Pancreatic serous cystadenoma masquerading as malignancy.

Pancreatic cysts include benign, premalignant and malignant lesions. Distinguishing them preoperatively remains challenging due to overlapping features. Serous cystadenomas are benign but can mimic other neoplasms, including pancreatic neuroendocrine tumours. We describe a case of a female in her 80s with an incidentally detected pancreatic tail mass and a history of resected melanoma. 18F-fluorodeoxyglucose positron emission tomography (PET) showed mild uptake, while chromogranin-A and urinary 5-hydroxyindoleacetic acid were slightly elevated. Magnetic resonance imaging (MRI) demonstrated a complex cystic lesion with a central scar favouring serous cystadenoma. However, gallium-68 PET and endoscopic ultrasound morphology raised suspicion for a pancreatic neuroendocrine tumour, with gallium uptake suggesting somatostatin receptor expression. Fine needle aspiration was non-diagnostic. Given the discordant findings and inability to exclude malignancy, robotic distal pancreatectomy and splenectomy were performed. Histopathology confirmed a benign serous cystadenoma. This case highlights the diagnostic challenges of pancreatic cysts and the potential for conflicting multimodal investigations.