Thoracopagus Conjoined Twins: A Case Report with Multiple Anomalies

Introduction

Conjoined twins are rare congenital anomalies, which usually resulting from a defect of blastogenesis during early embryonic period. The overall incidence ranges from 1/50,000 to 1/100,000 of live births [1]. Out of all pattern of conjoined twins, thoracophagus conjoined twins are the most common one, in which there is face to face fusion of thorax along with variable involvement of abdominal part occurs [2]. There are variable numbers of theories for formation of thoracopagus twins but embryo logically, there are two different theories to explain the formation of conjoined twins. Firstly the ’Fission theory’ which explains that, on 13th day after fertilization the embryonic disc undergoes an incomplete separation [3]. While, the second ‘fusion theory’ stress on two separate mono-ovulatory embryonic discs undergoing a secondary association. Recently the “Fusion Theory” has been accepted well [4]. According to some authors, thoracopagus twins result from the union of the cardiac analgen and the septum transversum, leaving the cranial end of the early disc. As a result of which the development of head and neck including face and the brain becomes normal, but thorax get united [5]. Thus conjoined twins are identical twins and comes under the class of the monochorionic and monoamniotic (1-2%) group. So it has been also believed that, in this two separate organizing centers which appear simultaneously in the single germ disc may overlap their differentiating influence to such an extent that two embryos are incompletely separated from each other. The genetic basis for pathogenesis of conjoined twins is that, it’s mainly due to misexpression of genes such as Goosecoid. This Goosecoid is responsible for initiation of primitive streak and ventralization of mesoderm [Langman Textbook of Medical Embryology]. The left- right asymmetries in these twins are regulated by a cascade of genes. A gene named sonic hedgehog which expressed in the notochord and serve as a midline barrier, represses or block the expression of left sided genes on the right embryo [6]. In a similar way, a gene ‘snail’ regulates right sidedness in the embryo. So these genes may also play certain role in formation of conjoined twins. The morphological changes which usually occur in the thoracopagus twins are external and internal. Externally chest wall and abdomen is usually affected with some changes in gentalias and face. Internally in the thorax, there is one large complex heart with multiple ventricles and duplicate aortic arches. In abdomen, majority of cases are having large fused liver along with some shared part of gastrointestinal tract. So, in thoracopagus mainly the fusion of viscera is a factor for asymmetry. Liver is shared in almost all cases followed by heart but gastrointestinal tract is shared only in about half of the cases [7].

Case Report

The specimen of thoracopagus conjoined twin had been received from pathology department, which was preserved in 10 % formalin for autopsy purpose. After the ethical approval it was brought to the anatomy department for the purpose of dissection and study. The history has been taken from the department of gynecology and obstetrics department of PGIMS, Rohtak. History revealed that it was a case of still born 34 Weeks twin pregnancy which were born to a G2P0A1, 30 years old Indian-Asiatic Women with no history of previous twin pregnancy in her family, in both maternal and paternal side. The pregnancy was uncomplicated with no history of any kind of infection, ingestion of drug or exposure to radiation during pregnancy. The history taken from gynecology and obstetrics department also revealed that, stillborn infants were approximately of equal in size and their combined weight was 2.8 Kilograms. The specimen was immediately put in 10% formalin and sent to pathology department for academic interest and to analyze various anomalies. As per our findings the external morphological details were, the heads were hyper-extended and both twins have kyphosis. They were conjoined along the midline of the thorax to the umbilicus, which was single for both the twins. Out of two babies, one was having cleft lip. On cut section umbilical cord showed five vessels. To look for further details and study purpose, baby having cleft lip with cleft palate has been labeled as Twin- A and another with normal face labeled as Twin-B (Figure 1). There were many features which were common in both the twins but lot more features were varied in both the twins which were described separately in there description.

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Discussion

Conjoined twins are monozygotic or identical twins which develops from a single fertilized egg which splits into two embryos but do not fully separate from each other during the blastula stage between the 13th to 15th day after fertilization [8]. They are classified according to most prominent site of conjugation. The thoracopagus is the most common variety with an incidence of 0.5% and omphalopagus is the least common variety. The earliest antenatal diagnosis of thoracopagus twins reported in the literature was made by transvaginal sonography as early as 8th weeks of gestation. Even after the diagnosis, overall survival rate for conjoined twins is approximately 25% [9]. The overall incidence is higher in female with a ratio of 3:1.This is because, the XX Karyotype may confer a survival benefit and the process of X-inactivation overlaps with timing of monozygote twinning [10]. The actual pathogenesis is still not well defined but either incomplete fission of the developing embryo or the development of co-dominant axis with apposition of part of the axis that leads to conjunction [11, 12, 13]. After making the diagnosis of the conjoined twins, 3-D ultra-sonography, CT and MRI are the other methods to diagnose the characteristic and severity of abnormality. During early stages of pregnancy, usually in 1st trimester, termination can be offered to the family. Surgical

separation may range from simple procedure to very complex lengthy surgeries with good to bad prognostic outcome, depending upon the point of attachment and the internal organs they shared especially the degree of cardiac fusion. Most cases of separation are extremely risky and life threatening. For cardiac evaluation, full cardiac catheterization with selective angiography is essential before separation is considered.

Conclusion

Conjoined thoracopagus twins are associated with a high prenatal mortality. If they are diagnosed before viability, termination should be done with the consent of parents. A vaginal delivery is preferred for still birth and for those who do not survive. The degree of fusion of the heart determines the outcome.

The Conflict of Interest

The authors state that they have no conflict of interest with institution

Ethical Approvals

No ethical approval is required. Specimen was taken from pathology museum.

Contribution

Research is a collective work done by all the authors. First author have done the dissection part along with the help of other authors. All the references were collected together.