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Zohdy YM, Alawieh AM, Bray D, Pradilla G, Garzon-Muvdi T, Ashram YA. An Artificial Neural Network Model for Predicting Postoperative Facial Nerve Outcomes After Vestibular Schwannoma Surgery. Neurosurgery 2024; 94:805-812. [PMID: 37962366 DOI: 10.1227/neu.0000000000002757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Accepted: 09/25/2023] [Indexed: 11/15/2023] Open
Abstract
BACKGROUND AND OBJECTIVES The emergence of machine learning models has significantly improved the accuracy of surgical outcome predictions. This study aims to develop and validate an artificial neural network (ANN) model for predicting facial nerve (FN) outcomes after vestibular schwannoma (VS) surgery using the proximal-to-distal amplitude ratio (P/D) along with clinical variables. METHODS This retrospective study included 71 patients who underwent VS resection between 2018 and 2022. At the end of surgery, the FN was stimulated at the brainstem (proximal) and internal acoustic meatus (distal) and the P/D was calculated. Postoperative FN function was assessed using the House-Brackmann grading system at discharge (short-term) and after 9-12 months (long-term). House-Brackmann grades I-II were considered good outcome, whereas grades III-VI were considered fair/poor. An ANN model was constructed, and the performance of the model was evaluated using the area under the ROC curve for internal validation and accuracy, sensitivity, specificity, and positive and negative predictive values for external validation. RESULTS The short-term FN outcome was grades I-II in 57.7% and grades III-VI in 42.3% of patients. Initially, a model using P/D had an area under the curve of 0.906 (internal validation) and an accuracy of 89.1% (95% CI: 68.3%-98.8%) (external validation) for predicting good vs fair/poor short-term FN outcomes. The model was then refined to include only muscles with a P/D with a proximal latency between 6 and 8 ms. This improved the accuracy to 100% (95% CI: 79%-100%). Integrating clinical variables (patient's age, tumor size, and preoperative HB grade) in addition to P/D into the model did not significantly improve the predative value. A model was then created to predict the long-term FN outcome using P/D with latencies between 6 and 8 ms and had an accuracy of 90.9% (95% CI: 58.7%-99.8%). CONCLUSION ANN models incorporating P/D can be a valuable tool for predicting FN outcomes after VS surgery. Refining the model to include P/D with latencies between 6 and 8 ms further improves the model's prediction. A user-friendly interface is provided to facilitate the implementation of this model.
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Affiliation(s)
- Youssef M Zohdy
- Department of Neurosurgery, Emory University, Atlanta , Georgia , USA
| | - Ali M Alawieh
- Department of Neurosurgery, Emory University, Atlanta , Georgia , USA
| | - David Bray
- Department of Neurosurgery, Emory University, Atlanta , Georgia , USA
| | - Gustavo Pradilla
- Department of Neurosurgery, Emory University, Atlanta , Georgia , USA
| | | | - Yasmine A Ashram
- Department of Physiology, Faculty of Medicine, Alexandria University, Alexandria , Egypt
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Torres-Carretero L, Otero-Rodríguez Á, Alejos-Herrera MV, Vázquez-Casares G, García-Martín A, Garrido-Ruiz PA. [Utility of the intraoperative neurophysiological monitoring as a prognostic value of postoperative facial paresis in vestibular schwannomas]. NEUROCIRUGIA (ENGLISH EDITION) 2023; 34:238-246. [PMID: 36931931 DOI: 10.1016/j.neucie.2022.09.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Accepted: 09/07/2022] [Indexed: 03/17/2023]
Abstract
BACKGROUND AND OBJECTIVE Intraoperative neurophysiological monitoring allows us to predict the functional status of the facial nerve after vestibular schwannoma surgery. Due to the great variability of the neurophysiological protocols used for it, the goal of this study is to determine the prognostic ability of our neurophysiological protocol. MATERIAL AND METHODS We have performed a statistical analysis of the neurophysiological monitoring data collected from patients operated between March 2009 and July 2021 at the Neurosurgery Service of Salamanca according to their functional status, both in the immediate post-surgical period and one year after surgery. RESULTS A number of 51 patients between 46 and 63 years old (median: 54) were analyzed. We have found significant differences studying the threshold value of the stimulation intensity of the facial nerve and the variation of the Cortico-bulbar Evoked Motor Potentials (P=0.043 and P=0.011, respectively) between the patients with good and bad clinical situation after surgery. The most discriminating intensity threshold value was 0.35mA (Sensitivity: 85%; Specificity: 48%). No statistical relationship was found in the study group one year after surgery. CONCLUSIONS Our intraoperative monitoring protocol allows us to predict the clinical situation of patients in the immediate postoperative period and improve information for the patient and her relatives after surgery. We cannot, however, use these parameters to predict the functional situation one year after surgery and make clinical decisions in this regard.
