A volumetric MRI study of the hippocampus and the parahippocampal region after unilateral medial temporal lobe resection

Remote effects of temporal lobe epilepsy surgery: Long-term morphological changes after surgical resection

OBJECTIVE

Epilepsy surgery is an effective treatment for drug-resistant patients. However, how different surgical approaches affect long-term brain structure remains poorly characterized. Here, we present a semiautomated method for quantifying structural changes after epilepsy surgery and compare the remote structural effects of two approaches, anterior temporal lobectomy (ATL), and selective amygdalohippocampectomy (SAH).

METHODS

We studied 36 temporal lobe epilepsy patients who underwent resective surgery (ATL = 22, SAH = 14). All patients received same-scanner MR imaging preoperatively and postoperatively (mean 2 years). To analyze postoperative structural changes, we segmented the resection zone and modified the Advanced Normalization Tools (ANTs) longitudinal cortical pipeline to account for resections. We compared global and regional annualized cortical thinning between surgical treatments.

RESULTS

Across procedures, there was significant cortical thinning in the ipsilateral insula, fusiform, pericalcarine, and several temporal lobe regions outside the resection zone as well as the contralateral hippocampus. Additionally, increased postoperative cortical thickness was seen in the supramarginal gyrus. Patients treated with ATL exhibited greater annualized cortical thinning compared with SAH cases (ATL: -0.08 ± 0.11 mm per year, SAH: -0.01 ± 0.02 mm per year, t = 2.99, P = 0.006). There were focal postoperative differences between the two treatment groups in the ipsilateral insula (P = 0.039, corrected). Annualized cortical thinning rates correlated with preoperative cortical thickness (r = 0.60, P < 0.001) and had weaker associations with age at surgery (r = -0.33, P = 0.051) and disease duration (r = -0.42, P = 0.058).

SIGNIFICANCE

Our evidence suggests that selective procedures are associated with less cortical thinning and that earlier surgical intervention may reduce long-term impacts on brain structure.

Longitudinal hippocampal diffusion-weighted imaging and T2 relaxometry demonstrate regional abnormalities which are stable and predict subfield pathology in temporal lobe epilepsy

OBJECTIVE

High-resolution (1 mm isotropic) diffusion tensor imaging (DTI) of the hippocampus in temporal lobe epilepsy (TLE) patients has shown patterns of hippocampal subfield diffusion abnormalities, which were consistent with hippocampal sclerosis (HS) subtype on surgical histology. The objectives of this longitudinal imaging study were to determine the stability of focal hippocampus diffusion changes over time in TLE patients, compare diffusion and quantitative T2 abnormalities of the sclerotic hippocampus, and correlate presurgical mean diffusivity (MD) and T2 maps with postsurgical histology.

METHODS

Nineteen TLE patients and 19 controls underwent two high-resolution (1 mm isotropic) DTI and 1.1 × 1.1 × 1 mm³  T2 relaxometry scans (in a subset of 16 TLE patients and 9 controls) of the hippocampus at 3T, with a 2.6 ± 0.8 year inter-scan interval. Within-participant hippocampal volume, MD and T2 were compared between the scans. Contralateral hippocampal changes 2.3 ± 1.0 years after surgery and ipsilateral preoperative MD maps versus postoperative subfield histopathology were evaluated in eight patients who underwent surgical resection of the hippocampus.

RESULTS

Reduced volume and elevated MD and T2 of sclerotic hippocampi remained unchanged between longitudinal scans. Focal regions of elevated MD and T2 in bilateral hippocampi of HS TLE were detected consistently at both scans. Regions of high MD and T2 correlated and remained consistent over time. Volume, MD, and T2 remained unchanged in postoperative contralateral hippocampus. Regional elevations of MD identified subfield neuron loss on postsurgical histology with 88% sensitivity and 88% specificity. Focal T2 elevations identified subfield neuron loss with 75% sensitivity and 88% specificity.

