Introduction
Facial paralysis is a debilitating disease process that poses significant physical and psychosocial impacts to patients. Facial paralysis resulting from salivary gland tumors can be due to the direct invasion of a malignant tumor, injury, or transection of the facial nerve during tumor removal. Sunderland classified nerve injury into five degrees :
1st degree injury is the temporary interruption of conduction at the site of injury.
2nd degree injury occurs when the axon is disrupted, and the distal portion undergoes Wallerian degeneration.
3rd degree injury is interfascicular injury, and the continuity of the endoneurial tube is lost. Axons are no longer confined to the endoneurial tubes, resulting in axon misrouting leading to synkinesis.
4th degree injury occurs when fasciculi are disrupted and disorganized. Regenerating axons are free to enter interfascicular tissue, leading to poor recovery.
5th degree injury indicates epineurial injury or transection of the nerve. Some regenerating axons may reach the distal stump depending on the distance between the nerve ends, but large numbers of the axons escape into the intervening tissues.
Evaluation
Prior to salivary gland surgery, the patient’s facial function should be thoroughly and systematically examined in a zonal fashion. Areas of muscle weakness should be noted before surgery, as well as areas with signs of nerve irritation, including muscle twitching, fasciculation, or spasm. Photographs and video-recordings are essential for documentation and for comparison after the surgery; these are taken at rest and during volitional movements (brow elevation, gentle and full effort eye closure, blink, lip pucker, gentle and full effort smile, lower lip depression). Spontaneous and emotional smile can be elicited by showing a funny videoclip.
An ideal facial nerve grading system is currently lacking. The House–Brackmann (HB) scale is the most commonly used grading system worldwide. However, the inter-rater and intra-rater reliability is only fair. Moreover, it is unable to track changes during recovery. The revised version, HB II or Facial Nerve Grading Scale 2.0, is a regional scale that has a low inter-observer variability. However, it is not widely adopted. The Sunnybrook Facial Grading Scale is a regional weighted scale that is sensitive to subtle changes during recovery with high intra- and inter-observer reliability, and is the most widely used scale for rehabilitative therapists. The eFACE is an electronic facial assessment scale, introduced in 2015 by Banks et al., which comprises a clinician-graded visual analog scale that rates 15 facial features. It was demonstrated to have high inter-rater and intra-rater correlations and has strong correlation with the Sunnybrook facial grading scale.
Management
Facial paralysis can be expected or unexpected. Expected facial paralysis is related to the resection of the facial nerve or its branches with the tumor, which should be included in the plan of tumor extirpation. Reconstruction should be immediate during operation as the distal stump will no longer be receptive to stimulation after 72 h. Otherwise, it would not be able to accurately identify the muscle that the distal branches innervate thereafter. Various reconstructive options are discussed in this chapter ( Fig. 50.1 ).
Interim Facial Paralysis Management
Periocular management is crucial in the treatment of facial paralysis to prevent exposure corneal keratopathy. Upper lid stretching is a non-surgical method for eye closure. However, it has to be done four times a day. Lubricating eye drops and taping during sleep are essential for corneal protection. A moisture chamber and scleral lens are alternatives to keep the cornea moist and protected.
When a prolonged recovery is expected, a temporary color-matched external weight can be taped onto the upper lid. However, this may not be aesthetically pleasing, and the result is suboptimal in patients with upper lid skin laxity. Alternatively, a thin profile platinum implant can be placed into the upper eyelid. This can easily be removed once the lid function spontaneously returns. Temporary tarsorrhaphy is a simple and yet most predictable option for lagophthalmos, but it is less aesthetically favorable.
