Interictal cerebral metabolism in partial epilepsies of neocortical origin

Feasibility of dose reduction for [18F]FDG-PET/MR imaging of patients with non-lesional epilepsy

The aim of the study was to evaluate the effect of reduced injected [18F]FDG activity levels on the quantitative and diagnostic accuracy of PET images of patients with non-lesional epilepsy (NLE).Nine healthy volunteers and nine patients with NLE underwent 60-min dynamic list-mode (LM) scans on a fully-integrated PET/MRI system. Injected FDG activity levels were reduced virtually by randomly removing counts from the last 10-min of the LM data, so as to simulate the following activity levels: 50 %, 35 %, 20 %, and 10 % of the original activity. Four image reconstructions were evaluated: standard OSEM, OSEM with resolution recovery (PSF), the A-MAP, and the Asymmetrical Bowsher (AsymBowsher) algorithms. For the A-MAP algorithms, two weights were selected (low and high). Image contrast and noise levels were evaluated for all subjects while the lesion-to-background ratio (L/B) was only evaluated for patients. Patient images were scored by a Nuclear Medicine physician on a 5-point scale to assess clinical impression associated with the various reconstruction algorithms.The image contrast and L/B ratio characterizing all four reconstruction algorithms were similar, except for reconstructions based on only 10 % of total counts. Based on clinical impression, images with diagnostic quality can be achieved with as low as 35 % of the standard injected activity. The selection of algorithms utilizing an anatomical prior did not provide a significant advantage for clinical readings, despite a small improvement in L/B (< 5 %) using the A-MAP and AsymBowsher reconstruction algorithms.In patients with NLE who are undergoing [18F]FDG-PET/MR imaging, the injected [18F]FDG activity can be reduced to 35 % of the original dose levels without compromising.

Prognostic value of high-frequency oscillations combined with multimodal imaging methods for epilepsy surgery

Background:

The combination of high-frequency oscillations (HFOs) with single-mode imaging methods has been proved useful in identifying epileptogenic zones, whereas few studies have examined HFOs combined with multimodal imaging methods. The aim of this study was to evaluate the prognostic value of ripples, an HFO subtype with a frequency of 80 to 200 Hz is combined with multimodal imaging methods in predicting epilepsy surgery outcome.

Methods:

HFOs were analyzed in 21 consecutive medically refractory epilepsy patients who underwent epilepsy surgery. All patients underwent positron emission tomography (PET) and deep electrode implantation for stereo-electroencephalography (SEEG); 11 patients underwent magnetoencephalography (MEG). Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in predicting surgical outcome were calculated for ripples combined with PET, MEG, both PET and MEG, and PET combined with MEG. Kaplan-Meier survival analyses were conducted in each group to estimate prognostic value.

Results:

The study included 13 men and 8 women. Accuracy for ripples, PET, and MEG alone in predicting surgical outcome was 42.9%, 42.9%, and 81.8%, respectively. Accuracy for ripples combined with PET and MEG was the highest. Resection of regions identified by ripples, MEG dipoles, and combined PET findings was significantly associated with better surgical outcome (P < 0.05).

Conclusions:

Intracranial electrodes are essential to detect regions which generate ripples and to remove these areas which indicate good surgical outcome for medically intractable epilepsy. With the assistance of presurgical noninvasive imaging examinations, PET and MEG, for example, the SEEG electrodes would identify epileptogenic regions more effectively.

18 F-FDG-PET hypometabolic pattern reveals multifocal epileptic foci despite limited unique stereotyped seizures

PURPOSE

Interictal positron emission tomography (PET) with ¹⁸F-FDG has largely proved its utility in presurgical evaluation of drug-resistant epilepsies (DRE) and in the surgical outcomes. Interictal hypometabolism topography is related to the neuronal networks involved in the seizure onset zone (SOZ) and spread pathways. ¹⁸F-FDG PET has a good prognostic value for post-surgical outcome, especially in cases with unique focal ictal semiology and a limited extent of hypometabolism. Surprisingly few patients have similar limited ictal features but extended hypometabolism. The objective of this study is to show that stereoelectro encephalography (SEEG) provides an explanation for this large hypometabolism, which impacts the surgical strategy.

METHODS

A cohort of 248 patients underwent ¹⁸F-FDG PET and SEEG to explore for refractory epilepsy in two close tertiary epilepsy centers between January 2009 and December 2017. From this cohort, a subset of patients was selected with extended PET metabolism despite showing unique and limited ictal features in scalp EEG. The surgical outcome of this subset of patients has been analysed with respect to their FDG-PET and SEEG to understand the relationship between PET/SEEG/ presentation and surgical outcome.

RESULTS

We report a series of seven patients with DRE and unique stereotyped ictal semiology but extensive ¹⁸F-FDG-PET hypometabolism revealing unexpected multifocal SOZ using SEEG. All SOZ were encompassed by the hypometabolic area.

CONCLUSION

Our results demonstrate the necessity of accounting for the discrepancy between limited symptoms and widespread hypometabolism which can reveal multifocal SOZ. In those patients, surgical possibilities should be considered carefully.

The Role of SPECT and PET in Epilepsy

OBJECTIVE. The purpose of this article is to summarize the role of molecular imaging of the brain by use of SPECT, FDG PET, and non-FDG PET radiotracers in epilepsy. CONCLUSION. Quantitative image analysis with PET and SPECT has increased the diagnostic utility of these modalities in localizing epileptogenic onset zones. A multi-modal platform approach integrating the functional imaging of PET and SPECT with the morphologic information from MRI in presurgical evaluation of epilepsy can greatly improve outcomes.

Utility of Absolute Quantification in Non-lesional Extratemporal Lobe Epilepsy Using FDG PET/MR Imaging

The purpose of this study was to establish a non-invasive clinical PET/MR protocol using [¹⁸F]-labeled deoxyglucose (FDG) that provides physicians with regional metabolic rate of glucose (MRGlc) values and to clarify the contribution of absolute quantification to clinical management of patients with non-lesional extratemporal lobe epilepsy (ETLE). The study included a group of 15 patients with non-lesional ETLE who underwent a dynamic FDG PET study using a fully-integrated PET/MRI system (Siemens Biograph). FDG tracer uptake images were converted to MRGlc (μmol/100 g/min) maps using an image derived input function that was extracted based on the combined analysis of PET and MRI data. In addition, the same protocol was applied to a group of healthy controls, yielding a normative database. Abnormality maps for ETLE patients were created with respect to the normative database, defining significant hypo- or hyper-metabolic regions that exceeded ±2 SD of normal regional mean MRGlc values. Abnormality maps derived from MRGlc images of ETLE patients contributed to the localization of hypo-metabolic areas against visual readings in 53% and increased the confidence in the original clinical readings in 33% of all cases. Moreover, quantification allowed identification of hyper-metabolic areas that are associated with frequently spiking cortex, rarely acknowledged in clinical readings. Overall, besides providing some confirmatory information to visual readings, quantitative PET imaging demonstrated only a moderate impact on clinical management of patients with complex pathology that leads to epileptic seizures, failing to provide new decisive information that would have changed classification of patients from being rejected to being considered for surgical intervention.

