Morphogenesis of experimental encephalocele (Cranioschisis occulta)

Small spheno-ethmoidal meningoencephalocele versus ethmoidal mucocele in spontaneous intracranial hypotension

Background

Meningoencephalocele is defined as an abnormal sac of brain tissue and meninges extending beyond natural skull margins, often leading to cerebrospinal fluid (CSF) leakage. When this condition arises in the spheno-ethmoidal region, the diagnosis becomes more challenging as it can be mistaken for other nasal pathologies, such as mucocele.

Research question

We show in this case report a non-congenital sphenoethmoidal meningoencephalocele causing rhinoliquoral fistula and spontaneous intracranial hypotension.

Results

this 65-year-old woman presented with sporadic rhinoliquorrhoea associated with orthostatic headache, nausea and dizziness. Brain MRI revealed a small lesion of an ethmoidal sinus, which was successfully treated with endoscopic endonasal surgery. Histology confirmed the presence of meningoencephalic tissue positive for S100 protein on immunohistochemistry.

Conclusions

When dealing with lesions of the paranasal sinuses in contact with the anterior skull base, rhinoliquorrhoea presence suggests meningoencephalocele. In dubious cases, a proper workup, including a thorough clinical history and neurological examination, specific imaging, and a direct search of CSF-like markers, is essential to support the differential diagnosis. In such cases, a transnasal endoscopic surgical approach is recommended to obtain a final histological diagnosis and to perform eventual dural plastic surgery.

The Current Status of the Surgical Management of Complex Spinal Cord Lipomas: Still Navigating the Labyrinth?

This review summarises the classification, anatomy and embryogenesis of complex spinal cord lipomas and describes in some detail the technique of total lipoma resection and radical reconstruction of the affected neural placode. Its specific mission is to tackle two main issues surrounding the management of complex dysraphic lipomas: whether total resection confers better long-term benefits than partial resection and whether total resection does better than conservative treatment, i.e. no surgery, for asymptomatic lipomas. Accordingly, the 24-year progression-free survival data of the senior author and colleagues' series of over 300 cases of total resection are compared with historical data from multiple series (including our own) of partial resection, and total resection data specifically for asymptomatic lesions are compared with the two known series of non-surgical treatment of equivalent patients. These comparisons so far amply support the author's recommendation of total resection for most complex lipomas, with or without symptoms. The notable exception is the asymptomatic chaotic lipoma, whose peculiar anatomical relationship with the neural tissue defies even our aggressive surgical approach, and consequently projects worse results (admittedly of small number of cases) than for the other two lipoma subtypes of dorsal and transitional lesions. Prophylactic resection of asymptomatic chaotic lipomas is therefore not currently endorsed. We have also recently found that some dorsal lipomas with clear outline of the conus on preoperative imaging had a significantly better long-term prognosis of preserving neurourological functions without surgery. Whether this subset of lipomas should be managed conservatively until symptoms arise is now an open question awaiting a longer follow-up of a larger cohort of such patients.

Encephalocele: know it to deal with it

Background

Encephaloceles refer to the herniation of intracranial contents through the defect in the dura and calvarium. This article aims to equip the radiologists with all the necessary information to approach a case of encephalocele in a systematic manner and report in an organized format. Thus reduce the reporting time without overlooking any detail.

Main text

An extensive literature review was performed searching through the standard textbooks and electronic databases to obtain thorough information on the various encephaloceles particularly from a radiological point of view. The author’s observations were also incorporated in the review. Among the available imaging modalities, magnetic resonance imaging is the most versatile and considered the imaging modality of choice because of superior anatomic resolution in the characterization of central nervous system malformation. This study provides the reporting radiologist with a methodical guide to approach a case of encephalocele discussing the imaging protocol, relevant anatomy, classification, associated abnormalities, and imaging prognostic factors.

Conclusion

Encephalocele has always been a subject of predicament for radiologists. Understanding the relevant terminologies, anatomy, imaging protocols, classification, associated malformations/anomalies, and imaging prognostic factors will help to methodically approach each case and provide a systematic and comprehensive report.

Morphometric characteristics of anencephalic skulls - A comparative study

Anencephaly is the most severe form of a neural tube defect resulting from the incomplete occlusion of the anterior neuropore in the fourth week of development and associated with a severely underdeveloped brain mass. As desmal ossification of the neurocranium is induced by the presence of soft tissues (brain), no bone develops as direct consequence of the missing brain. The cranial base, by contrast, is formed by chondral ossification, which is genetically determined, and thus present also in anencephaly. Morphometric characteristics of anencephalic skulls, however, have not yet been investigated in sufficient detail before. In this study we therefore comparatively assessed macroscopic morphological-anatomical and cephalometric CT data on structures and dimensions of 11 macerated anencephalic and 4 normal neonatal skulls highlighting skeletal morphological differences. The most striking results were the missing skullcap and the greatly changed morphology of the existing skull bones, which were reduced in size. The parameters of the skull base, the transverse orbital diameter and maxillary width were significantly smaller in anencephalic skulls. The morphology of the viscerocranium appeared similar to that of normal neonatal skulls. The results of this study can be used in diagnosis and skeletal classification for anencephaly. This can help identify bones that are incomplete, fragmented and taphonomically altered, which is often the case in historical and forensic studies.

Surgical Management of Complex Spinal Cord Lipomas : A New Perspective

This review summarises the classification, anatomy and embryogenesis of complex spinal cord lipomas, and describes in some detail the new technique of total lipoma resection and radical reconstruction of the affected neural placode. Its specific mission is to tackle two main issues surrounding the management of complex dysraphic lipomas : whether total resection confers better long term benefits than partial resection, and whether total resection does better than conservative treatment, i.e., no surgery, for asymptomatic lipomas. Accordingly, the 24 years progression-free survival data of the author and colleagues’ series of over 350 cases of total resection are compared with historical data from multiple series (including our own) of partial resection, and total resection data specifically for asymptomatic lesions are compared with the two known series of non-surgical treatment of equivalent patients. These comparisons amply support the author’s recommendation of total resection for most complex lipomas, with or without symptoms. The notable exception is the asymptomatic chaotic lipoma, whose peculiar anatomical relationship with the neural tissue defies even our aggressive surgical approach, and consequently projects worse results (admittedly of small number of cases) than for the other two lipoma subtypes of dorsal and transitional lesions. Prophylactic resection of asymptomatic chaotic lipomas is therefore not currently endorsed.

Surgical management of complex spinal cord lipomas: how, why, and when to operate. A review

This review summarizes the classification, anatomy, and embryogenesis of complex spinal cord lipomas, and it describes in some detail the new technique of total lipoma resection and radical reconstruction of the affected neural placode. Its specific mission is to tackle two main issues surrounding the management of complex dysraphic lipomas: whether total resection confers better long-term benefits than partial resection and whether total resection fares better than conservative treatment-i.e., no surgery-for asymptomatic lipomas. Accordingly, the 24-year progression-free survival data of the author and colleagues' series of over 300 cases of total resection are compared with historical data from multiple series (including the author and colleagues' own) of partial resection, and total resection data specifically for asymptomatic lesions are compared with the two known series of nonsurgical treatment of equivalent numbers of patients. These comparisons amply support the author's recommendation of total resection for most complex lipomas, with or without symptoms. The notable exception is the asymptomatic chaotic lipoma, whose peculiar anatomical relationship with the neural tissue defies even this aggressive surgical approach and consequently projects worse results (admittedly of a small number of cases) than for the other two lipoma subtypes of dorsal and transitional lesions. Prophylactic resection of asymptomatic chaotic lipomas is therefore not currently endorsed.

Cefaloceli

I cefaloceli sono difetti congeniti o acquisiti del cranio e della dura attraverso i quail possono erniare diverse strutture intracraniche. Un semplice difetto osseo della teca cranica in sede mediana o paramediana non attraversato da un prolasso delle strutture intracraniche prende il nome di cranio bifido occulto. I cefaloceli congeniti possono essere suddivisi in quattro gruppi a seconda del contenuto del tessuto erniato attraverso il difetto osseo:

– Meningoceli, le strutture erniate consistono in meningi e liquor. – Meningoencefaloceli, oltre a meningi e liquor ernia pure parte dell'encefalo. Se l'encefalo erniato comprende anche parte del sistema ventricolare il cefalocele prende il nome di idroencefalomeningocele. – Glioceli, il tessuto erniato è formato da una raccolta di liquor delimitata da tessuto neurogliale. – Cefaloceli atresici, forme fruste di cefaloceli localizzate in sede parietale o occipitale.

I disrafismi cranici congeniti sono piu rari dei disrafismi spinali: l'incidenza dei cefaloceli varia da 0.3 a 4 per 10.000 nati. La sede più frequente dei cefaloceli è la regione occipitale anche se nelle popolazioni orientali predomina le sede fronto-etmoidale. Vi è una prevalenza femminile per le localizzazioni occipitali e maschile per quelle parietali e sincipitali.

A seconda della loro sede i cefaloceli sono classificati in quattro gruppi: occipitali, della volta cranica, fronto-etmoidali (sincipitali) e del basicranio.

Da un punto di vista diagnostico: l'ecografia è di fondamentale importanza per la diagnosi prenatale delle anomalie più grossolane; lo studio del difetto osseo va condotto sia con i radiogrammi convenzionali che con studi di Tomografia Computerizzata (TC) con successive ricostruzioni tridimensionali; mentre la valutazione della componente erniata parenchimale e vascolare deve essere effettuata mediante la Risonanza Magnetica (RM) e la angiografia RM.

Parietal and occipital encephalocele in same child: A rarest variety of double encephalocele

An encephalocele is a protrusion of the brain and/or meninges through a defect in the skull. Based on the location of the skull defect they are classified into sincipital, basal, occipital or parietal varieties. Occurrence of more than one Encephalocele in a patient is very rare and very few cases of double encephalocele are reported. We report an interesting case where a parietal and an occipital encephalocele were present together. The patient was a 2 months boy who was brought to us with complaints of two swelling on the scalp since birth. Neuroimaging studies confirmed it to be a case of double encephalocele. The rarity of the findings prompted us to report this case. The presentation and management of the case along with and review of the relevant literature is presented.

Total Resection of Complex Spinal Cord Lipomas: How, Why, and When to Operate?

This article shows the long-term advantage of total resection of complex spinal cord lipomas over partial resection and over non-surgical treatment for children with asymptomatic lipomas. The classification, embryogenesis, and technique of total resection of complex lipomas are described. The 20-year outcome of 315 patients who had total resection is measured by overall progression-free survival (PFS, Kaplan-Meier), and by subgroup Cox multivariate hazard analysis for the influence of four variables: lipoma type, symptoms, prior surgery, and post-operative cord-sac ratio. These results are compared to 116 patients who underwent partial resection, and to two published series of asymptomatic lipomas followed without surgery. The PFS after total resection for all lipomas is 88.1% over 20 years vs. 34.6% for partial resection at 10.5 years (p < 0.0001). The PFS for total resection of asymptomatic virgin lipomas rose to 98.8% vs. 60% and 67% for non-surgical treatment. Partial resection also compares poorly to non-surgical treatment for asymptomatic lipomas. Multivariate analyses show that a low cord-sac ratio is the only independent variable that predicts good outcome. Pre-operative profiling shows the ideal patient for total resection is a young child with a virgin asymptomatic lipoma, who, with a PFS of 99.2%, is essentially cured. The technique of total resection can be learned by any neurosurgeon. Its long-term protection against symptomatic recurrence is better than partial resection and conservative management. The surgery should be done at diagnosis, except for asymptomatic small infants in whom surgery should be postponed till 6 months to minimize morbidity.

Lateral posterior fossa encephalocele with associated migrational disorder of the cerebellum in an infant

Encephaloceles are acquired or congenital defects in which intracranial contents protrude through a defect in the calvaria. The embryogenesis of these lesions is incompletely understood. The vast majority of lesions occur at or near the anatomical midline. The authors present an extremely rare case of a laterally oriented, pathologically proven encephalocele associated with a posterior fossa cyst and cerebellar migrational defect in an infant. The authors review past and current theories of encephalocele formation as it relates to this case.

