Theoretical and analytical embryology of conjoined twins: part II: adjustments to union

The application value of prenatal ultrasound in conjoined twins

OBJECTIVE

To evaluate the application and effectiveness of prenatal ultrasound in diagnosing and managing conjoined twins.

METHODS

A retrospective analysis was conducted on 20 cases of conjoined twins diagnosed at our hospital between January 2016 and December 2022. The types of conjoined twins, ultrasonographic characteristics, and associated anomalies were assessed.

RESULTS

The gestational age at diagnosis ranged from 10 to 35 weeks, with an average of 14.21 ± 5.69 weeks. Thirteen cases were detected in the first trimester, five in the early second trimester, one at 23 + 2 weeks, and one at 35 weeks. Thoracopagus was the most common type (11 cases, 55%), followed by omphalopagus (4 cases, 20%), cephalopagus (4 cases, 20%), and parapagus dicephalus (1 case, 5%). In the first trimester, the most common abnormalities observed included increased nuchal translucency (NT), cystic hygroma, hydrops fetalis, and generalized edema. Major birth defects identified in conjoined twins were omphalocele (3 cases), congenital heart malformations (3 cases), neural tube defects (2 cases), urachal cyst (1 case), and umbilical cyst (1 case). Pregnancy was terminated in 18 cases, one case resulted in spontaneous abortion during the second trimester, and one case was delivered by cesarean section at 37 weeks, with successful separation and recovery.

CONCLUSION

Prenatal ultrasound is the primary diagnostic tool for conjoined twins. It effectively assesses the extent of twin fusion, provides critical information for clinical decision-making, and aids in the management of obstetric care.

Monochorionic triplet pregnancy complicated by conjoined twins and early twin-twin transfusion syndrome

BACKGROUND

The condition of monozygotic, monochorionic triplet fetuses with a pair of conjoined twins is extremely rare (close to one in a million births), presents challenges in its management, and with poor prognosis.

CASE REPORT

We report a case of monochorionic diamniotic triplet pregnancy, ultrasound at 14 weeks shows a pair of conjoined thoracopagus fetuses, sharing heart, liver, and umbilical cord, in addition to omphalocele. The third fetus, without malformations, presents signs of early heart failure compatible with twin-to-twin transfusion syndrome. It was decided to carry out expectant management where at 18 weeks, intrauterine death of the three fetuses occurs. An abortion is performed by hysterotomy.

CONCLUSIONS

The treatment in these cases is discussed, three management options have been proposed: expectant management, selective reduction of the conjoined fetuses, or termination of the pregnancy. A review of the literature found only 12 cases with this combination of pathologies, in which only 3 normal fetuses (25%) survived and none of the conjoined twins survived. To our knowledge, this case is the first of a monochorionic triplet pregnancy with conjoined fetuses complicated with early twin-to-twin transfusion.

Overview of Swine Congenital Malformations Associated with Abnormal Twinning

A review of congenital malformations in swine relating to abnormal twinning was carried out. The aim was to describe and estimate these defects. Among the recorded twins, the most common defect was the syncephalus thoracopagus or cephalothoracopagus. A couple of dicephali and diprosopus congenital anomalies were also registered. At last, some cases of thoraco-omphalopagus piglets were surveyed. There was also a report of an acardiac twin (hemiacardius acephalus) and a case of a conjoined parasitic twin. The pathogenetic mechanisms of this condition, frequently reported in veterinary practice, are discussed. The importance of embryonic imperfect twinning is commonly associated with dystocia.

Brain malformations in diprosopia observed in clinical cases, museum specimens and artistic representations

BACKGROUND

Diprosopus is a rare malformation of still unclear aetiology. It describes a laterally double faced monocephalic and single-trunk individual and has to be distinguished from the variant Janus type diprosopus.

RESULTS

We examined seven double-faced foetuses, five showing true diprosopus, and one each presenting as monocephalic Janiceps and parasitic conjoined twins. Four of the foetuses presented with (cranio)rachischisis, and two had secondary hydrocephaly. Three foetuses showed cerebral duplication with concordant holoprosencephaly, Dandy-Walker cyst and/or intracranial anterior encephalocele. In the Janiceps twins, cerebral duplication was accompanied by cerebral di-symmetry. In the parasitic twins the cyclopic facial aspects were suggestive of concordant holoprosencephaly. In one of the true diprosopus cases, pregnancy was achieved after intracytoplasmic sperm injection. Whole-exome sequencing, perfomed in one case, did not reveal any possible causative variants.The comparison of our double-faced foetuses to corresponding artistic representations from the Tlatilco culture allowed retrospective assignment of hairstyles to brain malformations.

