Focal cortical dysplasia: comparison of MRI and FDG-PET

EANM practice guidelines for an appropriate use of PET and SPECT for patients with epilepsy

Epilepsy is one of the most frequent neurological conditions with an estimated prevalence of more than 50 million people worldwide and an annual incidence of two million. Although pharmacotherapy with anti-seizure medication (ASM) is the treatment of choice, ~30% of patients with epilepsy do not respond to ASM and become drug resistant. Focal epilepsy is the most frequent form of epilepsy. In patients with drug-resistant focal epilepsy, epilepsy surgery is a treatment option depending on the localisation of the seizure focus for seizure relief or seizure freedom with consecutive improvement in quality of life. Beside examinations such as scalp video/electroencephalography (EEG) telemetry, structural, and functional magnetic resonance imaging (MRI), which are primary standard tools for the diagnostic work-up and therapy management of epilepsy patients, molecular neuroimaging using different radiopharmaceuticals with single-photon emission computed tomography (SPECT) and positron emission tomography (PET) influences and impacts on therapy decisions. To date, there are no literature-based praxis recommendations for the use of Nuclear Medicine (NM) imaging procedures in epilepsy. The aims of these guidelines are to assist in understanding the role and challenges of radiotracer imaging for epilepsy; to provide practical information for performing different molecular imaging procedures for epilepsy; and to provide an algorithm for selecting the most appropriate imaging procedures in specific clinical situations based on current literature. These guidelines are written and authorized by the European Association of Nuclear Medicine (EANM) to promote optimal epilepsy imaging, especially in the presurgical setting in children, adolescents, and adults with focal epilepsy. They will assist NM healthcare professionals and also specialists such as Neurologists, Neurophysiologists, Neurosurgeons, Psychiatrists, Psychologists, and others involved in epilepsy management in the detection and interpretation of epileptic seizure onset zone (SOZ) for further treatment decision. The information provided should be applied according to local laws and regulations as well as the availability of various radiopharmaceuticals and imaging modalities.

Cortical surface analysis for focal cortical dysplasia diagnosis by using PET images

Focal cortical dysplasia (FCD) is a neurological disorder distinguished by faulty brain cell structure and development. Repetitive and uncontrollable seizures may be linked to FCD's aberrant cortical thickness, gyrification, and sulcal depth. Quantitative cortical surface analysis is a crucial alternative to ineffective visual inspection. This study recruited 42 subjects including 22 FCD patients who underwent surgery and 20 healthy controls (HC). For the FCD patients, T1-weighted and PET images were obtained by a PET-MRI scanner, and the confirmed epileptogenic zone (EZ) was collected from postsurgical follow-up. For the HCs, CT and PET images were obtained by a PET-CT scanner. Cortical thickness, gyrification index, and sulcal depth were calculated using a computational anatomical toolbox (CAT12). A cluster-based analysis is carried out to determine each FCD patient's aberrant cortical surface. After parcellating the cerebral cortex into 68 regions by the Desikan-Killiany atlas, a region of interest (ROI) analysis was conducted to know whether the feature in the FCD group is significantly different from that in the HC group. Finally, the features of all ROIs were utilised to train a support vector machine classifier (SVM). The classification performance is evaluated by the leave-one-out cross-validation. The cluster-based analysis can localize the EZ cluster with the highest accuracy of 54.5 % (12/22) for cortical thickness, 40.9 % (9/22) and 13.6 % (3/22) for sulcal depth and gyrification, respectively. Moderate concordance (Kappa, 0.6) is observed between the confirmed EZs and identified clusters by using the cortical thickness. Fair concordance (Kappa, 0.3) and no concordance (Kappa, 0.1) is found by using sulcal depth and gyrification. Significant differences are found in 46 of 68 regions (67.7 %) for the three measures. The trained SVM classifier achieved a prediction accuracy of 95.5 % for the cortical thickness, while the sulcal depth and the gyrification obtained 86.0 % and 81.5 %. Cortical thickness, as determined by quantitative cortical surface analysis of PET data, has a greater ability than sulcal depth and gyrification to locate aberrant EZ clusters in FCD. Surface measures might be different in many regions for FCD and HC. By integrating machine learning and cortical morphologies features, individual prediction of FCD seems to be feasible.

Pediatric Imaging Using PET/MR Imaging

PET/MR imaging is a one-stop shop technique for pediatric diseases allowing not only an accurate clinical assessment of tumors at staging and restaging but also the diagnosis of neurologic, inflammatory, and infectious diseases in complex cases. Moreover, applying PET kinetic analyses and sequences such as diffusion-weighted imaging as well as quantitative analysis investigating the relationship between disease metabolic activity and cellularity can be applied. Complex radiomics analysis can also be performed.

Predicting mood decline following temporal lobe epilepsy surgery in adults

OBJECTIVE

To develop a model to predict the probability of mood decline in adults following temporal lobe resection for the treatment of pharmacoresistant epilepsy.

METHODS

Variable selection was performed on 492 patients from the Cleveland Clinic using best subsets regression. After completing variable selection, a subset of variables was requested from four epilepsy surgery centers across North America (n = 100). All data were combined to develop a final model to predict postoperative mood decline (N = 592). Internal validation with bootstrap resampling was performed. A clinically significant increase in depressive symptoms was defined as a 15% increase in Beck Depression Inventory-Second Edition score and a postoperative raw score > 11.

RESULTS

Fourteen percent of patients in the Cleveland Clinic cohort and 22% of patients in the external cohort experienced clinically significant increases in depressive symptoms following surgery. The final prediction model included six predictor variables: psychiatric history, resection side, relationship status, verbal fluency score, age at preoperative testing, and presence/absence of malformation of cortical development on magnetic resonance imaging. The model had an optimism-adjusted c-statistic of .70 and good calibration, with slight probability overestimation in higher risk patients.

