Abstract
A 75-year-old woman was referred for evaluation of a pancreatic cystic lesion. Serum tumor markers were normal. Contrast-enhanced computed tomography revealed a 35 mm cystic lesion in the pancreatic body with a 7 mm enhancing mural nodule. Magnetic resonance imaging showed slight T1 hyperintensity, T2 hypointensity, and diffusion restriction of the nodule. Contrast-enhanced endoscopic ultrasound demonstrated a broad-based mural nodule with a slightly irregular surface, heterogeneous internal echogenicity, and persistent enhancement from the early to late phases. The lesion was preoperatively diagnosed as branch-duct intraductal papillary mucinous neoplasm (IPMN) with high-risk stigmata, and middle pancreatectomy was performed. Histopathological examination showed that the cystic lesion was a gastric-type IPMN. The mural nodule consisted primarily of pleomorphic and spindle-shaped atypical cells in a hyalinized stroma with focal multinucleated giant cells. Transition from adenocarcinoma to undifferentiated carcinoma identified in the superficial layer led to the final diagnosis of spindle cell-type undifferentiated carcinoma arising from IPMN. This rare case suggests that even a small mural nodule in a pancreatic cystic lesion may exhibit histologically aggressive features. However, preoperative diagnosis of undifferentiated carcinoma of the pancreas remains challenging. Therefore, when a mural nodule is detected in a pancreatic cystic lesion, the treatment strategy, including the surgical procedure, should be carefully considered.