Caudal duplication syndrome: more evidence for theory of caudal twinning

Caudal duplication syndrome is a rare entity in which structures derived from the embryonic cloaca and notochord are duplicated to various extents. The term encompasses a spectrum and often is quoted as one type of incomplete separation of monovular twins. The authors present more evidence giving credence to caudal twining as the mechanism behind the syndrome. The authors report successful surgical management of a full-term infant with a constellation of anomalies of caudal duplication syndrome.

The Chiari II malformation: cause and impact

INTRODUCTION

It is the Chiari II malformation and its effects that determine the quality of life of the individual born with spina bifida.

DISCUSSION

The cause of this malformation has been a source of debate for many years. Understanding the cause enables strategies for the management of problems created by this malformation to be developed. An open neural tube defect allows fluid to escape from the cranial vesicles, altering the intracranial environment and leads to all of the brain changes seen in the Chiari II malformation. Decompression of the intracranial vesicles causes overcrowding, decrease in the size of the third ventricle, and changes in the fetal skull. It also permanently links the intracranial ventricular system to the spinal cord central canal.

Pathobiology and genetics of neural tube defects

PURPOSE

Neural tube defects (NTDs), including spina bifida and anencephaly, are common congenital malformations that occur when the neural tube fails to achieve proper closure during early embryogenesis. Based on epidemiological and clinical data obtained over the last few decades, it is apparent that these multifactorial defects have a significant genetic component to their etiology that interacts with specific environmental risk factors. The purpose of this review article is to synthesize the existing literature on the genetic factors contributing to NTD risk.

RESULTS

To date, there is evidence that closure of the mammalian neural tube initiates and fuses intermittently at four discrete locations. Disruption of this process at any of these four sites may lead to an NTD, possibly arising through closure site-specific genetic mechanisms. Candidate genes involved in neural tube closure include genes of the folate metabolic pathway, as well as those involved in folate transport.

CONCLUSIONS

Although extensive efforts have focused on elucidating the genetic risk factors contributing to the etiology of NTDs, the population burden for these malformations remains unknown. One group at high risk for having children with NTDs is epileptic women receiving antiepileptic medications during pregnancy. Efforts to better understand the genetic factors that may contribute to their heightened risk, as well as the pathogenesis of neural tube closure defects, are reviewed herein.

Omphalocele-exstrophy-imperforate anus-spinal defects (OEIS) in triplet pregnancy after IVF and CVS

BACKGROUND

Omphalocele-exstrophy-imperforate anus-spinal defects (OEIS) complex is a rare sporadic condition.

CASE

We identified an infant with major malformations resembling OEIS. He was the product of a 30-week triplet pregnancy conceived by in vitro fertilization (IVF) and evaluated by chorionic villi sampling (CVS). In this article, we review the possible pathogenetic mechanisms in this case, including IVF, multiple gestation, trauma to the uterus or uterine vessels following CVS, and placenta accreta.

CONCLUSIONS

We conclude that the cumulative effects of all or some of these factors may have resulted in uteroplacental insufficiency adequate to produce this phenotype. This case provides additional evidence for the uterine vascular pathogenesis of OEIS complex in humans.

In vitro high-field magnetic resonance imaging-documented anatomy of a fetal myelomeningocele at 20 weeks' gestation. A contribution to the rationale of intrauterine surgical repair of spina bifida

OBJECT

It remains uncertain if closure of a myelomeningocele at midgestation changes the neurological condition at birth in an infant born with spina bifida. The authors conducted a study to provide a detailed analysis of the morphology of the spinal cord with the myelomeningocele at the time fetal surgery usually is performed.

METHODS

The myelomeningocele of a 20-week-gestation-age fetus was examined, and data were compared with those obtained in a neurologically intact specimen of the same age. In vitro high-field 9.4-tesla magnetic resonance (MR) microscopy was used to examine the fetal material. High-field MR spectroscopy provided images in the three orthogonal planes with a resolution comparable with low-power optical microscopy. The authors observed that the fetal cord of the myelomeningocele specimen was tapered and tethered at S3-4 while the conus medullaris in the normal fetus reaches L-4. No neurulation defects were noted. The axial MR images clearly revealed the nonfusion of the mesodermal structures. The absence of neurulation defects suggests that at least in some cases of spina bifida the spinal cord initially is well developed but is damaged later on chemically and mechanically. This might be an argument in favor of intrauterine myelomeningocele repair. By 20 weeks' gestation, however, the deformation of the cord inside the myelomeningocele is severe. An optimization of the preoperative assessment by means of MR imaging therefore might be considered a valuable contribution to intrauterine surgery. The in vitro high-field MR microscopic findings of this study could be used as references for clinical intrauterine MR imaging.

CONCLUSIONS

The detailed in vitro high-field MR analysis of a 20-week-gestation-age fetus with spina bifida demonstrated that an improvement of the preoperative intrauterine imaging should be pursued to detect those cases without neurulation defects and with minimal deformation of the spinal cord.

Ectopic expression ofGcm1induces congenital spinal cord abnormalities

Brief ectopic expression of Gcm1 in mouse embryonic tail bud profoundly affects the development of the nervous system. All mice from 5 independently derived transgenic lines exhibited either one or both of two types of congenital spinal cord pathologies: failure of the neural tube to close (spina bifida) and multiple neural tubes (diastematomyelia). Because the transgene is expressed only in a restricted caudal region and only for a brief interval (E8.5 to E13.5), there was no evidence of embryonic lethality. The dysraphisms develop during the period and within the zone of transgene expression. We present evidence that these dysraphisms result from an inhibition of neuropore closure and a stimulation of secondary neurulation. After transgene expression ceases, the spinal dysraphisms are progressively resolved and the neonatal animals, while showing signs of scarring and tissue resorption, have a closed vertebral column. The multiple spinal cords remain but are enclosed in a single spinal column as in the human diastematomyelia. The animals live a normal life time, are fertile and do not exhibit any obvious weakness or motor disabilities.

