Characterization of nodular neuronal heterotopia in children

Laser Ablation of Periventricular Nodular Heterotopia for Medically Refractory Epilepsy

OBJECTIVE

Periventricular nodular heterotopia (PVNH) is the most common neuronal heterotopia, frequently resulting in pharmaco-resistant epilepsy. Here, we characterize variables that predict good epilepsy outcomes following surgical intervention using stereo-electroencephalography (SEEG) -informed magnetic resonance-guided laser interstitial thermal therapy (MRgLITT).

METHODS

A retrospective review of consecutive cases from a single high-volume epilepsy referral center identified patients who underwent SEEG evaluation for PVNH to characterize the intervention and outcomes.

RESULTS

Thirty-nine patients underwent SEEG-guided MRgLITT of the seizure onset zone (SoZ) in PVNH and associated epileptic tissue. PVNH and polymicrogyria (PMG) were densely sampled with a mean of 16.5 (SD = 2)/209.4 (SD = 36.9) SEEG probes/recording contacts per patient. Ablation principally targeted just the PVNH and cortex that was abnormal on imaging was ablated (5 patients) only if implicated in the SoZ. Volumetric analyses revealed a high percentage of PVNH SoZ ablation (96.6%, SD = 5.3%) in unilateral and bilateral (92.9%, SD = 7.2%) cases. Mean follow-up duration was 31.4 months (SD = 20.9). Seizure freedom (ILAE 1) was excellent: unilateral PVNH without other imaging abnormalities, 80%; PVNH with mesial temporal sclerosis (MTS) or PMG, 63%; bilateral PVNH, 50%. SoZ ablation percentage significantly impacted surgical outcomes (p < 0.001).

INTERPRETATION

PVNH plays a central role in seizure genesis as revealed by dense recordings and selective targeting by LITT. MRgLITT represents a transformative technological advance in PVNH-associated epilepsy with seizure control outcomes consistent with those seen in focal lesional epilepsies. In localized unilateral cases and otherwise normal imaging, PVNH ablation without invasive recordings may be considered, and this approach deserves to be explored further. ANN NEUROL 2024;96:1174-1184.

Over 30 Years of DiI Use for Human Neuroanatomical Tract Tracing: A Scoping Review

In the present study, we conducted a scoping review to provide an overview of the existing literature on the carbocyanine dye DiI, in human neuroanatomical tract tracing. The PubMed, Scopus, and Web of Science databases were systematically searched. We identified 61 studies published during the last three decades. While studies incorporated specimens across human life from the embryonic stage onwards, the majority of studies focused on adult human tissue. Studies that utilized peripheral nervous system (PNS) tissue were a minority, with the majority of studies focusing on the central nervous system (CNS). The most common topic of interest in previous tract tracing investigations was the connectivity of the visual pathway. DiI crystals were more commonly applied. Nevertheless, several studies utilized DiI in a paste or dissolved form. The maximum tracing distance and tracing speed achieved was, respectively, 70 mm and 1 mm/h. We identified studies that focused on optimizing tracing efficacy by varying parameters such as fixation, incubation temperature, dye re-application, or the application of electric fields. Additional studies aimed at broadening the scope of DiI use by assessing the utility of archival tissue and compatibility of tissue clearing in DiI applications. A combination of DiI tracing and immunohistochemistry in double-labeling studies have been shown to provide the means for assessing connectivity of phenotypically defined human CNS and PNS neuronal populations.

Grey matter heterotopia subtypes show specific morpho-electric signatures and network dynamics

Grey matter heterotopia (GMH) are neurodevelopmental disorders associated with abnormal cortical function and epilepsy. Subcortical band heterotopia (SBH) and periventricular nodular heterotopia (PVNH) are two well-recognized GMH subtypes in which neurons are misplaced, either forming nodules lining the ventricles in PVNH, or forming bands in the white matter in SBH. Although both PVNH and SBH are commonly associated with epilepsy, it is unclear whether these two GMH subtypes differ in terms of pathological consequences or, on the contrary, share common altered mechanisms. Here, we studied two robust preclinical models of SBH and PVNH, and performed a systematic comparative assessment of the physiological and morphological diversity of heterotopia neurons, as well as the dynamics of epileptiform activity and input connectivity. We uncovered a complex set of altered properties, including both common and distinct physiological and morphological features across heterotopia subtypes, and associated with specific dynamics of epileptiform activity. Taken together, these results suggest that pro-epileptic circuits in GMH are, at least in part, composed of neurons with distinct, subtype-specific, physiological and morphological properties depending on the heterotopia subtype. Our work supports the notion that GMH represent a complex set of disorders, associating both shared and diverging pathological consequences, and contributing to forming epileptogenic networks with specific properties. A deeper understanding of these properties may help to refine current GMH classification schemes by identifying morpho-electric signatures of GMH subtypes, to potentially inform new treatment strategies.

Stereo-EEG Evaluation and Surgical Treatment in Patients With Drug-Resistant Focal Epilepsy Associated With Nodular Heterotopia

PURPOSE

Nodular heterotopia (NH) is a common cause of drug-resistant epilepsy. Only limited studies detail the treatment of NH with laser interstitial thermal therapy and none analyze the relation between epileptogenicity and NH location.

METHODS

We retrospectively studied nine patients with drug-resistant epilepsy and NH who underwent stereoelectroencephalography and subsequent epilepsy surgery. Nodular heterotopia in the frontal lobes or along the bodies of the lateral ventricles was classified as anterior NH. Nodular heterotopia in the trigones, temporal or occipital horns, or temporal lobes was classified as posterior NH. Nodular heterotopia in both anterior and posterior locations was classified as diffuse NH. Interictal and ictal stereoelectroencephalography were analyzed, and patients were followed postoperatively to assess outcomes.

RESULTS

Of the six patients who underwent nine laser interstitial thermal therapy procedures either in isolation or in combination with other surgical therapies, four patients were Engel Ia, one was Engel IIb, and one was Engel IIIa, with an average follow-up of 22.8 months. All patients with posterior NH had interictal epileptiform abnormalities and seizures originating from the posterior NH. None of the patients with anterior NH had epileptiform activity recorded from their NH.

