Acoustic neuromas, also known as vestibular schwannomas, are noncancerous tumors that grow in the ear, and that can affect hearing and balance. Otolaryngology–head and neck surgeon Francis Creighton, M.D., and neurosurgeon Christopher Jackson, M.D., offer insights about these rare tumors and their treatment options.

What is acoustic neuroma (vestibular schwannoma)?

Acoustic neuromas are noncancerous, usually slow growing tumors that form along the branches of the eighth cranial nerve (also called the vestibulocochlear nerve). This nerve leads from the brain to the inner ear and branches into divisions that play important roles in both hearing and balance.

Acoustic neuromas arise from Schwann cells, which wrap around and support nerve fibers, hence the name vestibular schwannoma. Schwannomas can occur on any cranial or peripheral nerve in the body, but in the brain, acoustic neuromas are the most common schwannomas.

Acoustic neuromas typically begin growing where the central nervous system transitions into the peripheral nervous system, called the porus acusticus.

Are acoustic neuromas dangerous?

Many acoustic neuromas do not grow, and though not always, most that do grow tend to do so slowly. They typically do not invade and destroy tissue like cancerous tumors do. However, they can cause symptoms as they grow and push on important surrounding structures.

A growing acoustic neuroma can cause compression of the nerves that enable facial sensation and movement of the facial muscles. With larger tumors, compression of the nerves important for swallowing, speaking and eye movement can occur.

Even if acoustic neuroma is not growing, it can cause worsening hearing loss and balance function.

If a growing acoustic neuroma is left untreated, it can cause a dangerous buildup of fluid in the brain or it can compress the cerebellum and brain stem, which can be life threatening. This is rare for patients whose tumors are properly diagnosed and treated.

Acoustic Neuroma Survival Rate

Though acoustic neuromas can cause lasting problems, such as hearing loss, death from these tumors is rare if they are properly diagnosed and treated.

Types of Acoustic Neuromas (Vestibular Schwannomas)

There are two types of acoustic neuromas:

• Sporadic, unilateral acoustic neuromas. These tumors only grow on one side of the body in 95% of patients. They occur from sporadic (sudden), nonhereditary mutations. These unilateral acoustic neuromas may develop at any age, but most commonly occur in people between the ages of 30 and 60.
• Genetic, bilateral acoustic neuromas. Acoustic neuromas on both sides of the body only occur in people who have the genetic disorder neurofibromatosis type 2, a mutation in chromosome 22 that affects the gene responsible for production of Schwann cells. These patients often have other schwannoma-like tumors throughout the body, and treatments for these tumors are often different from the treatment for unilateral tumors.

Acoustic Neuroma Symptoms

Hearing loss, dizziness, tinnitus and other symptoms of an acoustic neuroma can be caused by other, more common ear problems, and it is important to consult a doctor for a diagnosis. Because acoustic neuromas often grow on the balance and hearing nerve, the most common symptoms they cause are:

One-sided Hearing Loss

Over 90% of people with acoustic neuromas develop some degree of one-sided (unilateral) hearing loss. People with this type of hearing loss may have difficulty hearing in noisy settings and locating where a sound is coming from. If a person tends to hold a phone to a certain ear or has a hard time following conversation in a crowded room, these may be signs of hearing loss.

The hearing loss usually gets worse over the years and may lead to total deafness in one ear. In some people (about 5% of patients), hearing loss may develop suddenly. The loss may be partial or total, and spontaneous recovery is possible. Sudden hearing loss may be the first event that leads to a diagnosis, or it may occur months or years before the tumor is discovered.

Hearing loss can occur from compression or infiltration of the tumor on the hearing nerve, or from secretion of substances toxic to hearing. It can affect the range of sounds heard, as well as the clarity of sound. Hearing loss can occur even if the tumor is not growing.

A small portion of patients with acoustic neuroma may not yet have hearing loss from the tumor. Mild hearing loss due to an acoustic neuroma might not even be noticeable, which can result in a delayed diagnosis.

Ear Fullness

People with an acoustic neuroma might have a sensation of fullness in the ear, as if water is in it. This sensation is typically caused by the hearing loss from the tumor.

Noise in the Ear (Tinnitus)

Tinnitus is a very common symptom of acoustic neuromas and many other inner ear conditions. People with acoustic neuromas may experience a high-pitched tone in the ear affected by the tumor. In other cases, the tinnitus can sound like hissing, buzzing or roaring — like when putting a seashell to the ear.

While most patients with acoustic neuromas have both tinnitus and hearing loss in one ear, some may experience tinnitus without losing hearing. Tinnitus can come and go or be constant — with single or multiple tones — and can sound quiet or overwhelmingly loud.

Balance Problems and Vertigo

Because acoustic neuromas arise from the vestibular nerve responsible for balance, unsteadiness or balance problems may be early symptoms of acoustic neuroma. Nearly half of people with acoustic neuromas notice these symptoms, which tend to worsen if the tumor grows. Large acoustic neuromas may compress parts of the cerebellum, which may lead to falls. Patients tend to fall toward the side of the tumor.