Experimental split cord malformations

OBJECTIVE

To induce experimental split cord malformations (SCMs) produced through the surgical induction of a dorsal midline fistula.

METHODS

In addition, the theory of embryogenesis of SCMs was verified by examining the developmental process of this experimentally induced anomaly. In Cynopus pyrrhogaster (amphibian) embryos (stage 18), the neural plate and notochord were split regionally to construct a fistula that appeared to be the ectopic neurenteric canal. Following this procedure, the embryonic development was traced morphologically and histologically.

RESULTS

Following the incubation and breeding period, split cord malformation was observed in some animals. Scoliosis, spina bifida, vertebral anomaly and subcutaneous manifestations were also observed with SCMs.

CONCLUSIONS

The observations made in these experimentally induced SCMs are consistent with the findings in human SCMs. We report an experimental animal model of split cord malformation, in which double spinal cords were developed in the spinal canal. In addition, we examined the embryogenesis of SCMs. This study indicates that SCMs may arise through a process of dorsal midline fistula of the neural plate.

Embryonic hydromyelia: cystic dilatation of the lumbosacral neural tube in human embryos

In a large collection of human embryos (the Kyoto Collection of Human Embryos, Kyoto University), we encountered five cases with abnormal dilatation of the neural tube at the lumbosacral level. In these examples, the central canal was enlarged, and the roof plate of the neural tube was extremely thin and expanded. The mesenchymal tissue was scarce or lacking between the roof plate and the surface ectoderm. This type of anomaly was assumed to be formed after neural tube closure and may be an early form of spina bifida. In two of the cases, some abnormal cells were found ectopically between the thin roof plate and the surface ectoderm. Morphologically, these cells resembled those forming spinal ganglia and could be of the neural crest origin. Since neural crest cells are pluripotent and can differentiate into a variety of tissues, such ectopic cells might undergo abnormal differentiation into teratomatous tumors and/or lipomas, which are frequently associated with spina bifida. We also discuss the definition of spina bifida and the classification of neural tube defects from the embryological and pathogenic viewpoints and propose a new classification of neural tube defects.

Magnetic resonance imaging of spinal dysraphism

Spinal cord development occurs through three consecutive periods. Gastrulation (weeks 2-3) is characterized by conversion of the embryonic disk from a bilaminar to a trilaminar arrangement and establishment of a notochord. Primary neurulation (weeks 3-4) produces the uppermost nine tenths of the spinal cord. Secondary neurulation and retrogressive differentiation (weeks 5-6) result in formation of the conus tip and filum terminale. Defects in these early embryonic stages produce spinal dysraphisms, which are characterized by anomalous differentiation and fusion of dorsal midline structures. Spinal dysraphisms may be categorized clinically into two subsets. In open spinal dysraphisms, the placode (non-neurulated neural tissue) is exposed to the environment. These disorders include myelomeningocele, myeloschisis, hemimyelomeningocele, and hemimyelocele, and are always associated with a Chiari II malformation. Closed spinal dysraphisms are covered by intact skin, although cutaneous stigmata usually indicate their presence. Two subsets may be identified based on whether a subcutaneous mass is present in the low back. Closed spinal dysraphisms with mass comprise lipomyeloschisis, lipomyelomeningocele, meningocele, and myelocystocele. Closed spinal dysraphisms without mass comprise complex dysraphic states (ranging from complete dorsal enteric fistula to neurenteric cysts, split cord malformations, dermal sinuses, caudal regression, and spinal segmental dysgenesis), bony spina bifida, tight filum terminale, filar and intradural lipomas, and persistent terminal ventricle. Magnetic resonance imaging is the imaging method of choice for investigation of this complex group of disorders.

Development of lumbosacral spina bifida: three-dimensional computer graphic study of human embryos at Carnegie stage twelve

There is still some controversy as to whether sacral spina bifida in humans is the result of a defect of the primary or secondary neural tube. As somites are related to the development of vertebrae and the primary neural tube is related to the development of the spinal cord in embryos, it is very important to determine the number of somites in normal human embryos at the time of closure of the primary neural tube to understand the contribution of primary neural tube defects to the development of spina bifida. However, in the literature, the number of somites in stage 12 human embryos is still controversial. The aim of this study is to find the number of somites in human embryos at Carnegie stage 12. Four human embryos at Carnegie stage 12 were selected from the laboratory of the Congenital Anomaly Research Center in Japan. The neural tube and somites were reconstructed from their slices by a three-dimensional computer graphic reconstruction technique. The reconstructed embryos were examined from multidirectional magnified images. Thirty-three pairs of somites were present in all these reconstructed embryos. As the 33rd pair of somites corresponds to the fifth sacral segment, the presence of 33 pairs of somites at Carnegie stage 12 suggests that spina bifida develops from defects of the primary neural tube.

MR spectrum in spinal dysraphism

Spinal dysraphism is a general term which encompasses a wide variety of anomalies of the spine, all of which result from imperfect midline fusion of the embryonic neural tube. This term refers to large defects that involve the spine and not to small vertical clefts commonly seen within the spinal process of L5 or S1. We present a spectrum of MR imaging findings selected from a retrospective review of 100 patients of spinal dysraphism evaluated at our institution.

