Mobilization of the Anterior/Posterior Inferior Cerebellar Artery on the Cerebellar Surface in Microvascular Decompression Surgery for Hemifacial Spasm: Potential Effect on Hearing Preservation

Mobilization of the Anterior/Posterior Inferior Cerebellar Artery on the Cerebellar Surface in... Abstract BACKGROUND The infrafloccular approach in microvascular decompression (MVD) for hemifacial spasm (HFS) reduces the risk of postoperative hearing impairment. However, location of the anterior/posterior inferior cerebellar artery (AICA/PICA) on the cerebellar surface in the surgical route requires mobilization to maintain the approach direction for the protection of hearing function. OBJECTIVE To evaluate the effectiveness of mobilization of the AICA/PICA on the cerebellar surface in the surgical route. METHODS Retrospective review of 101 patients dividing their cases into 2 groups, the mobilized group and nonmobilized group. Surgical results, brainstem auditory evoked potentials (BAEPs), age, and duration of microsurgery were compared. In the mobilized group, whether the artery was responsible for the HFS or not, and whether the artery branched perforators to the cerebellar surface or choroid plexus or not, were analyzed. RESULTS No permanent hearing impairment occurred in any patient. The AICA/PICA was mobilized in 26 patients. No significant difference was found in surgical results, BAEP findings, and duration of microsurgery between the 2 groups, but age was younger in the mobilized group (P < .01). The mobilized artery was responsible in 14 cases and branched perforators in 7 cases in the mobilized group. The perforators did not obstruct mobilization. CONCLUSION Mobilization of the AICA/PICA from the cerebellar surface is a useful technique to maintain the infrafloccular approach in MVD for HFS. This technique reduces the risk of postoperative hearing impairment. Hearing loss, Hemifacial spasm, Infrafloccular approach, Microvascular decompression, Mobilization of artery ABBREVIATIONS ABBREVIATIONS AICA anterior inferior cerebellar artery BAEPs brainstem auditory evoked potentials CNs cranial nerves CP cerebellopontine fREZ facial root exit zone HFS hemifacial spasm MVD microvascular decompression PICA posterior inferior cerebellar artery Microvascular decompression (MVD) is a well-known procedure that can cure hemifacial spasm (HFS). In our facility, MVD is performed with the transposition method through the lateral suboccipital infrafloccular approach, which offers the advantages of adequate surgical space for exposure of the facial root exit zone (fREZ) and prevents postoperative hearing impairment.1 However, this procedure requires complete exposure of the lower cranial nerves (CNs) for the caudolateral direction of the surgical access,2 and the corner formed by the auditory nerve (CN VIII) and glossopharyngeal nerve (CN IX) is the entrance to the attached segment3 of the fREZ (Figure 1A).4 Consequently, the microsurgical working space is limited, so the key to successful decompression is correct exposure of this space. FIGURE 1. View largeDownload slide Illustrations of the surgical exposure for the infrafloccular approach in microvascular decompression for left hemifacial spasm. A, Final view of the approach showing complete exposure of the lower CNs (CNs IX, X, and XI) and the corner formed by the auditory nerve (CN VIII) and glossopharyngeal nerve (CN IX) at the entrance to the attached segment (asterisk) of the fREZ. B, Artery passing from the left cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface as well as the left vertebral artery medial to the lower CNs is present. The artery on the cerebellar surface is obstructing the surgical route. C and D, The vertebral artery is transposed with a Teflon sling and the PICA C or AICA D on the cerebellar surface is mobilized and fixed to the petrous bone with a Teflon sling. The fREZ is correctly exposed. © 2017 Kenichi Amagasaki. FIGURE 1. View largeDownload slide Illustrations of the surgical exposure for the infrafloccular approach in microvascular decompression for left hemifacial spasm. A, Final view of the approach showing complete exposure of the lower CNs (CNs IX, X, and XI) and the corner formed by the auditory nerve (CN VIII) and glossopharyngeal nerve (CN IX) at the entrance to the attached segment (asterisk) of the fREZ. B, Artery passing from the left cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface as well as the left vertebral artery medial to the lower CNs is present. The artery on the cerebellar surface is obstructing the surgical route. C and D, The vertebral artery is transposed with a Teflon sling and the PICA C or AICA D on the cerebellar surface is mobilized and fixed to the petrous bone with a Teflon sling. The fREZ is correctly exposed. © 2017 Kenichi Amagasaki. Occasionally we encounter vascular components along the approach route. The anterior inferior cerebellar artery (AICA) or posterior inferior cerebellar artery (PICA) can be observed passing from the cerebellopontine (CP) cistern toward the lateral and caudal directions on the cerebellar surface (Figure 1B). Eventually, such an artery crosses the approach route and obstructs manipulations during the decompression at the fREZ, so the approach may be changed to the lateral or rostral direction. However, such change in direction can cause hearing impairment due to stretching of CN VIII.2 Therefore, to continue with the pure infrafloccular approach, the artery must be dissected and isolated from the cerebellar surface and mobilized toward the petrous bone to prevent deviation of the infrafloccular route from the caudal direction (Figure 1C and 1D). The present study investigated the use of this mobilizing process and evaluated the anatomic and clinical results. METHODS Patients The medical records of 101 consecutive patients with HFS who underwent MVD were retrospectively reviewed. All patients were treated at our hospital between October 2015 and September 2016. The study was approved by the hospital ethics committee, after obtaining waivers of consent from all patients. Table 1 summarizes the clinical characteristics of the 101 patients including the offending vessels. TABLE 1. Summary of Demographic and Clinical Characteristics Variable Value Mean age (range), y 50.9 (24-75) Female/male 65/36 Right/left 36/65 Offending vessel  Anterior inferior cerebellar artery 71  Posterior inferior cerebellar artery 45  Vertebral artery 39 Variable Value Mean age (range), y 50.9 (24-75) Female/male 65/36 Right/left 36/65 Offending vessel  Anterior inferior cerebellar artery 71  Posterior inferior cerebellar artery 45  Vertebral artery 39 View Large TABLE 1. Summary of Demographic and Clinical Characteristics Variable Value Mean age (range), y 50.9 (24-75) Female/male 65/36 Right/left 36/65 Offending vessel  Anterior inferior cerebellar artery 71  Posterior inferior cerebellar artery 45  Vertebral artery 39 Variable Value Mean age (range), y 50.9 (24-75) Female/male 65/36 Right/left 36/65 Offending vessel  Anterior inferior cerebellar artery 71  Posterior inferior cerebellar artery 45  Vertebral artery 39 View Large Microvascular Decompression MVD was performed with the transposition method through the infrafloccular approach under routine monitoring of brainstem auditory evoked potentials (BAEPs), as described previously,1 as well as modification to avoid usage of the brain retractor. All microsurgical procedures in this series were performed by the same operator (K.A.). Intraoperative BAEP Monitoring Intraoperative BAEP monitoring was performed in the same way as previously described.1 Patients were divided into 4 groups on the basis of the greatest intraoperative latency prolongation or amplitude reduction of wave V compared with the preoperative baseline as follows: group 1, greatest latency prolongation of less than 1.0 ms without amplitude reduction of more than 50%; group 2, greatest latency prolongation of more than 1.0 ms, or amplitude reduction of more than 50% without latency prolongation of more than 1.0 ms; group 3, greatest latency prolongation of more than 1.0 ms and amplitude reduction of more than 50%; and group 4, complete loss of V wave (including transient loss). Mobilization of the AICA/PICA from the Cerebellar Surface During the approach through the infrafloccular route, if the operator considered that the surgical route was obstructed by the AICA or PICA on the cerebellar surface from the CP cistern, the artery was dissected and isolated from the cerebellar surface, then mobilized toward the petrous bone direction. The operator was entirely responsible for this decision-making, based on whether the surgical manipulation was disturbed by the artery or not. This procedure was first introduced more than 10 yr ago by Yutaka Takusagawa and has since been continued by the first author (K.A.). Consequently, the patients could be classified into the mobilized group or the nonmobilized group. The mobilized artery was identified as the AICA or PICA based on both preoperative magnetic resonance imaging and surgical findings. Age and duration of microscopic surgery in both groups were compared. The mobilized group was further analyzed to identify whether the artery was responsible for