The balance system can compensate for the loss of balance, so it may stabilize.

True vertigo (the sensation of spinning or tilting) is not commonly associated with acoustic neuromas, but it can sometimes occur due to tumor growth or bleeding.

Other Signs of Acoustic Neuroma

Acoustic neuromas can also put pressure on other important cranial nerves that are adjacent to where these tumors grow.

• Numbness in the face can result from a tumor pressing on the trigeminal nerve. There may be ongoing or periodic numbness and facial tingling on the side of the acoustic neuroma. Tingling (paresthesia) may be near the corner of the mouth or on the cheek. There may also be eye irritation or redness due to numbness in the eye that prevents appropriate blink reflexes. 
• Facial twitching or weakness can result from the tumor pressing on the facial nerve. This can cause twitching (tics or spasms) of the eye, eyebrow, forehead or mouth muscles. Less often, you might notice weakness in the face. Facial weakness often does not occur until acoustic tumors grow quite large, and it is less common at the time of diagnosis.
• Swallowing problems can occur from the tumor pressing on the vagal and hypoglossal nerves. These nerves control several aspects important to swallowing, including sensation in the throat and movement of vocal cords and the tongue.
• Change in taste and tear production is a less common symptom, but it should be evaluated by a doctor. The facial nerve helps control taste and tear formation. Pressure on the nerve can cause dry eye or even unexpected tears, as well as changes in taste perception.
• Headache and pressure: As the acoustic neuroma grows, it can press on the lining of the inside of the skull (the dura). The dura has sensory fibers that can transmit the sensation of the pressure. The headache that results from the acoustic neuroma can be dull or aching, and it is usually on one side of the head. The pain may radiate to the neck or the top or front of the head.

These symptoms can be caused by many other, more common health issues such as cholesteatoma, labyrinthitis and vestibular neuritis, and Meniere’s disease. If you have more than a few of these symptoms (especially if they don’t go away or become worse), your doctor can help you decide whether more testing is necessary.

Serious Complications of Acoustic Neuroma

If untreated, an acoustic neuroma can grow large enough to cause pressure on the brain stem. The tumor can block the flow of cerebrospinal fluid (CSF) between the brain and the spinal cord, causing a buildup of the fluid in the brain.

Because the skull is a closed structure, excess fluid in the brain (hydrocephalus) can press against the brain, causing unsteady movement and lack of coordination (ataxia), headaches and confusion.

Acoustic Neuromas in Children

Although they are more common in adults, acoustic neuromas can occur in children and teens, and may grow large before they are diagnosed. Children with acoustic neuromas most often have the genetic disorder neurofibromatosis type 2. In children with this disorder, acoustic neuromas may arise on both sides. 

Symptoms of acoustic neuroma in children are usually hearing loss, headache and unsteady gait (ataxia), elevated pressure inside the skull, tinnitus and dizziness. Acoustic neuromas are more likely to grow back in children than in adults if surgery does not remove all of the tumor.

Acoustic Neuroma (Vestibular Schwannoma) Diagnosis

Because symptoms of these tumors resemble those of other middle and inner ear conditions, they may be difficult to diagnose. Diagnosis usually starts with an ear examination, a hearing test and imaging. Based on the symptoms, your doctor will help determine if you need a computerized tomography (CT) and magnetic resonance imaging (MRI). MRI is much more sensitive than CT for detecting acoustic neuromas. If your doctor is concerned that you might have this tumor, MRI is the preferred test. Early diagnosis offers the best opportunity for successful treatment.

Acoustic neuroma diagnosis includes:

• Hearing test (audiometry). This is a test of hearing function that measures how well you hear sounds and speech. It is usually the first test performed to diagnose acoustic neuroma. A doctor asks you to listen to sounds and speech while you are wearing earphones attached to a machine that records responses and measures hearing function. If you have an acoustic neuroma, your audiogram may show the following.
• Increased pure tone average (PTA). This metric evaluates how loud a sound frequency needs to be before you hear it.
• Increased speech reception threshold (SRT). This metric evaluates how loud speech needs to be before you hear it. Similar to pure tone average, the higher the score, the worse the hearing.
• Decreased speech discrimination (SD). This metric evaluates how many words you can detect, one ear at a time. The lower the score, the worse the hearing.
• Imaging scans of the head. If other tests point to a possibility of acoustic neuroma, MRI can confirm the diagnosis. MRI with a contrast dye can help pinpoint the tumor. If an acoustic neuroma is present, it will soak up more dye than normal brain tissue and appear clearly on the scan. MRI commonly shows a densely "enhancing" (bright) tumor in the internal auditory canal.

Acoustic Neuroma (Vestibular Schwannoma) Causes

Of acoustic neuromas, 95% occur without any specific cause.

