Intraoperative corticobulbar motor evoked potentials reliably predict facial nerve function in elderly patients with cerebellopontine angle tumors. a clinical and neurophysiology study

Abstract BACKGROUND Cerebellopontine angle (CPA) surgery for extra-axial lesions in elderly patients could be hampered by concerns regarding functional outcomes. However, an overall ageing society warrants an improved approach. Intraoperative neuromonitoring is crucial for facial nerve (FN) preservation: intraoperative cortico-bulbar facial motor evoked potentials (FMEPs) can be effectively coupled to standard techniques. In a previous work, we validated the use of FMEPs as preditors of early and late post-operative FN function (FNF). Aim of this study was to re-evaluate FMEP role in patients beyond 65 years of age. METHODS An institutional series of 83 patients was reported. A pair of needle electrodes was used to record FMEP from orbicularis oculi (OOc) and orbicularis oris (OOr) muscles; baseline, final and minimum values were recorded. From FMEP amplitudes, minimum-to-baseline (MBR) and final-to-baseline (FBR) amplitude ratios, and recovery value (RV=FBR-MBR), were calculated. These indices were correlated to early (at discharge) and late (at 1-year) post-operative FNF. RESULTS 23 (27.7%) patients were older than 65 years. Among these, 52.2% and 81% had a good early and late FNF, respectively. Early and late FNF were not associated to age (p > 0.99 and p=0.72, respectively). In elderly patients, higher FBR (from OOc and OOr) and MBR (from OOc) were associated to a good early FN recovery (p=0.01, p=0.009, and p=0.03, respectively). Conversely, MBR from OOr was the only parameter significantly associated with late FN function (p=0.049). ROC analysis confirmed that, in elderly patients, the most accurate index for predicting late FN function was MBR as measured from OOr (AUC=0.869, cut-off value 12.5%). The most accurate index for predicting early FN function was FBR from OOc (AUC=0.865). CONCLUSION Cortico-bulbar FMEPs are reliable predictors of early and late post-operative FNF in elderly patients and allow a safe and feasible surgery in this important cohort.