HFS or not, and whether the artery supplied perforators to the cerebellar surface or choroid plexus or not. Evaluation of HFS and Complications Cases of HFS were evaluated in March 2017 and the outcome was classified into 4 categories: no spasm, improved, persistent, and recurrence. Any neurological deficit persisting in March 2017 was recorded as permanent. No formal hearing tests for the evaluation of hearing function were conducted except in patients who reported hearing problems at preoperative interviews. On admission, subjective hearing levels were recorded bilaterally on the medical charts as 0 (deaf) to 10 (normal) by finger scratching beside the ears. After the surgery, hearing levels were checked in the same way at least three times a day including immediately after surgery, and similarly recorded. If a definitive decreased hearing score compared with the preoperative condition was recorded, the patient was referred to the otolaryngologist for evaluation. Detailed protocols of hearing-function testing were described previously.1 Patients with symptoms of lower CN (CN IX/X) palsy, such as dysphasia and/or hoarseness, were also referred to the otolaryngologist for evaluation of laryngeal and pharyngeal function. Statistical Analysis Parameters of the 2 groups were compared as follows. Chi-square test was used to analyze the surgical results, Fisher's exact test for BAEP findings, t-test for age, and Mann–Whitney test for duration of microsurgery. IBM SPSS Statistics version 23.0 (IBM Inc, Armonk, New York) for Microsoft Windows (Microsoft, Redmond, Washington) was used for the analysis and P-values of less than .05 were interpreted as significant. RESULTS Table 2 summarizes the clinical data of the mobilized and nonmobilized groups. In total, HFS disappeared in 77 patients, improved in 15 patients, persisted in 8 patients, and recurred in 1 patient in the follow-up period of 6 to 18 mo. There was no statistically significant surgical effect in these surgical groups (P = .88). Ipsilateral hearing decreased to level 5 postoperatively in 1 patient in the mobilized group, but recovered within a few days, and the audiogram a week after the surgery showed no laterality in hearing. Two permanent neurological impairments were recorded. One patient in the mobilized group suffered from permanent facial palsy and another patient in the nonmobilized group suffered from permanent mild hoarseness, but these symptoms were still improving at the end of the follow-up period. CSF leakage was observed in 2 patients; 1 required repair and the other was stopped with lumbar taps. Minor subarachnoid hemorrhage with no neurological symptoms was observed in 1 patient. Intraoperative BAEP findings indicated 58 patients in group 1, 26 in group 2, 16 in group 3, and 1 in group 4. There was no significant difference in BAEP findings between the surgical groups (P = .40). The duration of microsurgery was not statistically significant between the surgical groups (P = .06), but age was significantly lower in the mobilized group (P = .01). The dissected artery was the PICA in 19 cases and the AICA in 7 cases. The artery was responsible for the HFS in 14 cases. Perforators to the cerebellar surface or choroid plexus were observed in 7 cases, but all branched in the caudal side only and none restricted the mobilization of the artery for the infrafloccular route. Three typical cases in the mobilized group are presented. Table 2. Clinical Data of Mobilized and Nonmobilized Groups Mobilized (n = 26) Nonmobilized (n = 75) P Value Surgical effect .88*  No spasm 21 56  Improved 4 11  Persisted 1 7  Recurrence 0 1 Complications  Auditory nerve palsy (transient) 1 0  Lower cranial nerves palsy (transient) 2 4  Lower cranial nerves palsy (permanent) 0 1  Abducens nerve palsy (transient) 0 1  Facial nerve palsy (permanent) 1 0  Cerebrospinal fluid leakage 0 2  Minor subarachnoid haemorrhage 0 1 Brainstem auditory evoked potentials .40**  Group 1 16 42  Group 2 5 21  Group 3 4 12  Group 4 1 0 Mean age ± SD, y 46.3 ± 11.9 52.5 ± 10.6 .01*** Median duration of microsurgery (range), min 84.0 (41 - 231) 73.0 (35 - 144) .06**** Mobilized artery  AICA (responsible for hemifacial spasm) 7 (5)  PICA (responsible for hemifacial spasm) 19 (9)  Origin of perforators to cerebellar surface/choroid plexus 7 Mobilized (n = 26) Nonmobilized (n = 75) P Value Surgical effect .88*  No spasm 21 56  Improved 4 11  Persisted 1 7  Recurrence 0 1 Complications  Auditory nerve palsy (transient) 1 0  Lower cranial nerves palsy (transient) 2 4  Lower cranial nerves palsy (permanent) 0 1  Abducens nerve palsy (transient) 0 1  Facial nerve palsy (permanent) 1 0  Cerebrospinal fluid leakage 0 2  Minor subarachnoid haemorrhage 0 1 Brainstem auditory evoked potentials .40**  Group 1 16 42  Group 2 5 21  Group 3 4 12  Group 4 1 0 Mean age ± SD, y 46.3 ± 11.9 52.5 ± 10.6 .01*** Median duration of microsurgery (range), min 84.0 (41 - 231) 73.0 (35 - 144) .06**** Mobilized artery  AICA (responsible for hemifacial spasm) 7 (5)  PICA (responsible for hemifacial spasm) 19 (9)  Origin of perforators to cerebellar surface/choroid plexus 7 AICA, anterior inferior cerebellar artery; PICA, posterior inferior cerebellar artery; SD, standard deviation *Chi square test, **Fisher's exact test, ***t-test, ****Mann-Whitney test. View Large Table 2. Clinical Data of Mobilized and Nonmobilized Groups Mobilized (n = 26) Nonmobilized (n = 75) P Value Surgical effect .88*  No spasm 21 56  Improved 4 11  Persisted 1 7  Recurrence 0 1 Complications  Auditory nerve palsy (transient) 1 0  Lower cranial nerves palsy (transient) 2 4  Lower cranial nerves palsy (permanent) 0 1  Abducens nerve palsy (transient) 0 1  Facial nerve palsy (permanent) 1 0  Cerebrospinal fluid leakage 0 2  Minor subarachnoid haemorrhage 0 1 Brainstem auditory evoked potentials .40**  Group 1 16 42  Group 2 5 21  Group 3 4 12  Group 4 1 0 Mean age ± SD, y 46.3 ± 11.9 52.5 ± 10.6 .01*** Median duration of microsurgery (range), min 84.0 (41 - 231) 73.0 (35 - 144) .06**** Mobilized artery  AICA (responsible for hemifacial spasm) 7 (5)  PICA (responsible for hemifacial spasm) 19 (9)  Origin of perforators to cerebellar surface/choroid plexus 7 Mobilized (n = 26) Nonmobilized (n = 75) P Value Surgical effect .88*  No spasm 21 56  Improved 4 11  Persisted 1 7  Recurrence 0 1 Complications  Auditory nerve palsy (transient) 1 0  Lower cranial nerves palsy (transient) 2 4  Lower cranial nerves palsy (permanent) 0 1  Abducens nerve palsy (transient) 0 1  Facial nerve palsy (permanent) 1 0  Cerebrospinal fluid leakage 0 2  Minor subarachnoid haemorrhage 0 1 Brainstem auditory evoked potentials .40**  Group 1 16 42  Group 2 5 21  Group 3 4 12  Group 4 1 0 Mean age ± SD, y 46.3 ± 11.9 52.5 ± 10.6 .01*** Median duration of microsurgery (range), min 84.0 (41 - 231) 73.0 (35 - 144) .06**** Mobilized artery  AICA (responsible for hemifacial spasm) 7 (5)  PICA (responsible for hemifacial spasm) 19 (9)  Origin of perforators to cerebellar surface/choroid plexus 7 AICA, anterior inferior cerebellar artery; PICA, posterior inferior cerebellar artery; SD, standard deviation *Chi square test, **Fisher's exact test, ***t-test, ****Mann-Whitney test. View Large Case 1 A 67-yr-old female underwent MVD for left HFS. After the dural incision, a PICA was identified passing from the CP cistern to the lateral and caudal direction on the cerebellar surface (Figure 2A, Video 1, Supplemental Digital Content: 0’20”). On approach to the left fREZ, the AICA was observed as the responsible artery (Figure 2B, Video 1, Supplemental Digital Content: 0’40”). However, the PICA crossed the entrance of the surgical space formed by CN VIII and CN IX, and obstructed further manipulations at the fREZ. Therefore, the PICA loop was dissected and isolated from the cerebellar surface and mobilized in the direction of the petrous bone (Figure 2C, Video 1, Supplemental Digital Content: 1’20”). After mobilization, a wide surgical space for the infrafloccular route was obtained (Figure 2D, Video 1, Supplemental Digital Content: 1’30”), and finally the AICA was securely transposed. Intraoperative BAEP findings showed no remarkable change in the V wave (group 1). FIGURE 2. View largeDownload slide Intraoperative images of case 1 with left hemifacial spasm. A, During opening of the left cerebellomedullary fissure, a PICA passing from the cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface is exposed. The dotted line indicates the margin of the auditory nerve (CN VIII). B, AICA (asterisk) is confirmed as the responsible artery by observation of the fREZ through the angle formed by CN VIII and the glossopharyngeal nerve (CN IX), but the PICA crosses the approach route. C, PICA is mobilized in the petrous bone direction. Vertebral artery is transposed with a Teflon sling medial to the PICA and lower cranial nerves. D, After mobilization of the PICA showing ensuring a wide space between CN VIII and CN IX, with no obstruction to the AICA (asterisk) at the fREZ. FIGURE 2. View largeDownload slide Intraoperative images of case 1 with left hemifacial spasm. A, During opening of the left cerebellomedullary fissure, a PICA passing from the cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface is exposed. The