Retroperitoneal Foregut Duplication Cyst Containing Gastric, Respiratory, and Pancreatic Tissue Misinterpreted as an Adrenal Mass on Imaging: A Case Report and Review of the Literature.

Foregut duplication cyst is most commonly seen in the posterior mediastinum without communication with adjacent organs or presence of other malformations and typically shows ectopic gastric or respiratory epithelium. The finding of ectopic pancreatic tissue is extremely rare. A 15-year-old female patient presented with elevated blood pressure, intermittent right flank pain for 18 months. An abdominal MRI revealed a 4 cm right cystic retroperitoneal mass, initially thought to arise from the right adrenal gland. Intraoperatively, the mass was centered in the retroperitoneum between the right adrenal gland and kidney, without attachments to these organs and no communication with other structures, and it was completely excised. Gross examination revealed a 3.5 cm well-circumscribed solid and cystic mass with orange-white cut surface and cloudy fluid surrounded by variable amounts of adipose tissue. On microscopic examination, the cysts were lined by respiratory and gastric antral/oxyntic-type mucosa, surrounded by muscularis mucosae, submucosal tissue, muscularis propria, and perienteric tissue. Within the muscular propria, exocrine pancreatic tissue was also noted. The patient is well with 7-months of follow up. This case is the first one reporting gastric, respiratory, and pancreatic epithelia.