Case Report: Pancreatic sclerosing epithelioid mesenchymal neoplasm (SEMN) with novel pancreatic duct obstruction in a middle-aged female.

Pancreatic sclerosing epithelioid mesenchymal neoplasms (SEMN) are extremely rare mesenchymal tumors, with only approximately 10 cases reported globally to date, resulting in limited understanding of their clinical, imaging, and pathological characteristics. We present a 55-year-old female admitted to our hospital following the incidental detection of a pancreatic mass during a routine health check-up. The patient had no specific clinical symptoms or relevant medical history. Preoperative multimodal imaging-including computed tomography (CT), dynamic contrast-enhanced MRI (dynamic contrast MRI), and positron emission tomography (PET)/CT-revealed a 1.6 × 1.4 cm solid lesion at the pancreatic body-neck junction, with a novel, previously unreported radiological feature: main pancreatic duct (MPD) interruption and distal dilation. Combined with postoperative histopathological findings of direct tumor infiltration into the MPD wall and disruption of ductal epithelium, this confirmed true ductal invasion rather than mechanical compression. Due to overlapping imaging manifestations with common pancreatic tumors, initial differential diagnosis strongly favored pancreatic neuroendocrine tumor (pNET). A preoperative attempt at duodenoscopic pancreatic duct stenting was performed to restore ductal patency and facilitate organ-sparing resection; however, the procedure failed, presumably due to tumor infiltration of the MPD. Intraoperative frozen section analysis was unable to definitively characterize the lesion, prompting laparoscopic spleen-preserving distal pancreatectomy (SPDP) to ensure complete resection and rule out malignancy. Postoperative histopathology demonstrated nests of epithelioid and spindle cells embedded within a dense sclerotic stroma, and immunohistochemical staining (Vimentin+, CK8/18+, CD99+; Syn-, CgA-, INSM1-) confirmed the diagnosis of SEMN. The patient had an uneventful postoperative recovery, with no evidence of recurrence or metastasis at the one-year follow-up. This case expands the clinical and imaging spectrum of SEMN by documenting its occurrence in middle-aged females and identifying MPD obstruction as a novel radiological phenotype. It further highlights the diagnostic pitfalls of SEMN due to imaging overlap with prevalent pancreatic tumors, and provides valuable insights for preoperative differential diagnosis and individualized surgical management-particularly the necessity of adapting resection strategies when minimally invasive ductal interventions fail to enable organ-sparing procedures. Collectively, our findings underscore the importance of integrating preoperative imaging, interventional outcomes, intraoperative observations, and postoperative immunohistochemical results to avoid misdiagnosis of this rare entity.