ACOUSTIC NEUROMA

Acoustic Neuroma is a benign tumor arising from the eighth (hearing and balance) cranial nerve. This nerve travels from the brainstem to the inner ear. The nerve transmits sound and balance information from the inner ear to the brain. The facial nerve travels with the hearing and balance nerve. This nerve allows for movement of the muscles of the face.

Acoustic Neuromas are typically slow growing tumors. They usually arise in the inner ear canal and expand towards the brainstem. While these tumors do not directly invade the brain, they may push on the brainstem. If left untreated, continued tumor growth can be life threatening. When diagnosed, these tumors may be described as small (less than 1.5cm), medium (1.5 to 2.5cm) and large (more than 2.5cm).

Acoustic Neuromas are relatively rare. They are diagnosed in about one person in 100,000. These tumors are usually identified between the ages of 30 and 60. While acoustic neuromas are not typically hereditary, there is an inherited condition of neurofibromatosis which may lead to acoustic neuroma formation.

Symptoms
Acoustic Neuromas will present most often with hearing loss in one ear. This is the presenting symptom in 90% of patients. The hearing loss is usually slowly progressive, although occasionally the loss may be sudden. Ringing in one ear, also called tinnitus, often a symptom of hearing loss, may be an early sign of an acoustic neuroma. Since this is a tumor arising from the hearing and balance nerve, dizziness or imbalance may be seen. Larger tumors may press on related structures, such as the trigeminal nerve. This would result in facial numbness or tingling. Larger tumors may also result in increasing intracranial pressure causing headaches and mental confusion. When this occurs, treatment becomes urgent.

Diagnosis
Initial testing to diagnose an acoustic neuroma is usually a hearing exam or audiogram. If hearing loss is seen in one ear, further testing is required. Usually magnetic resonance imaging (MRI) is performed. This imaging study will show the eighth cranial nerve and will clearly define an acoustic neuroma if it is present. Some patients are not able to undergo an MRI. In these situations computerized tomography (CT) with contrast may be performed. While not as sensitive in diagnosing tumors, CT may reveal larger tumors.

Treatment
There are three options available in managing acoustic neuromas. This includes observation, radiation and micrsurgical removal. The choice of management option is made between the patient and physician after careful consideration of multiple factors including the patient's age, physical condition and tumor size.

Observation
Acoustic Neuromas are slow growing tumors. Because of this, careful observation may be a reasonable option in managing these growths. This is particularly the case in smaller tumors found in older individuals. In these situations, MRI's are performed periodically. If tumor growth is seen, then treatment may be necessary. If no growth is seen, then observation is continued with serial MRI perhaps on an annual basis. Another situation in which observation may be indicated is when the tumor is present in a better or only hearing ear. In this situation, serial MRI is performed. When tumor growth is seen or hearing loss develops, treatment then may become necessary.

Radiation
Stereotactic Radiation or "radiosurgery" is a relatively new option in treatment of acoustic neuromas. This treatment is based on the idea that radiation delivered precisely to the tumor will arrest tumor growth. This procedure may be performed in a single dose treatment on an outpatient basis or in multi-dose treatment over a period of several days to several weeks. This treatment option is limited to small or medium size tumors. The advantage of this treatment is its noninvasive nature, with limited recovery time. Facial weakness or paralysis, facial numbness and hearing loss may still be seen with this treatment modality. Further, tumor growth may still occur in spite of the radiation. In these circumstances, further treatment may be required. As this is a relatively new treatment option, long term results for this modality are not available. Radiation may have effects on normal tissue and because of this, the potential for undiscovered problems may exist.

Microsurgery
When surgery is considered, preoperative planning will consider the possibilities of partial tumor removal or total resection. This decision is made after considering various factors including patient age, tumor size and overall health.

Partial Tumor Removal
Partial tumor removal is considered in order to avoid intraoperative complications. At times, older individuals may have larger tumors which may be life threatening. In these patients, subtotal removal may reduce the threat to life, while avoiding debilitating conditions such as facial paralysis, at the same time taking into account one's life expectancy. This option is considered with the understanding that there may be the need for further treatment in the future if tumor growth is seen.

Total Tumor Removal
Typically, most tumors are removed in their entirety. In these situations, the goals of surgery in descending order are total tumor removal, facial nerve preservation and in select situations, hearing preservation. There are three surgical approaches which are be used alone or in combination. The approach to be utilized depends on tumor size, status of hearing and patient health.

Translabyrinthine Approach
The translabyrinthine approach is performed through an incision behind the ear. The mastoid is opened and the inner ear is removed. The facial nerve is identified within the ear and followed into the tumor. This allows the surgeon to definitively locate the facial nerve prior to tumor removal. Further, this approach minimizes retraction of the brain reducing postoperative morbidity. This approach is considered when there is no useful hearing.

Retrosigmoid Approach
This approach is performed through an incision behind the mastoid portion of the ear. The underlying bone is removed and the dura (lining of the brain) opened. This allows the surgeon to visualize the tumor from the inner ear to the brainstem. By operating behind the inner ear, hearing preservation is an option. The disadvantage is that the facial nerve is located in behind the tumor and is not directly seen until a portion of tumor is removed. Also the cerebellum (a portion of the brain) must be retracted which may result a bit longer recovery.

Middle Fossa Approach
This approach is performed through an incision above the ear. The underlying bone is removed and the temporal lobe (a portion of the brain) is retracted. This allows for tumor removal while attempting to preserve hearing. One disadvantage of this approach is the risk of retraction of the temporal lobe. Also, the facial nerve may need to be mobilized to facilitate tumor removal, increasing the risk of facial weakness, although typically temporary.
The patient and surgeon should have a detailed dicussion of which approach to utilize. Each has advantages and disadvantages although excellent results are seen with each approach.

Conclusion
There is no right or wrong way to manage acoustic neuromas. The treatment decision is made after careful and thoughtful consultation between the patient, family and physician.

Acoustic Neuroma Association