Two is a Crowd: Two is a Crowd: On the Enigmatic Etiopathogenesis of Conjoined Twinning.

In this article, we provide a comprehensive overview of multiple facets in the puzzling genesis of symmetrical conjoined twins. The etiopathogenesis of conjoined twins remains matter for ongoing debate and is currently cited-in virtually every paper on conjoined twins-as partial fission or secondary fusion. Both theories could potentially be extrapolated from embryological adjustments exclusively seen in conjoined twins. Adoption of these, seemingly factual, theoretical proposals has (unconsciously) resulted in crystallized patterns of verbal and graphic representations concerning the enigmatic genesis of conjoined twins. Critical evaluation on their plausibility and solidity remains however largely absent. As it appears, both the fission and fusion theories cannot be applied to the full range of conjunction possibilities and thus remain matter for persistent inconclusiveness. We propose that initial duplication of axially located morphogenetic potent primordia could be the initiating factor in the genesis of ventrally, laterally, and caudally conjoined twins. The mutual position of two primordia results in neo-axial orientation and/or interaction aplasia. Both these embryological adjustments result in conjunction patterns that may seemingly appear as being caused by fission or fusion. However, as we will substantiate, neither fission nor fusion are the cause of most conjoined twinning types; rather what is interpreted as fission or fusion is actually the result of the twinning process itself. Furthermore, we will discuss the currently held views on the origin of conjoined twins and its commonly assumed etiological correlation with monozygotic twinning. Finally, considerations are presented which indicate that the dorsal conjunction group is etiologically and pathogenetically different from other symmetric conjoined twins. This leads us to propose that dorsally united twins could actually be caused by secondary fusion of two initially separate monozygotic twins. An additional reason for the ongoing etiopathogenetic debate on the genesis of conjoined twins is because different types of conjoined twins are classically placed in one overarching receptacle, which has hindered the quest for answers. Clin. Anat. 32:722-741, 2019. © 2019 Wiley Periodicals, Inc.

Conjoined twins: From conception to separation, a review.

Conjoined twins are suggested to result from aberrant embryogenesis. The two main theories proposed to explain the phenomena are fission and fusion. The incidence rate is 1 in 50,000 births; however, since about 60% of the cases are stillborn, the true incidence is approximated at 1 in 200,000. There is a higher predisposition towards female than male gender with a ratio of 3:1. Conjoined twins are classified based upon the site of attachment. The extent of organ sharing, especially the heart, determines the possibility and prognosis of a separation procedure. Meticulous preoperative evaluation, planning, and preparedness of the team are crucial for a successful separation. Separation of conjoined twins poses several technical, legal, and ethical issues. Clin. Anat. 30:385-396, 2017. © 2017 Wiley Periodicals, Inc.

Separation of Craniopagus Twins.

Separation of craniopagus twins is fraught by ethical issues. The surgery is high risk and may involve the sacrifice of one twin. We review surgical successes in separation of craniopagus twins and consider ethical and legal concepts affecting the decision to undertake such procedures. Our discussion considers how Gillett's potentiality principle and the concept of moral permissibility may be used to arrive at fair and realistic decisions.

Separation of craniopagus conjoined twins with a staged approach.