SIGNIFICANCE

Clinicians can utilize our nomogram via a paper tool or online calculator to estimate the risk of postoperative mood decline for individual patients prior to temporal lobe epilepsy surgery.

The predictive value of hypometabolism in focal epilepsy: a prospective study in surgical candidates

PURPOSE

FDG PET is an established tool in presurgical epilepsy evaluation, but it is most often used selectively in patients with discordant MRI and EEG results. Interpretation is complicated by the presence of remote or multiple areas of hypometabolism, which leads to doubt as to the true location of the seizure onset zone (SOZ) and might have implications for predicting the surgical outcome. In the current study, we determined the sensitivity and specificity of PET localization prospectively in a consecutive unselected cohort of patients with focal epilepsy undergoing in-depth presurgical evaluation.

METHODS

A total of 130 patients who underwent PET imaging between 2006 and 2015 matched our inclusion criteria, and of these, 86 were operated on (72% with a favourable surgical outcome, Engel class I). Areas of focal hypometabolism were identified using statistical parametric mapping and concordance with MRI, EEG and intracranial EEG was evaluated. In the surgically treated patients, postsurgical outcome was used as the gold standard for correctness of localization (minimum follow-up 12 months).

RESULTS

PET sensitivity and specificity were both 95% in 86 patients with temporal lobe epilepsy (TLE) and 80% and 95%, respectively, in 44 patients with extratemporal epilepsy (ETLE). Significant extratemporal hypometabolism was observed in 17 TLE patients (20%). Temporal hypometabolism was observed in eight ETLE patients (18%). Among the 86 surgically treated patients, 26 (30%) had hypometabolism extending beyond the SOZ. The presence of unilobar hypometabolism, included in the resection, was predictive of complete seizure control (p = 0.007), with an odds ratio of 5.4.

CONCLUSION

Additional hypometabolic areas were found in one of five of this group of nonselected patients with focal epilepsy, including patients with "simple" lesional epilepsy, and this finding should prompt further in-depth evaluation of the correlation between EEG findings, semiology and PET. Hypometabolism confined to the epileptogenic zone as defined by EEG and MRI is associated with a favourable postoperative outcome in both TLE and ETLE patients.

Focal Cortical Dysplasia and Refractory Epilepsy: Role of Multimodality Imaging and Outcome of Surgery

BACKGROUND AND PURPOSE

Focal cortical dysplasia (FCD) is one of the most common causes of drug resistant epilepsy. Our aim was to evaluate the role of presurgical noninvasive multimodality imaging techniques in selecting patients with refractory epilepsy and focal cortical dysplasia for epilepsy surgery and the influence of the imaging modalities on long-term seizure freedom.

MATERIALS AND METHODS

We performed a retrospective analysis of data of 188 consecutive patients with FCD and refractory epilepsy with at least 2 years of postsurgery follow-up. Predictors of seizure freedom and the sensitivity of neuroimaging modalities were analyzed.

RESULTS

MR imaging showed clear-cut FCD in 136 (72.3%) patients. Interictal FDG-PET showed focal hypo-/hypermetabolism in 144 (76.6%); in 110 patients in whom ictal SPECT was performed, focal hyperperfusion was noted in 77 (70.3%). Focal resection was the most common surgery performed in 112 (59.6%). Histopathology revealed FCD type I in 102 (54.3%) patients. At last follow-up, 124 (66.0%) were seizure-free. Complete resection of FCD and type II FCD were predictors of seizure freedom. Localization of FCD on either MR imaging or PET or ictal SPECT had the highest sensitivity for seizure freedom at 97.5%. Among individual modalities, FDG-PET had the highest sensitivity (78.2%), followed by MR imaging (75.8%) and ictal SPECT (71.8%). The sensitivity of MR imaging to localize type I FCD (60.8%) was significantly lower than that for type II FCD (84.8%, P < .001). Among 37 patients with subtle MR imaging findings and a focal FDG-PET pattern, 30 patients had type I FCD.

CONCLUSIONS

During presurgical multimodality evaluation, localization of the extent of the epileptogenic zone in at least 2 imaging modalities helps achieve seizure freedom in about two-thirds of patients with refractory epilepsy due to FCD. FDG-PET is the most sensitive imaging modality for seizure freedom, especially in patients with type I FCD.

Longitudinal Findings of MRI and PET in West Syndrome with Subtle Focal Cortical Dysplasia

BACKGROUND AND PURPOSE

Despite the development of neuroimaging, identification of focal cortical dysplasia remains challenging. The purpose of this study was to show the longitudinal changes of MR imaging and FDG-PET in patients with West syndrome and subtle focal cortical dysplasia.

MATERIALS AND METHODS

Among 52 consecutive patients with West syndrome, 4 were diagnosed with subtle focal cortical dysplasia on 3T MR imaging. MR imaging and PET findings were evaluated longitudinally at onset and at 12 and 24 months of age.

RESULTS

At the onset of West syndrome, MR imaging demonstrated focal signal abnormalities of the subcortical white matter in 2 patients. In the other 2 patients, focal subcortical high-intensity signals became visible on follow-up T2WI as myelination progressed. PET at onset showed focal cortical hypometabolism in 3 patients, with 1 of these patients also having focal hypermetabolism and 1 having normal findings. On PET at 24 months, hypometabolism persisted in 2 patients and disappeared in 1, and hypermetabolism disappeared in 1. In 1 patient with normal MR imaging and PET findings at onset, focal hyperintensity and hypometabolism first appeared at 24 months of age. The findings on MR imaging and PET in these patients evolved differently with brain maturation and the clinical course.

CONCLUSIONS

Subtle focal cortical dysplasia can be undetectable on MR imaging at the onset of West syndrome and is not always accompanied by hypometabolism or hypermetabolism on PET. Longitudinal MR imaging and PET studies may be useful for detecting such lesions. Even in West syndrome with a congenital structural abnormality, PET findings evolve differently with brain maturation and the clinical condition.

