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.

Recent Advances in Intraoperative Brainstem Auditory Evoked Potential Monitoring during Microvascular Decompression Surgery for Hemifacial Spasm.

Brainstem auditory evoked potential (BAEP) testing during microvascular decompression (MVD) is very important in the treatment of hemifacial spasm (HFS). The reason for this is that the vestibulocochlear nerve is located immediately next to the facial nerve, so the vestibulocochlear nerve may be affected by manipulation during surgery. BAEP testing for detecting vestibulocochlear nerve damage has been further developed for use during surgery. In most HFS patients with normal vestibulocochlear nerves, the degree of vestibulocochlear nerve damage caused by surgery is well-reflected in the BAEP test waveforms. Therefore, real-time testing is the best way to minimize damage to the vestibulocochlear nerve. The purpose of this study was to review the most recently published BAEP test waveforms that were obtained during MVD surgery to determine the relationship between vestibulocochlear nerve damage and BAEP waveforms.

Lateral Spread Response: Unveiling the Smoking Gun for Cured Hemifacial Spasm.

Hemifacial spasm (HFS) is a rare disorder characterized by involuntary facial muscle contractions. The primary cause is mechanical compression of the facial nerve by nearby structures. Lateral spread response (LSR) is an abnormal muscle response observed during electromyogram (EMG) testing and is associated with HFS. Intraoperative monitoring of LSR is crucial during surgery to confirm successful decompression. Proper anesthesia and electrode positioning are important for accurate LSR monitoring. Stimulation parameters should be carefully adjusted to avoid artifacts. The disappearance of LSR during surgery is associated with short-term outcomes, but its persistence does not necessarily indicate poor long-term outcomes. LSR monitoring has both positive and negative prognostic value, and its predictive ability varies across studies. Early disappearance of LSR can occur before decompression and may indicate better clinical outcomes. Further research is needed to fully understand the implications of LSR monitoring in HFS surgery.

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.

Chronological Patterns of Long-Term Outcomes After Microvascular Decompression for Hemifacial Spasm Over 5 Years.

BACKGROUND: The postoperative course of hemifacial spasm (HFS) varies. We analyzed the clinical outcomes from 1 to ≥5 years after microvascular decompression (MVD) in patients with HFS. METHODS: Between July 2004 and January 2015, 528 patients who were followed up for ≥5 years after MVD for HFS were included. We evaluated chronological patterns of clinical outcomes from 1 to ≥5 years. The outcomes at 2, 3, 4, and ≥5 years postoperatively were individually compared with those at 1 year postoperatively, and the relationships between clinical features, surgical findings, and outcomes over time were analyzed. RESULTS: Eight groups were created according to the similarity in the pattern of clinical outcomes from 1 to ≥5 years postoperatively. Individual postoperative outcomes at 2-4 years were consistent with those at 1 year postoperatively, whereas postoperative outcomes at ≥5 years were not (P = 0.020). There was substantial to moderate agreement between the outcomes at 1 year and at 2-4 years postoperatively, but the agreement decreased over time. Patients without diabetes (P = 0.015), an intraoperative offending vessel without a vein (P = 0.005), and intraoperative discoloration of the facial nerve (P = 0.036) showed better outcomes at ≥5 years postoperatively. CONCLUSIONS: Long-term outcomes from 1 to ≥5 years after MVD in patients with HFS were diverse. Nondiabetes, intraoperative offending vessel without a vein, and intraoperative discoloration of the facial nerve were better prognostic factors for outcomes at ≥5 years postoperatively. It is advisable to consider these results when evaluating the long-term outcomes of this surgery.

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.

Prognostic Value of Lateral Spread Response Recorded 1 Month After Microvascular Decompression for the Treatment of Hemifacial Spasm.

