• Vol. 34 No. 10, 646–649
  • 15 November 2005

Fetus-in-fetu in the Pelvis: Report of a Case and Literature Review



Introduction: Fetus-in-fetu is an extremely rare condition in which a malformed fetus is found in the body of its twin. To our knowledge, fewer than 100 cases have been reported. Wide variations of presentation have been described, although its embryo-pathogenesis and differentiation from a teratoma have not been well established. Clinical Picture: We describe a male neonate with a fetoid-like mass in his pelvis associated with bilateral undescended testes. The mass was detected on prenatal ultrasound scans. The diagnosis of fetus-in-fetu was considered prenatally and confirmed on a computed tomography scan after birth. Outcome: The mass was successfully excised. Histological examination, accompanied by a review of the literature, confirmed that the mass had features consistent with a fetus-in-fetu. Conclusions: Although an extremely rare clinical entity, fetus-in-fetu can be diagnosed prior to surgery with current imaging modalities. When it arises in the retroperitoneum of a male infant, it can hinder the descent of the testes. Complete excision is curative.

Baby A was delivered at 37-week and 4-day gestation via elective caesarean section. His mother was a healthy 33- year-old with a previous uneventful pregnancy. There was no history of consanguinity and no family history of multiple pregnancies. In the current pregnancy, there was no maternal illness, history of drug intake or exposure to radiation. A fetal anomaly scan at 20-week gestation showed a grossly normal, singleton fetus. An intra-abdominal mass in the fetus was detected on a growth scan at 31 weeks. A repeat scan at 33 weeks confirmed the presence of a cystic mass with solid components. It was behind the bladder and measured 65 mm x 31 mm with a volume of 25 cm3. The solid component within measured 29 mm x 16 mm x 16 mm. The mass was thought to represent either a well-differentiated teratoma or a fetus-in-fetu.

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