Low incidence of abnormal (18)FDG-PET in children with new-onset partial epilepsy: a prospective study

The vasodilator naftidrofuryl attenuates short-term brain glucose hypometabolism in the lithium-pilocarpine rat model of status epilepticus without providing neuroprotection

Status epilepticus (SE) triggered by lithium-pilocarpine is a model of epileptogenesis widely used in rats, reproducing many of the pathological features of human temporal lobe epilepsy (TLE). After the SE, a silent period takes place that precedes the occurrence of recurrent spontaneous seizures. This latent stage is characterized by brain glucose hypometabolism and intense neuronal damage, especially at the hippocampus. Importantly, interictal hypometabolism in humans is a predictive marker of epileptogenesis, being correlated to the extent and severity of neuronal damage. Among the potential mechanisms underpinning glucose metabolism impairment and the subsequent brain damage, a reduction of cerebral blood flow has been proposed. Accordingly, our goal was to evaluate the potential beneficial effects of naftidrofuryl (25 mg/kg i.p., twice after the insult), a vasodilator drug currently used for circulatory insufficiency-related pathologies. Thus, we measured the effects of naftidrofuryl on the short-term brain hypometabolism and hippocampal damage induced by SE in rats. 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) positron emission tomography (PET) neuroimaging along with various neurohistochemical assays aimed to assess brain damage were performed. SE led to both severe glucose hypometabolism in key epilepsy-related areas and hippocampal neuronal damage. Although naftidrofuryl showed no anticonvulsant properties, it ameliorated the short-term brain hypometabolism induced by pilocarpine. Strikingly, the latter was neither accompanied by neuroprotective nor by anti-inflammatory effects. We suggest that naftidrofuryl, by acutely enhancing brain blood flow around the time of SE improves the brain metabolic state but this effect is not enough to protect from the damage induced by SE.

Longitudinal changes of focal cortical glucose hypometabolism in adults with chronic drug resistant temporal lobe epilepsy

A high proportion of patients with drug-resistant temporal lobe epilepsy (TLE) show focal relative hypometabolism in the region of the epileptogenic zone on [¹⁸F]-Fluorodeoxyglucose positron emission tomography (FDG PET). However, whether focal (hypo)metabolism changes over time has not been well studied. We analysed repeated [¹⁸F]-FDG PET scans of patients with TLE to determine longitudinal changes in glucose metabolism. Adults (n = 16; 9 female, 7 male) diagnosed with drug resistant chronic TLE were assessed. Each patient had two [¹⁸F]-FDG PET scans that were 2-95 months apart. Region-of-interest analysis was performed on MR images onto which PET scans were coregistered to determine the relative [¹⁸F]-FDG uptake (normalised to pons) in the bilateral hippocampi and temporal lobes. Statistical Parametric Mapping analysis investigated global voxel-wise changes in relative metabolism between timepoints. Normalised [¹⁸F]-FDG uptake did not change with time in the ipsilateral (baseline 1.14 ± 0.03, follow-up 1.19 ± -0.04) or contralateral hippocampus (baseline 1.18 ± 0.03, follow-up 1.19 ± 0.03). Uptake in the temporal neocortex also remained stable (ipsilateral baseline 1.35 ± 0.03, follow-up 1.30 ± 0.04; contralateral baseline 1.38 ± 0.04, follow-up 1.33 ± 0.03). The was no relationship between change in uptake on the repeated scans and the time between the scans. SPM analysis showed increases in metabolism in the ipsilateral temporal lobe in 2/16 patients. No areas of decreased metabolism concordant to the epileptogenic zone were identified. [¹⁸F]-FDG uptake showed no significant changes over time in patients with drug-resistant TLE. This suggests that repeating FDG-PET scans in patients with subtle or no hypometabolism is of low clinical yield.

