MRI volume loss of subcortical structures in unilateral temporal lobe epilepsy

Quantitative susceptibility mapping identifies hippocampal and other subcortical grey matter tissue composition changes in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is associated with widespread brain alterations. Using quantitative susceptibility mapping (QSM) alongside transverse relaxation rate (R 2 * ), we investigated regional brain susceptibility changes in 36 patients with left-sided (LTLE) or right-sided TLE (RTLE) secondary to hippocampal sclerosis, and 27 healthy controls (HC). We compared three susceptibility calculation methods to ensure image quality. Correlations of susceptibility andR 2 * with age of epilepsy onset, frequency of focal-to-bilateral tonic-clonic seizures (FBTCS), and neuropsychological test scores were examined. Weak-harmonic QSM (WH-QSM) successfully reduced noise and removed residual background field artefacts. Significant susceptibility increases were identified in the left putamen in the RTLE group compared to the LTLE group, the right putamen and right thalamus in the RTLE group compared to HC, and a significant susceptibility decrease in the left hippocampus in LTLE versus HC. LTLE patients who underwent epilepsy surgery showed significantly lower left-versus-right hippocampal susceptibility. SignificantR 2 * changes were found between TLE and HC groups in the amygdala, putamen, thalamus, and in the hippocampus. Specifically, decreased R2 * was found in the left and right hippocampus in LTLE and RTLE, respectively, compared to HC. Susceptibility andR 2 * were significantly correlated with cognitive test scores in the hippocampus, globus pallidus, and thalamus. FBTCS frequency correlated positively with ipsilateral thalamic and contralateral putamen susceptibility and withR 2 * in bilateral globi pallidi. Age of onset was correlated with susceptibility in the hippocampus and putamen, and withR 2 * in the caudate. Susceptibility andR 2 * changes observed in TLE groups suggest selective loss of low-myelinated neurons alongside iron redistribution in the hippocampi, predominantly ipsilaterally, indicating QSM's sensitivity to local pathology. Increased susceptibility andR 2 * in the thalamus and putamen suggest increased iron content and reflect disease severity.

Brain but not serum BDNF levels are associated with structural alterations in the hippocampal regions in patients with drug-resistant mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy is the most common type of focal epilepsy, imposing a significant burden on the health care system worldwide. Approximately one-third of patients with this disease who do not adequately respond to pharmacotherapy are considered drug-resistant subjects. Despite having some clues of how such epileptic activity and resistance to therapy emerge, coming mainly from preclinical models, we still witness a scarcity of human data. To narrow this gap, in this study, we aimed to estimate the relationship between hippocampal and serum levels of brain-derived neurotrophic factor (BDNF), one of the main and most widely studied neurotrophins, and hippocampal subfield volumes in patients with drug-resistant mesial temporal epilepsy undergoing neurosurgical treatment. We found that hippocampal (but not serum) BDNF levels were negatively correlated with the contralateral volumes of the CA1 and CA4 subfields, presubiculum, subiculum, dentate gyrus, and molecular layer of the hippocampus. Taken together, these findings are generally in accordance with existing data, arguing for a proepileptic nature of BDNF effects in the hippocampus and related brain structures.

Event-based modeling in temporal lobe epilepsy demonstrates progressive atrophy from cross-sectional data

OBJECTIVE

Recent work has shown that people with common epilepsies have characteristic patterns of cortical thinning, and that these changes may be progressive over time. Leveraging a large multicenter cross-sectional cohort, we investigated whether regional morphometric changes occur in a sequential manner, and whether these changes in people with mesial temporal lobe epilepsy and hippocampal sclerosis (MTLE-HS) correlate with clinical features.

METHODS

We extracted regional measures of cortical thickness, surface area, and subcortical brain volumes from T1-weighted (T1W) magnetic resonance imaging (MRI) scans collected by the ENIGMA-Epilepsy consortium, comprising 804 people with MTLE-HS and 1625 healthy controls from 25 centers. Features with a moderate case-control effect size (Cohen d ≥ .5) were used to train an event-based model (EBM), which estimates a sequence of disease-specific biomarker changes from cross-sectional data and assigns a biomarker-based fine-grained disease stage to individual patients. We tested for associations between EBM disease stage and duration of epilepsy, age at onset, and antiseizure medicine (ASM) resistance.

RESULTS

In MTLE-HS, decrease in ipsilateral hippocampal volume along with increased asymmetry in hippocampal volume was followed by reduced thickness in neocortical regions, reduction in ipsilateral thalamus volume, and finally, increase in ipsilateral lateral ventricle volume. EBM stage was correlated with duration of illness (Spearman ρ = .293, p = 7.03 × 10-16 ), age at onset (ρ = -.18, p = 9.82 × 10-7 ), and ASM resistance (area under the curve = .59, p = .043, Mann-Whitney U test). However, associations were driven by cases assigned to EBM Stage 0, which represents MTLE-HS with mild or nondetectable abnormality on T1W MRI.

SIGNIFICANCE

From cross-sectional MRI, we reconstructed a disease progression model that highlights a sequence of MRI changes that aligns with previous longitudinal studies. This model could be used to stage MTLE-HS subjects in other cohorts and help establish connections between imaging-based progression staging and clinical features.

Topographic divergence of atypical cortical asymmetry and atrophy patterns in temporal lobe epilepsy

Temporal lobe epilepsy, a common drug-resistant epilepsy in adults, is primarily a limbic network disorder associated with predominant unilateral hippocampal pathology. Structural MRI has provided an in vivo window into whole-brain grey matter structural alterations in temporal lobe epilepsy relative to controls, by either mapping (i) atypical inter-hemispheric asymmetry; or (ii) regional atrophy. However, similarities and differences of both atypical asymmetry and regional atrophy measures have not been systematically investigated. Here, we addressed this gap using the multisite ENIGMA-Epilepsy dataset comprising MRI brain morphological measures in 732 temporal lobe epilepsy patients and 1418 healthy controls. We compared spatial distributions of grey matter asymmetry and atrophy in temporal lobe epilepsy, contextualized their topographies relative to spatial gradients in cortical microstructure and functional connectivity calculated using 207 healthy controls obtained from Human Connectome Project and an independent dataset containing 23 temporal lobe epilepsy patients and 53 healthy controls and examined clinical associations using machine learning. We identified a marked divergence in the spatial distribution of atypical inter-hemispheric asymmetry and regional atrophy mapping. The former revealed a temporo-limbic disease signature while the latter showed diffuse and bilateral patterns. Our findings were robust across individual sites and patients. Cortical atrophy was significantly correlated with disease duration and age at seizure onset, while degrees of asymmetry did not show a significant relationship to these clinical variables. Our findings highlight that the mapping of atypical inter-hemispheric asymmetry and regional atrophy tap into two complementary aspects of temporal lobe epilepsy-related pathology, with the former revealing primary substrates in ipsilateral limbic circuits and the latter capturing bilateral disease effects. These findings refine our notion of the neuropathology of temporal lobe epilepsy and may inform future discovery and validation of complementary MRI biomarkers in temporal lobe epilepsy.

Magnetic resonance imaging (MRI) volumetry in children with nonlesional epilepsy, does it help?

