Intraoperative Neurophysiological Monitoring during Microvascular Decompression Surgery for Hemifacial Spasm

Optimal method for reliable lateral spread response monitoring during microvascular decompression surgery for hemifacial spasm

In this study, we propose an optimal method for monitoring the key electrophysiological sign, the Lateral Spread Response (LSR), during microvascular decompression (MVD) surgery for hemifacial spasm (HFS). Current monitoring methods and interpretations of LSR remain unclear, leading to potential misinterpretations and undesirable outcomes." We prospectively collected data from patients undergoing MVD for HFS, including basic demographics, clinical characteristics, and surgical outcomes. Stimulation intensity was escalated by 1 mA increments to identify the optimal range for effective LSR. We designated the threshold at which we can observe LSR as THR1 and THR2 for when LSR disappears, with high-intensity stimulation (30 mA) designated as THR30. Subsequently, we compared abnormal muscle responses (AMR) between the optimal range (between THR1 and THR2) and THR30. Additionally, we conducted an analysis to identify and assess factors associated with artifacts and their potential impact on clinical outcomes. As stimulation intensity increases, the onset latency to detect AMR was shortened. The first finding of the study was high intensity stimulation caused artifact that mimic the wave of LSR. Those artifacts were observed even after decompression thus interfere interpretation of disappearance of LSR. Analyzing the factors related to the artifact, we found the AMR detected at onset latency below 9.6 ms would be the lateral spreading artifact (LSA) rather than true LSR. To avoid false positive LSR from LSA, we should stepwise increase stimulation intensity and not to surpass the intensity that cause LSR onset latency below 10 ms.

Surgical treatment of hemifacial spasms: how to predict failure and complications through a series of 200 patients

Primary hemifacial spasm (pHFS) is a benign but disabling movement disorder caused by a neurovascular conflict involving the facial nerve. Surgical treatment by microvascular decompression (MVD) is the most effective therapeutic. Predictors of surgical failure and surgical complications are still lacking. The aim of this study is to identify such predictors through the retrospective analysis of a series of 200 consecutive patients. All patients who underwent MVD for pHFS from January 1991 to December 2017 were included. All patients had at least two years follow-up. In addition to the demographic data, the outcome and the complications were collected. The primary outcome analysis showed that 7.5% of patients had a recurrence. Multiple and AICA related neurovascular conflicts were statistically associated to a higher recurrence rate after MVD (respectively p < 0.001 and p = 0.02). Permanent facial palsy occurred in 2.5% of patients, hearing loss in 9.0% (2.0% of complete unilateral impairment) and dizziness in 2.5%. The risk of each of these peripheral neurological impairments was statistically increased by a long duration between the first pHFS symptom and the MVD (p < 0.001). In case of recurrence, a second MDV was offered. Long term follow-up showed that all patients had a complete resolution of the HFS. Post-operative complication rate was not significantly increased after a second MVD. Multiple and AICA related neurovascular conflicts are associated to a higher risk of surgical failure. When a pHFS recurrence occurs, a second surgical procedure is associated with excellent outcome without significant increase of post-operative complications and should therefore be recommended.

Outcomes after Microvascular Decompression for Hemifacial Spasm without Definite Radiological Neurovascular Compression at the Root Exit Zone

The purpose of this study was to investigate the outcome of microvascular decompression (MVD) in patients with hemifacial spasm (HFS) who have no definite radiological neurovascular compression (NVC). Sixteen HFS patients without radiological NVC on preoperative MRI underwent MVD surgery. The symptoms were left-sided in fourteen (87.5%) and right-sided in two patients (12.5%). Intraoperatively, the most common vessel compressing the facial nerve was the AICA (8, 44.4%), followed by arterioles (5, 27.8%), veins (4, 22.2%), and the PICA (1, 5.6%). The most common compression site was the cisternal portion (13, 76.5%) of the facial nerve, followed by the REZ (4, 23.5%). One patient (6.3%) was found to have multiple NVC sites. Arachnoid type (7, 50%) was the most common compressive pattern, followed by perforator type (4, 28.6%), sandwich type (2, 14.3%), and loop type (1, 7.1%). A pure venous compression was seen in two patients, while a combined venous-arterial "sandwich" compression was detected in two patients. Symptom improvement was observed in all of the patients. Only one patient experienced recurrence after improvement. Based on our experience, MVD surgery can be effective for primary HFS patients with no definite radiological NVC. MVD can be considered if the patient shows typical HFS features, although NVC is not evident on MRI.

Microvascular decompression for hemifacial spasm: Complications after 292 procedures without neurophysiological monitoring

Background

Hemifacial spasm (HFS) is characterized by involuntary, progressive, and intermittent spasms in the upper and lower facial muscles. Due to the high success rate, microvascular decompression (MVD) is the treatment of choice, and intraoperative neuromonitoring (INM) is considered useful for achieving safe surgery. Still, most centers do not have this technology.

Methods

We analyzed 294 patients with HFS treated with MVD without INM. We only included patients with a neurovascular etiology while excluding other causes, such as tumors. As part of the postoperative evaluation, we assessed preoperative magnetic resonance imaging and pure-tone audiometry.

Results

The main complication was peripheral facial paralysis in 50 patients, followed by hypoacusis in 22 patients and deafness in 17 patients, associated with a failed surgical outcome (P = 0.0002). The anterior inferior cerebellar artery (AICA) was an offending vessel, and the involvement of more than one vessel was significantly associated with the development of facial nerve palsy (P = 0.01). AICA was also associated with hearing impairment (P = 0.04). Over 90% of immediate complications improve in the follow-up (6 months), and one patient did not show a cure for initial HFS.

