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Department of Otolaryngology Health-Related Library

Acoustic Neuroma

Important Things to Know About an Acoustic Neuroma

  1. An acoustic neuroma is a benign tumor.
  2. An acoustic neuroma can be cured by removal.
  3. Sometimes the tumor's growth pattern and necessary manipulation during removal affect nearby cranial nerves and the brainstem.

What Is an Acoustic Neuroma?

An acoustic neuroma (sometimes termed a neurinoma or schwannoma) is a benign (non-cancerous) tissue growth that arises on the eighth cranial nerve. The eighth cranial nerve is really two separate nerves, one part associated with transmitting hearing and the other with sending balance information to the brain from the inner ear. These nerves lie adjacent to each other as they pass through the bony canal leading from the inner ear to the brain. This tiny connective opening, called the internal auditory canal, varies in length from .4 to 1.2 centimeters (.15 to .45 inches) and it is here that acoustic neuromas usually begin to grow from the sheath surrounding the eighth nerve. The seventh or facial nerve which serves facial movement also passes through here, as well as important blood vessels.

What Causes an Acoustic Neuroma and What Is Its Growth Pattern?

The cause of acoustic neuroma is unknown, except for a small percentage of individuals in whom both sides are involved. In these instances, there is often a hereditary factor.

Acoustic neuromas usually grow very slowly, sometimes over a period of many years. They characteristically remain within their lining (encapsulated), and displace normal tissue very slowly, so that the body accommodates as long as possible to this abnormal growth.

How Often Do Acoustic Neuromas Occur?

Small, non-symptomatic acoustic neuromas have been found on autopsy in 2.4% of the general population. Estimates of occurrence of acoustic neuromas which causes symptoms range from 1 in every 3,500 persons to 5 in every million people. More women than men are affected, and most acoustic neuroma surgery is performed between the ages of 30 and 60.

Symptoms

There is no typical pattern of symptoms causes by a developing acoustic neuroma, thus making early diagnosis a challenge. However, there usually are indications pointing to the possibility of an acoustic tumor, which means that persons with "inner ear" problems should be completely evaluated to eliminate acoustic neuroma as the symptom cause. It may be that less serious problems such as Meniere's disease or a hardening of bone of the middle ear (otosclerosis) are the cause of these symptoms.

In over 90% of those with a tumor, the first symptom is a reduction in hearing in one ear caused by nerve failure, often accompanied by ear noise or ringing. The loss of hearing is usually subtle and worsens very slowly, although occasionally a sudden loss of hearing is noted. There may be a feeling of fullness in the affected ear. Unfortunately, since the hearing loss is often mild and there is no pain, some people merely shift the phone to the opposite ear or make other compromises for the one-sided hearing loss rather than seek medical evaluation.

Since the balance portion of the eighth cranial nerve is where the tumor arises, unsteadiness and balance problems may occur early in the growth of the neuroma, and may or may not continue as the balance function is destroyed on the affected side. The remainder of the balance system sometimes compensates for this loss, and thus balance problems may be forgotten after some time.

As the tumor presses on other nerves and tissue, facial sensation may be affected, with numbness and facial tingling felt constantly or intermittently. Facial nerve spasms may occur, and headaches and unsteady gait caused by tumor pressure on the cerebellum may be experienced.

Identifying the Tumor

Advances in medicine have made possible the identification of small acoustic neuromas, that is, those still confined to the internal auditory canal. After auditory tests reveal loss of speech discrimination ("I can hear sound in that ear, but I can't understand what's being said,") a brainstem auditory evoked response (BAER) test may be done. This test provides information on the passage of a harmless electrical impulse along the circuit provided by the acoustic nerve from the ear through the brainstem pathways. This can indicate whether there is a poorly functioning acoustic nerve.

The CT scan also has proved to be a powerful tool in locating acoustic neuromas. Although small tumors still confined to the canal may not show on the plain CT scan, air or contrast materials introduced into the body will enhance the tumor. Newer generation CT scanners have also improved identification of small acoustic tumors.

Magnetic Resonance Imaging (MRI) is a recently developed diagnostic system which is very effective in identifying acoustic neuromas. MRI uses modern computer technology to process the results of passing momentary harmless magnetic pulses and radio frequency waves through the portion of the body being studied. The image which is formed clearly defines an acoustic neuroma if it is present.

