Statistical parametric mapping of regional glucose metabolism in mesial temporal lobe epilepsy

Focal decreases of cortical GABAA receptor binding remote from the primary seizure focus: what do they indicate?

PURPOSE

To determine the electroclinical significance and histopathological correlates of cortical gamma-aminobutyric acid(A)(GABA(A)) receptor abnormalities detected in and remote from human neocortical epileptic foci.

METHODS

Cortical areas with decreased(11)C-flumazenil (FMZ) binding were objectively identified on positron emission tomography (PET) images and correlated to intracranial electroencephalography (EEG) findings, clinical seizure variables, histology findings, and surgical outcome in 20 patients (mean age, 9.9 years) with intractable partial epilepsy of neocortical origin and nonlocalizing magnetic resonance imaging (MRI).

RESULTS

Focal decrease of cortical FMZ binding was detected in the lobe of seizure onset in 17 (85%) patients. Eleven patients (55%) had 17 remote cortical areas with decreased FMZ binding outside the lobe of seizure onset. Thirteen of those 16 (81%) of the 17 remote cortical regions that were covered by subdural EEG were around cortex showing rapid seizure spread on intracranial EEG. Remote FMZ PET abnormalities were associated with high seizure frequency and, when resected, showed gliosis in all six cases where material was available. Higher number of unresected cortical regions with decreased FMZ binding was associated with poorer surgical outcome.

CONCLUSIONS

Focal decreases of cortical GABA(A) receptor binding on PET may include cortical regions remote from the primary focus, particularly in patients with high seizure frequency, and these regions are commonly involved in rapid seizure propagation. Although these regions may not always need to be resected to achieve seizure freedom, a careful evaluation of cortex with decreased GABA(A) receptor binding prior to resection using intracranial EEG may facilitate optimal surgical outcome in patients with intractable neocortical epilepsy.

Voxel-based T2 relaxation rate measurements in temporal lobe epilepsy (TLE) with and without mesial temporal sclerosis

INTRODUCTION

Quantitative measurements of T(2) relaxation in the hippocampus for focus lateralization in mesial temporal lobe epilepsy (mTLE) are well established. Less is known to what degree such relaxation abnormalities also affect regions beyond the ipsilateral hippocampus. Therefore, the aim of this study was to characterize extent and distribution pattern of extrahippocampal relaxation abnormalities in TLE with (TLE-MTS) and without MRI evidence of mesial-temporal sclerosis (TLE-no).

METHODS

Double spin echo images (TE1/2: 20/80 ms) acquired in 24 TLE-MTS and 18 TLE-no were used to calculate relaxation rate maps. These maps were analyzed by SPM2 and by selecting regions of interest (ROI) in the hippocampus and several extrahippocampal brain regions.

RESULTS

In TLE-MTS, the results of the SPM and ROI analysis were in good agreement and showed the most severe relaxation rate decreases in the ipsilateral hippocampus but also in other ipsilateral temporal regions, orbitofrontal, and parietal regions and to a lesser degree in contralateral frontal regions. The relaxation rate decreases in TLE-no were confined to small regions in the ipsilateral anterior inferior and medial temporal lobe in the SPM analysis while ROI analysis showed additional regions in the ipsilateral hippocampus, amygdala, and anterior cingulate.

CONCLUSION

TLE-MTS showed extensive, widespread but predominantly ipsilateral temporal and also extratemporal T(2) relaxation rate decreases. In contrast, the findings of the SPM and ROI analyses in TLE-no suggested that if relaxation rate decreases are present, they are less uniform and generally milder than in TLE-MTS. This further supports the hypothesis that TLE-no is a distinct clinicopathological entity from TLE-MTS and probably heterogeneous in itself.

"Magnetic resonance imaging negative positron emission tomography positive" temporal lobe epilepsy: FDG-PET pattern differs from mesial temporal lobe epilepsy

PURPOSE

Some patients with temporal lobe epilepsy (TLE) lack evidence of hippocampal sclerosis (HS) on MRI (HS-ve). We hypothesized that this group would have a different pattern of 2-deoxy-2-[F-18]fluoro-D-glucose (FDG)-positron emission tomography (PET) hypometabolism than typical mesial TLE/HS patients with evidence of hippocampal atrophy on magnetic resonance imaging (MRI) (HS+ve), with a lateral temporal neocortical rather than mesial focus.

PROCEDURES

Thirty consecutive HS-ve patients and 30 age- and sex-matched HS+ve patients with well-lateralized EEG were identified. FDG-PET was performed on 28 HS-ve patients and 24 HS+ve patients. Both groups were compared using statistical parametric mapping (SPM), directly and with FDG-PET from 20 healthy controls.

RESULTS

Both groups showed lateralized temporal hypometabolism compared to controls. In HS+ve, this was antero-infero-mesial (T = 17.13); in HS-ve the main clustering was inferolateral (T = 17.63). When directly compared, HS+ve had greater hypometabolism inmesial temporal/hippocampal regions (T = 4.86); HS-ve had greater inferolateral temporal hypometabolism (T = 4.18).

CONCLUSIONS

These data support the hypothesis that focal hypometabolism involves primarily lateal neocortical rather than mesial temporal structures in 'MRI-negative PET-positive TLE.'