CONCLUSION

Laser interstitial thermal therapy alone or in combination with other surgical therapies is an effective treatment in those with drug-resistant epilepsy because of NH, even in those with extensive NH and broad seizure onset. We observed a trend suggesting that posterior NH are more likely to be epileptogenic compared with anterior NH and recommend that in patients with anterior NH, alternative epilepsy etiologies and stereoelectroencephalography implantation strategies be considered.

Testing the suitability of neuroanatomical tracing method in human fetuses with long years of postmortem delay

PURPOSE

Human tissues in gross anatomical archives with long years of postmortem delays are considered suboptimal relative to recently fixed materials for neuroanatomical tracing studies, yet efficacy of neuroanatomical tracing on archival fetal tissues largely unexplored. We aimed to explore the suitability of human archival tissue in neuroanatomical tracing with lipophilic carbocyanine dyes.

METHODS

We used crystal and paste forms 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) and analogues for neuroanatomical tracing on different peripheral nerves in 15-18-year archival old formalin-fixed human fetuses. We employed bright-field, fluorescent and confocal microscopy to visualize the peripheric nerve traces, spinal cord and vibratome cut sections. Fluorescent signal of the dyes on epineurium and on axonal membranes were visualized under fluorescence and confocal microscopes and performance of the dye diffusion was assessed by semi-quantitative image analysis.

RESULTS

We followed up seven lipophilic dye embeddings in 16-28 gestational week-old human fetuses (n = 4) with 16.75 ± 1.29-year postmortem delay. The mean distance of distally moved carbocyanine dye diffusion measured on epineurium was detected as 25.11 ± 9.1 mm.

CONCLUSION

Based on the results of 13 distinct studies performed neuroanatomical tracing with human tissues in the immediate postmortem hours or days, average traced distance was 16.32 ± 15.95 mm, and a 95% confidence interval lower limit of 4.9 mm and upper limit of 27.73 mm. The tracing distances we observed in our current study fall entirely within this confidence interval. To our awareness, this is the first report to demonstrate that specific neuroanatomical tracing presented in axonal membrane level on peripheral nerves is possible on gross anatomical repositories.

Quantitative 1H-MRS reveals metabolic difference between subcategories of malformations of cortical development

PURPOSE

To figure out the spectra features of malformations of cortical development (MCDs) and the differences between MCDs subcategories.

METHODS

Twenty patients and 18 controls were studied. The patients included two subcategories: disorders of migration (DOM) and postmigration (DOPM). Spectra of patients were acquired from both the lesion and the normal-appearing contralateral side (NACS), and they were compared to those of the controls obtained from the frontal lobe.

RESULTS

Compared to the controls, a decreased NAA (P = 0.002) was identified in MCDs. After dividing the MCDs into the DOM and DOPM, we found that NAA reduction was only notable in the DOM (P = 0.007). Moreover, Ins and Cr of the DOPM were higher than those of the controls (P = 0.017 and 0.013) and the DOM (P = 0.027 and 0.001). Compared to the NACS, a decreased NAA (P = 0.042) and an increased Ins (P = 0.039) were identified in the lesion of MCDs. After dividing the MCDs into the DOM and DOPM, we found no significant differences in the DOM, but Ins, Cr, and Glx of the lesion were higher than those of the NACS (P = 0.007, 0.005 and 0.047) in the DOPM. In addition, we found that Cr and Glx correlated positively to the seizure frequency (P = 0.003 and 0.016).

CONCLUSION

Decreased NAA was the prominent abnormality confirmed in MCDs. Spectra of different MCDs subcategories were different: the DOM was characterized by decreased NAA, while the DOPM was characterized by increased Ins.

Tensor-valued diffusion MRI differentiates cortex and white matter in malformations of cortical development associated with epilepsy

Objective:

Delineation of malformations of cortical development (MCD) is central in presurgical evaluation of drug-resistant epilepsy. Delineation using magnetic resonance imaging (MRI) can be ambiguous, however, because the conventional T₁- and T₂-weighted contrasts depend strongly on myelin for differentiation of cortical tissue and white matter. Variations in myelin content within both cortex and white matter may cause MCD findings on MRI to change size, become undetectable, or disagree with histopathology. The novel tensor-valued diffusion MRI (dMRI) technique maps microscopic diffusion anisotropy, which is sensitive to axons rather than myelin. This work investigated whether tensor-valued dMRI may improve differentiation of cortex and white matter in the delineation of MCD.

Methods:

Tensor-valued dMRI was performed on a 7 T MRI scanner in 13 MCD patients (age = 32 ± 13 years) featuring periventricular heterotopia, subcortical heterotopia, focal cortical dysplasia, and polymicrogyria. Data analysis yielded maps of microscopic anisotropy that were compared with T₁-weighted and T₂-fluid-attenuated inversion recovery images and with the fractional anisotropy from diffusion tensor imaging.

Results:

Maps of microscopic anisotropy revealed large white matter-like regions within MCD that were uniformly cortex-like in the conventional MRI contrasts. These regions were seen particularly in the deep white matter parts of subcortical heterotopias and near the gray-white boundaries of focal cortical dysplasias and polymicrogyrias.

Significance:

By being sensitive to axons rather than myelin, mapping of microscopic anisotropy may yield a more robust differentiation of cortex and white matter and improve MCD delineation in presurgical evaluation of epilepsy.

Reading deficits correlate with cortical and subcortical volume changes in a genetic migration disorder

Periventricular nodular heterotopia (PNH) is the most common type of epileptogenic neuronal migration disorder, and often presents with epilepsy and reading disability. The functional role of ectopic nodules has been widely studied. However, the associated structural cortical and subcortical volumetric alterations have not been well characterized. Moreover, it is unknown whether a correlation between volumetric changes and behavioral problems exists.40 subjects with bilateral PNH and 40 matched healthy controls were enrolled in this study. The total cerebral, gray matter, white matter, and cerebrospinal fluid (CSF) volumes were compared between the two groups. Furthermore, structural and functional correlations were evaluated between volumetric changes and reading disability.There were no significant differences detected in total cerebral, gray matter or CSF volumes between the two groups, but there was a significant trend of larger gray-matter volume in PNH. Specifically, smaller white matter volumes were found in the PNH patients. Moreover, the volume of white matter was negatively related to time in the digit rapid naming task and a similar but insignificant trend was seen between the volume of gray matter and backward digit span.These findings suggest that reading disability exists in our sample of bilateral PNH. Periventricular nodules would have normally migrated to the overlying cortex. However, the total cerebral, gray matter, and CSF volumes were unaffected. Alterations in neuronal migration may have an impact in the white matter associated reading dysfluency, that is, visually normal.