SIGNIFICANCE

Diffusion and T2 abnormalities in ipsilateral and contralateral hippocampi remained unchanged between the scans suggesting permanent microstructural alterations. MD and T2 demonstrated good sensitivity and specificity to detect hippocampal subfield neuron loss on postsurgical histology, supporting the potential that high-resolution hippocampal DTI and T2 could be used to diagnose HS subtype before surgery.

Deep learning-based automated segmentation of resection cavities on postsurgical epilepsy MRI

Accurate segmentation of surgical resection sites is critical for clinical assessments and neuroimaging research applications, including resection extent determination, predictive modeling of surgery outcome, and masking image processing near resection sites. In this study, an automated resection cavity segmentation algorithm is developed for analyzing postoperative MRI of epilepsy patients and deployed in an easy-to-use graphical user interface (GUI) that estimates remnant brain volumes, including postsurgical hippocampal remnant tissue. This retrospective study included postoperative T1-weighted MRI from 62 temporal lobe epilepsy (TLE) patients who underwent resective surgery. The resection site was manually segmented and reviewed by a neuroradiologist (JMS). A majority vote ensemble algorithm was used to segment surgical resections, using 3 U-Net convolutional neural networks trained on axial, coronal, and sagittal slices, respectively. The algorithm was trained using 5-fold cross validation, with data partitioned into training (N = 27) testing (N = 9), and validation (N = 9) sets, and evaluated on a separate held-out test set (N = 17). Algorithm performance was assessed using Dice-Sørensen coefficient (DSC), Hausdorff distance, and volume estimates. Additionally, we deploy a fully-automated, GUI-based pipeline that compares resection segmentations with preoperative imaging and reports estimates of resected brain structures. The cross-validation and held-out test median DSCs were 0.84 ± 0.08 and 0.74 ± 0.22 (median ± interquartile range) respectively, which approach inter-rater reliability between radiologists (0.84-0.86) as reported in the literature. Median 95 % Hausdorff distances were 3.6 mm and 4.0 mm respectively, indicating high segmentation boundary confidence. Automated and manual resection volume estimates were highly correlated for both cross-validation (r = 0.94, p < 0.0001) and held-out test subjects (r = 0.87, p < 0.0001). Automated and manual segmentations overlapped in all 62 subjects, indicating a low false negative rate. In control subjects (N = 40), the classifier segmented no voxels (N = 33), <50 voxels (N = 5), or a small volumes<0.5 cm3 (N = 2), indicating a low false positive rate that can be controlled via thresholding. There was strong agreement between postoperative hippocampal remnant volumes determined using automated and manual resection segmentations (r = 0.90, p < 0.0001, mean absolute error = 6.3 %), indicating that automated resection segmentations can permit quantification of postoperative brain volumes after epilepsy surgery. Applications include quantification of postoperative remnant brain volumes, correction of deformable registration, and localization of removed brain regions for network modeling.

Expression of Circ_Satb1 Is Decreased in Mesial Temporal Lobe Epilepsy and Regulates Dendritic Spine Morphology

Mesial temporal lobe epilepsy (mTLE) is a chronic disease characterized by recurrent seizures that originate in the temporal lobes of the brain. Anti-epileptic drugs (AEDs) are the standard treatment for managing seizures in mTLE patients, but are frequently ineffective. Resective surgery is an option for some patients, but does not guarantee a postoperative seizure-free period. Therefore, further insight is needed into the pathogenesis of mTLE to enable the design of new therapeutic strategies. Circular RNAs (circRNAs) have been identified as important regulators of neuronal function and have been implicated in epilepsy. However, the mechanisms through which circRNAs contribute to epileptogenesis remain unknown. Here, we determine the circRNA transcriptome of the hippocampus and cortex of mTLE patients by using RNA-seq. We report 333 differentially expressed (DE) circRNAs between healthy individuals and mTLE patients, of which 23 circRNAs displayed significant adjusted p-values following multiple testing correction. Interestingly, hippocampal expression of circ_Satb1, a circRNA derived from special AT-rich sequence binding protein 1 (SATB1), is decreased in both mTLE patients and in experimental epilepsy. Our work shows that circ_Satb1 displays dynamic patterns of neuronal expression in vitro and in vivo. Further, circ_Satb1-specific knockdown using CRISPR/CasRx approaches in hippocampal cultures leads to defects in dendritic spine morphology, a cellular hallmark of mTLE. Overall, our results identify a novel epilepsy-associated circRNA with disease-specific expression and previously unidentified cellular effects that are relevant for epileptogenesis.

