Fetus in fetu
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Fetus in fetu (or foetus in foetu) is a developmental abnormality in which a mass of tissue resembling a fetus forms inside the body. There are two theories of origin concerning "fetus in fetu". One theory is that the mass begins as a normal fetus but becomes enveloped inside its twin. The other theory is that the mass is a highly developed teratoma. "Fetus in fetu" is estimated to occur in 1 in 500,000 live births.
Classification as life
A fetus in fetu can be considered alive, but only in the sense that its component tissues have not yet died or been eliminated. Thus, the life of a fetus in fetu is akin to that of a tumor in that its cells remain viable by way of normal metabolic activity. However, without the gestational conditions in utero with the amnion and placenta, a fetus in fetu can develop into, at best, an especially well differentiated teratoma; or, at worst, a high-grade metastatic teratocarcinoma. In terms of physical maturation, its organs have a working blood supply from the host, but all cases of fetus in fetu present critical defects, such as no functional brain, heart, lungs, gastrointestinal tract, or urinary tract. Accordingly, while a fetus in fetu can share select morphological features with a normal fetus, it has no prospect of any life outside of the host twin. Moreover, it poses clear threats to the life of the host twin on whom its own life depends.
Theories of development
There are two main theories about the development of fetus in fetu.
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 their survival depends on the survival of their 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 unable to survive on its own. As the host twin has to "feed" the enveloped twin from the nutrients received over a single umbilical cord, they usually die before birth.
Examples from history and in the media
An early example of the phenomenon was described in 1808 by George William Young. 
Cases of fetus in fetu sometimes attract worldwide media attention. These cases are a small minority of the known cases and rarely overlap with cases reported in the medical literature, but they are widely accessible.
- In June 1999, the case of Sanju Bhagat, a man from Nagpur, India attracted attention for the length of time (36 years) he had carried his parasitic "twin" inside his body, and the size of the growth, that had connected directly to his blood supply. Much of the size of the swelling was accumulated sebaceous secretions and hair shed from the parasite's skin.
- Alamjan Nematilaev was the surviving host of a fetus in fetu. In 2003, aged 7, his school physician in Kazakhstan referred him to a hospital after movements were detected in the boy's enlarged abdomen. An operation intended to remove a cyst uncovered the fetus of Alamjan's identical twin brother, which had lived as a 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 March 2006, doctors in Pakistan removed two fetuses from inside a two-month-old baby girl.
- In November 2006, a Chilean boy in Santiago was diagnosed with fetus in fetu shortly before birth.
- In August 2007, two-month-old Eljie Millapes from Baguio, the Philippines, was diagnosed with fetus in fetu. The parents of Millapes were alarmed by the abnormal growth of the abdomen of their baby. Doctors later discovered that she was suffering from fetus in fetu.
- In May 2008, a two-inch (5 cm) embryo was removed from the belly of a 9-year-old girl at Larissa General Hospital in Greece after she was diagnosed with a tumor on the right side of her belly. The embryo was a fetus with a head, hair and eyes, but no brain or umbilical cord.
- On June 30, 2008, in China, a newborn baby with this condition had an extra penis growing out of its back. Doctors spent three hours removing it, and the child was fine afterward.
- In October 2008, a doctor in the United States removed a brain tumor from Sam Esquibel that consisted of a foot and other body parts. This may have been a case of fetus in fetu or it may have been a teratoma.
- In September 2009, one-year-old Kang Mengru from China was "pregnant" with her own twin. After 10 hours of complex surgery to remove the fetus, Kang's family was told she could return home at the end of the month. She made a full recovery. 
- In November, 2010, a baby girl born in Hong Kong was found to have two 8-10 week old fetuses in her abdomen, originally thought to be tumors. They were removed by surgery. Reported by the Hong Kong Medical Journal in February 2015. 
- In September 2011, a 41-year-old man in Arjawinangun Public Hospital, Cirebon, Indonesia was diagnosed with a tumor in his abdomen. An operation was performed on October 4, 2011, which revealed the suspected tumor to actually be a fetus.
- In January 2016, an 18-year-old teenager in India had a successful operation to remove a retained twin from his abdomen after suffering chronic stomach pains. 
Examples in fiction
- Many of Philip K. Dick's works have an "unborn" twin, such as Dr. Bloodmoney.
- Jonas Venture Jr. of The Venture Bros. cartoon series is a fetus in fetu who manages to survive extraction from his encapsulating twin, Doctor Thaddeus Venture.
- Stephen King's The Dark Half proposes the possible delayed awakening of an unborn twin in the protagonist's body and mind.
- In the 1990 film Total Recall, George/Kuato, the mutant leader of the resistance attached to his unmutated brother
- Black Jack by Osamu Tezuka has a chapter dealing with the condition. After being removed, the fetus in fetu is given a prosthetic body and becomes the title character's sidekick for the rest of the series.
- The concept is also the central theme of the novel Passenger by Billy Cowie (published by Old Street Publishing 2008) where the main character Milan discovers his sister Roma is embedded in himself and spends the remainder of the book attempting to communicate with her.