Background

Epilepsy is a chronic condition characterized by repeated spontaneous seizures. It affects up to 1% of the population worldwide. Children with magnetic resonance imaging (MRI) negative (or “nonlesional”) focal epilepsy constitute the most challenging pharmacoresistant group undergoing pre-neurosurgical evaluation. Volumetric magnetic resonance imaging (VMRI) is a non-invasive brain imaging technique done to measure the volume and structure of specific regions of the brain. It is useful for many things, but primarily for discovering atrophy (wasting away of body tissue) and measuring its progression. The aim of this study is to assess role of volumetric magnetic resonance imaging in evaluation of nonlesional childhood epilepsy in which no specific findings detected in conventional MRI.

Results

There were 20 children with normal MRI brain volumetry (33.3%) and 40 children (66.6%) with abnormal MRI brain volumetry.

Grey matter volume in the abnormal group was significantly higher (P value was 0.001*) than the normal group (mean ± S.D 934.04 ± 118.12 versus 788.57 ± 57.71 respectively). White matter volume in the abnormal group was significantly smaller (P value was < 0.0001*) than in the normal group (mean ± S.D 217.79 ± 65.22 versus 418.07 ± 103.76 respectively). Right hippocampus CA4-DG volume in the abnormal volume group was found to be significantly smaller (P value < 0.0001*) than that of the normal group volume (mean ± S.D 0.095 ± 0.04 versus 0.32 ± 0.36 respectively). Right hippocampus subiculum volume in the abnormal volume group were found to be significantly smaller (P value was < 0.0001*) than that of the normal group volume (mean ± S.D 0.42 ± 0.11 versus 0.84 ± 0.09 respectively). Thalamus volume in the abnormal group was significantly smaller (P value 0.048*) than in the normal group (mean ± S.D 10.235 ± 3.22 versus 11.82 ± 0.75 respectively). Right thalamus was significantly smaller (P value was 0.028*) than in the normal group (mean ± S.D 5.01 ± 1.62 versus 5.91 ± 0.39 respectively). The sensitivity of the right hippocampus subiculum volume and right hippocampus CA4-DG was 100%. The sensitivity of white matter volume and grey matter volume and thalamus was 85% and 75% and 55% respectively. The specificity of the right hippocampus subiculum volume and right hippocampus CA4-DG was 90% and 90% respectively. The specificity of the right hippocampus subiculum volume and right hippocampus CA4-DG and grey matter volume and white matter volume and total hippocampus and thalamus was 100%. The specificity of brain volume was 60%. The accuracy of the right hippocampus subiculum volume and right hippocampus CA4-DG was 100%. The specificity of white matter volume, grey matter volume, thalamus, total hippocampus, and brain volume was 97%, 87%, 65%, 61%, and 57% respectively.

Conclusion

Volumetric magnetic resonance imaging is a promising imaging technique that can provide assistance in evaluation of nonlesional pharmacoresistant childhood epilepsy.

The Cross Talk between Underlying Mechanisms of Multiple Sclerosis and Epilepsy May Provide New Insights for More Efficient Therapies

Despite the significant differences in pathological background of neurodegenerative diseases, epileptic seizures are a comorbidity in many disorders such as Huntington disease (HD), Alzheimer's disease (AD), and multiple sclerosis (MS). Regarding the last one, specifically, it has been shown that the risk of developing epilepsy is three to six times higher in patients with MS compared to the general population. In this context, understanding the pathological processes underlying this connection will allow for the targeting of the common and shared pathological pathways involved in both conditions, which may provide a new avenue in the management of neurological disorders. This review provides an outlook of what is known so far about the bidirectional association between epilepsy and MS.

People with mesial temporal lobe epilepsy have altered thalamo-occipital brain networks

While temporal lobe epilepsy (TLE) is a focal epilepsy, previous work demonstrates that TLE causes widespread brain-network disruptions. Impaired visuospatial attention and learning in TLE may be related to thalamic arousal nuclei connectivity. Our prior preliminary work in a smaller patient cohort suggests that patients with TLE demonstrate abnormal functional connectivity between central lateral (CL) thalamic nucleus and medial occipital lobe. Others have shown pulvinar connectivity disturbances in TLE, but it is incompletely understood how TLE affects pulvinar subnuclei. Also, the effects of epilepsy surgery on thalamic functional connectivity remains poorly understood. In this study, we examine the effects of TLE on functional connectivity of two key thalamic arousal-nuclei: lateral pulvinar (PuL) and CL. We evaluate resting-state functional connectivity of the PuL and CL in 40 patients with TLE and 40 controls using fMRI. In 25 patients, postoperative images (>1 year) were also compared with preoperative images. Compared to controls, patients with TLE exhibit loss of normal positive connectivity between PuL and lateral occipital lobe (p < 0.05), and a loss of normal negative connectivity between CL and medial occipital lobe (p < 0.01, paired t-tests). FMRI amplitude of low-frequency fluctuation (ALFF) in TLE trended higher in ipsilateral PuL (p = 0.06), but was lower in the lateral occipital (p < 0.01) and medial occipital lobe in patients versus controls (p < 0.05, paired t-tests). More abnormal ALFF in the ipsilateral lateral occipital lobe is associated with worse preoperative performance on Rey Complex Figure Test Immediate (p < 0.05, r = 0.381) and Delayed scores (p < 0.05, r = 0.413, Pearson's Correlations). After surgery, connectivity between PuL and lateral occipital lobe remains abnormal in patients (p < 0.01), but connectivity between CL and medial occipital lobe improves and is no longer different from control values (p > 0.05, ANOVA, post hoc Fischer's LSD). In conclusion, thalamic arousal nuclei exhibit abnormal connectivity with occipital lobe in TLE, and some connections may improve after surgery. Studying thalamic arousal centers may help explain distal network disturbances in TLE.

Deep brain stimulation of the anterior nuclei of the thalamus relieves basal ganglia dysfunction in monkeys with temporal lobe epilepsy

Aims

Deep brain stimulation of the anterior nuclei of the thalamus (ANT‐DBS) is effective in temporal lobe epilepsy (TLE). Previous studies have shown that the basal ganglia are involved in seizure propagation in TLE, but the effects of ANT‐DBS on the basal ganglia have not been clarified.

Methods

ANT‐DBS was applied to monkeys with kainic acid–induced TLE using a robot‐assisted system. Behavior was monitored continuously. Immunofluorescence analysis and Western blotting were used to estimate protein expression levels in the basal ganglia and the effects of ANT stimulation.

Results

The seizure frequency decreased after ANT‐DBS. D1 and D2 receptor levels in the putamen and caudate were significantly higher in the ANT‐DBS group than in the epilepsy (EP) model. Neuronal loss and apoptosis were less severe in the ANT‐DBS group. Glutamate receptor 1 (GluR1) in the nucleus accumbens (NAc) shell and globus pallidus internus (GPi) increased in the EP group but decreased after ANT‐DBS. γ‐Aminobutyric acid receptor A (GABA_A‐R) decreased and glutamate decarboxylase 67 (GAD67) increased in the GPi of the EP group, whereas the reverse tendencies were observed after ANT‐DBS.

Conclusion

ANT‐DBS exerts neuroprotective effects on the caudate and putamen, enhances D1 and D2 receptor expression, and downregulates GPi overactivation, which enhanced the antiepileptic function of the basal ganglia.

Cerebrocerebellar structural covariance in temporal lobe epilepsy with hippocampal sclerosis

PURPOSE

The purpose of the study was to evaluate cerebral morphological changes in temporal lobe epilepsy with hippocampal sclerosis (TLE-HS) and their relationship to the cerebellum.

