An acoustic neuroma, otherwise known as a vestibular schwannoma is a benign (non-cancerous) tissue growth that arises on the eighth cranial nerve leading from the brain to the inner ear. Functions associated with this nerve include transmitting sound and balance.
These tumors usually grow slowly over a period of years. They expand in size at their site of origin and when large can displace normal brain tissue. The brain is not invaded by the tumor, but the tumor pushes the brain as it enlarges. The slowly enlarging tumor protrudes from the internal auditory canal into an area behind the temporal bone called the cerebellopontine angle. Acoustic neuroma is the most common type of tumor to occur within the cerebellopontine angle in the brain (between the cerebellum and pons). Of tumors in this region, 80% are acoustic neuromas followed by meningiomas. Tumors are typically described as small (less than 1.5 cm), medium (1.5 cm to 2.5 cm) or large (more than 2.5 cm).
Acoustic neuroma tumors usually arise from the sheath (lining) of the vestibular component 8th cranial (vestibulo-cochlear) nerve, which is critical in balance function. The nerve lining is made up of Schwann cells.
- Benign (non-cancerous)
- Slow growing
- Also referred to a neurinoma, schwannoma, or vestibular schwannoma
- Diagnoses in 1 person per 100,000 people per year
- More common in women than men
Acoustic neuroma is the most common type of tumor to occur within the cerebellopontine angle in the brain (between the cerebellum and pons). Of tumors in this region, 80% are acoustic neuromas followed by meningiomas.
Symptoms of Acoustic Neuroma
Because acoustic neuromas commonly grow slowly over many years, the body adapts to the gradual changes caused by the tumor and symptoms tend to occur very subtly and gradually. Symptoms of acoustic neuroma commonly include:
- Progressive or sudden hearing loss in one ear (the most common initial symptom)
- Tinnitus (ringing in the ear) in one ear
- Problems understanding telephone conversations
- Unsteady walk
- Larger lesions can manifest with facial numbness, headache, and imbalance
Acoustic neuromas are benign tumors. As the tumor grows, it can cause problems with hearing, balance and facial movement. An acoustic neuroma can be life threatening when they grow large enough to compress the brain stem significantly.
Causes of Acoustic Neuromas
Acoustic neuromas are thought to arise when there is a defect in a certain tumor suppressor gene. It is unknown why this genetic defect occurs. A high association of acoustic neuroma exists with the genetic disorder neurofibromatosis type 2 (NF2).
Diagnosis of Acoustic Neuroma
Acoustic neuromas are easily diagnosed by current technology. The best method that is currently available for the diagnosis of acoustic neuromas is Magnetic Resonance Imaging (MRI) of the brain with a contrast media (dye). An acoustic neuroma can be diagnosed with almost complete accuracy using the MRI scan. Most patients tolerate MRI scans very well, but there are a few limitations.
Other tests useful for diagnosing acoustic neuromas from other disorders are:
- CT scan
- Auditory Brainstem Evoked Responses (ABR)
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