Continuous Facial Nerve Monitoring Research Articles

[Intraoperative Neuromonitoring in Vestibular Schwannoma Surgery].

Vestibular schwannoma surgery necessitates intraoperative neuromonitoring to secure long-term tumor control by sufficient tumor removal and preservation of neural function. Therein, facial nerve function can be assessed in real-time and quantitatively by intraoperative continuous facial nerve monitoring with repetitive direct stimulation. The ABR and, further, CNAP, are closely monitored for the continuous assessment of the hearing function. In addition, the evoked masseter and extraocular electromyograms, SEP, MEP, and neuromonitoring of the lower cranial nerves are implemented as needed. In this article, we introduce our neuromonitoring techniques during vestibular schwannoma surgery with an illustrative video.

Extradural Transjugular Transsigmoid Approach with High Cervical Exposure for Glomus Jugulare Tumor.

Surgical removal of glomus jugulare tumors is challenging owing to the complex anatomy of the temporal bone and craniocervical region, aggressive tumor invasion into the nearby structures, and their hypervascularity. However, recent advances in skull base techniques, intraoperative neuromonitoring, and radiological interventions have enabled their relatively safe resection, while giving priority to functional preservation. This video demonstrates a case of a glomus jugulare tumor treated by the extradural transjugular transsigmoid approach with high-cervical exposure and tympamoplasty, after preoperative embolization. A 47-year-old woman presented with progressive hearing disturbance, pulsatile tinnitus, and hemifacial spasm. Neuroimaging displayed a hypervascular tumor occupying the temporal bone, extending to the cervical region through the jugular foramen, and to the external auditory canal. Preoperative feeder occlusion was successfully performed without any additional symptoms, while carefully evaluating the provocative test. Near-total resection of the tumor was achieved through the transjugular transsigmoid approach with high-cervical exposure under detailed neuromonitoring, including continuous facial nerve monitoring and auditory brainstem response. In this patient, in whom the tumor did not invade intradurally and the sigmoid sinus was already occluded preoperatively, the sinus was managed only by coagulation, to avoid unnecessary dural opening and the risk of cerebrospinal fluid leakage. Anterior facial nerve rerouting was not required since the tumor removal was accomplished through the corridor above and below the fallopian bridge. The patient had no new neurological deficits, and her pulsatile tinnitus and hemifacial spasm disappeared after the surgery. Her hearing disturbance improved postoperatively. The link to the video can be found at: https://youtu.be/gqf3dxHlv_0 .

Hearing preservation in vestibular schwannoma surgery via retrosigmoid transmeatal approach.

Advances in various diagnostic and/or treatment modalities, including radiological imaging, neuromonitoring, and microsurgical techniques, have resulted in treatments of vestibular schwannomas being aimed at preserving facial and hearing functions while achieving optimal tumor control. We describe our surgical technique for hearing preservation in vestibular schwannoma surgery. The retrosigmoid transmeatal approach under continuous neuromonitoring (auditory brainstem response, cochlear nerve action potentials, and continuous facial nerve monitoring) enables gross-total resection of vestibular schwannomas, while preserving hearing and facial functions. Radiological assessment and microsurgical techniques, such as meticulous tumor dissection, are also essential for functional preservation with sufficient tumor removal.

Minimally Invasive Approach for Resection of Masseteric Vascular Malformations.

Vascular malformations (VMs) in the head and neck region often cause esthetic as well as functional problems for patients. Intramuscular VMs (IVM), such as those in the masseter, can cause severe facial asymmetry and typically are excised transcutaneously to facilitate wide exposure and safe dissection from the facial nerve. This requires extensive dissection, prolonged healing, and can lead to suboptimal facial scarring. We describe the technique of resecting large IVMs of the masseter muscle in 3 patients using an entirely intraoral approach with continuous nerve monitoring and without visible facial scarring or secondary deformity. Preoperative injection of sclerotherapy was performed to reduce intra-operative bleeding and optimize resection. Successful excision was performed without complication in 3 patients to date. Total average operating room time was 120 minutes (range 95-145 minutes). Estimated blood loss was 213 mL (range 180-240 mL). The patients were discharged home either post-operative day (POD) 1 or 2, with 1 returning to work POD 4. Facial nerve function was normal postoperatively and no hematomas developed. Subjective masticatory function was equivalent to preoperative levels in all patients. Intraoral excision of VMs of the masseter muscle can be safely performed without added risk or complication. Continuous facial nerve monitoring allows minimally invasive approaches to be considered with less risk of iatrogenic facial nerve injury. We purport that this is a safe and effective method with substantially better esthetic outcomes compared with traditional transcutaneous approaches.

