Introduction

Acoustic tumors are non-cancerous fibrous growths (originating from the balance or hearing nerve), that do not spread (metastasize) to other parts of the body. They constitute 6 to 10 percent of all brain tumors.

These growths are located deep inside the skull and are adjacent to vital brain centers. The first noticeable signs or symptoms are usually related to ear functions and include ear noise and/or disturbances in hearing and balance. As the tumors enlarge, they involve other surrounding nerves having to do with more vital functions. Headaches may develop as a result of the 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. In others, severe. multiple symptoms develop rather rapidly.

Great care is taken before, during and after surgery. This is done in order to preserve life, the most important objective of surgery. A secondary objective of surgery is to preserve (for future life), as many vital structures as possible. For many, a completely normal life results following surgery. Some patients experience a minimum physical handicap, while for a few patients maximum physical handicap may persist.

To accomplish the preservation of life with a minimum of future physical disturbance, this surgery, with pre- and postoperative care, is performed by a team. This team includes an internist, an anesthesiologist, a specially trained surgical nurse, a neurosurgeon, and an otologist (ear specialist). The neurosurgeon is co-surgeon with the otologist.

Size of Tumor

Risks 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 the likelihood of complications. The removal of an acoustic tumor (large or small), is a major surgical procedure with the possibility of serious complications. The risk involved in the removal of these tumors must never be minimized.

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

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.

Surgical Approaches

The choice of surgical approach depends upon the size of the tumor and the level of residual hearing. It is possible to save useful hearing in only a minority of cases. If hearing preservation is successful, the preserved hearing is not better than the pre-operative level – and may be worse. The larger the tumor, the less chance for hearing preservation. In some cases with poor pre-operative hearing or large tumor, it is better to sacrifice the hearing in order to remove the tumor. All procedures are performed under general anesthesia.

Translabyrinthine Approach
This involves an incision behind the ear. The mastoid and inner ear structures are removed to expose the tumor. The tumor is totally removed. Rarely, only partial removal is accomplished. The mastoid defect is closed with fat taken from the abdomen.

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

Middle Fossa Approach
An incision is made above the ear, and the brain is elevated to expose the tumor. The tumor is totally removed in most cases. Every effort is made to preserve the hearing and still remove the tumor. In about 50 percent 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.

Retrosigmoid Approach
An incision is made behind the ear and the brain is elevated to expose the tumor. The tumor is totally removed in most cases. Every effort is made to preserve the hearing and still remove the tumor. In some cases, it is necessary to sacrifice the hearing to achieve tumor removal. In about 50 percent 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. Following this approach, some patients may experience persistent headaches.

Radiation Therapy
Since acoustic tumors are benign growths, we do not routinely advise radiation treatment. Radiation therapy is not risk-free and does not result in disappearance of the tumor. Hearing loss, facial paralysis, and serious complications have also occurred after radiation therapy. After this treatment, some patients have experienced continued tumor growth and have required surgical removal, which is much more difficult due to the effects of the radiation.

Risks and Complications of Acoustic Tumor Surgery

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

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.

Tinnitus
Tinnitus (ear noise) remains the same as before surgery in most cases. In 10 percent 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 five percent 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 tumor usually damages the balance systems, tumor removal frequently results in improvement in any pre-operative unsteadiness. Dizziness is common following surgery and may be severe for a few days. Imbalance or unsteadiness on head motion is prolonged until the normal balance mechanism in the opposite ear compensates for the loss in the operated ear – usually in one to four months. A few patients may notice unsteadiness for several years, especially when they are fatigued.

Facial Paralysis
Acoustic tumors are in intimate contact with the facial nerve, which both closes the eye and ensures movement for the muscles of facial expression. Temporary paralysis of the facial nerve is common following removal of acoustic tumor. Weakness may persist for 6 to 12 months. A few patients experience permanent residual weakness

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 and facial nerve monitoring, 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 five percent of cases), a second operation may be performed to connect the facial nerve to a nerve in the neck (facial hypoglossal anastomosis).

In five percent of cases, the facial nerve passes through the interior of the acoustic tumor. On occasion, the tumor may even originate from the facial nerve (facial nerve neuroma). In either instance, it is 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.

When it is not possible to reconnect or replace the facial nerve, a second operation may be performed (at a later time), to reanimate the face. One option is a facial hypoglossal anastomosis, connecting the nerve in the neck to the facial nerve. Another option is called the facial reanimation operation. The temporalis muscle (one of the chewing muscles) is attached to the muscles of the face to help move them.

Eye Complications
Should facial paralysis develop, the eye may become dry and unprotected. Care by an eye specialist may be indicated. It may be necessary to apply artificial tears, to tape the eye shut, even to sew the eyelid closed. When prolonged facial nerve paralysis is expected, an eye specialist may insert a spring eyelid-closing device. This keeps the eye moist as well as providing comfort and improved appearance.

Other Nerve Weakness
In the rare case, acoustic tumors may be in contact with the nerves which supply the eye muscles, the face, the mouth and throat. These areas may be injured with resultant double vision, numbness of the throat, face and tongue, weakness of the shoulder, weakness of the voice and difficulty swallowing. These problems may be permanent.

Postoperative headache
Headache following acoustic tumor removal is common in the early postoperative period. In some cases, headache may be prolonged.

Low Back Pain
Low back pain due to blood within the fluid space around the nerve roots is usually temporary and will respond to heat and physical therapy.

Brain Complications And Death
Acoustic tumors are located adjacent to vital brain centers which control breathing, blood pressure, and heart functions. As the tumor enlarges, it may become attached to these brain centers and usually becomes intertwined with the blood vessels supplying these areas of the brain.

Careful tumor dissection, with the help of an operating microscope, usually prevents complications. If the blood supply to the vital brain centers is disturbed, serious complications may result: loss of muscle control, paralysis, and even death. However, death occurs rarely as the result of acoustic tumor removal.

Postoperative Spinal Fluid Leak
Acoustic tumor surgery results in a temporary leak of cerebral spinal fluid (fluid surrounding the brain). This leak is closed prior to the completion of surgery with fat removed from the abdomen. Occasionally this leak reopens and further surgery may be necessary to close it.

Postoperative Bleeding and Brain Swelling
Bleeding and brain swelling may develop after acoustic tumor surgery. If this occurs, a subsequent operation may be necessary to re-open the wound to stop bleeding and allow the brain to expand. This complication can result in paralysis or death.

Postoperative Infection
Infection occurs in less than 10 percent of the patients following surgery. This infection is usually in the form of meningitis, an infection of the fluid and tissues surrounding the brain. When this complication occurs, hospitalization is prolonged. Treatment with high doses of antibiotics is often indicated. Complications from antibiotic treatment are rare.

Transfusion Reaction
It may be necessary to administer blood transfusions during acoustic tumor surgery. Immediate adverse reactions to transfusions are uncommon. A late complication of transfusions may be viral infections. In most cases, a unit of the patient’s own blood can be stored before surgery for later use.

Conclusion

The standard treatment for acoustic tumors is surgical removal. The earlier they are diagnosed and removed, 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 reached for whatever risks are necessary to remove these tumors. The risks of surgery are less than the risks of leaving the tumor untreated.