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Prognostic value of intra-operative abnormal muscle response monitoring during microvascular decompression for long-term outcome of hemifacial spasm
Journal of Clinical Neuroscience 19 (2012) 44–48
Contents lists available at SciVerse ScienceDirect
Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Clinical Study
Prognostic value of intra-operative abnormal muscle response monitoring during microvascular decompression for long-term outcome of hemifacial spasm Li Jiping a, Zhang Yuqing a, Zhu Hongwei a, Li Yongjie b,⇑ a b
Department of Functional Neurosurgery of Xuanwu Hospital, Capital Medical University, Beijing 100053, China Beijing Institute of Functional Neurosurgery, 45 Changchun Avenue, Xicheng District, Beijing 100053, China
a r t i c l e
i n f o
Article history: Received 13 February 2011 Accepted 2 April 2011
Keywords: Abnormal muscle response Hemifacial spasm Intra-operative monitoring Microvascular decompression
a b s t r a c t The reliability of intra-operative abnormal muscle response (AMR) monitoring as an indicator of postoperative outcome in patients with hemifacial spasm (HFS) is under debate. The primary aim of this study was to evaluate the correlation between intra-operative AMR changes and long-term post-operative outcome. We monitored intra-operative AMR during microvascular decompression (MVD) in consecutive patients with HFS (n = 104). Patients in this study were divided into two groups based on whether their AMR disappeared or persisted following MVD. Ninety patients were followed-up, and the mean duration from surgery to final follow-up examination was 3.7 years. Fourteen patients were lost to follow-up. AMR disappeared during surgery for 80 patients; of these, 74 achieved complete resolution of HFS, five had persistent HFS, and one patient developed a recurrence of HFS. Of the 10 patients with persistent AMR despite effective MVD, eight patients achieved complete resolution, one patient had persistent HFS, and one developed recurrent HFS. The long-term clinical outcome of HFS after MVD did not significantly correlate with intra-operative AMR changes (p = 0.791). Therefore, we suggest that intra-operative AMR monitoring may not be a reliable indicator of long-term post-operative outcome for HFS. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
2. Materials and methods
Hemifacial spasm (HFS) is an involuntary twitching or contraction of the facial muscles on one side of the face, and is thought to be caused by neurovascular compression of the facial nerve at its root exit zone (REZ).1,2 The most effective treatment for HFS is microvascular decompression (MVD). Abnormal muscle response (AMR),3 also termed lateral spread response,4 is observed in patients with HFS by electrically stimulating one branch of the facial nerve recording from the muscles innervated by other braches of the facial nerve by electromyography. In most patients with HFS, AMR disappears within seconds when the offending vessels are removed from the facial nerve during MVD.5–8 Accordingly, intraoperative AMR monitoring is a useful indicator to identify the offending vessels and to confirm adequate decompression.9–11 However, debate exists regarding the reliability of intra-operative AMR monitoring as an indicator of post-operative outcome. We investigated whether AMR findings obtained during MVD adequately reflect post-operative outcome in patients with HFS. Because the symptoms of HFS after MVD significantly improve over time,12,13 we measured the correlation between intra-operative AMR changes and the long-term post-operative outcome.
This study included 104 consecutive patients (34 male, 70 female; mean age = 47.5 years, range = 19–72 years) who were diagnosed with primary HFS and treated with MVD at our department between November 2006 and July 2007. The duration of HFS before surgery ranged from 4 months to approximately 20 years, and the mean duration was 7.9 years. To display the anatomic relationship between the vessels and facial nerve, all patients were assessed pre-operatively using three-dimensional time-of-flight magnetic resonance angiography. Intra-operative AMR monitoring was performed using Nicolet Viking Select electromyography monitor (Nicolet Biomedical, Madison, WI, USA). Prior to the induction of anesthesia, paired stimulating needle electrodes were inserted intradermally over the zygomatic branch of the facial nerve, and recording needle electrodes were inserted into the ipsilateral mentalis muscle (Fig. 1). Electrical stimulation used for AMR monitoring employed 0.1 millisecond (ms) rectangular waves at the following settings: (i) 5– 20 mA; (ii) band pass filter 20–3000 Hz; (iii) sensitivity 20–200 uv; and (iv) analysis time 50 ms. Operations were performed under general anesthesia, but muscle relaxants were only used for intubation. A small craniectomy was performed below the asterion and a dural opening. Subsequently, the flocculus and choroid plexus were gently retracted
⇑ Corresponding author. Tel.: +86 10 8319 8882; fax: +86 10 8316 3174. E-mail address: [email protected] (Y. Li). 0967-5868/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jocn.2011.04.023
J. Li et al. / Journal of Clinical Neuroscience 19 (2012) 44–48
45
Fig. 1. Schematic diagram showing the insertion position of the paired stimulating needle electrodes intradermally over the zygomatic branch of the facial nerve, and the recording needle electrodes into the ipsilateral mentalis muscle.