Structural and functional reorganization of contralateral hippocampus after temporal lobe epilepsy surgery

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Postoperative changes of contralateral hippocampus in temporal lobe epilepsy.

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No obvious hippocampal volume change was observed after successful surgery.

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Surgical manipulation may lead to a transient functional connectivity reduction.

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Increased functional connectivity mostly involved bilateral frontal regions.

Objective

To explore the structural and functional reorganization of contralateral hippocampus in patients with unilateral mesial temporal lobe epilepsy (mTLE) who achieved seizure-freedom after anterior temporal lobectomy (ATL).

Methods

We obtained high-resolution structural MRI and resting-state functional MRI data in 28 unilateral mTLE patients and 29 healthy controls. Patients were scanned before and three and 24 months after surgery while controls were scanned only once. Hippocampal gray matter volume (GMV) and functional connectivity (FC) were assessed.

Results

No obvious GMV changes were observed in contralateral hippocampus before and after successful surgery. Before surgery, ipsilateral hippocampus showed increased FC with ipsilateral insula (INS) and temporoparietal junction (TPJ), but decreased FC with widespread bilateral regions, as well as contralateral hippocampus. After successful ATL, contralateral hippocampus showed: (1) decreased FC with ipsilateral INS at three months follow-up, without further changes; (2) decreased FC with ipsilateral TPJ, postcentral gyrus and rolandic operculum at three months, with an obvious increase at 24 months follow-up; (3) increased FC with bilateral medial prefrontal cortex (MPFC) and superior frontal gyrus (SFG) at three months follow-up, without further changes.

Conclusions

Successful ATL may not lead to an obvious structural reorganization in contralateral hippocampus. Surgical manipulation may lead to a transient FC reduction of contralateral hippocampus. Increased FC between contralateral hippocampus and bilateral MPFC and SFG may be related to postoperative functional remodeling.

Establishing Surface Correspondence for Post-surgical Cortical Thickness Changes in Temporal Lobe Epilepsy

In pre- and post-surgical surface shape analysis, establishing shape correspondence is necessary to investigate the postoperative surface changes. However, structural absence after the operation accompanies focal non-rigid changes, which leads to challenges in existing surface registration methods. In this paper, we present a fully automatic particle-based method to establish surface correspondence that can handle partial structural abnormality in the temporal lobe resection. Our method optimizes the coordinates of points which are modeled as particles on surfaces in a hierarchical way to reduce a chance of being trapped in a local minimum during the optimization. In the experiments, we evaluate the effectiveness of our method in comparison with conventional spherical registration (FreeSurfer) on two scenarios: cortical thickness changes in healthy controls within a short scan-rescan time window and patients with temporal lobe resection. The post-surgical scan is acquired at least 1 year after the presurgical scan. In region of interest-wise (ROI-wise) analysis, no changes on cortical thickness are found in both methods on the healthy control group. In patients, since there is no ground truth available, we instead investigated the disagreement between our method and FreeSurfer. We see poorly matched ROIs and large cortical thickness changes using FreeSurfer. On the contrary, our method shows well-matched ROIs and subtle cortical thickness changes. This suggests that the proposed method can establish a stable shape correspondence, which is not fully captured in a conventional spherical registration.

Quantitative brain imaging analysis of neurological syndromes associated with anti-GAD antibodies

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The pattern of cortical atrophy is present throughout all anti-GAD phenotypes.

