Three-dimensional ultrasonographic features of diamniotic conjoined twins with body stalk anomaly.

BACKGROUND: Since conjoined twins were thought to be monoamniotic in the past, diamniotic conjoined twins would be improbable theoretically. Body stalk anomaly is a severe defect of the body wall, which is rare among twins. Body stalk anomaly in monochorionic diamniotic conjoined twins has never been reported prenatally so far as we know. CASE PRESENTATION: Here we present an extremely rare case of concordant body stalk anomaly in monochorionic diamniotic conjoined twins. Ultrasonography at 9 + 5 weeks revealed one chorionic and two amniotic cavities, close apposition of abdomen, limited movement, and common umbilical vessels. Follow-up ultrasonography at 11 + 6 weeks and 13 + 2 weeks showed close apposition of the lower abdominal region with cystic structures and a small bowel-like mass between the two fetuses. Three-dimensional ultrasonography assisted in observing the entire appearance of both twins in earlier first trimester, including amnioticity, conjoined region and umbilical vessels. We attribute this diamniotic conjoined twin in our case to the fusion theory. A single yolk sac was observed, challenging the idea that yolk sac number predicts amnionicity. Identification of single yolk sac and its allantois may form a common body stalk during this fusion, leading to concordant body stalk anomaly in monochorionic diamniotic twins. CONCLUSIONS: Our case may provide important insights into both ultrasonographic features and embryogenesis of this extremely rare anomaly.

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.

Xenopus, an ideal model organism to study laterality in conjoined twins.

Conjoined twins occur at low frequency in all vertebrates including humans. Many twins fused at the chest or abdomen display a very peculiar laterality defect: while the left twin is normal with respect to asymmetric organ morphogenesis and placement (situs solitus), the organ situs is randomized in right twins. Although this phenomenon has fascinated already some of the founders of experimental embryology in the 19th and early 20th century, such as Dareste, Fol, Warynsky and Spemann, its embryological basis has remained enigmatic. Here we summarize historical experiments and interpretations as well as current models, argue that the frog Xenopus is the only vertebrate model organism to tackle the issue, and outline suitable experiments to address the question of twin laterality in the context of cilia-based symmetry breakage.

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.

Dicephalous v. diprosopus sharks: record of a two-headed embryo of Galeus atlanticus and review of the literature.

As far as is known, this paper gives the first description of a two-headed shark embryo belonging to an oviparous species, Galeus atlanticus (Carcharhiniformes: Scyliorhinidae). The specimen was detected among 797 embryos intended for cardiovascular studies, which represents a defect incidence of 0·13%. Each head had a mouth, two eyes, a brain, a notochord and five gill openings on each side. The two heads fused behind the gills. On the single body, there were four anticipated dorsal fins, two anterior, right and left and two posterior, right and left. Ventrally, the specimen possessed two pairs of pectoral fins, a pair of pelvic fins and one anal fin. Two adjacent notochords, two neural tubes and two dorsal aortas ran along the body, which bent 180° at its posterior portion. There were two hearts, two oesophaguses, two stomachs, two livers, but a single intestine with a spiral valve. Previous reports of conjoined twins in sharks are scarce and only refer to oviparous and ovoviviparous species. Seven dicephalous sharks reported so far were similar to the specimen described here, namely, with two totally separated heads on one body. Instead, only one case of diprosopus shark has been reported; it had a single body and a single head with partial duplication of the face. Two further cases described in the literature as dicephalous or simply as abnormal sharks should be better regarded as diprosopus, while another three cases, also considered dicephalous, showed a mixture of characteristics of diprosopia and dicephalia.

Salmonid fish: model organisms to study cardiovascular morphogenesis in conjoined twins?

BACKGROUND: There is a gap in knowledge regarding the cardiovascular system in fish conjoined twins, and regarding the cardiovascular morphogenesis of conjoined twins in general. We examined the cardiovascular system in a pair of fully developed ventrally conjoined salmonid twins (45.5 g body weight), and the arrangement of the blood vessels during early development in ventrally conjoined yolk sac larvae salmonid twins (<0.5 g body weight). RESULTS: In the fully developed twins, one twin was normal, while the other was small and severely malformed. The mouth of the small twin was blocked, inhibiting respiration and feeding. Both twins had hearts, but these were connected through a common circulatory system. They were joined by the following blood vessels: (i) arteria iliaca running from arteria caudalis of the large twin to the kidney of the small twin; (ii) arteria subclavia running from aorta dorsalis of the large twin to aorta dorsalis of the small twin; (iii) vena hepatica running from the liver of the small twin into the sinus venosus of the large twin. Among the yolk sac larvae twins investigated, distinct vascular connections were found in some individuals through a joined v. vitellina hepatica. CONCLUSIONS: Ventrally conjoined fish twins can develop cardiovascular connections during early development, enabling a normal superior twin to supply a malfunctioning twin with oxygen and nutrients. Since the yolk sac in salmonids is transparent, twinning in salmonids may be a useful model in which to study cardiovascular morphogenesis in conjoined twins.

