FDG-PET in children and adolescents with partial seizures: role in epilepsy surgery evaluation

Semiquantitative analysis of cerebral [18F]FDG-PET uptake in pediatric patients

BACKGROUND

Glycolytic metabolism in the brain of pediatric patients, imaged with [18F]  fluorodeoxyglucose-positron emission tomography (FDG-PET) is incompletely characterized.

OBJECTIVE

The purpose of the current study was to characterize [18F]FDG-PET brain uptake in a large sample of pediatric patients with non-central nervous system diseases as an alternative to healthy subjects to evaluate changes at different pediatric ages.

MATERIALS AND METHODS

Seven hundred ninety-five [18F]FDG-PET examinations from children < 18 years of age without central nervous system diseases were included. Each brain image was spatially normalized, and the standardized uptake value (SUV) was obtained. The SUV and the SUV relative to different pseudo-references were explored as a function of age.

RESULTS

At all evaluated ages, the occipital lobe showed the highest [18F]FDG uptake (0.27 ± 0.04 SUV/year), while the parietal lobe and brainstem had the lowest uptake (0.17 ± 0.02 SUV/year, for both regions). An increase [18F]FDG uptake was found for all brain regions until 12 years old, while no significant uptake differences were found between ages 13 (SUV = 5.39) to 17 years old (SUV = 5.52) (P < 0.0001 for the whole brain). A sex dependence was found in the SUVmean for the whole brain during adolescence (SUV 5.04-5.25 for males, 5.68-5.74 for females, P = 0.0264). Asymmetries in [18F]FDG uptake were found in the temporal and central regions during infancy.

CONCLUSIONS

Brain glycolytic metabolism of [18F]FDG, measured through the SUVmean, increased with age until early adolescence (< 13 years old), showing differences across brain regions. Age, sex, and brain region influence [18F]FDG uptake, with significant hemispheric asymmetries for temporal and central regions.

Expression of fructose-1,6-bisphosphatase 1 is associated with [18F]FDG uptake and prognosis in patients with mesial temporal lobe epilepsy

OBJECTIVES

To determine whether fructose-1,6-bisphosphatase 1 (FBP1) expression is associated with [¹⁸F]FDG PET uptake and postsurgical outcomes in patients with mesial temporal lobe epilepsy (mTLE) and to investigate whether the molecular mechanism involving gamma-aminobutyric acid type A receptor (GABA_AR), glucose transporter-3 (GLUT-3), and hexokinase-II (HK-II).

METHODS

Forty-three patients with mTLE underwent [¹⁸F]FDG PET/CT. Patients were divided into Ia (Engel class Ia) and non-Ia (Engel class Ib-IV) groups according to more than 1 year of follow-up after surgery. The maximum standard uptake value (SUV_max) and asymmetry index (AI) of hippocampus were measured. The relationship among the SUV_max, AI, prognosis, and FBP1 expression was analyzed. A lithium-pilocarpine acute mTLE rat model was subjected to [¹⁸F]FDG micro-PET/CT. Hippocampal SUV_max and FBP1, GABA_AR, GLUT-3, and HK-II expression were analyzed.

RESULTS

SUV_max was higher in the Ia group than in the non-Ia group (7.31 ± 0.97 vs. 6.56 ± 0.96, p < 0.05) and FBP1 expression was lower in the Ia group (0.24 ± 0.03 vs. 0.27 ± 0.03, p < 0.01). FBP1 expression was negatively associated with SUV_max and AI (p < 0.01). In mTLE rats, the hippocampal FBP1 increased (0.26 ± 0.00 vs. 0.17 ± 0.00, p < 0.0001), and SUV_max, GLUT-3 and GABA_AR levels decreased significantly (0.73 ± 0.12 vs. 1.46 ± 0.23, 0.20 ± 0.01 vs. 0.32 ± 0.05, 0.26 ± 0.02 vs. 0.35 ± 0.02, p < 0.05); no significant difference in HK-II levels was observed. In mTLE patients and rats, FBP1 negatively correlated with SUV_max and GLUT-3 and GABA_AR levels (p < 0.05).

CONCLUSION

FBP1 expression was inversely associated with SUV_max in mTLE, which might inhibit [¹⁸F]FDG uptake by regulating GLUT-3 expression. High FBP1 expression was indicative of low GABA_AR expression and poor prognosis.

KEY POINTS

• It is of paramount importance to explore the deep pathophysiological mechanisms underlying the pathogenesis of mesial temporal lobe epilepsy and find potential therapeutic targets. • [¹⁸F]FDG PET has demonstrated low metabolism in epileptic regions during the interictal period, and hypometabolism may be associated with prognosis, but the pathomechanism of this association remains uncertain. • Our results support the possibility that FBP1 might be simultaneously involved in the regulation of glucose metabolism levels and the excitability of neurons and suggest that targeting FBP1 may be a viable strategy in the diagnosis and treatment of mesial temporal lobe epilepsy.