Utility of MRI, PET, and ictal SPECT in presurgical evaluation of non-lesional pediatric epilepsy

Children with epilepsy and normal structural MRI pose a particular challenge in localization of epileptic foci for surgical resection. Many of these patients have subtle structural lesions such as mild cortical dysplasia that can be missed by conventional MRI but may become detectable by optimized and advanced MRI acquisitions and post-processing. Specificity of objective analytic techniques such as voxel-based morphometry remains an issue. Combination of MRI with functional imaging approaches can improve the accuracy of detecting epileptogenic brain regions. Analysis of glucose positron emission tomography (PET) combined with high-resolution MRI can optimize detection of hypometabolic cortex associated with subtle cortical malformations and can also enhance presurgical evaluation in children with epileptic spasms. Additional PET tracers may detect subtle epileptogenic lesions and cortex with enhanced specificity in carefully selected subgroups with various etiologies; e.g., increased tryptophan uptake can identify epileptogenic cortical dysplasia in the interictal state. Subtraction ictal SPECT can be also useful to delineate ictal foci in those with non-localizing PET or after failed surgical resection. Presurgical delineation of language and motor cortex and the corresponding white matter tracts is increasingly reliable by functional MRI and DTI techniques; with careful preparation, these can be useful even in young and sedated children. While evidence-based pediatric guidelines are still lacking, the data accumulated in the last decade strongly indicate that multimodal imaging with combined analysis of MRI, PET, and/or ictal SPECT data can optimize the detection of subtle epileptogenic lesions and facilitate seizure-free outcome while minimizing the postsurgical functional deficit in children with normal conventional MRI.

Correlation of FDG-PET hypometabolism and SEEG epileptogenicity mapping in patients with drug-resistant focal epilepsy

OBJECTIVE

Interictal [18F]fluorodeoxyglucose-positron emission tomography (FDG-PET) is used in the presurgical evaluation of patients with drug-resistant focal epilepsy. We aimed at clarifying its relationships with ictal high-frequency oscillations (iHFOs) shown to be a relevant marker of the seizure-onset zone.

METHODS

We studied the correlation between FDG-PET and epileptogenicity maps in an unselected series of 37 successive patients having been explored with stereo-electroencephalography (SEEG).

RESULTS

At the group level, we found a significant correlation between iHFOs and FDG-PET interictal hypometabolism only in cases of temporal lobe epilepsy. This correlation was found with HFOs, and the same comparison between FDG-PET and ictal SEEG power of lower frequencies during the same epochs did not show the same significance.

SIGNIFICANCE

This finding suggests that interictal FDG-PET and ictal HFOs may share common underlying pathophysiologic mechanisms of ictogenesis in temporal lobe epilepsy, and combining both features may help to identify the seizure-onset zone.

The impact of positron emission tomography imaging on the clinical management of patients with epilepsy

Clinical positron emission tomography (PET) imaging of human epilepsy has a 30-year history, but it is still searching for its exact role among rapidly advancing neuroimaging techniques. The vast majority of epilepsy PET studies used this technique to improve detection of epileptic foci for surgical resection. Here, we review the main trends emerging from three decades of PET research in epilepsy, with a particular emphasis on how PET imaging has impacted on the clinical management of patients with intractable epilepsy. While reviewing the latest studies, we also present an argument for a changing role of PET and molecular imaging in the future, with an increasing focus on epileptogenesis and newly discovered molecular mechanisms of epilepsy. These new applications will be facilitated by technological advances, such as the use of integrated PET/MRI systems and utilization of novel radiotracers, which may also enhance phenotype-genotype correlations and assist rational, individualized treatment strategies.

Functional imaging: PET

Among various neuroimaging techniques used for the evaluation of children with intractable epilepsy, positron emission tomography (PET) employing various PET tracers plays a very important role, especially in localizing areas of focal cortical dysplasia. This is particularly important in infants, where incomplete myelination may limit the structural information provided by MRI. In children with tuberous sclerosis, PET can differentiate between epileptogenic and nonepileptogenic tubers, previously not thought to be possible with neuroimaging. PET may reveal cortical or subcortical abnormalities in various epilepsy syndromes, such as infantile spasms and Landau-Kleffner syndrome. Various other applications of PET have included the investigation of epileptic networks, secondary epileptic foci, dual pathology, and neuroinflammation. Finally, PET can also be used to evaluate various cognitive processes and their underlying neurological substrates and can help in addressing the issue of brain plasticity and reorganization, related to epilepsy.

On the relation between sensory deafferentation, pain and thalamic activity in Wallenberg's syndrome: A PET-scan study before and after motor cortex stimulation

Decrease of thalamic blood flow contralateral to neuropathic pain has been described by several groups, but its relation with sensory deafferentation remains unclear. Here we report one instance where the thalamic effects of sensory deafferentation could be dissociated from those of neuropathic pain. A 50-year-old patient underwent a left medullary infarct leading to right-sided thermal and pain hypaesthesia up to the third right trigeminal division, as well as in the left face. During the following months the patient developed neuropathic pain limited to the left side of the face. Although the territory with sensory loss was much wider in the right (non painful) than in the left (painful) side of the body, PET-scan demonstrated significant reduction of blood flow in the right thalamus (contralateral to the small painful area) relative to its homologous region. After 3 months of right motor cortex stimulation the patient reported 60% relief of his left facial pain, and a new PET-scan showed correction of the thalamic asymmetry. We conclude that thalamic PET-scan hypoactivity contralateral to neuropathic pain does not merely reflect deafferentation, but appears related to the pain pathophysiology, and may be normalized in parallel with pain relief. The possible mechanisms linking thalamic hypoactivity and pain are discussed in relation with findings in epileptic patients, possible compensation phenomena and bursting thalamic discharges described in animals and humans. Restoration of thalamic activity in neuropathic pain might represent one important condition to obtain successful relief by analgesic procedures, including cortical neurostimulation.

Multimodality imaging in the surgical treatment of children with nonlesional epilepsy

OBJECTIVES

To evaluate the diagnostic value of individual noninvasive presurgical modalities and to study their role in surgical management of nonlesional pediatric epilepsy patients.

