FACIAL NERVE PROBLEMS
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. Facial nerve disorders are accompanied at times by a hearing impairment. This impairment may or may not be related to the facial nerve problem.
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 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 twitching, weakness or paralysis of the face, dryness of the eye or the 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 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.
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.
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 not 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.
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.
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 fibrous 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.
A nonmalignant fibroid growth may grow in the facial nerve itself, producing a gradually progressive facial nerve paralysis. Removal of this facial nerve neuroma requires severing the facial nerve. Usually it is possible to graft it at the time with a skin sensation nerve from the neck.
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 relieve 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.
Circulatory disturbances of the nervous system may cause facial nerve paralysis. The most common example of this is a stroke. A stroke usually has many other symptoms which indicate the cause of the problem. Treatment is managed by the internist, neurologist, or neurosurgeon.
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.
Treatment of facial paralysis may be either medical or surgical.
Medical treatment is instituted to decrease the swelling. This treatment may be continued until the nerve shows signs of recovery.
Surgical treatment is indicated in select patients. The type of surgery required depends on the reason for weakness and duration of symptoms. Surgery may be used in order to treat the underlying reason for the weakness or to rehabilitate the paralyzed face and eye.