Correlations of interictal FDG-PET metabolism and ictal SPECT perfusion changes in human temporal lobe epilepsy with hippocampal sclerosis

BACKGROUND

The pathophysiological role of the extensive interictal cerebral hypometabolism in complex partial seizures (CPS) in refractory mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE-HS) is poorly understood. Our aim was to study ictal-interictal SPECT perfusion versus interictal fluorodeoxyglucose (FDG)-PET metabolic patterns.

METHODS

Eleven adults with refractory unilateral mTLE-HS, who were rendered seizure free after epilepsy surgery, were included. All had an interictal FDG-PET and an interictal and ictal perfusion SPECT scan. FDG-PET data were reconstructed using an anatomy-based reconstruction algorithm, which corrected for partial volume effects, and analyzed semi-quantitatively after normalization to white matter activity. Using Statistical Parametric Mapping (SPM), we compared interictal metabolism of the patient group with a control group. We correlated metabolic with ictal perfusion changes in the patient group.

RESULTS

Global cerebral grey matter glucose metabolism in patients was decreased 10-25% compared with control subjects. Interictal PET hypometabolism and ictal SPECT hypoperfusion were maximal in the ipsilateral frontal lobe. Ictal frontal lobe hypoperfusion was associated with crossed cerebellar diaschisis. The ipsilateral temporal lobe showed maximal ictal hyperperfusion and interictal hypometabolism, which was relatively mild compared with the degree of hypometabolism affecting the frontal lobes.

CONCLUSION

Interictal hypometabolism in mTLE-HS was greatest in the ipsilateral frontal lobe and represented a seizure-related dynamic process in view of further ictal decreases. Crossed cerebellar diaschisis suggested that there is a strong ipsilateral frontal lobe inhibition during CPS. We speculate that surround inhibition in the frontal lobe is a dynamic defense mechanism against seizure propagation, and may be responsible for functional deficits observed in mTLE.

Relationship between bilateral temporal hypometabolism and EEG findings for mesial temporal lobe epilepsy: Analysis of 18F-FDG PET using SPM

PURPOSE

To investigate the clinical significance of bilateral temporal hypometabolism (BTH) for patients with mesial temporal lobe epilepsy (MTLE) by using statistical parametric mapping (SPM).

METHODS

Interictal 18F-FDG PET scans were performed for 29 patients with surgically treated MTLE. Clinical data, interictal epileptiform discharges (IEDs), ictal scalp EEG and intracarotid amobarbital test (IAT) were analyzed. To assess an 18F-FDG PET image, an SPM analysis as well as visual interpretation were applied.

RESULTS

In 9 of 29 patients, the 18F-FDG PET scan revealed BTH by the SPM analysis, while only 3 patients showed BTH by the visual assessment. When the patients were classified into the unilateral temporal hypometabolism (UTH) and BTH groups based on the SPM results, bitemporal IEDs occurred significantly more frequently in the BTH group than in the UTH group (66.7% versus 22.2%). Bilateral independent seizure onset seen on the scalp EEG and bitemporal epilepsy were present only in the BTH group. Lateralized ictal onset was present less frequently in the BTH group than in the UTH group (44.4% versus 83.3%). There was no statistically significant difference in age at onset, duration of epilepsy, generalized seizure, history of febrile convulsion and CNS infection, lateralization throughout the whole tracing, lateralization on the IAT test, and surgical outcome between the UTH and BTH groups.

CONCLUSION

Bilaterality of the EEG findings correlated with BTH on 18F-FDG PET by the SPM method. Our results suggest that analysis of 18F-FDG PET by using SPM may have a role in predicting those patients with bitemporal excitability or bitemporal independent epileptogenicity, and these patients should be monitored carefully.

Statistical voxel-wise analysis of ictal SPECT reveals pattern of abnormal perfusion in patients with temporal lobe epilepsy

OBJECTIVE

To investigate the pattern of perfusion abnormalities in ictal and interictal brain perfusion SPECT images (BSI) from patients with temporal lobe epilepsy (TLE).

METHOD

It was acquired interictal and ictal BSI from 24 patients with refractory TLE. BSIs were analyzed by visual inspection and statistical parametric mapping (SPM2). Statistical analysis compared the patients group to a control group of 50 volunteers. The images from patients with left-TLE were left-right flipped.

RESULTS

It was not observed significant perfusional differences in interictal scans with SPM. Ictal BSI in SPM analysis revealed hyperperfusion within ipsilateral temporal lobe (epileptogenic focus) and also contralateral parieto-occipital region, ipsilateral posterior cingulate gyrus, occipital lobes and ipsilateral basal ganglia. Ictal BSI also showed areas of hypoperfusion.

CONCLUSION

In a group analysis of ictal BSI of patients with TLE, voxel-wise analysis detects a network of distant regions of perfusional alteration which may play active role in seizure genesis and propagation.

Voxel-based assessment of spinal tap test-induced regional cerebral blood flow changes in normal pressure hydrocephalus

OBJECTIVE

Normal pressure hydrocephalus (NPH) is a cause of dementia that may be amended by medical intervention. Its diagnosis is therefore of major importance and the establishment of response criteria to cerebrospinal fluid (CSF) shunting is essential. One of these criteria is the clinical response to spinal tap. The accuracy of the spinal tap test could potentially be improved by adding neuroimaging of regional cerebral blood flow (rCBF) changes to the response criteria. Statistical parametric mapping (SPM) is a voxel-based method of image analysis that may be used to statistically assess the significance of rCBF changes. The objective of this study was to evaluate, by SPM, spinal tap test-induced rCBF changes in patients with NPH syndrome.

