Abstracts

Rationale: Mapping of eloquent function is a crucial factor in tailoring epilepsy surgery including focal resections for medically intractable pediatric epilepsy. Stereo EEG has recently become more widely for invasive EEG monitoring, necessitating changes in standard functional mapping techniques previously optimized for subdural electrodes. Here we report the use of rapid real time high gamma frequency mapping for eloquent function in children and adolescents with medically intractable epilepsy who underwent invasive EEG monitoring with stereo EEG, for seizure localization and functional mapping prior to staged therapeutic surgical intervention. Methods: Seven patients (5 boys and 2 girls, mean age 13.2 +/- 4.1 years) who underwent stereo EEG recording for medically intractable epilepsy were identified between December 2018 and June 2019 at Boston Children’s Hospital (BCH). During the stereo EEG study, rapid real time high gamma frequency functional mapping was performed using the cortiQ system (g.tec medical engineering, Graz and Scheidlberg, Austria ). The cortiQ system was approved for use in invasive EEG monitoring cases by BCH. Custom-made stimulation paradigms were developed for each case, tailored to the functional level and ability for cooperation. Table 1 summarizes the locations for depth electrode placement. Confirmatory testing for function was performed with cortical stimulation testing in all cases. Results: In all cases, functional testing was able to detect increased high gamma frequency activity in areas activated by the paradigm-related tasks, without complications. The cortiQ system obtained functional mapping data without compromising the stereo EEG data to capture seizures and localize onset. The passive mapping paradigms used did not alter or have any negative impact on the stereo EEG recordings themselves. Areas of activation included expressive language, auditory, and sensory motor function in the relevant areas as well as the basal temporal area for specific auditory tasks (Table 1). Temporal lobe was activated during musical listening and playing in a highly trained musician. Confirmatory testing for function with cortical stimulation testing was generally concordant with the results of the high gamma frequency mapping. Conclusions: Rapid real-time, high-gamma frequency functional mapping appears to be a feasible and valid method of localizing important neurological function in children and adolescents undergoing invasive EEG monitoring for epilepsy surgery. This method can be used not only with subdural electrodes but also with multiple stereo EEG depth electrodes. Building on these initial findings, additional adjustments of the system for recording with stereo EEG depth electrodes may further optimize the use of this technology and improve the capacity for functional mapping with stereo EEG recordings. Funding: No funding