Disorders of the Facial Nerve
Disorders of the facial nerve can occur in men, women, and children, but they are more prominent among men and women over 40 years of age, people with diabetes, upper respiratory ailments, weak immune systems, or pregnant women. Cases of facial paralysis can be permanent or temporary, but in all circumstances there are treatments designed to improve facial function.
The facial nerve resembles a telephone cable and contains 7,000 individual nerve fibers. Each fiber carries electrical impulses to a specific facial muscle. Information passing along the fibers of this nerve allows us to laugh, cry, smile, or frown, hence the name, “the nerve of facial expression.”
When half or more of these individual nerve fibers are interrupted, facial weakness occurs. If these nerve fibers are irritated, then movements of the facial muscles appear as spasms or twitching. The facial nerve not only carries nerve impulses to the muscles of the face, but also to the tear glands, to the saliva glands, and to the muscle of the stirrup bone in the middle ear (the stapes). It also transmits taste from the front of the tongue.
The facial nerve passes through the base of the skull in transit from the brain to the muscles that control facial expressions. After leaving the brain, the facial nerve enters the temporal bone through the internal auditory canal, a small bony tube, in very close association with the hearing and balance nerves. Along its inch-and-a-half course through a small canal within the temporal bone, the facial nerve winds around the three middle ear bones, in back of the eardrum, and then through the mastoid (the bony area behind the part of the ear that is visible).
Causes
Infections, injuries, or tumors can cause facial nerve disorders, but the most common cause of facial weakness is Bell’s palsy. This disorder, which often comes on suddenly and reaches its peak within 48 hours, is probably due to the body’s response to a virus. When there is a virus, the facial nerve within the ear (temporal bone) swells, and this pressure on the nerve in the bony canal damages it.
Evaluation and Treatment
A variety of diagnostic tests are used to determine the cause of facial nerve dysfunction. These include audiologic and balance tests, CTs and MRI imaging, and electrodiagnostic tests of the facial nerve. Depending on the cause of facial nerve dysfunction a variety of medical and surgical options are available to eliminate the source of damage and restore function.