Hemifacial spasm retrospective case series studies [Neurosurgery Wiki]

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====== Hemifacial spasm retrospective case series studies ======

===== 2023 =====
Al Menabbawy et al. reviewed a prospectively maintained [[database]] for MVDs performed from 2005 until 2021 and extracted relevant data including patient demographics, offending vessel(s), operative technique, outcome, and different complications. Descriptive statistics with uni- and multivariable analyses for the factors that may influence the seventh, eighth, and lower cranial nerves were performed.

Data from 420 patients were obtained. Three hundred seventeen of 344 patients (92.2%) with a minimum follow-up of 12 months had a favorable outcome. The mean follow-up (standard deviation) was 51.3 ± 38.7 months. Immediate complications reached 18.8% (79/420). Complications persisted in only 7.14% of patients (30/420) including persistent hearing deficits (5.95%) and residual facial palsy (0.95%). Temporary complications included CSF leakage (3.10%), lower cranial nerve deficits (3.57%), meningitis (0.71%), and brainstem ischemia (0.24%). One patient died because of herpes encephalitis. Statistical analyses showed that the immediate postoperative disappearance of spasms and male gender are correlated with postoperative facial palsy, whereas combined vessel compressions involving the vertebral artery (VA) and anterior inferior cerebellar artery can predict postoperative hearing deterioration. VA compressions could predict postoperative lower cranial nerve deficits.

MVD is safe and effective for treating HFS with a low rate of permanent morbidity. Proper patient positioning, sharp arachnoid dissection, and endoscopic visualization under facial and auditory neurophysiological monitoring are the key points to minimize the rate of complications in MVD for HFS
((Al Menabbawy A, El Refaee E, Elwy R, Shoubash L, Matthes M, Schroeder HWS. Preemptive strategies and lessons learned from complications encountered with microvascular decompression for hemifacial spasm. J Neurosurg. 2023 Jun 23:1-12. doi: 10.3171/2023.4.JNS23557. Epub ahead of print. PMID: 37382346.)).

===== 2019 =====


A retrospective analysis of the clinical data of 600 patients with HFS subjected to MVD from March 2016 to May 2018 was performed. Student t test, chi-square test, logistic regression analysis, and multivariate analysis of variance were used to analyze the correlation between delayed cure and its related factors.

Among the 600 patients enrolled, 117 had delayed cure after MVD. The shortest duration of delayed cure was 4 days, and the longest was 540 days, with an average of 108 days. The frequency of delayed improvement in these patients was not associated with sex, age, or offending vessel type (p > 0.05); however, delayed cure was positively correlated with the course of the disease, grade of HFS severity, and disappearance of abnormal muscle responses during the operation (p < 0.05). Moreover, a longer disease course was associated with more severe related symptoms and a longer duration of postoperative delayed cure.

MVD is an effective treatment for HFS. Given that postoperative delayed cure was unavoidable, even with accurate identification of the offending vessel and sufficient decompression of the root exit zone, delayed cure should be considered in patients undergoing reoperation due to lack of remission or relapse after the operation. Additionally, the timing of efficacy assessments should be delayed
((Li MW, Jiang XF, Wu M, He F, Niu C. Clinical Research on Delayed Cure after
Microvascular Decompression for Hemifacial Spasm. J Neurol Surg A Cent Eur
Neurosurg. 2019 Oct 10. doi: 10.1055/s-0039-1698461. [Epub ahead of print] PubMed
PMID: 31600810.
)).
----


Among more than 2500 patients who underwent [[microvascular decompression for hemifacial spasm]], 23 patients received a second [[MVD]] in the  [[Kyung Hee University Hospital]] from January 2002 to December 2017. Three-dimensional [[Time-of-flight magnetic resonance angiography]] and reconstructed imaging were used to identify the culprit vessel and its conflict upon [[root exit zone]] (REZ) of the [[facial nerve]]. They reviewed patients' medical records and operation [[video]]s to identify the missing points of the first surgery.