Diabetic embryopathy in C57BL/6J mice. Altered fetal sex ratio and impact of the splotch allele

Maternal diabetes (types 1 and 2) induces a broad array of congenital malformations, including neural tube defects (NTDs), in humans. One of the difficulties associated with studying diabetic embryopathy is the rarity of individual malformations. In an attempt to develop a sensitive animal model for maternal diabetes-induced NTDs, the present study uses chemically induced diabetes in an inbred mouse model with or without the splotch (Sp) mutation, a putatively nonfunctional allele of Pax3. Pax3 deficiency has been associated with an increase in NTDs. Female C57BL/6J mice, either with or without the Sp allele, were injected intravenously with alloxan (100 mg/kg), and plasma glucose was measured 3 days later. A wide range of hyperglycemia was induced, and these diabetic mice were bred to C57BL/6J males, some carrying the Sp allele. Gestational-day-18 fetuses were examined for developmental malformations. Fetuses from matings in which either parent carried the Sp allele were genotyped by polymerase chain reaction. Maternal diabetes significantly decreased fetal weight and increased the number of resorptions and malformations, including NTDs. A significant correlation was found between the level of maternal hyperglycemia and the malformation rate. The sex ratio for live fetuses in diabetic litters was significantly skewed toward male fetuses. Matings involving the Sp allele yielded litters with significantly higher percentages of maternal diabetes-induced spina bifida aperta but not exencephaly, and this increase was shown to be associated with the presence of a single copy of the Sp allele in affected fetuses. Thus, Pax3 haploinsufficiency in this murine model of diabetic embryopathy is associated with caudal but not cranial NTDs.

Tethered cord syndrome and occult spinal dysraphism

Tethered cord syndrome is a progressive form of neurological deterioration that results from spinal cord tethering by various dysraphic spinal abnormalities. The syndrome, treatments, outcomes, and current controversies are reviewed.

A human YAC transgene rescues craniofacial and neural tube development in PDGFRalpha knockout mice and uncovers a role for PDGFRalpha in prenatal lung growth

The platelet-derived growth factor alpha-receptor (PDGFRalpha) plays a vital role in the development of vertebrate embryos, since mice lacking PDGFRalpha die in mid-gestation. PDGFRalpha is expressed in several types of migratory progenitor cells in the embryo including cranial neural crest cells, lung smooth muscle progenitors and oligodendrocyte progenitors. To study PDGFRalpha gene regulation and function during development, we generated transgenic mice by pronuclear injection of a 380 kb yeast artificial chromosome (YAC) containing the human PDGFRalpha gene. The YAC transgene was expressed in neural crest cells, rescued the profound craniofacial abnormalities and spina bifida observed in PDGFRalpha knockout mice and prolonged survival until birth. The ultimate cause of death was respiratory failure due to a defect in lung growth, stemming from failure of the transgene to be expressed correctly in lung smooth muscle progenitors. However, the YAC transgene was expressed faithfully in oligodendrocyte progenitors, which was not previously observed with plasmid-based transgenes containing only upstream PDGFRalpha control sequences. Our data illustrate the complexity of PDGFRalpha genetic control, provide clues to the location of critical regulatory elements and reveal a requirement for PDGF signalling in prenatal lung growth, which is distinct from the known requirement in postnatal alveogenesis. In addition, we found that the YAC transgene did not prolong survival of Patch mutant mice, indicating that genetic defects outside the PDGFRalpha locus contribute to the early embryonic lethality of Patch mice.

Spinal dysraphism: a review of neuroradiological features with embryological correlations and proposal for a new classification

Our purpose was to review the neuroradiological features of spinal dysraphism and to correlate them with clinical findings and up-to-date embryological theory. We also aimed to formulate a working classification which might prove useful in clinical practice. We reviewed series of 986 children referred to our Spina Bifida Centre in the past 24 years. There were 353 children with open spinal (OSD) and 633 with closed (skin-covered) spinal (CSD) dysraphism. By far the most common open abnormality was myelomeningocele, and all patients with OSD had a Chiari II malformation. CSD was categorised clinically, depending on the presence of a subcutaneous mass in the back. CSD with a mass mainly consisted of lipomas with dural defects and meningoceles, and accounted for 18.8 % of CSD. CSD without a mass were simple (tight filum terminale, intradural lipoma) or complex (split cord malformations, caudal regression). Our suggested classification is easy to use and to remember and takes into account clinical and MRI features; we have found it useful and reliable when making a preoperative neuroradiological diagnosis in clinical practice.

The detection of spina bifida before 10 gestational weeks using two- and three-dimensional ultrasound

We present three cases of spina bifida during the embryonic period detected by ultrasound before 10 weeks' gestational age. The last-menstrual-period-based ages ranged from 9 weeks 1 day to 9 weeks 4 days and the crown rump lengths ranged from 22 mm to 28 mm. The cases were identified prospectively in a program of targeted ultrasound examination of high-risk pregnancies, using a 7.5 MHz annular array transvaginal transducer. The use of 3D ultrasound made additional diagnostic ultrasound tomograms possible, but was not necessary for the definite diagnosis. The scalloping of the frontal bones and the Arnold Chiari malformation did not occur before 12 weeks.

Zic2 regulates the kinetics of neurulation

Mutation in human ZIC2, a zinc finger protein homologous to Drosophila odd-paired, causes holoprosencephaly (HPE), which is a common, severe malformation of the brain in humans. However, the pathogenesis is largely unknown. Here we show that reduced expression (knockdown) of mouse Zic2 causes neurulation delay, resulting in HPE and spina bifida. Differentiation of the most dorsal neural plate, which gives rise to both roof plate and neural crest cells, also was delayed as indicated by the expression lag of a roof plate marker, Wnt3a. In addition the development of neural crest derivatives such as dorsal root ganglion was impaired. These results suggest that the Zic2 expression level is crucial for the timing of neurulation. Because the Zic2 knockdown mouse is the first mutant with HPE and spina bifida to survive to the perinatal period, the mouse will promote analyses of not only the neurulation but also the pathogenesis of human HPE.

