Twitching, weakness or paralysis of the face is a symptom of some disorder involving the facial nerve. It is not a disease in itself. The disorder may be caused by many different diseases, including circulatory disturbances, injury, infection or tumor.
FUNCTION OF THE FACIAL NERVE
The facial nerve resembles a telephone cable and contains hundreds of individual nerve fibers. Each fiber carries electrical impulses to a specific facial muscle. Acting as a unit this nerve allows us to laugh, cry, smile, or frown, hence the name, “the nerve of facial expression”. Each of the two facial nerves not only carries nerve impulses to the muscles of one side of the face, but also carries nerve impulses to the tear glands, saliva glands, to the muscle of the small middle ear bone (stapes) and transmits taste fibers from the front of the tongue and pain fibers from the ear canal. As such, a disorder of the facial nerve may result in twitching, weakness or paralysis of the face, dryness of the eye or the mouth, loss of taste and, occasionally, increased sensitivity to loud sound an pain in the ear.
An ear specialist is often called upon to manage facial nerve problems because of the close association of this nerve with the ear structures. After leaving the brain the facial nerve enters the temporal bone (ear bone) through a small bony tube (the internal auditory canal) in very close association with the hearing and balance nerves. Along its inch and a half course through a small bony canal in the temporal bone the facial nerve winds around the three middle ear bones, in back of the eardrum, and then through the mastoid to exit below the ear. Here it divides into many branches to supply the facial muscles. During its course through the temporal bone, the facial nerve gives off several branches: to the tear gland, to the stapes muscle, to the tongue and saliva glands and to the ear canal.
DIAGNOSIS OF FACIAL NERVE DISORDERS
Abnormality of facial nerve function may result from circulatory changes, infections, tumors or injuries. An extensive evaluation may be necessary to determine the cause of the disorder and localize the area of nerve involvement.
Tests of the hearing are done to determine if the nerve disorder has involved the delicate hearing mechanism. When the face is totally paralyzed, special hearing tests (auditory brainstem response audiometry and acoustic reflex tests) may be necessary to localize the problem area.
X-rays may be taken to determine if there is any infection, tumor, or bone fracture. In some cases it may be necessary to obtain special studies such as computerized tomography (CT scan) or magnetic resonance imaging (MRI).
A test of the eye’s ability to tear is frequently necessary to help determine the location of the facial nerve involvement.
An ENG (electronystagmography) test of the balance canals is advised in some cases to clarify the cause or location of the facial nerve disorder.
There are three electrical tests of the facial nerve function that we may use: nerve excitability test, electroneuronography and electromyography.
Nerve Excitability Test
The facial nerve excitability test helps us to determine the extent of nerve fiber damage in cases of total paralysis. The test may be normal despite the paralysis, indicating a better outlook for return of function. In such cases the excitability test may be repeated every day or so to detect any change which would indicate progressive deterioration.
Electroneuronography involves the use of a computer to measure the muscle response to electrical stimulation of the facial nerve. Recording electrodes are glued to the face and the facial nerve is stimulated with small electrical currents. Muscle contractions are recorded by the computer.
Electromyography may be indicated in cases of long-standing paralysis. This test helps us to know if the nerve and muscles are recovering.
CAUSES OF FACIAL NERVE DISORDERS
The most common condition resulting in facial nerve weakness or paralysis is Bell’s palsy, named after Sir Charles Bell who first described the condition. The underlying cause of Bell’s palsy is now known, but it may well be due to a virus infection of the nerve. We know that the nerve swells in its tight bony canal. This swelling results in pressure on the nerve fibers and their blood vessels. Treatment is directed at decreasing the swelling and restoring the circulation so that the nerve fibers may again function normally. At times normal function is not restored.
Herpes Zoster Oticus A condition similar to Bell’s palsy is herpes zoster oticus, “shingles” of the facial nerve. In this condition there is not only facial weakness but often hearing loss, unsteadiness and painful ear blisters. These additional symptoms usually subside spontaneously but some hearing loss may remain.
Injuries of the Facial Nerve
The most common cause of facial nerve injury is skull fracture. This injury may occur immediately or may develop some days later due to nerve swelling.
Injury to the facial nerve may occur in the course of operations on the ear. This complication, fortunately, is very uncommon. It may occur, however, when the nerve is not in its normal anatomical position (congenital abnormality) or when the nerve is so distorted by the mastoid or middle ear disease that it is not identifiable. In rare cases it may be necessary to remove a portion of the nerve in order to eradicate the disease.
