Effect of seizure on hippocampus in mesial temporal lobe epilepsy and neocortical epilepsy: an MRS study

Detection of Hippocampal Subfield Asymmetry at 7T With Automated Segmentation in Epilepsy Patients With Normal Clinical Strength MRIs

While the etiology of hippocampal sclerosis (HS) in epilepsy patients remains unknown, distinct phenotypes of hippocampal subfield atrophy have been associated with different clinical presentations and surgical outcomes. The advent of novel techniques including ultra-high field 7T magnetic resonance imaging (MRI) and automated subfield volumetry have further enabled detection of hippocampal pathology in patients with epilepsy, however, studies combining both 7T MRI and automated segmentation in epilepsy patients with normal-appearing clinical MRI are limited. In this study, we present a novel application of the automated segmentation of hippocampal subfields (ASHS) software to determine subfield volumes of the CA1, CA2/3, CA4/DG, and the subiculum using ultra high-field 7T MRI scans, including T1-weighted MP2RAGE and T2-TSE sequences, in 27 patients with either mesial temporal lobe epilepsy (mTLE) or neocortical epilepsy (NE) compared to age and gender matched healthy controls. We found that 7T improved visualization of structural abnormalities not otherwise seen on clinical strength MRIs in patients with unilateral mTLE. Additionally, our automated segmentation algorithm was able to detect structural differences in volume and asymmetry across hippocampal subfields in unilateral mTLE patients compared to controls. Specifically, amongst unilateral mTLE patients with longer disease durations, volume loss was observed in the ipsilateral CA1 and CA2/3 subfields and contralateral CA1. There were no differences in subfield volumes in patients with NE compared to controls. We report the first application of 7T with automated segmentation to characterize the relationship between disease duration burden and asymmetry across specific hippocampal subfields in this population. Disease duration was found to have a statistically significant positive relationship with subfield asymmetry within the unilateral mTLE cohort. These findings highlight the ability of 7T MRI and automated segmentation to provide novel qualitative and quantitative information in epilepsy patients who are otherwise MRI-negative at clinical field strengths.

Usefulness of magnetic resonance spectroscopy in mesial temporal sclerosis: a systematic review

BACKGROUND

Magnetic resonance spectroscopy (MRS) provides non-invasive information about metabolic features in different regions of the brain affected by mesial temporal sclerosis (MTS).

PURPOSE

To review articles analyzing the most common alterations in biochemical parameters in MTS and the applications of MRS in presurgical assessment.

METHODS

We undertook a systematic literature search for MRS in MTS in PubMed, SCOPUS, and Cochrane based on the MESH terms ""Magnetic Resonance Spectroscopy", "Proton Magnetic Resonance Spectroscopy", "Carbon-13 Magnetic Resonance Spectroscopy", "1H-MRS", "31P-MRS", "mesial temporal sclerosis", "hippocampal sclerosis", "mesial temporal seizure", and "mesial temporal epilepsy".

RESULTS

Of the initial 134 articles found, 30 were selected after the exclusion process. Of these, 13 detected a decrease in N-acetylaspartate (NAA), 9 showed a decreased in the ratio NAA/Cho+Cr, and 8 demonstrated a decreased in the ratio NAA/Cr, all of them in the ipsilateral hippocampus. Nine studies also found reduced NAA levels in extrahippocampal regions.

CONCLUSIONS

The main findings were a decrease in NAA in the ipsilateral hippocampus. In addition, NAA levels were low outside the hippocampus so MTS could be a more extensive disease. Patients without MTS also presented a decrease in NAA in the ipsilateral hippocampus although NAA was even lower in the MTS patients. Thus, MRS could be useful in the presurgical evaluation to locate the epileptogenic focus, but not specific for the diagnosis of MTS.

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.

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.

Cognitive disorders associated with epilepsy: diagnosis and treatment

INTRODUCTION

Cognitive disorders are common in patients with epilepsy. Their aetiology is multifactorial, being affected by the type and location of the epileptogenic lesion, epileptic syndrome, type of seizures, age of onset, frequency and severity. Timely diagnosis and treatment can help to reduce their impact on the patient's quality of life.

RESULTS

The most significant cognitive deficits are associated with focal epilepsy, although some, usually mild, neuropsychological disorders can be found in idiopathic generalized epilepsy. The use of antiepileptic drugs (AEDs) can cause additional neuropsychological disorders that are of particular concern in learning-age children and elderly patients with cognitive disorders before the start of treatment. Recent studies have raised the concern that the use of some AEDs during pregnancy may cause cognitive disorders in the child exposed to them in utero. Cognitive disorders can also present as a complication of surgery for refractory epilepsy. Some risk factors for significant memory loss after surgery for temporal lobe epilepsy have been described. They include intervention in the dominant hemisphere, good preoperative function and poor functional reserve in the contralateral hippocampus.

