Presurgical localization of primary motor cortex in pediatric patients with brain lesions by the use of spatially filtered magnetoencephalography.

OBJECTIVE: The objective of this study was to confirm the efficacy of spatially filtered magnetoencephalography for the preoperative localization of primary motor cortex in pediatric patients with focal lesions in the region of the sensorimotor cortex.
METHODS: We recorded movement-related magnetoencephalographic activity in 10 pediatric patients (age range, 7-18 years; mean age, 12.5 years) undergoing presurgical evaluation for focal brain lesion resection. Participants made transient movements of the right and left index finger in response to a visual cue. The premovement motor field component in the averaged brain response was localized with a newly developed beamformer spatial filter algorithm. Cortical mapping of motor cortex intraoperatively was conducted in 5 of the 10 patients.
RESULTS: The motor field time-locked to electromyography onset was successfully localized to cortical areas corresponding to the hand region primary motor cortex in 95% of cases (9 of 10 from nonlesional hemisphere; 10 of 10 from lesional hemisphere). Intraoperative electrocortical stimulation activated the expected muscles at motor field coregistered cortical source locations in all cases tested (n = 5). Using these methods, we also found that displacement of the sensorimotor cortex by space-occupying tumors did not interfere with the localization of motor cortex.
CONCLUSION: We conclude that noninvasive localization of the primary motor cortex can be reliably performed by using spatially filtered magnetoencephalography techniques, which provide a robust and accurate measurement of motor cortical function for the purpose of surgical guidance.