[¹⁸F]FDG‐PET and Whole‐Scalp MEG Localization of Epileptogenic Cortex

Abstract

Summary:Purpose: To evaluate combined [ I 'F]fluorodeoxyglucose ("F-FDG) positron emission tomography (PET) and 122-channel whole-scalp magnetoencephalography (MEG) in lateralizing the epileptogenic cortex in patients whose routine presurgical evaluations gave discordant results about the location of the epileptic focus.Methods: Nine patients (five women, four men) aged 13-40 years were studied. Subdural EEG (SEEG) was recorded from eight patients. Six patients were operated on.Results: In seven of nine patients, PET and MEG agreed in localizing the epileptogenic cortex. When PET and MEG were in congruence, SEEG agreed with the findings. In five of six operated-on patients, PET and MEG results were congruent, and the outcome of the operation was successful. Two patients had discordant PET and MEG results. In one patient, PET showed bitemporal hypometabolism, whereas MEG showed epileptiform activity in the right parietal lobe. The surgical outcome of the palliative temporal lobectomy was poor. Another patient had unilateral temporal hypometabolism in PET and bitemporal activity in MEG. She was not operated on.Conclusions: In most patients, PET and MEG were congruent in locating the epileptogenic cortex. Thus the combination of these techniques may provide useful support for the localization of the seizure onset and reduce the need for invasive procedures. Key Words: [ '8F]FDG-PET-PET-MEGEpilepsy-Epilepsy surgery.Epilepsy surgery has become increasingly common in treating patients with drug-resistant focal epilepsy. Preoperative evaluations are performed to identify the primary epileptogenic zone [i.e, the area of brain tissue necessary and sufficient for the generation of habitual ictal events (l)], to detect the number of additional zones, and to determine their locations with respect to irretrievable cortical areas. Routine preoperative evaluation, with magnetic resonance imaging (MRI), interictal and ictal scalp electroencephalography (EEG), video monitoring, and neuropsychological tests, usually locates the epileptogenic area with reasonable accuracy. However, if the results disagree, invasive ictal EEG recording with subdural (SEEG) or intracerebral electrodes is usually needed to identify the region triggering the seizure. Noninvasive techniques with high sensitivity and specificity are being sought to reduce invasive and timeconsuming procedures in the subgroup of patients with epilepsy and with controversial preoperative evaluation.In patients with temporal lobe epilepsy (TLE), ['sF]fluorodeoxyglucose (FDG) positron emission tomography (PET) usually shows interictal focal decrease of cortical glucose uptake (2-4). FDG-PET indicates regional glucose hypometabolism in 70-89% of patients with TLE, and the congruence with scalp EEG recordings increases to -100% if the MRI is abnormal (5-1 1). PET is already accepted as an essential part of presurgical evaluation in most epilepsy surgery centers (12).Magnetoencephalography (MEG) measures extracranial magnetic fields resulting mainly from electrical currents i...

Surgical Implications of Neuromagnetic Spike Localization in Temporal Lobe Epilepsy

“…Spike localization by magnetoencephalography (MEG) has been compared with localization by intracranial EEG (2,(9)(10)(11)(12)(13)(14), positron emission tomography (PET) (15) and single-photon emission computed tomography (SPECT) (9). Previous studies suggested that the localization accuracy of MEG was higher than that of conventional scalp EEG (10,14) because of the absence of disturbance by the inhomogeneous conductivity of cranial tissues.…”

Magnetoencephalography in presurgical epilepsy evaluation

“…So far, only few studies addressed the question of the diagnostic yield of MEG, because most commonly only those patients who actually exhibited spikes on MEG were presented [29] or only patients with frequent interictal spikes on scalp EEG were referred for MEG recordings [30]. In one study where patients randomly selected from a presurgical epilepsy program were evaluated, epileptiform discharges on MEG could be recorded in 73% of cases [31].…”

“…MEG source localizations showed good agreement with the ultimate localization of the epileptogenic zone in all three patients. In the study of Lamusuo et al [29], four patients with temporal lobe epilepsy and normal MRI scans were included. While MEG and PET yielded converging localizing evidence in these patients, no attempt was made to attribute MEG locations to subcompartments of the temporal lobe.…”

“…So far, only a few MEG studies presented patients with clearly defined nonlesional temporal lobe epilepsy [29,31,32,62].…”

Magnetoencephalography: Clinical application in epilepsy

“…Indirect confirmation mainly comes from studies demonstrating co-localization with known epileptogenic substrates either visible on functional or structural imaging or confirmed with subsequent IC-EEG and successful surgical outcomes with supportive histopathology [7,10,11,13,15,16,18,[23][24][25][26][27][28][29][30].…”