8 patients had incomplete decompression, such as single-vessel decompression of multiple offending vessels. Teflon was not detected at the REZ, but was found in other locations in 12 patients. Three patients had severe adhesion with previous Teflon around the REZ. Nineteen patients had excellent surgical outcomes at immediate postoperative evaluation; 20 patients showed spasm disappearance at 1 year after surgery and 3 patients showed persistent symptoms. Neuro-vascular contacts around REZ of facial nerve were revealed on MRI of incomplete decompression and Teflon malposition patient groups. There were no clear neuro-vascular contacts in the patients with severe Teflon adhesion.

The decision on secondary MVD for persistent or recurrent spasm is troubling. However, if the neurovascular contact was observed in the MRI of the patient and there were offending vessels, the surgical outcome might be favorable
((Park CK, Lee SH, Park BJ. Surgical Outcomes of Revision Microvascular
Decompression for Persistent or Recurrent Hemifacial Spasm after Surgery:
Analysis of radiological and intraoperative findings. World Neurosurg. 2019 Aug
2. pii: S1878-8750(19)32107-2. doi: 10.1016/j.wneu.2019.07.191. [Epub ahead of
print] PubMed PMID: 31382068.
)).
----
A total of 539 patients with [[hemifacial spasm]] (HFS) underwent [[MVD]] treatment in the [[Xinhua Hospital]] between January 2014 and June 2017. Among them, 83 patients had received [[botulinum toxin]] (BT) injection before surgery and were recorded as BT group. Eighty-three patients underwent [[acupuncture]] before surgery and were recorded as acupuncture group. Five patients received both BT injection and acupuncture before surgery and were recorded as mixed group. A total of 368 patients who had not received any treatment before surgery were recorded as simple MVD group. Zhang et al. calculated the immediate and long-term remission rates after surgery. Abnormal Muscle Response (AMR) and Compound Motor Action Potential (CMAP) monitoring were routinely performed during surgery.

Immediate remission rate after surgery was 96.4% (80/83) in BT group, 100% (83/83) in acupuncture group, 100% (5/5) in mixed group, and 95.1% (350/368) in simple MVD group, and the immediate remission rate of BT group is significantly higher than that of simple MVD group (p = 0.04). Long-term remission rate: the remission rates of the four groups were 94.0% (78/83), 97.6% (81/83), 100.0% (5/5) and 92.7%(341/368), respectively, and there is no statistical difference between them (p > 0.05). The amplitude of one branch or several branches of CMAP on the affected side was lower than the healthy side in BT or acupuncture treatment patients.

A preoperative BT injection or acupuncture treatment do not reduce the postoperative remission rate of HFS patients treated with MVD, and the amplitude of CMAP on the affected side was lower than the healthy side.
((Zhang WB, Min LZ, Zhong WX, Tao BB, Li B, Sun QY, Wang XQ. Surgical effect and
electrophysiological study of patients with hemifacial spasm treated with
botulinum toxin or acupuncture before microvascular decompression. Clin Neurol
Neurosurg. 2019 Jul 12;184:105417. doi: 10.1016/j.clineuro.2019.105417. [Epub
ahead of print] PubMed PMID: 31351214.
)).
----
Teton et al., from the Department of Neurosurgery, University of [[Michigan]], [[Ann Arbor]] and [[Portland]] retrospectively analyzed patients with [[hemifacial spasm]] who underwent [[MVD]] at a single institution, combined with a modified [[HFS-7]] telephone questionnaire. [[Kaplan-Meier survival analysis]] was used to determine event-free survival, and the [[Wilcoxon signed rank test]] was used to compare pre- and postoperative HFS-7 scores.

Thirty-five patients underwent MVD for HFS between 2002 and 2018 with subsequent 3D reconstructions of preoperative images. The telephone questionnaire response rate was 71% (25/35). If patients could not be reached by telephone, then the last clinic follow-up date was recorded and any recurrence noted. Twenty-four patients (69%) were symptom free at longest follow-up. The mean length of follow-up was 2.4 years (1 month to 8 years). The mean symptom-free survival time was 44.9 ± 5.8 months, and the average symptom-control survival was 69.1 ± 4.9 months. Four patients (11%) experienced full recurrence. Median HFS-7 scores were reduced by 18 points after surgery (Z = -4.013, p < 0.0001). Three-dimensional reconstructed images demonstrated that NVC most commonly occurred at the attached segment (74%, 26/35) of the facial nerve within the fREZ and least commonly occurred at the traditionally implicated transition zone (6%, 2/35).

