In an article written by Timothy Cain, MD, acoustic neuromas count for 6% of all intracranial tumors, 30% of brain stem tumors. Of tumors in that region, the cerebellopontine angle, 85% are AN’s (Dizziness-and-balance.com, 2009).
The acoustic neuroma, also called vestibular schwannoma, is a benign tumor that affects not only the hearing but also the balance and more of its victims. The tumor is caused by overproduction of Schwann cells which “normally wrap around nerve fibers like onion skin to help support and insulate nerves.” (NICDC, 2009) Research shows that the growth may be caused by a genetic defect and is associated with the production of an abnormal protein called “Merlin”. (University of Minnesota, 2007)
AN Causes Unilateral Loss of Balance and Hearing
In order to better understand the effect of an acoustic neuroma, it helps to first understand the structure of the ear. The auditory canal is a tube that runs from the ear to the brain and measures between 0.4 to 1.2 cm long. Through it pass several nerves, including some for hearing and even facial nerves for feeling and muscle control. Acoustic neuromas typically first affect the 8th or vestibulo-cochlear nerve. These nerves are associated with hearing and balance. Symptoms can include loss of equilibrium and a number of hearing disorders, from tinnitus (ringing in the ears) to hearing loss. More often than not, the loss of balance and hearing are limited to one side (unilateral).
As it grows, the tumor takes on a mushroom sort of shape. This bulging out stretches the neighboring 7th nerve, a facial nerve for muscle movement, feeling and blood vessels. Pressure on that nerve can cause tingling in the jaw and loss of muscle control in the face.
Acoustic Neuroma Detectable on MRI or X-ray
In the confines of the canal, the tumor grows to the point that it fills the space, putting pressure on the bony walls of the canal. In many but not all cases, the tumor causes bone erosion and swelling of the canal. At this point, the tumor can be seen on MRI or X-ray images.
For unknown reasons, the tumor always grows from the ear toward the brain and never the other way around. Growth is not always regular. The tumor may stop growing for a time, only to resume later without warning.
AN’s Can Become Life Threatening
Left unchecked, the acoustic neuroma may eventually put pressure on the brainstem or cerebellum and can even threaten the life of the victim.
Acoustic neuromas are difficult to find before they grow and become symptomatic. Once the tinnitus, hearing loss or loss of balance are noticeable, hearing tests and proper ear examinations are in order, followed by CT and MRI exams as ordered by the doctor. If a tumor is discovered, surgery is the most frequent treatment. There are different types of surgeries depending on the size and location of the tumor. Radiation therapy is another treatment option that may be used alone or in conjunction with surgery.
Sources:
Acoustic Neuromas: the Basic Facts – University of Michigan, Department of Otolaryngology, June 2007
Vestibular Schwannoma (Acoustic Neuroma) and Neurofibromatosis: National Institute on Deafness, February 2004
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