Mediobasal prosencephalic defects, including holoprosencephaly and cyclopia, in relation to the development of the human forebrain

An osteological assessment of cyclopia by micro-CT scanning

PURPOSE

Imaging modalities such as micro-CT scanning and three-dimensional reconstruction are providing a mechanism for detailed analysis of skeletal components not only of normal specimens but also through revisitation of the abnormal. The aim of this study was to analyse the craniofacial skeleton of five human fetuses with cyclopia by means of micro-CT scanning and three-dimensional reconstruction.

MATERIALS AND METHODS

The study consisted of five cyclopean individuals from the paediatric collection of the School of Anatomical Sciences, University of the Witwatersrand. The specimens ranged in age from 22 to 42 weeks of gestation. The osteological features of each bone of the skull were analysed with the aid of micro-CT scanning and analysis using VG studiomax software.

RESULTS

A detailed analysis of all the bones of the skull revealed that the upper two-thirds of the viscerocranium and the anterior region of the basicranium were the most affected regions of the cyclopean fetuses. The ethmoid, nasal, inferior concha and the lacrimal bones were absent in all the cases of cyclopia. Major abnormalities were found in the premaxillary region which affected the development of the anterior dentition.

CONCLUSION

This study supports the suggestion that the malformations of the visceral bones are secondary to defective development of the presphenoid and mesethmoid cartilages. The ethmoidal bones are important midline struts during normal development and their absence in cyclopia leads to non-laterality of facial features.

Congenital eye anomalies: More mosaic than thought?

The eye is a sensory organ that primarily captures light and provides the sense of sight, as well as delivering non-visual light information involving biological rhythms and neurophysiological activities to the brain. Since the early 1990s, rapid advances in molecular biology have enabled the identification of developmental genes, genes responsible for human congenital diseases, and relevant genes of mutant animals with various anomalies. In this review, we first look at the development of the eye, and we highlight seminal reports regarding archetypal gene defects underlying three developmental ocular disorders in humans: (1) holoprosencephaly (HPE), with cyclopia being exhibited in the most severe cases; (2) microphthalmia, anophthalmia, and coloboma (MAC) phenotypes; and (3) anterior segment dysgenesis (ASDG), known as Peters anomaly and its related disorders. The recently developed methods, such as next-generation sequencing and genome editing techniques, have aided the discovery of gene mutations in congenital eye diseases and gene functions in normal eye development. Finally, we discuss Pax6-genome edited mosaic eyes and propose that somatic mosaicism in developmental gene mutations should be considered a causal factor for variable phenotypes, sporadic cases, and de novo mutations in human developmental disorders.

Sonographic Evaluation of Holoprosencephaly

Holoprosencephaly is a complex brain anomaly in which the primitive forebrain (prosencephaly) fails to properly divide into cerebral hemispheres. The frequency of holoprosencephaly has been estimated to be 1 in every 5,200 to 16,000 live births. The complex cerebral and facial anomalies that are observed in infants and fetuses with holoprosencephaly will challenge the sonographer who encounters them. Prenatal detection of the milder forms is particularly difficult; the infant with mild holoprosencephaly may live for years in a vegetative state. Knowledge of the range of malformations encountered in holoprosencephaly will help the sonographer accurately identify the findings.

Lack of motor neuron differentiation is an intrinsic property of the mouse secondary neural tube

The cranial part of the amniote neural tube is formed by folding and fusion of the ectoderm-derived neural plate (primary neurulation). After posterior neuropore closure, however, the caudal neural tube is formed by cavitation of tail bud mesenchyme (secondary neurulation). In mouse embryos, the secondary neural tube expresses several genes important in early patterning and induction, in restricted domains similar to the primary neural tube, yet it does not undergo neuronal differentiation, but subsequently degenerates. Although the secondary neural tube, isolated from surrounding tissues, is responsive to exogenous Sonic Hedgehog proteins in vitro, motor neuron differentiation is never observed. This cannot be attributed to the properties of the secondary notochord, since it is able to induce motor neuron differentiation in naive chick neural plate explants. Taken together, these results support that the lack of motor neuron differentiation is an intrinsic property of the mouse secondary neural tube.

Early pathogenesis of holoprosencephaly

Holoprosencephaly (HPE) is one of the most common malformations encountered in early human embryos. It is assumed that more than 90% of HPE embryos die in utero and are eliminated by spontaneous abortion. Embryonic HPE displays some characteristic craniofacial phenotypes, which are not necessarily comparable to those in postnatal HPE cases. In this article, we summarize our studies on HPE in human embryos and discuss the pathogenesis of HPE malformations.

Congenital hypopituitarism: clinico-radiological correlation

BACKGROUND

Non-tumoral causes constitute a major group of childhood hypopituitarism. The structural abnormalities of the stalk and the pituitary gland correlate with number and severity of concurrent hormone deficiencies. We describe clinico-radiological correlates in patients with non-tumoral hypopituitarism.

PATIENTS AND METHODS

Thirty-one children (23 boys) with congenital hypopituitarism, aged 1-17 years, with a peak GH levels of < 7 ng/ml after two pharmacological stimuli (insulin induced hypoglycemia [IIH] and clonidine) were included in the study. MRI tetrad of absent or hypoplastic pituitary, empty sella, redundant or absent stalk and absent/ectopic posterior pituitary bright spot (EPPBS) was considered as a radiological diagnostic criterion and these abnormalities were correlated with number of hormone deficiencies, severity of GH deficiency and mode of presentation at the time of delivery.