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Affiliation(s)
| | | | | | | | - Andoni García-Martín
- Servicio de Neurocirugía, Hospital Universitario de Salamanca, Salamanca, España
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Rampp S, Holze M, Scheller C, Strauss C, Prell J. Neural networks for estimation of facial palsy after vestibular schwannoma surgery. J Clin Monit Comput 2023; 37:575-583. [PMID: 36333576 PMCID: PMC10068649 DOI: 10.1007/s10877-022-00928-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Revised: 09/22/2022] [Accepted: 10/04/2022] [Indexed: 11/06/2022]
Abstract
PURPOSE Facial nerve damage in vestibular schwannoma surgery is associated with A-train patterns in free-running EMG, correlating with the degree of postoperative facial palsy. However, anatomy, preoperative functional status, tumor size and occurrence of A-trains clusters, i.e., sudden A-trains in most channels may further contribute. In the presented study, we examine neural networks to estimate postoperative facial function based on such features. METHODS Data from 200 consecutive patients were used to train neural feed-forward networks (NN). Estimated and clinical postoperative House and Brackmann (HB) grades were compared. Different input sets were evaluated. RESULTS Networks based on traintime, preoperative HB grade and tumor size achieved good estimation of postoperative HB grades (chi2 = 54.8), compared to using tumor size or mean traintime alone (chi2 = 30.6 and 31.9). Separate intermediate nerve or detection of A-train clusters did not improve performance. Removal of A-train cluster traintime improved results (chi2 = 54.8 vs. 51.3) in patients without separate intermediate nerve. CONCLUSION NN based on preoperative HB, traintime and tumor size provide good estimations of postoperative HB. The method is amenable to real-time implementation and supports integration of information from different sources. NN could enable multimodal facial nerve monitoring and improve postoperative outcomes.
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Affiliation(s)
- Stefan Rampp
- Department of Neurosurgery, University Hospital Halle (Saale), Ernst-Grube Str. 40, 06120, Halle, Germany.
- Department of Neurosurgery, University Hospital Erlangen, Schwabachanlage 6, 91054, Erlangen, Germany.
| | - Magdalena Holze
- Department of Neurosurgery, University Hospital Halle (Saale), Ernst-Grube Str. 40, 06120, Halle, Germany
| | - Christian Scheller
- Department of Neurosurgery, University Hospital Halle (Saale), Ernst-Grube Str. 40, 06120, Halle, Germany
| | - Christian Strauss
- Department of Neurosurgery, University Hospital Halle (Saale), Ernst-Grube Str. 40, 06120, Halle, Germany
| | - Julian Prell
- Department of Neurosurgery, University Hospital Halle (Saale), Ernst-Grube Str. 40, 06120, Halle, Germany
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Gazia F, Callejo À, Pérez-Grau M, Lareo S, Prades J, Roca-Ribas F, Amilibia E. Pre- and intra-operative prognostic factors of facial nerve function in cerebellopontine angle surgery. Eur Arch Otorhinolaryngol 2023; 280:1055-1062. [PMID: 35907000 PMCID: PMC9899719 DOI: 10.1007/s00405-022-07556-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2022] [Accepted: 07/12/2022] [Indexed: 02/07/2023]
Abstract
PURPOSE The study assesses whether pre- and intraoperative factors linked to electromyography and direct electrical stimulation (DES) of facial nerve can predict facial nerve function in the short- (12 days) and long-term (1 year) after cerebellopontine angle (CPA) tumor resection. METHODS 157 patients who underwent surgical resection of CPA tumors with facial nerve monitoring. Pre-operative factors (age, tumor size, pure tone average), surgical time and intra-operative parameters regarding facial function, minimum stimulation threshold (MST), compound muscle action potential (CMAP) and the difference between proximal and distal CMAP (DPDC) were evaluated. RESULTS A correlation between tumor size, MST, CMAP and facial function in both short and long term was found. A higher grade of immediate facial paralysis corresponded to a higher risk of poor outcome after one year. A postoperative House-Brackmann (HB) score of V or VI was correlated with poor outcome in 88.8% and 93.8% of cases. A risk of HB 3 or more, in the long term, was correlated with a tumor size of 20.2 mm. Using an MST of 0.1 mA, for long-term predictions, sensitivity and specificity were 0.62 (95% CI 0.46-0.75) and 0.73 (95% CI 0.61-0.82), respectively. With a CMAP cut-off < 200 µV, for long-term prediction, sensitivity was 0.73 (95% CI 0.53-0.87) and specificity 0.73 (95% CI 0.55-0.85). CONCLUSION The assessment based on the cut-offs described increases the ability to predict facial function. Improving predictive accuracy enables surgeons to address patients' expectations and to establish an intervention timeline for planning facial reanimation.