The Method for Placement of an Intraoperative Continuous Facial Nerve Stimulating Electrode in Acoustic Neuroma Surgery: Technical Note.

Preservation of facial nerve (FN) function is the most important goal in acoustic neuroma (AN) surgery. We have been using intraoperative continuous facial nerve monitoring (ICFNm) of evoked electromyography during AN surgery. ICFNm is very useful, and we can identify the real-time functions of the FN. Some surgeons have experienced difficulty with placing the ICFN stimulating electrode (SE). We therefore show how to place the ICFN SE. We mostly perform AN surgery with a retrosigmoid approach (RSA). A craniotomy with four burr holes is performed. We dissect the arachnoid membrane along the accessory nerve from the cisterna magna to the glossopharyngeal nerve. When we are able to identify the root exit zone (REZ) of the FN near the brainstem, we place the ICFN SE on it. However, when a large tumor covers the REZ, we have to debulk the tumor to create a space between the tumor and the glossopharyngeal nerve. After that, we can place the SE on the REZ. A method for placement of the ICFN SE is needed for some techniques of AN surgery. Once we learn how to place the SE, we can identify continuous FN function during AN surgery. This method is useful for the preservation of postoperative FN function in AN surgery.

Surgical Management of Internal Auditory Canal and Cerebellopontine Angle Facial Nerve Schwannoma

To investigate the long-term patient outcomes after tumor debulking for internal auditory canal facial schwannoma (FNS). Retrospective case review. Tertiary referral center. Patients operated on between 1998 and 2010 for a preoperative diagnosis of vestibular schwannoma with the intraoperative identification FNS instead. Diagnostic and therapeutic. House-Brackmann facial nerve score immediately and at long-term follow-up (>1 yr); recurrence of tumor. Sixteen patients were identified who were presumed to have vestibular schwannoma but intraoperatively were diagnosed with facial nerve schwannoma. Eleven underwent debulking surgery (67%-99% tumor removal), 2 underwent decompression only, 2 were diagnosed with nervus intermedius tumors and had total tumor removal with preservation of the motor branch of cranial nerve VII, and 1 had complete tumor removal with facial nerve grafting. Five of 11 debulking patients underwent the middle cranial fossa approach for tumor removal; the remainder had translabyrinthine resections. One debulking patient was lost to follow-up. Nine of 10 patients with long-term follow-up had House-Brackmann Grade I or II facial function. One patient had recurrence of the tumor that required revision surgery with total removal and facial nerve grafting. Tumor debulking for FNS provides an opportunity for tumor removal and excellent facial nerve function. Continuous facial nerve monitoring is vital for successful debulking surgery. FNS debulking is feasible via the middle cranial fossa approach. Serial postoperative imaging is warranted to monitor for recurrence.

Intraoperative real-time continuous facial nerve monitoring in acoustic neuroma surgery

