A Discussion of Facial Nerve Problems
A Discussion of Facial Nerve Problems
Spasm, 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, 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 from the brain 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.” The facial nerve 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 a 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 spasm, weakness or paralysis of the face, dryness of the eye or mouth, loss of taste and, occasionally, increased sensitivity to loud sound and 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 travels near the three middle ear bones, in back of the ear drum, 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. The facial nerve does not supply the muscle used in chewing.
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 felt to be due to a viral infection of the nerve or inflammation 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.
Herpes Zoster Oticus
A condition similar to Bell’s palsy is herpes zoster oticus or “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 or unsteadiness may remain.
Injuries of the Facial Nerve
The most common cause of facial nerve injury is due to a 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 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 a tumor.
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.
Acoustic Tumors: The most common tumor to involve the facial nerve is a nonmalignant tumor to the hearing and balance nerve called an acoustic neuroma (vestibular schwannoma). Although there is rarely any weakness of the face before surgery, tumor removal sometimes results in weakness or paralysis due to the close proximity of the facial nerve. 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. In that case, the face is totally paralyzed until the nerve is repaired and has had a chance to regrow. 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, connecting a tongue or shoulder nerve to the facial nerve.
Facial Nerve Neuroma: A nonmalignant growth may grow in the facial nerve itself, producing a gradually progressive facial nerve paralysis.
It may be necessary to severe or remove a portion of the facial nerve in order to remove a facial nerve neuroma. An attempt is made to sew the nerve ends together at the time of surgery or to insert a nerve graft. The nerve used in grafting is taken from a skin sensation nerve in the neck. Total paralysis will be present until the nerve regrows through the graft, usually a period of 6 to 24 months. At times, a nerve procedure is necessary later, connecting a tongue nerve to the facial nerve (hypoglassal-facial anastomosis). In all of these situations there will be some permanent facial weakness.
Removal of a facial nerve neuroma may necessitate removal of the inner ear structures. If this is necessary, it results in a total loss of hearing in the operated ear and temporary severe dizziness. Persistent unsteadiness is uncommon.
Acute or chronic middle ear or mastoid 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 cyst). Mastoid surgery is performed to eradicate the infection and relieve nerve pressure. Some permanent facial weakness may remain.
Tumors and 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, in brain diseases there are usually many other symptoms which indicate the cause of the problem. Treatment is managed by the neurotologist in conjunction with an internist, neurologist, or neurosurgeon.
Hemifacial spasm is an uncommon disease which results in spasmotic contractions of one side of the face. Extensive investigation is necessary at times to establish the diagnosis correctly. In some cases, a hemifacial spasm is caused by an irritation of the facial nerve by a blood vessel near the brain. Examination of the nerve and correction of the irritation, if present, is possible by a surgical approach.
DIAGNOSIS OF FACIAL NERVE DISORDERS
An extensive evaluation is often 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. Facial nerve disorders are accompanied at times by a hearing impairment. When the face is totally paralyzed, a special hearing test (stapedius reflex) helps to localize the problem area.
ABR (auditory Brainstem response) testing is a sophisticated computerized hearing test which evaluates the neural pathways of hearing through the Brainstem. These are pathways closely related to those of facial function. Abnormalities here help to further define the nature of the facial nerve disorder.
Hearing is measured in decibels (dB). A hearing level of 0 to 25 dB is considered serviceable hearing for conversational purposes.
Special testing of the balance portion of the inner ear may be necessary in some cases to clarify the cause or location of the facial nerve disorder. Conventional balance testing involves measuring the eye movements relative to stimulation of the ear in a test called electronystagmography (ENG).
MRI (magnetic resonance imaging) and CT (computer tomography) are both head scans highly capable of determining if the facial nerve disorder is due to tumor, infection, bone fracture or vascular conditions such as stroke. In some cases, it may be necessary to obtain special x-ray studies of the blood vessels (angiography) in the area of the brain or ear.
Nerve Stimulation Tests
Facial nerve stimulation or nerve excitability tests help to determine the magnitude of nerve fiber damage in cases of facial paralysis. It is an estimation of the health of the nerve and may be useful in helping to predict ultimate functional recovery of the paralysis. Despite the presence of obvious facial paralysis, these tests are capable of indicting the degree of damage which is occurring. These tests may be repeated regularly, perhaps daily; so as to detect any change, for better or worse, in the overall process of paralysis.
Nerve excitability testing includes maximum stimulation tests (MST) and the more sophisticated electroneurongraphy (ENOG) or evoked electromyography (EEMG).
In cases of long-standing facial paralysis, an EMG (electromygraph) may be requested. This test helps determine the status of nerve and facial muscles in the recovery process.