METHODS

Forty patients with NPH syndrome underwent hexamethylpropylene amine oxime (HMPAO) brain single photon emission computed tomography (SPECT) before and after a spinal tap test (1-day split-dose protocol). The differences in rCBF between these pairs of scans were analysed by SPM in the whole group and between subgroups divided according to gait improvement at the spinal tap test.

RESULTS

In the whole group of patients, there was no statistical difference between pre- and post-spinal tap SPECT images. SPM analysis of patients grouped as a function of their clinical response to the spinal tap test revealed a significant post-spinal tap rCBF increase in the bilateral dorsolateral frontal and left mesiotemporal cortex in clinically responding compared with non-responding patients.

CONCLUSION

According to SPM analysis, gait improvement at the spinal tap test in patients with NPH syndrome is associated with an rCBF increase localized in the bilateral dorsolateral frontal and left mesiotemporal cortex.

Diagnostic performance of 18F-FDG PET and ictal 99mTc-HMPAO SPET in pediatric temporal lobe epilepsy: quantitative analysis by statistical parametric mapping, statistical probabilistic anatomical map, and subtraction ictal SPET

We investigated the diagnostic performance of 18F-FDG PET and ictal (99m)Tc-HMPAO SPET in pediatric temporal lobe epilepsy (TLE). Twenty-one pediatric TLE patients were enrolled in this study. Their diagnoses were confirmed by histology and post-surgical outcome (Engel class I or II). The patients' ages were 18 or younger (15+/-3 years). Of the 21 patients, 21 patients underwent 18F-FDG PET scan and 15 underwent ictal (99m)Tc-HMPAO SPET. Preoperative PET and/or ictal SPET images were reviewed by simple visual assessment and by statistical parametric mapping (SPM). Asymmetric indices (AI) were calculated using statistical probabilistic anatomical map (SPAM) on 18F-FDG PET. In nine patients who underwent both ictal and interictal SPET, SISCOM (subtraction ictal SPET coregistered to MR template) was performed. PET correctly localized epileptogenic zones in 20 of 21 (95%) by visual assessment. SPM analysis of PET correctly localized epileptogenic zones in 18 of 21 (86%). Ictal SPET correctly localized epileptogenic zones in 12 of 15 (80%) by visual assessment. SPM analysis of ictal SPET correctly localized epileptogenic zones in 12 of 15 (80%). SISCOM correctly localized 8 of 9 (89%), which was equal to that of visual assessment of ictal SPET. The AIs of the temporal lobes by PET were -15+/-8.4 in the left and 9.9+/-8.9 in the right TLE (normal control: -2.9+/-2.8), and correctly localized epileptogenic zones in all cases. As is found in adult TLE, PET and ictal SPET efficiently localized epileptogenic zones in pediatric TLE. SPM analysis of PET or ictal SPET could be used as an aid to visual assessment. Moreover, SISCOM was equal visual assessment of ictal SPET images in terms of lesion localizations.

The Effects on Cognitive Performance of Tailored Resection in Surgery for Nonlesional Mesiotemporal Lobe Epilepsy

PURPOSE

Mesiotemporal lobe epilepsy (MTLE) can be treated with different surgical approaches. In tailored resections, neocortex is removed beyond "standard" margins when spikes are present in the electrocorticogram. We hypothesized that these larger resections are justified because spiking neocortex is dysfunctional. This would imply that in patients with spikes (a) postoperative cognitive performance is not affected, and (b) preoperative performance is worse than without spikes.

METHODS

We studied 80 operated-on MTLE patients with pathologically confirmed nonlesional hippocampal sclerosis. All patients were left-sided language dominant and underwent cognitive tests 6 months pre- and postoperatively. A repeated measures analysis of variance (ANOVA) was performed, looking for within- and between-subjects interactions with presence of intraoperative neocortical spikes.

RESULTS

Intraoperatively, neocortical spikes were present in 61% of patients. Improved postoperative cognitive outcome was seen only in left-sided patients with spikes. Their performance IQ (PIQ) increased by 8.1 points (95% confidence interval, 3.8-12.3; p = 0.02), and visual naming latency by 12.8 s (95% CI, 2.1-23.5; p = 0.07). Conversely, in left-sided patients without spikes, naming latency declined by 7.5 s (95% CI, -2.3-17.2; p = 0.07). Preoperative scores were comparable except for a 15.3-point (95% CI, 0.1-30.5; p = 0.02) lower VIQ in left-sided patients without spikes.

CONCLUSIONS

Tailoring does not harm cognitive performance and is, in left-sided MTLE, associated with postoperative improvement. Left-sided MTLE without neocortical spikes has lower verbal scores, which tend to decline after standard resection and may represent a special pathophysiologic entity.

PET in seizure disorders

PET imaging has been widely used in the evaluation and management of patients with seizure disorders. The ability of PET to measure cerebral function is ideal for studying the neurophysiologic correlates of seizure activity during both ictal and interictal states. PET imaging is also valuable for evaluating patients before surgical interventions to determine the best surgical method and maximize outcomes. PET will continue to play a major role, not only in the clinical arena, but also in investigating the pathogenesis and treatment of various seizure disorders.

