Presurgical FDG-PET also provides information regarding the functional deficit zone, the area of the brain that shows abnormal function during the interictal period. FDG-PET can identify focal abnormalities in the setting of a negative anatomic MRI brain scan [16]. Poor seizure outcomes following surgery have been described in the setting of bilateral temporal lobe hypometabolism in TLE [8]. A limitation of FDG-PET is the lack of precision in defining the margins of the epileptogenic zone [8]. Comparison of interictal PET and ictal SPECT demonstrated localization of lesions in 77.7% and 7.3% of patients, respectively [45]. FDG-PET, combined with other localizing modalities, such as perfusion ictal-interictal SPECT and MRI gray matter segmentation, has shown improved abilities to detect and predict the extent of epileptic foci [28]. FDG-PET co-registered with MRI may be an effective adjunctive study as it has been shown that MRI gray matter segmentation co-registered with FDG-PET resulted in higher correspondence to intracranial EEG than without segmentation [46]. MEG MEG records brain electrical activity, which can be localized in 3-D by using detectors and induction coils in a superconducting environment [47]. In contrast to EEG, MEG does not suffer from deterioration of signals due to the skull and scalp [48]. In one study, 85% of patients with concordant and specific MEG findings were seizure- free following surgery, compared with only 37% of individuals with MEG findings that were nonspecific or discordant with the region of resection [49]. One of the largest cases series of MEG utilization in 455 patients demonstrated a 70% sensitivity in detecting epileptic activity [50]. Though there have been significant advances in source localization techniques, MEG is still performed in only a minority of presurgical evaluation of epilepsy, and the clinical value of MEG in surgical epilepsy treatment is less clear compared with MRI [48].
Seizures and Epilepsy. Presurgical FDG-PET also provides information regarding the functional deficit zone, the area of the brain that shows abnormal function during the interictal period. FDG-PET can identify focal abnormalities in the setting of a negative anatomic MRI brain scan [16]. Poor seizure outcomes following surgery have been described in the setting of bilateral temporal lobe hypometabolism in TLE [8]. A limitation of FDG-PET is the lack of precision in defining the margins of the epileptogenic zone [8]. Comparison of interictal PET and ictal SPECT demonstrated localization of lesions in 77.7% and 7.3% of patients, respectively [45]. FDG-PET, combined with other localizing modalities, such as perfusion ictal-interictal SPECT and MRI gray matter segmentation, has shown improved abilities to detect and predict the extent of epileptic foci [28]. FDG-PET co-registered with MRI may be an effective adjunctive study as it has been shown that MRI gray matter segmentation co-registered with FDG-PET resulted in higher correspondence to intracranial EEG than without segmentation [46]. MEG MEG records brain electrical activity, which can be localized in 3-D by using detectors and induction coils in a superconducting environment [47]. In contrast to EEG, MEG does not suffer from deterioration of signals due to the skull and scalp [48]. In one study, 85% of patients with concordant and specific MEG findings were seizure- free following surgery, compared with only 37% of individuals with MEG findings that were nonspecific or discordant with the region of resection [49]. One of the largest cases series of MEG utilization in 455 patients demonstrated a 70% sensitivity in detecting epileptic activity [50]. Though there have been significant advances in source localization techniques, MEG is still performed in only a minority of presurgical evaluation of epilepsy, and the clinical value of MEG in surgical epilepsy treatment is less clear compared with MRI [48].