Squamoid Cyst of Pancreatic Ducts: A Case Series Describing Novel Immunohistochemistry, Cytology, and Quantitative Cyst Fluid Chemistry

Abstract

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.

Impact of Pancreatic Cyst Fluid CEA Levels on the Classification of Pancreatic Cysts Using the Papanicolaou Society of Cytology Terminology System for Pancreaticobiliary Cytology

“…3,6 Although only four of the cases had surgical follow-up of adenocarcinoma, no clear identification of a difference in CEA level between malignant and premalignant lesions could be established, in agreement to previous reports. 14 Interestingly, review of these two cases confirmed the original surgical diagnoses: one was an epidermoid/lymphoepithelial cyst for which abnormal high CEA levels have already been reported 15,16 and the other was a case of chronic pancreatitis with complicated pseudocyst formation. This is especially important because it can dictate surgical intervention.…”

“…6,7 Even though two of our cases had false-positive elevated CEA levels, specificity of the new classification was still high, in agreement to a similar recently published study. 14 Interestingly, review of these two cases confirmed the original surgical diagnoses: one was an epidermoid/lymphoepithelial cyst for which abnormal high CEA levels have already been reported 15,16 and the other was a case of chronic pancreatitis with complicated pseudocyst formation. Elevated CEA levels have also been described earlier on some patients with pancreatitis, and it may be misleading in isolated individual cases.…”

Experience and future perspectives on the use of the Papanicolaou Society of Cytopathology Terminology System for reporting pancreaticobiliary cytology

“…This is especially true for cysts where the use of the PB System with its multimodal approach incorporating biochemical and radiological analysis into the cytological diagnosis has reportedly decreased the number of nondiagnostic samples and increased both sensitivity and negative predictive value for the detection of mucinous cysts . Although mucinous neoplasms may present with a low CEA, cyst fluid with an elevated CEA level above 192 ng/mL is highly specific for a mucinous neoplasm with only rare exceptions such as lymphoepithelial cysts or very rarely, pseudocysts …”

“…[11][12][13] Although mucinous neoplasms may present with a low CEA, cyst fluid with an elevated CEA level above 192 ng/mL is highly specific for a mucinous neoplasm with only rare exceptions such as lymphoepithelial cysts or very rarely, pseudocysts. 11,14,15 Atypical remains a diagnosis of indeterminate atypia for both pancreas and bile duct brushings (BDBs). The main reasons reported for atypical diagnoses include low cellularity and scant mucinous material.…”

Benign Tumors and Tumorlike Lesions of the Pancreas

“…Preoperative differential diagnosis of these may be difficult, especially in the setting of elevated fluid CEA levels and acellular cytology 94, 95 . However, their distinction at the microscopic level is fairly straight forward 90 .…”