Possible evidence for secondary degeneration of central nervous system in the pathogenesis of anencephaly and brain dysraphia. A study in young human fetuses

Prenatal diagnosis of acrania/exencephaly/anencephaly sequence (AEAS): additional structural and genetic anomalies

OBJECTIVES

To analyse additional structural and genetic anomalies in fetuses with acrania/exencephaly/anencephaly sequence (AEAS).

METHODS

A retrospective analysis of 139 fetuses with AEAS diagnosed between 2006 and 2020 in a single tertiary referral ultrasound department.

RESULTS

The median gestational age at diagnosis decreased from 15 weeks in 2006 to 13 weeks in 2020 (- 0.21 per each year; p = 0.009). In 103 fetuses, the defects were limited to the neural tube (NTD) (74.1%), in 36 fetuses (25.9%), there were additional structural non-NTD anomalies. The most common were ventral body wall defects present in 17.8% (23/139), followed by anomalies of the limbs (7.2%; 10/139), face (6.5%; 9/139) and heart (6.5%; 9/139). Genetic anomalies were diagnosed in 7 of the 74 conclusive results (9.5%; 7/74; trisomy 18, n = 5; triploidy, n = 1; duplication of Xq, n = 1). In univariate logistic regression models, male sex, limb anomalies and ventral body wall defects significantly increased the risk of genetic anomalies (OR 12.3; p = 0.024; OR 16.5; p = 0.002 and OR 10.4; p = 0.009, respectively).

CONCLUSIONS

A significant number of fetuses with AEAS have additional structural non-NTD anomalies, which are mostly consistent with limb body wall complex. Genetic abnormalities are diagnosed in almost 10% of affected fetuses and trisomy 18 is the most common aberration. Factors that significantly increased the odds of genetic anomalies in fetuses with AEAS comprise male sex, limb anomalies and ventral body wall defects.

Neural tube defects: Different types and brief review of neurulation process and its clinical implication

Neural Tube Defects are the most typical congenital malformations, with almost 300,000 cases annually worldwide. The incidence varies amongst geographical ranges from 0.2 to up to 11 per 1000 live births. In India, incidence is reportedly higher in north than south and can be attributable to diet and genetic variances. Etiology is multifactorial. Severe forms of whitethorn are allied with syndromes. Primary neurulation and secondary neurulation are the most crucial steps in the formation and closure of the neural tube; any interruption can lead to mild to severe NTDs depending on the level of insult during embryogenesis. Various molecular and cellular events take place simultaneously for neural tube bending and closure of the neural tube. Neurological deficit in the newborn is contingent on the level of defect and severity of the structures affected. Survival of the newborn also depends on the severity of the lesion. Folic acid supplementation in all prospective mothers, preferably 4 weeks before conception and at least 12 weeks after conception, can prevent NTDs in folic responsive groups. But there is a significant number of other causes leading to neural tube defects apart from folic acid. Hydrocephalus is the commonest abnormality allied with NTDs in syndromic cases.

An Unusual First-Trimester Ultrasound Presentation of the Acrania-Anencephaly Sequence: The "Turkish Turban" Sign

A previously unrecognized first-trimester presentation of the acrania-anencephaly sequence is described. Ultrasound features included a constriction ring around the external base of the developing skull and an enlarged globular head, resembling a Turkish turban, with large cystic spaces replacing the brain. This constellation of findings was noted in 3 first-trimester fetuses. In 2 of them, it was possible to identify the amniotic membrane attached to the constriction ring. One case presented with anencephaly and fetal demise at 16 weeks. The other 2 women terminated the pregnancies and aborted anencephalic fetuses. This subtype of the acrania-anencephaly sequence could represent an earlier segmental rupture of the amnion, which subsequently entraps the developing fetal skull.

Vascular mechanism of axonal degeneration in peripheral nerves in hemiplegic sides after cerebral hemorrhage: An experimental study

Background

Though retrograde neuronal death and vascular insufficiency have been well established in plegics following intracerebral hemorrhage, the effects of plegia on arterial nervorums of peripheral nerves have not been reported. In this study, the histopathological effects of the intracerebral hemorrhage on the dorsal root ganglions and sciatic nerves via affecting the arterial nervorums were investigated.