METHODS

The study cohort included 21 patients with intractable TLE-HS (14 left-sided, 7 right-sided) and 38 healthy controls (HC). All patients later underwent anteromedial temporal lobe resection. All subjects were examined using a 1.5-T magnetic resonance imaging (MRI). Volumes of distinct cerebral and cerebellar structures were measured using voxel-based morphometry. The structural covariance of temporal lobe structures, insula, and thalamus with cerebellar substructures was examined using partial least squares regression.

RESULTS

Morphological changes were more significant in the group with left TLE-HS when comparing left-sided with right-sided structures as well as when comparing patients with controls. The gray matter volume (GMV) of the temporal lobe structures was smaller ipsilaterally to the seizure onset side in most cases. There was a significant amygdala enlargement contralateral to the side of hippocampal sclerosis in both patients with right and left TLE-HS as compared with controls. Selected vermian structures in patients with left but not right TLE-HS had significantly larger GMV than the identical substructures in controls. The structural covariance differed significantly between patients with left and right TLE-HS as compared with HC. The analysis revealed significant negative covariance between anterior vermis and mesial temporal structures in the group with left TLE-HS. No significance was observed for the group with right TLE-HS.

CONCLUSION

There is significant asymmetry in the GMV of cerebral and cerebellar structures in patients with TLE-HS. Morphological changes are distinctly more pronounced in patients with left TLE-HS. The observed structural covariance between the cerebellum and supratentorial structures in TLE-HS suggests associations beyond the mesial temporal lobe structures and thalamus.

NR4A1 Methylation Associated Multimodal Neuroimaging Patterns Impaired in Temporal Lobe Epilepsy

DNA hypermethylation has been widely observed in temporal lobe epilepsy (TLE), in which NR4A1 knockdown has been reported to be able to alleviate seizure severity in mouse model, while the underlying methylation-imaging pathway modulated by aberrant methylation levels of NR4A1 remains to be clarified in patients with TLE. Here, using multi-site canonical correlation analysis with reference, methylation levels of NR4A1 in blood were used as priori to guide fusion of three MRI features: functional connectivity (FC), fractional anisotropy (FA), and gray matter volume (GMV) for 56 TLE patients and 65 healthy controls. Post-hoc correlations were further evaluated between the identified NR4A1-associated brain components and disease onset. Results suggested that higher NR4A1 methylation levels in TLE were related with impaired temporal-cerebellar and occipital-cerebellar FC strength, lower FA in cingulum (hippocampus), and reduced GMV in putamen, temporal pole, and cerebellum. Moreover, findings were also replicated well in both patient subsets with either right TLE or left TLE only. Particularly, right TLE patients showed poorer cognitive abilities and more severe brain impairment than left TLE patients, especially more reduced GMV in thalamus. In summary, this work revealed a potential imaging-methylation pathway modulated by higher NR4A1 methylation in TLE via data mining, which may impact the above-mentioned multimodal brain circuits and was also associated with earlier disease onset and more cognitive deficits.

Longitudinal MRI Evaluation of Ischemic Stroke in the Basal Ganglia of a Rhesus Macaque (Macaca mulatta) with Seizures

An adult rhesus macaque developed seizures after the induction of ischemic stroke. Initially, on the day of surgery, a focal ischemic lesion was present exclusively in the right caudate nucleus. By 48 h after stroke induction, the lesion had extended into the putamen, when a seizure was observed. Our report highlights the temporal changes in infarction of unilateral basal ganglia after acute stroke and the accompanying clinical symptoms. This unusual case may provide additional information regarding the involvement of the basal ganglia in seizures, given that prior case reports and studies usually have not described the temporal and spatial evolution of the lesion before clinical symptoms emerge.

Grey matter volume in healthy and epileptic beagles using voxel-based morphometry - a pilot study

BACKGROUND

One of the most common chronic neurological disorders in dogs is idiopathic epilepsy (IE) diagnosed as epilepsy without structural changes in the brain. In the current study the hypothesis should be proven that subtle grey matter changes occur in epileptic dogs. Therefore, magnetic resonance (MR) images of one dog breed (Beagles) were used to obtain an approximately uniform brain shape. Local differences in grey matter volume (GMV) were compared between 5 healthy Beagles and 10 Beagles with spontaneously recurrent seizures (5 dogs with IE and 5 dogs with structural epilepsy (SE)), using voxel-based morphometry (VBM). T1W images of all dogs were prepared using Amira 6.3.0 for brain extraction, FSL 4.1.8 for registration and SPM12 for realignment. After creation of tissue probability maps of cerebrospinal fluid, grey and white matter from control images to segment all extracted brains, GM templates for each group were constructed to normalize brain images for parametric statistical analysis, which was achieved using SPM12.

RESULTS

Epileptic Beagles (IE and SE Beagles) displayed statistically significant reduced GMV in olfactory bulb, cingulate gyrus, hippocampus and cortex, especially in temporal and occipital lobes. Beagles with IE showed statistically significant decreased GMV in olfactory bulb, cortex of parietal and temporal lobe, hippocampus and cingulate gyrus, Beagles with SE mild statistically significant GMV reduction in temporal lobe (p < 0.05; family- wise error correction).

CONCLUSION

These results suggest that, as reported in epileptic humans, focal reduction in GMV also occurs in epileptic dogs. Furthermore, the current study shows that VBM analysis represents an excellent method to detect GMV differences of the brain between a healthy dog group and dogs with epileptic syndrome, when MR images of one breed are used.

Adhesio interthalamica and cavum septum pellucidum in mesial temporal lobe epilepsy

The absence of the adhesio interthalamica (AI; also called interthalamic adhesion or massa intermedia) and the presence of a large cavum septum pellucidum (CSP) later in life have been related to neurodevelopmental alterations and have not been systematically investigated in epilepsy to date. This study carried out a MRI evaluation of the AI and CSP in a large sample with mesial temporal lobe epilepsy (MTLE). A total of 179 patients, classified according to the side of the epileptogenic focus, and 156 age- and sex-balanced healthy controls were assessed. Between-group comparisons of the prevalence and length of both AI and CSP were conducted. Neuropsychological assessments were also performed in 160 MTLE patients. The patients exhibited reduction in the AI prevalence (P < 0.05; FDR-uncorrected) and length (P < 0.05; FDR-corrected) when compared to controls. Patients without AI showed lower scores in a proportion of neuropsychological tests than patients with AI. No CSP differences were found between MTLE patients and controls. These results support that AI anomalies have clinical significance in MTLE, as well as indicate that neurodevelopmental alterations may be implicated in this disorder.

A meta-analysis on progressive atrophy in intractable temporal lobe epilepsy: Time is brain?

OBJECTIVE

It remains unclear whether drug-resistant temporal lobe epilepsy (TLE) is associated with cumulative brain damage, with no expert consensus and no quantitative syntheses of the available evidence.

METHODS

We conducted a systematic review and meta-analysis of MRI studies on progressive atrophy, searching PubMed and Ovid MEDLINE databases for cross-sectional and longitudinal quantitative MRI studies on drug-resistant TLE.

