An acoustic neuroma is a benign (non-cancerous) tumour. In most cases, these tumors grow slowly over a period of years, but sometimes the rate of growth is more rapid. They arise from the cells of the schwann cell lining of the vestibular or auditory nerve, hence are sometimes referred to as ‘Acoustic Schwannomas’, ‘Vestibular Schwannomas’ or ‘Vestibular Neuromas’. Also known as the vestibulochocheal or eighth cranial the nerve runs from the brain stem to the inner ear and carries signals from the sounds we hear and also gives us the sensation of balance. They may present as sizeable by the time that symptoms become apparent.
Radiosurgery for acoustic neuromas is well established and can be useful in the treatment of both unilateral and bilateral neuromas. Although typically limited to the treatment of neuromas below 4cm in diameter, radiosurgery can be planned to preserve any residual hearing in the side being treated. The choice of treatment may be based on tumour size, hearing in the ear at time of diagnosis, patient age and health, and patient preference.
Symptoms can be mild or severe, and multiple symptoms might develop rather rapidly.These include declining hearing, tinnitus (a ringing noise) and loss of balance. The first signs or symptoms usually are related to ear function and include tinnitus (ear noise/ringing in the ear) and often disturbances in hearing on one side. As the eight cranial nerve runs alongside the seventh (facial) nerve which enables us to move one half of our facial muscles a loss of movement on one side of the face (similar to a Bells Palsy) can sometimes occur. In rare cases the tumour can press on the fifth (trigeminal nerve) and cause numbness or rarely, facial pain.
What are the causes?
The cause of acoustic neuroma is not well understood however, it is currently thought that one-sided sporadic acoustic neuromas arise due to a spontaneous mutation (alteration in genetic material) on chromosome 22. This produces an overproduction of the Schwann cells and the formation of a lump, as they multiply producing a tumour filling the canal housing these nerves.
How common are acoustic neuromas?
The incidence is approximately 2 per 100,000 per year, accounting for 8 out of 100 cases of primary brain tumours. That equates to 1200 new diagnoses per year assuming a UK population of 60 million. Based on MRI studies, the true prevalence may be around 0.05% (1 in 200) of the population, which equates to 30,000 people, also assuming a UK population of 60 million. They have an increasing incidence with age, and are often found more commonly in women. Some genetic conditions such as NF-II can also lead to an increased risk of Acoustic Neuromas.
Diagnosing acoustic neuromas
The diagnosis of this condition is made after the patient reports symptoms. There is then a careful examination of the ear and the hearing and balance systems, along with a complete neurological examination and then sophisticated audiometry to test the hearing along with a clinical balance assessment. An MRI scan is used to make the final diagnosis and this is the gold standard diagnostic test.
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