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Posted on 10/08/2001 1:05:17 PM PDT by Reelect President Dubya

Answers to frequently asked questions about acoustic neuromas.

What is an Acoustic Neuroma?

An acoustic neuroma (sometimes termed a neurolemmoma or schwannoma) is a benign (non-cancerous) 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 associated with transmitting sound and the other sending 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 2 cm (0.8 inches) long and it is here that acoustic neuromas originate from the sheath surrounding the eighth nerve. The facial nerve provides motion of the muscles of facial expression.

Acoustic neuromas usually grow slowly over a period of years. They expand in size at their site of origin and when large can displace normal brain tissue. The brain is not invaded by the tumor, but the tumor pushes the brain as it enlarges. The slowly enlarging tumor protrudes from the internal auditory canal into an area behind the temporal bone called the cerebellopontine angle. The tumor now assumes a pear shape with the small end in the internal auditory canal. Larger tumors can press on another nerve in the area (the trigeminal nerve) which is the nerve of facial sensation. Vital functions to sustain life can be threatened when large tumors cause severe pressure on the brainstem and cerebellum part of the brain. Tumors are typically described as small (less than 1.5 cm), medium (1.5 cm to 2.5 cm) or large (more than 2.5 cm).

Are Acoustic Neuromas hereditary?

No. Although there is an inheritable condition called neurofibromatosis which can lead to acoustic neuroma formation in some people, most acoustic neuromas occur spontaneously without any evidence of an inheritable pattern.

How often do Acoustic Neuromas occur?

Asymptomatic acoustic neuromas have been found during autopsy in less than one in one-hundred or perhaps as few as .01% of the general population. Acoustic neuromas large enough to cause hearing loss and other symptoms occur in about one person in 100,000. Most acoustic neuromas are diagnosed in patients between the ages of 30 and 60.

Symptoms of Acoustic Neuroma

Early symptoms are easily overlooked, thus making diagnosis a challenge. However, there usually are symptoms pointing to the possibility of an acoustic neuroma. The first symptom in 90% of those with a tumor is a reduction in hearing in one ear, often accompanied by ear noise or tinnitus. The loss of hearing is usually subtle and worsens slowly, although occasionally a sudden loss of hearing is noted. There may be a feeling of fullness in the affected ear. These early symptoms are sometimes mistaken for normal changes of aging, and diagnosis is often delayed.

Since the balance portion of the eighth nerve is where the tumor arises, unsteadiness and balance problems may occur during the growth of the neuroma. The remainder of the balance system sometimes compensates for this loss, and no imbalance will be noticed. Larger tumors can press on the trigeminal nerve, causing facial numbness and tingling, constantly or intermittently. Increase of intracranial pressure may be experienced with headaches, clumsy gait and mental confusion. This is a life-threatening complication requiring urgent treatment.

Identifying the tumor

Advances in medicine have made possible the identification of small acoustic neuromas; that is, those still confined to the internal auditory canal. Routine auditory tests may reveal a loss of hearing and speech discrimination (the patient can hear sound in that ear, but cannot understand what is being said).

An audiogram should be performed to effectively evaluate hearing in both ears. This test is important to begin the diagnosis of acoustic neuroma. Magnetic resonance imaging (MRI) is the diagnostic test that is preferred for identifying acoustic neuromas. Gadolinium, an enhancing material, is required to reveal the tumor. The image formed clearly defines an acoustic neuroma if it is present. Currently, this imaging study is the preferred test for identifying acoustic neuromas.

An auditory brainstem response test (ABR, BAER, or BSER) may be done in some cases. This test provides information on the passage of an electric impulse along the circuit from the inner ear to the brainstem pathways. An acoustic neuroma can interfere with the passage of this electrical impulse through the hearing nerve at the site of tumor growth in the internal auditory canal. This implies the possible diagnosis of an acoustic neuroma when the test is positive.

When a MRI is not available or cannot be performed, a computerized tomography scan (CT scan), with contrast, is suggested for patients in whom an acoustic neuroma is suspected. The CT scan and audiogram can provide valuable information to determine the presence of an acoustic neuroma. However, the MRI is nearly 100% accurate in identifying the presence of an acoustic neuroma and should be performed.

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