Microvascular decompression of the root emerging zone for hemifacial spasm: evaluation by fusion magnetic resonance imaging and technical considerations

Object

The root exit zone (RExZ) of the facial nerve has been considered to be the target in microvascular decompression (MVD) for hemifacial spasm. However, more proximal segments with oligodendrocyte-derived myelin, where the facial nerve root emerges at the pontomedullary sulcus and adheres to the brainstem surface (root emerging zone [REmZ]), may also be susceptible to neurovascular compression. This study evaluated the predictive value of magnetic resonance (MR) imaging in detecting and assessing the features of vascular compression, especially in the pontomedullary sulcus, and describes the technical considerations of MVD procedures for the more proximal segments of the facial nerve.

Methods

Twenty patients treated with MVD underwent three-dimensional constructive interference in steady-state MR imaging and three-dimensional time-of-flight MR angiography. Their fusion images were used to evaluate the anatomical neurovascular relationships and intraoperative findings were analyzed.

Results

Most offending arteries at the REmZ and the RExZ of the facial nerve were correctly identified by fusion MR imaging. During surgery, neurovascular contacts were identified at one or more segments of the facial nerve in all patients. The REmZ of the facial nerve was affected in 55 % of the patients. The most common offending vessel at the REmZ was the posterior inferior cerebellar artery rather than the anterior inferior cerebellar artery. The key procedure to explore the deep-seated REmZ in the pontomedullary sulcus was full dissection of the lower cranial nerves to the brainstem origin.

Conclusions

Our definition more correctly describes the specific anatomical relationship of the facial nerve origin from the brainstem and the clinically relevant target for MVD surgery. Fusion MR imaging is very useful to identify neurovascular contacts at both the RExZ and the REmZ of the facial nerve.     

Fusion imaging of three-dimensional magnetic resonance cisternograms and angiograms for the assessment of microvascular decompression in patients with hemifacial spasms

OBJECT: The precise preoperative assessment of the complex nerve-vessel relationship at the root exit zone (RExZ) of the facial nerve is important when planning microvascular decompression (MVD) in patients with hemifacial spasms. The authors have developed an imaging technique-the fusion of 3D magnetic resonance (MR) cistemography and coregistered 3D MR angiography images-that allows clear visualization of the spatial relationship between the vessels and the rootlet of the facial nerve at the brainstem. METHODS: The authors reconstructed 3D MR cisternograms and 3D MR angiograms by using a perspective volume-rendering algorithm that they applied to the volumetric data sets of the following modalities: MR cisternography (a T,-weighted 3D fast spin echo sequence) and coregistered MR angiography (a 3D time-of-flight sequence). The complex anatomical relationship between the offending vessels and the facial nerve RExZ was inspected preoperatively by examining the fusion images from various perspectives within the cerebellopontine angle cistern, within the affected facial nerve, and through the simulated surgical route. The reconstructed 3D findings of the nerve-vessel relationship were compared with the intraoperative findings. Postoperatively, the fused 3D MR imaging technique was used to confirm that microsurgical dissection and the interposed prosthesis had succeeded in maintaining the causative vessels in a position away from the RExZ. CONCLUSIONS: The fusion of 3D MR cisternograms and 3D MR angiograms may prove useful in the pre- and postoperative assessment of MVD in patients with hemifacial spasm.     

Surgical treatment of hemifacial spasm with zone-4 offending vessel

Background

Increasing evidence shows that vascular compression on any of the four zones of facial nerve may cause hemifacial spasms. Vascular compression on zone 4 (the cisternal portion) of the nerve is quite common, but only a very small percentage of such compression will elicit hemifacial spasm, because zone 4 is less susceptible than zone 3 (the root exit zone). Therefore, it seems difficult for the neurosurgeons to distinguish the real culprit vessels in zone 4. Here, our experience in treating vascular compression located in zone 4 of the facial nerve is reported.

Methods

Twelve patients of HFS due to compression of zone 4 were treated with microvascular decompression (MVD) surgery with the aid of combined monitoring of abnormal muscle response (AMR) and Z-L response (ZLR).

