INTRODUCTION

Both the anatomy and innervation of the facial nerve are complex. It bears efferent motor fibers to the facial muscles (including the stylomastoid, stapedius and posterior belly of the digastric), pre-ganglionic parasympathetic fibers (to the lacrimal, submaxilla, submandibular, sublingual and nasal seromucous glands), afferent fibers for our sense of taste (anterior two-thirds of the tongue, palate and tonsillar fossa), facial muscles afferent propioception and skin afference for the external acoustic meatus and conchae (1).

Peripheral facial paralysis bear great functional and cosmetic consequences for the patient. Most of the nerve fibers are motor, and they mobilize the muscles of the face responsible for mimicry. Their paralysis have a cosmetic effect due to facial cosmetic and function asymmetry due to changes in tearing and peribuccal muscle tone. Cosmetics is essential in the professional and social lives of people. This impairment brings enormous psychological consequences to the affected individuals.

Although Bell's palsy is the most common cause of peripheral facial palsy, cerebellopontine angle tumors and traumatic paralysis, specially that by gun shot wound, cause severe facial paralysis and in a proximal portion of the nerve (2).

Nerve repair by end-to-end anastomosis or by autologous grafting is the technique that yields the best result. However, in many of these cases the nerve proximal stump can't be obtained due to the impossibility of identifying the nerve because of intense local fibrosis, surgical risk related to its location in the posterior fossa, close to the brain stem and the very possibility of intra and post operative complications such as bleeding and fistulas, which make it impossible to perform these anastomosis. When this happens, the facial nerve may be reanimated in other ways (3): nerve replacement by innervation of another cranial nerve; transfer contralateral facial nerve (cross face); muscle transpositions/transfers.

Muscle transpositions and transfers use muscle groups that have reinnervation but not from the facial nerve, or muscle groups from other sites in the body together with their nerve bundle. In nerve replacement techniques the donor nerves were sacrificed so that the facial nerve could be reanimated, often times bringing about important sequelae (4). Anastomosis techniques between the facial and the hypoglossal nerves are the most described for replacement (3,5-7), however, motor deficits and hemiglossal atrophy may result from this technique, and represent the main criticisms for its performance (8,9).

Since Korte, in 1901 (8) proposed the first description of using the hypoglossal nerve to reinnervate the facial, many replacement surgical techniques have been published (3,10). Other cranial nerves have also been used for this purpose, such as the accessory, trigeminus and glossopharyngeal (5), always considering the binomial: facial movement and sequelae in the region previously innervated by the donor nerve. The neural compatibility achieved with the hypoglossal nerve was better than that with the other ones, mainly due to their functional similarities (1,6,11). Both have close cortical representation and the tongue enjoys broad representation.

The techniques initially proposed advocated the complete section of the hypoglossal and its end anastomosis with the facial nerve or with a graft from the distal facial stump all the way to the hypoglossal using either the sural or the auricular magnus nerve (3,8,10).

Due to the very complexity of the facial nerve fibers, achieving total mobility is an impossible goal for this procedure, where the basic functional activity such as muscle tonus during rest and capacity to suck, chew and speak are the essential goals (1). The results obtained with this repair techniques are the most reliable because they use the facial nerve conduction system and the tonotopy of the distal fibers 3,11,12).

The goal of this study is to describe and compare the funicular end-to-end anastomosis technique (FEEAT) with the neural replacement techniques already described in the literature.

MATERIAL AND METHODS

Twenty six patients, (16 males and 7 females, M:F ratio = 2.3) underwent FEEAT technique. Average age was of 36.5 years (minimum of 7 and maximum of 60). Twenty (87%) patients presented class 5 peripheral facial paralysis, three (13%) patients had class 4 on the House Brackmann (13) scale prior to surgery (Table 1). The paralysis etiology may be seen on Table 2.
The maximum time span between the facial paralysis and the surgical repair was of 18 months and the minimum time was of 3 months, with average time of 11 months.

The facial nerve was affected by primary lesion in 10 cases, by trauma (fracture or FAF) in 9 cases or during surgery in 4 cases.
The location of the damage was in the intracranial portion of the nerve or in the first intratemporal portion (internal acoustic meatus and labyrinth segment). In all cases the proximal stump was not accessible for repair. We then carried out the neural replacement technique with the nervus hypoglossus.

