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.     

Separation of craniopagus twins: the Brisbane experience

Introduction There are many problems facing the neurosurgeon when separating craniopagus twins. The condition is rare, with an incidence of 1 in 2.5 million births. As such there is a paucity of information in the literature regarding strategies for separation. Survival rates Over the last 20 years, there has been a gradual improvement in survival rates due to a combination of improved imaging, surgical/anaesthetic techniques and postoperative care. Currently, survival rates following surgery are at 50–60%. More information regarding this condition is needed to make surgical separation a safer event.Aim The aim of this article is to discuss the preoperative work-up, technical details of surgery, postoperative care and lessons learned with respect to the separation of craniopagus twins.     

A developmental theory of the superior sagittal sinus(es) in craniopagus twins

Introduction Based on the study of the vascular anatomy of craniopagus twins, and particularly that of Ladan and Laleh, a theory is hypothesised regarding the embryological formation of the sagittal sinuses.Theory and discussion The superior sagittal sinus develops in contact with the calvarium bone within the inter-periosteal leptomeningeal space following a signal from the midline of the telencephalic vesicle derived from a single prosencephalic one. The position of the falx cerebri and most likely in the deepest part, the corpus callosum, points to the position of this midline.     

The embryology of conjoined twins

Introduction Attention is drawn to the spontaneous incidence of twinning, both dizygotic and monozygotic in different mammalian species. Conjoined twinning, however, only arises when the twinning event occurs at about the primitive streak stage of development, at about 13–14 days after fertilisation in the human, and is exclusively associated with the monoamniotic monochorionic type of placentation. It is believed that the highest incidence of conjoined twinning is encountered in the human. While monozygotic twinning may be induced experimentally following exposure to a variety of agents, the mechanism of induction of spontaneous twinning in the human remains unknown. All agents that are capable of acting as a twinning stimulus are teratogenic, and probably act by interfering with the spindle apparatus.Discussion The incidence of the various types of conjoined twinning is discussed. Information from the largest study to date indicates that the spontaneous incidence is about 10.25 per million births. The most common varieties encountered were thoraco-omphalopagus (28%), thoracopagus (18.5%), omphalopagus (10%), parasitic twins (10%) and craniopagus (6%). Of these, about 40% were stillborn, and 60% liveborn, although only about 25% of those that survived to birth lived long enough to be candidates for surgery. Conjoined twinning occurs by the incomplete splitting of the embryonic axis and, with the exception of parasitic conjoined twins, all are symmetrical and the same parts are always united to the same parts. Fusion of monozygotic twins is no longer believed to be the basis of conjoined twinning. Accounts are provided of the anatomical features of each of the commonly encountered varieties.     

The separation of Guatemalan craniopagus twins

Case report The particularities of the surgical procedure for the separation of craniopagi twins performed at UCLA in 2002 are presented. The main difficulty for the neurosurgeons was that the twins shared a common sagittal sinus and that one of the sisters had a poorly developed collateral venous system, thus anticipating a set of postoperative clinical problems. During surgery, the response of the brain to the progressive occlusion of the venous bridges was monitored with EEG and Doppler ultrasound. One of the sisters had a large intracerebral hematoma that was evacuated and later developed hydrocephalus, which was treated with a ventriculoperitoneal shunt.Outcome One of the sisters had a basically uneventful recovery while the other contracted E. coli meningitis 8 months after surgery, thus impairing her motor and cognitive development.Discussion The details and intricacies of the anesthesia and plastic surgery are also outlined.     

Separation of craniopagus twins in the era of modern neuroimaging, interventional neuroradiology, and frameless stereotaxy

Introduction Craniopagus twinning is a rare embryological event occurring in 1 in 2.5 million births.Case report We present our recent experience with the separation of total vertical craniopagus twins in the modern era of neuroimaging and interventional neuroradiology. Three-dimensional CT images revealed the twins heads were axially rotated 30°. MRI showed deficient dura between the brains of the twins, and some sharing of parietal brain tissue. Cerebral angiography showed a dominant arterial circulation of one twin with unilateral middle cerebral artery (MCA) branches feeding the other twin. The twins shared a common superior sagittal sinus in its middle segment where a circular sinus was formed. Prior to surgery, endovascular separation of the twins arterial and venous circulations was achieved in part using tantalum coils for the MCA feeders in one twin, and balloon occlusion of the anterior superior sagittal sinus of the other. Using the ISG wand intraoperatively, surgery proceeded stepwise and included the circumferential removal of bone and opening of the dura, separation of the twins brains along leptomeningeal planes, and identification of the major draining veins from the superficial cerebral cortex. Discussion The separation of craniopagus twins demands a multidisciplinary team approach. Utilizing preoperative neuroendovascular techniques to occlude shared vascular anastomotic channels, complex total vertical craniopagus twins can now be successfully separated in a one-stage procedure.     

