Abstracts

Rationale: As mesial temporal lobe epilepsy (mTLE) without the hippocampal sclerosis (HS) shows no apparent abnormality in MRI, it is difficult to decide the lesion side. Invasive study such as subdural electrode monitoring (SEM) is needed to detect the focus of epilepsy. We evaluate preoperative magnetoencephalography (MEG) and FDG-positron emission tomography (PET), and SEM of mTLE without HS.Methods: Ten patients with intractable mTLE without HS were examined. Eight of ten cases were MRI normal mTLE and two cases were hypertrophic amygdala mTLE. We analyzed FDG-PET by visual finding and 3DSRT (three dimensional stereotaxic ROI template). Preoperative MEG was recorded with simultaneous EEG during 30-40 min. We searched the epileptogenic zone to all cases using subdural electrodes of bilateral temporal lobe: chronically-implanted electrocorticogram (ECoG) over the lateral, basal, and mesial temporal area. Moreover, MEG and ECoG were simultaneously measured at a magnetic shield room in interictal period. All cases received the operation: selective amygdalohippcampectomy.Results: In two cases of MRI negative mTLE, the FDG low uptake was consistent with the result of ECoG. One case of hypertrophic amygdala mTLE showed high uptake of FDG in lesion side. In four cases of MRI negative mTLE and one case of hypertrophic amygdala mTLE, the dipole accumulation in MEG showed the lesion same as the result of ECoG. However the dipole scattering was not typical TLE pattern, anterior temporal type. MEG always could not detect spikes whereas intracranial EEG detected. The Spike detective ratio by MEG was less than 10%. Conclusions: Although FDG-PET is most reliable study for epilepsy among other nuclear medical modalities, it is difficult to determine the lesion side by FDG-PET in mTLE without the HS. MEG hardly detects mesial temporal lobe epileptic spikes probably because their signal sources are too deep and not constantly horizontal to the scalp surface. If the back ground activity is high in comparison with MEG spikes, it becomes difficult to detect these spikes. Our results correspond to the previous reports. On the other hand, some spikes could be detected in MEG of ten cases. It means that we may omit invasive surgery for some cases. MEG may useful tool for some mTLE without HS.