In more complicated ear problems, such as tumors of the hearing and balance nerve, the facial nerve may be injured and at times the nerve must be severed to allow complete removal of the tumor.
The most common tumor to involve the facial nerve is a nonmalignant fibroid tumor of the hearing and balance nerve, the acoustic tumor. Although there is rarely any weakness of the face before surgery, tumor removal sometimes results in weakness or paralysis. This weakness usually subsides in several months without treatment.
It may be necessary to remove a portion of the facial nerve in order to remove the acoustic tumor. It may be possible to sew the nerve ends together at the time of surgery or to insert a nerve graft. At times a nerve anastomosis procedure is necessary later, connecting a tongue nerve to the facial nerve (hypoglossal-facial anastomosis). In either case the face is totally paralyzed until the nerve re-grows (6 to 15 months).
Facial Nerve Neuroma
A nonmalignant fibroid growth may grow in the facial nerve itself, producing a gradually progressive facial nerve paralysis. Removal of this facial nerve neuroma require severing the facial nerve. Usually it is possible to graft it at the time with a skin sensation nerve from the neck. Total paralysis will be present until the nerve re-grows through the graft, usually a period of 6 to 15 months. There will be some permanent facial weakness.
When the portion of the facial nerve nearest the brain is destroyed by the tumor, a hypoglossal-facial nerve anastomosis procedure is necessary.
Removal of a facial nerve neuroma may necessitate removal of the inner ear structures. If this were necessary, it would result in a total loss of hearing in the operated ear and temporary severe dizziness. Persistent unsteadiness is uncommon.
Post-Operative Facial Nerve Weakness
Delayed weakness or paralysis of the face following reconstructive middle ear surgery (myringoplasty, tympanoplasty, stapedectomy) is uncommon, but occurs at times due to swelling of the nerve during the healing period.
Fortunately, this type of facial nerve weakness usually subsides spontaneously in several weeks and rarely requires further surgery.
Acute or chronic middle ear infections occasionally cause a weakness of the face due to swelling or direct pressure on the nerve. In acute infections the weakness usually subsides as the infection is controlled and the swelling around the nerve subsides.
Facial nerve weakness occurring in chronically infected ears is usually due to pressure from a cholesteatoma (skin-lined cyst). Mastoid surgery is performed to eradicate the infection and relive nerve pressure. Some permanent facial weakness may remain.
Hemifacial spasm is an uncommon disease which results in spasmodic contractions of one side of the face. Extensive investigation is necessary at times to establish the diagnosis correctly.
Hemifacial spasm is caused by pressure of a blood vessel on the facial nerve near the brain. Displacement of the blood vessel from the facial nerve is possible through a retrosigmoid approach.
In this operation the area between the brain and the inner ear is exposed by removing the mastoid bone behind the inner ear. The complications related to this surgery are the same as those stated for the middle fossa approach.
Circulatory disturbances of the nervous system may cause facial nerve paralysis. The most common example of this is a stroke.
As opposed to other conditions listed in this booklet, a stroke usually has many other symptoms which indicate the cause of the problem. Treatment is managed by the internist, neurologist, or neurosurgeon.
COMPLICATIONS RESULTING FROM FACIAL NERVE PARALYSIS
The most serious complication that may develop as the result of total facial nerve paralysis is an ulcer of the cornea of the eye. It is most important that the eye on the involved side be protected from this complication.
Closing the eye with the finger is an effective way of keeping the eye moist. One should use the back of the finger rather than the tip in doing this to insure that the eye is not injured.
Glasses should be worn whenever you are outside. This will help prevent particles of dust from becoming lodged in the eye.
If the eye is dry, you may be advised to use artificial tears. The drops should be used as often as necessary to keep the eye moist. Ointment may be prescribed for use at bedtime. A Moisture Chamber may be recommended to prevent evaporation of tears.
At times it is necessary to tape the eyelid closed with tape. It is best for a family member to do this to insure that the eye is firmly closed and will not be injured by the tape.
If facial weakness is anticipated following surgery a silk thread is sometimes placed in the lid to help close it. When lid closure is adequate this is easily removed.
In some cases of long standing paralysis, it may be necessary to insert a closing spring into the eyelid or perform some other procedure to help the eyelid close.