Internodular functional connectivity in heterotopia-related epilepsy

Objective

A vast network involving the nodules and overlying cortices is believed to be responsible for the epileptogenicity in gray matter heterotopia with multiple nodules, which often associated with difficult‐to‐treat epilepsy. We sought to determine if functional magnetic resonance imaging (fMRI) could detect internodular functional connectivity (FC), and if this connectivity reflects an actual synchronized neuronal activity and partakes in epileptogenicity.

Methods

We studied 16 epilepsy patients with multiple heterotopic nodules; eight underwent subsequent intracerebral EEG. We examined the internodular FC using fMRI and its correspondence with internodular synchrony of intracerebral interictal activity. We then compared the spreading speed of ictal activity between connected and unconnected nodules; and the FC among possible combinations of nodule pairs in terms of their involvement at seizure onset.

Results

Seventy nodules were studied: 83% have significant connection to at least one other nodule. Among the 49 pairs studied with intracerebral EEG, (1) synchronized interictal activity is more prevalent in fMRI‐connected pairs (P < 0.05), (2) ictal activity spreads faster between connected pairs (P < 0.0001), and (3) stronger FC was observed between pairs in which both nodules were involved at seizure onset (P < 0.01).

Interpretation

fMRI could reliably and noninvasively detect the FC between heterotopic nodules. These functional connections correspond to the synchrony of interictal epileptic activity between the nodules and to the ability of nodules to generate synchronous seizure onsets or rapid seizure spread. These findings may help in understanding the complexity of the epileptogenic network in multiple heterotopic nodules and better targeting the likely epileptogenic nodules.

Association between scalp and intracerebral electroencephalographic seizure-onset patterns: A study in different lesional pathological substrates

OBJECTIVE

Our purpose was to determine the correlation between scalp electroencephalography (EEG) and intracerebral EEG (iEEG) seizure-onset patterns in patients with focal lesional epilepsy to determine whether scalp seizure-onset patterns can be specific to intracerebral seizure-onset patterns and to lesion type.

METHODS

We retrospectively analyzed 61 patients with focal epilepsy and a structural magnetic resonance imaging (MRI)-visible lesion, who first underwent extensive scalp recordings and then iEEG studies (stereo-EEG) for presurgical evaluation, and who showed an iEEG seizure onset in the lesional/perilesional area. Five seizure-onset patterns were recognized on scalp EEG, and 7 on iEEG, and in each patient, only the predominant scalp and iEEG seizure-onset patterns were compared. Because scalp and iEEG recordings were acquired at different times, we followed strict criteria based on semiology and topography to match scalp with intracerebral seizures.

RESULTS

Seventy-one pairs of seizure-onset patterns matched between scalp and iEEG were identified. Each scalp pattern did not correspond to a single intracerebral pattern, but there were significant associations: (1) paroxysmal fast activity (≥13 Hz) at scalp onset was associated with low-voltage fast activity at iEEG onset (P < .001), with malformations of cortical development (P < .001), and with superficial seizure-onset zone based on iEEG (P < .001); (2) rhythmic slow activity (<13 Hz) at scalp onset was associated with low-frequency high-amplitude periodic spikes at iEEG onset (P = .0014), with medial temporal atrophy/sclerosis (P < .001), and with deep seizure-onset zone (P < .001); and (3) repetitive epileptiform discharge at scalp onset was associated with a burst of high-amplitude polyspikes at iEEG onset (P = .0002).

SIGNIFICANCE

Our results disclosed that in focal epilepsy patients with seizures generated in an MRI-visible lesion, some scalp seizure-onset patterns are highly associated with a specific intracerebral pattern, with specific pathologies, and with the depth of seizure-onset zone. These findings allow the interpretation of scalp seizure-onset patterns to be significantly more informative.

Pathophysiological analyses of periventricular nodular heterotopia using gyrencephalic mammals

Although periventricular nodular heterotopia (PNH) is often found in the cerebral cortex of people with thanatophoric dysplasia (TD), the pathophysiology of PNH in TD is largely unknown. This is mainly because of difficulties in obtaining brain samples of TD patients and a lack of appropriate animal models for analyzing the pathophysiology of PNH in TD. Here we investigate the pathophysiological mechanisms of PNH in the cerebral cortex of TD by utilizing a ferret TD model which we recently developed. To make TD ferrets, we electroporated fibroblast growth factor 8 (FGF8) into the cerebral cortex of ferrets. Our immunohistochemical analyses showed that PNH nodules in the cerebral cortex of TD ferrets were mostly composed of cortical neurons, including upper layer neurons and GABAergic neurons. We also found disorganizations of radial glial fibers and of the ventricular lining in the TD ferret cortex, indicating that PNH may result from defects in radial migration of cortical neurons along radial glial fibers during development. Our findings provide novel mechanistic insights into the pathogenesis of PNH in TD.

Subcortical band heterotopia in rat offspring following maternal hypothyroxinaemia: structural and functional characteristics

Thyroid hormones (TH) play crucial roles in brain maturation and are important for neuronal migration and neocortical lamination. Subcortical band heterotopia (SBH) represent a class of neuronal migration errors in humans that are often associated with childhood epilepsy. We have previously reported the presence of SBH in a rodent model of low level hypothyroidism induced by maternal exposure to the goitrogen, propylthiouracil (PTU). In the present study, we report the dose-response characteristics of this developmental malformation and the connectivity of heterotopic neurones with other brain regions, as well as their functionality. Pregnant rats were exposed to varying concentrations of PTU through the drinking water (0-10 p.p.m.) beginning on gestational day 6 to produce graded levels of TH insufficiency. Dose-dependent increases in the volume of the SBH present in the corpus callosum were documented in the adult offspring, with a clear presence at concentrations of PTU that resulted in minor (< 15%) reductions in maternal serum thyroxine as measured when pups were weaned. SBH contain neurones, oligodendrocytes, astrocytes and microglia. Monoaminergic and cholinergic processes were prevalent and many of the axons were myelinated. Anatomical connectivity of SBH neurones to cortical neurones and the synaptic functionality of these anatomical connections was verified by ex vivo field potential recordings. SBH persisted in adult offspring despite a return to euthyroid status on termination of exposure and these offspring displayed an increased sensitivity to seizures. Features of this model are attractive with respect to the investigation of the molecular mechanisms of cortical development, the effectiveness of therapeutic intervention in hypothyroxinaemia during pregnancy and the impact of the very modest TH imbalance that accompanies exposure to environmental contaminants.

