Lateralization of temporal lobe epilepsy based on regional metabolic abnormalities in proton magnetic resonance spectroscopic images

Simultaneous high-resolution whole-brain MR spectroscopy and [18F]FDG PET for temporal lobe epilepsy

PURPOSE

Precise lateralizing the epileptogenic zone in patients with drug-resistant mesial temporal lobe epilepsy (mTLE) remains challenging, particularly when routine MRI scans are inconclusive (MRI-negative). This study aimed to investigate the synergy of fast, high-resolution, whole-brain MRSI in conjunction with simultaneous [18F]FDG PET for the lateralization of mTLE.

METHODS

Forty-eight drug-resistant mTLE patients (M/F 31/17, age 12-58) underwent MRSI and [18F]FDG PET on a hybrid PET/MR scanner. Lateralization of mTLE was evaluated by visual inspection and statistical classifiers of metabolic mappings against routine MRI. Additionally, this study explored how disease status influences the associations between altered N-acetyl aspartate (NAA) and FDG uptake using hierarchical moderated multiple regression.

RESULTS

The high-resolution whole-brain MRSI data offers metabolite maps at comparable resolution to [18F]FDG PET. Visual examinations of combined MRSI and [18F]FDG PET showed an mTLE lateralization accuracy rate of 91.7% in a 48-patient cohort, surpassing routine MRI (52.1%). Notably, out of 23 MRI-negative mTLE, combined MRSI and [18F]FDG PET helped detect 19 cases. Logistical regression models combining hippocampal NAA level and FDG uptake improved lateralization performance (AUC=0.856), while further incorporating extrahippocampal regions such as amygdala, thalamus, and superior temporal gyrus increased the AUC to 0.939. Concurrent MRSI/PET revealed a moderating influence of disease duration and hippocampal atrophy on the association between hippocampal NAA and glucose uptake, providing significant new insights into the disease's trajectory.

CONCLUSION

This paper reports the first metabolic imaging study using simultaneous high-resolution MRSI and [18F]FDG PET, which help visualize MRI-unidentifiable lesions and may thus advance diagnostic tools and management strategies for drug-resistant mTLE.

MR Image Changes of Normal-Appearing Brain Tissue after Radiotherapy

Simple Summary

Radiotherapy is one of the most important treatment options against cancer. Irradiation of cancerous tissue either directly destroys the cancer cells or damages them such that they cannot reproduce. One side-effect of radiotherapy is that tumor-surrounding normal tissue is inevitably also irradiated, albeit at a lower dose. The resulting long-term damage can significantly affect cognitive performance and quality of life. Many studies investigated the effect of irradiation on normal-appearing brain tissues and some of these correlated imaging findings with functional outcome. This article provides an overview of the examination of radiation-induced injuries using conventional and enhanced MRI methods and summarizes conclusions about the underlying tissue changes. Radiation-induced morphologic, microstructural, vascular, and metabolic tissue changes have been observed, in which the effect of irradiation was evident in terms of decreased perfusion and neuronal health as well as increased diffusion and atrophy.

Abstract

Radiotherapy is part of the standard treatment of most primary brain tumors. Large clinical target volumes and physical characteristics of photon beams inevitably lead to irradiation of surrounding normal brain tissue. This can cause radiation-induced brain injury. In particular, late brain injury, such as cognitive dysfunction, is often irreversible and progressive over time, resulting in a significant reduction in quality of life. Since 50% of patients have survival times greater than six months, radiation-induced side effects become more relevant and need to be balanced against radiation treatment given with curative intent. To develop adequate treatment and prevention strategies, the underlying cause of radiation-induced side-effects needs to be understood. This paper provides an overview of radiation-induced changes observed in normal-appearing brains measured with conventional and advanced MRI techniques and summarizes the current findings and conclusions. Brain atrophy was observed with anatomical MRI. Changes in tissue microstructure were seen on diffusion imaging. Vascular changes were examined with perfusion-weighted imaging and susceptibility-weighted imaging. MR spectroscopy revealed decreasing N-acetyl aspartate, indicating decreased neuronal health or neuronal loss. Based on these findings, multicenter prospective studies incorporating advanced MR techniques as well as neurocognitive function tests should be designed in order to gain more evidence on radiation-induced sequelae.

Interictal Single-Voxel Proton Magnetic Resonance Spectroscopy of the Temporal Lobe in Dogs With Idiopathic Epilepsy

Proton magnetic resonance spectroscopy (H1-MRS) could provide insight into the metabolic pathophysiology of the temporal lobe of canine brain after seizure. Currently, there is no evidence-based data available on MRS of temporal lobe in dogs with idiopathic epilepsy (IE). The aim of this prospective, cross-sectional study was to evaluate the interictal metabolic activity of the temporal lobe in IE dogs compared to a control group with the use of H1-MRS. Ten healthy dogs and 27 client-owned dogs with IE underwent 1.5-Tesla magnetic resonance imaging (MRI) and single-voxel H1-MRS. The MRS studies were acquired as spin echoes with a repetition time (TR) of 2,000 ms and an echo time (TE) of 144 ms. A cubic voxel (10 ×10 ×10 mm) was positioned bilaterally into the region of the left and right temporal lobe, including a middle part of the hippocampus and the amygdala. The N-acetylaspartate (NAA)-to-creatine (NAA/Cr), NAA-to-choline (NAA/Cho), choline-to-creatine (Cho/Cr), and choline-to-NAA (Cho/NAA) ratios were determined in both hemispheres and compared to controls. No significant differences in all metabolite ratios between epileptic dogs and the control group could be found. A time-dependent decrease in the NAA/Cho ratio as well as an increase in the Cho/NAA ratio was found with proximity in time to the last seizure. We found no correlation between metabolite ratios and age or sex in this animal group. Time span from the last seizure to the acquisition of MRS significantly correlated with NAA/Cho and Cho/NAA ratio. We conclude that without a time relation, metabolite ratios in dogs with IE do not differ from those of the control group.