RESULTS

We screened 2,976 records and assessed eligibility of 248 full-text articles. Forty-two articles met the inclusion criteria for quantitative evaluation. We observed a predominance of cross-sectional studies, use of different clinical indices of progression, and high heterogeneity in age-control procedures. Meta-analysis of 18/1 cross-sectional/longitudinal studies on hippocampal atrophy (n = 979 patients) yielded a pooled effect size of r = -0.42 for ipsilateral atrophy related to epilepsy duration (95% confidence interval [CI] -0.51 to -0.32; p < 0.0001; I² = 65.22%) and r = -0.35 related to seizure frequency (95% CI -0.47 to -0.22; p < 0.0001; I² = 61.97%). Sensitivity analyses did not change the results. Narrative synthesis of 25/3 cross-sectional/longitudinal studies on whole brain atrophy (n = 1,504 patients) indicated that >80% of articles reported duration-related progression in extratemporal cortical and subcortical regions. Detailed analysis of study design features yielded low to moderate levels of evidence for progressive atrophy across studies, mainly due to dominance of cross-sectional over longitudinal investigations, use of diverse measures of seizure estimates, and absence of consistent age control procedures.

CONCLUSIONS

While the neuroimaging literature is overall suggestive of progressive atrophy in drug-resistant TLE, published studies have employed rather weak designs to directly demonstrate it. Longitudinal multicohort studies are needed to unequivocally differentiate aging from disease progression.

Planimetry investigation of the corpus callosum in temporal lobe epilepsy patients

Objective:

To evaluate the effects of temporal lobe epilepsy (TLE) on corpus callosum (CC) morphometry in patients with TLE.

Methods:

This retrospective study was conducted at the Faculty of Medicine, Tekirdag Namik Kemal University, Tekirdag, Turkey between November 2010 and December 2013. The epileptic syndrome diagnosis was based on International League Against Epilepsy criteria, and this study was conducted on the MRIs of 25 epilepsy patients and 25 control subjects. We classified the patients according to their duration of epilepsy <10 and ≥10 years. The projection area length (PAL) of the CC was also estimated. Total brain volumes (TBV) were measured on CT images.

Results:

The mean values of TBV for patients with TLE and the control group were not statistically different, but the CC PAL values were statistically different. The mean CC PAL values of under and over 25 years of age in patients with TLE were statistically different. The mean values of TBV of under and over 10 years duration of TLE were small statistically, but the CC PAL values were statistically different.

Conclusion:

The results indicate a clear influence of TLE on the structure of the CC rather than TBV.

Hemispheric asymmetries in cortical and subcortical anatomy

Previous research studies have reported many hemispherical asymmetries in cortical and subcortical anatomy, but only a subset of findings is consistent across studies. Here, we used improved Freesurfer-based automated methods to analyse the properties of the cortex and seven subcortical structures in 138 young adult subjects. Male and female subjects showed similar hemispheric asymmetries in gyral and sulcal structures, with many areas associated with language processing enlarged in the left hemisphere (LH) and a number of areas associated with visuospatial processing enlarged in the right hemisphere (RH). In addition, we found greater (non-directional) cortical asymmetries in subjects with larger brains. Asymmetries in subcortical structures included larger LH volumes of thalamus, putamen and globus pallidus and larger RH volumes of the cerebellum and the amygdala. We also found significant correlations between the subcortical structural volumes, particularly of the thalamus and cerebellum, with cortical area. These results help to resolve some of the inconsistencies in previous studies of hemispheric asymmetries in brain anatomy.

Quantitative MRI in refractory temporal lobe epilepsy: relationship with surgical outcomes

Medically intractable temporal lobe epilepsy (TLE) remains a serious health problem. Across treatment centers, up to 40% of patients with TLE will continue to experience persistent postoperative seizures at 2-year follow-up. It is unknown why such a large number of patients continue to experience seizures despite being suitable candidates for resective surgery. Preoperative quantitative MRI techniques may provide useful information on why some patients continue to experience disabling seizures, and may have the potential to develop prognostic markers of surgical outcome. In this article, we provide an overview of how quantitative MRI morphometric and diffusion tensor imaging (DTI) data have improved the understanding of brain structural alterations in patients with refractory TLE. We subsequently review the studies that have applied quantitative structural imaging techniques to identify the neuroanatomical factors that are most strongly related to a poor postoperative prognosis. In summary, quantitative imaging studies strongly suggest that TLE is a disorder affecting a network of neurobiological systems, characterized by multiple and inter-related limbic and extra-limbic network abnormalities. The relationship between brain alterations and postoperative outcome are less consistent, but there is emerging evidence suggesting that seizures are less likely to remit with surgery when presurgical abnormalities are observed in the connectivity supporting brain regions serving as network nodes located outside the resected temporal lobe. Future work, possibly harnessing the potential from multimodal imaging approaches, may further elucidate the etiology of persistent postoperative seizures in patients with refractory TLE. Furthermore, quantitative imaging techniques may be explored to provide individualized measures of postoperative seizure freedom outcome.

Increasing structural atrophy and functional isolation of the temporal lobe with duration of disease in temporal lobe epilepsy

BACKGROUND

Due to pharmacoresistant seizures and the underutilization of surgical treatments, a large number of temporal lobe epilepsy (TLE) patients experience seizures for years or decades. The goal of this study was to generate a predictive model of duration of disease with the least number of parameters possible in order to identify and quantify the significant volumetric and functional indicators of TLE progression.

METHODS

Two cohorts of subjects including 12 left TLE, 21 right TLE and 20 healthy controls (duration = 0) were imaged on a 3T MRI scanner using high resolution T1-weighted structural MRI and 20 min of resting functional MRI scanning. Multivariate linear regression methods were used to compute a predictive model of duration of disease using 49 predictors including functional connectivity and gray matter volumes computed from these images.

RESULTS

No model developed from the full set of data accurately predicted the duration of disease across the entire range from 3 to 50 years. We then performed the regression on 35 subjects with durations of disease in the range 10 to 35 years. The resulting predictive model showed that longer durations were associated with reductions in functional connectivity from the ipsilateral temporal lobe to the contralateral temporal lobe, precuneus and mid cingulate, and with decreases in volume of the ipsilateral hippocampus and pallidum.

CONCLUSIONS

Functional and volumetric parameters accurately predicted duration of disease in TLE. The findings suggest that TLE is associated with a gradual functional isolation and significant progressive structural atrophy of the ipsilateral temporal lobe over years of duration in the range of 10-35 years. Furthermore, these changes can also be detected in the contralateral hemisphere in these patients, but to a lesser degree.

The consequences of refractory epilepsy and its treatment

Seizures in some 30% to 40% of patients with epilepsy fail to respond to antiepileptic drugs or other treatments. While much has been made of the risks of new drug therapies, not enough attention has been given to the risks of uncontrolled and progressive epilepsy. This critical review summarizes known risks associated with refractory epilepsy, provides practical clinical recommendations, and indicates areas for future research. Eight international epilepsy experts from Europe, the United States, and South America met on May 4, 2013, to present, review, and discuss relevant concepts, data, and literature on the consequences of refractory epilepsy. While patients with refractory epilepsy represent the minority of the population with epilepsy, they require the overwhelming majority of time, effort, and focus from treating physicians. They also represent the greatest economic and psychosocial burdens. Diagnostic procedures and medical/surgical treatments are not without risks. Overlooked, however, is that these risks are usually smaller than the risks of long-term, uncontrolled seizures. Refractory epilepsy may be progressive, carrying risks of structural damage to the brain and nervous system, comorbidities (osteoporosis, fractures), and increased mortality (from suicide, accidents, sudden unexpected death in epilepsy, pneumonia, vascular disease), as well as psychological (depression, anxiety), educational, social (stigma, driving), and vocational consequences. Adding to this burden is neuropsychiatric impairment caused by underlying epileptogenic processes ("essential comorbidities"), which appears to be independent of the effects of ongoing seizures themselves. Tolerating persistent seizures or chronic medicinal adverse effects has risks and consequences that often outweigh risks of seemingly "more aggressive" treatments. Future research should focus not only on controlling seizures but also on preventing these consequences.