CONCLUSION

Brain malformations in patients with diprosopus may not be regarded as an independent event but rather as a sequel closely related to the duplication of the notochord and neural plate and as a consequence of the cerebral and associated craniospinal structural instabilities.

A Case of Ischiopagus Dicephalus Conjoined Twins with Tetrabrachius Bipus from Dessie, Ethiopia

The development of conjoined twins always catches the eyes of researchers and clinicians. Beyond the rareness of the cases, how they develop is a debatable issue. This report presented a case of ischiopagus conjoined twins who had two heads (dicephalus), four upper extremities (tetrabrachius), and were joined below the chest with two lower extremities (bipus). The twin’s mother was referred from a primary hospital to Dessie Comprehensive Specialized Hospital for proper management of twin pregnancy, where a cesarean section was performed. The mother and her husband have no family history of birth defects or exposure to known teratogens. On imaging, the twins had separate hearts, lungs, and kidneys but a single liver, spleen, stomach, and intestine. They also shared genitourinary structures: a single penis with sub-coronal hypospadias and one imperforate anus. In addition, their placenta was single with one umbilical vein and two umbilical arteries. The conjoined twins had multiple accompanying cardiovascular anomalies but no external craniofacial, extremity, or brain anomalies. They passed away after 36 hours of follow-up in the neonatal intensive care unit at Dessie Comprehensive Specialized Hospital.

Cross-cultural representations of conjoined twins

Conjoined twinning is a rare birth defect estimated to occur in about 1 in 50,000 to 100,000 births. The mechanism of conjoined twinning is not proven. Different forms of conjoined twinning are observed with the thoracopagus form being the most common. The rate of conjoined twinning is similar across all major populations. A dramatic malformation of this type would be an extraordinary occurrence leading people to reflect on the spiritual or supernatural nature of such an event. Therefore, it is not surprising that artifacts that seem to depict different forms of conjoined twins are seen across diverse cultures. In this article, we present a survey of these cultural artifacts including anatomic classification based on external anatomy and an exploration of the cultural and spiritual contexts associated with the artifacts. A key finding is that the most common form of conjoined twinning in the artifacts is parapagus (both dicephalus and diprosopus) in contrast to thoracopagus, the most common form in epidemiologic studies. Potential reasons for this difference are discussed. Evidence is presented to support the speculation that these objects represent artistic impressions of actual conjoined twinning events.

The Outcomes of Surgical Separation in Thoracopagus Twins with Conjoined Hearts: An Analysis of the Literature

We sought to perform a comprehensive review of reported cases of conjoined thoracopagus twins with cardiovascular conjunction to determine the overall survival after separation and factors that might be associated with survival. We performed a systematic review of cases of thoracopagus twins with conjoined cardiovascular systems reported in the English medical literature using Embase, PubMed, Web of Science, and Scopus. We employed standard statistical methods to analyze differences among groups. We identified 102 unique cases of thoracopagus twins (69% female) with some degree of cardiovascular conjunction who had undergone surgical separation. We identified 6 distinct types of cardiovascular union. Median age was 47 days (IQR 12, 120). Survival to at least hospital discharge occurred in 51% (105/204). Median age at separation was lower in emergent (9 days, IQR 1, 25) versus elective cases (93 days, IQR 49, 180) (p < 0.0001). Survival to hospital discharge was higher in those who underwent elective separation (70%, 93/132 total children versus 17%, 12/72) (p < 0.0001). Survival was associated with the type of cardiovascular union (p < 0.0001). The separation of thoracopagus twins with cardiovascular conjunction is higher than expected. Increased survival is associated with elective separation, older age, and shared pericardium only. These findings suggest survival could be improved with better delineation of degree of union and delayed separation.

