Abstracts

Rationale: Co-registered EEG and functional MRI (EEG-fMRI) technique allows the non-invasive delineation of epileptogenic networks. Studies in patients with temporal lobe epilepsy have been carried out (Kobayashi et al. Epilepsia 2006;47:343), but the value of EEG-fMRI for patients with frontal lobe epilepsy (FLE) is unknown. EEG -fMRI can be useful in the pre-operative work-up of difficult epilepsy cases (Zijlmans et al. Brain 2007;130:2343), and it might be promising especially in non lesional FLE patients, which are often rejected for surgery due to an unclear seizure focus. Methods: Sixteen FLE patients were studied with EEG-fMRI using a 3T scanner: 8 were lesional (cortical dysplasia, 3; atrophic lesion, 2; tumor, 2; and 1 with an inflammatory lesion) and 8 were non lesional. Spikes identified on the EEG were used to build a regressor which was convolved with four different hemodynamic response functions with peaks at 3, 5, 7 and 9s. Significant responses were defined with a t>3.1 (p=0.05, corrected for multiple comparisons). We compared the localisation of the spike and in lesional cases of the lesion, to the localisation of the BOLD response. In non lesional cases the structural MRIs were reviewed for subtle abnormalities in areas that showed BOLD responses. Results: A BOLD response was observed in each patient. Six lesional patients showed a concordance between spike localisation, lesion and BOLD response (3 showed activations, 2 deactivations and 1 activation and deactivation). In non-lesional patients a concordance between spike localisation and BOLD was found in 7 (all activations). In one case, a revision of structural MRI revealed an increase in grey matter thickness without abnormal signal in the right anterior cingulate gyrus (figure). This cortex was eventually resected and histology showed a focal dysplasia. One other patient underwent invasive recordings and was operated. Histology showed a subtle but extended polymicrogyria not visible on structural MRI even after revision. However, EEG-fMRI had shown activation just adjacent to the resected pathological area. In the remaining non lesional patients a revision of structural MRI did not give evidence for subtle structural abnormalities in regions of BOLD signal changes. Conclusions: Lesional FLE patients show a good correspondence between spike localisation, lesion and BOLD signal changes. In non lesional FLE, EEG-fMRI may help to detect subtle structural abnormalities when reviewing structural MRIs guided by EEG-fMRI results. BOLD signal changes may also point to structural pathologies not visible on structural MRI. This study shows that EEG-fMRI can add useful information in the presurgical evaluation of non lesional FLE patients.