Efficacy of transcranial motor-evoked potentials in avoiding the postoperative neurologic deficit for brain tumors with allocation in eloquent regions

Background: Motor-evoked potentials (MEPs) are the well proven method to assess the descending motor pathways and detect neurological impairment. Muscle action potentials of the upper or lower limbs are the responses to the central stimulation. This study aimed to elucidate the clinical efficacy of TcMEP monitoring during resection surgeries of tumors from eloquent brain areas. Material and methods: TcMEP monitoring data of 83 patients were prospectively reviewed. The patient’s age varied between 16 and 81 years, 44 males (53.0%), 39 females (46.4%). None of these patients had a neurological deficit before the surgery. The MEPs were evoked by transcranial electrical stimulation through spiral electrodes placed over the primary motor cortex and were recorded by needle electrodes inserted into the following muscles: biceps, abductor pollicis brevis, and anterior tibialis muscles. MEPs were continuously recorded throughout surgery. The following stimulation parameters were used: number of pulses – 5, duration of each pulse – 0.5 ms, inter-pulse interval between – 2-4 ms, stimulation intensity –50-150 mA. When MEP amplitudes decreased by more than 50%, MEP stimulation was repeated and MEP changes were reported to the surgeon. Results: No postoperative motor deficit was found in 71 out of 83 patients with stable MEP amplitudes. Postoperative paresis developed in 12 patients. MEP decrease in amplitude (>50%) occurred in six patients (7.2%). Two patients had permanent paresis, caused by vascular injury during tumor resection. Conclusions: Monitoring of motor-evoked potentials during brain tumors operations located within or adjacent to eloquent brain regions is an effective technique to detect acute intraoperative injury and to avoid postoperative neurologic deficit