An acoustic neuroma, neurinoma, auditory tumor, or vestibular schwannoma, is a benign, non-cancerous tumor that develops on the 8th cranial (vestibulo-cochlear or auditory) nerve that connects the ear to the brain.
Figure showing the ear and an acoustic neuroma growing from the vestibulo component of the vestibulo-cochlear or auditory nerve (eighth cranial nerve). The acoustic neuroma is stretching both the facial nerve (cranial nerve seven) and the cochlear branch of the vestibulocochlear nerve.
Acoustic neuromas usually grow very slowly over a period of many years. Acoustic neuromas typically remain within their capsule or lining and displace the surrounding nerves and brain tissue very slowly. The acoustic neuroma growth rate does not appear to be consistent, and the acoustic neuroma tumor might grow for a while and appear to stop, only to start again later.
Acoustic neuromas tend to grow from the ear side toward the brain, and once the acoustic neuroma grows to fully occupy the internal auditory canal, it often begins to erode the walls of the canal; however this bony erosion does not always occur. As the acoustic neuroma erodes the auditory canal, it enlarges to the point that it can be detected on CT or MRI.
Estimates of acoustic neuromas that produce symptoms range from 1 in every 3,500 to 5 in every million people. It appears that women are more affected than men and most acoustic neuromas are diagnosed between the ages of 30 & 60 years.
A small percentage of individuals with acoustic neuromas have the hereditary condition neurofibromatosis type 2 (NF-2), and people with neurofibromatosis type 2 do NOT manifest acoustic neuromas until the average age of 48.
Schematic showing the genetic inheritance pattern of people with neurofibromatosis type 2.
People with neurofibromatosis type 2 may also have an acoustic neuroma on both of the two 8th cranial nerves with an aggressive growth pattern and often involve adjacent nerves.
At first, people with an acoustic neuroma may have no symptoms or mild symptoms that can include, loss of hearing on one side, ringing in the affected ear, and dizziness and balance problems. The acoustic neuroma tumor can also eventually cause numbness or paralysis of the face (as it pushes against and stretches the facial nerve). If the acoustic neuroma grows large enough, it can press against the brain, becoming life-threatening.
Figure showing the acoustic neuroma pressing against and deforming the brain.
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