Antioxidant drug therapy as a neuroprotective countermeasure of nerve agent toxicity

The use of chemical warfare agents is an ongoing, significant threat to both civilians and military personnel worldwide. Nerve agents are by far the most formidable toxicants in terms of their lethality and toxicity. Nerve agents initiate neurotoxicity by the irreversible inhibition of acetylcholinesterase and resultant accumulation of acetylcholine in excitable tissues. The cholinergic toxidrome presents as miosis, lacrimation, diarrhea, fasciculations, seizures, respiratory arrest and coma. Current medical countermeasures can attenuate acute mortality and confer limited protection against secondary neuronal injury when given rapidly after exposure. However, there is an urgent need for the development of novel, add-on neuroprotective therapies to prevent mortality and long-term toxicity of nerve agents. Increasing evidence suggests that pathways other than direct acetylcholinesterase inhibition contribute to neurotoxicity and secondary neuronal injury. Among these, oxidative stress is emerging as a key therapeutic target for nerve agent toxicity. In this review, we discuss the rationale for targeting oxidative stress in nerve agent toxicity and highlight research investigating antioxidant therapy as a neuroprotective medical countermeasure to attenuate oxidative stress, neuroinflammation and neurodegeneration.

Objective PET study of glucose metabolism asymmetries in children with epilepsy: Implications for normal brain development

Clinical interpretation of cerebral positron emission tomography with 2-deoxy-2[F-18]fluoro-d-glucose (FDG-PET) images often relies on evaluation of regional asymmetries. This study was designed to establish age-related variations in regional cortical glucose metabolism asymmetries in the developing human brain. FDG-PET scans of 58 children (age: 1-18 years) were selected from a large single-center pediatric PET database. All children had a history of epilepsy, normal MRI, and normal pattern of glucose metabolism on visual evaluation. PET images were analyzed objectively by statistical parametric mapping with the use of age-specific FDG-PET templates. Regional FDG uptake was measured in 35 cortical regions in both hemispheres using an automated anatomical labeling atlas, and left/right ratios were correlated with age, gender, and epilepsy variables. Cortical glucose metabolism was mostly symmetric in young children and became increasingly asymmetric in older subjects. Specifically, several frontal cortical regions showed an age-related increase of left > right asymmetries (mean: up to 10%), while right > left asymmetries emerged in posterior cortex (including portions of the occipital, parietal, and temporal lobe) in older children (up to 9%). Similar trends were seen in a subgroup of 39 children with known right-handedness. Age-related correlations of regional metabolic asymmetries showed no robust gender differences and were not affected by epilepsy variables. These data demonstrate a region-specific emergence of cortical metabolic asymmetries between age 1-18 years, with left > right asymmetry in frontal and right > left asymmetry in posterior regions. The findings can facilitate correct interpretation of cortical regional asymmetries on pediatric FDG-PET images across a wide age range.

Applications of global quantitative 18F-FDG-PET analysis in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is a prevalent neurodegenerative disease associated with various neuropsychiatric disorders and decreased quality of life. Much has been said about the use of fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG-PET), magnetic resonance imaging (MRI), and computed tomography in the qualitative assessment of TLE. However, research into the applications of quantitative measurements to treat and diagnose TLE is severely lacking in the literature. Global quantitative analysis using 18F-FDG-PET is a powerful tool in the metabolic assessment of TLE, and can more accurately identify seizure lateralization and the potential effects of treatment as compared with visual assessments and traditional biopsy region-of-interest quantification. Therefore, there is a pressing need to introduce these novel methods to the treatment of TLE. Although 18F-FDG-PET is most commonly used for visual assessments, qualitative analysis is associated with high levels of interobserver and intraobserver variability. Semiquantitative analysis using standardized uptake value is a more consistently accurate measure of the hypometabolic patterns seen in TLE patients. Novel methods of global quantitative analysis developed in our laboratory have the potential to improve TLE assessment by limiting variability and correcting for the partial volume effect. It is of great importance to adopt these techniques into the mainstream diagnosis and treatment of TLE in order to improve patient care worldwide.

Cerebral glucose hypometabolism is associated with mitochondrial dysfunction in patients with intractable epilepsy and cortical dysplasia

OBJECTIVES

Metabolic imaging studies, such as positron emission tomography (PET), allow for an assessment of physiologic functioning of the brain, and [(18)F]fluoro-2-deoxyglucose (FDG)-PET is now a commonly used technique in presurgical epilepsy evaluations. Focal interictal decreases in glucose consumption are often but inconsistently concordant with the ictal onset area, and the underlying mechanisms are poorly understood. The current study tests the hypothesis that areas of glucose hypometabolism, determined by FDG-PET, are associated with mitochondrial dysfunction in patients with medically intractable epilepsy associated with isolated focal cortical dysplasia (FCD).

METHODS

Measures of electron transport chain (ETC) functioning and mitochondrial abnormalities (ETC complex biochemistry, protein kinase B subtype 1 (Akt1), glial fibrillary acidic protein (GFAP)) were assessed in surgical resection specimens that had hypometabolic abnormalities and those that were normal on FDG-PET. Determination of FDG-PET abnormalities was based on coregistration of statistical parametric mapping (SPM) results with postsurgical images.

RESULTS

Twenty-two patients (11 male, 11 female; mean age at the time of surgery 10.5 ± 4.4 years), with pathologically confirmed FCD, were included in this retrospective review. Complex IV function was found to be significantly reduced in areas of hypometabolism (p = 0.014), whereas there was a trend toward a significant reduction in complex II and III function in areas of hypometabolism (p = 0.08, p = 0.059, respectively). These decreases were independent of cortical dysplasia severity (p = 0.321) and other clinical epilepsy measures.

