Acoustic Neuroma Causes and Risk Factors

An acoustic neuroma, also known as a vestibular schwannoma, is a non-cancerous, slow-growing tumor that develops on the main nerve connecting your inner ear to your brain. This nerve is crucial for hearing and balance. While the exact cause is often unknown, a genetic condition called neurofibromatosis type 2 (NF2) is a known risk factor.

What is Acoustic Neuroma Causes and Risk Factors?

An acoustic neuroma is a non-cancerous (benign) tumor that grows slowly on the vestibulocochlear nerve, which is the eighth cranial nerve. This nerve connects your inner ear to your brain and is vital for both hearing and balance. Understanding its causes and risk factors helps explain why these tumors develop.

Acoustic neuromas are also called vestibular schwannomas. They form on the Schwann cells, which are cells that cover and support nerve fibers. When these cells grow abnormally, they can form a tumor. Because the tumor grows on the nerve responsible for hearing and balance, its presence can interfere with the signals sent to the brain. This interference leads to the common symptoms associated with the condition. These tumors are almost always benign, meaning they are not cancerous and do not spread to other parts of the body. However, as they grow, they can press on important nerves and brain structures, leading to various symptoms and potential complications.

Symptoms

Symptoms of an acoustic neuroma usually develop slowly over time as the tumor grows and presses on surrounding nerves. The most common initial symptoms involve hearing and balance, often affecting only one side of your head. These can include hearing loss, ringing in the ear, and dizziness.

The earliest and most common symptom is a gradual loss of hearing in one ear. This hearing loss can be subtle at first, making it difficult to notice. You might also experience a ringing or buzzing sound in the affected ear, a condition known as tinnitus. Another common symptom is a feeling of unsteadiness or dizziness, sometimes described as vertigo. This happens because the tumor affects the part of the nerve responsible for balance. You might feel off-balance, especially when walking or standing. As the tumor grows larger, it can press on other nearby nerves. This pressure can lead to numbness or weakness in your face, or even difficulty with facial expressions. In very rare cases, a very large tumor might cause headaches or problems with coordination.

Causes & risk factors

The primary known cause of acoustic neuroma is a genetic mutation on chromosome 22, specifically involving the NF2 gene. This mutation is directly linked to an inherited condition called neurofibromatosis type 2 (NF2), which is the main risk factor for developing these tumors, often in both ears.

In most cases of acoustic neuroma, the exact cause is not known. These are called sporadic cases. However, scientists have identified a clear genetic link for some individuals. The known cause involves a defective gene on chromosome 22. This gene, called NF2, normally produces a protein known as merlin or schwannomin. This protein helps control the growth of Schwann cells, which are the cells that cover nerves. When the NF2 gene is defective, the merlin protein is not produced correctly. This allows Schwann cells to grow unchecked, leading to the formation of tumors like acoustic neuromas. This genetic mutation is the underlying cause for people with neurofibromatosis type 2 (NF2). Neurofibromatosis type 2 (NF2) is the main risk factor for acoustic neuromas. It is an inherited disorder that causes non-cancerous tumors to grow on nerves throughout the body. People with NF2 almost always develop acoustic neuromas in both ears. Radiation exposure to the head has also been suggested as a possible, though not definitive, risk factor.

How it's diagnosed

Diagnosing an acoustic neuroma typically begins with a physical exam and a detailed discussion of your symptoms. If an acoustic neuroma is suspected, your doctor will usually recommend specific hearing tests and imaging scans, with magnetic resonance imaging (MRI) being the most effective way to confirm the diagnosis.

Your doctor will first ask about your symptoms, such as hearing loss, ringing in your ears, or balance problems. They will also perform a physical examination, which may include checking your balance and reflexes. If an acoustic neuroma is suspected, a hearing test called audiometry is often performed. This test measures your ability to hear sounds at different pitches and volumes. It can help identify the type and degree of hearing loss. The most definitive diagnostic tool is a magnetic resonance imaging (MRI) scan of your head, often performed with a special dye (contrast). An MRI can clearly show the presence, size, and location of an acoustic neuroma, even very small ones. Other imaging tests like computed tomography (CT) scans may be used if an MRI is not possible, but they are less effective at detecting these tumors.