Characterizing the hyper- and hypometabolism in temporal lobe epilepsy using multivariate machine learning

Mesial temporal lobe epilepsy (MTLE) is the most common type of focal epilepsy, presenting both structural and metabolic abnormalities in the ipsilateral mesial temporal lobe. While it has been demonstrated that the metabolic abnormalities in MTLE actually extend beyond the epileptogenic zone, how such multidimensional information is associated with the diagnosis of MTLE remains to be tested. Here, we explore the whole-brain metabolic patterns in 23 patients with MTLE and 24 healthy controls using [¹⁸ F]fluorodeoxyglucose PET imaging. Based on a multivariate machine learning approach, we demonstrate that the brain metabolic patterns can discriminate patients with MTLE from controls with a superior accuracy (>95%). Importantly, voxels showing the most extreme contributing weights to the classification (i.e., the most important regional predictors) distribute across both hemispheres, involving both ipsilateral negative weights over the anterior part of lateral and medial temporal lobe, posterior insula, and lateral orbital frontal gyrus, and contralateral positive weights over the anterior frontal lobe, temporal lobe, and lingual gyrus. Through region-of-interest analyses, we verify that in patients with MTLE, the negatively weighted regions are hypometabolic, and the positively weighted regions are hypermetabolic, compared to controls. Interestingly, despite that both hypo- and hypermetabolism have mutually contributed to our model, they may reflect different pathological and/or compensative responses. For instance, patients with earlier age at epilepsy onset present greater hypometabolism in the ipsilateral inferior temporal gyrus, while we find no evidence of such association with hypermetabolism. In summary, quantitative models utilizing multidimensional brain metabolic information may provide additional assistance to presurgical workups in TLE.

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.

Evolution of lobar abnormalities of cerebral glucose metabolism in 41 children with drug-resistant epilepsy

OBJECTIVE

We analyzed long-term changes of lobar glucose metabolic abnormalities in relation to clinical seizure variables and development in a large group of children with medically refractory epilepsy.

METHODS

Forty-one children (25 males) with drug-resistant epilepsy had a baseline positron emission tomography (PET) scan at a median age of 4.7 years; the scans were repeated after a median of 4.3 years. Children with progressive neurological disorders or space-occupying lesion-related epilepsy and those who had undergone epilepsy surgery were excluded. The number of affected lobes on 2-deoxy-2(18 F)-fluoro-D-glucose-PET at baseline and follow-up was correlated with epilepsy variables and developmental outcome.

RESULTS

On the initial PET scan, 24 children had unilateral and 13 had bilateral glucose hypometabolism, whereas 4 children had normal scans. On the follow-up scan, 63% of the children showed an interval expansion of the hypometabolic region, and this progression was associated with persistent seizures. In contrast, 27% showed less extensive glucose hypometabolism at follow-up; most of these subjects manifested a major interval decrease in seizure frequency. Delayed development was observed in 21 children (51%) at baseline and 28 (68%) at follow-up. The extent of glucose hypometabolism at baseline correlated with developmental levels at the time of both baseline (r = .31, P = .05) and follow-up scans (r = .27, P = .09).

SIGNIFICANCE

In this PET study of unoperated children with focal epilepsy, the lobar pattern of glucose hypometabolism changed over time in 90% of the cases. The results support the notion of an expansion of metabolic dysfunction in children with persistent frequent seizures and its association with developmental delay, and support that optimized medical treatment to control seizures may contribute to better neurocognitive outcome if no surgery can be offered.

The Role of Radionuclide Imaging in Epilepsy, Part 1: Sporadic Temporal and Extratemporal Lobe Epilepsy

Epilepsy is one of the most common yet diverse neurologic disorders, affecting almost 1%-2% of the population. Presently, radionuclide imaging such as PET and SPECT is not used in the primary diagnosis or evaluation of recent-onset epilepsy. However, it can play a unique and important role in certain specific situations, such as in noninvasive presurgical localization of epileptogenic brain regions in intractable-seizure patients being considered for epilepsy surgery. Radionuclide imaging can be particularly useful if MR imaging is either negative for lesions or shows several lesions of which only 1 or 2 are suspected to be epileptogenic and if electroencephalogram changes are equivocal or discordant with the structural imaging. Similarly, PET and SPECT can also be useful for evaluating the functional integrity of the rest of the brain and may provide useful information on the possible pathogenesis of the neurocognitive and behavioral abnormalities frequently observed in these patients.