Consistent left-right asymmetry cannot be established by late organizers in Xenopus unless the late organizer is a conjoined twin.

How embryos consistently orient asymmetries of the left-right (LR) axis is an intriguing question, as no macroscopic environmental cues reliably distinguish left from right. Especially unclear are the events coordinating LR patterning with the establishment of the dorsoventral (DV) axes and midline determination in early embryos. In frog embryos, consistent physiological and molecular asymmetries manifest by the second cell cleavage; however, models based on extracellular fluid flow at the node predict correct de novo asymmetry orientation during neurulation. We addressed these issues in Xenopus embryos by manipulating the timing and location of dorsal organizer induction: the primary dorsal organizer was ablated by UV irradiation, and a new organizer was induced at various locations, either early, by mechanical rotation, or late, by injection of lithium chloride (at 32 cells) or of the transcription factor XSiamois (which functions after mid-blastula transition). These embryos were then analyzed for the position of three asymmetric organs. Whereas organizers rescued before cleavage properly oriented the LR axis 90% of the time, organizers induced in any position at any time after the 32-cell stage exhibited randomized laterality. Late organizers were unable to correctly orient the LR axis even when placed back in their endogenous location. Strikingly, conjoined twins produced by late induction of ectopic organizers did have normal asymmetry. These data reveal that although correct LR orientation must occur no later than early cleavage stages in singleton embryos, a novel instructive influence from an early organizer can impose normal asymmetry upon late organizers in the same cell field.

The North American Fetal Therapy Network Registry data on outcomes of radiofrequency ablation for twin-reversed arterial perfusion sequence.

OBJECTIVE: To report the North American Fetal Therapy Network (NAFTNet) Registry data on the outcomes of using radiofrequency ablation to treat twin-reversed arterial perfusion (TRAP). METHODS: This was a retrospective review of the records of all patients who underwent percutaneous radiofrequency ablation of an acardiac twin after referral to 12 NAFTNet institutions between 1998 and 2008. Maternal, fetal and neonatal data were analyzed. The primary outcome was neonatal survival to 30 days of age. All participating sites conducted this study under institutional review board approval. RESULTS: Of the 98 patients identified, there were no maternal deaths and no women required blood transfusions. Most women (76 of 98; 78%) stayed in the hospital for ≤1 day after the procedure. Mean gestational age at delivery was 33.4 weeks overall and 36.0 weeks for survivors. Median gestational age at delivery was 37.0 weeks. Survival of the pump twin to 30 days was 80% in the overall cohort. CONCLUSION: The NAFTNet registry data suggest that radiofrequency ablation of the acardiac twin is an effective treatment for TRAP sequence.

Polarity proteins are required for left-right axis orientation and twin-twin instruction.

Two main classes of models address the earliest steps of left-right patterning: those postulating that asymmetry is initiated via cilia-driven fluid flow in a multicellular tissue at gastrulation, and those postulating that asymmetry is amplified from intrinsic chirality of individual cells at very early embryonic stages. A recent study revealed that cultured human cells have consistent left-right (LR) biases that are dependent on apical-basal polarity machinery. The ability of single cells to set up asymmetry suggests that cellular chirality could be converted to embryonic laterality by cilia-independent polarity mechanisms in cell fields. To examine the link between cellular polarity and LR patterning in a vertebrate model organism, we probed the roles of apical-basal and planar polarity proteins in the orientation of the LR axis in Xenopus. Molecular loss-of-function targeting these polarity pathways specifically randomizes organ situs independently of contribution to the ciliated organ. Alterations in cell polarity also disrupt tight junction integrity, localization of the LR signaling molecule serotonin, the normally left-sided expression of Xnr-1, and the LR instruction occurring between native and ectopic organizers. We propose that well-conserved polarity complexes are required for LR asymmetry and that cell polarity signals establish the flow of laterality information across the early blastoderm independently of later ciliary functions. genesis 50:219-234, 2012. © 2011 Wiley Periodicals, Inc.

Dicephalic parapagus conjoined twins: a rare second trimester sonographic diagnosis.

