Awake Brain Tumor Resection Protocol

As previously described (11 (link)), the critical points of awake surgery include patient position, awake anesthesia, neuronavigation, intraoperative ultrasound, DES mapping, and tumor resection. All patients were anesthetized by administration of propofol and remifentanil by target-controlled infusion, using a laryngeal mask airway for intubation during the craniotomy. The ipsilateral critical sensory scalp nerves, pin insertion, and scalp incision sites were injected with local anesthetic (0.67% lidocaine and 0.33% ropivacaine) with 1:200,000 adrenaline to provide rapid and long-lasting local anesthesia while reducing bleeding. Anesthesia was withdrawn to wake up the patient. The location of the tumor was detected intraoperatively using ultrasound before brain mapping and tumor resection. DES mapping was performed using a 5-mm interval bipolar electrical nerve stimulator (Osiris NeuroStimulator; inomed Medizintechnik GmbH, Emmendingen, Germany) with a frequency of 60 Hz, a pulse duration of 1 ms, a current of 2–6 mA (usually 3–4 mA), and a duration of 1 s for motor and sensory tasks and 4 s for language or other cognitive tasks. Positive motor area stimulation was assumed when movements of the contralateral limb or face were induced. Positive stimulation affecting sensory areas was considered when an abnormal feeling was generated in the contralateral limb or face. Positive stimulation of language areas was considered when the patient exhibited counting arrest, anomia, speech repetition, or other language disturbances without twitching of the mouth. After cortical mapping, the lesion was removed by alternating resection and regular subcortical stimulation.
To protect functional pathways, the patient was asked to continue to move their arm and hand or leg, count numbers, or name pictures when the resection moved closer to the subcortical structures. If the patient experienced weakness of the limb, abnormal language, or abnormal sensation, subcortical DES was performed immediately with the same stimulation parameters. If the above-mentioned positive reaction occurred, it was confirmed to be an essential subcortical conduction pathway. The resection was then interrupted in this direction and was continued in other directions. If no positive response occurred, after the patient’s function recovered, resection was continued until the subcortical areas (positive stimulation) or normal meninges (such as the falx cerebri, fissures), ventricles, or arachnoid borders were encountered, or when more than 1 cm outside of normal white matter surrounding the tumor could be visualized. Tumors were resected 2 mm from the sulci near the eloquent brain areas and then were resected inside the pia mater to avoid damage to the vital supplying arteries in the subarachnoid space. Lesions were safely removed to the greatest extent possible to preserve the cortical and subcortical structures of critical functional areas, drainage veins, and supplying arteries.