Acoustic Neuroma

What is an acoustic neuroma?

An acoustic neuroma, also called a vestibular schwannoma, is a tumor that grows from the nerves responsible for balance and hearing. It is a slow growing tumor that arises from the Schwann cells forming the covering of the vestibulocochlear nerve. As the tumor grows, it expands from its origin inside the internal auditory cana out into the space between the brainstem and the bone known as the cerebellopontine angle. The pear-shaped tumor can continue to get bigger which causes it to compress the trigeminal nerve that is responsible for facial sensations. Eventually, the tumor can compress the brainstem. Acoustic neuromas are classified according to their size as small (less than 1.5 cm), medium (1.5 to 2.5 cm), or large (more than 2.5 cm).

What causes acoustic neuromas?

The cause of acoustic neuromas is largely unknown. No environmental factor (such as cell phones or diet) has been scientifically proven to cause these tumors. Acoustic neuromas can be sporadic or caused by an inherited condition called neurofibromatosis type 2 (NF-2). Sporadic tumors occur 95% of the time, while 5% of acoustic neuromas occur with NF-2.

Neurofibromatosis is a rare disease that occurs in two forms. Type 1 causes tumors to grow on nerves throughout the body, especially the skin. Type 2 can cause acoustic neuromas on both the left and right sides, creating the possibility of complete deafness if the tumors grow unchecked. The presence of bilateral acoustic tumors affects the choice of treatment, as hearing preservation is a prime objective.

What are the symptoms?

Acoustic neuroma symptoms follow the size and growth of the tumor. The most common first symptom is hearing loss in the affected ear, which often goes unrecognized or is mistaken for a normal change of aging. Small tumors, which are typically limited to the bony canal, cause hearing loss in one ear, tinnitus (ringing in the ears), and unsteadiness or dizziness. As the tumor expands, hearing loss may worsen facial weakness may occur, and balance problems may occur. Large tumors can compress the brainstem and the trigeminal nerve. As brainstem compression becomes severe, the fourth ventricle collapses and hydrocephalus results, causing persistent headache and visual problems.

Diagnosing acoustic neuroma tumors:

The doctor will ask about your personal and family medical history and will perform a complete physical examination. In addition to checking your general health, the doctor will perform a neurological exam. This will include checks for mental status and memory, cranial nerve function (sight, hearing, smell, tongue and facial movement), muscle strength, coordination, reflexes, and response to pain. Diagnostic tests may include:

Audiogram
Electronystagmography (ENG)
MRI
Computed Tomography (CT)
Auditory Brainstem Response (ABR)

What treatments are available?

The treatment that is right for you will depend on your age, general health, hearing status, and the tumor size. The larger the tumor, the more complex the treatment. Therefore, early recognition, diagnosis and treatment are essential. Because patients and acoustic neuromas differ, it is important to seek treatment at a medical center that offers the full range of options, including surgery, radiosurgery, and hearing or facial rehabilitation. A neurosurgeon, otologic surgeon, and radiation oncologist work as a team to treat acoustic neuromas. Treatment options may include:

Observation (“watch and wait”): Acoustic neuromas that are small and have few symptoms may be observed with MRI scans every year until tumor growth or symptoms change. The average acoustic neuroma growth rate is 0.66 to 1.5mm per year. In 40% to 50% of observed patients, tumor growth or progression of symptoms will prompt the need for surgery or radiosurgery. Observation may be the best option for older patients with other health conditions or patients with a tumor in their only hearing ear.
Acoustic neuroma surgery: Surgical removal is a common treatment for acoustic neuromas, especially large ones. Priorities in surgery are: first, the maintenance of facial nerve function; second, the preservation of socially useful hearing in the affected ear; and third, complete tumor removal. While total tumor removal may result in a cure, it also carries a higher risk of hearing and facial nerve damage. During tumor removal, a probe is used to stimulate and monitor the nerves and brainstem function. Because acoustic tumors grow slowly, small remnants of tumor capsule may be left attached to critical nerves. Partial removal may be advocated to reduce the chances of facial nerve damage. If the tumor remnant grows, radiosurgery may be used.

