Fetus in fetu

Overview
Fetus in fetu (or fœtus in fœtu) is a developmental abnormality containing entire organ systems, even major body parts such as torso or limbs. The abnormality occurs in 1 in 500,000 live births.

Theories of development
There are two main theories about the development of fetus in fetu; one simple, the other complex.

Teratoma theory
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.

Examples

 * 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.