Extraoperative electrical stimulation mapping in epilepsy presurgical evaluation: a proposal and review of the literature.

ABSTRACT

BACKGROUND: Electrical stimulation mapping (ESM) is an important tool for the localization of the seizure onset zone (SOZ) in patients with medically resistant epilepsy (MRE). ESM is the gold standard for the identification of eloquent cortex in epilepsy surgery candidates. However, there is no standard protocol outlining how to perform ESM, to obtain the most useful information possible. The objective of this study, after reviewing the literature concerning ESM, is to propose a unifying technique to validate reliable data across different centers. METHODS: In this manuscript we summarize this technique from its origin to present, and review protocols used in other centers. We also describe a protocol that has been used in our institution, which utilizes depth electrodes. RESULTS: The most common type of ESM uses a "close-loop" system, bipolar and high frequency stimulation (50 Hz). We propose to use a pulse width of 300 µs, current spanning 1-6 mA in depth electrodes and 1-11 mA in subdural-grids. Stimulation time of 5 s maximum and at least 10 s break in between the stimulations. CONCLUSIONS: ESM is a useful tool for understanding eloquent cortex as well as the epilepsy network, although there is no clear consensus regarding how it should be performed.