Frontoethmoidal meningoencephalocele: appraisal of 200 operated cases

OBJECT

Frontoethmoidal mengingoencephaloceles (fMECs) are frequently observed in Cambodia, especially in poor families. The authors describe issues related to the surgical treatment of fMECs in Cambodia at the end of a humanitarian program that provided surgery free of charge to patients and their families.

METHODS

The authors reviewed 257 cases of fMEC involving patients who presented to their institution, the Children's Surgical Center in Phnom Penh, between 2004 and 2009. They treated 200 of these patients surgically (108 males, 92 females; 89% younger than 18 years) using a "low-cost" management plan with no routine pre- or postoperative investigations. Initially, surgery was performed by visiting foreign surgeons who taught the procedures to resident surgeons. Patients were not charged for consultations or treatment and received at least 1 follow-up examination 6 months postoperatively.

RESULTS

The nasoethmoidal type was the most frequent fMEC encountered (69%). Many patients had associated ophthalmological issues (46% of cases). Only 1 familial case was detected. Combined neurosurgical and facial procedures were successfully standardized and learned by surgeons initially unfamiliar with fMEC management. A neurosurgical approach avoided the need for a facial incision in 42 cases, improving cosmetic results. The most common postoperative issues were a temporary CSF leak (24 cases [12%]) and/or infection (28 cases [14%]). There were 3 deaths directly related to the operations. Cosmetic results were good in 145 cases, average in 27, poor in 7, and worse than preoperative appearance in 6 patients. Fifteen patients were lost to follow-up. The parents of 87% of the children were rice farmers. Questionnaire results confirmed that fMEC has important social and educational consequences for the affected children and that these consequences can be partially improved by fMEC correction.

CONCLUSIONS

This experience in fMEC management demonstrates that local surgeons can treat these malformations with limited surgical materials and in a nonspecialized infrastructure after principles of treatment have been learned and if they are carefully respected. Surgery for fMEC can thus be more accessible to a larger number of patients in developing countries. Moreover, local treatment facilitates better postoperative and follow-up care.

Long-term outcome of total and near-total resection of spinal cord lipomas and radical reconstruction of the neural placode: part I-surgical technique

OBJECTIVE

Partial resection of complex spinal cord lipomas is associated with a high rate of symptomatic recurrence caused by retethering, presumably promoted by a tight content-container relationship between the spinal cord and the dural sac, and incomplete detachment of the terminal neural placode from residual lipoma. Since 1991, we have performed more than 250 total/near-total resections of complex lipomas with radical reconstruction of the neural placodes. Sixteen years of follow-up have proven the long-term benefits of this technique. Part I of this series introduces our technique of total resection and reports the immediate surgical results. Part II will analyze the long-term outcomes of both total and partial resection and identify the factors affecting outcome.

METHODS

From 1991 to 2006, 238 patients (age range, 2 months-72 years) with dorsal, transitional, and chaotic lipomas underwent total or near-total lipoma resection and radical placode reconstruction. Eighty-four percent of the patients were children younger than 18 years and 16% were adults. The technique consisted of wide bony exposure, complete unhinging of the lateral adhesions of the lipoma-placode assembly from the inner dura, untethering of the terminal conus, radical resection of the fat off the neural plate along a white fibrous plane at the cord-lipoma interface, meticulous pia-to-pia neurulation of the supple neural placode with microsutures, and expansile duraplasty with a bovine pericardial graft. Elaborate electrophysiological monitoring was used.

RESULTS

Three postoperative observations concern us. The first is that of the 238 patients, 138 (58%) had no residual fat on postoperative magnetic resonance imaging; 81 patients (36%) had less than 20 mm3 of residual fat, the majority of which were small bits enclosed by neurulation; and 19 patients (8%), mainly of the chaotic lipoma group, had more than 20 mm of fat. There are no significant differences in the amount of residual fat among lipoma types, but redo lipomas are more likely than virgin (previously unoperated on) lipomas to have residual fat by a factor of 2 (P = 0.0214). The second concern is that the state of the reconstructed placode is objectively measured by the cord-sac ratio, obtained by dividing the sagittal diameter of the reconstructed neural tube by the sagittal diameter of the thecal sac. A total of 162 patients (68%) had cord-sac ratios less than 30% (low), 61 (25.6%) had ratios between 30% and 50% (medium), and only 15 (6.3%) had high ratios of more than 50%. Seventy-four percent of patients with virgin lipomas had low cord-sac ratios compared with 56.3% in the redo lipoma patients. The overall distribution of cord-sac ratio is significantly different between redo and virgin lipomas (P = 0.00376) but not among lipoma types. Finally, the incidence of combined neurological and urological complications was 4.2%. The combined cerebrospinal fluid leak and wound infection/dehiscence incidence was 2.5%. Both sets of surgical morbidity compared favorably with the published rates reported for partial resection.

CONCLUSION

Total/near-total resection of spinal cord lipomas and complete reconstruction of the neural placode can be achieved with low surgical morbidity and a high yield of agreeable postoperative cord-sac relationship. Some large rambling transitional lipomas and most chaotic lipomas are the most difficult lesions to resect and tend to have less favorable results on postresection magnetic resonance imaging.

Treatment of frontoethmoidal meningoencephalocele in Cambodia: a low-cost procedure for developing countries

OBJECT

Frontoethmoidal meningoencephaloceles (MECs) are a relatively common abnormality in southeast Asia, with disastrous consequences for the sufferer. In Cambodia, a lack of skilled neuro- and craniofacial surgeons, and the cost of surgery limit the possibilities for appropriate treatment of patients with these lesions. The authors developed a low-cost humanitarian program with the goals of treating frontoethmoidal MECs, ensuring careful postoperative follow-up, and teaching Khmer surgeons how to treat these malformations.

METHODS

This program was facilitated by two nongovernmental organizations: Rose Charities Cambodia provided the facilities, patients, and local staff, and "Médecins du Monde" provided visiting surgeons and anesthesiologists. All operations were free of charge for all patients. A strict follow-up program was organized to evaluate the surgical results, the social impact of the surgery, and the satisfaction levels of the children and their parents.