Interactions between in vivo neuronal-glial markers, side of hippocampal sclerosis, and pharmacoresponse in temporal lobe epilepsy

OBJECTIVE

To evaluate the interactions of metabolic neuronal-glial changes with the presence and hemispheric-side of hippocampal sclerosis (HS) and its potential role in predicting pharmacoresistance in temporal lobe epilepsy (TLE).

METHODS

We included structural magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (¹ H-MRS) metabolic data for 91 patients with unilateral TLE and 50 healthy controls. We measured the values of total N-acetyl aspartate/total creatine (tNAA/tCr), glutamate/tCr (Glu/tCr), and myo-inositol/tCr (mIns/tCr). To assess the influence of the pharmacoresponse and hemispheric-side of HS on metabolic data, the relationship between clinical and MRI data, and the predictive value of NAA/Cr, we used analysis of variance/covariance and built a logistic regression model. We used bootstrap simulations to evaluate reproducibility.

RESULTS

Bilateral tNAA/tCr reduction was associated with pharmacoresistance and with left HS, a decrease of Glu/tCr ipsilateral to the seizure focus was associated with pharmacoresistance, and ipsilateral mIns/tCr increase was related to pharmacoresistance and the presence of left HS. The logistic regression model containing clinical and ¹ H-MRS data discriminated pharmacoresistance (area under the curve [AUC] = 0.78). However, the reduction of tNAA/tCr was the main predictor, with the odds 2.48 greater for pharmacoresistance.

SIGNIFICANCE

Our study revealed a spectrum of neuronal-glial changes in TLE, which was associated with pharmacoresistance, being more severe in left-sided HS and less severe in MRI-negative TLE. These noninvasive, in vivo biomarkers provide valuable additional information about the interhemispheric differences in metabolic dysfunction, seizure burden, and HS, and may help to predict pharmacoresistance.

Long term sequelae of amygdala enlargement in temporal lobe epilepsy

PURPOSE

Amygdala enlargement (AE) has been reported in drug resistant lesional and non-lesional temporal lobe epilepsy (TLE). Its contribution to development of intractability of epilepsy is at best uncertain. Our aim was to study the natural course of AE in a heterogenous group of TLE patients with follow-up imaging and clinical outcomes.

METHODS

A prospective observational study in patients with TLE with imaging features of AE recruited from epilepsy clinics between 1994 and 2018. Demographic data, details of epilepsy syndrome, outcomes and follow up neuroimaging were extracted.

RESULTS

Forty-two patients were recruited including 19 males (45 %). Mean age at onset of epilepsy was 30.6 years and mean duration of epilepsy was 19.9 years. On MRI, 33 patients had isolated unilateral AE and eleven had AE with hippocampal enlargement (HE). Twenty (48 %) underwent temporal resections with most common histopathology being amygdalar gliosis (40 %). Engel Class IA outcome at last follow up (mean, 10 years) was 60 %. Thirty-four patients had neuroimaging follow up of at least 1 year (mean, 5 years). AE resolved in 6, persisted in 25, evolved into bilateral HS in 1, bilateral mesial temporal atrophy in 1 and ipsilateral mesial temporal atrophy in 1. Resolution of AE was associated with better seizure free outcomes (p = 0.013).

CONCLUSIONS

TLE with AE is associated with favourable prognosis yet not benign. Over 50 % were drug resistant and surgical outcomes were similar to mTLE. Resolution of AE on follow up neuroimaging was associated with better seizure free outcomes.

Magnetic Resonance Spectroscopy and its Clinical Applications: A Review

In vivo NMR spectroscopy is known as magnetic resonance spectroscopy (MRS). MRS has been applied as both a research and a clinical tool in order to detect visible or nonvisible abnormalities. The adaptability of MRS allows a technique that can probe a wide variety of metabolic uses across different tissues. Although MRS is mostly applied for brain tissue, it can be used for detection, localization, staging, tumour aggressiveness evaluation, and tumour response assessment of breast, prostate, hepatic, and other cancers. In this article, the medical applications of MRS in the brain, including tumours, neural and psychiatric disorder studies, breast, prostate, hepatic, gastrointestinal, and genitourinary investigations have been reviewed.

Brain metabolite values in children with breath-holding spells

Breath-holding spells are benign, paroxysmal events with apnea and postural tone changes after a crying episode in infants. The objective of this study was to investigate the pathologies in brain metabolite values in the absence of seizure in children with breath-holding spells by using magnetic resonance spectroscopy (MRS). Brain MRS examination was performed on 18 children with breath-holding spells and 13 neurologically normal children who were included as the control group. There was no significant difference in terms of N-acetyl aspartate (NAA), choline (Cho), creatine (Cr), and myoinositol (mI) levels and also in terms of NAA/Cr, Cho/Cr, and mI/Cr ratios between the patients and the control group (all P>0.05). Our study suggested that there is no permanent neuronal damage in patients with breath-holding spells. This result confirms the previous studies, which reported no permanent neuronal damage in patients with breath-holding spells.

