Impact of Motor-Evoked Potential Monitoring on Facial Nerve Outcomes after Vestibular Schwannoma Resection

Abstract

Objectives: Assess the utility of intraoperative transcranial facial motor-evoked potential (FMEP) monitoring in predicting and improving facial function after vestibular schwannoma (VS) resection. Study Design: Retrospective chart review. Methods: Data were obtained from 82 consecutive VS resections meeting inclusion criteria. Sixty-two cases were performed without FMEP and 20 with FMEP. Degradation of FMEP response was defined as a final-to-baseline amplitude ratio of 0.5 or less. House-Brackmann (HB) grade was assessed preoperatively, postoperatively, at follow-up assessments, and it was compared between pre-and post-FMEP cohorts. Positive predictive value (PPV) and negative predictive value (NPV), sensitivity, and specificity of FMEP degradation in predicting facial weakness were calculated. Results: In the pre-FMEP group, at length of follow-up (LOF) ⩾9 months, 83.9% (52/62) of patients exhibited HB 1-2 outcome. In the post-FMEP cohort, 75.0% (15/20) exhibited HB 1-2 function at LOF ⩾9 months. There was no difference in rates of HB 1-2 outcomes between groups in the immediate postoperative period (P = .35) or at long-term follow-up (P = 1.0). With respect to predicting immediate postoperative facial function, FMEP demonstrated high specificity (88.9%) and moderate sensitivity (54.5%). The PPV and NPV for immediate postoperative facial function were 85.7% and 61.5%, respectively. With respect to long-term (⩾9 months LOF) facial function, intraoperative FMEP was moderately sensitive (71.4%) and highly specific (84.6%); PPV was moderate (71.4%), and NPV was high (84.6%). Conclusions: Intraoperative FMEP is highly specific and moderately sensitive in predicting postoperative facial function for patients undergoing VS resection, but its use may not be associated with improved facial nerve outcomes.

Sensitivity and Negative Predictive Value of Motor Evoked Potentials of the Facial Nerve

“…Sensitivity and negative predictive values were found to be higher than those reported recently by Tawfik et al 19 This observation can be explained by the fact that a single alarm criterion was applied across different lesion types. This criterion The numbers of true positive (TP; permanent MEP decrease above that threshold at the end of resection and new deficits), true negative (TN; MEP decrease under that threshold at the end of resection and no deficit), and false negative (FN; MEP decrease under that threshold at the end of resection but new deficits) are indicated with sensitivity (TP/(TP þ FN)) and with negative predictive value (TN/(TN þ FN)).…”

“…This alarm criterion could have led to a lower sensitivity, with FN cases, and could have contributed to the conclusion that neuromonitoring did not decrease the rate of facial nerve deterioration. 19 Seidel et al 16 reported a low complication rate using continuous direct electrical stimulation during the resection of vestibular schwannomas. In the present series, direct electrical stimulation was usually performed temporarily and was not always done before the observation of MEP decreases.…”

“…A 50% decrease in MEP amplitude has been reported as reliable in some studies 17,18 but not strict enough in others. [19][20][21] In this context, the objective of this retrospective study was to analyze the validity of the alarm criterion applied at the time of surgery, that is, a reproducible 50% decrease in MEP amplitude in neurosurgeries performed for vestibular schwannomas or for other lesions of the cerebellopontine angle.…”

Therapy of Sporadic and NF2-Related Vestibular Schwannoma

“…Function preservation of surrounding structures and mainly the 7 th nerve is an important part of VS surgery. The surgical outcome in sporadic VS is associated with the following factors: tumor size, adhesion to the brainstem and CNs, the use of CN monitoring technology and surgeon's experience [64][65][66][67][68][69]. Surgical treatments include subtotal resection (STR), near-total resection (NTR) and total resection [70].…”

Delayed Facial Nerve Palsy Following Resection of Vestibular Schwannoma: Clinical and Surgical Characteristics

“…The introduction of intraoperative facial electromyographic (EMG) recordings has allowed the surgeon to monitor FN function during surgery and better accomplish an atraumatic dissection. A robust FN response to direct stimulation has been associated with excellent postoperative FN function, although precise metrics have yet to be defined and this phenomenon is sparsely described with relation to DFNP (6,9,12,14,(24)(25)(26).…”