RESULTS

Forty-five children and seven young adults with MECs were treated using a rather simple surgical technique. Of the three types of MECs encountered, the most frequent was the nasoethmoidal type (43 cases). The most common postoperative issue was a temporary CSF leak (in 16 patients). Cosmetic results were considered excellent or good in 40 patients, average in nine, and poor in one; two patients were lost to follow-up. The overall cost of each operation was estimated to be $380 (US dollars), far less than a standard MEC operation would cost in a more developed country. At the end of this humanitarian program, Khmer surgeons were able to treat standard cases of frontoethmoidal MECs without the help of foreigners.

CONCLUSIONS

Patients in developing nations who have limited access to standard neurosurgical care can be treated for frontoethmoidal MECs with few complications and a satisfactory cost-to-benefit ratio.

Chlorambucil-induced postclosure exencephaly and axial skeletal abnormalities in rat fetuses

Open neural tube defects (NTD) are reported to arise from failure of the embryonic neural folds to close or rupture of a previously closed neural tube. The critical period for dysmorphogenesis of the neural tube by either mechanism is of clinical importance. We had previously reported that single doses of cyclophosphamide (CPA), administered to pregnant rats resulted in reopening of the closed neural tube. The objective of the present study was to determine if other antineoplastic drugs also had similar ability to cause rupture of the closed neural tube. Therefore, single doses of chlorambucil dissolved in bicarbonate buffer were administered to Wistar rats on one of gestation days (GD) 11 through 14 (i.e., well after closure of the neural tube) and fetuses were examined on GD 20. It was observed that the window of susceptibility extended from GD 11 through 14 and that a single dose of 10 mg/kg of the drug was most effective. The affected fetuses had the prosencephalon and mesencephalon parts of the brain protruding through a wide opening of the cranial roof. The exposed brain tissue was hemorrhagic and covered by a thin, transparent and often porous membrane. The cranial vault was missing. Numerous malformations of the axial skeleton and of several nonneural organs were found to accompany the brain defect. Electron microscopic and light microscopic studies revealed extensive cell death, fragmentation, and phagocytosis of dead cells and vacuolization of the neuroepithelium (NE) within 12 h of the drug treatment. Cell death per se was not pronounced in the cranial mesenchyme (ME). The vacuoles in the NE coalesced into small cavities. The ME failed to proliferate adequately and organize itself into the cranial vault primordium. Hemorrhage and disorganization of the NE was progressive. The fluid that escaped into the interstitium seemed to extend into the cysts that developed in the ME externally and into the ventricular system internally. The edema of the ME thus might have contributed to disruption of precursor mesenchymal tissue and consequently to malformation of the cranial bones. Large hematomas and cysts also developed on the basal aspect of the crumbling brain vesicles and appeared to lift the neural tissue out of the shallow cranial cavity. As previously reported for CPA, these data provide evidence for the ability of chlorambucil to cause postclosure exencephaly in rat fetuses for a susceptible period that is considerably long.

Sodium valproate augments spontaneous neural tube defects and axial skeletal malformations in TO mouse fetuses [corrected]

The TO mouse exhibits a low incidence (3.65%) of spontaneous exencephaly at birth. The objectives of this study were to determine if sodium valproate (VPA) would augment this background frequency of exencephaly and to characterize its gross and histologic bases. Single doses of 200, 400, or 600 mg/kg of VPA were administered on one of gestation days (GD) 7 to 10 and fetuses were collected on GD 18. Significant augmentation of the background incidence of exencephaly was observed in the GD 7 and 8 treatment groups. Absence of the skull vault, hemorrhage, and degeneration of the exposed brain, polyhydramnios, and a female excess characterized the abnormality. Exencephalic embryos were markedly growth retarded. In addition to craniofacial and urogenital anomalies, severe axial skeletal malformations were found to be consistently associated with exencephaly. Morphometric evaluation of the alizarin red-stained skeleton confirmed significant skeletal growth inhibition. Histologic sections of GD 10 embryos revealed early onset of treatment-related growth retardation. Arrest of closure appeared to affect intermittent segments of the neural tube. The closure defect sometimes only involved the surface ectoderm of the dorsal midline. The unclosed neural tube was at times covered by a continuous layer of surface ectoderm. Cell death per se was not pronounced in the neuroepithelium. The mesenchyme was generally sparse and edema was obvious in embryos with partial closure. Growth inhibition of the optic and otic primordia was marked by pronounced cell death in these structures as well as in the otic and trigeminal ganglia and in the pharyngeal arch mesenchyme. Evidence for neural crest cell migration was also recorded. These data indicate that VPA interacts with genetic susceptibility, augments the frequency of exencephaly, and also induces other malformations in the TO mouse. The widespread malformations of the cranifacial structures are suggestive of the preferential effect of VPA on the neural crest or its derivatives.

Cerebellar dermoid tumor and occipital meningocele in a monozygotic twin: clues to the embryogenesis of craniospinal dysraphism

A case of monochorionic/monoamnionic twin with discordant occipital developmental malformations is presented. One female twin appeared to have an occipital meningocele with cerebellar aplasia and died immediately after birth. The other twin presented with signs and symptoms of raised intracranial pressure at the age of 7 months. Severe hydrocephalus was present due to an infected intracerebellar dermoid tumor with a contiguous occipital dermal sinus. The clinical and pathological characteristics are described and the different theories concerning twinning, embryogenesis, and dysmorphology in relation to neural tube defects are discussed. Analysis of the features of these monozygotic twins indicates that a meningocele is not a post-neurulation disorder but results from deficient neurulation, probably due to mesodermal insufficiency.

Neural tube defects in the parietal region of human embryos: failure to close or closure-reopening?

This is a follow-up study to earlier investigations on neural tube defects (NTD) in the Kyoto collection of human embryos. It includes an extensive examination of abnormal embryos which have been photographed and serially sectioned following routine histological preparation. Two new types of NTD are described in the parietal region (the roof of the third ventricle) which had previously been overlooked. These anomalies were found most commonly in embryos at the developmental period. Carnegie stage [CS] 16-23 (embryonic days 38-52). Hypotheses are advanced regarding the genesis of NTD and whether encephaloceles and NTD are part of a spectrum of malformation. This study also reinforces evidence that the occurrence of NTD is significantly higher in the embryonic period than at birth. Animal studies, using the guinea-pig are discussed with regard to the investigation of hypotheses put forward to explain the genesis of NTD.

