Subdural grid-and-strips are used routinely in pre-surgical evaluations for people with drug-resistant epilepsy (DRE). Thin-film polyimide electrodes (NeuroOne Evo, 0.08mm) which have been approved for clinical use, are thinner and better conform to brain convolutions than current market grids.

We present two patients with DRE who underwent intracranial EEG (iEEG) monitoring with thin-film polyimide subdural electrode grid-and-strip electrodes as well as traditional EEG for pre-surgical evaluation. Patient 1 had a prior left mesial temporal lobe ablation with seizure recurrence. They underwent left temporal craniotomy with implantation of two subdural grids, three strips and additional depth electrodes. IEEG demonstrated two habitual seizures arising from anterior temporal subdural strips. Functional mapping identified the basal-temporal and Wernicke’s speech areas. Left anterior temporal lobectomy was performed and he remains seizure free 9 months post-resection. Patient 2 underwent bilateral stereoEEG electrode placement with coverage in the frontal/temporal/insular regions and subdural strip electrodes. IEEG demonstrated seizure onset from the left hippocampus and right hippocampal spikes. Given bilateral findings, they underwent Responsive Neurostimulation System implantation.

The two patients underwent subdural electrode placements without complications. IEEG recordings were comparable between NeuroOne Evo and traditional electrodes in terms of integrity, artifactual content and signal recording characteristics. The thinner profile of the Evo grid tail facilitated dura closure and reduced mass effect compared to traditional grids. By trimming material from the tip of the subdural strip, the electrode was placed through a burr hole without difficulty. Recording from these grids contributed to pre-surgical evaluation and led to surgical interventions.

Our initial experience suggests that thin-film electrodes are a viable option for subdural iEEG that could safely minimize intracranial mass effect/brain shift and improve surgical ease of use.