Root Exit Zone Of Facial Nerve Research Articles

Interposition and transposition techniques of vascular decompression for hemifacial spasm

To analyze the vessels compressing facial nerve root exit zone and efficacy of interposition and transposition techniques of vascular decompression for hemifacial spasm. Vascular compression was evaluated in 110 patients. Implant interposition between vessels and nerve was performed in 52 cases, transposition of arteries without contact between implants and nerve - in 58 patients. Compressing vessels were anterior (44), posterior (61) inferior cerebellar, vertebral (28) arteries and veins (4). Multiple compressing vessels were found in 27 cases. Premeatal meningioma and jugular schwannoma were accompanied by vascular compression in 2 cases. Immediate regression of symptoms was observed in 104 patients, partial regression - in 6 patients. Transient facial paresis (4) and impaired hearing (5) were noted after implant interposition. Redo vascular decompression was performed in one case. The most common compressing vessels were cerebellar arteries, vertebral artery and veins. Transposition of arteries is highly effective technique with low incidence of VII-VII nerve dysfunction but relatively slow regression of symptoms.

A Novel Approach to Microvascular Decompression for Hemifacial Spasm: Method Description and Associated Outcomes.

Microvascular decompression (MVD) is the only potential cure for hemifacial spasm (HFS). However, traditional techniques such as the interposition method may have limited effect in some cases. Alternative techniques have been proposed; however, they can be more complex or difficult to perform than the standard approach. To describe a safe decompression technique-the "shelter method"-which involves creating a shelter-like space around the facial nerve root exit zone and present associated outcomes. Medical records and intraoperative findings of 92 patients with HFS who underwent MVD using the shelter method between April 1997 and March 2017 were retrospectively reviewed. As a historical control group, we included 53 patients who had undergone MVD by the traditional interposition method before March 1989. The patients were divided into 3 subgroups according to the arteries involved and degree or direction of arterial compression to the seventh nerve. Patient outcomes were assessed as excellent, good, fair, and poor according to the MVD scoring system of the Japan Society for MVD Surgery. In the shelter method group, complete disappearance of HFS was achieved in 87 patients (94.6%). The curative rate of the shelter method group was significantly higher than that of the interposition method group. The overall complication rates were significantly lower in the shelter method group than in the interposition method group. Our findings indicate high curative and low complication rates of the shelter method, suggesting that it helps treat HFS caused by various types of arterial compression.

Fully Endoscopic Microvascular Decompression for Hemifacial Spasm Using Improved Retrosigmoid Infrafloccular Approach: Clinical Analysis of 81 Cases.

Microvascular decompression (MVD) is widely accepted as the preferred treatment for hemifacial spasm (HFS). Endoscopy has been implemented to provide a comprehensive view of neurovascular conflicts and minimize the damage caused by brain retraction while exploring the facial nerve root exit zone of the brain stem. To preliminarily evaluate the surgical safety and efficacy of fully endoscopic MVD for HFS using an improved retrosigmoid infrafloccular approach. The clinical data of 81 patients with HFS who underwent fully endoscopic MVD using an improved endoscopic retrosigmoid infrafloccular approach from June 2019 to December 2020 were retrospectively analyzed. The reliability and advantages of this surgical technique in the treatment of HFS were evaluated according to the intraoperative situation, outcomes of postoperative symptoms, and main complications. During the follow-up period, 77 cases (95.1%) were completely cured, with immediate facial twitch disappearance in 56 cases and a delayed cure in 21 cases; in 4 cases (4.9%), there was no obvious improvement. There were no cases of recurrence. There were 4 cases (4.9%) of transient facial paralysis after MVD, all of which were completely cured in 3 months. Three cases (3.7%) had hearing loss postoperatively, of whom 2 showed good improvement. At the end of the follow-up period, 1 case (1.2%) still had tinnitus. There were no cases of postoperative intracranial hemorrhage, cerebellar swelling, or death. Fully endoscopic MVD using an improved retrosigmoid infrafloccular approach not only has the advantages of panoramic surgical visualization but also takes into account the requirements of minimally invasive surgery.