RESULTS

Twenty (66%) children had vertex presentation, nine breech, and two children were delivered by lower segment Cesarean section (LSCS). Seven (78%) out of nine in the breech delivery group, 14 (70%) out of 20 in the vertex group and one out of two (50%) in the LSCS group had multiple pituitary hormone deficiencies (MPHD) (p = 0.665). Hypoplastic pituitary gland and posterior pituitary abnormalities were more frequent in patients with isolated growth hormone deficiency (IGHD) as opposed to MPHD (87.5% vs 65.2%, p = 0.08, 63% vs 47%, p = 0.64), whereas empty sella and stalk abnormalities were found more frequently in MPHD than in the IGHD group (76% vs 50%, p = 0.45 and 82.6% vs 37.5%, p = 0.01). Higher frequency of MR abnormalities was found in those with a peak GH response of < 3 ng/ml irrespective of the number of other pituitary hormone deficiencies (82.6% vs 37.5%, p = 0.02). Sixteen patients had MRI tetrad and it was more prevalent in the IGHD than in the MPHD group (75% and 44%, p = 0.01) and correlated with the severity of GH deficiency (r = 0.57, p = 0.01). The imaging abnormalities were also more prevalent in children with breech as compared to vertex presentation and correlated with severity of GH deficiency (100% vs 60%, p = 0.03, r = 0.52).

CONCLUSION

Imaging abnormalities are frequent in patients with non-tumoral hypopituitarism and correlate best with severity of GH deficiency rather than number of hormone deficiencies and breech presentation.

3-D reconstruction of a human fetus with combined holoprosencephaly and cyclopia

Background

The purpose of this study was to examine a human fetus with combined holoprosencephaly and cyclopia by means of histology and 3-D reconstruction to determine the internal structure and extent of the malformation.

Methods

The head from a human fetus at 20 weeks gestation and a diagnosis of holoprosencephaly and cyclopia was investigated histologically and three-dimensionally reconstructed with CAD techniques. The cranial bones, blood vessels, nerves, eye and brain anlagen were reconstructed.

Results

The 3-D reconstruction revealed both severe malformation and absence of the facial midline bones above the maxilla, and a malformation of the maxilla and sphenoid bone. The mandible, posterior cranial bones, cranial nerves and blood vessels were normal. A synophthalmic eye with two lenses was found. The prosencephalon was a single small protrusion above the diencephalon. No nasal cavity was present. Above the single eye a proboscis was found.

Conclusion

The absence of the facial midline bones above the maxilla and the presence of a proboscis as a nose-like structure above the cyclopic eye both mean that there was a developmental defect in the fronto-nasal facial process of this fetus.

Holoprosencephaly: An Antenally-diagnosed Case Series and Subject Review

Introduction: Holoprosencephaly (HPE) is an uncommon congenital failure of forebrain development. Although the aetiology is heterogeneous, chromosomal abnormalities or a monogenic defect are the major causes, accounting for about 40% to 50% of HPE cases. At least 7 genes have been positively implicated, including SHH, ZIC2, SIX3, TGIF, PTCH1, GLI2, and TDGF1. Clinical Picture: Twelve antenatally- and 1 postnatally-diagnosed cases are presented in this study. These comprised 6 amniotic fluid, 3 chorionic villus, 2 fetal blood, 1 peripheral blood, and 1 product of conception. Outcome: The total chromosome abnormality rate was 92.3%, comprising predominantly trisomy 13 (66.7%). There was 1 case of trisomy 18, and 3 cases of structural abnormalities, including del13q, del18p, and add4q. Conclusion: Despite the poor outcome of an antenatally-diagnosed HPE and the likely decision by parents to opt for a termination of pregnancy, karyotyping and/or genetic studies should be performed to determine if a specific familial genetic or chromosomal abnormality is the cause. At the very least, a detailed chromosome analysis should be carried out on the affected individual. If the result of highresolution karyotyping is normal, Fluorescence in situ hybridisation (FISH) and/or syndromespecific testing or isolated holoprosencephaly genetic testing may be performed. This information can be useful in making a prognosis and predicting the risk of recurrence. Key words: Chromosomes, Genes, Karyotyping, Trisomies

