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The eighth cranial nerve - also known as the auditory or vestibulocochlear nerve - consists of the vestibular and cochlear divisions, which runs from the inner ear to the brain. The cochlear division is responsible for transmitting information about hearing and vestibular division is responsible for balance.
An acoustic neuroma is a benign tumour that develops when the specialized (Schwann) cells surrounding the vestibular division of the auditory nerve, grow at an abnormal rate in the internal auditory canal. The tumour if left untreated, can grow into the auditory canal and all the way through to the brain.
Acoustic neuromas generally grow slowly, so symptoms develop gradually. The main ones - dizziness, hearing loss and ringing in the ears (tinnitus) - are due to the effects of the tumour pressing on the auditory nerve. If the tumour grows large enough, it also may press on the nearby facial nerve and cause facial paralysis or tingling. Although the tumors are not cancerous, they can become life threatening if they grow so large that they press on brain structures that control vital body functions.
People with a hereditary disease called neurofibromatosis have a higher risk of developing acoustic neuromas and can develop tumours on both sides of the head.
Because the tumour grows so slowly, the symptoms are easy to miss or misinterpret. The earliest and most common symptoms of an acoustic neuroma are a gradual reduction in hearing in one ear and tinnitus, a ringing or noisy sound in the ear.
Other possible symptoms that may occur, depending on the extent of the tumour, include: dizziness, loss of balance or clumsiness facial paralysis, numbness or tingling, headache, a feeling of something clogging the ear, or mental confusion.
Most of these tumours grow slowly, taking years before they become large enough to cause symptoms. Once diagnosed, they must be treated or carefully observed; they do not resolve on their own.
Occasionally, doctors may recommend no action at all beyond regular monitoring. This is because an acoustic neuroma typically grows at a slow rate in the initial stages. However, in most cases, treatment is required. Options may include:
Surgery ? microsurgery techniques are used to remove the tumour. However, side effects can include loss of hearing, and facial nerve damage.
Stereotactic procedure ? a non-invasive device that directs gamma radiation at the tumour. Side effects may also be experienced with this procedure.
All patients will require close follow-up. Patients and their physicians need to pay close attention for hearing loss, balance and facial muscle weakness. Hearing tests and MRIs will be performed periodically to assess changes in growth or new growth.
Acoustic neuromas are not malignant and do not spread to other parts of the body.
However, some untreated neuromas can grow very aggressively and cause severe and permanent damage to nerves, ear and brain tissue. Hearing loss and balance problems related to the tumour may remain, even after treatment by surgery or radiation. If an acoustic neuroma is diagnosed early, when the tumour is small, treatment is more likely to preserve hearing.
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