Hemifacial Spasm: Endoscopic Assistance in Facial Nerve Decompression With Lateral Spread Response Corroboration: 2-Dimensional Operative Video

This video depicts the case of a 48-yr-old female with 3 yr of progressive left hemifacial spasm (HFS) refractory to medication. Magnetic resonance imaging showed a large anterior inferior cerebellar artery (AICA) and also a labyrinthine artery loop around the facial nerve (FN) root exit zone. A large bony eminence was also noted in the superior and lateral aspects of the porous acousticus (PA). She preferred surgery if "cure" was possible in lieu of Botox injections. A left retro sigmoid craniotomy was performed with brainstem auditory evoked responses (BAERs) and FN monitoring along with lateral spread response (LSR) assessment. The large bony prominence was drilled in its lateral aspect. Despite this, visualization was still limited and therefore we utilized a 30-degree-angled endoscope to observe the vessels caudal and cranial to the FN. This view prompted us to then drill further at the PA to decompress the FN as well as mobilize the labyrinthine artery away from the nerve. The LSR showed a dramatic improvement when FN decompression was accomplished, and then a further improvement with arterial mobilization and Teflon pledget placement. The BAERS remained at baseline throughout. FN function and hearing were intact on postoperative clinical assessment. Her symptomatic improvement was recorded at 12 mo after surgery. This video illustrates a more complex case of microvascular decompression with skull base concepts and techniques. The patient provided consent for the procedure and use of her images and operative video for publication.

Spasm Freedom Following Microvascular Decompression for Hemifacial Spasm: Systematic Review and Meta-Analysis

Hemifacial spasm (HFS) is a debilitating disorder characterized by intermittent involuntary movement of muscles innervated by the facial nerve. HFS is caused by neurovascular compression along the facial nerve root exit zone and can be treated by microvascular decompression (MVD). The goal was to determine rates and predictors of spasm freedom after MVD for HFS. A literature search using the key terms "microvascular decompression" and "hemifacial spasm" was performed. The primary outcome variable was spasm freedom at last follow-up. Analysis was completed to evaluate for variables associated with spasm-free outcome. A total of 39 studies including 6249 patients were analyzed. Overall spasm freedom rate was 90.5% (5652/6249) at a follow-up of 1.25 ± 0.04 years. There was no significant relationship between spasm freedom versus persistent spasm and age at surgery, timing of follow-up, gender, disease duration, side of disease, or vessel type. Spasm freedom was more likely after an initial surgery versus a redo MVD (odds ratio 4.16, 95% confidence interval 1.99-8.68; P < 0.01). MVD works well for HFS with cure rates >90% at 1-year follow-up in 6249 patients from 39studies. A significant predictor of long-term spasm freedom at 1 year was an initial MVD as compared to repeat MVD. The majority of published manuscripts on MVD for HFS are heterogeneous single-institutional retrospective studies. As such, a large-scale meta-analysis reporting outcome rates and evaluating significant predictors of spasm freedom provides utility in the absence of randomized controlled studies.

Utilization of 3D imaging reconstructions and assessment of symptom-free survival after microvascular decompression of the facial nerve in hemifacial spasm.

