Heterotopia associated with hippocampal sclerosis: an under-recognized cause of early onset epilepsy in children operated on for temporal lobe epilepsy.

PURPOSE: The aim of this study is to report on 52 children operated on for pharmacoresistant temporal lobe epilepsy, with special emphasis on histopathology and correlation with clinical features. METHODS: Charts were retrospectively analyzed. All children underwent comprehensive clinical, electrophysiological and radiological investigations before surgery. Surgical procedures were tailored according to scalp, foramen ovale and eventually depth electrode recordings. Histopathology was compared with clinical variables (χ (2) and Fisher's exact tests). Outcome was evaluated using the Engel scale. RESULTS: Developmental tumor was found in 14 cases, malformation of cortical development (MCD) in 26, isolated hippocampal sclerosis (HS) in 5 and gliosis in 7. Dual pathology (DP) affected 18 patients and the main extrahippocampal lesion consisted of microscopic sub-cortical heterotopias (HS-HT) for 15 patients who shared a particular clinical pattern: a history of febrile seizures (FS) and/or brain injury, early onset of epilepsy without latent period from FS to the first temporal seizure, and a particularly good outcome following surgery. CONCLUSION: In our pediatric temporal lobe surgery series, the prevalence for MCD and for DP was higher than in adult series. Age at seizure onset depends on pathology, and is earlier when involving the neocortex rather than only the hippocampus. We identify the association HS-HT (the most frequent DP in this series), with particular clinical features.

Transmission of the BSE agent to mice in the absence of detectable abnormal prion protein.

The agent responsible for transmissible spongiform encephalopathies (TSEs) is thought to be a malfolded, protease-resistant version (PrPres) of the normal cellular prion protein (PrP). The interspecies transmission of bovine spongiform encephalopathy (BSE) to mice was studied. Although all of the mice injected with homogenate from BSE-infected cattle brain exhibited neurological symptoms and neuronal death, more than 55 percent had no detectable PrPres. During serial passage, PrPres appeared after the agent became adapted to the new host. Thus, PrPres may be involved in species adaptation, but a further unidentified agent may actually transmit BSE.

Selective destruction of mossy fibers and granule cells with preservation of the GABAergic network in the inferior region of the rat hippocampus after colchicine treatment.

Lesions induced by colchicine injection into the rat hippocampus were investigated by means of electron microscopy and GABA immunocytochemistry. Granule cells were nearly completely destroyed 3 days after colchicine injection; since the necrosis of their axonal endings was delayed, an anterograde degeneration of the mossy fibers had probably taken place. The selectivity of the lesions was not limited to granule cells, for some pyramidal neurons in CA1 pyramidal layer were damaged. It was, however, striking to observe that throughout the hippocampal structure GABAergic neurons were spared from the effects of colchicine. For instance, GABAergic neurons were found in the vicinity of the completely destroyed granule cell layer. GABAergic neurons and terminals were also present in the CA3 region where the GABA-containing terminals formed a dense network of synapses with somata and dendrites of pyramidal cells. It was interesting to note that, consistent with previous studies, the GABAergic neurons in CA3 are innervated by mossy fibers. We conclude that after colchicine treatment the destruction of the granule cells was not associated with a lesion of the GABAergic network. This selective lesion provides a useful model with which to study the properties of CA3 neurons deprived of their major excitatory input but with an intact inhibitory network.

Gabaergic neurons of the hippocampus: development in homotopic grafts and in dissociated cell cultures.

The hippocampus taken from E18-E19 rat embryos was dissociated into a cell suspension and was either grafted into the hippocampus of adult rats or cultured. The growth of GABAergic neurons was examined using a GABA directed antiserum. The implanted tissue was capable of survival and growth without exhibiting a laminar organization. Most of the various morphological neuronal types could be observed, establishing different types of synapses; however, granule neurons were rarely encountered. A substantial proportion of GABA-positive neurons was detected within the graft with profuse labelling of the neuropil. In cultures issued from the same cell suspension, GABA-immunoreactive neurons were numerous and had different morphologies. Altogether these data suggest that GABA neurons express a high potential for growth and sprouting in vitro and in vivo.

Kainate-induced apoptotic cell death in hippocampal neurons.