The development of the neural crest in the human

The first systematic account of the neural crest in the human has been prepared after an investigation of 185 serially sectioned staged embryos, aided by graphic reconstructions. As many as fourteen named topographical subdivisions of the crest were identified and eight of them give origin to ganglia (Table 2). Significant findings in the human include the following. (1) An indication of mesencephalic neural crest is discernible already at stage 9, and trigeminal, facial, and postotic components can be detected at stage 10. (2) Crest was not observed at the level of diencephalon 2. Although pre-otic crest from the neural folds is at first continuous (stage 10), crest-free zones are soon observable (stage 11) in Rh.1, 3, and 5. (3) Emigration of cranial neural crest from the neural folds at the neurosomatic junction begins before closure of the rostral neuropore, and later crest cells do not accumulate above the neural tube. (4) The trigeminal, facial, glossopharyngeal and vagal ganglia, which develop from crest that emigrates before the neural folds have fused, continue to receive contributions from the roof plate of the neural tube after fusion of the folds. (5) The nasal crest and the terminalis-vomeronasal complex are the last components of the cranial crest to appear (at stage 13) and they persist longer. (6) The optic, mesencephalic, isthmic, accessory, and hypoglossal crest do not form ganglia. Cervical ganglion 1 is separated early from the neural crest and is not a Froriep ganglion. (7) The cranial ganglia derived from neural crest show a specific relationship to individual neuromeres, and rhombomeres are better landmarks than the otic primordium, which descends during stages 9-14. (8) Epipharyngeal placodes of the pharyngeal arches contribute to cranial ganglia, although that of arch 1 is not typical. (9) The neural crest from rhombomeres 6 and 7 that migrates to pharyngeal arch 3 and from there rostrad to the truncus arteriosus at stage 12 is identified here, for the first time in the human, as the cardiac crest. (10) The hypoglossal crest provides cells that accompany those of myotomes 1-4 and form the hypoglossal cell cord at stages 13 and 14. (11) The occipital crest, which is related to somites 1-4 in the human, differs from the spinal mainly in that it does not develop ganglia. (12) The occipital and spinal portions of the crest migrate dorsoventrad and appear to traverse the sclerotomes before the differentiation into loose and dense zones in the latter. (13) Embryonic examples of synophthalmia and anencephaly are cited to emphasize the role of the neural crest in the development of cranial ganglia and the skull.

Midline "brain in brain": an unusual variant of holoprosencephaly with anterior prosomeric cortical dysplasia

INTRODUCTION

We report three cases of brain malformation presenting with a midline mass of dysplastic cortex that we have termed "brain in brain" malformation.

RESULTS

The three cases have holoprosencephalic features, including bilateral hemispheric continuity across the midline, single ventricle, midline facial defect and missing olfactory bulbs. All three cases have a midline conglomerate mass of deeply infolded, cortex-lined fissures with major arterial branches, heterotopia and large amount of white matter. The dysplastic mass of cortex and white matter extended into the third ventricle. The cortex and white matter of the dysplastic lesion was continuous with the cortex and white matter, respectively, of the cerebral hemispheres.

CONCLUSION

The midline "brain in brain" malformations have some similarities to subcortical heterotopia and extracerebral glioneuronal heterotopia. However, the continuity with the cerebral hemispheres and extension into the ventricle were not reported in subcortical or glioneuronal heterotopia. The common involvement of the midline cortex and extension into the third ventricle implied an anterior segmental prosencephalic abnormality (prosomeres 5/6). However, its pathogenesis remains to be explained.

Computerized three-dimensional analysis of the heart and great vessels in normal and holoprosencephalic human embryos

The developing heart and great vessels undergo drastic morphogenetic changes during the embryonic period. To analyze the normal and abnormal development of these organs, it is essential to visualize their structures in three and four dimensions, including the changes occurring with time. We have reconstructed the luminal structure of the hearts and great vessels of staged human embryos from serial histological sections to demonstrate their sequential morphological changes in three dimensions. The detailed structures of the embryonic heart and major arteries in normal and holoprosencephalic (HPE) human embryos could be reconstructed and visualized, and anatomical structures were analyzed using 3D images. By 3D analysis, cardiac anomalies such as double-outlet right ventricle and malrotation of the heart tube were identified in HPE embryos, which were not easily diagnosed by histological observation. Reconstruction and analysis of 3D images are useful for the study of anatomical structures of developing embryos and for identifying their abnormalities.

Embryonic holoprosencephaly: pathology and phenotypic variability

Holoprosencephaly (HPE) is one of the major brain anomalies caused by the failure of cleavage of the prosencephalon during the early stage of development. Over 200 cases of HPE in the Kyoto Collection of Human Embryos were observed grossly and histologically, with special emphasis on the anomalies of the brain, face and eye. The facial anomalies of HPE human embryos after Carnegie stage (CS) 18 could be classified into cyclopia, synophthalmia, ethmocephaly, cebocephaly, and premaxillary agenesis, similarly as the classical classification for postnatal cases. On the other hand, HPE embryos at CS 13-17 showed some characteristic facies which are different from those in older embryos. In the present paper, pathology and phenotypic variability in HPE embryos were discussed from the embryopathological point of view. Recently, the molecular mechanism of HPE has been clarified by the techniques of gene manipulation, and various HPE genes have been identified by gene analysis of familial HPE cases. HPE is one of the major CNS anomalies which have been extensively studied and provides a clue to the mechanisms of normal and abnormal development of craniofacial structures.

Coincidence of semilobar holoprosencephaly and Chiari II malformation: correlation of prenatal diagnostics and neuropathologic findings

As holoprosencephaly and Chiari II malformation differ considerably, both in pathogenesis and in phenotypic localization, the coincidence of both entities is extremely rare. The case presented is, to our knowledge, the first published report comprising a combination of a semilobar holoprosencephaly associated with a Chiari II malformation and a myelomeningocele diagnosed prenatally and confirmed by postmortem neuropathologic evaluation. These findings indicate that in the case of pre- and postnatal detection of a myelomeningocele and/or Chiari II malformation, possible additional intracranial malformation, such as a semilobar holoprosencephaly, should also be taken into account and vice versa.

Phenotypic variability in human embryonic holoprosencephaly in the Kyoto Collection

BACKGROUND

Holoprosencephaly (HPE) is one of the most common developmental disorders of the brain associated with specific craniofacial dysmorphogenesis. Although numerous postnatal cases have been reported, early phases of its pathogenesis are not well understood. We examined over 200 cases of HPE human embryos both grossly and histologically, and studied their phenotypic variability and stage-specific characteristics.