Results

All of the 12 patients had a zone 4 compression. In addition, there were vascular compressions on zone 3 (the root exit zone) and/or zone 2 (the attached segment) in six cases. AMR was absent in two cases, unstable in one case, and persisted after vascular decompression in another one case. ZLR was stable before decompression of zone 4 and disappeared after decompression in all cases. After MVD surgery, 11 patients were cured and one patient achieved good resolution of spasm. One patient had postoperative transient tinnitus.

Conclusions

The neurosurgeon should not ignore vascular compression at zone 4, especially when compressions at zones 2 and 3 co-exist. With the aid of AMR and ZLR, we are able to judge whether offending vessels exist at zone 4.     

Preoperative assessment of microvascular decompression for hemifacial spasm with fusion imaging of 3D MR cisternogram/angiogram

The preoperative assessment of microvascular decompression (MVD) for hemifacial spasm has been performed with MRI, but assessment of the compressive status by 2D imaging has a number of limitations. We used a fusion image of the 3D MR cisternogram and co-registered 3D MR angiogram, reconstructed from MR cisternogram, obtained by 3D fast spin-echo sequence, and MR angiography, 3D time-of-flight and spoiled-gradient recalled sequences, for the preoperative assessment of the offending artery in 10 patients with hemifacial spasm. The anatomical relationship of the nerve-vessel complex was assessed on the simulated images, and compared with the intraoperative findings. The fusion image of the 3D MR cisternogram/angiogram depicted contours of the brain, nerves, and vessels clearly, and that allowed precise assessment of the pathogenic compression of the facial nerve by the offending vessels, comparative to the operative findings. The fusion imaging of the 3D MR cisternogram/angiogram may provide useful information in the surgical planning of MVD for hemifacial spasm.     

Hemifacial spasm due to vascular compression of the distal portion of root exit zone of the facial nerve: report of two cases

It has been generally assumed that only vascular contact at the root exit zone (REZ) of the facial nerve can cause hemifacial spasm. We treated two cases of hemifacial spasm in which compression of the distal site of the REZ of the facial nerve produced symptoms. The microvascular decompression for the patients showed excellent results. Extreme care must be taken not to stretch the internal auditory artery during surgical manipulation. The ABR monitoring is useful to prevent the postoperative hearing loss. It must be kept in mind that the compression of distal portions of the facial nerve may be responsible for hemifacial spasm in cases in which neurovascular compression at the REZ is not confirmed intraoperatively.     

Demonstration of neurovascular compression in trigeminal neuralgia and hemifacial spasm with magnetic resonance imaging: comparison with surgical findings in 60 consecutive cases

BACKGROUND: Until recently, it has been impossible to demonstrate vascular compression at the root entry or exit zone (REZ) of the trigeminal nerve and facial nerve in patients with trigeminal neuralgia (TN) and hemifacial spasm (HFS) preoperatively, although surgical findings have revealed apparent neurovascular compression and its correction has resulted in a good outcome in most cases. Revealing the anatomic correlation between nerves and vessels at the REZ preoperatively would be useful to predict operative findings. METHODS: To assess whether the vascular contact of the nerve at the REZ could be demonstrated preoperatively, high-resolution magnetic resonance tomographic angiography (MRTA) was performed in 21 patients with TN and 39 with HFS. Neuroradiological findings were compared with the operative findings in all patients. Contralateral asymptomatic nerves were evaluated as a control. RESULTS: MRTA correctly identified offending vessels in 14 (67%) of the 21 TN and 34 (87%) of the 39 HFS patients. Failure to identify neurovascular contact was noted in the cases with compression by veins or small arteries, thickened arachnoid, or distal compression. Neurovascular contact was also observed in 15% of the asymptomatic nerves. The deformity of the nerve seemed to be a more important factor for determining operative indication. CONCLUSIONS: MRTA could demonstrate offending vessels in TN and HFS at a high rate and was useful to predict operative findings. MRTA gave supportive evidence of surgical indications in patients with TN and HFS, although attention should be paid to the fact that MRTA did not necessarily detect all of the offending vessels.     