TREATMENT OF FACIAL NERVE DISORDERS
Medical treatment is instituted to decrease the swelling. This treatment may be continued until the nerve shows signs of recovery
Decompression of the facial nerve. Surgical decompression of the facial nerve is indicated in cases of paralysis when the electrical test show that the nerve function has significantly deteriorated. This operation is performed under general anesthesia and requires hospitalization for from 2 to 7 days. The rigid bone around the swollen nerve is removed, relieving pressure so that the circulation may be restored.
The degree and rapidity of recovery of facial nerve function depends upon the amount of damage present in the nerve at the time of surgery. Recovery may take from 3 to 12 months and may not be complete. Fortunately, it is unusual to develop a hearing impairment following surgery but this depends on the extent of surgery needed in the individual case.
Facial nerve graft. A facial nerve graft is necessary at times if facial nerve damage is extensive. A skin sensation nerve is removed from the neck and transplanted into the ear bone to replace the diseased portion of the facial nerve. Total paralysis will be present until the nerve re-grows through the graft. This usually takes 6 to 15 months. Some facial weakness is permanent.
TYPES OF FACIAL NERVE SURGERY
Middle Fossa Approach
An incision is made above the ear and the brain with its dense covering is elevated. Bone over the facial nerve can be removed to allow decompression or inspection. This allows exposure of the nerve in the internal auditory canal, at the geniculate ganglion and into the middle ear.
Through an incision behind the ear, bone over the facial nerve can be removed as it passes across the middle ear and mastoid.
Hypoglossal-Facial Nerve Anastomosis
When it is not possible for a facial nerve connection by other means, the nerve to the muscles of one side of the tongue is connected to the facial nerve. This hypoglossal-facial nerve anastomosis is usually performed 9 to 12 months after the tumor removal.
Surgery is performed under general anesthesia. The previous incision behind the ear is opened and extended into the neck. The nerve to the tongue (hypoglossal nerve) is cut, either partially or completely, and then connected to the facial nerve.
In 6 to 12 months, when the tongue nerve grows into the facial nerve, a variable degree of facial motion returns. Facial appearance may be nearly normal at rest. There will be some persistent weakness of the face. On moving the face, all of the muscles tend to contract at once, and some face motion may occur when speaking.
Weakness and wasting of one half of the tongue develops following cutting of the hypoglossal nerve. This results in some difficulty in speaking, chewing and swallowing. Although the tongue weakness is permanent, it is rare for a severe disability to persist.
Botlinum Toxin Injection for Treatment of Synkinesis
Patients with synkinesis may lack the ability to independently move different segments of the face. They typically complain of involuntary eyelid closure with common movements of the mouth such as puckering, eating, or smiling. Excessive closure of the eye may, in addition to the obvious cosmetic deformity, result in visual impairment. Synkinesis may also occur on the lower portion of the face where tightness or inappropriate muscle contraction occurs with common facial movements. Mass movement on the affected side of the face is most commonly seen several months after the onset of the severe facial paralysis. This occurs as a result of the misdirected nerve fibers re-innervating the wrong facial muscles.
Botulinum toxin can be used to alleviate synkinesis muscle movements that occur as a result of facial paralysis. Small doses of botulinum toxin are injected into the affected muscle group. In addition to synkinesis, these injections may also be used for benign essential blepharospasm and hemifacial spasm. The injection typically lasts three to four months in controlling the synkinesis. Repeat injections are required to sustain benefit over long periods of time.
Facial Reanimation Surgery
In some patients, additional techniques are used to achieve facial symmetry and movement, usually in patients with long-standing facial paralysis. These methods can also be used in combination with a facial nerve graft or hypoglossal-facial anastomosis. These procedures are not considered cosmetic, as the facial paralysis is a functional deficit.
Common problems encountered with the paralyzed eye include: failure to close, brow droop, and laxity of the lower lid. In some patients, the eye has been sewn shut (tarsorrhaphy) to protect it. It is now possible to open the tarsorrhaphy and place a spring in the upper lid to enable it to close voluntarily. Brow droop can also be corrected by a brow lift and several procedures are available to tighten the lower lid. Eye surgery is usually done by an ophthalmologist, who is part of the facial disorders team.
A crooked smile, which results from drooping of the corner of the mouth, troubles many patients with facial paralysis. Besides the obvious disfigurement, it can cause difficulties with eating and talking.
The temporalis muscle, a chewing muscle not innervated by the facial nerve, can be sewn into the corner of the mouth. This usually gives symmetry at rest and allows the patient to voluntarily smile by clenching his teeth. The incisions are usually in the hair above the ear and at the corner of the mouth. Immediately after surgery, the corner of the mouth is pulled up very high. This is the over-correction factor that is needed to counter the effects of gravity. Within 6 weeks, most patients develop a balanced smile and are able to move the corner of the mouth. Practice is required to achieve the best results.
