A new method for monitoring abnormal muscle response in hemifacial spasm: A prospective study

Microvascular decompression for hemifacial spasm after Bell's palsy: a retrospective clinical study

OBJECTIVE

This study aimed to investigate the clinical characteristics of hemifacial spasm (HFS) after Bell's palsy and to evaluate the therapeutic efficacy of microvascular decompression (MVD).

METHODS

A retrospective analysis was conducted on 18 patients who underwent MVD for HFS after Bell's palsy at our institution between January 1, 2017, and December 31, 2021. Clinical presentations, intraoperative findings, postoperative outcomes, and complications were comprehensively assessed.

RESULTS

Neurovascular compression (NVC) was identified in all the 18 patients. The offending vessels included anterior inferior cerebellar artery (AICA) in 6 patients (33.3%), posterior inferior cerebellar artery (PICA) in 7 patients (38.9%), vertebral artery (VA) combined with AICA in 3 patients (16.7%), and VA alongside PICA in 2 patients (11.1%). Notably, marked arachnoid membrane adhesion was evident in 11 patients (61.1%). 15(83.3%) patients were cured immediately after MVD, delayed relief was found in 3 (16.7%) patients. During the follow-up period, recurrence was not documented. Surgical complications were limited to facial paralysis in 3 patients and auditory impairment in 1 patient. No additional surgical complications were recorded.

CONCLUSIONS

In patients manifesting HFS after Bell's palsy, NVC predominantly underlies the etiology. MVD is a reliably safe and efficacious therapeutic intervention.

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.

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.

Optimized EEG based mood detection with signal processing and deep neural networks for brain-computer interface

Electroencephalogram (EEG) is a very promising and widely implemented procedure to study brain signals and activities by amplifying and measuring the post-synaptical potential arising from electrical impulses produced by neurons and detected by specialized electrodes attached to specific points in the scalp. It can be studied for detecting brain abnormalities, headaches, and other conditions. However, there are limited studies performed to establish a smart decision-making model to identify EEG's relation with the mood of the subject. In this experiment, EEG signals of 28 healthy human subjects have been observed with consent and attempts have been made to study and recognise moods. Savitzky-Golay band-pass filtering and Independent Component Analysis have been used for data filtration.Different neural network algorithms have been implemented to analyze and classify the EEG data based on the mood of the subject. The model is further optimised by the usage of Blackman window-based Fourier Transformation and extracting the most significant frequencies for each electrode. Using these techniques, up to 96.01% detection accuracy has been obtained.

Applying a deep convolutional neural network to monitor the lateral spread response during microvascular surgery for hemifacial spasm

BACKGROUND

Intraoperative neurophysiological monitoring is essential in neurosurgical procedures. In this study, we built and evaluated the performance of a deep neural network in differentiating between the presence and absence of a lateral spread response, which provides critical information during microvascular decompression surgery for the treatment of hemifacial spasm using intraoperatively acquired electromyography images.

METHODS AND FINDINGS

A total of 3,674 image screenshots of monitoring devices from 50 patients were prepared, preprocessed, and then adopted into training and validation sets. A deep neural network was constructed using current-standard, off-the-shelf tools. The neural network correctly differentiated 50 test images (accuracy, 100%; area under the curve, 0.96) collected from 25 patients whose data were never exposed to the neural network during training or validation. The accuracy of the network was equivalent to that of the neuromonitoring technologists (p = 0.3013) and higher than that of neurosurgeons experienced in hemifacial spasm (p < 0.0001). Heatmaps obtained to highlight the key region of interest achieved a level similar to that of trained human professionals. Provisional clinical application showed that the neural network was preferable as an auxiliary tool.

CONCLUSIONS

A deep neural network trained on a dataset of intraoperatively collected electromyography data could classify the presence and absence of the lateral spread response with equivalent performance to human professionals. Well-designated applications based upon the neural network may provide useful auxiliary tools for surgical teams during operations.

Beyond the observation of all or nothing: The clinical significance of the pre-decompression instability of abnormal muscle response in Microvascular decompression for Hemifacial spasm

BACKGROUND

In microvascular decompression (MVD) surgery, abnormal muscle response (AMR) monitoring was utilized to confirm sufficient decompression. However, the AMR seems to contain more information that could improve surgical results.

