Continuous Facial Nerve Stimulating Burr for Otologic Surgeries

Abstract

To evaluate a continuous facial nerve (FN) stimulating burr (the StimBurGard) during otologic/neurotologic procedures in terms of safety and reliability when drilling in contact with the Fallopian canal (FC) of the mastoid segment of the FN. Prospective clinical trial. Tertiary referral center. Thirty-five patients operated through translabyrinthine (TL) approach for vestibular schwannoma removal were divided into 3 groups. Group 1 (5 patients): the stimulation current was set at 3 and then at 2 mA visualizing the localization of the burr when the first response at 100-μV threshold was obtained in the mastoid cavity. Group 2 (15 patients): exposure of the FC in the mastoid segment during TL approach was stopped when the first response was obtained at 1-mA stimulation; FC thickness in the second genu and mastoid segment of the FC was evaluated on a postoperative computed tomographic (CT) scan, and FC dehiscence observed on CT scan was compared with surgical observation. Group 3 (15 patients), exposure of the FC was performed as routinely done during a TL approach and surgical observation of FC dehiscence; stimulation values in mA at the 100 μV threshold and FC thickness on postoperative CT scan were evaluated. In all cases, the stimulation value at the cerebellopontine angle root of the FN with a 100-μV response threshold was measured before tumor resection. Group 1: stimulation at 3 mA occurred in aditus ad antrum and at 2 mA near the FC. Group 2: mean thickness of 1.09 ± 0.69 mm with 2 cases of radiologic dehiscence of the FN. Group 3: the stimulation threshold was 0.6 ± 0.37 mA, and the thickness was 0.41 ± 0.56 mm with 9 cases of uncovered FN (p = 0.0082). In all patients, FN at brainstem was stimulated at 0.03 mA before VS dissection. Continuous FN stimulating burr by means of the StimBurGard system is a safe and effective tool for FN stimulation and identification. The integrity of FC is preserved in most cases when the stimulation intensity is 1 mA.