Portuguese Version

Year:  1974  Vol. 40   Ed. 2 - (6º)

Artigos Originais

Pages: 145 to 148

Neurectomy of the Eighth Nerve

Author(s): Michel Portmann and
Jean-Pierre Bebear (Bordeaux - France)

Neurectomy of the VIIIth nerve is not a new operation. In was being performed before the last war for Menieré s Disease via the posterior cranial fossa approach by Dandy W. E.1, Aubry M. and Ombredanne M.z. Actually it is W. House3 who deserves the credit for reintroducing to Otology this operation but via a different approach. He used the middle cranial fossa approach which carried little risk because it was extradural. This technique was similar to the approach used by Frazier for the retro-gasserian neurectomy.

1 - Indications for Neurectomy of the VIIIth Nerve

Neurectomy of the VIIIth nerve via the middle cranial fossa finds its place in the treatment of many disorders causing vertigo, tinnitus or intolerable resonance. Vestibular Neurectomy: Scarpectomy Vertigo of labyrinthine origin is treatable by vestibular neurectomy. Naturally medical treatment must always be tried first.

a) Meniere's Disease. - If the syndrome is classical with only a slight hearing loss we prefer decompression of the endolymphatic sac using the technique of G. Portmann. If it is a longstanding case of Menieré s Disease with almost a total hearing loss a peripheral destruttion is sufficient. But if the results of the endolymphatic sac are unsatisfactory with a recurrence of the symptoms then a vestibular neurectomy is indicated.

b) Meniere-14 e Syndromer. - In the case where the disorder is not typical of Meniere's Disease the crisis of "hydrops" is due to a diffuse vascular insufficiency involving the retrolabyrinthine area. This is the arca of Scarpa's ganglion. In such a case a vestibular neureztomy is indicated. In cases with relatively good hearing this technique usually maintains then preoperative level of hearing.

c) Vertiginous Syndromes` due to a vestibular neuronitis (viral, intrameatal arachnoiditis, ischemia, etc.). - In regards to surgical treatment a vestibular neuretomy is always indicated.

d) Peripheral Vestibular Syndromes following infection (otitis media, labyrinthitis, following radical middle ear operations). - Vestibular neurectorny via the middle cranial fossa approach produces excellent results. A great advantage of this approach is that in is aseptic.

Total Neurectomy: Scarpectomy plus cochlear Neurectomy. Patients presenting with an almost total and irreversible sensorineural hearing loss plus tinnitus or an intolerable resonance in a noisy environment can be relieved by a total neurectomy. The middle cranial fossa or translabyrinthine approach can be used for these cases. The selection of the patients is important. It is necessary to define the vestibular and auditory problems as well as the psychiatric state such as depressive or anxious tendencies. All these factors must be considered. The intervention may be inadvisable if the psychiatric symptoms are excessive.

