Anatomy of the Vestibulocochlear Nerve

The vestibulocochlear nerve is located in the internal auditory meatus (internal auditory canal). The nerve is responsible for equilibrium and hearing. Conditions of the vestibulocochlear nerve include vestibular neuritis, labyrinthitis, and acoustic neuroma. 

Anatomy

The vestibulocochlear is made up of two nerves—the cochlear nerve, which is responsible for hearing, and the vestibular nerve, which is responsible for balance. As one of the 12 cranial nerves, it runs between the pons (the middle of the brainstem) and the medulla oblongata (the lower part of the brainstem).

The vestibular part of the nerve then travels from the inner ear in a group of nerve cells called the vestibular ganglion. The cochlear part of the nerve travels from the cochlea in the inner ear in the spiral ganglion. 

Function

The function of the vestibulocochlear nerve is purely sensory. It has no motor function. It communicate ssound and equilibrium information from the inner ear to the brain.

The cochlea, the part of the inner ear where the cochlear part of the nerve originates, detects soundwaves. These then travel from the spiral ganglion to the brain.

The vestibular apparatus, where the vestibular part of the nerve originates, detects changes in the head’s position based on gravity. Then the position of the head communicates information about balance to the brain.

Associated Conditions

Conditions of the vestibulocochlear nerve can affect balance and hearing. An otologist or neurotologist commonly work with disorders associated with the vestibulocochlear nerve.

Vestibular Neuritis and Labyrinthitis

Vestibular neuritis is a disorder of the inner ear that affects the vestibular part of the vestibulocochlear nerve, which is responsible for equilibrium. When this part of the nerve swells, it interferes with information it would normally send to the brain about balance. 

Labyrinthitis is a closely related condition to vestibular neuritis that impacts both the vestibular and cochlear parts of the nerve. The onset of both conditions is often sudden.

Symptoms of vestibular neuritis and labyrinthitis can include:

• Sudden-onset, severe vertigo
• Dizziness 
• Imbalance
• Nausea and vomiting
• Difficulty concentrating
• Tinnitus (labyrinthitis only)
• Hearing loss (labyrinthitis only) 

Symptoms generally resolve after a couple of days. Some people experience dizziness and balance problems for several months. These disorders may be caused by a viral or bacterial infection. 

Diagnosis for vestibular neuritis and labyrinthitis can be made by an otologist or a neurotologist. Your healthcare provider may refer you to an audiologist for hearing and balance tests. If symptoms persist longer than a few weeks, your healthcare provider may order magnetic resonance imaging (MRI) to rule out other conditions.

Acoustic Neuroma

Acoustic neuroma is a noncancerous tumor that grows on the vestibulocochlear nerve. Tumors may grow on one or both nerves, with unilateral acoustic neuromas (those affecting one ear) being more common.

People who have had neck or face radiation or who have neurofibromatosis type 2 (NF2) are at higher risk for developing an acoustic neuroma. 

Symptoms of acoustic neuroma include:

• One-sided hearing loss
• Headaches
• Clumsiness and confusion
• A feeling of fullness in the ear
• Tinnitus
• Dizziness and balance problems
• Facial numbness

Diagnosis of acoustic neuroma may include hearing tests, brainstem auditory evoked response (BAER), and MRI.

Rehabilitation

Treatment for conditions of the vestibulocochlear nerve usually involves managing symptoms until they resolve. Sometimes further intervention, like medication or surgery is required.

Vestibular neuritis and labyrinthitis are managed with medication to manage nausea and dizziness. These medications should not be taken for more than several days.

If a virus is suspected, antiviral medications may also be prescribed. Sometimes steroids are also used, although the benefits of steroids are not conclusive.

Balance rehabilitation may be recommended if symptoms persist for more than a few weeks. Rehabilitation consists of body posture balance, and vision and head-turn exercises. Most people with vestibular neuritis and labyrinthitis fully recover.

Treatment of acoustic neuroma depends on the size of the tumor and a person’s general health. Treatment options include watchful waiting, surgery, and radiation.

Surgical removal is done via craniotomy, surgical removal of part of the skull to access the brain. “Keyhole” craniotomy is the less invasive surgery option. In a keyhole craniotomy, a surgeon makes a small incision behind the ear in order to access the affected nerve.

Translabyrinthine craniotomy is a more invasive surgery that may be chosen for larger tumors and if hearing is already compromised. A surgeon makes an incision in the scalp behind the ear and removes the mastoid bone and a portion of the inner ear bone in order to access the tumor. This surgery results in complete hearing loss.

Post-treatment, people may benefit from hearing aids or cochlear implants. If facial nerves are damaged during surgery, plastic surgery may restore facial functioning.