METHODS

We retrospectively studied 14 children (3-18 years) with nonlesional intractable focal epilepsy. Clinical characteristics, surgical outcome, localizing features on 3 presurgical diagnostic tests (subtraction peri-ictal SPECT coregistered to MRI [SISCOM], statistical parametric mapping [SPM] analysis of [18F] FDG-PET, magnetoencephalography [MEG]), and intracranial EEG (iEEG) were reviewed. The localization of each individual test was determined for lobar location by visual inspection. Concordance of localization between each test and iEEG was scored as follows: 2=lobar concordance; 1=hemispheric concordance; 0=discordance or nonlocalization. Total concordance score in each patient was measured by the summation of concordance scores for all 3 tests.

RESULTS

Seven (50%) of 14 patients were seizure-free for at least 12 months after surgery. One (7%) had only rare seizures and 6 (43%) had persistent seizures. MEG (79%, 11/14) and SISCOM (79%, 11/14) showed greater lobar concordance with iEEG than SPM-PET (13%, 3/14) (p<0.05). SPM-PET provided hemispheric lateralization (71%, 10/14) more often than lobar localization. Total concordance score tended to be greater for seizure-free patients (4.7) than for non-seizure-free patients (3.9).

CONCLUSIONS

Our data suggest that MEG and SISCOM are better tools for lobar localization than SPM analysis of FDG-PET in children with nonlesional epilepsy. A multimodality approach may improve surgical outcome as well as selection of surgical candidates in patients without MRI abnormalities.

Presurgical epilepsy localization with interictal cerebral dysfunction

Localization of interictal cerebral dysfunction with 2-[(18)F]fluoro-2-D-deoxyglucose (FDG) positron emission tomography (PET) and neuropsychological examination usefully supplements electroencephalography (EEG) and brain magnetic resonance imaging (MRI) in planning epilepsy surgery. In MRI-negative mesial temporal lobe epilepsy, correlation of temporal lobe hypometabolism with extracranial ictal EEG can support resection without prior intracranial EEG monitoring. In refractory localization-related epilepsies, hypometabolic sites may supplement other data in hypothesizing likely ictal onset zones in order to intracranial electrodes for ictal recording. Prognostication of postoperative seizure freedom with FDG PET appears to have greater positive than negative predictive value. Neuropsychological evaluation is critical to evaluating the potential benefit of epilepsy surgery. Cortical deficits measured with neuropsychometry are limited in lateralizing and localizing value for determination of ictal onset sites, however. Left temporal resection risks iatrogenic verbal memory deficits and dysnomia, and neuropsychological findings are useful in predicting those at greatest risk. Prognostication of cognitive risks with resection at other sites is less satisfactory.

Longitudinal Change in Outcome of Frontal Lobe Epilepsy Surgery

BACKGROUND:

Although the outcome of epilepsy surgery changes with time, few studies have considered longitudinal changes after frontal lobe epilepsy (FLE) surgery.

OBJECTIVE:

To assess the longitudinal changes after FLE surgery.

METHODS:

Resection of the seizure onset zone was performed in 76 patients with FLE. Invasive monitoring was performed in 56 of these 76. Awake craniotomy was performed in 43 of the 76 patients. More than 50% of patients were followed up for at least 7 years. The mean follow-up was 81 months.

RESULTS:

For all patients, the seizure-free rate was 79% at 6 months, 64% at 1 year, 55% at 2 years, and 55% at 7 years. For patients with cortical dysplasia, the seizure-free rate was 72% at 6 months, 53% at 1 year, 51% at 2 years, and 46% at 7 years. For patients with tumor, the seizure-free rate was 89% at 6 months, 83% at 1 year, 83% at 2 years, and 74% at 7 years. Patients with tumor showed better outcome than those with cortical dysplasia (P = .04). Although the overall seizure-free rate became stable after 2 years, individual status changed for up to 5 years. Seizures recurred in 11 patients within 1 year (early recurrence) and in 12 patients by 1 to 5 years (late recurrence). Antiepileptic drug (AED) medication was adjusted in all patients with recurrence. Patients with late recurrence had a more favorable response (Engel class I or II) than early recurrence (P &lt; .01).

CONCLUSION:

The overall seizure outcome changes mostly during the first year. However, individual seizure status changes for up to 5 years. The outcome of late recurrence is favorable to AED adjustment.

Quantitative brain surface mapping of an electrophysiologic/metabolic mismatch in human neocortical epilepsy

The spatial relationship between an intracranial EEG-defined epileptic focus and cortical hypometabolism on glucose PET has not been precisely described. In order to quantitatively evaluate the hypothesis that ictal seizure onset and/or rapid seizure propagation, detected by subdural EEG monitoring, commonly involves normometabolic cortex adjacent to hypometabolic cortical regions, we applied a novel, landmark-constrained conformal mapping approach in 14 children with refractory neocortical epilepsy. The 3D brain surface was parcellated into finite cortical elements (FCEs), and hypometabolism was defined using lobe- and side-specific asymmetry indices derived from normal adult controls. The severity and location of hypometabolic areas vs. ictal intracranial EEG abnormalities were compared on the 3D brain surface. Hypometabolism was more severe in the seizure onset zone than in cortical areas covered by non-onset electrodes. However, similar proportions of the onset electrodes were located over and adjacent to (within 2 cm) hypometabolic regions (46% vs. 41%, respectively), whereas rapid seizure spread electrodes preferred these "adjacent areas" rather than the hypometabolic area itself (51% vs. 22%). On average, 58% of the hypometabolic regions had no early seizure involvement. These findings strongly support that the seizure onset zone often extends from hypometabolic to adjacent normometabolic cortex, while large portions of hypometabolic cortex are not involved in seizure onset or early propagation. The clinical utility of FDG PET in guiding subdural electrode placement in neocortical epilepsy could be greatly enhanced by extending grid coverage to at least 2 cm beyond hypometabolic cortex, when feasible.

Advances in neuroimaging in patients with epilepsy

Intractable seizures can have a devastating effect on the development of a child. In children with intractable epilepsy that is refractory to medication, surgical treatment may be needed. Magnetic resonance imaging is an essential neuroimaging tool to assist in the identification of an epileptogenic substrate. The interpretation of MR images should be done in the context of clinical knowledge of the seizure symptomatology and electroencephalographic findings. Quantitative processing of structural MR data and advanced MR imaging such as diffusion tensor imaging and MR spectroscopy have the potential to identify subtle lesions that may otherwise have been missed. In addition to lesion localization, identification of eloquent cortex and white matter tracts are also an essential component of epilepsy surgery workup. Functional MR imaging maps the sensorimotor cortex and also lateralizes language. Diffusion tensor imaging tractography can be used to map the corticospinal tracts and the optic radiations. In addition to MR imaging, magnetoencephalography and nuclear medicine studies such as PET and SPECT scanning may be used to lateralize seizure focus when clinical, electrophysiological, and structural MR imaging findings are discordant.

