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.     

Surgical anatomy for hemifacial spasm

Classically in the cerebello-pontine angle the facial (CN VII) and vestibular-cochlear (CN VIII) nerves should run parallel with the anterior inferior cerebellar artery, whereas the lower nerves (CN IX-XI) continue with the posterior-inferior-cerebellar artery (PICA). In fact, this is not always true, particularly when dealing with hemispasm surgery where the relationships between CN VII, CN VIII and PICA are often different and closer. Knowledge of anatomical bases in surgical situation will help neurosurgeons to appreciate anatomical nuances, that are important to increase effectiveness and safety of hemifacial spasm surgery.     

Imaging of hemifacial spasm

Almost all primary hemifacial spasms are associated with one or more neurovascular conflicts, most often at the root exit zone in the immediate vicinity of the brainstem. Imaging has first to exclude a secondary hemifacial spasm and secondly to search for and characterize the responsible neurovascular conflict(s). Magnetic resonance imaging should include high-resolution anatomical hyper T2-weighted sequences and magnetic resonance angiography by using 1.5 or even better 3 Tesla magnets. The most frequent vascular compressions are from the anterior-inferior cerebellar artery, the posterior-inferior cerebellar artery and the vertebrobasilar artery; venous conflicts are very rare. Conflicts are often multiple; also, the same vessel may compress the facial nerve in two places. Also, conflicts may be aided by particular anatomical circumstances, including arterial dolichoectasia, posterior fossa with a small volume or bony malformations.     

Diagnosis of primary hemifacial spasm

The diagnosis of primary hemifacial spasm (pHFS), due to a benign compression of the facial motor nerve by a vessel, within or close to its root exit zone, is often made with delay. Misdiagnosis includes psychogenic spasm, tics, facial myokymia or blepharospasm, but in fact post-facial palsy synkinesis (post-paralytic HFS) is the closest clinical condition, because it is limited to the territory of the facial nerve of a single hemiface. The differential diagnosis between these two entities, whose pathophysiological mechanisms are very different, can be made by electroneuromyographic (ENMG) examination. In addition, magnetic resonance imaging (MRI) is essential to show the offending vessel at the origin of pHFS and the absence of other causes of nerve compression. However, the diagnosis cannot be made on MRI basis alone, since a neurovascular conflict can be present in clinically asymptomatic subjects. This article reviews the clinical, MRI, and ENMG features in favour of a pHFS diagnosis as well as the various differential diagnoses of this involuntary facial movement disorder.     

Microvascular decompression for hemifacial spasm: Outcome on spasm and complications. A review

Over the last decades microvascular decompression (MVD) has been established as the curative treatment of the primary Hemifacial Spasm (HFS), proven to be linked in almost all cases to a neurovascular compression of the facial nerve. Because the disease is not life-threatening and MVD not totally innocuous, efficacy and safety have to be weighted before decision taken of indicating surgery. The authors have been charged by the French Speaking Society of Neurosurgery to conduct a detailed evaluation of the probability of relief of the spasm that MVD is able to obtain, together with its potential complications. For the review, the authors have gone through the reports available from the Pubmed system. Eighty-two publications have been read and analysed, totalizing more than 10,000 operated cases. In most series, the percentage of patients with total relief ranged between 85% and 90%. Relief was obtained after a certain delay in as many as in 33% ± 8% of the patients in many series. For those, delay lasted around one year in 12% of them. When effect of MVD was considered achieved, relief remained permanent in all but 1%–2% of the long-term followed patients. As regards to complications, risk of permanent cranial nerve deficit was evaluated at 1%–2% for facial palsy, 2%–3% for non-functional hearing loss, 0.5%–1% for lower cranial nerve dysfunction. Risk of stroke was at 0.1% and mortality at 0.1%. CSF leakage and related complications could be reduced at less than 2% in most series provided careful closing techniques be applied. Complications were at a higher rate in repeated MVD. MVD is an effective curative method for almost all the patients affected with primary HFS. Because MVD for HFS is functional surgery, scrupulous consideration of its potential risks, together with the ways to avoid complications are of paramount importance. When MVD is estimated to have failed, it is wise to wait one year before considering to repeat surgery, as number of patients may benefit from delayed effect. This is the more so as important as repeated surgery entails a higher rate of complications.     

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.     

