The nervous system consists of the brain and the spinal cord and all the connections these have withe the various tissues of the body. Most nerves in the body are connected first to the spinal cord, which runs through the space within each vertebra, and then to the brain.
There are 12 paiirs of nerves which arise directly from the brain and pass through the openings in the skull to reach their locations. There are called the cranial nerves. The eighth cranial nerve (properly known as the ‘vestibulocochlear’ nerve is the one which serves hearing and balance. It is really in two parts: one part of the nerve is associated with transmitting sound information and the other with sending balance information to the brain from the hearing and balance organs located within the inner ear.
An acoustic neuroma is a benign (non-cancerous_ growth that arises from the sheath surrounding the eighth cranial nerve. The term ‘acoustic neuroma’ is, strictly speaking, incorrect because the tumour arises usually on the part of the eigth nerve which deals with balance rather than sound. It also is a tumour of the covering (sheath) of the nerve rather than the nerve itself.
Despite these inaccuracies, the term hs stuck. True acoustic neuromas occur in conjunction with a fairly rare hereditary condition called neurofibromatosis 2, in which multiple cranial nerve tumours arise.
Acoustic neuroma is diagnosed only once per year per 100,000 people so from that point of view it is uncommon. However small acoustic neuromes, not causing any symptoms, can be found in up to nearly 3% of elderly people. There is no known cause for these tumours, other than the hereditary type. They usually grow lowly over a period of years and when large may press on normal brain tissue. Larger tumours can press on another nerve in the same area (the fifth cranial nerve or ‘trigeminal’ nerve) which is the nerve concerned with facial sensation.
What are the symptoms of acoustic neuroma?
- Reduction in hearing on one ear which is usually subtle and worsens slowly
- Ear noise or tinnitus in one ear.
- Unsteadiness and balance problems (since the balance portion of the eighth nerve is where the tumour arises).
- Facial numbness and tingling may occur if the tumour is large, and so presses on the fifth cranial nerve.
- Headaches, clumsy gait and mental confusion may be experienced in the pressure on the brain arises
The pattern of symptoms depends mainly on the exact place along the nerve that the tumour arises, which in turn determines which of the local structures (nerves & brain tissue) are pressed on first. As the tumors keep on growing a young person who develops acoustic neuroma will almost always eventually develop symptoms from it.
How is acoustic neuroma diagnosed?
- Routine hearing tests may reveal a loss of hearing and speech discrimination (the patient can hear sound in that ear but cannot understand what is being said).
- An auditory brainstem response test (ABR) may be done in some cases. This test measures the speed at whcih an electric impulse from the inner ear passes to the brain. The test is positive when an acoustic neuroma slows the signal down.
- Magnetic resonance imaging (MRI) with a contrast dye is the most commonly performed type of scan to reveal an acoustic neuroma.
How is acoustic neuroma treated?
There is no medication known to have a substantial effect on growth or to shrink acoustic neuroma tumours. There are three options:
- Conservative management or ‘wait and see’: This involves periodic monitoring with serial hearing tests and/or MRI scans. It is usually reserved for tumours of less than one centimetre in size.
- Radtiation treatment may be employed when the risk of surgery is high because of other medical problems.
- Surgical removal of the tumour performed by a neuro-otologist (specialist in hearing and nervous system disorders) and a nerosurgeon. Surgery is the preferred treatment option in most cases and may also allow preservation of hearing.
All forms of treatment carry some risks. As the facial nerve, which controls the muscles of the side of the face, usually runs across the tumour there can be a high risk of facial nerve damage from surgery. This can lead to paralysis of one side of the face.
Removal of the tumour might interfere with balance, leading to ‘vertigo’ – an unpleasant feeling of unsteadiness. Because the tumour is in an awkward place with other important brain structures immediately around it there are risks of damage for example to the nerves controlling eye movement and swallowing.
The risk to a person’s hearing varies slightly with the surgical approach and the technical problems in an individual person’s case, but complete loss of hearing on the affected side is a real risk that needs to be considered.
These risks diminish when the surgical team has a high level of experience in operating on acoustic neuroma, but they should be fully discussed in advance with the patient.
Increasing interest is being shown in very accurate X-ray treatment – called ‘stereotactic radiotherapy’. In this the X-rays are guided precisely to the site of the tumour. Although still being researched this treatment can be used either on its own or in combination with surgery, usually to reduce the size of the tumour before the surgeon operates
All credit for information in this post belongs to: http://www.netdoctor.co.uk/diseases/facts/acousticneuroma.htm
