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Published on: November 1, 2024
A novel method in predicting immediate postoperative facial nerve function post acoustic neuroma excision
Vincent Y W Lin1, David Houlden, Allison Bethune
1Department of Otolaryngology-Head and Neck Surgery, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada. vincent.lin@sunnybrook.ca
Summary
Facial nerve function after acoustic neuroma surgery can be predicted by comparing direct stimulation response amplitude to transcutaneous stimulation amplitude. Higher percentages and amplitude progression indicate better immediate postoperative facial nerve outcomes.
Area of Science:
- Neurosurgery
- Nerve Monitoring
- Facial Nerve Function
Background:
- Acoustic neuroma surgery requires precise facial nerve preservation.
- Intraoperative facial nerve monitoring is crucial for predicting postoperative function.
Purpose of the Study:
- To evaluate the predictive value of facial nerve stimulation response amplitude ratios and progression for immediate postoperative facial nerve function (House-Brackmann Grade 1 or 2) after acoustic neuroma surgery.
Main Methods:
- Intraoperative recordings of frontalis, orbicularis oculi, and orbicularis oris muscles.
- Direct facial nerve stimulation at the pontomedullary junction and transcutaneous stimulation at the stylomastoid region were performed.
- Response amplitudes were analyzed to calculate ratios and assess progression with increasing stimulus intensities.
Main Results:
- A compound action potential >50% of maximum showed a 93% positive predictive value for normal/near-normal function.
- Amplitude increase >5 microV had a 77% positive predictive value and 87% sensitivity.
- Stimulus intensity of 0.3 mA at the root exit zone with >20% compound action potential yielded 81% positive predictive value and 81% sensitivity.
Conclusions:
- The ratio of direct pontomedullary junction stimulation response amplitude to maximal stylomastoid stimulation response amplitude predicts immediate postoperative facial nerve function.
- Response amplitude progression with increasing stimulus intensity also serves as a reliable predictor of normal to near-normal facial nerve function.