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The radiomic features correctly classify anti-GAD patients versus healthy subjects.

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The different neurological anti-GAD phenotypes should be considered as a continuum.

Neurological disorders associated with anti-glutamic acid decarboxylase (GAD) autoimmunity are rare and include a variety of neurological syndromes: stiff-person syndrome, cerebellar ataxia or limbic encephalitis. The diagnosis remains challenging due to the variety of symptoms and normal brain imaging.

The morphological MRI of 26 patients (T1-weighted and Fluid-attenuated inversion recovery (FLAIR)-weighted images) was analyzed at the initial stage of diagnosis, matched by age and sex to 26 healthy subjects. We performed a vertex-wise analysis using a generalized linear model, adjusting by age, to compare the brain cortical thickness of both populations. In addition, we used a voxel-based morphometry of cerebellum thickness obtained by CEREbellum Segmentation (CERES), as well as the hippocampus volumetry comparison using HIPpocampus subfield Segmentation (HIPS). Finally, we extracted 62 radiomics features using LifeX to assess the classification performance using a random forest model to identify an anti-GAD related MRI.

The results suggest a peculiar profile of atrophy in patients with anti-GAD, with a significant atrophy in the temporal and frontal lobes (adjusted p-value < 0.05), and a focal cerebellar atrophy of the V-lobule, independently of the anti-GAD phenotype. Finally, the MRIs from anti-GAD patients were correctly classified when compared to the control group, with an area under the curve (AUC) of 0.98.

This study suggests a particular pattern of cortical atrophy throughout all anti-GAD phenotypes. These results reinforce the notion that the different neurological anti-GAD phenotypes should be considered as a continuum due to their similar cortical thickness profiles.

Preservation of Memory Despite Unresected Contralateral Hippocampal Volume Loss After Resection of Hippocampal Sclerosis in Seizure-Free Patients

OBJECTIVE

To determine postoperative long-term changes of hippocampal volume (HV) correlating with cognitive functions in patients who underwent surgery for hippocampal sclerosis with postoperative freedom from seizures.

METHODS

We studied 1.5T magnetic resonance imaging before and after surgery in 24 patients (mean ± SD age, 36.9 ± 11.0 years) with hippocampal sclerosis. We performed serial magnetic resonance imaging at 6 months to 1 year, 1-2 years, 2-3 years, and 3-5 years postoperatively. We compared HVs of 24 patients with HVs of 14 age-matched control subjects. We analyzed correlations between consecutive HVs and seizure duration and age at surgery. We compared consecutive changes in HVs between dominant and nondominant hemispheres with concurrent cognitive functions.

RESULTS

Preoperative HVs of unresected contralateral hippocampus were significantly smaller than HVs of control subjects (P < 0.01). Unresected contralateral HV changes compared with preoperative HVs were -3.6% ± 6.9%, -2.3% ± 8.5%, -3.6% ± 10.2% (P < 0.05), and -5.0% ± 9.5% (P < 0.05) at consecutive postoperative periods. Largest change in HVs at 3-5 years was significantly correlated with older age at surgery (P < 0.05). Unresected contralateral dominant 14 HVs remained consistently smaller than nondominant 10 HVs up to 5 years with statistical significance (P < 0.05). Verbal memory was preserved in 14 patients with unresected contralateral smaller dominant hippocampus.

CONCLUSIONS

In seizure-free patients after hippocampal sclerosis resection , unresected contralateral HV significantly declined with older age at surgery. Visual memory was preserved regardless of side and volume loss. Despite significantly reduced HVs, verbal memory was preserved with the unresected contralateral dominant hippocampus. Earlier surgical intervention may have lower potential risk for memory decline secondary to postoperative HV loss.