Hemifacial spasm (HFS), largely caused by neurovascular compression (NVC) of the facial nerve, is a rare condition characterized by paroxysmal, unilateral, involuntary contraction of facial muscles. It has long been suggested that these symptoms are due to compression at the transition zone of the facial nerve. The aim of this study was to examine symptom-free survival and long-term quality of life (QOL) in HFS patients who underwent microvascular decompression (MVD). A secondary aim was to examine the benefit of utilizing fused MRI and MRA post hoc 3D reconstructions to better characterize compression location at the facial nerve root exit zone (fREZ). The authors retrospectively analyzed patients with HFS who underwent MVD at a single institution, combined with a modified HFS-7 telephone questionnaire. Kaplan-Meier analysis was used to determine event-free survival, and the Wilcoxon signed-rank test was used to compare pre- and postoperative HFS-7 scores. Thirty-five patients underwent MVD for HFS between 2002 and 2018 with subsequent 3D reconstructions of preoperative images. The telephone questionnaire response rate was 71% (25/35). If patients could not be reached by telephone, then the last clinic follow-up date was recorded and any recurrence noted. Twenty-four patients (69%) were symptom free at longest follow-up. The mean length of follow-up was 2.4 years (1 month to 8 years). The mean symptom-free survival time was 44.9 ± 5.8 months, and the average symptom-control survival was 69.1 ± 4.9 months. Four patients (11%) experienced full recurrence. Median HFS-7 scores were reduced by 18 points after surgery (Z = -4.013, p < 0.0001). Three-dimensional reconstructed images demonstrated that NVC most commonly occurred at the attached segment (74%, 26/35) of the facial nerve within the fREZ and least commonly occurred at the traditionally implicated transition zone (6%, 2/35). MVD is a safe and effective treatment that significantly improves QOL measures for patients with HFS. The vast majority of patients (31/35, 89%) were symptom free or reported only mild symptoms at longest follow-up. Symptom recurrence, if it occurred, was within the first 2 years of surgery, which has important implications for patient expectations and informed consent. Three-dimensional image reconstruction analysis determined that culprit compression most commonly occurs proximally along the brainstem at the attached segment. The success of this procedure is dependent on recognizing this pattern and decompressing appropriately. Three-dimensional reconstructions were found to provide much clearer characterization of this area than traditional preoperative imaging. Therefore, the authors suggest that use of these reconstructions in the preoperative setting has the potential to help identify appropriate surgical candidates, guide operative planning, and thus improve outcome in patients with HFS.

Microvascular decompression for hemifacial spasm : Surgical techniques and intraoperative monitoring

Primary hemifacial spasm with few exceptions is due to the vascular compression of the facial nerve that can be evidenced with high resolution MRI. Microvascular decompression is the only curative treatment for this pathology. According to literature review detailed in chapter “conflicting vessels”, the compression is located at the facial Root Exit Zone (REZ) in 95% of the cases, and in 5% distally at the cisternal or the intrameatal portion of the root as the sole conflict or in addition to one at brainstem/REZ. Therefore, exploration has to be performed on the entire root, from the ponto-medullary fissure to the internal auditory meatus. Because microvascular decompression is functional surgery, the procedure should be as harmless as possible and with a high probability of permanent efficacy. Besides facial palsy, main complications are hearing loss, tinnitus and gait disturbances. Causes are cochlea/labyrinth ischemia due to manipulations of their nutrient arteries and/or stretching of the eight nerve complex. To minimize the latter, the approach should not be with lateral-to-medial retraction of the cerebellar hemisphere, but along an infra-floccular trajectory, from below. In fact, most of the neurovascular conflicts are situated ventro-caudally to facial REZ at the brainstem, particularly those from a megadolicho-vertebrobasilar artery and its posterior inferior-cerebellar branch. Also, care should be taken not to cause any injury of the manipulated vessels or stretching of their perforators to brainstem. Heating from bipolar coagulation must be avoided. The inserted material used to maintain the offending vessel(s) away must not be neo-compressive. Intraoperative neuromonitoring is considered to be useful for achieving safe surgery at least until the learning curve has reached an optimal level, particularly BrainstemAuditory Evoked Potentials recordings. Increase in latency and/or decrease in amplitude of wave V warn excessive stretching or damage to the cochlear nerve, and decrease in amplitude of wave I signals possible ischemia of the cochlea. Free-running EMG of the facial muscles may warn against excessive manipulation of the facial nerve. Recording of the lateral spread responses – which are a sign of hyperexcitabilty of the facial motor system – may provide information on completeness of the decompression.