The role of PET imaging in the management of patients with central nervous system disorders

PET will continue to play a critical role in both clinical and research applications with regard to CNS disorders. PET is useful in the initial diagnosis of patients presenting with CNS symptoms and can help clinicians determine the best course of therapy. PET studies can also be useful for studying the response to therapy. From the research perspective, the various neurotransmitter and other molecular tracers currently available or in development will provide substantial information about pathophysiologic process in the brain. As such applications become more widely tested, their introduction into the clinical arena will further advance the use of PET imaging in the evaluation and management of CNS disorders.

Metabolic Changes of Subcortical Structures in Intractable Focal Epilepsy

PURPOSE

Intractable focal epilepsy is commonly associated with cortical glucose hypometabolism on interictal 2-deoxy-2[18F]-fluoro-D-glucose (FDG) positron emission tomography (PET). However, subcortical brain structures also may show hypometabolism on PET and volume changes on magnetic resonance imaging (MRI) studies, and these are less well understood in terms of their pathophysiology and clinical significance. In the present study, we analyzed alterations of glucose metabolism in subcortical nuclei and hippocampus by using FDG-PET in young patients with intractable epilepsy.

METHODS

Thirty-seven patients (mean age, 7.5 years; age range, 1-27 years) with intractable frontal (n = 23) and temporal (n = 14) lobe epilepsy underwent FDG-PET scanning as part of their presurgical evaluation. Normalized glucose metabolism was measured in the thalamus and caudate and lentiform nuclei, as well as in hippocampus, both ipsi- and contralateral to the epileptic focus, and correlated with duration and age at onset of epilepsy, presence or absence of secondary generalization, location of the epileptic focus, and extent of cortical glucose hypometabolism.

RESULTS

Long duration of epilepsy was associated with lower glucose metabolism in the ipsilateral thalamus and hippocampus. Duration of epilepsy was a significant predictor of ipsilateral thalamic glucose metabolism in both temporal and frontal lobe epilepsy. Presence of secondarily generalized seizures also was associated with lower normalized metabolism in the ipsilateral thalamus and hippocampus. Extent of cortical hypometabolism did not correlate with subcortical metabolism, and glucose metabolism in the caudate and lentiform nuclei did not show any correlation with the clinical variables.

CONCLUSIONS

The findings suggest that metabolic dysfunction of the thalamus ipsilateral to the seizure focus may become more severe with long-standing temporal and frontal lobe epilepsy, and also with secondary generalization of seizures.

Qualitative and quantitative imaging of the hippocampus in mesial temporal lobe epilepsy with hippocampal sclerosis

MR imaging allows the in vivo detection of hippocampal sclerosis (HS) and has been instrumental in the delineation of the syndrome of mesial temporal lobe epilepsy with HS (mTLE-HS). MR features of HS include hippocampal atrophy with an increased T2 signal. Quantitative MR imaging accurately reflects the degree of hippocampal damage.Ictal single photon emission computed tomography (SPECT) in mTLE-HS shows typical perfusion patterns of ipsilateral temporal lobe hyperperfusion, and ipsilateral frontoparietal and contralateral cerebellar hypoperfusion. Interictal 18fluoro-2-deoxyglucose positron emission tomography (PET) shows multiregional hypometabolism, involving predominantly the ipsilateral temporal lobe. 11C-flumazenil PET shows hippocampal decreases in central benzodiazepine receptor density. Future strategies to study the etiology and pathogenesis of HS should include longitudinal MR imaging studies,MR studies in families with epilepsy and febrile seizures, stratification for genetic background, coregistration with SPECT and PET, partial volume correction and statistical parametric mapping analysis of SPECT and PET images.

Statistical parametric mapping of 5-HT1A receptor binding in temporal lobe epilepsy with hippocampal ictal onset on intracranial EEG

Experimental data in animals show that 5-HT(1A) receptors are predominantly located in limbic areas and suggest that serotonin, via these receptors, mediates an antiepileptic and anticonvulsant effect. In this PET study, we used an antagonist of the 5-HT(1A) receptor, [(18)F]MPPF, to assess the extent of 5-HT(1A) receptor binding changes in a group of seven temporal lobe epilepsy (TLE) patients with hippocampal ictal onset demonstrated by intracerebral EEG recording. On the basis of MRI-measured hippocampal volumes (HV), patients were classified into "normal HV" or "hippocampal atrophy" (HA). Voxel-based analyses (SPM99) were performed to objectively assess the differences in [(18)F]MPPF binding potential (BP) between patients (taken as a group or as individuals) and a database of 48 controls subjects. In the full group of patients, a significant decreased BP was detected ipsilateral to the epileptogenic zone in the hippocampus, temporal pole, insula, and temporal neocortex. This result was confirmed in the subgroup of patients with HA. In patients with normal HV, the BP decrease was restricted to the temporal pole. TLE patients also demonstrated an increased BP in various regions contralateral to the epileptogenic zone. These data suggest that in TLE patients with hippocampal seizure onset, the decrease in 5-HT(1A) receptor binding partly reflects hippocampal neuronal loss, but is also observed in various regions involved in temporo-limbic epileptogenic networks that appeared normal on MRI. Further studies are warranted to evaluate the clinical usefulness of [(18)F]MPPF-PET as compared to other established PET tracers in drug resistant TLE.

