Twin or Siamese twins (anatomically united twins)

Twin or Siamese twins (anatomically united twins)

Joint twins fascinated generations, being considered deities and even feared for their appearance. They are recognized as legendary figures or "monsters" from the circus. With the passage of time, they were perceived by the society to be completely separate, due to the physical and emotional connection between the two twins. The name of Siamese twins comes from the place where the first pair of united twins was born, in Siam (Thailand today).
Considered rare, the conjoined twins are still born and have a probability of survival in the first years of life of 1 to 3 cases.
A small portion of the surviving twins will be fit for separation. But the operation is not a common procedure because it is extremely risky and must be performed in a specialized medical setting.
Separation of the united twins not only requires skill, but sometimes life-saving decisions such as sacrificing one in order to increase the life chances of the other must be taken. The prognosis is reserved and depends very much on the united parties and the bodies that the two Siamese share.
The survival rate of the conjoined twins is 5-25%, and the success of separation by operation of 75% (with the survival of one or both).
Although few pairs of Siamese twins have lived to maturity, it is difficult to describe such a connection between two persons with a common existence.
With the improvement of surgical techniques, more and more Siamese twins have been separated, even if the risks are very high and often one or both of them die. The decision to separate them is primarily a matter of ethics and morals, considering the risks of the operation and the probability that one of the conjoined twins will die to save the other.
Formation of joint twins
There are two theories related to the formation of conjunct twins. It seems that the most accepted is the "fission theory" which argues that the formation of the conjoined twins takes place when the fertilized egg splits into two, in the case of twin pregnancy, and this process is interrupted by producing two partially formed, united embryonic bodies. between them.
The fission theory is quite old and has been proven and proven over the years with the scientific progress of embryology. According to newer studies, the fertilized egg first splits and then the two embryonic parts of the uterine cavity merge. The embryo, in the first months of development, consists of 3 layers of cells. They look for cells of the same type nearby to form unit organs. In fact, it is an abnormal cell signal that makes it possible to link cells from different embryos.
This process is most easily understood in Siamese craniophage twins (united at the level of the skull).
The last cellular layer of the embryo is responsible for the formation of the neural tube that results in the spinal cord and brain. It is formed as if you were running a strip of paper inside a tube until the edges come together. Spina bifida is a type of paralysis, a consequence of the improper welding of these edges of the neural tube. When two neural tubes are about to form, from the two twins, the cell layers can be "recognized" as having the same conformation and can be united.
The opinions are divided on the origin and the period of formation of Siamese twins. Most likely, they formed shortly after the conception period.
Joint twins are of two types:

- You disengaged
- which come from eggs fertilized by different sperm;

- Multiple monozygotes
- which does not separate from each other during the division of the fertilized egg.
Thus, the two twins will be united in some parts of the body and can share tissues, organs and limbs.
Like monozygotic twins, Siamese are of the same sex and race. It is estimated that 70% of the pairs of Siamese twins are girls. But this anomaly is quite rare, having an incidence of 1 to 85,000 births and 1 to 200 of the pairs of monozygotic twins.

Classification of types of joint twins

- most cases were registered in India or Africa.
- The determining factors incriminated are the genetic and environmental ones. These factors endanger the separation of the two twins on the 13th day after fertilization of the embryos.
- there were no cases of triplets or quadruplets united.
Types of joint twins
Joint twins are usually classified by their place of union (the Greek word "pagos" means "which is united") for the particularization of each case.
Classification of types of joint twins

1. A union that does not involve sharing the same heart or umbilicus

• Craniophages:
union at the cranial level - represents 2% of all the conjoined twins. These twins share the same skull box, with different necks and bodies. Separating them can be very difficult because parts of the brain and common blood vessels are involved.
Craniophages can also be divided by the cranial portion where they are united:
- Vertical craniophage - join at the top of the head, making an angle of 180 ° between them;
- occipital craniophages - united at the level of the head;
- frontal craniophages- united at the forehead level;
- parietal craniophages - join in the side of the head.