Organelle and cellular abnormalities associated with hippocampal heterotopia in neonatal doublecortin knockout mice

Heterotopic or aberrantly positioned cortical neurons are associated with epilepsy and intellectual disability. Various mouse models exist with forms of heterotopia, but the composition and state of cells developing in heterotopic bands has been little studied. Dcx knockout (KO) mice show hippocampal CA3 pyramidal cell lamination abnormalities, appearing from the age of E17.5, and mice suffer from spontaneous epilepsy. The Dcx KO CA3 region is organized in two distinct pyramidal cell layers, resembling a heterotopic situation, and exhibits hyperexcitability. Here, we characterized the abnormally organized cells in postnatal mouse brains. Electron microscopy confirmed that the Dcx KO CA3 layers at postnatal day (P) 0 are distinct and separated by an intermediate layer devoid of neuronal somata. We found that organization and cytoplasm content of pyramidal neurons in each layer were altered compared to wild type (WT) cells. Less regular nuclei and differences in mitochondria and Golgi apparatuses were identified. Each Dcx KO CA3 layer at P0 contained pyramidal neurons but also other closely apposed cells, displaying different morphologies. Quantitative PCR and immunodetections revealed increased numbers of oligodendrocyte precursor cells (OPCs) and interneurons in close proximity to Dcx KO pyramidal cells. Immunohistochemistry experiments also showed that caspase-3 dependent cell death was increased in the CA1 and CA3 regions of Dcx KO hippocampi at P2. Thus, unsuspected ultrastructural abnormalities and cellular heterogeneity may lead to abnormal neuronal function and survival in this model, which together may contribute to the development of hyperexcitability.

Magnetic resonance diffusion tensor imaging metrics in perilesional white matter among children with periventricular nodular gray matter heterotopia

BACKGROUND

Despite pharmacological and surgical interventions, some children with periventricular nodular heterotopia (PNH) remain refractory to treatment, which suggests more diffuse pathology potentially involving perilesional white matter.

OBJECTIVE

The purpose of this study was to evaluate MR diffusion tensor imaging (MRDTI) metrics within perilesional white matter in children with PNH.

MATERIALS AND METHODS

Six children with PNH (four boys; average age 3.2 years, range 2 months to 6 years) were studied with MRDTI at 3 T. Fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) were quantified within perilesional white matter at distances of 5 mm, 10 mm, 15 mm, and 20 mm from focal areas of PNH and compared to location-matched ROIs in six healthy control patients (two boys, average age 3.3 years, range 2-6 years). Statistical significance was set at an overall level of α = 0.05, corrected for multiple comparisons.

RESULTS

Perilesional white matter showed significantly decreased fractional anisotropy and elevated mean and radial diffusivity at all evaluated distances. No significant differences in axial diffusivity were detected at any distance.

CONCLUSION

PNH is associated with microstructural white matter abnormalities as indicated by abnormal perilesional MRDTI metrics detectable at least 20 mm from visible nodular lesions.

New insights into genotype-phenotype correlations for the doublecortin-related lissencephaly spectrum

X-linked isolated lissencephaly sequence and subcortical band heterotopia are allelic human disorders associated with mutations of doublecortin (DCX), giving both familial and sporadic forms. DCX encodes a microtubule-associated protein involved in neuronal migration during brain development. Structural data show that mutations can fall either in surface residues, likely to impair partner interactions, or in buried residues, likely to impair protein stability. Despite the progress in understanding the molecular basis of these disorders, the prognosis value of the location and impact of individual DCX mutations has largely remained unclear. To clarify this point, we investigated a cohort of 180 patients who were referred with the agyria-pachygyria subcortical band heterotopia spectrum. DCX mutations were identified in 136 individuals. Analysis of the parents' DNA revealed the de novo occurrence of DCX mutations in 76 cases [62 of 70 females screened (88.5%) and 14 of 60 males screened (23%)], whereas in the remaining cases, mutations were inherited from asymptomatic (n = 14) or symptomatic mothers (n = 11). This represents 100% of families screened. Female patients with DCX mutation demonstrated three degrees of clinical-radiological severity: a severe form with a thick band (n = 54), a milder form (n = 24) with either an anterior thin or an intermediate thickness band and asymptomatic carrier females (n = 14) with normal magnetic resonance imaging results. A higher proportion of nonsense and frameshift mutations were identified in patients with de novo mutations. An analysis of predicted effects of missense mutations showed that those destabilizing the structure of the protein were often associated with more severe phenotypes. We identified several severe- and mild-effect mutations affecting surface residues and observed that the substituted amino acid is also critical in determining severity. Recurrent mutations representing 34.5% of all DCX mutations often lead to similar phenotypes, for example, either severe in sporadic subcortical band heterotopia owing to Arg186 mutations or milder in familial cases owing to Arg196 mutations. Taken as a whole, these observations demonstrate that DCX-related disorders are clinically heterogeneous, with severe sporadic and milder familial subcortical band heterotopia, each associated with specific DCX mutations. There is a clear influence of the individual mutated residue and the substituted amino acid in determining phenotype severity.

Bilateral posterior periventricular nodular heterotopia: a recognizable cortical malformation with a spectrum of associated brain abnormalities

BACKGROUND AND PURPOSE

Bilateral posterior PNH is a distinctive complex malformation with imaging features distinguishing it from classic bilateral PNH associated with FLNA mutations. The purpose of this study was to define the imaging features of posterior bilateral periventricular nodular heterotopia and to determine whether associated brain malformations suggest specific subcategories.

MATERIALS AND METHODS

We identified a cohort of 50 patients (31 females; mean age, 13 years) with bilateral posterior PNH and systematically reviewed and documented associated MR imaging abnormalities. Patients were negative for mutations of FLNA.