We have examined the role apoptosis plays in epileptic brain damage using intra-amygdaloid injection of kainate. With the silver staining technique of Gallyas, argyrophylic (dying) neurons were observed, a few hours after the injection, in the amygdala and in the vulnerable pyramidal neurons of the hippocampal CA3 region. In both areas, cell death has apoptotic features, including: (i) nuclear chromatin condensation and marginalization with light and electron microscopy; (ii) DNA fragmentation with a typical ladder pattern on agarose gel electrophoresis; (iii) positive nuclear labelling with a selective in situ DNA fragmentation staining method. Combined in situ DNA labelling and silver staining showed that the DNA fragmentation occurred in dying neurons. CA1 or granule cells which do not degenerate following intra-amygdaloid injection of kainate were not stained with the in situ DNA labelling or the argyrophylic technique. Administration of diazepam blocked the kainate-induced seizures and prevented DNA fragmentation in CA3 but not in the amygdala. Therefore, apoptosis contributes to the local and distant damage induced by kainate.

GABAergic mechanisms in the CA3 hippocampal region during early postnatal life.

The developmental pattern of GABAergic neurons in the rat hippocampus during the first week of postnatal life shows several particularities both from a morphological and physiological point of view: (1) GABA immunoreactive neurons which are initially localized in a deep and superficial layer, progressively disappear from these two layers. From the end of the first postnatal week, GABAergic neuronal somata appear throughout the whole hippocampus, but GABA immunoreactive terminal structures are not frequent until the second postnatal week. (2) Intracellular observations in slices reveal the presence in CA3 pyramidal neurons between P0 and P6 (postnatal days) of spontaneous giant depolarizing potentials (GDPs); these are mediated by GABA acting on GABAA receptors and modulated presynaptically by NMDA receptors. During this period of development, GABA and GABAA analogues have a depolarizing action at resting membrane potential. Bicuculline at this developmental stage blocks completely spontaneous and evoked synaptic potentials. During the second postnatal week, when GABA responses shift from depolarizing to hyperpolarizing, bicuculline induces spontaneous interictal discharges. It is suggested that the positive feedback of the GABAergic interneuron on the pyramidal neuron during the first week of life may account for the generation of GDPS which may play an important role in synaptogenesis.

Effects of undernutrition on glial maturation.

Rats of Wistar strain were conceived and breast-fed until the 25th day by mothers maintained on a low protein (5%) and low caloric (21 calories/day) diet, producing a severe deficiency in weight body growth (more than 50% at the 10th day) and of the weight of the central nervous system (40% on the 15th day) both in the cerebral hemispheres and the spinal cord. Histological and biochemical analysis of the central nervous system shows: (1) Glial proliferation is insufficient and delayed, the number of glial cells is reduced by 50% on the 10th day in the cuneatus and gracilis tracts and the density of the glial cells is reduced by 50% in the corpus callosum at the 19th day. (2) Maturation of the glial cells is greatly retarded, especially in the corpus callosum a structure which matures late. On the 19th day, the majority of the cells in this structure still have a glioblastic appearence, whereas in the normal rat, at this age the majority of the glial cells are oligodendrocytes. (3) These abnormalities of glial maturation agree well with the delay of the increase of DNA, RNA and protein measured in the spinal cord and cerebral hemispheres. (4) There is a defect in myelination assessed by estimation of the density of the myelin fibres, and a definitive reduction in the caliber of the spinal tracts.

Developmental changes of synapses in the cerebellar cortex of the rat. A quantitative analysis.

Synaptogenesis in the molecular layer of the vermis cortex in Wistar rats between 1 and 25 days after birth was investigated. After staining with OSO4, the following parameters were measured: the density of synaptic profiles; the percentage of the neuropil area occupied by synapses; the mean diameter of the boutons; and the numerical density of synapses in a defined volume. The detailed topographical analysis enabled us to show the following: the first synapses appear diffusely in the molecular layer; after the 10th day a synaptic gradient is present between the depth and the surface area (this gradient can be found by the count of the synapses and by studying the spatial distribution of the synaptic area); this gradient is no longer seen at the 25th day, when the density of synapses is relatively uniform throughout the whole molecular layer.

Distribution of GABAergic neurons in late fetal and early postnatal rat hippocampus.

