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Acoustic Neuroma

Mitchell K. Schwaber, M.D.
Richard Prass, M.D.
Nashville Ear, Nose and Throat Clinic

• General Comments
• Treatment
• Surgical Approaches
• Risks and Complications of Surgery
• Partial vs. Total Removal of an Acoustic Tumor
• Concluding Remarks

General Comments

Acoustic tumors and most skull base tumors are nonmalignant fibrous growths, originating from the balance or hearing nerve, that do not spread (metastasize) to other parts of the body. They constitute six to ten percent of all brain tumors. These growths are located deep inside the skull and are adjacent to vital brain centers. The first signs or symptoms one notices usually are related to ear function and include ear noise and disturbances in hearing and balance. As the tumors enlarge, they involve other surrounding nerves having to do with more vital functions. Headache may develop as a result of increased pressure on the brain. If allowed to continue over a long period of time, this pressure on the brain is ultimately fatal.

In most cases these tumors grow slowly over a period of years. In others, the rate of growth is more rapid. In some the symptoms are mild, and in others severe, multiple symptoms develop rather rapidly. The patient with an acoustic tumor has a serious problem. Therefore many diagnostic procedures are used to be as certain as possible of an accurate diagnosis. The most important objective is to stop the tumor from growing. A secondary objective is to preserve for future life as many vital structures as possible. For some, a completely normal life results following treatment. For others degrees of physical handicap may persist.

To accomplish these goals, treatment is handled by a team. This team includes an internist, an anesthesiologist, a specially trained surgical nurse, a neurosurgeon, an otologist (ear specialist), and a radiation oncologist.

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Treatment

In general, these lesions are managed in 3 ways, depending on tumor size, symptoms, and the age and health of the patient.

These 3 options are observation, fractionated sterotactic radiation, and surgery. These are discussed below:

1. Observation is chosen when the tumor is small, or not thought to be growing. Observation requires office visits, hearing checks, and MRI scans periodically. If tumor growth occurs, or symptoms develop, other treatment options are then chosen.
2. Fractionated Stereotactic Radiation is another option for some patients to treat the acoustic tumor with multiple doses of radiation, specifically targeted to the tumor. This treatment is for small to medium size tumors with good hearing and no vertigo. Your doctor plays an important role in determining the amount and extent of therapy. Radiation therapy is performed as an outpatient and takes about 1 week. The other advantage of the treatment is that is preserves hearing and facial nerve function in most cases. The disadvantages are that the tumor must be carefully followed on MRI scans because 10-15% of tumors may not respond and continue to grow larger. In these cases where the tumor does not respond, the surgery is more complicated. Other risks can also occur, including facial numbness and coordination difficulties, but these are rare.
3. Surgery is chosen in cases where the tumor is large, when hearing is poor, or if vertigo is a significant problem. Risk and complications of acoustic tumor surgery vary with the size of the tumor: the larger the tumor, the more serious the complications, and the more likelihood of complications. The removal of an acoustic tumor whether large or small, is a major surgical procedure, with possibilities of serious complications, including death. The risk involved in the removal of these tumors must never be minimized.

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Surgical Approaches

These tumors are ones which have extended from the bony canal into the brain cavity but has not yet produced pressure on the brain itself. The operation for this sized tumor is performed under general anesthesia using an operating microscope. The surgical approach is made through an incision behind the ear and mastoid bone. The tumor is then removed totally. Occasionally only partial removal is accomplished. The defect is closed.

Two types of procedures are used.

• The translabyrinthine approach sacrifices the hearing and balance mechanism of the inner ear. Consequently, the ear is 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 in one to four months.
• The transtemporal-suboccipital approach is performed through an incision behind the ear overlying the skull base. 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. The transtemporal-suboccipital approach allows preservation of hearing in small tumors 40% of the time. Although the balance mechanism has been removed on the operated ear the balance mechanism of the opposite ear usually provides stabilization for the patient in one to four months. Every attempt is made to preserve the facial nerve.

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Risks and Complications of Acoustic Tumor Surgery

It is not possible to list every complication that might occur before, during or following a surgical procedure. The following discussion is included to indicate some of the risks and complications peculiar to acoustic tumor surgery. In general, the smaller the tumor at the time of surgery, the less chance of complications. As the tumor enlarges the incidence of complications becomes increasingly greater. Also, surgery after fractionated radiation is associated with more complications.

Hearing Loss:

In small tumors it is sometimes possible to save the hearing by removing the tumor. Most tumors are larger, however, and the hearing is lost in the involved ear as a result of the surgical procedure. Therefore, following surgery the patient hears only with the remaining good ear. Hearing can be replaced with implantable aids in some cases.