A case of monocephalus, tetrabrachious and tetrapod in female newborn goat

All conjoined twins are originally born as a result of fertilizing one zygote (egg) and also called monozygotic twins experiencing an incomplete division of an embryo into two portions of the embryo usually causing the formation of the primary streak stage. The main reason for the creation of this defect is not obvious. Dead twin goat with one head, one trunk, four anterior limbs, and four posterior organs was referred to the Laboratory of the Faculty of Veterinary Medicine, Islamic Azad University, Shoushtar Branch, Shoushtar, Iran. The radiographic and three-dimensional images showed one normal skull and pelvic bone vertebral column. The ribs and sternum of the newborn goat were quite normal and confirmed two pairs of extra limbs. There were no doubles in describing the internal organs. This report seems to be the first report regarding a case of a monocephalus, tetrabrachius, and tetrapod newborn goat.

A parapagus dicephalus tripus tribrachius conjoined twin with a unique morphological pattern: a case report

Background

Conjoined twinning is a rare congenital malformation with an incidence of about 1.5 per 100,000 births. Because no consensus has been reached regarding the dysmorphology, thorough descriptions of conjoined twins as part of teratological collections can be useful to increase knowledge of this congenital malformation. In this case report, we describe a parapagus dicephalus twin from the collection of the Department of Anatomy of the University Medical Center Utrecht in the Netherlands. External anatomical characteristics were assessed through a detailed macroscopic examination and internal characteristics by means of whole-body computed tomography and magnetic resonance imaging (3 Tesla).

Case presentation

Macroscopic examination showed a Caucasian male parapagus dicephalus tripus tribrachius conjoined twin a type of conjoined twinning in which there are two heads side by side, one rump, and three upper and three lower limbs. In addition, anencephaly was observed in the left twin. Radiological imaging showed a normal central nervous system in the right twin and absence of the calvaria, cerebrum, diencephalon, and mesencephalon in the left twin. There was clear duplication of the vertebral column, rib cage, respiratory system, and gastrointestinal system at least up to and including the first part of the duodenum. The heart consisted of a monoatrium with two separate ventricles. There was a fused liver with a single gallbladder, a single spleen, three kidneys, two bladders, and duplication of the penis. The third upper and lower extremities were articulating with a fused glenoid and acetabulum, respectively. The third foot showed both polydactyly and syndactyly of the toes.

Conclusion

This case report describes a unique case of a male dicephalus parapagus tripus tribrachus conjoined twin discordant for anencephaly. Radiological imaging proved to be an adequate noninvasive method to provide insights into the internal (dys)morphology of this specific specimen, improving its scientific and educational value. This approach could be generally applied to other teratological specimens, thereby strengthening arguments regarding pathogenetic hypotheses, which may lead to new or improved insights into both normal and abnormal embryonic development.

"I" and "Me": The Self in the Context of Consciousness

James (1890) distinguished two understandings of the self, the self as "Me" and the self as "I". This distinction has recently regained popularity in cognitive science, especially in the context of experimental studies on the underpinnings of the phenomenal self. The goal of this paper is to take a step back from cognitive science and attempt to precisely distinguish between "Me" and "I" in the context of consciousness. This distinction was originally based on the idea that the former ("Me") corresponds to the self as an object of experience (self as object), while the latter ("I") reflects the self as a subject of experience (self as subject). I will argue that in most of the cases (arguably all) this distinction maps onto the distinction between the phenomenal self (reflecting self-related content of consciousness) and the metaphysical self (representing the problem of subjectivity of all conscious experience), and as such these two issues should be investigated separately using fundamentally different methodologies. Moreover, by referring to Metzinger's (2018) theory of phenomenal self-models, I will argue that what is usually investigated as the phenomenal-"I" [following understanding of self-as-subject introduced by Wittgenstein (1958)] can be interpreted as object, rather than subject of experience, and as such can be understood as an element of the hierarchical structure of the phenomenal self-model. This understanding relates to recent predictive coding and free energy theories of the self and bodily self discussed in cognitive neuroscience and philosophy.

Three-dimensional ultrasound for prenatal assessment of conjoined twins: additional advantages?