Mini-review: toward understanding mechanisms of genetic neural tube defects in mice

We review the data from studies of mouse mutants that lend insight to the mechanisms that lead to neural tube defects (NTDs). Most of the 50 single-gene mutations that cause neural tube defects (NTDs) in mice also cause severe embryonic-lethal syndromes, in which exencephaly is a nonspecific feature. In a few mutants (e.g., Trp53, Macs, Mlp or Sp), other defects may be present, but affected fetuses can survive to birth. Multifactorial genetic causes, as are present in the curly tail stock (15-20% spina bifida), or the SELH/Bc strain (15-20% exencephaly), lead to nonsyndromic NTDs. The mutations indicate that "spina bifida occulta," a dorsal gap in the vertebral arches over an intact neural tube, is usually genetically and developmentally unrelated to exencephaly or "spina bifida" (aperta). Almost all exencephaly or spina bifida aperta of genetic origin is caused by failure of neural fold elevation. The developmental mechanisms in genetic NTDs are considered in terms of distinct rostro-caudal zones along the neural folds that likely differ in mechanism of elevation. Failure of elevation leads to: split face (zone A), exencephaly (zone B), rachischisis (all of zone D), or spina bifida (caudal zone D). The developmental mechanisms leading to these genetic NTDs are heterogeneous, even within one zone. At the tissue level, the mutants show that the mechanism of failure of elevation can involve, e.g., (1) slow growth of adjacent tethered tissue (curly tail), (2) defective forebrain mesenchyme (Cart1 or twist), (3) defective basal lamina in surface ectoderm (Lama5), (4) excessive breadth of floorplate and notochord (Lp), (5) abnormal neuroepithelium (Apob, Sp, Tcfap2a), (6) morphological deformation of neural folds (jmj), (7) abnormal neuroepithelial and neural crest cell gap-junction communication (Gja1), or (8) incomplete compensation for a defective step in the elevation sequence (SELH/Bc). At the biochemical level, mutants suggest involvement of: (1) faulty regulation of apoptosis (Trp53 or p300), (2) premature differentiation (Hes1), (3) disruption of actin function (Macs or Mlp), (4) abnormal telomerase complex (Terc), or (5) faulty pyrimidine synthesis (Sp). The NTD preventative effect of maternal dietary supplementation is also heterogeneous, as demonstrated by: (1) methionine (Axd), (2) folic acid or thymidine (Sp), or (3) inositol (curly tail). The heterogeneity of mechanism of mouse NTDs suggests that human NTDs, including the common nonsyndromic anencephaly or spina bifida, may also reflect a variety of genetically caused defects in developmental mechanisms normally responsible for elevation of the neural folds.

Transgenic rescue of congenital heart disease and spina bifida in Splotch mice

Pax3-deficient Splotch mice display neural tube defects and an array of neural crest related abnormalities including defects in the cardiac outflow tract, dorsal root ganglia and pigmentation. Pax3 is expressed in neural crest cells that emerge from the dorsal neural tube. Pax3 is also expressed in the somites, through which neural crest cells migrate, where it is required for hypaxial muscle development. Homozygous mutant Splotch embryos die by embryonic day 14. We have utilized the proximal 1.6 kb Pax3 promoter and upstream regulatory elements to engineer transgenic mice reproducing endogenous Pax3 expression in neural tube and neural crest, but not the somite. Over expression of Pax3 in these tissues reveals no discernible phenotype. Breeding of transgenic mice onto a Splotch background demonstrates that neural tube and neural crest expression of Pax3 is sufficient to rescue neural tube closure, cardiac development and other neural crest related defects. Transgenic Splotch mice survive until birth at which time they succumb to respiratory failure secondary to absence of a muscular diaphragm. Limb muscles are also absent. These results indicate that regulatory elements sufficient for functional expression of Pax3 required for cardiac development and neural tube closure are contained within the region 1.6 kb upstream of the Pax3 transcriptional start site. In addition, the single Pax3 isoform used for this transgene is sufficient to execute these developmental processes. Although the extracellular matrix and the environment of the somites through which neural crest migrates is known to influence neural crest behavior, our results indicate that Pax3-deficient somites are capable of supporting proper neural crest migration and function suggesting a cell autonomous role for Pax3 in neural crest.

Accessory limbs associated with spina bifida - a second look

An accessory limb associated with spina bifida was already reported by the authors. We had then described it as a result of a very early splitting of the limb bud arising from the paraxial mesoderm. We have subsequently seen three other such cases, which are described in this report as well as a review of five other cases in the literature. It is proposed that the growth of the accessory limb occurs from a mesodermal blastema that is a result of de-differentiation from Schwann cells.

Fibronectin expression in the developing human spinal cord, nerves, and ganglia

AIM

Analysis of developmental role of fibronectin during differentiation of the human spinal cord, nerves, and ganglia.

METHODS

Seven normal human embryos and fetuses between the 7th and 9th developmental week and a 9-week fetus with cervical spina bifida were histologically examined on hematoxylin and eosin stained serial paraffin sections of thoracic axial segments. Monoclonal antibody to the human cell fibronectin fragment was used for immunohistochemical detection of fibronectin.

RESULTS

In the 7th and 8th week of development, fibronectin was weakly expressed in the ventricular and intermediate zones of the spinal cord. Intense fibrillar expression was found in the marginal zone of the spinal cord - first over the ventral gray horns and later over the lateral and dorsal gray horns, and along the pathways of ventral and dorsal roots of the spinal nerves and in the spinal ganglia. At 9th week, fibronectin expression disappeared in the ventricular and intermediate zones a nd became weak and granular in the marginal zone of the spinal cord. In the spinal cord of a 9-week malformed fetus with cervical spina bifida, fibronectin expression was completely absent. Fibronectin was expressed in the nerves and ganglia throughout the investigated period, both in normal and malformed human conceptuses.

CONCLUSION

Transient expression of fibronectin in the human spinal cord coincided with the most intense neuronal differentiation. Temporal and spatial expression of fibronectin during normal development, and its absence in a malformed human fetus suggests developmental role of fibronectin for the normal formation of the spinal cord.