- My Big Fat Greek Wedding's Aunt Voula casually mentions a "lump" that turned out to be her "unborn twin" in passing after the Miller family is accepted as in-laws to the lead character.
- The TV show X-Files episode "Humbug" (Season 2) centers on a fetus in fetu that is able to leave the host-twin's body for a limited time.
- The comedy/horror film Basket Case centers on a man's murderous parasitic brother.
- In the comedy series The Office (U.S. TV series) Dwight attributes his strength to the dead fetus he absorbed at birth.
- In the comedy series Community (TV series), Chang states that he consumed his twin sibling's fetus in utero.
- In the opening chapter of the manga Jin by Motoka Murakami, a patient undergoing surgery to remove a brain tumor surprised everyone when instead of a tumor, something that appeared to be a fetus in fetu was removed from his brain.
- In the animated comedy South Park, Nurse Gollum is said to have a fictional but related condition called "conjoined twin myslexia".
- In the medical TV drama series Grey's Anatomy ("We Gotta Get Out of this Place"), a man becomes emotionally attached to his "brother".
- In the 1978 horror movie The Manitou a woman suffers from a growing tumor on her neck, that X-rays show contains a fetus.
- Chua, JHY; 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.
- Grant P, Pearn JH (May 1969). "Foetus-in-foetu". Med. J. Aust. 1 (20): 1016–9. PMID 5815070. — source not consulted; cited here following Hoeffel CC, Nguyen KQ, Phan HT, et al. (June 2000). "Fetus in fetu: a case report and literature review". Pediatrics 105 (6): 1335–44. doi:10.1542/peds.105.6.1335. PMID 10835078.
- "Journal of Medical Case Reports | Full text | Fetus in fetu : a case report". Jmedicalcasereports.com. Retrieved 2012-11-22.
- Basu A, Jagdish S, Iyengar KR, Basu D (October 2006). "Fetus in fetu or differentiated teratomas?". Indian J Pathol Microbiol 49 (4): 563–5. PMID 17183856.
- George William Young (1808). "Case of A Foetus found in the Abdomen of a Boy" (PDF). Ncbi.nlm.gov. Retrieved 2012-11-22.
- "Man With Twin Living Inside Him - A Medical Mystery Classic - ABC News". Abcnews.go.com. 2006-08-23. Retrieved 2012-11-22.
- Alok Jha. "How did that boy end up with his twin growing inside him? (July 17, 2003) | Science | Retrieved 23 May 2014". London: The Guardian.
- "Surgeons remove two fetuses from infant - Health | NBC News". MSNBC. 2006-03-28. Retrieved 2012-11-22.
- "Boy born with fetus in his stomach - Health - Health care - More health news | NBC News". MSNBC. 2006-11-24. Retrieved 2012-11-22.
- "Fetus inside a baby; 'broken' food | Public Affairs | GMA News Online | The Go-To Site for Filipinos Everywhere". Gmanews.tv. 2007-08-01. Retrieved 2012-11-22.
- "Bearing Your Own Twin - ABC News". Abcnews.go.com. 2008-05-16. Retrieved 2012-11-22.
- Thomson, Katherine (June 10, 2008). "Baby Born With Second Penis On Back (PHOTO)". Huffington Post.
- "'I've never seen anything like it,' doctor says of newborn's brain surgery | brain, sam, doctor - Top Stories - Colorado Springs Gazette, CO". Gazette.com. 2008-12-15. Retrieved 2012-11-22.
- "Baby born with 'foot in brain'". BBC (London). December 19, 2008. Retrieved 2008-12-21.
US surgeons operating on a brain tumour in a baby boy found a tiny foot inside his head.
- "China's Kang Mengru survives twin foetus removal in Zhenzhou | Mail Online". London: Dailymail.co.uk. 2009-09-22. Retrieved 2012-11-22.
- Pang Kristine KY, Chao, Nicholas SY, Tsang, TK; et al. (February 2015). "From observation to aetiology: a case report of a twin fetus-in-fetu and a revisit of the known rarity". Hong Kong Medical Journal 21 (1): 80–83. doi:10.12809/hkmj133925.
- "Report of a Case and Literature Review : Fetus in Fetu Laki-laki Hamil Selama 41 Tahun ( Pregnancy in Male For About 41 Years ) « Dr Herry S Yudha Utama SpB MHKes FInaCS". Herrysetyayudha.wordpress.com. 2011-11-23. Retrieved 2012-11-22.
- Dr. Herry Setya Yudha Utama SpB MHKes FInaCS ICS (2011-11-22). "Dr Herry Setya Yudha Utama SpB. MHKes. FInaCS. ICS: Case Report and Literatur Review : Fetus in Fetu Laki-laki Hamil Selama 41 Tahun ( Pregnancy in Male For About 41 Years )". Herryyudha.blogspot.com. Retrieved 2012-11-22.
- Clee, Nicholas (2007-03-02). "The marriage of music and science". The Guardian (London).
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