Small Tumor

A small acoustic tumor is still confined within the bony canal that extends from the inner ear to the brain. Through this canal pass the hearing, balance and facial nerves and the blood vessels which supply the inner ear.

The operation for removal of a small tumor is performed under general anesthesia using the operating microscope. The surgical approach (middle fossa approach) is through an incision in front of and above the ear.

The tumor is totally removed in most cases. On rare occasions only partial removal can be accomplished. Every effort is made to preserve the hearing and still remove the tumor. In about 50% of cases the tumor involves the hearing nerve or the artery leading to the inner ear, and total loss of hearing results in the operated ear.

Medium Tumor

A medium sized acoustic tumor is one which has extended from the bony canal into the brain cavity, but has not yet produced pressure on the brain itself.

The operation for a medium sized tumor is performed under general anesthesia using an operating microscope. The surgical approach (translabyrinthine-suboccipital approach) is made through an incision behind the ear, overlying the mastoid bone. The mastoid and the inner ear structures are removed to expose the tumor. The tumor is then totally removed. Occasionally only partial removal is accomplished. The mastoid bone defect is closed with fat taken from the abdomen.

The translabyrinthine-suboccipital approach sacrifices the hearing and balance mechanism of the inner ear. Consequently, the ear is made permanently deaf. Although the balance mechanism has been removed on the operated ear, the balance mechanism of the opposite ear usually provides stabilization for the patient within one to four months.

Large Tumor

A large acoustic tumor is one which has extended out of the bony canal into the brain cavity and is sufficiently large to produce pressure on the brain and disturb vital brain centers.

Operations for large acoustic tumors require extensive removal of bone to properly expose the tumor and control the large blood vessels which obstruct access to the tumor. For this reason, special vascular studies (arteriograms) may be required along with other procedures necessary to diagnose and establish the size of the acoustic tumor.

The operation for a large tumor is performed under general anesthesia using an operating microscope. The surgical approach (translabyrinthine-suboccipital approach) is through an incision behind the ear, overlying the mastoid bone. The mastoid, inner ear structures and a portion of the skull are removed to expose the tumor. The tumor is then totally removed unless vital sign changes occur. If there are changes in the blood pressure, pulse rate or respiration rate, the surgery must be terminated before the tumor is totally removed. In this case a second operation to complete the tumor removal is usually necessary. The mastoid bone defect is closed with fat taken from the abdomen.

In large tumors, it is often necessary to monitor the patient's general status by inserting a small tube (arterial line) into an artery in the arm or leg. When this is necessary there may be pain in the hand or foot following surgery. Occasionally a blood clot forms in the artery following surgery. Should this complication occur, further surgery may be necessary to remove the clot. A very rare complication of this arterial line monitoring is loss of a finger, toe or even a hand or a foot.

The translabyrinthine-suboccipital approach sacrifices the hearing and balance mechanism of the inner ear. Consequently, the ear is made permanently deaf. Although the balance mechanism has been removed on the operated ear, the balance mechanism of the opposite ear usually provides stabilization for the patient within one to four months.

Treatment of an Acoustic Neuroma

At the present time, the only treatment that can cure the patient is removal of the tumor by surgery. Within the last two decades, microsurgical techniques have been pioneered and refined. Finely scaled surgical instruments, alternate cutting and tumor-reducing tools, and the operating microscope used by surgeons trained and experienced in this delicate removal process have made possible an extremely low mortality rate. The doctors are also able to minimize contact with nerves and tissue just adjacent to the tumor.

The location and size of the tumor, and the surgeon's preference will determine whether a sub-occipital (posterior fossa) or a translabyrinthine approach to the tumor site is used.

Postoperatively, one to several days may be spent in intensive care with careful monitoring. Immediate problems which may develop during this time can include headache and decreased mental alertness due to development of a blood clot of obstruction of the flow of cerebrospinal fluid. Other early problems may include cerebrospinal fluid leak and meningitis, an infection controlled with antibiotics which necessitates a longer hospitalization.

Another treatment, developed in Sweden, is the use of a special form of radiation therapy. At the present time, the long term benefits and the incidence of temporary or permanent side effects are not known.

