Spatial Electrophysiological Mapping of Tumour and Peritumoural Cortex During Glioma-Related Epilepsy Surgery
A. O’Donnell¹,3; R. Kilbride¹; K. Sweeney2; D. O’Brien2; M. O’Neill3; M.O. Cunningham4
¹Department of Clinical Neurophysiology, Beaumont Hospital, Dublin
2Department of Neurosurgery, Beaumont Hospital, Dublin
3Department of Neuro-Medical Physics, Beaumont Hospital, Dublin
4Discipline of Physiology, School of Medicine, Trinity College Dublin
Abstract:
Introduction
Intraoperative electrocorticography (ioECoG) enables direct recording of cortical electrical activity and can assist identification of epileptogenic cortex during epilepsy surgery¹˒². High-frequency oscillations (HFOs), including ripples and fast ripples, have emerged as potential complementary biomarkers to interictal spikes3-6. However, their spatial distribution within glioma, peritumoural and macroscopically normal cortex, and their relationship with subsequent tissue resection and seizure outcome, remain incompletely understood.
Aims and Objectives
This prospective study aims to characterise the spatial electrophysiological profile of tumour, peritumoural and normal cortex during glioma-related epilepsy (GRE) surgery. Specifically, the distribution of HFOs, interictal spikes and delta, theta, alpha and beta activity will be mapped to anatomically defined tissue regions using intraoperative neuronavigation. Electrophysiological characteristics will subsequently be related to tissue resection and 12-month postoperative seizure outcome to investigate whether specific electrophysiological features, and their resection, are associated with seizure outcome.
Methods
Patients with GRE undergoing glioma resection are prospectively recruited. ioECoG is recorded using an 8-contact subdural strip electrode (DIXI Medical) and Xltek Quantum EEG system at a sampling rate of 2048 Hz. A reproducible three-position electrode-placement protocol was developed to achieve systematic spatial sampling using an electrode routinely employed for functional cortical mapping. The strip is positioned sequentially at three cortical locations, rotating 60° around a central reference position, with two minutes of continuous ioECoG recorded at each position.
Neuronavigation snapshots are acquired at predefined strip contacts at each position, supplemented by intraoperative photographs incorporating identifiable vascular or gyral landmarks. Individual recording contacts are subsequently localised on three-dimensional brain reconstructions and classified as tumour, peritumoural or normal cortex.
Recordings are analysed for interictal spikes, ripples (80–250 Hz), fast ripples (250–500 Hz), and delta, theta, alpha and beta activity. Postoperative imaging delineates the resection cavity, allowing the resection status of spatially mapped tissue to be determined. Electrophysiological characteristics and their resection will subsequently be related to 12-month seizure outcome.
Results
Seven patients (N=7) with low-grade glioma have been recruited and analysed to date. HFOs were identified in two patients (2/7), while interictal spikes were identified in four (4/7), involving tumour, peritumoural and/or normal cortex. Two ioECoG recordings were performed in awake patients (2/7) and five under steady-state propofol anaesthesia (5/7). Spatial and frequency-band analyses are ongoing, together with prospective assessment of postoperative seizure outcome.
Conclusion
Systematic spatial ioECoG sampling across glioma, peritumoural and normal cortex is feasible using a reproducible three-position strip-electrode protocol. Preliminary findings demonstrate HFOs in 2/7 and interictal spikes in 4/7 patients. Integration of spatial electrophysiological characteristics with resection mapping and 12-month seizure outcome will determine whether specific electrophysiological features, and their resection, have potential clinical utility in GRE surgery.
Ethical approval
Beaumont Hospital Medical Research Ethics Committee approval REF25/06