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.     

Neurovascular compression (conflict)]

Since Dandy first reported vascular compression of the trigeminal nerve, the concept of neurovascular compression syndrome for trigeminal neuralgia and hemifacial spasm (HFS) has been accepted, and neurovascular decompression has been performed for this condition. The further investigations indicated that some other clinical syndromes such as glossopharyngeal neuralgia, disabling positional vertigo, tinnitus, geniculate neuarlgia, spasmodic torticolis, essential hypertension, cyclic oculomotor spasm with paresis and superior oblique myokymia also may be initiated by vascular compression of the glossopharyngeal, cochleovestibular, intermediate, accessory, oculomotor and trochlear nerves or the ventrolateral medulla oblongata. In this study several hypotheses regarding the development of cranial nerves vascular compression syndromes are presented. It is alsoemphasized the value of high-resolution magnetic resonance tomographic angiography for visualization of vascular compression. The most frequent clinical syndromes caused by vascular compressionof the cranial nerves are discussed regarding the pathogenesis, symptomes and therapy. We present our series of 124 patients with preoperative evidently positive finding of vascular compression to the trigeminal nerve (MRI). Microvascular decompression (MVD) was performed in all of them. Initial postoperative result was excellent in 110/124 (89%) patients,while in 11/124 (9%) patients the pain relief was satisfactory. In the remaining three patients MVD failed. Recurrence of pain after two years reached 19%. Complications were related to diplopia associated with transient fourth nerve dysfunction in 5 (4%) patients, facial motor dysfunction in 4 (3%) patients, transient facial hypesthesia in 27 (22%) patients and partially hearing loss in 4 (3%) patients. Cerebellar hemorrhagic infarction occurred in 1 (0.8%) patient and cerebrospinal fluid leaks appeared in two (1.6%) cases. There was no lethal outcome.     

Microvascular Decompression of the Facial Nerve for the Treatment of Hemifacial Spasm: Preoperative Magnetic Resonance Imaging Related to Clinical Outcomes

Summary  Background. The objective of this study was to investigate the role of preoperative three dimensional short-range magnetic resonance angiography (3D-TOF MRA) in predicting the clinical outcomes following microvascular decompression for the treatment of hemifacial spasm.  Method. Preoperative magnetic resonance (MR) imaging was performed on all patients with hemifacial spasm (564 cases) between January 1992 and September 1998. Of the 564 patients, 440 patients were included in this retrospective study. The presence of vascular contact, offenders, and anomalies in the vertebro-basilar system, were determined by 3D-TOF MRA prior to microvascular decompression of the facial nerve. The preoperative findings were compared with the surgical findings and clinical outcomes.  Findings. A correlation was found between the clinical outcome (p<0.01) and the presence of a vascular indentation at the root entry zone (REZ) of the facial nerve. A shift of the vertebrobasilar system to the symptomatic side was found in 214 (48.6%) patients with hemifacial spasm, compared to only 10 (13.5%) patients in the control group (p<0.01). The unilateral vertebral artery was observed in 43 (9.8%) patients with hemifacial spasm and in 8 (10.8%) of the control patients. A hypoplasia of the artery was found in 8 (1.8%) patients with hemifacial spasm and in 1 (1.4%) control patient. The compressing offenders in the patients, discovered by MRI in conjunction with MRA, were as follows: 45.9% (202 patients) in the anterior inferior cerebellar artery (AICA), 34.8% (153 patients) in the posterior inferior cerebellar artery (PICA), 12.5% (55 patients) in the vertebral artery (VA) and 6.8% (30 patients) in multiple vessels. In contrast to the compressing offenders seen on the MRA, the offenders confirmed during surgery were as follows: 43% (189 patients) in the AICA, 36.4% (160 patients) in the PICA, 1.4% (6 patients) in the VA, 19% (84 patients) in multiple vessels, and 0.2% (1 patient) in the vein.  In our long-term follow-up series of the 440 patients with hemifacial spasm, an excellent surgical outcome was obtained in 86.3% of cases and a good outcome was achieved in 6.4% (mean follow-up duration, 45.5 months).  Interpretation. Preoperative 3D-TOF MRA can identify the relationship between the facial nerve and adjacent vessels in patients with a hemifacial spasm and assist in preoperative planning. This study suggests that 3D-TOF MRA is useful for selecting appropriate patients for surgical treatment and, to some extent, as an additional role for predicting the clinical outcome.     

