Temporal lobectomy for epilepsy: recovery of the contralateral hippocampus measured by (1)H MRS

Central nervous system manifestation of lupus erythematosus resembling brain abscess

Manifestations of central nervous system involvement are one of the leading causes of morbidity and mortality in patients suffering from systemic lupus erythematosus. It frequently involves the central nervous system and sometimes need to be differentiated from lesions of infectious etiology, thus representing a major diagnostic dilemma. We present the case of a male adolescent with a known history of idiopathic thrombocytopenic purpura who presented with a seizure ictus and a space-occupying lesion, which posed significant diagnostic challenges to specify its characteristics.

Hippocampal MRS and subfield volumetry at 7T detects dysfunction not specific to seizure focus

Ultra high-field 7T MRI offers sensitivity to localize hippocampal pathology in temporal lobe epilepsy (TLE), but has rarely been evaluated in patients with normal-appearing clinical MRI. We applied multimodal 7T MRI to assess if focal subfield atrophy and deviations in brain metabolites characterize epileptic hippocampi. Twelve pre-surgical TLE patients (7 MRI-negative) and age-matched healthy volunteers were scanned at 7T. Hippocampal subfields were manually segmented from 600μm isotropic resolution susceptibility-weighted images. Hippocampal metabolite spectra were acquired to determine absolute concentrations of glutamate, glutamine, myo-inositol, NAA, creatine and choline. We performed case-controls analyses, using permutation testing, to identify abnormalities in hippocampal imaging measures in individual patients, for evaluation against clinical evidence of seizure lateralisation and neuropsychological memory test scores. Volume analyses identified hippocampal subfield atrophy in 9/12 patients (75%), commonly affecting CA3. 7/8 patients had altered metabolite concentrations, most showing reduced glutamine levels (62.5%). However, neither volume nor metabolite deviations consistently lateralized the epileptogenic hippocampus. Rather, lower subiculum volumes and glutamine concentrations correlated with impaired verbal memory performance. Hippocampal subfield and metabolic abnormalities detected at 7T appear to reflect pathophysiological processes beyond epileptogenesis. Despite limited diagnostic contributions, these markers show promise to help elucidate mnemonic processing in TLE.

Quantitative magnetic resonance imaging in neuropsychiatric systemic lupus erythematosus

Neuropsychiatric symptoms are common in systemic lupus erythematosus (SLE) but are poorly understood.Although there is a wide spectrum of clinical manifestations, brain histologyoften simply shows a bland vasculopathy. Magnetic resonance techniques such as magnetic resonance spectroscopy, magnetization transfer imaging and diffusion weighted imaging have been used to try to improve our understandingof the pathophysiologicalmechanisms involved in neuropsychiatric lupus (NPSLE). This article reviews the current literature on the use of these techniques and their possible future role as diagnostic tools in NPSLE.

Proton magnetic resonance spectroscopy in focal cortical dysplasia at 3T

PURPOSE

Focal cortical dysplasia (FCD) type II is a frequent cause of medically intractable epilepsy. On conventional MRI diagnosis may be difficult. The purpose of our study was to assess the metabolic characteristics of MRI-typical or neuropathologically confirmed FCD II lesions at 3T.

METHODS

In a prospective study, 13 patients with drug-resistant epilepsy and MRI diagnosis of FCD II (seven neuropathologically confirmed) were investigated by single-volume proton magnetic resonance spectroscopy ((1)H MRS). We performed an intra-individual comparison placing spectroscopic volumes of interest in the lesion and in the apparently normal contralateral hemisphere. Spectroscopic results were correlated with clinical data.

RESULTS

Matched pair analysis revealed a significant increase in absolute choline (Cho) concentration in the lesion volume (+32%, p=0.015) compared to the control volume. This increase was associated with a significant decrease in N-acetyl-aspartate (NAA) concentration (-13%; p=0.008). Mean myo-inositol (Ins) levels were distinctly (+36%) but not significantly (p=0.051) elevated. Lesional creatine (Cr) concentration correlated significantly with the frequency of seizures (Spearman-Rho r=0.898; p=0.002), while concentrations of NAA, Cho and Ins did not correlate with clinical or imaging parameters.

CONCLUSION

MR spectroscopy revealed a characteristic metabolic pattern in FCD II lesions that helps to distinguish normal from epileptogenic tissue.

Advances in imaging explosive blast mild traumatic brain injury

In the past, direct physical evidence of mild traumatic brain injury (mTBI) from explosive blast has been difficult to obtain through conventional imaging modalities such as T1- and T2-weighted magnetic resonance imaging (MRI) and computed tomography (CT). Here, we review current progress in detecting evidence of brain injury from explosive blast using advanced imaging, including diffusion tensor imaging (DTI), functional MRI (fMRI), and the metabolic imaging methods such as positron emission tomography (PET) and magnetic resonance spectroscopic imaging (MRSI), where each targets different aspects of the pathology involved in mTBI. DTI provides a highly sensitive measure to detect primary changes in the microstructure of white matter tracts. fMRI enables the measurement of changes in brain activity in response to different stimuli or tasks. Remarkably, all three of these paradigms have found significant success in conventional mTBI where conventional clinical imaging frequently fails to provide definitive differences. Additionally, although used less frequently for conventional mTBI, PET has the potential to characterize a variety of neurotransmitter systems using target agents and will undoubtedly play a larger role, once the basic mechanisms of injury are better understood and techniques to identify the injury are more common. Finally, our MRSI imaging studies, although acquired at much lower spatial resolution, have demonstrated selectivity to different metabolic and physiologic processes, uncovering some of the most profound differences on an individual by individual basis, suggesting the potential for utility in the management of individual patients.

Recovery from emotion recognition impairment after temporal lobectomy

Mesial temporal lobe epilepsy (MTLE) can be associated with emotion recognition impairment that can be particularly severe in patients with early onset seizures (1–3). Whereas, there is growing evidence that memory and language can improve in seizure-free patients after anterior temporal lobectomy (ATL) (4), the effects of surgery on emotional processing are still unknown. We used functional magnetic resonance imaging (fMRI) to investigate short-term reorganization of networks engaged in facial emotion recognition in MTLE patients. Behavioral and fMRI data were collected from six patients before and after ATL. During the fMRI scan, patients were asked to make a gender decision on fearful and neutral faces. Behavioral data demonstrated that two patients with early onset right MTLE were impaired in fear recognition while fMRI results showed they lacked specific activations for fearful faces. Post-ATL behavioral data showed improved emotion recognition ability, while fMRI demonstrated the recruitment of a functional network for fearful face processing. Our results suggest that ATL elicited brain plasticity mechanisms allowing behavioral and fMRI improvement in emotion recognition.