Comparative Lateralizing Ability of Multimodality MRI in Temporal Lobe Epilepsy

Purpose. The objective is to compare lateralizing ability of three quantitative MR (qMRI) modalities to depict changes of hippocampal architecture with clinical entities in temporal lobe epilepsy. Methods. We evaluated 14 patients with clinical and EEG proven diagnosis of unilateral TLE and 15 healthy volunteers. T1-weighted 3D dataset for volumetry, single-voxel ¹H MR spectroscopy (MRS), and diffusion tensor imaging (DTI) were performed for bilateral hippocampi of all subjects. Results. Individual volumetric measurements provided accurate lateralization in 85% of the patients, spectroscopy in 57%, and DTI in 57%. Higher lateralization ratios were acquired combining volumetry-spectroscopy (85%), spectroscopy-DTI (85%), and volumetry-DTI (100%). Significantly decreased NAA/(Cho+Cr) ratios (p = 0.002) and increased FA (p = 0.001) values were obtained in ipsilateral to epileptogenic hippocampus. Duration of epilepsy and FA values showed a significant negative correlation (p = 0.016, r = −0.847). The history of febrile convulsion associated with ipsilateral increased ADC values (p = 0.015, r = 0.851) and reduced NAA/(Cho+Cr) ratios (p = 0.047, r = −761). Conclusion. Volumetry, MRS, and DTI studies provide complementary information of hippocampal pathology. For lateralization of epileptogenic focus and preoperative examination, volumetry-DTI combination may be indicative of diagnostic accuracy.

Utility of magnetic resonance spectroscopic imaging for human epilepsy

This review discusses the potential utility of broad based use of magnetic resonance (MR) spectroscopic imaging for human epilepsy and seizure localization. The clinical challenges are well known to the epilepsy community, intrinsic in the variability of location, volumetric size and network extent of epileptogenic tissue in individual patients. The technical challenges are also evident, with high performance requirements in multiple steps, including magnet homogeneity, detector performance, sequence design, speed of acquisition in addition to large territory spectral processing. We consider how MR spectroscopy and spectroscopic imaging has been informative for epilepsy thus far, with specific attention to what is measured, the interpretation of such measurements and technical performance challenges. Examples are shown from medial temporal lobe and neocortical epilepsies are considered from 4T, 7T and most recently 3T.

Decreased expression of proteins involved in energy metabolism in the hippocampal granular layer of rats submitted to the pilocarpine epilepsy model

Long-term structural and functional changes in the hippocampus have been identified as the primary physiopathological basis for temporal lobe epilepsy. These changes include reactive gliosis and granule cell axonal sprouting within the dentate gyrus. The intimate mechanisms of these changes are beginning to be revealed. Here, we show the possibility of using laser capture microdissection (LCM) to isolate the dentate granular cell layer of Wistar rats submitted to the pilocarpine model of epilepsy. Using two-dimensional gel electrophoresis (2-D PAGE) and mass spectrometry for laser-captured cells, we identified molecular events that could be altered as part of the epileptic pathogenic process. According to our results, eight proteins related to energy metabolism were differentially expressed between both the control and pilocarpine-treated animals. These results provide, for the first time, new molecular insights into the altered protein profile of the epileptogenic dentate gyrus and can contribute to a better understanding of the phenomena involved in the genesis and maintenance of the epileptic state.

Brain mitochondrial metabolic dysfunction and glutamate level reduction in the pilocarpine model of temporal lobe epilepsy in mice

Although certain metabolic characteristics such as interictal glucose hypometabolism are well established for temporal lobe epilepsy (TLE), its pathogenesis still remains unclear. Here, we performed a comprehensive study of brain metabolism in a mouse model of TLE, induced by pilocarpine-status epilepticus (SE). To investigate glucose metabolism, we injected mice 3.5-4 weeks after SE with [1,2-(13)C]glucose before microwave fixation of the head. Using (1)H and (13)C nuclear magnetic resonance spectroscopy, gas chromatography-mass spectrometry and high-pressure liquid chromatography, we quantified metabolites and (13)C labeling in extracts of cortex and hippocampal formation (HF). Hippocampal levels of glutamate, glutathione and alanine were decreased in pilocarpine-SE mice compared with controls. Moreover, the contents of N-acetyl aspartate, succinate and reduced nicotinamide adenine dinucleotide (phosphate) NAD(P)H were decreased in HF indicating impairment of mitochondrial function. In addition, the reduction in (13)C enrichment of hippocampal citrate and malate suggests decreased tricarboxylic acid (TCA) cycle turnover in this region. In cortex, we found reduced (13)C labeling of glutamate, glutamine and aspartate via the pyruvate carboxylation and pyruvate dehydrogenation pathways, suggesting slower turnover of these amino acids and/or the TCA cycle. In conclusion, mitochondrial metabolic dysfunction and altered amino-acid metabolism is found in both cortex and HF in this epilepsy model.

Neuroimaging biomarkers for epilepsy: advances and relevance to glial cells

Glial cells play an important role in normal brain function and emerging evidence would suggest that their dysfunction may be responsible for some epileptic disease states. Neuroimaging of glial cells is desirable, but there are no clear methods to assess neither their function nor localization. Magnetic resonance imaging (MRI) is now part of a standardized epilepsy imaging protocol to assess patients. Structural volumetric and T2-weighted imaging changes can assist in making a positive diagnosis in a majority of patients. The alterations reported in structural and T2 imaging is predominantly thought to reflect early neuronal loss followed by glial hypertrophy. MR spectroscopy for myo-inositol is a being pursued to identify glial alterations along with neuronal markers. Diffusion weighted imaging (DWI) is ideal for acute epileptiform events, but is not sensitive to either glial cells or neuronal long-term changes found in epilepsy. However, DWI variants such as diffusion tensor imaging or q-space imaging may shed additional light on aberrant glial function in the future. The sensitivity and specificity of PET radioligands, including those targeting glial cells (translocator protein) hold promise in being able to image glial cells. As the role of glial function/dysfunction in epilepsy becomes more apparent neuroimaging methods will evolve to assist the clinician and researcher in visualizing their location and function.