Three-Dimensional Probabilistic Maps of Mesial Temporal Lobe Structures in Children and Adolescents' Brains

The hippocampus and the adjacent perirhinal, entorhinal, temporopolar, and parahippocampal cortices are interconnected in a hierarchical MTL system crucial for memory processes. A probabilistic description of the anatomical location and spatial variability of MTL cortices in the child and adolescent brain would help to assess structure-function relationships. The rhinal sulcus (RS) and the collateral sulcus (CS) that border MTL cortices and influence their morphology have never been described in these populations. In this study, we identified the aforementioned structures on magnetic resonance images of 38 healthy subjects aged 7-17 years old. Relative to sulcal morphometry in the MTL, we showed RS-CS conformation is an additional factor of variability in the MTL that is not explained by other variables such as age, sex and brain volume; with an innovative method using permutation testing of the extrema of structures of interest, we showed that RS-SC conformation was not associated with differences of location of MTL sulci. Relative to probabilistic maps, we offered for the first time a systematic mapping of MTL structures in children and adolescent, mapping all the structures of the MTL system while taking sulcal morphology into account. Our results, with the probabilistic maps described here being freely available for download, will help to understand the anatomy of this region and help functional and clinical studies to accurately test structure-function hypotheses in the MTL during development. Free access to MTL pediatric atlas: http://neurovault.org/collections/2381/.

Influences of temporal lobe epilepsy and temporal lobe resection on olfaction

Although temporal lobe epilepsy (TLE) and resection (TLR) impact olfactory eloquent brain structures, their influences on olfaction remain enigmatic. We sought to more definitively assess the influences of TLE and TLR on olfaction using three well-validated olfactory tests and measuring  the tests' associations with the volume of numerous temporal lobe brain structures. The University of Pennsylvania Smell Identification Test and an odor detection threshold test were administered to 71 TLE patients and 71 age- and sex-matched controls; 69 TLE patients and controls received an odor discrimination/memory test. Fifty-seven patients and 57 controls were tested on odor identification and threshold before and after TLR; 27 patients and 27 controls were similarly tested for odor detection/discrimination. Scores were compared using analysis of variance and correlated with pre- and post-operative volumes of the target brain structures. TLE was associated with bilateral deficits in all test measures. TLR further decreased function on the side ipsilateral to resection. The hippocampus and other structures were smaller on the focus side of the TLE subjects. Although post-operative volumetric decreases were evident in most measured brain structures, modest contralateral volumetric increases were observed in some cases. No meaningful correlations were evident pre- or post-operatively between the olfactory test scores and the structural volumes. In conclusion, we demonstrate that smell dysfunction is clearly a key element of both TLE and TLR, impacting odor identification, detection, and discrimination/memory. Whether our novel finding of significant post-operative increases in the volume of brain structures contralateral to the resection side reflects plasticity and compensatory processes requires further study.

Long-term postoperative atrophy of contralateral hippocampus and cognitive function in unilateral refractory MTLE with unilateral hippocampal sclerosis

OBJECTIVE

This study aimed to evaluate long-term atrophy in contralateral hippocampal volume after surgery for unilateral MTLE, as well as the cognitive outcome for patients submitted to either selective transsylvian amygdalohippocampectomy (SelAH) or anterior temporal lobe resection (ATL).

METHODS

We performed a longitudinal study of 47 patients with MRI signs of unilateral hippocampal sclerosis (23 patients with right-sided hippocampal sclerosis) who underwent surgical treatment for MTLE. They underwent preoperative/postoperative high-resolution MRI as well as neuropsychological assessment for memory and estimated IQ. To investigate possible changes in the contralateral hippocampus of patients, we included 28 controls who underwent two MRIs at long-term intervals.

RESULTS

The volumetry using preoperative MRI showed significant hippocampal atrophy ipsilateral to the side of surgery when compared with controls (p<0.0001) but no differences in contralateral hippocampal volumes. The mean postoperative follow-up was 8.7 years (± 2.5 SD; median=8.0). Our patients were classified as Engel I (80%), Engel II (18.2%), and Engel III (1.8%). We observed a small but significant reduction in the contralateral hippocampus of patients but no volume changes in controls. Most of the patients presented small declines in both estimated IQ and memory, which were more pronounced in patients with left TLE and in those with persistent seizures. Different surgical approaches did not impose differences in seizure control or in cognitive outcome.

