(374) Language mapping in children with Stereo EEG, using rapid real time high-gamma frequency functional mapping

Mapping of eloquent brain function is essential when tailoring epilepsy surgery, including focal resections for medically intractable pediatric epilepsy. Stereo EEG has become more widely used compared to subdural electrodes, for invasive EEG monitoring. We report rapid real time high gamma frequency mapping for localizing language function, in children and adolescents with medically intractable epilepsy who underwent invasive EEG monitoring using stereo EEG recordings, to optimize surgical intervention.    

Methods:

Fifteen patients (9 boys and 6 girls, mean age 12.2 +/- 4.3 years) who underwent stereo EEG recording for medically intractable epilepsy were identified between December 2018 and February 2020, at Boston Children’s Hospital. Six of these patients (4 boys and 2 girls, mean age 11.0 +/- 4.1 years) had electrode placement in the dominant left inferior frontal and superior temporal regions, and underwent functional mapping of expressive and receptive language.  

During the stereo EEG study, rapid real time high gamma frequency functional mapping was performed using the CortiQ system (gtec, Austria). The CortiQ system was approved for use in invasive EEG monitoring cases by Boston Children's Hospital. Custom-made stimulation paradigms were developed for each case, tailored to the functional level and ability to cooperate for testing. Confirmatory testing for function was performed with cortical stimulation in all cases. 

Results:

The functional testing was able to detect increased high gamma frequency activity in areas activated by the paradigm-related tasks. CortiQ system was able to obtain functional mapping data without compromising the stereo EEG data to capture seizures and localize onset. The passive mapping paradigms used did not alter or negatively impact the stereo EEG recording itself.  

Expressive language was localized in the inferior frontal regions in three cases. This facilitated direct cortical stimulation testing. Auditory responses were localized in three cases; differentiation between primary auditory responses and receptive language function was performed with additional cortical stimulation testing. Overall, results from confirmatory testing for function with cortical stimulation testing were generally concordant with the results of the high gamma frequency mapping.

Conclusions:

Rapid real time high-gamma frequency functional mapping appears to be very useful in assisting localization of language function in children undergoing invasive EEG monitoring for epilepsy surgery. This method can be used with subdural electrodes as well as with multiple depth electrodes placed in stereo EEG recordings. Carefully planned electrode placement will be necessary to cover the relevant regions to localize language function. The expressive language region may be easier to access in the superficial inferior frontal gyrus, while receptive language region may have more challenges to access, in the posterior superior temporal gyrus and also in the planum temporale, within the sylvian fissure. However, more accurate stereotactic placement of the depth electrodes in such deeper regions could be a potential advantage with stereo EEG compared to subdural electrode placement. Further improvement in tailored planning of the electrode placement, for recording with stereo EEG recordings will be necessary, to further optimize the use of this technology.

Funding: Please list any funding that was received in support of this abstract.: No funding was received in support of this abstract.