RESULTS

Nodules were often noncontiguous (n = 28) and asymmetric (n = 31). All except 1 patient showed associated developmental brain abnormalities involving a spectrum of posterior structures. A range of posterior fossa abnormalities affected the cerebellum, including cerebellar malformations and posterior fossa cysts (n = 38). Corpus callosum abnormalities (n = 40) ranged from mild dysplasia to agenesis. Posterior white matter volume was decreased (n = 22), and colpocephaly was frequent (n = 26). Most (n = 40) had associated cortical abnormalities ranging from minor to major (polymicrogyria), typically located in the cortex overlying the PNH. Abnormal Sylvian fissure morphology was common (n = 27), and hippocampal abnormalities were frequent (n = 37). Four family cases were identified-2 with concordant malformation patterns and 2 with discordant malformation patterns.

CONCLUSIONS

The associations of bilateral posterior PNH encompass a range of abnormalities involving brain structures inferior to the Sylvian fissures. We were unable to identify specific subgroups and therefore conceptualize bilateral posterior PNH as a continuum of infrasylvian malformations involving the posterior cerebral and hindbrain structures.

Novel pathological abnormalities of deep brain structures including dysplastic neurons in anterior striatum associated with focal cortical dysplasia in epilepsy

OBJECT

Some patients are not seizure free even after epileptogenic cortical resection. The authors recently described a case of frontal lobe epilepsy cured after the resection of periventricular white matter and striatum, in which dysplastic neurons were revealed. The authors attempted to confirm similar cases.

METHODS

They reviewed the records of 8 children with frontal lobe epilepsy who had daily (7) or monthly (1) seizures and underwent resections including deep brain structures.

RESULTS

Five patients underwent multiple resections. Neuroimaging of the deep structures showed the transmantle sign in 3 patients, ictal hyperperfusion in 6, reduced iomazenil uptake in 2, and spike dipole clustering in 6. All patients became seizure free postoperatively. Focal cortical dysplasia of various types was diagnosed in all patients. Dysmorphic neurons were found in the cortex and subcortical white matter of 5 patients. The striatum was verified in 3 patients in whom dysmorphic neurons were scattered. In the periventricular white matter, prominent astrocytosis was evident in all cases.

CONCLUSIONS

Pathological abnormalities such as dysmorphic neurons and astrocytosis in deep brain structures would play a key role in epileptogenesis.

Abnormal structural and functional brain connectivity in gray matter heterotopia

PURPOSE

Periventricular nodular heterotopia (PNH) is a malformation of cortical development associated with epilepsy and dyslexia. Evidence suggests that heterotopic gray matter can be functional in brain malformations and that connectivity abnormalities may be important in these disorders. We hypothesized that nodular heterotopia develop abnormal connections and systematically investigated the structural and functional connectivity of heterotopia in patients with PNH.

METHODS

Eleven patients were studied using diffusion tensor tractography and resting-state functional connectivity MRI with bold oxygenation level-dependent (BOLD) imaging. Fiber tracks with a terminus within heterotopic nodules were visualized to determine structural connectivity, and brain regions demonstrating resting-state functional correlations to heterotopic nodules were analyzed. Relationships between these connectivity results and measures of clinical epilepsy and cognitive disability were examined.

KEY FINDINGS

A majority of heterotopia (69%) showed structural connectivity to discrete regions of overlying cortex, and almost all (96%) showed functional connectivity to these regions (mean peak correlation coefficient 0.61). Heterotopia also demonstrated connectivity to regions of contralateral cortex, other heterotopic nodules, ipsilateral but nonoverlying cortex, and deep gray matter structures or the cerebellum. Patients with the longest durations of epilepsy had a higher degree of abnormal functional connectivity (p = 0.036).

SIGNIFICANCE

Most heterotopic nodules in PNH are structurally and functionally connected to overlying cortex, and the strength of abnormal connectivity is higher among patients with the longest duration of epilepsy. Along with prior evidence that cortico-cortical tract defects underlie dyslexia in this disorder, the current findings suggest that altered connectivity is likely a critical substrate for neurologic dysfunction in brain malformations.

Assessment of gray matter heterotopia by magnetic resonance imaging

AIM: To evaluate magnetic resonance imaging (MRI) features of different types of gray matter heterotopia.

METHODS: Between June 2005 and December 2009, the medical records and MRI studies of patients with gray matter heterotopia were reviewed. The MRI morphologic findings of heterotopia were recorded along with the presence and type of associated cranial malformations. Available clinical and electrophysiological data were also recorded.

RESULTS: 20 patients were included in the study. Their ages ranged from 9 mo to 39 years with a mean age of 15 years. All patients suffered from epileptic seizures. According to the location of heterotopia, patients were classified into three groups: subependymal (12), subcortical (5) and band (3) heterotopia.

CONCLUSION: MRI was useful in diagnosing and differentiating between various types of gray matter heterotopia. The severity of clinical manifestations of heterotopia was related to the location and pattern of heterotopia. Determination of heterotopia type and its extent is useful for management planning and predicting prognosis.

Cerebral cortical development in rodents and primates

Rodents and primates both show considerable variation in the overall size, the radial and tangential dimensions, folding and subdivisions into distinct areas of their cerebral cortex. Our current understanding of brain development is based on a handful of model systems. A detailed comparative analysis of the cellular and molecular mechanisms that regulate neural progenitor production, cell migration, and circuit assembly can provide much needed insights into the working of neocortical evolution. From the limited comparative data currently available, it is apparent that the emergence and variation of the neuronal progenitor cells have led to the production of increased neuronal populations and the evolution of the cortex. Further diversification and compartmentalization of the germinal zone together with changing proportions of radial glia in the ventricular zone and various intermediate progenitors in the subventricular zone may have been the driving force behind increased cell numbers in larger brains both in rodents and primates. Radial and tangential migratory patterns are both present in rodents and primates, but in different proportions. There are apparent differences between mouse and human in the generation and elaboration of the interneuronal subtypes and also in gene expression patterns associated with the appearance of distinct cortical areas. The increased cortical dimensions and the formation of a more elaborate cortical architecture in primates require a larger and more compartmentalized transient subplate zone during development. More comparative analysis in rodent and primate species with large, small, and smooth and folded brains is needed to reveal the biological significance of the alterations in these cortical developmental programs.