CONCLUSIONS

We observed small declines in cognitive scores with most of these patients, which were worse in patients with left-sided resection and in those who continued to suffer from postoperative seizures. We also demonstrated that manual volumetry can reveal a reduction in volume in the contralateral hippocampus, although this change was mild and could not be detected by visual analysis. These new findings suggest that dynamic processes continue to act after the removal of the hippocampus, and further studies with larger groups may help in understanding the underlying mechanisms.

Modulation of encoding and retrieval by recollection and familiarity: mapping the medial temporal lobe networks

Medial temporal lobe (MTL) structures are crucial for episodic memory. However, it remains unclear how these structures are involved in encoding and retrieval processes as a function of recollection and familiarity. To better elucidate MTL organization of these two processes, we implemented an fMRI protocol in which both encoding and retrieval of words were scanned in 21 healthy adults. During encoding, subjects were requested to bind each word to an emotional context (pleasant or unpleasant). Retrieval consisted of a Remember/Know procedure in two stages: first, subjects had to recognize the word, followed by the retrieval of the associated emotional context. fMRI data were reported in eight manually delineated MTL regions of interest (in the head, body and tail of the hippocampus, the entorhinal, perirhinal and parahippocampal cortices, the amygdala and the temporopolar cortex). Results obtained in 19 subjects showed four MTL patterns of activity consisting in activations of parahippocampal cortex and hippocampus in episodic encoding and retrieval and perirhinal cortex involvement in familiarity. These results are in line with the Binding of Item and Context (BIC) model predictions. Additionally, some new findings specified the familiarity MTL neural substrate by showing precise entorhinal activations during retrieval of familiar words, as well as hippocampal and amygdala deactivations in encoding of these words. Finally, we emphasize that among all four memory processes, episodic retrieval (recollection effect) was the only one eliciting strong bilateral activations in all MTL structures. These results should be considered for future studies on MTL dysfunction in patients with temporal lobe damage.

Comprehensive brain MRI segmentation in high risk preterm newborns

Most extremely preterm newborns exhibit cerebral atrophy/growth disturbances and white matter signal abnormalities on MRI at term-equivalent age. MRI brain volumes could serve as biomarkers for evaluating the effects of neonatal intensive care and predicting neurodevelopmental outcomes. This requires detailed, accurate, and reliable brain MRI segmentation methods. We describe our efforts to develop such methods in high risk newborns using a combination of manual and automated segmentation tools. After intensive efforts to accurately define structural boundaries, two trained raters independently performed manual segmentation of nine subcortical structures using axial T2-weighted MRI scans from 20 randomly selected extremely preterm infants. All scans were re-segmented by both raters to assess reliability. High intra-rater reliability was achieved, as assessed by repeatability and intra-class correlation coefficients (ICC range: 0.97 to 0.99) for all manually segmented regions. Inter-rater reliability was slightly lower (ICC range: 0.93 to 0.99). A semi-automated segmentation approach was developed that combined the parametric strengths of the Hidden Markov Random Field Expectation Maximization algorithm with non-parametric Parzen window classifier resulting in accurate white matter, gray matter, and CSF segmentation. Final manual correction of misclassification errors improved accuracy (similarity index range: 0.87 to 0.89) and facilitated objective quantification of white matter signal abnormalities. The semi-automated and manual methods were seamlessly integrated to generate full brain segmentation within two hours. This comprehensive approach can facilitate the evaluation of large cohorts to rigorously evaluate the utility of regional brain volumes as biomarkers of neonatal care and surrogate endpoints for neurodevelopmental outcomes.