• Xipophagy:
union at the sacral level (19% of the conjoined twins). The common parts are the spine in the terminal portion and the pelvis, the two twins having their own limbs. Over time, many pairs of xifopags have been known to live to maturity. Surgical separation is performed, but with the risk of paralysis. Xipophages are also called ileophages.

2. Unification on the midline at the level of the navel

• Chest pain:
united in the upper part of the trunk, most of the time they share the same heart (35% of all the conjoined twins). Recovery is always very risky, often the two twins dying shortly after the operation.

• Cephalophagy:
these joint twins are united at the level of the upper thorax and at the level of the head with the faces in opposite directions. It is an extremely rare situation and often the twins do not share the same heart. They can be united only at the level of the head and neck, but due to the cranial malformations are not compatible with life after separation.

• Cephalothorax:
are a combination of cephalophages and thoracophages. The joint twins are glued to the head, neck and chest with separate limbs. Dividing the heart and brain and they have a very poor prognosis of survival.

• Paragliders:
they are joined laterally in the lower half of the body, usually having 3 legs. Theoretically these twins are xifotoracoischiopagi taking into account the parts where they are united.

• Ischiopagias:
unite at the level of the pelvis (pelvis) face with the spine at 180 ° from each other. They may have a common leg or separate legs. Usually, the common foot is not controlled by any of the twins being rudimentary for locomotion. 14% of the conjoined twins are hamstrings.

• Omphalopagi:
are those twins bound in the middle portion of the trunk: from the sternum to the pubic area. In the abdominal area they can share the same liver or other organs of the digestive system. These joint twins are usually easy to separate surgically.

3. Rare forms of conjoined twins

• Asymmetries
between the two Siamese twins they meet when one of them is smaller, less developed and dependent on the other.

Very rarely, when one of the twins cannot develop during the fetal period, it is embedded in the body of the other. This malformation is called fetus in fetus and is found at the birth of a healthy baby with traces or fetal pieces in his body.

Causes and diagnosis of pregnancy with twin twins

Causes of formation of conjoined twins
Twin pregnancy results when the fertilized egg is divided into two fetuses. Separation usually occurs within the first two weeks of pregnancy. If the separation is delayed, the twins suffer malformations, uniting. The connection portion between the two joint twins will be established according to the period when the egg divides and the position of the division area. However, the cause of the division delay is not known.
Diagnosis and screening tests
The increased size of the uterus compared to the normal and the presence of high heart rate are early signs of twin pregnancy. The confirmation is made ultrasound only in the 12th week. If it is a pregnancy with twin twins on ultrasound, you can see a single placenta devoid of separating membranes. But the contours of the bodies are difficult to distinguish. After the 20th week of pregnancy any imaging test can recognize the anatomical parts divided by the two twins.
50% of pregnancies with joint twins are accompanied by an excessive amount of amniotic fluid (polyhydroamnios). This change increases the risk of complications during pregnancy: premature rupture of membranes, developmental problems and even intrauterine death.
Most commonly, conjoined twins cannot be born naturally. Of the cases compatible with life, half reach the age at which they are able to be surgically separated.
The treatment of this malformation is highly dependent on the circumstances.
Many parents choose to stop the pregnancy. The prognosis and chances of success of a separation operation weigh heavily in making this decision. If babies have a common heart or brain, separation is risky.
If the parents still choose to keep the pregnancy, then the mother and children will be monitored permanently. Caesarean section is planned two or four weeks before the deadline.
After the birth of the conjoined twins it is decided by the doctors and parties whether they will be separated or not. Emergency separation is practiced when one of the twins dies and may endanger the other's life. Usually, the intervention is done two or four months after the birth with a survival rate of 80%.
There are other factors that depend on the possibility of the separation operation:
• If the twins have common vital organs.
• If the twins are healthy enough to support the intervention.
• Finding solutions for the reconstruction of the separate parts.
• Good prognosis.
• Problems encountered after separation.
If separation is not possible or the parents do not agree to separation, twins can continue specialized care to have a better life.
Black Delia
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