Conjoined twins are a rare, but serious, complication of monozygotic twins. Early prenatal diagnosis of conjoined twins is increasingly made with transvaginal ultrasound and color Doppler studies. Most prenatally diagnosed conjoined twins are terminated due to the high perinatal mortality, but advancement in pediatric surgery has allowed for successful postnatal separation in a small number of cases, and some parents may consider this option over termination of pregnancy. It is important to get a detailed prenatal ultrasound for the site and extent of fusion for an accurate categorization. Three-dimensional ultrasound (3DUS) provides images that can facilitate counselling for the parents. Additional information that impacts on diagnosis, prognostication, and perinatal management of conjoined twins could be obtained from selective use of 3DUS, particularly those with atypical fetal union. Most of the proposed additional benefits of 3DUS are based on case reports. Magnetic resonance imaging (MRI) has been increasingly used for the purpose of identifying intricate organ sharing. Because of the rarity of this condition, and the heterogeneity of fetal fusion, added benefits of either 3DUS or MRI for prenatal diagnosis and perinatal management of conjoined twins have not been demonstrated by well-conducted clinical trials. This article aims to review clinical application of various 3DUS display modes in prenatal assessment of conjoined twins, focusing on their potential additional benefits, risks and misuses. 3DUS may help detecting additional findings that are not possible with 2DUS, but, it has not been scientifically shown to improve the survival rate of the twins or reduce maternal morbidity.

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.

Diprosopus: Systematic review and report of two cases

BACKGROUND

Diprosopus is a subtype of symmetric conjoined twins with one head, facial duplication and a single trunk. Diprosopus is a very rare congenital anomaly.

METHODS

This is a systematic review of published cases and the presentation of two new cases born in Argentina. We estimated the prevalence of conjoined twins and diprosopus using data from the National Network of Congenital Anomalies of Argentina (RENAC).

RESULTS

The prevalence of conjoined twins in RENAC was 19 per 1,000,000 births (95% confidence interval, 12-29). Diprosopus prevalence was 2 per 1,000,000 births (95% confidence interval, 0.2-6.8). In the systematic review, we identified 31 diprosopus cases. The facial structures more frequently duplicated were nose and eyes. Most frequent associated anomalies were: anencephaly, duplication of cerebral hemispheres, craniorachischisis, oral clefts, spinal abnormalities, congenital heart defects, diaphragmatic hernia, thoracic and/or abdominal visceral laterality anomalies. One of the RENAC cases and three cases from the literature had another discordant nonmalformed twin.

CONCLUSION

The conjoined twins prevalence was similar to other studies. The prevalence of diprosopus was higher. The etiology is still unknown. The presence of visceral laterality anomalies may indicate the link between diprosopus and the alteration or duplication of the primitive node in the perigastrulation period (12-15 days postfertilization). Pregnancies of more than two embryos may be a risk factor for diprosopus. Given the low prevalence of this defect, it would be useful to perform studies involving several surveillance systems and international consortiums. Birth Defects Research (Part A), 2016. © 2016 Wiley Periodicals, Inc. Birth Defects Research (Part A) 106:993-1007, 2016. © 2016 Wiley Periodicals, Inc.

Parasitic twin--a supernumerary limb associated with spinal malformations. A case report

We describe a case of rachipagus parasitic twin with spinal cord malformations (lipomyelomeningocele and tethered cord) in a 7-month-old Ethiopian infant. The parasitic mass had a well-formed foot, ankle and lower leg and a small sinus that resembled an anus. Magnetic resonance imaging scans revealed spinal malformations including a distal syringohydromyelia. The mass was successfully resected and the dural attachment was closed. Histopathological examination confirmed the diagnosis. Postoperatively, the child had unchanged, intact neurological function in both lower limbs. Almost all rachipagus parasitic twins are associated with spinal malformations. They should, therefore, be operated on by surgeons experienced in myelomeningocele surgery.

Dicephalus Parapagus Conjoined Twins Diagnosed by First-Trimester Ultrasound

Conjoined twins are a rare phenomenon, occurring in 1% of monochorionic twin gestation, with an incidence of 1 : 50 000 to 1 : 100 000. Many conjoined twins have abnormalities incompatible with life, so early prenatal diagnosis is very important for optimal management of both pregnancy and delivery. We report a case of dicephalus parapagus conjoined twins, sharing a single heart, diagnosed at 12 weeks' gestation. With early ultrasound diagnosis, we were able to provide appropriate and timely prenatal counseling to the family.

In utero and postnatal imaging findings of parasitic conjoined twins (ischiopagus parasiticus tetrapus)

Conjoined twins are a rare developmental anomaly with a reported prevalence of 1.47 per 100,000 births. We present an uncommon case of a parasitic ischiopagus tetrapus with a parasitic ischiopagus partial twin joined to the complete fetus at the level of the ischium diagnosed in utero by fetal MRI. The correct prenatal diagnosis led to birth by caesarean section. Prenatal MRI findings are presented and corroborated by postnatal imaging delineating the full extent and associated anomalies of this rare malformation. Differential diagnosis of duplicated lower extremities is discussed.

