Rapid and low-invasive functional brain mapping by realtime visualization of high gamma activity for awake craniotomy

Abstract

For neurosurgery with an awake craniotomy, the critical issue is to set aside enough time to identify eloquent cortices by electrocortical stimulation (ECS). High gamma activity (HGA) ranging between 80 and 120 Hz on electrocorticogram (ECoG) is assumed to reflect localized cortical processing. In this report, we used realtime HGA mapping and functional magnetic resonance imaging (fMRI) for rapid and reliable identification of motor and language functions. Three patients with intra-axial tumors in their dominant hemisphere underwent preoperative fMRI and lesion resection with an awake craniotomy. All patients showed significant fMRI activation evoked by motor and language tasks. After the craniotomy, we recorded ECoG activity by placing subdural grids directly on the exposed brain surface. Each patient performed motor and language tasks and demonstrated realtime HGA dynamics in hand motor areas and parts of the inferior frontal gyrus. Sensitivity and specificity of HGA mapping were 100% compared to ECS mapping in the frontal lobe, which suggested HGA mapping precisely indicated eloquent cortices. The investigation times of HGA mapping was significantly shorter than that of ECS mapping. Specificities of the motor and language-fMRI, however, did not reach 85%. The results of HGA mapping was mostly consistent with those of ECS mapping, although fMRI tended to overestimate functional areas. This novel technique enables rapid and accurate functional mapping.

Electrocorticographic Temporal Alteration Mapping: A Clinical Technique for Mapping the Motor Cortex with Movement-Related Cortical Potentials

“…Compared with scalp MRCPs, intracranial MRCPs (iMRCPs) extracted from ECoG have much larger (up to 150 microvolt) voltage and higher spatial resolution. iMRCP components are often visible in very few adjacent electrode contacts and span a few square centimeter with steep amplitude gradients, suggesting close proximity to the cortical generators (Breshears et al, 2010; Roland et al, 2010; Ogawa et al, 2014; Taplin et al, 2016). With a systematical analysis of MRCPs, researchers can understand models of these cognitive processes and locate the brain regions that implicate specific cognitive processes.…”

“…However, only a few attempts tried to use ECoG in the intraoperative settings instead of after-surgery monitoring for motor and speech/language cortex localization (Breshears et al, 2010; Roland et al, 2010; Ogawa et al, 2014; Taplin et al, 2016). The practicality and potential value of ECoG-based mapping in the operating room is still largely unexplored.…”

Electrocorticography-Based Real-Time Functional Mapping for Pediatric Epilepsy Surgery

“…Obviously, this approach might only be applied with older or more emotionally mature pediatric patients who are able to undergo awake craniotomy. In fact, such a novel approach of visualizing neuronal brain activity in real time intraoperatively has already been developed and tested in adult tumor patients by Dr. Kamada and his group in the Department of Neurosurgery, School of Medicine, Asahikawa Medical University, Hokkaido, Japan 32,55,56 (►Fig. 6).…”

“…They utilized RTFM after craniotomy when applying grids to the exposed brain surface. 32 Both motor and language functional mappings were performed. When the results of the frontal lobe mapping for Broca area were compared with extraoperative ESM results, a 100% concordance for both sensitivity and specificity was observed.…”

Awake right hemisphere brain surgery

“…Eloquent regions are subject to substantial anatomical variance among patients, and the use of preoperative functional MRI (fMRI) has allowed neurosurgeons to identify the eloquent brain areas in a patient-specific manner [10][11][12][13]. Combined with intraoperative neuronavigation, fMRI has further enhanced the safety of awake craniotomies for resection of tumors or epileptic foci, which previously had the potential to significantly damage eloquent regions of the brain [5,[14][15][16].…”