to expose the REZ of the facial nerve, and the REZ was examined for vascular contact. The offending vessels were dissected and moved away from the REZ. To separate the offending vessels from the REZ, interposing polytetrafluoroethylene (TeflonÒ) patches were placed between the vessels and the brainstem. AMR recordings were obtained at each stage of the MVD procedure as follows: (i) before anesthesia (baseline response); (ii) opening of the dura; (iii) retraction of the cerebellum; (iv) removal of cerebrospinal fluid; (v) dissecting the offending vessels; (vi) polytetrafluoroethylene interposition; (vii) termination of the microsurgical procedure; (viii) infusion of physiological saline; and (ix) closure of the dura. If AMR did not disappear following MVD, or if AMR reappeared after the release of cerebellar retraction, we started again with a further decompressive procedure. If AMR persisted following confirmation that no offending vessels remained, we completed the microsurgical procedure. All patients were contacted by telephone at the last follow-up in November 2010. Statistical analysis was performed using the Statistical Package for the Social Sciences version 16.0, and the relationship between the intra-operative AMR and the long-term results were analyzed by Fisher’s exact test. The level for statistical significance was p < 0.05.
(9.6%) patients despite effective decompression (Figs. 3 and 4). The mean duration from surgery to the final follow-up examination was 3.7 years (range = 3.2–4.0 years), and 14 patients were lost to follow-up. The remaining 90 patients were divided into two groups. Group I included 80 patients in whom AMR disappeared completely following MVD, and Group II included 10 patients in whom AMR persisted despite decompression. Seven of the 10 patients in Group II experienced a decrease in AMR amplitude to approximately 50–87.5% of that before surgery (mean = 69.6%), and pre-operative waveforms persisted in three patients. The results of MVD are summarized in Table 1. In Group I, 74 of 80 patients achieved complete relief from HFS, five patients had persistent HFS, and one patient developed recurrent HFS 6 months after surgery. In Group II, eight of 10 patients achieved complete relief from HFS, one patient in whom the AMR amplitude decreased had mild HFS, and one patient in whom pre-operative AMR persisted developed recurrent HFS 3 months after surgery. There was no significant difference in the long-term clinical results between the two groups (p = 0.791, Fisher’s exact test). AMR findings obtained during MVD did not reflect the long-term post-operative outcome of HFS.
3. Results
4. Discussion
Valid AMR were obtained for all patients prior to surgery; the mean latency was 12.6 ± 3.2 ms (Fig. 2). Following MVD, AMR disappeared in 94 (90.4%) patients, and AMR persisted in 10
AMR is an abnormal electromyogram response characteristic of patients with HFS, the latency of which is approximately 9–10 ms and the amplitude 0.1–0.2 mV, and its presence strongly supports a
46
J. Li et al. / Journal of Clinical Neuroscience 19 (2012) 44–48
Fig. 2. Pre-operative recordings showing abnormal muscle response: (A) five consecutive single recordings of a patient before surgery (A1–A5); and (B) constant and strongly overlapping waveforms.
Fig. 3. Intra-operative recordings of abnormal muscle response (AMR): (A1–5) before anesthesia (baseline response); during (A6) craniotomy and after (A7) dural opening; (A8, A9) cerebellar retraction with removal of the cerebrospinal fluid; (A10) interposition of polytetrafluoroethylene between the vessel and the brainstem after mobilization of the offending vessels; (A11) additional insertion of polytetrafluoroethylene; (A12) release of the cerebellar retraction; (A13) infusion of physiological saline; (A14) dura mater suturing; (A15) skin suturing. AMR disappeared after microvascular decompression.
diagnosis of HFS.3 In this study, all patients had characteristic AMR. Intra-operative AMR monitoring is used in HFS because it has been shown to instantaneously disappear after the offending vessels have been removed from the facial nerve REZ; and recompression of the vessels leads to a reappearance of AMR.5–8 It has been hypothesized that the disappearance of AMR is indicative of adequate decompression; and that this correlates with resolution of HFS after surgery. Conversely, the persistence of AMR indicates inadequate decompression and the persistence of HFS.
