Magnetoencephalography using auditory evoked fields (AEFs) for tone-burst stimulus is one of the most established methods to localize auditory cortices on the upper surface of the bilateral temporal lobes. The N100m of the AEFs is localized near the border of the Heschl gyrus and the planum temporale. This study investigated whether N100m can be used as a physiological landmark of the posterior language area (PLA) in 10 patients with left temporal lobe gliomas. Preoperative AEF sources were projected into the surgical field using a frameless stereotactic system in two patients. Lateral projection of the N100m dipole to the cortical surface corresponded to the PLA identified by cortical stimulation during the awake condition. The location of the PLA was correlated to the N100m source position after surgery in another patient. The other seven patients underwent resection surgery without intraoperative language mapping. The lateral projection point of the N100m source was projected to the surgical field by a stereotactic guidance system. The lateral projection point and the surrounding area were preserved. No patient developed language dysfunction after surgery. The present results suggest that the N100m of the AEFs for tone-burst stimulus can be used as a simple and practical landmark of the PLA.
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