METHOD

Patients' records of HFS treated with MVD under AMR monitoring, from January 2018 to December 2019 in our centre, were retrospectively reviewed. MVD procedures were performed via a suboccipital retrosigmoid approach, and AMR monitoring was performed. Pre-Decompression Instability (PDI) of AMR before the final decompression, including amplitude inconsistency and waveform chaos, was inspected and notified to the surgeon.

RESULT

165 cases were found with full follow-up data. In these cases, PDI was recognized in 144 cases. And in the remaining 21 cases, the AMR disappeared abruptly or continued to exist to the end of the MVD surgery. When PDI appeared, the rate of electrophysiological relief was significantly higher (91.7 % vs 66.7 %, P = 0.001). In cases with PDI appearance during MVD procedure, the rate of neurological dysfunction was lower (13.2 % vs 38.1 %, P = 0.004). The relief rate the PDI group tended to be higher without statistical significance.

CONCLUSION

The appearance and observation of pre-decompression instability of AMR monitoring made a positive impact on the surgical outcomes of MVD surgeries. The advent of PDI indicates that the key step of the procedure has arrived. The timely notification of the PDI advent improved the surgical outcomes of MVD surgery by increasing the electrophysiological relief rate, reducing the incidence of neurological dysfunction, and possible elevation of the relief rate. Therefore, continuous intra-operative communication between the surgeon and electrophysiological monitoring staff should be encouraged.

Advances in Intraoperative Neurophysiology During Microvascular Decompression Surgery for Hemifacial Spasm

Microvascular decompression (MVD) is a widely used surgical intervention to relieve the abnormal compression of a facial nerve caused by an artery or vein that results in hemifacial spasm (HFS). Various intraoperative neurophysiologic monitoring (ION) and mapping methodologies have been used since the 1980s, including brainstem auditory evoked potentials, lateral-spread responses, Z-L responses, facial corticobulbar motor evoked potentials, and blink reflexes. These methods have been applied to detect neuronal damage, to optimize the successful decompression of a facial nerve, to predict clinical outcomes, and to identify changes in the excitability of a facial nerve and its nucleus during MVD. This has resulted in multiple studies continuously investigating the clinical application of ION during MVD in patients with HFS. In this study we aimed to review the specific advances in methodologies and clinical research related to ION techniques used in MVD surgery for HFS over the last decade. These advances have enabled clinicians to improve the efficacy and surgical outcomes of MVD, and they provide deeper insight into the pathophysiology of the disease.

Prevention of Superior Petrosal Vein Injury during Microvascular Decompression for Trigeminal Neuralgia: Operative Nuances

Background The superior petrosal vein (SPV) often obscures the surgical field or bleeds during microvascular decompression (MVD) for the treatment of trigeminal neuralgia. Although SPV sacrifice has been proposed, it is associated with multiple complications. We have performed more than 4,500 MVDs, including approximately 400 cases involving trigeminal neuralgia. We aimed to describe our operative technique and nuances to avoid SPV injury.

Methods We have provided a detailed description of our institutional protocol, including the anesthesia technique, neurophysiologic monitoring, patient positioning, surgical approach, and SPV management. The surgical outcomes and treatment-related complications were retrospectively analyzed.

Results No SPVs were sacrificed intentionally or accidentally during our MVD protocol for trigeminal neuralgia. In the 344 operations performed during 2006 to 2020, 269 (78.2%) patients did not require medication postoperatively, 58 (16.9%) tolerated the procedure with adequate medication, and 17 (4.9%) did not respond to MVD. Postoperatively, 35 (10.2%), 1 (0.3%), and 0 patients showed permanent trigeminal, facial, or vestibulocochlear nerve dysfunction, respectively. Wound infection occurred in five (1.5%) patients, while cerebrospinal fluid leaks occurred in three (0.9%) patients. Hemorrhagic complications appeared in four (1.2%) patients but these were unrelated to SPV injury. No surgery-related mortalities were reported.