Endoscope-assisted decompression of facial nerve for treatment of hemifacial spasm

Microvascular decompression has become the sole method for a curative treatment of primary hemifacial spasm. Finding the responsible conflicting artery is not always easy as its location can be deeply situated within the cerebellopontine/medullary fissure at the facial root exit zone. Sole or additional offending vessel(s) may be at the meatus of the internal auditory canal (5% of the cases). Identifying the compressive vessel(s) and performing decompression is in most cases possible without cerebellar retraction by classical microsurgical techniques. However, in a number of patients the neurovascular conflict may be hidden in spite of the direct illumination of the operative microscope. Therefore, assistance by endoscopy can be useful and contribute as a minimally invasive approach. The author reports his own experience in a series of 553 patients operated on over the past three decades. A total of 93.6% had complete relief of their spasm (11% after repeated surgery). Relief was delayed in 20.8% of these patients. Recurrence was rare (0.3%). There was no mortality and morbidity was low: deafness occurred in 0.6%. There was no permanent postoperative facial palsy. CSF leakage amounted to 1% in the last period of surgery. In conclusion, the author advocates combining the use of both the endoscopy for exploration and the microscope for decompression.

The conflicting vessels in hemifacial spasm: Literature review and anatomical-surgical implications

Since several decades, it has been established that so-called primary hemifacial spasm is linked to neuro-vascular conflicts in the facial nerve, especially its root exit zone (REZ). Based on our review of the detailed publications of literature (2489 patients), together with our own series (340 patients), the responsible vessels found at surgery were: the posterior inferior cerebellar artery in 47.2%, the anterior inferior cerebellar artery in 45.9%, the vertebro-basilar artery in 17.5%, another (smaller) artery in 11.7%. Participation of veins was very diversely estimated according to series: 4.9% on average. Multiple neuro-vascular conflicts in a same individual were frequently observed, in the order of 20 to 30% according to authors, 37% in our series. Also, abnormal conformation of the posterior fossa may play a role, such as flatness of the posterior fossa or exiguity of the cerebello-pontine angle cistern. Whatever, most neurovascular conflicts are located at brainstem and/or ventrocaudally to the facial REZ, in the order of 95% of the patients. The anatomical location and conformation of the compressive vessel(s) are crucial in determining the difficulties to identify the responsible conflict(s) and to perform effective and safe decompression. Main difficulties are encountered in cases with arteriosclerotic megadolicho-vertebrobasilar artery, at brainstem, especially when PICA and/or AICA come in association, or for neurovascular conflict(s) located at the cisternal or the intrameatal portions of the facial root. Later ones can be alone or in addition to NVC at brainstem/REZ.

New insights into the pathophysiology of primary hemifacial spasm

Primary hemifacial spasm (pHFS) is due to a benign compression of the facial motor nerve by an offending vessel, leading to increased nerve excitability. Facial nerve hyperexcitability presents two different aspects. First, there is a spontaneous and ectopic generation of action potentials on the incriminated nerve and then this ectopic impulse can propagate and spread “laterally” from one facial nerve branch to another. This results in spontaneous and synkinetic spasms affecting one hemiface. Although the increase in excitability certainly concerns the nucleus of the facial motor nerve in the brainstem, it seems unlikely that the primary origin of this hyperexcitability and the associated phenomenon of lateral spreading strictly originate at the nuclear level. In fact, the mechanisms causing facial nerve hyperexcitability per se remain unknown. The leading implication of a structural nerve lesion, such as segmental demyelination, induced by vessel compression, is also unconvincing. In contrast, a functional mechanical factor increasing nerve excitability is extremely probable, that it is either due to compression or stretch resulting from the neurovascular conflict. Axonal ion channel changes are obviously associated with this mechanism. Then the lateral spreading of nerve fibre hyperexcitability probably results from an ephaptic process, the “cross-talk” between axons being located in the region of the conflict or in the transition zone between central and peripheral myelin, at the end of the facial nerve root exit zone. In any event, pHFS is due to a functional increase in facial nerve excitability triggered by an offending vessel and this clearly explains the remarkable and rapid efficacy of surgical microvascular decompression.

Microvascular decompression for hemifacial spasm: A systematic review of vascular pathology, long term treatment efficacy and safety.