Pax3 and Pax7 are expressed in commissural neurons and restrict ventral neuronal identity in the spinal cord

Pax3 and Pax7 are transcription factors sharing high sequence identity and overlapping patterns of expression in particular in the dorsal spinal cord. Analysis of Pax3 and Pax7 double mutant mice demonstrates that both genes share redundant functions to restrict ventral neuronal identity in the spinal cord. In their absence, the En1 expression domain is expanded dorsally but that of Evx1 is not affected. In addition, Pax3 and Pax7 are expressed in commissural neurons and double mutant embryos exhibit highly reduced ventral commissure. Our findings reveal two distinct regulatory pathways for spinal cord neurogenesis, only one of which is dependent on Pax3/7 and 6.

[Prenatal diagnosis and outcome of patients with spina bifida]

The frequency of new cases of myelomeningocele has largely decreased in the last 10 years in several countries of western Europe; the emergence of widespread prenatal diagnosis is probably one of the main reasons. However, the outcome of spina bifida which eludes the prenatal diagnosis, or in cases where termination was refused by parents, remains badly known. To our knowledge, there is no recent data on the outcome of children with spina bifida. Moreover, available data, depending on their European or American origin, indicate different functional outcomes. This led us to re-evaluate the mechanisms involved in the prenatal diagnosis of spina bifida and the outcome of our patients with spina bifida. The aim of this paper is to give a short description of the "rules and principles" of prenatal diagnosis as it is applied in our centres, as well as a brief overview of the outcome of 137 cases of spina bifida. In the retrospective study, three major aspects were evaluated: 1) frequency and types of surgeries and their benefits; 2) socio-psychological adaptation of the patients; 3) educational level and learning disabilities.

A novel embryogenetic mechanism for Currarino's triad: inadequate dorsoventral separation of the caudal eminence from hindgut endoderm

Currarino's triad is a congenital malformation involving the combination of anorectal stenosis, a presacral mass (most often a teratoma or ventral menigocele) and an anterior sacral bony defect (scimitar sacrum). Current theories regarding its embryogenesis are difficult to reconcile with our current understanding of caudal neuraxial and hindgut development. Caudal neuraxial structures develop from the caudal eminence (or tail bud), which normally separates from the hindgut endoderm concurrent with ingrowth of the posterior notochord during late gastrulation. We describe the first reported association of Currarino's triad with a caudal split cord malformation. It has previously been proposed that split cord malformations and related 'complex dysraphic malformations' involving abnormalities of one or more of the three primary germ layers arise through disordered midline axial integration during gastrulation. The presence of a split cord malformation in a patient with Currarino's triad suggests that the two disorders share a common embryogenetic pathway. We propose that the malformations of Currarino's triad arise through a failure of dorsoventral separation of the caudal eminence from the hindgut endoderm during late gastrulation.

Comparison of lectin binding patterns in malformed and normal human embryos and fetuses

Altered glycosylation in the course of disease detectable by changes in lectin binding patterns has been well established for adult tissues, but only a few authors have described carbohydrate entities during normal human embryonic and fetal development. Whether alterations in carbohydrate patterns occur in human embryonic and fetal tissues, affected by malformations, remains to be investigated. We, therefore, examined human embryos and fetuses at corresponding developmental stages with and without malformations (spina bifida, exencephaly, cleft lip and cleft palate, and dysmelia) with respect to their lectin binding patterns for the lectins RCA I, PNA, WGA, SBA, SNA, Con A, and LTA. Our results demonstrated that during the development of malformations, the affected tissue sites exhibited a different carbohydrate pattern from normally developed specimens. Furthermore, tissues known to be sites of secondary malformation, accompanying the primary defect, although displaying a histologically normal appearance, also showed an altered carbohydrate pattern. This might indicate a possible general alteration in the carbohydrate pattern in the course of development of malformations in man.

[Congenital defects of the spinal part of the neural tube]

The abnormal closure of the neural tube results in defects of the nervous system development, which are referred to as dysraphism. Considering successive steps of the development of the human foetus, it can be estimated that spinal cord malformations arise from pathologies of early foetal development between 17th and 28th day gestational age. This time period comprises a development of the neural plate and subsequently neural tube. The development is completed with a closure of a posterior aperture of the neural tube (caudal neuropore). Congenital malformations are often caused by defective closure of the caudal neuropore. The neural plate develops about 17th day gestational age, the cerebral vesicle appears about 21st day and the neural tube forms between 17th and 20th day. The rostral neuropore closes on the day 25th as does the caudal neuropore on the day 28th. The embryo is 2.5 mm long at the time. Noxious factors acting during that period can affect normal closure of the caudal neuropore and distort the process of spinal cord canalization. The resultant defect is called spina bifida. This is the most severe form of dysraphism-rachischisis. Meninges are also affected in this defect. They cannot cover the neural canal and on the margins of the lesion are replaced by epithelium. In milder types of the defect lack of a complete bony framework is concealed by soft tissues, forming a sac of variable size over the lesion. Spina bifida can be subdivided according to the sac structure: meningocoele, meningocysticoele, meningomyelocoele, meningomyelocystocoele. Central canal pathologies constitute another form of spinal cord malformations presenting as hydromyelia. Abnormal closure of the neural tube may affect development of the vertebral column and spinal cord along their entire length or only at a certain portion. Malformations are seen most frequently in the lumbo-sacral and then cervical regions.

Body wall defects in two sibs

We describe 2 sibs, a male fetus with an unusual lumbar hernia and spina bifida occulta, and a female fetus with a median abdominoschisis. The first fetus had some signs of lumbocostovertebral syndrome (LCVS), which consists of a congenital lumbar hernia and associated abnormalities such as absent or hypoplastic ribs, hemivertebrae, and scoliosis. Abdominoschisis has not been described in LCVS, and the given abnormalities in the 2 sibs have not been published to date. One can hypothesize that vascular disruption of a somite or a group of somites may result in the described abdominal wall defects. We conclude that these abnormalities could be coincidental in the 2 sibs or could have a related, probably multifactorial, cause.