Nuclear Medicine in Pediatric Neurology and Neurosurgery: Epilepsy and Brain Tumors

In pediatric drug-resistant epilepsy, nuclear medicine can provide important additional information in the presurgical localization of the epileptogenic focus. The main modalities used are interictal (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) and ictal regional cerebral perfusion study with single-photon emission computed tomography (SPECT). Nuclear medicine techniques have a sensitivity of approximately 85% to 90% in the localization of an epileptogenic focus in temporal lobe epilepsy; however, in this clinical setting, they are not always clinically indicated because other techniques (eg, icterictal and ictal electroencephalogram, video telemetry, magnetic resonance imaging [MRI]) may be successful in the identification of the epileptogenic focus. Nuclear medicine is very useful when MRI is negative and/or when electroencephalogram and MRI are discordant. A good technique to identify the epileptogenic focus is especially needed in the setting of extra-temporal lobe epilepsy; however, in this context, identification of the epileptogenic focus is more difficult for all techniques and the sensitivity of the isotope techniques is only 50% to 60%. This review article discusses the clinical value of the different techniques in the clinical context; it also gives practical suggestions on how to acquire good ictal SPECT and interictal FDG-PET scans. Nuclear medicine in pediatric brain tumors can help in differentiating tumor recurrence from post-treatment sequelae, in assessing the response to treatment, in directing biopsy, and in planning therapy. Both PET and SPECT tracers can be used. In this review, we discuss the use of the different tracers available in this still very new, but promising, application of radioisotope techniques.

"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.'

The Blood?Brain Barrier and Epilepsy

During the past several years, there has been increasing interest in the role of the blood-brain barrier (BBB) in epilepsy. Advances in neuroradiology have enhanced our ability to image and study the human cerebrovasculature, and further developments in the research of metabolic deficiencies linked to seizure disorders (e.g., GLUT1 deficiency), neuroinflammation, and multiple drug resistance to antiepileptic drugs (AEDs) have amplified the significance of the BBB's relationship to epilepsy. Prior to 1986, BBB research in epilepsy focused on three main areas: ultrastructural studies, brain glucose availability and transport, and clinical uses of AEDs. However, contrast-based imaging techniques and medical procedures such as BBB disruption provided a framework that demonstrated that the BBB could be reversibly disrupted by pathologic or iatrogenic manipulations, with important implications in terms of CNS drug delivery to "multiple drug resistant" brain. This concept of BBB breakdown for therapeutic purposes has also unveiled a previously unrecognized role for BBB failure as a possible etiologic mechanism in epileptogenesis. Finally, a growing body of evidence has shown that inflammatory mechanisms may participate in the pathological changes observed in epileptic brain, with increasing awareness that blood-borne cells or signals may participate in epileptogenesis by virtue of a leaky BBB. In this article we will review the relationships between BBB function and epilepsy. In particular, we will illustrate consensus and divergence between clinical reality and animal studies.

Prognostic Factors in Neocortical Epilepsy Surgery: Multivariate Analysis

PURPOSE

Defining prognostic factors for neocortical epilepsy surgery is important for the identification of ideal candidates and for predicting the prognosis of individual patients. We use multivariate analysis to identify favorable prognostic factors for neocortical epilepsy surgery.

METHODS

One hundred ninety-three neocortical epilepsy patients, including 91 without focal lesions on MRI, were included. Sixty-one had frontal lobe epilepsy (FLE), 80 had neocortical temporal lobe epilepsy (nTLE), 21 had parietal lobe epilepsy (PLE), and 22 had occipital lobe epilepsy (OLE). The primary outcome variable was patient status >or=2 years after surgery (i.e., seizure free or not). Clinical characteristics and the recent presurgical diagnostic modalities were considered as probable prognostic factors. Univariate and standard multiple logistic regression analyses were used to identify favorable prognostic factors.

RESULTS

The seizure-free rate was 57.5%. By univariate analysis, a focal lesion on MRI, localized ictal onset on surface EEG, epilepsies other than FLE, localized hypometabolism on fluorodeoxyglucose-positron emission tomography (FDG-PET), and pathologies other than cortical dysplasia were significantly associated with a seizure-free outcome (p<0.05). Multivariate analysis revealed that a focal lesion on MRI (p=0.003), correct localization by FDG-PET (p=0.007), and localized ictal onset on EEG (p=0.01) were independent predictors of a good outcome.

CONCLUSIONS

The presence of a focal lesion on MRI, correct localized hypometabolism on FDG-PET, or localized ictal rhythms on EEG were identified as predictors of a seizure-free outcome. Our results suggest that these findings allow the selection of better candidates for neocortical epilepsy surgery.

The role of FDG-PET, ictal SPECT, and MEG in the epilepsy surgery evaluation

2-[18F]Fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET), ictal single-photon-emission computed tomography (ictal SPECT), and magnetoencephalography (MEG) represent three established functional imaging tests that offer unique information toward the localization of epilepsy for surgery evaluation and treatment. When these tests are combined with high-resolution magnetic fresonance imaging (MRI), epilepsy related structure and function disturbances may be localized with a degree of confidence and understanding not possible with electroencephalography (EEG), even ictal recordings with intracranial electrodes, the mainstay of tools for seizure localization. Use of these alternative tests allows an increased percentage of patients to be considered for surgical treatment. In particular, the additional information provided by these techniques has been demonstrated to help those patients with nonlocalizing MRI or extratemporal lobe epilepsy. Studies that address optimal use of these tests (alone and in combination) will build toward the next major advancement in the surgical treatment of epilepsy by allowing better patient selection, less risk, and better surgical outcomes. Ultimately, appropriate use of these tests, combined with more comprehensive functional brain mapping (e.g., with MEG or functional MRI), may lead to completely noninvasive epilepsy surgery evaluation.

Molecular vibrational analysis and MAS-NMR spectroscopy study of epilepsy drugs encapsulated in TiO2-sol–gel reservoirs

A nanostructured matrix, consisting of titania, was designed in such a way that an antiepileptic drug could be encapsulated and released according to a well-defined time release schedule. The titania was synthesized by a sol-gel method in which titanium n-butoxide was used as the precursor for the formation of the sol. The synthesis was optimized to yield a homogeneous particle size with a high porosity and an anatase crystal structure. The antiepilectic drugs, phenytoine or valproic acid, were added during the gelation stage in order to obtain a homogeneous gel phase. The resulting nanostructured matrix including the drug showed only weak attractive forces, such as London forces, dipole-dipole coupling, and in some cases hydrogen bonds. The resulting assembly, referred to as a reservoir, was characterized using conventional FTIR and NMR spectroscopic techniques. Theoretical simulation studies were performed so as to obtain an understanding of the equilibrium electrostatic potential distribution and the relative charges on the titania and the anticonvulsants.