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Affiliation(s)
- Francesco Gazia
- Department of Otorhinolaryngology, Hospital Universitari Germans Trias i Pujol, Universitat Autònoma de Barcelona (UAB), Carretera del Canyet, Badalona, 08916, Barcelona, Spain
- Unit of Otorhinolaryngology, Department of Adult and Development Age Human Pathology "Gaetano Barresi", University of Messina, Messina, Italy
| | - Àngela Callejo
- Department of Otorhinolaryngology, Hospital Universitari Germans Trias i Pujol, Universitat Autònoma de Barcelona (UAB), Carretera del Canyet, Badalona, 08916, Barcelona, Spain
| | - Marta Pérez-Grau
- Department of Otorhinolaryngology, Hospital Universitari Germans Trias i Pujol, Universitat Autònoma de Barcelona (UAB), Carretera del Canyet, Badalona, 08916, Barcelona, Spain
| | - Susana Lareo
- Department of Otorhinolaryngology, Hospital Universitari Germans Trias i Pujol, Universitat Autònoma de Barcelona (UAB), Carretera del Canyet, Badalona, 08916, Barcelona, Spain
| | - José Prades
- Department of Otorhinolaryngology, Hospital Universitari Germans Trias i Pujol, Universitat Autònoma de Barcelona (UAB), Carretera del Canyet, Badalona, 08916, Barcelona, Spain
| | - Francesc Roca-Ribas
- Department of Otorhinolaryngology, Hospital Universitari Germans Trias i Pujol, Universitat Autònoma de Barcelona (UAB), Carretera del Canyet, Badalona, 08916, Barcelona, Spain
| | - Emilio Amilibia
- Department of Otorhinolaryngology, Hospital Universitari Germans Trias i Pujol, Universitat Autònoma de Barcelona (UAB), Carretera del Canyet, Badalona, 08916, Barcelona, Spain.
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D’Alessandris QG, Menna G, Stifano V, Della Pepa GM, Burattini B, Di Domenico M, Izzo A, D’Ercole M, Lauretti L, Montano N, Olivi A. A Study on the Role of Intraoperative Corticobulbar Motor Evoked Potentials for Improving Safety of Cerebellopontine Angle Surgery in Elderly Patients. Diagnostics (Basel) 2023; 13:diagnostics13040710. [PMID: 36832198 PMCID: PMC9955429 DOI: 10.3390/diagnostics13040710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 02/09/2023] [Accepted: 02/10/2023] [Indexed: 02/16/2023] Open
Abstract
Preservation of facial nerve function (FNF) during neurosurgery for cerebellopontine angle (CPA) tumors is paramount in elderly patients. Corticobulbar facial motor evoked potentials (FMEPs) allow assessment intraoperatively of the functional integrity of facial motor pathways, thus improving safety. We aimed to evaluate the significance of intraoperative FMEPs in patients 65 years and older. A retrospective cohort of 35 patients undergoing CPA tumors resection was reported; outcomes of patients aged 65-69 years vs. ≥70 years were compared. FMEPs were registered both from upper and lower face muscles, and amplitude ratios (minimum-to-baseline, MBR; final-to-baseline, FBR; and recovery value, FBR minus MBR) were calculated. Overall, 78.8% of patients had a good late (at 1 year) FNF, with no differences between age groups. In patients aged ≥70 years, MBR significantly correlated with late FNF. At receiver operating characteristics (ROC) analysis, in patients aged 65-69 years, FBR (with 50% cut-off value) could reliably predict late FNF. By contrast, in patients aged ≥70 years, the most accurate predictor of late FNF was MBR, with 12.5% cut-off. Thus, FMEPs are a valuable tool for improving safety in CPA surgery in elderly patients as well. Considering literature data, we noticed higher cut-off values for FBR and a role for MBR, which suggests an increased vulnerability of facial nerves in elderly patients compared to younger ones.