In our study, only three of 80 patients (3.8%) in whom AMR disappeared completely following MVD showed no significant improvement during the follow-up period. Two of the three patients (patients 78 and 79 in Group I) experienced significant improvement in the initial post-operative months, but their symptoms later reappeared. This subsequent recurrence of HFS may be attributed to other causes such as movement of the implant or the development of compression in new vessels. The third patient in the group (patient 77 in Group I), who experienced a 50% decrease
47
J. Li et al. / Journal of Clinical Neuroscience 19 (2012) 44–48
Fig. 4. Intra-operative abnormal muscle response (AMR) (A) before surgery and (B) changes after microvascular decompression (MVD) showing: (A1) AMR disappeared after MVD (patients in Group I); (A2) AMR persisted but amplitude decreased (in seven of 10 patients in Group II); (A3) pre-operative waveforms persisted, despite MVD (in three of 10 patients in Group II).
Table 1 Intra-operative abnormal muscle response (AMR) recording and the long-term results of microvascular decompression (MVD) for hemifacial spasm (HFS)
Group I
Group II
Patient
AMR changes
Results of MVD
1–74 75 76 77 78 79 80
Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared
Complete relief HFS reduced 90% HFS reduced 90% HFS reduced 50% HFS reduced 20% HFS unchanged Recurrence, HFS reduced 90%
1
Amplitude 60.0% Amplitude 50.0% Amplitude 80.0% Amplitude 75.0% Amplitude 87.5% Amplitude 60.0% Amplitude 75.0% Amplitude Amplitude Amplitude
reduced
Complete relief
reduced
Complete relief
reduced
Complete relief
reduced
Complete relief
reduced
Complete relief
reduced
Complete relief
reduced
HFS reduced 40%
unchanged unchanged unchanged
Complete relief Complete relief Recurrence, HFS aggravated
2 3 4 5 6 7 8 9 10
in symptoms after surgery, had a less common form of HFS characterized by involuntary twitching of the forehead muscle on the right side of the face. The findings of our study, as also shown by previous studies (see Table 2), suggest that the disappearance of AMR following MVD indicates a high likelihood of post-operative long-term relief from HFS. The debate over the reliability of intra-operative AMR monitoring as an indicator of post-operative outcome remains focused on whether the persistence of AMR following decompression always correlates with a poor outcome. Previous studies have shown evidence that AMR may be an unreliable predictor of long-term outcome. For example, in studies reported by Kiya et al. and Hatem et al., all patients experienced resolution of HFS despite persistent AMR upon completion of the operation.16,17 Similarly, Kong et al. reported 22 of 33 patients (66.7%) and Joo et al. reported 26 of 32
Table 2 Reports of abnormal muscle response monitoring Yearref
Follow-up period (months)
No. of HFS outcome and AMR findings patients HFS cured/AMR HFS not persisted cured/ (amplitude AMR decreased) disappeared
19878 19919 199614 199715 200110 200116 200117 200518 200619 200720 200821 200922 Present study
1–24 3–36 12–66 (36) 6–24 (12) >12 >3 12–36 12–74 (61) 67–118 (87) 12–55 (35.8) >6 1–28.6 (10.7) 39–47 (44.4)
67 8 40 132 74 38 33 60 51 263 72 69 90
2/44 0/7 2/38 5/70 8/69 0/21 1/23 3/53 2/44 22/230 4/40 5/53 6/80
16/23 (14/16) 1/1 0/2 44/62 (41/58) 4/5 17/17 10/10 6/7 (5/6) 5/7 (5/6) 22/33 26/32 15/16 8/10 (6/7)
Mean follow-up period shown in parentheses. AMR = abnormal muscle response, HFS = hemifacial spasm.
