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Risk Factors and Origins of Acoustic Neuroma

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Receiving a diagnosis of an acoustic neuroma can be a challenging experience. During this process, it’s common for patients to wonder, “Where do acoustic neuromas come from?” and “What increases the risk of developing an acoustic neuroma?”

Knowing the answers to these questions can help you cope with the diagnosis. They are also important to make informed decisions on management options. In this article, we’ll discuss the origins of acoustic neuromas and what factors increase the risk of their development.

What Is an Acoustic Neuroma?

An acoustic neuroma, also known as a vestibular schwannoma, is a benign growth that occurs on the eighth cranial nerve of your inner ear. These tumors place pressure on the nerve, causing problems with hearing and balance. An acoustic neuroma can also begin to press on the brainstem, and nerves responsible for controlling facial muscles and interpreting facial sensation as it grows.

                                            Figure 1: MRI of a patient’s brain with a large acoustic neuroma (left) and a drawing of a large acoustic neuroma pressing on the surrounding brain structures as well as brainstem (right).

Figure 1: MRI of a patient’s brain with a large acoustic neuroma (left) and a drawing of a large acoustic neuroma pressing on the surrounding brain structures as well as brainstem (right).

Despite the risks present in the growth of acoustic neuromas, the prognosis for this condition is generally favorable. When an acoustic neuroma develops, it usually grows slowly. As a result, symptoms may not appear until years after the neuroma first appears.

Common symptoms of an acoustic neuroma include hearing loss, poor balance, tinnitus in the affected ear, and vertigo. The hearing loss may be partial or complete, and it may occur gradually or suddenly. Hearing loss occurs on one side in most cases of acoustic neuroma.

Origin of Acoustic Neuromas

Acoustic neuromas are abnormal growth of cells (Schwann cells) that form the myelin sheath that insulates certain nerves. An acoustic neuroma can be due to a sporadic (random) mutation or a problem with a gene on chromosome 22. This gene produces a protein that suppresses tumor development and controls the growth of Schwann cells.

When mutated, these tumors have the propensity to grow in an uncontrolled fashion from the Schwann cells surrounding the eighth cranial nerve. Many mutations of chromosome 22 are associated with a genetic disorder called neurofibromatosis type 2 (NF2) that is inherited from previous generations.

What Is Neurofibromatosis Type 2?

NF2 is a genetic mutation that occurs on chromosome 22 that prevents a protein (merlin) from suppressing cell growth in Schwann cells. NF2 is an autosomal dominant disorder, which means one parent with the genetic disorder can pass it down to their children. Though this change can be present at birth, symptoms don’t typically appear in people until their late teens or early twenties.

                                            Figure 2: Depiction of common NF2 tumor types throughout the body.

Figure 2: Depiction of common NF2 tumor types throughout the body.

The most commonly seen symptom of NF2 is the growth of benign tumors on the nerves in the brain and spinal cord. Patients with NF2 may develop acoustic neuromas, as well as retinal tumors and cataracts.  Acoustic neuromas associated with NF2 are commonly bilateral (both sides). It is important to note that only 5% of patients with acoustic neuromas have NF2.

Other Risk Factors for Acoustic Neuroma

While NF2 is currently the only confirmed risk factor for acoustic neuromas, there may be others. Acoustic neuromas generally develop in people aged 30 to 60, with older populations at higher risk. There are no differences in risk among ethnicities, but women are more likely to be diagnosed with an acoustic neuroma than men.

One case-control study found an elevated risk of developing an acoustic neuroma in patients exposed to loud noises with little or no ear protection. Most patients reported exposure to loud noises with leisurely activity, such as concerts, sporting events, and clubs. Persistent exposure to occupational noises correlated with a significant risk of developing tinnitus and other hearing problems but not to the development of acoustic neuromas.

Like many tumors, exposure to low radiation levels around the head or neck is a risk factor for developing an acoustic neuroma. The risk is higher if you were exposed to radiation during childhood.

Despite the role that stress plays in many immune and nervous system disorders, there has been no correlation between high levels of stress and development of an acoustic neuroma. However, stress can exacerbate symptoms that may already exist.

Can You Prevent an Acoustic Neuroma?

In short, there is no way to prevent an acoustic neuroma. Avoiding risk factors such as unnecessary radiation may reduce chances of developing acoustic neuromas and other tumors. Genetic testing may be possible if one or both parents have a family history of NF2 and can help to inform the patient about family planning and potential for developing tumors in the future.

Key Takeaways

  • Acoustic neuromas are caused by unregulated cell growth of Schwann cells, which surround nerves.
  • Chromosome 22 gene mutations are associated with an increased risk of developing acoustic neuromas.
  • Neurofibromatosis type 2 (NF2), an inherited disorder, is associated with bilateral acoustic neuromas.