METHODS

Among over 44,000 human embryos in the Kyoto Collection of Human Embryos, 221 embryos have been diagnosed as HPE. Their developmental stages ranged from Carnegie stage (CS) 13 to CS 23. They were examined grossly and were also serially sectioned for detailed histological analysis.

RESULTS

HPE embryos after CS 18 were classified into complete (true) cyclopia, synophthalmia (partially fused eyes in a single eye fissure), closely apposed separate eyes (possible forerunners of ethmocephaly and cebocephaly), and milder HPE with median cleft lip (premaxillary agenesis). At CS 13-17, when facial morphogenesis is not completed, HPE embryos had some facial characteristics that are specific to these stages and different from those in older HPE embryos. The midline structures of the brain, including the pituitary gland, were lacking or seriously hypoplastic in HPE embryos. Complete cyclopia was found in two cases after CS 18 but none at earlier stages.

CONCLUSIONS

The early development of HPE in human embryos was systematically studied for the first time. The pathogenesis of craniofacial abnormalities, especially eye anomalies, in HPE was discussed in the light of recent studies with mutant laboratory animals.

[Congenital malformations of the brain. 2: Malformations of the corpus callosum and holoprocencephalies]

The corpus callosum is formed between the 7th and the 20th gestational week. If this process is disrupted, partial or complete callosal agenesis may ensue. As large parts of the supra- and infratentorial brain are created during this critical period, associated anomalies need always to be searched for when callosal agenesis is present. Associations with neuro-genetic syndromes also exist. The corpus callosum is generally formed from front to back ("front-to-back rule"). Therefore, a partial callosal agenesis usually involves the posterior portion of the corpus callosum, while a secondary lesion of the corpus callosum does not follow this rule. Holoprosencephalies are a notable exception to this rule, as the frontal part of the corpus callosum is absent in spite of their classification as congenital malformations. They represent a disturbance of the differentiation and cleavage of the prosencephalon with a disruption of the separation of the cerebral hemispheres. Holoprosencephalies can be due to genetic causes, but also to intrauterine infections or other teratogenic causes. The holoprosencephalies are subdivided into alobar, semilobar and lobar holoprosencephalies. This article aims to describe the most important features of callosal agenesis and holoprosencephalies highlighting the respective imaging characteristics.

Ethmocephaly caused by de novo translocation 18;21--prenatal diagnosis

Ethmocephaly is a rare anomaly associated with partial failure of cleavage of the prosencephalon. Morphologically, it is closely related to cyclopia. We present an extremely rare case of ethmocephaly diagnosed in utero and caused by an unbalanced de novo translocation 18;21.

Extramedullary hematopoiesis within a frontoethmoidal encephalocele in a newborn with holoprosencephaly

We present the first report of extramedullary hematopoiesis (EMH) in an encephalocele. The patient was a new-born with semilobar holoprosencephaly, a frontoethmoidal encephalocele, and a large subdural hematoma. The encephalocele appeared as a hemorrhagic mass, protruding from the forehead to cover the right eye, without involvement of the sinuses or nasopharynx. Computerized tomography and magnetic resonance imaging studies ruled out other forms of holoprosencephaly and confirmed the continuity of the brain with the extruded mass. Immunohistochemistry confirmed the presence of an atrophic epithelium covering the mass. Histologic examination of the encephalocele revealed EMH both within and adjacent to malformed cerebral cortex, with a tendency for the hematopoietic cells to line up in columns within malformed cerebral cortex. We propose that a single event during the fourth week of gestation could both interrupt closure of the neural tube, giving rise to the encephalocele, and impair migration of the neural crest, leading to holoprosencephaly secondary to failure of neural crest derivatives to induce basomedial telencephalic differentiation. EMH may have been induced from hematopoietic stem cells in the richly vascular meningeal component of the encephalocele, in response to anemia and hypoxia.

Towards a greater understanding of the pathogenesis of holoprosencephaly

Holoprosencephaly is a malformation of the cerebral hemispheres resulting in the absence of the inter-hemispheric fissure along with other defects of brain development. Frequently midline defects of the craniofacial structures are also present. This malformation sequence has been of interest for many years because of the well recognized genetic and environmental pathogeneses, although the molecular pathogenesis remained elusive. Recent studies have begun clarifying the molecular pathogenesis of holoprosencephaly. Herein is reviewed the syndromes associated with holoprosencephaly, the pathology of this disorder, genetic and environment factors, and a current understanding of the molecular pathogenesis of this disorder.

Molecular mechanisms of holoprosencephaly

Holoprosencephaly (HPE) is the most common developmental defect of the forebrain in humans. Several distinct human genes for holoprosencephaly have now been identified. They include Sonic hedgehog (SHH), ZIC2, and SIX3. Many additional genes involved in forebrain development are rapidly being cloned and characterized in model vertebrate organisms. These include Patched (Ptc), Smoothened (Smo), cubitus interuptus (ci)/Gli, wingless (wg/Wnt, decapentaplegic (dpp)/BMP, Hedgehog interacting protein (Hip), nodal, Smads, One-eyed pinhead (Oep), and TG-Interacting Factor (TGIF). However, further analysis is needed before their roles in HPE can be established. Here we present an overview of the presently known genes causing human holoprosencephaly and describe candidate genes involved in forebrain development identified in other systems. A model is discussed for how these genes may interact within and between several different signaling pathways to direct the formation of the forebrain.

