Abstracts

Rationale: The cortical Electric Stimulation Mapping (ESM) procedure is used as a standard approach to localize and continuously monitor the condition of the eloquent cortex and corticospinal tract during the neurosurgical intervention. Eliciting the motor responses using the standard ESM paradigm developed for adults is problematic in approximately 20% of young children. We have therefore developed and tested a novel ESM protocol, which uses intense (up to peak-peak 100 mA), high frequency (500 Hz) and short stimulation pulses (15×40 µs). We have previously reported a high reliability of this method in preventing and predicting postsurgical motor deficits in all age groups of children. The aim of the present study was to prove the safety of the protocol.  Methods: The novel ESM paradigm was tested in selected 10 children indicated to extensive temporal lobe resections. We monitored a hypothetical destructive thermal effects of high intense currents by the high-resolution thermography camera (VarioCAM-HD, zoom lens, 1024x768 pixels, 10 fps, 0.05°C resolution). As a part of routine intraoperative electrocorticography (ECoG) performed during temporal lobe surgeries, subdural strips were placed over the lateral temporal neocortex, always within the region included in the resection. ECoG continued during the stimulation in order to exclude induction of electrographic seizures. Intensity of the stimulation current was gradually increased from 10 to 100 mA. If 39°C brain tissue temperature was reached or an electrographic seizure activity was recorded, the stimulation was immediately stopped.The exact site of the electrical stimulation was marked by color ink at the resected brain specimen and histopathologically evaluated using the hematoxylin eosin, luxol fast blue, PAS and cresyl violet staining to detect possible morphological changes induced by the stimulation. Results: Thermography monitoring revealed the short-time increase of temperature in 1 mm surrounding of stimulating electrode using stimulation current above 40 mA. The maximal applicable current 100 mA cause local temperature increasing 0.4°C. The used ESM current intense variated 22.9±21.2 mA. The 22.5 % of cases (6±3.4 years) required higher intense stimulation (>40 mA) with the hypothetical unproven risk of the thermal lesion.No stimulation-induced morphological changes (i.e. regression changes of neurons and glial cell, necrosis, leucostasis, the vessel wall changes etc.) were found by the detailed histopathological evaluation. Conclusions: The safety control of high-intense pulses used in our novel ESM protocol proved low non-destructive thermal effect of stimulation. Any micro-thermal lesions were not observed by the histopathology. We stress inconsiderable risks of the novel ESM method are acceptable in comparison to uncontrolled surgery in eloquent motor brain structures. Funding: Supported by MH CZ–DRO, University Hospital Motol, Prague, Czech Republic 00064203 and AZV 15-30456A.