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Object: In this paper, the authors' goal was to determine the utility of monitoring the abnormal muscle response (AMR) or "lateral spread" during microvascular decompression surgery for hemifacial spasm., Methods: The authors' experience with AMR as well as the data available in the English-language literature regarding resolution or persistence of AMR and the resolution or persistence of hemifacial spasm at follow-up was pooled and subjected to a meta-analysis., Results: The pooled OR revealed by the meta-analysis was 4.2 (95% CI 2.7-6.7). The chance of a cure if the AMR was abolished during surgery was 4.2 times greater than if the lateral spread persisted., Conclusions: The AMR should be monitored routinely in the operating room, and surgical decision-making in the operating room should be augmented by the AMR.

Background: Retromastoid craniectomy and microvascular decompression of cranial nerve VII for hemifacial spasm is a well accepted and effective treatment. Risks of the operation relate to the surgical approach in general and to the seventh nerve in particular. Delayed facial weakness is an unusual and little-described complication of the procedure. The purpose of this review is to describe this complication and the characteristics of the patients so affected., Methods: Between 1972 and 1996, 985 patients have undergone microvascular decompression for hemifacial spasm. During this time, 28 patients (2.8%) undergoing decompression of the facial nerve and 1 patient undergoing decompression of the cochlear nerve for tinnitus developed delayed facial palsy., Results: The weakness was at least a House Grade III or worse and was complete in 11 of the patients. The time to occurrence averaged 12 days, with a tight range of 7 to 16 days. There were no factors such as duration of symptoms, intraoperative findings, or preoperative botulinum injections that were predictive of this postoperative weakness. In all patients there was almost complete recovery (House Grade I or II)., Conclusions: Delayed facial weakness after MVD of CN VII can occur in up to 3% of cases. The onset of weakness after operation is consistent in its timing, occurring on average 12 days after the procedure. Although the etiology of this complication is uncertain, the palsy spontaneously resolves with a good or excellent outcome.

The authors report the results of 782 microvascular decompression procedures for hemifacial spasm in 703 patients (705 sides), with follow-up study from 1 to 20 years (mean 8 years). Of 648 patients who had not undergone prior intracranial procedures for hemifacial spasm, 65% were women; their mean age was 52 years, and the mean preoperative duration of symptoms was 7 years. The onset of symptoms was typical in 92% and atypical in 8%. An additional 57 patients who had undergone prior microvascular decompression elsewhere were analyzed as a separate group. Patients were followed prospectively with annual questionnaires. Kaplan-Meier methods showed that among patients without prior microvascular decompression elsewhere, 84% had excellent results and 7% had partial success 10 years postoperatively. Subgroup analyses (Cox proportional hazards model) showed that men had better results than women, and patients with typical onset of symptoms had better results than those with atypical onset. Nearly all failures occurred within 24 months of operation; 9% of patients underwent reoperation for recurrent symptoms. Second microvascular decompression procedures were less successful, whether the first procedure was performed at Presbyterian-University Hospital or elsewhere, unless the procedure was performed within 30 days after the first microvascular decompression. Patient age, side and preoperative duration of symptoms, history of Bell's palsy, preoperative presence of facial weakness or synkinesis, and implant material used had no influence on postoperative results. Complications after the first microvascular decompression for hemifacial spasm included ipsilateral deaf ear in 2.6% and ipsilateral permanent, severe facial weakness in 0.9% of patients. Complications were more frequent in reoperated patients. In all, one operative death (0.1%) and two brainstem infarctions (0.3%) occurred. Microvascular decompression is a safe and definitive treatment for hemifacial spasm with proven long-term efficacy.

The syndrome of tic convulsif consists of ipsilateral concurrent trigeminal neuralgia and hemifacial spasm. Since Cushing's 1920 description of this syndrome in three patients, 37 additional cases have been reported in the world literature. Of the 15 with adequate operative descriptions, 10 had vascular abnormalities and five had tumors. The authors report 11 cases of tic convulsif treated by microvascular decompression of both the fifth and seventh cranial nerves. At operation, 21 of 22 nerves were found to have root entry zone vascular compression. One trigeminal nerve was considered normal. One seventh nerve had a tumor displacing the anterior inferior cerebellar artery into its root entry zone. The average follow-up period in this series was 6 years 2 months (range 1 to 8 1/2 years). Eight patients (73%) were pain-free, two (18%) had frank recurrences, and one (9%) had mild discomfort. Eight patients (73%) were totally free of facial spasm, and two others (18%) had only a trace of residual spasm. These results are comparable to those achieved by treating the individual syndromes with microvascular decompression. Therefore, microvascular decompression of both the fifth and seventh cranial nerves is recommended as the treatment of choice in tic convulsif.