Evaluation of subcortical grey matter abnormalities in patients with MRI-negative cortical epilepsy determined through structural and tensor magnetic resonance imaging

Background

Although many studies have found abnormalities in subcortical grey matter (GM) in patients with temporal lobe epilepsy or generalised epilepsies, few studies have examined subcortical GM in focal neocortical seizures. Using structural and tensor magnetic resonance imaging (MRI), we evaluated subcortical GM from patients with extratemporal lobe epilepsy without visible lesion on MRI. Our aims were to determine whether there are structural abnormalities in these patients and to correlate the extent of any observed structural changes with clinical characteristics of disease in these patients.

Methods

Twenty-four people with epilepsy and 29 age-matched normal subjects were imaged with high-resolution structural and diffusion tensor MR scans. The patients were characterised clinically by normal brain MRI scans and seizures that originated in the neocortex and evolved to secondarily generalised convulsions. We first used whole brain voxel-based morphometry (VBM) to detect density changes in subcortical GM. Volumetric data, values of mean diffusivity (MD) and fractional anisotropy (FA) for seven subcortical GM structures (hippocampus, caudate nucleus, putamen, globus pallidus, nucleus accumbens, thalamus and amygdala) were obtained using a model-based segmentation and registration tool. Differences in the volumes and diffusion parameters between patients and controls and correlations with the early onset and progression of epilepsy were estimated.

Results

Reduced volumes and altered diffusion parameters of subcortical GM were universally observed in patients in the subcortical regions studied. In the patient-control group comparison of VBM, the right putamen, bilateral nucleus accumbens and right caudate nucleus of epileptic patients exhibited a significantly decreased density Segregated volumetry and diffusion assessment of subcortical GM showed apparent atrophy of the left caudate nucleus, left amygdala and right putamen; reduced FA values for the bilateral nucleus accumbens; and elevated MD values for the left thalamus, right hippocampus and right globus pallidus A decreased volume of the nucleus accumbens consistently related to an early onset of disease. The duration of disease contributed to the shrinkage of the left thalamus.

Conclusions

Patients with neocortical seizures and secondary generalisation had smaller volumes and microstructural anomalies in subcortical GM regions. Subcortical GM atrophy is relevant to the early onset and progression of epilepsy.

Does epilepsy cause a reversion to immature function?

Seizures have variable effects on brain. Numerous studies have examined the consequences of seizures, in light of the way that these may alter the susceptibility of the brain to seizures, promote epileptogenesis, or functionally alter brain leading to seizure-related comorbidities. In many -but not all- situations, seizures shift brain function towards a more immature state, promoting the birth of newborn neurons, altering the dendritic structure and neuronal connectivity, or changing neurotransmitter signaling towards more immature patterns. These effects depend upon many factors, including the seizure type, age of seizure occurrence, sex, and brain region studied. Here we discuss some of these findings proposing that these seizure-induced immature features do not simply represent rejuvenation of the brain but rather a de-synchronization of the homeostatic mechanisms that were in place to maintain normal physiology, which may contribute to epileptogenesis or the cognitive comorbidities.

Neurobehavioral comorbidities of pediatric epilepsies are linked to thalamic structural abnormalities

PURPOSE

Neurobehavioral comorbidities are common in pediatric epilepsy with enduring adverse effects on functioning, but their neuroanatomic underpinning is unclear. Striatal and thalamic abnormalities have been associated with childhood-onset epilepsies, suggesting that epilepsy-related changes in the subcortical circuit might be associated with the comorbidities of children with epilepsy. We aimed to compare subcortical volumes and their relationship with age in children with complex partial seizures (CPS), childhood absence epilepsy (CAE), and healthy controls (HC). We examined the shared versus unique structural-functional relationships of these volumes with behavior problems, intelligence, language, peer interaction, and epilepsy variables in these two epilepsy syndromes.

METHODS

We investigated volumetric differences of caudate, putamen, pallidum, and thalamus in children with CPS (N = 21), CAE (N = 20), and HC (N = 27). Study subjects underwent structural magnetic resonance imaging (MRI), intelligence, and language testing. Parent-completed Child Behavior Checklists provided behavior problem and peer interaction scores. We examined the association of age, intelligence quotient (IQ), language, behavioral problems, and epilepsy variables with subcortical volumes that were significantly different between the children with epilepsy and HC.

KEY FINDINGS

Both children with CPS and CAE exhibited significantly smaller left thalamic volume compared to HC. In terms of developmental trajectory, greater thalamic volume was significantly correlated with increasing age in children with CPS and CAE but not in HC. With regard to the comorbidities, reduced left thalamic volumes were related to more social problems in children with CPS and CAE. Smaller left thalamic volumes in children with CPS were also associated with poor attention, lower IQ and language scores, and impaired peer interaction.

SIGNIFICANCE

Our study is the first to directly compare and detect shared thalamic structural abnormalities in children with CPS and CAE. These findings highlight the vulnerability of the thalamus and provide important new insights on its possible role in the neurobehavioral comorbidities of childhood-onset epilepsy.

Evaluation of corpus callosum morphometry in patients with mesial temporal lobe epilepsy with hippocampal sclerosis

PURPOSE

The purpose of the study was to evaluate the effects of mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) on corpus callosum (CC) morphometry in large and pathologically proven MTLE-HS patients.

METHODS

We measured certain CC dimensions in 103 patients and 33 healthy controls using in vivo magnetic resonance imaging. In particular, we compared the two groups in relation to the clinical (localization of the HS, duration of epilepsy, frequency of seizures and length of seizures) and demographical (age, gender, handedness) features. Students' t test, two-way ANOVA and Spearman test were used for statistical analysis.

RESULTS

There was no significant difference between CC morphometry with respect to age and handedness among patients. The differences between the genders, however, were significant favouring longer diameters in males. We found significant decrease in the dimensions of the genu, body, isthmus and splenium of the CC in the MTLE-HS group, but there was no reduction in the size of the rostrum.

CONCLUSIONS

This general reduction in the size of the CC except for the rostrum was thought to be the result of cortical atrophy secondary to the disease. Concerning the preserved rostral part of the CC, it was thought that the fibers of the frontal lobe pass through different pathways than the tracts in the rostrum.