Automated Online Quantification Method for 18F-FDG Positron Emission Tomography/CT Improves Detection of the Epileptogenic Zone in Patients with Pharmacoresistant Epilepsy

Aims

To assess the validity of an online method to quantitatively evaluate cerebral hypometabolism in patients with pharmacoresistant focal epilepsy as a complement to the visual analysis of the ¹⁸F-FDG positron emission tomography (PET)/CT exam.

Methods

A total of 39 patients with pharmacoresistant epilepsy and probable focal cortical dysplasia [22 patients with frontal lobe epilepsy (FLE) and 17 with temporal lobe epilepsy (TLE)] underwent a presurgical evaluation including EEG, video-EEG, MRI, and ¹⁸F-FDG PET/CT. We conducted the automated quantification of their ¹⁸F-FDG PET/CT data and compared the results with those of the visual-PET analysis conducted by experienced nuclear medicine physicians. For each patient group, we calculated Cohen’s Kappa coefficient for the visual and quantitative analyses, as well as each method’s sensitivity, specificity, and positive and negative predictive values.

Results

For the TLE group, both the visual and quantitative analyses showed high agreement. Thus, although the quantitative analysis could be used as a complement, the visual analysis on its own was consistent and precise. For the FLE group, on the other hand, the visual analysis categorized almost half of the cases as normal, revealing very low agreement. For those patients, the quantitative analysis proved critical to identify the focal hypometabolism characteristic of the epileptogenic zone. Our results suggest that the quantitative analysis of ¹⁸F-FDG PET/CT data is critical for patients with extratemporal epilepsies, and especially those with subtle MRI findings. Furthermore, it can easily be used during the routine clinical evaluation of ¹⁸F-FDG PET/CT exams.

Significance

Our results show that quantification of ¹⁸F-FDG PET is an informative complementary method that can be added to the routine visual evaluation of patients with subtle lesions, particularly those in the frontal lobes.

Focal Cortical Dysplasia in Childhood Epilepsy

Focal cortical dysplasia is a common cause of medication resistant epilepsy. A better understanding of its presentation, pathophysiology and consequences have helped us improved its treatment and outcome. This paper reviews the most recent classification, pathophysiology and imaging findings in clinical research as well as the knowledge gained from studying genetic and lesional animal models of focal cortical dysplasia. This review of this recently gained knowledge will most likely help develop new research models and new therapeutic targets for patients with epilepsy associated with focal cortical dysplasia.

Does F-18 FDG-PET substantially alter the surgical decision-making in drug-resistant partial epilepsy?

OBJECTIVE

There is a dearth of information on the critical utility of positron emission tomography (PET) in choosing candidates for epilepsy surgery especially in resource-poor countries where it is not freely available. This study aimed to critically analyze the utility of FDG-PET in the presurgical evaluation and surgical selection of patients with DRE based on the results obtained through its use in our comprehensive epilepsy program.

METHODS

From 2008 to 2012, 117 patients with drug-resistant epilepsy underwent F-18 fluoro-deoxy-glucose (FDG) PET in our center. We utilized their data to audit the utility of PET in choosing/deferring patients for surgery.

RESULTS

Of the 117 patients (age: 5-42years) who underwent F-18 FDG-PET, 64 had normal MRI, and 53 had lesions. Electroclinical data favored temporal ictal onset in 48 (41%), extratemporal in 60 (51.3%), and uncertain lobar localization in 9 (7.7%). The topography of PET hypometabolism was localizing in 53 (45.3%), lateralizing in 12 (10.3%), and 52 (44.4%) had either normal or discordant results. In the nonlesional group, focal hypometabolism was concordant to the area of ictal onset in 27 (41.5%) versus 38 (58.5%) in the lesional group (p=0.002). Greater concordance was noted in temporal lobe epilepsy (TLE) (78.0%) as compared to extratemporal epilepsy (ETPE) (28.6%) (p<0.001). Positron emission tomography was more concordant in patients with mesial temporal sclerosis than in those with other lesions (82.8% versus 50%) (p=0.033). Positron emission tomography helped in surgical decision-making in 68.8% of TLE and 23.3% of ETPE cases. Overall, 37 patients (31.6%) were directly selected for resective surgery based on PET results.

CONCLUSIONS

Positron emission tomography, when utilized judiciously, remained an ancillary tool in the surgical selection of one-third of patients with drug-resistant partial epilepsy, although its utility as an independent tool is not very promising.

Electro- and magneto-encephalographic spike source localization of small focal cortical dysplasia in the dorsal peri-rolandic region

OBJECTIVE

Small focal cortical dysplasia (FCD) may be ambiguous or overlooked on magnetic resonance (MR) imaging. Source localization of EEG and magnetoencephalography (MEG) spikes was evaluated to confirm the diagnosis of small FCD.

METHODS

This study included 6 epilepsy patients with a single small lesion on MR imaging suggesting FCD within a single gyrus among 181 consecutive epilepsy patients admitted to our epilepsy monitoring unit over 27 months. Stereotypical interictal spikes were detected on simultaneous EEG and MEG recordings and the onset-related source of averaged spikes was estimated.

RESULTS

All 6 patients had unique clinical characteristics as follows: leg sensori-motor seizures in 5 patients and eye version in 1 patient; a small MR imaging lesion suggesting FCD in the dorsal peri-rolandic region, which had been overlooked until our evaluation; and both EEG and MEG dipoles were estimated adjacent to the MR imaging lesion.

CONCLUSIONS

Source localization of EEG and MEG spikes can confirm the diagnosis of FCD based on a single small MR imaging lesion, which was overlooked by previous examination of MR images.

SIGNIFICANCE

Examination of MR images should be based on spike source localization as well as seizure semiology to identify subtle MR imaging abnormalities.

Can we increase the yield of FDG-PET in the preoperative work-up for epilepsy surgery?