dotted line indicates the margin of the auditory nerve (CN VIII). B, AICA (asterisk) is confirmed as the responsible artery by observation of the fREZ through the angle formed by CN VIII and the glossopharyngeal nerve (CN IX), but the PICA crosses the approach route. C, PICA is mobilized in the petrous bone direction. Vertebral artery is transposed with a Teflon sling medial to the PICA and lower cranial nerves. D, After mobilization of the PICA showing ensuring a wide space between CN VIII and CN IX, with no obstruction to the AICA (asterisk) at the fREZ. Case 2 A 31-yr-old male underwent MVD for right HFS. Opening the cerebellomedullary fissure revealed an artery on the cerebellar surface originating from the CP cistern (Figure 3A, Video 2, Supplemental Digital Content: 0’10”), and obstructing the approach to the responsible artery (Figure 3B, Video 2, Supplemental Digital Content: 0’40”). Therefore, the artery was dissected and isolated from the cerebellar surface, and mobilized in the direction of the petrous bone. Observation of the fREZ after mobilization revealed that the artery was a lateral branch from the AICA, which bifurcated in the CP cistern, and the medial branch was responsible for the HFS (Figure 3C, Video 2, Supplemental Digital Content: 1’10”). Mobilization of the lateral branch facilitated mobilization of the main trunk of the AICA, and finally the medial branch was securely transposed in the anterocaudal direction (Figure 3D, Video 2, Supplemental Digital Content: 1’40”). Intraoperative BAEP findings showed 1.2 ms delay of the V wave but the amplitude was unchanged (group 2). FIGURE 3. View largeDownload slide Intraoperative images of case 2 with right hemifacial spasm. A, On approach to the cerebellopontine cistern from the caudal side, an artery passing from the cistern to the lateral and caudal direction on the cerebellar surface is present. The dotted line indicates the margin of the auditory nerve (CN VIII). B, The responsible artery (asterisk) is confirmed by observation of the facial root exit zone (fREZ) through the angle formed by CN VIII and the glossopharyngeal nerve, but the artery to the cerebellar surface crosses the approach route. C, Mobilized artery is the lateral branch from the anterior inferior cerebellar artery, and the medial branch is the responsible artery (asterisk). D, Transposition of the medial branch in the anterocaudal direction and fixing to the petrous bone with a Teflon sling (asterisk) achieves complete decompression of the artery from the attached segment of the fREZ. FIGURE 3. View largeDownload slide Intraoperative images of case 2 with right hemifacial spasm. A, On approach to the cerebellopontine cistern from the caudal side, an artery passing from the cistern to the lateral and caudal direction on the cerebellar surface is present. The dotted line indicates the margin of the auditory nerve (CN VIII). B, The responsible artery (asterisk) is confirmed by observation of the facial root exit zone (fREZ) through the angle formed by CN VIII and the glossopharyngeal nerve, but the artery to the cerebellar surface crosses the approach route. C, Mobilized artery is the lateral branch from the anterior inferior cerebellar artery, and the medial branch is the responsible artery (asterisk). D, Transposition of the medial branch in the anterocaudal direction and fixing to the petrous bone with a Teflon sling (asterisk) achieves complete decompression of the artery from the attached segment of the fREZ. Case 3 A 50-yr-old male underwent MVD for left HFS. Approaching the CP angle from the caudal side revealed a PICA on the cerebellar surface (Figure 4A). During dissection of the artery in the caudal direction, the artery branched a perforator to the cerebellar surface (Figure 4B). However, the perforator did not disturb the mobilization of the artery in the direction of the petrous bone, and the proximal part of the artery compressing the attached segment3 of the fREZ was safely transposed. BAEP findings showed no remarkable change in the V wave (group 1). FIGURE 4. View largeDownload slide Intraoperative image of case 3 with left hemifacial spasm. A, Posterior inferior cerebellar artery (PICA) passing from the cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface is present. The dotted line indicates the margin of the auditory nerve. B, Perforator to the cerebellar surface from the PICA is isolated from the cerebellar surface at the caudal side. FIGURE 4. View largeDownload slide Intraoperative image of case 3 with left hemifacial spasm. A, Posterior inferior cerebellar artery (PICA) passing from the cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface is present. The dotted line indicates the margin of the auditory nerve. B, Perforator to the cerebellar surface from the PICA is isolated from the cerebellar surface at the caudal side. DISCUSSION MVD for HFS carries the risk of damage to CN VIII.5-8 The infrafloccular approach is useful for the avoidance of auditory impairment.1,2 The surgical technique presented in this paper demonstrates how to continue with the infrafloccular approach if the surgical route is obstructed by an arterial component. The absence of permanent hearing impairment reconfirms that the infrafloccular approach is absolutely advantageous for prevention of postoperative hearing impairment. Surgery without use of the retractor is ideal for the prevention of hearing impairment in MVD. Presence of the AICA/PICA crossing the surgical route limits the entrance to the fREZ and the decompression procedure (Figures 2B and 3B). Therefore, a brain retractor may be applied for better exposure. However, if the artery is dissected and isolated from the cerebellar surface, the cerebellum can be retracted easily with a single dissector and the need for the fixed brain retractor decreases. Our previous study showed that the frequency of use of the retractor affected delay and diminishment of the V wave of the BAEP.1 Later, with the improvement of surgical skills, surgery could be achieved without use of the retractor. In our previous study, flattening of the V wave was observed in 7% (7/100) of cases,1 whereas the present series observed flattening in only 1% (1/101) of cases. In the patient with flattening of the V wave in the mobilized group, who suffered from transient decreased hearing, manipulation of the cisternal portion3 of fREZ and CN VIII during the decompression was necessary, so that the dissecting process of the artery on the cerebellar surface was not directly related to the BAEP change. There are some other advantages of this surgical technique. First, this procedure also allows complete transposition if the dissected artery is responsible for HFS, as observed in 14 cases. Our target of the decompression process is complete isolation of the vessel from the fREZ. Therefore, transposition of the responsible vessel to the petrous bone direction is often ideal. Isolation of the AICA/PICA from the cerebellar surface facilitates the mobilization so that complete transposition can be safely achieved. Secondly, this technique can reduce discomfort of the surgeon during the surgery. Since the surgical space for the final decompression process is deeply located and limited, the surgeon is always concerned about comfort of manipulation during the microscopic procedure. The larger space without any obstructive component in the surgical route and the lower chance of warning BAEP findings result in more confidence that safe decompression can be achieved. The size of the cistern is one of the related factors, and our finding that the mobilized group was significantly younger suggests that this technique is especially useful in cases with the narrow cistern. The microsurgical duration of both groups was not significantly different, but tended to be longer in the mobilized group. Dissection and isolation of the artery from the cerebellar surface may take additional time. However, the dissection process is not a complex procedure with experience. The arachnoid membrane along the artery can be carefully incised and correct isolation of the artery from the cerebellar surface can be achieved. Perforators to the cerebellar surface or choroid plexus were observed in some cases, but only in the caudal side and no cerebellar injury occurred. Finally, skill and technique in MVD surgery vary with the surgeon and can reflect the surgical results. A previous study of MVD indicated 3 complications directly related to operative technique: cerebellar injury, CSF leakage, and hearing loss.5 In our series, 2 patients had CSF leakage, but no other complications occurred. Therefore, we believe that the technique presented in this paper achieves better results in MVD for HFS. Limitations There are some limitations in this study. One is the method of evaluating hearing function. Strict bedside evaluation of hearing is done routinely but pure tone audiometry is not a part of our protocol. Only some patients were evaluated with pure tone audiometry including otolaryngologist consultation.1 However, we assume that bedside evaluation provides useful information about everyday hearing because we are always depending on subjective reporting. The other limitation is the short follow-up period. In this series, the efficacy of the surgery was low compared with our previous series even though the surgical method was similar.1,4 The longest follow-up periods of the previous study were 22 and 26 mo, compared to 18 mo in the present study. Shorter follow-up period may have affected the surgical results. CONCLUSION Mobilization of the AICA/PICA from the cerebellar surface is a useful technique for adequate exposure of the surgical space during MVD for HFS. With this technique, the infrafloccular approach from the caudal side can be maintained throughout the surgery and reduces risk of postoperative hearing impairment. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Amagasaki K , Watanabe S , Naemura K , Nakaguchi H . Microvascular decompression for hemifacial spasm: how can we protect auditory function? ? Br J Neurosurg . 2015 ; 29 ( 3 ): 347 - 352 . Google Scholar CrossRef Search ADS PubMed 2. Hitotsumatsu T , Matsushima T , Inoue T . Microvascular decompression for treatment of trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia: three surgical approach variations: technical note . Neurosurgery . 2003 ; 53 ( 6 ): 1436 - 1443 ; discussion 1442-1433 . Google Scholar CrossRef Search ADS PubMed 3. Campos-Benitez M , Kaufmann AM . Neurovascular compression findings in hemifacial spasm . J Neurosurg . 2008 ; 109 ( 3 ): 416 - 420 . Google Scholar CrossRef Search ADS PubMed 4. Amagasaki K , Kurita N , Watanabe S et al. Lower cranial nerve palsy after the infrafloccular approach in microvascular decompression for hemifacial spasm . Surg Neurol Int . 2017 ; 8 : 67 . Google Scholar CrossRef Search ADS PubMed 5. McLaughlin MR , Jannetta PJ , Clyde BL , Subach BR , Comey CH , Resnick DK . Microvascular decompression of cranial nerves: lessons learned after 4400 operations . J Neurosurg . 1999 ; 90 ( 1 ): 1 - 8 . Google Scholar CrossRef Search ADS PubMed 6. Ying T , Thirumala P , Shah A et al. Incidence of high-frequency hearing loss after microvascular decompression for hemifacial spasm . J Neurosurg . 2013 ; 118 ( 4 ): 719 - 724 . Google Scholar CrossRef Search ADS PubMed 7. Jung NY , Lee SW , Park CK , Chang WS , Jung HH , Chang JW . Hearing outcome following microvascular decompression for hemifacial spasm: series of 1434 cases . World Neurosurg . 2017 ; 108 : 566 - 571 . Google Scholar CrossRef Search ADS PubMed 8. El Damaty A , Rosenstengel C , Matthes M et al. A new score to predict the risk of hearing impairment after microvascular decompression for hemifacial spasm . Neurosurgery . 2017 ; 81 ( 5 ): 834 - 843 . Google Scholar PubMed Acknowledgement We appreciate Dr Yutaka Takusagawa for his pioneering surgical work and the help of Ms Yuimi Marumoto for assistance with statistical analysis. Supplemental digital contentis available for this article at www.operativeneurosurgery-online.com. Supplemental Digital Content 1. Video. Case 1. Supplemental Digital Content 2. Video. Case 2. COMMENTS As pointed out by the authors, there is no doubt that the (classical) infrafloccular approach to the fREZ and neighboring brainstem is the way to perform MVD for HFS with both efficacy and safety. As a matter of fact, more than 90% of the neurovascular compressions responsible for HFS are located ventrocaudally at the fREZ.1 Further, this trajectory revealed the safest to avoid stretching the VIIIth nerve, and consequently create hearing and/or vestibular disturbances with corresponding sequelae. This has been demonstrated for a long time by BAEP studies.2,3 When AICA with its cerebellar surface course makes an obstacle to the fREZ and neighboring brainstem, it has to be dissected free for a long portion and transposed apart. The way described in this article has given satisfaction to the authors, as they did not notice significant hearing complications in the corresponding group of their patients. However, in spite of the inoccuity in the hands of the authors’ study, we think it wise to insist on the risk –by manipulating the AICA and the labyrinthine artery (its tributary to the cochlea) – of producing (by mechanical reflex) some vasospasm. Decrease in amplitude of peak I on BAEP trace can be a useful warning of threatening cochlear ischemia4,5,6,7 that should incite irrigation of those arteries with warm saline, together with a few droplets of Papaverine in 10% solution, before damage becomes irreversible. Marc Sindou Lyon, France 1. Li S.T , Sun H . Surgical Techniques of Microvascular Decompression for Hemifacial Spasm . In “ Microvascular Decompression Surgery ”, Li Zhong Sekula (eds), Springer , Heidelberg , 2016 , pages 79 – 93 Google Scholar CrossRef Search ADS 2. Sindou M , Fobe J. L. , Ciriano D. , Fischer C. Hearing prognosis and intraoperative guidance of BAEPs in MVD . Laryngoscope , 1992 , 102 : 678 – 682 Google Scholar CrossRef Search ADS PubMed 3. Hatayama T , Moller A.R. Correlation between latency and amplitude of peak V in the BAEPs Intraoperative recordings in MVD operations . Acta Neurochir ., 1998 , 140 : 681 – 687 Google Scholar CrossRef Search ADS PubMed 4. Polo G , Fischer C. , Sindou M.P. , Marneffe V. Brain 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 , 54 : 97 – 106 Google Scholar CrossRef Search ADS PubMed 5. Sindou M . Microvascular decompression for primary hemifacial spasm. Importance of intra-operative neurophysiological monitoring , Acta Neurochir ., 2005 , 147 : 1019 – 1026 Google Scholar CrossRef Search ADS PubMed 6. Jo KW , Kim JW. , Kong DS. , Hong SH. , Park K. The patterns risk factors of hearing loss following MVD for HFS . Acta Neurochir . 2011 , 153 : 1023 – 1030 Google Scholar CrossRef Search ADS PubMed 7. Li S.T. , Ying T.T. Intra operative monitoring in “Microvascular Decompression Surgery ”, Li S.T. , Zhong J. , Sekula R.F. (eds), Springer , Heidelberg , 2016 , chap 12, pages 151 – 170 The authors of this paper share their experience with management of HFS using an infrafloccular approach for MVD. Out of 101 analyzed cases, the arterial trunk of AICA/PICA was located on the cerebellar surface and had to be mobilized to allow safe approach to the VII-VIII cranial nerve complex in 26 patients. Despite this arterial mobilization – or because of it –the results were essentially the same in those who did and did not have such mobilization. The authors routinely use the “sling technique” to keep the artery away from the nerve root. This surgical nuance does usually require somewhat larger exposure and more arterial manipulation than simple placement of Teflon felt pledgets between the vessel and the nerve root. I am not sure how prevalent is the use of slings in MVD for HFS; it is conceivable, however, that at some point it will become a preferred approach for MVD. Overall, I applaud the authors' thoroughness in documenting the surgical nuance that most of us use from time to time already – the need for arterial dissection is routinely determined during the surgical approach. It is, however, nice to know that such additional manipulation does not make the procedure significantly longer and, when properly addressed, the adherence of artery to the cerebellum dose not negatively affect the overall outcome. Konstantin Slavin Chicago, Illinois Without a doubt, the “infrafloccular” approach to MVD of the facial nerve is the preferred approach for this operation. This manuscript emphasizes avoidance of fixed retraction and mobilization of AICA and PICA along the cerebellar surface and petrous dura1. These are important concepts. The use of transposition of AICA/PICA to the petrous dura is a nice adjunct to the operation. For years, I have also used “slings” fashioned from a variety of materials in many of my patients undergoing MVD for hemifacial spasm or trigeminal neuralgia. I avoid, however, slinging AICAs with short brainstem perforators as brainstem infarction may eventuate. The major limitation of this study, however, is the technique used to evaluate preoperative and postoperative hearing function. The use of a “finger scratch” technique is not only inexact but is misleading. A patient with significantly decreased hearing or even unilateral deafness may believe that he or she can hear in the deaf ear with “finger scratch” for a period of time. Undoubtedly, if all patients in this series underwent pure tone audiometry preoperatively and postoperatively, some amount of hearing loss would have been detected. Overall, however, the manuscript nicely illustrates important technical nuances of successful MVD of the facial nerve, and the authors are to be congratulated. Raymond F. Sekula Jr Pittsburgh, Pennsylvania 1. Thirumala P , Frederickson AM , Balzer J , Crammond D , Habeych ME , Chang YF , Sekula RF . Reduction in high-frequency hearing loss following technical modifications to microvascular decompression for hemifacial spasm . J Neurosurg . 2015 Oct ; 123 ( 4 ): 1059 – 64 . Epub 2015 Jul 10 Google Scholar CrossRef Search ADS PubMed Copyright © 2018 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Operative Neurosurgery Oxford University Press

Mobilization of the Anterior/Posterior Inferior Cerebellar Artery on the Cerebellar Surface in Microvascular Decompression Surgery for Hemifacial Spasm: Potential Effect on Hearing Preservation