Meningoceles, meningomyeloceles, and encephaloceles: a neuro-dermatopathologic study of 132 cases

Because there have been few comprehensive histopathologic studies of meningomyeloceles and related malformations, we undertook a systematic study of these lesions. One hundred and thirty two cases were obtained from our surgical pathology files; these included 38 meningoceles, 71 meningomyeloceles, and 23 encephaloceles. Tissue sections were stained with hematoxylin and eosin; special stains included trichrome, alcian blue, Fontana-Masson, Nissl, Holzer, and immunoperoxidase for glial fibrillary acidic protein. Epithelial changes included ulceration, atrophy, or nevoid hyperplasia of the epidermis, and loss of appendages. Mesodermal features included fibrous zones resembling dura, subarachnoid tissue or scar (99% of cases), increased numbers of blood vessels (83%), hypertrophy of arrector pili muscle (42%), lipoma formation (38%), and immature skeletal muscle fibers (5%) that rarely intermingled with neuropil-like matrix. The latter tissue was identified in 71% of cases and included neurons, astrocytes, oligodendroglia, and ependyma. Forty-eight percent of cases included peripheral nerve fibers or roots, and some fibers formed onion bulb or Pacinian corpuscle-like structures. Meningothelial cells were observed in 26% of cases and sometimes formed recognizable whorls. Choroid plexus was noted in 3 cases, one example showing an unusual dystrophic calcification that formed long parallel spicules. Pigmented dendritic cells were observed within zones of fibrous tissue in 10% of cases. These malformations involve complex arrangements of cutaneous, neuroectodermal, and mesodermal elements. Because they may be encountered by dermatopathologists, familiarity with the microscopic features of dysraphic lesions is essential.

Cephalic axial skeletal-neural dysraphic disorders: embryology and pathology

Three fundamental types of cephalic axial skeletal-neural dysrapic disorders are analyzed, including: cranioschisis aperta with encephaloschisis (anencephaly and/or exencephaly), cranioschisis occulta with occipital encephalocele, and the Chiari malformation (occipital bone hypoplasia) with compression, deformation and displacement of hindbrain, cerebellum, and medulla. Both clinical and experimental (vitamin A induced) examples of these malformations are used. The study establishes that these are not simple neurological (neural tube defects) disorders as it has been generally assumed, but complex developmental malformations affecting primarily the formation of the axial basicranium (causing skeletal defects) and the elevation of the neural folds and neurocranium (causing neural defects), and, secondarily, the topography of the facial skeleton or viscerocranium (causing oropharyngeal defects). The pathology of these skeletal, neural, and oropharyngeal defects is analyzed, their embryonic origin explored, and their developmental interrelationships discussed. The study proposes that an early paraxial mesodermal insufficiency may be the original anomaly common to all the different malformations that constitutes this heterogeneous group of dysraphic disorders. At any time during the segmental formation of the embryonic skeletal-neural axis a simple reduction in the number of paraxial mesodermal cells produced by the Hensen node/primitive streak complex, could impair the formation of the axial skeleton as well as the elevation of the neural folds thus interfering with their closure. The final type of malformation is determined by variations of the degree, time of occurrence, and duration of the paraxial mesodermal insufficiency.

Subtorcular occipital encephaloceles. Anatomical considerations relevant to operative management

Three cases of occipital encephalocele, one with associated myelomeningocele, are presented. All received preoperative evaluation with magnetic resonance imaging. Such studies provide optimal demonstration of the cerebral and hindbrain anatomy to guide operative treatment and formulate prognosis. Review of available radiographic, operative, and pathological information suggests that most, if not all, occipital encephaloceles are associated with an anomaly of the hindbrain, and the usual anomaly is a rhombic roof encephalocele. In such cases, the site of cranial herniation is caudal to the torcula, regardless of the presence or absence of occipital lobe tissue within the sac. Experimental and clinical analysis suggests that occipital encephaloceles most likely arise from abnormalities in the development of the skull base.

Central nervous system malformations induced by triamcinolone acetonide in nonhuman primates: pathology

Triamcinolone acetonide (TAC) was administered to pregnant macaques (Macaca mulatta [15] and M. radiata [7]) during gestational days (GD) 23 to 41 using various dosing schedules. A daily dose of 10 mg/kg is approximately equal to 100 x the human dose equivalent. The brains of the fetuses and infants were studied grossly and histologically. All cases displayed either the mild form of the TAC-induced syndrome (craniofacial dysmorphia, cranium bifidum occultum, meningocele, and mild distortion of the midbrain) or the more severe form (occipital encephalocele, hydrocephalus, severe distortion of the midbrain or midbrain "beaking," shunting of cerebrospinal fluid, and craniofacial malformations). The dysmorphology was dose-related, with severity increasing at higher doses or with increased numbers of treatments. Individual cases were assessed for the severity of the syndrome by comparison of like components between groups. The lesions observed were morphologically comparable to those described in spontaneous human cases; the TAC-induced occipital encephaloceles were associated with brainstem and cerebellar abnormalities, and, with the less severe form of the syndrome, brainstem abnormalities were occasionally present, with occipital meningoceles. Controversy exists concerning the significance and temporal development of the midbrain changes. However, the associated alteration in aqueduct conformation may have been responsible for functional compromise and ensuing hydrocephalus.

Central nervous system malformations induced by triamcinolone acetonide in nonhuman primates: pathogenesis

The pathogenetic sequence for TAC-induced encephalocele is in agreement with hypotheses proposing that neural tube closure is followed by protrusion of the mesencephalon, with subsequent growth and development resulting in herniation of the cerebrum and cerebellum. This model could serve to clarify the pathogenesis of encephalocele and to stimulate further study in comparing this defect to other dysraphic states. Triamcinolone acetonide (TAC) was administered intramuscularly (10 mg/kg) to 16 pregnant rhesus monkeys (Macaca mulatta) for 5 alternate days of pregnancy, beginning on gestational day (GD) 23. Conceptuses were removed by hysterotomy at GD 35, 42, 50, or 70 and examined grossly and histologically. Length, area, and perimeter of the tectum and aqueduct area and perimeter were measured with an image analyzer. Changes in treated specimens were suggestive of forces within or ventral to the tectum resulting in dorsal protrusion, rostral-posterior stretching, and attenuation. The angle of the cephalic, pontine, and cervical flexures was also measured. The more acute angle of the cephalic flexure and less acute cervical flexure of treated specimens could represent altered orientation secondary to a mesenchymal deficiency. However, the less acute angle of the pontine flexure in treated specimens suggests an intrinsic alteration in the neural tube. This suggests that encephalocele may result from a combination of mesenchymal and neural tube abnormalities.