Glucose Metabolic Profile by Visual Assessment Combined with Statistical Parametric Mapping Analysis in Pediatric Patients with Epilepsy

PET with ¹⁸F-FDG has been used for presurgical localization of epileptogenic foci; however, in nonsurgical patients, the correlation between cerebral glucose metabolism and clinical severity has not been fully understood. The aim of this study was to evaluate the glucose metabolic profile using ¹⁸F-FDG PET/CT imaging in patients with epilepsy. Methods: One hundred pediatric epilepsy patients who underwent ¹⁸F-FDG PET/CT, MRI, and electroencephalography examinations were included. Fifteen age-matched controls were also included. ¹⁸F-FDG PET images were analyzed by visual assessment combined with statistical parametric mapping (SPM) analysis. The absolute asymmetry index (|AI|) was calculated in patients with regional abnormal glucose metabolism. Results: Visual assessment combined with SPM analysis of ¹⁸F-FDG PET images detected more patients with abnormal glucose metabolism than visual assessment only. The |AI| significantly positively correlated with seizure frequency (P < 0.01) but negatively correlated with the time since last seizure (P < 0.01) in patients with abnormal glucose metabolism. The only significant contributing variable to the |AI| was the time since last seizure, in patients both with hypometabolism (P = 0.001) and with hypermetabolism (P = 0.005). For patients with either hypometabolism (P < 0.01) or hypermetabolism (P = 0.209), higher |AI| values were found in those with drug resistance than with seizure remission. In the post-1-y follow-up PET studies, a significant change of |AI| (%) was found in patients with clinical improvement compared with those with persistence or progression (P < 0.01). Conclusion:¹⁸F-FDG PET imaging with visual assessment combined with SPM analysis could provide cerebral glucose metabolic profiles in nonsurgical epilepsy patients. |AI| might be used for evaluation of clinical severity and progress in these patients. Patients with a prolonged period of seizure freedom may have more subtle (or no) metabolic abnormalities on PET. The clinical value of PET might be enhanced by timing the scan closer to clinical seizures.

Neuroimaging of epilepsy

Imaging is pivotal in the evaluation and management of patients with seizure disorders. Elegant structural neuroimaging with magnetic resonance imaging (MRI) may assist in determining the etiology of focal epilepsy and demonstrating the anatomical changes associated with seizure activity. The high diagnostic yield of MRI to identify the common pathological findings in individuals with focal seizures including mesial temporal sclerosis, vascular anomalies, low-grade glial neoplasms and malformations of cortical development has been demonstrated. Positron emission tomography (PET) is the most commonly performed interictal functional neuroimaging technique that may reveal a focal hypometabolic region concordant with seizure onset. Single photon emission computed tomography (SPECT) studies may assist performance of ictal neuroimaging in patients with pharmacoresistant focal epilepsy being considered for neurosurgical treatment. This chapter highlights neuroimaging developments and innovations, and provides a comprehensive overview of the imaging strategies used to improve the care and management of people with epilepsy.

FDG-PET in healthy and epileptic Lagotto Romagnolo dogs and changes in brain glucose uptake with age

Regional cerebral metabolism and blood flow can be measured noninvasively with positron emission tomography (PET). 2-[(18) F]fluoro-2-deoxy-D-glucose (FDG) widely serves as a PET tracer in human patients with epilepsy to identify the seizure focus. The goal of this prospective study was to determine whether juvenile or adult dogs with focal-onset epilepsy exhibit abnormal cerebral glucose uptake interictally and whether glucose uptake changes with age. We used FDG-PET to examine six Lagotto Romagnolo dogs with juvenile epilepsy, two dogs with adult-onset epilepsy, and five control dogs of the same breed at different ages. Three researchers unaware of dog clinical status visually analyzed co-registered PET and magnetic resonance imaging (MRI) images. Results of the visual PET analyses were compared with electroencephalography (EEG) results. In semiquantitative analysis, relative standard uptake values (SUV) of regions of interest (ROI) drawn to different brain regions were compared between epileptic and control dogs. Visual analysis revealed areas of hypometabolism interictally in five out of six dogs with juvenile epilepsy in the occipital, temporal, and parietal cortex. Changes in EEG occurred in three of these dogs in the same areas where PET showed cortical hypometabolism. Visual analysis showed no abnormalities in cerebral glucose uptake in dogs with adult-onset epilepsy. Semiquantitative analysis detected no differences between epileptic and control dogs. This result emphasizes the importance of visual analysis in FDG-PET studies of epileptic dogs. A change in glucose uptake was also detected with age. Glucose uptake values increased between dog ages of 8 and 28 weeks and then remained constant.