微血管减压术治疗颅神经功能亢进性疾患

目的 评价微血管减压术(mierovaseular decompression,MVD)治疗颅神经功能亢进性疾患的疗效.方法 2002年10月-2007年1月,采用MVD治疗106例颅神经功能亢进性疾患.男47例,女59例;年龄42～85岁,平均62岁.三叉神经痛56例,面肌痉挛33例,痉挛性斜颈17例.MRI检查血管压迫神经根明显者60例(56.6%),可疑者33例(31.1%),无压迫者13例(12.3%).病程2～300个月,中位病程54个月.术前典型表现为相应支配区的神经激惹症状.结果 术中发现三叉神经痛患者最常见责任血管为小脑上动脉,共25例(44.6%):面肌痉挛患者为小脑前下动脉,共11例(33.3%):痉挛性斜颈患者为椎基底动脉共14例(82.4%).术后31例发生面瘫、听力下降、面部麻木、眩晕、颈肩疼痛、转颈无力及皮下积液(29.2%),均经对症处理后愈合或改善.患者均获随访,随访时间6～42个月.根据Kobata等疗效评定标准,三叉神经痛者治愈47例(83.9%),面肌瘁挛治愈27例(81.8%),痉挛性斜颈治愈7例(41.2%),总有效率为90.6%;5例(4.7%)无效者,2例再次手术治愈,余放弃治疗.5例(4.7%)于术后3～8个月复发,2例再次手术治愈,1例行伽玛刀治疗好转,余放弃治疗.结论 MVD治疗因血管压迫相关颅神经导致的疾病有较好疗效.完备的术前评估、娴熟的显微手术技巧和术中电生理监护是提高疗效和减少并发症的关键.     

Assessment of neurovascular compression in patients with trigeminal neuralgia with a boundary fusion three-dimensional magnetic resonance cisternogram/angiogram

Precise assessment of the complex nerve-vessel relationship at the root entry zone (REZ) the trigeminal nerve is useful for the planning of the microvascular decompression (MVD) in patients with trigeminal neuralgia. We have applied a boundary imaging of fusion three-dimensional (3D) magnetic resonance (MR) cisternogram/angiogram. The boundary imaging allows virtual assessment of the spatial relationship of the neurovascular compression at the REZ of the trigeminal nerve. The boundary images depicted complex anatomical relationship of the offending vessels to the trigeminal nerve REZ. The presence of offending vessels, compressive site, and degree of neurovascular compression were assessed from various viewpoints in thl cistern and virtually through the brainstem and trigeminal nerve per se. The 3D visualization of the nerve-vessel relationship with fusion images was consistent with the intraoperative findings. The boundary fusion 3D MR cisternogram/angiogram may prove a useful adjunct for the diag nosis and decision-making process to execute the MVD in patients with trigeminal neuralgia.     

Hemifacial spasm due to tumor, aneurysm, or arteriovenous malformation.