Identification of abnormal neuronal metabolism outside the seizure focus in temporal lobe epilepsy

PURPOSE

The aim of this study was to identify metabolically abnormal extrahippocampal brain regions in patients with temporal lobe epilepsy with (TLE-MTS) and without (TLE-no) magnetic resonance imaging (MRI) evidence for mesial-temporal sclerosis (MTS) and to assess their value for focus lateralization by using multislice 1H magnetic resonance spectroscopic imaging (MRSI).

METHODS

MRSI in combination with tissue segmentation was performed on 14 TLE-MTS and seven TLE-no and 12 age-matched controls. In controls, N-acetylaspartate/(creatine + choline) [NAA/(Cr+Cho)] of all voxels of a given lobe was expressed as a function of white matter content to determine the 95% prediction interval for any additional voxel of a given tissue composition. Voxels with NAA/(Cr+Cho) below the lower limit of the 95% prediction interval were defined as "pathological" in patients and controls. Z-scores were used to identify regions with a higher percentage of pathological voxels than those in controls.

RESULTS

Reduced NAA/(Cr+Cho) was found in ipsilateral temporal and parietal lobes and bilaterally in insula and frontal lobes. Temporal abnormalities identified the epileptogenic focus in 70% in TLE-MTS and 83% of TLE-no. Extratemporal abnormalities identified the epileptogenic focus in 78% of TLE-MTS but in only 17% of TLE-no.

CONCLUSIONS

TLE is associated with extrahippocampal reductions of NAA/(Cr+Cho) in several lobes consistent with those brain areas involved in seizure spread. Temporal and extratemporal NAA/(Cr+Cho) reductions might be helpful for focus lateralization.

Differential effects of left versus right mesial temporal lobe epilepsy on Wechsler intelligence factors

This study investigates the effects of left versus right mesial temporal lobe epilepsy (MTLE) on Wechsler intelligence factors. In the left MTLE group, the Verbal Comprehension (VC) factor score was significantly lower than the Perceptual Organization (PO) factor score, whereas in the right MTLE group, the PO factor score was significantly lower than the VC factor score. The VC factor score was significantly lower for the left than the right MTLE group, whereas the PO factor score was significantly lower for the right than the left MTLE group. Thus, left versus right MTLE was associated with relative deficits in verbal versus nonverbal intelligence, respectively. These findings indicate that lateralized cognitive deficits in unilateral MTLE patients are not limited to the learning-memory domain but include more global intelligence functions.

Pathophysiology and functional consequences of human partial epilepsy: lessons from positron emission tomography studies

Positron emission tomography (PET) is a powerful clinical and research tool that, in the past two decades, has provided a great amount of novel data on the pathophysiology and functional consequences of human epilepsy. PET studies revealed cortical and subcortical brain dysfunction of a widespread brain circuitry, providing an unprecedented insight in the complex functional abnormalities of the epileptic brain. Correlation of metabolic and neuroreceptor PET abnormalities with electroclinical variables helped identify parts of this circuitry, some of which are directly related to primary epileptogenesis, while others, adjacent to or remote from the primary epileptic focus, may be secondary to longstanding epilepsy. PET studies have also provided detailed data on the functional anatomy of cognitive and behavioral abnormalities associated with epilepsy. PET, along with other neuroimaging modalities, can measure longitudinal changes in brain function attributed to chronic seizures as well as therapeutic interventions. This review demonstrates how development of more specific PET tracers and application of multimodality imaging by combining structural and functional neuroimaging with electrophysiological data can further improve our understanding of human partial epilepsy, and helps more effective application of PET in presurgical evaluation of patients with intractable seizures.

Quantification of human brain benzodiazepine receptors using [18F]fluoroethylflumazenil: a first report in volunteers and epileptic patients

Fluorine-18 fluoroethylflumazenil ([18F]FEF) is a tracer for central benzodiazepine (BZ) receptors which is proposed as an alternative to carbon-11 flumazenil for in vivo imaging using positron emission tomography (PET) in humans. In this study, [18F]FEF kinetic data were acquired using a 60-min two-injection protocol on three normal subjects and two patients suffering from mesiotemporal epilepsy as demonstrated by abnormal magnetic resonance imaging and [18F]fluorodeoxyglucose positron emission tomography. First, a tracer bolus injection was performed and [18F]FEF rapidly distributed in the brain according to the known BZ receptor distribution. Thirty minutes later a displacement injection of 0.01 mg/kg of unlabelled flumazenil was performed. Activity was rapidly displaced from all BZ receptor regions demonstrating the specific binding of [18F]FEF. No displacement was observed in the pons. Plasma input function was obtained from arterial blood sampling, and metabolite analysis was performed by high-performance liquid chromatography. Metabolite quantification revealed a fast decrease in tracer plasma concentration, such that at 5 min post injection about 70% of the total radioactivity in plasma corresponded to [18F]FEF, reaching 24% at 30 min post injection. The interactions between [18F]FEF and BZ receptors were described using linear compartmental models with plasma input and reference tissue approaches. Binding potential values were in agreement with the known distribution of BZ receptors in human brain. Finally, in two patients with mesiotemporal sclerosis, reduced uptake of [18F]FEF was clearly observed in the implicated left hippocampus.