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

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

Neurosurgical management of frontal lobe epilepsy in children

OBJECT

Pediatric frontal lobe epilepsy (FLE) remains a challenging condition for neurosurgeons and epileptologists to manage. Postoperative seizure outcomes remain far inferior to those observed in temporal lobe epilepsies, possibly due to inherent difficulties in delineating and subsequently completely resecting responsible epileptogenic regions. In this study, the authors review their institutional experience with the surgical management of FLE and attempt to find predictors that may help to improve seizure outcome in this population.

METHODS

All surgically treated cases of intractable FLE from 1990 to 2008 were reviewed. Demographic information, preoperative and intraoperative imaging and electrophysiological investigations, and follow-up seizure outcome were assessed. Inferential statistics were performed to look for potential predictors of seizure outcome.

RESULTS

Forty patients (20 male, 20 female) underwent surgical management of FLE during the study period. Patients were an average of 5.6 years old at the time of FLE onset and 11.7 years at the time of surgery; patients were followed for a mean of 40.25 months. Most patients displayed typical FLE semiology. Twenty-eight patients had discrete lesions identified on MRI. Eight patients underwent 2 operations. Cortical dysplasia was the most common pathological diagnosis. Engel Class I outcome was obtained in 25 patients (62.5%), while Engel Class II outcome was observed in 5 patients (12.5%). No statistically significant predictors of outcome were found.

CONCLUSIONS

Control of FLE remains a challenging problem. Favorable seizure outcome, obtained in 62% of patients in this series, is still not as easily obtained in FLE as it is in temporal lobe epilepsy. While no statistically significant predictors of seizure outcome were revealed in this study, patients with FLE continue to require extensive workup and investigation to arrive at a logical and comprehensive neurosurgical treatment plan. Future studies with improved neuroimaging and advanced invasive monitoring strategies may well help define factors for success in this form of epilepsy that is difficult to control.

Epilepsy imaging study guideline criteria: commentary on diagnostic testing study guidelines and practice parameters

Recognition of limited economic resources, as well as potential adverse effects of "over testing," has increased interest in "evidence-based" assessment of new medical technology. This creates a particular problem for evaluation and treatment of epilepsy, which are increasingly dependent on advanced imaging and electrophysiology, since there is a marked paucity of epilepsy diagnostic and prognostic studies that meet rigorous standards for evidence classification. The lack of high quality data reflects fundamental weaknesses in many imaging studies but also limitations in the assumptions underlying evidence classification schemes as they relate to epilepsy, and to the practicalities of conducting adequately powered studies of rapidly evolving technologies. We review the limitations of current guidelines and propose elements for imaging studies that can contribute meaningfully to the epilepsy literature.

Transient focal cortical increase of interictal glucose metabolism in Sturge-Weber syndrome: implications for epileptogenesis

PURPOSE

To investigate clinical correlates and longitudinal course of interictal focal cortical glucose hypermetabolism in children with Sturge-Weber syndrome (SWS).

METHODS

Fluorodeoxyglucose positron emission tomography (FDG-PET) scans of 60 children (age range 3 months to 15.2 years) with Sturge-Weber syndrome and epilepsy were assessed prospectively and serially for focal hypo- or hypermetabolism. Thirty-two patients had two or more consecutive PET scans. Age, seizure variables, and the occurrence of epilepsy surgery were compared between patients with and without focal hypermetabolism. The severity of focal hypermetabolism was also assessed and correlated with seizure variables.

KEY FINDINGS

Interictal cortical glucose hypermetabolism, ipsilateral to the angioma, was seen in nine patients, with the most common location in the frontal lobe. Age was lower in patients with hypermetabolism than in those without (p=0.022). In addition, time difference between the onset of first seizure and the first PET scan was much shorter in children with increased glucose metabolism than in those without (mean: 1.0 vs. 3.6 years; p=0.019). Increased metabolism was transient and switched to hypometabolism in all five children where follow-up scans were available. Focal glucose hypermetabolism occurred in 28% of children younger than the age of 2 years. Children with transient hypermetabolism had a higher rate of subsequent epilepsy surgery as compared to those without hypermetabolism (p=0.039).