Association of the severity of cortical damage with the occurrence of spontaneous seizures and hyperexcitability in an animal model of posttraumatic epilepsy

Posttraumatic epilepsy is a common consequence of traumatic brain injury in humans. Major predictors for the development of posttraumatic epilepsy include the severity of injury and occurrence of cortical contusions. The effect of the size or location of the cortical lesion on the risk of epileptogenesis, however, is poorly understood. Here, we investigated the extent and location of cortical damage and its association with a lowered seizure threshold and the occurrence of spontaneous seizures in rats (n=77) that had experienced moderate or severe lateral fluid-percussion brain injury (FPBI) 12 months earlier. Spontaneous seizures were detected with video-electroencephalography monitoring and a lowered seizure threshold was determined based on a pentylenetetrazol (PTZ) test. Cortical atrophy was evaluated from thionin-stained sections using the Cavalieri estimation in four different experiments in which rats developed either spontaneous recurrent seizures (i.e., epilepsy) or a lowered seizure threshold. Our data show that damage to the cortex ipsilateral to the injury was more severe and extended more caudally in epileptic animals than in those without epilepsy (p<0.05 and p<0.001 for 2 independent experiments). Further, the extent of the cortical damage correlated positively with chronically increased hyperexcitability (number of spikes in PTZ test) in animals with traumatic brain injury (r=-0.54, p<0.05; r=-0.72, p<0.01 for 2 independent experiments). Specifically, cortical lesions located at the level of the perirhinal, entorhinal, and postrhinal cortices were associated with a lowered seizure threshold and seizures. The severity of the cortical injury did not correlate with the severity of hippocampal damage. These findings indicate that, like in humans, the severity of cortical injury correlates with epileptogenesis and epilepsy in an experimental model of posttraumatic epilepsy.

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.

Stereotactic radiofrequency amygdalohippocampectomy in the treatment of mesial temporal lobe epilepsy

PURPOSE

Minimally invasive percutaneous single trajectory stereotactic radiofrequency amygdalohippocampectomy was used to treat mesial temporal lobe epilepsy (MTLE). The aim of the study was to evaluate complications and effectiveness of this procedure.

MATERIALS AND METHODS

A group of 51 patients with MTLE was treated using stereotactic thermo-lesion of amygdalohippocampal complex under local anaesthesia. The target was reached through the occipital approach with a single trajectory using MRI stereotactic localisation. Thermocoagulation of the amygdalohippocampal complex was planned according to the individual anatomy of each patient. Amygdalohippocampectomy was performed using a string electrode with a 10-mm active tip, and 16-38 lesions (median = 25) were performed in all patients along the 30- to 45-mm trajectory (median = 35) in the amygdalohippocampal complex.

RESULTS

The procedure was well tolerated by all patients with no severe permanent morbidity; meningitis was recorded in two patients (4%), hematoma was detected in four patients, clinically insignificant in three of them, and one patient required temporary ventricular drainage (2%). Thirty-two patients were followed up over at least 2 years, and the clinical outcomes were evaluated by Engel's classification; 25 of them (78%) were Engel I, five (16%) were Engel II, and two (6%) were Engel IV.

CONCLUSIONS

Stereotactic amygdalohippocampectomy is a minimally invasive procedure with low morbidity and good results that can be the method of choice in selected patients with MTLE.

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.

Role of the medial temporal lobe in time estimation in the range of minutes

This study examined the role of medial temporal lobe structures in verbal estimation and production of time intervals. Left medial temporal lobe lesions produced deficits in both tasks, whereas right medial temporal lobe lesions only disturbed time production. Although both tasks require adequate use of chronometric units, they seem to be subserved by distinct cognitive processing and to depend on different neural substrates. Verbal estimation of intervals in retrospect seems to depend mainly on contextual memory, and production of intervals depends more specifically on the mental load devoted to time. These findings, documenting for the first time the role of each temporal lobe in duration estimation within the range of minutes, are discussed in light of memory-based and attentional models of time.