Functions of Facial Nerve

The facial nerve resembles a telephone cable and contains 7000 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." When half or more of the individual nerve fibers that make up the facial nerve are inter-rupted, facial weakness is noted. If these nerve fibers are irritated, abnormal movements of the facial muscles appear as spasms or twitching of the face. The facial nerve not only carries nerve impulses to the muscles of the face, but also carries nerve impul-ses to the tear glands, to the saliva glands, to the mus-cle of a small bone in the middle ear (the stapes), and transmits taste fibers from the front of the tongue. Since the function of the facial nerve is so complex, many symptoms may occur when the fibers of the fa-cial nerve are disrupted. A disorder of the facial nerve may result in twitching, weakness, or paralysis of the face, in dryness of the eye or the mouth, or in disturbance of taste. An otolaryngology-head and neck surgeon is called upon to manage facial nerve problems be-cause of the close association of this nerve with the ear structures (Figure 1). After leaving the brain the facial nerve enters the temporal bone (ear bone) through a small bony tube (the internal auditory ca-nal) 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 inner middle ear bones, a sack of the eardrum, and then through the mastoid (the bony area behind the part of the ear which is visible). After the facial nerve leaves the mastoid it divides again into many branches which supply the various facial muscles. The facial nerve gives off many branches as it courses through the temporal bone: to the tear gland, to the stapes mus-cle, to the tongue, and, to the saliva glands.

Diagnosis, Prognosis and Treatment of Facial Nerve Disorders

The three questions most often asked by the pa-tient with a problem in facial nerve function are:

• What is the cause? (diagnosis),
• When can I ex-pect recovery? (prognosis)
• What can be done to bring about recovery at the earliest possible moment? (treatment). In order to answer these three questions the otolaryngology-head and neck surgeon must perform an extensive evaluation of each patient to determine the cause of the disorder and to attempt to localize the area of the facial nerve which is involved as well so that the best treatment can be prescribed.

Diagnosis

The most common cause of facial weakness which comes on suddenly is referred to as "Bell's palsy." This disorder is thought to be due to the body's re-sponse to a particular virus; in reaction to the virus the facial nerve within the ear bone swells and this pressure on the nerve in the bony canal damages it. In order to be sure that this is the cause of the facial weakness and that it is not due to some rare cause or other disease, a special set of questions will be asked. The patient will be examined and a series of tests may be performed. The most common tests are:

• Hearing Test: Tests of hearing are done to determine if the damage to the nerve has involved the delicate hearing mechanism.
• Balance Test: Balance tests may be needed to deter-mine if the balance nerve is involved.
• Test Test: A test of the eye's ability to produce tears may help the physician to determine the location and severity of facial nerve disease.
• Taste Test: A test of taste may be beneficial in localiz-ing the area of the facial nerve which is affected.
• Salivation Test:A test to measure the flow of saliva may be administered; this test may help to predict the location and severity of facial nerve involvement
• X-RaysX-rays may be obtained to determine if there is infection, tumor, bone fracture, or other abnormality in the area where the facial nerve lies.
• Electrical Test:he facial nerve is stimulated in some cases to determine the severity of involvement. This test may have to be repeated daily to detect pro-gression of disease.

Prognosis

After the evaluation has been completed, the most likely cause of facial nerve disorder may become clear and the second question, "When can I expect recovery to begin" can be answered. This will be dis-cussed by your physician.

Treatment

Not all facial nerve problem require specfic treatment. Many will recover spontaneously.