Facial Nerve Sacrifice
Before the operation, a clear discussion with the patient should be undertaken and they should be psychologically well prepared for the postoperative facial paralysis. The choice of reconstruction depends on the patient’s age, motivation, expectation, and the length of preoperative facial paralysis. But the most important factor is the availability of proximal and distal stumps. Usually in salivary gland surgery, both the proximal and distal stumps can be traced, even into the intratemporal portion. Tensionless primary neurorrhaphy is possible if only a short segment of facial nerve or branch is resected. Study has shown that a gap between nerve ends >6 mm may require interpositional grafting. Nerve graft can be harvested from the great auricular nerve, the medial antebrachial cutaneous nerve of the arm, or the sural nerve. The great auricular nerve is advantageous because of its proximity and diameter ( Figs. 50.2 , 50.3 ). However, its use may be limited in the case of highly neurotropic tumors. The medial antebrachial cutaneous nerve is a preferred choice because its branching pattern provides excellent coaptation to distal stumps. In cases when the anterolateral thigh free flap is planned for defect coverage and contouring, the motor nerve to the vastus lateralis can be harvested with no additional donor morbidity ( Figs. 50.4 , 50.5 ). Due to poor topographic arrangement of the facial nerve, synkinesis or dyskinesis is inevitable.
Very often, adjuvant radiotherapy is required after resection of a parotid malignancy. It is generally accepted that radiotherapy or brachytherapy plus radiotherapy does not affect the functional recovery of patients with nerve grafts. Treatment of synkinesis will be discussed later in this chapter. Occasionally, when a neurotropic tumor with extensive perineural spread limits the proximal stump availability, nerve reinnervation or substitution should be applied. Cross facial nerve graft (CFNG), originally developed by Scaramella and Smith, with sural nerve is the best option in terms of achieving a spontaneous and emotional smile. However, several factors must be considered when reinnervating the native facial muscles with a CFNG ( Fig. 50.6 ). Favorable outcomes are related to the donor axonal count and there is a significant negative correlation between age and the axonal load. The duration of paralysis before surgery is important. Outcome of CFNG may be suboptimal if the preoperative facial paralysis interval is 6 months or more. With CFNG, there is always concern about whether the normal side would be weakened. Cooper et al. demonstrated that the gross motion of the normal hemiface is not permanently impaired with CFNG when donor nerves are carefully selected. The masseteric nerve is a good alternative, as it is in close proximity to the distal stump so that an interpositional graft is not required ( Figs. 50.7 , 50.8 ). It is located 3 cm in front of the tragus and 1 cm below the zygomatic arch. The branch descends towards the oral commissure between the deep and middle layer of the masseter. The subzygomatic triangle approach, introduced by Collar et al., is another rapid method to identify the nerve with minimal dissection using the zygomatic arch, the temporomandibular joint, and the frontal branch of facial nerve as landmarks. Failure rates are lower with the masseteric nerve than that of CFNG, owing to its denser axonal load and single coaptation. Sacrificing of this nerve will not cause significant donor site morbidity. Muscle contraction will be evident as early as 2 months. However, with masseteric to facial transfer, the patient needs to bite down to create a smile. In a study by Hontanilla and Cabello, 56.66% of patients with masseteric nerve transfer were able to achieve a spontaneous smile. Women were shown to have a higher achievement with an earlier onset. All these patients underwent a daily mirror biofeedback exercise, starting from 1 month after surgery. This is possible because of brain plasticity and the close proximity of the cortical smile area and the jaw-clenching area. Hypoglossal facial transfer has been performed for years to reinnervate the facial muscles. Multiple modifications including a mini-hypoglossal transfer technique have been adopted to reduce tongue morbidity. However, the rate of achieving a spontaneous smile with hypoglossal facial transfer was lower than that with masseteric nerve. Moreover, masseteric and hypoglossal nerve transfer can also be used as a “babysitter” procedure for CFNG. The non-facial nerve innervates the muscle earlier, provides trophic support to the muscle, and prevents irreversible muscle damage. Then axons from the CFNG come in for spontaneity. In rare situations, with large tumor resection in which the distal stump or even the facial muscles are resected, a muscle transfer procedure should be performed to replace the native muscle. However, the choice of donor nerve is debatable. For patients who require immediate smile restoration, lengthening temporalis myoplasty or temporalis tendon transfer can be considered.