Hemifacial spasm (HS) is a rare disorder caused by the compression of facial nerve root exit zone (REZ) at the brainstem by a vascular loop. Microvascular decompression (MVD) is a popular treatment modality for HS. The purpose of this study was to determine the long-term efficacy and safety of MVD for HS by assessing the effect of the procedure from the literature published over the last 25 years. A systematic data review from 1992 to 2015 using specific eligibility criteria yielded 27 studies on MVD for HS, the data of which were pooled and subjected to a meta-analysis. The pooled odds ratio (OR) revealed by the meta-analysis showed that anterior inferior cerebellar artery was the most common offending vessel in 37.8% (95% confidence interval [CI]: 27.8-47.7%) of the patients. Complete resolution of HS was seen in 88.5% (95% CI: 86.7-90.4%) of the patients after a long-term follow up. The complication rate was low following MVD, the most common being temporary facial paresis in 5.9% (95% CI: 4.3-7.5%) of patients. MVD is a safe and effective treatment for HS with long-term benefits and a low complication rate.

Evaluating Transient Hemifacial Spasm that Reappears After Microvascular Decompression Specifically Focusing on the Real Culprit Location of Vascular Compression

Even although microvascular decompression is the standard treatment for hemifacial spasm (HFS), the treatment is not always 100% successful. Some patients experience the reappearance of HFS after temporary relief after surgery. We analyzed our data to elucidate the reasons for and prognosis of HFS reappearance, specifically focusing on exact compressive location of the facial nerve. The patients were divided into 2 groups: group A, the patients whose symptoms of spasm disappeared immediately after surgery but recurred within a month, and group B, the patients whose symptoms of spasm completely disappeared and never recurred. We adopted the terms of subdivision in the facial nerve root exit zone: RExP, root exit point; AS, attached segment; RDP, root detachment point; TZ, transition zone; and CP, distal cisternal portion. Among 115 patients, 56 (48.7%) belonged to group A and 59 (51.3%) to group B. In 54 of the 56 patients in group A (96.4%), the reappearing HFS disappeared gradually over several weeks. The precise location of compression in group A was at the RExP in 46.4% of the patients, AS in 33.9%, RDP in 16.1%, and TZ in 3.6%, and the RExP compression was significantly more frequent compared with in group B. After microvascular decompression for HFS, almost half of the patients experienced transient HFS recurrence despite sufficient decompression of the facial nerve. However, in most cases, recurrent HFS gradually resolved over a period. Based on the compression location, the surgeon could anticipate recurrence of transient HFS.

Outcome of microvascular decompression for hemifacial spasm associated with the vertebral artery.

We retrospectively compared the outcome of microvascular decompression (MVD) for hemifacial spasm (HFS) associated with the vertebral artery (VA) with that of MVD for HFS unrelated to the VA. Between April 2008 and April 2015, 22 patients with VA-associated HFS underwent MVD at our institution. The median follow-up period was 28months (range, 12-90months). Results were classified as excellent in 19 patients (86%), good in one (5%), fair in one (5%), and poor in one (5%). Immediate complications developed in five patients (23%), and one of these complications (5%) was permanent. The surgical outcome of MVD for VA-associated HFS was similar to that of MVD for HFS unrelated to the VA; however, the incidence of complications was significantly more frequent in patients whose VA compressed the more proximal portion of the facial nerve root exit zone from the caudal side at the pontomedullary sulcus. We conclude that preoperative evaluation of VA compression patterns is important to predict the difficulty of the planned MVD procedure.

Microvascular Decompression Surgery for Hemifacial Spasm.

This study aims to investigate the operative efficacy, surgical complication rate, and surgical strategy of microvascular decompression (MVD) for hemifacial spasm (HFS). Clinical data of 46 patients with HFS who underwent MVD were retrospectively analyzed. During surgery, it was found that the facial nerve root exit zone was compressed by the following arterial vessels: anterior inferior cerebellar artery in 24 patients (52.17%); posterior inferior cerebellar artery in 14 patients (30.43%); vertebral artery and a small artery in 7 patients (15.22%); and vertebral artery in 1 patient (2.18%). Symptoms of 38 patients were immediately remitted completely after surgery and symptoms of 8 patients were significantly reduced. Main complications included dizziness and tinnitus in 9 patients, hearing loss in 5 patients, cerebrospinal fluid leakage in 1 patient, and infection in 2 patients. No patient died during surgery. MVD is the preferred choice for treating idiopathic hemifacial spasm, and hearing impairment is the main complication. Skilled microsurgical techniques, as well as identifying and completely decompressing offending vessels, are the key to ensuring a successful microvascular decompression.