BACKGROUND: The predictive value of intraoperative disappearance of the lateral spread response (LSR) during microvascular decompression surgery for hemifacial spasm treatment is unclear. Studies evaluating the clinical implications of the LSR recorded during the postoperative period are also limited. OBJECTIVE: To analyze the LSR 1 month postoperatively and to evaluate its prognostic value until 1 year postsurgery. METHODS: In total, 883 patients who underwent microvascular decompression between 2016 and 2018 were included. LSR was recorded preoperatively, intraoperatively before decompression, intraoperatively after decompression, and 1 month postoperatively. The outcomes were evaluated at 1 week, 1 month, and 1 year postoperatively. RESULTS: The presence of preoperative and intraoperative LSR after decompression did not predict the postoperative outcome at 1 year. In 246 patients (27.9%), the postoperative LSR at 1 month was not identical to that recorded intraoperatively after decompression. Postoperative LSR at 1 month was associated with a worse outcome at 1 month (P < .0001) and 1 year (P = .0002) postoperatively. Patients with residual symptoms and a LSR 1 month postoperatively were more likely to show residual symptoms 1 year postoperatively, with a positive predictive value of 50.7%. CONCLUSION: Unlike the intraoperative LSR, the LSR at 1 month postoperatively showed prognostic value in predicting 1-year postoperative outcomes and was useful for identifying patients with a high risk of unfavorable outcomes. Thus, confirming the presence of postoperative LSR is necessary.

Factors Influencing Patient Satisfaction after Microvascular Decompression for Hemifacial Spasm: A Focus on Residual Spasms.

INTRODUCTION: Patients with hemifacial spasm (HFS) experience improvement in symptoms after microvascular decompression (MVD); however, patient satisfaction is sometimes low. This study aimed to analyze the relationship between residual spasms and patient satisfaction, identify factors affecting satisfaction, and investigate the degree of improvement in spasms which result in patient satisfaction after surgery. METHODS: 297 patients who completed a questionnaire after MVD for HFS between March 2020 and June 2020 were included. Information on surgical outcomes and patient satisfaction was collected using the questionnaire, and their relationships were analyzed. RESULTS: Among the 297 patients, the mean residual spasm percentage and patient satisfaction score were negatively correlated with 14.0% and 8.8 points, respectively. In addition to residual spasms, discomfort caused by persistent spasms, psychological problem-solving, better social life, and interpersonal relationship improvement were associated with satisfaction. There was no significant association between the presence of complications and satisfaction. There was no significant difference in the satisfaction score at up to 30% residual spasm, and the patients with 0-30% residual spasm had a satisfaction score of 7 points or higher. CONCLUSION: Residual spasms and discomfort from residual spasms decreased patient satisfaction after MVD for HFS. It is then necessary to perform accurate surgical resolution to improve surgical outcomes and provide adequate management to reduce postoperative discomfort and anxiety, and ultimately to enhance satisfaction. Residual spasms of up to 30% compared with the preoperative severity can be considered a good outcome when evaluating surgical outcomes.

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.

Association of Thyroid Hypofunction with Clinical Outcomes after Microvascular Decompression for Hemifacial Spasm.

INTRODUCTION: Data regarding the association between thyroid dysfunction and hemifacial spasm (HFS) are limited. We conducted a single-center, retrospective study to investigate the predictive value of thyroid dysfunction in patients with HFS after microvascular decompression (MVD). METHODS: Between July 2004 and January 2015, 156 patients who were tested for thyroid hormones after MVD for HFS were enrolled in the present study. We assessed their detailed history, clinical manifestations, serum thyroid hormone levels, and surgical outcomes. The patients were classified into low and high groups based on thyroid hormone concentrations, and clinical outcomes were evaluated in each group. RESULTS: In a total of 156 patients with a median follow-up period of 40.9 months, the improvement rate was 87.8%. The patients were classified into low (76, 48.7%) or high (80, 51.3%) groups based on serum thyroxine (T4) levels. There was a difference between the 2 groups in terms of postoperative outcomes following MVD (p = 0.020). There were no differences in the outcomes according to serum tri-iodothyronine (T3) levels as well as other factors associated with the outcomes. CONCLUSIONS: We found that decreased serum T4 levels are associated with poor postoperative outcomes among patients with HFS. Further studies are needed to examine the clinical benefit of thyroid hormone replacement therapy for patients with suboptimal T4 concentrations as well as active thyroid hormone screening for patients with HFS.

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.

A prewarning sign for hearing loss by brainstem auditory evoked potentials during microvascular decompression surgery for hemifacial spasm.