Partial Removal

Incomplete removal of the tumor is elected by some patients and their surgeons to reduce the risk of complication, with the realization that further surgery may be needed in the future.

Occasionally, because of apparent disturbance of patient vital brain centers during surgery, the operation is terminated before the tumor is totally removed. In many instances, total removal is possible at a later date. If the surgeon determines observation of the remaining tumor to be wiser, this course will be followed.

Afterward

Removal of an acoustic neuroma is a complex and delicate process. In general, the smaller the tumor at the time of surgery, the less chance of complications. As the tumor enlarges, the chance of complications becomes increasingly greater. Thus there may be problems with the cranial nerves affected by the tumor after surgery which may or may not have been present before the tumor was removed.


Postoperative Instructions

Tumor Patients

  1. You may resume your regular activities as you feel like it. Set your own pace. Please refrain from lifting anything heavier than 25 pounds for at least six months. If you have a tendency toward constipation, take a stool softener to lessen the need to strain while having a bowel movement.
  2. Your hair, including the incision site, may be washed as soon as the staples have been removed from the incision. This normally occurs about one week after surgery.
  3. Things to watch for when you get home:
  4. Do not blow your nose forcibly for two weeks following surgery.
  5. If you have facial weakness following surgery, please see an ophthalmologist immediately upon your return home. Your eye will need attention. Remember to wear a plastic eye shield at night and to keep the eye moist throughout the daytime hours by placing drops (artificial tears) in the eye every 30 minutes and/or using a moisture shield.
  6. Should you have any difficulty upon returning home, please call us directly instead of consulting your local physician. Once we have assessed the situation, we will contact your doctor with specific instructions for your care.
  7. You will need to see your referring doctor about six weeks after returning home.

Residual Problems

Immediate Post Op

In the days and perhaps weeks after surgery there is a possibility of extreme fatigue and increased drowsiness, although some experience "survival euphoria" and a renewed sense of energy. A period of emotional "lows" is not unusual as the patient begins to adjust to his or her physical changes.

One symptom which may not occur until after discharge from the hospital is a nasal "drip" of clear fluid which may be particularly noticeable when bending over. This should be reported promptly to your surgeon so that the possibility of a leak of cerebrospinal fluid can be checked.

Hearing Loss

With small tumors it may be possible to save hearing. Monitoring of hearing function during surgery is a technique currently being perfected to assist in this preservation. However, in medium or large tumors (those which protrude into the brain) the hearing usually has been partially or totally lost, and cannot be restored. This means that the patient will continue having problems locating sound, hearing on the deaf side and understanding speech over low background noise. For some, a CROS aid will help. A 30 day free trial should be allowed before purchase.

Tinnitus

Ear noises usually remain the same as before surgery, though in a few cases ear noise begins after tumor removal. A masking device may help some people affected by tinnitus.

Facial Weakness or Paralysis

Since the facial nerve, which controls muscles of facial expression, is in close contact with acoustic neuromas, it is usually necessary for the surgeon to manipulate and sometimes remove portions of this nerve. In some cases, even though the nerve is still intact after surgery, nerve damage or swelling may cause temporary, or in a small percentage of cases, permanent facial paralysis.

Nerve regeneration is a slow process and it may take up to a year for recovery to be noticeable. If facial recovery is not observed after some time, a second operation may be performed to connect the healthy portion of the facial nerve to a nerve in the neck, usually the nerve leading to one side of the tongue. This procedure is called a hypoglossal facial nerve anastomosis and restores some but not all facial movement. There may be some loss of tongue function. There are also other procedures which adapt available muscles and nerves to aid in toning or reanimating the sagging face. When it is necessary to remove a portion of the nerve at the time of surgery, the facial nerve may be reconnected immediately, or a graft inserted.

Eye Problems

Studies show that at least half of those who have had an acoustic neuroma removed have long term eye discomfort and other eye problems, particularly if the tumor was medium or large. It is important to see an eye specialist if problems occur.

Loss of eyelid function and/or altered tear production can cause "scratchiness" and irritation because the eye may be dry and unprotected. There are various surgical procedures which can provide protection to the cornea. They include a canthoplasty (bringing together tendons in either or both corners of the eye), a spring implantation in the upper lid, an elastic prosthesis secured around the upper and lower lids, a gold weight implantation in the upper lid, and a tarsorrhaphy (sewing the lids together).