MVD is a safe and effective treatment that significantly improves QOL measures for patients with HFS. The vast majority of patients (31/35, 89%) were symptom free or reported only mild symptoms at longest follow-up. Symptom recurrence, if it occurred, was within the first 2 years of surgery, which has important implications for patient expectations and informed consent. Three-dimensional image reconstruction analysis determined that culprit compression most commonly occurs proximally along the brainstem at the attached segment. The success of this procedure is dependent on recognizing this pattern and decompressing appropriately. Three-dimensional reconstructions were found to provide much clearer characterization of this area than traditional preoperative imaging. Therefore, the authors suggest that use of these reconstructions in the preoperative setting has the potential to help identify appropriate surgical candidates, guide operative planning, and thus improve outcome in patients with HFS
((Teton ZE, Blatt D, Holste K, Raslan AM, Burchiel KJ. Utilization of 3D imaging
reconstructions and assessment of symptom-free survival after microvascular
decompression of the facial nerve in hemifacial spasm. J Neurosurg. 2019 Jul
12:1-8. doi: 10.3171/2019.4.JNS183207. [Epub ahead of print] PubMed PMID:
31299649.
)).
----
A study included 21 patients who underwent redo MVD over the last two decades. Their medical charts were retrospectively reviewed for preoperative medical history, prior and redo MVD intraoperative findings, and prior and redo MVD postoperative outcomes.

Redo MVDs were 2nd operations in 20 patients and 3rd procedure in one patient. The median interval between prior and redo MVD was 46.3 months (range, 14.4-188.2). 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 prior MVD failure. MVD failure was caused by neglected offending vessels in ten patients, insufficient decompression in seven patients, and untouched neurovascular compression sites in four patients. Spasm-free rates after redo MVD were 80.5% at one year and 90.5% in the last year of follow-up (median 15.8 months; range, 3.6-152.0. Permanent hearing loss and facial palsy were each observed in two (9.5%) patients. Additionally, one patient experienced cerebellar infarction and another experienced vocal cord palsy.

Redo MVD remains a feasible treatment option for HFS patients who have failed to benefit from prior MVD, but is associated with higher risks of cranial nerve and vascular injuries
((Lee S, Park SK, Lee JA, Joo BE, Park K. Missed Culprits in Failed
Microvascular Decompression Surgery for Hemifacial Spasm and Expenses for Redo
Surgery. World Neurosurg. 2019 May 31. pii: S1878-8750(19)31508-6. doi:
10.1016/j.wneu.2019.05.231. [Epub ahead of print] PubMed PMID: 31158550.
)).

----

Jani et al., from the [[University of Pittsburgh Medical Center]], [[prospective]]ly recruited 27 patients without [[facial pain]] who were undergoing [[microvascular decompression]] for [[hemifacial spasm]] and had undergone high-resolution preoperative [[MRI]]. [[Neurovascular contact]]/compression (NVC/C) by [[artery]] or [[vein]] was assessed both intraoperatively and by MRI, and was stratified into 3 types: simple contact, [[compression]] (indentation of the surface of the nerve), and [[deformity]] (deviation or distortion of the nerve).

Intraoperative evidence of NVC/C was detected in 23 patients. MRI evidence of NVC/C was detected in 18 patients, all of whom had intraoperative evidence of NVC/C. Thus, there were 5, or 28% more patients in whom NVC/C was detected intraoperatively than with MRI (Kappa = 0.52); contact was observed in 4 of these patients and compression in 1 patient. In patients where NVC/C was observed by both methods, there was agreement regarding the severity of contact/compression in 83% (15/18) of patients (Kappa = 0.47). No patients exhibited deformity of the nerve by imaging or intraoperatively.

