Cytological Identification of a Rhabdoid Variant of Pancreatic Neuroendocrine Neoplasm.

Pancreatic neuroendocrine tumors (PanNETs) are rare epithelial neoplasms with endocrine differentiation. Although most PanNETs exhibit typical cytological features, uncommon morphological variants occasionally occur. We report the first case of a rhabdoid-type PanNET diagnosed solely by cytology. A 48-year-old woman was incidentally found to have a pancreatic head mass. Endoscopic ultrasound-guided fine-needle aspiration cytology revealed tumor cells with eccentric nuclei, granular chromatin, and prominent eosinophilic intracytoplasmic inclusions, which were highlighted by Giemsa staining. Immunocytochemistry demonstrated strong cytokeratin positivity within the inclusions along with the expression of neuroendocrine markers. This case underscores that rhabdoid-type PanNET can be diagnosed through the cytological identification of distinctive intracytoplasmic inclusions and confirmed by immunocytochemistry. Awareness of this rare phenotype is essential for accurate diagnosis and improved clinicopathological understanding of PanNET variants.