Early cognitive and behavioral problems in children with nodular heterotopia

Adults with periventricular nodular heterotopia (PNH) have epilepsy and dyslexia, but most have normal intelligence. It is not known whether PNH-related reading difficulty can be detected earlier in childhood or whether associated behavioral problems are present. We studied 10 children with PNH, 3 of whom did not have seizures, and 10 matched controls with neuropsychological testing and parental rating instruments at two time points separated by about 1 year. Children with PNH performed significantly worse than controls on a task related to reading fluency. In addition, those with PNH showed significantly worse adaptive skills, and a measure of conduct problems significantly worsened over time. Mood and behavioral problems were reported more commonly, though not significantly so, in children with PNH. These findings demonstrate that reading dysfluency can be evident in children with nodular heterotopia, even in the absence of epilepsy, but also highlight difficulties with behavior in this population.

Diuretics and epilepsy: will the past and present meet?

Clinical studies from over half a century ago suggested efficacy of a variety of diuretics in focal and generalized epilepsies as well as in status epilepticus, but these findings have not been translated into modern epilepsy training or practice. Recent advances in our understanding of neuronal maturation and the pathophysiology of neonatal seizures provide fresh insight into the mechanisms by which diuretics might reduce susceptibility to seizures. In vitro and in vivo rodent studies and human epilepsy surgical cases have shown that specific diuretic agents targeting the cation-chloride cotransporters decrease neuronal synchrony and neuronal hyperexcitability. These agents are thought to convey their antiepileptic activity by either expanding the extracellular space or promoting a cellular chloride transport balance that reflects a more developmentally "mature," less excitable state. It may be time to reexamine whether diuretics could serve as adjunctive therapies in the treatment of refractory epilepsies.

Cerebral volumetric analysis over time in children with malformations of cortical development: a quantitative investigation

Malformations of cortical development are common neurological disorders characterized by disruptions in the normal development of cerebral gray and white matter during fetal life. We performed a quantitative, partly longitudinal investigation of cerebral volumes in a cohort of children with cortical malformations to investigate how their anatomical abnormalities change over time. Cortical malformation subjects showed volumetric curves that were comparable with those reported for healthy individuals, and reached peak cerebral volume, gray matter volume, and white matter volume at ages similar to those reported for healthy children. Volumes of heterotopic gray matter, however, demonstrated increases that were out of proportion to changes in cortical volume or caudate nucleus volume, suggesting that misplaced gray matter can have a unique pattern of maturation. Our findings demonstrate that overall brain growth in children with cortical malformations appears to mirror that of the healthy population, although malformed regions can show distinct growth patterns.

Renewed focus on the developing human neocortex

Many specifically human psychiatric and neurological conditions have developmental origins. Rodent models are extremely valuable for the investigation of brain development, but cannot provide insight into aspects that are specifically human. The human brain, and particularly the cerebral cortex, has some unique genetic, molecular, cellular and anatomical features, and these need to be further explored. Cortical expansion in human is not just quantitative; there are some novel types of neurons and cytoarchitectonic areas identified by their gene expression, connectivity and functions that do not exist in rodents. Recent research into human brain development has revealed more elaborated neurogenetic compartments, radial and tangential migration, transient cell layers in the subplate, and a greater diversity of early-generated neurons, including predecessor neurons. Recently there has been a renaissance of the study of human brain development because of these unique differences, made possible by the availability of new techniques. This review gives a flavour of the recent studies stemming from this renewed focus on the developing human brain.

ERK1 and ERK2 are required for radial glial maintenance and cortical lamination

ERK1/2 is involved in a variety of cellular processes during development, but the functions of these isoforms in brain development remain to be determined. Here, we generated double knockout (DKO) mice to study the individual and combined roles of ERK1 and ERK2 during cortical development. Mice deficient in Erk2, and more dramatically in the DKOs, displayed proliferation defects in late radial glial progenitors within the ventricular zone, and a severe disruption of lamination in the cerebral cortex. Immunohistochemical analyses revealed that late-generated cortical neurons were misplaced and failed to migrate the upper cortical layers in DKO mice. Moreover, these mice displayed fewer radial glial fibers, which provide architectural guides for radially migrating neurons. These results suggest that extracellular signal-regulated kinase signaling is essential for the expansion of the radial glial population and for the maintenance of radial glial scaffolding. Tangential migration of interneurons and oligodendrocytes from the ganglionic eminences (GE) to the dorsal cortex was more severely impaired in DKO mice than in mice deficient for Erk2 alone, because of reduced progenitor proliferation in the GE of the ventral telencephalon. These data demonstrate functional overlaps between ERK1 and ERK2 and indicate that extracellular signal-regulated kinase signaling plays a crucial role in cortical development.

Surgically treated movement disorders associated with heterotopia: report of 2 cases

Heterotopic gray matter has been implicated in epilepsy; however, not much is known regarding heterotopia beyond epilepsy. Here, the authors describe 2 pediatric patients with deep heterotopias contiguous with basal ganglia structures. These heterotopias appear to have manifested as movement disorders. One patient presented with a left-sided myoclonus and choreiform movements associated with a right caudate heterotopia; she experienced vast improvement after resection of periventricular heterotopia. The other patient presented with progressive dystonia and a ballistic movement disorder. Initial bilateral globus pallidus internus stimulation resulted in successful treatment of the dystonia; however, her movement disorder worsened. After an extensive workup, including STATISCOM (statistical ictal SPECT coregistered to MR imaging), the patient underwent cortical stimulation with improvement in her movement disorder. To the best of our knowledge, these cases are the first reported instances of heterotopic gray matter associated with movement disorders. Both patients experienced significant improvements following resection of their heterotopias.

