[A case of epidermoid cyst in the intrapancreatic accessory spleen mimicking pancreatic malignant tumor].

We report a rare case of an epidermoid cyst in the intrapancreatic accessory spleen with producing CA19-9. A 42-year-old woman was referred to department of internal medicine of our hospital due to growing cystic lesion at the pancreatic tail. Laboratory tests on admission revealed a high serum CA19-9 (102.0 U/mL). Ultrasound sonography detected a 25-mm monolocular cystic tumor with thick capsule and septum. The capsule and septum was enhanced on computed tomography. Endoscopic examination of upper gastrointestinal tract and colon revealed normal. CA19-9 was elevated up to 147.3 U/mL after 2-month follow-up, and she was referred to department of digestive surgery. We suspected a mucinous cystic neoplasm or endocrine tumor, and distal pancreatectomy was performed. The surgical specimen showed a septate cyst surrounded by brown solid tissue resembling normal spleen. The patient was discharged on postoperative day 11. Histological diagnosis was an epidermoid cyst originated from an intrapancreatic accessory spleen. Immunohistochemical analysis of CA19-9 in the epidermoid cyst showed clear staining of the inner epithelium of the cyst. The serum CA19-9 value was confirmed to decline to normal 1 month after resection.