Methods

This study was conducted on 13 male hybrid rabbits. Three animals were taken as control group and did not undergo surgery. The remaining 10 subjects were anesthetized and were injected with 0.50 ml of autologous blood into their right sensory-motor region. All rabbits were followed-up for two months and then sacrificed. Endothelial cell numbers and volume values were estimated a three dimensionally created standardized arterial nervorums model of lumbar 3. Neuron numbers of dorsal root ganglions, and axon numbers in the lumbar 3 nerve root and volume values of arterial nervorums were examined histopathologically. The results were analyzed by using a Mann-Whitney-U test.

Results

Left hemiplegia developed in 8 animals. On the hemiplegic side, degenerative vascular changes and volume reduction in the arterial nervorums of the sciatic nerves, neuronal injury in the dorsal root ganglions, and axonal injury in the lumbar 3 were detected. Statistical analyses showed a significant correlation between the normal or nonplegic sides and plegic sides in terms of the neurodegeneration in the dorsal root ganglions (p < 0.005), axonal degeneration in the lumbar 3 nerve roots (p < 0.005), endothelial cell degeneration in the arterial nervorums (p < 0.001), and volume reduction in the arterial nervorums (p < 0.001).

Conclusion

Intracerebral hemorrhage resulted in neurodegeneration in the dorsal root ganglion and axonolysis in the sciatic nerves, endothelial injury, and volume reduction of the arterial nervorums in the sciatic nerves. The interruption of the neural network connection in the walls of the arterial nervorums in the sciatic nerves may be responsible for circulation disorders of the arterial nervorums, and arterial nervorums degeneration could result in sciatic nerves injury.

Ganglionary mechanisms of spasticity and ileus in cerebral hemorrhage: an experimental study

OBJECTIVE

The effects of retrograde neuronal death is well determined in dorsal root ganglia (DRG) after peripheral nerve injury, but the effects of intracerebral hemorrhage on the DRG has not been well known. In this study, it was investigated if hemorrhagic lesions of sensory-motor cortex cause neurodegeneration on DRG.

MATERIALS AND METHODS

This study was conducted on 23 male hybrid rabbits. Three of 23 animals were examined as control. Left parietal burr-hole surgery was applied to remaining 20 animals and autolog blood of 0.25ml injected into left sensory-motor region under general anesthesia. All rabbits were followed-up for two months and sacrificed. L(5) DRG's were observed histopathologically. The results were analyzed with Mann-Whitney U-test.

RESULTS

Right spastic hemiplegia developed only in 16 operated animals and 10 of them were developed ileus. The number of degenerated neurons in DRG was higher in the plegic side than in the non-plegic side (p<0.001). But, the difference between the non-plegic side of the study group and control group did not meaningful (p>0.05).

CONCLUSION

Intracerebral hemorrhages affecting the sensory-motor cortex may result in neurodegeneration in DRG. Sensitive reflex arches of striated muscles and bowels may be disturbed due to DRG degeneration and results in spasticity and/or ileus.

Subclassification of anencephalic human fetuses according to morphology of the posterior cranial fossa

Anencephaly is a designation for congenital absence of the cranial vault with cerebral hemispheres completely missing or decreased to small masses attached to the base of the skull. The etiology is unknown. Whether the bony tissue or soft brain tissue is a primary factor is also unknown. The present study has focused on the posterior cranial fossa in anencephaly. The goal is to determine whether differences in the posterior cranial fossa could provide a basis for subclassification of anencephalic fetal skeletons. Twenty-three human anencephalic fetuses, at gestational ages 13 to 22 weeks, were studied. Radiologic and cephalometric analyses, including measurements of bone sizes and different angles, were performed. Permission for autopsy of the central nervous system was not available. For comparison of anencephalic findings with normal conditions, standards from a recent publication were used. Foot length served as a parameter for age comparison. The study showed 2 morphologic types of the posterior cranial fossa. One type had a fossa cranial morphology close to normal morphology, whereas the other had a malformed and much smaller posterior cranial fossa. The latter condition was presumed to be due to a primary error in chondral and cranial development. The current skeletal subgrouping might be essential for clinicians' or pathologists' future assessment of the autopsy results. The skeletal subgrouping should, if possible, be associated with karyotyping and analysis of the central nervous system. The goal is to distinguish between congenital conditions resulting in anencephaly and acquired conditions resulting in anencephaly.

