Multichannel magnetoencephalographic mapping of sensorimotor cortex for epilepsy surgery.

Preliminary reports have shown a close correlation between the anatomic location of evoked magnetic somatosensory fields and intraoperative evoked somatosensory potentials in patients with mass lesions. We have performed magnetic source imaging (MSI) of sensory and motor (MER) evoked responses or fields on 4 patients with frontal convexity epileptic foci. The method involves (1) graphic overlaying of magnetoencephalography evoked field data and three-dimensional (3D) phase contrast magnetic resonance angiographic data on 3D MRI surface cortical renderings, and (2) correlating these data with intraoperative stimulation-mapped sensory and/or motor responses and local cortical venous anatomy. Our initial results indicate that the location of MSI evoked sensory data correlates closely with the results of intraoperative stimulation mapping. MSI MERs have tended to show a less discrete spatial topography, involving areas of cortex extending beyond the motor strip.