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.     

Neurovascular compression findings in hemifacial spasm

OBJECT: It is generally accepted that hemifacial spasm (HFS) is caused by pulsatile vascular compression upon the facial nerve root exit zone. This 2-3 mm area, considered synonymous with the Obersteiner-Redlich zone, is a transition zone (TZ) between central and peripheral axonal myelination that is situated at the nerve's detachment from the pons. Further proximally, however, the facial nerve is exposed on the pontine surface and emerges from the pontomedullary sulcus. The incidence and significance of neurovascular compression upon these different segments of the facial nerve in patients with HFS has not been previously reported. METHODS: The nature of neurovascular compression was determined in 115 consecutive patients undergoing their first microvascular decompression (MVD) for HFS. The location of neurovascular compression was categorized to 1 of 4 anatomical portions of the facial nerve: RExP = root exit point; AS = attached segment; RDP = root detachment point that corresponds to the TZ; and CP = distal cisternal portion. The severity of compression was defined as follows: mild = contact without indentation of nerve; moderate = indentation; and severe = deviation of the nerve course. Success in alleviating HFS was documented by telephone interview conducted at least 24 months following MVD surgery. RESULTS: Neurovascular compression was found in all patients, and the main culprit was the anterior inferior cerebellar artery (in 43%), posterior inferior cerebellar artery (in 31%), vertebral artery (in 23%), or a large vein (in 3%). Multiple compressing vessels were found in 38% of cases. The primary culprit location was at RExP in 10%, AS in 64%, RDP in 22%, and CP in 3%. The severity of compression was mild in 27%, moderate in 61%, and severe in 12%. Failure to alleviate HFS occurred in 9 cases, and was not related to compression location, severity, or vessel type. CONCLUSIONS: The authors observed that culprit neurovascular compression was present in all cases of HFS, but situated at the RDP or Obersteiner-Redlich zone in only one-quarter of cases and rarely on the more distal facial nerve root. Since the majority of culprit compression was found more proximally on the pontine surface or even pontomedullary sulcus origin of the facial nerve, these areas must be effectively visualized to achieve consistent success in performing MVD for HFS.     

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.     

Delayed facial palsy after microvascular decompression for hemifacial spasm due to reactivation of varicella-zoster virus

We report a patient suffering from delayed facial palsy after microvascular decompression (MVD) for hemifacial spasm, in whom the pathogenesis was proved. A 56-year-old man with a left hemifacial spasm was admitted to our hospital. Preoperative MR imaging showed that the left anterior inferior cerebellar artery (AICA) was compressing the left facial nerve. The causative vessel was defined as AICA during surgery, and MVD was performed successfully. Seven days later, the patient showed severe left facial palsy. Serum antibody of varicella-zoster virus (VZV) was increased, and Gd enhanced MR imaging demonstrated an enhancement of a geniculate ganglion of the left facial nerve, indicating inflammation. These findings suggested that delayed facial palsy after MVD was caused by a re-activation of VZV. The facial palsy disappeared completely over a period of nine months.     

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.     

Atypical Hemifacial Spasm

Summary  Among 155 cases of hemifacial spasm (HFS), the authors found two cases of atypical HFS (1.3%) in which spasm started with the orbicularis oris and buccinator muscles, and gradually spread upward to involve the orbicularis occuli muscle, whereas the reverse process is usually seen in cases of typical HFS. The compression site in cases of atypical HFS is the posterior/rostral aspect of the facial nerve (FN), whereas it was the anterior/caudal aspect of the FN in all cases of typical HFS except for one. The meatal loop of the anterior inferior cerebellar artery (AICA) compressed the FN when the vessel passed between the FN and the eighth cranial nerve (8th N). These findings suggest that the topographical organization in the FN in the cerebellopontine cistern may be reversed to a peripheral distribution: the fibres on the posterior/rostral side of the FN innervate the lower part of the facial muscles, and those in the anterior/caudal side of the nerve innervate the upper part of the facial muscles. When examining patients with HFS, we must very carefully determine whether patients have typical or atypical HFS, to determine whether blood vessels (usually the meatal loop of the AICA) between the FN and the 8th N as well as at the root exit zone of the FN are to be decompressed.     

Combined intraoperative monitoring of abnormal muscle response and Z-L response for hemifacial spasm with tandem compression type

Background

Multiple neurovascular compression is present in about 38 % cases of hemifacial spasm (HFS). In these cases, the vertebral artery (VA) compresses another vessel, which in turn compresses the nerve. This type was named as “the tandem type”. In the tandem type, the real offending vessel is often concealed by the VA. It is sometimes neglected by the surgeons. In this study, we report our experience in using abnormal muscle response (AMR) and ZL-Response (ZLR) simultaneously as intraoperative monitoring for MVD surgery of HFS with “the tandem type” vascular compression involving VA.

