Endoscopic ultrasonography-guided fine-needle aspiration cytology of surgically confirmed cystic pancreatic neuroendocrine tumors: A Mayo Clinic experience

Introduction: Endoscopic ultrasonography-guided fine-needle aspiration (EUS-FNA) cytology is widely used to evaluate solid and cystic pancreatic lesions preoperatively. Pancreatic neuroendocrine tumors (PanNETs) are typically solid, but when they are cystic, differentiation from other pancreatic cystic neoplasms can be challenging. We examined cases of cystic PanNETs (cPanNETs) from 3 Mayo Clinic Hospitals focusing on the EUS-FNA cytology. Materials and methods: A total of 21 EUS-FNA cases of cPanNETs with histology confirmation were identified from the Mayo Clinic Health System database. The patients' demographic data, clinical, radiological, and EUS characteristics were obtained. EUS-FNA cytology and surgical pathology were reviewed. Results: Among the 21 patients with cPanNETs, only 2 of 21 cases had suggestion of cPanNET on preoperative imaging (computed tomography/magnetic resonance imaging). On EUS, most cPanNETs (16/ of 21) had ≥1 high-risk stigmata or worrisome feature per the Sendai Consensus guidelines. None of the cases had an elevated carcinoembryonic antigen level. EUS-FNA cytology was positive or suspicious for cPanNET in 15 of 21 cases (71.4%). Immunohistochemical stains of neuroendocrine markers were performed on all the positive or suspicious cases and showed positivity for ≥1 neuroendocrine marker. All cases had surgical resection and the diagnosis of cPanNET was confirmed on each case. Conclusions: Although computed tomography/magnetic resonance imaging has a low specificity for detecting cPanNETs, high-risk features on EUS and low carcinoembryonic antigen levels should raise the suspicion for cPanNET. EUS-FNA cytology along with immunohistochemical stains has a high accuracy in establishing the preoperative diagnosis of cPanNET.