SIGNIFICANCE

This study suggests an association between glucose hypometabolism and reduced mitochondrial complex IV functioning, which is independent of the degree of cortical dysplasia. This supports the role of cellular energy failure as a potential mechanism for intractable epilepsy.

Positron emission tomography in seizure disorders

Positron emission tomography (PET) has been widely used in the study of seizure disorders. As a research tool, PET has been used to determine the pathophysiology of different seizures disorders, prognostic and diagnostic information, and the response to various interventions. PET imaging has also been used clinically to help with the detection of seizure foci. With the continued development of a large array of radiopharmaceuticals that can evaluate all of the components of different neurotransmitter systems as well as cerebral blood flow and metabolism, PET imaging will continue to play a key role in research and clinical applications for seizure disorders.

Objective detection of epileptic foci by 18F-FDG PET in children undergoing epilepsy surgery

PET has been used for the presurgical localization of epileptic foci for more than 20 y; still, its clinical role in children with intractable epilepsy remains unclear, largely because of variable analytic approaches and different outcome measures. The purpose of the present study was to evaluate and optimize the performance (lateralization and lobar localization value of epileptic foci) of objective voxel-based analysis of (18)F-FDG PET scans in a pediatric epilepsy population.

METHODS

Twenty children with intractable focal epilepsy (mean age ± SD, 11 ± 4 y; age range, 6-18 y) who underwent interictal (18)F-FDG PET, followed by 2-stage epilepsy surgery with chronic subdural electrocorticographic monitoring, and were seizure-free after surgery were included in this study. PET images were analyzed using both a visual-analysis and a statistical parametric mapping (SPM) method. Lateralization value and performance of lobar localization (in lateral and medial surfaces of all lobes, total of 8 regions in each epileptic hemisphere), calculated for 3 different statistical thresholds, were determined against intracranial electrocorticography-determined seizure-onset region and surgical resection site.

RESULTS

SPM using a statistical threshold of P less than 0.001 provided 100% correct lateralization, which was better than visual assessment (90%). Although visual and SPM analyses (with both P < 0.001 and P < 0.0001 thresholds) performed similarly well (with a sensitivity and specificity of 74% or above) in the localization of seizure-onset regions, SPM detected 7 of 9 seizure-onset regions, mostly in medial cortices, that were missed by visual assessment. Also, SPM performed equally well in both hemispheres, compared with visual analysis, which performed better in the left hemisphere. No statistical difference in performance was observed between visual and SPM analyses of children with abnormal versus normal MRI findings or of children with gliosis versus developmental pathology. Clinical variables, such as age, duration of epilepsy, age of seizure onset, and time between PET and last seizure, showed no correlation with sensitivity or specificity of either visual analysis or SPM analysis.

CONCLUSION

SPM analysis, using a young adult control group, can be used as a complementary objective analytic method in identifying epileptogenic lobar regions by (18)F-FDG PET in children older than 6 y.

PET in Epilepsy and Other Seizure Disorders

Positron emission tomography (PET) imaging has been widely used in the evaluation and management of patients with seizure disorders. The ability of PET to measure cerebral function makes it ideal for studying the neurophysiologic correlates of seizure activity during ictal and interictal states. PET imaging is also useful for evaluating patients before surgical interventions to determine the best surgical method and maximize outcomes. Thus, PET will continue to play a major role not only in the clinical arena but in further investigations of the pathogenesis and management of various seizure disorders. This article reviews the literature regarding the current uses and indications for PET in the study and management of patients with seizure disorders.

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.

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.

EEG Source Imaging in Pediatric Epilepsy Surgery: A New Perspective in Presurgical Workup

PURPOSE

Epilepsy is a relatively frequent disease in children, with considerable impact on cognitive and social life. Successful epilepsy surgery depends on unambiguous focus identification and requires a comprehensive presurgical workup, including several neuroimaging techniques [magnetic resonance imaging, positron emission tomography (PET), and single-photon emission computed tomography (SPECT)]. These may be difficult to apply in younger or developmentally delayed children or both, requiring sedation, and hence, a significant workforce. Modern electric source imaging (ESI) provides accurate epileptic source-localization information in most patients, with minimal patient discomfort or need for cooperation. The purpose of the present study was to determine the usefulness of ESI in pediatric EEG recordings performed with routine electrode arrays.

METHODS

Preoperative EEGs recorded from 19 to 29 scalp electrodes were reviewed, and interictal epileptiform activity was analyzed by using a linear source-imaging procedure (depth-weighted minimum norm) in combination with statistical parametric mapping.

RESULTS

In 27 (90%) of 30 patients, the ESI correctly localized the epileptogenic region. These numbers compare favorably with the results from other imaging techniques in the same patients (PET, 82%; ictal SPECT, 70%). In extratemporal epilepsy, ESI was correct in all cases, and in temporal lobe epilepsy, in 10 of 13 cases. In two temporal lobe patients showing less-accurate ESI results, 128-electrode data could be analyzed, and in both cases, the 128-electrode ESI was correct.