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Congress of Neurological Surgeons
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Copyright © 2018 by the Congress of Neurological Surgeons
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2332-4252
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2332-4260
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10.1093/ons/opy128
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Abstract

Abstract BACKGROUND The infrafloccular approach in microvascular decompression (MVD) for hemifacial spasm (HFS) reduces the risk of postoperative hearing impairment. However, location of the anterior/posterior inferior cerebellar artery (AICA/PICA) on the cerebellar surface in the surgical route requires mobilization to maintain the approach direction for the protection of hearing function. OBJECTIVE To evaluate the effectiveness of mobilization of the AICA/PICA on the cerebellar surface in the surgical route. METHODS Retrospective review of 101 patients dividing their cases into 2 groups, the mobilized group and nonmobilized group. Surgical results, brainstem auditory evoked potentials (BAEPs), age, and duration of microsurgery were compared. In the mobilized group, whether the artery was responsible for the HFS or not, and whether the artery branched perforators to the cerebellar surface or choroid plexus or not, were analyzed. RESULTS No permanent hearing impairment occurred in any patient. The AICA/PICA was mobilized in 26 patients. No significant difference was found in surgical results, BAEP findings, and duration of microsurgery between the 2 groups, but age was younger in the mobilized group (P < .01). The mobilized artery was responsible in 14 cases and branched perforators in 7 cases in the mobilized group. The perforators did not obstruct mobilization. CONCLUSION Mobilization of the AICA/PICA from the cerebellar surface is a useful technique to maintain the infrafloccular approach in MVD for HFS. This technique reduces the risk of postoperative hearing impairment. Hearing loss, Hemifacial spasm, Infrafloccular approach, Microvascular decompression, Mobilization of artery ABBREVIATIONS ABBREVIATIONS AICA anterior inferior cerebellar artery BAEPs brainstem auditory evoked potentials CNs cranial nerves CP cerebellopontine fREZ facial root exit zone HFS hemifacial spasm MVD microvascular decompression PICA posterior inferior cerebellar artery Microvascular decompression (MVD) is a well-known procedure that can cure hemifacial spasm (HFS). In our facility, MVD is performed with the transposition method through the lateral suboccipital infrafloccular approach, which offers the advantages of adequate surgical space for exposure of the facial root exit zone (fREZ) and prevents postoperative hearing impairment.1 However, this procedure requires complete exposure of the lower cranial nerves (CNs) for the caudolateral direction of the surgical access,2 and the corner formed by the auditory nerve (CN VIII) and glossopharyngeal nerve (CN IX) is the entrance to the attached segment3 of the fREZ (Figure 1A).4 Consequently, the microsurgical working space is limited, so the key to successful decompression is correct exposure of this space. FIGURE 1. View largeDownload slide Illustrations of the surgical exposure for the infrafloccular approach in microvascular decompression for left hemifacial spasm. A, Final view of the approach showing complete exposure of the lower CNs (CNs IX, X, and XI) and the corner formed by the auditory nerve (CN VIII) and glossopharyngeal nerve (CN IX) at the entrance to the attached segment (asterisk) of the fREZ. B, Artery passing from the left cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface as well as the left vertebral artery medial to the lower CNs is present. The artery on the cerebellar surface is obstructing the surgical route. C and D, The vertebral artery is transposed with a Teflon sling and the PICA C or AICA D on the cerebellar surface is mobilized and fixed to the petrous bone with a Teflon sling. The fREZ is correctly exposed. © 2017 Kenichi Amagasaki. FIGURE 1. View largeDownload slide Illustrations of the surgical exposure for the infrafloccular approach in microvascular decompression for left hemifacial spasm. A, Final view of the approach showing complete exposure of the lower CNs (CNs IX, X, and XI) and the corner formed by the auditory nerve (CN VIII) and glossopharyngeal nerve (CN IX) at the entrance to the attached segment (asterisk) of the fREZ. B, Artery passing from the left cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface as well as the left vertebral artery medial to the lower CNs is present. The artery on the cerebellar surface is obstructing the surgical route. C and D, The vertebral artery is transposed with a Teflon sling and the PICA C or AICA D on the cerebellar surface is mobilized and fixed to the petrous bone with a Teflon sling. The fREZ is correctly exposed. © 2017 Kenichi Amagasaki. Occasionally we encounter vascular components along the approach route. The anterior inferior cerebellar artery (AICA) or posterior inferior cerebellar artery (PICA) can be observed passing from the cerebellopontine (CP) cistern toward the lateral and caudal directions on the cerebellar surface (Figure 1B). Eventually, such an artery crosses the approach route and obstructs manipulations during the decompression at the fREZ, so the approach may be changed to the lateral or rostral direction. However, such change in direction can cause hearing impairment due to stretching of CN VIII.2 Therefore, to continue with the pure infrafloccular approach, the artery must be dissected and isolated from the cerebellar surface and mobilized toward the petrous bone to prevent deviation of the infrafloccular route from the caudal direction (Figure 1C and 1D). The present study investigated the use of this mobilizing process and evaluated the anatomic and clinical results. METHODS Patients The medical records of 101 consecutive patients with HFS who underwent MVD were retrospectively reviewed. All patients were treated at our hospital between October 2015 and September 2016. The study was approved by the hospital ethics committee, after obtaining waivers of consent from all patients. Table 1 summarizes the clinical characteristics of the 101 patients including the offending vessels. TABLE 1. Summary of Demographic and Clinical Characteristics Variable Value Mean age (range), y 50.9 (24-75) Female/male 65/36 Right/left 36/65 Offending vessel  Anterior inferior cerebellar artery 71  Posterior inferior cerebellar artery 45  Vertebral artery 39 Variable Value Mean age (range), y 50.9 (24-75) Female/male 65/36 Right/left 36/65 Offending vessel  Anterior inferior cerebellar artery 71  Posterior inferior cerebellar artery 45  Vertebral artery 39 View Large TABLE 1. Summary of Demographic and Clinical Characteristics Variable Value Mean age (range), y 50.9 (24-75) Female/male 65/36 Right/left 36/65 Offending vessel  Anterior inferior cerebellar artery 71  Posterior inferior cerebellar artery 45  Vertebral artery 39 Variable Value Mean age (range), y 50.9 (24-75) Female/male 65/36 Right/left 36/65 Offending vessel  Anterior inferior cerebellar artery 71  Posterior inferior cerebellar artery 45  Vertebral artery 39 View Large Microvascular Decompression MVD was performed with the transposition method through the infrafloccular approach under routine monitoring of brainstem auditory evoked potentials (BAEPs), as described previously,1 as well as modification to avoid usage of the brain retractor. All microsurgical procedures in this series were performed by the same operator (K.A.). Intraoperative BAEP Monitoring Intraoperative BAEP monitoring was performed in the same way as previously described.1 Patients were divided into 4 groups on the basis of the greatest intraoperative latency prolongation or amplitude reduction of wave V compared with the preoperative baseline as follows: group 1, greatest latency prolongation of less than 1.0 ms without amplitude reduction of more than 50%; group 2, greatest latency prolongation of more than 1.0 ms, or amplitude reduction of more than 50% without latency prolongation of more than 1.0 ms; group 3, greatest latency prolongation of more than 1.0 ms and amplitude reduction of more than 50%; and group 4, complete loss of V wave (including transient loss). Mobilization of the AICA/PICA from the Cerebellar Surface During the approach through the infrafloccular route, if the operator considered that the surgical route was obstructed by the AICA or PICA on the cerebellar surface from the CP cistern, the artery was dissected and isolated from the cerebellar surface, then mobilized toward the petrous bone direction. The operator was entirely responsible for this decision-making, based on whether the surgical manipulation was disturbed by the artery or not. This procedure was first introduced more than 10 yr ago by Yutaka Takusagawa and has since been continued by the first author (K.A.). Consequently, the patients could be classified into the mobilized group or the nonmobilized group. The mobilized artery was identified as the AICA or PICA based on both preoperative magnetic resonance imaging and surgical findings. Age and duration of microscopic