Vestibular Schwannoma (Acoustic Neuroma)
Vestibular Schwannomas, also called Acoustic Neuromas, are benign growths that occur along the nerve that connects the inner ear to the brain (vestibulocochlear nerve). This nerve controls hearing and balance. They arise from the Schwann cells, which are cells that surround the nerves. Vestibular schwannomas can cause loss of hearing or problems with balance.
What Are the Causes of Vestibular Schwannoma?
A malfunction in a gene on chromosome 22 has been found to cause vestibular schwannomas. This gene normally produces a protein that controls the growth of Schwann cells covering the nerve. Certain risk factors make it more likely that people can develop a vestibular schwannoma:
- Genetic factors
- People with a genetic syndrome called neurofibromatosis type 2 (NF 2) are more likely to develop schwannomas.
- NF 2 patients will often develop vestibular schwannoma on both sides, or on other nerves.
- Prolonged exposure to loud noise
- Previous radiation therapy to the head and neck area during childhood
- Genetic factors
What Are the Symptoms of Vestibular Schwannoma?
Symptoms usually arise because the schwannoma grows large enough to put pressure on the nerves that control hearing, or the surrounding brain. The most common symptoms of vestibular schwannomas are:
- Hearing loss. This usually happens slowly over years, so a patient may not even be aware of the hearing loss. This is most commonly just on one side.
- Tinnitus, a ringing sound in the affected ear
- Balance problems or a feeling of leaning to one side
- Numbness, pain or weakness of the facial muscles
What Are the Treatment Options?
There are several ways to treat vestibular schwannomas including observation, surgery or radiation therapy. The aim of treatment is relieve symptoms, while preserving the function of the nerve.Generally active treatment will be recommended if the schwannoma is causing significant symptoms, or if it is found to be growing rapidly. Active treatment is more likely to be recommended if the patient is young or the schwannoma is particularly large.
Most vestibular schwannomas are slow growing and may not cause a patient any significant problems over their lifetime. If the tumour is small, a “watch and wait” approach maybe recommended with repeat imaging (usually MRI scans every 6 to 12 months) and hearing tests, rather than treating the schwannoma straight away. If during observation there is rapid growth, evidence of hearing loss or development of new symptoms then active treatment should be considered.
Removing the schwannoma with surgery can stop symptoms getting any worse by relieving pressure on the nerve. This may involve accessing the tumour through the inner ear, or through an incision through the skull. If the schwannoma is completely removed it is very unlikely to grow back, however there is a risk of damaging nerves during surgery, which could cause further hearing loss or damage to the nerve controlling the facial muscles. Some patients may also experience headaches following surgery.
If the tumour is located too close to important nerves or blood vessels it may not be able to be completely resected. If residual tumour is left behind, then this can re-grow following surgery in approximately 15% of patients.
Radiation therapy can also be used to treat vestibular schwannoma. Radiation therapy for schwannoma is most commonly given as stereotactic radiosurgery or stereotactic radiation therapy (a single dose or just a few doses). Conventional fractionated radiation therapy (small doses given once a day, 5 days a week for 5 to 6 weeks) can also be used, usually for larger tumours. The aim of radiation therapy is to stop the growth of the tumour, and preserve the function of the nerve as much as possible.
Stereotactic radiosurgery involves multiple high energy X-ray beams that are focused precisely on the tumour and avoiding the surrounding normal structures. It is non–invasive (that is NOT surgery despite the name) and usually involves just a single treatment. The patient needs to be kept extremely still during treatment to ensure accuracy, so a special immobilisation face mask or head ring is used during treatment.
Stereotactic Radiation Therapy
Stereotactic radiation therapy is similar treatment to radiosurgery but the treatment is given over 5 to 10 sessions, rather than one single dose.
Fractionated Radiation Therapy
Fractionated radiation therapy uses the same high energy X-ray beams to treat the tumour but treatment is delivered given in small doses (or fractions) each day over a period of 5-6 weeks.
How effective is radiation therapy?
Radiation therapy is very effective in controlling vestibular schwannomas.
Stereotactic techniques (see above) are able to achieve local control rates of between 91 to 100% at 10 years post treatment.
What are the side effects of radiation therapy?
Most patients do not notice any immediate side effects with stereotactic radiation therapy for vestibular schwannoma, although headache or nausea can occur rarely. Long term side effects following radiation therapy for vestibular schwannoma can occur months or years after treatment. The main concern is damage to the cranial nerves in the region.
Overall the risk of damage to the cranial nerves with modern radiation therapy techniques is low at less than 5%. Other possible side effects include:
- Tumour expansion. In some cases the tumour can slightly increase in size at around 6-12 months.
- Hearing loss. This can occur in 30-40% of patients at 10 years. Hearing tends to decline slowly over years, and is more likely to happen in older patients, larger tumours, or patients with a greater degree of hearing loss prior to treatment.
- With any exposure to radiation there is a very small increase in the risk of developing another second cancer in the future
The best person to discuss radiation therapy with is a Radiation Oncologist. You can ask your surgeon or General Practitioner for a referral to a Radiation Oncologist for a discussion whether radiation therapy is a suitable treatment option for you.
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