Craniopagus parasiticus

Craniopagus parasiticus is an extremely rare type of parasitic twinning occurring in about 4 to 6 of 10,000,000 births. In craniopagus parasiticus, a parasitic twin head with an undeveloped body is attached to the head of a developed twin. Fewer than a dozen cases of this type of conjoined twin have been documented in the literature. Most infants with this condition are stillborn, or die shortly after birth.