Craniopagus parasiticus is an extremely rare condition of parasitic twinning; it is characterized by the conjoining of twins at the head. The primary cause is unclear; genetic scientists are still investigating the development of this condition [7]. In the development of normal monozygotic twins, one egg is fertilized by a single sperm. Then the egg splits into two, frequently during the two-cell stage. If the splitting of the egg occurs during the initial blastocyst phase, two inner cell masses tend to form, consequently the twins share the same placenta and chorion results, but with distinct amnions. It is also possible for the egg to divide into two but have one blastocyst. This results in one blastocyst and one inner cell mass. In such cases, during development the twins have a tendency to share the same chorion, placenta, and amnion. This is the one of the most likely reasons for the occurrence of conjoined twins. It is also probable that such an abnormality has a part in craniopagus parasiticus [8, 9]. On the other hand, it is known that parasitic twins form in the utero and start development in the embryo, but the twins fail to completely split into two. In this condition, the dominant embryo fully develops, while the other embryo’s development is extremely restricted during gestation [2].
One hypothesis for the development of craniopagus parasiticus is that a single zygote leads to the development of two fetuses but separation fails either during the second or fourth week of gestation. This is known as fission theory. Another hypothesis is that craniopagus parasiticus is caused by a lack of blood supply to the second twin brought about by the degeneration of the umbilical cord, thereby halting the development of the fetus [10]. The main difference between a parasitic twin and conjoined twins is that the parasitic twin fails to develop during gestation, while the normal twin develops fully [11].
Only ten cases of craniopagus parasitic twins have been documented in the literature. Recently, Manar Maged, the normal twin of craniopagus parasitic twins, underwent surgery, which is an indication that a normal twin can survive. Manar Maged was able to survive without any signs of paralysis until a few days before her second birthday when she died due to a severe infection in her brain [12].
In our case, a pregnant woman was referred from a rural health center for prolonged second stage labor. On her arrival at our hospital an obstetrician decided to do a caesarean section because she was unable to deliver vaginally. During the procedure, a baby girl weighing 4200 g was delivered but unexpectedly she was a craniopagus parasitic twin; the placenta was single and normal. We evaluated the delivered baby by using a skull X-ray, an ultrasound of the co-twin, and an ultrasound of the abdomen of the normal twin. Doppler ultrasound confirmed that the parasitic conjoined twin had no connection with the brain or related structures of the normal twin, and the only communication was soft tissue and vessels arising from carotid vessels.
After necessary counselling and preparation was completed, a 6-hour successful separation surgery was done 1 week after her birth. Postoperation, she easily suckled breast and had no neurological deficit. Two weeks after separation she was discharged in a good healthy condition with an arrangement for postnatal follow up. A pathological examination of the parasitic twin revealed two deformed lower limbs, one of which was rudimentary. Dissection of the mass of the body showed the intestine but no chest organs or abdominal organs. The long bones of the parasitic twin’s bilateral lower limbs and some pelvic bone were seen. There was a rudimentary labium but no vaginal opening (see Figs. 1, 2, 3, 4, and 5).
In conclusion, the causes of craniopagus parasiticus are still unknown due to a rarity of cases and the limited number of studies on it. There have been only nine or ten cases of craniopagus parasiticus, of which only three survived past birth and were documented in the literature. We hope that genetic scientists and researchers continue to investigate this case because they might find explanations of the birth defect, and provide answers and improve the prognosis and the life chances of twins with craniopagus parasiticus. In our case, the baby girl is in good health and suckling breast milk after a successful separation was performed.