PURPOSE

[(18)F] Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) is a semi-invasive, interictal method of localization of hypometabolic epileptic foci. FDG-PET can be useful in the clinical work-up prior to epilepsy surgery, especially in equivocal cases. We investigated whether we could increase the yield of presurgical FDG-PET in patients with difficult epilepsy requiring chronic subdural electrocorticography (ECoG).

METHODS

We retrospectively studied patients with refractory focal epilepsy in whom there was uncertainty about the focus localization and who underwent FDG-PET and ECoG. Two experts (epileptologist and nuclear medicine radiologist) together systematically re-assessed the scans visually (PETRE), blinded to their initial reports. Scans were also re-analyzed by comparing them to a normal control dataset with Statistical Parametric Mapping (SPM), using a liberal (PETSPM1), and strict (PETSPM2) statistical threshold. Regions with hypometabolism and regions containing the seizure onset zone (SOZ) in ECoG were marked as positive anatomical regions (PARs). We compared the concordance of these PARs for the different PET re-assessments. We calculated the sensitivity, specificity and accuracy of the PET results for the SOZ. The added value of the re-assessments was evaluated with emphasis on scans initially reported as negative.

RESULTS

41 Patients (63% extra-temporal) were included. PETRE identified the SOZ best, with a sensitivity of 62% and specificity of 93%. PETSPM1 had a sensitivity of 62% and specificity 69%, for PETSPM2 this was 35% and 85% respectively. The overlap between PETRE vs. PETSPM1 and vs. PETSPM2 was 71% and 37%. Visual re-assessment and PETSPM1 identified the SOZ in four out of five scans that were initially reported as negative.

CONCLUSIONS

Pre-surgical re-assessment of PET scans is worthwhile in epilepsy patients who undergo ECoG, especially when results were reported as negative before. Visual re-assessment itself has a higher combined specificity, sensitivity and accuracy than SPM analysis alone. SPM analysis could be used as a guide for visual (re-)assessment, because of its high sensitivity.

[PET and SPECT in epilepsy]

Epilepsy is one of the most frequent chronic neurological disorders, affecting 1-2% of the population. Patients with complex partial drug resistant episodes may benefit from a surgical treatment consisting in the excision of the epileptogenic area. Localization of the epileptogenic area was classically performed with video-EEG and magnetic resonance (MR). Recently, functional neuroimaging studies of Nuclear Medicine, positron emission tomography (PET) and single photon emission tomography (SPECT) have demonstrated their utility in the localization of the epileptogenic area prior to surgery. Ictal SPECT with brain perfusion tracers show an increase in blood flow in the initial ictal focus, while PET with (18)FDG demonstrates a decrease of glucose metabolism in the interictal functional deficit zone. In this review, the basic principles and methodological characteristics of the SPECT and PET in epilepsy are described. The ictal SPECT injection mechanism, different patterns of perfusion based on the time of ictal, postictal or interictal injection are detailed and the different diagnostic sensitivities of each one of these SPECT are reviewed. Different methods of analysis of the images with substraction and fusion systems with the MR are described. Similarly, the injection methodology, quantification and evaluation of the images of the PET in epilepsy are described. Finally, the main clinical indications of SPECT and PET in temporal and extratemporal epilepsy are detailed.

Focal cortical dysplasia and epilepsy surgery

Focal cortical dysplasia (FCD) is the most commonly encountered developmental malformation that causes refractory epilepsy. With advances in neuroimaging techniques, in particular MRI, recent studies have revealed a higher prevalence of FCD than previously estimated and have improved the preoperative identification and classification of these abnormalities. However, MRI frequently does not show any abnormalities in patients with pathologically proven FCD. In this situation, functional neuroimaing such as FDG-PET and ictal SPECT can be helpful. FCD is thought to be intrinsically epileptogenic, because the dysplastic tissues contain aberrant neural networks that are highly susceptible to abnormal excitation. The response to the medical treatment of epilepsy has been documented as consistently poor. Therefore, surgical resection has been an important alternative treatment for patients with intractable epilepsy related to FCD. Incomplete resection of FCD has been consistently known to be a poor prognostic factor. However, the complete removal of FCD is often difficult because the demarcation of the lesion is frequently poor, and dysplastic tissues tend to be more extensive than is apparent on MRI. Evidence indicates that even patients with MRI abnormalities who have resective epilepsy surgery for FCD have worse surgical outcomes than those of patients who have surgery for other focal lesional epilepsy syndromes. Careful planning of evelauation using intracranial electrodes is necessary for successful epilepsy surgery.

Focal cortical dysplasia - review

Focal cortical dysplasia is a malformation of cortical development, which is the most common cause of medically refractory epilepsy in the pediatric population and the second/third most common etiology of medically intractable seizures in adults.Both genetic and acquired factors are involved in the pathogenesis of cortical dysplasia. Numerous classifications of the complex structural abnormalities of focal cortical dysplasia have been proposed - from Taylor et al. in 1971 to the last modification of Palmini classification made by Blumcke in 2011. In general, three types of cortical dysplasia are recognized.Type I focal cortical dysplasia with mild symptomatic expression and late onset, is more often seen in adults, with changes present in the temporal lobe.Clinical symptoms are more severe in type II of cortical dysplasia usually seen in children. In this type, more extensive changes occur outside the temporal lobe with predilection for the frontal lobes.New type III is one of the above dysplasias with associated another principal lesion as hippocampal sclerosis, tumor, vascular malformation or acquired pathology during early life.Brain MRI imaging shows abnormalities in the majority of type II dysplasias and in only some of type I cortical dysplasias.THE MOST COMMON FINDINGS ON MRI IMAGING INCLUDE: focal cortical thickening or thinning, areas of focal brain atrophy, blurring of the gray-white junction, increased signal on T2- and FLAIR-weighted images in the gray and subcortical white matter often tapering toward the ventricle. On the basis of the MRI findings, it is possible to differentiate between type I and type II cortical dysplasia. A complete resection of the epileptogenic zone is required for seizure-free life. MRI imaging is very helpful to identify those patients who are likely to benefit from surgical treatment in a group of patients with drug-resistant epilepsy.However, in type I cortical dysplasia, MR imaging is often normal, and also in both types the lesion seen on MRI may be smaller than the seizure-generating region seen in the EEG. The abnormalities may also involve vital for life brain parts, where curative surgery will not be an option. Therefore, other diagnostic imaging techniques such as FDG PET, MEG, DTI and intra-cranial EEG are widely used to establish the diagnosis and to decide on management.With advances in both genetics and neuroimaging, we may develop a better understanding of patients with drug-resistant epilepsy, which will help us to provide more successful pharmacological and/or surgical treatment in the future.

