Blink Reflex for Facial Nerve Monitoring: A Feasibility Study

Background: Facial nerve preservation remains a challenge during cerebellopontine angle (CPA) surgery, especially vestibular schwannoma resection. The reliability of using the blink reflex to guide surgical resection and its prognostic role in facial nerve outcomes remains uncertain. In this study, we assess the feasibility of using blink reflex for intraoperative facial nerve monitoring in patients undergoing translabyrinthine resection of vestibular schwannomas.

Methods: Twelve patients with presumed vestibular schwannomas who underwent translabyrinthine resection were included in the study. A standardized facial nerve monitoring setup that has been tested and refined by our neuromonitoring team was used. The first stimulating electrode was placed over the supraorbital foramen, the second stimulating electrode was placed ~1 cm superior to it. Two recording electrodes were used. An active recording electrode was placed subdermally in the orbicularis oculi muscle directly below the pupil and a reference electrode was placed next to the lateral canthus. The early component of evoked action potential responses (R1), which represents the disynaptic pathway between the main sensory nucleus of the trigeminal nerve and the ipsilateral facial nucleus, was recorded at baseline and throughout the surgery for each patient for both the ipsilateral and contralateral sides of the surgery. A stimulus train of 4 to 7 individual pulses was used to elicit a response with a pulse duration of 200 to 400 ms, inter-pulse duration of 0.5 to 2 ms, and intensity of 40 to 80 mA. Facial nerve function was assessed with the House-Brackmann (HB) grading system postoperatively.

Results: Baseline R1 responses were reliably obtained in 11/12 patients for the ipsilateral side of the surgery and 9/12 for the contralateral side. In the remaining patients, the R1 response was present but variable. In 8/12 patients, ipsilateral R1 response remained stable throughout the case, in 3 patients there was an ipsilateral decrease in R1 response amplitude at the end of the case, while the contralateral side was stable. In one patient the amplitude decreased bilaterally, this was considered a technical issue as facial nerve function was stable postoperatively. Postoperative HB score was stable in 8/12 patients. Four patients had postoperative deficits (HB score of II in three patients, HB of V in one patient). In patients with postoperative facial nerve deficit, three had decreased ipsilateral R1 response amplitude at the end of the case. The remaining patient had a stable R1 response bilaterally and a facial nerve triggered EMG response of 300 μV at an intensity of 0.05 mA at the end of the case.

Conclusions: The study demonstrates the feasibility of recording blink reflex reliably intraoperatively and opens the potential for neuromonitoring of blink reflex during vestibular schwannoma surgery. Blink reflex can provide feedback without interruption of surgery as opposed to direct stimulation. Further studies are needed to determine the prognostic role of the blink reflex in predicting postoperative facial nerve function, especially as compared with triggered EMG.

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Artikel online veröffentlicht:
01. Februar 2023