Craniopagus parasiticus is a rare condition characterized by parasitic twinning of newborns. It occurs in around 4 to 6 births out of 10,000,000 births. In this form of parasitic twinning, the head of a parasitic twin with an incompletely formed body is connected to the head of a fully formed and developed twin. Most babies with the condition are stillborn, or tend to die just after birth. There are not more than a dozen cases of craniopagus parasiticus that have been documented in literature.
The terms used to describe parasitic twinning has not been always consistent in the past. A parasitic twin, by definition, is attached to the other twin in a specific part or location of the body of the developed twin. The twin with developed body is considered as an autosite, while underdeveloped twin is termed as a parasite. It is possible for the autosite to also suffer from defects or abnormalities. However, in most cases, the autosite is developed sufficiently so as to be able to live on its own.
Causes and development of craniopagus parasiticus
Doctors are unaware about the exact cause craniopagus parasiticus development. However, the underdeveloped twin is regarded as the parasitic twin by all medical experts. It is known that parasitic twins form in the utero when the embryo does not fully split into two during the development of monozygotic twins into an embryo. The failure of the embryo to completely split results in the dominated development of one embryo, while the development of the other is extremely restricted. The main difference between conjoined twins and parasitic twins is the fact that, in the latter the development of one of the twins which is the parasitic twin stops during gestation, but the autosite twin continues developing fully.
During the development of normal monozygotic twins, a single sperm fertilizes one embryo. The egg then fully splits or divides into 2, usually during the 2-cell stage. If the splitting of the egg occurs during the initial blastocyst phase, 2 inner cell masses tend to form, subsequently resulting in the sharing of the same placenta and chorion by the twins, but with different amnions. It is also possible for the egg to divide into 2 but continue to have 1 blastocyst. This results in one blastocyst and one inner cell mass. In such cases, the twins tend to share the same chorion, placenta, and amnion during development. This is considered as one of the most probable causes of the occurrence of conjoined twins. It is also possible for such anomaly to have a part in the occurrence of craniopagus parasiticus.
As per one hypothesis, craniopagus parasiticus may occur due to connection of the placental and somatic vascular systems of the developing twins as well as degeneration of the parasitic twin’s umbilical cord. This hypothesis thus indicates that the condition may occur because of deficient blood flow to one of the twins.
As per another hypothesis, when a single zygote that is developing into 2 fetuses fails to split at the head area during the 2nd week of gestation, then it can trigger the commencement of craniopagus parasiticus. Some experts however think that this anomaly occurs during the later stages of development, somewhere near the 4th week of gestation. It is believed there is fusion of the 2 embryos near the front open neuropore during the 4th week of gestation.
Craniopagus parasiticus appears to be more prevalent in male infants than females. Out of the total of 9 reported cases of the condition, 7 were males. As the number of documented cases is so small, it cannot be said with certainty that the above observation has major relevance. It can however offer some data about whether the condition has a specific genetic predisposition.
Treatment of craniopagus parasiticus
As the rate of survival of craniopagus parasiticus patients after birth is very slim, surgical removal of the parasitic twin is considered as the best treatment option.
Surgical correction of the condition is however considered as extremely dangerous because only once has it been successful. The main problem with surgical removal of the parasitic twin is the fact that the arteries of the brain are interwoven in such a complex manner that controlling bleeding can be very difficult. Doctors are of the opinion that severing the arterial supply of the parasitic twin can help improve the chances of survival of the autosite twin.
Cases of craniopagus parasiticus
Out of the ten odd cases of craniopagus parasiticus reported in modern medical documentation and literature, only 3 survived after birth.
- The first case that was ever recorded is that of the ‘two-headed boy of Bengal’ reported by Everard Home. The boy was born in the year 1783. He died in 1787 due to a cobra bite. The skull/head of the boy is now kept in preservation as part of the Hunterian Museum’s collection at the Royal Society of Surgeons of London.
- Rebeca Martínez born on Dec 10, 2003, in the Dominican Republic, had a parasitic twin. She was the first baby with craniopagus parasiticus to have undergone a surgical operation, wherein the head of the parasitic twin was removed. After an operation that lasted for 7 hours, Rebecca died on Feb 7, 2004.
- Manar Maged is another infant with craniopagus parasiticus to have survived after birth. She was born in 2004 in Cairo, Egypt. Her underdeveloped parasitic twin sister Islaam’s head was attached to the head of Manar in an upward facing direction. Islaam had no limbs, but could blink, smile, and cry. When Manar was 10 months old, she became very ill and was taken to a hospital in Cairo. The doctors decided to surgically remove the parasitic twin, else both of them would end up dying. A 13-hour surgery was then carried out on Feb 19, 2005. Islaam died after the surgery as she was using the blood supply of Manar. Fourteen months later, Manar also died due to severe brain infection and other complications of the surgery. Manar was featured in Body Shock, a British documentary series, as well as in an episode of the world-famous The Oprah Winfrey Show.