Focal cortical dysplasia type IIa and IIb: MRI aspects in 118 cases proven by histopathology

INTRODUCTION

This study aims to review the magnetic resonance imaging (MRI) aspects of a large series of patients with focal cortical dysplasia type II (FCD II) and attempt to identify distinctive features in the two histopathological subtypes IIa and IIb.

METHODS

We retrospectively reviewed the MRI scans of 118 patients with histological proven FCD IIa (n = 37) or IIb (n = 81) who were surgically treated for intractable epilepsy.

RESULTS

MRI was abnormal in 93 patients (79 %) and unremarkable in 25 (21 %). A dysplastic lesion was identified in 90 cases (97 %) and classified as FCD II in 83 and FCD non-II in seven cases. In three cases, the MRI diagnosis was other than FCD. There was a significant association between the presence of cortical thickening (p = 0.002) and the "transmantle sign" (p < 0.001) and a correct MRI diagnosis of FCD II. MRI positivity was more frequent in the patients with FCD IIb than in those with FCD IIa (91 % vs. 51 %), and the detection rate of FCD II was also better in the patients with type IIb (88 % vs. 32 %). The transmantle sign was significantly more frequent in the IIb subgroup (p = 0.003).

CONCLUSIONS

The rates of abnormal MRI results and correct MRI diagnoses of FCD II were significantly higher in the IIb subgroup. Although other MRI stigmata may contribute to the diagnosis, the only significant correlation was between the transmantle sign and FCD IIb.

[Imaging in epilepsy: functional studies]

Neuroimaging studies play a fundamental role in the diagnosis and evaluation of epilepsy. Technological advances in neuroimaging techniques have made it possible to obtain functional as well as structural information. The pathophysiology of epilepsy consists of an abnormal increase in cerebral activity that can be appreciated on neuroimaging techniques like functional magnetic resonance imaging (fMRI), PET, and SPECT. In patients with epilepsy that is refractory to drug therapy, the main aim of surgery is to control seizures and thus to improve the quality of life. In the preoperative workup of these patients, fMRI has an increasingly important role, evaluating the location of functional areas that must be safeguarded during surgery.

Anatomy-based reconstruction of FDG-PET images with implicit partial volume correction improves detection of hypometabolic regions in patients with epilepsy due to focal cortical dysplasia diagnosed on MRI

PURPOSE

Detection of hypometabolic areas on interictal FDG-PET images for assessing the epileptogenic zone is hampered by partial volume effects. We evaluated the performance of an anatomy-based maximum a-posteriori (A-MAP) reconstruction algorithm which combined noise suppression with correction for the partial volume effect in the detection of hypometabolic areas in patients with focal cortical dysplasia (FCD).

METHODS

FDG-PET images from 14 patients with refractory partial epilepsy were reconstructed using A-MAP and maximum likelihood (ML) reconstruction. In all patients, presurgical evaluation showed that FCD represented the epileptic lesion. Correspondence between the FCD location and regional metabolism on a predefined atlas was evaluated. An asymmetry index of FCD to normal cortex was calculated.

RESULTS

Hypometabolism at the FCD location was detected in 9/14 patients (64%) using ML and in 10/14 patients (71%) using A-MAP reconstruction. Hypometabolic areas outside the FCD location were detected in 12/14 patients (86%) using ML and in 11/14 patients (79%) using A-MAP reconstruction. The asymmetry index was higher using A-MAP reconstruction (0.61, ML 0.49, p=0.03).

CONCLUSION

The A-MAP reconstruction algorithm improved visual detection of epileptic FCD on brain FDG-PET images compared to ML reconstruction, due to higher contrast and better delineation of the lesion. This improvement failed to reach significance in our small sample. Hypometabolism outside the lesion is often present, consistent with the observation that the functional deficit zone tends to be larger than the epileptogenic zone.

[18F] fluorodeoxyglucose-positron-emission tomography and MR imaging coregistration for presurgical evaluation of medically refractory epilepsy

Epilepsy is a chronic disorder affecting approximately 1% of the population of the world. Approximately one third of patients with epilepsy remain refractory to medical therapy. For these patients, surgery is a curative option. In order for surgery to be considered, precise localization of the structural abnormality is needed. When MR imaging findings are normal, more sensitive techniques such as positron-emission tomography (PET) can help find the abnormality. Combining MR imaging and PET information increases the sensitivity of the presurgical evaluation. In this review, we discuss the clinical applications of coregistration of [(18)F] fluorodeoxyglucose (FDG)-PET with MR imaging for medically refractory epilepsy. Because FDG-PET/MR imaging coregistration has been a routine component of the presurgical evaluation for patients with epilepsy at our institution since 2004, we also included cases from our data base that exemplify the utility of this technology to obtain better postsurgical outcomes.