Artificial tears or eye lubricant may be needed for a short time or permanently. Taping part of the lids together, using protective glasses and moisture chamber, using bandage contact lenses and avoiding eye irritants can also help.

In a few patients, double vision may be due to pressure on one of the cranial nerves (usually the sixth) which controls the muscles that move the eyes.

Taste Disturbance and Mouth Dryness or Excessive Salivation

There may be some alteration in taste and amount of saliva secretion for a short time following surgery. In a few cases, this may be prolonged. For others, increased salivation occurs while chewing, or there may be increased tear production while eating. The appetite may be affected for a time.

Swallowing, Throat and Voice Problems

For a small percentage of patients, surgery for acoustic neuromas affects the nerves which control the throat, swallowing and voice. Hoarseness and difficulty swallowing usually improve slowly.

Balance Problems

The vestibular portion of the eighth nerve almost always is removed during surgery. Usually this portion of the nerve has already been destroyed. Dizziness is common following surgery and may be severe for a time. After a while, the balance apparatus in the normal ear should compensate for the loss, but the compensation may never be perfect, particularly when the person is fatigued or when there is a sudden change in motion. Maintaining good health through proper diet and moderate exercise can be a key to balance improvement and general vitality.

Fatigue

Fatigue sometimes remains a problem long after other post-operation symptoms have disappeared. It is important to adjust one's pace in harmony with one's energy level.

Headache

Headaches are a problem for some while still hospitalized. The causes may vary from tension from holding the head rigidly to intracranial changes. If severe headaches persist well after hospital discharge, medical help should be sought.

Dental Care

If the patient suffers from facial paralysis, food tends to "get lost" in the mouth on the affected side. This can lead to dental problems. Washing out the mouth while hospitalized is important, and careful mouth rinsing should be continued as well as brushing and flossing several times daily.

Protecting the Outer Ear

It is important to provide sensible protection for the remaining good ear. Avoid extreme and sudden loud noises, such as firearms and some cordless phones. Some physicians also suggest follow-up CT scans and/or audiograms for a period of time after acoustic neuroma removal.

Psychologic Coping

For some, adjustment to the changes after acoustic neuroma removal is challenging. In addition to changes in hearing, appearance may change, and the patient may have other impairments.

The Acoustic Neuroma Association

The Acoustic Neuroma Association is a patient organized and administered information and mutual-aid group, founded in 1981. It is an incorporated, non-profit organization, recognized as such by the IRS. The Acoustic Neuroma Association publishes a quarterly newsletter, distributes patient information booklets, presents a biennial national symposium, provides access to a network of local support groups, compiles a Registry of statistical data on acoustic neuroma treatment, and maintains a Home Page on the Internet for patient information and discussion.

The purposes of the association are:

  1. To provide support and information for patients who have been diagnosed with or treated for acoustic neuroma or other benign tumor affecting the cranial nerves.
  2. To furnish information on patient rehabilitation to physicians and health care personnel.
  3. To promote and support research on acoustic neuroma and its effects.
  4. To educate the public regarding symptoms suggestive of acoustic neuroma, thus promoting early diagnosis and successful treatment.

For further information, contact:

Acoustic Neuroma Association

P.O. Box 12402

Atlanta, GA 30335

Phone: (404) 237-8023
Fax: (404) 237-2704
E-mail: ANAUSA@aol.com
Website: http://www.ANAUSA.org