[The main etiopathogenic mechanisms of neurocutaneous diseases]

Neurocutaneous syndromes constitute a large and complex group of diseases in which recent medical advances, particularly in the field of molecular biology and genetics, have afforded a deeper understanding of the way in which these diseases originate. In this article, we review the advances concerning pathogenic mechanisms. First, we discuss the malformations disorders of the central nervous system associated with skin disorders, which range from spinal and/or cranial dysraphism with skin lesions to fustrated forms of malformations of the neural tube, such us membranous aplasia cutis. Neurocutaneous vascular disorders can be due to malformational disease, such as in Sturge-Weber syndrome, as well as to autoimmune diseases. The analysis of mutations affecting the capacity for migration and differentiation of melanocyte precursors enables us to gain a better understanding of disorders of the cells of the neural crest, such as piebaldism and Waardenburg's syndrome. Mutations in tumor suppressor genes play an important part in the development of hamartomatous and neoplastic lesions in neurofibromatosis and tuberous sclerosis. Genetic mosaicism, both of the functional and the genomic kind, accounts for the great diversity of phenotypes and the distribution of neurocutaneous diseases. Lastly, neurocutaneous syndromes such as the paracrinopathies form an attractive hypothesis, which is as yet to be confirmed.

Embryogenesis. Why do we need a new explanation for the emergence of spina bifida with lipoma?

Spina bifida with lipoma is a human malformation that most often affects the lumbosacral area. It is a complex morphological type. Its origin is controversial, and none of the previous hypotheses can be retained in view of the most recent advances in experimental embryogenesis. Contrary to earlier opinions, adipocytes cannot arise from meninges, vessels or glial cells and spina bifida cannot be explained by incarceration of mesodermal tissues during primary neurulation or developmental defect at the level of the tail bud. Spina bifida with lipoma, which actually involves all the derivatives of the so-called dorsal mesoderm, must therefore result from abnormal development of this mesoderm, which is induced by the dorsal neural tube. The location of the primary defect (dorsal mesoderm or neural tube) remains to be established.

Neural tube defects and abnormal brain development in F52-deficient mice

F52 is a myristoylated, alanine-rich substrate for protein kinase C. We have generated F52-deficient mice by the gene targeting technique. These mutant mice manifest severe neural tube defects that are not associated with other complex malformations, a phenotype reminiscent of common human neural tube defects. The neural tube defects observed include both exencephaly and spina bifida, and the phenotype exhibits partial penetrance with about 60% of homozygous embryos developing neural tube defects. Exencephaly is the prominent type of defect and leads to high prenatal lethality. Neural tube defects are observed in a smaller percentage of heterozygous embryos (about 10%). Abnormal brain development and tail formation occur in homozygous mutants and are likely to be secondary to the neural tube defects. Disruption of F52 in mice therefore identifies a gene whose mutation results in isolated neural tube defects and may provide an animal model for common human neural tube defects.

Brca1 deficiency results in early embryonic lethality characterized by neuroepithelial abnormalities

The breast and ovarian cancer susceptibility gene, BRCA1, has been cloned and shown to encode a zinc-finger protein of unknown function. Mutations in BRCA1 account for at least 80% of families with both breast and ovarian cancer, as well as some non-familial sporadic ovarian cancers. The loss of wild-type BRCA1 in tumours of individuals carrying one nonfunctional BRCA1 allele suggests that BRCA1 encodes a tumour suppressor that may inhibit the proliferation of mammary epithelial cells. To examine the role of BRCA1 in normal tissue growth and differentiation, and to generate a potential model for the cancer susceptibility associated with loss of BRCA1 function, we have created a mouse line carrying a mutation in one Brca1 allele. Analysis of mice homozygous for the mutant allele indicate that Brca1 is critical for normal development, as these mice died in utero between 10 and 13 days of gestation (E10-E13). Abnormalities in Brca1-deficient embryos were most evident in the neural tube, with 40% of the embryos presenting with varying degrees of spina bifida and anencephaly. In addition, the neuroepithelium in Brca1-deficient embryos appeared disorganized, with signs of both rapid proliferation and excessive cell death.

Alterations in cranial morphogenesis in the Lp mutant mouse

The effects of exencephaly on cranial morphogenesis were studied at 10 to 12 days of gestation in the loop-tail (Lp) mutant mouse in which the hindbrain and spinal cord fail to close. At the level of the hindbrain, the otocysts became displaced ventrally in abnormal (Lp/Lp) embryos, and the everted neuroepithelium showed a diminished "luminal" reaction to the lectins WGA and Con A, as compared with normal embryos. Also, occasional clusters of rounded cells that resembled presumptive neural crest cells and that labeled with WGA, Con A, and anti-N-CAM were observed at the everted tips of the open neural folds. By 12 days' gestation, there was a loss of integrity in some areas of the neuroepithelium. However, despite the topographic and neuroepithelial distortions, normal differentiation of a roof plate-like neuroepithelium occurred at the ends of the everted neural folds. In addition, the mesenchyme showed normal condensations that labeled with WGA, Con A, and anti-N-CAM in the perinotochordal basicranium and periotic regions. Thus, in this mutant mouse model of neural dysraphism, some features of cranial morphogenesis and differentiation appear to be dependent on timely and proper closure of the cranial neural tube, whereas other aspects may proceed independently of neural closure.

