The recognition of epithelial cells with high-grade atypia (HGA) in the cyst fluid of an intraductal papillary mucinous neoplasm (IPMN) identifies a cyst at high risk of invasive carcinoma. To the best of the authors' knowledge, the cytological features of HGA have not been systematically analyzed to define diagnostic criteria.
Cell groups from patients with histologically confirmed branch-duct IPMNs were evaluated by 2 cytopathologists with expertise in pancreatic cytology. A consensus interpretation categorized the cell groups as having either low-grade (LG) or high-grade (HG) morphology. Characteristics regarding cell size and architecture, nuclear and cytoplasmic features, and background necrosis were analyzed. Performance characteristics were assessed using the Fisher exact test at 95% confidence intervals.
Sixty cell groups yielded 27 LG and 25 HG morphological groups. No consensus was reached for 8 groups, which were excluded from statistical analysis. Five features that were found to be significantly different between the LG and HG groups included: 1) cell size <  a 12-μm duodenal enterocyte for HG and size equal for LG; 2) an increased nuclear-to-cytoplasmic (N/C) ratio; 3) marked nuclear membrane abnormalities; 4) abnormal chromatin pattern; and 5) background necrosis. The 3 most accurate features for the identification of HGA were background necrosis (88%), abnormal chromatin pattern (84%), and an increased N/C ratio (82%).
IPMN cyst fluid at high-risk of malignancy can be recognized most accurately by the presence of epithelial cells with HGA showing an increased N/C ratio, an abnormal chromatin pattern, and background necrosis.