Case Profiles of Noninvasive Functional Brain Imaging as an Alternative to Cortical Stimulation Mapping

Cortical stimulation mapping (CSM) has long been considered the gold-standard for localizing the eloquent cortex in the presurgical evaluation of patients with epilepsy and brain tumors. In recent years, however, the introduction of non-invasive brain mapping techniques- namely functional magnetic resonance imaging (fMRI), magnetoencephalography (MEG) and transcranial magnetic stimulation (TMS)- have presented an alternative to CSM for identifying the central sulcus and specifying the motor cortex, as well as approximating expressive and receptive language cortices, particularly in cases where invasive monitoring may not be practical. Moreover, the efficacy of the non-invasive methods as a viable substitute for CSM has been attested to in a number of comparison studies in clinical cohorts. In this paper, we present two case studies which demonstrate the utility of the non-invasive functional mapping techniques (MEG and TMS) during presurgical evaluation. Specifically, we first report an instance of preserved sensorimotor function within an area of frontal polymicrogyria coincident with the ictal onset zone in a female with intractable symptomatic partial epilepsy; second, we present findings from a female patient where language localized to the boundary of a left temporal lobe ganglioglioma. In both cases, the outcome of the non-invasive techniques was deemed to be of sufficient utility to defer surgery and seek alternative treatment measures, in order to preserve function and reduce morbidity.