A Discussion of Acoustic Neuroma (Vestibular Schwannoma) Tumours

General Comments

Acoustic tumours are non-malignant 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 tumours.

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 tumours 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 tumours 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 tumour has a serious problem. Therefore, many diagnostic procedures are used to be as certain as possible of an accurate diagnosis.

Great care is exerted before, during, and after surgery in these cases in order to preserve life. The preservation of life is the most important objective of surgery in these most difficult cases. A secondary objective of surgery is to preserve for future life as many vital structures as possible. For some, a completely normal life results following surgery; for others, minimum, or at times even maximum degrees of physical handicap may persist.

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

Size of Tumour

Risks and complications of acoustic tumour surgery vary with the size of the tumour: the larger the tumour, the more serious the complications, and the more likelihood of complications.

Small Tumour

A small acoustic tumour 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.

Medium Tumour

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

Large Tumour

A large acoustic tumour 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 the vital brain centers.

Surgical Approaches

The surgeons at Norwest ENT Group and the North Shore Skull Base Institute, offer all three microsurgical options. The choice of surgical approach depends upon the size of the tumour and level of residual hearing. It is possible to save hearing in only a minority of cases; if hearing preservation is successful the preserved hearing is not better than the preoperative level, and is usually worse. The larger the tumour, the lower the chances for hearing preservation. In some cases with poor preoperative hearing or large tumour, it is better to sacrifice the hearing in order to remove the tumour.

Translabyrinthine approach (through the ear)

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This involves an incision behind your ear under general anesthesia. The mastoid and inner ear structures are removed to expose the tumour. The tumour is then removed totally. Occasionally, 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. Consequently, the ear is made 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 (above the ear)

Under general anesthesia, an incision is made above the ear, and the brain is elevated to expose the tumour. Every effort is made to preserve the hearing and still remove the tumour. In about 50 to 60% of cases, the tumour involves the hearing nerve or the artery leading to the inner ear and total loss of hearing results in the operated ear.

Retrosigmoid approach (behind the ear)

Under general anesthesia, an incision is made behind the ear and the brain is elevated to expose the tumour. The tumour is totally removed in most cases. On rare occasions only partial removal is accomplished. Every effort is made to preserve the hearing and still remove the tumour. In some cases it is necessary to sacrifice the hearing to achieve tumour removal. In about 50 to 60% of cases, the tumour 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 tumours are benign growths, we do not routinely advise radiation treatment. Radiation therapy is not risk-free and does not result in disappearance of the tumour. Hearing loss, facial paralysis, and serious complications have also occurred after radiation therapy. After this treatment, some patients have experienced continued tumour growth and have required surgical removal, which is much more difficult due to the effects of radiation.

Hearing Impairment
FOLLOWING SURGERY

Following acoustic tumour surgery, the patient is usually deaf in the operated ear. When the hearing has deteriorated prior to surgery, the patient already has become aware of problems: location of the direction of sound, hearing a person on the deaf side, and the major problem – understanding speech in difficult listening situations.

The patient must learn to watch a speaker carefully in difficult listening situations, using his eyes to help the brain understand words which may sound very much the same, but appear different on the lips (example: pope, coke, soap, dope, cope). Considerable help also may be obtained with a BAHA.

The Bone Anchoured Implant (BAHA) (contra lateral routing of sound) is an instrument that receives sound on the deaf side, amplifies it, and then routes it to the good hearing ear. Usually a second day surgery procedure is required to insert the BAHA implant.

Risks & Complications

OF ACOUSTIC TUMOUR 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 tumour surgery.

In general, the smaller the tumour at the time of surgery, the less chance of complications. As the tumour enlarges, the incidence of complication becomes increasingly greater.

Hearing Loss

In small tumours, it is sometimes possible to save the hearing by removing the tumour. Most tumours 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% of the patients, the tinnitus may be more noticeable.

Taste Disturbance & 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 & Balance Disturbance

In acoustic tumour 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 usually has been damaged by the tumour 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 30% 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 tumour or the removal of the tumour. Difficulty in coordination in arm and leg movements (ataxia) may result.

Facial Paralysis

Acoustic tumours are in intimate contact with the facial nerve – the nerve which controls movement of the muscles which close the eye, as well as the muscles of facial expression. Temporary paralysis of the face and muscles which close the eye is common following removal of an acoustic tumour. Weakness may persist for six to twelve months and there may be 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 tumour in the internal auditory canal. Careful tumour 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 the 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 tumour. On occasion, the tumour 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 tumour 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 a 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, a specialist may insert a gold weight eyelid closing device. This keeps the eye moistened, as well as provides comfort and improved appearance.

Other Nerve Weaknesses

Acoustic tumours may contact 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 perm-anent.

Brain Complications & Death

Acoustic tumours are located adjacent to vital brain centers which control breathing, blood pressure, and heart function. As the tumour enlarges, it may become attached to these brain centers, and usually becomes inter-twined with the blood vessels supplying these areas of the brain.

Careful tumour dissection with the help of an operating microscope usually avoids complications. If the blood supply to vital brain centers is disturbed, serious compli-cations may result: loss of muscle control, paralysis, even death. In our experience, death occurs rarely as the result of the removal of small acoustic tumours, and occurs in less than 1% of the larger tumours.

Postoperative Spinal Fluid Leak

Acoustic tumour 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 & Brain Swelling

Bleeding and brain swelling may develop after acoustic tumour surgery. If this occurs, a subsequent operation may be necessary to reopen the wound to arrest bleeding and allow the brain to expand. This complication can result in paralysis or death.

Postoperative Infection

Infection occurs in less than 10% of the patients following surgery. This infection is usually in the form of meningitis, an infection of the fluid and tissue surrounding the brain. When this complication occurs, hospitalization is prolonged. Treatment with high doses of antibiotics is often indicated. These antibiotics can cause allergic reactions, may suppress the body’s blood forming tissues, or may produce hearing loss in the good ear. Fortunately, these antibiotic complications are rare.

Transfusion Reaction

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

Concluding Remarks

The standard treatment for large acoustic tumours is surgical removal. Current research suggests that smaller tumours can be left alone and observed with serial MRI scanning. 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 tumour. Unfortunately, a very careful check of all patients with these symptoms does not always result in an early diagnosis of acoustic tumours. In some cases, the tumour becomes relatively large before a definite diagnosis can be established..

Should you have any questions pertaining to the problem of your tumour, please discuss them with Dr Nirmal Patel.

Adapted from the Patient Discussion Booklet
Series of the University of Utah Otolaryngology.
Reprinted by Permission.

Reproduction in part or whole of this material is restricted by copyright law unless express permission is granted by the Norwest ENT Group.

For more information on our acoustic neuroma services, please go to:

www.sanami.com.au


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