57.2.1 Congenital Facial Nerve Palsy

This is present at birth. This is the most common form of facial paralysis seen in pediatric setting. It may be isolated with the involvement of the facial nerve and its musculature only, or it may be part of a syndrome. It may be the result of developmental defects or of traumatic etiology. It is estimated that facial paralysis occurs in 2.0% of live births ¹

Birth weight greater than 3500 grams, forceps-assisted delivery, and prematurity are all risk factors associated with traumatic facial palsy. The presence of multisystem dysmorphia and multiple cranial nerve abnormalities tend to favor developmental abnormalities, although isolated facial palsy can be of developmental origin. ²

A well-recognized form of congenital facial palsy is Möbius syndrome, which is typically accompanied by impairment of ocular abduction. In addition, two loci for isolated facial palsy of developmental origin have been identified, designated hereditary congenital facial paresis 1 and 2 on chromosomes 3q21–22 and 10q21.3–22.1, respectively. ^{3 – 5} Other syndromes are also associated with facial palsies, including hemifacial microsomia (the most common unilateral syndromatic facial palsy), Poland syndrome, osteopetrosis, trisomy 13 and 18. ⁶

The difference between developmental and traumatic facial palsies in the perinatal period is that some or complete recovery of function favors traumatic lesions. Early motor nerve conduction study also helps distinguish these etiologies.

57.2.2 Möbius Syndrome

This syndrome, sometimes called Möbius sequence, is a congenital facial palsy (unilateral or bilateral) with abnormalities of abducens nerve (cranial nerve VI) function, though other cranial nerves (III, IV, V, VIII) may be involved. ^{7 , 8} Postmortem analysis has shown hypoplasia of the motor nucleus of the facial nerve with small or absent facial nerve rootlets exiting the brainstem. ⁹ Möbius syndrome is also associated with trunk and limb anomalies in about one-third of patients. The incidence of Möbius syndrome is estimated to be about 1 in 200,000 live births. A genetic cause has not yet been identified, ¹⁰ but linkage points to a distinct locus at 13q12.2–13. ¹¹ There is some overlap with the hereditary congenital facial paresis syndromes.

57.2.3 Acquired Facial Nerve Palsy

Approximately one-half of all acquired cases qualify for the label “Bell’s palsy,” previously defined as an acute facial nerve palsy of unknown cause.

The diagnosis of idiopathic (Bell’s) facial nerve palsy is based upon the following criteria:

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  A diffuse involvement of all of the distal branches of the facial nerve is present.

  
  
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  Onset is acute, over a day or two; the course is progressive, reaching maximal clinical weakness/paralysis within 3 weeks or less from the first day of visible weakness; recovery of some degree of function usually occurs within 6 months.

  
  
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  Associated prodrome, ear pain, or dysacusis may be reported.

The most common identified cause of acute onset facial nerve palsy in children has in the past been acute otitis media. However, Lyme disease may be a more common cause in endemic areas than otitis media. ¹²

Patients with Lyme disease and facial nerve palsy may have other clinical features of Lyme disease, but many have no other symptoms, nor a history of tick bite or erythema migrans. ¹³ Painless, nontender swelling and erythema of the face preceding the facial palsy are distinctive features that may be present and help confirm the clinical diagnosis. ¹⁴ The likelihood that Lyme disease is the cause of a seventh nerve palsy diminishes in either nonendemic areas or at a time of year when Lyme disease is not prevalent. In pediatric patients with low immunization rates and acute facial paralysis, varicella-zoster virus reactivation has been identified in up to 37 percent of cases. ¹⁵ Most such cases are characterized by the absence of rash (i.e., zoster sine herpete) while a few are notable for the presence of typical zoster lesions in the auditory canal and auricle, termed the Ramsay Hunt syndrome. HIV infection rarely causes facial palsy. If it does, onset is at the time of seroconversion, when a CSF lymphocytosis usually is present. ¹⁶

Several other disorders should be considered in the differential diagnosis of facial nerve palsy. Cholesteatoma should be suspected if the onset of facial palsy is gradual. ¹⁷ The Melkersson–Rosenthal syndrome is characterized by facial paralysis, episodic facial swelling, and a fissured tongue, typically beginning in adolescence but with recurrent episodes of facial palsy. ¹⁸ Sarcoidosis should be considered, especially in patients with bilateral facial palsy. Severe systemic hypertension has been linked to unilateral primary facial nerve palsy in children and adolescents and rarely in adults. ¹⁹ Hypertension should be suspected in a pediatric patient, if facial palsy is associated with headache, altered level of consciousness, vomiting, convulsions, or focal central nervous system deficit.

Other acquired causes for facial paralysis are temporal bone trauma and cranial neoplasm (whether from the primary tumor or due to iatrogenic cause following treatment).

57.6.1 Indications

Acute traumatic/iatrogenic facial paralysis should be reconstructed within 72 hours from injury onset, if proximal and distal facial nerve stumps are present on the paralyzed side.

In an acute facial nerve damage such as in trauma or operation, immediate primary repair must be considered within 72 hours. For acute traumatic injuries primary repair of the nerve, direct or using nerve grafts, renders the best outcome. ²⁴

The advantages of acute repair include the ability to perform intraoperative nerve stimulation (which aids in locating the nerve stumps), to optimize motor nerve recovery, and to adequately gain exposure and mobilize nerve ends without the interference of scar tissue.

Nerve ends have been reported to still contain neurotransmitters within 72 hours of injury, and from a histopathologic standpoint, nerve ends have symmetrically apposed fascicles immediately after transection but then become increasingly difficult to match, as Schwann cell proliferation, fibrosis, and angiogenesis occur at each end. ²⁵

In cases of immediate injury due to penetrating trauma, surgical exploration should be undertaken. The wound should be copiously irrigated and appropriate antibiotics should be administered.