A sphenoorbital encephalocele--clinical, radiological, and morphological findings

We report here on congenital sphenoorbital encephalocele which could not be disclosed by computed tomography including contrast medium application or by orbital sonography. Surgery and histological examination were necessary to establish correct the diagnosis.

Light microscopic studies on the pathogenesis of exencephaly and cranioschisis induced in the rat after neural tube closure

Administration of a single dose of cyclophosphamide (20 mg/kg) to Charles Foster (CF) rats on day 12 of gestation (i.e., well after neural tube closure) results in exencephaly in almost 100% of living fetuses at term (Padmanabhan, '84). Following the same treatment, embryos/fetuses were collected at various intervals of time (from 8 hr to day 19 of gestation) and studied histologically. At 10 hr after treatment, the neuroepithelium (NE) of the brain vesicles and the neural crest-derived ganglia exhibited pronounced cell death. By day 13, cell death appeared to be more intense and extensive in the NE; the mesenchyme (ME) was less proliferative and was loosely organized. In the following days, the NE presented vacuolizations which coalesced into cavities; these cavities were often bilaterally symmetrical, contained free neuroblasts and erythrocytes, and subsequently opened into the ventricles. The choroid plexus hypertrophied, the ventricles distended, and the NE gradually became very thin. The hypertrophied capillaries of the ME cleaved through the NE, thus delaminating an outer stratum. Subcutaneous blebs developed over the brain vesicles and communicated with the cavities in the brain. Thus the ventricles and the blebs came into direct communication. The ME dorsal and lateral to the brain was loose, and at no site was it organized into the skull primordium. By day 19, there were clear and multiple discontinuities in the walls of the brain. Initial cell death and vacuolization in the NE, inhibition of ME proliferation followed by hypertrophy of the choroid plexus, and possibly enhanced intraventricular pressure and hemorrhage and edema of the ME seem to underlie this process of reopening of the closed neural tube.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental analysis of cephalic axial dysraphic disorders in arsenic-treated hamster embryos

Parenteral injection of pregnant golden hamsters with inorganic arsenic salts early in gestation results, by term, in markedly elevated embryonic-fetal mortality (approximately equal to 50%) and, in surviving fetuses, a high (approximately equal to 90%) incidence of cephalic axial dysraphic disorders ("neural tube defects"), particularly exencephaly/anencephaly and encephaloceles. The present investigation traces the day by day development of these embryopathic effects of arsenic in the hamster with an emphasis on the pathogenesis of cephalic axial dysraphic disorders. Pregnant golden hamsters were given an intraperitoneal injection of sodium arsenate (20 mg/kg) on the 8th day (08.00) of their 16 day gestation period. Matched control dams were injected with an equivalent volume of distilled water by the same route and at the same stage of gestation. Experimental and control dams were sacrificed beginning 24 h after treatment and at regular daily intervals thereafter until term. Embryos and fetuses delivered from sacrificed dams were examined for abnormalities both grossly and histologically. In embryos delivered earliest after treatment (24-48 h) the principal deleterious effect of arsenic observed was retarded growth (elevation, approximation, and fusion) of the cephalic neural folds. This growth retardation ranged in severity among embryos. In the most severely afflicted there was a site wherein the opposing cephalic neural folds had completely failed to appose and fuse ("closure"). This failure of closure of all four tissue components of the neural folds (surface ectoderm, paraxial mesoderm, neural crest cells, neuroectoderm) resulted in a persistent dorsal opening in the head, i.e., cranioschisis aperta. The extent and appearance of this opening varied from a small, ovoid aperture in the dorsal midbrain (mesencephalic) region of the head to a widely open cleft involving the fore and hindbrain regions as well as the midbrain region. In less severely afflicted early embryos, the cephalic neural folds had elevated and met in the dorsal midline but had only incompletely fused, i.e., cranioschisis occulta. Microscopic study of these latter embryos revealed that in the affected region(s), complete closure of the surface ectoderm component of the neural folds had taken place, but only partial closure of the mesoderm, neural crest and neuroectoderm components. The different types of cephalic axial dysraphic disorders presenting in arsenic-treated fetuses delivered at later gestational stages (predominantly exencephaly and encephaloceles) could all be traced back and related to one or the other of these early forms of disturbed neurulation.

Neural tube defects: a review of human and animal studies on the etiology of neural tube defects

Although neural tube defects are a common congenital anomaly, their etiology is not known. Human studies have emphasized the pathology and epidemiology of the defects and suggest that in the majority of cases the etiology is multifactorial. Factors which appear possibly to be important are genetic predisposition, maternal illness, and fetal drug exposure. Animal studies have utilized naturally occurring neural tube defects and teratologically induced lesions. No animal model has been convincingly established as the equivalent of human neural tube defects. However, animal models have allowed investigation of the mechanisms of suggested human teratogens and determination of the pathogenesis of naturally occurring animal defects. Their most important contribution has been in furthering the understanding of the normal mechanisms of neural tube closure. It may be through this understanding that the etiology of human neural tube defects will be determined.

Developmental toxicity of the cyanogenic glycoside linamarin in the golden hamster

Cassava, a staple food in many tropical countries, has been suspected as a cause of human congenital defects. Ingestion of the material during pregnancy has been reported to induce limb defects, microcephaly, open eye, and growth retardation in rats. Linamarin is a natural cyanogenic glycoside that occurs in high concentrations in cassava. In the present study, pregnant hamsters received an oral dose of 70,100, 120 or 140 mg/kg linamarin or an equivalent volume of isotonic saline during the early primitive streak stage of gestation. A dose of 120 or 140 mg/kg of the glycoside was associated with an increased incidence of vertebral and rib anomalies as well as the production of encephaloceles in the offspring. These larger doses of linamarin also resulted in obvious maternal toxicity. Linamarin treatment had no effect on fetal body weight, ossification of fetal skeletons, embryonic mortality, or litter size. Although ingestion of the cyanogenic glycoside was associated with a significant teratogenic response, the effects occurred only at doses that elicited signs of maternal intoxication.