Prenatal sonographic diagnosis of acrania associated with amniotic bands

We describe the prenatal sonographic findings in 2 cases of amniotic band sequence-related acrania. In the first case, sonography demonstrated acrania, asymmetric facial clefts, and digital fusion on the hands and feet. In the second case, sonography demonstrated acrania and amniotic bands adhering to the brain, face, and body. This report highlights the importance of a careful search for amniotic bands and a detailed survey of the fetus' face, digits, and body in the sonographic evaluation of fetal acrania.

First-trimester echogenic amniotic fluid in the acrania-anencephaly sequence

OBJECTIVE

To describe the association between echogenic amniotic fluid and first-trimester fetal acrania.

METHODS

Nine fetuses with acrania were examined between 11 weeks' and 13 weeks 6 days' menstrual age for the presence of echogenic free-floating particles in the amniotic fluid. Cases were classified into 3 types according to the echogenicity of the amniotic fluid: similar to (type 0), slightly greater than (type 1), and clearly more echogenic than (type 2) that of the extracelomic fluid.

RESULTS

In 1 pregnancy, no free-floating particles were identified (type 0). In 6 cases, small free-floating particles scattered within the amniotic cavity were identified, making the amniotic fluid slightly more echogenic than the extracelomic fluid (type 1). In the remaining 2 cases, the amniotic fluid was homogeneously and clearly more echogenic than the extracelomic fluid (type 2).

CONCLUSIONS

A high percentage (89%) of fetuses with acrania had echogenic amniotic fluid, suggesting that this finding could potentially be used as a marker of fetal acrania in the first trimester. This finding also supports the hypothesis of the transition from acrania to anencephaly, with the unprotected brain undergoing progressive destruction from the first trimester, leading to the classic finding of anencephaly in the second trimester.

Reviewing old concepts at the start of a new millenium: growth restriction, adrenal hypoplasia, and thymomegaly in human anencephaly

BACKGROUND

Anencephaly has been associated frequently with intrauterine growth retardation (IUGR), consistently with adrenal hypoplasia, and occasionally with an enlarged thymus. Few studies have analyzed the relationship between gestational age (GA), IUGR, associated anomalies and thymomegaly in anencephaly. The aims of our study were to evaluate this relationship and to highlight the usefulness of anencephaly as a model when investigating immune-endocrine interactions.

METHODS

Fifty-two anencephalics' autopsies were reviewed retrospectively. Body weight, adrenal, and thymus weights were compared to prenatal, postnatal, and stillborn control values, and between associated and isolated anencephalic cases (presenting with and without other unrelated anomalies). Comparisons of adrenal and thymus weights were done by GA and by body weight. Thymus weight:body weight (TW:BW) ratios were compared to expected values.

RESULTS

Anencephalics' body and adrenal weights were lower than their control values, whereas thymus weights did not differ. Body and thymus weights were twice as high in isolated than in associated anencephaly, whereas adrenal weights did not differ. Anencephalics TW:BW ratios were higher than their control values, higher in cases with IUGR, and higher in isolated rather than associated cases. When distributed by GA, thymus weights in anencephaly increased at a higher-than-expected rate.

CONCLUSIONS

Our results suggest that adrenal hypoplasia is invariably present in anencephaly, and depending on an underdeveloped pituitary gland, seems to be independent of its etiology. On the contrary, IUGR mainly exists in associated cases and thymus enlargement mainly exists in isolated cases, suggesting a relationship with the underlying cause.

