Abstracts

Rationale: Mapping eloquent brain function is essential when tailoring surgery for medically intractable pediatric epilepsy. Recently Stereo EEG (SEEG) has become more widely used compared to subdural electrodes, for invasive EEG monitoring. We report rapid real time high gamma frequency mapping (RTFM) for localizing motor and sensory function, in children and adolescents with medically intractable epilepsy, who underwent invasive EEG monitoring with using SEEG recordings, to optimize surgical intervention.

Methods: 25 patients (14 male and 11 female, mean age 12.5 +/- 4.5 years) who underwent SEEG recording for medically intractable epilepsy were identified between December 2018 and March-February 2021, at Boston Children’s Hospital.

16 of these patients (8 male and 8 female, mean age 12.0 +/- 4.3 years) had electrode placement in the peri rolandic regions (left side in 6 cases, right side in 10 cases), and underwent functional mapping of motor and sensory function.

During the SEEG study, RTFM was performed using the CortiQ system (gtec, Austria). CortiQ system was approved for use in invasive EEG monitoring cases, at 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: RTFM was able to detect increased high gamma frequency activity (60-170 Hz) in regions/areas activated by the paradigm-related tasks. CortiQ system was able to perform functional mapping data without compromising the SEEG data, to capture seizures and localize onset.

Motor function was localized in the precentral regions in 13 cases, and sensory function was localized in the postcentral region in 8 cases (5 cases had localization of both motor and sensory function). Motor function was localized for face in 8, hand in 5, and leg in 2 cases; sensory function was localized for face in 3, hand in 6, and leg in 0 cases, respectively.

Results from confirmatory testing with cortical stimulation testing were generally concordant with results from RTFM.

Conclusions: RTFM with high gamma frequency appears to be very useful in assisting localization of motor and sensory function in children and adolescents undergoing invasive EEG monitoring for epilepsy surgery, not only with subdural electrodes, but also with multiple depth electrodes placed in SEEG recordings.

RTFM was able to provide functional data confirmed with multiple paradigms, also assess regions with low seizure threshold or high threshold for function where cortical simulation could be limited, and overall improve localization.

Motor and sensory function of hand and face areas were detected more often, likely associated with the placement of SEEG electrodes; this also could be due to larger cortical areas represented for hand and face compared to leg, in primary motor and sensory areas.

Carefully tailored planning of electrode placement for SEEG recordings will be necessary for covering the relevant regions of motor and sensory function and further optimizing use of this technology.

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