Coexistent pathology in chronic epilepsy patients with neoplasms

Neoplasms are a well-established cause of medically intractable or chronic epilepsy. Certain tumors, including gangliogliomas and dysembryoplastic neuroepithelial tumors, are well known to be associated with cortical dysplasia. This study retrospectively examines the incidence of coexistent pathology in patients with tumors and chronic epilepsy. This study is a retrospective review of 270 tumors arising in patients with medically intractable epilepsy encountered during a 20-year period (1989-2009). Coexistent pathology was noted in 50 of 270 (17.8%) patients, including 27 males (54%) with a mean age at surgery of 18 years (range 1-52 years). The vast majority of lesions (n=40) (80%) were located in the temporal lobe and less commonly in the parietal lobe (n=4) and the occipital lobe (n=3). Tumor diagnoses included ganglioglioma (n=29), dysembryoplastic neuroepithelial tumor (n=10), low-grade glial/glioneuronal neoplasm (n=5), low-grade astrocytoma (n=2), angiocentric glioma (n=1), low-grade mixed glioma (n=1), dysembryoplastic neuroepithelial tumor/ganglioglioma mixed tumor (n=1), and meningioangiomatosis (n=1). Forty-one (82%) tumors represented WHO grade-I neoplasms. Concomitant pathology included malformation of cortical development (cortical dysplasia) in 40 patients (80%) (Palmini et al type-I: n=37; Palmini et al type-II: n=3). Hamartias were identified in 10 patients (20%), hippocampal sclerosis in four patients (8%), and nodular heterotopia in one patient (2%). The true incidence of coexistent pathology (17.8% in this study) was likely underrepresented, given the limited extent of adjacent non-tumoral tissue sampling in cases of resected tumor. Coexistent pathology may account for the incidence of recurrent or residual epilepsy in patients who undergo tumor resection.

Gray matter volumes and cognitive ability in the epileptogenic brain malformation of periventricular nodular heterotopia

Periventricular nodular heterotopia (PNH) is a brain malformation clinically characterized by the triad of epilepsy, normal intelligence, and dyslexia. We investigated the structure-function relationship between cerebral volumes and cognitive ability in this disorder by studying 12 subjects with PNH and 6 controls using volumetric analysis of high-resolution anatomical MRI and neuropsychological testing. Total cerebral volumes and specific brain compartment volumes (gray matter, white matter, and cerebrospinal fluid) in subjects with PNH were comparable to those in controls. There was a negative correlation between heterotopic gray matter volume and cortical gray matter volume. Cerebral and cortical volumes in PNH did not correlate with Full Scale IQ, unlike in normal individuals. Our findings support the idea that heterotopic nodules contain misplaced neurons that would normally have migrated to the cortex, and suggest that structural correlates of normal cognitive ability may be different in the setting of neuronal migration failure.

Neuronal migration disorders

Lissencephaly-pachygyria-severe band heterotopia are diffuse neuronal migration disorders (NMDs) causing severe, global neurological impairment. Abnormalities of the LIS1, DCX, ARX, TUBA1A and RELN genes have been associated with these malformations. NMDs only affecting subsets of neurons, such as mild subcortical band heterotopia and periventricular heterotopia, cause neurological and cognitive impairment that vary from severe to mild deficits. They have been associated with abnormalities of the DCX, FLN1A, and ARFGEF2 genes. Polymicrogyria results from abnormal late cortical organization and is inconstantly associated with abnormal neuronal migration. Localized polymicrogyria has been associated with anatomo-specific deficits, including disorders of language and higher cognition. Polymicrogyria is genetically heterogeneous and only in a small minority of patients a definite genetic cause has been identified. Mutations of the GPR56 and SRPX2 genes have been related to isolated polymicrogyria. Focal migration abnormalities associated with abnormal cell types, such as focal cortical dysplasia, are highly epileptogenic and variably influence the functioning of the affected cortex. The functional consequences of abnormal neuronal migration are still poorly understood. Conservation of function in the malformed cortex, its atypical representation, and relocation outside the malformed area are all possible. Localization of function based on anatomic landmarks may not be reliable.

Different structures involved during ictal and interictal epileptic activity in malformations of cortical development: an EEG-fMRI study

Malformations of cortical development (MCDs) are commonly complicated by intractable focal epilepsy. Epileptogenesis in these disorders is not well understood and may depend on the type of MCD. The cellular mechanisms involved in interictal and ictal events are notably different, and could be influenced independently by the type of pathology. We evaluated the relationship between interictal and ictal zones in eight patients with different types of MCD in order to better understand the generation of these activities: four had nodular heterotopia, two focal cortical dysplasia and two subcortical band heterotopia (double-cortex). We used the non-invasive EEG-fMRI technique to record simultaneously all cerebral structures with a high spatio-temporal resolution. We recorded interictal and ictal events during the same session. Ictal events were either electrical only or clinical with minimal motion. BOLD changes were found in the focal cortical dysplasia during interictal and ictal epileptiform events in the two patients with this disorder. Heterotopic and normal cortices were involved in BOLD changes during interictal and ictal events in the two patients with double cortex, but the maximum BOLD response was in the heterotopic band in both patients. Only two of the four patients with nodular heterotopia showed involvement of a nodule during interictal activity. During seizures, although BOLD changes affected the lesion in two patients, the maximum was always in the overlying cortex and never in the heterotopia. For two patients intracranial recordings were available and confirm our findings. The dysplastic cortex and the heterotopic cortex of band heterotopia were involved in interictal and seizure processes. Even if the nodular gray matter heterotopia may have the cellular substrate to produce interictal events, the often abnormal overlying cortex is more likely to be involved during the seizures. The non-invasive BOLD study of interictal and ictal events in MCD patients may help to understand the role of the lesion in epileptogenesis and also determine the potential surgical target.

Malformations of cortical development and epilepsy

Malformations of cortical development (MCDs) are macroscopic or microscopic abnormalities of the cerebral cortex that arise as a consequence of an interruption to the normal steps of formation of the cortical plate. The human cortex develops its basic structure during the first two trimesters of pregnancy as a series of overlapping steps, beginning with proliferation and differentiation of neurons, which then migrate before finally organizing themselves in the developing cortex. Abnormalities at any of these stages, be they environmental or genetic in origin, may cause disruption of neuronal circuitry and predispose to a variety of clinical consequences, the most common of which is epileptic seizures, A large number of MCDs have now been described, each with characteristic pathological, clinical, and imaging features. The causes of many of these MCDs have been determined through the study of affected individuals, with many MCDs now established as being secondary to mutations in cortical development genes. This review will highlight the best-known of the human cortical malformations associated with epilepsy. The pathological, clinical, imaging, and etioiogic features of each MCD will be summarized, with representative magnetic resonance imaging (MRI) images shown for each MCD, The malformations tuberous sclerosis, focal cortical dysplasia, hemimegalencephaiy, classical iissencephaly, subcortical band heterotopia, periventricular nodular heterotopia, polymicrogyria, and schizencephaly will be presented.

Functional interactions in brain networks underlying epileptic seizures in bilateral diffuse periventricular heterotopia

OBJECTIVE

Our aim was to investigate relationships between heterotopic and remote cortical structures at seizure initiation, in a patient with bilateral periventricular nodular heterotopias (BPNH) explored by intracerebral electrodes.