Cranio-facial skeletal development in three human synophthalmic holoprosencephalic fetuses

In three human fetuses with synophthalmic holoprosencephaly (8, 14, 23 wks. p.c.) and two normal human fetuses (9 and 13 wks. p.c.) the anatomy of the cranial base, facial cranium and their relation to the notochord was studied using serial histological sections and computer aided three-dimensional reconstruction methods. Mesethmoidal cartilage differentiation was variably deficient in all three holoprosencephalic cases. The premaxillary bones were rudimentary with missing tooth buds. The development of the sphenoid bone was defective in two of the holoprosencephalic cases (8, 14 wks. p.c.). The notochord terminated normally within the sphenoid body in all investigated cases. Our results indicate that in holoprosencephaly there is a general defect in the midline cranial cartilage differentiation rostral to the notochord.

Cyclopamine-induced holoprosencephaly and associated craniofacial malformations in the golden hamster: anatomic and molecular events

Holoprosencephaly is a complex congenital malformation of the brain and is often associated with a spectrum of facial anomalies ranging from normocephaly or nondiagnostic changes to cleft lip/palate (premaxillary dysgenesis), cebocephaly, ethmocephaly, and cyclopia. The primary insult is thought to occur during gastrulation, when prechordal mesenchyme and overlying anterior neural plate undergo complex developmental interactions. Exposure to cyclopamine, a steroid isolated from the desert plant Veratrum californicum, causes holoprosencephaly in mammalian embryos. We have begun to study the pathogenesis of cyclopamine-induced holoprosencephaly and associated craniofacial anomalies in Syrian golden hamsters (Mesocricetus auratus). Embryos were exposed to a single maternal dose of cyclopamine during gastrulation on embryonic day (E) 7.0. By E13.0, 62% of fetuses showed craniofacial malformations, including premaxillary dysgenesis, ocular hypotelorism, and cebocephaly. Facial anomalies were associated with absence of the premaxilla and abnormalities of the midline cranial base, particularly the ethmoid and sphenoid bones. Histological sections from cyclopamine-treated embryos at earlier stages showed marked deficiency of cranial mesenchyme derived from the rostral neural crest. Expression of two transcription factors, HNF-3 beta and Hox-b5, which have been implicated in specification of rostral and caudal neural crest cells, respectively, were examined immunohistochemically. Treatment with cyclopamine caused a transient loss of HNF-3 beta immunoreactivity in prechordal mesenchyme, but had no effect on Hox-b5 expression. The findings suggest that an early event in the pathogenesis of cyclopamine-induced holoprosencephaly may be altered expression of selected proteins in the prechordal mesenchyme and floor plate with secondary impaired development of the adjacent neural plate and cranial neural crest.

Epidemiology of holoprosencephaly and phenotypic characteristics of affected children: New York State, 1984-1989

Holoprosencephaly is a congenital defect of the median structures of the brain and face. The epidemiology is poorly known due to the paucity of population-based studies. This study describes the epidemiology of holoprosencephaly in a large population, using cases identified through the New York State Congenital Malformations Registry, and born in 1984-1989. We describe the craniofacial abnormalities present, their frequency, and their cooccurrence, and we examine the correspondence between the severity of craniofacial abnormalities, chromosomal abnormalities, and severity of the brain defect. Liveborn cases totaled 78, yielding a prevalence of 4.8 per 100,000 live births. Prevalence among girls was nearly double that in boys, and was 4.2 times higher among infants of mothers under age 18 compared to infants of older mothers. Only 9.8% of all cases had no craniofacial abnormalities other than the brain defect. Eye malformations were present in 76.8%, nose malformations in 69.5%, ear malformations in 50%, and oral clefts in 41.5%. These malformations arise at different times during gestation. The variability in patterns of cooccurrence suggests variability in the developmental pathways and/or timing of developmental derangements which result in holoprosencephaly. This, in turn, is consistent with a model of multiple causes. Children with alobar holoprosencephaly tended to have the most severe craniofacial anomalies, but the correspondence was not 100%. Craniofacial phenotype does not consistently discriminate between cytogenetically normal and abnormal cases.

Development and differentiation of pituitary cells

Classically, it was thought that the adenohypophyseal gland originated from the oral ectoderm. Its development has been the object of numerous studies over many years. However, several questions are still raised about its origin, differentiation, and commitment. The adenohypophyseal gland could originate from the anterior ridge of the neural plate. Glandular adenohypophyseal cells are committed very early in embryonic life. Interactions between adenohypophyseal presumptive territory and neighboring tissues can exist very soon, as early as at the open neural stage. The expression of a given phenotype by the committed cells seems to be controlled by a number of differentiation and/or transcription factors. In view of all these studies, performed with the use of different in vivo and in vitro models, classical concepts of the embryology of the adenohypophyseal gland need to be reevaluated. Indeed, many questions remain unanswered concerning the molecular mechanisms of known and unknown factors controlling development of the adenohypophyseal gland.

Magnetic resonance imaging of brain anomalies in fetal alcohol syndrome

OBJECTIVE

Postmortem studies of fetuses, infants, and young children with fetal alcohol syndrome (FAS) have demonstrated a variety of severe central nervous system (CNS) anomalies. We undertook this magnetic resonance study (1) to assess the spectrum of CNS anomalies that occur in a clinical sample of typical patients with FAS who are medically stable; and (2) to examine the relationship between CNS and facial anomalies.