Treatment options

Treatment for an acoustic neuroma depends on the tumor's size, growth rate, your symptoms, and overall health. Options range from watchful waiting for small, slow-growing tumors to surgery or radiation therapy for larger or symptomatic tumors. Your doctor will discuss the best approach for your specific situation.

For small, slow-growing acoustic neuromas that cause few or no symptoms, your doctor may recommend watchful waiting. This involves regular MRI scans to monitor the tumor's growth over time. If the tumor remains stable, no active treatment may be needed. If the tumor is growing or causing significant symptoms, surgery may be an option. The goal of surgery is to remove as much of the tumor as possible while preserving nerve function. This is a complex procedure performed by neurosurgeons. Radiation therapy, specifically stereotactic radiosurgery, is another treatment choice. This method uses highly focused radiation beams to stop the tumor from growing or to shrink it. It is a non-invasive procedure that can be effective for many patients. Your doctor will help you weigh the benefits and risks of each treatment option.

Recovery & outlook

The recovery and long-term outlook after an acoustic neuroma diagnosis vary greatly depending on the tumor's size, the chosen treatment, and individual factors. Many people experience a good quality of life, but potential long-term effects can include some degree of hearing loss, balance issues, or facial weakness.

After treatment, recovery can involve managing any remaining symptoms or side effects. For example, some degree of hearing loss or ringing in the ear may persist. Balance issues might also continue, and some people may need physical therapy to help improve their stability. If the facial nerve was affected by the tumor or during treatment, you might experience temporary or permanent facial weakness or numbness. This can impact facial expressions and eye closure. Your medical team will monitor these effects and suggest ways to manage them. Regular follow-up appointments, including MRI scans, are important to monitor for any tumor recurrence or new symptoms. The overall outlook is generally positive, especially with early diagnosis and appropriate treatment. Most acoustic neuromas are benign and do not shorten life expectancy, but they can affect your quality of life.

When to see a doctor

You should see a doctor if you experience persistent or worsening symptoms that could indicate an acoustic neuroma. These include new or worsening hearing loss in one ear, persistent ringing in one ear, or unexplained problems with balance and dizziness. Early evaluation can lead to timely diagnosis and treatment.

It is important to seek medical attention if you notice any new or persistent changes in your hearing, especially if it affects only one ear. This includes a gradual decrease in your ability to hear or a constant ringing sound (tinnitus). Also, consult your doctor if you experience unexplained dizziness, vertigo, or problems with your balance. These symptoms, particularly when combined with hearing changes, warrant a medical evaluation. While acoustic neuromas are not cancerous, early diagnosis allows for monitoring and treatment before the tumor grows large enough to cause more severe or permanent damage to nerves and brain structures. Your doctor can perform initial tests and refer you to specialists if needed.

Frequently asked questions

Can an acoustic neuroma be cancerous?

No, an acoustic neuroma is almost always a non-cancerous (benign) tumor. It does not spread to other parts of the body, but it can cause problems by pressing on nearby nerves and brain structures as it grows.

Is acoustic neuroma hereditary?

In most cases, acoustic neuromas are not hereditary and occur randomly. However, a specific genetic condition called neurofibromatosis type 2 (NF2) is an inherited disorder that causes acoustic neuromas, often in both ears.

How fast does an acoustic neuroma grow?

Acoustic neuromas are typically slow-growing tumors. Their growth rate can vary, but they often grow only a few millimeters per year, or sometimes not at all. This slow growth is why symptoms often develop gradually over time.

Can an acoustic neuroma affect both ears?

Yes, an acoustic neuroma can affect both ears, but this is rare. It almost exclusively occurs in individuals with the genetic condition neurofibromatosis type 2 (NF2). In most sporadic cases, the tumor affects only one ear.

What is the main risk factor for acoustic neuroma?

The main known risk factor for developing an acoustic neuroma is having neurofibromatosis type 2 (NF2). This inherited genetic disorder causes tumors to grow on nerves, including the vestibulocochlear nerve.

Can radiation exposure cause acoustic neuroma?

Radiation exposure to the head has been suggested as a possible risk factor for acoustic neuroma, but the link is not definitively strong. Most cases occur without any clear cause or known exposure.

Sources

• MedlinePlus — Acoustic Neuroma Causes and Risk Factors
• Mayo Clinic — Acoustic Neuroma Causes and Risk Factors
• Cochrane Library — Acoustic Neuroma Causes and Risk Factors