Presurgical assessment of memory-related brain structures: the Wada test and functional neuroimaging

Medial temporal lobe structures are known to play a major role in memory processing. Recent work has revealed that extratemporal structures (e.g. the frontal lobe and thalamus) may also be important in memory function. In candidates for epilepsy surgery, particularly in those with temporal lobe seizures, presurgical evaluation of memory function is essential, since seizures may originate in the neural substrate that is critical for memory. In this article, we review the tools used for presurgical evaluation and their contribution to the understanding of memory function, focusing on the Wada test, [18F]fluorodeoxy-glucose positron emission tomography ([18F]FDG-PET) and functional magnetic resonance imaging (fMRI). We also explore perspectives on future studies that may elucidate the role of the temporal and extratemporal structures in memory function and the mechanisms of cerebral plasticity.

Detection of inter-hemispheric asymmetries of brain perfusion in SPECT

Technetium-99m HMPAO and technetium-99m ECD single photon emission computed tomography (SPECT) imaging is commonly used to highlight brain regions with altered perfusion. It is particularly useful in the investigation of intractable partial epilepsy. However, SPECT suffers from poor spatial resolution that makes interpretation difficult. In this context, we propose an unsupervised voxel neighbourhood based method to assist the detection of significant functional inter-hemispheric asymmetries in brain SPECT, using anatomical information from MRI. For each MRI voxel, the anatomically homologous voxel in the contralateral hemisphere is identified. Both homologous voxel coordinates are then mapped into the SPECT volume using SPECT-MRI registration. Neighbourhoods are then defined around each SPECT voxel and compared to obtain a volume of inter-hemispheric differences. A volume including only the statistically significant inter-hemispheric differences is deduced from this volume using a non-parametric approach. The method was validated using realistic analytical simulated SPECT data including known asymmetries (in size and amplitude) as ground truth (gold standard). Detection performance was assessed using an ROC (receiver operating characteristic) approach based on the measures of the overlap between known and detected asymmetries. Validation with computer-simulated data demonstrates the ability to detect asymmetric zones with relatively small extension and amplitude. The registration of these detected functional asymmetries on the MRI enables good anatomical localization to be achieved.

FDG-PET images quantified by probabilistic atlas of brain and surgical prognosis of temporal lobe epilepsy

PURPOSE

This study evaluated the relation between hypometabolism, diagnosed by fluorodeoxyglucose positron emission tomography (FDG-PET), and the surgical outcome of a large and homogeneous series of cases of mesial temporal lobe epilepsy (mTLE), by using a probabilistic atlas of the human brain (statistical probabilistic anatomical maps: SPAM).

METHODS

Ninety-five surgically proven intractable mTLE patients and 22 age-matched controls were spatially normalized to the average brain PET template of international consortium of brain mapping (ICBM). The diagnosis of mTLE was confirmed by the presence of hippocampal sclerosis on magnetic resonance imaging (MRI) and video-EEG monitoring. Counts from normalized PET images were multiplied by the probability from 98 volumes of interest (VOIs) of SPAM. Asymmetric indexes (AIs) reflecting the severity of hypometabolism were calculated by counts of selected 12 VOIs from SPAM images in both temporal lobes. Extent of hypometabolism was determined by the number of voxels showing decreased metabolism in each VOI segmented by SPAM.

RESULTS

Of the 95 patients studied, 76 (80%) were seizure free, and 19 (20%) had postoperative seizures for the > or =2-year follow-up period. No significant association between the severity of hypometabolism in each VOI of the temporal lobe and surgical outcome was identified (p > 0.05). The number of voxels showing decreased hypometabolism was not significantly different between the good- and poor-outcome groups (p > 0.05).

CONCLUSIONS

Our results demonstrated that focal severity and extent of hypometabolism quantified by a probabilistic atlas of brain were not related to the surgical outcome in mTLE patients who had hippocampal sclerosis on MRI. We should develop a more localized and specified anatomic map for mTLE for further results.

Insular cortex involvement in mesiotemporal lobe epilepsy: a positron emission tomography study

Somesthetic and emotional symptoms that are common in patients with mesial temporal lobe epilepsy are usually related to hippocampo-amygdalar complex involvement. Recent stereo-electroencephalographic studies have shown a relationship between such symptoms and epileptic insular discharges. To further investigate this problem, we carried out a positron emission tomography study using fluorodeoxyglucose (18F-FDG) and flumazenil (11C-FMZ) in mesial temporal lobe epilepsy patients. The aim of our study was to assess the existence of a cortical insular involvement in order to examine its clinical correlates and the relationship between the postoperative outcome and the insular involvement. Fluorodeoxyglucose and flumazenil-positron emission tomography studies were carried out in 18 patients with mesial temporal lobe epilepsy patients. A statistical parametric mapping (SPM96) was performed to analyze the data in comparison to 18 healthy volunteers. For each set of fluorodeoxyglucose and flumazenil images a group and an individual analysis were performed. In addition, a region of interest analysis was performed to validate the results. Focusing on the metabolic abnormalities, we also investigated the role of insular cortex in the symptoms experienced by the patients and the prognostic value of insular metabolic abnormalities. Highly significant hypometabolism and BZR binding decreases were detected in the insular cortex. Results were similar using the region of interest approach. Insular involvement (mainly ipsilateral to the seizure focus) was present in 60% of the patients. Emotional symptoms correlated with hypometabolism in the anterior part of the ipsilateral insular cortex, whereas somesthetic symptoms correlated with hypometabolism in the posterior part. No relationship between postoperative outcome and ipsilateral insular hypometabolism was found. Unilateral mesial temporal lobe epilepsy is associated with insular hypometabolism and benzodiazepine receptor loss. Our results also suggest that the anterior part of the insular cortex is involved in the emotional symptoms and the posterior insular cortex is involved in the somesthetic symptoms. Hypometabolism located in the insula did not influence postoperative outcome after anterior lobectomy.

