Acoustic Neuroma

An acoustic neuroma (sometimes termed a vestibular schwannoma or neurolemmoma) is a benign (noncancerous) tissue growth that arises on the eighth cranial nerve leading from the brain to the inner ear. This nerve has two distinct parts. One part is associated with transmitting sound, and the other sends balance information to the brain from the inner ear. These pathways, along with the facial nerve, lie adjacent to each other as they pass through a bony canal called the internal auditory canal. This canal is approximately 1-inch long. Acoustic neuromas originate in this canal from the sheath surrounding the eighth nerve.


Diagnosis

Magnetic resonance imaging (MRI) is the preferred diagnostic test for identifying acoustic neuromas.

Other tests used to diagnose acoustic neuroma and to differentiate it from other causes of dizziness or vertigo include:

* Computed tomography (CT) scan of the head
* Audiology (a test for hearing)
* Caloric stimulation (a test for vertigo)
* Electronystagmography (a test of equilibrium and balance)
* Brain stem auditory evoked response (BAER, a test of hearing and brain stem function)


Treatment

Observation
Acoustic neuromas are sometimes discovered by physicians while evaluating a patient for another medical condition, or when the tumor is very small with subtle symptoms. Because the tumors are slow-growing, if discovered when they are very small, careful observation over time may be appropriate for some patients.

A small tumor diagnosed in an elderly patient may require only observation of its growth rate, if disabling symptoms are not present. If the tumor likely will not need to be treated during the patient's normal life expectancy, treatment and its potential risks and complications can be avoided. Some tumors don't appear to grow at all.

Observation also may be the preferred therapy for those who have a tumor in their only hearing ear or better-hearing ear. In such cases, growth is monitored and treatment is considered only if hearing is lost or the tumor size becomes life-threatening.

In these patients, magnetic resonance imaging (MRI) of the head is done periodically to monitor tumor growth. If there is no growth, observation is continued. If the tumor is growing, however, treatment may become necessary.

Microsurgical Removal
The goal of surgery is to remove the tumor and avoid any new neurologic deficits such as facial weakness or hearing loss. Success in achieving these goals depends a great deal on the tumor's size and configuration and the patient's hearing status prior to surgery.

Microscopic surgery for acoustic neuromas is done under general anesthesia. Usually, patients stay in the hospital four to five days after surgery.

Several surgical approaches can be used to remove acoustic neuromas. The choice depends on the location, tumor size, the patient's hearing level and the surgeon's skill and experience.

Each approach has advantages and disadvantages, but excellent results have been achieved in all approaches. The surgeon and patient should have a thorough discussion before selecting the approach.

Partial Tumor Removal
Some patients and their surgeons prefer partial removal of an acoustic neuroma, especially if the tumor is large. This decision includes the understanding that more surgery or stereotactic radiosurgery may be needed in the future.