Methods

Fourteen “tandem type” patients treated with microvascular decompression surgery (MVD) surgery were included. ZLR and AMR were recorded simultaneously to identify the offending vessels in operation.

Results

After MVD surgery, 13 patients achieved excellent resolution of spasm. In one case, the patient failed to attain resolution in the first operation, underwent early reoperation and had good resolution. There were no operative deaths or serious operative complications. In all 14 cases, we found that VA compressed the anterior inferior cerebellar artery (AICA) or posterior inferior cerebellar artery (PICA), which in turn compressed the root exit zone (REZ). A typical ZLR was identified from the AICA or PICA but not from the VA. AMR was absent in one case and persisted in one case. After the VA was transposed, the typical AMR was unchanged, unstable or disappeared, and ZLR from the AICA/PICA also existed. AMR and ZLR did not disappear until AICA/PICA was sufficiently decompressed.

Conclusions

The combination of AMR and ZLR provides more useful information than does the AMR alone, and ZLR may be the only useful intraoperative monitoring for MVD surgery in times when AMR is absent or persists. ZLR played a crucial role in finding the real offending vessel, which was often concealed by the VA in tandem type.     

Prediction of Vertebral Artery Compression in Patients with Hemifacial Spasm Using Oblique Sagittal MR Imaging

Summary  To discriminate between the various compressing vessels of the facial nerves in patients with hemifacial spasm, pre-operative oblique sagittal gradient-echo MR imaging was performed. Forty-two patients underwent pre-operative MR imaging and microvascular decompression. The MR images were divided according to findings into three groups as follows: Group A, a thick and/or long high-intensity line along the root exit zone (REZ) of the facial nerve; Group B, a thin and/or short high-intensity line along the REZ; and Group C, an unreliable image around the REZ. Fifteen images were classified as Group A, 19 as Group B, and 8 as Group C. In Group A, vertebral artery (VA) compression was confirmed intra-operatively in 12 cases and posterior inferior cerebellar artery (PICA) or anterior inferior cerebellar artery (AICA) compression in 3. In Group B, PICA or AICA compression was confirmed intra-operatively in all cases. In Group C, PICA or AICA compression was confirmed intra-operatively in 7 cases and no compression in one. In all cases of VA compression of the facial nerve, the oblique sagittal gradient-echo images demonstrated a thick and/or long high intensity line along the REZ. Oblique sagittal gradient-echo MR imaging is a useful pre-operative planning aid, which can predict the possibility of VA compression prior to microvascular decompression for hemifacial spasm.     

Outcomes of surgical treatment for hemifacial spasm associated with the vertebral artery: severity of compression,indentation, and color change

Object  

The object of surgical treatment for hemifacial spasm (HFS) is the exclusion of pulsatile neurovascular compression of the root exit zone (REZ). However, spasm persists transiently or permanently in some cases even after complete decompression. In particular, we mainly experience these results when the vertebral artery (VA) is the offender. Hence, we verified color changes of the nerve and indentations from within the operative field in HFS patients with the VA as the offender. So, we reviewed retrospectively the records of those patients who were treated with microvascular decompression (MVD) in order to assess the relationship between operative findings and clinical results.     

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.     

A surgical case of hemifacial spasm caused by a tortuous,enlarged, and calcified vertebral artery

Microvascular decompression (MVD) is an established procedure to treat hemifacial spasm and trigeminal neuralgia. However, this cannot be done in some cases in which ecstatic vertebrobasilar arteries are involved. In these instances, alternative techniques must be used. We encountered a patient with hemifacial spasm caused by a calcified, enlarged, and tortuous vertebral artery. To obtain safe and certain neurovascular decompression of the facial nerve, the tortuous and calcified vertebral artery was surgically repositioned by placing layers of Teflon felt at two regions between the brain stem and the artery. After surgery hemifacial spasm completely disappeared. This method is thought to be a useful option for the treatment of hemifacial spasm caused by a tortuous, enlarged, or calcified vertebral artery.     

Disappearance of hemifacial spasm following spinal drainage: a case report

This report is concerned with a case of right hemifacial spasm (HFS) occurring in a 65-year-old woman, who incidentally had a left internal carotid-ophthalmic artery aneurysm. The aneurysm was successfully treated by clipping its neck. However, spinal drainage had to be performed postoperatively in order to prevent possible cerebrospinal fluid (CSF) rhinorrhea, as the roof of the sphenoid sinus was accidentally opened during the aneurysm surgery. Liquorrhea was observed and stopped on the 5th postoperative day. The drain was then removed only to be reset because CSF rhinorrhea recurred 8 days later, when the HFS began to subside. When the spinal drain was finally removed 9 days later, the HFS was scarcely seen. The HFS was thought to be due to the compression of the right facial nerve by the ipsilateral AICA. The draining of the CSF might have changed the amount and flow of the liquor and consequently the positional relationship among the facial nerve, the AICA and the arachnoid membrane, resulting in neurovascular decompression.     