OBJECTIVE: We aimed to define the prewarning sign of brainstem auditory evoked potentials (BAEPs) associated with cerebellar retraction (CR) during microvascular decompression surgery for hemifacial spasm. METHODS: A total of 241 patients with a latency prolongation of 1 ms or an amplitude decrement of 50% of wave V were analyzed. According to BAEPs before significant changes during CR, patients were classified into Groups A (latency prolongation of wave I [≥0.5 ms] without prolongation of the I-III interpeak interval [<0.5 ms]) and B (no latency prolongation of wave I [<0.5 ms] with prolongation of the I-III interpeak interval [≥0.5 ms]). BAEPs and postoperative hearing loss (HL) were compared between the two groups. RESULTS: Group B comprised 160 (66.4%) patients. With maximal changes in wave V, latency prolongation (≥1 ms) with amplitude decrement (≥50%) was more common in Group B (p < 0.018). At the end of the operation, wave V loss was observed in 11 patients, including 10 patients from Group B. Five patients developed postoperative HL; all were from Group B. CONCLUSIONS: Latency prolongation of wave III during CR was associated with serious BAEPs changes and postoperative HL. SIGNIFICANCE: Latency prolongation of wave III is a significant prewarning sign.

Significance of wave I loss of brainstem auditory evoked potentials during microvascular decompression surgery for hemifacial spasm.

OBJECTIVE: We sought to define the significance of wave I loss of brainstem auditory evoked potentials (BAEPs) during microvascular decompression (MVD) surgery for hemifacial spasm. METHODS: Out of 670 patients, 36 showed wave V loss during MVD surgery. These patients were classified into the following two groups based on wave I loss: Total wave loss, including wave I loss, and wave V loss with persistent wave I. We analyzed the differences in postoperative complications between the groups. We also investigated when wave I loss occurred during MVD surgery. RESULTS: Of the 36 patients, 24 (66.7%) exhibited wave I persistence and 12 (33.3%) exhibited total wave loss. The patients who showed total wave loss were significantly more likely to exhibit postoperative hearing loss (p = 0.009). In addition, these patients exhibited a significantly higher frequency of postoperative complications such as dizziness and tinnitus (p = 0.002 and p = 0.031, respectively). Total wave loss occurred more frequently after the decompressive procedure of MVD surgery. CONCLUSIONS: Total wave loss, including wave I loss, was more closely associated with severe postoperative complications. Total wave loss occurred more frequently after the decompressive procedure of MVD surgery. SIGNIFICANCE: These findings suggest the significance of wave I loss of BAEPs.

Clinical Outcome After Microvascular Decompression According to the Progression Rates of Hemifacial Spasm.

OBJECTIVE: The progression rate for clinical manifestations in hemifacial spasm (HFS) varies; however, little is known about the factors contributing to this. The purpose of this study was to identify independent factors affecting the rate of symptom progression and to evaluate clinical outcomes according to progression rates. METHODS: The study enrolled 1335 patients who underwent microvascular decompression for HFS between July 2004 and January 2015. We assessed detailed history, clinical manifestations, and outcomes. Based on the duration and severity of symptoms, patients were classified into rapidly progressive and slowly progressive groups. We identified predisposing factors affecting the differences between the 2 groups and evaluated the clinical outcome in each group. RESULTS: Of 1335 patients with HFS, 825 (61.8%) were classified as rapidly progressive, and 510 (38.2%) were classified as slowly progressive. In univariable and multivariable analyses, younger age at surgery, older age at symptom onset, and absence of intraoperative facial nerve indentation were significant predisposing factors for rapid progression. The rapidly progressive group had worse outcomes than the slowly progressive group following microvascular decompression. CONCLUSIONS: In this study, patients with rapidly progressive HFS had worse clinical outcomes. Therefore, patients with rapidly progressive symptoms should be warned in advance that the prognosis may be worse after microvascular decompression. This study is also useful to understand the differences in symptom progression rates in HFS in order to inform patients about symptom progression.

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.

Vascular Complications in Microvascular Decompression: A Survey of 4000 Operations.

