Intraoperative Electrically-evoked ABRs in Patients Undergoing Vestibular Schwannoma Surgery

This is a feasibility study being conducted prior to development of a penetrating cochlear nerve stimulating electrode. Experiments will be conducted in patients who are undergoing surgery for resection of a vestibular schwannoma (VS). In the normal course of such a surgical procedure, the cochlear nerve is exposed and, in many cases, the cochlear nerve is resected or function of the cochlear nerve is otherwise disrupted. Typically, recording electrodes are placed on the scalp for the purpose of recording sound-evoked auditory brainstem responses (ABRs), which serve as a measure of the functional status of the cochlear nerve. In this intraoperative experimental procedure, a conventional bipolar nerve stimulating electrode will be placed in contact with the cochlear nerve and the nerve will be stimulated with electrical pulses. Activation of the auditory system by the electrical pulses will be evaluated by measurement of electrically-evoked ABRs, using the same scalp electrodes that are typically used for measurement of sound-evoked ABRs. The cochlear-nerve stimulating electrode will be in place only during the actual intraoperative test. No device will remain in the patient. The intraoperative experimental procedure is not intended to as a therapeutic measure for the patient's VS.