Dear Editor: We were very pleased to read the letter to the editor from Acioly et al. They estimated the intraoperative continuous monitoring of evoked facial nerve electromyograms we reported [1] as "a new device for an old concept," and we agree with their assessment. Because the first step for starting continuous monitoring of the facial nerve is to identify the root exit zone (REZ), the authors expressed concern about a case in which a large acoustic neuroma obstructed the REZ of the facial nerve because of anatomical distortion of the brainstem. In Kohno's experience, there have been only four cases (0.7%) out of 550 surgically treated patients with acoustic neuromas, in which he could not identify the REZ of the facial nerve, a very low percentage despite the fact that large tumors (Koos 3 and 4) account for 84% of cases. For a large tumor, internal decompression of the tumor is necessary to find the REZ of the facial nerve. Until we start continuous monitoring, we can notice that the facial nerve is mechanically stimulated by the free-running spontaneous facial electromyography. Therefore, we do not consider the possibility of facial nerve impairment before starting continuous monitoring. An important part of developing new surgical methodologies is to keep them simple, effective and easy to perform. For a new method to become popular and widely used over time, however, certain techniques and tips are required for every operation in the neurosurgical field. In particular with acoustic neuroma surgery, all neurosurgeons know that individual technique and experience must be considered. The authors express concern about movement of the electrode for continuous stimulation; however, we actually replace it at most twice or three times in a surgery, with minimum adjustment within a minute. To be sure, there are tips for stabilizing the electrode to prevent movement. As we described in our paper, we use a small cotton pad to fix the electrode in place. The authors also refer to the necessity of placing recording needle electrodes on three muscles (frontalis, orbicularis oculi and oris). Actually, electromyograms from three muscles vary in initial voltages and intraoperative changes, and there is the possibility that problems with a needle electrode or an electrical cord might occur. Therefore, we believe that setting recording electrodes on all of these three muscles is effective and necessary. The monitoring by transcranial facial motor-evoked potentials (FMEP), which is recommended by Alcioly et al., is surely effective, particularly until the surgeon finds the REZ of the facial nerve. However, body movement at electrical stimulation is considered a problem. In FMEP, as they point out, it is necessary to stop microsurgical procedures to record electromyograms from the viewpoint of safety. We consider FMEP to be a different type of monitoring compared to our method, which allows us to assess the condition of the facial nerve continuously during the process of dissecting the tumor from the facial nerve in real-time without stopping microsurgical procedures. M. Kohno (*) Department of Neurosurgery & Stroke Center, Tokyo Metropolitan Police Hospital, 4-22-1, Nakano, Nakano-Ku, Tokyo 164-0001, Japan e-mail: mkouno-nsu@umin.ac.jp

Śródoperacyjne monitorowanie czynności nerwu twarzowego w chirurgii ślinianki przyusznej

The route of the facial nerve in its extracranial part determines the technique of parotid gland surgery. Permanent facial nerve paralysis after parotidectomy is not rare. It is the most devastating complication for the patient and surgeon. Facial nerve monitoring by observing or palpating the face during the surgery is a long-standing practice. Using an EMG device is a standard procedure at present. Evaluation of the effectiveness of intraoperative facial nerve monitoring for parotid gland surgery. Fifty three patients operated on due to parotid gland tumour in the Head and Neck Surgery and Laryngological Oncology Department of the Greater Poland Cancer Center in 2007–2008. All patients had been provided with EMG and ENG examinations of the facial nerve before the surgery and continuous facial nerve monitoring during the operation. Facial nerve function after surgery was assessed according to the House-Brackmann grading system. Six (12%) patients presented facial nerve dysfunction after surgery. Three (6%) patients had temporary paralysis grade III H-B with complete recovery in 6 weeks. Three (6%) patients with deep lobe tumour had grade V H-B with complete recovery in one patient after 3 months, and two (4%) patients had grade III H-B after one year since the surgery. Intraoperative facial nerve monitoring should be a standard procedure during parotid gland surgery in most clinical situations.

Continuous Facial Nerve Monitoring during Pleomorphic Adenoma Recurrence Surgery

Surgery of recurrent pleomorphic adenoma (RPA) is known to lead to a high facial nerve complication rate. The efficacy of the continuous facial nerve monitoring (CFNM) technique remains to be proven in RPA surgery. The goal was thus to evaluate facial nerve palsy rates and the recovery period after parotidectomy for RPA using CFNM by way of continuous electromyography and to compare these rates and the operation time with those of patients who had undergone surgery without facial nerve monitoring. Cohort study. Forty-seven patients were referred for RPA (1981-2003). Among them, 32 (18 unmonitored and 14 monitored) patients displayed no preoperative facial palsy, and histologic analyses revealed evidence of recurrence. The operation time and the extent and duration of postoperative facial nerve palsy were examined in both groups (monitored vs. unmonitored). Both groups had a similar clinical appearance distribution. Facial nerve paralysis was estimated using the House-Brackmann grading scale. CFNM reduced the intensity of facial nerve paralysis independently of the kind of surgery performed. The complete deficit rates were 0% for the monitored group and 5.6% for the unmonitored group. Postoperative facial nerve paralysis was significantly lower (P = .01) in the monitored group than in the unmonitored group. CFNM improved the duration of facial paralysis (P = .001) in the monitored group. The operation time was significantly lower in the monitored group than in the unmonitored group (P = .001). Routine use of CFNM during RPA surgery improves the surgical outcome. The facial nerve deficit can be reduced, and the recovery of facial nerve function is faster.