Neuronal overmaturation in dysraphism: ontogenic expression of neuropeptides in the fetal brain and developmental anomalies in exencephaly

Starting from knowledge obtained in our previous studies of experimental dysraphism in chick embryos, the entity of neuronal overgrowth observed in exencephaly was further investigated. The ontogenic expression of neuron-specific enolase (NSE), vasoactive intestinal polypeptide (VIP), and somatostatin was analyzed both in chick exencephaly of the natural product and in normal chick fetuses by carrying out immunohistochemical studies. In normal fetuses, immunostained elements positive for NSE first appeared in the spinal gray matter on postincubation day 16 and increased in intensity during the fetal period. By postnatal day 2, the cerebral peduncle, brain stem neurofibers, molecular layer of the cerebellum, corpus striatum, and piriform cortex became immunoreactive. No immunohistochemical reaction to VIP was observed during these stages. Somatostatin-positive elements were not identified during the fetal period, except in limited regions, such as the corpus striatum, which appeared to have weakly positive staining on day 21. The exencephalic fetuses, however, demonstrated extremely advanced neuronal maturation, with intense immunoreactivity already being manifest in various regions, including the corpus striatum, piriform cortex, spinal gray matter, and brain stem nuclei, on day 16 of the fetal period. Somatostatin-positive elements also appeared at this stage in chick exencephaly, but such immunoreactivity was localized, particularly in the overgrown foci. The present study showed that the neuronal maturation process in some neurons of exencephalic brain and spinal cord was definitely further advanced than that in normal controls. A possible clinical application of NSE and somatostatin measurement as markers for dysraphic states in the fetus is suggested.

Interaction between undulated and Patch leads to an extreme form of spina bifida in double-mutant mice

The aetiology of spina bifida involves genetic and environmental factors, which may be why major genes contributing to pathogenesis have not been identified. Here we report that undulated-Patch double-mutant mice have a phenotype reminiscent of an extreme form of spina bifida occulta in humans. This unexpected phenotype in double-mutant but not single-mutant mice shows that novel congenital anomalies such as spina bifida can result from interaction between products of independently segregating loci. This example of digenic inheritance may explain the often sporadic nature of spina bifida in humans.

Spina bifida: role of neural tissue damage during pregnancy in producing spinal paralysis

Spina bifida is one of the most common human birth defects. In fetuses with open spina bifida, the spinal cord remains exposed to the amniotic fluid (AF) throughout gestation. Results of prenatal examinations suggest that affected fetuses exhibit leg movement until the third trimester but become paralyzed later in pregnancy, several months after the initial spinal cord defect occurred. Clinical observations suggest that after the initial defect in neural tube closure, the spinal cord may be subjected to continuous, progressive damage related to contact with the AF. We urge clinicians and scientists to test the AF damage hypothesis by studying prenatal fetal activity in humans and through experimental studies. If this hypothesis is correct, the onset of spinal paralysis in affected fetuses may be prevented by protecting the spinal cord tissues before major nerve damage occurs. If the course of this disease process could be altered, both the patient and family would benefit from the reduction in the misery of the disabling neurologic condition as well as from the acute and long-term cost of medical care.

Caudal agenesis and associated caudal spinal cord malformations

Caudal agenesis is a rare congenital anomaly resulting from an insult to the structures of the caudal eminence. It may be associated with anomalies of other structures derived from the caudal eminence: the hindgut and the urogenital system. Patients are more likely to present first to the pediatric surgeon (for evaluation of gastrointestinal anomalies), the urologist (for urogenital malformation or dysfunction), or the orthopedic surgeon (for lower extremity abnormalities), than to the neurosurgeon. Characteristic external features of the buttocks, hips, and lower extremities may suggest the diagnosis. MR imaging is the diagnostic modality of choice and should be used in all patients with suggestive external features or other caudal anomalies. The level of bone anomaly corresponds well to the level of weakness but not sensory loss. Sensation is usually relatively preserved. The caudal spinal cord is often truncated in cases of high bone lesions and tethered, with occasional association with a dysraphic lesion, in cases of low bone lesions. Early neurosurgical intervention is preferred in all cases of recognized occult spinal dysraphism. Progressive neurologic deficits may develop later in life in patients with unrecognized tethered cord or dural stenosis and require neurosurgical repair on diagnosis. A better understanding of the embryology of the caudal region and investigation of the teratogens that may interfere with this stage of development should lead to more effective treatment and prevention of caudal agenesis and the associated caudal anomalies.

In utero surgery rescues neurological function at birth in sheep with spina bifida

We hypothesize that the neurologic deficit associated with open spina bifida is not directly caused by the primary defect but rather is due to chronic mechanical and chemical trauma since the unprotected neural tissue is exposed to the intrauterine environment. We report here that exposure of the normal spinal cord to the amniotic cavity in midgestational sheep fetuses leads to a human-like open spina bifida with paraplegia at birth, indicating that the exposed neural tissue is progressively destroyed during pregnancy. When open spina bifida was repaired in utero at an intermediate stage, the animals had near-normal neurologic function. The spinal cord was deformed but largely preserved. These findings suggest that secondary neural tissue destruction during pregnancy is primarily responsible for the functional loss and that timely in utero repair of open spina bifida might rescue neurologic function.

Mechanisms of mutant genes in spina bifida: a review of implications from animal models

Spina bifida (spinal neural tube defects) has been shown to be caused by an abnormality in closure of the neural tube. Basic scientific research has rapidly progressed in experimental embryology and molecular genetics to give new insights into the pathogenesis of defective neural tube closure. The chick and the mouse have proved to be the best animal models for study because of similarities to human neurulation. The embryonic mechanisms for spina bifida appear to be under the control of mutant early regulating genes and modifying genes. Faulty early gene function in chicks and mice has been reported to result in abnormalities of neuronal and nonneuronal tissues important for neural tube closure. Research efforts are being aimed at understanding the inductive interactions and downstream target sites for early regulating genes. Elucidation of the genetic roadmap for the control of neurulation will give further insights into the causes of spina bifida.