Glossary of Terms

Acoustic
pertaining to hearing
Acoustic Neuroma
benign tumor of the eighth cranial nerve
Anastomosis
the surgical joining of two organs - can be muscles, nerves, blood vessels
Arteriogram (Angiogram)
A type of X-ray which demonstrates the vascular system after an injection of dye. Used in some patients to determine type, size and exact location of a cranial tumor.
Audiogram
A chart of hearing acuity recorded during hearing tests
Benign
Not malignant, not cancerous
Bilateral
Pertaining to both sides of the body
Brainstem
Connects the upper brain to the spinal cord, less than 3 inches (7.6 cm) long. The pons is one part of the brainstem.
CT Scan (Computerized Tomography)
A special X-ray test which creates a cross-sectional picture of any part of the body. This X-ray can distinguish between tissue, fluid, fat and bone, and after intravenous injection of a dye will show an acoustic neuroma unless the tumor is very small.
Cerebellopontine Angle
Space bounded by the petrous (mastoid) bone, brainstem and cerebellum and through which cranial nerves six through eleven pass
Cerebellum
Located behind the brainstem, extending from the brainstem toward each mastoid bone, it is the part of the brain that controls muscular coordination.
Cranial Nerves
There are two sets of twelve cranial nerves each. Each set involves one side of the body. The cranial nerves control the sensory and muscle functions around the eyes, face and throat.
CROS Hearing Aid (Contralateral Routing of Sound)
A CROS aid is used with one-sided deafness. It receives sound on the deaf side, amplifies it and carries it to the good ear.
CSF (Cerebrospinal fluid)
A watery fluid, continuously being produced and absorbed, which flows in the ventricles (cavities) within the brain and around the surface of the brain and spinal cord.
Hydrocephalus
Enlargement of the normal CSF containing cavities (ventricles) within the brain due to impairment of flow or absorption of the CSF.
Magnetic Resonance Imaging (MRI)
A body imaging system employing a magnet which surrounds the patient. A magnetic field causes small harmless movements of the atoms in the area of the body being studied. A low energy radio wave is then passed through the same area and the minute change this imparts to the atoms in the magnetic field causes signals to be emitted which are picked up and analyzed by modern computer technology. An image of the tissue is produced in clear detail.
Neuroma
Benign growth originating on a nerve
Neurofibromatosis
A familial condition characterized by developmental changes in the nervous system, muscles, bones and skin. The central form may produce bilateral acoustic neuromas.
Pons
Located at the base of the brain in front of the cerebellum. This section of the cranium is a mass of nerve tissue which coordinates the activities of the various lobes of the brain.
Posterior Fossa
The cavity in the back of the skull which contains the cerebellum, brainstem and cranial nerves 5-12.
Sensorineural Hearing Loss
Deafness caused by failure of the acoustic nerve
Shunt
A tube implanted in the cranium to balance the flow of cerebrospinal fluid, and used in the treatment of hydrocephalus.
Tinnitus
Buzzing, ringing and other internally produced noises
Translabyrinthine
Surgical approach to an acoustic neuroma through the mastoid bone and inner ear (labyrinth)
Unilateral
Involving only one side
Vertigo
Dizziness. A symptom sometimes caused by an acoustic neuroma.
Vestibular
Associated with the balance system

Bibliography

The Diagram Group, THE BRAIN, A USER'S MANUAL, New York, G.P. Putnam's Sons, 1982.

Holvey, D.N., Ed., MERCK MANUAL OF DIAGNOSIS AND THERAPY, Rahway, N.J., Merck, Sharp & Dohme Research Laboratories, 1972.

Martuza, R.L., Parker, S.W., Nadol, J.B., Davis, K.R., Ojemann, R.G.: Diagnosis of Cerebellopontine Angle Tumors. CLINICAL NEUROSURGERY, 1985, 32:177-213.

House, W.F., Luetje, C.M., eds., ACOUSTIC TUMORS: Vol 1, DIAGNOSIS, Vol 2, MANAGEMENT. Baltimore, University Park Press, 1979.

Information Office, National Institute of Neurological Diseases and Stroke, ACOUSTIC NEUROMA: HOPE THROUGH RESEARCH. DHEW Publ. #NIH 73-204, 1973.

Ojemann, R.G., Levine, R.A., Montgomery, W.M.: Evoked Potentials to Preserve Hearing in Unilateral Acoustic Neuroma Removal. J NEURO SURG, 1984, 61:938-948.

Otologic Medical Group, Inc. A DISCUSSION OF ACOUSTIC NEUROMAS, Los Angeles, Rev. 1982.

Segal, Gail. A PRIMER OF BRAIN TUMORS. Chicago, Association for Brain Tumor Research, 1978.

Tortorelli, B.A.: Acoustic Neuroma: An Overview of the Disorder and Nursing Care for These Patients. JOURNAL OF NEUROSURGICAL NURSING, 1971 Vol 13,4:170-176.

DeFillip, G.J., Buchheit, W.A.: Magnetic Resonance Imaging of Acoustic Neuromas. NEUROSURGERY, 1985, 16:763-765.