OVERVIEW

What does the facial nerve mean?

The facial nerve is a mixed nerve that primarily controls the movement of facial expression muscles. It secondarily transmits taste sensations and regulates the secretion of salivary and lacrimal glands. It is also responsible for conveying skin sensations from areas such as the inner and external ear canals.

• The motor fibers of the facial nerve originate from the facial nerve nucleus, accompany the vestibulocochlear nerve into the internal auditory canal, descend through the facial nerve canal, pass over the geniculate ganglion at the bend of the facial nerve, and branch into the stapedius nerve and chorda tympani. Finally, they exit the skull through the stylomastoid foramen, traverse the parotid gland, and innervate all facial expression muscles (except the masticatory muscles and levator palpebrae superioris), as well as the auricular muscles, occipitalis, platysma, and stapedius muscle.

• The sensory fibers of the facial nerve are divided into taste fibers and general somatic sensory fibers. The peripheral processes of the taste fibers branch from the geniculate ganglion, leave the facial nerve within the facial canal to form the chorda tympani, join the lingual nerve, and terminate in the taste buds of the anterior two-thirds of the tongue, transmitting taste sensations from this region. The central processes enter the pons lateral to the motor branch and terminate in the solitary nucleus along with the taste fibers of the glossopharyngeal nerve.

• The parasympathetic fibers of the facial nerve arise from the superior salivatory nucleus in the pons, travel via the intermediate nerve → chorda tympani → lingual nerve to the submandibular ganglion. The postganglionic fibers regulate the secretion of the sublingual and submandibular glands. Fibers responsible for lacrimal gland secretion join the greater petrosal nerve via the intermediate nerve, reach the pterygopalatine ganglion, and the postganglionic fibers innervate the lacrimal gland.

What disorders are associated with facial nerve dysfunction?

Facial nerve dysfunction includes Bell's palsy, facial spasm, facial neuritis, and other facial nerve disorders.

Domestic textbooks often equate Bell's palsy with facial neuritis, but Bell's palsy has multiple possible causes, and facial neuritis is merely the most common etiology of facial paralysis.

SYMPTOMS

What are the characteristics of facial nerve dysfunction?

Since the facial nerve is involved, symptoms mostly affect areas innervated by it, such as:

• Facial paralysis: Inability to frown, incomplete or absent eye closure, flattened nasolabial fold, drooping mouth corner, mouth deviation when grinning, air leakage when puffing cheeks or blowing, and buccinator muscle paralysis.
• Loss of taste.
• Hearing abnormalities.
• Facial muscle spasms: Involuntary twitching on one side of the face under fatigue or stress, resembling "grimacing."

In most cases, unilateral facial nerve involvement leads to asymmetrical symptoms on both sides of the face.

CAUSES

What are the common causes of facial nerve dysfunction?

Facial nerve dysfunction has various causes, including infections, space-occupying compression, trauma, and congenital or genetic factors. Some cases have no identifiable cause, medically termed as "idiopathic."

• Infections: Otitis media, herpes simplex virus infection, varicella-zoster virus infection, HIV infection, etc., may trigger facial neuritis, leading to other facial nerve disorders.
• Compression: Tumors, tissue edema, hemangiomas, or adjacent blood vessels can compress the facial nerve, causing dysfunction.
• Trauma: Brain or facial injuries may damage the facial nerve, resulting in functional impairment.
• Congenital or genetic factors: Many facial nerve dysfunctions are inherited or congenital. Premature birth or birth trauma may also cause facial nerve damage in newborns.

DIAGNOSIS

What tests are needed for facial nerve dysfunction?

• Physical examination: A detailed and careful physical examination can help locate the site of the lesion.
• Electromyography (EMG): Electrodes are placed on the muscles or needle electrodes are used to assess muscle function. Needle electrodes may cause a stinging sensation, similar to an injection, but it is tolerable.
• Head imaging tests: If intracranial lesions are suspected as the cause of facial nerve dysfunction, imaging tests such as an MRI scan of the head may be required.

TREATMENT

Which department should I see for facial nerve dysfunction?

Neurology, Neurosurgery, Maxillofacial Surgery.

What are the treatment options for facial nerve dysfunction?

• Oral medication: Most facial nerve dysfunction is treated with medication. Corticosteroids are often the first choice for Bell's palsy, while carbamazepine and other antiepileptic drugs or sedatives like diazepam are commonly used for hemifacial spasm.
• Botulinum toxin injections: Mainly used to treat hemifacial spasm.
• Surgery: For space-occupying lesions causing facial nerve dysfunction, surgery can remove the lesion to relieve pressure on the facial nerve. For hemifacial spasm caused by adjacent blood vessel compression, surgery can separate the facial nerve and blood vessels under a microscope using special materials.

DIET & LIFESTYLE

See specific diseases for details.

PREVENTION

See specific diseases for details.