Changes in memory function in children and young adults with temporal lobe epilepsy: a follow-up study

This longitudinal study explored change in memory function from childhood to young adulthood in temporal lobe epilepsy (TLE). The 24 participants (11 left TLE; 13 right TLE) had a mean age of 16.10 years (SD=4.13 years), and 14 had undergone surgery since initial assessment. Contrary to baseline, verbal memory deficits were lateralized (left<right on paired associate learning, p=.009, and delay, p=.02). Change over time interacted with laterality on a complex non-verbal memory task (p=.05), with the right but not the left group improving. A three-way time-by-laterality-by-surgery interaction was significant for delayed facial recognition (p=.05), with surgical groups improving irrespective of laterality. Non-surgical groups remained stable, although there was a trend for the right to improve and the left to decline. Results were independent of seizure variables, mood and IQ and suggest that memory in left TLE tends to remain stable over time and improve in right TLE.

Hippocampal atrophy in temporal lobe epilepsy: the 'generator' and 'receiver'

OBJECTIVE

Some patients with unilateral medial temporal lobe epilepsy (MTLE) display bilateral hippocampal atrophy on MRI, even though seizures originate in only one hippocampus. The correct identification of the epileptogenic hippocampus (the 'generator') vs the non-epileptogenic (the 'receiver') may lead to better surgical planning and results.

MATERIALS AND METHODS

We studied 14 patients with MTLE (eight left and six right) who became seizure free after unilateral hippocampal resection, with hippocampal sclerosis confirmed by histology. Hippocampal tridimensional morphometry was performed comparing patients and healthy controls employing a voxel-wise Wilcoxon test. Results were corrected for multiple comparisons with the application of a False Discovery Rate (FDR)-corrected threshold for q < 0.05.

RESULTS

Patients with MTLE showed atrophy involving the ipsilateral hippocampus and the contralateral hippocampus, more pronouncedly within the ipsilateral hippocampus in the anterior-inferior aspect of the hippocampal head (left MTLE, left hippocampus x = -28, y = -16, z = -24, Z = 3.6; right MTLE, right hippocampus x = 22, y = -11, z = -27, Z = 2.9). On the contralateral hippocampus, the atrophy was more noticeable in the posterior head and body areas.

CONCLUSION

The epileptogenic hippocampal atrophy has an anatomically distinct pattern compared with the contralateral hippocampus. This information may help guide the presurgical assessment of MTLE.

[Memory improvement in patients with temporal lobe epilepsy at one-year postoperative]

INTRODUCTION

Several studies have assessed the impact of surgery on both anterograde and remote memory in patients with temporal lobe epilepsy (TLE). The majority of results have shown an extensive memory deficit in patients after temporal resection (TL). However, few protocols have used a prospective longitudinal design. Moreover, the postoperative delays were variable from one study to the next, instead of regular monitoring to identify the potential effect of time elapsed after surgery on memory performance. In addition, some studies have not used strict inclusion criteria to establish homogeneous patient groups. Finally, the impact of surgery on memory has been often assessed by comparing memory skills between epileptic patients and healthy controls. Our aim was to examine the impact of TL on memory in patients with TLE, recruited according to clear-cut clinical criteria. Moreover, we focused on memory performance progression per se in epileptic patients pre- and postoperatively, rather than on memory performance analysis expressed as "deficient" or "normal".

METHODS

We assessed 30 patients with unilateral TLE (17 right TLE and 13 left TLE) on four anterograde memory tests and six remote memory tasks. Patients completed all tests preoperatively, and 5 and 12 months after TL.

RESULTS

Five months after surgery, performance was equivalent to the preoperative scores for both groups in anterograde memory tasks and remote memory tests. One year after TL, patients with right TLE showed enhanced performance in the verbal anterograde memory tests and in retrieving recent autobiographical memories. Results for left TL showed improved scores only in a recognition memory test of faces.

CONCLUSIONS

In the present study, surgical patients were "double winners" gaining seizure freedom and potential of memory stability or recovery. The gain was observed only 12 months after surgery and following temporal resection lateralisation. Our data showed postoperative memory improvement in patients with temporal lobe epilepsy presenting with specific clinical characteristics.

Magnetoencephalographic and magnetic resonance spectroscopy evidence of regional functional abnormality in mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (mTLE) with mesial temporal sclerosis (MTS) is a recognized epilepsy syndrome which is successfully treated with mesial temporal lobe resection. However, recent studies suggest that mTLE is more than a "focal" disease process. The objective of our study was to determine the presence and extent of functional abnormalities outside of a defined structural abnormality in epilepsy patients with mTLE. We used a prospective age-matched controlled design to study eight consecutive patients with MTS who were undergoing epilepsy surgery evaluation. Magnetoencephalography was used to localize the sources of electromagnetic abnormality. Proton magnetic resonance spectroscopy ((1)H-MRS) measured integrated peak areas for N-acetyl compounds (NAA) and choline-containing compounds (Cho) to determine regions of metabolic abnormality. All eight subjects had predominant electromagnetic abnormality in the temporal lobe ipsilateral to the MTS. All eight subjects had lower NAA/Cho ratios in the region of electromagnetic abnormality when compared to the homologous contralateral region (P < 0.001). Four subjects had predominant MEG spiking outside the mesial temporal region. Surgery-free outcome for the group with neuroimaging abnormalities outside of the medial temporal lobe is 50%. The region of maximal electromagnetic abnormality is outside the hippocampus in some patients with mTLE. These regions also demonstrate functional abnormalities. Our findings support the concept that mTLE is a more diffuse process than the hippocampal structural abnormality, which may impact surgical outcome.

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.