Surgical outcome and prognostic factors of cryptogenic neocortical epilepsy

Surgical treatment of cryptogenic neocortical epilepsy is challenging. The aim of this study was to evaluate surgical outcomes and to identify possible prognostic factors including the results of various diagnostic tools. Eighty-nine patients with neocortical epilepsy with normal magnetic resonance imaging (35 patients with frontal lobe epilepsy, 31 with neocortical temporal lobe epilepsy, 11 with occipital lobe epilepsy, 11 with parietal lobe epilepsy, and 1 with multifocal epilepsy) underwent invasive study and focal surgical resection. Patients were observed for at least 2 years after surgery. The localizing values of interictal electroencephalogram (EEG), ictal scalp EEG, interictal 18F-fluorodeoxyglucose positron emission tomography (FDG-PET), and subtraction ictal single-photon emission computed tomography were evaluated. Seventy-one patients (80.0%) had a good surgical outcome (Engel class 1-3); 42 patients were seizure free. Diagnostic sensitivities of interictal EEG, ictal scalp EEG, FDG-PET, and subtraction ictal single-photon emission computed tomography were 37.1%, 70.8%, 44.3%, and 41.1%, respectively. Localization by FDG-PET and interictal EEG was correlated with a seizure-free outcome. The localizing value of FDG-PET was greatest in neocortical temporal lobe epilepsy. The focalization of ictal onset and also ictal onset frequency in invasive studies were not related to surgical outcome. Concordance with two or more presurgical evaluations was significantly related to a seizure-free outcome.

Occipital lobe epilepsy: clinical characteristics, surgical outcome, and role of diagnostic modalities

PURPOSE

To assess the role of various diagnostic modalities, to identify surgical prognostic factors and concordances with presurgical evaluations, and to characterize the clinical features of occipital lobe epilepsy (OLE), we studied 26 patients who were diagnosed as having OLE and underwent epilepsy surgery.

METHODS

Diagnoses were established by standard presurgical evaluations, which included magnetic resonance imaging (MRI), fluorodeoxyglucose-positron emission tomography (FDG-PET), ictal single-photon emission computed tomography (SPECT), scalp video-EEG monitoring, and intracranial EEG monitoring. After epilepsy surgery, patients were followed up for >2 years.

RESULTS

Sixteen (61.5%) of the 26 became seizure free after surgery, and another eight patients had a favorable outcome. Sixteen of the 26 patients experienced a type of visual aura (i.e., visual hallucination, visual illusion, blindness, or a field defect). Nine patients had both automotor seizures and secondary generalized tonic-clonic seizures at different times. Interictal EEG showed correctly localizing spikes in 10 of the 16 patients who became seizure free, and in three of the 10 non-seizure-free patients. MRI correctly localized the lesion in seven of these 16 seizure-free patients, and in three of the 10 non-seizure-free patients. FDG-PET correctly localized the lesion in eight of the 16 seizure-free patients, and in three of nine non-seizure-free patients. Ictal SPECT was performed in 19 patients and correctly localized the lesion in only three of 12 seizure-free patients, and in four of seven non-seizure-free patients. Ictal EEG correctly localized the lesion in 13 of the 16 seizure-free patients, and in five of the 10 non-seizure-free patients. No significant relation was found between the diagnostic accuracy of any modality and surgical outcome. The localizations of epileptogenic zones by these different diagnostic methods were complementary. The concordance of three or more modalities was significantly observed in seizure-free patients (p = 0.042). However, no definite relation was observed between the presence of lateralizing clinical seizure manifestation and surgical outcome (p = 0.108).

CONCLUSIONS

Some specific auras indicated an occipital epilepsy onset. Various diagnostic methods can be useful to diagnose OLE, and a greater concordance between presurgical evaluation modalities indicates a better surgical outcome.

Identification of the epileptogenic lobe in neocortical epilepsy with proton MR spectroscopic imaging

PURPOSE

The aim of this study was to evaluate the usefulness of multislice magnetic resonance spectroscopic imaging (MRSI) in combination with tissue segmentation for the identification of the epileptogenic focus in neocortical epilepsy (NE).

METHODS

Twenty patients with NE (10 with MRI-visible malformations, 10 with normal MRI) and 19 controls were studied. In controls, N-acetylaspartate NAA/Cr and NAA/Cho of all voxels of a given lobe were expressed as a function of white matter, and thresholds were determined by calculating the 95% prediction intervals (PIs) for NAA/Cr and NAA/Cho. Voxels with NAA/Cr or NAA/Cho values less than the 95% PI were defined as "pathological." Z-scores were calculated. Depending on the magnitude of those z-scores, we used two different methods (score-localization or forced-localization) to identify in a given subject the lobe with the highest percentage of pathological voxels, which was supposed to represent the epileptogenic lobe.

RESULTS

MRSI correctly identified the lobe containing the epileptogenic focus as defined by EEG in 65% of the NE patients. MRSI localization of the focus was correct in 70% of the patients with an MRI-visible malformation and in 60% of the patients with normal MRI. Of the patients, 15% had metabolically abnormal brain regions outside the epileptogenic lobe, and 35% of the patients had evidence for secondary hippocampal damage.

CONCLUSIONS

MRSI may be helpful for the identification of the epileptogenic focus in NE patients, even in NE with normal MRI.

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.

The role of positron emission tomography with [18F]fluorodeoxyglucose in the evaluation of the epilepsies

Cerebral glucose metabolic mapping using positron emission tomography (PET) and 2-[18F]fluoro-2-deoxyglucose (FDG) has been extensively studied in the epilepsies. Regions of interictal glucose hypometabolism are highly associated with cerebral sites of seizure generation-propagation in focal epilepsies. The volume of reduced glucose metabolism is often widespread and even bilateral in focal epilepsies, although ictal onset zones typically are located at the sites of most severe hypometabolism within a larger volume of hypometabolism.

Parietal Lobe Epilepsy: The Semiology, Yield of Diagnostic Workup, and Surgical Outcome

PURPOSE

To characterize the clinical features, the prognostic value, and diagnostic sensitivities of various presurgical evaluations and the surgical outcomes in parietal lobe epilepsy (PLE), we describe 40 patients who were diagnosed as having PLE, including 27 surgically treated patients.

METHODS

The diagnosis was established by means of a standard presurgical evaluation, including magnetic resonance imaging (MRI), fluorodeoxyglucose-positron emission tomography (FDG-PET), ictal single-photon emission tomography (SPECT), and scalp video-electroencephalography (EEG) monitoring, with additional intracranial EEG monitoring in selected cases.