CONCLUSIONS

The heterogeneity of different types of epilepsy makes case-control studies difficult; however, thanks to the growing interest in the neuropsychological deficits associated with epilepsy, we now know some factors that could lead to the appearance of these disorders and their prognosis. Special care must be taken to detect cognitive side effects associated with AEDs, which seem to be more common with classic than with new AEDs, and in those patients receiving polytherapy. Neuropsychological assessment should be routinely performed before epilepsy surgery to predict possible postsurgical cognitive deficits.

Facial emotion recognition impairment in chronic temporal lobe epilepsy

PURPOSE

To evaluate facial emotion recognition (FER) in a cohort of 176 patients with chronic temporal lobe epilepsy (TLE).

METHODS

FER was tested by matching facial expressions with the verbal labels for the following basic emotions: happiness, sadness, fear, disgust, and anger. Emotion recognition performances were analyzed in medial (n = 140) and lateral (n = 36) TLE groups. Fifty healthy subjects served as controls. The clinical and neuroradiologic variables potentially affecting the ability to recognize facial expressions were taken into account.

RESULTS

The medial TLE (MTLE) group showed impaired FER (86% correct recognition) compared to both the lateral TLE patients (FER = 93.5%) and the controls (FER = 96.4%), with 42% of MTLE patients recording rates of FER that were lower [by at least 2 standard deviations (SDs)] than the control mean. The MTLE group was impaired compared to the healthy controls in the recognition of all basic facial expressions except happiness. The patients with bilateral MTLE were the most severely impaired, followed by the right and then the left MTLE patients. FER was not affected by type of lesion, number of antiepileptic drugs (AEDs), aura semiology, or gender. Conversely, the early onset of seizures/epilepsy was related to FER deficits. These deficits were already established in young adulthood, with no evidence of progression in older MTLE patients.

CONCLUSION

These results on a large cohort of TLE patients demonstrate that emotion recognition deficits are common in MTLE patients and widespread across negative emotions. We confirm that early onset seizures with right or bilateral medial temporal dysfunction lead to severe deficits in recognizing facial expressions of emotions.

Involvement of Nitric Oxide in Spatial Memory Deficits in Status Epilepticus Rats

Status epilepticus (SE) is associated with a significant risk of cognitive impairment, and the increase of nitric oxide (NO) releasing has been reported during SE. We investigated the effects of neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole (7-NI) and inducible nitric oxide synthase (iNOS) inhibitor, aminoguanidine (AG), on spatial performance of rats in the Morris water maze. Treatment with 7-NI, but not with AG, improved the performance of rats after SE not only in acquisition of the task but also in probe test. Furthermore, the level of SE-induced malondialdehyde (MDA), end product of lipid peroxidation, was significantly decreased only in animals receiving 7-NI injection. Taken together, the results of the present study provided evidence that the NO pathway contributed to oxidative stress after SE, and nNOS/NO pathway may underlie one of the potential mechanisms contributing to SE-induced spatial memory deficits.

Carbamazepine treatment recovered low N-acetylaspartate+N-acetylaspartylglutamate (tNAA) levels in the megencephaly mouse BALB/cByJ-Kv1.1(mceph/mceph)

Megencephaly mice (BALB/cByJ-Kv1.1(mceph/mceph)) display excessive brain growth and seizures related to a mutation within the potassium channel gene Kv1.1 producing a malfunctioning protein. (1)H Magnetic resonance spectroscopy (MRS) provides means to study brain transmitters and metabolites in vivo. We applied MRS to pinpoint differences in hippocampus between mceph/mceph and wild type (wt) mice. Carbamazepine (CBZ) protects against brain overgrowth in mceph/mceph. Therefore, the effects of durable oral CBZ treatment on the MR spectra were investigated. LCModel was used for spectra quantification and multivariate data analysis applied to detect group differences. mceph/mceph mice had lower levels of N-acetylaspartate+N-acetylaspartylglutamate (tNAA) and choline-containing (tCho) compounds compared to wt mice. Glutamate, glutamine, taurine and myo-inositol levels were similar in wt and mceph/mceph. Furthermore, CBZ treatment recovered tCho and tNAA levels in mceph/mceph. Thus, distinct differences in MRS spectra between mceph/mceph and wt mice were depicted and treatment effects of CBZ were monitored using MRS.