There was moderate agreement between imaging and operative findings with respect to both the presence and severity of NVC/C
((Jani RH, Hughes MA, Gold MS, Branstetter BF, Ligus ZE, Sekula RF Jr.
Trigeminal Nerve Compression Without Trigeminal Neuralgia: Intraoperative vs
Imaging Evidence. Neurosurgery. 2019 Jan 1;84(1):60-65. doi:
10.1093/neuros/nyx636. PubMed PMID: 29425330.
)).
===2017===
Endoscopic-assisted microvascular decompression (MVD) was performed in 42 patients with HFS with complicated local anatomy from Janurary 2008 to Janurary 2012 in the Department of Neurosurgery, Hospital Affiliated with Nanjing Medical University of Wuxi, Wuxi, [[China]]., in the event of a significant blind spot, endoscopic exploration was performed with multi-angle 360-degree observation, including exploration of the brainstem facial nerve root exit zone (REZ) and exploration of the distal end of the nerve, and the relationships between blood vessels and nerves were carefully determined. After surgery, endoscopic examination was performed again to rule out vascular omissions, avascular excessive stretch, kinking, or formation of new compressions. The relevant data of all cases were retrospectively analyzed.

All patients were followed for 18-30 months, 41 patients had complete remission without recurrence (97.6%), 3 cases recovered to grade 0 from discharge grade I, 1 case of hearing loss was fully restored in 6 months, and 1 case of grade II was not significant increased to the end of follow-up.

Neuroendoscopy is an effective supplement to traditional MVD in treating HFS. In particular, in patients with complicated or abnormal local anatomy (for example small posterior fossa volume, abnormal fullness of the cerebellar flocculus, petrous bone block, local thickening of arachnoid adhesions, and unidentified offending vessels), neuroendoscopy can greatly improve the effectiveness of surgery
((Zhi M, Lu XJ, Wang Q, Li B. Application of neuroendoscopy in the surgical
treatment of complicated hemifacial spasm. Neurosciences (Riyadh). 2017
Jan;22(1):25-30. doi: 10.17712/nsj.2017.1.20150567. PubMed PMID: 28064327.
)).
===2016===
A retrospective analysis of 370 patients who underwent microvascular decompression for HFS was performed. The patients were divided into four groups based on the offending arteries, namely [[anterior inferior cerebellar artery]] (AICA), [[posterior inferior cerebellar artery]] (PICA), [[vertebral artery]], and multiple offending arteries. Affected side, age at onset, presence of hypertension, and sigmoid sinus area and dominance were compared between groups. The mean age of patients with a left HFS was significantly greater than that of patients with a right HFS (P=0.009). The AICA affected primarily the right side and PICA and multiple offending arteries the left side (P<0.001). Side of sigmoid sinus dominance was significantly different among groups (P<0.001). The offending arteries in HFS may be related to these differences. AICA was associated with right-sided symptoms, younger age at onset, and presence of left dominant sigmoid sinus, while PICA was associated with left-sided symptoms, older age at onset, and smaller right sigmoid sinus area
((Chung M, Han I, Chung SS, Huh R. Side predilections of offending arteries in
hemifacial spasm. J Clin Neurosci. 2016 Jul;29:106-10. doi:
10.1016/j.jocn.2015.10.041. PubMed PMID: 26898581.
)).
----

Twenty-six patients underwent late redo MVD in our institution from January 1, 2011 to December 31, 2015. The clinical features, surgical findings, outcomes, and complications of the repeat MVD were analyzed retrospectively.

Twenty-four (92.3 %) patients were cured immediately after the redo MVD. Delayed relief was found in two (7.7 %) patients; it took 6 days and 2 weeks for them to obtain complete relief. No recurrence was found during follow-up. Surgical complications including three (11.5 %) facial paralysis and one (3.8 %) hearing loss.