Sonographic markers of exencephaly at 9 + 3 weeks of gestation

Following the introduction of transvaginal sonography, several first trimester diagnoses of the exencephaly anencephaly sequence have been reported, with the earliest being described at 10 weeks of gestation. We report a case with a high index of suspicion for exencephaly at 9 weeks and 3 days because of three sonographic features: the cranial pole of the embryo was smaller than the chest, the cranial pole bulged dorsally and the surface of the cranium was irregular. The diagnosis was confirmed by a repeat ultrasound examination at 11 + 4 weeks and by autopsy after termination of pregnancy.

First-trimester sonographic diagnosis of Cantrell's pentalogy with exencephaly

We report a case of Cantrell's pentalogy with exencephaly detected by sonography at 11 weeks 4 days' menstrual age and confirmed at autopsy. Cantrell's pentalogy consists of defects of the lower sternum, anterior diaphragm, midline supraumbilical abdominal wall, and diaphragmatic pericardium with ectopia cordis. Exencephaly involves acrania with a disorganized mass of brain tissue. Both conditions are rare; the combination of the 2 has been reported only twice before. To our knowledge, this is the earliest reported diagnosis of the 2 conditions by prenatal sonography.

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.

Prenatal Diagnosis of Exenceplhaly

Exencephaly is a rare congenital anomaly, thought to be a precursor of anencephaly. Like anencephaly, this abnormality is characterized by absence of the cranial vault above the orbits. However, unlike anencephaly, discrete, sometimes disorganized, brain tissue can be identified above the cranial defect. In this article, the authors report a case of exencephaly diagnosed prenatally during transvaginal ultrasound examination, with anatomic and pathologic correlation.

Crown-chin length in normal and anencephalic fetuses at 10 to 14 weeks' gestation

OBJECTIVE

Our goal was to establish a reference range for the fetal crown-chin length at 10 to 14 weeks' gestation and to determine its usefulness in the prenatal detection of anencephaly in the first trimester.

STUDY DESIGN

Women attending our center for transabdominal ultrasonographic screening at 10 to 14 weeks' gestation were prospectively recruited for this study. The crown-chin length was measured in a sagittal view of the fetal head, which included the fetal profile, from the highest point of the head to the most anterior aspect of the jaw. Nomograms for the crown-chin length and the ratio of the crown-chin length to the crown-rump length according to gestational age were generated. Additionally, the crown-chin length and the ratio of the crown-chin length to crown-rump length were obtained from a subset of 13 anencephalic fetuses and plotted against the reference range.

RESULTS

In normal fetuses the crown-chin length increased (Crown-chin length = 65.2 x Gestational age in days - 28.4; r = 0.74%, p <0.0001) and the ratio of the crown-chin length to the crown-rump length decreased (Ratio of crown-chin length to crown-rump length -17.2 x Gestational age in days + 60.5; r = 0.23, p <0.0001) with advancing gestation. In anencephalic fetuses crown-chin length measurements and the ratio of the crown-chin length to the crown-rump length were below the 5th percentile in 77% and 62% of the cases, respectively. The slope of change in the ratio of the crown-chin length to the crown-rump length with gestational age was significantly different in anencephalic fetuses compared with normal fetuses (t = 2.7, p <0.003).

CONCLUSION

Measurement of the crown-chin length at 10 to 14 weeks' gestation provides a technique that can assist in the early recognition of anencephaly.

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

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

Exencephaly in autosomal dominant brachydactyly syndrome

Exencephaly was diagnosed at 17 weeks in a 27-year-old primigravida with abnormalities of the hands and a family history suggestive of autosomal dominant brachydactyly and clinodactyly. In this family there was also a history of 'anencephaly'. To our knowledge, this is the first report on the association of exencephaly and autosomal dominant brachydactyly. As the relationship between hand and cranial anomalies is well established, we suggest that this association in our case could be due to a defect in the same gene.