Challenges in the surgical treatment of epilepsy patients with cortical dysplasia

Cortical dysplasia (CD) is the most common malformation of cortical development in epilepsy surgery patients. Patients with mild Palmini type I CD represent about 50% of the surgical cases, and these lesions tend to occur most often in the temporal lobe, often associated with hippocampal sclerosis. By comparison, patients with severe type II CD present at younger ages, often with multilobar extratemporal lesions, and more aggressive seizures. The presurgical evaluation in CD patients can be challenging, as no single test is 100% accurate. Based on retrospective cohort studies, the accuracy of investigations are: interictal scalp electroencephalography (EEG), 50%; ictal scalp EEG, 65%; magnetic resonance imaging (MRI), 66%; fluorodeoxyglucose-positron emission tomography (FDG-PET), 81%; and ictal single photon emission computed tomography (SPECT), 57%. Intracranial electrodes are used in about 50% of patients with CD. Contemporary series report that 62% of patients with CD are seizure free after resective neurosurgery, with higher rates for complete (77%) compared with incomplete (20%) removal of the lesion. Morbidity (<3%) and mortality (0.2%) are low for patients with CD undergoing epilepsy neurosurgery. Future challenges include the noninvasive identification of patients with CD with 100% accuracy, evaluation of long-term outcomes in surgical patients, and devising new treatments based on a better understanding of the neurobiology leading to seizures in CD tissue.

Assessment and surgical outcomes for mild type I and severe type II cortical dysplasia: a critical review and the UCLA experience

Recent findings on the clinical, electroencephalography (EEG), neuroimaging, and surgical outcomes are reviewed comparing patients with Palmini type I (mild) and type II (severe) cortical dysplasia. Resources include peer-reviewed studies on surgically treated patients and a subanalysis of the 2004 International League Against Epilepsy (ILAE) Survey of Pediatric Epilepsy Surgery. These sources were supplemented with data from University of California, Los Angeles (UCLA). Cortical dysplasia is the most frequent histopathologic substrate in children, and the second most common etiology in adult epilepsy surgery patients. Cortical dysplasia patients present with seizures at an earlier age than other surgically treated etiologies, and 33-50% have nonlocalized scalp EEG and normal magnetic resonance imaging (MRI) scans. 2-((18)F)Fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) is positive in 75-90% of cases. After complete resection, 80% of patients are seizure free compared with 20% with incomplete resections. Compared with type I, patients with type II cortical dysplasia present at younger ages, have higher seizure frequencies, and are extratemporal. Type I dysplasia is found more often in adult patients in the temporal lobe and is often MRI negative. These findings identify characteristics of patients with mild and severe cortical dysplasia that define surgically treated epilepsy syndromes. The authors discuss future challenges to identifying and treating medically refractory epilepsy patients with cortical dysplasia.

FDG-PET/MRI coregistration improves detection of cortical dysplasia in patients with epilepsy

OBJECTIVE

Patients with cortical dysplasia (CD) are difficult to treat because the MRI abnormality may be undetectable. This study determined whether fluorodeoxyglucose (FDG)-PET/MRI coregistration enhanced the recognition of CD in epilepsy surgery patients.

METHODS

Patients from 2004-2007 in whom FDG-PET/MRI coregistration was a component of the presurgical evaluation were compared with patients from 2000-2003 without this technique. For the 2004-2007 cohort, neuroimaging and clinical variables were compared between patients with mild Palmini type I and severe Palmini type II CD.

RESULTS

Compared with the 2000-2003 cohort, from 2004-2007 more CD patients were detected, most had type I CD, and fewer cases required intracranial electrodes. From 2004-2007, 85% of type I CD cases had normal non-University of California, Los Angeles (UCLA) MRI scans. UCLA MRI identified CD in 78% of patients, and 37% of type I CD cases had normal UCLA scans. EEG and neuroimaging findings were concordant in 52% of type I CD patients, compared with 89% of type II CD patients. FDG-PET scans were positive in 71% of CD cases, and type I CD patients had less hypometabolism compared with type II CD patients. Postoperative seizure freedom occurred in 82% of patients, without differences between type I and type II CD cases.

CONCLUSIONS

Incorporating fluorodeoxyglucose-PET/MRI coregistration into the multimodality presurgical evaluation enhanced the noninvasive identification and successful surgical treatment of patients with cortical dysplasia (CD), especially for the 33% of patients with nonconcordant findings and those with normal MRI scans from mild type I CD.

Disorders of cortical formation: MR imaging features

The purpose of this article was to review the embryologic stages of the cerebral cortex, illustrate the classification of disorders of cortical formation, and finally describe the main MR imaging features of these disorders. Disorders of cortical formation are classified according to the embryologic stage of the cerebral cortex at which the abnormality occurred. MR imaging shows diminished cortical thickness and sulcation in microcephaly, enlarged dysplastic cortex in hemimegalencephaly, and ipsilateral focal cortical thickening with radial hyperintense bands in focal cortical dysplasia. MR imaging detects smooth brain in classic lissencephaly, the nodular cortex with cobblestone cortex with congenital muscular dystrophy, and the ectopic position of the gray matter with heterotopias. MR imaging can detect polymicrogyria and related syndromes as well as the types of schizencephaly. We concluded that MR imaging is essential to demonstrate the morphology, distribution, and extent of different disorders of cortical formation as well as the associated anomalies and related syndromes.

Cortical glucose metabolism correlates negatively with delta-slowing and spike-frequency in epilepsy associated with tuberous sclerosis

The mechanism of altered glucose metabolism seen on positron emission tomography (PET) in focal epilepsy is not fully understood. We determined the association between interictal glucose metabolism and interictal neuronal activity, using PET and electrocorticography (ECoG) measures derived from 865 intracranial electrode sites in 11 children with focal epilepsy associated with tuberous sclerosis complex (TSC) (age: 0.5-16 years) undergoing epilepsy surgery. A multiple linear regression analysis was applied to each patient, to determine whether the glucose uptake at each electrode site on interictal PET was predicted by ECoG amplitude powers and interictal spike-frequency measured in the given electrode site. The regression slopes as well as R-square values (an indicator of fitness of the regression models) were finally averaged across the 11 patients. The mean regression slope for delta amplitude power was -0.0025 (95% CI: -0.0045 to -0.0004; P = 0.02 based on one-sample t-test) and that for spike frequency was -0.023 (95% CI: -0.042 to -0.0038; P = 0.02). On the other hand, the mean regression slopes for the remaining ECoG amplitude powers (theta, alpha, sigma, beta, and gamma activities) were not significantly different from zero. The mean R-square value was 0.39. These results suggest that increased delta-slowing and frequent spike activity were independently and additively associated with glucose hypometabolism in children with focal epilepsy associated with TSC. Association between frequent interictal spike activity and low glucose metabolism may be attributed to slow-wave components following spike discharges on ECoG recording, and a substantial proportion of the variance in regional glucose metabolism on PET could be explained by electrophysiological traits derived from conventional subdural ECoG recording.

