Applications of Magnetoencephalography in Epilepsy and Tumor Surgery

Abstract

Magnetoencephalography (MEG), which represents the most novel example of noninvasive functional mapping techniques, has contributed to the surgical management of epilepsy and brain tumors in two ways. First, in the case of epilepsy, MEG localization of interictal activity has facilitated placement of subdural (grid, strip, and depth) electrodes that are necessary for accurately localizing the ictal onset zone. Second, MEG has emerged as a reliable and accurate tool for localizing motor, somatosensory, and language-specific cortexes as well as determining hemispheric dominance for language in surgical candidates. In this chapter, we first present a general description of MEG, including background on instrumentation, underlying neurophysiology, and its applications in contemporary clinical practice. Subsequently, we review evidence demonstrating the utility of MEG as a noninvasive tool for approximating the ictal onset zone in addition to localizing eloquent cortex and determining the spatial relation of this cortex to epileptogenic tissue and mass lesions. Furthermore, the utility of MEG in presurgical mapping is discussed in light of some methodologic caveats, with recommendations on optimizing its contributions in clinical practice.