Abstracts

Rationale: Mapping for eloquent brain function is essential in tailoring pediatric epilepsy surgery. Stereo EEG (SEEG) has become more widely used compared to subdural electrodes for invasive EEG monitoring. Functional mapping with SEEG has challenges as well as advantages compared to subdural electrodes. We report rapid real time high gamma frequency mapping (RTFM) for localization of language function in children, adolescents and young adults with medically intractable epilepsy who underwent SEEG recordings.   

Methods: A total of 34 patients (20 male, 14 female, mean age 13.0 ± 4.4 years) who underwent SEEG for medically intractable epilepsy were identified, between December 2018 and April 2022 at Boston Children’s Hospital. 12 patients (7 male, 5 female, mean age 11.9 ± 4.2 years) had electrode placement in the dominant left inferior frontal and superior temporal regions, and underwent expressive and receptive language mapping. During SEEG, RTFM was performed with the CortiQ system (gtec, Austria), which was approved for use in invasive EEG monitoring, by Boston Children's Hospital. Custom-made stimulation paradigms for each case were tailored to functional level and ability to cooperate for testing. Confirmatory testing for function was performed with cortical stimulation in all cases.

Results: RTFM detected increase in high gamma frequency activity, in areas activated by  paradigm-related tasks. RTFM was performed without compromising SEEG recordings to capture seizures and localize onset. Paradigms used did not induce any seizures, or negatively impact the SEEG recording. Expressive language was localized in the inferior frontal regions in 4 cases. Auditory responses through combined paradigms were localized in the superior temporal regions in 8 cases. Further differentiation between primary auditory responses and receptive language function was performed with additional cortical stimulation testing. Results from confirmatory functional testing with cortical stimulation were generally concordant with RTFM.

Conclusions: RTFM appears very useful for mapping language function during invasive EEG monitoring for epilepsy surgery. RTFM can be used with subdural electrodes as well as with depth electrodes in SEEG. Carefully planned electrode placement is essential, to cover the relevant regions for language mapping when indicated. Accessing expressive language region may be easier, in the superficial inferior frontal gyrus. Accessing receptive language region may have more challenges, in particular within the sylvian fissure, including planum temporale. More accurate stereotactic placement of depth electrodes in deeper regions can be performed with SEEG, while placement of subdural electrodes in the sylvian fissure is very challenging. Thus SEEG has greater advantages for localization of receptive language function. Also RTFM has advantages compared to cortical stimulation, simultaneously recording the whole network of implanted electrodes, and with no concerns of inducing seizures or tissue injury, during mapping sessions. Optimized planning of electrode placement for SEEG is still necessary for RTFM, which appears to have advantages with language mapping.

Funding: None