Intraoperative Mapping and Monitoring of the Pyramidal Tract Using Endoscopic Depth Electrodes

OBJECTIVE: To evaluate motor function during neuro-endoscopic resectioning of deep-seated brain tumors using endoscopically guided depth electrodes. METHODS: For 12 cases of thalamic tumors, including high-grade gliomas, germinomas, and malignant lymphomas, depth electrodes were inserted using endoscopic guides between the tumor and the pyramidal tract in the thalamus. Motor-evoked potentials (MEPs) were continuously recorded during neuroendoscopic resectioning of the tumors. RESULTS: Monitoring of MEP responses using depth electrodes in all 12 cases was successful. The minimum stimulus intensity threshold required to induce MEP responses was 3 mA. Gross total or subtotal resections were successful with this technique for all patients with glioma. No additional neurologic impairments were found after surgery in any of the cases. CONCLUSIONS: Continuous MEP measurement using depth electrodes can serve as a new monitoring technique for endoscopic resectioning of deep-seated brain tumors.