RESULTS

Among the 40 patients, 27 experienced at least one type of aura. The most common auras were somatosensory (13 patients), followed by affective, vertiginous, and visual auras. The patients had diverse manifestations. Eighteen patients showed simple motor seizure, followed by automotor seizure, and dialeptic seizure. Two patients manifested generalized tonic-clonic seizures only, and 19 patients experienced more than one type of seizure. The surgical outcome was favorable in 22 of 26 patients including 14 who were seizure free. Patients with localized MRI abnormality had a higher probability to be seizure free, with marginal significance (p = 0.062), whereas other diagnostic modalities failed to predict the surgical outcome. In the seizure-free group, localization sensitivity was 64.3% by MRI, 50% by PET, 45.5% by ictal SPECT, and 35.7% by ictal EEG. The concordance rate of the various diagnostic modalities was higher in the seizure-free group than in the non-seizure-free group, although it did not reach statistical significance.

CONCLUSIONS

Seizures, in the case of PLE, can manifest themselves in a wider variety of ways than was previously thought. Surgical outcome was favorable in most of the patients. MRI abnormality and concordance of different diagnostic modalities were associated with high seizure-free rate.

Contralateral motor automatisms in neocortical temporal lobe epilepsy

BACKGROUND

The lateralizing value of the motor automatisms is generally doubted in most patients with temporal lobe epilepsy. However, subgroup analysis of the seizures of temporal lobe origin suggests a role for motor automatisms in discriminating seizures of neocortical versus mesial temporal lobe origin.

METHODS

Video-EEG of a patient with well-defined neocortical temporal lobe epilepsy was reviewed to assess the localizing value of motor automatisms.

RESULTS

We report a patient with left upper extremity motor automatisms and clonic movements of the proximal left lower extremity with altered awareness as the sole manifestations of right temporal neocortical seizures.

CONCLUSION

Early onset unilateral motor automatisms without dystonic posturing can localize the seizure origin to the contralateral temporal lobe neocortex.

Positron emission tomography and single photon emission computed tomography in epilepsy care

Radiopharmaceutical brain imaging is clinically applied in planning resective epilepsy surgery. Cerebral sites of seizure generation-propagation are highly associated with regions of hyperperfusion during seizures, and with glucose hypometabolism interictally. For surgical planning in epilepsy, the functional imaging modalities currently established are ictal single photon emission computed tomography (SPECT) with [(99m)Tc]technetium-hexamethylpropyleneamine oxime (HMPAO) or with [(99m)Tc]technetium-ethylene cysteine dimer (ECD), and interictal positron emission tomography (PET) with 2-[(18)F]fluoro-2-deoxyglucose (FDG). Ictal SPECT and interictal FDG PET can be used in presurgical epilepsy evaluations to reliably: (1) determine the side of anterior temporal lobectomy, and in children the area of multilobar resection, without intracranial electroencephalographic recording of seizures; (2) select high-probability sites of intracranial electrode placement for recording ictal onsets; and, (3) determine the prognosis for complete seizure control following anterior temporal lobe resection. Coregistration of a patient's structural (magnetic resonance) and functional images, and statistical comparison of a patient's data with a normal data set, can increase the sensitivity and specificity of these SPECT and PET applications to the presurgical evaluation.

Metabolic parameters of epilepsy: adjuncts to established antiepileptic drug therapy

Hughlings Jackson at the turn of the century defined epilepsy as a disorder originating in a "morbid nutrition" of the neuron. With the advances in modern neurochemistry, it is becoming increasingly clear that a chronic seizure predisposition or a lowering of the brain's discharge threshold can be demarcated by a number of biochemical markers. They include a tendency for an increased release of glutamate with or without GABAergic impairment, (intra)neural tissue alterations in water redistribution/osmolarity or other distortions of the cytoarchitecture, and an elevation of ionic calcium inside the cell. These changes are dominantly shared parameters of the seizure prone brain. Magnetic resonance spectroscopy (MRS) shows that cerebral levels of glutamate + glutamine (Glx) are increased interictally in epileptogenic regions in human partial epilepsy; other findings using this technique suggest damage to (cellular/mitochondrial) membranes, denoted by N-acetyl-aspartic acid (NAA) changes and a decreased energy capability. The merging of previous in vitro and ex vivo findings in neurophysiology and neurochemistry with magnetic resonance spectroscopy technology provides a powerful new methodology to interpret and to obtain clinical insight into the metabolic alterations that underlie an epileptogenic process. In this review some of these basic neurochemical and electrophysiological mechanisms are discussed. In addition, certain adjuncts to established antiepileptic drug therapy are suggested in the hope that over the long term they may help in correcting the primary metabolic deficits.

Role of neuroimaging in the management of seizure disorders

Neuroimaging is one of the most important advances made in the past decade in the management of seizure disorders. Magnetic resonance imaging (MRI) has increased substantially the ability to detect causes of seizure disorders, to plan medical or surgical therapy, and to prognosticate the outcome of disorders and therapy. However, MRI must be performed with techniques that will maximize the detection of potentially epileptogenic lesions, especially in candidates for epilepsy surgery. Functional imaging has an established role in evaluating patients for epilepsy surgery. It is relied on when results from standard diagnostic methods, such as clinical information, electroencephalography, and MRI, are insufficient to localize the seizure focus. Also, functional imaging is a reportedly reliable alternative to invasive methods for identifying language, memory, and sensorimotor areas of the cerebral cortex. Despite the availability of multimodality imaging, the epileptogenic zone is not determined solely by a single imaging modality. Evidence and experience have shown that concordance of results from clinical, electrophysiologic, and neuroimaging studies is needed to identify the epileptogenic zone accurately. With modern techniques in image processing, multimodality imaging can integrate the location of abnormal electroencephalographic, structural, and functional imaging foci on a "map" of the patient's brain. Computer image-guided surgery allows surgically exact implantation of intracranial electrodes and resection of abnormal structural or functional imaging foci. These techniques decrease the risk of morbidity associated with epilepsy surgery and enhance the probability of postsurgical seizure control.

Frontal lobe tumoral epilepsy: clinical, neurophysiologic features and predictors of surgical outcome

PURPOSE

To review the clinical, neurophysiologic features and surgical outcomes in patients with frontal lobe tumors and chronic intractable seizures.

METHODS

Medical records of patients with intractable epilepsy who underwent resection or stereotactic biopsy of frontal lobe tumor (confirmed by surgical pathology) seen between 1985 and 1999 at Yale University School of Medicine Epilepsy Center were reviewed for age at diagnosis, age at onset of seizures, delay between seizure onset and tumor diagnosis, types and frequencies of seizures, EEG results, use of anticonvulsants, extent of surgery, pathological diagnosis, and tumor recurrence.