METHODOLOGY

Magnetic resonance imaging was performed on a series of 10 patients (4 children, 3 adolescents, and 3 adults) who met criteria for FAS. We systematically evaluated each scan for brain anomalies and compared total brain tissue volume with that of healthy child, adolescent, and adult control subjects.

RESULTS

Six patients had some type of midline anomaly, ranging from partial to complete callosal agenesis (three patients) to hypoplastic corpus callosum (one patient), cavum septi pellucidi (three patients), and cavum vergae (two patients). These midline anomalies were associated with a greater number of facial anomalies. Other brain anomalies identified included micrencephaly, ventriculomegaly, and hypoplasia of the inferior olivary eminences.

CONCLUSION

Patients with classic FAS have a high incidence of midline brain anomalies. This finding is consistent with the concept that the midline CNS is a developmental field that is particularly susceptible to the teratogenic effects of alcohol. Furthermore, patients with more severe facial dysmorphologic characteristics are more likely to have midline brain anomalies. In addition, we observed a high incidence of micrencephaly with a wide range of severity.

The development of the corpus callosum in semilobar and lobar holoprosencephaly

OBJECTIVE

The objective of this study was to determine whether and how a true corpus callosum develops in milder cases of holoprosencephaly.

MATERIALS AND METHODS

The MR scans of seven patients with holoprosencephaly and a callosum-like structure were reviewed. The anatomy of the callosum-like structure and the pericallosal anatomy were evaluated.

RESULTS

Six of the seven cases had a posterior corpus callosum. The seventh case was indeterminate because lack of myelination prevented confirmation that the callosum-like structure consisted only of white matter. In each case the posterior corpus callosum formed posterior to white matter which spanned the interhemispheric fissure beneath a layer of cortical gray matter.

CONCLUSION

A posterior corpus callosum can develop in holoprosencephaly because the first callosal axons use the white matter of the undivided hemispheres as a bridge to cross the interhemispheric fissure.

Fetal alcohol syndrome: craniofacial and central nervous system manifestations

Magnetic resonance imaging (MRI) is undertaken on fetal alcohol syndrome (FAS) subjects to document central nervous system (CNS) anomalies. The abnormalities found include agenesis and hypoplasia of the corpus callosum, cavum septi pellucidi, cavum vergae, ventriculomegaly, hypoplasia of inferior olivary eminences, small brain stem, and micrencephaly. Craniofacial anomalies range from the well-recognized FAS physiognomy to the more severe frontonasal "dysplasia" (median cleft face). CNS and craniofacial abnormalities are predominantly symmetric and central or midline. The association of these anomalies becomes self-evident with recognition of the concept of the midline as a special developmental field, vulnerable to adverse factors during embryogenesis and fetal growth and development.

Generalized chorea in an infant with semilobar holoprosencephaly

We report chorea in an infant with holoprosencephaly. Congenital structural brain disease has not been a reported cause of chorea. Cranial magnetic resonance imaging revealed small, fused frontal lobes with hypoplastic caudates. Our patient responded to symptomatic treatment with dopamine-depleting agents. It is likely that the mechanism for the chorea was a dysfunction of the striatum. The differential diagnosis of childhood chorea should include holoprosencephaly.

Interactions between adenohypophyseal, hypothalamic and nasal presumptive territories during early neurulation process

In chick embryo, the adenohypophysis shows close morphological relationships with hypothalamic and nasal presumptive territories. However, we do not know how long the adenohypophysis depends on its surrounding tissues for its development and differentiation nor do we know anything about factors and mechanisms invovled. This study was undertaken to investigate whether any interactions between these neighbouring tissues influence adenohypophyseal cell growth and differentiation. The ablation of the presumptive hypothalamus and neurohypophysis results in the failure of hypothalamic and infundibular process development. However, the adenohypophysis was present, although it was drastically modified. Moreover, gonadotrophs and corticotrophs can be detected in the developing adenohypophyseal tissue. After the ablation of nasal presumptive territory, from where GnRH neurons originate, the adenohypophyseal length and the number of gonadatrophs and corticotrophs are not significantly altered when compared to control embryos. These results suggest that the presumptive hypothalamus and neurohypophysis are committed during open neural stage. At the following stages, these territories may act to promote the future adenohypophysis development and morphogenesis. However, it seems that pituitary cells are committed from the very early embryonic stages, but interactions between the presumptive adenohypophysis and adjacent territories before the open neural stage cannot be ruled out.

[Holoprosencephaly: study of 6 cases]

The aim of this study is to classify and analyse macroscopic aspects of the brain and facies in holoprosencephaly. The six cases reported were examined at the Department of Pathology of FFFCMPA. Data observed in this study are compared to those registered in the literature.

Holoprosencephaly in a long-tailed macaque (Macaca fascicularis): a case report

A long-tailed macaque fetus with ethmocephaly, alobar holoprosencephaly, and arhinia is reported. This fetus was exposed to an antiprogestational agent, RU 486 (2.5 mg/kg intramuscular, once daily), during gestational days 15-18. Three hypotheses are proposed to explain these malformations: (1) they are a direct result of drug exposure, (2) they are a secondary effect of treatment and the result of decreased blood supply to the developing embryo due to an incomplete abortion, and (3) they represent a spontaneous occurrence.

