Acoustic Neuroma (Vestibular Schwannoma)

What an acoustic neuroma is

The vestibulocochlear nerve (the eighth cranial nerve) carries hearing and balance signals from the inner ear to the brainstem through a narrow bony channel, the internal auditory canal. A vestibular schwannoma grows from the Schwann cells that wrap the balance part of this nerve. As it grows, it presses on the hearing nerve, and if large, on the facial nerve, the trigeminal nerve (facial sensation), the cerebellum and the brainstem.

It is benign: it does not spread to other parts of the body. Most grow slowly, about 1 to 2 mm a year, and some never grow at all.

Symptoms

• Hearing loss in one ear: usually gradual over months to years, especially for high pitches and speech clarity. About 1 in 10 people have a sudden drop in hearing.
• Tinnitus in one ear: ringing, hissing or roaring.
• Unsteadiness: a vague imbalance rather than spinning, because the brain compensates for the slowly failing balance nerve. Some people have episodes of vertigo, which can be confused with Ménière's disease.
• Ear fullness or pressure.
• Facial numbness or tingling when the tumor is larger and presses on the trigeminal nerve.
• Facial weakness or twitching: uncommon before treatment.
• Headache, clumsiness and vision changes only with very large tumors that block fluid flow in the brain (hydrocephalus).

Any asymmetric hearing loss or tinnitus, meaning one ear worse than the other, should be investigated.

Causes and risk factors

Most acoustic neuromas occur sporadically, from a gene change (in the NF2 gene) in a single nerve cell, with no known cause. Risk factors include:

• NF2-related schwannomatosis (neurofibromatosis type 2): an inherited condition causing tumors on both hearing nerves, usually appearing in teens and young adults. See neurofibromatosis.
• Radiation to the head and neck in childhood.

The evidence linking mobile phone use to acoustic neuroma is inconsistent and has not established a causal link.

Diagnosis

1. Hearing test (audiogram): shows sensorineural hearing loss worse in one ear, often with poor word recognition out of proportion to the hearing loss.
2. MRI with gadolinium contrast: the gold standard. It shows the tumor and its size, even tumors of a few millimeters.
3. Balance testing: may show reduced function in the affected ear.
4. Auditory brainstem response (ABR): a hearing nerve test used when MRI is not possible.

Many tumors are now found early, or by chance on scans done for other reasons.

Treatment options

Treatment depends on tumor size, growth, hearing, age, health and personal preference. Specialist teams usually include a neurotologist and neurosurgeon.

Observation ("watch and scan")

Small tumors that are not causing major symptoms are often monitored with MRI after 6 to 12 months, then yearly, and less often if stable. A large proportion of small tumors do not grow for years. Hearing may still decline gradually.

Stereotactic radiosurgery

Highly focused radiation (such as Gamma Knife or CyberKnife) is aimed at the tumor in one or a few sessions without an incision. The goal is to stop growth rather than remove the tumor. It is used for small to medium tumors and in people who are older or not fit for surgery. Tumor control rates are high, though hearing may still decline over time.

Microsurgery

The tumor is removed through the skull by one of three approaches, depending on size and hearing:

• Retrosigmoid: behind the ear; can preserve hearing.
• Middle fossa: above the ear; for small tumors when hearing preservation is the goal.
• Translabyrinthine: through the inner ear; good facial nerve access but sacrifices hearing in that ear.

Surgery is preferred for large tumors pressing on the brainstem, or for younger people who want the tumor removed.

Risks of treatment

• hearing loss in the affected ear
• facial weakness, usually temporary but sometimes permanent
• imbalance in the weeks after surgery while the brain adjusts
• headache, cerebrospinal fluid leak, and rarely infection or stroke

Living with acoustic neuroma

• Hearing aids help if some hearing remains.
• CROS hearing aids or bone-conduction implants route sound from the deaf side to the good ear.
• Cochlear implants are an option for some people when the nerve is preserved.
• Vestibular rehabilitation (balance exercises) helps the brain compensate.
• Tinnitus management with sound therapy and counseling.
• Eye care: if facial weakness prevents full eye closure, lubricating drops and protection prevent corneal damage.

Outlook

Acoustic neuroma is not life-threatening in most people because it is benign and slow-growing. Long-term tumor control is excellent with both radiosurgery and surgery. The main lasting effects are hearing loss in the affected ear and, less often, facial weakness or imbalance.

Frequently asked questions

Is an acoustic neuroma cancer?

No. Acoustic neuromas are benign tumors that do not spread to other parts of the body. However, they can grow and press on nearby nerves and the brainstem, so they need monitoring or treatment depending on their size and growth.

What are the first symptoms of an acoustic neuroma?

The most common first symptoms are gradual hearing loss in one ear and ringing in that ear. Some people notice difficulty understanding speech on the phone on one side, or mild unsteadiness. Any one-sided hearing loss or tinnitus should be checked.

How is an acoustic neuroma diagnosed?

A hearing test shows one-sided nerve hearing loss, and an MRI scan with contrast confirms the tumor. MRI can detect tumors only a few millimeters across, so it is the standard test when hearing loss or tinnitus is asymmetric.

Does an acoustic neuroma always need surgery?

No. Many small tumors are monitored with regular MRI scans because they grow slowly or not at all. Growing tumors can be treated with focused radiation instead of surgery. Surgery is mainly used for larger tumors or when removal is preferred.

Can hearing be saved with acoustic neuroma?

Sometimes. Hearing is more likely to be preserved when the tumor is small and hearing is good at diagnosis. Some surgical approaches and radiosurgery aim to preserve hearing, but hearing often declines over the years regardless of treatment.