An acoustic neuroma is a benign tumor.

An acoustic neuroma can be cured by removal.

Sometimes the tumor's growth pattern and necessary manipulation during removal affect nearby cranial nerves and brain stem.

What is an acoustic neuroma?

An acoustic neuroma (sometimes termed neurinoma or schwannoma) is a benign (non-cancerous) tissue growth that arises on the eighth cranial nerve. The eighth cranial nerve is two separate nerves, one part associated with transmitting hearing and other with sending balance information to the brain from the inner ear. These nerves lie adjacent to each other as they pass through the bony canal leading from the inner ear to the brain. This connective opening, called the internal auditory canal, is about one centimeter (0.4 inches) long, and it is here that acoustic neuromas usually arise from the sheath surrounding the eighth nerve. The nerve (seventh or facial) which serves facial movement also passes through this canal, as do important blood vessels.

What causes acoustic neuromas and what is its growth pattern?

The cause of most acoustic neuromas is unknown.There is a small group of patients who have neurofibromatosis type 2, which is genetically determined.

Acoustic Neuromas usually grow slowly over a period of many years. They characteristically remain within their lining (encapsulated) and displace normal tissue. The body accommodates to this abnormal growth. An acoustic neuroma first distorts the eighth nerve, then presses on the seventh nerve. The slowly enlarging tumor protrudes from the internal auditory canal into an area behind the temporal bone called the cerebellopontine angle. It now assumes a pear shape, with the small end in the canal. The tumor presses on adjacent nerves, such as the fifth, or trigeminal, which is the nerve of facial sensation. Ultimately, the tumor can press on the brainstem, which can be life threatening.

How often do acoustic neuromas occur?

Asymptomatic acoustic neuromas have been found during autopsy in 2.4% of the general population. Estimates of symptomatic acoustic neuromas range from one in every 3,500 persons to five in every million people. More women than men are affected, and most acoustic neuromas are diagnosed between the ages of thirty and sixty.

What are the symptoms of an acoustic neuroma?

1. Early symptoms are easily overlooked, thus making diagnosis a challenge. However, there usually are symptoms pointing to the possibility of an acoustic tumor, which means that persons with "inner ear" hearing problems should be completely evaluated to eliminate acoustic neuroma as the cause. It may be that less serious problems, such as Meniere's disorder or a hardening bone of the middle ear (otosclerosis), are the cause.

2. The first symptom in over 90% of those with a tumor is a reduction in hearing in one ear, oftentimes accompanied by ear or ringing. The loss of hearing is usually subtle and worsens very slowly, although occasionally a sudden loss of hearing is noted. There may be feeling of fullness in the affected ear. Unfortunately, since the hearing loss is often mild and there is no pain, some people shift the phone to the opposite ear or make other compromises for the one-sided hearing loss rather than seeking medical evaluation.

3. Unsteadiness and balance problems may occur early in the growth of the neuroma since the balance portion of the eighth cranial nerve is where the tumor arises. The remainder of the balance system sometimes compensates for this loss, and thus balance problems may be forgotten after some time.

4. As the tumor presses on other cranial nerves, facial sensation may be affected, with numbness and facial tingling felt constantly or intermittently. Headaches and unsteady gait caused by increased intracranial pressure may be experienced.

How do you identify the tumor?

Advances in medicine have made possible the identification of small acoustic neuromas, that is those still confined to the internal auditory canal. After routine auditory tests reveal loss of hearing and speech discrimination ("I can hear a sound in that ear, but I can't understand what is being said."), an auditory brainstem response test (ABR, BAER, BSER) may be done. This test provides information on the passage of an electrical impulse along the circuit from the ear to the brainstem pathways. The results imply the cause of a poorly-functioning acoustic nerve. A detailing "imaging" usually is ordered if there is an abnormality in the ABR test, which suggests the presence of an acoustic tumor.

The CT scan has proven to be a powerful tool in locating acoustic neuromas. Although small tumors still confined to the internal auditory canal may not show on the plain CT scan, air or contrast materials introduced into the body will enhance the tumor.

Magnetic Resonance Imaging (MRI) is a more recently developed diagnostic test which is very effected in identifying acoustic neuromas. MRI uses modern computer technology to process the results of passing momentary harmless magnetic pulses and radio frequency waves through the portion of the body being studied. The image which is formed clearly defines an acoustic neuroma if it is present. Gadolinium, a contrast material, is required to enhance the tumor. Currently, this imaging study is preferred.