Abstracts

RATIONALE: We have used whole cortex MEG (MSI) to localize sensorimotor cortex of hand and foot in 30 patients with epilepsy and tumors to plan surgery. We report here 3 cases with seizure zones or tumors immediately adjacent to sensorimotor cortex where whole cortex MEG clearly added non-redundant, useful non-invasive information and allowed more complete resection. METHODS: We used a whole cortex neuromagnetometer with 100 dc SQUIDs and 68 sensor sites (C.T.F. Systems) in a magnetically shielded room (B.T.i., Vacuumschmelze). We recorded somatosensory evoked fields (SEFs) after stimulation of median nerve at the wrist or posterior tibial nerve at the ankle at motor threshold. We coregistered MRI T1 images with MEG sensors. We used a single equivalent current dipole (ECD) in a sphere fit to the MRI CSF boundary optimizing least squares fit between data and model with a downhill simplex. We imaged best fitting MEG ECDs on MRI. Patients had intracranial recordings and cortical stimulations confirming location of central fissure. RESULTS: In the first patient the MEG map of tibial nerve SEF allowed resection of an astrocytoma immediately anterior to foot motor cortex in interhemispheric fissure. The patient had the anticipated transient edema in the immediate post-operative period but thereafter no detectable postoperative deficit, with normal individual toe movements. In the second patient, the MEG map of median nerve SEF allowed resection of a seizure zone immediately anterior to hand motor cortex. In the third patient, the MEG map of median SEF allowed resection of a seizure zone immediately anterior to motor cortex. In both these patients, there was no postoperative deficit, with normal individual fine finger movements. CONCLUSIONS: Whole cortex MEG coregistered with MRI (MSI) adds essential non-invasive information to assist surgery for tumors and epilepsy immediately adjacent to sensorimotor cortex. 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 epilepsy or tumors near sensorimotor areas. Supported by NIH NS20806 and RR13276.