Acoustic Neuroma Causes and Symptoms
An acoustic neuroma (also called a vestibular schwannoma) is a rare, non-cancerous growth that can affect hearing and balance.
Initial symptoms are tinnitus (or ringing in the ear) and hearing disturbances on one side.
The average growth rate of the tumor is about 1.5 millimeters per year, but several studies have demonstrated that up to half of tumors show little to no growth over long periods of time (5 to 10 years). No environmental or dietary factors are known to influence the growth rate of acoustic neuromas.
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Cause of Acoustic Neuroma
For most acoustic neuromas, the cause at the cellular level is the failure of a "governor" gene to suppress the growth of Schwann cells—those cells responsible for coating nerve fibers with insulation. Without suppression, these cells grow to produce the neuroma.
Radiation exposure to the head is the only environmental influence that has been definitively linked with an increased incidence of acoustic neuroma. No evidence currently exists for an association between cell phone use and the development of these tumors.
Acoustic neuroma is not generally considered an inherited disease; however, five percent of cases are associated with a genetic disorder called neurofibromatosis type 2 (NF2). These individuals show two-sided vestibular tumors often associated with other tumors around the brain and/or in the spine. Most acoustic neuromas are sporadic (nonhereditary).
Acoustic Neuroma Symptoms
Symptoms of vestibular schwannoma can be associated with the size of the tumor but this is not always the case. Many patients experience few symptoms even with a large tumor. Small tumors are defined at 2 centimeters or less, medium tumors are between 2 and 4 centimeters, and large tumors are over 4 centimeters. Smaller tumors are often associated with few symptoms, while large compressive tumors can be life-threatening.
Acoustic neuromas arise from the balance or vestibular nerves in an area called the cerebellopontine angle. The tumors often occur in the internal auditory canal, which contains the facial nerve, the cochlear or auditory nerve, and the two balance or vestibular nerves. Larger tumors project inward from the internal auditory canal and displace the adjacent cerebellum and brainstem.
Although acoustic neuromas emerge from the balance nerve, patients rarely have severe dizziness but may experience unsteadiness. The most common symptom of acoustic neuroma is single-sided hearing loss and fullness often associated with tinnitus or head noise. Unless the tumor is very large, it rarely affects the facial nerve or facial expressions.