surgery in both groups were compared. The mobilized group was further analyzed to identify whether the artery was responsible for HFS or not, and whether the artery supplied perforators to the cerebellar surface or choroid plexus or not. Evaluation of HFS and Complications Cases of HFS were evaluated in March 2017 and the outcome was classified into 4 categories: no spasm, improved, persistent, and recurrence. Any neurological deficit persisting in March 2017 was recorded as permanent. No formal hearing tests for the evaluation of hearing function were conducted except in patients who reported hearing problems at preoperative interviews. On admission, subjective hearing levels were recorded bilaterally on the medical charts as 0 (deaf) to 10 (normal) by finger scratching beside the ears. After the surgery, hearing levels were checked in the same way at least three times a day including immediately after surgery, and similarly recorded. If a definitive decreased hearing score compared with the preoperative condition was recorded, the patient was referred to the otolaryngologist for evaluation. Detailed protocols of hearing-function testing were described previously.1 Patients with symptoms of lower CN (CN IX/X) palsy, such as dysphasia and/or hoarseness, were also referred to the otolaryngologist for evaluation of laryngeal and pharyngeal function. Statistical Analysis Parameters of the 2 groups were compared as follows. Chi-square test was used to analyze the surgical results, Fisher's exact test for BAEP findings, t-test for age, and Mann–Whitney test for duration of microsurgery. IBM SPSS Statistics version 23.0 (IBM Inc, Armonk, New York) for Microsoft Windows (Microsoft, Redmond, Washington) was used for the analysis and P-values of less than .05 were interpreted as significant. RESULTS Table 2 summarizes the clinical data of the mobilized and nonmobilized groups. In total, HFS disappeared in 77 patients, improved in 15 patients, persisted in 8 patients, and recurred in 1 patient in the follow-up period of 6 to 18 mo. There was no statistically significant surgical effect in these surgical groups (P = .88). Ipsilateral hearing decreased to level 5 postoperatively in 1 patient in the mobilized group, but recovered within a few days, and the audiogram a week after the surgery showed no laterality in hearing. Two permanent neurological impairments were recorded. One patient in the mobilized group suffered from permanent facial palsy and another patient in the nonmobilized group suffered from permanent mild hoarseness, but these symptoms were still improving at the end of the follow-up period. CSF leakage was observed in 2 patients; 1 required repair and the other was stopped with lumbar taps. Minor subarachnoid hemorrhage with no neurological symptoms was observed in 1 patient. Intraoperative BAEP findings indicated 58 patients in group 1, 26 in group 2, 16 in group 3, and 1 in group 4. There was no significant difference in BAEP findings between the surgical groups (P = .40). The duration of microsurgery was not statistically significant between the surgical groups (P = .06), but age was significantly lower in the mobilized group (P = .01). The dissected artery was the PICA in 19 cases and the AICA in 7 cases. The artery was responsible for the HFS in 14 cases. Perforators to the cerebellar surface or choroid plexus were observed in 7 cases, but all branched in the caudal side only and none restricted the mobilization of the artery for the infrafloccular route. Three typical cases in the mobilized group are presented. Table 2. Clinical Data of Mobilized and Nonmobilized Groups Mobilized (n = 26) Nonmobilized (n = 75) P Value Surgical effect .88*  No spasm 21 56  Improved 4 11  Persisted 1 7  Recurrence 0 1 Complications  Auditory nerve palsy (transient) 1 0  Lower cranial nerves palsy (transient) 2 4  Lower cranial nerves palsy (permanent) 0 1  Abducens nerve palsy (transient) 0 1  Facial nerve palsy (permanent) 1 0  Cerebrospinal fluid leakage 0 2  Minor subarachnoid haemorrhage 0 1 Brainstem auditory evoked potentials .40**  Group 1 16 42  Group 2 5 21  Group 3 4 12  Group 4 1 0 Mean age ± SD, y 46.3 ± 11.9 52.5 ± 10.6 .01*** Median duration of microsurgery (range), min 84.0 (41 - 231) 73.0 (35 - 144) .06**** Mobilized artery  AICA (responsible for hemifacial spasm) 7 (5)  PICA (responsible for hemifacial spasm) 19 (9)  Origin of perforators to cerebellar surface/choroid plexus 7 Mobilized (n = 26) Nonmobilized (n = 75) P Value Surgical effect .88*  No spasm 21 56  Improved 4 11  Persisted 1 7  Recurrence 0 1 Complications  Auditory nerve palsy (transient) 1 0  Lower cranial nerves palsy (transient) 2 4  Lower cranial nerves palsy (permanent) 0 1  Abducens nerve palsy (transient) 0 1  Facial nerve palsy (permanent) 1 0  Cerebrospinal fluid leakage 0 2  Minor subarachnoid haemorrhage 0 1 Brainstem auditory evoked potentials .40**  Group 1 16 42  Group 2 5 21  Group 3 4 12  Group 4 1 0 Mean age ± SD, y 46.3 ± 11.9 52.5 ± 10.6 .01*** Median duration of microsurgery (range), min 84.0 (41 - 231) 73.0 (35 - 144) .06**** Mobilized artery  AICA (responsible for hemifacial spasm) 7 (5)  PICA (responsible for hemifacial spasm) 19 (9)  Origin of perforators to cerebellar surface/choroid plexus 7 AICA, anterior inferior cerebellar artery; PICA, posterior inferior cerebellar artery; SD, standard deviation *Chi square test, **Fisher's exact test, ***t-test, ****Mann-Whitney test. View Large Table 2. Clinical Data of Mobilized and Nonmobilized Groups Mobilized (n = 26) Nonmobilized (n = 75) P Value Surgical effect .88*  No spasm 21 56  Improved 4 11  Persisted 1 7  Recurrence 0 1 Complications  Auditory nerve palsy (transient) 1 0  Lower cranial nerves palsy (transient) 2 4  Lower cranial nerves palsy (permanent) 0 1  Abducens nerve palsy (transient) 0 1  Facial nerve palsy (permanent) 1 0  Cerebrospinal fluid leakage 0 2  Minor subarachnoid haemorrhage 0 1 Brainstem auditory evoked potentials .40**  Group 1 16 42  Group 2 5 21  Group 3 4 12  Group 4 1 0 Mean age ± SD, y 46.3 ± 11.9 52.5 ± 10.6 .01*** Median duration of microsurgery (range), min 84.0 (41 - 231) 73.0 (35 - 144) .06**** Mobilized artery  AICA (responsible for hemifacial spasm) 7 (5)  PICA (responsible for hemifacial spasm) 19 (9)  Origin of perforators to cerebellar surface/choroid plexus 7 Mobilized (n = 26) Nonmobilized (n = 75) P Value Surgical effect .88*  No spasm 21 56  Improved 4 11  Persisted 1 7  Recurrence 0 1 Complications  Auditory nerve palsy (transient) 1 0  Lower cranial nerves palsy (transient) 2 4  Lower cranial nerves palsy (permanent) 0 1  Abducens nerve palsy (transient) 0 1  Facial nerve palsy (permanent) 1 0  Cerebrospinal fluid leakage 0 2  Minor subarachnoid haemorrhage 0 1 Brainstem auditory evoked potentials .40**  Group 1 16 42  Group 2 5 21  Group 3 4 12  Group 4 1 0 Mean age ± SD, y 46.3 ± 11.9 52.5 ± 10.6 .01*** Median duration of microsurgery (range), min 84.0 (41 - 231) 73.0 (35 - 144) .06**** Mobilized artery  AICA (responsible for hemifacial spasm) 7 (5)  PICA (responsible for hemifacial spasm) 19 (9)  Origin of perforators to cerebellar surface/choroid plexus 7 AICA, anterior inferior cerebellar artery; PICA, posterior inferior cerebellar artery; SD, standard deviation *Chi square test, **Fisher's exact test, ***t-test, ****Mann-Whitney test. View Large Case 1 A 67-yr-old female underwent MVD for left HFS. After the dural incision, a PICA was identified passing from the CP cistern to the lateral and caudal direction on the cerebellar surface (Figure 2A, Video 1, Supplemental Digital Content: 0’20”). On approach to the left fREZ, the AICA was observed as the responsible artery (Figure 2B, Video 1, Supplemental Digital Content: 0’40”). However, the PICA crossed the entrance of the surgical space formed by CN VIII and CN IX, and obstructed further manipulations at the fREZ. Therefore, the PICA loop was dissected and isolated from the cerebellar surface and mobilized in the direction of the petrous bone (Figure 2C, Video 1, Supplemental Digital Content: 1’20”). After mobilization, a wide surgical space for the infrafloccular route was obtained (Figure 2D, Video 1, Supplemental Digital Content: 1’30”), and finally the AICA was securely transposed. Intraoperative BAEP findings showed no remarkable change in the V wave (group 1). FIGURE 2. View largeDownload slide Intraoperative images of case 1 with left hemifacial spasm. A, During opening of the left cerebellomedullary fissure, a PICA passing from the cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface is exposed. The dotted line indicates the margin of the auditory nerve (CN VIII). B, AICA (asterisk) is confirmed as the responsible artery by observation of the fREZ through the angle formed by CN VIII and the glossopharyngeal nerve (CN IX), but the PICA crosses the approach route. C, PICA is mobilized in the petrous bone direction. Vertebral artery is transposed with a Teflon sling medial to the PICA and lower cranial nerves. D, After mobilization of the PICA showing ensuring a wide space between CN VIII and CN IX, with no obstruction to the AICA (asterisk) at the fREZ. FIGURE 2. View largeDownload slide Intraoperative images of case 1 with left hemifacial spasm. A, During opening of the