RISKS AND COMPLICATIONS OF FACIAL NERVE SURGERY
All patients notice some hearing impairment in the operated ear immediately following surgery. This is due to swelling and fluid collection in the mastoid and middle ear. This swelling usually subsides within 2 to 4 weeks and the hearing returns to its preoperative level. In an occasional case, scar tissue forms and results in a permanent hearing impairment. It is rare to develop a severe impairment.
Dizziness is common immediately following surgery due to swelling in the mastoid and irritation of the inner ear structures. Some unsteadiness may persist for a few days postoperatively. On rare occasions, dizziness is prolonged.
Related to Middle Fossa Approach
The middle fossa approach to the facial nerve, absolutely necessary in some cases, is a more serious operation.
Hearing and balance disturbances are more likely following this surgery. Permanent impairment is, nonetheless, uncommon.
A hematoma (collection of blood under the skin incision) develops in a small percentage of cases, prolonging hospitalization and healing. Re-operation to remove the clot may be necessary if this complication occurs.
A cerebral spinal fluid leak (leak of fluids surrounding the brain) develops in an occasional case. Re-operation may be necessary to stop the leak.
Infection is a rare occurrence following facial nerve surgery. Should it develop, however, after a middle fossa approach, it could lead to meningitis, an infection in the fluid surrounding the brain. Fortunately, this complication is very rare.
Temporary paralysis of half the body has occurred following a middle fossa operation, due to brain swelling. This complication is, however, extremely rare.
Complications Related to Hypoglossal-Facial Anastomosis
A hematoma (collection of blood under the skin incision) develops in a small percentage of cases, prolonging hospitalization and healing. Re-operation to remove the clot may be necessary of this complication occurs.
Infection is a rare occurrence following hypoglossal-facial anastomosis.
Complications Related to Botlinum Toxin Injection
“Botulinum toxin is a safe therapy when administered in the appropriate dosage by experienced physicians. Side effects are generally transitory, well tolerated and amenable to treatment. Persisting complications are distinctly rare and serious side effects are uncommon.” – NIH Consensus Statement 1990.
The most common side effect from botulinum toxin injection for facial synkinesis is worsening of the facial paralysis. This is usually temporary with symptoms resolving over the course of several weeks. Dry eye complications may occur when used around the eye. Eye care, as described earlier, is usually prescribed.
Complications Related to Facial Reanimation Surgery
Eye: Risks and complications can occur after eye surgery and should be discussed with the ophthalmologist.
Mouth: Infection at the incision sites may occur and can usually be treated with antibiotics. Readmission to the hospital and re-operation is rarely required.
A hematoma (collection of blood under the skin incisions) develops in a small percentage of patients. Re-operation to remove the blood clot is rarely needed.
Temporalis muscle retraction occurs in some patients with weak facial tissues. The sutures between the muscle and the weakened tissue cannot hold adequately and the temporalis muscle retracts into the cheek. Re-operation is needed to reattach the temporalis muscle to the mouth tissues. Usually, scar tissue from the first operation provides adequate anchoring of the temporalis muscle for reattachment.
Fullness over the cheekbone occurs in all patients. This results from the temporalis muscle as it passes to the mouth. While this is noticeable, rarely is it objectional.
Further revision surgery is required in some patients. Because of individual variability, it is impossible to predict healing results exactly. To achieve the desired results, minor touch-up or fine tuning surgery may be required after complete healing has occurred.
No reanimation operation can achieve “normal” facial movement – the patient can never be made exactly as he was before the paralysis. The aim of this surgery is to achieve the best possible facial function and improved appearance. Unfortunately, restoration of entirely “normal” facial function is still beyond our ability today. With continued research, we hope to continue to improve our results of the treatment of facial paralysis.
During the period of recovery of facial function, exercise may be recommended. Exercising the muscles by wrinkling the forehead, closing the eyes tightly, and smiling forcefully may be beneficial.
We do not usually recommend electrical stimulation of the facial muscles.
In some patients with stable partial facial movement, it is possible to improve their function with facial retraining. This is a form of physical therapy that involves mirror exercises. It allows the patient to make the best use of the facial function that the patient possesses. Generally, it is not recommended until approximately one year after the onset of the paralysis.