側頭葉神経膠腫における聴覚誘発磁界

Auditory evoked magnetic fields in cases with temporal lobe glioma

I．はじめに

　聴覚野は側頭葉上面に存在し，一側耳の聴覚刺激に対しても両側性に反応することが知られている^{1,4,6,13,15,16，19,24,26,29）}が，頭皮上記録による聴覚誘発電位では両側半球由来の信号が重畳して観察されるため左右の聴覚機能を分離して評価できなかった^3,6,14,28）．一方で，聴覚誘発脳磁界は左右半球由来の信号を明確に分離できるのが特徴である．すでにわれわれはヘルメット型脳磁計による健常例の検討から，中・長潜時成分における振幅，潜時，信号源位置の左右差について報告している^{10-12,19,20）}．

　本研究では，側頭葉神経膠腫が大脳皮質聴覚機能に与える影響を調べるため，純音刺激による聴覚誘発磁界を計測し健常人データとの比較検討を行った^{10-12,19,20）}．

Auditory evoked magnetic field (AEF) is known to be suitable to separate left and right hemispheric activi-ties while auditory evoked potential is not. To evaluate cortical auditory function in ten patients with temporal lobe gliomas, we measured AEF for monaural tone sti-muli using a helmet-shaped 66-channel MEG system. Latency of the N100m, the most prominent peak with a latency around 90 ms, was measured in the hemisphere contralateral to the stimulus onset. In five patients, the N100m latency was within our normal range (mean±2 s.d.). In these five cases, tumor was located in the anterior or the inferior part of the temporal lobe. We observed significant delay of the N100m latency in fourpatients and disappearance of the N100m in another pa-tient. In the later five patients, tumor extended to the superior and posterior part of the temporal lobe. AEFcan be used to evaluate cortical auditory function noninvasively in cases with temporal lobe gliomas.