left cerebellomedullary fissure, a PICA passing from the cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface is exposed. The dotted line indicates the margin of the auditory nerve (CN VIII). B, AICA (asterisk) is confirmed as the responsible artery by observation of the fREZ through the angle formed by CN VIII and the glossopharyngeal nerve (CN IX), but the PICA crosses the approach route. C, PICA is mobilized in the petrous bone direction. Vertebral artery is transposed with a Teflon sling medial to the PICA and lower cranial nerves. D, After mobilization of the PICA showing ensuring a wide space between CN VIII and CN IX, with no obstruction to the AICA (asterisk) at the fREZ. Case 2 A 31-yr-old male underwent MVD for right HFS. Opening the cerebellomedullary fissure revealed an artery on the cerebellar surface originating from the CP cistern (Figure 3A, Video 2, Supplemental Digital Content: 0’10”), and obstructing the approach to the responsible artery (Figure 3B, Video 2, Supplemental Digital Content: 0’40”). Therefore, the artery was dissected and isolated from the cerebellar surface, and mobilized in the direction of the petrous bone. Observation of the fREZ after mobilization revealed that the artery was a lateral branch from the AICA, which bifurcated in the CP cistern, and the medial branch was responsible for the HFS (Figure 3C, Video 2, Supplemental Digital Content: 1’10”). Mobilization of the lateral branch facilitated mobilization of the main trunk of the AICA, and finally the medial branch was securely transposed in the anterocaudal direction (Figure 3D, Video 2, Supplemental Digital Content: 1’40”). Intraoperative BAEP findings showed 1.2 ms delay of the V wave but the amplitude was unchanged (group 2). FIGURE 3. View largeDownload slide Intraoperative images of case 2 with right hemifacial spasm. A, On approach to the cerebellopontine cistern from the caudal side, an artery passing from the cistern to the lateral and caudal direction on the cerebellar surface is present. The dotted line indicates the margin of the auditory nerve (CN VIII). B, The responsible artery (asterisk) is confirmed by observation of the facial root exit zone (fREZ) through the angle formed by CN VIII and the glossopharyngeal nerve, but the artery to the cerebellar surface crosses the approach route. C, Mobilized artery is the lateral branch from the anterior inferior cerebellar artery, and the medial branch is the responsible artery (asterisk). D, Transposition of the medial branch in the anterocaudal direction and fixing to the petrous bone with a Teflon sling (asterisk) achieves complete decompression of the artery from the attached segment of the fREZ. FIGURE 3. View largeDownload slide Intraoperative images of case 2 with right hemifacial spasm. A, On approach to the cerebellopontine cistern from the caudal side, an artery passing from the cistern to the lateral and caudal direction on the cerebellar surface is present. The dotted line indicates the margin of the auditory nerve (CN VIII). B, The responsible artery (asterisk) is confirmed by observation of the facial root exit zone (fREZ) through the angle formed by CN VIII and the glossopharyngeal nerve, but the artery to the cerebellar surface crosses the approach route. C, Mobilized artery is the lateral branch from the anterior inferior cerebellar artery, and the medial branch is the responsible artery (asterisk). D, Transposition of the medial branch in the anterocaudal direction and fixing to the petrous bone with a Teflon sling (asterisk) achieves complete decompression of the artery from the attached segment of the fREZ. Case 3 A 50-yr-old male underwent MVD for left HFS. Approaching the CP angle from the caudal side revealed a PICA on the cerebellar surface (Figure 4A). During dissection of the artery in the caudal direction, the artery branched a perforator to the cerebellar surface (Figure 4B). However, the perforator did not disturb the mobilization of the artery in the direction of the petrous bone, and the proximal part of the artery compressing the attached segment3 of the fREZ was safely transposed. BAEP findings showed no remarkable change in the V wave (group 1). FIGURE 4. View largeDownload slide Intraoperative image of case 3 with left hemifacial spasm. A, Posterior inferior cerebellar artery (PICA) passing from the cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface is present. The dotted line indicates the margin of the auditory nerve. B, Perforator to the cerebellar surface from the PICA is isolated from the cerebellar surface at the caudal side. FIGURE 4. View largeDownload slide Intraoperative image of case 3 with left hemifacial spasm. A, Posterior inferior cerebellar artery (PICA) passing from the cerebellopontine cistern to the lateral and caudal direction on the cerebellar surface is present. The dotted line indicates the margin of the auditory nerve. B, Perforator to the cerebellar surface from the PICA is isolated from the cerebellar surface at the caudal side. DISCUSSION MVD for HFS carries the risk of damage to CN VIII.5-8 The infrafloccular approach is useful for the avoidance of auditory impairment.1,2 The surgical technique presented in this paper demonstrates how to continue with the infrafloccular approach if the surgical route is obstructed by an arterial component. The absence of permanent hearing impairment reconfirms that the infrafloccular approach is absolutely advantageous for prevention of postoperative hearing impairment. Surgery without use of the retractor is ideal for the prevention of hearing impairment in MVD. Presence of the AICA/PICA crossing the surgical route limits the entrance to the fREZ and the decompression procedure (Figures 2B and 3B). Therefore, a brain retractor may be applied for better exposure. However, if the artery is dissected and isolated from the cerebellar surface, the cerebellum can be retracted easily with a single dissector and the need for the fixed brain retractor decreases. Our previous study showed that the frequency of use of the retractor affected delay and diminishment of the V wave of the BAEP.1 Later, with the improvement of surgical skills, surgery could be achieved without use of the retractor. In our previous study, flattening of the V wave was observed in 7% (7/100) of cases,1 whereas the present series observed flattening in only 1% (1/101) of cases. In the patient with flattening of the V wave in the mobilized group, who suffered from transient decreased hearing, manipulation of the cisternal portion3 of fREZ and CN VIII during the decompression was necessary, so that the dissecting process of the artery on the cerebellar surface was not directly related to the BAEP change. There are some other advantages of this surgical technique. First, this procedure also allows complete transposition if the dissected artery is responsible for HFS, as observed in 14 cases. Our target of the decompression process is complete isolation of the vessel from the fREZ. Therefore, transposition of the responsible vessel to the petrous bone direction is often ideal. Isolation of the AICA/PICA from the cerebellar surface facilitates the mobilization so that complete transposition can be safely achieved. Secondly, this technique can reduce discomfort of the surgeon during the surgery. Since the surgical space for the final decompression process is deeply located and limited, the surgeon is always concerned about comfort of manipulation during the microscopic procedure. The larger space without any obstructive component in the surgical route and the lower chance of warning BAEP findings result in more confidence that safe decompression can be achieved. The size of the cistern is one of the related factors, and our finding that the mobilized group was significantly younger suggests that this technique is especially useful in cases with the narrow cistern. The microsurgical duration of both groups was not significantly different, but tended to be longer in the mobilized group. Dissection and isolation of the artery from the cerebellar surface may take additional time. However, the dissection process is not a complex procedure with experience. The arachnoid membrane along the artery can be carefully incised and correct isolation of the artery from the cerebellar surface can be achieved. Perforators to the cerebellar surface or choroid plexus were observed in some cases, but only in the caudal side and no cerebellar injury occurred. Finally, skill and technique in MVD surgery vary with the surgeon and can reflect the surgical results. A previous study of MVD indicated 3 complications directly related to operative technique: cerebellar injury, CSF leakage, and hearing loss.5 In our series, 2 patients had CSF leakage, but no other complications occurred. Therefore, we believe that the technique presented in this paper achieves better results in MVD for HFS. Limitations There are some limitations in this study. One is the method of evaluating hearing function. Strict bedside evaluation of hearing is done routinely but pure tone audiometry is not a part of our protocol. Only some patients were evaluated with pure tone audiometry including otolaryngologist consultation.1 However, we assume that bedside evaluation provides useful information about everyday hearing because we are always depending on subjective reporting. The other limitation is the short follow-up period. In this series, the efficacy of the surgery was low compared with our previous series even though the surgical method was similar.1,4 The longest follow-up periods of the previous study were 22 and 26 mo, compared to 18 mo in the present study. Shorter follow-up period may have affected the surgical results. CONCLUSION Mobilization of the AICA/PICA from the cerebellar surface is a useful technique for adequate exposure of the surgical space during MVD for HFS. With this technique, the infrafloccular approach from the caudal side can be maintained throughout the surgery and reduces risk of postoperative hearing impairment. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Amagasaki K , Watanabe S , Naemura K , Nakaguchi H . Microvascular decompression for hemifacial spasm: how can we protect auditory function? ? Br J Neurosurg . 2015 ; 29 ( 3 ): 347 - 352 . Google Scholar CrossRef Search ADS PubMed 2. Hitotsumatsu T , Matsushima T , Inoue T . Microvascular decompression for treatment of trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia: three surgical approach variations: technical note . Neurosurgery . 2003 ; 53 ( 6 ): 1436 - 1443 ; discussion 1442-1433 . Google Scholar CrossRef Search ADS PubMed 3. Campos-Benitez M , Kaufmann AM . Neurovascular compression findings in hemifacial spasm . J Neurosurg . 2008 ; 109 ( 3 ): 416 - 420 . Google Scholar CrossRef Search ADS PubMed 4. Amagasaki K , Kurita N , Watanabe S et al. Lower cranial nerve palsy after the infrafloccular approach in microvascular decompression for hemifacial spasm . Surg Neurol Int . 2017 ; 8 : 67 . Google Scholar CrossRef Search ADS PubMed 5. McLaughlin MR , Jannetta PJ , Clyde BL , Subach BR , Comey CH , Resnick DK . Microvascular decompression of cranial nerves: lessons learned after 4400 operations . J Neurosurg . 1999 ; 90 ( 1 ): 1 - 8 . Google Scholar CrossRef Search ADS PubMed 6. Ying T , Thirumala P , Shah A et al. Incidence of high-frequency hearing loss after microvascular decompression for hemifacial spasm . J Neurosurg . 2013 ; 118 ( 4 ): 719 - 724 . Google Scholar CrossRef Search ADS PubMed 7. Jung NY , Lee SW , Park CK , Chang WS , Jung HH , Chang JW . Hearing outcome following microvascular decompression for hemifacial spasm: series of 1434 cases . World Neurosurg . 2017 ; 108 : 566 - 571 . Google Scholar CrossRef Search ADS PubMed 8. El Damaty A , Rosenstengel C , Matthes M et al. A new score to predict the risk of hearing impairment after microvascular decompression for hemifacial spasm . Neurosurgery . 2017 ; 81 ( 5 ): 834 - 843 . Google Scholar PubMed Acknowledgement We appreciate Dr Yutaka Takusagawa for his pioneering surgical work and the help of Ms Yuimi Marumoto for assistance with statistical analysis. Supplemental digital contentis available for this article at www.operativeneurosurgery-online.com. Supplemental Digital Content 1. Video. Case 1. Supplemental Digital Content 2. Video. Case 2. COMMENTS As pointed out by the authors, there is no doubt that the (classical) infrafloccular approach to the fREZ and neighboring brainstem is the way to perform MVD for HFS with both efficacy and safety. As a matter of fact, more than 90% of the neurovascular compressions responsible for HFS are located ventrocaudally at the fREZ.1 Further, this trajectory revealed the safest to avoid stretching the VIIIth nerve, and consequently create hearing and/or vestibular disturbances with corresponding sequelae. This has been demonstrated for a long time by BAEP studies.2,3 When AICA with its cerebellar surface course makes an obstacle to the fREZ and neighboring brainstem, it has to be dissected free for a long portion and transposed apart. The way described in this article has given satisfaction to the authors, as they did not notice significant hearing complications in the corresponding group of their patients. However, in spite of the inoccuity in the hands of the authors’ study, we think it wise to insist on the risk –by manipulating the AICA and the labyrinthine artery (its tributary to the cochlea) – of producing (by mechanical reflex) some vasospasm. Decrease in amplitude of peak I on BAEP trace can be a useful warning of threatening cochlear ischemia4,5,6,7 that should incite irrigation of those arteries with warm saline, together with a few droplets of Papaverine in 10% solution, before damage becomes irreversible. Marc Sindou Lyon, France 1. Li S.T , Sun H . Surgical Techniques of Microvascular Decompression for Hemifacial Spasm . In “ Microvascular Decompression Surgery ”, Li Zhong Sekula (eds), Springer , Heidelberg , 2016 , pages 79 – 93 Google Scholar CrossRef Search ADS 2. Sindou M , Fobe J. L. , Ciriano D. , Fischer C. Hearing prognosis and intraoperative guidance of BAEPs in MVD . Laryngoscope , 1992 , 102 : 678 – 682 Google Scholar CrossRef Search ADS PubMed 3. Hatayama T , Moller A.R. Correlation between latency and amplitude of peak V in the BAEPs Intraoperative recordings in MVD operations . Acta Neurochir ., 1998 , 140 : 681 – 687 Google Scholar CrossRef Search ADS PubMed 4. Polo G , Fischer C. , Sindou M.P. , Marneffe V. Brain 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 , 54 : 97 – 106 Google Scholar CrossRef Search ADS PubMed 5. Sindou M . Microvascular decompression for primary hemifacial spasm. Importance of intra-operative neurophysiological monitoring , Acta Neurochir ., 2005 , 147 : 1019 – 1026 Google Scholar CrossRef Search ADS PubMed 6. Jo KW , Kim JW. , Kong DS. , Hong SH. , Park K. The patterns risk factors of hearing loss following MVD for HFS . Acta Neurochir . 2011 , 153 : 1023 – 1030 Google Scholar CrossRef Search ADS PubMed 7. Li S.T. , Ying T.T. Intra operative monitoring in “Microvascular Decompression Surgery ”, Li S.T. , Zhong J. , Sekula R.F. (eds), Springer , Heidelberg , 2016 , chap 12, pages 151 – 170 The authors of this paper share their experience with management of HFS using an infrafloccular approach for MVD. Out of 101 analyzed cases, the arterial trunk of AICA/PICA was located on the cerebellar surface and had to be mobilized to allow safe approach to the VII-VIII cranial nerve complex in 26 patients. Despite this arterial mobilization – or because of it –the results were essentially the same in those who did and did not have such mobilization. The authors routinely use the “sling technique” to keep the artery away from the nerve root. This surgical nuance does usually require somewhat larger exposure and more arterial manipulation than simple placement of Teflon felt pledgets between the vessel and the nerve root. I am not sure how prevalent is the use of slings in MVD for HFS; it is conceivable, however, that at some point it will become a preferred approach for MVD. Overall, I applaud the authors' thoroughness in documenting the surgical nuance that most of us use from time to time already – the need for arterial dissection is routinely determined during the surgical approach. It is, however, nice to know that such additional manipulation does not make the procedure significantly longer and, when properly addressed, the adherence of artery to the cerebellum dose not negatively affect the overall outcome. Konstantin Slavin Chicago, Illinois Without a doubt, the “infrafloccular” approach to MVD of the facial nerve is the preferred approach for this operation. This manuscript emphasizes avoidance of fixed retraction and mobilization of AICA and PICA along the cerebellar surface and petrous dura1. These are important concepts. The use of transposition of AICA/PICA to the petrous dura is a nice adjunct to the operation. For years, I have also used “slings” fashioned from a variety of materials in many of my patients undergoing MVD for hemifacial spasm or trigeminal neuralgia. I avoid, however, slinging AICAs with short brainstem perforators as brainstem infarction may eventuate. The major limitation of this study, however, is the technique used to evaluate preoperative and postoperative hearing function. The use of a “finger scratch” technique is not only inexact but is misleading. A patient with significantly decreased hearing or even unilateral deafness may believe that he or she can hear in the deaf ear with “finger scratch” for a period of time. Undoubtedly, if all patients in this series underwent pure tone audiometry preoperatively and postoperatively, some amount of hearing loss would have been detected. Overall, however, the manuscript nicely illustrates important technical nuances of successful MVD of the facial nerve, and the authors are to be congratulated. Raymond F. Sekula Jr Pittsburgh, Pennsylvania 1. Thirumala P , Frederickson AM , Balzer J , Crammond D , Habeych ME , Chang YF , Sekula RF . Reduction in high-frequency hearing loss following technical modifications to microvascular decompression for hemifacial spasm . J Neurosurg . 2015 Oct ; 123 ( 4 ): 1059 – 64 . Epub 2015 Jul 10 Google Scholar CrossRef Search ADS PubMed Copyright © 2018 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

Operative NeurosurgeryOxford University Press

Published: May 22, 2018

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