RESULTS

Thirty-seven patients were included. Mean age at seizure onset was 31.6 years, and at tumor diagnosis was 36.2 years. Mean duration between onset of seizures and tumor diagnosis was 6.1 years. Seventeen patients had auras. Seizure frequency averaged 7.6 seizures per week, with 58% of patients having more than one seizure type. All patients used anticonvulsants, with 90% eventually using polytherapy. All patients eventually underwent at least one surgical procedure. Only 13 (35.1%) patients were class I. Twelve (32.4%) patients were class II, seven (18.9%) class III, and five (13.5%) class IV. No statistically significant differences were seen between good and poor long-term seizure outcome in relation to specific tumor pathology, seizure types, or type of resection.

CONCLUSIONS

Long-term surgical outcomes in tumoral frontal lobe epilepsy are more favorable than those in nontumoral intractable frontal lobe epilepsy (65% class I or II) and less favorable than those in other tumoral epilepsy (overall, 70% class I). Frontal location of intracranial neoplasm may predict a less favorable long-term epilepsy prognosis than tumoral epilepsy in general, an observation for which several explanations are proposed.

Pre-surgical evaluation and surgical outcome of 41 patients with non-lesional neocortical epilepsy

Pre-surgical evaluation and the surgical treatment of non-lesional neocortical epilepsy is one of the most challenging areas in epilepsy surgery. The aim of this study was to evaluate the surgical outcome and the diagnostic role of ictal scalp electroencephalography (EEG), interictal (18)F-fluorodeoxyglucose-positron emission tomography (FDG-PET), and ictal technetium-99m hexamethylpropyleneamine oxime single photon emission tomography ( (99m)Tc-HMPAO SPECT). In 41 non-lesional neocortical epilepsy patients (16 frontal lobe epilepsy, 11 neocortical temporal lobe epilepsy, seven occipital lobe epilepsy, four parietal lobe epilepsy, and three with multifocal onset) who underwent surgical treatment between December 1994 and July 1998, we evaluated the surgical outcome with a follow-up of at least 1 year. The localizing and lateralizing values of ictal scalp EEG, interictal FDG-PET, and ictal SPECT were evaluated in those patients with good surgical outcome. Ictal scalp EEG had the highest diagnostic sensitivity in the localization of epileptogenic foci (69.7% vs. 42.9% for FDG-PET and 33.3% for ictal SPECT; P= 0.027). However, no significant difference was found in the lateralization of the epileptogenic hemisphere among the three modalities (78.8% for ictal scalp EEG, 57.2% for FDG-PET, and 55.5% for ictal SPECT; P= 0.102). During a mean follow-up of 2.77 +/- 1.12 years, 33 (80.5%) showed good surgical outcome (seizure free or seizure reduction >90%), including 16 (39.0%) seizure free patients. Ictal scalp EEG was the most useful diagnostic tool in the localization of epileptogenic foci. Interictal FDG-PET and ictal SPECT were found to be useful as complementary and, sometimes, independent modalities. Many patients with non-lesional neocortical epilepsy would benefit from surgical treatment.

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.

CPD - education and self-assessment: functional imaging in epilepsy

Functional imaging plays a growing role in the clinical assessment and research investigation of patients with epilepsy. This article reviews the literature on functional MRI (fMRI) investigation of EEG activity, fMRI evaluation of cognitive and motor functions, magnetic resonance spectroscopy (MRS), single photon emission computed tomography (SPECT) and positron emission tomography (PET) in epilepsy. The place of these techniques in clinical evaluation and their contribution to a better neurobiological understanding of epilepsy are discussed.

Thalamic asymmetry on interictal SPECT in patients with frontal lobe epilepsy

BACKGROUND

Interictal brain single photon emission computed tomography (SPECT) is useful for the detection of seizure focus. Recent reports indicate a hypoperfusion in the ipsilateral thalamus as a seizure focus on interictal SPECT in temporal lobe epilepsy. In frontal lobe epilepsy (FLE), however, the alteration of perfusion in the thalamus has not been well documented. This study aimed to assess whether perfusion analysis on the thalamus may add useful information for the detection of epileptic foci in patients with FLE.

METHODS

Interictal brain SPECT was performed in 11 patients with FLE. The asymmetry index for the thalamus and frontal area in the SPECT image was calculated in order to compare the laterality of the seizure foci.

RESULTS

Thalamic asymmetry was seen in seven patients (64%), while cortial asymmetry was seen in six patients (55%). The concordance with the lateralization of the seizure foci was 6/7 (86%) in the thalamus, and 4/6 (67%) in the frontal area. Four patients showed only thalamic asymmetry. Concordance with the lateralization of the seizure focus was found in all of them.

CONCLUSION

These preliminary results suggest that hypoperfusion in the thalamus may have a complementary role to lateralize the epileptic foci in patients with FLE.

[Neurofunctional tests in presurgical strategies for partial epilepsies]

The presurgical evaluation of drug-resistant partial epilepsies primarily relies on two major investigations, including a long term video-EEG monitoring which aimed at recording the patient's typical seizures, and a specifically designed high quality magnetic resonance imaging (MRI). The latter demonstrates an abnormality within the epileptogenic lobe in the majority of cases, which might not, however, necessarily match the epileptogenic zone. Numerous functional neuro-imaging techniques have been progressively added to the pre-surgical evaluation of refractory partial epilepsies, such as the study of cerebral glucose metabolism, benzodiazepine receptor availability, and methionine incorporation using positron emission tomography (PET), the evaluation of ictal cerebral blood flow changes using single photon emission computerized tomography (SPECT), the measurement of N-acetyl-aspartate concentration with magnetic resonance spectroscopy, and the mapping of eloquent areas using functional MRI. These investigations can help to confirm the origin of seizure onset previously suggested by MRI and electro-clinical data, and provide independent prognostic information regarding the chance of a successful surgical treatment. Moreover, functional neuro-imaging data can have a critical diagnostic value when MRI is strictly normal or shows multifocal abnormalities. However, the variety and rapid evolution of functional neuro-imaging techniques makes it difficult to propose a standard protocol. Finally, it remains mandatory to proceed to an intracranial EEG investigation in a substantial number of patients, including the majority of those suffering from an extra-temporal epilepsy.

Seizures of temporal lobe epilepsy: identification of subtypes by coherence analysis using stereo-electro-encephalography

OBJECTIVES

Two subtypes of temporal lobe epilepsy (TLE) according to the structures initially involved during seizures are currently recognized: medial TLE (MTLE) and lateral (or neocortical) TLE (LTLE). A few reports have suggested that the classification of TLE subtypes might be larger according to variations in the interactions between medial structures and the neocortex. In this study, we analyzed these interactions using coherence analysis of stereo-encephalographic (SEEG) signals during spontaneous seizures.

