High Quality Content by WIKIPEDIA articles! Craniopagus parasiticus is a rare type of Craniopagus occurring in about 4 to 6 of 10,000,000 births. Craniopagus itself occurs when the skulls of conjoined twins are fused together, but they have separate bodies. The occurrence is only about 1 in 2,500,000 births, which only accounts for 2% of conjoined twins. Craniopagus parasiticus, is even more rare with only about nine documented cases in the literature. In craniopagus parasiticus a parasitic twin head with an undeveloped (or underdeveloped) body is attached to the head of a developed twin. Most individuals with this condition are stillborn, or die shortly after or during surgery.