The separation of craniopagus conjoined twins is a very rare and complex challenge. As with many rare challenges, it presents initially as a deceptively simple problem requiring only the most basic clinical techniques. As in many reconstructive problems, this paradigm mandates that the neurosurgical team performs the separation with the plastic surgeons providing closure at the end of the separation. Historically, these approaches have included, as with the separation of many other types of conjoined twins, the use of tissue expansion before separation followed by separation surgery. In the best hands, at the most capable medical centers, the mortality reported in the literature for the past 50 years is greater than 50%. Craniofacial surgery frequently demands a coordinated effort between plastic surgery and neurosurgery and many other specializations; separating craniopagus twins takes this coordination to a stratospheric level. It is, however, this coordination that is of paramount importance. Success clearly requires an understanding of the complex interrelationship between the "separation" and the "reconstruction" and that decisions made for 1 aspect of the surgery will have a profound impact on another aspect of the surgery. The impact can be disastrous or, if planned well, can be advantageous.We were contacted to evaluate craniopagus conjoined male infant twins for separation. Radiographic studies suggested that the brains were separate, and their medical team suggested that they were "fit for separation." We reviewed the literature and reviewed our colleagues' experiences with similar cases around the world. It became clear that whether separation had been unsuccessful or successful, a variety of issues accompanied surgery as follows: (1) massive intraoperative hemorrhage, (2) cerebral edema, (3) venous infarcts, (4) swelling of flaps, and (5) dehiscence of repairs with cerebrospinal fluid (CSF) leak, meningitis, or brain exposure. Although the initial plan was to separate the twins in the same fashion as in previous cases (ie, single-stage separation surgery preceded by tissue expansion of the scalp), it was clear that this approach increases cerebral venous pressure during the separation component of surgery and therefore set up a cascade of events favoring failure rather than success. Wishing to favor success, we elected to design an open-ended multistaged separation to improve venous collateral circulation. We believe that this would improve venous drainage, prevent increased venous pressure, diminish cerebral edema, and favor the integrity of the dura and flap repair that would in turn lessen the risk of CSF leak. The stages would also allow the twins to recover from each stage before progressing to the next stage while continuing to receive nutritional support and physical therapy. Four major stages for 9 ½ months led to their successful separation. There has been no CSF leak or meningitis. To our knowledge, this technique has since been applied to 2 other sets of craniopagus with similar outcomes.A review of the pertinent literature, our rationale, and methodology are discussed in this article.

Preoperative Evaluation of Craniopagus Twins: Anatomy, Imaging Techniques, and Surgical Management.

Craniopagus twins are a rare congenital malformation in which twins are conjoined at the head. Although there is high prenatal and postnatal mortality for craniopagus twins, successful separation has become more common due to advances in neuroimaging, neuroanesthesia, and neurosurgical techniques. Joined brain tissue, shared arteries and veins, and defects in the skull and dura make surgery technically challenging, and neuroimaging plays an important role in preoperative planning. Drawing on our experience from consultation for multiple successful separations of craniopagus twins, we discuss what radiologists need to know about the anatomy, classification, imaging techniques, and surgical management of craniopagus twins.

Di-symmetric cephalopagus conjoined twins described by Hovorakova et al.: some additions and corrections.

This article provides some additions and corrections on a recently published case report concerning a pair of di-symmetrical cephalopagus conjoined twins. Eight different types of conjoined twins can be distinguished; one is cephalopagus, which is fourth in rarity of occurrence. Between 17 and 24% of cephalopagus is of the male sex. More than 30 case reports of di-symmetrical cephalopagus can be traced in Western literature, the oldest one described and illustrated in 1569.

[Conjoined twins--rare biological phenomenon. Case report].

Authors are discussing a rear case of multiple pregnancy--conjoined twins. The case is personal by exact antenatal diagnosis and delivering is made by the author. It is proposed a classification of conjoined twins and theoretical interpretation of pathological mechanism of fusion.

Conjoined twins: Pre-birth management, changes to NRP, and transport.

The management of conjoined twins is complex and requires careful preparation. Pre-birth management includes prenatal counseling, which is important due to the overall poor prognosis. In instances of trial of life, the delivery must be tailored to address the anticipated anatomy based on prenatal imaging and anticipated physiology. A multidisciplinary team is essential to anticipate and address the ergonomic challenges and medical issues related to organ fusion, cross-circulation and associated anomalies. There are several suggested modifications to the current Neonatal Resuscitation Program algorithm including modifications to initial assessment, airway management, administration of chest compressions, obtaining emergency access, and medication dosing. Simulation is essential to address challenges, practice Neonatal Resuscitation Program modifications, delineate clear roles during delivery and practice communication. This paper offers a discussion of unique issues associated with delivery of conjoined twins and recommendations on how to approach these challenges based on our experience and available literature.