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

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

Neuroimaging in epilepsy

Epilepsy is a common neurological disorder with diverse etiologies. Neuroimaging plays an important role in workup of patients with epilepsy. It helps to identify brain pathologies that require specific treatment; and also in formulating syndromic and etiological diagnoses so as to give patients and their relatives an accurate prognosis. Magnetic resonance imaging, specially the 3 tesla MRI is the imaging of choice because of its ability to detect small lesions like mesial temporal sclerosis, cortical dysplasias, small tumors, etc that are not detected by conventional MR or CT scan of brain. Identification of these lesions often helps in managing refractory epilepsies more effectively. However, cost and non-availability of MR in large part of the country necessitate the use of CT as an alternative. CT is often the initial investigation and also useful in acute situations. Functional imagings are used for pre-surgical work-up of refractory epilepsy cases with an aim to identify the epileptogenic focus and to delineate functional areas nearing the focus.

The effect of behavior therapy on caudate N-acetyl-l-aspartic acid in adults with obsessive-compulsive disorder

Previous studies suggest that baseline differences in neuronal markers between patients with obsessive-compulsive disorder (OCD) and healthy controls no longer exist following successful pharmacotherapy. The current study used proton magnetic resonance spectroscopy (MRS) to investigate differences in absolute concentrations of neurochemicals (i.e., N-acetyl-l-aspartic; NAA) in the head of the caudate nucleus (HOC) and orbital frontal white matter (OFWM) between 15 adults with OCD and a sex- and age-matched control group, as well as the effects of behavior therapy on these chemicals. Behavior therapy was associated with a significant increase in left HOC NAA. When the analyses were restricted to only pairings with complete data (OCD patient, control, post-treatment), the levels of left HOC NAA were significantly lower in patients compared to controls, and increased significantly with treatment. Exploratory analyses suggested that levels of NAA and Cr (creatine) in the right OFWM may be significantly lower in the OCD group than the control group. The results raise the possibility that successful behavioral treatment may be associated with increases in markers of neuronal viability, although other associations found in the literature were not replicated.

Mesial temporal lobe epilepsy: How do we improve surgical outcome?

Surgery has become the standard of care for patients with intractable temporal lobe epilepsy, with anterior temporal lobe resection the most common operation performed for adults with hippocampal sclerosis. This procedure leads to significant improvement in the lives of the overwhelming majority of patients. Despite improved techniques in neuroimaging that have facilitated the identification of potential surgical candidates, the short-term and long-term success of epilepsy surgery has not changed substantially in recent decades. The basic surgical goal, removal of the amygdala, hippocampus, and parahippocampal gyrus, is based on the hypothesis that these structures represent a uniform and contiguous source of seizures in the mesial temporal lobe epilepsy (MTLE) syndrome. Recent observations from the histopathology of resected tissue, preoperative neuroimaging, and the basic science laboratory suggest that the syndrome is not always a uniform entity. Despite clinical similarity, not all patients become seizure-free. Improving surgical outcomes requires a re-examination of why patients fail surgery. This review examines recent findings from the clinic and laboratory. Historically, we have considered MTLE a single disorder, but it may be time to view it as a group of closely related syndromes with variable type and extent of histopathology. That recognition may lead to identifying the appropriate subgroups that will require different diagnostic and surgical approaches to improve surgical outcomes.

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.

Functional and structural changes in the memory network associated with left temporal lobe epilepsy

Understanding functional plasticity in memory networks associated with temporal lobe epilepsy (TLE) is central to predicting memory decline following surgery. However, the extent of functional reorganization within memory networks remains unclear. In this preliminary study, we used novel analysis methods assessing network-level changes across the brain during memory task performance in patients with TLE to test the hypothesis that hippocampal functions may not readily shift between hemispheres, but instead may show altered intra-hemispheric organization with unilateral damage. In addition, we wished to relate functional differences to structural changes along specific fibre pathways associated with memory function. Nine pre-operative patients with intractable left TLE and 10 healthy controls underwent functional MRI during complex scene encoding. Diffusion tensor imaging was additionally performed in the same patients. In our study, we found no evidence of inter-hemispheric shifts in memory-related activity in TLE using standard general linear model analysis. However, tensor independent component analysis revealed significant reductions in functional connectivity between bilateral MTL, occipital and left orbitofrontal regions among others in left TLE. This altered orbitofrontal activity was directly related to measures of fornix tract coherence in patients (P < 0.05). Our results suggest that specific fibre pathways, potentially affected by MTL neurodegeneration, may play a central role in functional plasticity in TLE and highlight the importance of network-based analysis approaches. Relative to standard model-based methods, novel objective functional connectivity analyses may offer improved sensitivity to subtle changes in the distribution of memory functions relevant for surgical planning in TLE.

Use of short echo time two-dimensional 1H-magnetic resonance spectroscopy in temporal lobe epilepsy with negative magnetic resonance imaging findings

We evaluated short echo time two-dimensional 1H magnetic resonance spectroscopy (2D-1HMRS) with the point-resolved spatial selection (PRESS) protocol in temporal lobe epilepsy (TLE) patients with negative magnetic resonance imaging (MRI) findings and described the characteristics of 2D-(1)HMRS in the epileptic focus. Thirty-eight TLE patients with negative conventional MRI findings and 10 healthy controls were studied by 2D-1HMRS. A 128-channel prolonged video-electroencephalographic (EEG) method was used as the standard for epileptogenic focus localization to evaluate N-acetyl aspartate/(choline + creatine + phosphocreatine) (NAA/[Cho + Cr-PCr]), glutamate + glutamine/creatine (Glx/Cr-PCr) and myo-inositol/Cr-PCr ratios in patients with negative MRI findings. The 2D-1HMRS showed that 32/38 patients and all healthy controls had stable baselines and good signal-to-noise ratios. Compared with the healthy controls, 32 patients showed abnormal NAA/(Cho + Cr-PCr) ratios in the hippocampus and, in 25 of these patients, focus lateralization agreed with the EEG. It is concluded that short echo time 2D-1HMRS with the PRESS protocol can help find abnormalities in lateralization of temporal epilepsy in patients with negative MRI findings.

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.