Conclusion

MVD is the method with the highest long-term cure rates for treating HFS; however, we must inquire into the multiple factors of the patient and the surgeon to predict surgical outcomes. INM is not a must during MVD for HFS. We recommend its use depending on the availability and mainly on the surgeon's skills, for surgeons.

Intraoperative Monitoring of the Facial Nerve during Microvascular Decompression for Hemifacial Spasm

This review article discusses the clinical significance of intraoperative neurophysiological monitoring (IONM), provides recommendations for monitoring protocols, and considers the interpretation of results in microvascular decompression (MVD) for hemifacial spasm (HFS). The lateral spread response (LSR) is an important monitoring parameter during MVD. It helps to identify the responsible blood vessel and confirms its thorough decompression from the facial nerve. The disappearance of the LSR during surgery is associated with favorable clinical outcomes. Standard and revised monitoring protocols and the confirmation of LSR persistence and disappearance are also discussed. The blink reflex and other facial nerve monitoring modalities, such as free-running electromyography, facial motor evoked potentials, F-waves, and the Z-L response, are further considered.

Lateral spread response of different facial muscles during microvascular decompression in hemifacial spasm

OBJECTIVE

Interpreting lateral spread response (LSR) during microvascular decompression (MVD) for hemifacial spasm (HFS) is difficult when LSRs observed in different muscles do not match. We aimed to analyze LSR patterns recorded in both the orbicularis oris (oris) and mentalis muscles and their relationships with clinical outcomes.

METHODS

The data of 1288 HFS patients who underwent MVD between 2015 and 2018 were retrospectively reviewed. LSR was recorded in the oris and mentalis muscles through centrifugal stimulation of the temporal branch of the facial nerve after preoperative mapping. The disappearance of LSR following surgery, clinical outcomes, and the characteristics of LSR in oris were analyzed.

RESULTS

After surgery, LSR remained in 100 (7.7%) and 279 (21.6%) of the mentalis and oris muscles, respectively. The postoperative outcome correlated with LSR disappearance in the mentalis, not with that in the oris.

CONCLUSION

LSR patterns differed in each muscle and may not be correlated with clinical outcomes. LSR in the mentalis and oris muscles should be interpreted differently.

SIGNIFICANCE

We describe a monitoring protocol characterized by preoperative facial nerve mapping, antidromic stimulation, and recording from multiple muscles. We analyze differences in LSRs in the mentalis and oris muscles and suggest technical points for interpretation.

Awake CT-guided percutaneous stylomastoid foramen puncture and radiofrequency ablation of facial nerve for treatment of hemifacial spasm

OBJECTIVE

Hemifacial spasm (HFS) is a debilitating neuromuscular disorder with limited treatment options. The current study describes a novel minimally invasive procedure that provided effective and sustained relief for patients with HFS. The authors provide a detailed description of the awake CT-guided percutaneous radiofrequency ablation (RFA) of the facial nerve for treatment of HFS, and they examine its clinical efficacy. This is the first time in the literature that this procedure has been applied and systematically analyzed for HFS.

METHODS

Patients with a history of HFS were recruited between August 2018 and April 2020. Those with a history of cerebellopontine lesions, coagulopathy, ongoing pregnancy, cardiac pacemaker or defibrillator implants, or who declined the procedure were excluded from the study. Fifty-three patients who met the study criteria were included and underwent awake CT-guided RFA. Under minimal sedation, a radiofrequency (RF) needle was used to reach the stylomastoid foramen on the affected side under CT guidance, and the facial nerve was localized using a low-frequency stimulation current. Patients were instructed to engage facial muscles as a proxy for motor monitoring during RFA. Ablation stopped when the patients' hemifacial contracture resolved. Patients were kept for inpatient monitoring for 24 hours postoperatively and were followed up monthly to monitor resolution of HFS and complications for up to 19 months.

RESULTS

The average duration of the procedure was 32-34 minutes. Postoperatively, 91% of the patients (48/53) had complete resolution of HFS, whereas the remaining individuals had partial resolution. A total of 48 patients reported mild to moderate facial paralysis immediately post-RFA, but most resolved within 1 month. No other significant complication was observed during the study period. By the end of the study period, 5 patients had recurrence of mild HFS symptoms, whereas only 2 patients reported dissatisfaction with the treatment results.

CONCLUSIONS

The authors report for the first time that awake CT-guided RFA of the facial nerve at the stylomastoid foramen is a minimally invasive procedure and can be an effective treatment option for HFS.

Clinical Application of Diffusion Tensor Imaging in Diagnosis and Prognosis of Hemifacial Spasm

OBJECTIVE

The purpose of this study was to test the application of diffusion tensor imaging (DTI) in patients with hemifacial spasm (HFS), to make more accurate diagnoses before surgery and to judge the degree of recovery more accurately after surgical microvascular decompression. To our knowledge, this is the first study to test the validity of DTI for diagnosis and postsurgical evaluation of HFS.

METHODS

We included 40 patients with HFS who underwent DTI scanning before microvascular decompression. They were followed up with DTI 6 months and 1 year after surgery. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were obtained and compared.

RESULTS

In patients with HFS, the FA value of the affected side (mean FA, 0.46 ± 0.03) was significantly lower than that of the healthy side (mean FA, 0.43 ± 0.04; P < 0.05), and the ADC value of the affected side (mean FA, 1.60 ± 0.14) was significantly higher than that of the healthy side (mean ADC, 1.50 ± 0.12; P < 0.05). Compared with those before surgery, the FA values of both follow-up patients increased significantly, whereas their ADC values decreased significantly.

CONCLUSIONS

The use of DTI improves diagnosis and treatment of HFS.