The surgical principles of conjoined twin separation.

The surgical management of conjoined twin separation is a complex, multidisciplinary process that requires extensive pre operative planning and organization for optimal outcomes. Identification of detailed anatomic relationships is necessary prior to the separation. The use of 3D modeling is extremely helpful for conceptualization of the operation. The principles of the separation are dependent on the type of twin, although each variant of symmetric twins has certain commonalities related to their embryology that can be considered when planning the operation. The use of tissue expansion in the pre operative planning stage is highly recommended due to known issues with closure after separation. In order to ensure a safe, successful operation, we recommend organized pre operative planning meetings with at least one simulation of the separation event with multidisciplinary involvement.

The craniopagus malformation: classification and implications for surgical separation.

Craniopagus twins (CPT) are an uncommon, highly fascinating accident of nature. The clinical pathology of this complex entity is reviewed and placed in perspective. A logical classification aids understanding of the anomaly, and is essential to gauge outcome from separation attempts. 'Partial forms' lack significant shared dural venous sinuses (SDVS) and 'Total forms' with SDVS also exhibit more severe compressional brain distortion. Our classification consists of Partial Angular (PA), Partial Vertical (PV), Total Angular (TA) and Total Vertical (TV, formerly O'Connell Types I-III). Total vertical has a continuous cranium, and inter-twin axial facial rotation <40 degrees (Type I), 140-180 degrees (Type II) or intermediate (Type III). The term 'Angular' denotes an inter-twin longitudinal angle below 140 degrees , regardless of axial rotation. Our review categorized 64 well-delineated CPT, including 41 operative separation attempts in small children since initial success in 1952. Just over one-half were TV, almost one-third TA, and partial forms accounted for the remaining one-sixth. About 30% of CPT had shared or fused brain tissue, and a similar percentage of TA twins shared a posterior fossa. Partial forms had significantly higher birth weights, were separated at an earlier age (6 versus 11 months) and had lower mortality and better outcome compared with Total forms. A multi-staged surgical separation for Total CPT had a significantly better mortality than single-staged separation. Discussion emphasizes embryological, anatomical and clinical aspects of the malformation, with emphasis upon obstacles to a successful outcome.

Successful separation of two pairs of conjoined twins in Ile Ife, Nigeria: case reports.

Conjoined twins are rare phenomena occurring in one in 1 in 50,000 live births. Successful surgical separation of conjoined twins is a major undertaking requiring careful planning by a multidisciplinary team. Reports of seperation of joined twins in developing countries like Nigeria are rare. Ten cases of conjoined twins were separated between 1936 and January 2003 (including the authors two new cases). There were five omphalopagus, two pygopagus, two heterpagus and one ishiopagus twins. Three underwent emergency separation with 83.3% mortality while seven underwent elective seperation with 64.3% survival. The overall mortality rate was 50%. Despite the absence of advanced technological resource selected group of conjoined twins can be successfully separated in a developing country like Nigeria. An improvement in facilities and availability of trained personnel in likely to be associated with improved outcome.

Classification and clinical evaluation.

Conjoined twins represent a great challenge for most pediatric specialists including pediatric surgeons, anesthetists, neonatologists, urologists, neurosurgeons, and orthopedic surgeons. This anomaly can be classified according to the type of twins׳ fusion. Various organs can be fused making the separation difficult. Conjoined twins are usually diagnosed antenatally by ultrasound. Detailed fetal echocardiography is necessary to counsel the parents during pregnancy. Postnatally, the majority of the conjoined twins can be thoroughly investigated using various imaging techniques. This allows careful planning of the operation. However, in approximately one-third of the patients an urgent operation is required at birth without a complete assessment of the joining. This is associated with a poorer outcome.

Prenatal diagnosis and obstetric management.