The authors report eight cases of so-called symptomatic hemifacial spasm. They had gross pathological lesions such as a tumor (one epidermoid, one neurinoma, and two meningiomas), vascular malformation (one medullary venous malformation and two arteriovenous malformations), and aneurysm. In all four cases with a tumor, no artery compressed the facial nerve at the root exit zone. In three of the four cases, the hemifacial spasm disappeared after removal of the tumor in contact with the facial nerve. Compression or encasement of the facial nerve by the tumor was the pathogenesis of the hemifacial spasm in these three cases. The remaining case with tumor (tentorial meningioma) did not have a mass or vessel that directly compressed the facial nerve at the root exit zone. However, the hemifacial spasm disappeared after the removal of the tumor. In a case with a medullary venous malformation with arterial component, an engorged draining vein compressed the root exit zone of the facial nerve. In the remaining three vascular cases--two cases of arteriovenous malformation and a case of saccular aneurysm--enlarged feeding arteries and an aneurysm directly compressed the root exit zone of the facial nerve. Not only arterial or venous but also mass compression can cause hemifacial spasm in some symptomatic cases. Surgical decompression of the facial nerve from the causative organic lesion is the primary choice of treatment.     

Microvascular decompression for hemifacial spasm: a long-term follow-up of 1,169 consecutive cases

We analyzed the records of 1,169 patients with hemifacial spasm (HFS) who underwent microvascular decompression (MVD) and were followed up for more than 6 months from January 1987. The mean follow-up duration was 23.8 months (6-145 months). Excellent surgical outcome was obtained in 90.5% and good in 4.5%, giving an overall success rate of 95.0%. There was statistically significant relationship between vertebral artery (VA) shift and side of symptom. Permanent facial weakness and hearing impairment were 1.4% and 2.3%, respectively. There were no anatomical differences at the root entry zone (REZ) and significant differences of surgical outcome in young HFS (34 patients). Factors such as type of offender, severity of compression on the facial nerve root, and the degree of decompression of the REZ on postoperative MRI did not correlate with surgical outcome.     

Preoperative assessment of trigeminal neuralgia and hemifacial spasm using constructive interference in steady state-three-dimensional Fourier transformation magnetic resonance imaging

Results of microvascular decompression (MVD) for trigeminal neuralgia (TN) and hemifacial spasm (HFS) may be improved by accurate preoperative assessment of neurovascular relationships at the root entry/exit zone (REZ). Constructive interference in steady state (CISS)-three-dimensional Fourier transformation (3DFT) magnetic resonance (MR) imaging was evaluated for visualizing the neurovascular relationships at the REZ. Fourteen patients with TN and eight patients with HFS underwent MR imaging using CISS-3DFT and 3D fast inflow with steady-state precession (FISP) sequences. Axial images of the cerebellopontine angle (CPA) obtained by the two sequences were reviewed to assess the neurovascular relationships at the REZ of the trigeminal and facial nerves. Eleven patients subsequently underwent MVD. Preoperative MR imaging findings were related to surgical observations and results. CISS MR imaging provided excellent contrast between the cranial nerves, small vessels, and cerebrospinal fluid (CSF) in the CPA. CISS was significantly better than FISP for delineating anatomic detail in the CPA (trigeminal and facial nerves, petrosal vein) and abnormal neurovascular relationships responsible for TN and HFS (vascular contact and deformity at the REZ). Preoperative CISS MR imaging demonstrated precisely the neurovascular relationships at the REZ and identified the offending artery in all seven patients with TN undergoing MVD. CISS MR imaging has high resolution and excellent contrast between cranial nerves, small vessels, and CSF, so can precisely and accurately delineate normal and abnormal neurovascular relationships at the REZ in the CPA, and is a valuable preoperative examination for MVD.     

Classification of neurovascular compression in typical hemifacial spasm: three-dimensional visualization of the facial and the vestibulocochlear nerves