patients (81.3%) in whom AMR persisted but who had no HFS.20,21 Conversely, some investigators divided their patients with persistent AMR into two groups according to amplitude changes: (i) AMR decreased (reduction of P 50%); and (ii) no change in AMR (reduction < 50%).8,15,18 These studies found that patients with decreased AMR after MVD showed good outcome compared with patients with persistent, unchanged AMR. However, in our study, both decreased AMR or no change in AMR were correlated with good post-operative outcome. We suggest that patients can achieve excellent results, even if AMR persists after the initial decompression, if an effective and thorough decompression is performed. The exact mechanism of post-operative persistence of AMR despite effective decompression has not yet been sufficiently delineated. AMR is caused by a cross-transmission of antidromic activity, and intra-operative measurements of neural conduction time in parts of the facial nerve in patients with HFS who undergo MVD indicate that abnormal cross-transmission occurs at a central site, probably in the facial nucleus.23 In studies in which chronic electrical stimulation was applied to the facial nucleus of rats,
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J. Li et al. / Journal of Clinical Neuroscience 19 (2012) 44–48
kindling-like hyperactivity of the facial nucleus was determined to be the cause of the AMR.24 We assume that the persistence of AMR following complete decompression of the facial nerve REZ may be attributed to the remaining hyperexcitability of the facial nucleus. Consistent with this hypothesis, Ishikawa et al. reported that AMR was recorded, and subsequently disappeared, in seven patients within 1 month after complete relief of HFS. Patients continued to demonstrate improvement in their AMR status during the follow-up period.25 This has also been described in other reports,2,26 in which hyperexcitability of the facial nucleus required several months to normalize, and then AMR disappeared. Although AMR does not always disappear completely despite effective decompression, intra-operative AMR monitoring can provide useful assistance during surgery. In our experience, if AMR is absent after decompression, we close the incision. If AMR persists after the decompression, further microsurgical procedure is performed until we can confirm that no visible contact exists between the facial nerve and blood vessels. The persistence of AMR can provide surgeons with a warning of insufficient decompression, supporting further exploration to avoid missing offending vessels. This information is particularly useful for patients with HFS who have vascular compression in the distal portion of the facial nerve or facial nerve compression by multiple vessels. Similarly, AMR can be useful for patients in whom recompression results from excessive insertion of polytetrafluoroethylene or the change of positional relationship between the offending vessels and the facial nerve after release of the cerebellar retraction and infusion of physiological saline.14 Therefore, we encourage routine application of intra-operative AMR monitoring during MVD for HFS which should be continued until the end of surgery. 5. Conclusion The persistence of AMR after decompression did not always indicate post-operative persistent HFS if an effective and thorough decompression was performed, and the long-term outcome of HFS did not always correlate with the disappearance or persistence of AMR. Therefore, AMR may not be a reliable indicator of long-term post-operative outcome. Nonetheless, intra-operative AMR monitoring can be useful in guiding neurosurgeons to obtain sufficient decompression, and we advocate routine intra-operative AMR monitoring during MVD for HFS. References 1. Moller AR. The cranial nerve vascular compression syndrome: II. A review of pathophysiology. Acta Neurochir (Wien) 1991;113:24–30. 2. Moller AR. Vascular compression of cranial nerves: II: pathophysiology. Neurol Res 1999;21:439–43. 3. Moller AR, Jannetta PJ. On the origin of synkinesis in hemifacial spasm: results of intracranial recordings. J Neurosurg 1984;61:569–76.
4. Nielsen VK. Pathophysiology of hemifacial spasm: I. Ephaptic transmission and ectopic excitation. Neurology 1984;34:418–26. 5. Moller AR, Jannetta PJ. Hemifacial spasm: results of electrophysiologic recording during microvascular decompression operations. Neurology 1985;35:969–74. 6. Moller AR, Jannetta PJ. Microvascular decompression in hemifacial spasm: intraoperative electrophysiological observations. Neurosurgery 1985; 16:612–8. 7. Moller AR, Jannetta PJ. Physiological abnormalities in hemifacial spasm studied during microvascular decompression operations. Exp Neurol 1986;93:584–600. 8. Moller AR, Jannetta PJ. Monitoring facial EMG responses during microvascular decompression operations for hemifacial spasm. J Neurosurg 1987;66:681–5. 9. Haines SJ, Torres F. Intra-operative monitoring of the facial nerve during decompressive surgery for hemifacial spasm. J Neurosurg 1991;74:254–7. 10. Mooij JJ, Mustafa MK, van Weerden TW, et al. Hemifacial spasm: intraoperative electromyographic monitoring as a guide for microvascular decompression. Neurosurgery 2001;49:1365–71. 11. Sindou MP. Microvascular decompression for primary hemifacial spasm: importance of intra-operative neurophysiological monitoring. Acta Neurochir (Wien) 2005;147:1019–26. 12. Li CS. Varied patterns of postoperative course of disappearance of hemifacial spasm after microvascular decompression. Acta Neurochir (Wien) 2005;147:617–20. 13. Oh ET, Kim E, Hyun DK, et al. Time course of symptom disappearance after microvascular decompression for hemifacial spasm. J Korean Neurosurg Soc 2008;44:245–8. 