METHODS

Stereoelectroencephalography (SEEG) was performed in a man with BPNH and refractory epilepsy to investigate the hypothesis of right temporal lobe epilepsy and the possible involvement of heterotopic structures during seizures. SEEG signals were analyzed with quantification of functional coupling between different brain structures during seizures, using nonlinear regression. We have used Z-score transformation of correlation values to reflect the change from the preictal period. Relationships between BPNH and cortical structures were investigated using analysis of stimulation-induced potentials.

RESULTS

Three spontaneous seizures were recorded and analyzed. Signal analysis of interdependencies in two seizures demonstrated a large initial network involving both heterotopia and cortical structures. Stimulations of heterotopia induced responses in remote cortical structures.

CONCLUSIONS

Distinct epileptogenic networks were identified, in which leader structures were either the heterotopic or the mesial temporal structures, with functional connections between heterotopic and cortical areas.

SIGNIFICANCE

These results confirm that a vast epileptogenic network, including heterotopic and cortical neurons, may be responsible for seizure generation in BPNH. This may explain certain surgical failures in this group.

Modest thyroid hormone insufficiency during development induces a cellular malformation in the corpus callosum: a model of cortical dysplasia

There is a growing body of evidence that subtle decreases in maternal thyroid hormone during gestation can impact fetal brain development. The present study examined the impact of graded levels of thyroid hormone insufficiency on brain development in rodents. Maternal thyroid hormone insufficiency was induced by exposing timed-pregnant dams to propylthiouracil (PTU) at doses of 0, 1, 2, 3, and 10 ppm in the drinking water from gestational d 6 through weaning on postnatal d 30. An examination of Nissl-stained sections of the brains from developmentally hypothyroid offspring killed on postnatal d 23 revealed the presence of a heretofore unreported bilateral cellular malformation, a heterotopia, positioned within the white matter of the corpus callosum of both hemispheres. Immunohistochemical techniques were used to determine that this heterotopia primarily consists of neurons born between gestational d 17-19 and exhibits a dose-dependent increase in size with decreases in thyroid hormone levels. Importantly, this structural abnormality is evident at modest levels of maternal thyroid hormone insufficiency ( approximately 45% reductions in T(4) with no change in T(3)), persists in adult offspring despite a return to normal hormonal status, and is dramatically reduced in size with prenatal thyroid hormone replacement. Developmental exposure to methimazole, another goitrogen, also induced formation of this heterotopia. Whereas the long-term consequence of this cortical malformation on brain function remains to be determined, the presence of the heterotopia underscores the critical role thyroid hormone plays in brain development during the prenatal period and provides a new model in which to study mechanisms of cortical development and cortical dysplasia.

Periventricular nodular heterotopia: A challenge for epilepsy surgery

Pharmacoresistant focal epilepsies due to periventricular nodular heterotopia are a diagnostic and therapeutic challenge because of the need of invasive presurgical diagnostics and the selection of an optimal surgical approach. Invasive investigations in previous studies showed that focal epileptic activity can be correlated predominantly either with one of the nodular heterotopia or with neocortical epileptogenic zones distant to the periventricular nodules. Up to now, invasive recordings were required for localization of epileptic activity and its correlation to heterotopia. The following case presentation reports on a non-invasive approach using magnetic source imaging (MSI) combined with intraoperative ECoG. MSI combines preoperative data from magnetic resonance imaging (MRI) with magnetoencephalography (MEG). The MSI data for definition of the localization of the epileptic activity and functional important areas were coregistered with the intraoperative high-field-MRI and diffusion tensor imaging-based fiber tracking (DTI) of the visual pathway using a neuronavigational system. A neuronavigation-guided surgical resection of the epileptogenic area was performed leaving the heterotopia and the visual tract fibers intact. Postoperatively preservation of the visual fields was documented and the frequency of seizures was markedly reduced.

Epidemiology of hemimegalencephaly: a case series and review

Hemimegalencephaly (HME) is a congenital brain malformation characterized by unilateral enlargement of the cerebral hemisphere. Clinically, HME is typically associated with hemiparesis, psychomotor retardation, and intractable seizures usually apparent soon after birth. HME is often an isolated finding, but it has been described as an occasional feature of a large number of syndromes, many of which may not be readily identified at birth. There are a multitude of case series and reports of HME in the English literature; however, there is no comprehensive, unbiased, detailed survey characterizing the proportion of cases of HME that are associated with a syndrome. We performed a retrospective study of all cases of HME seen at our institution from 1990 to 2003. Of the 15 cases of HME identified, 53% (8/15) were non-syndromic and 47% (7/15) of the cases were associated with a known or suspected genetic syndrome. In patients with syndromic HME, many of the syndromic features were not readily discernible at birth or in early infancy. It is, therefore, imperative to continually evaluate any infant with HME for signs and symptoms of these and other syndromes. Knowing the relative differential diagnosis will lead to a more comprehensive evaluation, improvement in expectant management, and appropriate counseling of families before considering radical surgical options such as hemispherectomy.

Layer positioning of late-born cortical interneurons is dependent on Reelin but not p35 signaling

We tested the response of interneurons to the absence of Reelin signaling or p35 in the mouse neocortex. We provide three independent strands of evidence to demonstrate that layering of late-born (but not early-born) interneurons is regulated by Reelin signaling. First, early-born and late-born interneurons behaved differently in mice lacking Reelin or disabled 1 (Dab1). Early-born interneurons showed layer inversion, whereas late-born interneurons did not demonstrate layer inversion but were randomly distributed across the cortex. Second, in p35 mutant brains (in which Reelin signaling is intact), late-born interneurons are appropriately positioned in the upper layers despite the malpositioning of all other cortical neurons in these mice. Third, transplanted late-born interneuron precursors (wild type) into Dab1(-/-) cortices showed appropriate upper layer segregation. Together, these results indicate that, in the absence of Reelin signaling, late-born interneurons fail to laminate properly, and this is restored in an environment in which Reelin signaling is intact. These studies suggest different mechanisms for the stratification of cortical interneurons. Whereas the early-born interneurons appear to be associated with projection neuron layering, late-born interneurons rely on Reelin signaling for their correct lamination.