but the cytology and quantitative fluid chemistry profiles from fine-needle aspiration have not been reported. This case series discusses the cytology and cyst fluid chemistry profiles in 2 SCPDs and describes morphologic and immunohistochemical features that have not been previously reported. Fine-needle aspiration of 2 SCPDs yielded acellular debris lacking mucin or exfoliated squamous cells. Two cysts had elevated fluid carcinoembryonic antigen (CEA) and amylase levels. Positive immunohistochemical staining included cytokeratin 5/6, pCEA, synaptophysin, and chromogranin (both focal). MUC2 and MUC5AC showed negativity in all cases, while PAX8 showed negative nuclear staining. An accurate preoperative diagnosis of SCPD is potentially difficult in the setting of elevated fluid CEA levels, and acellular cytology as a mucinous cyst cannot be confidently excluded.