Methanol-induced neural tube defects in mice: pathogenesis during neurulation

A spectrum of cephalic neural tube defects was observed in near-term (gestation day [GD] 17) mouse fetuses following maternal inhalation of methanol at a high concentration (15,000 ppm) for 6 hr/day during neurulation (GD 7-9). Dysraphism, chiefly exencephaly, occurred in 15% of fetuses, usually in association with reduction or absence of multiple bones in the craniofacial skeleton and ocular anomalies (prematurely open eyelids, cataracts, retinal folds). Measurements of cerebrocortical width in grossly normal, methanol-exposed fetuses revealed significant semiquantitative differences in the thicknesses of the frontal cortex and its constituent layers (neuroepithelium, intermediate cortex/subventricular plate, and cortical layer 1) as well as apparent increases in subventricular plate cellularity relative to controls. Subsequently, the early morphogenesis of these neural changes was investigated in neurulating mouse embryos to define tissue-specific patterns of methanol-induced damage that lead to cephalic axial dysraphism. Following daily 6-hr maternal inhalations of 15,000 ppm methanol during GD 7-8, the cephalic neural fold margins were swollen, blunted, and poorly elevated on GD 8.5 and 9 relative to controls. Histopathology of exposed GD 8.5 embryos revealed microcephaly in association with reductions in the cell density and mitotic index of at least 47% in the cranial mesoderm. The mitotic index in the embryonic neuroepithelium was also reduced by 55%, and groups of neural crest cells were displaced to the neural folds dorsal to the foregut (relative to the more ventral location in the facial regions of control embryos). When examined on GD 9.5 and 10.5, maternal methanol exposure (15,000 ppm for 6 hr/day) during GD 7-9 resulted in stunting, delayed rotation, and microcephaly in over 90% of the affected embryos. Persistent patency of the anterior neuropore and prosencephalic hypoplasia were seen in > 40% and up to 90% of embryos, respectively. Shallow optic vesicles, stunted branchial arches, scoliosis, and hydropericardium were also observed. Many 10.5-day-old embryos were edematous. Occult dysraphism, recognized grossly by abnormally narrow cephalic conformation and histopathologically by the absence of mesoderm in the mesencephalon, was present in at least 21% of methanol-exposed embryos on GD 9.5 and 10.5. Nile blue vital dye staining of methanol-exposed embryos revealed no difference in dye accumulation between control and treated embryos on GD 8.5, 9.0, or 9.5. There were no apparent dysmorphogenic effects in control embryos at any stage of development.(ABSTRACT TRUNCATED AT 400 WORDS)

Hydantoin syndrome with holoprosencephaly: a possible rare teratogenic effect

We report on a newborn girl with lobar holoprosencephaly and clinical signs of hydantoin syndrome. During pregnancy the mother was treated with diphenylhydantoin and primidon for psychomotor and petit mal seizures. The possible relationship between hydantoin syndrome, holoprosencephaly, and maternal intake of anticonvulsants during pregnancy is discussed.

Update of sporadic microphthalmos and coloboma. Non-inherited anomalies

The majority of patients with microphthalmos and colobomas have genetic disorders. This is a survey of non-inherited, sporadic microphthalmos. Such cases may occur in the Goldenhar, CHARGE and VATER associations; it may also be due to teratological agents, for instance maternal ingestion of drugs, maternal infection, fever or irradiation. In these cases it is possible that neural crest cell development is abnormal. Some drugs, for instance retinoic acid are regulators of Hox genes which control an ordered sequence of differentiation; coloboma or microphthalmos may appear if deregulation occurs. Large choristomas of the anterior segment of the eye may be associated with microphthalmos or anophthalmos. Encephaloceles or orbital tumours may deform the growing eye and are another cause of non-inherited microphthalmos.

Holoprosencephaly with retroprosencephalic extracerebral cyst

The authors report holoprosencephaly combined with an enormous extracerebral glio-ependymal cyst in the superior cistern of a 10-week-old boy. The cyst had compressed the holosphere at the floor of the anterior fossa and had caused herniation of the cerebellar vermis and tonsils at the foramen magnum, along with ascending cervical roots. This uncommon combination of lesions clinically may mimic hydranencephaly or hydrocephalus.

The cavum septi pellucidi in term and preterm newborn infants

We reviewed cranial sonographic studies done on 108 normal newborn infants to determine the prevalence and variability in size of the cavum septi pellucidi (CSP). Infants were classified according to gestational age by 2-week intervals. At 24 weeks, only four normal scans were identified. Between 26 and 34 weeks, ten consecutive normal scans were used since all infants had a CSP. At 36, 38, and 40 weeks, all normal scans were counted in order to obtain a prevalence estimate. A CSP was seen in all normal infants below 36 weeks of gestational age. At 36, 38, and 40 weeks, only 69%, 54%, and 36%, respectively, had CSPs. There was no significant change in the width, depth, or area of the CSP with age, birth weight, or biparietal diameter. A CSP greater than 0.95 cm in width or greater than 0.81 cm in depth is outside the normal range and may represent anomalous development of the midline structures of the brain.