We suggested that repeat MVD can be performed 2 years after the first MVD if the spasm was not resolved. Repeat MVD for HFS is effective
((Jiang C, Xu W, Dai Y, Lu T, Jin W, Liang W. Failed microvascular decompression
surgery for hemifacial spasm: a retrospective clinical study of reoperations.
Acta Neurochir (Wien). 2016 Nov 5. [Epub ahead of print] PubMed PMID: 27817006.
)).
----

Three hundred seventy-two patients received microvascular decompression (MVD) under intraoperative electrophysiological monitoring in Nanjing Drum Tower Hospital in 2014; the characteristic AMR of HFS was observed in 359 patients during the operation. And the 359 patients were divided into two groups based on whether AMR had remained before the beginning of the decompression procedure for offending vessels. Thirty-three patients who showed a permanent disappearance of AMR before the beginning of decompression were regarded as group I. Dural opening and the succeeding CSF drainage produced a permanent disappearance of AMR in 13. During the dissection of lateral cerebellomedullary cistern, a permanent disappearance of AMR was found in 20 patients. Thirty-two patients were cured immediately; delayed resolution (7 days after surgery) was found in one patient. No complications were observed and no recurrence was found during the follow-up period in the 33 patients. In the other 326 patients (group II), AMR disappeared temporarily before the beginning of the decompression procedure for offending vessels in 42 patients. After decompression, AMR disappeared completely in 305 patients. Two hundred sixty-seven patients were cured immediately and 57 patients got a delayed resolution (2 days to 45 weeks after surgery). The two left did not get a complete abolition of spasm. Three cases of hearing loss, one hoarseness, and nine delayed facial paralysis were observed. The reason of early abnormal muscle response disappearance may be that the degree of neurovascular compression was not serious; these patients were more likely to get an immediate cure. Continuous intraoperative electrophysiological monitoring of AMR is necessary
((Jiang C, Xu W, Dai Y, Lu T, Jin W, Liang W. Early permanent disappearance of
abnormal muscle response during microvascular decompression for hemifacial spasm:
a retrospective clinical study. Neurosurg Rev. 2016 Dec 15. [Epub ahead of print]
PubMed PMID: 27981401.
)).
----

Between June 2005 and May 2014, 13 patients with facial hemispasm were operated, underwent microvascular decompression. The age, sex, duration of symptoms before surgery, and surgical finds, were all evaluated. In addition, postoperative results were also analyzed.

Seven patients were women and 6 were men. The average age of the patients was 53 years. The average time between onset of symptoms and surgery ranged from 3 to 9 years. In all cases the facial hemispasm was typical, one with concomitant trigeminal neuralgia, observed in all neurovascular compression intraoperative. In decreasing order of frequency, the cause of compression was anterior inferior cerebellar artery, posterior inferior cerebellar artery, dolicomega basilar artery and dolicomega vertebral artery. The average time of postoperative follow-up after the surgery was 24 months. Complete relief from spasm occurred in 62%; 30% disappearance after 3 weeks-2 months (8% partial) and in 8% had no improvement. Regarding postoperative complications: 3 patients had facial paresis II-III in House-Brackman scale and 1 patient presented CSF leak. None of the patients in the serie had hearing loss or deafness.

The microvascular decompression for facial hemispasm is a safe an effective procedure, which allows complete resolution of the disease in most cases
((Campero A, Herreros IC, Barrenechea I, Andjel G, Ajler P, Rhoton A.
[Microvascular decompression in hemifacial spasm: 13 cases report and review of
the literature]. Surg Neurol Int. 2016 Apr 1;7(Suppl 8):S201-7. doi:
10.4103/2152-7806.179545. Spanish. PubMed PMID: 27127708; PubMed Central PMCID:
PMC4828948.
)).
----

42 patients included in the analysis consisted of 22 females and 20 males, with an average follow-up duration of 76 months (range 24-132 months). Intraoperative investigation revealed that an artery other than the VA was responsible for the neurovascular compression in all cases : posterior inferior cerebellar artery (PICA) in 23 patients (54.7%) and anterior inferior cerebellar artery (AICA) in 11 patients (26.2%). All patients became symptom-free after MVD. Neither recurrence nor postoperative neurological deficit was noted during the 2-year follow-up, except in one patient who developed permanent deafness. Cerebrospinal fluid (CSF) leak occurred in three patients, and one required dural repair.