Failed microvascular decompression surgery for hemifacial spasm due to persistent neurovascular compression: an analysis of reoperations.

OBJECT Microvascular decompression (MVD) surgery for hemifacial spasm (HFS) is potentially curative. The findings at repeat MVD in patients with persistent or recurrent HFS were analyzed with the aim to identify factors that may improve surgical outcomes. METHODS Intraoperative findings were determined from review of dictated operative reports and operative diagrams for patients who underwent repeat MVD after prior surgery elsewhere. Clinical follow-up was obtained from the hospital and clinic records, as well as telephone questionnaires. RESULTS Among 845 patients who underwent MVD performed by the senior author, 12 had been referred after prior MVD for HFS performed elsewhere. Following repeat MVD, all patients improved and complete spasm resolution was described by 11 of 12 patients after a mean follow-up of 91 ± 55 months (range 28-193). Complications were limited to 1 patient with aggravation of preexisting hearing loss and mild facial weakness and 1 patient with aseptic meningitis without sequelae. Significant factors that may have contributed to the failure of the first surgery included retromastoid craniectomies that did not extend laterally to the sigmoid sinus or inferiorly to the posterior fossa floor in 11 of 12 patients and a prior surgical approach that focused on the cisternal portion of the facial nerve in 9 of 12 patients. In all cases, significant persistent neurovascular compression (NVC) was evident and alleviated more proximally on the facial root exit zone (fREZ). CONCLUSIONS Most HFS patients will achieve spasm relief with thorough alleviation of NVC of the fREZ, which extends from the pontomedullary sulcus root exit point to the Obersteiner-Redlich transition zone.

Characteristic anatomical conformation of the vertebral artery causing vascular compression against the root exit zone of the facial nerve in patients with hemifacial spasm.

Hemifacial spasm (HFS) is caused by tortuous offending vessels near the facial nerve root exit zone. However, the definitive mechanism of offending vessel formation remains unclear. We hypothesized that vascular angulation and tortuosity, probably caused by uneven vertebral artery blood flow, result in vascular compression of the facial nerve root exit zone. The authors observed two anatomical characteristics of the vertebrobasilar arterial system in 120 subjects in the surgical group and 188 controls. The presence of the dominant vertebral artery (DVA) and laterality of the vertebrobasilar junction (VBJ) were observed. We also analyzed the morphological characteristics of the surgical group showing the presence of DVA. The morphological characteristics were classified into three types: type I had the VBJ and DVA on the same side, type II had the VBJ within 2 mm of the midline, and type III had the VBJ opposite the DVA. The DVA was more prevalent in the surgical group than in the control group (71 % versus 54 %, P < 0.05). The surgical group patients with HFS on the left were more likely to have a DVA on the left (P < 0.05) and with HFS on the right were more likely to have a DVA on the right (P < 0.01) compared with controls. The direction of the VBJ was more common on the same side as the DVA, which corresponds with the laterality of the HFS. In the surgical group with the DVA and HFS on the same side, type I was predominant, but in the surgical group with a contralateral DVA and HFS, type III was predominant. The presence of a DVA and shifting of the VBJ on the same side plays a role in the angulation and tortuosity of vessels in the perivertebrobasilar junction, resulting in neurovascular compression of the facial nerve root exit zone and thereby causing HFS.

Improved preservation of function during acoustic neuroma surgery.