Traitement neurochirurgical du spasme hémifacial primaire par décompression vasculaire microchirurgicale

In nearly all cases, primary hemifacial spasm is related to arterial compression of the facial nerve in the root exit zone at the brainstem. The offending arterial loops originate from the posterior inferior cerebellar, anterior inferior cerebellar, or vertebrobasilar artery. In as many as 40% of the patients, neurovascular conflicts are multiple. The cross-compression at the brainstem is almost always seen on magnetic resonance imaging combined with magnetic resonance angiography. Botulinum toxin can be useful by alleviating the symptoms, but the effects are inconstant and only transient. The definitive conservative treatment is microvascular decompression (MVD), which cures the disease in 85 to 95% of patients. In expert hands, the MVD procedure can be done with relatively low morbidity. Because cure of spasms is frequently delayed - by several months to even a few years -, we do not recommend early reoperation in patients with failure or until at least 1 year of follow-up. Delayed cure could well be explained by the slow reversal of the plastic changes in the facial nucleus that may have caused the symptoms.     

Microvascular decompression for primary hemifacial spasm. Importance of intraoperative neurophysiological monitoring

Summary There is considerable evidence that primary Hemi-Facial Spasm (HFS) is in almost all cases related to a vascular compression of the facial nerve at its Root Exit Zone (REZ) from brainstem, and that Micro-Vascular Decompression (MVD) constitutes its curative treatment. Clinical as well as electrophysiological features plead for mechanisms of the disease in structural lesions at the neural fibers (putatively: focal demyelination at origin of ephapses) and functional changes in the nuclear cells (hyperactivity of the facial nucleus). Lateral Spread Responses (LSRs) elicited by stimulation of the facial nerve branches testify of these electrophysiological perturbations. Monitoring LSRs during surgery is feasible; however the practical value of their intraoperative disappearance as control-test of an effective decompression remains controversial. MVD allows cure of the disease in most cases. Because the VIIIth nerve is at risk during surgery, intraoperative monitoring of Brainstem Auditory Evoked Potentials (BEAPs) is of value to reduce occurrence of hearing loss. Increase in latency of Peak V and decrease in amplitude of Peak I are warning-signals of an excessive stretching of the the cochlear nerve and impairment of the cochlear vascular supply, respectively.     

Chronologic analysis of symptomatic change following microvascular decompression for hemifacial spasm: value for predicting midterm outcome

The objectives of this study are to categorize the patterns of symptomatic change and to chronologically analyze them. From January 2004 to February 2006, microvascular decompression was performed on 236 consecutive patients. Follow-up time was at least over 1 year (mean, 17.1 months). We categorized the postoperative courses into five different groups according to the similarity of the temporal changes of the residual symptoms. The symptomatic change during each follow-up interval was chronologically analyzed among five different groups. The five improvement patterns included group A (immediate recovery without relapse), group B (temporary relapse followed by cure), group C (slow but steady improvement that leads to cure after one or more months), group D (recurrence with sustained symptoms), and group E (no improvement or improvement to some extent that does not lead to cure). The symptomatic change in the successful groups (groups A, B, and C) differed from that in the unsatisfactory groups (groups D and E), especially during the follow-up interval between postoperative 3 weeks and 3 months (p = 0.014). This finding was true with (p = 0.029) or without (p = 0.015) the relapse curve. Therefore, we can predict the postoperative result as early as 3 months after the surgery. Overall cure rate in this series (93.2%) was nearly correspondent to the estimated cure rate at the first postoperative year (93.4%). Postoperative 3 months can be the most efficient and earliest time to predict the postoperative result.     

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.     

不同剂量舒芬太尼术后镇痛方案对面肌痉挛微血管减压术后恶心呕吐的影响

目的:观察面肌痉挛微血管减压术后应用不同剂量舒芬太尼镇痛方案对术后恶心呕吐不良反应的影响。方法:回顾性纳入行微血管减压术的面肌痉挛女性患者183例,在相同麻醉方法的基础上根据术后是否使用舒芬太尼镇痛泵及其不同剂量将患者分为舒芬太尼2 μg/kg组（A组,60例）、舒芬太尼1 μg/kg组（B组,60例）和未使用镇痛泵组...     

微血管减压术治疗面肌痉挛的远期效果

目的：探讨微血管减压术治疗面肌痉挛1年以上的远期疗效。方法：对1987年7月至1999年6月间329例患者的临床资料及随访结果进行回顾性分析。结果：本组患者随访1－3年97例，痉挛完全缓解92．7％，明显缓解3．1％，部分缓解2．1％，无改变2．1％；3－5年77例，完全缓解92．2％，明显缓解3．9％，部分缓解1．3％，无改变占2．6％；5－10年121例，完全缓解90．9％，明显缓解4．1％，部分缓解2．5％，无改变2．5％；10年以上34例，痉挛综合缓解91．2％，明显缓解5．9％，无改变2．95。329例中主观满意度≥80％者占82．1％，痉挛复发率5．2％，并发症发生率5．5％，。结论：采用微血管减压术治疗面肌痉挛，尽量减少对脑神经及血管损伤，不遗漏面神经根附近的责任血管，是提高远期疗效养活并发症的重要环节。     