57.6.2 Technique

An operative microscope is usually used for all nerve repair cases as it aids in accurate placement of epineural sutures and minimize damage to nerve tissue.

The proximal and distal portions of the nerve must be identified. The use of an electric nerve stimulator can be useful in identification of distal branches. The nerve ends must be neurolyzed from the surrounding scar tissue bed. During this step, it is critical to avoid physical damage (i.e., crushing or tearing) to the nerve ends.

Adequate exposure also entails injured nerve end resection in order to find healthy nerve tissue and facilitate fascicle apposition. Given the healing process initiated at the nerve ends after traumatic injury, more end resection is required as the time from injury increases. In cases whereby there is uncertainty of the viability of the nerve, an intraoperative histology is used.

Repair must be achieved with minimal tension. Even in the setting of a fresh nerve laceration, some tension exists because of the elastic nature of nerves. A failure to hold an end-to-end repair with a single 9–0 suture is a sign of undue tension. ²⁶ As tension on the neurorrhaphy seems to diminish perfusion and neural regeneration, if there is insufficient length of nerve for primary repair, an interpositional graft from the great auricular nerve, sural nerve, or other suitable donor nerve should be performed.

A few epineural sutures are placed, the preferred suture material being nylon with caliber typically 9–0 or 10–0. The repair should be on the looser rather than the tighter side. The most destructive error is a repair that is too tight, whereby opposing fascicles are forced to pass each other. Repairing the back wall first in a slightly loose fashion is helpful to initially align the nerve ends and to keep the back wall fascicles contained. Repairing the remainder of the nerve so that the fascicles barely touch is the goal. At the end of the repair, there should be no deformity to the nerve. At the repair site, the edges of the nerve should be flushed without any kinks. No fascicles should be escaping the repair site. If minimal, this situation can be salvaged by a minimal trimming of escaping fascicles. Otherwise, the repair should be repeated but in a looser fashion.

Coaptation of the nerve at a site more proximal than the stylomastoid foramen should be avoided, when possible, as the arrangement of nerve fibers in this region is less organized in terms of geographical distribution to the face; thus, wrong re-routing can lead to greater synkinesia.

57.7.1 Indications

Recent facial paralysis reconstruction should be managed not later than a year after injury onset.

Recent Paralysis is defined for a paralysis in which the mimetic musculature may be reactivated by provision of neural input, and the time limit is generally 18 to 24 months.

Preoperative EMG may help to rule out early irreversible atrophy, which seldom develops earlier than 12 months after the onset of palsy, particularly in cases of recurrent facial palsy, palsy caused by radiotherapy, and Ramsay–Hunt syndrome. Patients with recent paralyses have fibrillations of the mimetic musculature, and if these fibrillations cannot be recorded, the paralysis must be considered long-standing.

By reactivation of the mimetic musculature of the face, the muscle tone can be preserved. The patient will gain better facial symmetry by preventing the dogmatic facial sagging of the affected side, better eye closure (with innervation of the orbicularis occuli) and better oral continence (with innervation of the orbicularis oris).

In the past, if a functional facial nerve branch was available only on the contralateral face, a cross-face nerve graft was used to relay facial nerve input across the face to the BZMC.

Axons from the contralateral facial nerve regenerate through the sheath of the graft and innervate the muscle over 4 to 6 months. ^{27 – 29}

Because muscle atrophy could develop while the facial nerve regenerates, an ipsilateral motor nerve (nerve to the masseter muscle) was transposed and connected to the facial nerve to serve as a temporary innervator (“babysitter”) to the muscle. In that way muscle tone was preserved while waiting for the cross-face grafts to grow across, and eventually spontaneous smiling would be restored. ^{23 , 30} Yet from the author’s experience, this type of reanimation by itself will usually result in a strong, unsightly, mass action created by the masseter-to-facial nerve anastomosis but a weak muscle contraction coming from the cross-face grafting, so even with the preservation of muscle tone and the added compliance of the orbicularis oris and occuli, a poor, nonspontaneous, and unsightly smile will result.

Since we have noticed that a cross-face nerve graft did not deliver a strong smile in the last-described situation, it is now the author’s choice, even in recent paralysis, to use masseter-to-facial anastomosis, which will be responsible for the eye and mouth tone, together with a cross-face nerve graft followed by a second-stage free gracilis muscle transfer that will be responsible for the spontaneity of the smile.

In this approach, in the first stage the distal stump of the facial nerve at the affected side is re-innervated. This innervation can be either based on an ipsilateral facial nerve if present (in cases where the nerve was cut or partially dissected) or by a cross-cranial nerve re-innervation (mostly facial-to-masseter nerve) as a permanent innervation.

At the same surgery, a cross-face nerve graft is coapted to the lower trunks of the normal contralateral facial nerve, and then tunneled across the face through the upper lip and banked for the second stage.

Within 2 to 3 months, the paralyzed facial muscles will regain tone and then will begin to function in a mass pattern motion.

At a second stage (9 months later), a free muscle is transferred and the cross-face nerve graft is used to innervate the free muscle. Within 3 to 6 months, spontaneous facial motion is initiated by the contralateral facial nerve that should take control of the transferred muscle.

In cases where the masseter nerve was used to innervate the mimetic muscles, if the masseter nerve action is still noticeable at the BZMC and unsightly, the facial nerve branches to the BZMC can be transected at a later procedure so that the smile will be solely produced by the transferred muscle.