The induction of microphthalmia, encephalocele, and other head defects following hyperthermia during the gastrulation process in the rat

The aim of this study was to ascertain whether there is a period during early embryonic development of the rat that is particularly sensitive to hyperthermia. Pregnant Sprague-Dawley rats were partially immersed in a water bath at 43.5 degrees C until their core temperatures, monitored by a rectal thermistor probe, were elevated to 43.5 degrees C. The procedure was repeated 6 hours later. The regimen of two heatings was performed over a range of development from early gastrulation (8 days 18 hours) to about the 12 somite stage (10 days 18 hours). The rats were killed on days 17-19 and the fetuses were examined. Each group contained a minimum of five litters. The main teratogenic effect of the hyperthermia was the induction of one or more head defects, notably microphthalmia, encephalocele (either a single, large, parietal encephalocele or multiple small protuberances), and maxillary hypoplasia. Microphthalmia was the most common defect with approximately 90% of surviving fetuses having small eyes when heating occurred between 9 days 6 hours and 10 days 0 hours (9.06 and 10.00). Encephaloceles were induced by heating between 9.00 and 10.00 with a peak sensitivity between 9.12 and 9.18 when 57% of surviving fetuses were affected. Maxillary hypoplasia resulted from heating between 9.06 and 10.06 with up to 20% of surviving fetuses being affected. Control rats were exposed to the same experimental procedure in a water bath at 38 degrees C on 9.12 and 9.18, the gestational time most sensitive to hyperthermia induced malformations. There were no abnormal fetuses in the controls. The critical period identified spans 9 days 6 hours to 10 days 0 hours gestational age. In developmental terms this includes a large proportion of the gastrulation process.

Malformations of the axial skeleton in cranioschisis aperta and exencephaly in rat fetuses induced after neural tube closure

Single doses of cyclophosphamide were administered (IP) to groups of Wistar rats, on different days of gestation after neural tube closure (days 12-15) and fetuses were collected on day 20. A very large number of the fetuses treated during days 12-14 exhibited cranioschisis and exencephaly. Ethanol fixed, alizarin red stained specimens were observed for axial skeletal abnormalities. The exencephalic ones lacked ossified skulls. The basicranial bones were either under ossified or had undergone extensive fusion resulting in reduction in cranial volume. The basicraniovertebral angle was obtuse. The vertebral bodies and arches showed varying degrees of hypoplasia, fusion and/or agenesis. The development of ribs and sternebrae was also extensively affected. Treatment on day 15 did not induce exencephaly but the axial skeleton was hypoplastic. Wavy ribs were a remarkable feature of these fetuses. All exencephalic fetuses had subcutaneous haemorrhages; many of them were obviously oedematous. These data indicate that the susceptible period for induction of these anomalies does not stop at neuropore closure.

Experimental induction of cranioschisis aperta and exencephaly after neural tube closure. A rat model

Administration of single doses of cyclophosphamide to pregnant rats on days 12-14 of gestation (i.e. well after closure of the neural tube) resulted in cranioschisis and exencephaly in 100% of fetuses observed at term. In these fetuses the brain was covered by atrophic epidermis devoid of skin appendages and a highly vascular loose mesoderm without the osseous skull vault and the meninges. There were obvious hemorrhages in the brain tissue and in the ventricles. The thin walls of the distended ventricles showed breaks through which the ventricles communicated with the exterior and with the cavities in the brain. The choroid plexus had hypertrophied and denuded neuroepithelium could be found in the ventricles. Associated anomalies included edema, hemorrhage, exophthalmia, micrognathia, defects of the skull base, an increase in the basiocranio vertebral angle, reduction deformities of the limbs, etc. Chronological observations indicated a progressive distension of the ventricular system of the brain. A very high incidence of cranioschisis and exencephaly and the consistency of associated pathology validate the point that this is an excellent experimental model for investigating the pathogenetic mechanisms of these serious malformations.

Structure-activity relationships of retinoids in developmental toxicology. I. Studies on the nature of the polar terminus of the vitamin A molecule

The teratogenic activities of all-trans-retinoyl fluoride, all-trans-3-retinylidene-2,4-pentanedione, all-trans-2-retinylidene-1,3-cyclopentanedione, all-trans-2-retinylidene-5,5-dimethyl-1,3-cyclohexanedione, all-trans-2-retinylidene-5-p-methoxyphenyl-1,3-cyclohexanedione, all-trans-2-retinylidene-1,3-cyclooctanedione, all-trans-5-[2,6-dimethyl-8-(2,6,6-trimethylcyclohexen-1-yl)-1,3, 5,7-octatetrae n-1-yl]tetrazole, ethyl all-trans-9-(exo-2-bicyclo[2.2.1.]heptyl)-3,7-dimethyl-2,4,6,8- nonatetraenoate, ethyl all-trans-4-[2-methyl-4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1,3- butadien-1-yl]benzoate, 13-cis-N-(4-hydroxyphenyl)retinamide, and 13-cis-N-(2-hydroxyethyl)retinamide were determined in the hamster and compared with that of all-trans-retinoic acid. Administration of a single oral dose of the retinoids failed to induce signs of the hypervitaminosis A intoxication syndrome in any of the dams, and the maternal weight gain was not significantly different from the vehicle control value, except following intubation of the retinamides where maternal weight gain was significantly depressed. All of the retinylidene 1,3-diketones studied here were devoid of significant teratogenic activity. The retinamides failed to induce either an elevated mean litter frequency of malformed fetuses or a syndrome of anomalies similar to that induced by administration of an equimolar dose of all-trans-retinoic acid. All of the other retinoids induced a syndrome of malformations similar to that induced by administration of all-trans-retinoic acid and were associated with a significant increase in the number of litters containing one or more malformed fetuses and an elevated mean litter frequency of malformed fetuses. The teratogenic activity in the hamster of this series of retinoids was independent of structural modifications in either the beta-cyclogeranylidene ring or the polyene chain of the molecule. The results of the present study suggest that the changes in teratogenic activity associated with structural modification of vitamin A at C15 were primarily dependent upon the presence of or biotransformation to a free carboxyl or a moiety with an equivalent pKa at C15, not upon the molecular size of the substituent or the stereochemical position about C13. Since major structural modifications of vitamin A were made without the substantial loss of teratogenic activity, the structural requirements of retinoids for induction of terata were not extraordinarily exacting.