Intracranial EEG power and metabolism in human epilepsy

EEG power and high frequency activity in the seizure onset zone has been increasingly considered for its relationship with seizures in animal and human studies of epilepsy. We examine the relationship between quantitative EEG measures and metabolic imaging in epilepsy patients undergoing intracranial EEG (icEEG) analysis for seizure localization. Patients with mesial temporal lobe epilepsy (MTLE) and neocortical epilepsy (NE) were studied. Metabolic imaging was performed with MR spectroscopic imaging using N-acetyl aspartate (NAA) and creatine (Cr). All data were acquired from the mesial temporal lobe such that a direct comparison of the same anatomical regions between the two groups could be performed. While no difference was seen in the total power recorded from the mesial temporal lobe, the MTLE group had significantly greater power in the high frequency bands. There was a significant positive exponential relationship between total icEEG power with NAA/Cr in MTLE, R=+0.84 and p<0.001, which was not seen in NE. There was also a significant negative relationship between fractional gamma power with NAA/Cr in MTLE, R=-0.66 and p<0.02, also not seen in NE. These data argue that within the seizure onset zone, the tight correlation between total power and NAA/Cr suggests that total electrical output is powered by available mitochondrial function. These data are also consistent with the hypothesis that high frequency activity is an abnormal manifestation of tissue injury.

Novel approaches to imaging epilepsy by MRI

As the concept of a network of injury has emerged in the treatment of epilepsy, the importance of evaluating that network noninvasively has also grown. Recently, studies utilizing magnetic resonance spectroscopic imaging, manganese-enhanced MRI and functional (f)MRI measures of resting state connectivity have demonstrated their ability to detect injury and dysfunction in cerebral networks involved in the propagation of seizures. The ability to noninvasively detect neuronal injury and dysfunction throughout cerebral networks should improve surgical planning, provide guidance for placement of devices that target network propagation and provide insights into the mechanisms of recurrence following resective surgery.

Proton MR spectroscopy of metabolite concentrations in temporal lobe epilepsy and effect of temporal lobe resection

PURPOSE

To use proton Magnetic Resonance Spectroscopy (MRS) to measure in vivo temporal lobe GABA and glutamate plus glutamine (GLX) concentrations in patients with temporal lobe epilepsy (TLE) attributable to unilateral hippocampal sclerosis (HS) before and following anterior temporal lobe resection (ATLR).

METHODS

We obtained quantitative short echo time MRS in both temporal lobes of 15 controls and 16 patients with TLE and HS, and repeat spectra in 10 patients after ATLR. We measured the concentrations of N-acetyl aspartate+N-acetyl aspartyl-glutamate (NAAt), creatine plus phosphocreatine (Cr), and glutamate+glutamine (GLX) using a metabolite-nulled sequence designed to minimize macromolecule artifact. GABA concentrations were measured using a previously described double quantum filter.

RESULTS

In patients with TLE, NAAt/Cr was reduced in ipsilateral and contralateral temporal lobes. No significant variation in GLX/Cr or GABA+/Cr was evident in any group although GABA+/Cr was highest in the ipsilateral temporal lobe in TLE. After ATLR there was a trend to normalization of NAAt/Cr in the contralateral temporal lobe but no change in individual metabolite concentrations, GLX/Cr or GABA+/Cr compared to pre-surgery levels.

DISCUSSION

Temporal lobe epilepsy was associated with bilateral reduction in NAAt/Cr but not significant abnormality in GABA+/Cr or GLX/Cr. Normalization of NAAt/Cr in the contralateral temporal lobe was seen following successful ATLR.

1H MR spectroscopy in histopathological subgroups of mesial temporal lobe epilepsy

The aim of the study was to analyze the lateralizing value of proton magnetic resonance spectroscopy ((1)H MRS) in histopathologically different subgroups of mesial temporal lobe epilepsies (MTLE) and to correlate results with clinical, MRI and seizure outcome data. A group of 35 patients who underwent resective epilepsy surgery was retrospectively studied. Hippocampal (1)H MR spectra were evaluated. Metabolite concentrations were obtained using LCModel and NAA/Cr, NAA/Cho, NAA/(Cr+Cho), Cho/Cr ratios and coefficients of asymmetry were calculated. MRI correctly lateralized 89% of subjects and (1)H MRS 83%. MRI together with (1)H MRS correctly lateralized 100% of patients. Nineteen subjects had "classical" hippocampal sclerosis (HS), whereas the remaining 16 patients had "mild" HS. Nineteen patients had histopathologically proven malformation of cortical development (MCD) in the temporal pole; 16 subjects had only HS. No difference in (1)H MRS findings was found between patients in different histopathological subgroups of MTLE. Our results support the hypothesis that (1)H MRS abnormalities do not directly reflect histopathological changes in MTLE patients. Subjects with non-lateralized (1)H MRS abnormalities did not have a worse postoperative seizure outcome. We found no significant impact of contralateral (1)H MRS abnormality on post-surgical seizure outcome.

Spectroscopic imaging of the pilocarpine model of human epilepsy suggests that early NAA reduction predicts epilepsy

Reduced hippocampal N-acetyl aspartate (NAA) is commonly observed in patients with advanced, chronic temporal lobe epilepsy (TLE). It is unclear, however, whether an NAA deficit is also present during the clinically quiescent latent period that characterizes early TLE. This question has important implications for the use of MR spectroscopic imaging (MRSI) in the early identification of patients at risk for TLE. To determine whether NAA is diminished during the latent period, we obtained high-resolution (1)H spectroscopic imaging during the latent period of the rat pilocarpine model of human TLE. We used actively detuneable surface reception and volume transmission coils to enhance sensitivity and a semiautomated voxel shifting method to accurately position voxels within the hippocampi. During the latent period, 2 and 7 d following pilocarpine treatment, hippocampal NAA was significantly reduced by 27.5 +/- 6.9% (P < 0.001) and 17.3 +/- 6.9% (P < 0.001) at 2 and 7 d, respectively. Quantitative estimates of neuronal loss at 7 d (2.3 +/- 7.7% reduction; P = 0.58, not significant) demonstrate that the NAA deficit is not due to neuron loss and therefore likely represents metabolic impairment of hippocampal neurons during the latent phase. Therefore, spectroscopic imaging provides an early marker for metabolic dysfunction in this model of TLE.