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.     

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 28 months (range, 12–90 months). 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.     

Electrophysiological investigation of hemifacial spasm: F-waves of the facial muscles

Summary In patients with hemifacial spasm (HFS), the spasm is due to cross-compression of the facial nerve by a blood vessel. There are currently two hypotheses for the mechanism of HFS: 1) the spasm is caused by ephaptic transmission and an increase in excitability at the site of compression; and 2) the spasm is caused by hyperexcitability in the facial nerve nucleus. In peripheral nerves, F-waves, which result from the backfiring of antidromically activated anterior horn cells, have been proposed as indices of proximal motoneuron conduction and anterior horn cell excitability. Enhancement of the F-waves indicates increased anterior horn cell excitability. We have therefore measured F-waves in the facial muscle of HFS patients in order to investigate the exitability of the facial nerve nucleus.The authors obtained facial nerve evoked responses from 20 HFS patients before microvascular decompression (MVD), 10 HFS patients after MVD and 10 healthy controls. The F-waves, obtained with surface electrodes from the mentalis muscle, were the second response after the M-wave. On the patient's spasm side, the F-wave duration, F/M amplitude ratio and frequency of F-wave appearance significantly increased compared with those of the normal side or healthy controls; minimum latency and chronodispersion did not significantly differ between these groups. In patients whose spasm disappeared completely following MVD, the abnormal muslce response (lateral spread), which is a characteristic sign of HFS, and the enhancement of the F-wave eventually also disappeared. Because of the correlation between HFS and F-waves, the authors' study supports the hypothesis that the cause of HFS is hyperexcitability of the facial motonucleus.     

Immediate disappearance of hemifacial spasm after partial removal of ponto-medullary junction anaplastic astrocytoma: case report

Hemifacial spasm (HFS) is generally caused by a neurovascular conflict (NC) at the root exit zone (REZ) of the facial nerve at the brainstem. Although a direct compression to the seventh cranial nerve (CN) by the anterior inferior cerebellar artery (AICA) is generally the most frequent cause, secondary HFS may be related to other pathological conditions. HFS due to an intracranial mass lesion is exceptionally rare and it has been reported in very few cases. The online database was searched for English-language articles reporting cases of HFS due to brainstem mass lesions and the possible pathophysiological mechanisms involved in its genesis. A 47-year-old man affected by an anaplastic astrocytoma of the brainstem at the level of the ponto-medullary junction developed right HFS. He underwent a subtotal surgical removal of the tumor with complete resolution of the HFS. This is the ninth reported case of HFS caused by an intrinsic brainstem tumor. The exceptional rarity of the relationship between intra-axial tumors and peripheral HFS was analyzed.     

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.     

Intra-operative monitoring of two facial muscles in hemifacial spasm surgery

BackgroundHemifacial spasm (HFS) is a chronic facial nerve disorder characterized by spontaneous muscle contractions. Microvascular decompression (MVD) is the neurosurgical treatment of choice. Intraoperative neurophysiologic monitoring (IOM) during MVD can help determine when adequate decompression is performed.MethodsMVD with IOM was performed on 16 patients with HFS that included recording the abnormal lateral spread response (LSR) in lower facial muscles, considered as neurophysiologic marker of HFS. Two lower facial muscles were monitored as opposed to a standard monitoring of a single muscle.ResultsAll patients underwent preoperative thin cut MRI confirming the presence of neurovascular conflict. Patients underwent small retrosigmoid craniotomy and MVD. In 13 cases, the LSR guided the surgeon to continue MVD until the response was unobtainable from all recorded lower facial muscles. In four of those (30%), the LSR persisted on one of the recorded muscle and prompted further exploration and decompression until complete disappearance of LSR in all recorded muscles. In two cases, the LSR disappeared after dural opening and never recurred during the procedure, therefore the completion of MVD was based on non reappearance of LSR. In one case, the LSR persisted despite apparent complete decompression of the nerve. Fourteen patients had complete relief of their symptoms after surgery, one had partial improvement and the one with persistent LSR was unchanged.ConclusionEvaluation of the LSR by monitoring of two lower facial muscles provides valuable neurosurgical guidance during MVD for HFS. This simple modification of intra-operative monitoring may improve prediction of satisfactory MVD and HFS resolution.     

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.     

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.