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Affiliation(s)
- Quintino Giorgio D’Alessandris
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
- Department of Neuroscience, Neurosurgery Section, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Largo Agostino Gemelli, 8, 00168 Rome, Italy
| | - Grazia Menna
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
- Department of Neuroscience, Neurosurgery Section, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Largo Agostino Gemelli, 8, 00168 Rome, Italy
| | - Vito Stifano
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
| | - Giuseppe Maria Della Pepa
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
| | - Benedetta Burattini
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
- Department of Neuroscience, Neurosurgery Section, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Largo Agostino Gemelli, 8, 00168 Rome, Italy
| | - Michele Di Domenico
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
| | - Alessandro Izzo
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
| | - Manuela D’Ercole
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
| | - Liverana Lauretti
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
- Department of Neuroscience, Neurosurgery Section, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Largo Agostino Gemelli, 8, 00168 Rome, Italy
| | - Nicola Montano
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
- Department of Neuroscience, Neurosurgery Section, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Largo Agostino Gemelli, 8, 00168 Rome, Italy
- Correspondence: ; Tel.: +39-0630154120 or +39-0630154358; Fax: +39-063051343
| | - Alessandro Olivi
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, 00168 Rome, Italy
- Department of Neuroscience, Neurosurgery Section, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Largo Agostino Gemelli, 8, 00168 Rome, Italy
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Torres-Carretero L, Otero-Rodríguez Á, Alejos-Herrera MV, Vázquez-Casares G, García-Martín A, Garrido-Ruiz PA. Utilidad de la monitorización neurofisiológica intraoperatoria como valor pronóstico de la parálisis facial posquirúrgica en schwannomas vestibulares. Neurocirugia (Astur) 2022. [DOI: 10.1016/j.neucir.2022.09.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Della Pepa GM, Stifano V, D'Alessandris QG, Menna G, Burattini B, Di Domenico M, Izzo A, D'Ercole M, Lauretti L, Olivi A, Montano N. Intraoperative Corticobulbar Motor Evoked Potential in Cerebellopontine Angle Surgery: A Clinically Meaningful Tool to Predict Early and Late Facial Nerve Recovery. Neurosurgery 2022; 91:406-413. [PMID: 35612564 DOI: 10.1227/neu.0000000000002039] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Accepted: 04/03/2022] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Intraoperative neuromonitoring is crucial for facial nerve preservation in cerebellopontine angle (CPA) surgery. Among the available techniques, the role of intraoperative corticobulbar facial motor evoked potentials (FMEPs) is unclear. OBJECTIVE To evaluate the significance of intraoperative FMEPs as indicators for early and late postoperative facial nerve function (FNF) in CPA tumor resection and the feasibility of their integration with standard monitoring techniques. METHODS An institutional series of 83 patients who underwent surgery under intraoperative monitoring for CPA extra-axial tumor resection was reported. A pair of needle electrodes was used to record FMEP from orbicularis oculi (OOc) and orbicularis oris (OOr) muscles at baseline, at the end of surgery and minimum values recorded. From FMEP amplitudes, minimum-to-baseline amplitude ratio (MBR), final-to-baseline amplitude ratio (FBR), and recovery value, intended as FBR minus MBR, were calculated. These indices were correlated with early and late postoperative FNF. RESULTS Our analysis demonstrated that higher FBR (both from OOc and OOr) and MBR (from OOr only) were associated with a good early and late FNF; a higher MBR from OOc was significantly associated with a good late FNF. The most accurate index in predicting early FNF was FBR measured from OOr with a cutoff of 35.56%, whereas the most accurate index in predicting late FNF was FBR as measured from OOc with a cutoff of 14.29%. CONCLUSION Our study confirmed that FMEPs are reliable predictors of early and late postoperative FNF in CPA surgery and could be easily integrated with standard intraoperative neuromonitoring techniques.