CONCLUSIONS

ESI with standard clinical EEG recordings provides excellent localizing information in pediatric patients, in particular in extratemporal lobe epilepsy. The lower yield in temporal lobe epilepsy seems to be due to undersampling of basal temporal areas with routine scalp recordings.

Longitudinal changes in cortical glucose hypometabolism in children with intractable epilepsy

In children with partial epilepsy, there is increasing evidence to suggest that not all cortical regions showing glucose hypometabolism on positron emission tomography (PET) represent epileptogenic cortex but that some hypometabolic areas might be the result of repeated seizures. Most of the supportive data, however, have come from cross-sectional imaging studies. To evaluate longitudinal changes in cortical glucose hypometabolism, we compared two sequential [(18)F]fluorodeoxyglucose (FDG) PET scans performed 7 to 44 months apart in 15 children with intractable nonlesional partial epilepsy. The extent of hypometabolic cortex on the side of the electroencephalography-verified epileptic focus and its changes between the two PET scans were measured and correlated to clinical seizure variables. The change in seizure frequency between the two PET scans correlated positively with the change in the extent of cortical glucose hypometabolism (r = .8, P <.001). Most patients with persistent or increased seizure frequency (one or more seizures per day) showed enlargement in the area of hypometabolic cortex on the second PET scan. In contrast, patients whose seizure frequency had decreased below daily seizures between the first and second PET scans showed a decrease in the size of the hypometabolic cortex. These results support the notion that the extent of cortical glucose hypometabolism on PET scanning can undergo dynamic changes, and these are, at least partly, related to the frequency of seizures. The findings have implications on how aggressively persistent seizures should be treated in children. (J Child Neurol 2006;21:26-31).

The Prognostic Value of [18F]FDG-PET in Nonrefractory Partial Epilepsy

PURPOSE

Regional abnormalities of cerebral glucose metabolism, as identified by 18-fluorodeoxyglucose positron emission tomography (FDG-PET) have prognostic value regarding the outcome of epilepsy surgery in patients with refractory partial epilepsy. The value of FDG-PET abnormalities in nonrefractory patients has not been investigated systematically. This study examines whether FDG-PET could be used for early identification of nonrefractory epilepsy in patients who will become pharmacoresistant later during the course of their disease.

METHODS

We investigated interictal abnormalities of cerebral glucose metabolism by using FDG-PET in 125 consecutive patients with nonrefractory cryptogenic partial epilepsy and normal cranial magnetic resonance imaging (MRI), and we compared relative changes in seizure frequency in 90 patients after > or =2 years of follow-up.

RESULTS

Regional asymmetry of tracer distribution was seen in 43 of the 90 patients. Forty-one patients had regional glucose hypometabolism in the temporal and two patients in an extratemporal region. No difference between patients with and without a hypometabolic focus was found regarding seizure freedom after follow-up. This held true also for the subgroup of patients with epilepsy onset within 1 year before admission. Only patients with regional glucose metabolism showed an increase in seizure frequency. Multivariate analysis showed that only anticonvulsive treatment before index admission and the possibility of localizing the epileptogenic focus by using all available clinical and EEG data were independently associated with continuing seizures after a median follow-up period of 43 months.

CONCLUSIONS

Regional hypometabolism in FDG-PET is not significantly associated with a lower likelihood of successful anticonvulsant drug therapy in patients with nonrefractory partial epilepsy. Careful analysis of all routinely available clinical and neurophysiologic data has a much better predictive power to identify patients with medically refractory epilepsy early in the course of the disease. However, if PET data are available, they could help in identifying patients with a less benign course.

Assessment of the role of FDG PET in the diagnosis and management of children with refractory epilepsy

PURPOSE

We performed a retrospective analysis of the results of FDG PET scans in children with refractory epilepsy referred to our centre over an 8-year period, with a view to ascertaining the impact of FDG PET on subsequent patient management.

METHODS

A questionnaire was used to assess the impact of FDG PET scan on diagnosis, management and clinical decision-making processes for epilepsy surgery from the managing clinician's perspective. FDG PET scan results were also compared with MRI, EEG and SPECT results and coded according to whether the FDG PET scan provided independent information and localisation of epileptogenic regions.

RESULTS

A total of 118 eligible patients under the age of 14 years were identified, with questionnaires being completed on 113 evaluable patients (96%). The pre-PET management plan consisted of consideration for surgery in 92 patients (81%) and medical therapy for the remaining 21 patients (19%). Managing physicians rated FDG PET as providing information additional to that obtained with other investigations regarding epileptogenic sites in 88 patients (77%). FDG PET had either a minor or a major impact on clinical management in 58 patients (51%), principally with regard to surgical candidacy.

CONCLUSION

FDG PET has a definite role in the assessment of paediatric patients with refractory epilepsy who are being considered for surgery. In the future, analysis of FDG PET data in specific subpopulations of children with refractory epilepsy may lead to novel insights regarding aetiology.

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.

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.

Subcortical [18F]fluorodeoxyglucose uptake in lesional epilepsy in patients with intracranial tumour

BACKGROUND

We hypothesized that in patients with intracerebral tumours a subcortical metabolical shift may be present when the underlying pathology can, itself, be the epileptogenic focus. We also assumed that by studying the alterations in glucose metabolism beyond the tumour's borders we could identify a modulator area.