Volume estimation of the thalamus using freesurfer and stereology: consistency between methods

Freely available automated MR image analysis techniques are being increasingly used to investigate neuroanatomical abnormalities in patients with neurological disorders. It is important to assess the specificity and validity of automated measurements of structure volumes with respect to reliable manual methods that rely on human anatomical expertise. The thalamus is widely investigated in many neurological and neuropsychiatric disorders using MRI, but thalamic volumes are notoriously difficult to quantify given the poor between-tissue contrast at the thalamic gray-white matter interface. In the present study we investigated the reliability of automatically determined thalamic volume measurements obtained using FreeSurfer software with respect to a manual stereological technique on 3D T1-weighted MR images obtained from a 3 T MR system. Further to demonstrating impressive consistency between stereological and FreeSurfer volume estimates of the thalamus in healthy subjects and neurological patients, we demonstrate that the extent of agreeability between stereology and FreeSurfer is equal to the agreeability between two human anatomists estimating thalamic volume using stereological methods. Using patients with juvenile myoclonic epilepsy as a model for thalamic atrophy, we also show that both automated and manual methods provide very similar ratios of thalamic volume loss in patients. This work promotes the use of FreeSurfer for reliable estimation of global volume in healthy and diseased thalami.

Epilepsy as progressive disorders: what is the evidence that can guide our clinical decisions and how can neuroimaging help?

There is evidence that some types of epilepsy progress over time, and an important part of this knowledge has derived from neuroimaging studies. Different authors have demonstrated structural damage more pronounced in individuals with a longer duration of epilepsy, and others have been able to quantify this progression over time. However, others have failed to demonstrate progression possibly due to the heterogeneity of individuals evaluated. Currently, temporal lobe epilepsy associated with hippocampal sclerosis is regarded as a progressive disorder. Conversely, for other types of epilepsy, the evidence is not so clear. The causes of this damage progression are also unknown although there is consistent evidence that seizure is one of the mechanisms. The conflicting data about epilepsy progression can be a challenge for clinical decisions for an individual patient. Studies with homogenous groups and longer follow-up are necessary for appropriate conclusions about the real burden of damage progression in epilepsies, and neuroimaging will be essential in this context.

Epileptogenesis in the developing brain

The neonatal brain has poorly developed GABAergic circuits, and in many of them GABA is excitatory, favoring ictogenicity. Frequently repeated experimental seizures impair brain development in an age-dependent manner. At critical ages, they delay developmental milestones, permanently lower seizure thresholds, and can cause very specific cognitive and learning deficits, such as the permanent impairment of neuronal spatial maps. Some types of experimental status epilepticus cause neuronal necrosis and apoptosis, and are followed by chronic epilepsy with spontaneous recurrent seizures, others appear relatively benign, so that seizure-induced neuronal injury and epileptogenesis are highly age-, seizure model-, and species-dependent. Experimental febrile seizures can be epileptogenic, and hyperthermia aggravates both neuronal injury and epileptogenicity. Antiepileptic drugs, the mainstay of treatment, have major risks of their own, and can, at therapeutic or near-therapeutic doses, trigger neuronal apoptosis, which is also age-, drug-, cell type-, and species-dependent. The relevance of these experimental results to human disease is still uncertain, but while their brains are quite different, the basic biology of neurons in rodents and humans is strikingly similar. Further research is needed to elucidate the molecular mechanisms of epileptogenesis and of seizure- or drug-induced neuronal injury, in order to prevent their long-term consequences.

Ictal dystonia and secondary generalization in temporal lobe seizures: a video-EEG study

The aim of this study was to determine whether the occurrence of unilateral ictal limb dystonia (ID) during complex partial seizures (CPS) reduces the possibility of contralateral propagation (CP) and secondary generalization (SG) in patients with temporal lobe epilepsy (TLE). We assessed 216 seizures recorded in 33 patients with pharmacoresistant TLE. All patients underwent video-EEG telemetry prior to surgical treatment with good postoperative outcomes (Engel I). Ictal limb dystonia was observed in 16 of the 33 patients (48%) and 58 of the 216 seizures (26.8%). We found highly significant differences in the frequency of SG between seizures with ID and seizures without ID (2/58 vs. 41/158; 3.45% vs. 25.95%; p<0.001). Contralateral propagation was seen in 13 of the 57 analyzed seizures with ID compared to 85 of the 158 seizures without ID (22.8% vs. 53.8%; p<0.001). Among the CPS without SG, we found that the mean duration of seizures with ID was significantly longer than the duration of seizures without ID (81.66±40.10 vs. 68.88±25.01 s; p=0.011). Our findings that CP and SG occur less often in patients with ID, yet the duration of CPS without SG is longer in patients with ID, suggest that the basal ganglia might inhibit propagation to the contralateral hemisphere but not ictal activity within the unilateral epileptic network.

Do the basal ganglia inhibit seizure activity in temporal lobe epilepsy?

There is substantial evidence in the literature that the basal ganglia (BG), namely the striatum and pallidum, are involved in temporal lobe epilepsy (TLE). The BG are probably not involved in elaborating clinical seizures, as they do not produce specific epileptiform activity and there is no evident change in the electrical activity in the BG immediately after seizure onset. The data we obtained by direct ictal recording in the BG [1,2], as well as a large body of experimental and clinical evidence reported by other groups, suggest an inhibitory role of the BG during temporal lobe seizures. The BG may have a remote influence on cortical oscillatory processes related to control of epileptic seizures via their feedback pathways to the cortex.

Voxel-based statistical analysis of fractional anisotropy and mean diffusivity in patients with unilateral temporal lobe epilepsy of unknown cause

PURPOSE

To determine regional alterations of fractional anisotropy (FA) and mean diffusivity (MD) in patients with magnetic resonance imaging (MRI)-negative temporal lobe epilepsy with unknown cause (TLEu) using diffusion tensor imaging (DTI) and voxel-based statistics (VBS).

METHODS

Ten patients with left TLEu and no abnormality on conventional MRI and 81 age-matched neurological healthy controls were studied. VBS analyses were used to compare FA and MD differences between patients and controls. All results were reported using stringent statistical thresholds corrected for multiple comparisons.

RESULTS

Patients with TLEu had widespread and bilateral reduction of white matter FA, encompassing the temporal lobes, entire corpus callosum, thalamus, and other regions relative to controls. Increased MD was more spatially limited in patients, but was also observed in the thalamus. FA of the putamen was significantly increased bilaterally in patients relative to controls, which correlated with increasing macroscopic atrophy of the putamen.

DISCUSSION

Water diffusion abnormalities are widespread and bilaterally distributed in patients with unilateral TLEu, which are beyond the resolution of conventional MRI. FA alterations are more widespread relative to MD alterations. This is the first study to show evidence of interrelated microscopic (ie, FA increase) and macroscopic (ie, atrophy) alterations of the putamen in patients with TLEu.

Extratemporal damage in temporal lobe epilepsy: magnetization transfer adds information to volumetric MR imaging

BACKGROUND AND PURPOSE

MTS is characterized by gliosis and atrophy of the hippocampus and related limbic structures. However, the damage is not limited to those structures with atrophy and has been reported in extratemporal regions. Because volumetric studies are nonspecific, the pathophysiology of the brain damage remains to be solved. MTI is an MR imaging technique more sensitive to subtle neuropathologic changes than conventional MR imaging. Here we combined MTI with VBM analysis to evaluate extratemporal damage in patients with TLE.

MATERIALS AND METHODS

We studied 23 healthy controls and 21 patients with TLE with mean ages, respectively, of 37.6 ± 10.9 and 38.6 ± 9.02 years. All subjects had a full clinical follow-up and MR imaging. We processed the images with VBM for volumetric analysis of WM and GM, as well as with voxel-based analysis of MTR for macromolecular integrity analysis.