We show evidence that the motonucleus of the facial nerve is involved in producing the synkinesis in patients with hemifacial spasm. These results were obtained by recording from the intracranial portion of the facial nerve and from the orbicularis oculi muscle in patients operated upon for hemifacial spasm during electrical stimulation of the mandibular branch of the facial nerve. Also, the electromyographic response from the same muscle was recorded when the facial nerve was electrically stimulated at a location near the brainstem. The results show that it is unlikely that the symptoms of patients with hemifacial spasm can be explained on the basis of ephaptic transmission at the site of lesion of the facial nerve.

Electrophysiologic recordings were made from patients with hemifacial spasm (HFS) during microvascular decompression (MVD) operations to see if spasm and synkinesis are caused by ephaptic transmission at the site of lesion (root entry zone [REZ] of the facial nerve). The response from the orbicularis oculi muscle to electrical stimulation of the marginal mandibular nerve had a 2.2-msec longer latency (average of 16 patients) than the sum of the conduction times of the parts of the facial nerve that would be involved if the response was the result of ephaptic transmission at the REZ of the seventh cranial nerve. Similar results were obtained when the zygomatic branch of the facial nerve was stimulated. These results indicate that the facial motonucleus is involved in HFS.

The pathophysiology of hemifacial spasm was studied using electrophysiologic recordings made during neurosurgical operations to relieve it by microvascular decompression of the facial nerve near its entrance into the brain stem. Electrical stimulation of the temporal or the marginal mandibular branch of the facial nerve resulted in a response not only from the muscles that were innervated by the branch of the facial nerve that was stimulated, but also from other muscles, as evidenced by EMG recordings. This "lateral spread" of antidromic activity was facilitated by stimulation at a high rate (50 pps): the response increased five- to tenfold within a few seconds. When the repetition rate was reduced to the initial low stimulus rate (2 to 5 pps), facilitation continued for periods lasting from a few seconds to several minutes. The amplitude of the response of the supraorbital reflex (blink reflex), which can be elicited in patients with hemifacial spasm intraoperatively on the affected side despite the use of inhalation anesthesia, also increased after brief stimulation at a high rate (50 pps). After the facial nerve had been decompressed, both the lateral spread response and the blink reflex response were absent. These results support the hypothesis that hemifacial spasm is the result of hyperexcitability of the facial motor nucleus and facilitation of cross-transmissions between cells in the nucleus that innervate different parts of the face.

Facial electromyographic (EMG) responses were monitored intraoperatively in 67 patients with hemifacial spasm who were operated on consecutively by microvascular decompression of the facial nerve near its exit from the brain stem. At the beginning of the operation, electrical stimulation of the temporal or the zygomatic branch of the facial nerve gave rise to a burst of EMG activity (autoexcitation) and spontaneous EMG activity (spasm) that could be recorded from the mentalis muscle in all patients. In some patients, the spontaneous activity and the autoexcitation disappeared after the dura was incised or when the arachnoid was opened, but stimulation of the temporal branch of the facial nerve caused electrically recordable activity in the mentalis muscle (lateral spread) with a latency of about 10 msec that lasted until the facial nerve was decompressed in all but one patient, in whom it disappeared when the arachnoidal membrane was opened. When the facial nerve was decompressed, this lateral spread of antidromic activity disappeared totally in 44 cases, in 16 it was much reduced, and in seven it was present at the end of the operation at about the same strength as before craniectomy. In four of these last seven patients there was still very little improvement of the spasm 2 to 6 months after the operation; these four patients underwent reoperation. In two of the remaining three patients, the spasm was absent at the 3- and 7-month follow-up examination, respectively, and one had mild spasm. Of the 16 patients in whom the lateral spread response was decreased as a result of the decompression but was still present at the end of the operation, 14 had no spasm and two underwent reoperation and had mild spasm at the last examination. Of the 44 patients in whom the lateral spread response disappeared totally, 42 were free from spasm and two had occasional mild spasm at 6 and 13 months, respectively, after the operation. Monitoring of facial EMG responses is now used routinely by the authors during operations to relieve hemifacial spasm, and is performed simultaneously with monitoring of auditory function for the purpose of preserving hearing. The usefulness of monitoring both brain-stem auditory evoked potentials recorded from electrodes placed on the scalp and compound action potentials recorded directly from the eighth cranial nerve is evaluated.

Hemifacial spasm is usually an isolated symptom resulting from facial nerve root compression. Three patients had, in addition, tinnitus, hearing loss, facial sensory loss, diminished gag reflex, dysphagia, and dysarthria. Acoustic reflexes were abnormal, and facial nerve conduction studies showed evidence of ephaptic transmission and ectopic excitation. Brain CT and metrizamide cisternography were normal. Surgical exploration showed compression of cranial nerve roots by posterior inferior cerebellar artery branches. After decompression, symptoms abated, and electrical signs of hemifacial spasm disappeared. Vascular compression of nerve roots in the cerebellopontine recess may cause multiple cranial neuropathy.

Recordings were made from facial muscles and the facial nerve near its entrance into the brain stem in patients with hemifacial spasm (HFS). The purpose of this study was to determine if the synkinesis commonly seen in patients with HFS could be linked to ephaptic transmission at the presumed site of the lesion (at the root entry zone (REZ) of the facial nerve). When the mandibular branch of the facial nerve was electrically stimulated, a response could be recorded from the orbicularis oculi muscles during the operation. The latency of the earliest response was 11.03 +/- 0.66 msec (mean response of seven patients +/- standard deviation (SD]. With equivalent stimulation a response could also be recorded from the facial nerve near the REZ; the latency of this response was 3.87 +/- 0.36 msec. Stimulation of the facial nerve at the same location yielded a response from the orbicularis oculi muscle, with a latency of 4.65 +/- 0.25 msec. The latency of the earliest response from the orbicularis oculi muscle to stimulation of the marginal mandibular branch of the facial nerve (11.3 msec) is thus larger than the sum of the conduction times from the points of stimulation of the marginal mandibular branch to the REZ of the facial nerve and from the REZ of the facial nerve to the orbicularis oculi muscle (8.52 +/- 0.38 msec). It is therefore regarded as unlikely that the earliest response of the orbicularis oculi muscle to stimulation of the mandibular branch of the facial nerve is a result of "crosstalk" in the facial nerve at a location near the REZ, and it seems more likely that HFS caused by injury of the facial nerve is a result of reverberant activity in the facial motonucleus, possibly caused by mechanisms that are similar to kindling.

The blink reflex cannot normally be elicited during surgical anesthesia using inhalation anesthetics. However, in patients with hemifacial spasm (HFS) the early component of the reflex response (R1) can be elicited on the affected side but not on the unaffected side during such anesthesia. The electromyographic (EMG) response from the mentalis muscle to stimulation of the supraorbital nerve was recorded during microvascular decompression (MVD) of the facial nerve to relieve HFS and compared to the response from the same muscle to stimulation of the zygomatic branch of the facial nerve in four patients. During the operation before the facial nerve was decompressed, contractions in both the orbicularis oculi and the mentalis muscles could be elicited by stimulation of the supraorbital nerve (mean latencies 12.2 +/- 1.9 and 12.9 +/- 2.0 ms, respectively). When the facial nerve had been decompressed the blink reflex could no longer be elicited, and there was no response from the mentalis muscle to stimulation of the zygomatic branch of the facial nerve. Compound action potentials (CAP) recorded from the 7th cranial nerve in response to stimulation of the supraorbital nerve had latencies of 7.5 ms +/- 1.4 ms to the negative peak.

In patients with hemifacial spasm, pathological changes were found in the facial nerve resulting from neurovascular compression-distortion. These changes are simular to those noted in trigeminal neuralgia.

Hemifacial spasm (HFS) in childhood is extremely rare. Two patients with HFS in childhood and eight adults who had the onset of HFS before the age of 20 were treated with microvascular decompression of the facial nerve at the nerve root entry zone. The two children were both girls and had typical HFS on the right side. Of the eight adults, five were men and three were women. Six had typical and two had atypical HFS. Six had HFS on the left side, and two had HFS on the right. Vascular cross compression was found at the nerve root entry zone in all cases. The average follow-up period was 7.3 years (range, 1 1/2 to 11 years). All but one patient had complete relief of their HFS immediately or after delay. In one adult, the compressing artery could not be decompressed without damaging the nerves. One adult patient had two recurrences 1 year after the first operation and 6 months after the second; this patient had complete relief after a third operation. Complications included temporary mild facial weakness in four patients and moderate hearing impairment in the patient who had three operations. These results are comparable to those of HFS of adult onset. Microvascular decompression is recommended as the treatment of choice for HFS during childhood.

The syndrome of hemifacial spasm occurs as a consequence of compression, almost universally by blood vessels, of the root entry zone of the facial nerve. The vascular compression is usually obvious at operation, but may be subtle. The author describes a case in which a venule running in an anterior-posterior direction across the caudal aspect of the root entry zone of the facial nerve, which was thought to be causing the spasm, was coagulated and divided. A small, more distal arteriole, probably not contributory, was decompressed away from the nerve. After operation, the patient improved gradually, and she remains free of facial spasm or weakness. This is the most subtle vascular compression seen by the author and his colleagues in over 400 microvascular decompressions for hemifacial spasm.