Intra-operative monitoring by facial electromyographic responses during microvascular decompressive surgery for hemifacial spasm

Summary The facial electromyographic response was monitored intraoperatively in 40 patients with hemifacial spasm who were operated on by microvascular decompression of the facial nerve. All 40 patients showed an abnormal facial electromyographic response (lateral spread response) with a latency of about 10 msec after stimulation. The abnormal response resolved before decompression in 22, resolved immediately with decompression in 16, and failed to resolve in two. Of the 38 patients in whom the abnormal response disappeared during surgery, 36 were postoperatively free from hemifacial spasm and two had mild hemifacial spasm. The two patients in whom the lateral spread response did not disappear during surgery showed persistent hemifacial spasm.In conclusion. Disappearance of the lateral spread response during surgery correlated with the absence of hemifacial spasm in the early postoperative period. The prognosis of hemifacial spasm was good in cases in whom the lateral spread response disappeared. Therefore, the authors think that intra-operative facial electromyography is very useful in assessing the efficacy of microvascular decompression and in predicting the prognosis of hemifacial spasm.     

Hemifacial spasm associated with other cranial nerve syndromes: Literature review

Hyperactive dysfunction may affect all cranial nerves in the posterior fossa. According to literature review and personal experience, hemifacial spasm was found to be associated not only with the most frequent cranial nerve syndromes, namely: trigeminal neuralgia, vago-glossopharyngeal neuralgia or VIIIth nerve disturbances manifested by vertigo, tinnitus, hearing decrease, but also with rarer syndromes like geniculate neuralgia, masticatory spasm etc. Also, a number of publications have pointed out the relatively high incidence of the coexistence of hemifacial spasm and systemic blood hypertension; both can be cured by vascular decompression of the ventrolateral aspect of the medulla and IX-Xth route entry zone (REZ) together with the facial REZ. Even more complex clinical presentations have been encountered, corresponding to disturbances in several cranial nerve nuclei. Some could be attributed to neurovascular conflicts from elongated arteries invaginated into the brainstem, and cured by microvascular decompression surgery. When confronted with such complex, and therefore misleading, syndrome, it is advised to search for vascular conflicts at the brainstem using high-resolution MRI exploration.     

Hemifacial spasm caused by a tortuous recurrent perforating artery: A case report

IntroductionWhen the culprit vessel in hemifacial spasm (HFS) is hard to determine, this is a challenge in microvascular decompression (MVD) surgery. In such a situation, small arteries such as perforators to the brainstem might be suspected. But small arteries are omnipresent near the facial nerve root exit/entry zone (fREZ). How to decide whether a given small artery is responsible for HFS is unclear.MethodWe report a case with a previously unreported form of neurovascular impingement, in which the culprit was found to be the recurrent perforating artery (RPA) from the anterior inferior cerebellar artery (AICA). An aberrant anatomic configuration of the RPA was found intraoperatively, which we thought was responsible for generating focal pressure on the facial nerve.Case reportA 62-year-old woman presented with a 1-year history of paroxysmal but increasingly frequent twitching in her right face. MRI showed tortuosity of the vertebral artery and apparently marked neurovascular impingement on the asymptomatic left side, while only the right AICA could be implicated as the possible culprit. Hemifacial spasm was diagnosed based on the typical clinical manifestation, and MVD was performed. The pre-meatal segment of the AICA was found not to be impinging the facial nerve at any susceptible portion near the fREZ: root exit point, attached segment, or root detachment point. The real culprit was in fact the RPA. This occult culprit vessel was tortuous, forming a coil-shaped twist which was interposed between the facial nerve and the intermediate nerve near the root detachment point. Focal pressure atrophy of the nerve was clearly observed at the compressing site. The patient achieved total spasm relief immediately after surgery, and remained spasm-free at 1-year follow-up, without any postoperative complications.ConclusionMVD is the only curative treatment for hemifacial spasm, but with a failure rate of around 10%. Mistaking the real culprit has been reported to be the most likely reason for surgical failure. Therefore, intraoperative identification of atypical occult forms of vascular compression is of importance to improve surgical outcome. In the present case, the RPA formed a coil-shaped twist, which inflicted focal vascular compression causing hemifacial spasm. We recommend careful inspection of the recurrent perforating artery during MVD for HFS, and decompressing any such neurovascular impingement.     