Clinical outcome of continuous facial nerve monitoring during primary parotidectomy.

To assess whether continuous facial nerve monitoring during parotidectomy is associated with a lower incidence of facial nerve paresis or paralysis compared with parotidectomy without monitoring and to assess the cost of such monitoring. A retrospective analysis of outcomes for patients who underwent parotidectomy with or without continuous facial nerve monitoring. University medical center. Fifty-six patients undergoing parotidectomy in whom continuous electromyographic monitoring was used and 61 patients in whom it was not used. (1) The incidence of early and persistent facial nerve paresis or paralysis and (2) the cost associated with facial nerve monitoring. Early, unintentional facial weakness was significantly lower in the group monitored by electromyograpy (43.6%) than in the unmonitored group (62.3%) (P=.04). In the subgroup of patients without comorbid conditions or surgeries, early weakness in the monitored group (33.3%) remained statistically lower than the rate of early weakness in the unmonitored group (57.5%) (P=.03). There was no statistical difference in the final facial nerve function or incidence of permanent nerve injury between the groups or subgroups. After multivariate analysis, nonmonitored status (odds ratio [OR], 3.22), advancing age (OR, 1.47 per 10 years), and longer operative times (OR, 1.3 per hour) were the only significant independent predictive variables significantly associated with early postoperative facial weakness. The incremental cost of facial nerve monitoring was $379. The results suggest that continuous electromyographic monitoring of facial muscle during primary parotidectomy reduces the incidence of short-term postoperative facial paresis. Advantages and disadvantages of this technique need to be considered together with the additional costs in deciding whether routine use of continuous monitoring is a useful, cost-effective adjunct to parotid surgery.

Preservation of facial, cochlear, and other nerve functions in acoustic neuroma treatment

Between March 1966 and September 1992, 1400 acoustic neuromas were treated in Paris, France, by surgical excision. The findings over the last 7 years are presented. The translabyrinthine approach has been used in more than 85% of cases. Where hearing preservation is attempted, the middle fossa approach has been adapted for intracanilicular tumors and the retrosigmoid approach for small tumors extending into the cerebellopontine angle, in which the fundus of the internal meatus is free of tumor. The main goal is to achieve a grade I or II result in facial function within 1 month of surgery. Results improved during 1991 after the introduction of continuous facial nerve monitoring and the use of the Beaver mini-blade for dissection of tumor from nerve. With these techniques, facial function of grade I or II at 1 month improved from 20% to 52% for large tumors (larger than 3 cm), from 42% to 81% for medium tumors (2 to 3 cm). and from 70% to 92% for small tumors (up to and including 2 cm extracanalicular). The facial nerve was at greater risk using the retrosigmoid or middle fossa approaches than by the translabyrinthine route. Since 1985, success in hearing preservation has changed little, with useful hearing being preserved in 38.2% of cases operated on by means of the retrosigmoid route and a 36.4% of cases after the middle fossa approach. In older patients with good hearing and small tumors, observation with periodic MRI scanning is recommended. Despite earlier diagnosis, the number of patients suitable for hearing preservation surgery remains very limited and careful selection is required. Trigeminal nerve signs were present in 20% of cases preoperatively, in 10% postoperatively, and recovered spontaneously. Palsies of the other cranial nerves after surgery were much rarer and were as follows: sixth nerve (abducens), 0.5%; ninth nerve (glossopharyngeal), 1.4%; and tenth nerve (vagus), 0.7%. The importance of preservation of function of the nervus intermedius of Wrisberg is stressed. These results emphasize the advantages of the translabyrinthine approach, offering greater security to the facial nerve and lower morbidity.