Cranial base and vertebral column in human anencephalic fetuses

The purpose of the present study was to investigate the axial skeleton related to the notochord in human anencephalic fetuses in order to elucidate the pathogenesis. Fifteen second trimester fetuses were examined. The spine and the cranial base were dissected and radiographed. Comparison with normal fetuses was performed. Two patterns of abnormal ossification were seen. Anencephalic cases without cervical rachischisis (Groups I and II) differed markedly from cases with cervical rachischisis (Group III). Morphological characteristics, such as bilateral narrowing of the basilar part of the occipital bone combined with normal cranio-caudal dimension, were found in cases without cervical rachischisis. In these cases frontal clefting of vertebral corpora occurred. Caudocranial shortening of the basilar part of the occipital bone was found in cases with cervical rachischisis, where complete median clefting of vertebral corpora also occurred. Because the vertebral corpora and the basilar part of the occipital bone develop around the notochord, which interacts also in the process of neurulation, the defects might indicate a notochordal insufficiency. The study showed that when the initial closure of the neural groove failed, the skeletal deviations were more extensive. The study supports the hypothesis that the notochord is an important clue to an understanding of the pathogenesis in anencephaly.

Ultrasound assessment of congenital spinal anomalies presenting in infancy

Sonography of the infant spine can rapidly and safely exclude or confirm the presence of a congenital malformation. This article reviews the embryology of the spinal cord, abnormal and normal sonographic findings, and findings associated with occult dysraphic lesions. Patient selection for sonographic assessment is also discussed. Illustrations of normal anatomy and the more common dysraphic lesions are provided.

Anencephaly with spinal dysraphism, cleft lip and palate and limb reduction defects

We report three unrelated fetuses presenting with anencephaly, spinal dysraphism, cleft lip and palate and limb reduction defects. Review of the literature suggests that this association may be more commonly found than previously recognized and may indicate severe disturbance in early embryogenesis.

Midline maxillofacial skeleton in human anencephalic fetuses

The purpose of this study was to describe the midline maxillofacial skeleton (the axial skeleton anterior to the sella turcica) in 15 human anencephalic fetuses (14-19 weeks of gestation) by radiography and histology, and to relate the findings to skeletal patterns in the remaining part of the axial skeleton. Four patterns in the maxillofacial skeleton were recognized: normal structures, slightly deformed (6 cases); cleft palate (3 cases); incomplete nasal septum (3 cases); multilocular ethmoid cartilage (3 cases). No association was found between skeletal patterns in the different parts of the axial skeleton. The study demonstrates the existence of a developmental borderline in the anencephalic axial skeleton in the region of the sella turcica. It is presumed that this borderline indicates the boundary between skeletal tissue developed around the notochord (posterior axial skeleton) and the anterior skeletal components derived from neural crest cells.

Multifactorial inheritance of neural tube defects: localization of the major gene and recognition of modifiers in ct mutant mice

Neural tube defects (NTD) in humans have been considered to have a multifactorial aetiology, however the participating genes have not been identified. The curly-tail (ct) mutant mouse develops NTD that resemble the human malformations in location, pathology and associated abnormalities. Moreover, there appears to be multifactorial influence on the incidence of NTD in offspring of curly-tail mice. We now describe a linkage analysis that localizes the ct gene to distal chromosome 4 in mice. Further analysis using recombinant inbred strains demonstrates the presence of at least three modifier loci that influence the incidence of NTD. This study provides definitive evidence for multifactorial inheritance in a mouse model of human NTD.

Syringomyelia: a brief review of ontogenetic, experimental and clinical aspects

The generally accepted definition of syringomyelia is that it is a chronically progressive illness characterized by the presence of cavities or syrinxes in the spinal cord. As manifold as the terminology of syringomyelia are the hypotheses of the etiology. Nowadays with MRI without and with gadolinium it is possible to recognize intramedullar cavities safely, the MR especially the cine-MR provides information on pathophysiological details of the flow and intracavitary pressure dependent pulsations of the CSF. Animal models and the findings of own experimental studies have enabled us to study a form of syringomyelia which very closely resembles that brought about by dysrhaphic malformations in the human being and to examine the effectiveness of certain types of surgical therapy. In this paper the term syringomyelia is only used for dysrhaphic cavities in the medulla. After our experience with 61 patients with syringomyelia now we perform the operative decompression of the craniocervical transition as the first step in the operative treatment of the progressive syringomyelia combined with severe craniocervical malformations. In cases with insufficient treatment response we suggest the syringoarachnoid shunting of persisting large intramedullar cavities.

[Overgrowth and DNA synthesis of neuroepithelium in embryonic stages of induced Long-Evans rat myeloschisis]

Overgrowth of the myeloschisis, namely the excessive amount of the neural plate tissue, has been reported in the human myeloschisis. However, it is still debatable how the overgrowth develops and whether the overgrowth is the cause, or the secondary effect of spinal dysraphism. The author induced myeloschisis in the fetuses of Long-Evans rats by the administration of ethylenethiourea (ETU) to pregnant rats on day 10 of gestation. The fetuses were removed 1 hour after the treatment with bromodeoxyuridine (BrdU) to the dams on day 14 and 21. The fetuses were fixed in alcohol and embedded in paraffin. H-E staining and the immunohistologic examination were performed on the staining patterns to anti-neurofilament (NFP), anti-glial fibrillary acidic protein (GFAP) and anti-BrdU antibody by ABC method. On day 14, the lateral portion of everted neural plate showed a loose arrangement of cells and there was rosette formation in the mesoderm. On day 21, cell necrosis was observed at the dorsolateral portion of myeloschisis, although the ventral portion showed almost normal cytoarchitecture and was positive to NFP and GFAP. The cause of myeloschisis in this model is supposed to be the local and direct cytotoxic effect of ETU to neuro-ectodermal junction. On day 14, control animals contained few BrdU-incorporated cells at the basal plate of neural tube. In contrast, everted neural plate showed an active uptake of BrdU diffusely in the subependymal matrix layer cells. Overgrowth was not yet identified. On day 21, overgrowth of myeloschisis was found in spite of a few positive cells to BrdU which was identical to the control animals. These findings seem to suggest that cells in the myeloschisis retain their ability of DNA synthesis for longer periods of development and overgrowth found on day 21 is possibly a secondary effect of spinal dysraphism in this model.