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Acoustic Neuroma / Vestibular Schwannoma

WHAT IS AN ACOUSTIC NEUROMA?

An acoustic neuroma is a tumor of the cells surrounding the nerve that transmits balance information from the inner ear to the brain. It is not malignant; that is, it does not produce cells that travel to other places in the body and start additional tumors. Nonetheless, an acoustic neuroma is a problem because it slowly grows toward the brain’s hearing, breathing, and blood pressure centers and compresses them. Untreated, acoustic neuromas can create serious neurological problems and even become life-threatening. Acoustic neuromas large enough to cause these symptoms are rare, occurring in only 1 out of 100,000 people per year. They generally happen in people between the ages of 30 and 60.

Acoustic neuromas typically start in the canal through which the nerves of hearing, balance, and facial function run from the inner ear to the brain (figure reference). The tumors are classified by size: small (under 2 cm), medium (2-4 cm), (large 4-6 cm), and giant (more than 6 cm).

Acoustic neuromas are also called vestibular schwannomas.

WHAT ARE THE SYMPTOMS OF AN ACOUSTIC NEUROMA?

The patient begins to experience symptoms when nerves and brain structures are compressed by the growing mass. Early symptoms include hearing loss, ringing in the ear (tinnitus), and dizziness. Sometimes mild to moderate pain is felt behind and slightly above the ear. Paradoxically, smaller tumors are more prone to produce pain in this location compared to large tumors. As noted above, acoustic neuromas are relatively rare. Many other syndromes also cause similar symptoms; diagnostic work is essential to arrive at the correct interpretation of symptoms.

Later on, more serious neurological symptoms such as headaches and mental confusion occur as the brain is compressed by the growing tumor. The tumor creates fluid pressure outside and within the brain, a condition called hydrocephalus. The patient may lose feeling in the face and control over the facial muscles, since the nerve that controls the face runs through the area where the tumor occurs. For similar reasons, swallowing and voice quality may be affected.

WHAT CAUSES ACOUSTIC NEUROMAS?

The vast majority of tumors are sporadic, meaning there is no genetic inheritance pattern. In these cases, the tumor occurs in only one ear.

However, in rare cases acoustic neuromas are caused by an inherited genetic disorder. These are called NF2 (neurofibromatosis type 2) tumors. Because the cause is genetic, both ears may be affected. In many cases, the damaged NF2 genes cause problems in other areas of the body as well. The damaged genes have been identified, making it possible to test whom within a family carries it. NF2 is autosomal dominant, which means the children of a parent with NF2 have a 50% chance of inheriting the gene that causes the syndrome. A CEI Neurotologist will be able to distinguish between the sporadic and genetic form of acoustic neuromas, and can discuss the implications of either with you.

HOW ARE ACOUSTIC NEUROMAS DIAGNOSED

Physicians look for acoustic neuromas with diagnostic testing and/or imaging studies. One test consists of emitting clicks into both ears, one at a time, and recording brainwave activity in the neural system. Comparison of the two ears can show if an acoustic neuroma is present in one of them. Another imaging test is magnetic resonance imaging (MRI) with injection of a contrast agent (usually gadolinium) which will clearly shows an acoustic neuroma if one is present. Gadolinium cannot be used in all patients, so if this test is ordered for you, please review your entire medical history in detail with the radiologist performing this test.

ACOUSTIC NEUROMA TREATMENT OPTIONS

There are three possible courses of action: observation, radiation, and surgery.

Observation. A few acoustic neuromas (less than five percent) do not grow, or grow very slowly. If there are complicating factors such as advanced age or medical problems that would make other therapies more risky, we may recommend simply observing the tumor on a regular basis.

Radiation. As with other kinds of cancers, radiation can be used to stop tumor growth. However, this is usually not the best approach for treating acoustic neuromas due to their proximity to the brain, and the fact that radiation can occasionally make acoustic neuromas turn malignant. Moreover, radiation occasionally fails to fully eliminate acoustic neuromas; and the tumor can reoccur. If this happens, it is even more difficult to surgically remove the tumor due to scarring from the radiation.

When radiation therapy is used, it is delivered either in a single large dose or repeated smaller doses. Narrow beams of radiation are aimed at the acoustic neuroma from various angles, with the goal of focusing radiation on the target area and minimizing damage to surrounding tissue. This technique is called stereotactic radiation therapy. When it is delivered in repeated small doses, it is called fractionated stereotactic radiation therapy.

Surgery. Surgery is the treatment chosen for the majority of cases, with recurrence rates under 1%. Fortunately, acoustic neuromas tend to compress brain tissue rather than growing into it, allowing for surgical removal with a low likelihood of damage to critical structures. One such structure is the facial nerve, which controls movement and sensation in the face. During surgery, the facial nerve is monitored with a probe that reports when the nerve is put at risk from the surgeon’s motions. The surgeon’s goal is always to preserve as much facial function and hearing as possible while eliminating the tumor.

There are three surgical methods for removing an acoustic neuroma:

a. Retrosigmoid: The surgeon opens the skull about three inches behind the ear. The cerebellum, the part of the brain surrounding the acoustic neuroma, is gently retracted to expose the tumor. The advantage of this approach is that hearing can sometimes be preserved. This is also called the sub-occipital approach.

b. Middle fossa: An opening is created above the ear, and the surgeon drills toward the tumor while staying outside the dura covering of the brain. Bone is removed over the internal auditory canal to expose the tumor. This approach most often used when preservation of hearing is a primary goal.

c. Translabyrinthine: This approach may be used when the patient has no remaining hearing in the ear, or when other approaches are not feasible. The surgeon drills immediately behind the outer ear and removes bone with the goal of exposing the tumor as completely as possible. The advantage of this method is that no part of the brain need be retracted, and the facial nerve can easily be seen.