SIGNIFICANCE

Interictal glucose hypermetabolism in young children with SWS is most often seen within a short time before or after the onset of first clinical seizures, that is, the presumed period of epileptogenesis. Increased glucose metabolism detected by PET predicts future demise of the affected cortex based on a progressive loss of metabolism and may be an imaging marker of the most malignant cases of intractable epilepsy requiring surgery in SWS.

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.

Epilepsy duration impacts on brain glucose metabolism in temporal lobe epilepsy: results of voxel-based mapping

OBJECTIVE

[(18)F]Fluorodeoxyglucose positron emission tomography ([(18)F]FDG-PET) is a valuable method for detecting focal brain dysfunction associated with epilepsy. Evidence suggests that a progressive decrease in [(18)F]FDG uptake occurs in the epileptogenic cortex with an increase in the duration of epilepsy. In this study, our aim was to use statistical parametric mapping (SPM) to test the validity of this relationship in a retrospective study of patients with temporal lobe epilepsy (TLE).

METHODS

[(18)F]FDG-PET scans of 46 adult patients with pharmacoresistant unilateral TLE (25 RTLE and 21 LTLE) were subjected to SPM analysis.

RESULTS

Forty-six patients were diagnosed with nonlesional TLE, 16 of whom had hippocampal sclerosis (HS). The average duration of epilepsy was 17.4 +/- 12.3 years (3-46 years), <5 years in 10 patients and >or=10 years in 30 patients. Visual analysis of [(18)F]FDG-PET scans revealed hypometabolism in the epileptogenic temporal cortex in 31 (67%) patients. After SPM analysis of all [(18)F]FDG-PET images, hypometabolism was unilateral and reported in lateral and mesial structures of the epileptogenic temporal cortex in addition to the ipsilateral fusiform and middle occipital gyrus. Subsequent analysis revealed that temporal lobe hypometabolism was present only in patients with longer epilepsy duration (>or=10 years) in parahippocampal gyrus, uncus, and middle and superior temporal gyrus (P < 0.05 corrected). Epilepsy duration was inversely correlated with decreased glucose uptake in the inferior temporal gyrus, hippocampus, and parahippocampal gyrus of the epileptogenic temporal cortex (P < 0.05). Age at seizure onset did not affect the correlation between epilepsy duration and glucose uptake except in the inferior temporal gyrus (P < 0.05).

CONCLUSION

Voxel-based mapping supports the assertion that glucose hypometabolism of the epileptogenic temporal lobe cortex and other neighboring cortical regions increases with longer epilepsy duration in TLE.

Role of subdural electrocorticography in prediction of long-term seizure outcome in epilepsy surgery

Since prediction of long-term seizure outcome using preoperative diagnostic modalities remains suboptimal in epilepsy surgery, we evaluated whether interictal spike frequency measures obtained from extraoperative subdural electrocorticography (ECoG) recording could predict long-term seizure outcome. This study included 61 young patients (age 0.4-23.0 years), who underwent extraoperative ECoG recording prior to cortical resection for alleviation of uncontrolled focal seizures. Patient age, frequency of preoperative seizures, neuroimaging findings, ictal and interictal ECoG measures were preoperatively obtained. The seizure outcome was prospectively measured [follow-up period: 2.5-6.4 years (mean 4.6 years)]. Univariate and multivariate logistic regression analyses determined how well preoperative demographic and diagnostic measures predicted long-term seizure outcome. Following the initial cortical resection, Engel Class I, II, III and IV outcomes were noted in 35, 6, 12 and 7 patients, respectively. One child died due to disseminated intravascular coagulation associated with pseudomonas sepsis 2 days after surgery. Univariate regression analyses revealed that incomplete removal of seizure onset zone, higher interictal spike-frequency in the preserved cortex and incomplete removal of cortical abnormalities on neuroimaging were associated with a greater risk of failing to obtain Class I outcome. Multivariate logistic regression analysis revealed that incomplete removal of seizure onset zone was the only independent predictor of failure to obtain Class I outcome. The goodness of regression model fit and the predictive ability of regression model were greatest in the full regression model incorporating both ictal and interictal measures [R(2) 0.44; Area under the receiver operating characteristic (ROC) curve: 0.81], slightly smaller in the reduced model incorporating ictal but not interictal measures (R(2) 0.40; Area under the ROC curve: 0.79) and slightly smaller again in the reduced model incorporating interictal but not ictal measures (R(2) 0.27; Area under the ROC curve: 0.77). Seizure onset zone and interictal spike frequency measures on subdural ECoG recording may both be useful in predicting the long-term seizure outcome of epilepsy surgery. Yet, the additive clinical impact of interictal spike frequency measures to predict long-term surgical outcome may be modest in the presence of ictal ECoG and neuroimaging data.

