Cytology Histology Correlation of Pancreatic Fine Needle Aspiration Biopsy Samples: Pitfalls and Lessons Learned

Summary: Introduction: Cytology-histology correlation (CHC) is a useful quality assurance tool which helps to identify sources of systematic error and improve diagnostic accuracy. Here we report our experience with CHC of pancreatic fine needle aspiration biopsy (FNAB) samples. Materials and Methods: Under IRB approval, the internal cytopathology laboratory quality assurance database was searched for cases of pancreatic FNAB with subsequent surgical pathology (SP) samples during a 20-month period. The final FNAB and SP reports were compared. The pancreatic FNAB cases were categorized according to the WHO System for Reporting of Pancreaticobiliary Cytopathology. Results: Forty correlation events were identified with the following FNAB diagnostic categories: 14 malignant, 2 suspicious, 3 pancreaticobiliary neoplasm: high-risk/grade (Pan-high), 11 pancreaticobiliary neoplasm: low-risk/grade (Pan-low), 4 atypical, 3 negative, and 3 nondiagnostic. The 16 malignant/suspicious cases were malignant on SP, including 9 neuroendocrine tumors (NET) and 7 adenocarcinomas. Two Pan-high cases correlated with the SP, including 1 intraductal papillary mucinous neoplasm (IPMN) with high grade dysplasia (HG) and 1 intraductal oncocytic papillary neoplasm, both with microscopic foci of invasion. One Pan-high showed IPMN with low grade dysplasia (LG). Four Pan-low cases correlated with the SP (2 IPMN with LG, 2 mucinous cystic neoplasms), and 6 Pan-low had IPMN with LG and focal HG. One case with an acellular aspirate but elevated CEA and low glucose classified as Pan-low was lymphoepithelial cyst on SP. Conclusions: Pancreatic FNAB CHC showed a high rate of correlation. Discrepancies occurred most often in the Pan-high and Pan-low categories. Intermediate grade dysplasia in the SP accounted for interpretation as HG dysplasia on FNAB. HG dysplasia may be focal, and not sampled on FNAB. One case illustrated a pitfall when relying solely on biochemical analysis to classify a cyst fluid, as CEA and glucose may lead to a false assessment of mucinous cyst.