The neural bases of obsessive-compulsive disorder in children and adults

Functional imaging studies have reported with remarkable consistency hyperactivity in the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), and caudate nucleus of patients with obsessive-compulsive disorder (OCD). These findings have often been interpreted as evidence that abnormalities in cortico-basal ganglia-thalamo-cortical loops involving the OFC and ACC are causally related to OCD. This interpretation remains controversial, however, because such hyperactivity may represent either a cause or a consequence of the symptoms. This article analyzes the evidence for a causal role of these loops in producing OCD in children and adults. The article first reviews the strong evidence for anatomical abnormalities in these loops in patients with OCD. These findings are not sufficient to establish causality, however, because anatomical alterations may themselves be a consequence rather than a cause of the symptoms. The article then reviews three lines of evidence that, despite their own limitations, permit stronger causal inferences: the development of OCD following brain injury, pediatric autoimmune neuropsychiatric disorders associated with streptococcal infection, and neurosurgical lesions that attenuate OCD. Converging evidence from these various lines of research supports a causal role for the cortico-basal ganglia-thalamo-cortical loops that involve the OFC and ACC in the pathogenesis of OCD in children and adults.

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.

Non-invasive detection of hippocampal sclerosis: correlation between metabolite alterations detected by (1)H-MRS and neuropathology

We assessed (1)H-MRS as a screening tool for detection of hippocampal sclerosis in patients with temporal lobe epilepsy (TLE). (1)H-MRS was carried out in the hippocampus of 23 patients with unilateral TLE. Metabolite alterations detected by (1)H-MRS correlated with degree of segmental neuronal cell loss and amount of astrogliosis. Positive correlation was found between total N-Acetylaspartate (tNAA) reduction and neuronal density in hippocampal CA1 (P < 0.001), CA3 (P = 0.015), and CA4 subfields (P = 0.031) and the dentate gyrus (P = 0.006). Neuronal cell loss in CA1 turned out to be the most predictive and only significant variable for tNAA reduction (P = 0.027). The association between myo-inositol (m-Ins) and astroglial glial fibrillary acidic protein (GFAP) expression revealed significantly increased m-Ins concentrations associated with diffuse astrogliosis (m-Ins = 6.4 +/- 1.1 institutional units) compared with gliosis restricted to isolated sectors of the hippocampus (i.e. hilus) (m-Ins = 5.2 +/- 1.2 institutional units) (P = 0.039). A negative correlation was found between m-Ins and neuronal loss in the CA4 subfield of the hippocampus (P = 0.028). Our results support (1)H-MRS as a suitable non-invasive method for preoperative identification of hippocampal sclerosis in patients with TLE. The extent of tNAA reduction correlates with hippocampal neuronal cell density. Furthermore, m-Ins is associated with the extent of hippocampal astrogliosis.

Neurometabolism in human epilepsy

PURPOSE

Because of the large and continuous energetic requirements of brain function, neurometabolic dysfunction is a key pathophysiologic aspect of the epileptic brain. Additionally, neurometabolic dysfunction has many self-propagating features that are typical of epileptogenic processes, that is, where each occurrence makes the likelihood of further mitochondrial and energetic injury more probable. Thus abnormal neurometabolism may be not only a chronic accompaniment of the epileptic brain, but also a direct contributor to epileptogenesis.

METHODS

We examine the evidence for neurometabolic dysfunction in epilepsy, integrating human studies of metabolic imaging, electrophysiology, microdialysis, as well as intracranial EEG and neuropathology.

RESULTS

As an approach of noninvasive functional imaging, quantitative magnetic resonance spectroscopic imaging (MRSI) measured abnormalities of mitochondrial and energetic dysfunction (via 1H or 31P spectroscopy) are related to several pathophysiologic indices of epileptic dysfunction. With patients undergoing hippocampal resection, intraoperative 13C-glucose turnover studies show a profound decrease in neurotransmitter (glutamate-glutamine) cycling relative to oxidation in the sclerotic hippocampus. Increased extracellular glutamate (which has long been associated with increased seizure likelihood) is significantly linked with declining energetics as measured by 31P MR, as well as with increased EEG measures of Teager energy, further arguing for a direct role of glutamate with hyperexcitability.

DISCUSSION

Given the important contribution that metabolic performance makes toward excitability in brain, it is not surprising that numerous aspects of mitochondrial and energetic state link significantly with electrophysiologic and microdialysis measures in human epilepsy. This may be of particular relevance with the self-propagating nature of mitochondrial injury, but may also help define the conditions for which interventions may be developed.

Magnetic resonance spectroscopy in animal models of epilepsy

The noninvasive localization of the epileptogenic zone continues to be a challenge in many patients that present as candidates for possible epilepsy surgery. Magnetic resonance imaging (MRI) techniques provide accurate anatomical definition, but despite their high resolution, these techniques fail to visualize the pathological neocortical and hippocampal changes in a sizable number of patients with focal pathologies. Further, visualized lesions on MRI may not all produce seizures. One of the keys to the understanding of the epileptogenic zone lies in the recognition of the metabolic alterations that occur in the setting of epileptic seizures. Magnetic resonance spectroscopy (MRS) is a valuable tool that can be used to study the metabolic changes seen in both acute and chronic animal models of epilepsy. Such study allows for the identification of epileptic tissue with high sensitivity and specificity. We present here a review of the use of MRS in animal models of epilepsy.

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.