METHODS

Sixty-seven patients with supratentorial brain tumour associated epilepsy were investigated interictally, in normoglycaemic conditions, by using [18F]fluorodeoxyglucose positron emission tomography (FDG PET). The studies were analysed semiquantitatively by calculating standardized uptake values and asymmetry indices. Normal subjects and patients with non-epileptic brain lesions were used as controls.

RESULTS

Compared to normal controls frontal and temporal tumours showed significant changes in thalamic FDG uptake, which reflected hypometabolism of the affected side. It was noted in occipito-medial cortex in temporal tumours and in lentiform nucleus in frontal tumours as well. Comparison to lesional brains only proved that there was significant hypometabolism in lentiform nucleus in temporal tumours.

CONCLUSIONS

The quantified values obviously reflect biological changes. The observed subcortical hypometabolism is most likely secondary to underlying pathology. Although seizures in tumorous patients do not originate from subcortical structures their influence on cortical sites of seizure initiation could be explained by defective subcortical regulation of cortical excitability.

Interictal patterns of cerebral glucose metabolism, perfusion, and magnetic field in mesial temporal lobe epilepsy

PURPOSE

To characterize the epileptogenic condition of patients with mesial temporal lobe epilepsy, the interictal patterns of glucose metabolism, perfusion, and magnetic field in the temporal lobe were evaluated by using [18F]fluorodeoxyglucose-positron emission tomography, [99mTc]-ethylcysteinate dimer-single photon emission computed tomography, and magnetoencephalography (MEG).

METHODS

Twenty-one patients with mesial temporal lobe epilepsy related to hippocampal sclerosis were studied. The ictal-onset area was located by continuous video-EEG monitoring. Quantitative analysis of glucose metabolism and perfusion in the temporal lobe was performed, and the cerebral magnetic field was evaluated to measure the equivalent current dipole (MEG-ECD).

RESULTS

Although hypometabolism and hypoperfusion in the temporal lobe were lateralized with the ictal-onset area in 16 (76.2%) and in 11 (52.4%) respectively, they were localized in diverse ways without any coupling. MEG-ECD was distributed in diverse ways unrelated to the ictal-onset area: ipsilateral medial temporal origin in five (23.8%), ipsilateral lateral temporal origin in two (9.5%), ipsilateral mixed (medial and lateral) temporal origin in six (28.6%), bilateral temporal origin in four (19.0%), and contralateral temporal origin in two (9.5%).

CONCLUSIONS

MEG-ECD was distributed in varied ways with the disorder and uncoupling of glucose metabolism and perfusion in the temporal lobe. These results may help resolve the clinical controversy over the possibility that the cortical irritative area generating the interictal epileptic discharge is distinct from the ictal-onset area, and also may have some functional implications in identifying different brain compartments in the generation of metabolic signals.

[Clinical impact of 18F-fluorodeoxyglucose positron emission tomography in the diagnosis of brain diseases]

In this review it will be discussed in which neurological disorders positron emission tomography can yield important diagnostic information. Because positron emission tomography is an expensive method indications have to be clearly defined. One important question concerns the differentiation of tumor recurrence and scar due to radiation therapy or an operation. The grading of brain tumors is another application. In HIV patients fluorodeoxyglucose positron emission tomography can separate lymphoma and toxoplasmosis. In the evaluation of dementia positron emission tomography can help to clarify the differential diagnosis. Another important area is the presurgical evaluation of epilepsy patients and patients with cerebrovascular disease in whom a surgical revascularisation procedure is planned. In extrapyramidal disorders, positron emission tomography can often help to establish the final diagnosis.

Neuroradiology of the central nervous system in childhood

The purpose of this article is to familiarize readers with new imaging applications, identify the relative strengths of imaging modalities, and emphasize practical applications of imaging the child's nervous system. Because of recent advances in MRI, the article emphasizes the expanding role of MRI in evaluating children with neurologic disease.

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.

Structural and functional imaging in children with partial epilepsy

Imaging plays an increasingly important role in the evaluation of children with complex partial seizures. Most partial epilepsy, especially of temporal lobe origin, begins during childhood. Structural imaging with high-resolution MRI can help identify the etiology of partial seizure disorders in many children. MRI studies also show the more widespread effect of seizures on brain structure. Progressive volume loss of the hippocampal formation in some patients with temporal lobe epilepsy provides evidence that continued seizures may be associated with progressive neuronal injury. FDG-PET studies show regional decreases in glucose consumption in the cortical zone from which seizures arise. Functional abnormalities often are more extensive than the seizure focus. Studies in children with recent-onset epilepsy show that metabolic abnormalities are considerably less common than in adults with partial epilepsy, supporting the notion that in some patients there may be progressive metabolic changes that occur with continued seizures. Functional MRI may be used to identify language areas in children with partial epilepsy. fMRI language tasks reliably identify the dominant hemisphere for language dominance when compared to the intracarotid amytal procedure. Tests of verbal fluency and semantic decision identify frontal lobe language areas, while reading text paradigms and auditory passage paradigms are better for identifying temporal language areas. A panel of paradigms is best used to identify language areas in children being considered for epilepsy surgery. fMRI is a valuable tool for elucidating the impact of chronic neurologic disease states on the functional organization of language networks during development.