14. Isu T, Kamada K, Mabuchi S, et al. Intra-operative monitoring by facial electromyographic responses during microvascular decompressive surgery for hemifacial spasm. Acta Neurochir (Wien) 1996;138:19–23. 15. Shin JC, Chung UH, Kim YC, et al. Prospective study of microvascular decompression in hemifacial spasm. Neurosurgery 1997;40:730–4. 16. Kiya N, Bannur U, Yamauchi A, et al. Monitoring of facial evoked EMG for hemifacial spasm: a critical analysis of its prognostic value. Acta Neurochir (Wien) 2001;143:365–8. 17. Hatem J, Sindou M, Vial C. Intra-operative monitoring of facial EMG responses during microvascular decompression for hemifacial spasm. Prognostic value for long-term outcome: a study in a 33-patient series. Br J Neurosurg 2001;15:496–9. 18. Yamashita S, Kawaguchi T, Fukuda M, et al. Abnormal muscle response monitoring during microvascular decompression for hemifacial spasm. Acta Neurochir (Wien) 2005;147:933–7. 19. Fukuda M, Yamashita S, Kawaguchi T, et al. Abnormal muscle response monitoring during microvascular decompression for hemifacial spasm and long term results. No Shinkei Geka 2006;34:583–9. 20. Kong DS, Park K, Shin BG, et al. Prognostic value of the lateral spread response for intra-operative electromyography monitoring of the facial musculature during microvascular decompression for hemifacial spasm. J Neurosurg 2007;106:384–7. 21. Joo WI, Lee KJ, Park HK, et al. Prognostic value of intra-operative lateral spread response monitoring during microvascular decompression in patients with hemifacial spasm. J Clin Neurosci 2008;15:1335–9. 22. Sekula Jr RF, Bhatia S, Frederickson AM, et al. Utility of intraoperative electromyography in microvascular decompression for hemifacial spasm: a meta-analysis. Neurosurg Focus 2009;27:E10. 23. Moller AR. Hemifacial spasm: ephaptic transmission or hyperexcitability of the facial motor nucleus? Exp Neurol 1987;98:110–9. 24. Yamakami I, Oka N, Higuchi Y. Hyperactivity of the facial nucleus produced by chronic electrical stimulation in rats. J Clin Neurosci 2007;14:459–63. 25. Ishikawa M, Ohira T, Namiki J, et al. Electrophysiological investigation of hemifacial spasm after microvascular decompression: F waves of the facial muscles, blink reflexes, and abnormal muscle responses. J Neurosurg 1997;86:654–61. 26. Shin JC, Kim YC, Park CI, et al. Intra-operative monitoring of microvascular decompression in hemifacial spasm. J Yonsei Med 1996;37:209–13.
Contents lists available at SciVerse ScienceDirect
Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Clinical Study
Prognostic value of intra-operative abnormal muscle response monitoring during microvascular decompression for long-term outcome of hemifacial spasm Li Jiping a, Zhang Yuqing a, Zhu Hongwei a, Li Yongjie b,⇑ a b
Department of Functional Neurosurgery of Xuanwu Hospital, Capital Medical University, Beijing 100053, China Beijing Institute of Functional Neurosurgery, 45 Changchun Avenue, Xicheng District, Beijing 100053, China
a r t i c l e
i n f o
Article history: Received 13 February 2011 Accepted 2 April 2011
Keywords: Abnormal muscle response Hemifacial spasm Intra-operative monitoring Microvascular decompression
a b s t r a c t The reliability of intra-operative abnormal muscle response (AMR) monitoring as an indicator of postoperative outcome in patients with hemifacial spasm (HFS) is under debate. The primary aim of this study was to evaluate the correlation between intra-operative AMR changes and long-term post-operative outcome. We monitored intra-operative AMR during microvascular decompression (MVD) in consecutive patients with HFS (n = 104). Patients in this study were divided into two groups based on whether their AMR disappeared or persisted following MVD. Ninety patients were followed-up, and the mean duration from surgery to final follow-up examination was 3.7 years. Fourteen patients were lost to follow-up. AMR disappeared during surgery for 80 patients; of these, 74 achieved complete resolution of HFS, five had persistent HFS, and one patient developed a recurrence of HFS. Of the 10 patients with persistent AMR despite effective MVD, eight patients achieved complete resolution, one patient had persistent HFS, and one developed recurrent HFS. The long-term clinical outcome of HFS after MVD did not significantly correlate with intra-operative AMR changes (p = 0.791). Therefore, we suggest that intra-operative AMR monitoring may not be a reliable indicator of long-term post-operative outcome for HFS. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
2. Materials and methods
Hemifacial spasm (HFS) is an involuntary twitching or contraction of the facial muscles on one side of the face, and is thought to be caused by neurovascular compression of the facial nerve at its root exit zone (REZ).1,2 The most effective treatment for HFS is microvascular decompression (MVD). Abnormal muscle response (AMR),3 also termed lateral spread response,4 is observed in patients with HFS by electrically stimulating one branch of the facial nerve recording from the muscles innervated by other braches of the facial nerve by electromyography. In most patients with HFS, AMR disappears within seconds when the offending vessels are removed from the facial nerve during MVD.5–8 Accordingly, intraoperative AMR monitoring is a useful indicator to identify the offending vessels and to confirm adequate decompression.9–11 However, debate exists regarding the reliability of intra-operative AMR monitoring as an indicator of post-operative outcome. We investigated whether AMR findings obtained during MVD adequately reflect post-operative outcome in patients with HFS. Because the symptoms of HFS after MVD significantly improve over time,12,13 we measured the correlation between intra-operative AMR changes and the long-term post-operative outcome.
