ACOUSTIC NEUROMA-THE BASIC FACTS Diagnosis

Advances in medicine, especially imaging technology have made the identification of small AN's possible. After routine auditory tests reveal loss of hearing and speech discrimination (i.e. "I can hear sound in that ear, but can't understand what's being said") a special test for hearing which records responses from the brain-stem called the auditory brainstem response test (ABR, BAER, BSER) may be done. The results of this test detect the cause of a poorly functioning 8th nerve. Once an abnormality in the ABR test suggesting an AN is found, imaging is done to confirm the diagnosis. At our institute however, we do not perform the ABR test in all patients to diagnose an acoustic neuroma as majority of the patients can be diagnosed by imaging techniques (MRI/CT scans) which is the gold standard. CT scan has proven to be a powerful tool in locating AN's. The only drawback is that small tumors confined to the internal auditory canal (IAC) may not show on plain CT scan. Such cases require air or contrast materials to be introduced into the body in order to enhance the tumor. MRI is a more recently developed diagnostic test which has become the gold standard for diagnosis of AN. Gadolinium is the contrast material used to define & enhance the tumor.

Small tumors

A small tumor is also called intracanalicular because it is confined within the bony internal auditory canal (figure). A patient with such a tumor may have hearing loss, ringing in the ear or ear noise, and vertigo or dizziness.

Medium tumors

A medium sized acoustic neuroma is one which has extended from the bony canal into the brain cavity, but has not yet produced pressure on the brain itself (figure). Patients with such tumors have worsening of their hearing, difficulty in balance, in addition to dizziness, and occasionally, the onset of headaches due to irritation of the lining of the brain called dura. Some patients may experience numbness of the mid-face or diminished sensation in the eye during the later stages.

Large tumors

A large tumor is one which is extended out of the internal auditory canal in to the brain cavity and is sufficiently large to produce pressure on the brain and disturb vital centers in the brain (figure). During this stage, all previous symptoms worsen; facial twitch and weakness may occur, and finally patient may develop hydrocephalus due to the blockage of the cavity which contains CSF-the resultant symptoms are headache, visual loss and double vision.

For more information, you may visit the Acoustic Neuroma Association website