Varied patterns of postoperative course of disappearance of hemifacial spasm after microvascular decompression

Summary Background. The precise course of resolution of postoperative residual HFS after a single MVD has not been well categorised quantitatively in the literature. Not all patients with HFS were cured immediately after a single MVD; some of them exhibited a gradual disappearance of the HFS over a period of time. The time course of the gradual resolution of HFS is categorised and the situation of re-exploration in a few patients whose HFS persisted or recurred is determined.Methods. The results of 547 MVDs in 545 Chinese patients were reviewed using the database from the authors personal records between January 1992 and December 2002. Different outcomes were observed and divided into four categories according to the variable convalescent period: type 1, spasm cured immediately; type 2, spasm persisted with milder severity and faded away gradually from 7 days to as long as 2 years; type 3, spasm ceased immediately but recurred after 3 days and ran the same course as in type 2; type 4, failed.Findings. Four hundred and seventy-nine patients followed a type 1 course, which constituted an 87.9% immediate success rate. Forty-one patients (7.5%) followed a type 2 course, including three whose spasm persisted for more than 2 years. Twenty-three patients (4.2%), including one with venous compression, followed a type 3 course with their spasm ceased within three months. All of them had typical vascular loop compression. Another patient with a venous contact failed to respond positively to the first MVD underwent re-operation within 2 months. Re-operation was also performed in one patient four days after the first MVD due to persisting and even more severe spasm. These two patients were categorized type 4 as they failed the first MVD (0.4%). Late recurrence was noted in five patients from 1 to 2 years after the first MVD, only one of whom underwent re-exploration and was then cured again.Conclusions. Approximately 80% of the patients with HFS achieved immediate excellent results after a single MVD, the rest of the patients exhibited residual but usually milder spasms, which resolved gradually over a period of time. According to the patterns of the residual or persisting spasms, the situation and timing of re-exploration can be determined without difficulty. The surgeon should be concerned about missing the responsible vessels in patients with typical HFS who completely failed the first MVD.     

Fusiform aneurysm of the vertebral artery presenting with hemifacial spasm treated by microvascular decompression

Summary We report a rare case of symptomatic hemifacial spasm caused by a fusiform vertebral artery aneurysm. A 59-year-old woman presented with left hemifacial spasm of 18 months duration. Magnetic resonance imaging showed an enlarged a fusiform aneurysm of the left vertebral artery which compressed the seventh cranial nerve at its exit from the caudal pons. Microvascular decompression of the facial nerve with moving of the aneurysm resulted in complete relief of the hemifacial spasm. No enlargement of the aneurysm was shown on follow-up for a period of 6 years.     

Trigeminal neuralgia and hemifacial spasm caused by a tortuous vertebrobasilar system

The case of a 66-year-old woman who developed both trigeminal neuralgia and hemifacial spasm caused by a tortuous vertebrobasilar system is reported. Vertebral angiography showed a dilated and elongated basilar artery overlying the porus acusticus of the internal auditory canal. Double-contrast computed tomography scanning was very useful in evaluating this abnormality. Vascular decompression was performed by using a fenestration clip.     

Frequency and prognosis of delayed facial palsy after microvascular decompression for hemifacial spasm

Summary Background. Microvascular decompression (MVD) for hemifacial spasm (HFS) provides a long-term cure rate. Delayed facial palsy (DFP) is not an unusual complication, but it has only been sporadically described in the literature. The purpose of this report is to evaluate the incidence of delayed facial palsy after MVD and its clinical course and final results. Methods. From January, 1998 to April, 2004, 410 patients underwent microvascular decompression for hemifacial spasm at our Institute. During this time, 21 patients (5.4%) developed delayed facial weakness; eighteen of them were given steroid medication and they were followed up in the out-patient clinic. Findings. Twenty-one patients developed DFP after microvascular decompression an incidence of 5.4%. There were seventeen women (81.0%) among the 21 patients with DFP who were included in this study. In twenty of them, the symptoms of HFS improved completely after the operation, but the spasm remained with one of them. The onset of palsy occurred between postoperative day 7 and 23 (average: 12.1 days). The palsy was at least Grade II or worse on the House-Brackmann (HB) scale. The time to recovery averaged 5.7 weeks (range: 25 days–17 weeks); 20 patients improved to complete recovery and 1 patient remained with minimal weakness, as Grade II on the HB scale, at the follow-up examination. Conclusion. Our findings demonstrated that the incidence of DFP was not so low as has been reported the literature, and it did not have any striking predisposing factors. Even though the degree of facial palsy was variable, almost all patients exhibited a complete recovery without any further special treatment. The etiology of DFP and its association with herpes infection should be further clarified.