Treatment of facial nerve weakness or paralysis may be supportive, medical, eye care, surgical, or a combination of all four.
Medical treatment is instituted to decrease the swelling. It often involves the use of steroids. This treatment may be continued until the nerve shows sign of recovery.
The most serious complications that may develop as the result of total facial nerve paralysis are 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. Contact lenses should
not be worn in this situation. The advice of your eye doctor should be sought.
If the eye is dry, you may be advised to use eye drops. The drops should be used as often as necessary to keep the eye moist. Ointment may be prescribed for use at bedtime.
The best protection for night/sleep hours is to place a clear eye guard over the eye. This can be secured in place with tape. Eye care must be compulsive! Any eye problems or irritation which does not quickly pass should warrant consultation with your eye doctor as soon as possible.
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 easily removed.
In some cases of long-standing paralysis, it may be necessary to insert a weight into the eyelid to close the eye or perform some other procedure to help the eyelid close (i.e. tarsorrhaphy).
Surgical treatment for facial paralysis is very controversial. Surgery to decompress the swelling facial nerve is indicated in very special and well defined circumstances. Surgical facial nerve treatment is not applicable to everyone.
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 18 months and may not ever 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.
Mastoid decompression of the facial nerve. Surgical decompression of the facial nerve is indicated in cases of paralysis when the electrical tests show that the nerve function is deteriorating or a fracture is present. This operation is performed under general anesthesia and requires hospitalization for 1 to 2 days. Through an incision behind the ear the mastoid bone around the nerve is removed, allowing repair of a nerve or relieving pressure so that the circulation may be restored.
Middle fossa facial nerve decompression. This procedure involves making an incision above the ear, and making a small opening in the skull. This procedure allows pressure to be relieved from the nerve or repair of a nerve, if injured.
Retrosigmoid facial nerve decompression. In certain conditions such a hemifacial spasm or facial nerve tumors, the facial nerve may need to be investigated where it enters the brain. This is performed through an incision behind the ear and removal of either the mastoid bone or a portion of the skull just behind the mastoid. This exposes the area between the brain and the inner ear to allow appropriate treatment.
Translabyrinthine facial nerve decompression and repair. In certain situations, the hearing and balance function of the inner ear is destroyed by the same process causing the facial paralysis. Usually this is trauma or a tumor. In this instance, the inner ear structures for balance and hearing may be removed to give greater access to repair the facial nerve.
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 regrows through the graft. This usually takes 6 to 15 months. Some facial weakness is permanent.
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. Usually, this occurs when the facial nerve is severed during tumor surgery or trauma and may be performed immediately or up to several years after the injury. 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 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.
RISKS AND COMPLICATIONS OF FACIAL NERVE SURGERY
The surgeon carefully weighs the risks and complications of each procedure for the individual patient. Surgery is not recommended unless the benefits derived from surgery to optimize the return of facial nerve function far outweigh the risks and complications of surgery. Patients are required to carefully study the risks and complications of surgery so they may make a thoughtful, informed consent if surgery is decided upon by the patient and the surgeon. Patient questions are encouraged so the patient has a clear understanding of the facial nerve problem and the options available for management.
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 2-4 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, unless a translabyrinthine approach was utilized.
Dizziness is common immediately following surgery due to swelling in the mastoid and unsteadiness may persist for a few days postoperatively. On rare occasions dizziness is prolonged.
A hematoma (collection of blood under the skin incision) develops in a small percentage of cases, prolonging hospitalization and healing. Re-operation may be necessary to remove the blood.
A cerebral spinal fluid leak (leak of fluid 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 an intracranial procedure, it could lead to meningitis (infection in the fluid surrounding the brain). Fortunately, this complication is very rare.
Brain injury or stroke, which may lead to paralysis or other neurologic disability, has occurred following intracranial operations for facial nerve repair. This complication is, however, extremely rare.
Related to Intracranial Surgery
The middle fossa, retrolabyrinthine/retrosigmoid, and translabyrinthine approaches to the facial nerve, absolutely necessary in some cases, are more serious operations. Hearing and balance disturbances are more likely following this surgery.
Related to Anesthesia
Operations on the facial nerve usually are performed under general anesthesia. There are risks involved with any anesthesia and you may discuss this with the anesthesiologist if desired.
During the period of recovery of facial function, exercises may be recommended. Exercising the muscles by wrinkling the forehead, closing the eyes tightly, and smiling forcefully may be beneficial.
Electrical stimulation of the facial muscles is usually not recommended. Electromyographic biofeedback may be used during rehabilitation of the facial nerve injury to educate and instruct patients in facial muscle contraction.
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