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.

Evolution of cortical metabolic abnormalities and their clinical correlates in Sturge-Weber syndrome

BACKGROUND

The natural course of Sturge-Weber syndrome (SWS) is poorly understood, although neurological symptoms are often progressive.

AIMS

To track longitudinal changes in brain glucose metabolism measured with positron emission tomography (PET) and their relation to clinical changes during the early course of SWS.

METHODS

Fourteen children (age 3 months to 3.9 years at enrollment) with SWS and unilateral leptomeningeal angioma underwent two consecutive glucose metabolism PET scans with a mean follow-up time of 1.2 years. Longitudinal changes of the extent of cortical glucose hypometabolism on the angioma side were measured and correlated with age, clinical seizure frequency and hemiparesis.

RESULTS

An increase in the size of the hypometabolic cortex was seen in 6 children, coinciding with an age-related increase in cortical glucose metabolism measured in unaffected contralateral cortex. These 6 patients were younger both at the initial (mean age 0.75 vs. 2.8 years; p<0.001) and the second scan (mean age 1.8 vs. 4.2 years; p=0.001) than those with no change in the extent of hypometabolic cortex (n=6). The area of cortical hypometabolism decreased in the two remaining children, and this was associated with resolution of an initial hemiparesis in one of them. Seizure frequency between the two scans was higher in children who showed progressive enlargement of cortical hypometabolism, as compared to those with no progression (p=0.008).

CONCLUSIONS

In SWS, detrimental metabolic changes occur before 3 years of age coinciding with a sharp increase of developmentally regulated cerebral metabolic demand. Progressive hypometabolism is associated with high seizure frequency in these children. However, metabolic abnormalities may remain limited or even partially recover later in some children with well-controlled seizures. Metabolic recovery accompanied by neurological improvement suggests a window for therapeutic intervention in children with unilateral SWS.

PET tracer technology for monitoring focal epilepsies

Studies using positron emission tomography (PET) have advanced our pathophysiological and biochemical understanding of focal and generalized epilepsies. H(2) (15)O PET allows quantification of cerebral blood flow and (18)F-fluorodeoxyglucose-PET quantification of cerebral glucose metabolism. Neurotransmitters are directly responsible for modulating synaptic activity and newer PET tracers can provide information about synaptic activity and specific ligand-receptor relationships, which are important for epileptogenesis and the spread of epileptic activity.

Functional neuroimaging in the preoperative evaluation of children with drug-resistant epilepsy

FUNCTIONAL NEUROIMAGING: Although the primary imaging modality in the management of epilepsy is magnetic resonance imaging MRI, functional neuroimaging with positron-emission tomography (PET) and single photon emission computed tomography (SPECT) often provides complementary information and, in a number of situations, provides unique information that cannot be obtained with MRI. The most commonly used PET tracers used for epilepsy evaluation are 2-deoxy-2-[(18)F]fluoro-D: -glucose (FDG) and [(11)C]flumazenil (FMZ). Recently, interictal PET with alpha-[(11)C]methyl-L: -tryptophan was found to be highly specific for the epileptic focus and can differentiate between epileptogenic and nonepileptogenic lesions in the same patient (e.g., in patients with tuberous sclerosis).

DISCUSSION

In this review, we discuss clinical applications of these three PET tracers in drug-resistant temporal and extratemporal lobe epilepsy, selected epilepsy syndromes of childhood, lesional and nonlesional epilepsy, and the challenges of imaging secondary epileptic foci. A brief discussion of SPECT applications in epilepsy is also included. With further development of new tracers highly sensitive and specific for epileptogenic brain regions, the presurgical evaluation of refractory epilepsy will be greatly facilitated. Approximately 0.5 to 1.0% of the population suffer from epilepsy, of which 15-20% are intractable. Infants and children, whose seizures have a focal onset are refractory to anticonvulsants and are prolonged, tend to have the worst cognitive outcome [Meador KJ, Neurology 58 (Suppl 5):S21-S26, 2002]. Seizures themselves affect the developing brain and contribute to an adverse neurologic outcome (Holmes, Pediatric Neurology 33:1-110, 2005).