This study included 104 consecutive patients (34 male, 70 female; mean age = 47.5 years, range = 19–72 years) who were diagnosed with primary HFS and treated with MVD at our department between November 2006 and July 2007. The duration of HFS before surgery ranged from 4 months to approximately 20 years, and the mean duration was 7.9 years. To display the anatomic relationship between the vessels and facial nerve, all patients were assessed pre-operatively using three-dimensional time-of-flight magnetic resonance angiography. Intra-operative AMR monitoring was performed using Nicolet Viking Select electromyography monitor (Nicolet Biomedical, Madison, WI, USA). Prior to the induction of anesthesia, paired stimulating needle electrodes were inserted intradermally over the zygomatic branch of the facial nerve, and recording needle electrodes were inserted into the ipsilateral mentalis muscle (Fig. 1). Electrical stimulation used for AMR monitoring employed 0.1 millisecond (ms) rectangular waves at the following settings: (i) 5– 20 mA; (ii) band pass filter 20–3000 Hz; (iii) sensitivity 20–200 uv; and (iv) analysis time 50 ms. Operations were performed under general anesthesia, but muscle relaxants were only used for intubation. A small craniectomy was performed below the asterion and a dural opening. Subsequently, the flocculus and choroid plexus were gently retracted
⇑ Corresponding author. Tel.: +86 10 8319 8882; fax: +86 10 8316 3174. E-mail address: [email protected] (Y. Li). 0967-5868/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jocn.2011.04.023
J. Li et al. / Journal of Clinical Neuroscience 19 (2012) 44–48
45
Fig. 1. Schematic diagram showing the insertion position of the paired stimulating needle electrodes intradermally over the zygomatic branch of the facial nerve, and the recording needle electrodes into the ipsilateral mentalis muscle.
to expose the REZ of the facial nerve, and the REZ was examined for vascular contact. The offending vessels were dissected and moved away from the REZ. To separate the offending vessels from the REZ, interposing polytetrafluoroethylene (TeflonÒ) patches were placed between the vessels and the brainstem. AMR recordings were obtained at each stage of the MVD procedure as follows: (i) before anesthesia (baseline response); (ii) opening of the dura; (iii) retraction of the cerebellum; (iv) removal of cerebrospinal fluid; (v) dissecting the offending vessels; (vi) polytetrafluoroethylene interposition; (vii) termination of the microsurgical procedure; (viii) infusion of physiological saline; and (ix) closure of the dura. If AMR did not disappear following MVD, or if AMR reappeared after the release of cerebellar retraction, we started again with a further decompressive procedure. If AMR persisted following confirmation that no offending vessels remained, we completed the microsurgical procedure. All patients were contacted by telephone at the last follow-up in November 2010. Statistical analysis was performed using the Statistical Package for the Social Sciences version 16.0, and the relationship between the intra-operative AMR and the long-term results were analyzed by Fisher’s exact test. The level for statistical significance was p < 0.05.
(9.6%) patients despite effective decompression (Figs. 3 and 4). The mean duration from surgery to the final follow-up examination was 3.7 years (range = 3.2–4.0 years), and 14 patients were lost to follow-up. The remaining 90 patients were divided into two groups. Group I included 80 patients in whom AMR disappeared completely following MVD, and Group II included 10 patients in whom AMR persisted despite decompression. Seven of the 10 patients in Group II experienced a decrease in AMR amplitude to approximately 50–87.5% of that before surgery (mean = 69.6%), and pre-operative waveforms persisted in three patients. The results of MVD are summarized in Table 1. In Group I, 74 of 80 patients achieved complete relief from HFS, five patients had persistent HFS, and one patient developed recurrent HFS 6 months after surgery. In Group II, eight of 10 patients achieved complete relief from HFS, one patient in whom the AMR amplitude decreased had mild HFS, and one patient in whom pre-operative AMR persisted developed recurrent HFS 3 months after surgery. There was no significant difference in the long-term clinical results between the two groups (p = 0.791, Fisher’s exact test). AMR findings obtained during MVD did not reflect the long-term post-operative outcome of HFS.