Comparative analysis of MR imaging, Ictal SPECT and EEG in temporal lobe epilepsy: a prospective IAEA multi-center study

BACKGROUND AND PURPOSE

MR imaging, ictal single-photon emission CT (SPECT) and ictal EEG play important roles in the presurgical localization of epileptic foci. This multi-center study was established to investigate whether the complementary role of perfusion SPECT, MRI and EEG for presurgical localization of temporal lobe epilepsy could be confirmed in a prospective setting involving centers from India, Thailand, Italy and Argentina.

METHODS

We studied 74 patients who underwent interictal and ictal EEG, interictal and ictal SPECT and MRI before surgery of the temporal lobe. In all but three patients, histology was reported. The clinical outcome was assessed using Engel's classification. Sensitivity values of all imaging modalities were calculated, and the add-on value of SPECT was assessed.

RESULTS

Outcome (Engel's classification) in 74 patients was class I, 89%; class II, 7%; class III, 3%; and IV, 1%. Regarding the localization of seizure origin, sensitivity was 84% for ictal SPECT, 70% for ictal EEG, 86% for MRI, 55% for interictal SPECT and 40% for interictal EEG. Add-on value of ictal SPECT was shown by its ability to correctly localize 17/22 (77%) of the seizure foci missed by ictal EEG and 8/10 (80%) of the seizure foci not detected by MRI.

CONCLUSIONS

This prospective multi-center trial, involving centers from different parts of the world, confirms that ictal perfusion SPECT is an effective diagnostic modality for correctly identifying seizure origin in temporal lobe epilepsy, providing complementary information to ictal EEG and MRI.

Subfield-specific loss of hippocampal N-acetyl aspartate in temporal lobe epilepsy

PURPOSE

In patients with mesial temporal lobe epilepsy (MTLE) it remains an unresolved issue whether the interictal decrease in N-acetyl aspartate (NAA) detected by proton magnetic resonance spectroscopy ((1)H-MRS) reflects the epilepsy-associated loss of hippocampal pyramidal neurons or metabolic dysfunction.

METHODS

To address this problem, we applied high-resolution (1)H-MRS at 14.1 Tesla to measure metabolite concentrations in ex vivo tissue slices from three hippocampal subfields (CA1, CA3, dentate gyrus) as well as from the parahippocampal region of 12 patients with MTLE.

RESULTS

In contrast to four patients with lesion-caused MTLE, we found a large variance of NAA concentrations in the individual hippocampal regions of patients with Ammon's horn sclerosis (AHS). Specifically, in subfield CA3 of AHS patients despite of a moderate preservation of neuronal cell densities the concentration of NAA was significantly lowered, while the concentrations of lactate, glucose, and succinate were elevated. We suggest that these subfield-specific alterations of metabolite concentrations in AHS are very likely caused by impairment of mitochondrial function and not related to neuronal cell loss.

CONCLUSIONS

A subfield-specific impairment of energy metabolism is the probable cause for lowered NAA concentrations in sclerotic hippocampi of MTLE patients.

Bilateral white matter diffusion changes persist after epilepsy surgery

PURPOSE

Bilateral white matter diffusion tensor imaging (DTI) abnormalities have been reported in patients with temporal lobe epilepsy (TLE) and unilateral mesial temporal sclerosis (MTS), but it is unknown whether these are functional or structural changes. We performed a longitudinal study in patients with unilateral MTS who were seizure-free for 1 year after surgery to determine whether the observed presurgical white matter diffusion abnormalities were reversible.

METHODS

Eight TLE patients with unilateral MTS who were seizure-free after anterior temporal resection and 22 healthy subjects were recruited. DTI was performed before surgery and at 1-year follow-up. Tractography and region-of-interest (ROI) analyses were performed in the fornix, cingulum, genu, and splenium of the corpus callosum and external capsules. Diffusion tensor parameters were compared between groups and before and after surgery in the patient group.

RESULTS

The fornix, cingulum, and external capsules showed preoperative bilateral abnormal diffusion parameters (i.e., decreased diffusion anisotropy and increased mean and perpendicular diffusivities). The fornix and cingulum ipsilateral to the resected mesial temporal structures showed signs of wallerian degeneration at 1-year follow-up. The contralateral tracts of the fornix, cingulum, and external capsules, as well as the genu of the corpus callosum, failed to show a normalization of their diffusion parameters.

CONCLUSIONS

The irreversibility of the white matter DTI abnormalities on seizure freedom suggests underlying structural abnormalities (e.g., axonal/myelin degradation) as opposed to functional changes (e.g., fluid shifts due to seizures) in the white matter.

Postoperative Recovery of Hippocampal Contralateral Diffusivity in Medial Temporal Lobe Epilepsy

PURPOSE

To search for a recovery after surgery of mean diffusivity (MD) values in the contralateral nonsclerotic hippocampus of patients with medial temporal lobe epilepsy (MTLE) and hippocampal sclerosis (HS).

METHODS

Twenty-four MTLE patients (12 right-sided and 12 left-sided MTLE) and 36 healthy volunteers were investigated using diffusion tensor imaging. A region-of-interest approach was used to measure pre- and postoperative interictal hippocampal MD values in patients.

RESULTS

Diffusion abnormalities in contralateral nonsclerotic hippocampus recovered after surgery (p<0.0001). A subgroup of 14 patients exhibited a clear increase in MD values whereas the remaining 10 patients were stable. No significant difference was found between the two subgroups for each of the electroclinical data studied including early postoperative outcome, all patients being either seizure free or with rare persistent auras.

CONCLUSIONS

This finding suggests that diffusion abnormalities in contralateral hippocampus may represent a functional mechanism linked to the active epileptic process.

