The diagnosis of an acoustic neuroma is often triggered by a patient’s symptoms. The most common presenting feature of acoustic neuromas, occurring in 90% of patients, is unilateral hearing loss. When "pure tone audiometry" is used, the most common finding is high frequency hearing loss. The hearing loss is progressive in most patients, but in approximately 12% of patients the hearing loss may occur suddenly. Other symptoms of the acoustic neuroma include asymmetric tinnitus (ringing in the ear), dizziness and disequilibrium (difficulty with balance). Because symptoms of these tumors resemble other middle and inner ear conditions, they may be difficult to diagnose. Preliminary diagnostic procedures include ear examination and hearing test. Computerized tomography (CT) and magnetic resonance imaging (MRI) scans help to determine the location and size of the tumor. Early diagnosis offers the best opportunity for successful treatment.
- Hearing test (audiometry): A test of hearing function, which measures how well the patient hears sounds and speech, is usually the first test performed to diagnose acoustic neuroma. The patient listens to sounds and speech while wearing earphones attached to a machine that records responses and measures hearing function. The audiogram may show increased "pure tone average" (PTA), increased "speech reception threshold" (SRT) and decreased "speech discrimination" (SD).
- Brainstem auditory evoked response (BAER): This test is performed in some patients to provide information on brain wave activity as a response to clicks or tones. The patient listens to these sounds while wearing electrodes on the scalp and earlobes and earphones. The electrodes pick up and record the brain's response to these sounds.
- Scans of the head: If other tests show that the patient may have acoustic neuroma, magnetic resonance imaging (MRI) is used to confirm the diagnosis. MRI uses magnetic fields and radio waves, rather than x-rays, and computers to create detailed pictures of the brain. It shows visual “slices” of the brain that can be combined to create a three-dimensional picture of the tumor. A contrast dye is injected into the patient. If an acoustic neuroma is present, the tumor will soak up more dye than normal brain tissue and appear clearly on the scan. The MRI commonly shows a densely "enhancing" (bright) tumor in the internal auditory canal.
- An acoustic neuroma typically grows on one of the branches of the 8th cranial nerve—the nerve that serves as the conduit for information from the ear to support hearing and balance.
- More than 80% of patients having acoustic neuromas have tinnitus. Tinnitus is usually described as hissing, ringing, buzzing or roaring. Tinnitus is often said to be high pitched. In some patients the tinnitus is a pure tone, and in others the tinnitus is a noise. Many patients with acoustic neuroma have combined tinnitus and hearing loss.
(Printed with permission of Johns Hopkins Medicine) http://www.hopkinsmedicine.org/