OBJECT: In this paper, the authors introduce a method of noninvasive anatomical analysis of the facial nerve-vestibulocochlear nerve complex and the depiction of the variable vascular relationships by using 3D volume visualization. With this technique, a detailed spatial representation of the facial and vestibulocochlear nerves was obtained. Patients with hemifacial spasm (HFS) resulting from neurovascular compression (NVC) were examined. METHODS: A total of 25 patients (13 males and 12 females) with HFS underwent 3D visualization using magnetic resonance (MR) imaging with 3D constructive interference in a steady state (CISS). Each data set was segmented and visualized with respect to the individual neurovascular relationships by direct volume rendering. Segmentation and visualization of the facial and vestibulocochlear nerves were performed with reference to their root exit zone (REZ), as well as proximal and distal segments including corresponding blood vessels. The 3D visualizations were interactively compared with the intraoperative situation during microvascular decompression (MVD) to verify the results with the observed microneurosurgical anatomy. RESULTS: Of the 25 patients, 20 underwent MVD (80%). Microvascular details were recorded on the affected and unaffected sides. On the affected sides, the anterior inferior cerebellar artery (AICA) was the most common causative vessel. The posterior inferior cerebellar artery, vertebral artery, internal auditory artery, and veins at the REZ of the facial nerve (the seventh cranial nerve) were also found to cause vascular contacts to the REZ of the facial nerve. In addition to this, the authors identified three distinct types of NVC within the REZ of the facial nerve at the affected sides. The authors analyzed the varying courses of the vessels on the unaffected sides. There were no bilateral clinical symptoms of HFS and no bilateral vascular compression of the REZ of the facial nerve. The authors discovered that the AICA is the most common vessel that interferes with the proximal and distal portions of the facial nerve without any contact between vessels and the REZ of the facial nerve on the unaffected sides. CONCLUSIONS: Three-dimensional visualization by direct volume rendering of 3D CISS MR imaging data offers the opportunity of noninvasive exploration and anatomical categorization of the facial nerve-vestibulocochlear nerve complex. Furthermore, it proves to be advantageous in establishing the diagnosis and guiding neurosurgical procedures by representing original MR imaging patient data in a 3D fashion. This modality provides an excellent overview of the entire neurovascular relationship of the cerebellopontine angle in each case.     

面神经根显微神经血管减压梳理牵拉术治疗特发性半面痉挛

目的：解除特发性半面痉挛的病因，提高治愈率。方法：采用乙状窦后进路面神经根显微神经血管减压梳理牵拉术。结果：４３８例特发性半面痉挛，术后随访１～８年以上，治愈４１７例（９５．２％），复发１４例（３．４％）。结论：特发性半面痉挛的病因主要为血管压迫面神经根及其周围的脑干表面，另一病因为面神经核功能异常。认为面神经根显微神经血管减压梳理牵拉术是一种解除病因的治疗方法，治愈率高，复发率低。     

Postoperative Oblique Sagittal MR Imaging of Microvascular Decompression for Hemifacial Spasm

Summary  Pre-operative and postoperative oblique sagittal gradient-echo magnetic resonance (MR) imaging was used to evaluate microvascular decompression of the facial nerves in 26 patients with hemifacial spasm. The pre-operative MR images were divided into two groups as follows: 22 images in Group I, clear imaging of a high-intensity line and/or spot at the root exit zone (REZ) of the facial nerve; and 4 in Group II, and unreliable image around the REZ. Surgery found that the causative vessel was the vertebral artery (VA) in 9 cases and the anterior inferior cerebellar artery (AICA) or the posterior inferior cerebellar artery (PICA) in 13 cases in Group I, and the AICA or the PICA in the 4 cases in Group II. Postoperative MR imaging showed clear decompression as the high-intensity line and/or spot completely separated from the REZ by a low- and/or iso- intensity area in 9 cases of VA compression repositioned to the petrous dura mater, in 11 cases of PICA or AICA compression treated by shredded Teflon pledgets in Group I and in 3 cases in Group II. Postoperative MR imaging showed an incomplete separation of any high-intensity line and/or spot in the REZ in 2 cases of PICA or AICA compression in Group I and in one in Group II. The outcome was excellent in 22 of 23 cases with clear decompression, and in 1 of 3 cases of unclear decompression. Hemifacial spasm persisted in 3 cases. Oblique sagittal gradient-echo MR imaging is a useful method for postoperative follow-up which can demonstrate changes around the REZ of the facial nerve if hemifacial spasm recurs.     