Conjoined twins are rare, representing 1 in 50,000 to 1 in 200,000 live births, and the prognosis is generally poor. Accurate prenatal diagnosis by an experienced multidisciplinary team using a combination of imaging modalities allows parents to make fully informed choices. This may include termination of pregnancy, which is easier and safer at the earlier gestations at which diagnosis is now being made; continuing with the pregnancy but accepting that only palliative care is appropriate after birth; or planned intensive care and separation of the twins after birth. Delivery will invariably be by cesarean section in order to minimize the risk of peripartum harm to both mother and babies.

The separation procedure.

The various stages of the separation are carefully planned but despite this, variations which will change the schedule of the procedure may exist. In general the operation commences on the opposite side from the main procedure and then the twins are turned for the remainder of the operation. Each type of conjoined twin is different but basically thoracopagus involves the hearts, omphalopagus involves the liver and small intestine and ischiopagus involves the large intestine and genito-urinary system. Our results are presented together with interesting cases from which lessons have been learned.

Craniopagi: anatomical characteristics and classification.

The incidence, embryology, anatomical features of the site of junction, associated abnormalities, and survival of the 79 craniopagi reported from 1496 to 1987 have been reviewed. All craniopagi upon whom sufficient information is available have been classified on the basis of the deepest shared anatomical structure.

Multi-detector row CT for depicting anatomic features of cephalothoracopagus varieties: revised approach.

Conjoined twins can be classified on the basis of the site of union; thus, three main types can be described: (a) ventral union, (b) dorsal union, and (c) rarer forms of union. Ventral union is characterized by the fusion of the two embryos on the ventral side (eg, the abdomen). Dorsal union twins are joined on the dorsal aspect (eg, the vertebral column or occipital bone). Ventral union twins include the group of crucipage twins (ventral midline structures at 90 degrees to the dorsal midline structures), which show interesting features in the organization of the midline. Twins conjoined at the head and chest are called cephalothoracopagus twins. The cephalothoracopagus variety called "Janus" is characterized by the presence of two opposite faces, which are composite structures half of which belong to one twin and half to the other. A complete set of five variants of cephalothoracopagus is presented and, to the authors' knowledge, analyzed for the first time with multi-detector row helical computed tomography. This modality is an invaluable tool for obtaining high-resolution images of the brain, chest, abdomen, and spine and for demonstrating organ position, shared viscera, and limited vascular anatomy. In addition, data acquired in three-dimensional volumes can further be manipulated and then reconstructed. For this purpose, the authors developed dedicated software for three-dimensional reconstruction to analyze data from specimens preserved in formalin. The anatomic findings are discussed here for their embryologic value and to revise the classification of cephalothoracopagus twins. These data offer detailed information for accurate comprehension of imaging studies and for theoretical studies concerning the formation of several anatomic structures.

Prenatal ultrasound diagnosis of conjoined twins.

Four cases of conjoined twins are presented. On the basis of these cases and a review of the literature we present the ultrasonographic features to diagnose this rare condition prenatally in its various forms. Recommendations to avoid misdiagnosis are given. Consequences of this diagnosis and assessment of shared organs are discussed for counselling and obstetrical care.

Anatomic description of conjoined twins: a plea for standardized terminology.

The function of language is communication, but accurate communication is impossible unless the language is mutually understood. In an extensive review of the literature of conjoined twins, considerable difficulty was encountered in interpreting the variations in nomenclature--the designation of the different types of union as well as the identification of the individual twins and their anatomic relationship to one another. For example, the term thoracopagus often includes twins with either one or two hearts; the former rarely (if ever) is capable of surviving, but the latter often do survive. Labeling them as thoracopagus and omphalopagus, respectively, will permit more meaningful comparison between the two types. A simple, logical system of terminology is proposed.

Antenatal diagnosis of cephalothoracopagus twins in a triplet pregnancy. A case report.

The occurrence of conjoined twins in a triplet pregnancy is rare. Cephalothoracopagus twins were diagnosed on ultrasonography at 17 weeks' gestation. This is the first case of conjoined twins in a triplet pregnancy diagnosed early enough antenatally to allow vaginal pregnancy termination.