Fetiform teratoma with amnionitis causing rapid abdominal distension in an infant: a case report

Introduction Fetiform teratoma is an extremely rare condition usually presenting in infancy with a bizarre truncal mass containing incomplete well differentiated organoid tissue. Fetiform teratoma containing amnion has not previously been described. Case Presentation A 5-month-old malnourished female presented with a multicystic retroperitoneal mass causing progressive abdominal distension. Initial biopsy suggested pancreatic tissue, leading to a provisional diagnosis of a pancreatic pseudocyst, with mesenteric lymphatic malformation also considered. Rapid accumulation of ascites over 2 weeks led to respiratory collapse and abdominal compartment syndrome despite repeated large volume drainage. At laparotomy, a cystic-and-solid mass at the mesenteric root between the porta hepatis and superior mesenteric artery origin was resected. Histology demonstrated inflamed amniotic membrane, accounting for the escalating fluid production, alongside benign mature and immature tissues of the central nervous system, ophthalmic, respiratory and various connective tissues, consistent with fetiform teratoma with overlapping features of fetus in fetu. Postoperatively, the patient required ventilatory and nutritional support but improved steadily, with resolution of ascites, and normalization of biochemical derangements. She was discharged on postoperative day 15 and remains well at 6-year follow-up. Conclusion Inflammation of amnion in fetiform teratoma can lead to the production of a large amount of fluid and can result in rapid abdominal distension.