Surgery of epilepsy associated with focal lesions in childhood

OBJECT

Surgery in children with epilepsy is a new, evolving field. The important practical issues have been to define strategies for choosing the most suitable candidates and the type and optimal timing of epilepsy surgery. This study was undertaken to elucidate these points.

METHODS

To identify the factors that correlated with outcome, the authors analyzed a series of 200 children (aged 1-15 years (mean 8.7 years) who underwent surgery between 1981 and 1996 at the Hôpital Necker-Enfants Malades. In 171 cases (85.5%) the epilepsy was medically refractory and was associated with focal cortical lesions. Surgery consisted of resection of the lesion without specifically attempting to identify and remove the "epileptogenic area. "In the group of children whose seizures were medically refractory, the mean follow-up period was 5.8 years. According to Engel's classification, 71.3% of these children became seizure free (Class 1a,) whereas 82% were in Class I. A multivariate statistical analysis revealed that among all the factors studied, the success of surgery in a patient in whom there was a good clinical/electroencephalogram/imaging correlation depended on the patient's having undergone a minimally traumatic operation, a complete resection of the lesion, and a short preoperative seizure duration. After the surgical control of epilepsy, behavior disorders were more improved (31% of all patients) than cognitive function (25%). The patient age at onset, duration and frequency of seizures, intractability of the disease to therapy, and seizure characteristics were correlated with cognitive, behavioral, and academic performance pre- and postoperatively. Multivariate statistical analysis revealed that cognitive dysfunction correlated highly with the duration of epilepsy prior to surgery, whereas behavioral disorders correlated more with seizure frequency.

CONCLUSIONS

These data must be taken into account when selecting patients for surgical treatment and when deciding the timing of surgery. Early surgical intervention allows for optimum brain development.

Presurgical evaluation and surgical outcome of temporal lobe epilepsy

The authors analyzed 22 patients younger than 18 years of age with temporal lobe epilepsy (TLE) treated surgically. Patients underwent a comprehensive presurgical evaluation, including video-electroencephalogram. Fifty-five percent had a history of febrile seizures. Eighty-two percent had auraes and most exhibited oroalimentary and gestural automatisms. Contralateral dystonic posturing was present in 36% and postictal dysphasia in 54% of patients with left-sided resections. Cranial magnetic resonance imaging (MRI) was abnormal in 59% of patients. MRI revealed changes consistent with mesial temporal sclerosis in 8 (47%) of 17 patients without lesions. Fluorodeoxyglucose-positron emission tomography (PET) scans revealed ipsilateral temporal hypometabolism (PET-TH) in 12 (85.7%) of 14 patients. The intracarotid amobarbital procedure revealed impaired memory of the epileptogenic side in 59% of patients. Seventeen patients underwent en-bloc resections and five lesionectomies and resection of the epileptogenic area. There was no surgical morbidity or mortality. Forty-three percent had hippocampal sclerosis, 28.5% gliosis, 14% low-grade tumors, 9.5% cavernous angiomas, and 5% had no pathologic findings. Follow-up (6 months to 12 years) was available for 21 patients; 76% became seizure free, 19% had rare seizures, and 5% had a worthwhile improvement. TLE can be safely treated surgically in younger patients with excellent results. The clinical manifestations were similar to adult patients. PET-TH was present even at a younger age, suggesting that the focal functional deficits appear early in patients with medically refractory TLE, which may help in the early identification of these patients.

Surgery in epilepsy associated with focal lesions in childhood

Surgery in children with epilepsy is a new, evolving field. The important practical issues have been to define strategies for choosing the most suitable candidates, as well as the type and the optimum timing of epilepsy surgery. This study was undertaken to illustrate these points.

To identify the factors that correlated with outcome, the authors analyzed a series of 200 children (aged 1–15 years, mean 8.7 years) who underwent surgery at the Hôpital Necker-Enfants Malades between 1981 and 1996. In 171 cases (85.5%) the epilepsy was medically refractory and was associated with focal cortical lesions. Surgery consisted of resection of the lesion without specifically attempting to identify and remove the "epileptogenic area."

In the group of children whose seizures were medically refractory, the mean follow-up period was 5.8 years. According to Engel's classification, 71.3% of these children became seizure free (Ia), whereas 82% were in Class I. A multivariate statistical analysis revealed that among all the factors studied, the success of surgery in a patient in whom there was a good clinical-electroencephalogram-imaging correlation, depended on the patients' having undergone a minimally traumatic operation, a complete resection of the lesion, and a short preoperative seizure duration.

After the surgical control of epilepsy, behavior disorders were more improved (31% of all patients) than cognitive function (25%). The patient age at onset, duration and frequency of seizures, intractability of the disease to therapy, and seizure characteristics, were correlated with cognitive, behavioral, and academic performance pre- and postoperatively. Multivariate statistical analysis revealed that cognitive dysfunction correlated highly with the duration of epilepsy prior to surgery, whereas behavioral disorders correlated more with seizure frequency.

