What is an Acoustic Neuroma?
An acoustic neuroma (also called a vestibular schwannoma) is a benign (non-cancerous) tissue growth that arises from the balance nerve. There are four balance (vestibular) nerves, two for each of the right and left ears. There is an upper (superior) and lower (inferior) balance nerve for each ear. The balance nerves are thin cords that stars at the base of the brain and travel through a small, bony canal (internal auditory canal) of the skull to the inner ear. Two other nerves, the hearing nerve and the facial nerve (7th cranial nerve), travel directly alongside the balance nerves through the internal auditory canal to the inner ear. Both the balance and hearing nerves are part of the 8th nerve complex.
Acoustic neuromas commonly develop inside the internal auditory canal. These tumors usually grow slowly over a period of many years. When acoustic neuromas grow in size, the tumor compresses the hearing nerve. Therefore, hearing loss is the first symptom in over 90% of patients with acoustic neuroma. Tinnitus (ear noise) is also a common symptom. Loss of balance, dizziness or facial weakness may develop as the tumor continues to grow.
Identifying the tumor
With appropriate tests it is now possible to identify tumors as small as 2-3mm in size. The first step in identifying a possible tumor is a thorough history and physical examination by a physician. Hearing testing is performed to identify any loss of hearing or speech understanding. An auditory brainstem response test (abbreviated ABR, BAER, or BSER) is ordered if there are any asymmetries in hearing testing between the right and left ears. An ABR provides information on the passage of an electrical impulse along the hearing nerve from the ear to the brain. Abnormal ABR results suggest a poorly functioning hearing nerve. A detailed "imaging" is ordered if there is an abnormality of the ABR test.
The most accurate imaging technique for acoustic neuroma identification is a magnetic resonance imaging (MRI). A properly performed MRI can identify acoustic neuromas as small as 2-3mm. MRI uses magnetic pulses and radio frequency waves to produce an image of a portion of the body being studied. Radiation is not used to perform an MRI. A contrast material, gadolinium, is given during the MRI to enhance the visibility of the tumor.
Since acoustic neuromas are benign, often slow-growing tumors, careful observation over a period of time may be appropriate for some patients. When a small tumor is discovered in an older patient, observation to study the growth rate of the tumor may be indicated if acute symptoms are not present. A MRI scan of the tumor and surrounding region must be performed periodically to determine if there is significant change in the size of the tumor. If the tumor does not grow, observation is continued. If the tumor increases in size, treatment may be recommended. For more information regarding observation, please click here.
There are several surgical approaches that may be used to remove an acoustic tumor. The type of approach is individualized depending on the patient's wishes, hearing level, other neurological symptoms, as well as the location and size of the tumor. The Ear Institute of Chicago is well versed in all surgical approaches for acoustic neuroma management. For more information regarding surgical removal, please click here.