N-Acetylaspartate in the CNS: from neurodiagnostics to neurobiology

The brain is unique among organs in many respects, including its mechanisms of lipid synthesis and energy production. The nervous system-specific metabolite N-acetylaspartate (NAA), which is synthesized from aspartate and acetyl-coenzyme A in neurons, appears to be a key link in these distinct biochemical features of CNS metabolism. During early postnatal central nervous system (CNS) development, the expression of lipogenic enzymes in oligodendrocytes, including the NAA-degrading enzyme aspartoacylase (ASPA), is increased along with increased NAA production in neurons. NAA is transported from neurons to the cytoplasm of oligodendrocytes, where ASPA cleaves the acetate moiety for use in fatty acid and steroid synthesis. The fatty acids and steroids produced then go on to be used as building blocks for myelin lipid synthesis. Mutations in the gene for ASPA result in the fatal leukodystrophy Canavan disease, for which there is currently no effective treatment. Once postnatal myelination is completed, NAA may continue to be involved in myelin lipid turnover in adults, but it also appears to adopt other roles, including a bioenergetic role in neuronal mitochondria. NAA and ATP metabolism appear to be linked indirectly, whereby acetylation of aspartate may facilitate its removal from neuronal mitochondria, thus favoring conversion of glutamate to alpha ketoglutarate which can enter the tricarboxylic acid cycle for energy production. In its role as a mechanism for enhancing mitochondrial energy production from glutamate, NAA is in a key position to act as a magnetic resonance spectroscopy marker for neuronal health, viability and number. Evidence suggests that NAA is a direct precursor for the enzymatic synthesis of the neuron specific dipeptide N-acetylaspartylglutamate, the most concentrated neuropeptide in the human brain. Other proposed roles for NAA include neuronal osmoregulation and axon-glial signaling. We propose that NAA may also be involved in brain nitrogen balance. Further research will be required to more fully understand the biochemical functions served by NAA in CNS development and activity, and additional functions are likely to be discovered.

A prospective study of the effects of anterior temporal lobectomy on emotion recognition and theory of mind

Nineteen patients evaluated facial emotional expressions and performed 'theory of mind' reasoning tasks before and after a temporal lobectomy for medically intractable epilepsy, and results were compared with the performance of 19 healthy controls. Following operation, which in all cases resulted in excision of the entire amygdala, there was no change in the ability to reason about the mental states of others, in line with the suggestion that the anterior temporal lobe is not necessary for theory of mind reasoning. However, following a left anterior temporal lobectomy, patients evaluated fearful facial expressions in a more normative manner. This may reflect the excision of a 'hyper-excitable' amygdala which pre-operatively misinterprets fearful expressions as containing blends of other emotions. Alternatively the results may represent an improvement in function of the right amygdala following the excision of a noxious inhibitory epileptogenic focus on the left. The finding complements earlier demonstrations that damage to the right amygdala is associated with impaired processing of fear; amelioration of right amygdala function may conversely be associated with an improvement.

The role of 1H magnetic resonance spectroscopy in pre-operative evaluation for epilepsy surgery. A meta-analysis

PURPOSE

We aimed to assess the additional pre-operative value of (1)H MRS in identifying the epileptogenic zone (EZ) for epilepsy surgery by performing a meta-analysis considering publications from 1992 to 2003.

METHODS

From an extensive computer and hand search 22 studies were included. For inclusion, studies had to report post-operative outcome and detailed diagnostic test results for each individual patient. Studies exclusively reporting on patients with brain tumors or on children were excluded.

RESULTS

Great heterogeneity among studies regarding methodological and technical aspects and concerning evaluation and interpretation of data was observed. Only patients with intractable temporal lobe epilepsy were presented. Sixty-four percent of all patients and 72% of patients with good outcome had an ipsilateral MRS abnormality concordant with the EZ. The positive predictive value of all patients with ipsilateral MRS abnormality for good outcome was 82%. An odds ratio weighted by inverse variance showed a 4.891 better chance of seizure free outcome [CI=1.965-12.172; Q=2.748; d.f.=5; critical chi2-value=11.07] in patients with an ipsilateral MRS abnormality when compared to patients with bilateral MRS abnormalities. Data for MRI-negative patients were conflicting. One study stressed a role for MRS in patients with bilateral hippocampal atrophy at MRI.

CONCLUSIONS

MRS still remains a research tool with clinical potential. Our findings indicate the connection of ipsilateral MRS abnormality to good outcome. The ability for prediction of post-operative outcome may depend on the assessed population. Prospective studies limited to non-localized ictal scalp EEG or MRI-negative patients are required for validation of these data.

Imaging in CNS lupus

The diagnosis of neuropsychiatric systemic lupus erythematosus (NPSLE) is complex not only on account of the heterogeneous nature of neurological presentation but also because of the difficulty of differentiating lupus-related pathology from other neuropsychiatric diseases. Magnetic resonance imaging (MRI) remains the gold standard for the non-invasive assessment of NPSLE but there are problems, both with sensitivity and specificity. Both T(2) quantitation and the use of gadolinium have shown promise in differentiating acute from chronic lesions. Nonetheless, the lack of sensitivity of conventional MRI has led to the exploration of other MR-based techniques. Magnetic resonance spectroscopy (MRS) allows the measurement of brain metabolites, whereas diffusion weighted imaging and diffusion tensor imaging allow assessment of white matter structure and integrity. MRS studies in NPSLE have consistently shown a reduction in N-acetyl aspartate (a neuronal marker). Diffusion weighted imaging has had only limited application in lupus and the results to date have shown abnormal diffusivity in lupus patients consistent with inflammation and loss of white matter structure. These techniques remain research tools at this early stage. Positron emission tomography (PET) and single photon emission computed tomography (SPECT) have also been explored as functional imaging tools in lupus and both appear to be more sensitive in detecting subtle brain changes in NPSLE but there are issues with specificity which deter their use in the clinical setting.

The myth of silent cortex and the morbidity of epileptogenic tissue: implications for temporal lobectomy

This article reviews two commonly held myths regarding temporal lobe epilepsy-it is a static disorder with minimal morbidity and mortality, and epileptogenic tissue impairs only the functions of the seizure focus-and one myth concerning temporal lobe functions-they contain areas of nonfunctional, "silent" cortex. Chronic temporal lobe epilepsy can cause progressive structural, cognitive, and behavioral changes. Aside from the seizure focus, primary epileptogenic cortex may have a deleterious influence on distant brain areas. Removing this "nociferous" cortex and reducing the antiepileptic drug burden can improve cognitive or behavioral and metabolic function in areas remote from the resection. Anterior temporal lobectomy often removes functional tissue that may or may not be epileptogenic. Because normal brain does not contain functionless, "silent" areas, the procedure can have negative as well as positive cognitive or behavioral consequences. To improve the outcomes of focal cortical resections for seizure control, we need to better define functional and nociferous cortex and more clearly understand their boundaries and interactions.

