The rarity of the condition as well as the challenge it presents in separating the twins has been difficult to understand. In recent years, with advancing medical technology, physicians have been able to successfully separate Ischiopagus twins. However, it depends on the organs shared, how closely joined the twins are, and what risks could rise from separating the twins during surgery. Since Ischiopagus twins usually share a gastrointestinal tract and other organs in the pelvic region, it takes months of planning to decide whether or not separation of the twins outweighs the complications and risks associated with surgery and reconstruction of organs. Surgery to separate conjoined twins has allowed surgeons to be able to study the mechanisms of embryogenesis as well as the physiological consequences of parabiosis.Separating ischiopagus tripus conjoined twins usually leaves the twins with one leg each. Prognosis
Depending upon what organs are shared among the twins and if they are surgically separable, usually only one of the twins makes it through the surgery or they both die due to complications either before or during the surgery. Now that successful surgery has been reported and more findings are becoming available due to research and pre-surgery evaluation, better surgery techniques and procedures will be available in the future to help increase the survival rate of ischiopagus twins as well as other conjoined twins. Epidemiology
Ischiopagus is a rare anomaly occurring in about 1 in every 100,000 live births and occurring in 1 out of 10 conjoined twin births.
The lower extremities are oriented at right angles to the axes of the thorax and the adjacent limbs near the union of the ischium belong to the opposite twin. Embryology
During embryonic development, twins can form from the splitting of a single embryo (monozygotic) which forms identical twins or the twins can arise from separate oocytes in the same menstrual cycle (dizygotic) which forms fraternal twins. Although the latter is more frequent, monozygotic is the reason conjoined twins can develop. In monozygotic twinning for conjoined twins such as ischiopagi, the twins form by the splitting of a bi-laminar embryonic disc after the formation of the inner cell masses. Thus, making the twins occupy the same amnion which can lead to a conjoining of the twins as a result of the twins not separating properly during the twinning process. Separation occurring between the seventh and thirteenth days should result in a monochorionic, monoamniotic identical twins sharing a yolk sac. If separation of the twins occur in the later stages of development prior to the appearance of the primitive streak and axial orientation, then it can be predicted that conjoined twins will develop. The origin of exactly what goes wrong to produce ischiopagus or any conjoined twin is a result by either incomplete fission or double overlapping inducing centers on the same germ disc.