Tinnitus:

Tinnitus (ear noise) remains the same as before surgery in most cases. In 10% of the patients the tinnitus may be more noticeable.

Taste Disturbance and Mouth Dryness:

Taste disturbance and mouth dryness is not uncommon for a few weeks following surgery. In 5% of patients this disturbance is prolonged. Dizziness and Balance Disturbance: In acoustic tumor surgery it is necessary to remove part or all of the balance nerve and, in most cases to remove the inner ear balance mechanism. Because the balance nerve usually has been damaged by the tumor already, its removal frequently results in improvement in any preoperative unsteadiness. Dizziness is common, nonetheless, following surgery and may be severe for days or a few weeks. Imbalance or unsteadiness on head motion is prolonged in 15% of the patients until the normal balance mechanism in the opposite ear compensates for the loss in the operated ear. Some patients notice unsteadiness when fatigued for several years. At times the blood supply to the portion of the brain responsible for coordination (cerebellum) is decreased by the tumor or the removal of the tumor. Difficulty in coordination in arm and leg movements (ataxia) may result.

Facial Paralysis:

Acoustic tumors are in intimate contact with the facial nerve, the nerve which controls movement of the muscles which close the eye. Facial paralysis may result from nerve swelling or nerve damage. Swelling of the facial nerve is common due to the fact that the nerve is usually compressed and distorted by the tumor in the internal auditory canal. Careful tumor removal, with the help of an operating microscope, usually results in preservation of the nerve but nerve stretching may result in swelling of the nerve with subsequent temporary paralysis. In these instances facial function is observed for a period of months following surgery. If it becomes certain that facial nerve function will not recover (approximately 5% of cases), a second operation may be performed to connect the facial nerve to a nerve in the neck (facial-hypoglossal anastomosis). In 5% of cases the facial nerve passes through the interior of the acoustic tumor. On occasions the tumor may even originate from the facial nerve (facial nerve neuroma). In either instance it is sometimes necessary to remove all or a portion of the nerve to accomplish tumor removal. When this is necessary it may be possible to immediately reconnect the facial nerve or to remove a skin sensation nerve from the upper part of the neck to replace the missing portion of the facial nerve. If this is not possible a second operation may be performed to connect the facial nerve to a nerve in the neck (facial-hypoglossal anastomosis).

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Partial vs. Total Removal of an Acoustic Tumor

Total removal of an acoustic tumor, without complications, is the goal of the management of these tumors. Partial removal of the tumor, regardless of its size, may be necessary if the patient's responses during surgery indicate disturbance of the vital brain centers that control respiration, blood pressure or heart function. If premature termination of the operation is necessary in the judgement of the operating surgeons, the remaining portion of the tumor may gradually enlarge again to produce symptoms. In this event, a subsequent operation may be necessary. This subsequent operation can often be then accomplished without significant changes in vital signs.

In the event your tumor is partially removed, you will be so informed. Usually the first operation reduces the size of the tumor sufficiently so that it has a chance to separate away from the vital brain centers and it can, therefore, be successfully removed at a later date.

In other cases, a course of continued observation is recommended. In this instance the tumor will be evaluated from time to time for possible regrowth and accordingly a decision made regarding its treatment.

Hearing Loss

If hearing loss occurs with treatment, it can be helped in some cases with hearing aids. These will be recommended depending on the level of hearing. Total loss of hearing can also be helped with BAHA type systems, including implantation of a bone-conducted hearing aid. Our goal is to restore functionality as much as possible.

Concluding Remarks

The earlier an acoustic tumor is diagnosed and treated, the less likely the possibility of serious complications. Many patients have unilateral hearing loss, head noise, and balance difficulties. Rarely are these symptoms due to an acoustic tumor. Unfortunately, a very careful check of all patients with these symptoms does not always result in an early diagnosis of acoustic tumors. In some cases the tumor becomes relatively large before a definite diagnosis can be established. The problem must be faced as it exists at the time of diagnosis and acceptance made of whatever risks are necessary to treat these tumors.

The statements made herein are based on our personal experiences in managing a large series of acoustic tumor cases. If you have any questions about yourself and a possible acoustic tumor, please discuss them with your doctor. We want to work with you to provide the best long term outcome. Feel free to consult a second otologist or neurosurgeon regarding your situation. If you are a patient of the Nashville ENT Clinic, your medical records can be sent to any consultant you desire.

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