Abstracts

RATIONALE: We used whole cortex MEG coregistered with MRI (MSI) to localize the epileptogenic zone in 13 patients with intractable extratemporal epilepsy considered for surgery. We report here two cases with non-lesional frontal lobe epilepsy near motor cortex where MEG clearly added non-redundant, useful information in our standardized epilepsy surgical protocol. One had prior surgery elsewhere, where resection was limited due to proximity of the epileptogenic zone to motor cortex. METHODS:_ The whole cortex neuromagnetometer had 100 dc SQUID channels and 68 sensor sites (C.T.F. Systems) in a magnetically shielded chamber (B.T.i., Vacuumschmelze). In each patient, we recorded over 100 interictal single spikes and median nerve somatosensory evoked fields (SEFs). We coregistered MRI T1 images with MEG sensors. We applied a single equivalent current dipole model (ECD) in a sphere fit to the MRI CSF boundary with optimization of least squares fit between model and data using a downhill simplex. We imaged the best fitting ECDs of all MEG spike on the coregistered MRI. RESULTS: In the first patient the map of the ECDs of single spikes formed a crescent on the posterior border of the prior resection, anterior to sensorimotor cortex. This justified reevaluation with subdural grids and a resection involving this region. In the second patient, the MEG showed ECDs of single spikes over sensorimotor frontal operculum, immediately anterior to hand motor cortex. This justified the placement of a subdural grid which confirmed localization and led to resection in this area. Motor strip was validated by cortical stimulations. There was no post-operative deficit in either patient. Follow-up will be presented. CONCLUSIONS: Whole cortex MEG coregistered with MRI (MSI) adds non-redundant information in extratemporal intractable partial epilepsy considered for surgery. Based on our experience in these and other patients, we have found whole cortex MEG clinically useful in presurgical evaluation. We now use whole cortex MEG routinely in extratemporal epilepsy as a part of our standard protocol of epilepsy presurgical evaluation. Supported by NIH NS20806 and RR13276.