Fetus in fetu

Anteroposterior abdominal radiograph shows a soft-tissue mass in the right hemiabdomen. The mass contains calcified osseous-appearing structures of varying sizes and shapes.
The postoperative specimen from the previous image shows a fairly well developed fetus lying on its back, with rudimentary digits.
A computed tomography scan of the same patient's abdomen pre-operation reveals a large retroperitoneal soft-tissue mass. There are long hyperdense opacities that resemble fetal bones.

Fetus in fetu (or foetus in foetu) is a rare developmental abnormality in which a mass of tissue resembling a fetus forms inside the body of its twin. An early example of the phenomenon was described in 1808 by George William Young.[1]

There are two hypotheses for the origin of a fetus in fetu. One hypothesis is that the mass begins as a normal fetus but becomes enveloped inside its twin.[2] The other hypothesis is that the mass is a highly developed teratoma. Fetus in fetu is estimated to occur in 1 in 500,000 live births.[3]

  1. ^ Young GW (1808). "Case of a Fœtus found in the Abdomen of a Boy". Medico-Chirurgical Transactions. 1: 236–264. PMC 2128792. PMID 20895115.
  2. ^ Chua JH, Chui CH, Sai Prasad TR, et al. (2005). "Fetus-in-fetu in the pelvis" (PDF). Annals of the Academy of Medicine Singapore. 34: 646–9. Archived from the original (PDF) on 2007-10-11.
  3. ^ Grant P, Pearn JH (May 1969). "Foetus-in-foetu". The Medical Journal of Australia. 1 (20): 1016–1019. doi:10.5694/j.1326-5377.1969.tb49866.x. PMID 5815070. S2CID 209072187. — source not consulted; cited here following Hoeffel CC, Nguyen KQ, Phan HT, Truong NH, Nguyen TS, Tran TT, Fornes P (June 2000). "Fetus in fetu: a case report and literature review". Pediatrics. 105 (6): 1335–1344. doi:10.1542/peds.105.6.1335. PMID 10835078.