Diffusion tensor imaging in medial temporal lobe epilepsy with hippocampal sclerosis

Interictal diffusion imaging studies in patients with medial temporal lobe epilepsy (MTLE) accompanied by hippocampal sclerosis (HS) have shown an increased diffusivity in the epileptogenic hippocampus. In this study, we wanted to explore the whole brain in order to determine if MTLE could have an impact on the organization and the architecture of a large cerebral network and to identify clinical factors that could mediate diffusion abnormalities. Diffusion tensor imaging (DTI) and statistical parametric mapping of the entire brain were performed in 35 well-defined MTLE patients and in 36 healthy volunteers. SPM analyses identified three abnormal areas: an increased diffusivity was detected in the epileptic hippocampus and the ipsilateral temporal structures associated with a decreased anisotropy along the temporal lobe, a decreased diffusivity was found in the contralateral non-sclerotic hippocampus, the amygdala, and the temporal pole, and finally, a decreased anisotropy was noted ipsilaterally in posterior extratemporal regions. Duration of epilepsy, age at onset, and the frequency of generalized tonic-clonic seizures or partial complex seizures did not correlate with the presence of diffusion abnormalities. Region of interest analysis in the hippocampus/parahippocampus demonstrated a correlation between lower ipsilateral diffusivity values and occurrence of epigastric aura and between higher anisotropy values in both hemispheres and history of febrile seizures. In conclusion, this study showed that diffusion abnormalities are not restricted to the pathologic hippocampus and involve a larger network. This pattern may indirectly reflect the epileptogenic network and may be interpreted as a cause or a consequence of epilepsy.

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

This study was performed to evaluate the effect of seizures on the bilateral hippocampus in mesial temporal lobe epilepsy (mTLE) and neocortical epilepsy by single voxel proton magnetic resonance spectroscopy (MRS). Forty-one patients with mTLE having unilateral hippocampal sclerosis and 43 patients with a neocortical epilepsy who underwent subsequent epilepsy surgery were recruited. Ninety-five percent confidence intervals of N-acetyl aspartate/choline (NAA/Cho) and NAA/creatine (NAA/Cr) ratios in 20 healthy control subjects were used as threshold values to determine abnormal NAA/Cho and NAA/Cr. NAA/Cho and NAA/Cr were significantly lower in the ipsilateral hippocampus of mTLE and neocortical epilepsy. Using asymmetry indices for patients with bilaterally abnormal ratios of NAA/Cho and NAA/Cr in addition to using unilateral abnormal ratio, the seizure focus was correctly lateralized in 65.9% of patients with mTLE and 48.8% of neocortical epilepsy patients. Bilateral NAA/Cho abnormality was significantly related to a poor surgical outcome in mTLE. No significant relationship was found between the results of NAA/Cho or NAA/Cr and surgical outcome in neocortical epilepsy. The mean contralateral NAA/Cr ratio of the hippocampus in mTLE was significantly lower in patients with a history of secondary generalized tonic-clonic seizure (SGTCS) than in those without. Our results demonstrate effects of seizures on the hippocampi in neocortical epilepsy and the relation between SGTCS and NAA/Cr of the contralateral hippocampus in mTLE. This proves the presence of a seizure effect on the hippocampus in neocortical epilepsy as well as in mTLE.

Interictal perceptual function in epilepsy

Epilepsy can affect perception. Ictal perceptual experiences are common, but interictal perceptual function may also be affected. This article reviews the English-language literature on interictal perceptual disturbances in epilepsy. Although most studies report impaired perceptual ability, heightened sensitivity has also been described. There is a compelling, though not absolute, correlation between affected sensory modality and underlying epilepsy syndrome. Olfaction is clearly affected in temporal lobe epilepsy, while visual information processing is disturbed in occipital lobe epilepsy. The cause of interictal perceptual dysfunction is unknown, but propagating epileptiform discharges may play a role. The presence of specific perceptual disturbances in focal epilepsy syndromes is consistent with the view that epilepsy is a network disease, with the potential to affect neural circuits distant from the seizure focus. The use of thoughtfully selected psychophysical perceptual tasks may provide additional insight into the cognitive impact of different epilepsy syndromes and of ablative epilepsy surgery.

Somatosensory processing is impaired in temporal lobe epilepsy

PURPOSE

Growing evidence suggests that temporal lobe epilepsy (TLE) is a network disease. In this view, the seizure focus may produce measurable deficits in specific cortical functions.

METHODS

A tactile grating orientation (GrOr) discrimination task associated with parietal lobe function was administered at the index fingertip to 15 subjects with medically intractable TLE and to 19 neurologically normal controls. TLE subjects were tested bilaterally at baseline while taking their usual antiepileptic drugs (AEDs), and off AEDs during inpatient video-EEG monitoring (n = 9). Three subjects also were tested after temporal lobectomy. t Tests were used to compare baseline performance between TLE subjects and controls, and between hands ipsilateral and contralateral to side of seizure onset, with Bonferroni correction for multiple comparisons. TLE subjects' baseline thresholds were compared with those obtained off AEDs by using a repeated measures analysis of variance.

RESULTS

TLE subjects were severely impaired bilaterally on the GrOr task, with mean discrimination thresholds nearly twice those of controls (p </= 0.001 for each hand). No significant difference was found in baseline performance between hands (p = 0.37), or between baseline and off-AED testing (p = 0.42). The three subjects tested after temporal lobectomy demonstrated improved performance compared with baseline, but statistics were not performed because of the small subject number.

CONCLUSIONS

Patients with medically intractable TLE have impaired tactile GrOr discrimination bilaterally that is not due to nonspecific effects of AEDs. This impaired perceptual ability may be reversible with surgical removal of the seizure focus.