II - Surgical Technique

The technique has been described many times therefore we will relate just the essential points. Neurectomy of the VIIIth nerve can be carried out by the sub-occipital, posterior translabyrinthine, anterior translabyrinthine or middle cranial fossa approaches. The middle cranial fossa approach is by far the most common that we use. The technique is as follows: - a vertical scalp incision is made 8 cm in length. It is 2 cm in front of a vertical line passing through the anterior margin of the external auditory canal. In extends from the base of the zygomatic arch to the upper border of the temporalis muscle. - the muscle incision is of the same length and is extended the bone. - self-retaining retractors are placed to retract the superficial tissues and further bony exposure is gained by elevation of the periosteum - a 4 cm x 4 cm cranio tomy is made in the bone usine oreferably the air-drill. The inferior margin of the craniotomy is as near as possible to the root of the zygoma and the temporal line. - the dura is elevated and then the House-Urban retractor is installed. - the drilling of the roof of the petrous pyramid is again preferably performed with the air-drill. The area of the internal auditory canal is in front of the arcuate eminence. The facial hiatus with greater superficial petrosal nerve is used as a landmark for the internal auditory canal. A number of other landmarks have been proposed 6, 7, 8. - fine hooks are used to remove the remaining bony shell over the internal auditory canal and the dura is opened in its length. After waiting for the initial rush of CSF escaping from the canal, the dura edges are folded back and the acoustico-facial bundle is identified. This is well-visualized due to the obliquity of the field. In is composed of the facial nerve antero-superiorly. The facial nerve is the closest to the reflected dura. The vestibular nerve is found posteriorly bound to the facial by anastomoses and is composed of a superior and inferior portion. Scarpa's ganglion is identified as a fuller and better vascularized portion of the nerve. The cochlear nerve is located inferiorly and is therefore hidden by the facial and vestibular nerve. The arterial system is generally well seen. An arterial loop from the cerebellar artery is usually situated between the two levels of nerves. - the duration of the procedure depends on whether a scarpectomy alone on a total neurectomy is performed. - Scarpectomy: in is recommended to use a magnification of 16 x or better 25 x - the facial nerve is well-visualized. In is the most antero-superior. In certain patients due to the obliquity of the approach, the facial nerve appears to be less anterior than usual bur in is always the most superiorly placed nerve within the internal auditory canal. - the dissection of the vestibular nerve is performed with the aid of small hooks and special scalpels. The vestibulo-facial anastomoses are carefully sectioned. - the distal end of the superior vestibular nerve is elevated by a hook and with the other hand sectioned with a scalpel or scissors. The inferior portion now seen is sectioned in the same manner. - the out ends of the vestibular nerve are grasped with a forceps or better the suction and carefully lifted up and dissected away from the cochlear nerve. With the curved scissors the proximal end of the vestibular nerve is sectioned. The fragment thus obtained contains Scarpa's ganglion which prevents the future regeneration of the nerve. - Total Neurectomy: if the panent presents with an almost total and irreversible sensorineural hearing loss plus tinnitus of a peripheral variety or an intolerable resonance in a noisy environment section of the cochlear nerve is indicated. This nerve is found in an inferior position in the canal. The operation consists of a vestibular nerve settion and then section of the cochlear nerve which is situated under the facial nerve. Once exposed an adequate section of the cochlear nerve is taken using a scalpel or scissors. - closure of the operative field is now performed. - a free graft of temporalis muscle or fascia or a muscle flap is used to close the dural defect of the internal auditory canal. This is designed to fit snugly. The expansion of the brain retains the graft in place. - the House-Urban retractor is removed carefully. The anesthetist simultaneously elevares the blood pressure to allow the brain "to swell" and retake its normal form. Careful hemostasis is performed using bipolar micro-electrocoagulation and absorbable hemostatic -agents such as surgicel. - the dura is maintained in an elevated position by passing silk sutures between the temporalis muscle and dura an the inferior margin of the craniotomy. This prevents the formation of a hematoma. Sulfa powder is placed on the outer surface of the temporal lobe dura. A drain is utilized and brought out through the inferior margin of the craniotomy. - the temporal bone fragment is replaced as a free bone graft. The drain exits through the lower margin. The temporalis muscle is suttured with catgut and the skin with nylon. The drain exits through the inferior portion of the incision.

III - Results of The Vlllth Nerve Neurectomy

In our hands more than 100 operations have already been performed. At present our followup is not sufficient to give the results of the entire series. It would be preferable to analyze a series of cases presented at the last Congrès de la Societé Francaise d'Oto-RhinoLaryngologie by ourselves in collaboration with J. M. Sterkera, R. Charachon and CH. Chouards; these statistics were derived from 165 cases operated on by members of this group since 1967.

Vertigo

Total relief of vertigo, vegetative and the accompanying neurological and tensional signs is assured in 95 % of cases. Recurrences occur in 5 % of cases and is totally unpredictable in the preoperative investigation. It has been cases of Meniere s Disease which have had recurrences after the endolymphatic sac decompression or labyrinthine destruction where the vestibular neurettomy has been so successful.

Instability

Most patients suffering from Meniere's Disease do not complain of any instability between crises of vertigo. During the post-operative period following vestibular neurectomy there are 3 phases of dysequilibrium, critical, acute and compensatory. A persistent destruttive type of nystagmus is seen only with eyes closed on the ENG in 80% of cases. 15 days post operatively there is no persistence of troublestome instability.

Audition

The progression of the hearing loss in Meniere's Disease ("vertigo which ends in deafness") is obviously of major interest in the pathophysiological evaluation of the treatment. In this chapter we will discuss multiple problems related to the hearing loss. In order to evaluate the hearing results in is convenient to clarify them as worsened, stabilized or improved. The long-term results must be evaluated and finally theories must be developed to explain how a vestibular nerve section is able to produce an improvement in cochlear function. We will first review the spontaneous development of the hearing loss in Meniere's Disease. The pure tone curve first presents with a low frequency loss with or without a loss at 1000 Hz. The loss in the low frequencies is approximattely 20-30 dB. This level is subject to fluctuation and the audition is able to return to normal between crises. As the crises continue the hearing loss reaches a second plateau of about 40 dB. The third plateau is about 70 dB and finally there is total deafness. This evolution is not constam and the hearing deficit is able to jump 2 to 3 levels immediately. Fluctuations of 15-30 dB can be seen at each plateau but are rather uncommon. Most frequently (45% of cases) the hearing loss stabilizes at one of these plateaus and produces a flat curve. Unfrequently there is an immediate flat curve or an immediate total hearing loss or only a high frequency loss. This last curve is atypical and not subject to fluctuation. The related variations in the speech intelligibility curve are very interesting to study. Diplacusis and recruitment ate typical of this disease and they can present before there are deficits in the pure tone audiogram. These distortions in hearing persist during the fluctuation of hearing level.