3. Results
4. Discussion
Valid AMR were obtained for all patients prior to surgery; the mean latency was 12.6 ± 3.2 ms (Fig. 2). Following MVD, AMR disappeared in 94 (90.4%) patients, and AMR persisted in 10
AMR is an abnormal electromyogram response characteristic of patients with HFS, the latency of which is approximately 9–10 ms and the amplitude 0.1–0.2 mV, and its presence strongly supports a
46
J. Li et al. / Journal of Clinical Neuroscience 19 (2012) 44–48
Fig. 2. Pre-operative recordings showing abnormal muscle response: (A) five consecutive single recordings of a patient before surgery (A1–A5); and (B) constant and strongly overlapping waveforms.
Fig. 3. Intra-operative recordings of abnormal muscle response (AMR): (A1–5) before anesthesia (baseline response); during (A6) craniotomy and after (A7) dural opening; (A8, A9) cerebellar retraction with removal of the cerebrospinal fluid; (A10) interposition of polytetrafluoroethylene between the vessel and the brainstem after mobilization of the offending vessels; (A11) additional insertion of polytetrafluoroethylene; (A12) release of the cerebellar retraction; (A13) infusion of physiological saline; (A14) dura mater suturing; (A15) skin suturing. AMR disappeared after microvascular decompression.
diagnosis of HFS.3 In this study, all patients had characteristic AMR. Intra-operative AMR monitoring is used in HFS because it has been shown to instantaneously disappear after the offending vessels have been removed from the facial nerve REZ; and recompression of the vessels leads to a reappearance of AMR.5–8 It has been hypothesized that the disappearance of AMR is indicative of adequate decompression; and that this correlates with resolution of HFS after surgery. Conversely, the persistence of AMR indicates inadequate decompression and the persistence of HFS.
In our study, only three of 80 patients (3.8%) in whom AMR disappeared completely following MVD showed no significant improvement during the follow-up period. Two of the three patients (patients 78 and 79 in Group I) experienced significant improvement in the initial post-operative months, but their symptoms later reappeared. This subsequent recurrence of HFS may be attributed to other causes such as movement of the implant or the development of compression in new vessels. The third patient in the group (patient 77 in Group I), who experienced a 50% decrease
47
J. Li et al. / Journal of Clinical Neuroscience 19 (2012) 44–48
Fig. 4. Intra-operative abnormal muscle response (AMR) (A) before surgery and (B) changes after microvascular decompression (MVD) showing: (A1) AMR disappeared after MVD (patients in Group I); (A2) AMR persisted but amplitude decreased (in seven of 10 patients in Group II); (A3) pre-operative waveforms persisted, despite MVD (in three of 10 patients in Group II).
Table 1 Intra-operative abnormal muscle response (AMR) recording and the long-term results of microvascular decompression (MVD) for hemifacial spasm (HFS)
Group I
Group II
Patient
AMR changes
Results of MVD
1–74 75 76 77 78 79 80
Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared
Complete relief HFS reduced 90% HFS reduced 90% HFS reduced 50% HFS reduced 20% HFS unchanged Recurrence, HFS reduced 90%
1
Amplitude 60.0% Amplitude 50.0% Amplitude 80.0% Amplitude 75.0% Amplitude 87.5% Amplitude 60.0% Amplitude 75.0% Amplitude Amplitude Amplitude
reduced
Complete relief
reduced
Complete relief
reduced
Complete relief
reduced
Complete relief
reduced
Complete relief
reduced
Complete relief
reduced
HFS reduced 40%
unchanged unchanged unchanged
Complete relief Complete relief Recurrence, HFS aggravated
2 3 4 5 6 7 8 9 10
in symptoms after surgery, had a less common form of HFS characterized by involuntary twitching of the forehead muscle on the right side of the face. The findings of our study, as also shown by previous studies (see Table 2), suggest that the disappearance of AMR following MVD indicates a high likelihood of post-operative long-term relief from HFS. The debate over the reliability of intra-operative AMR monitoring as an indicator of post-operative outcome remains focused on whether the persistence of AMR following decompression always correlates with a poor outcome. Previous studies have shown evidence that AMR may be an unreliable predictor of long-term outcome. For example, in studies reported by Kiya et al. and Hatem et al., all patients experienced resolution of HFS despite persistent AMR upon completion of the operation.16,17 Similarly, Kong et al. reported 22 of 33 patients (66.7%) and Joo et al. reported 26 of 32
Table 2 Reports of abnormal muscle response monitoring Yearref
Follow-up period (months)
No. of HFS outcome and AMR findings patients HFS cured/AMR HFS not persisted cured/ (amplitude AMR decreased) disappeared
19878 19919 199614 199715 200110 200116 200117 200518 200619 200720 200821 200922 Present study
1–24 3–36 12–66 (36) 6–24 (12) >12 >3 12–36 12–74 (61) 67–118 (87) 12–55 (35.8) >6 1–28.6 (10.7) 39–47 (44.4)
67 8 40 132 74 38 33 60 51 263 72 69 90
2/44 0/7 2/38 5/70 8/69 0/21 1/23 3/53 2/44 22/230 4/40 5/53 6/80
16/23 (14/16) 1/1 0/2 44/62 (41/58) 4/5 17/17 10/10 6/7 (5/6) 5/7 (5/6) 22/33 26/32 15/16 8/10 (6/7)
Mean follow-up period shown in parentheses. AMR = abnormal muscle response, HFS = hemifacial spasm.