Prevalence and significance of neurocognitive dysfunction in hepatitis C in the absence of correlated risk factors

Neurocognitive morbidity has been reported in individuals with chronic hepatitis C virus (HCV) infection, but the magnitude of such dysfunction in the absence of disease-correlated factors known to affect the central nervous system (e.g., substance abuse, cirrhosis, depression, interferon treatment) and the impact of any such change on functioning is unclear. We investigated a cohort of individuals with HCV, all of whom were carefully screened to exclude relevant comorbidities, to elucidate virus-related changes in the brain using neuropsychological tests and magnetic resonance spectroscopy (MRS). A cohort of 37 patients with chronic HCV infection was culled from 300 consecutive patients presenting to a tertiary care liver clinic. A comparison group of healthy controls (n = 46) was also assessed. Of 10 neurocognitive measures evaluated, the HCV group showed marginally poorer learning efficiency compared with controls; only 13% of patients demonstrated a clinical level of impairment on this test (defined as 1.5 SD below the normative standard). Although patients reported greater levels of fatigue and symptoms of depression, these factors did not correlate with the degree of learning inefficiency. With respect to MRS, the HCV group demonstrated increased choline and reduced N-acetyl aspartate relative to controls in the central white matter. Indicators of liver disease severity did not correlate with either memory or MRS abnormalities. In conclusion, while our findings support an association between hepatitis C and indicators of central nervous system involvement in a cohort of patients carefully screened to eliminate other factors influencing neurocognitive integrity, the clinical significance of these effects is limited.

Regional energetic dysfunction in hippocampal epilepsy

OBJECTIVES

There is increasing evidence for a dysfunctional metabolic network in human mesial temporal lobe epilepsy (MTLE). To further describe this, we evaluated the bioenergetic status in unilateral MTLE inter-regionally and in relation to neuropathology.

MATERIALS AND METHODS

We used whole brain high field (4 T) 31P MR spectroscopic imaging to determine in vivo PCr and ATP, studying n=22 patients (all candidates for hippocampal resection) and n=14 control volunteers. The degree of bioenergetic impairment was assessed by calculating the ratio of PCr to ATP.

RESULTS

Compared to controls, patients demonstrated significant decreases in PCr/ATP from the ipsilateral amygdala and pes (0.84 +/- 0.14, 0.87 +/- 0.10, respectively, patients vs 0.97 +/- 0.15, 0.98 +/- 0.16, controls). In patients, the ipsilateral thalamic energetics positively correlated with contralateral hippocampal energetics. In addition, the ipsilateral thalamic and striatal energetics negatively correlated with hippocampal total glial counts.

CONCLUSIONS

These data are consistent with a view that in MTLE, the bilateral hippocampi, ipsilateral thalamus and striatum are linked in their energetic depression, possibly reflecting the propagation of seizures throughout the brain.

Correlations between granule cell physiology and bioenergetics in human temporal lobe epilepsy

Human temporal lobe epilepsy (TLE) is associated with bioenergetic abnormalities including decreased phosphocreatine (PCr) normalized to ATP. The physiological consequences of these metabolic alterations have not been established. We hypothesized that impaired bioenergetics would correlate with alterations in physiological functions under conditions that strongly activate neural metabolism. We correlated several physiological variables obtained from epileptic human dentate granule cells studied in slices with hippocampal PCr/ATP measured using in vivo magnetic resonance spectroscopy. The physiological variables included: the ability to fire multiple action potentials in response to single stimuli, the inhibitory postsynaptic potential (IPSP) conductance and the responses to a 10 Hz, 10 s stimulus train. We noted a significant negative correlation between the ability to fire multiple spikes in response to single synaptic stimulation and PCr/ATP (P < 0.03) and a positive correlation between the IPSP conductance and PCr/ATP (P < 0.05). Finally, there was a strong correlation between PCr/ATP and the recovery of the membrane potential following a stimulus train (P < 0.01), with low PCr/ATP being associated with prolonged recovery times. These data suggest that the bioenergetic impairment seen in this tissue is associated with specific changes in excitatory and inhibitory neuronal responses to synchronized synaptic inputs.

Mesial temporal lobe epilepsy: a proton magnetic resonance spectroscopy study and a histopathological analysis

Object. Proton magnetic resonance (MR) spectroscopy imaging of the ratio of N-acetylaspartate (NAA) to creatine (Cr) has proved efficacious as a localizing tool in demonstrating the metabolic changes associated with temporal lobe epilepsy. To analyze the significance of these MR spectroscopy findings further, the authors explored the relationship between regional alterations in the NAA/Cr ratio in hippocampi measured preoperatively and histopathological findings in hippocampi resected in patients with intractable mesial temporal lobe epilepsy (MTLE).

Methods. Twelve patients in whom the diagnosis of MTLE had been made and 12 healthy volunteers with no known history of neurological disease underwent high-resolution 1H MR spectroscopy imaging of NAA and Cr (0.64 cm3 nominal voxel resolution) in five voxels spanning the anteroposterior length of the hippocampus. The authors correlated the NAA/Cr ratio with neuropathological findings in resected hippocampi, specifically glial fibrillary acidic protein (GFAP) immunoreactivity and pyramidal neuronal loss. A linear regression analysis of the ipsilateral NAA/Cr ratio revealed a statistically significant relation to the extent of hippocampal neuronal loss in only the CA2 sector (correlation coefficient [r] = −0.66, p < 0.03). The ipsilateral NAA/Cr ratio displayed significant regressions with GFAP immunoreactivity from all the CA sectors (r values ranged from −0.69 and p < 0.01 for the CA4 sector to −0.88 and p < 0.001 for the CA2 sector) except for the CA1. The extent of neuronal cell loss in every hippocampal subfield (r = 0.71−0.74, p < 0.007), except the CA2 (p = 0.08), correlated to the extent of neuronal cell loss in the dentate gyrus. There was no significant relationship between the duration or frequency of seizures and the mean ipsilateral NAA/Cr ratio; however, the mean density of GFAP-immunopositive cells correlated with seizure frequency (p < 0.03).

Conclusions. The NAA/Cr ratio may not measure the full extent of hippocampal neuronal cell loss. The significant association of the NAA/Cr ratio with the GFAP immunoreactivity of most CA sectors indicates that the NAA/Cr ratio may provide a more accurate measurement of recent neuronal injury caused by epileptic activity. The coupling between neuronal impairment and astroglial GFAP expression may indicate the close association between neuronal and glial dysfunction in patients with epilepsy.