RESULTS

In addition to MTR decrease in the temporal lobes, we found a significant decrease in GM and WM volumes. In the WM, the MTR decrease was correlated to volume loss detected by VBM, indicating that brain atrophy may explain part of the MTR decrease. We also found areas in which the MTR decrease was not associated with volume loss, suggesting an additional pathophysiologic process other than neuronal loss and atrophy underlying the MTR changes.

CONCLUSIONS

Our results support the hypothesis that there are widespread lesions in the brain, including the corpus callosum and the frontal lobe, affecting both GM and WM.

Microstructural and volumetric abnormalities of the putamen in juvenile myoclonic epilepsy

PURPOSE

Patients with juvenile myoclonic epilepsy (JME) show evidence of microstructural white matter (WM) damage of thalamocortical fiber tracts and changes of blood oxygen level dependent (BOLD) signal in a striatothalamocortical network. The objective of the present study was to investigate microstructural and volumetric alterations of the putamen in patients with JME using diffusion tensor imaging (DTI) and conventional magnetic resonance imaging (MRI).

METHODS

We performed DTI and MRI for 10 patients with JME and 59 age-matched neurologically healthy volunteers. Evaluation of microstructural damage was investigated using calculation of mean fractional anisotropy (FA) values in a priori regions of interest (ROIs) for the putamen, frontal lobe, and a thalamocortical region, after application of an improved eddy current correction method and a new statistical parametric mapping (SPM)-compatible toolbox incorporating intensive multicontrast FA image registration. Stereologic analysis on MRI was performed to estimate macroscopic volume of the putamen in both cerebral hemispheres for all subjects.

KEY FINDINGS

Relative to controls, patients had significantly reduced FA in the frontal lobe (p = 0.01) and thalamocortical fiber WM (p < 0.001). In contrast, putamen FA was bilaterally increased (p = 0.01) and correlated with decreasing putamen volume (r(2) = -0.63, p = 0.004) in patients only. Putamen FA correlated negatively with onset of JME (total: r(2) = -0.50, p = 0.01), duration of JME (r(2) = 0.52, p = 0.01), and thalamocortical fiber FA (r(2) = -0.47, p = 0.01).

SIGNIFICANCE

This is the first evidence of combined microstructural and macrostructural putamen abnormalities in patients with JME, with early age of onset and a longer duration of epilepsy being significant predictors for greater architectural alterations. These findings are consistent with studies indicating neurophysiologic abnormalities of frontostriatal networks in patients with JME, and may contribute to explain the frequent presentation of executive dysfunction in these patients. Confirmation and further exploration of the increase in putamen FA in patients with JME is required in larger samples.

Secondary Corpus Callosum Abnormalities Associated with Antiepileptic Drugs in Temporal Lobe Epilepsy

Epilepsy is more than a grey-matter disorder affecting large white matter connections of the brain with seizure generation and propagation. The mechanism for such changes remains unclear. The purpose of this study was to investigate the microstructural changes in the corpus callosum in temporal lobe epilepsy (TLE) patients and whether these abnormalities are related to antiepileptic drug (AED) therapy. Ten TLE patients receiving AED therapy, ten TLE patients with no therapy and ten controls were included in the study. The regions of interest in the corpus callosum were outlined to each Witelson region (WR). Fractional anisotrophy (FA), apparent diffusion coefficient (ADC), three main diffusivity values (λ1, λ2, λ3) and tractography were acquired from each WR. DTI indices of these tracts and each WR were compared between the three subject groups and correlates examined with clinical variables that included duration of epilepsy, gender, AED type and AED therapy exposure. In TLE subjects with receiving AED therapy significantly (p<0.05) decreased FA and increased ADC values of corpus callosum were obtained when compared to the other groups. There was no significant relationship between AED type and DTI indices. Analysis of eigen values in the splenium of corpus callosum (WR7) showed λ1 values were significantly decreased in relation to AED medication duration (p<0.05). FA values of rostrum and corpus showed a reduction with duration of epilepsy. TLE is associated with abnormal integrity of corpus callosum white matter tracts. AED therapy may cause additional damage on secondary degeneration and medication time effects especially on the splenium of corpus callosum.

Differences in corpus callosum volume and diffusivity between temporal and frontal lobe epilepsy

We analyzed volume and diffusivity measures of the corpus callosum (CC) in patients with temporal (TLE) and frontal (FLE) lobe epilepsy in comparison with healthy subjects. On high-resolution T1-weighted scans of 18 controls and 44 patients the volumes (cm(3)) of Witelson regions (WRs) and the entire CC were measured. The apparent diffusion coefficients (ADCs, 10(-5)mm(2)s(-1)) for the entire CC and three areas of interest were measured from co-registered ADC maps. The CC of patients with TLE and FLE, corrected for total brain volume, was smaller than that of controls. Patients' ADC values were higher than those of controls. Findings were significant for WR1, WR2, and WR6, the CC regions connecting the frontal and temporal lobes. Patients with FLE had smaller WR1 and higher ADC values; in patients with TLE, the findings were similar for WR6. Atrophy and increased diffusivity in subregions of the CC connecting homotopic contralateral cortical regions indicate anatomical abnormalities extending beyond the epileptogenic zone in FLE and TLE.

Update on neuroimaging in epilepsy

Neuroimaging in epilepsy is a very large and growing field. Researchers in this area have quickly adopted new methods, resulting in a lively literature. Basic features of common epilepsies are well known, but, outside of the specific area of epilepsy surgery evaluation, new methods evolving in the last few years have had limited new beneficial clinical impact. Here, an overview of the epilepsy neuroimaging literature of the last 5 years, with an emphasis on mesial temporal lobe epilepsy, idiopathic generalized epilepsies, presurgical evaluation and new developments in functional MRI is presented. The need for attention to clinical translation, as well as immediate opportunities and future trends in this field, are discussed.

Extrahippocampal integrity in temporal lobe epilepsy and cognition: thalamus and executive functioning

Chronic temporal lobe epilepsy (TLE) is characterized by the presence of extra-hippocampal brain abnormality and cognitive impairment in both memory and nonmemory domains. However, the link between structural integrity and cognition has not frequently been studied. Forty-six patients with TLE and 61 age-matched controls were studied to determine the predictive relationship between baseline thalamic volume and performance on measures of executive functioning evaluated 4 years later. As expected, the TLE group had lower baseline thalamic volumes than controls and also performed more poorly on measures of executive functioning. Total thalamic volume significantly predicted subsequent performance on all three measures of executive functioning. These findings were maintained when both hippocampal volume and frontal lobe volume were taken into account. These findings add to a growing literature demonstrating a link between extra-hippocampal volume abnormalities and cognitive functioning in TLE.

