FACIAL PARALYSIS

Author: Dr Wong Manzhi
The facial nerve is the nerve that controls movement of the muscles of the face. It is divided into five main branches which are responsible for important facial functions such as lifting of the eyebrows, eye closure and smiling. Paralysis results in severe impairment of the function and appearance of the face. In addition, taste sensation to the front of the tongue and tear production can be affected. 

The facial nerve originates in the brain and exits the skull below the ear, passing through the parotid salivary gland as it divides into branches that enter the facial muscles.

Facial paralysis can thus occur for a variety of reasons when the nerve is injured or interrupted along its course. These include salivary gland tumors, brain tumors, trauma or infections. It can also occur in children due to congenital abnormal development of the facial nerve. 

Even after recovery from facial paralysis, disorganized regeneration of the nerve can lead to troubling sequelae such as unwanted co-contractions of the muscles. 

BELL'S PALSY

Bell’s palsy is the leading cause of facial paralysis. The nerve becomes inflamed and swollen within its tight canal and is unable to function. This may be caused by a virus. There is some evidence that the culprit is often herpes simplex virus (HSV), the same virus that causes cold sores and genital herpes. Other viruses may also cause the condition, including herpes zoster virus, cytomegalovirus, and Epstein-Barr virus. Both genders and all races are affected equally; however diabetes and pregnancy increase the risk of developing Bell’s palsy.

Patients generally report being suddenly unable to move their face, with symptom onset over 48-72 hours.
  • Bell’s palsy diagnosis and initial management

    Patients who experience sudden facial paralysis should go to the Accident & Emergency Department immediately. After confirmation of the diagnosis, appropriate initial steps include oral steroids and antiviral treatment if indicated. Further non-urgent investigations such as hearing tests, computed tomography (CT scan), magnetic resonance imaging scan (MRI scan) as well as electrophysiological tests may need to be performed in certain patients. Other causes of facial paralysis such as tumor, trauma and inner ear infection must be ruled out.

  • Subsequent treatment and prognosis

    85% of patients can expect to recover fully from Bell’s palsy. 10% of patients can suffer from synkinesis and partial facial weakness. The remaining 5% of patients may be left with complete paralysis and will need surgery to restore functions such as smiling. Most people start to get better within 3 weeks of when their symptoms start, although it can take them up to 6 months to get completely back to normal. 


    Dry eyes and tearing are common complaints and are contributed by incomplete eyelid closure and inability to retain tears. Eye protection (with eye drops and taping at night) is important to prevent corneal ulceration which can lead to blindness in severe cases.


    “Synkinesis” refers to involuntary linked contractions between facial muscle groups. It can occur in the course of nerve recovery due to disorganized or abnormal facial nerve regeneration. For example, patients may notice that their eye spontaneously closes when they smile. They may also have sensations such as twitching, spasms and tightness around the eye or mouth. A rehabilitation program by dedicated physiotherapists is divided into phases depending on the stage of muscle recovery. The aim is to gently strengthen the facial muscles while preventing or reducing the development of synkinesis.  


    Botulinum toxin (Botox) injection is an important adjunct to weaken muscles that are in spasm or hyperactive. Effects last for up to 6 months for the first 2 years and thereafter, the duration of effect may be prolonged to 1 year. Surgical procedures such as blepharoplasty, brow lift, reduction of synkinetic muscles and smile reconstruction can improve symmetry and appearance. 


PAROTID GLAND AND BRAIN TUMORS

These are the other main causes of facial nerve paralysis. Acoustic neuroma is the most common type of brain tumor involved. It is a benign (non-cancerous) growth that occurs on the eight cranial nerve which lies adjacent to the facial nerve. The eight nerve carries hearing information and balance signals from the ear to the brain. Symptoms of an acoustic neuroma include hearing loss, tinnitus (perception of noise ringing in the ear) and vertigo (spinning sensation). A hearing test and MRI can establish the diagnosis and the tumor may require removal by a neurosurgeon.
 
The facial nerve divides into branches as it passes through the parotid salivary gland which lies just in front of the ear. Some or all of the facial nerve branches can be involved by malignant (cancerous) tumors of the parotid gland and may need to be removed together to ensure tumor clearance. 

