Screening & 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 the 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.
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.
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.
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.
Early symptoms of acoustic neuroma can occur in other conditions of the ear that can be easily overlooked. There is no typical pattern of symptoms which again makes early diagnosis of acoustic neuroma quite challenging. However, there are symptoms that act as indicators to the possibility if an acoustic neuroma. Patients with "inner ear" problems should be completely evaluated to rule out acoustic neuroma as a cause of these symptoms. It is possible that Meniere's disease or hardening of the bone of the middle ear (otosclerosis) could be causing these symptoms. Patients with acoustic neuroma may present the following symptoms:
- Hearing loss
- Ringing in the ears (tinnitus)
- Dizziness (vertigo)
- Difficulty in balance (imbalance or dysequilibrium)
- Fullness or pressure in the ears
- Facial numbness or paralysis (for very large tumors)
In over 90 percent of the patients with acoustic neuroma, the first symptom is a reduction in hearing in one ear due to involvement of the VIII nerve. This is usually accompanied by ringing in the ears or ear noise-also called "tinnitus". The hearing loss is usually subtle and worsens very slowly over a period of time. In some cases, there maybe a sudden loss of hearing. Some patients may experience a sense of fullness in the affected ear. Unfortunately, since hearing loss is often mild and there is no pain, patients tend to ignore the change in hearing and merely shift the phone to the opposite ear or make other compromises for the one-sided hearing loss rather than seek medical attention.
Vertigo & Imbalance
Since the tumor usually arises from the vestibular nerve which is responsible for balance, unsteadiness or balance problems may be one of the earlier symptoms in the growth of the tumor. Since the remainder of the balance system compensates for this loss, balance problems may be forgotten after some time.
As the tumor grows larger in size and starts pressing over other nerves, mainly the trigeminal nerve, facial sensation may be affected. The patients will then experience numbness and facial tingling, constantly or intermittently. Patients may also have facial tics or spasms. As the tumor grows larger or presses on the brainstem, the patient will experience headaches, facial weakness, vertigo and unsteady gait due to raised intracranial pressure.