Facial Nerve Monitoring Parameters As a Predictor of Postoperative Facial Nerve Outcomes after Vestibular Schwannoma Resection

Objective: To evaluate whether the intraoperative stimulus threshold and response amplitude measurements from facial electromyography can predict facial nerve function at 1 year after vestibular schwannoma resection. Study Design: Prospective study. Setting: Tertiary academic center. Patients: Seventy-four consecutive vestibular schwannoma patients. Intervention: The minimal stimulus intensity (in milliamperes) and electromyographic response amplitude (in microvolts) were recorded during stimulation applied to the proximal facial nerve after vestibular schwannoma removal. Main Outcome Measure: Facial nerve outcomes at 1 year were evaluated using the House-Brackmann scale. Analysis was then performed to evaluate whether these electrophysiologic recordings and tumor size could predict facial nerve functional outcomes. Results: Of the 74 patients, 66 of 74 (89%) had House-Brackmann Grade I or II facial nerve function and 8 of 74 (11%) had House-Brackmann Grade III-VI function at 1 year after surgery. If standards were set for intraoperative minimal stimulus intensity of 0.05 mA or less and response amplitude of 240 μV or greater, the authors were able to predict a House-Brackmann Grade I or II outcome in 56 of 66 (85%) patients at 1 year after surgery. With these same electrophysiologic parameters, only 1 of 8 (12%) House-Brackmann Grade III-VI patients also met this standard and thus gave a false-positive result. Logistic regression analysis of the data showed that both a stimulus threshold of 0.05 mA or less and a response amplitude of 240 μV or greater predicted a House-Brackmann Grade I or II outcome with a 98% probability. However, stimulus threshold or response amplitude alone had a much lower probability of the same result. In addition, although tumor size was found to independently predict facial nerve outcomes at 1 year, it did not improve the ability to predict facial nerve function over a model using stimulus intensity and amplitude alone. Conclusion: Individually, minimal stimulus intensity or response amplitude was less successful in predicting long-term postoperative facial nerve function. However, if both parameters are considered together, the study demonstrates that they are good prognostic indicators for facial nerve function at 1 year after surgery.

[1]  N. Surgery [Facial nerve grading system]. , 2006, Zhonghua er bi yan hou tou jing wai ke za zhi = Chinese journal of otorhinolaryngology head and neck surgery.

[2]  H. Winn,et al.  Delayed facial palsy after resection of vestibular schwannoma. , 2002, Journal of neurosurgery.

[3]  O. Sterkers,et al.  Predictive Factors of Long-term Facial Nerve Function after Vestibular Schwannoma Surgery , 2002, Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology.

[4]  Toshimitsu Kobayashi,et al.  Electromyographic Evaluation of Facial Nerve Damage in Acoustic Neuroma Surgery , 2001, Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology.

[5]  C. Strauss,et al.  Continuous electromyography monitoring of motor cranial nerves during cerebellopontine angle surgery. , 2000, Journal of neurosurgery.

[6]  P. Garrud,et al.  Impact of Facial Paralysis on Patients With Acoustic Neuroma , 2000, The Laryngoscope.

[7]  J. Helms,et al.  Quantitative parameters of intraoperative electromyography predict facial nerve outcomes for vestibular schwannoma surgery. , 2000, Neurosurgery.

[8]  R. Ramsden,et al.  Assessment of real-time clinical facial function during vestibular schwannoma resection. , 2000, The Laryngoscope.

[9]  J. Fenton,et al.  Prediction of postoperative facial nerve function in acoustic neuroma surgery. , 1999, Clinical otolaryngology and allied sciences.

[10]  K. Uemura,et al.  Intraoperative evoked facial muscle responses and recovery process of the facial nerve in acoustic neuroma surgery. , 1999, British journal of neurosurgery.

[11]  G. Magliulo,et al.  Facial nerve function after cerebellopontine angle surgery and prognostic value of intraoperative facial nerve monitoring: a critical evaluation. , 1998, American journal of otolaryngology.

[12]  D. Welling,et al.  Clinical Manifestations of Mutations in the Neurofibromatosis Type 2 Gene in Vestibular Schwannomas (Acoustic Neuromas) , 1998, The Laryngoscope.

[13]  L. Pitts,et al.  Comparison of response amplitude versus stimulation threshold in predicting early postoperative facial nerve function after acoustic neuroma resection. , 1998, The American journal of otology.

[14]  G. Schackert,et al.  Intraoperative Facial Nerve Monitoring (IFNM) Predicts Facial Nerve Outcome after Resection of Vestibular Schwannoma , 1998, Acta Neurochirurgica.

[15]  Y. Inoue,et al.  Aetiology of Delayed Facial Palsy after Vestibular Schwannoma Surgery: Clinical Data and Hypothesis , 1998, Acta Neurochirurgica.

[16]  D. Long,et al.  Facial nerve injury in acoustic neuroma (vestibular schwannoma) surgery: etiology and prevention. , 1997, Journal of neurosurgery.

[17]  M. McKenna,et al.  Delayed facial paralysis after acoustic neuroma surgery: factors influencing recovery. , 1996, The American journal of otology.

[18]  J. Kartush,et al.  Delayed facial palsy after acoustic neuroma resection: the role of viral reactivation. , 1996, The American journal of otology.

[19]  S. E. Børgesen,et al.  Cystic acoustic neuromas. Results of translabyrinthine surgery. , 1994, Archives of otolaryngology--head & neck surgery.

[20]  L. Pitts,et al.  Facial Nerve Outcome after Acoustic Neuroma Surgery: A Study from the Era of Cranial Nerve Monitoring , 1994, Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery.

[21]  H. Silverstein,et al.  Intraoperative facial nerve monitoring in acoustic neuroma surgery. , 1993, The American journal of otology.

[22]  N. Cohen,et al.  Intraoperative Monitoring of Facial Nerve Function in Cerebellopontine Angle Surgery , 1990, Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery.

[23]  W. Panje,et al.  Free gastroomental flap for head and neck reconstruction: assessment in an animal model. , 1989, American journal of otolaryngology.

[24]  M. Graham,et al.  Neurophysiologic intraoperative monitoring: II. Facial nerve function. , 1989, The American journal of otology.

[25]  J. Daube,et al.  Improved preservation of facial nerve function with use of electrical monitoring during removal of acoustic neuromas. , 1987, Mayo Clinic proceedings.