Facial palsy is the most common risk of otoneurosurgery. (O.N.S.) The object of this paper is to specify the preventive and curative methods of facial palsy according to our experience based on 156 operations. The facial nerve (7N.) is vulnerable for the following reasons: the lack of epineurium as the nerve traverses the cerellopontine angle and internal auditory canal (I.A.C.). The nerve has no protective sheath like in the fallopian canal. - The fragility of the nerve vascularisation. The geniculate ganglion is area poor in vascular anastomose; the petrosal vessels are the principal vascular pedicle of the labyrinthine segment of the nerve. This pedicle is specially exposed to surgical injury.
I - Techniques of Facial Nerve Preservation
1.° - in VESTIBULAR NEURECTOMY.
a) by the trans-labyrinthine approach, the risk of facial palsy is not more important than in middle ear surgery.
b) by the middle fossa approach, it is known from long that facial palsy is a possible complication of this approach. The facial weakness can arise immediately or after a few days, even fourteen days.
Tearing of the great superficial petrosal nerve (G. S.P.N.) is the pathogenesis mostly invoked. The ischiemic damage done to the genicula ganglion and the 7N. by interruption of the petrosal vessels explains the delay of installation of the palsy. The return comes when the nerve's oedema resolves. A facial weakness occured in 6% of our cases (over 100). The function returns ove or two weeks later, in all except one case. This case illustrates the ischiemic pathogenesis. The facial palsy appeared a few days after the operation. The return was incomplete (45%.) and a petrosal neuralgia developped. There was no other explanation than a tearing of the petrosal pedicle. Three years later the reoperation found an oedema of the petrosal nerve and a partial atrophy of the 7N. Obviously then, the best way to avoid a post operatory facial weakness is to spare the petrosal pedicle. That is one of the reasons of using "the technique of direct approach of the I.A.C.". In this technique the elevation of the dura is made in the biauricular axis, the meatal aera is exposed, the G.S.P.N. is seen in front of this aera. Then the drilling begins in the internal half of the I.A.C. far from the 7N. and the petrosal pedicle. When the I.A.C. is reached two precautions must be emphasized to prevent injury to the 7N.:
- firstly, the incision of the dura must be done on its posterior border - secondly, the drilling of the end of the I.A.C..must be very careful, specially when the vestibular fossa is deep. The drilling must be limitated to the posterior half of the far end of the I.A.C., using a 2mm. diamond burr. A larger burr could injure the 7N. which is situated in the anterior wall of the vestibular fossa.
2.° in ACOUSTIC TUMOR SURGERY.
In spite of recent progress in the methods of this surgery, facial palsy is still the principal risk, even in removal of intra canalar tumors.
a) technique of facial nerve preservation
The following observations are useful: - The 7N. must be identified at the end of the I.A.C. or in the fallopian aqueduct. The 7N. is more exposed to direct injury in the middle fossa approach for it is compressed between the dura and the tumor and is the first structure to be seen after the opening of the I.A.C. For this reason the trans-labyrinthine approach is prefered when hearing function is already lost. - The development of a plane of dissection between the 7N. and the tumor must be done with minimal tension to the verve. Ali forward tension on the tumor would stretch the nervous fibers. To minimize the tension, it is necessary to first remove a part of the tumor. Then during the verve dissection it is essential to protect the verve, because catching it with the suction tube is extremely dangerous since the verve fibers have no protective sheath. A cottonoid must be placed against the 7N. and the suction applied through this protection. "The cotton technique of dissection" is the key of facial preservation. - When the tumor has not penetrated between the 7N. and the cochlear nerve, this nerve is kept as a stake for the 7N. - A specially dangerous spot is at the porus where the 7N. adheres to the dura and can be difficult to dissect.
b) Results:
In 34 acoustic tumors totally removed, (intra and extra canalar, less than two centimeters), the trans-labyrinthine approach has been used 25 times, the middle fossa 9. The 7N. was anatomically preserved in 31 cases, transitory facial, palsy was observed in 14 cases. The palsy was permanent in 2 cases. The 7N. was interrupted during surgery in 3 cases. In short, 29 cases out of 34 (85%) had no or little facial weakness at ove year. 5 cases (15%) had permanent facial palsy. They were all tumors with expansion in the angle.