patients (81.3%) in whom AMR persisted but who had no HFS.20,21 Conversely, some investigators divided their patients with persistent AMR into two groups according to amplitude changes: (i) AMR decreased (reduction of P 50%); and (ii) no change in AMR (reduction < 50%).8,15,18 These studies found that patients with decreased AMR after MVD showed good outcome compared with patients with persistent, unchanged AMR. However, in our study, both decreased AMR or no change in AMR were correlated with good post-operative outcome. We suggest that patients can achieve excellent results, even if AMR persists after the initial decompression, if an effective and thorough decompression is performed. The exact mechanism of post-operative persistence of AMR despite effective decompression has not yet been sufficiently delineated. AMR is caused by a cross-transmission of antidromic activity, and intra-operative measurements of neural conduction time in parts of the facial nerve in patients with HFS who undergo MVD indicate that abnormal cross-transmission occurs at a central site, probably in the facial nucleus.23 In studies in which chronic electrical stimulation was applied to the facial nucleus of rats,
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kindling-like hyperactivity of the facial nucleus was determined to be the cause of the AMR.24 We assume that the persistence of AMR following complete decompression of the facial nerve REZ may be attributed to the remaining hyperexcitability of the facial nucleus. Consistent with this hypothesis, Ishikawa et al. reported that AMR was recorded, and subsequently disappeared, in seven patients within 1 month after complete relief of HFS. Patients continued to demonstrate improvement in their AMR status during the follow-up period.25 This has also been described in other reports,2,26 in which hyperexcitability of the facial nucleus required several months to normalize, and then AMR disappeared. Although AMR does not always disappear completely despite effective decompression, intra-operative AMR monitoring can provide useful assistance during surgery. In our experience, if AMR is absent after decompression, we close the incision. If AMR persists after the decompression, further microsurgical procedure is performed until we can confirm that no visible contact exists between the facial nerve and blood vessels. The persistence of AMR can provide surgeons with a warning of insufficient decompression, supporting further exploration to avoid missing offending vessels. This information is particularly useful for patients with HFS who have vascular compression in the distal portion of the facial nerve or facial nerve compression by multiple vessels. Similarly, AMR can be useful for patients in whom recompression results from excessive insertion of polytetrafluoroethylene or the change of positional relationship between the offending vessels and the facial nerve after release of the cerebellar retraction and infusion of physiological saline.14 Therefore, we encourage routine application of intra-operative AMR monitoring during MVD for HFS which should be continued until the end of surgery. 5. Conclusion The persistence of AMR after decompression did not always indicate post-operative persistent HFS if an effective and thorough decompression was performed, and the long-term outcome of HFS did not always correlate with the disappearance or persistence of AMR. Therefore, AMR may not be a reliable indicator of long-term post-operative outcome. Nonetheless, intra-operative AMR monitoring can be useful in guiding neurosurgeons to obtain sufficient decompression, and we advocate routine intra-operative AMR monitoring during MVD for HFS. References 1. Moller AR. The cranial nerve vascular compression syndrome: II. A review of pathophysiology. Acta Neurochir (Wien) 1991;113:24–30. 2. Moller AR. Vascular compression of cranial nerves: II: pathophysiology. Neurol Res 1999;21:439–43. 3. Moller AR, Jannetta PJ. On the origin of synkinesis in hemifacial spasm: results of intracranial recordings. J Neurosurg 1984;61:569–76.
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