Ischiopagus tripus conjoined twins in a western lowland gorilla (Gorilla gorilla)

Conjoined twinning is rare in man and non-human primates. The current report describes a case of ischiopagus tripus conjoined Western Lowland gorilla (Gorilla gorilla) twins. The female twins were joined at the umbilical and pelvic region, involving the liver, xiphoid, umbilicus, body wall and skin. Computed tomography revealed two complete spines. The combined pelvic space was formed by two sacra, each connected with two iliac bones. The twins were only conjoined by a common pubis. Cause of death was attributed to cardiac and circulatory collapse resulting from a large patent foramen ovale (8 mm in diameter) of one twin and neonatal asphyxia.

Conjoined twins detected in the first trimester: a review

Conjoined twinning occurs in 1 in 100 sets of monozygotic twins, 1 in 50,000 gestations or 1 in 250,000 live births. With the advent of ultrasound technology, prenatal diagnosis of conjoined twins is possible. This article provides a comprehensive review of conjoined twins detected in the first trimester including fetal gender, maternal age, parity, types of fusion, related ultrasound abnormalities, perinatal outcome and association with assisted reproduction.

A chick embryo with a yet unclassified type of cephalothoracopagus malformation and a hypothesis for explaining its genesis

Cephalothoracopagus embryos are conjoined twins, who share parts of their heads, necks and bodies. Our study aims at presenting a detailed morphological analysis of a cephalothoracopagus chick embryo of developmental stage 31. Because none of the existing theories can explain the genesis of the phenotype of this embryo, we also suggest a hypothesis, which explains it. Beside the cephalothoracopagus embryo, we investigated five control embryos. With the aid of the high-resolution episcopic microscopy (HREM) technique, we created digital volume data and three-dimensional (3D) computer models of the organs and arteries of the embryos. We used the 3D models for topological analysis and for measuring the diameters of the great intrathoracic arteries. The malformed embryo showed two body backs, each containing a notochord, spinal cord and dorsal aorta. The body backs continued into separated lower bodies. The embryo had a single, four-chambered heart, single respiratory tract and single upper alimentary tract. The topology of the pharyngeal arch arteries was normal, and the diameters of these arteries were similar to that of the control embryos. We classified the embryo we investigated as a yet unknown malformation and suggest a hypothesis explaining its genesis.

Conjoined hearts in thoracopagus twins

This study aimed to identify the anatomic and pathologic structural cardiac abnormalities in conjoined twins and to focus on those that have prevented the successful separation of conjoined hearts. A retrospective review was undertaken to examine consecutive cases of thoracopagus conjoined twins with conjoined hearts evaluated at The Children's Hospital of Philadelphia from 1 January 1980 through 6 October 2008. The records included autopsy and surgical findings as well as clinical reports. The study group included nine sets of conjoined twins with a mean gestational age at birth of 33.8 ± 5.5 weeks. Three twin pairs were stillborn. Five twin pairs died afterward. One pair died of cardiopulmonary failure. The median age at death was 22 days (range, 0-345 days). Major congenital heart disease was present in 94.4% (17/18) of the hearts, and 72.2% (13/18) of the hearts had single-ventricle physiology. Total anomalous pulmonary venous return occurred in 39% (7/18) of the cases. The clinical outcome for thoracopagus twins with conjoined hearts remains poor because of inability to separate conjoined and single ventricles. Surgical nonintervention and palliative care should be strongly considered for these patients.

Conjoined twins: a worldwide collaborative epidemiological study of the International Clearinghouse for Birth Defects Surveillance and Research

Conjoined twins (CT) are a very rare developmental accident of uncertain etiology. Prevalence has been previously estimated to be 1 in 50,000 to 1 in 100,000 births. The process by which monozygotic twins do not fully separate but form CT is not well understood. The purpose of the present study was to analyze diverse epidemiological aspects of CT, including the different variables listed in the Introduction Section of this issue of the Journal. The study was made possible using the International Clearinghouse for Birth Defects Surveillance and Research (ICBDSR) structure. This multicenter worldwide research includes the largest sample of CT ever studied. A total of 383 carefully reviewed sets of CT obtained from 26,138,837 births reported by 21 Clearinghouse Surveillance Programs (SP) were included in the analysis. Total prevalence was 1.47 per 100,000 births (95% CI: 1.32-1.62). Salient findings including an evident variation in prevalence among SPs: a marked variation in the type of pregnancy outcome, a similarity in the proportion of CT types among programs: a significant female predominance in CT: particularly of the thoracopagus type and a significant male predominance in parapagus and parasitic types: significant differences in prevalence by ethnicity and an apparent increasing prevalence trend in South American countries. No genetic, environmental or demographic significant associated factors were identified. Further work in epidemiology and molecular research is necessary to understand the etiology and pathogenesis involved in the development of this fascinating phenomenon of nature.