II - Technique of Facial Nerve Repair
The techniques are:
- end to end anastomosis
- free nerve graft
- heteronervous anastomosis
1.° The end_to end anastomosis
This technique gives the best results. The anastomosis is done with 6.0 suture material (silk or nylon). The stumps of the nerve being very thin allows only ove suture. Regeneration will happen if tension is not excessive. The rerouting technique can be used to get some length: The petrous nerve is cut and the 7N. is extracted from the fallopian aqueduct.
2.° The autogenous free nerve graft
The graft is taken from the great auricular nerve, the ends are sutured to the facial stumps. If the suture is not possible, the nerves are placed in a polyethylene or a collagen cylinder. The regeneration is longer than with the end to end anastomosis and the quality of facial motion is not as good. These two procedures are not, of course, always successful. But it is necessary to wait a long time (12 or even 14 months) to be sure regeneration is not coming. So we prefer if the nerve reconstruction was hazardous to dont loose to much time. After a minimum of six months, we reoperate and have a look on the 7N. in the mastoid. If the nerve is still completely atrophied in the mastoid area its indicates with a very great probability that regeneration will not happened. So we proceed immediately to a hetero-nervous anastomosis. This "surgical appraisement of the nerve state" is, in our mind, a useful procedure, although empirical.
3.° The heteronervous anastomosis
This is the last but not the least solution. The results are far better than with any plastic operations. The tonus returns four months after the anastomosis, and the face is normal in repose, the lagophthalmus is corrected. Voluntary mimic is obtained after exercises. The smile and the closing of eyelids returns. But in emotional mimic, the face remains not symmetrical. We have always performed the hypoglossal-facial (12-7N.) anastomosis. The 7N. is sectioned at its second genu and sutured to the 12N., which is sectioned anteriorly so that the anastomosis is done without tension. The descending branch of the 12N. is sutured to the peripheral stump of the main trunk to correct the hemilingual atrophy. The anastomosis can be done at the end of the primary operation or later. The best results are obtained when the anastomosis is performed during the four first months after nerve interruption. Our results in 10 cases were all satisfying though the delay in two cases were very long: the anastomosis were performed twelve and eighteen months after the 7N. interruption.
Summary - Abstract
1.° In vestibular neurectomy, facial weakness is rare and transitory. (6%). The technique of direct approach of the I.A.C. lessens the rate of facial weakness.
2.° In acoustic tumor surgery, facial palsy is the most common complication. (15%).
The cottonoid technique of dissection is essential to preserve the nerve.
3.° The facial repair is always possible. The technique of choice is the end to end suture, with rerouting if necessary. The two other techniques are the free graft and the hypoglossal-facial anastomosis. This last technique gives satisfying results which are far better and faster than with plastic procedures.
Bibliography
1. Perria, C., and Zini, C.: a pathogenic interpretation of the lesions of the facial nerve following operations in the middle fossa. Neurochirurgia 12:83-93 (may) 1969.
2. House, W. F., and Hitselberger, W. W.: preservation of the facial nerve in acoustic tumor surgery. Arch otolaryng. 88: 655-658. (der.) 1968.
3. Miehlke, A.: surgery of the facial nerve. Urban and Schwarzenberg, édit., Munich, 1973.
4. Sterkers, I. M.: Découverte du conduit auditif interne. Ann. d'O. L. (Paris). 90: 323-325, 1973.
5. id.: Anastomose hypoglosso-faciale. Ann. d'O. L., à paraitre.
* Pr coll. nédecine. 42 rue Ampere. 75017 Paris - France.
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