1H and 31P Spectroscopic Imaging of Epilepsy: Spectroscopic and Histologic Correlations

Although MRS measurements are useful in assessing the biochemical alterations underlying human epilepsy, to date their use has been limited primarily by three factors: (a) the lack of widespread methods and appropriate hardware for acquiring high-resolution spectroscopic imaging data, (b) difficulties in spectral interpretation associated with metabolic heterogeneity, and (c) difficulties in biological interpretation due to a lack of correlative histologic studies. In this work, we (a) describe approaches to overcome these hurdles, and (b) discuss the biological interpretation of the spectroscopic findings in TLE.

Correlation between 1H MRS and Memory before and after Surgery in Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis

PURPOSE

Proton magnetic resonance spectroscopy (1H MRS), which can demonstrate neuronal loss and gliosis, may be used as a sensitive tool for lateralization of temporal lobe epilepsy (TLE). Although the correlation between the memory functions and 1H MRS has been investigated, its predictive value after surgery has not been studied previously. This study evaluated memory and 1H MRS values of medically intractable patients with mesial TLE and hippocampal sclerosis (MTLE-HS) before and after selective amygdalohippocampectomy (SAH).

METHODS

Twenty-two patients underwent memory tests and 1H MRS investigation before and 6 months after SAH and were compared with nine control subjects.

RESULTS

The 1H MRS scores were found to be significantly low on the pathological side of the patients. Both right-sided 1H MRS of right TLE and left-sided 1H MRS values of left TLE patients were correlated only with verbal memory scores. Statistical analysis did not reveal any significance for nonverbal memory scores for both TLE groups on either side, which showed no significant correlation between material specificity and 1H MRS findings. Conversely, regression analyses demonstrated that high right- and low left-sided 1H MRS values obtained before surgery may predict a decline in verbal learning scores after surgery.

CONCLUSIONS

1H MRS can be considered as a useful tool to determine the lateralization in patients with MTLE-HS before the surgery. Although only a weak relation exists between the MRS values and memory scores, presurgical MRS scores may be predictive for a possible deterioration in verbal memory after surgery. However, further studies with higher numbers of cases are needed for confirmation of the results.

Hippocampal N-acetyl aspartate levels do not mirror neuronal cell densities in creatine-supplemented epileptic rats

For neuroprotective therapy of neurodegenerative diseases creatine treatment has gained special interest because creatine has been shown to cross the blood-brain barrier, accumulate in the human brain in vivo and cause delayed neuronal cell death in a large number of animal models. Here, we used the pilocarpine model of temporal lobe epilepsy to determine whether creatine administration is able to attenuate the epilepsy-associated decrease in hippocampal N-acetyl aspartate (NAA) concentrations, impairment of mitochondrial function and neuronal cell loss. In vivo1H-NMR spectroscopy showed, in epileptic rats after creatine administration, higher hippocampal NAA concentrations, suggesting improved neuronal survival. However, in vitro observation of hippocampal slices from creatine-treated epileptic rats revealed a more pronounced loss of pyramidal neurons and decrease in activity of mitochondrial enzymes in hippocampal subfields. This indicates that NAA concentrations measured by in vivo1H-NMR spectroscopy reflect alterations of metabolism rather than neuronal cell densities. Our data indicate an adverse effect of creatine on neuronal survival under conditions of enhanced neuronal activity.

Extraction of epileptogenic foci from PET and SPECT images by fuzzy modeling and data fusion

During the presurgical evaluation of medically intractable epilepsy, isotopic functional imagery provides an increasing amount of data concerning the potential location of the focus. The aim of this study is to facilitate the surgical decision by presenting an image fusion method able to extract epileptogenic foci from periictal single photon emission computed tomography (SPECT), interictal SPECT, fluoro-desoxy-glucose (FDG) position emission tomography (PET), and flumazenil PET. After spatial coregistration, the images are converted into fuzzy maps whose membership functions indicate the pathological degree of each voxel, according to each modality. These maps are then fused together thanks to a combination operator managing uncertainty (due to the sensitivity) and imprecision (due to poor resolution and partial volume effect) of the images. In the framework of possibilistic theory, this operator mimics the way the physicians evaluate and compare the various exams. The technique was successfully tested on simulated images with well-defined abnormalities, in terms of size and intensity. A preliminary clinical study was also performed and gave results in accordance with the "gold standard" investigation (deep electrodes or postsurgical outcome) in 11 patients out of 12.

Evidence of neuronal injury outside the medial temporal lobe in temporal lobe epilepsy: N-acetylaspartate concentration reductions detected with multisection proton MR spectroscopic imaging--initial experience

PURPOSE

To determine whether magnetic resonance (MR) spectroscopic imaging reveals metabolic changes, especially decreased N-acetylaspartate (NAA) concentrations outside the medial temporal lobe in patients with mesial temporal lobe epilepsy (TLE), consistent with neuropathologic findings of extratemporal neuronal impairment.

MATERIALS AND METHODS

Eleven patients with mesial TLE and 13 control subjects were examined with multisection MR spectroscopic imaging. Three MR spectroscopic imaging sections were acquired. Thirteen brain regions in each hemisphere and the midbrain were analyzed in each patient, and the NAA to creatine-phosphocreatine (Cr) plus choline-containing compounds (Ch) (NAA/[Cr + Ch]) ratios were determined. In addition, hemispheric and whole-brain values were calculated and statistically analyzed.

RESULTS

The NAA/(Cr + Ch) ratio in the ipsilateral hippocampus was significantly reduced, compared with that in the contralateral hippocampus (P <.002) and compared with that in control subjects (P <.03), confirming findings in previous studies. In patients, whole-brain NAA/(Cr + Ch) ratio outside the hippocampus was significantly lower than that in control subjects (P <.002). For the ipsilateral hemisphere in patients, NAA/(Cr + Ch) ratio was significantly lower than that in control subjects (P <.0002). Comparisons between individual brain regions revealed trends toward lower NAA/(Cr + Ch) ratios in many areas of the ipsilateral and, to a lesser extent, the contralateral hemisphere outside the hippocampus and temporal lobe, suggesting diffuse impairment.

CONCLUSION

Results suggest that repeated seizure activity damages neurons outside of the seizure focus.