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

Tinnitus: an underreported condition following microvascular decompression for hemifacial spasm

PURPOSE

While hearing loss is a well-known condition following microvascular decompression (MVD) for hemifacial spasm (HFS), tinnitus is an underreported one. This study aims to identify prevalence, characteristics, severity, and predictors of tinnitus following MVD for HFS.

METHODS

A single-center cohort of 55 HFS patients completed a questionnaire approximately 5 years following MVD. Data encompassed tinnitus presence, side, type, onset, and severity measured by a 10-point Visual Analogue Scale (VAS). Descriptive, correlation, and logistic regression analyses were conducted. RESULTS  : At surgery, participants' median age was 58 years (IQR 52-65). The median duration of HFS symptoms before surgery was 5 years (IQR 3-8), slightly predominant on the left (60%). Postoperative tinnitus was reported by 20 patients (36%), versus nine (16%) that reported preoperative tinnitus. Postoperative tinnitus was ipsilateral on the surgical side in 13 patients (65%), bilateral in six (30%), and contralateral in one (5%). Among patients with bilateral postoperative tinnitus, 33% did not have this preoperatively. Tinnitus was continuous in 70% of cases and pulsatile in 30%. Onset of new tinnitus was in 58% immediately or within days, in 25% within three months, and in 17% between three months and one year after surgery. The mean severity of postoperative tinnitus was 5.1 points on the VAS. Preoperative tinnitus and presence of arachnoid adhesions had suggestive associations with postoperative tinnitus in initial analyses (p = 0.005 and p = 0.065). However, preoperative tinnitus was the only significant predictor of postoperative tinnitus (p = 0.011).

CONCLUSION

Tinnitus is a common condition following MVD for HFS, with a moderate overall severity. Causes behind postoperative tinnitus remain obscure but could be related to those of postoperative hearing loss in this patient population. Clinicians should be aware of tinnitus following MVD and vigilantly monitor its occurrence, to facilitate prevention efforts and optimize outcome for HFS patients undergoing MVD.

Intraoperative Brainstem Auditory Evoked Potentials and Postoperative Nausea and Vomiting After Microvascular Decompression

BACKGROUND

We performed this study to investigate the effect of intraoperative brainstem auditory evoked potential (IBAEP) changes on the development of postoperative nausea and vomiting (PONV) after microvascular decompression (MVD) for neurovascular cross compression.

METHODS

A total of 373 consecutive cases were treated with MVD. The use of rescue antiemetics after surgery was used as an objective indicator of PONV. IBAEP monitoring was routinely performed in all.

RESULTS

The use of rescue antiemetics was significantly associated with female sex (OR = 3.427; 95% CI, 2.077-5.654; P < 0.001), PCA use (OR = 3.333; 95% CI, 1.861-5.104; P < 0.001), and operation time (OR = 1.017; 95% CI, 1.008-1.026; P < 0.001). A Wave V peak delay of more than 1.0 milliseconds showed a significant relation with the use of rescue antiemetics (OR = 1.787; 95% CI, 1.114-2.867; P = 0.016) and a strong significant relation with the use of rescue antiemetics more than 5 times (OR = 2.426; 95% CI, 1.372-4.290; P = 0.002).

CONCLUSIONS

A wave V peak delay of more than 1.0 milliseconds might have value as a predictor of PONV after MVD. More detailed neurophysiological studies will identify the exact pathophysiology underlying PONV after MVD.

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.

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.

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.

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.

Brainstem auditory evoked potential combined with high resolution cranial base CT can optimize the diagnosis of auditory nerve injury

PURPOSE

Auditory nerve injury is one of the most common nerve injury complications of skull base fractures. However, there is currently a lack of auxiliary examination methods for its direct diagnosis. The purpose of this study was to find a more efficient and accurate means of diagnosis for auditory nerve injury.

METHODS

Through retrospectively analyzing the results of brainstem auditory evoked potential (BAEP) and high-resolution CT (HRCT) in 37 patients with hearing impairment following trauma from January 1, 2018 to July 31, 2020, the role of the two inspection methods in the diagnosis of auditory nerve injury was studied. Inclusion criteria were patient had a clear history of trauma and unilateral hearing impairment after trauma; while exclusion criteria were: (1) severe patient with a Glasgow coma scale score ≤5 because these patients were classified as severe head injury and admitted to the intensive care unit, (2) patient in the subacute stage admitted 72 h after trauma, and (3) patient with prior hearing impairment before trauma. According to Goodman's classification of hearing impairment, the patients were divided into low/medium/severe injury groups. In addition, patients were divided into HRCT-positive and negative groups for further investigation with their BAEP results. The positive rates of BEAP for each group were observed, and the results were analyzed by Chi-square test (p < 0.05, regarded as statistical difference).

RESULTS

A total of 37 patients were included, including 21 males and 16 females. All of them were hospitalized patients with GCS score of 6-15 at the time of admission. The BAEP positive rate in the medium and severe injury group was 100%, which was significantly higher than that in the low injury group (27.27%) (p < 0.01). The rate of BEAP positivity was significantly higher in the HRCT-positive group (20/30, 66.7%) than in the HRCT-negative group (1/7, 14.3%) (p < 0.05). Twenty patients (54.05%) were both positive for BEAP and HRCT test, and considered to have auditory nerve damage. Six patients (16.22%) were both negative for BEAP and HRCT test, and 10 patients (27.03%) were BAEP-negative but HRCT-positive: all the 16 patients were considered as non-neurological injury. The rest 1 case (2.70%) was BAEP-positive but HRCT-negative, which we speculate may have auditory nerve concussion.

CONCLUSION

By way of BAEP combining with skull base HRCT, we may improve the accuracy of the diagnosis of auditory nerve injury. Such a diagnostic strategy may be beneficial to guiding treatment plans and evaluating prognosis.

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.

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.

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.

Predictive values of maximum changes of brainstem auditory evoked potentials during microvascular decompression for hemifacial spasm

BACKGROUND

Brainstem auditory evoked potentials (BAEPs) have been widely monitored to prevent hearing loss (HL) during microvascular decompression (MVD) for hemifacial spasm (HFS); however, their predictive value is still unclear. The aim of this study is to investigate the predictive values of the maximum changes in BAEPs and define the best warning indicator and a cutoff value (CV) during HFS-MVD.

METHODS

The clinical data of 93 HFS-MVD patients were retrospectively analysed. The maximum change rates of the latency and amplitude of waves I, III, and V and the interpeak latencies (IPLs) I-III, I-V, and III-V, when BAEPs change most during MVD, were defined. Pure tone audiometry was performed to evaluate hearing loss (HL). Logistic regression, propensity score, receiver operating curve (ROC), and area under the curve (AUC) were used to identify the predictive value of relevant indexes and to determine the CV (with the largest Youden index) of the best index at different levels of HL.

RESULTS

The AUCs of BAEPs for predicting HL were 0.98, 0.92, and 0.84 for 50 dB, 30 dB, and 10 dB, respectively. The amplitude of wave V (AwV) was the best single predictive index at all three HL levels. The CV of AwV was 55% (50 dB), 46% (30 dB), and 34% (10 dB). At 50 dB HL, the predictive value of IPLs I-V (AUC 0.89 with CV 0.6 ms) was better than that of LwV (AUC 0.82 with CV 1 ms).

CONCLUSION

BAEPs can predict HL well. AwV is the best single predictive index of all BAEPs. The reduction of AwV by 34% (watching), 46% (reporting), and 55% (warning) can be used as a sliding-scale warning sign. In addition, IPLs I-V (> 0.6 ms) and LwV (> 1 ms) should also be observed and reported during MVD.