Prenatal and developmental toxicology of arsenicals

A variety of species, including the human, have been shown to be susceptible to the embryotoxic effects of inorganic arsenic. Malformations of the axial skeleton, neurocranium, viscerocranium, eyes, and genitourinary systems as well as prenatal death followed a bolus dose of trivalent or pentavalent inorganic arsenic. Trivalent arsenic was more teratogenic than pentavalent arsenic; in contrast, the methylated metabolites of arsenic possessed only limited teratogenic activity. Administration of inorganic arsenic to mammals results in concentration of arsenic within the placenta and small amounts are deposited within the embryo. Studies concerning the pathogenesis of arsenic-induced axial skeletal lesions revealed early failure of neural fold elevation and a subsequent, persistent failure of closure of the neural tube. Physical factors, drugs and heavy metals may modify the response to a teratogenic dose of inorganic arsenic. Medical problems associated with industrial or agricultural arsenicalism are most often typified by chronic exposure; future studies should emphasize those routes of administration and types of exposure that are characteristic of arsenic intoxication.

Craniofacial and central nervous system malformations induced by triamcinolone acetonide in nonhuman primates: II. Craniofacial pathogenesis

This study further defines the craniofacial malformations induced by triamcinolone acetonide in the rhesus monkey. Ten timed-mated pregnant rhesus monkeys (Macaca mulatta) received intramuscular injections of 10 mg/kg TAC on days 23, 25, 27, 29, and 31 of gestation. Results of previous experiments with rhesus and bonnet monkeys and baboons indicated that specific craniofacial and brain malformations could be induced with TAC during this period of pregnancy (Hendrickx et al., '80). Stage-matched TAC-treated and control embryos (stages 17-18 and 22) and age-matched TAC-treated and control fetuses (50, 60, and 70 days gestation) were removed by hysterotomy. Stage 17-18 TAC embryos appeared grossly normal but histologic evaluation revealed a shortened anlage of the posterior cranial base. Stage 22 TAC embryos and all TAC fetuses exhibited craniofacial dysmorphia and encephalocele. The developing sphenoid was the earliest affected and most severely malformed bone. Its defects included reduced anterioposterior and transverse dimensions, reduced orbitosphenoid and alisphenoid, abnormal pituitary fossa, and reduced dorsum and tuberculum sellae. In addition, shortening of the posterior cranial base and decreased cranial base angle was a consistent finding in the treated embryos and fetuses. Decreased ossification and remodeling in the facial bones and abnormal position due to the malformed sphenoid occurred.

Axial skeletal malformations associated with cranioschisis aperta and exencephaly. The result of experimental intervention after the neural tube closure in rats

Maternal administration of a single dose of cyclophosphamide (20 mg/kg) after the neural tube closure (on day 12) resulted in exencephaly and cranioschisis in 100% of rat fetuses at term. Extensive hemorrhages and edema were regularly associated with these defects. Alizarin-red stained skeletal preparations revealed absence of skull vault, premature closure of basicranial synchondroses, exaggeration of the craniovertebral angle, and agencies and hypoplasia of the vertebrae, ribs and sternum. It is suggested that failure of the neural tube to close is not the primary cause of axial skeletal malformations and even after closure, the axial skeletal anlagen remains susceptible to teratogenic insult.

Cephaloceles: clinical and neuroradiological appearance. Associated cerebral malformations

Cephaloceles are congenital malformations with herniation of intracranial structures through a defect in the cranium. On the basis of a review of the literature and 31 personal observations the authors discuss the clinical and neuroradiological presentation of their various anatomical locations: sphenoidal, ethmoidal, frontal, occipital and parietal.

Morphogenesis of experimentally induced Arnold--Chiari malformation

The administration of a single dose of vitamin A to pregnant hamsters, early during the morning of their 8th day of gestation, induces types I and II Arnold--Chiari malformation (ACM), as well as various types of axial skeletal-dysraphic disorders known to be associated with the human disease. This new model provides a means of carrying comparative studies between the axial skeletal defects and neurological anomalies of this complex developmental malformation with those which characterize the other induced disorders related to it. Study of this experimental model has demonstrated that the basichondrocranium of fetuses with ACM is shorter than normal and slightly elevated (lordotic) in relation to the axis of the vertebral column. The shortness of the basichondrocranium of these fetuses is caused by the underdevelopment of the occipital bone specially noticeable in its basal component (basioccipital). This basic defect has resulted in a short and small posterior cerebral fossa which is inadequate to contain the developing nervous structures of that region. The developing cerebellum is displaced downward to an anomalous position just above the foramen magnum; and, the developing medulla is compressed or crowded into the small posterior cerebral fossa of affected fetuses. The lordotic elevation of the basichondrocranium is also responsible for the reduction of the pontine flexure and the increased angle of the cervical flexure of the hindbrain found in these fetuses. All of these neurological anomalies, which are characteristic and diagnostic of clinical ACm as well, are considered here to be secondary to the axial skeletal defects rather than primary abnormalities, as is generally believed. The peculiar type of protrusion of the odontoid process into the cranial cavity found in fetuses with ACM, as well as in those with cranioschisis aperta and occulta, is also considered to be caused by the slight depression of the underdeveloped basioccipital and therefore, comparable to the so-called basilar impression often described in clinical ACM. This study has emphasized various developmental features which are closely related with the morphogenesis of ACM, including: the somitic origin of the occipital bone, and the late growth of the cerebellum which is predominantly postnatal in almost all experimental animals. It has been pointed out that some developmental defects involving the occipital bone and the caudal vertebral column, such as those which characterize ACM type II, may be more closely related than previously recognized. It has been also pointed out that the so-called cerebellar herniation into the cervical spinal canal described in the human disease represents a late addition to this disorder which is related to the relatively late growth of the cerebellum...