Craniopagus parasiticus

Craniopagus parasiticus is a medical condition in which a parasitic twin head with an undeveloped (or underdeveloped) body is attached to the head of a developed twin.

Cases
There have only been ten documented cases of this phenomenon, though to-date there have been at least eighty separate cases of this phenomenon written about in various records. Only three ever have been documented by modern medicine to have survived birth.
 * On December 10, 2003, Rebeca Martínez was born in the Dominican Republic with this rare condition. She was the first baby born with the condition to undergo an operation to remove the second head. She died on February 7, 2004, after an 11-hour operation.`
 * On February 19, 2005, 10 month old Manar Maged underwent a successful 13-hour surgery in Egypt, but she died March 25, 2006 due to an infection in her brain. . Manar had been featured on an episode of The Oprah Winfrey Show and in the British documentary series BodyShock.
 * An earlier case was the so-called "Two-Headed Boy of Bengal," who was born in 1783 and died of a cobra bite in 1787. His skull remains in the collection of the Hunterian Museum of the Royal College of Surgeons of London.

Prognosis
Prognosis for craniopagus parasiticus is generally poor. As of 2007, only three cases are known to have survived childbirth. Everard Home described the first and longest-lived of these, the "Two-Headed Boy of Bengal", who survived until bitten by a cobra in 1787, at the age of four. More recent cases have attracted considerable media attention as well as efforts to correct the condition through surgery. An infant girl in the Dominican Republic died in 2004 from complications in surgery. Egyptian doctors, having studied evidence of that operation, successfully removed the parasitic twin from an infant, named Manar Maged, in 2005; however, she succumbed to an infection the following year. The twin removed in this case could smile, blink, cry, and tried to suckle but never developed a body (except a small remnant), or lungs and heart, and instead was dependent on oxygen and nutrients provided by Manar. The case illustrates that there is a continuum from craniopagus parasiticus to the phenomenon of the conjoined twin.