BACKGROUND: Vascular complications in posterior fossa surgery, even in microvascular decompression (MVD) involving a small cranial opening, can have catastrophic consequences. We analyzed these complications to determine the incidence, risk factors, prognosis, and preventive measures involved. METHODS: Between April 1997 and March 2018, 4000 consecutive patients with neurovascular compression syndrome were admitted and underwent MVD. We reviewed the medical records of patients who developed vascular complications after MVD, focusing on their past medical history, perioperative laboratory findings and images, surgical findings, and postoperative progress. RESULTS: Vascular complications developed in 28 patients (0.7%), including 24 with hemifacial spasm and 4 with trigeminal neuralgia. Twenty-two hemorrhagic (78.6%) and 6 ischemic (21.4%) complications occurred, with epidural hematoma the most frequent type identified. Ten patients (35.7%) patients were asymptomatic and 18 (64.3%) were symptomatic. Six patients (21.4%) underwent revision surgery, such as hematoma removal, craniectomy, or extraventricular drainage insertion. At the last follow-up, dizziness was the most commonly reported sequela from vascular complications. No deaths had occurred. CONCLUSIONS: Vascular complications are rare, but can be the most devastating adverse outcome of MVD surgery. Unusual signs and symptoms after MVD should prompt special attention to early management and patient safety.

Missed Culprits in Failed Microvascular Decompression Surgery for Hemifacial Spasm and Clinical Outcomes of Redo Surgery.

OBJECTIVE: To identify causes of recurrent hemifacial spasm (HFS) after initial microvascular decompression (MVD) and to assess the feasibility of redo MVD. METHODS: The study included 21 patients who underwent redo MVD over the last 2 decades. Their medical charts were retrospectively reviewed for preoperative medical history, previous and redo MVD intraoperative findings, and previous and redo MVD postoperative outcomes. RESULTS: Redo MVDs were the second operation in 20 patients and the third operation in 1 patient. The median interval between previous and redo MVD was 46.3 months (range, 14.4-188.2 months). Compression of offending vessels such as a vein or perforating artery located medial to or at the cisternal segment of the facial nerve was found to be a possible cause of previous MVD failure. MVD failure resulted from neglect of offending vessels in 10 patients, insufficient decompression in 7 patients, and untouched neurovascular compression sites in 4 patients. Spasm-free rates after redo MVD were 80.5% at 1 year and 90.5% in the last year of follow-up (median, 15.8 months; range, 3.6-152.0 months). Permanent hearing loss and facial palsy were each observed in 2 patients (9.5%). In addition, 1 patient each experienced cerebellar infarction and vocal cord palsy. CONCLUSIONS: Redo MVD remains a feasible treatment option for patients with HFS who failed to benefit from previous MVD, but it is associated with an increased risk of cranial nerve and vascular injuries.

Algorithm to Predict the Outcome of Microvascular Decompression for Hemifacial Spasm: A Data-Mining Analysis Using a Decision Tree.

OBJECTIVE: Although microvascular decompression (MVD) is the primary treatment for hemifacial spasm (HFS), the postoperative course is variable. This study aimed to develop a prediction model of the outcome of MVD in patients with HFS by investigating influential factors. METHODS: Electronic medical records of 1624 patients with HFS who underwent MVD from July 2004 to January 2015 were reviewed. The relationships between patient-related, disease-related, and surgery-related factors and postoperative outcome were analyzed using multinomial logistic regression. A predictive model for MVD outcome was developed using decision tree analysis. RESULTS: The mean follow-up duration after surgery was 30.2 months (median, 23.5 months; range, 6.0-133.3 months). For the 1624 patients, the overall improvement rate was 90.5%. Overall, 984 patients (60.6%) showed improvement of spasm immediately after surgery, 486 (29.9%) experienced delayed improvement, and 154 (9.5%) showed persistence of spasm. Outcome of patients with HFS after MVD was predicted by 4 items: postoperative delayed facial palsy, degree of preoperative spasm, intraoperative indentation on the facial nerve, and sex. The patients were classified into 6 categories and improvement of spasm immediately after surgery showed 35%-91%, delayed improvement 6%-46%, and persistence of spasm 0%-59%. The accuracy of the developed prediction model was 0.608. CONCLUSIONS: Male sex, mild degree of preoperative spasm, intraoperative indentation on the facial nerve, and postoperative delayed facial palsy were better favorable prognostic factors of MVD in patients with HFS. This novel algorithm may be useful to predict the outcome of MVD in these patients.