Fig. 2

a Abdominal CT at the time of detection (a) and preoperative CT (b) revealed low-density cystic tumor in the tail of the pancreas in all phases (arrow), but no septum or nodules were detected in the cyst. b Endoscopic ultrasound showed a cystic tumor with a septum (arrow). c Magnetic resonance imaging showed a low-intensity T1 signal and high-intensity T2 signal in the tumor. d The resected cyst specimen contained serous and yellow fluid. e Microscopic examination showed that the tumor was a unilocular cyst and had a thin septum. The epithelial cells were lined with a single layer of cuboidal pancreato-biliary cells (arrow) and had no sign of malignancy. The cellular ovarian stroma was present beneath the epithelium with hematoxylin and eosin staining. Immuno-pathologically, the tumor showed nuclear expression of an estrogen receptor and a progesterone receptor in the stromal cells, and the epithelial cells showed no expression of MUC1, 2, 5AC, and 6, which showed that the tumor had an ovarian-like-stroma but not MUC secretion. CT computed tomography, MUC mucin