The treatment approach to facial paralysis in tumor cases depends on the findings during the operation. A conservative approach is prudent if the surgeon who performs the tumor removal feels that the nerve was saved during the operation. Patients will require eye care and sometimes temporary surgical procedures on a case-by-case basis. If the nerve was cut during the operation or if the facial palsy does not resolve, then a more active approach must be taken. 

NERVE RECONSTRUCTION

If one or more facial nerve segments needs to be removed, they can be reconstructed using nerve grafts harvested from other areas of the body. This can be done either in the immediate setting (at the same time as the removal of the tumor) or as early as possible (within 3-6 months is preferable). 

The nerve grafts can be connected to the same side facial nerve, or if this is not available, to the healthy side facial nerve or to the nerve to the masseter muscle (one of the muscles for chewing). As nerves regenerate at a speed of 1mm/day, between 6-12 months may be required before the nerve reaches the muscle and is able to activate it again. Radiation therapy may slow the speed of nerve regeneration and affect the final muscle strength achieved. In addition, fibrosis of the surrounding tissues will result in a tightness and contracture.

If more than 18 months has elapsed from the time of onset of facial nerve paralysis, the facial muscles would usually have atrophied and spontaneous recovery cannot be expected. Replacement of muscle function using functional muscle transfer is the ideal solution to allow the patient to smile again.

SMILE RECONSTRUCTION

  • Static Methods: Fascia lata suspension

    A strip of fascia lata can be harvested from the thigh via a small incision. The fascia lata is a layer that covers the thigh muscles and is relatively strong. A piece of it can be used as a hammock to suspend the lip and angle of the mouth to more stable structures in the temple or upper cheek area. Although it is simple procedure that can be performed even under local anesthesia injections, the position of the lip is fixed is a slightly elevated position. In other words, patients do not have a dynamic smile. In addition, the fascia lata stretches with time and recurrence of lip drooping can be expected. Tightening of the fascia lata can be repeated in a second operation.


    Other techniques such as face lift cannot reanimate a smile. as they do not affect the facial muscles.  However they can be important adjuncts to improve the soft tissue drooping that also occurs in facial palsy. 


  • Dynamic Methods: Lengthening temporalis myoplasty

    The temporalis muscle is one of the muscles responsible for jaw movement. One can locate it by feeling the temple area while biting down. This muscle can be diverted for smiling, by stitching its end to the smiling muscles around the mouth. A smile can be produced immediately post-operation by biting down. However after going thru a post-operative rehabilitation program, a smile can be produced without conscious thought as early as few months after operation. Functional MRI has shown that the brain adapts by the process of cortical plasticity such that it recognizes the temporalis muscle as a “smiling muscle” instead of one for chewing.

  • Dynamic Methods: Free functioning muscle transfer

    When the facial muscles are in an atrophied state or are absent, muscle can be transferred from other parts of the body such as the back (Latissimus dorsi muscle) and thigh (Gracilis muscle) to replace them. After harvesting the muscle, there is no loss of function in the donor site as the body is designed with more than one muscle for the same job. The muscle is taken with its blood supply (artery and veins) and connected to blood vessels in the head and neck using microsurgery. Microsurgery is the joining of blood vessels under a microscope. The muscle is also harvested with its nerve which is connected to a branch of the healthy side facial nerve. After the nerve regenerates from the healthy side over a period 4-9 months, patients can smile as per normal without need for conscious activation. 

Other Procedures

There are 17 muscles of facial expression on each half of the face. Smiling is just one of the functions of the face. For example restoration of brow position with brow lift techniques can reduce skin hooding that obscures vision and also improve appearance. This can be accomplished either by endoscopic techniques or by direct brow lift (which will leave a hairline scar above the brow). As eye closure can be impaired leading to dry eyes and tearing, definitive eyelid reconstruction such as with levator recession or gold/platinum weight may be needed. The lower eyelid can be tightened with techniques such as limited tarsorraphy, canthopexy/canthoplasty or inferior retractor recession.