CONCLUSION

Therefore, in treating children with intractable epilepsy, it is important to consider seizure control and to give allowance for normal cognitive development.

Epileptogenesis and rational therapeutic strategies

The understanding of neurobiological mechanisms of epileptogenesis is essential for rational approaches for a possible disease modification as well as treatment of underlying causes of the epilepsies. More effort is necessary to translate results from basic investigations into new approaches for clinical research and to better understand a relationship with findings from clinical studies. The following report is a condensed synapsis in which molecular mechanisms of epileptogenesis, pharmacological modulation of epileptogenesis, evidence based therapy, refractoriness and prediction of outcome is provided in order to stimulate further collaborative international research.

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.

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.

Metabolic Changes of Subcortical Structures in Intractable Focal Epilepsy

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

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.

Multimodality imaging in partial epilepsies

PURPOSE OF REVIEW

The rapid expansion of novel applications and the development of new techniques in structural and functional imaging modalities present a troubling challenge to keep up with and harness potential valuable information created in this critical field of epilepsy localization and non-invasive in-vivo research.

RECENT FINDINGS

Recent advances in epilepsy imaging have centered on: (1) improving the localization of epileptogenic tissue beyond that of state-of-the-art structural magnetic resonance imaging; (2) monitoring the development and progression of epileptogenic pathology, particularly mesial temporal sclerosis; and (3) an investigation of the in-vivo structural and functional disturbances underlying and revealing mechanisms of partial epilepsy pathophysiology.

SUMMARY

The main impact of the progress in epilepsy localization with multimodality imaging is to allow more effective presurgical evaluation and the selection of patients with intractable seizures. By combining serial imaging findings and genetic studies, the major questions surrounding the development and progression of mesial temporal sclerosis with regard to the cause and consequence of epilepsy will soon be answered. Long-standing questions concerning in-vivo metabolic and neurotransmitter disturbances associated with partial epilepsy, detected and depicted (but not understood) with magnetic resonance spectroscopy and positron emission tomography, are finally being addressed.

Epilepsy Duration, Febrile Seizures, and Cerebral Glucose Metabolism

PURPOSE

Studies using magnetic resonance imaging have shown that reduced hippocampal volume is associated with a history of febrile seizures, the duration of epilepsy, and the number of generalized tonic-clonic seizures. It is uncertain whether these factors have the same influence on functional as on structural measures of the integrity of the epileptogenic zone.

METHODS

We used positron emission tomography (PET) with fluorine 18 2-deoxyglucose to study 91 patients with temporal lobe seizure foci localized by ictal video-EEG. PET was performed in the awake interictal resting state with ears plugged and eyes patched. We recorded surface EEG during injection (5 mCi) and the 30-min uptake period. We used a standard template to analyze PET scans.

RESULTS

A significant negative relation was found between the duration of epilepsy and hippocampal glucose metabolism ipsilateral to the epileptic focus. Patients with a history of either any febrile seizures, or complex, or prolonged febrile seizures, did not have greater hypometabolism ipsilateral to the epileptic focus than did patients without a febrile seizure history. We found no effect of generalized tonic-clonic seizure history.

CONCLUSIONS

Longer epilepsy duration is associated with greater hypometabolism, suggesting that epilepsy is a progressive disease.

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

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

Imaging the epileptic brain with positron emission tomography

Positron emission tomography (PET) has an established role in the noninvasive localization of epileptic foci during presurgical evaluation. [18F]fluorodeoxyglucose (FDG) PET is able to lateralize and regionalize potentially epileptogenic regions in patients who have normal MR imaging and is also useful in the evaluation of various childhood epilepsy syndromes, including cryptogenic infantile spasms and early Rasmussen's syndrome. Novel PET tracers that were developed to image neurotransmission related to gamma-aminobutyric acid (GABA) [with [11C]flumazenil] and serotonin-mediated [with alpha-[11C]methyl-L-tryptophan (AMT)] function provide increased specificity for epileptogenic cortex and are particularly useful when FDG PET shows large abnormalities of glucose metabolism. Detailed comparisons of PET abnormalities with intracranial electroencephalographic findings also improve our understanding of the pathophysiology of human epilepsy.