Reappearance of Cranial Nerve Dysfunction Symptoms Caused by New Artery Compression More than 20 Years after Initially Successful Microvascular Decompression: Report of Two Cases

Reappearance of symptoms of cranial nerve dysfunction is not uncommon after successful microvascular decompression (MVD). The purpose of this study was to report two quite unusual cases of recurrent and newly developed hemifacial spasm (HFS) caused by a new conflicting artery more than 20 years after the first successful surgery. In Case 1, the first MVD was performed for HFS caused by the posterior inferior cerebellar artery (PICA) when the patient was 38 years old. After 26 symptom-free years, HFS recurred on the same side of the face due to compression by the newly developed offending AICA. In Case 2, the patient was first operated on for trigeminal neuralgia by transposition of the AICA at 49 years old, but 20 symptom-free years after the first MVD, a new offending PICA compressed the facial nerve on the same side, causing HFS. These two patients underwent reoperation and gained satisfactory results postoperatively. Reappearance of symptoms related to compression of the root exit zone (REZ) by a new offending artery after such a long symptom-free interval since the first effective MVD is rare. Here, we describe two such unusual cases and discuss how to manage and prevent such reappearance of symptoms after a long time interval.     

Intraoperative monitoring of facial EMG responses during microvascular decompression for hemifacial spasm. Prognostic value for long-term outcome: a study in a 33-patient series

Lateral spread responses (LSR), an electrophysiological characteristic of hemifacial spasm (HFS), can be recorded during surgery. This work aims at evaluating the prognostic value of the persistence or suppression of the LSR at the end of the microvascular decompression (MVD) procedure of the facial nerve. Thirty-three patients with HFS, which had been evolving for 5.5 years, underwent MVD with intraoperative EMG. Monitoring required the placement of a needle in the frontalis and mentalis muscles. Responses were recorded after stimulation of inferior or superior branches of the facial nerve to search for abnormal ephaptic LSR. Preoperative abnormal LSRs were present in all patients. In 23 patients, LSR disappeared with vascular decompression and was not present upon closure. Among those patients, 20 were considered clinically cured and three still presented with mild/moderate spasm at 3-month follow-up. At late follow-up, 22 patients were free of spasm. One patient had recurrence of spasm at month 10. On the contrary, 10 patients had persistent abnormal LSR upon closure. Among those, seven were cured at early follow-up (3 months on average), whereas spasm disappeared at late follow-up (12 to 36 months) in the other three patients. The prognostic value of LSR monitoring is questionable; a good clinical result may be obtained in patients who presented with persistent LSR at the end of MVD. Delayed cure strongly supports the hypothesis that HFS is not only due to the mechanical pulsations of the elongated artery against the root exit zone of the facial nerve, but also to demyelination of the nerve and/or hyperactivity of the facial motornucleus generated by the neurovascular compression.     

Indications and Timings of Re-operation for Residual or Recurrent Hemifacial Spasm after Microvascular Decompression: Personal Experience and Literature Review

We reviewed reports about the postoperative course of hemifacial spasm (HFS) after microvascular decompression (MVD), including in our own patients, and investigated treatment for delayed resolution or recurrence of HFS. Symptoms of HFS disappear after surgery in many patients, but spasm persists postoperatively in about 10–40%. Residual spasm also gradually decreases, with rates of 1–13% at 1 year postoperatively. However, because delayed resolution is uncommon after 1 year postoperatively, the following is advised: (1) In patients with residual spasms after 1 year postoperatively (incomplete cure) or who again experience spasm ≥ 1 year postoperatively (recurrence), re-operation is recommended if the spasms are worse than before MVD. (2) When re-operation is considered, preoperative magnetic resonance imaging (MRI) findings and intraoperative videos should be reviewed to ensure that no compression due to a small artery or vein was missed, and to confirm that adhesions with the prosthesis are not causing compression. If any suspicious findings are identified, the cause must be eliminated. Moreover, because of the risk of nerve injury, decompression of the distal portion of the facial nerve should be performed only in patients in whom distal compression is strongly suspected to be the cause of symptoms. (3) Cure rates after re-operation are high, but complications such as hearing impairment and facial weakness have been reported in 10–20% of cases, so surgery must be performed with great care.