The ontogenesis of GABAergic neurons in the rat hippocampus was studied using an anti-GABA serum. GABA immunoreactivity appeared at the 18th day of gestation. At this stage, GABA-immunoreactive (GABA-IR) cells are grouped in two layers, one located deeply in the intermediate zone near the ventricular zone, and the other found superficially in the marginal zone near the hippocampal fissure. During the late embryonic and early postnatal life, GABA-IR neurons progressively disappeared from these two layers. The transient appearance of an abundant network of GABAergic neurons might be due to transient expression of GABA in some neurons or to cellular death. Later on, from the third postnatal day, the GABA-IR neurons appeared throughout the whole hippocampus according to a dorsoventral and lateromedial gradient. The setting of neuronal bodies preceded that of GABA-IR puncta (supposed to be mainly synaptic boutons) around the neuronal cell bodies and along the dendritic shafts. The puncta are only visible from the sixth day onwards and their number increased rapidly during the first 3 postnatal weeks. Our results indicate that GABA may have a role in neurotransmission in the hippocampus from a very early stage of development.

Development of mossy fiber synapses in hippocampal slice culture.

The mossy fiber synaptogenesis has been studied in hippocampal slice cultures. In vivo mossy fiber terminals contact the thorny excrescences of CA3 pyramidal neurons over a restricted portion, i.e. the proximal part of the apical dendrite. In organotypic cultures mossy fibers expand their terminal field and invade the infrapyramidal area of the CA3 region and the supragranular layer of the dentate gyrus. Newly formed mossy fiber synapses in CA3 region were examined, through electron microscopy, in cultures taken at various time intervals. The main events of the formation of newly formed mossy fiber synapses can be summarized as follows. During the first week following explantation mossy fiber axons contact the dendritic shaft of the pyramidal dendrite and establish both symmetrical and asymmetrical contacts. Subsequent modifications occur in the postsynaptic portion facing the mossy fiber bouton: (i) a massive accumulation of polyribosomes and coated vesicles in the subsynaptic cytoplasm; (ii) undulations of the plasma membrane; (iii) disappearance of neurotubules at postsynaptic sites and appearance of a fine network of filamentous material. Later on in culture, complex giant spines invaginate within the synaptic bouton. In conclusion this study shows that CA3 pyramidal neurons following deafferentation retain the capacity to form thorny excrescences, when contacted by mossy fibers. Moreover these results suggest a crucial role for mossy fibers to induce the formation of thorny excrescences in an heterotopic localization, i.e. over the basilar dendrites of CA3 pyramidal neurons.

Hippocampal plasticity in childhood epilepsy.

Quantitative autoradiography was used to study changes in high affinity (Kd = 12 nM) binding sites for kainic acid, a marker of mossy fibers, in the hippocampus of childhood epileptics. We found a highly significant increase in the density of kainate binding sites in the CA3 region and in the fascia dentata in childhood epileptics as compared to age matched controls. We suggest that anatomical plasticity occurs in the hippocampus of human epileptics as in experimental models of epilepsy. The increase in kainate binding sites may contribute to the development of epileptic seizures.

An unusual presentation of focal cortical dysplasia.

In a case of histologically proved focal cortical dysplasia, there was an absence of cortex-white matter delineation in the right parietooccipital area only on the T2-weighted images. This pattern correlated with the gross and histologic findings obtained on the resected cerebral tissue.

The cerebro-hepato-renal (Zellweger) syndrome: lamellar lipid profiles in adrenocortical, hepatic mesenchymal, astrocyte cells and increased levels of very long chain fatty acids and phytanic acid in the plasma.

Clinical, radiological, histological and biochemical aspects of two cases of cerebro-hepato-renal syndrome (CHRS) are reported. CT scan disclosed a demyelinating process and gyral abnormalities reflecting the observed neuropathological findings. Trilamellar and lamellar inclusions were found in brain astrocytes, hepatic mesenchymal and adrenal cells. The morphologic features of these inclusions are similar to those observed in childhood adrenoleukodystrophy, neonatal adrenoleukodystrophy and infantile Refsum's disease. In the two CHRS patients, increased plasma levels of very long chain fatty acids (C26:1, C26:0) and phytanic acid were in the same range as those observed in seven other instances of neonatal adrenoleukodystrophy. The presence of increased plasma levels of phytanic acid in these disorders suggests that phytanate oxidase activity is, at least, partially located in peroxisomes.

Microgyric and necrotic cortical lesions in twin fetuses: original cerebral damage consecutive to twinning?

