Acoustic Neuroma

An acoustic neuroma, also known as a vestibular schwannoma, is a rare, noncancerous (benign) tumor that grows slowly on the main nerve leading from your inner ear to your brain. This nerve, called the vestibulocochlear nerve, affects both hearing and balance. While not cancerous, the tumor can press on nerves and brain structures, leading to symptoms like hearing loss and balance problems.

What is Acoustic Neuroma?

An acoustic neuroma is a slow-growing, noncancerous tumor that develops on the vestibulocochlear nerve, which connects your inner ear to your brain. This nerve is responsible for sending sound and balance information to your brain. As the tumor grows, it can press on this nerve and nearby brain structures, leading to various symptoms, most commonly affecting hearing and balance.

Acoustic neuromas are typically benign, meaning they do not spread to other parts of the body like cancer. They are also known as vestibular schwannomas because they arise from Schwann cells, which cover the vestibular branch of the vestibulocochlear nerve. This nerve has two parts: one for hearing (cochlear nerve) and one for balance (vestibular nerve). These tumors are relatively rare, affecting about 1 in 100,000 people each year. They usually grow very slowly over several years. In some cases, the tumor may grow large enough to press on the brainstem, which can be life-threatening, though this is uncommon with early detection. Most acoustic neuromas are unilateral, meaning they affect only one ear. Bilateral acoustic neuromas, affecting both ears, are usually associated with a genetic disorder called neurofibromatosis type 2 (NF2).

Symptoms

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

The earliest and most common symptom is often a gradual hearing loss in one ear, which may be more noticeable for high-frequency sounds. About 9 out of 10 people (90%) with an acoustic neuroma experience this type of hearing loss. Sometimes, the hearing loss can be sudden. Another common symptom is ringing or buzzing in the affected ear, known as tinnitus. You might also experience problems with balance, such as unsteadiness or dizziness (vertigo). These balance issues can make you feel like you are spinning or that the world around you is moving. As the tumor grows larger, it can press on other nerves and brain areas, leading to additional symptoms. These might include numbness, tingling, or weakness on one side of your face, difficulty swallowing, hoarseness, headaches, or even confusion. These more severe symptoms are less common and usually indicate a larger tumor.

Causes & risk factors

The exact cause of most acoustic neuromas is unknown. They are thought to result from a problem with a gene on chromosome 22 that helps control the growth of Schwann cells. While most cases occur randomly without a clear reason, a specific genetic disorder called neurofibromatosis type 2 (NF2) is a known risk factor, accounting for a small percentage of cases.

Most acoustic neuromas are sporadic, meaning they occur without any known cause or family history. Researchers believe these tumors develop due to a malfunction in a gene located on chromosome 22. This gene normally produces a protein that helps regulate the growth of Schwann cells, which are cells that cover nerve fibers. When this gene doesn't work correctly, Schwann cells can grow uncontrollably, forming a tumor. The main known risk factor for acoustic neuroma is neurofibromatosis type 2 (NF2). This is a rare, inherited genetic disorder that causes benign tumors to grow on nerves throughout the body, including the vestibulocochlear nerves on both sides. If you have NF2, you are at a much higher risk of developing bilateral acoustic neuromas. Despite ongoing research, there is no strong scientific evidence to support other proposed risk factors, such as exposure to loud noise, cell phone use, or certain environmental factors. Most people who develop an acoustic neuroma have no identifiable risk factors other than, in rare cases, NF2.

How it's diagnosed

Diagnosing an acoustic neuroma typically begins with a thorough physical exam and a review of your symptoms. If an acoustic neuroma is suspected, a hearing test (audiometry) is usually the first step. The definitive diagnosis is made using magnetic resonance imaging (MRI) with contrast, which can clearly show the tumor's presence, size, and location.

If you experience symptoms like one-sided hearing loss or tinnitus, your doctor will likely refer you for a hearing test called audiometry. This test measures your ability to hear sounds at different pitches and volumes and can detect the specific type of hearing loss often associated with an acoustic neuroma. Another test, electronystagmography (ENG), might be used to check your balance by measuring eye movements. However, the most accurate and common way to diagnose an acoustic neuroma is with a magnetic resonance imaging (MRI) scan of your head. During an MRI, a special dye (contrast material) is often injected into your vein to make the tumor show up more clearly on the images. This imaging technique can detect even very small tumors and is crucial for confirming the diagnosis and planning treatment. In some cases, if an MRI is not possible, a computed tomography (CT) scan with contrast may be used, but it is less effective at detecting small acoustic neuromas than an MRI. Early diagnosis is important because it allows for more treatment options and better outcomes.

Treatment options

Treatment for an acoustic neuroma depends on several factors, including the tumor's size, growth rate, your symptoms, age, and overall health. Options range from simply monitoring the tumor to radiation therapy or surgery. Your healthcare team will discuss the best approach for your specific situation, aiming to preserve nerve function and manage symptoms.