METHODS

Twenty-seven patients with drug-resistant TLE, diagnosed from ictal SEEG recordings obtained during pre-surgical evaluation, were studied. Orthogonally implanted depth electrodes with multiple leads according to Talairach's method were used to sample medial and neocortical structures. Coherence analysis of ictal discharges was performed between two SEEG bipolar signals from adjacent leads located either in medial structures (amygdala and hippocampus) or in neocortical regions of the temporal lobe. A new algorithm, which was designed to reduce the bias inherent in coherence estimation, was used to compute the coherence.

RESULTS

We were able to classify TLE seizures (TLES) into 4 distinct categories: (1) 'medial' TLES, characterized by medial onset with later involvement of the neocortex in the form of a 'phasic' discharge. High ictal coherence values were observed between medial structures; (2) 'medial-lateral' TLES which started in medial structures with a fast low-voltage discharge (FLVD) which rapidly affects the neocortex (< or = 3 s). High coherence values were observed between medial and lateral structures; (3) 'lateral-medial' TLES, which are different from medial-lateral TLES in that the FLVD starts in the lateral neocortex and involves the amygdala and/or hippocampus almost immediately after; (4) 'lateral' TLES: characterized by a neocortical onset, a delayed involvement of medial structures (when present), and high coherence values between neocortical structures.

CONCLUSIONS

These results demonstrate the existence of numerous interactions between medial limbic structures and the neocortex during TLE seizures. Such findings could have implications for surgical strategies and the prognosis of epilepsy surgery, particularly when limited resection is indicated.

Visual and quantitative ictal EEG predictors of outcome after temporal lobectomy

PURPOSE

We investigated whether visual and quantitative ictal EEG analysis could predict surgical outcome after anteromesial temporal lobectomy (AMTL) in which mesial structures, basal, and temporal tip cortex were resected.

METHODS

We retrospectively reviewed 282 presurgical scalp-recorded ictal EEGs (21- to 27-channel) from 75 patients who underwent AMTL. We examined the pattern of seizure onset (frequency, distribution, and evolution) and estimated the principal underlying cerebral generators by using a multiple fixed dipole model that decomposes temporal lobe activity into four sublobar sources (Focus 1.1). We correlated findings with a 2-year postoperative outcome.

RESULTS

Sixteen patients had seizures with a well-lateralized, regular 5 to 9-Hz rhythm at onset, that most often had a temporal or subtemporal distribution. All patients became seizure free after surgery. In 51 patients, seizure onset was remarkable for lateralized slow rhythms (<5 Hz), which sometimes appeared as periodic discharges, were often irregular and stable only for short periods (<5 s), and had a widespread lateral temporal distribution. Among these a favorable surgical outcome was encountered in patients with seizures having prominent anterior-tip sources ( 16 of 17 seizure free), whereas those with dominant lateral or oblique sources had a less favorable outcome (three of 14 and 13 of 18, respectively). Irregular, nonlateralized slowing characterized seizure onsets in eight patients. Three patients became seizure free after surgery.

CONCLUSIONS

Both visual and quantitative sublobar source analysis of scalp ictal EEG can predict surgical outcome in most cases after AMTL and complement non-invasive presurgical evaluation.

Thalamocortical circuits causing remote hypometabolism during focal interictal epilepsy

The functional circuit causing depression of cerebral glucose metabolism in brain areas remote from an epileptic focus was investigated in experiments on the cortex of the rat. Epileptic activity was induced by direct epicortical application of Na-penicillin onto the motor cortical area Fr1/Fr2. The increased neuronal activity was associated with an increase of metabolism in the focal area and a decrease in somatosensory cortical areas. Metabolism was also massively increased in the thalamus, predominantly in the posterior nucleus. Stereotactic radiofrequency lesioning of this nucleus, 30 days prior to the induction of the epileptic focus, restricted the area with increase of metabolism to the upper cortical laminae, and abolished the cortical hypometabolism in the sensory cortex. It is suggested that the primary functional circuit affected by the acute epileptic focus in the present model consists of the motor cortex, the thalamic nucleus posterior and the somatosensory cortex.

Identification of frontal lobe epileptic foci in children using positron emission tomography

PURPOSE

Presurgical evaluation for intractable frontal lobe epilepsy (FLE) is difficult and invasive, partly because anatomic neuroimaging studies with computed tomography (CT) and magnetic resonance imaging (MRI) typically do not show a discrete lesion. In adult patients with FLE, functional neuroimaging of glucose metabolism with positron emission tomography (PET) is less sensitive in detecting focal metabolic abnormalities than in temporal lobe epilepsy (TLE). Comparable data on children with FLE are not available.

METHODS

We used high-resolution PET scanning of glucose metabolism to evaluate 13 children (age 17 months to 17 years; mean age 9.5 years) with intractable FLE being considered for surgical treatment. Only children with normal CT and MRI scans were included.

RESULTS

Hypometabolism including the frontal lobe was evident in 12 of the 13 children, was unilateral in 11 of 13, and was restricted to the frontal lobe in 8 of 13. One child showed bilateral frontal cortex hypometabolism and another had an ictal PET scan demonstrating unilateral frontal cortex hypermetabolism surrounded by hypometabolism. Additional hypometabolic areas outside the frontal cortex were observed in 5 children in parietal and/or temporal cortex. Localization of seizure onset on scalp EEG was available in 10 children and corresponded to the location of frontal lobe PET abnormality in 8. However, in 4 of the 10 children, the extent of hypometabolism exceeded the epileptogenic region indicated by ictal EEG. In 2 of the 13 children, the abnormality evident on EEG was more extensive than that evident on PET. In the remaining 3 children for whom only interictal EEG data were available, the PET foci did not correspond in location to the interictal EEG abnormalities. In 11 of the 13 children, the presumed region of seizure onset in the frontal lobe, as based on analysis of seizure semiology, corresponded to the locations of frontal lobe glucose metabolism abnormalities.

CONCLUSIONS

Although high-resolution PET appears to be very sensitive in localizing frontal lobe glucose metabolic abnormalities in children with intractable FLE and normal CT/MRI scans, the significance of extrafrontal metabolic disturbances requires further study; these may represent additional epileptogenic areas, effects of diaschisis, seizure propagation sites, or secondary epileptogenic foci.

Algorithm on the clinical evaluation of epilepsy

Epilepsy is an important public health problem because of its prevalence in the community and the economic disadvantage associated with its chronic morbidity. Uncontrolled seizures are potentially life-threatening and have adverse psychosocial consequences. Surgery is an effective but underutilized therapy for some patients with medically refractory seizures. However, this form of treatment demands precise localization of the epileptogenic zone. In recent years there have been major advances in the development of various imaging techniques for seizure localization. The best combination of diagnostic testing with regard to cost-benefit has been debated. A rational strategy for the deployment of these techniques is discussed.