Identifying the affected hemisphere by (1)H-MR spectroscopy in patients with temporal lobe epilepsy and no pathological findings in high resolution MRI

Up to 30% of patients with temporal lobe epilepsy (TLE) remain without remarkable changes in MRI. In this study we investigated the role of (1)H-MR spectroscopy ((1)H-MRS) in lateralizing the affected hemisphere in the mentioned patient group. Twenty-two consecutive patients diagnosed with TLE were investigated by high resolution MRI and (1)H-MRS. We examined the incidence and diagnostic accuracy of temporal metabolite alterations determined by Linear Combination of Model Spectra (L C Model) via water reference. Metabolite values of each hemisphere of TLE patients were compared with healthy controls. Results of metabolite alterations were related to intensive video EEG focus localization. Reduction of N-acetylaspartate + N-acetylaspartyl-glutamate (tNAA) in the affected hemisphere revealed identification in six of nine patients (66%) with unilateral TLE. Group comparison revealed a significant reduction of tNAA (6.1+/-0.8*) in the involved temporal lobe compared with controls (6.67+/-0.4*, P=0.026). Choline levels were significantly increased in the affected hemisphere (1.42+/-0.17*) compared with healthy controls (1.22+/-0.17*, P=0.035). The results of our study show that (1)H-MRS is able to identify the affected hemisphere of MRI negative TLE patients and can be used as an additive tool in multimodal focus localization.

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.

Proton magnetic resonance spectroscopy of mesial temporal sclerosis: Analysis of voxel shape and position to improve diagnostic accuracy

OBJECTIVE

To determine if change in voxel shape and position improves the lateralization of magnetic resonance (MR) spectroscopy to the side of the MR imaging and/or electroencephalography (EEG) abnormality in mesial temporal sclerosis.

METHODS

In 10 patients with unilateral mesial temporal sclerosis and 5 controls, MR spectroscopy was performed. Long echo time single-voxel spectroscopy was obtained in the right and left hippocampus. First, the standard 2-cm x 2-cm x 2-cm cubic voxels were placed bilaterally. Then, 1-cm x 2-cm x 4-cm rectangular voxels were used. With this rectangular voxel shape, more of the hippocampus and less of the adjacent medial temporal lobe were included in the interrogation voxel. N-acetylaspartate-to-creatine (NAA/Cr) ratios and choline-to-creatine (Cho/Cr) ratios were obtained. The difference between the affected and unaffected sides in the patients was calculated and compared with the controls. Additionally, the mean difference and standard deviation were determined. Predictive values and Student t tests were also performed.

RESULTS

In all 10 patients, using the NAA/Cr ratios, the rectangular voxel correctly identified the abnormal side. The cubic voxel only identified the abnormal side in 6 of the 10 patients, however. Additionally, the mean difference between the affected and unaffected sides was 0.30 for the rectangular voxel but only 0.003 for the cubic voxel; that is, there was no overall significant difference when using the cubic voxel (P = 0.007). No significant correlation between the affected and unaffected sides was found using the Cho/Cr ratios. No significant difference between the right and left sides was found in the controls.

CONCLUSION

Use of a 1-cm x 2-cm x 4-cm rectangular voxel places more of the hippocampus in the region of interrogation with less partial volume artifact from the adjacent brain parenchyma, which occurs with use of the standard 2-cm x 2-cm x 2-cm cubic voxel, resulting in improved correct lateralization of MR spectroscopy to the side of the MR imaging and/or EEG abnormality.

Extracellular N-acetylaspartate depletion in traumatic brain injury

N-Acetylaspartate (NAA) is almost exclusively localized in neurons in the adult brain and is present in high concentration in the CNS. It can be measured by proton magnetic resonance spectroscopy and is seen as a marker of neuronal damage and death. NMR spectroscopy and animal models have shown NAA depletion to occur in various types of chronic and acute brain injury. We investigated 19 patients with traumatic brain injury (TBI). Microdialysis was utilized to recover NAA, lactate, pyruvate, glycerol and glutamate, at 12-h intervals. These markers were correlated with survival and a 6-month Glasgow Outcome Score. Eleven patients died and eight survived. A linear mixed model analysis showed a significant effect of outcome and of the interaction between time of injury and outcome on NAA levels (p = 0.009 and p = 0.004, respectively). Overall, extracellular NAA was 34% lower in non-survivors. A significant non-recoverable fall was observed in this group from day 4 onwards, with a concomitant rise in lactate-pyruvate ratio and glycerol. These results suggest that mitochondrial dysfunction is a significant contributor to poor outcome following TBI and propose extracellular NAA as a potential marker for monitoring interventions aimed at preserving mitochondrial function.

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.

Temporal lobe magnetic resonance spectroscopic imaging following selective amygdalohippocampectomy for treatment-resistant epilepsy

OBJECTIVES

Magnetic resonance spectroscopic imaging (MRSI) may show circumscribed or extensive decreased brain N-acetyl aspartate (NAA)/creatine and phosphocreatine (Cr) in epilepsy patients. We compared temporal lobe MRSI in patients seizure-free (SzF) or with persistent seizures (PSz) following selective amygdalohippocampectomy (SAH) for medically intractable mesial temporal lobe epilepsy (mTLE). We hypothesized that PSz patients had more extensive temporal lobe metabolite abnormalities than SzF patients.

MATERIALS AND METHODS

MRSI was used to study six regions of interest (ROI) in the bilateral medial and lateral temporal lobes in 14 mTLE patients following SAH and 11 controls.

RESULTS

PSz patients had more temporal lobe ROI with abnormally low NAA/Cr than SzF patients, including the unoperated hippocampus and ipsilateral lateral temporal lobe.

CONCLUSION

Postoperative temporal lobe MRSI abnormalities are more extensive if surgical outcome following SAH is poor. MRSI may be a useful tool to improve selection of appropriate candidates for SAH by identifying patients requiring more intensive investigation prior to epilepsy surgery. Future prospective studies are needed to evaluate the utility of MRSI, a predictor of successful outcome following SAH.

Radiation-induced brain metabolic changes in the acute and early delayed phase detected with quantitative proton magnetic resonance spectroscopy

OBJECTIVE

Quantitative proton magnetic resonance spectroscopy (MRS) was performed before and after radiation therapy to estimate its usefulness for evaluating radiation-induced metabolic brain changes.