These data must be taken into account when selecting patients for surgical treatment and when deciding the timing of surgery. Early surgical intervention allows for optimum brain development.

Brain hypometabolism in a model of chronic focal epilepsy in rat neocortex

PURPOSE

Metabolic mapping of the human brain has become a widely used method for identifying and localizing epileptic foci. A reduction of glucose consumption usually is found interictally in the area of the focus. By contrast, animal models of acute epilepsy show a hypermetabolism in the epileptic focus. Here we investigated how metabolism is altered in an animal model of chronic epilepsy caused by focal injection of tetanus toxin into rat neocortex.

METHODS

A total of 27 male Wistar rats were anesthetized and injected into the motor or sensory cortex either with dissolved tetanus toxin or with the solvent only. Animals recovered for 7, 14, or 30 days and then were anesthetized again for quantitative 14C-deoxyglucose autoradiography. Data were analyzed with an imaging program, and regional cerebral glucose metabolism (rCMRGlc) was determined.

RESULTS

Injection of tetanus toxin into the motor cortex caused a focal hypometabolism which was confined to the cytoarchitectonic boundaries of the injected area, whereas sensory cortex injection caused a more widespread hypometabolism in all sensory cortical and connected, areas. None of the animals displayed focal hypermetabolism and we observed no significant time-dependent alteration of brain metabolism.

CONCLUSIONS

Tetanus toxin injection into the cortex of the rat induces chronic epileptic activity accompanied by a focal hypometabolism. The data suggest that the spread of the metabolic alterations depends on the connectivity of the injected cortical area.

FDG-PET and MRI in temporal lobe epilepsy: relationship to febrile seizures, hippocampal sclerosis and outcome

OBJECTIVE

To correlate the volumetric head magnetic resonance imaging (MRI) and fluorodeoxyglucose-positron emission tomography (FDG-PET) scan findings with the history, intracarotid amobarbital procedure, pathology, and outcome in patients with medically refractory temporal lobe epilepsy.

MATERIAL AND METHODS

Thirty-eight patients with temporal lobe epilepsy treated surgically following a comprehensive presurgical evaluation. Follow-up ranged from 12 to 44 months.

RESULTS

Volumetric MRI showed ipsilateral hippocampal atrophy in 29 (76%), and PET scan showed ipsilateral temporal hypometabolism (PET-TH) in 31 (81.5%) of patients. Eighty-three percent of those patients with hippocampal sclerosis on MRI (MRI-HS) had ipsilateral PET-TH. Sixty-six percent of patients with MRI-HS had a history of prolonged febrile convulsions or a childhood febrile illness accompanied by convulsions, and 77% of patients with MRI-HS had pathologically proven hippocampal sclerosis (HS). Ninety percent became seizure free or had rare seizures.

CONCLUSION

FDG-PET scans and head MRIs were complementary; 95% of patients had either MRI-HS or temporal hypometabolism. MRI-HS correlated with a history of febrile seizures and pathologically demonstrated hippocampal sclerosis. Ninety-three percent of patients had focal functional deficits on the epileptogenic side. Concordance between PET temporal hypometabolism and MRI-HS correlated with better outcome.

Extratemporal atrophy in patients with complex partial seizures of left temporal origin

Total cerebral, temporal lobe, hippocampal, caudate, and lenticular nuclei volumes were quantified from magnetic resonance images of 21 patients with left temporal lobe epilepsy and medically intractable complex partial seizures. These regional brain volumes were compared with the same measures in 19 controls. No significant differences in total cerebral, left temporal lobe, right temporal lobe, or total temporal lobe volumes were found. As expected, left hippocampal volumes were significantly smaller in the patients with epilepsy than in control subjects. The left hippocampus-to-right hippocampus volume ratio was significantly lower in patients than in control subjects. In addition to left hippocampal volumes, mean left thalamic, left caudate, and bilateral lenticular volumes were significantly smaller in the patients with epilepsy than in control subjects. The left-to-right thalamic volume ratio was also significantly lower in the patients with epilepsy compared with control subjects, but there were no significant group differences in caudate or lenticular ratios. These results show that medically intractable temporal lobe epilepsy is associated with volume loss in brain structures outside the presumably involved hippocampus. The pathophysiological significance of our findings is uncertain. They could be related to the underlying cause of the disorder. However, volume loss also may reflect damage due to involvement of these structures in recurrent seizure activity.

Is 11C-flumazenil PET superior to 18FDG PET and 123I-iomazenil SPECT in presurgical evaluation of temporal lobe epilepsy?

OBJECTIVE

To determine the contribution of 18FDG PET, 11C-flumazenil PET, and 123I-iomazenil SPECT to the presurgical evaluation of patients with medically intractable complex partial seizures.

METHODS

Presurgical evaluation was performed in 23 patients, who were considered candidates for temporal lobe resective surgery (14 females and nine males with a median age of 34 (range 13 to 50) years). The presurgical diagnosis was based on seizure semiology as demonstrated with ictal video recording, ictal and interictal scalp EEG recordings, and MRI.