Surgical treatment of intractable epilepsy associated with focal cortical dysplasia

Focal cortical dysplasias (FCDs) are congenital malformations of cortical development that are a frequent cause of refractory epilepsy in both children and adults. With advances in structural and functional neuroimaging, these lesions are increasingly being identified as a cause of intractable epilepsy in patients undergoing surgical management for intractable epilepsy. Comprehensive histological classification of FCDs with the establishment of uniform terminology and reproducible pathological features has aided in our understanding of FCDs as an epilepsy substrate. Complete resection of FCDs and the associated epileptogenic zone can result in a good surgical outcome in the majority of patients.

Disorders of cortical formation: MR imaging features

The purpose of this article was to review the embryologic stages of the cerebral cortex, illustrate the classification of disorders of cortical formation, and finally describe the main MR imaging features of these disorders. Disorders of cortical formation are classified according to the embryologic stage of the cerebral cortex at which the abnormality occurred. MR imaging shows diminished cortical thickness and sulcation in microcephaly, enlarged dysplastic cortex in hemimegalencephaly, and ipsilateral focal cortical thickening with radial hyperintense bands in focal cortical dysplasia. MR imaging detects smooth brain in classic lissencephaly, the nodular cortex with cobblestone cortex with congenital muscular dystrophy, and the ectopic position of the gray matter with heterotopias. MR imaging can detect polymicrogyria and related syndromes as well as the types of schizencephaly. We concluded that MR imaging is essential to demonstrate the morphology, distribution, and extent of different disorders of cortical formation as well as the associated anomalies and related syndromes.

Focal cortical malformations can show asymmetrically higher uptake on interictal fluorine-18 fluorodeoxyglucose positron emission tomography (PET)

Interictal fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) is a component of the presurgical evaluation of patients with medically intractable epilepsy, including patients with malformations of cortical development. The authors describe 3 cases of focal cortical malformations that displayed asymmetrically higher uptake on FDG-PET performed in the interictal state in patients undergoing evaluation for possible focal resection for refractory localization-related epilepsy. The evaluation included routine and prolonged video electroencephalography (EEG), magnetic resonance imaging (MRI), interictal FDG-PET with concurrent EEG, and single-photon emission computed tomography (SPECT). All 3 patients had focal cortical malformations on MRI corresponding to regions of asymmetrically higher uptake on FDG-PET. EEG confirmed that the FDG-PET studies were performed in the interictal state. The lesions included a large region of subcortical heterotopia in the right frontal lobe, a left temporal lobe dysplasia, and a region of subcortical heterotopia in the right occipital lobe. In both patients with subcortical heterotopia, there were other focal regions of cortical malformation that were not associated with abnormal or asymmetric uptake on FDG-PET. Previous reports describe decreased uptake on interictal PET in most cases of focal cortical malformations. Normal to increased uptake has been reported with band heterotopia. The authors demonstrate that other types of focal malformations of cortical development, including focal subcortical heterotopia and lobar dysplasia, can be associated with asymmetrically higher uptake on interictal FDG-PET.

Malformations corticales et épilepsie : apport de l’IRM

Malformations of cortical development are increasingly recognized as important causes of epilepsy, developmental delay and other neurological disorders. Our purpose is to present the relevance of the MRI in these pathologies with the clinical, genetic and therapeutic aspects. This classification is based on the three fundamental events of cortical formation: proliferation of neurons and glie in the periventricular zone, migration of postmitotic neurons to the periphery, subsequent cortical organization. MR analysis evaluates particularly the cortical thickness, sulcal and cortical morphology, gray-white matter junction, and looks for gray matter in abnormal location. These data coupled with the familial history, the seizure characteristics and genetic findings should allow an appropriate classification of the lesions. MR imaging allows the detection and classification of cortical malformations. MR imaging findings are primordial to consider surgery when the epilepsy becomes refractory to the anti-epileptic drugs. An adequate classification of these malformations should help to provide to the family an appropriate counseling both in terms of genetics and outcome.

Neuroimaging of Focal Cortical Dysplasia

Focal cortical dysplasia (FCD) is a common cause of pharmacoresistant epilepsy that is amenable to surgical resective treatment. The identification of structural FCD by magnetic resonance imaging (MRI) can contribute to the detection of the epileptogenic zone and improve the outcome of epilepsy surgery. MR epilepsy protocols that include specific T1 and T2 weighted, and fluid-attenuated inversion recovery (FLAIR) sequences give complementary information about the characteristic imaging features of FCD; focal cortical thickening, blurring of the gray-white junction, high FLAIR signal, and gyral anatomical abnormalities. Novel imaging techniques such as magnetic resonance spectroscopy (MRS), magnetization transfer imaging (MTI), and diffusion tensor imaging (DTI) can improve the sensitivity of MR to localize the anatomical lesion. Functional/metabolic techniques such as positron emission tomography (PET), ictal subtraction single photon emission computed tomography (SPECT), functional MRI (fMRI), and magnetic source imaging (MSI) have the potential to visualize the metabolic, vascular, and epileptogenic properties of the FCD lesion, respectively. Identification of eloquent areas of cortex, to assist in the surgical resection plan, can be obtained non-invasively through the use of fMRI and MSI. Although a significant number of FCD lesions remain unidentified using current neuroimaging techniques, future advances should result in the identification of an increasing number of these cortical malformations.