All of these procedures are regularly performed by the board certified otologists of the California Ear Institute. Each has advantages and disadvantages, and these will be discussed with you when surgery is being considered.

Follow-up Treatment

Once the acoustic neuroma has been eliminated, follow-up treatment consists of balance therapy and providing as much support as possible for the remaining hearing.

Since removal of the balance nerve is necessary in all cases of surgical treatment, rehabilitation of balance is always called for. Such therapy, also called vestibular rehabilitation, is usually successful. Most patients can return to close to their functioning level before the acoustic neuroma symptoms started. Vestibular rehabilitation consists of daily exercises prescribed by a physician or physical therapist that retrain the brain to make use of the balance information it is still getting, whether from the inner ears or from other sources such as vision or feedback from muscles. Fortunately, the brain is quite flexible and can usually compensate for loss of unilateral or bilateral balance function.

In rare cases, facial nerve transplantation may be required for those with advanced acoustic neuromas that result in permanent facial nerve paralysis.

Hearing loss in one or both ears can be treated in a number of ways, depending on the specific situation of the patient following removal of the neuroma.

a. Specialized hearing aids, called bi-cross hearing aids, route a sound signal from the deaf ear’s side to the hearing ear. These can be fitted by CEI audiologists who specialize in hearing restoration following removal of an acoustic neuroma.

b. Bone-Anchored Hearing Appliances (BAHAs) consist of surgically implanting a titanium device on the deafened side with the goal of transmitting sound vibrations directly through the skull to the intact cochlea and hearing nerve of the other ear. The device can be placed under either general anesthesia or under local anesthesia. This often results in marked improvement in cases where one ear is deaf but the other remains normal, as is usually the case with acoustic neuromas. Surgeons at CEI have placed over 400 BAHA devices in patients with single-sided deafness.

c. A cochlear implant can be used when hearing is lost in the inner ear (due to disruption of blood flow after surgery) but the hearing nerve remains intact. A cochlear implant uses an implanted electrode to stimulate the hearing nerve in such a way that the brain believes it is receiving sound from a functioning ear. In this situation, the patient is receiving sound input from two functioning ears rather than one.

d. An auditory brainstem implant (ABI) may be used in patients who have lost the hearing nerve in both ears. Like cochlear implants, ABIs use implanted electrodes to deliver sound information to the brain, except the electrodes are placed in the auditory center of the brain itself rather than the inner ear.

Cochlear implants and auditory brainstem implants as treatment for acoustic neuromas are generally reserved for cases where the cause is neurofibromatosis type 2 or von Recklinghausen's disease.

CONSEQUENCES OF AVOIDING TREATMENT

Left untreated, an acoustic neuroma will cause serious neurological problems, including facial paralysis which can lead to blindness, and brain damage severe enough to cause death. An acoustic neuroma always requires specialized and prompt treatment.

ADDITIONAL NOTES

Patients searching the Internet for information about this medical issue should know that generally it is the patients with the severest cases who take the time to write up their experiences for online reading. As a result, it is easy become overly alarmed and assume the worst. Patients should keep this in mind as they explore the available online research resources. As with all medical conditions, prompt treatment by experienced medical personnel give the best chance for a positive outcome.

CONCLUSION

An acoustic neuroma is a complex medical problem requiring skilled care at all stages from diagnosis to rehabilitation. Our philosophy at CEI entails educating you to make an informed decision. We structure our treatment plans with the following priorities: first, stop the tumor from being life-threatening; second, preserve facial nerve function; third, preserve hearing. Your surgeon will explain the treatment options based on your individual situation.

When CEI assembles an acoustic neuroma team for a patient, it includes a surgeon, an assistant surgeon, OR and post-op nurses, an audiologist, an anesthesiologist, vestibular therapists, and hearing restoration specialists. CEI has been in operation since 1968 and is Northern California’s most experienced otology practice group. We use tools including laser technology, imaging guidance and integration, hearing nerve monitoring, facial nerve monitoring, cranial nerve monitoring, tumor removal devices (including CUSA or Selector ultrasonic aspirators), specialized anesthesia techniques, and a clinical pathway protocol for postoperative treatment. CEI’s physicians have been involved in the development of many of the currently used techniques in each of these areas.

Click here to make an appointment with the California Ear Institute to consult with one of our board certified otologists regarding your ear-related condition.

USEFUL READINGS

a. Acoustic Neuroma Association, 60 Peachtree Parkway, Suite 108, Cumming, GA 30041-6899. Telephone: (770) 205-8211. Website: http://www.anausa.org.

b. “Vestibular Schwannoma (Acoustic Neuroma) and Neurofibromatosis.” National Institute on Deafness and Other Communication Disorders. 1 Communication Avenue,
Bethesda, MD 20892-3456. Telephone: (800) 241-1044. Website: http://www.nidcd.nih.gov/.

c. “Acoustic Neuroma: The Basic Facts.” University of Minnesota. http://www.med.umn.edu/otol/library/aneuroma.


 
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