Thoracopagus conjoined twins: a case report

Objective. Conjoined twin is a rarely seen congenital anomaly together with severe mortality and morbidity. The more common types of conjoined twins include the thoracopagus type, where the fusion is anterior, at the chest, and involves the heart. We are reporting one case of conjoined thoracopagus twins diagnosed by ultrasonography at 11 weeks. Case Report. In a multigravid pregnant woman who has been admitted to our clinic with a diagnosis of conjoined twins, thoracopagus, by ultrasonography at an 11-week gestation, termination of the pregnancy was performed. Conclusion. Making an early diagnosis with ultrasonographic examination gives the parents a chance to elect pregnancy termination.

Conjoined twins with mirror-image cleft lip and palate: case report in Brazil

The observation of mirror-image clefts in conjoined twins may suggest an influence from environmental factors (e.g., poor blood supply) on the appearance of clefts. The present paper reports on a pair of male thoracopagus twins born to a 20-year-old woman. The twins were stillborn. Both twins exhibited complete unilateral cleft lip and palate with mirror-image configuration, affecting the left side for twin A and the right side for twin B. The twins also shared some organs. The case is discussed with similar information in the literature, with reference to possible related etiologic factors. Reporting on such occurrences throughout the world is important to shed light on important aspects underlying the formation of clefts.

Anatomy of successfully separated thoracopagus-omphalopagus conjoined twins

The birth of conjoined twins occurs in approximately 1 in 50,000 to 1 in 100,000 deliveries, and the majority are either stillborn or die early in life. Approximately 184 successful separations have been described. The authors describe the preoperative radiologic evaluation of a set of thoracopagus-omphalopagus twins and their successful surgical separation. Preoperative radiologic imaging demonstrated that the twins did not share myocardium, but an ectopic cordis was present. The inferior vena cavae entered the right atria at more acute angles than normal. The liver was fused, two gallbladders were present, and there was a large bridging portal vein that crossed the hepatic isthmus of one twin to the conjoined twin's portal venous system. Replaced hepatic arteries originated from the superior mesenteric arteries. Each twin had separate kidneys, colons, and rectums. Preoperative tissue expansion was necessary, and the twins were separated at 5 1/2 months of life. Successful separation of twins conjoined by several organ systems requires a multispecialty approach. Preoperative knowledge of shared anatomy is necessary for adequate preparation and planning. Despite meticulous preoperative investigations, certain anatomy can only be discovered at the time of surgery, and the ability to adjust to these findings is imperative.

Imaging of conjoined twins

The incidence of conjoined twins is estimated to be around 1 in 250,000 live births. There is a distinct female predominance. In this paper the imaging of conjoined twins both antenatally and postnatally is reviewed, in particular taking into consideration recent advances with multidetector CT. Accurate counselling of parents regarding the likely outcome of the pregnancy and the likelihood of successful separation is dependent on good prenatal imaging with ultrasound and MRI. Planning of postnatal surgical separation is aided by accurate preoperative imaging which, depending on the conjoined area, will encompass many imaging modalities, but often relies heavily on CT scanning.

Congenital heart defects in conjoined twins: outcome after surgical separation of thoracopagus

In this study, we correlated cardiac malformations in the various types of conjoined twins with the proposed site of embryologic union and evaluated the possibility of survival after surgical separation. We conclude that surgical separation is only very rarely successful in twins with united hearts, whereas survival in twins with separate hearts is more dependent on the malformations of other viscera. This report deals primarily with conjoined twins in whom anomalies of the heart are the major factor in deciding whether surgical separation is feasible.