Description of the surgical technique
A simple mastoidectomy is made in order to access the facial nerve in its 3rd portion (mastoid) and release it up to where it emerges the stylomastoid foramen (Figure1). The nerve is sectioned in its 2nd turn without touching the ossicular chain. The nerve is then removed from the Fallopian channel and taken inferiorly through the stylomastoid foramen region, medially to the posterior belly of the digastric muscle.

The incision is then extended all the way to the neck, continuing the retroauricular incision made for the mastoidectomy and aligned with the anterior border of the sternocleidomastoideus muscle (in the anterior neck triangle). The nervus hypoglossus is then located postero-inferiorly to the posterior border of the digastric muscle, over the internal carotid artery and anterior to the internal jugular vein (Figure2).

We then locate its descending branch. Proximal to its descending branch we open a window in the epineurium in the lateral most portion of the hypoglossal nerve, in order to visualize the funiculi. We then section the most posterior and most lateral funiculus. The distal stump of the facial nerve that has been moved here is then sutured to the proximal stump of the hypoglossal nerve funiculus (Figure3).

If the length of the facial nerve is not enough to perform a tensionless anastomosis, the digastric and/or the sternocleidomastoideus muscles may be cut. Human fibrin glue (Tissucol®) was used to stabilize the anastomosis according to technique previously described by Bento (14,15). The surgical incision is then sutured in three planes: muscle, subcutaneous tissue and skin.
All patients underwent facial motor rehabilitation program to train the new movement ways.

RESULTS

The patients were followed up for 24 months. The facial mimicry motor function was assessed in sequential visits and by the same examiner in one month intervals. On the fourth month 20 patients already showed some signs of motor reinnervation, while the remaining three showed movement after 1 year. After 24 months the obtained results may be seen on Table 2. Both movement and functionality of the tongue were preserved in all cases.

DISCUSSION

The results attained by this technique showed acquisition of the facial musculature tonus during rest with improvement in its self feeding functionality. The HB has not always been the scale used to assess the paralysis, and this makes it difficult to compare studies. However, most of the authors consider gain in rest tonus and facial joint functionality for speech and feeding to be satisfactory results for this technique (2). In these studies, there was 100% tongue sequelae, and the association of a pre-existing lesion in other cranial nerves could have caused important definitive impairments for the patient. Considering the best support the hypoglossal nerve is able to donate to the facial nerve, 10% of the patients may not achieve facial reinnervation and even then have hemiglossal sequela, and since there is a large amount of fibers going to the facial nerve, there is an increase in the possibility of movement.
Results with the anastomosis between the terminal stump of the facial nerve and the lateral wall of the hypoglossal nerve, or with part of the hypoglossal, aim at reducing tongue movement sequela (5,6). In this technique the number of nervous fibers to the facial nerve would be less and so will be the tongue sequelae (3,11). The technique carried out without the sectioning of one third the thickness of the nervus hypoglossus and end-to-side anastomosis was initially carried out with the interposition of a nerve graft (3,4) (sural or auricularis magnum). In this case, the drawback is that there are two anastomosis, because the nerve transposition is made close to the parotid gland, not leaving enough facial nerve distal stump for direct suture to the nervus hypoglossus, thus needing the graft, and this led to worse results than those achieved by the author (3,7). Even sectioning half the nervus hypoglossus diameter, there were no tongue sequelae (1,5,6). The lateral graft shows that there is less tongue impairment, or no impairment at all, however there are worse results for facial reinnervation. The results achieved in the present study show facial nerve reinnervation (HB III or II) in approximately two-thirds of the patients, and compared to the aforementioned techniques, this shows better performance. FEEAT bears the same complication rates in relation to tongue atrophy when compared to the techniques that preserve part of the hypoglossus fibers, as in the side-to-end anastomosis.

CONCLUSION

FEEAT adds the possibility of having good facial mobility results (HB II or III), because the anastomosis is end-to-end and not side-to end, through the dissection of a specific funiculus. Therefore, there is less fiber damage and greater chance of reinnervation, preserving more nervus hypoglossus diameter, thus reducing the possibility of impairing the tongue motor function.

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