Restoration of cranial nerve functions during acoustic neuroma (AN) surgery is crucial for good outcome. The effects of minimizing the injury period and maximizing the recuperation period were investigated in 89 patients who consecutively underwent retrosigmoid unilateral AN surgery. Cochlear nerve and facial nerve functions were evaluated during AN surgery by use of continuous auditory evoked dorsal cochlear nucleus action potential monitoring and facial nerve root exit zone-elicited compound muscle action potential monitoring, respectively. Factors affecting preservation of function at the same (preoperative) grade were analyzed. A total of 23 patients underwent standard treatment and investigation of the monitoring threshold for preservation of function; another 66 patients underwent extended recuperation treatment and assessment of its effect on recovery of nerve function. Both types of final action potential monitoring response and extended recuperation treatment were associated with preservation of function at the same grade. Preservation of function was significantly better for patients who received extended recuperation treatment.

Significance of Arachnoid Dissection to Obtain Optimal Exposure of Lower Cranial Nerves and the Facial Nerve Root Exit Zone during Microvascular Decompression Surgery

This letter discusses the article2) entitled Delayed unilateral soft palate palsy without vocal cord involvement after microvascular decompression for hemifacial spasm recently published in J Korean Neurosurg Soc 53 : 364-367, 2013. In order to prevent cranial nerve palsies during microvascular decompression for hemifacial spasm, it is important to avoid retracting the cerebellum from the internal to the external side. Instead, it should be retracted from the lower to the upper side to obtain the optimal exposure of lower cranial nerves and the facial nerve root exit zone (FNREZ). The author of this manuscript devised an arachnoid dissection technique to expose the lower cranial nerves and the FNREZ. The retromastoid approach is most commonly conducted in the lateral decubitus position. The dura mater is incised along the sigmoid sinus, and the Cisterna magna is opened to drain the cerebrospinal fluid after careful retraction of the cerebellum from the lower to the upper side. The cerebellar cortical branches of the anterior inferior cerebellar artery (AICA), which is covered with an arachnoid membrane exterior to the lower cranial nerves, are exposed. Under the microscope, the outside of the arachnoid membrane is attached to the pia mater of the cerebellar cortical braches of AICA, which is dissected using an arachnoid knife and microscissors. At this point, the inner side of the arachnoid membrane of the cerebellar cortical braches of AICA should be preserved (Fig. 1). Next, the space between the cerebellar cortical braches of AICA and the cerebellar cortex is separated, and the sharp continuous arachnoid membrane dissection is extended towards the anterior and inferior end of lower cranial nerves modified by author's technique (Fig. 2)1). The cerebellar cortical branches of AICA are then retracted naturally towards the tentorium, and the choroid plexus, located in the lateral recess of the 4th ventricle, can be visualized. The offending artery and entire set of lower cranial nerves, facial nerves, including the FNREZ, can then be widely exposed (Fig. 3). Fig. 1 The outside of cortical anterior inferior cerebellar artery arachnoid membrane is dissected using microscissors. Fig. 2 The sharp coninuous arachnoid dissection is extended toward anterior and inferior end of lower cranial nerves. Fig. 3 The offending vessels and entire set of lower cranial nerves, facial nerve root exit zone are widely exposed. A : Left. B : Right. I think the significance of this arachnoid dissection procedures can prevent the lower cranial nerve palsies and also helpful to avoid cerebellar ischemia resulting from cerebellar cortical arterial compression/retraction during the operation.

Value of 3-Dimensional High-Resolution Magnetic Resonance Imaging in Detecting the Offending Vessel in Hemifacial Spasm

High-resolution 3-dimensional (3-D) magnetic resonance imaging (MRI) is widely used to predict the neurovascular anatomy within the cerebellopontine angle. To assess the value of 3-D steady-state free precession imaging (SSFP) and time-of-flight magnetic resonance angiography (TOF MRA) in detecting the offending vessels in hemifacial spasm in comparison to intraoperative endoscopic visualization. 42 patients underwent endoscope-assisted microvascular decompression (MVD). All available preoperative 3-D SSFP and TOF MRA images were checked. Intraoperative videos were captured by a high-definition endoscopic camera attached to endoscopes while exploring the area of facial nerve root exit zone (REZ). Evaluation of the 3-D images was performed by 2 independent groups of observers and compared with the operative findings. Three-D MRI had an average positive predictive value (PPV) of 89.1% in differentiating between simple and complex compression. Mean accuracy of the images in detection of the offending vessels was 83.3% and 77% according to the first and second groups of observers, respectively. Averaged inter-observer agreement between the 2 groups of observers was substantial, with an averaged Kappa coefficient (K) of 0.56. In the simple compression group, mean accuracy was 97% and 89.4% according to the first and second groups of observers, respectively. Averaged K for agreement was substantial (K = 0.65). According to endoscopic visualization, 3-D SSFP and TOF MRA images are accurate in detecting the offending vessels in simple compression of the facial nerve, and in predicting presence of a complex compression with variable sensitivity in identifying all offending vessels.

