MediFocus Guidebook
Acoustic Neuroma
160 Pages · Updated: 08/04/2014
MediFocus

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The Intelligent Patient Overview - Diagnosis of Acoustic Neuroma


Signs and Symptoms

The symptoms of acoustic neuromas often appear so gradually that a person does not recognize them - or becomes accustomed to them - and may not seek help until they become more severe. In fact, many of the small, asymptomatic acoustic neuromas are discovered incidentally when a person is being evaluated for another problem.

In a 1998 Members' Survey of the Acoustic Neuroma Association, reported symptoms prior to treatment were hearing loss (88%), imbalance (64%), tinnitus (64%), feeling of fullness (43%), headache (33%), facial numbness (22%), facial weakness (16%), facial twitching (13%) change in taste or smell (10%), and difficulty swallowing (7%). Many of these patients had large tumors.

Hearing Loss

The most common symptom of acoustic neuroma is the gradual reduction of hearing in one ear, which occurs in 80% to 90% of patients. Ear noise or tinnitus (ringing or roaring in the ears) often accompanies this. The hearing loss may be so subtle that it is often overlooked or associated with the normal process of aging.

Patients typically have a decreased ability to perceive and discriminate sounds, particularly those sounds at higher frequencies. Approximately 70% of people with acoustic neuromas have a high frequency pattern of hearing loss. A person may complain of difficulty hearing someone speak on the telephone in one ear, locating where sounds are coming from, or understanding the speech of soft-spoken people or young children.

The hearing loss typically worsens over a period of many years, eventually leading to total deafness in the affected ear. It is less common for people to experience a complete and sudden loss of hearing. When this does occur, it is often associated with a viral infection or vascular occlusion. Speech discrimination (the ability to hear and understand speech) is often affected much more greatly than pure tone hearing loss. Some patients may also experience both low and high frequency hearing loss. A small number of people may experience hearing loss in both ears while others may continue to experience normal hearing in one ear.

As the tumor grows and causes pressure on the acoustic nerve, people may also experience vertigo, nausea, balance problems, or unsteadiness because the eighth nerve where the tumor originates is associated with balance. In many cases, however, the balance system finds a way to compensate for the loss of one nerve and the symptom goes undetected, delaying diagnosis.

Tinnitus

Tinnitus - a ringing or roaring in the ears - is a very common symptom of acoustic neuromas. In the majority of cases, the tinnitus is high pitched and only occurs in the ear affected by the tumor. A small number of people may experience unilateral tinnitus. It is generally regarded as an early symptom of the disease.

Vertigo

True vertigo, a disabling sensation in which an individual feels that his/her surroundings are in a constant motion, occurs in about 19% of people with acoustic neuromas. It is more commonly caused in the early growth stages of the tumor as opposed to a large tumor at the time diagnosis.

Balance Problems

Approximately half of people with acoustic neuromas suffer from problems with balance. These problems appear to become more frequent with larger tumors.

Cerebellar dysfunction is characterized by intention tremor and gait ataxia (unsteadiness while walking). True cerebellar dysfunction is less common in people with acoustic neuromas and often limited to those people with large tumors. When this occurs, people tend to fall towards the side where the tumor is located.

Facial Nerve Dysfunction

Other cranial nerves may also be affected by tumor growth. If the seventh cranial (facial nerve) nerve is compressed, a person may experience facial weakness on the affected side, slurred speech, difficulty closing the eyelid, and decreased or absent corneal reflux.

Compression of the fifth cranial nerve is less common and may result in a person having facial paresthesia (a "pins and needles" tingling) or anesthesia (loss of feeling and sensation) and difficulty chewing. Facial numbness and tingling are often symptoms when larger tumors press against the trigeminal nerve. The numbness and tingling can occur intermittently or be constant.

Swallowing Problems

If the ninth (glossopharyngeal), 10th, or 12th cranial nerves are compressed, a person may experience difficulty swallowing and/or speaking. Difficulty swallowing can also be related to pressure against the trigeminal nerve.

Life-Threatening Symptoms

When a large tumor significantly compresses or distorts a person's brainstem, symptoms can include nausea, vomiting, and lethargy that can lead to coma, respiratory depression, and death. Immediate treatment should be sought.

Increased cranial pressure can lead to papilledema (swelling of the optic nerve) and life-threatening hydrocephalus (an abnormal increase in the amount of cerebrospinal fluid within the ventricles of the brain).

Differential Diagnosis

Thanks to medical advances, health care providers can often locate small acoustic neuromas when they are still confined to the internal auditory canal. Tumors are typically classified as small (up to .05 cm), medium (.05 cm to 2 cm) or large (2 cm to 4 cm or larger).

Diagnostic Testing

  • Simple auditory tests of both ears, such as an audiogram, can be used to determine if hearing loss is present or if there is speech discrimination (when a person can hear sound but does not understand what is being said). An audiogram is arranged from low to high frequencies as well as soft sounds to loud sounds. Hearing is measured in decibels (units of loudness). Any difficulty in understanding speech is also reported by the patient. Normal hearing ranges from 0 to 20 dB in all frequencies. If an audiogram is abnormal, and MRI is usually ordered to confirm diagnosis.

  • Magnetic resonance imaging (MRI) is most commonly used to identify and diagnose acoustic neuromas. With an MRI, harmless magnetic pulses and radio frequency waves are intermittently passed through the area of the body that is being tested. An enhancing material called gadolinium is used to detect if a tumor is present.

  • In those cases when an MRI cannot be performed, a computerized tomography scan (CT scan) may be ordered. Since an ordinary CT scan will not reveal small tumors still confined to the internal auditory canal, contrast materials are used to enhance the image of acoustic neuroma.

  • An auditory brainstem response test (ABR, BAER, or BSER) provides information as an electrical impulse travels from the inner ear to the brainstem pathways. When acoustic neuroma is present in the internal auditory canal, it typically disrupts the passage of the electrical impulse through the hearing nerve.

  • Electrocochleography (EcochG) to measure cochlear function may be helpful in determining the site and severity of hearing impairment. This test involves clicks and short tone bursts that are recorded through a transtympanic needle electrode.

  • Caloric stimulation with electronystagmography (ENG) is less commonly used. This test appears to lack specificity in identifying other inner ear problems and may appear as normal in people with acoustic neuromas.
While a CT scan and an audiogram can provide valuable information to aid diagnosis, an MRI is generally considered to be the most accurate diagnostic test for identifying the presence of an acoustic neuroma.



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