Conclusion MVD for the treatment of trigeminal neuralgia can be achieved safely without sacrificing the SPV. A key step is positioning the patient's vertex at a 10-degree elevation from the floor, which can ease venous return and loosen the SPV, making it less fragile to manipulation and providing a wider surgical corridor.

Usefulness of intraoperative monitoring in microvascular decompression for hemifacial spasm: a systematic review and meta-analysis

OBJECTIVE

To review the diagnostic accuracy and possible added value of Brainstem Auditory Evoked Potentials (BAEP) monitoring and Lateral Spread Response (LSR) monitoring in microvascular decompression surgery for hemifacial spasms.

METHODS

For this systematic review we followed the PRISMA guidelines. We searched different databases and bibliographies of articles. We included studies on BAEP and LSR monitoring that reported data on hearing outcome or efficacy. Selected studies were assessed for bias using the MINORS tool.

RESULTS

64 articles were selected for qualitative synthesis, 42 met inclusion criteria for meta-analysis. The overall incidence of hearing loss was 3.4%. For BAEP monitoring AUC and pooled OR with 95% confidence interval were 0.911 (0.753-0.933) and 7.99 (3.85-16.60) respectively. Short-term data on LSR monitoring showed an overall spasm relief rate of 89% with pooled OR, sensitivity and specificity with a 95% confidence interval of 8.80 (4.82-16.08), 0.911 (0.863-0.943) and 0.451 (0.342-0.564) respectively. Long-term data on LSR monitoring showed an overall spasm relief rate of 95% with pooled OR, sensitivity and specificity with a 95% confidence interval of 4.06 (2.15-7.64), 0.871 (0.817-0.911) and 0.39 (0.294-0.495) respectively.

CONCLUSION

The alarm criteria, a wave V latency prolongation of 1ms or a wave V amplitude decrement of 50%, proposed by the 'American Clinical Neurophysiology Society' are a sensitive predictor for postoperative hearing loss. Other BAEP wave changes, for example, complete loss of wave V, are more specific but correspond to irreversible damage and are therefore not useful as warning criteria. LSR monitoring has high diagnostic accuracy at short-term follow-up. At long-term follow-up, diagnostic accuracy decreases because most patients get spasm relief regardless of their LSR status. LSR persistence after surgery has a good long-term outcome, as long as an extensive exploration of the facial nerve has been performed.

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.

Challenging Microvascular Decompression Surgery for Hemifacial Spasm

OBJECTIVE

Microvascular decompression (MVD) is the most effective treatment for hemifacial spasm (HFS). However, surgical difficulties due to complex anatomy or revision surgery can endanger the functional integrity of the brainstem. We describe surgically challenging cases and provide operative guidance that may be helpful for neurosurgeons who perform MVDs.

METHODS

Of 3028 patients with HFS who underwent MVDs consecutively by a single neurosurgeon, complex or unusual cases associated with surgical difficulty were selected. Medical charts and images were reviewed, with the primary focus being intraoperative findings, operative techniques, and clinical outcomes. All MVDs were performed using the interposition method.

RESULTS

Surgically difficult cases were categorized into six types: tandem, perforator, atypical location, encircling, revision, and penetrating types. During the follow-up period (11.5-42.7 months; median 24.9 months), the spasm-free rate was 88.4%. Intraoperative changes in brainstem auditory evoked potentials were observed in 31.5% of patients. Immediate postoperative facial palsy and deafness were observed in 6.0% and 1.5% of patients, respectively. Revision surgery showed the highest surgical morbidity among the unusual HFS types. Detailed illustrations and descriptions of MVD in patients with surgically challenging HFS are provided.

CONCLUSIONS

Complex or unusual HFS types carry higher surgical risks in MVD. Neurosurgeons performing MVDs need to be prepared to manage complex HFS cases in order to achieve favorable clinical outcomes.