METHODS

Twenty patients with multiple brain metastases not having received any previous brain radiation were selected for the study. The total radiation dose varied from 40 (20 fractions) to 50 (25 fractions) Gy, with an opposition technique. MRS was performed just before irradiation, during the acute phase (n = 20, 8.5 +/- 4.6 days) and in the early delayed phase (n = 15, 3.6 +/- 0.5 months) after radiation. The concentration of N-acetyl-L-aspartate (NAA), choline-containing substance (Cho), and creatine/phosphocreatine (Cr) was quantified.

RESULTS

The concentration of NAA decreased (P = 0.05 versus before radiation), and the concentration of Cho increased (P = 0.006 versus before radiation) during the early delayed phase. The concentration of Cr was not changed before or after radiation.

CONCLUSIONS

Radiation-induced changes in brain metabolism were well detected with quantitative MRS in the early delayed phase. Quantitative MRS is a novel tool for estimating radiation-induced neurotoxicity.

Quantitative HMRS and MRI volumetry indicate neuronal damage in the hippocampus of children with focal epilepsy and infrequent seizures

PURPOSE

Seizures induce progressive morphologic and functional changes in particular in the hippocampus, but whether and at what stage the hippocampus is affected in children with focal, temporal, nonintractable epilepsy is poorly known. We have now studied eventual metabolic and volume changes in the hippocampus of children with nonsymptomatic focal epilepsy taking antiepileptic medication (AEDs) but still having infrequent seizures.

METHODS

Quantitative proton magnetic resonance spectroscopy ((1)HMRS) and volumetric MRI were used to study the hippocampal region of 11 pediatric outpatients (age 10 to 17 years) with cryptogenic localization-related epilepsy, and eight healthy volunteers (age 9 to 16 years) served as controls. The spectra were obtained bilaterally from the hippocampi by using the 1.5-T MR imager. The spectral resonance lines of N-acetyl group (NA), creatine and phosphocreatine group (Cr), choline-containing compounds (Cho), and myoinositol (mI) were analyzed quantitatively. The volume of the hippocampus was semiautomatically calculated.

RESULTS

The mean concentration of NA was significantly decreased both in the focus side (9.02 +/- 2.00 mM) and in the nonfocus side (8.88 +/- 2.09 mM) of the patients compared with the controls (10.76 +/- 1.86 mM), in particular if the children had a history of generalized tonic-clonic seizures. The mean concentrations of Cho, Cr, and mI did not differ significantly between the patients and controls. Moreover, the mean hippocampal volume of the focus side of patients was significantly reduced compared with that of the controls.

CONCLUSIONS

Metabolic changes in hippocampi were detected in children with nonsymptomatic localization-related epilepsy and infrequent seizures. Reduced NA could reflect neuronal metabolic dysfunction and/or neuronal damage, as indicated by our volumetric findings.

Neuroimaging of epilepsy: therapeutic implications

Neuroimaging has important applications in the diagnosis and treatment of patients with seizures and epilepsy. Having replaced computed tomography (CT) in many situations, MRI is the preferred imaging technique for patients with epilepsy. Advances in radionuclide-based techniques such as single-photon emission CT/positron emission tomography and electromagnetic source imaging with magnetoencephalography are providing new insights into the pathophysiology of epilepsy. In addition, techniques such as magnetic resonance spectroscopy are beginning to impact treatment. In this review, I discuss how these techniques are used in clinical practice but more importantly, how imaging findings play an increasing role in neurotherapeutics.

Interdependence of N-acetyl aspartate and high-energy phosphates in healthy human brain

Because cellular and extract data have suggested that N-acetylaspartate (NAA) reflects neuronal mitochondrial function, we evaluated the quantitative relationship between NAA, high-energy phosphates, and ADP levels in the hippocampus and occipital lobe of 15 healthy volunteers. The ADP levels are calculated using the creatine kinase equilibrium and quantified (31)P and total creatine measurements. Using high-field quantitative MR spectroscopic imaging, we find that NAA and ADP concentrations in the hippocampal body are 9.7 +/- 1.5mM and 35 +/- 8microM, respectively. In the occipital lobe, NAA and ADP are 11.9 +/- 1.9mM and 32 +/- 12microM, respectively. There is a statistically significant positive correlation between NAA and ADP, with R = +0.80, p < 2 x 10(-7)in the hippocampal body. In an adjacent hippocampal NAA voxel, the correlation between NAA and ADP had a R = +0.62, p < 3 x 10(-4), whereas, in the occipital lobe, R = +0.67, p < 5 x 10(-5). There was no significant relationship NAA and either ATP or phosphocreatine. This positive relationship of NAA with ADP suggests a directional process wherein energetics may modulate mitochondrial function.

Clinical applications of MR spectroscopy in epilepsy

1H and 31P spectroscopy detects relevant metabolite changes in patients with TLE. Numerous studies confirm reduction in NAA and in the ratio of PCr/Pi. In his 1999 review, Kuzniecky concluded that proton MRS, using single-voxel or chemical shift imaging, lateralizes temporal lobe epilepsy in 65% to 96% of cases, with bilateral changes seen in 35% to 45% of cases, whereas phosphorus MRS shows a lateralizing PCr/Pi ratio in 65% to 75% of the TLE patients. There are indications that these changes are reversible with seizure treatment. Improvements in MRS technology, such as the ability to calculate absolute concentrations, to account for differences be-tween gray and white matter and to achieve better spectral resolution by use of a higher magnetic field strength, will now allow more extensive use of this technique for patients with epilepsy.

