Abstracts

Rationale: The Electric Stimulation Mapping (ESM) is routinely used for intraoperative mapping of motor functions during neurosurgical procedures close to the eloquent motor cortex and corticospinal tract. Standard ESM protocols used in adults are nevertheless ineffective in about 20% of young children. We therefore developed a novel highly efficient ESM paradigm characterized by high intensity (=100 mA) and high frequency (500 Hz) currents delivered at a short-time sequence (30 ms). However, application of the pulses (up to 100 mA) has a potential risk of stimulated tissue overheating.In our previous works, ability of our ESM protocol to elicit motor responses was proven in all 65 children of different age (9.2±5.5 years) and types of epileptogenic lesions undergoing resective epilepsy surgery in the vicinity of the motor eloquent cortical and subcortical structures. We also conducted a safety control study using in vivo thermography in 13 subjects indicated to larger temporal lobe resections (10±4.6 years) that clearly showed non-destructive temperature effect of the proposed ESM protocol. This observation was supported by after-surgery histopathology in 17 subjects. Methods: Here we report an additional safety control study. Using COMSOL Multiphysic® software we developed the complex numerical model simulating the cerebral cortex including its perfusion, stimulation electrodes and electrical fields during ESM. The purpose of our simulation was to reveal an under-surface distribution of temperature with the high spatiotemporal resolution. Results: The simulation showed an increase of temperature up to 45°C only in the thin liquid film humidifying the cortex for less than 50 ms. The surface of the brain (pia matter) is heated up to 41°C by heat transfer in total volume less than 0.005 mm3. Importantly, the temperature immediately drops to the initial value before ESM. The probability of tissue damage computed using Arrhenius integral was estimated close to zero. The simulated electrical field and temperature distribution well corresponded to our previous in vivo thermography measurement. Conclusions: We conclude that the numerical simulation verified safety of our ESM protocol employing high intensity and high frequency currents. The results are in accordance with in vivo thermography and histopathological assessment. Discrete short-time tissue overheating is not destructive and possess only inconsiderable hypothetical risk of the brain tissue damage. Funding: Supported by AZV 15-30456A and MH CZ–DRO, University Hospital Motol, Prague, Czech Republic 00064203.