Development of anencephaly and its variants

Extreme variants of anencephaly in two human embryos of the same stage, namely 22 (54 days), shed new light on problems such as craniocerebral interrelationships and the timing of developmental events. Embryo X had a chondrocranium that possessed features typical of a holoacranial anencephalic skull and an extremely well-preserved brain, in which some of the neural tracts were comparable to those in a normal control. On the other hand, embryo Y of the same stage had a completely degenerated brain, although the chondrocranium was more nearly normal and represented the precursor of a meroacranial skull. A comparison of the two cases seems to indicate a certain independence between skull and brain. Moreover, it appears possible that the disturbances are related primarily to the skeletal, and only secondarily to the nervous, component. Comparisons with experimental data allow the conclusion that the maldevelopment involves mostly paraxial mesenchyme and little or no disturbance of neural crest. The timing of the mesenchymal defect is probably as early as stages 8 and 9 (18-20 days). This is also the time at which mesenchymal defects can result in failure of the neural tube to close.

Wide cavum septum pellucidum: a marker of disturbed brain development

A wide cavum septum pellucidum defined as a separation of greater than 1 cm of the leaves occurs uncommonly. Nine children with wide cavum septum pellucidum were studied; 8 were abnormal. Observed abnormalities included cognitive impairment (8), seizures (4), hypoplasia of the corpus callosum (4), optic nerve hypoplasia (2), and growth failure (4). The incidence of intellectual dysfunction, the association with midline anomalies of the brain, and growth failure all suggest that wide cavum septum pellucidum may represent part of a spectrum of midline brain anomalies.

An anatomic comparison of cebocephaly and ethmocephaly

Cebocephaly (hypotelorism, single-nostril nose) and ethmocephaly (hypotelorism, interorbital proboscis) lie in the middle of the spectrum of craniofacial changes associated with holoprosencephaly. Because these defects and thorough anatomic studies of them are rare, knowledge concerning morphologic as well as pathogenetic relationships is lacking. We report the autopsy findings and anatomic features of the dried skull of a 31 week fetus with cebocephaly and the craniofacial dissection of a 36 week fetus with ethmocephaly. Both manifested dysplastic changes of the ethmoid bone and anterior portion of the sphenoid bone, with concomitant hypotelorism and defects of the medial orbital walls. Through these latter defects, the eyes were joined in the ethmocephalic fetus (synophthalmia). Other changes of bone (single optic foramen, approximated maxillae, choanal atresia, thickened palate) and soft tissue (eccentric or fused extraocular muscles, single optic nerve) in both fetuses resembled those reported in other cases of cebocephaly and ethmocephaly, as well as cyclopia. In the 19th century, both cebocephaly and ethmocephaly were classified as two-orbit variants of cyclopia, a view supported by the present study.

Holoprosencephaly: examples of clinical variability and etiologic heterogeneity

Clinical variability and causal heterogeneity of holoprosencephaly is discussed in relation to several newborn infants with cyclopia (cases 4,5,6), cebocephaly (cases 2,3), and premaxillary agenesis (case 1). In subjects with holoprosencephaly, the presence of multiple malformations is an indicator of concomitant chromosome aberrations, as in present case 1 (Down syndrome) and case 3 (trisomy 13). Cases 5 and 6 are two monozygotic twins with the same type of cyclopia and alobar holoprosencephaly recognized by prenatal ultrasonography. The diagnostic importance of ultrasonographic, cytogenetic, and pathological studies is pointed out in view of etiologic evaluation, genetic counseling, and prevention of holoprosencephaly.

The human brain at stages 18-20, including the choroid plexuses and the amygdaloid and septal nuclei

The development of the human brain during the seventh embryonic week was studied in serial sections of 88 embryos, and graphic reconstructions were prepared. From stages 18 to 20 the cerebral hemispheres expand rapidly and become more and more distinct entities. The longitudinal fissure between them occupies approximately half of their rostrocaudal extent. In stage 20 they have progressed so far in organization that functional aspects (based on synapses in the primordial plexiform layer) are of importance. An advanced differentiation is also present in the amygdaloid body, which has at least four individual nuclei, and in the forebrain septum, which shows the nucleus of the diagonal band and the medial septal nucleus. This has a bearing on recent experimental studies that document the fundamental role of the septal nuclei with regard to behavioural and cognitive functions. Fibre connections between septal nuclei and hippocampus have appeared. A definitive internal capsule, however, is not yet present. The main connections with diencephalon and other parts of the brain are chiefly by fibres to or from the amygdaloid body by way of the lateral forebrain bundle. The olfactory areas are connected with the habenular nuclei by a well developed stria medullaris thalami. Globus pallidus externus, entopeduncular nucleus, and subthalamic nucleus are prominent features in the subthalamus. The main nucleus of the oculomotor nerve shows a dorsolateral and a ventromedial portion. The rhombic lip is mitotically active in all parts of the rhombencephalon, and seems to participate significantly in the formation of the intermediate layer of the cerebellum and of the cochlear nuclei. The sensory nucleus of the trigeminal nerve has appeared. In the cerebellum the cell layer thought to contain the future Purkinje cells develops. The cerebellar plate is organized into external and internal bulges, and is now connected with mid- and hindbrain through fibre bundles. The area thought to be the dentate nucleus and the supposed floccular region are especially rich in fibres. The accessory olivary nucleus appears in stage 19, and accessory nuclei of the abducent and hypoglossal nerves are evident in stage 20. The choroid plexuses of the fourth and lateral ventricles have appeared. In view of their advanced features, the study of embryos of stages 19-21 becomes increasingly relevant to questions of tissue transplantation.