The combination of pure tone loss and loss of intelligibility produces a useless ear. This development is particularly serious if the disease is bilateral. Spontaneous improvement or improvement under medical treatment become less frequent with time. Surgery is able to aggravate the already existing hearing loss. Among the operations utilized in Meniere's Disease only the endolymphatic decompression and the vestibular nerve section are followed by an improvement in hearing. The vestibulo-facial anastomoses have been demonstrated to contain sympathetic nervous fibers. Dividing these anastomoses during a vestibular nerve settion improves the hearing due to vasodilatation secondary to loss of sympathetic control. The other techniques have unpredictable results. They either conserve the hearing or increase the hearing loss. In the endolymphatic sac decompression the risk of increasing the deafness only arises if the posterior semicircular canal is opened by a mistake in technique. This error is not always avoidable. In the vestibular neurectomy an aggravation in the hearing loss is also due to technical errors. They are the opening of the cochlea if the facial nerve is used as a landmark for the internal auditory canal or opening of the posterior semicircular canal through the posterior wall near the distal end of the internal auditory canal if care is not taken to stay within the axis of the internal auditory canal. These two errors are avoidable if the internal auditory canal is located first at its inner portion as we stress. Less avoidable is a cochlear defett due to acoustic trauma from the drill.

Tinnitus

The relief of tinnitus by vestibular neurectomy occurs but is inconstant and unpredictable. A nociceptive stimulus produces intolerable tinnitus which in turn produces a non-habitual psychic component to which it is impossible to the patient to adapt. When tinnitus is the principal sympton bringing the patient for consultation the results of neurectomy have not been clear cut. On the contrary in the cases where tinnitus is variable, well localized and a secondary sympton in the affected ear it is partially relieved and not increased by the operation. In cases of Menieré s Disease with a total hearing loss a total neurectomy produces a complete disappearance of the tinnitus in 50% of cases. We finally emphasize that vestibular neurectomy or total neurectomy have never produced or exaggerated existing tinnitus in the operated ear. On
the other hand where tinnitus was the major sympton its disappearance has been followed by the appearance of tinnitus in the contralateral ear. Is it not possible that this is due to the loss of masking by the operared ear?

In conclusion the VIIIth Nerve Neurectomy must be proposed when definite outlined indications exist. It must not be considered any longer an operation of last resort. The middle cranial fossa approach is remarkably safe. The long term results are very satisfactory even in the cases where a strictly peripheral technique (endolymphatic sac decompression or labyrinthine destruction) did not produce satisfaccory relief of symptoms.

Bibliography

1. Dandy, W. E. - The Surgical Treatment of Meniere's Disease Surg. Gynec. Obstret., 1941, 72 (421-425)
2. Aubry, M. et Ombredanne, M. - Indications et Résultats de la chirurgie infra-cranienne du nerf auditif - Rapport à la Société Française d'O.R.L., 1937, Librairie Arnette, Paris
3. House, W. F. - Surgical Exposure of the Internal Auditory Canal and its contents through the middle fosse - Laryngoscope (St. Louis), 1961, 71/11 (1363-1385)
4. Portmann, M. - Aperçu sur les techniques chirurgicales concernant le conduit auditif interne - Cahiers d'O. R. L. (Montpellier), 1972, T. 7, n .I 7 (777-787)
5. Portmann, M., Sterkers, /. M., Charachon, R. et Chouard, CH. - Le Conduit Auditif Interne - Rapport à la Société Française d'O. R. L., 1973, Librairie Arnette, Paris
6. Portmann, M., Cohadon, F., Castel, J. P. et Leman, P. - Situation et rapports du Conduit Auditif Interne. Application à Pabord transpétreux de cette structure - Rev. de Laryngologie (Bordeaux), 1969, n.° 11-12 (643-660)
7. Fisch, U. - Neurectomy of the Vestibular Nerve - Surgical Technic - Indications and Results obtained in 70 cases - Rev. de laryngologie (Bordeaux), 1969, n.° 11-12 (661-685)
8. Pialoux, P., Freyss, G., Narcy, P., St. Macary, M., Davaine, F. - Contribution à l'anatomie stéréotaxique du Conduit Auditif Interne et de la première portion du facial - Ann. Otolaryng., Paris, 1972, n.° 89/7-8 (385-396)

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