Involvement of the vertebral artery in hemifacial spasm: clinical features and surgical strategy

The vertebral artery (VA)-involved hemifacial spasm (HFS) has distinctive clinical features and performing microvascular decompression (MVD) is challenging. We described the clinical presentations of VA-involved HFS and the outcomes of MVD using the interposition method. Between January 2008 and March 2015, MVD was performed in 271 patients with VA-involved HFS. Demographic characteristics, preoperative severity, intraoperative findings, spasm-free outcome, and complications were retrospectively evaluated. A control group of 1500 consecutive patients with non-VA-involved HFS was enrolled. VA-involved HFS was associated with older age (p < 0.001), less female predominance (p < 0.001), more left-sided predominance (p < 0.001), and rapid symptom progression before MVD (p < 0.001). The Teflon Fulcrum method allowed intraoperative identification of the neurovascular compression site in 92.6% of the cases, and showed more severe indentation on the facial nerve (p < 0.001). Changes in the brainstem auditory evoked potentials during MVD (p < 0.001) and postoperative non-serviceable hearing loss (p < 0.001) were more frequent in patients with VA-involved than in non-VA-involved HFS. The spasm-free outcome and overall complication rates after MVD were not significantly different between the groups. VA-involved HFS has distinctive clinical features and poses a major surgical challenge for MVD success. The interposition method is a feasible surgical strategy in VA-involved HFS.

Persistent abnormal muscle response after microvascular decompression for hemifacial spasm

To explore the causes of persistent abnormal muscle response (AMR) after microvascular decompression (MVD) for hemifacial spasm (HFS) and the clinical outcomes of these patients. MVDs performed in Nanjing Drum Tower Hospital in 2017 were retrospectively studied, and 326 patients with HFS were classified into two groups based on whether AMR disappeared or persisted following MVD. The clinical features, treatment efficacy and postoperative complications were compared between the two groups. 305 patients with disappeared AMR after decompression were classified as Group A. In Group B, the 21 patients exhibited persistent AMR after successful MVD. The preoperative duration of symptoms in Group B was significantly longer than that in Group A (P < 0.001), and no significant difference was identified between the two groups in terms of gender, side, age and offending vessels (P > 0.05). The immediate postoperative cure rate of Group A (88.9%)was significantly higher than that in Group B (28.6%, P < 0.001), furthermore, the two groups were not different in the long-term outcome and the incidence of surgical complications (P > 0.05). The long preoperative duration of HFS patients may account for persistent AMR after successful decompression, and it is more likely for these patients to get delayed cured, the long-term outcomes showed no difference compared to those in patients with disappeared AMR after MVD.

An Intraoperative Multibranch Abnormal Muscle Response Monitoring Method During Microvascular Decompression for Hemifacial Spasm

BACKGROUND

Intraoperative abnormal muscle response (AMR) is widely used as an indicator during microvascular decompression surgery for hemifacial spasm. Usually only 1 muscle is recorded, and not all patients show a response, leaving the surgery somewhat blinded. We propose an improved method to record from multiple muscles innervated by multiple branches of the facial nerve to increase the positive AMR detection rate.

METHODS

Retrospective analysis was performed of 1604 patients with hemifacial spasm undergoing microvascular decompression at a single center. All patients were monitored for AMR by stimulating the zygomatic branch of the facial nerve. Only mentalis was recorded in 158 cases (single-branch AMR). Orbicularis oris, frontalis, and mentalis were simultaneously monitored in 148 cases (3-branch AMR), and platysma was further added in the remaining 1298 cases (4-branch AMR). Positive AMR detection rates were compared across the groups.

RESULTS

Total positive AMR detection rates significantly increased as more muscles were included in monitoring and were 74.1% for single-branch AMR, 86.5% for 3-branch AMR, and 98.4% for 4-branch AMR. Detection rates from single muscles were not significantly different across the groups. For all available cases, rates were 73.5% from mentalis, 47.2% from frontalis, 64.1% from orbicularis oris, and 40.8% from platysma.

CONCLUSIONS

This new multibranch AMR monitoring method can effectively increase the positive detection rate to as high as 98.4%. It is expected to better assist surgery.

