S3493 Epidermoid Cyst Arising From an Intrapancreatic Accessory Spleen Initially Misdiagnosed as Intraductal Oncocytic Papillary Neoplasm

Introduction: Pancreatic cystic lesions (PCL) ranges from benign inflammatory pseudocysts to malignant neoplasms. Most PCLs are asymptomatic and benign, the challenge lies in accurately distinguishing low-risk lesions from those with malignant potential, as misclassification can lead to unnecessary surgical resections. Case Description/Methods: A 69 year-old woman with a history of type II diabetes mellitus was referred for evaluation of an asymptomatic pancreatic tail cyst. She denied abdominal pain, weight loss, history of pancreatitis and toxic habits. Previous evaluation with endoscopic ultrasound (EUS) in another institution revealed a unilocular cyst in the pancreatic tail measuring 31 × 27 mm with internal debris. Cyst fluid analysis showed an elevated carcinoembryonic antigen (CEA) level of 7,932 ng/mL and a low amylase level of 261 IU/L. Molecular analysis was negative for KRAS, GNAS mutations, and loss of heterozygosity. Histology showed fibrotic, mildly inflamed stroma lined by bland stratified epithelium. Immunohistochemistry revealed positivity for pancytokeratin and focal CD34 staining; ER, PR, inhibin, synaptophysin, and chromogranin were all negative. Ki-67 was low. Surveillance magnetic resonance imaging a year and a half later revealed a stable cyst without mural nodules or pancreatic ductal dilation. However, repeat imaging a year later showed cyst enlargement to 44 by 32 mm. EUS was repeated and found a unilocular pancreatic tail cyst with internal debris and no solid components. Amorphous debris and foamy macrophages were obtained from the fine needle aspiration (FNA) sample. Microforceps biopsy revealed histologic features of intraductal oncocytic papillary neoplasm (IOPN). Given the increasing size and malignant potential, the patient underwent robotic-assisted distal pancreatectomy. Postoperative histopathology revealed a unilocular cyst lined by non-keratinizing squamous epithelium surrounded by splenic tissue, consistent with an epidermoid cyst in an intrapancreatic accessory spleen. The patient recovered uneventfully. Discussion: This case demonstrates the risk of misdiagnosis of pancreatic cystic lesions despite an exhaustive evaluation including repeated EUS-FNA, microforceps biopsy with histopathology, and molecular analysis of cyst fluid. Nonetheless, it also highlights the importance of surveillance and close clinical follow-up of these patients with the aim of identifying premalignant lesions of the pancreas at an early curable stage.