Reliability and validity of MRI-based automated volumetry software relative to auto-assisted manual measurement of subcortical structures in HIV-infected patients from a multisite study

The automated volumetric output of FreeSurfer and Individual Brain Atlases using Statistical Parametric Mapping (IBASPM), two widely used and well published software packages, was examined for accuracy and consistency relative to auto-assisted manual (AAM) tracings (i.e., manual correction of automated output) when measuring the caudate, putamen, amygdala, and hippocampus in the baseline scans of 120 HIV-infected patients (86.7% male, 47.3+/-6.3y.o., mean HIV duration 12.0+/-6.3years) from the NIH-funded HIV Neuroimaging Consortium (HIVNC) cohort. The data was examined for accuracy and consistency relative to auto-assisted manual tracing, and construct validity was assessed by correlating automated and AAM volumetric measures with relevant clinical measures of HIV progression. When results were averaged across all patients in the eight structures examined, FreeSurfer achieved lower absolute volume difference in five, higher sensitivity in seven, and higher spatial overlap in all eight structures. Additionally, FreeSurfer results exhibited less variability in all measures. Output from both methods identified discrepant correlations with clinical measures of HIV progression relative to AAM segmented data. Overall, FreeSurfer proved more effective in the context of subcortical volumetry in HIV-patients, particularly in a multisite cohort study such as this. These findings emphasize that regardless of the automated method used, visual inspection of segmentation output, along with manual correction if necessary, remains critical to ensuring the validity of reported results.

Current themes in neuroimaging of epilepsy: brain networks, dynamic phenomena, and clinical relevance

Brain scanning methods were first applied in patients with epilepsy more than 30years ago. A very substantial literature now exists in this field, which is exponentially increasing. Contemporary neuroimaging studies in epilepsy reflect new concepts in the epilepsies, as well as current methodological developments. In particular, this area is emphasising the role of networks in epileptogenicity, the existence of dynamic phenomena which can be captured by imaging, and is beginning to validate the implementation of neuroimaging in the clinic. Here, recent studies of the last 5years are reviewed, covering the full range of neuroimaging methods with SPECT, PET and MRI in epilepsy.

The emerging architecture of neuropsychological impairment in epilepsy

A new literature is now under way, one linking cognitive abnormalities directly to indices of structural, functional, metabolic, and other neurobiologic markers of cerebral integrity, independent of their association with clinical epilepsy characteristics. These trends are reviewed in this article. The focus is on temporal lobe epilepsy (TLE) as a model with which to address the core points because this form of localization-related epilepsy has been very carefully studied from both a cognitive and imaging standpoint. Some pertinent historical issues are touched on first, followed by more detailed reviews of the cognitive and neuroimaging abnormalities that have been found in TLE, followed by an overview of studies examining direct structure-function relationships in TLE and other epilepsies.

Neuroanatomical correlates of cognitive phenotypes in temporal lobe epilepsy

OBJECTIVE

Previous research characterized three cognitive phenotypes in temporal lobe epilepsy, each associated with a different profile of clinical seizure and demographic characteristics, total cerebral (gray, white, cerebrospinal fluid) and hippocampal volumes, and prospective cognitive trajectories. The objective of this investigation was to characterize in detail the specific neuroanatomical abnormalities associated with each cognitive phenotype.

METHODS

High-resolution MRI scans of healthy controls (n=53) and patients with temporal lobe epilepsy (n=55), grouped by cognitive phenotype (minimally impaired; memory impaired; memory, executive function, and speed impaired), were examined with respect to patterns of gray matter thickness throughout the cortical mantle, as well as volumes of subcortical structures, corpus callosum, and regions of the cerebellum.

RESULTS

Increasing abnormalities in temporal and extratemporal cortical thickness, volumes of subcortical structures (hippocampus, thalamus, basal ganglia), all regions of the corpus callosum, and bilateral cerebellar gray matter distinguish the cognitive phenotypes in a generally stepwise fashion. The most intact anatomy is observed in the minimally impaired epilepsy group and the most abnormal anatomy is evident in the epilepsy group with impairments in memory, executive function, and speed.

CONCLUSION

Empirically derived cognitive phenotypes are associated with the presence, severity, and distribution of anatomic abnormalities in widely distributed cortical, subcortical, callosal, and cerebellar networks.

The psychosocial impact of epilepsy in adults

Although defined by the presence of recurrent seizures, epilepsy can be so much more and can include a very wide range of difficulties in cognition, psychiatric status, and social adaptive functioning. These psychosocial complications of epilepsy have a long history, generating calls for action by national commissions, public health agencies, and special action groups which are briefly summarized here. Next, a brief overview of the prevalence of psychosocial complications of epilepsy in population-based and other representative is presented. Finally, with a focus on the onset and development of psychosocial difficulties, the following points are stressed: (1) neurobiological factors likely contribute to psychosocial problems in a major way, but currently this contribution is poorly understood, and (2) although neurobiological factors may prove important, they operate in a social setting, and therefore, a full accounting of the etiology, treatment, and prevention of psychosocial problems in epilepsy will require an integrated biopsychosocial model and life span perspective.

Atrophy of basal ganglia nuclei and negative symptoms in temporal lobe epilepsy

Recent work has identified the presence of negative symptoms in a subset of temporal lobe epilepsy (TLE) patients. The authors hypothesized that negative symptoms in TLE are associated with disruption in the mesolimbic system. Basal ganglia and anterior cingulate region of interest volumes were compared between 22 TLE patients with negative symptoms, 22 TLE patients without negative symptoms, and 22 comparison subjects. The negative symptom group showed significantly reduced volumes in the putamen and globus pallidus. It appears that these structures within the broader mesolimbic system contribute to the phenomenon of negative symptoms in TLE.

Secondary white matter degeneration of the corpus callosum in patients with intractable temporal lobe epilepsy: a diffusion tensor imaging study

Imaging changes in patients with focal epilepsy are not only seen in areas where seizures arise but often also in remote locations. The mechanism for such changes is unknown. We aimed to investigate whether patients with temporal lobe epilepsy (TLE) have microstructural changes involving the posterior portion of the corpus callosum (CC), where it links the temporal lobes, using presurgical diffusion tensor imaging (DTI) sequences. Ten patients with medically intractable TLE (two mesial TLE, eight neocortical TLE) who had seizure-free surgical outcomes were compared with 10 healthy controls. The regions of interest were outlined at each Witelson region (WR). Fractional anisotropy (FA), apparent diffusion coefficient (ADC) and three principal diffusivity values (lambda1, lambda2, lambda3) were determined in each WR. We performed tractography originating at each WR. In the TLE patients, the FA values were lower at the splenium of the corpus callosum (WR 7) compared to controls (p<0.05). Analysis of Eigen values in that location revealed that lambda1 values were decreased while lambda2 and lambda3 values were increased (p<0.05). Tractography revealed the connection between both temporal lobes via WR 7. In conclusion, decreased FA values with decreased lambda1 and increased lambda2 and lambda3 at the splenium of CC suggest that the pathologic changes, Wallerian degeneration, extend to the corpus callosum in TLE patients. Seizure-induced damage may cause secondary white matter degeneration along the tapetum and through the splenium of the corpus callosum, a potential pathway of spread in temporal lobe seizures.

Growing old with epilepsy: the neglected issue of cognitive and brain health in aging and elder persons with chronic epilepsy

The purpose of this review is to examine what is known about cognitive and brain aging in elders with chronic epilepsy. We contend that much remains to be learned about the ultimate course of cognition and brain structure in persons with chronic epilepsy and concern appears warranted. Individuals with chronic epilepsy are exposed to many risk factors demonstrated to be associated with abnormal cognitive and brain aging in the general population, with many of these risk factors present in persons with chronic epilepsy as early as midlife. We suggest that a research agenda be developed to systematically identify and treat known modifiable risk factors in order to protect and promote cognitive and brain health in aging and elder persons with chronic epilepsy.