Mapping of Eloquent Cortex in Focal Epilepsy with Intracranial Electrodes

Abstract

Epilepsy surgery has revolutionized the management of treatment-resistant focal epilepsy. Its success is based on the total resection of the epileptogenic zone (EZ) in the absence of any neurologic (e.g., motor, sensory, and cognitive) deficits. Clearly, the ideal candidate is a patient with focal epilepsy with an EZ that does not involve eloquent cortex and is easily accessible to surgical resection and in whom the noninvasive studies of the presurgical evaluation can yield concordant data of the neurophysiologic (interictal and ictal electrographic recordings), structural (e.g., high-resolution brain MRI) and functional (e.g., positron emission tomography [PET]) neuroimaging studies and neuropsychological evaluation. Unfortunately such is not the case in a significant percentage of patients, for one of the following reasons: (1) the presurgical evaluation fails to yield concordant localizing data among the various diagnostic studies; (2) the epileptogenic zone cannot be localized or even lateralized in a reliable manner; (3) the epileptogenic zone appears to be close to or involve eloquent cortex. Under those circumstances, there is a need to recur to invasive EEG monitoring with intracranial electrodes. Specifically, these are the circumstances when intracranial recordings should be considered: