Microvascular decompression in patients with hemifacial spasm: report of 1200 cases

Microvascular decompression in patients with hemifacial spasm: report of 1200 cases

[  CMJ 2005;118(10):833-836  ]

 

YUAN Yue, WANG Yan, ZHANG Si-xun, ZHANG Li, LI Rui, GUO Jing

 

Background Microvascular Decompression (MVD) operation is the most reliable treatment for hemifacial spasm (HFS), but it causes many complications. The aim of this retrospective study was to investigate the factors relavent to the effects and postoperative complications of microvascular decompression on hemifacial spasm. 兰州大学第二医院神经外科张新定
Methods A total of 1200 HFS patients treated with MVD were studied retrospectively. The root exit zone (REZ) of the facial nerve was exposed through the infraflocculus approach, the offending vessels were identified and separated from the REZ, and a Teflon graft was interposed between the offending vessels and the brain stem. Brain stem auditory evoked potential (AEP) was monitored intraoperatively.
Results The offending vessels can be identified in all patients. The anteroinferior cerebellar artery was the main offending vessel (42.6%). Patients with vertebral artery compression had a multiple vascular compression fashion. Follow-up for 2-10 years (mean 4.2 years) showed that 88.7% patients were cured and 5.6% relieved， with an effective rate of 94.3%. Recurrence rate was 3.2%, and the ineffective rate was 2.6%. The most frequent complication was hearing dysfunction (2.8%).
Conclusions MVD is the most definitive treatment method of HFS. The key procedures of this operation include adequate exposure of the REZ, identification of the offending vessels, and proper positioning of Teflon grafts. Complications can be reduced effectively by utilizing a real-time AEP monitoring during the operation.

 

Idiopathic hemifacial spasm （HFS） presenting with paroxysmal uncontrolled spasm of the hemifacial muscle progresses slowly and is hard to recover by itself. This disease may affect visage of patients, causing physical and mental distress. The concept of vascular compression is based on the anatomic observations made by Dandy.［1］ Micro-vascular decompression (MVD) was initially developed by Gardner et al［2］ and was perfected and popularized by Jannetta.［3］ Many studies showed that MVD as a preferred method for treating HFS［4-9］ has not been perfect yet.［10,11］ From November 1991 to December 2001, 1200 HFS patients were treated with MVD at this hospital. The factors affecting the outcome and complications of MVD were analyzed with reference to the literature.

METHODS

Patients
In the 1200 patients, 485 were men and 715 women, aged 23 to 72 years (mean 53 years), and 657 presented with right-sided symptoms, and 543 left-sided symptoms. The duration of the symptoms ranged from 8 months to 23 years (mean 4.8 years). Computed tomography and magnetic resonance imaging were performed in all patients before operation to exclude the presence of other diseases such as tumor. In this series, 246 patients underwent magnetic resonance tomographic angiography (MRA), and the offending vessel was identified in 203 patients (82.5%).

Operative methods
Under general anesthesia, the patient lied on his side with the head drooping for 15° and rotating to the health side for 10°. The chin was slightly flexed, making the mastoid in the diseased side parallel to the operating table and the highest position of body in order to keep the axis of the operative microscope consistent with the operative entry easily. A “∫” shaped incision was made for 4-6 cm in parallel with the hairline. Retrosigmoid bur hole was made 2 cm in diameter and was close to the sigmoid sinus and condylus occipitalis. The operation was performed under a microscope immediately after the dura mater was opened in a “┻” shape. As the root exit zone (REZ) of the 7th nerve is behind the 9th and 10th nerves, the arachnoidal membrane over them was dissected throughly, and the root of the 9th and 10th nerves was exposed. The REZ of the 7th nerve can be fully exposed by retracting the flocculus and adjusting the head position and the axis of the microscope. The offending vessel was identified and moved away from the REZ of the 7th nerve. An appropriate Teflon graft was interposed between the offending vessel and the brain stem. The operation under the microscope lasted 30 minutes on average. Brain stem auditory evoked potential (BAEP) was monitored during the operation ( Fig. ).

Operative findings
In all patients, the offending vessel was identified in the REZ. The anteroinferior cerebellar artery (AICA) was found in 511 patients (42.6%), and the posteroinferior cerebellar artery (PICA) in 255 (21.3%). Both AICA and PICA were found in 154 patients (12.8%), AICA and the vertebral artery (VA) in 115 (9.6%), PICA and VA in 88 (7.3%), and AICA, PICA and VA in 77 (6.4%). RESULTSIn this series, symptoms disappeared immediately after operation in 797 patients (66.4%). In 403 patients with residual facial spasm, 267 patients showed disappearance of symptoms 20-160 days after operation. Postoperative complications included hearing disturbance in 61 patients, facial palsy in 59, tinnitus in 43, ataxia in 19, meningitis in 19, leakage of CSF in 16, and diplopia in 5; but no mortality and disability were found. All patients were followed up for 2-10 years (mean 4.2 years). In this series, 1064 patients (88.7%) were cured and 67 patients (5.6%) showed ameliorated symptoms, giving a total effective rate of 94.3%. Thirty-one patients (2.6%) showed no effect and 38 (3.2%) recurrent symptoms. Complications were ameliorated except deafness in 34 patients (2.8%) ( Table ).

DISCUSSION

MVD has become a definitive treatment for HFS because it is less invasive and produces excellent results including the preservation of vascular and neural function, and few complication.［12-14］ Kato et al［4］ summarized the results of long-term follow-up of 4865 HFS patients who had undergone MVD in 23 hospitals in Japan. They found symptom free in 83.7% of the patients， relief in 12.2%， operative failure in 4.1%, and complications in 3.9%. In these patients, 2.5% suffered from hearing disturbance and others from facial palsy, ataxia, and meningitis. With the development of microsurgery, the result of MVD has been improved significantly, but it is still far from a 100% cure rate. We emphasize that expertise of the operator and correct manipulation are related to a satisfactory result.

Our experience in MVD treatment of 1200 patients and literature review show the following key points for a successful operation: correct preoperative diagnosis and differential diagnosis; preoperative MRA for identifying affending vessels; microsurgical expertise and knowledge about local anatomy sufficient to identify the offending vessels, appropriate interposition of Teflon graft, and prevention of complications.［15-18］

HFS patients often demonstrate paroxysmal, uncontrolled tics in the orbicularis oculi, with subsequent downward progression over the muscles of the face, even the neck. Typical symptoms of hemifacial spasms are the main evidence of preoperative diagnosis. These symptoms should be different from blepharospasm, spasm after facial paralysis, hysteric blepharospasm and others. MRI and MRA are able to exclude secondary diseases and detect the offending vessels, and their path and distribution in most patients.

Operative position and incision are important to the exposure of the REZ. The offending vessels usually pass through and compress the REZ with a loop. The vessels lying on the distal portion of the 7th nerve, dissociating in the cerebellopontine cistern, or contacting and running parallel with the trunk of 7th nerve, should not be recognized as the offending vessels. If multiple vessels are observed in the REZ, the offending vessels usually run beneath the vascular plexus. The factors affecting the identification of the offending vessel are as follows: change of head position; poor exposure of the REZ; shift of the offending vessel because of retraction of the cerebellum or wide dissection of the arachnoid membrane. The inferoanterior cerebellar artery is the commonest offending vessel. As the unique affending vessels, the vertebral artery never is always combined with other affending vessels. The multiple offending vessels can be found in all patients with vertebral artery compression.

Manipulation of the offending vessel is to isolate and push it away from the REZ towards the skull base. Teflon graf is shaped as an elliptic loose wad, and interposed between the offending vessel and brain stem. Interposition between the offending vessel and the 7th nerve trunk should be avoided. The size of Teflon graft should be appropriate to cause neither new compression nor floating away in the cerebrospinal fluid, and the position should be ensured with gelfoam around the area. The offending vessel should not be twisted to disturb the blood supply to the brain stem. If the offending vessel is a large, twisted, sclerotic one such as the vertebral artery or gives off many short perforating arteries among the brain stem, the 7th and 8th nerves, the suspending method should be utilized. Shredded Teflon graft is shaped into a belt and coiled round the offending vessel, finally fixed to the dura mater. This method may improve the effect of decompression in the REZ, and avoid injury to small perforating arteries.

The reported rate of delayed resolution is 13%-50% and in our series it is 25.4% (305 patients).［15-18］ Delayed resolution is defined as the disappearance of spasm 1 to 12 weeks or more after MVD instead of immediately after MVD. Patients with a long history (more than 5 years) of HFS and/or multiple offending vessels and/or obvious arterial sclerosis are more likely to have delayed resolution. The symptoms of these patients are relieved during 6 months after MVD and most of them disappeared from 3 to 6 weeks after MVD. Thus the patient with symptoms persisting after MVD should be followed up for at least 6 months to evaluate the effect of MVD.

The rates of failed MVD and recurrent symptoms were 2.6% and 3.2% respectively in our series, in whom 23 patients with failed MVD and 19 with recurrent symptoms were subjected to second MVD.［19,20］ Intraoperative findings in this series showed that failed MVD and recurrent symptoms are due to incorrect identification or missing of the offending vessels after poor exposure of the REZ; incomplete decompression in the REZ of the 7th nerve because of inappropriate selection or interposition of implant graft; new compression caused by excessive implant graft; dislocation of implant graft; new compression caused by adhesion of the arachnoid membrane or the new offending vessel. Hence correct identification of the offending vessel and precise manipulation can improve the effect of MVD. The second operation is still effective in patients with failed MVD or recurrent symptoms after MVD.

Hearing disturbance as the main complication of MVD［12-16］ accounted for 3.2% in this series. The utilization of intraoperative BAEP monitoring can reduce the rate of hearing dysfunction significantly.［13,14,21］ A 50% decrease of amplitude of V wave is a critical point, at which manipulation should be very careful. If the amplitude of V wave is decreased by 75%, operation should be stopped to find out the cause and make the wave recover. Other complications such as facial palsy, tinnitus, ataxia, meningitis, leakage of CSF, diplopia and others can be controlled within 2-12 weeks after operation. The following points should be followed to avoid or reduce these complications: strict sterilization; avoidance of persistent or heavy retraction to the cerebellum and direct instrumental contact with nerves; protection of the small perforating artery especially the cochlear artery; and fine closure of incision.

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