One common approach for small, slow-growing tumors that cause few or no symptoms is observation, also known as "watch and wait." This involves regular MRI scans, typically every 6 to 12 months, to monitor the tumor's growth. If the tumor remains stable, no further treatment may be needed. This option is often considered for older individuals or those with other health conditions. Radiation therapy, specifically stereotactic radiosurgery, is a non-surgical option that uses highly focused radiation beams to stop the tumor from growing. Examples include Gamma Knife or CyberKnife. This treatment aims to control tumor growth while minimizing damage to surrounding healthy tissue. It is often used for small to medium-sized tumors and can be effective in preventing further hearing loss or other symptoms, though it may take months or years to see the full effect. Surgery, called a craniotomy, involves removing the tumor through an incision in the skull. This option is typically chosen for larger tumors, those causing significant symptoms, or tumors that continue to grow despite radiation. The goal of surgery is to remove as much of the tumor as safely possible while preserving facial nerve function and hearing. The specific surgical approach depends on the tumor's size and location. Each treatment option carries its own set of potential risks and benefits, which your doctor will explain in detail.

Recovery & outlook

The recovery and long-term outlook for an acoustic neuroma vary greatly depending on the tumor's size, the chosen treatment, and your individual response. Many people experience good outcomes, especially with early detection and treatment. However, some may face ongoing challenges like hearing loss, balance issues, or facial weakness, requiring rehabilitation and ongoing care.

If you undergo observation, your recovery involves regular follow-up MRI scans to track tumor growth. If the tumor remains stable, you may not experience significant changes to your daily life. However, if it grows, you may need to consider other treatments. Following radiation therapy, recovery is generally less intensive than surgery. You might experience temporary fatigue, headaches, or numbness. The goal of radiation is to stop tumor growth, and it can take several months to a year to see if the treatment was successful. Some people may still experience a decline in hearing or balance over time, even if the tumor stops growing. Surgical recovery can be more involved, often requiring a hospital stay of several days and a recovery period of several weeks to months. Potential side effects include continued hearing loss, tinnitus, balance problems, and facial weakness or numbness. Physical therapy and vestibular rehabilitation can help improve balance and reduce dizziness. While complete tumor removal is often possible, some people may have residual tumor that requires further monitoring or treatment. The vast majority of acoustic neuromas are benign, and with appropriate management, most people can lead full lives.

When to see a doctor

You should see a doctor if you experience new or worsening symptoms that could indicate an acoustic neuroma. These include unexplained hearing loss in one ear, persistent ringing in one ear (tinnitus), or problems with balance and dizziness. Early evaluation is important because it can lead to earlier diagnosis and potentially more effective treatment options.

It is particularly important to seek medical attention if you experience sudden hearing loss in one ear, as this could be a sign of an acoustic neuroma or another serious condition. While many causes of hearing loss are not serious, it's always best to have it checked by a healthcare professional. Also, pay attention to any persistent or worsening balance issues, such as feeling unsteady on your feet or frequent episodes of vertigo. If you notice any numbness, tingling, or weakness on one side of your face, or if you develop new, severe headaches, these could be signs of a larger tumor pressing on other nerves or brain structures, and you should seek prompt medical advice.

Frequently asked questions

Is an acoustic neuroma a type of brain cancer?

No, an acoustic neuroma is not a type of brain cancer. It is a noncancerous (benign) tumor. This means it does not spread to other parts of your body, and it usually grows slowly. However, if it grows large, it can still cause serious problems by pressing on important nerves and brain structures.

How fast do acoustic neuromas usually grow?

Acoustic neuromas typically grow very slowly, often just a few millimeters per year, or sometimes not at all. Some tumors may remain stable in size for many years. The growth rate can vary significantly from person to person, which is why observation with regular MRI scans is a common management strategy for smaller tumors.

Can acoustic neuromas come back after treatment?

After complete surgical removal, an acoustic neuroma is unlikely to return. However, if only part of the tumor is removed (subtotal resection) or if radiation therapy is used, there is a chance that the remaining tumor cells could grow again. Regular follow-up with MRI scans is important to monitor for any regrowth.

What are the long-term effects of an acoustic neuroma?

Long-term effects can vary widely depending on the tumor's size, location, and the treatment chosen. Common long-term effects may include some degree of hearing loss, ringing in the ear (tinnitus), and balance problems. Some people may also experience facial weakness or numbness, which can be temporary or permanent. Rehabilitation, such as physical therapy, can help manage these effects.

Are there any ways to prevent an acoustic neuroma?

Currently, there are no known ways to prevent an acoustic neuroma. Most cases occur randomly without a clear cause. The only known risk factor is a genetic condition called neurofibromatosis type 2 (NF2), which is inherited. If you have NF2, genetic counseling and regular screening may be recommended.

Can an acoustic neuroma affect my vision?

While an acoustic neuroma primarily affects hearing and balance, a very large tumor can, in rare cases, grow to press on brain structures that are involved in vision. This could potentially lead to vision changes. However, this is uncommon, and vision problems are not typical symptoms of most acoustic neuromas.

Sources

• MedlinePlus — Acoustic Neuroma
• Mayo Clinic — Acoustic Neuroma
• Cochrane Library — Acoustic Neuroma