Transposition of the VA using a bioglue-coated Teflon [[sling retraction technique]] is a safe and effective surgical technique for HFS involving the VA. A future prospective study to compare clinical outcomes between groups with and without use of this novel technique is required
((Lee SH, Park JS, Ahn YH. Bioglue-Coated Teflon Sling Technique in
Microvascular Decompression for Hemifacial Spasm Involving the Vertebral Artery. 
J Korean Neurosurg Soc. 2016 Sep;59(5):505-11. doi: 10.3340/jkns.2016.59.5.505.
PubMed PMID: 27651870; PubMed Central PMCID: PMC5028612.
)).
----

Joo et al., performed a preliminary study of 13 patients with HFS in 2010. They increased the stimulation rate from 10.1 Hz/sec to 100.1 Hz/sec by 10-Hz increments, and they elevated the average time from 100 times to 1000 times by 100-unit increments at a fixed stimulus rate of 43.9 Hz. After defining the optimal stimulation rate and the number of trials that needed to be averaged for IOM of BAEPs, they also identified the useful warning criteria for this protocol for MVD surgery. From January to December 2013, 254 patients with HFS underwent MVD surgery following the new IOM of BAEPs protocol. Pure-tone audiometry and speech discrimination scoring were performed before surgery and 1 week after surgery. To evaluate the usefulness of the new protocol, the authors compared the incidence of postoperative hearing impairment with the results from the group that underwent MVD surgery prior to the new protocol. 

Through a preliminary study, the authors confirmed that it was possible to obtain a reliable wave when using a stimulation rate of 43.9 Hz/sec and averaging 400 trials. Only a Wave V amplitude loss > 50% was useful as a warning criterion when using the new protocol. A reliable BAEP could be obtained in approximately 9.1 seconds. When the new protocol was used, 2 patients (0.8%) showed no recovery of Wave V amplitude loss > 50%, and only 1 of those 2 patients (0.39%) ultimately had postoperative hearing impairment. When compared with the outcomes in the pre-protocol group, hearing impairment incidence decreased significantly among patients who underwent surgery with the new protocol (0.39% vs 4.02%, p = 0.002). There were no significant differences between the 2 surgery groups regarding other complications, including facial palsy, sixth cranial nerve palsy, and vocal cord palsy. 

There was a significant decrease in postoperative hearing impairment after MVD for HFS when the new protocol for IOM of BAEPs was used. Real-time IOM of BAEPs, which can obtain a reliable BAEP in less than 10 seconds, is a successful new procedure for preventing hearing impairment during MVD surgery for HFS
((Joo BE, Park SK, Cho KR, Kong DS, Seo DW, Park K. Real-time intraoperative
monitoring of brainstem auditory evoked potentials during microvascular
decompression for hemifacial spasm. J Neurosurg. 2016 Nov;125(5):1061-1067.
PubMed PMID: 26824371.
)).
===2015===
A retrospective study evaluated the length of cerebellar retraction and the changes of intraoperative brainstem auditory evoked potential (BAEP) during microvascular decompression (MVD), and assessed the predictive value of the hearing loss as a prognostic indicator for the treatment outcome of hemifacial spasm (HFS).

This series included 1,518 consecutive patients affected with HFS who underwent MVD, during which BAEP was monitored. Patients were divided into two groups based on whether hearing loss occurred following decompression or not. Each patient underwent a similar procedure performed by one neurosurgeon. The two patients groups were matched with regard to sex, age, and degree of spasm.
RESULTS:

Among the 1,518 patients, 106 (6.98 %) displayed functional hearing changes. Hearing loss was permanent in 12 patients (0.79 %). Of the 1,412 patients with stationary hearing compared with preoperative audiometry, 96 patients were selected who were individually matched with respect to sex, age, and degree of spasm. BAEP changed immediately after cerebellar retraction in 7 of 12 hearing-loss patients, suggesting the importance of retraction on hearing outcomes. The distance from the cerebellar surface of the petrous temporal bone to the neurovascular compression point was measured. The median distance of cerebellar retraction in the hearing-loss group was 13.77 mm, which was longer than the median distance in the control group.