Extensive cortical necrosis associated with malformative microgyric-like lesions and with necrotic lesions of the white matter was observed in two male 25 week fetuses. These cases differed from previously reported cases of brain damage in monozygotic twins: both fetuses were affected and the lesions occurred early in pregnancy, before the end of neuronal migration, thus resulting in a cortical malformation associated with destructive lesions.

Bilateral porencephalic defect in a newborn after injection of benzol during pregnancy.

Porencephaly is usually considered to be a prenatal brain lesion due to a circulatory failure. We report a case of bilateral porencephaly with heterotopia and absence of the septum pellucidum in a newborn. The mother had received several injections of benzol during pregnancy with an intent of inducing abortion. The possibility of a causal relationship between the administration of benzol and the occurrence of the defect is supported by the existence of previously reported cases of cerebral malformations following maternal exposure to organic solvents.

Cardiac rhabdomyoma and tuberous sclerosis in three fetuses: a neuropathological study.

In spite of the development of modern imaging, most lesions of tuberous sclerosis (TS) remain difficult to detect before birth. Particularly, brain involvement at a fetal stage of development is poorly documented. We report three cases of fetuses examined after pregnancy was interrupted because of the detection of cardiac rhabdomyoma. In two of the three cases there were brain lesions suggestive of TS, including cortical tubers, subependymal nodules and scattered bizarre giant cells in the white matter. These observations confirm that brain lesions of TS can be present before birth; they can show, at an early period of development, an aspect quite similar to lesions described at an adult stage. The most characteristic cell abnormality is the so-called balloon cell. The majority of these cells exhibit a strong immunoreactivity with glial antibodies (GFAP, vimentin, S100). Immunoreactivity with neuronal markers (synaptophysin) is present in a small percentage of balloon cells.

Antenatal thalamic lesions in the newborn: two anatomoclinical cases.

We report two cases of antenatal bilateral thalamic lesions constituted by neuronal loss, gliosis and mineralized glial or neuronal cells. No etiology could be found. Neuroradiological findings were poorly correlated with histological changes. These cases are compared with the few previously reported cases of the same condition. We strongly recommend extensive etiological investigation as recurrence occurred in one family.

Menkes disease: a Golgi and electron microscopic study of the cerebellar cortex.

A neuropathological study of a case of Menkes disease is reported, illustrating the involvement of different types of neuronal cells. The cerebellum showed the most striking abnormalities: severe lack of internal granule cells. Purkinje cells with weeping willow pattern, numerous segmental enlargements of dendritic trunks and secondary branches, and presence of numerous eosinphilic spherical bodies in the molecular layer were the most conspicuous features. Using electron microscopy, the dendritic enlargements were observed to be made of both proliferated and enlarged mitochondria, and of saccules of smooth endoplasmic reticulum. The spheroid bodies in the molecular layer were mainly made of concentric lamellar structures which seemed to be proliferated smooth endoplasmic reticulum. The relationship between these morphological abnormalities and the metabolic disorder of Menkes disease is discussed.

[Cortical heterotopias: animal models and human disease]. / Hétérotopies corticales: modèles animaux et pathologie humaine.

Cortical heterotopia is defined as the misplacement of a group of neurons displaced to a precise localization in the neocortex and results from perturbed migration along the glial guide, either because of glial destruction or molecular anomalies. Heterotopic neurons are rarely dispersed but are rather grouped in nodules or bands. Heterotopic masses may lie in an ependymal or subcortical localization depending on whether they result from lack of migration or an arrested migration. Heterotopias can also occur in intra-cortical or extra-cortical localizations. The cause of heterotopia remains to be elucidated. Two genes situated on chromosome X have been implicated but non-genetic forms attributable to antenatal ischemia or toxic aggression during fetal development have also been observed. The presence of heterotopia is usually associated with epilepsy and sometimes with mental retardation. Seizures may be initiated within the heterotopic region then propagate via long projections to the neocortex which may also be malformed.

Cerebral lymphoma and HIV encephalitis in a case of paediatric AIDS, with pre-existing multicystic encephalomalacia.

A case of intracerebral malignant B cell lymphoma associated with encephalitis typical of Human Immunodeficiency Virus (HIV) infection is described in a 4 year old child, with post-transfusion Acquired Immune Deficiency Syndrome (AIDS) and severe pre-existing cystic encephalomalacia. This report further documents B cell lymphoma as the commonest cause of an intracerebral mass, and an important cause of death in paediatric AIDS. That more than one pathological process may be responsible for neurological symptoms in paediatric AIDS is also emphasised.