Acoustic neuroma causes
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]
Overview
Causes
The cause of acoustic neuromas is largely unknown. No environmental factor (such as cell phones or diet) has been scientifically proven to cause these tumors. They can be sporadic or caused by an inherited condition called neurofibromatosis type 2 (NF-2). Sporadic tumors occur 95% of the time, while 5% of acoustic tumors are caused by NF-2.
Neurofibromatosis is a rare disease that occurs in two forms. Type 1 causes tumors to grow on nerves throughout the body, especially the skin. Type 2 can cause acoustic tumors on both left and right sides, creating the possibility of complete deafness if the tumors grow unchecked. The presence of bilateral acoustic tumors affects the choice of treatment, as hearing preservation is a prime objective.
Both types of acoustic neuroma occur following a loss of the function of a gene on chromosome 22. A gene is a small section of DNA responsible for a particular trait like hair color or skin tone. This particular gene on chromosome 22 suppresses the growth of Schwann cells. When this gene malfunctions, Schwann cells can grow out of control. This gene may help suppress other types of tumor growth. In NF2 patients, the faulty gene on chromosome 22 is inherited.
Acoustic neuroma occurs in two forms: a sporadic form and a form associated with an inherited syndrome. About 95% of all cases are sporadic. The cause of the sporadic form is unclear. Some small studies have found an association of acoustic neuromas with cellular phone use or prolonged exposure to loud noises, but other studies do not find this link (Christensen et al 2004, Edwards et al 2006, Edwards et al 2007, Hardell et al 2003, Lonn et al 2004, Myung et al 2009, Schlehofer et al 2007, Schoemaker et al 2007). There is not hard evidence supporting a link between environmental factors and acoustic neuromas.
The inherited syndrome called neurofibromatosis type II (NF2). NF2 is rare; there are only several thousand affected individuals in the entire United States, corresponding to about 1 in 40,000 individuals. Roughly 5% of patients with acoustic neuroma have NF2.
The exact cause of an acoustic neuroma is unknown. Most cases seem to arise for no apparent reason (spontaneously). No specific risk factors for the development of these tumors have been identified.
A variety of potential risk factors for acoustic neuroma have been studied including prior exposure to radiation to the head and neck area (as is done to treat certain cancers) or prolonged or sustained exposure to loud noises (as in an occupational setting). Research is under way to determine the specific cause and risk factors associated with an acoustic neuroma.
In a small subset of cases, acoustic neuromas occur as part of a rare disorder known as neurofibromatosis type II. This rare genetic disorder is usually associated with acoustic neuromas affecting both ears at once (bilateral). (For more information on this disorder, choose “neurofibromatosis” as your search term in NORD’s Rare Disease Database.)
An acoustic neuroma arises from a type of cell known as the Schwann cell. These cells form an insulating layer over all nerves of the peripheral nervous system (i.e., nerves outside of the central nervous system) including the eighth cranial nerve. The eighth cranial nerve is separated into two branches the cochlear branch, which transmits sound to the brain and the vestibular branch, which transmits balance information to the brain. Most acoustic neuromas occur on the vestibular portion of the eighth cranial nerve. Because these tumors are made up of Schwann cells and usually occur on the vestibular portion of the eighth cranial nerve, many physicians prefer the use of the term vestibular schwannoma. However, the term acoustic neuroma is still used more often in the medical literature.
There is a growing body of evidence that sporadic defects in tumor suppressor genes may give rise to these tumors in some individuals. Other studies have hinted at exposure to loud noise on a consistent basis. One study has shown a relationship of acoustic neuromas to prior exposure to head and neck radiation, and a concomitant history of having had a parathyroid adenoma (tumor found in proximity to the thyroid gland controlling calcium metabolism). There are even controversies on hand-held cell phones. It remains to be seen whether or not the radiofrequency radiation has anything to do with acoustic neuroma formation. To date, no environmental factor (such as cell phones and diet) has been scientifically proven to cause these tumors. ANA does recommend that frequent cell phone users use a hands-free device to enable separation of the device from the head. Please refer to cell phone statement on our website
Neurofibromatosis type II occurs in individuals who have defective tumor suppressor gene located on chromosome 22q12.2. The defective protein produced by the gene is called merlin or schwannomin