Anesthetic Management for Thoracopagus Twins with Complex Cyanotic Heart Disease in the Magnetic Resonance Imaging Suite

We report a case of thoracopagus twins undergoing magnetic resonance imaging (MRI) studies under general anesthesia. The twins had a complex shared cardiac anatomy that posed additional challenges to an already-difficult anesthesia care area. This report emphasizes the approach to anesthetic management of conjoined twins in the MRI environment.

CLOACAL EXSTROPHY VARIANTS. CAN BLIGHTED CONJOINED TWINNING PLAY A ROLE?

PURPOSE

For normal single births with evidence of first trimester twinning, vanishing twin rates of 13% to 78% have been reported. We propose that blighting of a conjoined twin can result in an infant with a variation of cloacal exstrophy.

MATERIALS AND METHODS

We retrospectively reviewed the records of 26 patients with cloacal exstrophy treated from January 1989 to November 2003, all of whom had prenatal evaluations readily available to determine the presence of twinning. The criterion for establishing the prenatal diagnosis of twins was the documentation of 2 fetal heart tones on Doppler and/or 2 fetal poles on ultrasound.

RESULTS

All 26 patients had prenatal care including prenatal fetal Doppler studies and followup ultrasound. Of the patients 15 had classic cloacal exstrophy (58%) with no evidence of twin gestations documented. Of the 26 cloacal exstrophy cases 11 (42%) were cloacal exstrophy variants, including 8 of the 11 (73%) with consistent findings of twin gestation on prenatal studies. All 8 patients had documented 2 fetal heart tones in the first trimester, and 4 had 2 fetal poles in 1 amniotic sac on prenatal ultrasound. Five patients had subsequent ultrasound studies showing a single fetus by the second trimester. Two patients were born conjoined with 1 of the twins lifeless at birth in both cases.

CONCLUSIONS

We propose that blighted conjoined twinning may be a cause of cloacal exstrophy variant cases.

Management of other complications specific to monochorionic twin pregnancies

Monochorionic (MC) twins have a 3-10-fold higher perinatal mortality and morbidity than dichorionic twins. This is largely attributable to their common vascular architecture and the high rate of discordant fetal growth, growth restriction and congenital abnormalities. In the event of a single intrauterine death (IUD), intertwin agonal transfusion results in up to a 38% risk of death and a 46% risk of neurological injury to the co-twin. This chapter addresses the management of complications unique to MC twins. The primary aim of management is to prevent single IUD or, if inevitable, prevent agonal transfusion occurring by vascular occlusive selective feticide. Older fetoscopic techniques have been replaced by the simpler ultrasound-guided techniques of interstitial laser and bipolar cord occlusion. Their application in twin reversed-arterial perfusion sequence has been associated with a 50% reduction of perinatal mortality in the pump twin. Moreover, prophylactic interstitial laser therapy in early pregnancy might obviate the technical and clinical difficulties in the presence of fetal decompensation in later pregnancy. Recent strategies to reduce the high perinatal mortality due to cord entanglement in antenatally diagnosed monoamniotic twins including medical amnioreduction and elective caesarean delivery at 32 weeks, are also discussed.

Craniopagus twins: embryology, classification, surgical anatomy, and separation

INTRODUCTION

With recent advances in brain imaging and neurosurgical techniques, there has been a renewed interest in the surgical separation of craniopagus twins. Successful separation in recent cases, along with widespread publicity, has attracted craniopagus twins from all over the world to be referred to pediatric neurosurgical centers for evaluation and consideration for surgical separation.

SEPARATION OF BLOOD SUPPLY

It has become apparent, however, that the most critical decisions in surgical planning are related to separation of the blood supply to the conjoined brains. In fact, in craniopagus twins that survive pregnancy or the first few days of life, there is usually little shared brain tissue. The shared blood supply is far and away the more critical issue. It is very difficult to successfully separate craniopagus twins in one surgical procedure. Staged separation, with gradual re-routing of the shared blood supply, has been a successful alternative.

CASE STUDIES AND DISCUSSION

We discuss here our experience with three sets of craniopagus twins and our approach to staged separation.

Twinning

Twinning has fascinated human beings over the centuries. New technologies and large study groups have led to improved documentation of frequency and complications in twin pregnancies and long-term outcomes. Artificial reproductive technologies have led to a pronounced rise in numbers of dizygotic and monozygotic twins. Although spontaneous dizygotic twinning is clearly associated with increased concentration of follicle-stimulating hormone and ovulation of more than one egg, causes of monozygotic twinning remain illusive. Twin studies are used increasingly to study complex traits and disorders: however, caution is suggested, since twins might not be representative of a typical singleton pregnancy. Monozygotic twinning seems to represent an anomaly in itself, with an increased number of spontaneous abortions and structural congenital anomalies. Both monozygotic and dizygotic twins have growth rates that slow at 30 weeks in utero and might be programmed both developmentally and biochemically earlier in pregnancy to have different responses at birth and after birth compared with singletons.