Intraoperative early change of latencies in Facial nerve function during Microvascular Decompression studied in patients with Hemifacial Spasm

Background: Primary hemifacial spasm (HFS) is reported mainly as a result of cross compression of blood vessel and facial nerve at its root exit zone (REZ). Generation of HFS could be due to hyperexcitability of facial nerve since microvascular decompression (MVD) has been an effective treatment in clinical experince of authors. Multimodal Intraoperative monitoring (MIOM) has been frequently used for care and constant evaluation of facial nerve during MVD. In HFS patients F waves of the facial muscle which is known to be induced from backfiring of facial motor nucleus, Blink reflexes and Lateral spread (abnormal muscle responses) before, during and after MVD have been used to evaluate the excitability of the facial motor nucleus and the treatment outcome after MVD procedure. Methods: In 9 female HFS cases with abnormal lateral spread in their facial Electromyography (EMG), patients history, preoperative physical examination, electrodiagnosis and MIOM were perfored using a Moltimodal 40 channels electrophysiologic monitoring system (Nicolet Endeavor, VIASYS Healthcare, 2005, USA). Free run EMG, Stimulated EMG, bilateral blink reflexes and facial F waves were set for MIOM as indicators of MVD effectiveness. Bilateral Orbicularis Oris/Oculi muscles were used for surface EMG recordings. Antidromic stimulatin of facial nerve branches and direct bipolar stimulation of the nerve in REZ, before and after its vascular contact at the site of operation applied by surgen. In all subjects, recordings were scheduled a week before, intaoperatively and every 2 weeks up to 3 months after operation. Results: In affected side of the face before MVD, threshold of F wave was reduced and excitability of blink reflex EMG responses were enhanced compared to the normal side. These responses remaind the same intraoperatively. In post operation recordings F waves and Blink reflex responses were as before in 7 subjects up to fourth week after the surgery, although with lower amplitude of the responses. These responses and Lateral spread of EMGs disappeared completely after 6 weeks. In 2 other subject these abnormal findings reduced slowly and subsequently disappeared after 12 weeks. In all cases, introperative recordings of F wave latencies and the latencies of R1 and R2 responses of blink reflexes were reduced significantly even before 20 minutes of decompression (P Propofol or Propofol/Ketamine mixture plus narcotic is suitable to obtain stable reproducible F waves and EMGs. Atracurium or other nondepolarizing muscle relaxant should be avoided. Muscle relaxants, mean arterial pressure (MAP) below 70 mmHg may cause bilateral reduction or loss of reflex responces and EMGs. In all cases, there was no postoperative clinically detectable complication. Conclusions: MIOM could be useful technique in all patients undergoing any procedures around cranial nerves. Monitoring can practically reduce possibilities of neurologic deficit and reduce the potential risk of interventions around facial REZ. We conclude that in MVD for HFS, the use of stimulated EMGs for evaluating involved facial nerve is not sufficent because, practically, it could be limited to the efferent nerve fibers not the nucleuses.In these settings and similar procedures, if monitoring systems are avaiable, alternative multimodal methods with greater sensitivity and efficacy should be explored. MVD seems to be effective procedure for treatment of HFS and monitoring would help to optimise the MVD. The study also supports the hypothesis that the hyperexcitability of the facial motor nucleus may be the main cause of hemifacial spasm. To aquire and maintain MIOM modalities, close collaboration of the anesthesioloist is nessesary.