Management of pyopagus conjoined twins

Introduction Approximately 18% of conjoined twins (1 in 200,000 live births) are joined at the sacrum (pyopagus). As the joined structures are not life-threatening, there is generally a good prognosis, with time for investigation and planning of operative separation.Case report This paper reports on the management of pyopagus twin girls, the first in the UK delivered at 36 weeks by Caesarean section. The diagnosis had been made by ultrasound at 12 weeks and confirmed by MRI scan at 26 weeks gestation. Each twin had wasting and weakness below one knee, but no deficit in the other leg. The perineum had two urethras but only one anus. One infant had a colostomy in the immediate neonatal period. With appropriate further imaging, surgery was planned in two stages. First, a balloon expander was inserted in the bridging area. At 3 months of age a team comprising Plastic, Paediatric and Neurosurgeons undertook the definitive separation.Discussion Details of the multidisciplinary planning, operative separation and follow-up of these two children will be discussed.     

Craniopagus: the Thessaloniki–Rome experience

Object A case of two female Greek twins conjoined at the left frontal and orbital regions is described. These conjoined twins were transferred to the Pediatric Neurosurgical Unit of the Gemelli Hospital, Catholic University Medical School, at the age of 4 months for possible surgical division.Method Multiple diagnostic investigations, which included in particular advanced imaging techniques, demonstrated an independent cerebral vascularization of the two babies and excluded significant intracranial malformations. Such an accurate evaluation of the anatomy of the craniopagus at the level of the cranial junction allowed the feasibility of the surgical correction to be established.Conclusions The operation was carried out by a multidisciplinary team in a single stage. The operating team included two distinct teams of neurosurgeons and anesthesiologists as well as a plastic surgeons team. Both babies survived the operation. The postoperative course was uneventful. Both twins were discharged in good clinical and neurological condition after a 3-week period of hospitalization.     

Advanced “tactile” medical imaging for separation surgeries of conjoined twins

Background Understanding the anatomy of conjoined twins is difficult because of the rarity of this congenital malformation and the scarcity of reported cases in medical literature.New technology Advances in radiologic imaging, computer modeling, and sophisticated manufacturing techniques enable medical imaging datasets to be translated into accurate, solid, life-size models. These models, which can be designed to include various combinations of anatomical features revealed by established imaging modalities, are important for pre-surgical assessments and planning, as well as for reference during the actual operative procedure. In addition, they provide a valuable basis for communication between the groups of specialists who are involved in these cases.Case studies This article will describe the advances in technology behind this process and illustrate its value in two cases of craniopagus twins.     

Ethics and conjoined twins

Introduction

The birth of live conjoined twins in a community can draw considerable attention to the appropriate ethical issues.

Discussion

The management requires the skills of a multi-disciplinary team of clinicians who have seldom faced the challenge. The team leader must draw together principles of a medical, social, cultural, religious and legal nature in reaching the best outcome. Often the basic question is whether one child should die or both? At times the question is raised whether it is justifiable to sacrifice one life to save the other. In these days of high technology, surgeons can be tempted to go a bridge too far. In reaching this decision there can be numerous hidden conflicts of interest. Increasingly the final decision needs to be made and approved by the courts so as to protect the rights of the twins and to ensure surgical intervention is not an unlawful act.     

Anaesthesia for conjoined twins

Introduction Anaesthesia for conjoined twin surgery, whether prior to or for separation, is an enormous challenge to the paediatric anaesthesiologist.Discussion The site and complexity of the conjunction will affect airway management, acquisition of vascular access, the extent of blood loss, and the number of surgical specialties involved. Preoperative assessment and planning, with interdisciplinary communication and cooperation, is vital to the success of the operations. These twins require a dedicated team of anaesthetists for each child, and, consequently, duplication of all monitoring and equipment in one operating room is necessary. Meticulous attention to detail, monitoring, and vigilance are mandatory. Planning for the postoperative period in the intensive care unit (ICU), as well as the babies reconstruction and rehabilitation, is essential from the time of the initial admission.     