Surgical outcome and prognostic factors of pediatric epilepsy caused by cortical dysplasia

OBJECTS

We analyzed 30 patients with cortical dysplasia (CD) and epilepsy to evaluate the clinical characteristics and surgical outcome of both epilepsy control and neurocognition.

MATERIALS AND METHODS

The mean ages at seizure onset and at the time of the operation were 3.6 years (range, 1 month-12.6 years) and 10.3 years (range, 1.5-18.3 years), respectively. The mean follow-up period was 3.2 years (range, 1-5.3 years). (18)FDG-positron emission tomography was the most sensitive and magnetic resonance imaging was the most specific in localizing the lesion. Developmental/intellectual delay was predominant in the early-onset group (n=18, seizure onset <3 years), with intelligence tending to be normal in the late-onset group (n=12, seizure onset >or=3 years). Mild CD predominated in the late-onset epilepsy group and moderate or severe CD in the early-onset group (p=0.005). The surgical success rate of epilepsy control was 87%. A better outcome was obtained if the lesion was confined to the temporal lobe. School performance was favorable in 43%. The age at seizure onset and preoperative developmental/intellectual delay were the important prognostic factors in school performance as well as the epilepsy control. A total of 77% of patients had relatively good social adaptation. Successful epilepsy control and good school performance were affirmative conditions precedent to social adaptation.

CONCLUSIONS

Due to the favorable control of epilepsy and its effect on school performance and social adaptation, surgical treatment is strongly recommended for cortical dysplasia and intractable epilepsy.

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

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

Imaging structure and function in refractory focal epilepsy

Over the past decade there have been many advances in data acquisition and analysis for structural and functional neuroimaging of people with epilepsy. New imaging sequences and analysis techniques have increased the resolution of images such that underlying structural pathology can be seen in many patients with "cryptogenic" epilepsy. When an epileptogenic lesion is present, antiepileptic drugs alone rarely prevent seizures. However, the success of surgical treatment is improved when a structural lesion has been identified. Lesions might not overlap with the area of the cortex generating seizures and may continue into areas sustaining normal functions. To prevent postsurgical morbidity, the spatial relation between functionally important areas and the epileptogenic lesion must be assessed before surgery. In this review we describe the potential of different neuroimaging techniques to show lesions, assess neuronal function, and assist with the prognosis of postsurgical outcome in patients with refractory focal epilepsy.

Neuroimaging in disorders of cortical development

Malformations of cortical development are important causes of developmental delay and epilepsy. They are classified by the presumed stage during which normal development is interrupted: neuronal proliferation and differentiation, neuronal migration, and late migration/cortical organization. This article discusses the important malformations in each of these groups, how and why the malformations develop, and their imaging findings. A better understanding of these disorders helps in genetic counseling of the parents and may help in the treatment of associated epilepsy.

Diffusion tensor imaging in frontal lobe epilepsy

We report a 13-year-old female with refractory frontal lobe epilepsy in whom diffusion tensor imaging was useful for exploring subtle cortical malformation. She had frequent simple partial seizures characterized by clonic movement of the right upper extremity. Conventional magnetic resonance imaging was not conclusive. A diffusion tensor imaging revealed an increased apparent diffusion coefficient and reduced anisotropy in the left frontal lobe. Positron emission tomography disclosed hypermetabolism in the adjacent area. We could identify the relatively thick cortex with an indistinct gray-white matter junction in a thin-slice T(1)-weighted image.

Malformations of cortical development

Malformations of cortical development are an important cause of developmental delay and epilepsy. Proper identification of these malformations can greatly help in accurately counseling affected families and, in some cases, in the treatment of the epilepsy. Modem neuroimaging is an important tool in the diagnosis of these malformations.

Neocortical temporal FDG-PET hypometabolism correlates with temporal lobe atrophy in hippocampal sclerosis associated with microscopic cortical dysplasia

PURPOSE

Medically intractable temporal lobe epilepsy (TLE) due to hippocampal sclerosis (HS), with or without cortical dysplasia (CD), is associated with atrophy of the hippocampal formation and regional fluorodeoxyglucose positron-emission tomography (FDG-PET) hypometabolism. The relation between areas of functional and structural abnormalities is not well understood. We investigate the relation between FDG-PET metabolism and temporal lobe (TL) and hippocampal atrophy in patients with histologically proven isolated HS and HS associated with CD.

METHODS

Twenty-three patients underwent en bloc resection of the mesial and anterolateral neocortical structures. Ten patients were diagnosed with isolated HS; 13 patients had associated microscopic CD. Temporal lobe volumes (TLVs) and hippocampal volumes were measured. Magnetic resonance imaging (MRI) and PET were co-registered, and regions of interest (ROIs) determined as gray matter of the mesial, lateral, and anterior temporal lobe.

RESULTS

All patients (HS with or without CD) had significant ipsilateral PET hypometabolism in all three regions studied (p < 0.0001). In patients with isolated HS, the most prominent hypometabolism was in the anterior and mesial temporal lobe, whereas in dual pathology, it was in the lateral temporal lobe. TLVs and hippocampal volumes were significantly smaller on the epileptogenic side (p < 0.05). The PET asymmetries ipsilateral/contralateral to the epileptogenic zone and TLV asymmetries correlated significantly for the anterior and lateral temporal lobes (p < 0.05) in the HS+CD group, but not in the isolated HS group. Mesial temporal hypometabolism was not significantly different between the two groups.

CONCLUSIONS

Temporal neocortical microscopic CD with concurrent HS is associated with more prominent lateral temporal metabolic dysfunction compared with isolated HS in TL atrophy. Further studies are needed to confirm these findings and correlate the PET hypometabolic patterns with outcome data in patients operated on for HS with or without CD.