Joined at the Hip

Siamese twins, or conjoined twins, are twins that are connected at birth. The first case of documented Siamese twins was in Armenia in the year 945. The conjoined twin brothers were seen in Constantinople where they had traveled for medical evaluation. However, it is possible that Siamese twins predated the year 945 due to the fact that ancient Peruvian ceramics depict these twins in work that was constructed around 300 A.D. Now the term “Siamese twins” is politically incorrect and the term “conjoined twins” has taken its place. This name came from the twins Chang and Eng Bunker, who were joined at the torso and shared a liver. They lived in Thailand in from 1811-1874 but back then the country’s name was Siam. The twins got famous in P.T. Barnum’s traveling circus and were called the Siamese twins.

It cannot be medically proven at this time as to the cause of conjoined twins. Two theories stand however that can explain this phenomenon. The most accepted theory is called fission. Usually, when twins are born these two parts of the egg cell separate completely causing the development of two equal babies. In fission, the egg cell splits partially, developing in two almost separate balls of cells. Then the conjoined twins cells become confused about where they are in the body and they do not know which twin they are in. When babies are developing in the embryo and fetus stages in a normal, healthy child, their cells produce chemical messages telling other cells where they are. That way you do not have liver cells developing with heart cells and so on. In conjoined twins the cells might be making liver cells for one egg cell and put them in the other egg cell not knowing that it is a separate “baby” over there and that it is making a “bad order.” Because of this too many or not enough body parts can be made and they can end up in the wrong place, such as a single child with two heads or two hearts. Some debate whether this is really just one child with extreme abnormality, or if it is actually two children linked together.

The other theory of development of conjoined twins is called fusion. In the fusion theory the fertilized egg cell does completely separate into two cells, like it would in the normal development of twins. Stem cells are cells which search for similar cells and are present in fetuses are what cause the conjoinment. Stem cells from each fetus find stem cells on the other and then connect fusing the two babies together in that way. The theory of fusion is more recent due to the fact that stem cell research has only gone underway in the recent past.

Having conjoined twins should not be something a mother has to worry about because it is a quite rare happening. It is an estimated percentage that 1 in every 200,000 births results in a pair of conjoined twins. About half of these twins are born alive and a percentage of those born alive have abnormalities that make it impossible for them to live. The average survival rate for conjoined twins is 25 percent. About 75 percent of conjoined twins are females and there is a higher occurrence of conjoined twins in Southwest Asia and Africa.

There are two main types of conjoined twins: Diplopagus and Heteropagus. Diplopagus are twins joined equally, each with a nearly complete body. These twins only share a few organs or are attached in minimal ways. Heteropagus are twins joined very unequally. In this case there is usually one almost normal baby with a parasitic twin, such as a head coming off of his head or something like that. Parasitic twins result when the embryo does not separate completely at the normal stage of twin development. What happens next is one of the two halves develops normally and is dominant over the other half. That other half must cease development because it doesn’t have the resources to develop all the way because of the other’s dominance. When born, the parasitic half is incompletely formed or must depend completely on the other half for survival. In separation, the parasitic twin dies. The process of inclusion twinning is another thing that can happen naturally. In inclusion twinning the dominant twin just “absorbs” the parasitic twin during development and problems may or may not arise due to the success of development afterwards. It is possible that with inclusion twinning, that extra body parts can remain in the dominant twin.

Conjoined twins can be classified into many other categories based on their attachment. Thoracopagus is when the twins are joined at the thorax. The heart is always involved in Thoracopagus and due to this fact there are little chances for survival. Omphalopagus is the joining of the lower chest not including the heart, but including the liver, digestive system, diaphragm, and other organs. In Xiphopagous, the twins are joined only through cartilage and the survival rate is very high. In cases containing Pygopagus, the twins are joined back to back. Cephalopagus is a type of conjoinment in which the heads are fused together but the bodies are separated. Survival for these twins is rare due to abnormalities in the formation of the brain. Cephalothoracopagus is a condition where the twins are joined at the head and the thorax. Craniopagus occurs when the outer parts of the skulls are fused together but the bodies are separate. In Craniopagus Parasiticus, there is a body with a second head attached. Dicephalus is the occurrence of two heads, one body and extra limbs. Ischiopagus is the union of the lower half with separate sets of reproductive organs. Ischio-omphalopagus is the same thing with shared reproductive organs. Parapagus is the union of the lower half up to the chest, giving room for separate sets of shoulders. Diprosopus is when the twins have one head with two faces next to each other.

Usually, parents and doctors choose to separate the conjoined twins after birth. The first surgical separation of Siamese twins was in 1953. Since then, the operation has become much more successful due to advances in medical science. The place that the twins are attached and the organs that they share determine how complex the separation is. Most separations are very risky and can lead to death in one or both of the twins.