Intraoperative Neurophysiological Monitoring during Microvascular Decompression Surgery for Hemifacial Spasm

Hemifacial spasm (HFS) is due to the vascular compression of the facial nerve at its root exit zone (REZ). Microvascular decompression (MVD) of the facial nerve near the REZ is an effective treatment for HFS. In MVD for HFS, intraoperative neurophysiological monitoring (INM) has two purposes. The first purpose is to prevent injury to neural structures such as the vestibulocochlear nerve and facial nerve during MVD surgery, which is possible through INM of brainstem auditory evoked potential and facial nerve electromyography (EMG). The second purpose is the unique feature of MVD for HFS, which is to assess and optimize the effectiveness of the vascular decompression. The purpose is achieved mainly through monitoring of abnormal facial nerve EMG that is called as lateral spread response (LSR) and is also partially possible through Z-L response, facial F-wave, and facial motor evoked potentials. Based on the information regarding INM mentioned above, MVD for HFS can be considered as a more safe and effective treatment.

Altered facial muscle innervation pattern in patients with postparetic facial synkinesis

OBJECTIVES/HYPOTHESIS

Using surface electrostimulation, we aimed to use facial nerve mapping (FNM) in healthy subjects and patients with postparetic facial synkinesis (PPFS) to define functional facial target regions that can be stimulated selectively.

STUDY DESIGN

Single-center prospective cohort study.

METHODS

FNM was performed bilaterally in 20 healthy subjects and 20 patients with PPFS. Single-pulse surface FNM started at the main trunk of the facial nerve and followed the peripheral branches in a distal direction. Stimulation started with 0.1 mA and increased in 0.1 mA increments. The procedure was simultaneously video recorded and evaluated offline.

RESULTS

A total of 1,873 spots were stimulated, and 1,875 facial movements were evaluated. The stimulation threshold was higher on the PPFS side (average = 9.8 ± 1.0 mA) compared to the contralateral side (4.1 ± 0.8 mA) for all stimulation sites or compared to healthy subjects (4.1 ± 0.5 mA; all P < .01). In healthy subjects, selective electrostimulation ± one unintended coactivation was possible at all sites in >80% of cases, with the exception of pulling up the corner of the mouth (65%-75%). On the PPFS side, stimulation was possible for puckering lips movements in 60%/75% (selective stimulation ± one coactivation, respectively), blinking in 55%/80%, pulling up the corner of the mouth in 50%/85%, brow raising in 5%/85, and raising the chin in 0%/35% of patients, respectively.

CONCLUSIONS

FNM mapping for surgical planning and selective electrostimulation of functional facial regions is possible even in patients with PPFS. FNM may be a tool for patient-specific evaluation and placement of electrodes to stimulate the correct nerve branches in future bionic devices (e.g., for a bionic eye blink).

LEVEL OF EVIDENCE

2b Laryngoscope, 130:E320-E326, 2020.

Blink synkinesis monitoring during microvascular decompression for hemifacial spasm

BACKGROUND

In the present study, we investigated whether blink synkinesis monitoring during microvascular decompression (MVD) is effective for predicting long-term outcomes in patients with hemifacial spasm (HFS).

METHODS

This retrospective study included 69 patients who had undergone MVD for HFS at a tertiary hospital. All patients underwent intraoperative monitoring of blink synkinesis, lateral spread responses (LSRs), and facial nerve motor-evoked potentials (FNMEPs). Baseline signals were compared to those obtained following decompression with Teflon, and postoperative outcomes were recorded.

RESULTS

A total of 65 patients were observed with complete relief of symptoms after 1 year after MVD, while 61 patients were observed with initial disappearance of blink synkinesis, 57 patients were observed with initial elimination of the LSR, and 45 patients with initial decreases in FNMEP amplitude (>50%). The highest sensitivity and accuracy values were observed for blink synkinesis. Chi-square tests comparing the sensitivity of the three methods revealed that FNMEP monitoring was associated with significantly lower sensitivity values than the remaining methods. Combined use of blink synkinesis and LSRs did not significantly increase sensitivity (61/65 vs 62/65) or accuracy (62/69 vs 63/69).

CONCLUSION

Our results demonstrate that blink synkinesis monitoring is safe during MVD for HFS. Furthermore, blink synkinesis was associated with the highest sensitivity and predictive values among the three methods evaluated. These findings suggest that blink synkinesis can be regarded as the first choice for intraoperative monitoring during MVD. Concurrent use of blink synkinesis and LSR monitoring may maximize the ability to predict patient prognosis and determine the extent of decompression.