In vitro1H NMR spectroscopy shows an increase in N-acetylaspartylglutamate and glutamine content in the hippocampus of amygdaloid-kindled rats

We examined energy metabolism and amino acid content in the hippocampus of amygdaloid-kindled rats using (1)H NMR spectroscopy. Three weeks after the last stage 5 seizure, kindled rats were killed by microwave irradiation. The hippocampus was dissected out and subjected to MeOH/CHCl(3) extraction. All (1)H spectra were analyzed to quantify absolute concentrations using a non-linear least squares method, combined with a prior knowledge of chemical shifts. Saturation effects were compensated for by the T1 measurement of each component. Levels of energy metabolism-related compounds, phosphocreatine, creatine, glucose and succinate were the same in both kindled rats and sham controls. Lactate concentration had a tendency to increase, although this was not statistically significant. When compared with sham controls, levels of aspartate, glutamate, glycine and glutamine, as well as GABA and inositol, were increased in the ipsilateral but not the contralateral hippocampus. In contrast, levels of taurine, alanine and threonine were unchanged. Finally, N-acetylaspartylglutamate content was elevated, whereas N-acetyl-l-aspartate content was unaltered in the ipsilateral hippocampus of kindled animals. Our results suggest that amygdala kindling may affects amino acid metabolism, but not energy metabolism.

Chronic temporal lobe epilepsy: spatial extent and degree of metabolic dysfunction studied with magnetic resonance spectroscopy (MRS)

INTRODUCTION

Proton magnetic resonance spectroscopy ((1)H MRS) has been proposed as a lateralizing method for the presurgical evaluation of patients with medically intractable temporal lobe epilepsy (TLE). Studies have shown correlations between temporal lobe (TL) NAA and seizure frequency, and TL NAA/Cr and the duration of epilepsy in patients with TLE. This latter finding may suggest that progressive neuronal dysfunction may occur in both temporal lobes in patients with TLE, even when the seizures originate in only one temporal lobe. We analyzed our data in an attempt to find a possible correlation between extension of neuronal dysfunction based on NAA measures and duration of epilepsy.

METHODS

We studied 45 consecutive patients with the diagnosis of TLE, who were referred for presurgical evaluation. Duration of epilepsy was defined as the interval between the age of seizure onset and the time of the MRS examination. All studies were performed in the inter-ictal state, prior to intracranial monitoring or resection. We performed two-tailed Pearson correlation analysis between ipsilateral NAA/Cr and extension of the abnormality (voxels involved) and the duration of the seizure disorder in years.

RESULTS

The average duration of epilepsy in this group was 20 years. No significant correlation was found between duration of epilepsy and mean hippocampal NAA/Cr (r=-.131, p=.390); nor was a correlation found between duration of epilepsy in years or the extent of metabolic lesion (voxels involved) (r=-.264, p=.079).

CONCLUSIONS

Hippocampal NAA/Cr does not correlate with duration of epilepsy in TLE. Our findings suggest that cross-sectional group measures of hippocampal neuronal function do not suggest damage progression.

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.

Areas of Interictal Spiking Are Associated with Metabolic Dysfunction in MRI‐negative Temporal Lobe Epilepsy

PURPOSE

The objective of our study was to determine noninvasively whether metabolic dysfunction is present in focal areas of interictal electrophysiologic abnormality and whether metabolic dysfunction correlates with frequency of spiking.

METHODS

We used a prospective, power analysis-driven, age-matched design to study 20 subjects with nonlesional temporal lobe epilepsy by using magnetoencephalography (MEG) and proton magnetic resonance spectroscopy (1H-MRS). MEG was used to localize the source area of interictal spikes. 1H-MRS measured integrated peak areas for N-acetyl compounds (NAA) and choline-containing compounds (Cho) in both hippocampi, the MEG spike zone, and the region contralateral to the MEG spike zone in all subjects. 1H-MRS was performed in seven controls.

RESULTS

Fifteen of 20 subjects had a lower NAA/Cho ratio in the MEG spike zone compared with the contralateral homologous region. NAA/Cho was significantly decreased in the MEG spike zone (p < 0.01). NAA/Cho ratios were not significantly different between the hippocampus ipsilateral and contralateral to the spike activity, or from control hippocampi. NAA/Cho ratios did not correlate with spike frequency.

CONCLUSIONS

Metabolic dysfunction is present in focal areas of interictal spiking in nonlesional temporal lobe epilepsy. These findings confirm that functional abnormalities can be detected in vivo in radiographically normal-appearing cortex exhibiting abnormal excitability.

The role of relaxation time corrections for the evaluation of long and short echo time 1H MR spectra of the hippocampus by NUMARIS and LCModel techniques

1H MR spectroscopy is routinely used for lateralization of epileptogenic lesions. The present study deals with the role of relaxation time corrections for the quantitative evaluation of long (TE=135 ms) and short echo time (TE=10 ms) 1H MR spectra of the hippocampus using two methods (operator-guided NUMARIS and LCModel programs). Spectra of left and right hippocampi of 14 volunteers and 14 patients with epilepsy were obtained by PRESS (TR/TE=5000/135 ms) and STEAM (TR/TE=5000/10 ms) sequences with a 1.5-T imager. Evaluation was carried out using Siemens NUMARIS software and the results were compared with data from LCModel processing software. No significant differences between the two methods of processing spectra with TE=135 ms were found. The range of relaxation corrections was determined. Metabolite concentrations in hippocampi calculated from spectra with TE=135 ms and 10 ms after application of correction coefficients did not differ in the range of errors and agreed with published data (135 ms/10 ms: NAA=10.2+/-0.6/10.4+/-1.3 mM, Cho=2.4+/-0.1/2.7+/-0.3 mM, Cr=12.2+/-1.3/11.3+/-1.3 mM). When relaxation time corrections were applied, quantitative results from short and long echo time evaluation with LCModel were in agreement. Signal intensity ratios obtained from long echo time spectra by NUMARIS operator-guided processing also agreed with the LCModel 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.