Magnetoencephalography (MEG) data analyzed with novel spatial filtering methods, namely event-related beamforming (ERB), have shown success in localizing hand motor areas in healthy adults and in a group of pediatric patients with peri-Rolandic tumors. The validity of this method to localize the primary motor field in a pediatric tumor case was confirmed by intraoperative direct cortical stimulation. Currently, the reliability of this method has not been demonstrated. We report on a 16-year-old boy with localization-related epilepsy originating from his right hemisphere sensory cortex. Hand motor and sensory areas were identified preoperatively by ERB analysis of MEG data. The patient underwent invasive monitoring which localized the epileptic focus to right postcentral gyrus, immediately posterior to the MEG motor area and adjacent to the MEG sensory area. The patient received a gyrectomy of sensory cortex guided by intraoperative direct cortical stimulation to ensure sparing of hand motor cortex. Replication of the MEG motor mapping protocol postoperatively demonstrated reliable localization of the motor and sensory areas. We also discuss caveats for future applications of this protocol.

Keywords:
Magnetoencephalography, Presurgical mapping, Motor mapping, Event-related beamformer, Motor field, Movement-evoked field, Somatosensory-evoked field
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2009
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