Conjoined twins are 1 of the rarest and most challenging congenital malformations. It occurs if twinning is initiated after the embryonic disc and rudimentary amniotic sac have been formed. We report a very rare case of dicephalic parapagus that was diagnosed by transabdominal sonography.

Double Trouble: Complications in Twin Pregnancies.

With the increasing rate of twin pregnancies due to increase in maternal age and use of assisted reproduction, it is important to be aware of unique diseases which occur specifically to twin pregnancies, especially in monochorionic twin pregnancies. These entities include twin to twin transfusion syndrome, twin anemia polycythemia sequence, twin reversed arterial perfusion, cotwin demise, and conjoined twins. Early evaluation and documentation are imperative to guide management which ultimately leads to better patient outcomes.

Monocephalus dipygus parapagus: a suspected case of complete caudal duplication in a British Blue kitten.

Complete caudal duplication is an extremely rare type of conjoined twinning. This communication reports the birth and gross features of a live conjoined British Blue kitten born naturally to a healthy queen. The monocephalic dipygus kitten exhibited a normal skull and upper body, two separate pelves, four hind limbs and two tails. A cleft palate and bifurcation of rostral mandible were also noted. The absence of maternal dystocia was unusual for conjoined twinnings.

Diamniotic omphalopagus conjoined twins in a diamniotic pregnancy.

OBJECTIVE: To present antepartal diagnostic findings including 2D/3D ultrasonography in a rare case of conjoined twins with diamniotic placentation. METHODS: In ultrasonographic examination, a communicating structure containing solid and cystic components together with cord vessels was found between the fetuses. The long axes of the fetuses were not parallel and they moved independently. Bladder configurations were absent. A fetal membrane from the chorioidal plate was imaged. RESULTS: Postmortem pathological examination revealed that the twins were conjoined by way of fused cloacal exstrophy and omphalocele, and the separate amniotic cavities communicated via a fused allantoic cavity. The placenta was monochorionic and diamniotic. DNA analysis of the twins and the placenta confirmed the monozygotic origin. CONCLUSION: Visualization of the amniotic membrane does not rule out conjoined twins in rare cases of monochorionic twin pregnancies.

Minimally conjoined omphalopagi: emphasis on embryogenesis and possibility of emergency separation.

Minimally conjoined omphalopagus twins (MCOTs) has been recognized in the last decade as a special subgroup in which omphalopagus twins have union of peritoneal cavities through anterior lower abdominal wall defect with union of distal small intestine and patent urachal structures and associating anorectal malformation. A careful review of the current literature revealed that MCOTs have usually been separated in emergency situations within the first hours of life due to ruptured omphalocele, gastroschisis, stillbirth of one of the twins, intestinal obstruction, or requirement of enterostomy for cloacal anomaly. Pediatric surgeons should be familiar with MCOTs and ready for emergency separation with thorough knowledge of the anatomical relationships of the connecting structures and the embryologic basis for this anomaly. We present a new set of MCOTs separated in emergency conditions with a review of the relevant English literature. We give special emphasis to the common surgical characteristics and a brief discussion on the embryogenesis of this rare condition.

Prenatal and postnatal radiologic evaluation of conjoined twins.

Imaging of conjoined twins requires the use of multiple modalities, in both the prenatal and postnatal setting. Prenatal imaging, including both ultrasound and magnetic resonance imaging, benefits from an organized, worksheet-based approach, careful labelling of all images, and adoption of supplemental techniques. Postnatal imaging should be informed by the prenatal imaging findings and should be thoughtfully planned prior to performance. Complete evaluation prior to planned surgical separation will require the use of complementary modalities and multidisciplinary review and discussion.

Role of simulation in preparation for the care of conjoined twins-prenatal preparation to separation.

The rarity and complexity of conjoined twins creates a challenge for prenatal planning, delivery resuscitation, and postnatal management. The modality of simulation offers a safe practice environment for a multidisciplinary group consisting of neonatal providers, nurses, respiratory therapists, and surgeons in which to identify and address clinical decision making, procedural, and behavioral plans related to routine and emergency care of these patients. Simulation-based clinical rehearsals (SbCR) provide a unique opportunity to prepare for rare, complex, and patient specific clinical procedures and scenarios. This primer serves as a revisable tool that promotes the development of proper timing, technique, and confidence to allow for an optimal setting for delivery of safe care to conjoined twins. We describe the development and implementation of a simulation approach to all stages of care from the antenatal life, NICU care, to preparation for postnatal separation of conjoined twins.

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.