The facial nerve is the seventh of 12 nerves that exit directly through openings in the skull. These are known as cranial nerves. The facial nerve has several functions. It supplies motor impulses to the muscles of facial expression, allows the tongue to detect tastes and supplies the glands in the mouth. When the facial nerve is damaged, any or all of these functions can be impacted.
Fractures
When the bones of the skull are fractured by trauma, nerve damage can result. Fractures of the temporal bone are specifically prone to cause facial nerve damage. This is because the facial nerve travels through a series of openings in the temporal bone on its way to its exit near the base of the skull, through an opening called the stylomastoid foramen.
Tumors
Tumors in the skull can put pressure on the facial nerve, causing damage. A vestibular schwannoma is a tumor that develops from an overgrowth of Schwann cells in the inner ear.
Vestibular schwannomas are benign, but they can still cause problems such as deafness and loss of balance. They can also damage the facial nerve, since the facial nerve passes through the internal auditory canal in the inner ear on its way through the temporal bone. The department of neurosurgery at the International Neuroscience Institute in Hannover, German has noted that surgeries to preserve facial nerve function following the removal of a schwannoma are becoming increasingly effective.
Infectious Diseases
Certain diseases are particularly prone to affect the nervous system. After the initial outbreak of herpes, the herpes simplex virus remains dormant in the nerve bundles for the rest of an individual's life. It can reawaken and travel down the nerves, causing pain and muscle dysfunction, and has been reported to cause cases of facial neuralgia, or facial nerve pain.
The National Institutes of Health lists Lyme disease and HIV as other causes of facial nerve damage, specifically in cases of facial nerve palsy, which can manifest as facial paralysis or drooping, difficulty eating and taste impairment.
Sarcoidosis
Sarcoidosis is a disease whose cause remains unknown. It is characterized by inflammation of the lymph nodes, lungs, liver, eyes, skin, or other tissues, according to the National Institutes of Health. Facial nerve palsy has been observed in patients with sarcoidosis. The diagnosis is of this disease is sometimes made through nerve biopsies, which may reveal abnormal clusters of immune cells called granulomas.
References
- University of Michigan Medical School: Cranial Nerves : Facial Nerve
- PubMed: Surgical Treatment of Facial Nerve Paralysis in Fractures of the Temporal Bone
- PubMed: Using an End-to-side Interposed Sural Nerve Graft for Facial Nerve Reinforcement After Vestibular Schwannoma Resection Department of Neurosurgery, International Neuroscience Institute, Hannover, German
- Medline: Facial Nerve Palsy
- PubMed: Facial Neuralgia Associated with Recurrent Herpes Simplex
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