Preoperative measurement of the cerebellar retraction distance can be a valuable clue to predict and prevent postoperative hearing loss in MVD for HFS
((Lee MH, Lee HS, Jee TK, Jo KI, Kong DS, Lee JA, Park K. Cerebellar retraction 
and hearing loss after microvascular decompression for hemifacial spasm. Acta
Neurochir (Wien). 2015 Feb;157(2):337-43. doi: 10.1007/s00701-014-2301-8. Epub
2014 Dec 18. PubMed PMID: 25514867.
)).

=== 2012 ===
A prospective randomized controlled trial of 96 patients with HFS (ASA status I or II) undergoing MVD under general anesthesia. Patients are randomized to receive succinylcholine, vecuronium, or no muscle relaxant before intubation. Intraoperative LSR will be recorded until the dural opening. The primary outcome of this study is the rate of the LSR, and the secondary outcomes are post-intubation pharyngolaryngeal symptoms, the rate of difficult intubations, the rate of adverse hemodynamic events and the relationship between the measurement of LSR or not, and clinical success rates at 30 days after surgery.

This study aims to evaluate the impact of muscle relaxants on the rate of the LSR, and the study may provide evidence supporting the use of muscle relaxants before intubation in patients with HFS undergoing MVD surgery.

http://www.chictr.org/ ChiCTR-TRC-11001504 Date of registration: 24 June, 2011. The date the first patient was randomised: 30 September, 2011
((Fang Y, Zhang H, Liu W, Li Y. A comparison of three induction regimens using
succinylcholine, vecuronium, or no muscle relaxant: impact on the intraoperative 
monitoring of the lateral spread response in hemifacial spasm surgery: study
protocol for a randomised controlled trial. Trials. 2012 Sep 8;13:160. doi:
10.1186/1745-6215-13-160. PubMed PMID: 22958580; PubMed Central PMCID:
PMC3502586.
)).

===2005===
84 consecutive patients affected with hemifacial spasm who underwent microvascular decompression during which BAEPs were monitored. During surgery, Wave I, I to V interpeak interval, latency, and amplitude of Wave V were recorded and measured. Auditory function was studied before and after surgery and expressed as a pure tone average in all patients. Then, correlations were made between hearing impairment after surgery and intraoperative BAEP changes in an attempt to define warning values.

Seventy-four patients (88%) had no hearing loss after surgery (Group 1). Eight patients (9.5%) had hearing impairment with a decrease in pure tone average of more than 20 dB (Group 2). Two patients (2.3%) experienced a definitive and complete hearing loss on the side operated on (Group 3). Among intraoperative BAEP changes, latency of Peak V was the most frequently observed and the most significant phenomenon, especially during cerebellar retraction and the decompression step of the microvascular decompression procedure. In the group of patients without hearing loss (Group 1), the mean delay in latency of Peak V was 0.61 millisecond (standard deviation, +/-0.36 ms); in the group with hearing decrease (Group 2), the mean delay was 1.05 milliseconds (standard deviation, +/-0.64 ms); and in the group with deafness (Group 3), Wave V was abolished.

From a practical standpoint, three warning values, based on delay in latency of Peak V, were established for use during surgery: an initial one at 0.4 millisecond ("watching" signal) at the safety limit; a second one at 0.6 millisecond (risk "warning" signal), which is the mean value corresponding to the group of patients without postoperative hearing loss; and an ultimate one at 1 millisecond ("critical" warning), before irreversibility. These warnings should help the surgeon to avoid or correct maneuvers that are dangerous for hearing function, which is mandatory in functional surgery
((Polo G, Fischer C, Sindou MP, Marneffe V. Brainstem auditory evoked potential 
monitoring during microvascular decompression for hemifacial spasm:
intraoperative brainstem auditory evoked potential changes and warning values to 
prevent hearing loss--prospective study in a consecutive series of 84 patients.
Neurosurgery. 2004 Jan;54(1):97-104; discussion 104-6. PubMed PMID: 14683545.
)).
===== References =====