Conjoined twins cephalopagus janiceps monosymmetros: a case report

BACKGROUND

We present an extremely rare case of Janiceps type of female cephalopagus conjoined twins. Various pathological mechanisms that may be responsible for abnormal morphological development (limited to the conjoined part and normal morphological development in free lower abdomen and pelvis) are discussed.

METHODS

Conjoined twins were obtained from a hospital, fixed in formalin, and dissected to observe and report the abnormalities present.

RESULTS

Anatomical features included development of normal face on one side, rudimentary face (two pinna only) on the opposite side, two cerebra each connected to the eye ball of its own side byoptic nerve without any chiasma formation, two brain stems, two spinal cords, normally developed vertebral columns, four upper limbs, four lower limbs, a single shared foregut and small intestine up to Meckel's diverticulum beyond which it duplicated for the two twins, patent large intestines and anal canals. The genitourinary system was developed normally in both twins. The heart of one twin was relatively hypoplastic with the lungs. The liver was herniated on one side and the other side it was hypoplastic without any herniation. Gall bladder was absent on both sides. Conjoined hepatic ducts from both livers and the only pancreatic duct drained into esophagogastric junction.

CONCLUSIONS

We propose that the development of upper abnormally conjoined parts and lower normally developed parts of the body of both the twins may be attributed to the factors associated with variable degrees of the conjoining, dysgenetic (developmental) defects, and deformations because of crowding in utero.

Spinal cord involvement in pygopagus conjoined twins: case report and review of the literature

INTRODUCTION

Pygopagus conjoined twins are joined at the rump and have union of the gastrointestinal and genitourinary systems as well occasional involvement of neural elements.

CASE REPORT

We report a case where the terminal spinal cords were fused, despite which there was only a minor motor deficit in the lower limbs after separation. The pre-operative and intra-operative findings are described and issues of long-term follow-up discussed.

DISCUSSION

Seven other cases reported in the literature with varying degrees of involvement of the spinal cord and cauda equina are reviewed.

Atypical parasitic ischiopagus conjoined twins

Occurrence of asymmetrical or parasitic conjoined twins (CT) is rare, and currently they are classified analogically to the common unions of symmetrical CT. The authors report on an infant with a parasitic third limb attached to the left lateral aspect of the autosite trunk, in whom male gonadal tissue was found histologically. Parasite parts included complete left lower limb, hemipelvis, lumbosacral vertebral column, spinal cord, and one kidney with ureter and adrenal gland. Autosite anomalies comprised a small left diaphragmatic defect, omphalocele, exstrophy of cloaca, and lumbar meningomyelocele. The authors considered this case to be a rare atypical parasitic ischiopagus CT. The differential diagnosis of the type of twining and other entities with caudal duplications is analyzed briefly.

Parasitic conjoined twins: external, internal (fetuses in fetu and teratomas), and detached (acardiacs)

During the course of researching the embryologic etiology of conjoined twins, more than 1260 individual cases were collected from the literature and the reported abnormal anatomy tabulated and evaluated in the light of known embryology. It soon became apparent that the association of conjoined twins and their parasites with fetuses in fetu, acardiacs, and teratomas was more frequent than could be attributed to chance. These anomalous fetuses form a continuum, strongly suggesting that they are all variations of abnormal conjoined twinning, with the site of union and the extent of damage (or defect) of one embryo resulting in (1) an externally attached parasitic twin, (2) an enclosed fetus in fetu, (3) an internal teratoma, or (4) an acardiac connected via the placenta. Common patterns among them are a family history of twinning, the predominance of females, and the frequent presence of a twin or triplet accompanying the malformation. The several reports of chromosomal abnormality suggest that perhaps, at least on occasion, it is a genetically imperfect embryo that develops into a defective fetus. Of singular importance is the fact that rarely, if ever, is either a functional heart or a competent brain found in any of these abnormal fetuses, suggesting that the etiology of all of them is a primary cardiac malformation with secondary disruption in the development of the brain.