RESULTS

Eighteen patients had convergent findings in clinical semiology, interictal and ictal EEG with scalp and sphenoidal electrodes, and MRI that warranted surgery without depth EEG (DEEG). In five patients with insufficient precision of localisation, DEEG with intracerebral and subdural electrodes was performed. MRI showed abnormalities in 22 out of 23 patients. Of these 22, 18 had mesial temporal sclerosis. This was limited to the mesial temporal lobe in four and more widespread in the temporal lobe in 14 patients. In one patient only enlargement of the temporal horn was found and in three others only white matter lesions were detected. 18FDG PET showed a large area of glucose hypometabolism in the epileptogenic temporal lobe, with an extension outside the temporal lobe in 10 of 23 patients. Only in one of these patients DEEG showed extratemporal abnormalities that were concordant with a significant extratemporal extension of hypometabolism in 18FDG PET. 18FDG PET was compared with the results of scalp EEG: in none of the patients was an anterior temporal ictal onset in scalp EEG related to a maximum hypometabolism in the mesial temporal area. By contrast, the region of abnormality indicated by 11C-flumazenil PET was much more restricted, also when compared with DEEG findings. Extension of abnormality outside the lobe of surgery was seen in only two patients with 11C-flumazenil and was less pronounced compared with the intratemporal abnormality. Both 18FDG PET and 11C-flumazenil PET reliably indicated the epileptogenic temporal lobe. Thus these techniques provide valuable support for the presurgical diagnosis, especially in patients with non-lesional MRI or non-lateralising or localising scalp EEG recordings. In those patients in whom phase 1 presurgical evaluation on the basis of classic methods does not allow a localisation of the epileptogenic area, PET studies may provide valuable information for the strategy of the implantation of intracranial electrodes for DEEG. Previous studies have suggested that 11C-flumazenil binding has a closer spatial relationship with the zone of ictal onset than the area of glucose hypometabolism, but this study suggests rather that the decrease in the 11C-flumazenil binding simply reflects a loss of neurons expressing the benzodiazepine-GABA receptor. 11C-flumazenil PET did not prove to be superior to 18FDG PET.

CONCLUSION

In 21 patients sufficient material was obtained at surgery for a pathological examination. In 17 mesial temporal sclerosis, in one an oligodendroglioma grade B, in another a vascular malformation and in two patients no abnormalities were found. Although all 21 patients with pathological abnormality showed hypometabolic zones with 18FDG PET and a decreased uptake in 11C-flumazenil binding, there was no strong correlation between pathological diagnosis and functional abnormal areas in PET. Grading of medial temporal sclerosis according to the Wyler criteria showed no correlation with the degree of hypometabolism in either 18FDG or 11C-flumazenil PET. The interictal 123I-iomazenil SPECT technique was highly inaccurate in localising the lobe of surgery.

Three- to five-dimensional biomedical multisensor imaging for the assessment of neurological (dys) function

This report describes techniques and protocols implemented at the Geneva Canton University Hospitals (HUG) for the combination of various biomedical imaging modalities and sensors including electromagnetic tomography, to study, assess, and localize neurological (dys) function. The interest for this combination stems from the broad variety of information brought out by (functional) magnetic resonance imaging, magnetic resonance spectroscopy, computed tomography, single-photon emission tomography, positron emission tomography, and electromagnetic tomography. Combining these data allows morphology, metabolism, and function to be studied simultaneously, the complementary nature of the information from these modalities becoming evident when studying pathologies reflected by metabolic or electrophysiologic dysfunctions. Compared with other current multimodality approaches, the one at the HUG is totally compatible with both clinical and research protocols, and efficiently addresses the multidimensional registration and visualization issues. It also smoothly integrates electrophysiology and related data as fully featured modalities.

Usefulness of [18F]fluorodeoxyglucose positron emission tomography in pediatric epilepsy surgery

We sought to analyze our experience with pediatric epilepsy surgery patients to determine the place of [18F]fluorodeoxyglucose (FDG) positron emission tomography (FDG-PET) in the preoperative evaluation of such children relative to chronic invasive intracranial monitoring. Fifty-six children who received an interictal FDG-PET as part of a phase 1 epilepsy surgery evaluation were compared with 44 children who did not have this study in a retrospective analysis of 100 patients accrued over a 4-year period. There was no significant difference between the two groups of children in terms of age or follow-up or was there a significant difference between the FDG-PET group and the no-FDG-PET group in regard to the numbers of children who had surgery, the type of procedure done, whether chronic invasive intracranial monitoring was performed, or outcome. The hypometabolic area demonstrated on interictal FDG-PET was concordant with that of the epileptogenic zone as mapped out with ictal recordings from subdural electrodes in 2 of 13 patients in whom a complete data set was available for comparison. In the other 11 children there was either poor agreement between interictal FDG-PET and ictal electrocorticographic data or the interictal FDG-PET was normal in the face of an epileptogenic focus which was successfully mapped by invasive electrophysiologic techniques and excised. We conclude that one cannot exclude a child with intractable partial seizures from surgical consideration because the interictal FDG-PET is normal; nor is there sufficient correlation between the interictal hypometabolic area on FDG-PET and the epileptogenic zone in terms of anatomic location and size to justify forgoing chronic invasive intracranial monitoring in children with intractable partial seizures being evaluated for epilepsy surgery unless there is absolute concordance between all neuroimaging, clinical, and video-electroencephalographic data.