Prenatal diagnosis of exencephaly

This paper presents a sonographic diagnosis of exencephaly made during the last trimester of gestation. The sonogram showed the absence of bones in the cranial vault together with the presence of a disorganized cerebral mass, with loss of its normal anatomy. Post-partum examination of the newborn confirmed the findings of the sonogram. We briefly review the characteristics of exencephaly, its aetiology, and its relationship to anencephaly.

Progression of exencephaly to anencephaly in the human fetus--an ultrasound perspective

Exencephaly as a precursor of anencephaly is well delineated in animal studies. In humans, a similar though unproven embryologic sequence is postulated. In the case reported, serial ultrasound studies allowed us to identify a 16-week human exencephalic fetus and observe the cephalic changes during its progression to a classic anencephalic appearance.

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)

Immunoreactive keratin with foreign body reaction in anencephaly

Keratinous material, in the form of epithelial squames often with foreign body reaction and dense gliosis, was demonstrated in all of ten cases of anencephaly by a sensitive and specific immunohistochemical stain. In some cases keratin was not recognized on routine histological stains.

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.

A syndrome of arterial-occlusive retinopathy and encephalopathy

An analysis of two new cases and four previously reported cases produced evidence for a syndrome of arterial-occlusive retinopathy and encephalopathy. All six patients were women; they ranged in age from 21 to 40 years. The clinical features of this condition include multiple branch retinal arterial occlusions and encephalopathy in which behavioral and memory disturbances predominate early. Hearing loss is frequent. Except for cerebrospinal fluid pleocytosis and an increased cerebrospinal fluid protein level, there are few laboratory or radiographic abnormalities. The disease may be responsive to corticosteroid therapy. There are some similarities between this syndrome and systemic lupus erythematosus but it appears to be a distinct disease entity. A comparison of the retinal findings with those described in experimental allergic encephalitis suggests that this may be a virally induced immune-mediated disease. Although only four clearly documented examples of this syndrome have been reported, we suspect that cases may have been overlooked because of failure to recognize arterial branch occlusions in the peripheral retina.

Studies on the area cerebrovasculosa of anencephalic fetuses

The area cerebrovasculosa has been examined in 35 anencephalic fetuses and coronal sections prepared in 15 cases. A bilaterally symmetrical cystic mass is found covering the anterior and middle cranial fossae. The mass is generally walled with glial tissue, partially lined with ependyma and filled with abnormally vascular choroid plexus. The coverings of the cyst are conspicuously vascular and the overlying squamous epithelium is in continuity with hairy skin at the margins of the lesion. The posterior cranial fossa contains a variable quantity of medulla oblongata which has no connection with the cystic mass. The medulla and cervical cord are more nearly normal in that minority of cases with an intact foramen magnum. The degree of hindbrain development is correlated with previously reported presence of heterotopic glial tissue in the spinal subarachnoid space of some anencephalic fetuses (Bell, Gordon and Maloney, 1981; Bell, 1981, in press). These findings have led us to reject the widely accepted view that the area cerebrovasculosa is totally disorganised, and that anencealy is characterised by absence of the forebrain.

Temporal bone studies in anencephaly

The principal anatomical and histological features of the temporal bones of three anencephalics are described, one a twin-headed monster, with four temporal bones. These may be summarized as follows: Malformation of ossicles. Mondini type malformation of the cochlea. Occasionally cochlear hydrops or collapse of Reissner's membrane, following apparently on its rupture. Distension of the vestibular labyrinth and oedema of the perilymphatic spaces and membranes. Rupture of the saccular wall with 'sealing off' and repair of the tears and gaps by coagulated lymph material. Fibrous obliteration of the internal auditory meatus containing scanty nerves and neurones. Geniculate ganglion and facial nerve present and appear to be normally developed. The neuro-epithelial structures were well developed despite the total or partial absence of the central nervous system. The temporal bones of anencephalics offer an excellent source of comparative anatomy for the study of the pathology of Menière's disease and sensorineural lesions.

The examination of embryonic and fetal material in diagnostic histopathology laboratories

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