Fetus in fetu
Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Synonyms and keywords: Fœtus in fœtu
Fetus in fetu is a developmental abnormality containing entire organ systems, even major body parts such as torso or limbs.
- Alamjan Nematilaev was the surviving host of a fetus in fetu. In 2003, aged 7, his school physician in Kazakhstan referred him to hospital after movements were detected in the boy's enlarged stomach. An operation intended to remove a cyst uncovered the fetus of Alamjan's identical twin brother, which had lived as parasitic growth inside the boy throughout his entire life. The fetus was comparatively highly developed, with hair, arms, fingers, nails, legs, toes, genitals, a head, and a vague approximation of a face.
- In June 1999, Sanju Bhagat, a man from Nagpur, India, was rushed to a hospital due to difficulty breathing. There, a surgical team removed from his bulging belly a teratoma, a kind of tumor. The report described that the surgical team found a living half-formed "creature" inside Mr. Bhagat's belly.
- In November 2006, a Chilean boy in Santiago was diagnosed with fetus in fetu shortly before birth. 
Theories of Development
There are two main theories about the development of fetus in fetu; one simple, the other complex.
Fetus in fetu may be a very highly differentiated form of dermoid cyst, itself a highly differentiated form of mature teratoma.
Parasitic Twin Theory
Fetus in fetu may be a parasitic twin fetus growing within its host twin. Very early in a monozygotic twin pregnancy, in which both fetuses share a common placenta, one fetus wraps around and envelops the other. The enveloped twin becomes a parasite, in that its survival depends on the survival of its host twin, by drawing on the host twin's blood supply. The parasitic twin is anencephalic (without a brain) and lacks some internal organs, and as such is almost always unable to survive on its own.
Sometimes, however, the host twin survives and is delivered. The parasitic twin grows so large that it starts to harm the host, at which point doctors usually intervene. The condition causes the host to look pregnant, and can occur in both males and females.
Epidemiology and Demographics
The abnormality occurs in 1 in 500,000 live births.
- ↑ Chua, JHY (2005). "Fetus-in-fetu in the pelvis" (PDF). Annals of the Academy of Medicine Singapore. 34: 646–649. Unknown parameter
- ↑ "How did that boy end up with his twin growing inside him?" The Guardian, July 17, 2003, accessed June 4, 2007
- ↑ "The Boy Who Gave Birth to His Twin", Channel 4, December 2003, accessed June 4, 2007
- ↑ "Man With Twin Living Inside Him—A Medical Mystery Classic", ABC News
- ↑ "Chilean boy born with fetus in his stomach", MSNBC, November 24, 2006, accessed June 4, 2007
- ↑ Basu, A (Oct 2006). "Fetus in fetu or differentiated teratomas?". Indian Journal of Pathology and Microbiology. 49 (4): 563–565. Unknown parameter
- ↑ Grant P, Pearn JH Foetus-in-foetu. Med J Aust. 1969; 1:1016-1020 — source not consulted; cited here following Hoeffel CC, Nguyen KQ, Phan HT, Truong NH, Nguyen TS, Tran TT, Fornes P. Fetus in fetu: a case report and literature review. Pediatrics. 2000 Jun;105(6):1335-44. PMID 10835078 free full text
- Video clip of Sanju Bhagat's surgery, the fetus in fetu after removal, and interviews
- A fictional depiction of the problem.