Management of hydrocephalus in ilio-omphalopagus conjoined twins

One member of ilio-omphalopagus conjoined twins developed symptomatic hydrocephalus. Uneventful ventriculoperitoneal shunting improved the baby's condition. Technical aspects of the neurosurgical and anesthetic management in this case are discussed.     

3H-imipramine binding in human platelets: a study in normal twins

3H-imipramine binding was determined in freshly prepared intact platelets from 17 monozygotic (MZ) and 15 dizygotic (DZ) twin pairs, all of them male, adult, drug-free, and healthy volunteers. Sixteen males served as controls for determination of intraindividual variation of binding parameters. Both MZ and DZ twin pairs exhibited high intraclass correlations of Bmax values, but DZ twins were nearly as similar as MZ pairs. Interindividual variation of binding parameters is not large enough to reveal a significant genetic control.     

Dementia of frontal lobe type in monozygotic twins

A pair of monozygotic twins who are concordant for dementia of frontal lobe type are discussed. This is believed to be the first case report of twins with this type of dementia. The salient features of dementia of frontal lobe type are also discussed.     

Japanese monozygotic twins with Rett syndrome

We present a study of 28-year-old Japanese monozygotic female twins with Rett syndrome (RS). To our knowledge, this is the first report of monozygotic twins with RS from Japanese family. There are some differences between twins about seizures, scoliosis and stereotypical hand movements during adolescence. Monozygosity was confirmed by both blood typing and HLA titers.     

Identical twins with medulloblastoma occurring in infancy

Familial cerebellar medulloblastomas occurred in monozygotic twin siblings during infancy, and they had a rapid downhill course. Both twins underwent surgery for the tumours. This was followed by chemotherapy in the second twin. Both died after a short time. The tumours were seen to arise from the cerebellum and both had almost identical histomorphological features. To the best of our knowledge, this is the second report of familial medulloblastoma in twin siblings. Our observation suggests an underlying genetic influence in the histogenesis of these tumours. Received: 30 November 1997     

Ataxia telangiectasia in identical twins: unusual features

Summary The cases of identical twins with ataxia telangiectasia, early intellectual impairment and progressive spasticity are reported. Immunological tests revealed reduced levels of serum and salivary IgA, increased B cells, reduced T cells and raised -fetoprotein. CT scan performed in one of the twins was normal. The pathogenesis of the spasticity is discussed.     

Valproate-induced hyperammonaemia in two epileptic identical twins

Summary The cases of two epileptic identical twins are described, one of whom had presented an episode of valproate (VPA)-induced stupor associated with very high blood ammonia (NH₃) concentrations. Both twins showed a similar marked increase of venous NH₃ concentrations after the administration of a single loading dose of VPA (800 mg).     

Neurological abnormalities in schizophrenic twins.

BACKGROUND: Neurological abnormalities (NAs) are well recognized in schizophrenia, though their genetic and environmental determinants, and pathophysiological significance, are poorly understood. METHODS: Sixty-three twin pairs, varying in their zygosity and concordance for schizophrenia, and 73 unaffected control twin pairs were examined for total, primary and integrative NAs using the Neurological Evaluation Scale. RESULTS: NAs were increased in probands with schizophrenia compared to nonschizophrenic co-twins and to healthy control twins but there were no significant differences between patients from the concordant and discordant pairs. NAs in the nonpsychotic co-twins from discordant pairs were increased compared to control twins. There were no significant differences in NAs between the nonschizophrenic co-twins from monozygotic (MZ) and dizygotic (DZ) discordant pairs, but the within pair correlations were greater in the MZ compared to DZ pairs. NAs were modified in all groups by pre-morbid schizotypal traits, and in patients by anti-psychotic medication. CONCLUSIONS: NAs in schizophrenia are determined in part by genetic risk for the illness but the presence of premorbid schizotypal traits, and anti-psychotic medication confer additional risk for NAs.