Determination of regional cerebral function with FDG-PET imaging in neuropsychiatric disorders

Functional brain imaging using 18F fluorodeoxyglucose (FDG) and positron emission tomography (PET) has greatly enhanced our understanding of brain function both in normal conditions as well as in a wide variety of neuropsychiatric disorders. We review the uses of FDG PET in the diagnosis, management, and follow-up of patients with neuropsychiatric disorders. This article will also explore what FDG-PET imaging has revealed in these neuropsychiatric disorders and how these findings relate to both research and clinical applications.

Comparison of statistical parametric mapping and SPECT difference imaging in patients with temporal lobe epilepsy

PURPOSE

Statistical parametric mapping (SPM) is an image-analysis tool that assesses the statistical significance of cerebral blood flow (CBF) changes on a voxel-by-voxel basis, thereby removing the subjectivity inherent in conventional region-of-interest (ROI) analysis. Our platform of single-photon emission computed tomography (SPECT) ictal-interictal difference imaging in clinical epilepsy has been validated for localizing seizure onset. We extend the tools of SPM by further applying statistical measures for the significance of perfusion changes in individual patients to localize epileptogenic foci in patients with defined temporal lobe epilepsy by using paired scans in this preliminary study.

METHODS

Twelve patients with pairs of periictal and interictal SPECT scans were analyzed in this comparison study between SPECT difference imaging and SPM difference analysis by using a reference database of paired normal healthy images. These 12 patients possessed seizure foci localized to the mesial temporal lobe as confirmed by surgical outcome and by hippocampal sclerosis on pathology. SPM was used to identify clusters of increased or decreased CBF in each patient in contrast to our control group.

RESULTS

The regions having the most significant increased or decreased CBF by SPM analysis were in agreement with regions identified by conventional difference imaging and visual analysis by viewers blinded to the results of the SPM analysis. Differentiated further by time of radiopharmaceutical injection, six of seven patients injected within 100 s of seizure onset displayed hyperperfusion changes localized to the corresponding epileptogenic temporal lobe by both techniques. Among patients receiving injections after 100 s, both techniques showed primarily regions of hypoperfusion, which again were similar between these two methods.

CONCLUSIONS

The results provide strong evidence supporting SPM difference analysis in assessing regions of significant CBF change from baseline in concordance with our current clinically used technique of SPECT ictal--interictal difference imaging in epilepsy patients. Difference analysis using SPM could serve as a useful diagnostic tool in the evaluation of seizure focus in temporal lobe epilepsy.

Diagnostic performance of [18F]FDG-PET and ictal [99mTc]-HMPAO SPECT in occipital lobe epilepsy

PURPOSE

We investigated whether interictal F-18 fluorodeoxyglucose positron emission tomography ([18F]FDG-PET) or ictal [99mTc]-HMPAO single-photon emission computed tomography (SPECT) was useful to find epileptogenic zones in occipital lobe epilepsy (OLE).

METHODS

We reviewed visually and quantified patterns of hypometabolism in interictal [18F]FDG-PET and those of hyperperfusion in ictal SPECT in 17 OLE patients (27 plus minus 6.8 years old; M/F, 10/7; injection time, 30 plus minus 17 s). OLE was diagnosed based on invasive electroencephalography, surgery, and postsurgical outcome (Engel class I in all at an average of 26 months after surgery).

RESULTS

Epileptogenic zones were correctly localized in nine (60%) of 15 patients by interictal [18F]FDG-PET, and asymmetric indices corroborated visual diagnosis. Epileptogenic hemispheres were correctly lateralized in 14 (93%) of 15 patients on [18F]FDG-PET. Epileptogenic hemispheres were correctly lateralized in 13 (76%) of 17 patients using ictal SPECT, but localization was possible in only five (29%) patients. Interictal [18F]FDG-PET was helpful in two of the patients who showed no abnormality on magnetic resonance imaging (MRI) and no possible localization with ictal SPECT.

CONCLUSIONS

In OLE, ictal SPECT was helpful in lateralization, but less helpful in localization. Interictal [18F]FDG-PET was helpful in localization or lateralization of epileptogenic zones, even in patients with ambiguous MRI or ictal SPECT findings.