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Affiliation(s)
- Giuseppe Maria Della Pepa
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Vito Stifano
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Quintino Giorgio D'Alessandris
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Grazia Menna
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy.,Department of Neuroscience, Neurosurgery Section, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Benedetta Burattini
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy.,Department of Neuroscience, Neurosurgery Section, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Michele Di Domenico
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Alessandro Izzo
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Manuela D'Ercole
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Liverana Lauretti
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy.,Department of Neuroscience, Neurosurgery Section, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Alessandro Olivi
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy.,Department of Neuroscience, Neurosurgery Section, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Nicola Montano
- Department of Neurosurgery, Fondazione Policlinico Universitario A. Gemelli IRCCS, Università Cattolica del Sacro Cuore, Rome, Italy.,Department of Neuroscience, Neurosurgery Section, Università Cattolica del Sacro Cuore, Rome, Italy
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Arlt F, Kasper J, Winkler D, Jähne K, Fehrenbach MK, Meixensberger J, Sander C. Facial Nerve Function After Microsurgical Resection in Vestibular Schwannoma Under Neurophysiological Monitoring. Front Neurol 2022; 13:850326. [PMID: 35685739 PMCID: PMC9170892 DOI: 10.3389/fneur.2022.850326] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Accepted: 04/11/2022] [Indexed: 11/30/2022] Open
Abstract
Background The use of intraoperative neurophysiological monitoring, including direct nerve stimulation (especially the facial nerve), acoustic evoked potentials (AEP) and somatosensory evoked potentials (SSEP), is a helpful tool in the microsurgery of vestibular schwannoma to prevent nerve injury. Patient characteristics and intraoperative and postoperative variables might also influence the postoperative facial nerve function. The study was performed to investigate these variables and the intraoperative neurophysiological monitoring values. Methods Seventy-nine patients with vestibular schwannoma were included consecutively into this study. Intraoperative neurophysiological monitoring, including SSEP, AEP, and direct nerve stimulation for facial and trigeminal nerve electromyography, was performed utilizing digital data storage in all cases. The intensity (in volts) of the direct stimulation and the latency (in ms) for the orbicularis oculi and the orbicularis oris muscle and the amplitude (in mV) was measured. Univariate and multivariate statistical analyses concerning the different parameters was performed directly after the operation and in the subsequent follow-ups 3 and 6 months after the operation. Results The mean intensity was 0.79 V (SD.29). The latency and amplitude for the oris muscle was 5.2 ms (SD 2.07) and 0.68 mV (SD.57), respectively. The mean latency for the occuli muscle was 5.58 ms (SD 2.2) and the amplitude was 0.58 mV (SD 1.04). The univariate and multivariate statistical analyses showed significance concerning the postoperative facial nerve function and the amplitude of the direct stimulation of the facial nerve in the orbicularis oris muscle (p = 0.03), so repeated direct nerve stimulation might show FN function deterioration. The mean diameter of the tumors was 24 mm (range 10–57 mm). Cross total resection and near total was achieved in 76 patients (96%) and subtotal in three patients (4%). The preoperative House–Brakeman score (HBS) 1 was constant in 65 (82%) cases. The mortality in our series was 0%; the overall morbidity was 10%. The HBS was not influenced concerning the extent of resection. The mean follow-up was 28 months (range 6 to 60 months). The limitations of the study might be a low number of patients and the retrospective character of the study. Conclusion Intraoperative neurophysiological monitoring is crucial in vestibular schwannoma surgery. Repeated direct nerve stimulation and a detected decreased amplitude might show facial nerve function deterioration.
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