Complications of surgery may include facial weakness or paralysis, cerebrospinal fluid leak, persistent headache, meningitis, and stroke. Tumor recurrence is less than 5% after surgical removal.

Stereotactic Radiosurgery: The goal of radiosurgery is to stop or control tumor growth. It does not remove the tumor. Radiation is used to treat small and medium-sized acoustic neuromas (<2.5 cm). Using highly focused radiation beams, radiosurgery works by damaging the DNA inside cells and making them unable to divide and reproduce. The aim of radiation therapy is to maximize the dose to abnormal cells and minimize exposure to normal cells. The benefits of radiation are not immediate but occur over time. Gradually, the tumor stops growing and may shrink in size. Periodic MRI scans are necessary to monitor for tumor changes.

A stereotactic frame or mask is attached to the patient’s head to precisely localize the tumor on an MRI scan and to hold the head perfectly still during treatment. Highly focused beans of radiation are approximately one hour.

Complications after radiation may include hearing loss, facial weakness, facial sensory loss, radiation necrosis, and brainstem injury. There is also a slight risk of radiation-induced malignant tumors year after treatment. Radiation can cause scar tissue to develop around the tumor and facial nerve, making surgical removal more difficult should the tumor grow back.

Clinical trials: these are research studies in which new treatments — drugs, diagnostics, procedures, and other therapies — are tested in people to see if they are safe and effective. Research is always being conducted to improve the standard of medical care. Information about current clinical trials, including eligibility, protocol, and locations, are found on the web. Studies can be sponsored by the National Institutes of Health (see clinicaltrials.gov) as well as private industry and pharmaceutical companies (see centerwatch.com).

Recovery and prevention

Coping with the possibility of hearing loss and facial paralysis and deciding which treatment is best for you can be difficult. The Acoustic Neuroma Association collects and publishes outcomes data from member surveys on their website.

Hearing preservation is an important goal for patients with an acoustic neuroma, although it is not always possible. All treatment options carry a risk of hearing loss. The Gardner-Roberson Scale is used to measure useful hearing (1=good, 2=serviceable). Hearing loss in one ear affects your ability to tell where a sound is coming from. An audiologist or speech therapist can help you learn tips for coping with one-sided deafness. Certain types of hearing aids called CROS (Contralateral Routing of Sound) and BAHA (Bone-Anchored Hearing Aid) may be helpful. These hearing aids take sound that would normally enter the non-hearing ear and route the signal to the hearing ear.

Patients with NF-2 can develop bilateral acoustic neuromas, and many may eventually lose hearing in both ears. All NF-2 patients with bilateral acoustic neuromas should learn sign language before deafness occurs. An auditory brainstem implant (ABI) can be inserted during surgery to provide a sensation of hearing by bypassing the cochlea and directly stimulating the brainstem. The device doesn’t enable full range of hearing, but it does provide increased noise awareness. Most patients can hear noises, such as a ringing telephone, but the degree of hearing usefulness can vary greatly. An auditory brainstem implant, combined with lip reading, helps improve communication.

Balance problems can be improved with physical therapy, Pilates or Tai Chi. Dizziness is common and will persist until the opposite ear is able to compensate and stabilize, usually within 1 to 4 months. Persistent problems with balance, dizziness, or vertigo may require treatment with vestibular rehabilitation.

Facial exercises and massages are recommended to improve facial nerve function. The House-Brackmann Scale is used to evaluate facial nerve function before and after treatment. If a patient has facial weakness after treatment, eye care consists of artificial tears and lubricant until facial nerve function returns. If a patient has facial paralysis 1 year after surgery, the chance of further recovery is reduced. Consultation with an ENT surgeon who specializes in facial plastic and reconstructive surgery is recommended.

Acoustic neuromas sometimes recur after radiation or surgery. Periodic MRI scan (every 1 to 2 years) and hearing tests are important for long-term monitoring.

Support groups are available through the Acoustic Neuroma Association; call 770-205-8211.