Disparity of perfusion and glucose metabolism of epileptogenic zones in temporal lobe epilepsy demonstrated by SPM/SPAM analysis on 15O water PET, [18F]FDG-PET, and [99mTc]-HMPAO SPECT

PURPOSE

To elucidate uncoupling of perfusion and metabolism and its significance in epilepsy, 15O water and 18F fluorodeoxyglucose (FDG) positron emission tomography (PET) and Tc-99m hexamethyl-propyleneamine-oxime (HMPAO) single-photon emission computed tomography (SPECT) were examined by SPM (statistical parametric mapping) and quantitation by using SPAM (statistical probabilistic anatomic map).

METHODS

[15O]water and [18F]FDG-PET, and [99mTc]-HMPAO SPECT were performed in 25 patients (SPECT in 17 of 25) with medial temporal lobe epilepsy. For volume of interest (VOI) count analysis, the normalized counts using VOI based on SPAM templates of PET and SPECT were compared with those of the normal controls. Perfusion or metabolism was found abnormal if the Z score was >2 for each VOI. For SPM analysis, the differences between each patient's image and a group of normal control images (t statistic for p < 0.01) on a voxel-by-voxel basis were examined to find significant decreases in perfusion or metabolism.

RESULTS

With SPAM VOI count analysis, areas of hypoperfusion were found in 13 patients in the epileptogenic temporal lobes by [15O]water PET and areas of hypometabolism in 21 patients by [18F]FDG-PET. With voxel-based SPM analysis, the epileptogenic zones were localized in 15 by [15O]water PET and in 23 patients by [18F]FDG-PET. The localization by [15O]water PET was concordant with that of [18F]FDG-PET. The areas of hypoperfusion on [15O]water PET were absent or smaller than the areas of hypometabolism on [18F]FDG-PET. Interictal [99mTc]-HMPAO SPECT revealed the hypoperfused zones in seven of 17 patients on visual assessment.

CONCLUSIONS

SPAM VOI count and SPM analysis of [15O]water and [18F]FDG-PET and [99mTc]-HMPAO SPECT revealed that in the same patients, the areas of hypoperfusion were concordant with but smaller than the areas of hypometabolism. Discordance of perfusion and metabolic abnormalities represents an uncoupling of perfusion and metabolism in the epileptogenic zones, and this might explain the lower diagnostic accuracy of perfusion imaging in temporal lobe epilepsy.

Comparative study of hippocampal neuronal loss and in vivo binding of 5-HT1a receptors in the KA model of limbic epilepsy in the rat

A high density of 5-HT1a receptors is present in pyramidal hippocampal cells. Mapping of these receptors may be performed in vivo using the tracer no-carrier-added 4-(18)F-fluoro-N-2-(1-(2-methoxyphenyl)-1-piperazinyl)ethyl-N-2-pyridinyl-benzamide (MPPF). We tested the hypothesis of a relationship between MPPF binding and post-epileptic neuronal loss in the hippocampus. The model of limbic epilepsy induced by kainic acid (KA) in the rat was used. Rats were sacrificed at various times (1 h-240 days) after systemic injection of 10 mg/kg KA. Determination of MPPF binding in the brain was combined with a quantification of neuronal loss using DNA labeling with propidium iodide and confocal microscopy. Hippocampal MPPF binding varied according to time elapsed from KA injection. An initial decrease from day 1 to day 6 post injection was followed by a relative increase between day 6 and day 30. This effect was observed in rats which showed hippocampal neuronal loss but also in one rat which did not. In KA treated rats, statistically significant relationship between MPPF binding and neuronal count was found during the acute period (rats sacrificed 1 h-day 6 after KA injection) and the chronic phase (rats sacrificed beyond day 60 after KA injection). The late relative increase of MPPF binding suggests an epilepsy-induced increase of 5-HT1a receptors in the hippocampus. This effect needs to be further characterized before considering PET determination of hippocampal MPPF binding as a method of post-epileptic neuronal loss assessment.

Quantification of F-18 FDG PET images in temporal lobe epilepsy patients using probabilistic brain atlas

A probabilistic atlas of the human brain (Statistical Probabilistic Anatomical Maps: SPAM) was developed by the international consortium for brain mapping (ICBM). It is a good frame for calculating volume of interest (VOI) in many fields of brain images. After calculating the counts in VOI using the product of probability of SPAM images and counts in FDG images, asymmetric indices (AI) were calculated and used for finding epileptogenic zones in mesial temporal lobe epilepsy (mTLE). FDG PET images from 18 surgically confirmed mTLE patients and 22 age-matched controls were spatially normalized to the average brain MRI template of ICBM. Counts from normalized PET images were multiplied with the probability of 12 VOIs from SPAM images in both temporal lobes. Finally AI were calculated on each pair of VOIs, and compared with visual assessment. If AI of mTLE patients were not within 2.9 standard deviation from those of normal control group (P < 0.008; Bonferroni correction for P < 0.05), epileptogenic zones were considered to be found successfully. The counts of VOIs in the normal control group were symmetric (AI < 4.3%, paired t test P > 0.05) except for those of the inferior temporal gyrus (P < 0.001). By AIs in six pairs of VOIs, PET in mTLE had deficit on one side (P < 0.05). Lateralization was correct in only 14/18 of patients by AI, but 17/18 were consistent with visual inspection. In three patients with normal AI, PET images were symmetric on visual inspection. The asymmetric indices obtained by taking the product of the statistical probability anatomical map and FDG PET, correlated well with visual assessment in mTLE patients. SPAM is useful for the quantification of VOIs in functional images.