Are acoustic neuromas hereditary?

People who have neurofibromatosis type 2 (NF2) may inherit a genetic tendency to develop acoustic neuromas. Among patients with NF2, acoustic neuromas are typically present on both sides, and symptoms affect both ears. These patients represent about 5% of all patients with acoustic neuromas.

Acoustic Neuroma Treatment

After a diagnosis of an acoustic neuroma, the doctor will determine the best plan of action. The options include the following:

• Surgery to remove the tumor. This is a highly effective treatment for acoustic neuromas. Hearing loss that has already occurred from the tumor cannot be reversed, but the remaining hearing can be preserved in some cases. Surgical tumor removal can often address balance problems, facial numbness and other symptoms.
• Stereotactic radiosurgery. This form of radiation therapy delivers precisely targeted radiation to the tumor while avoiding the surrounding healthy tissue. Radiation does not cause the tumor to go away. Rather, the goal is to stop or slow the growth. Typically, radiation therapy is not recommended for young patients and those with larger tumors.
• Observation. This means waiting and watching, and it can be an option for some patients with acoustic neuroma. Because acoustic neuromas are usually slow growing, immediate intervention is not always necessary. For patients with very small tumors that don’t cause any symptoms, older patients and patients with serious medical problems, the doctor may recommend regular monitoring of the tumor using imaging such as MRI.

Priorities in treating acoustic neuromas are preserving facial nerve function, optimizing hearing outcomes and maintaining quality of life.  

Acoustic Neuroma Observation

Acoustic neuromas are noncancerous tumors, so they can often be closely monitored without treatment. After the initial diagnosis, unless the tumor is already very large or is causing significant symptoms, doctors may recommend getting an additional MRI after six to twelve months. This allows you and your doctor to determine if the tumor is growing. Tumors that are small, that are cause minor or no symptoms, and that are not growing can often continue to be observed with regular MRI. If the imaging shows that a tumor is growing, or if the tumor begins to cause significant symptoms, it might be time for treatment.

Acoustic Neuroma Surgery

Modern microsurgical advancements have made acoustic neuroma surgery procedures safer, more effective and easier to recover from.

The goals of surgery are to remove the tumor while preserving the facial nerve’s function. Hearing preservation after surgery for acoustic neuroma is possible but depends on several factors, including how well you hear before the surgery and how big the tumor is. Roughly half of patients with the smallest tumors who have useful hearing before surgery will maintain useful hearing after surgery. Hearing preservation is less likely for larger tumors. The risk of hearing and facial nerve complications after the surgery increases with larger acoustic neuroma size.

Surgeons have developed different approaches to remove acoustic neuromas — the best depends on tumor size and location, patient characteristics and the goals of surgery. The most commonly used approaches are suboccipital, translabyrinthine and middle fossa craniotomy.

• Suboccipital or retrosigmoid craniotomy. During this procedure, the surgeon accesses the acoustic neuroma from the back of the head. It offers the best view of the brainstem, particularly for the nerves involved in swallowing, which can be affected if a tumor is large. This approach is often recommended for patients with larger tumors. It also might preserve hearing for patients with smaller tumors, because the inner ear structures are preserved.
• Translabyrinthine craniotomy. During this procedure, the surgeon removes the bone behind the ear to access the tumor through the inner ear. This provides the best view of the entire length of the facial nerve and can require less retraction of the brain. However, it requires going through the structures of the inner ear and does not allow preservation of hearing. This approach is generally considered for patients who have no functional hearing.
• Middle fossa craniotomy. This is an option for patients with smaller acoustic neuromas and intact hearing. It is generally considered to provide the greatest chance of hearing preservation, but there is a slightly greater risk of facial nerve weakness after the surgery, and it cannot be performed for medium or large size tumors.

Image Guidance and Monitoring During Acoustic Neuroma Surgery

Monitoring of brain and nerve function is a critical part of acoustic neuroma surgery. A team of neurologists and electrophysiologists watches for any changes in facial and hearing nerve activity, as well as for changes in the brain. Being aware of such changes can help the surgeon avoid neurologic complications.

Stereotactic Radiosurgery for Acoustic Neuroma

Radiosurgery, also called stereotactic radiosurgery, is a noninvasive procedure that uses precisely focused, narrow beams of radiation to treat the acoustic neuroma while limiting the amount of radiation that affects surrounding structures, including the hearing, balance and facial nerves. This form of radiation therapy can reduce the growth of an acoustic neuroma. Doctors may recommend radiosurgery for older patients with acoustic neuromas who might be too fragile to endure more invasive treatment.  Radiosurgery may also be used in combination with surgery for large tumors that cannot be removed completely without permanently damaging the facial nerve or other structures.

Some studies report cancers developing within the field of radiation treatment for acoustic neuroma.

What if an acoustic neuroma returns after radiosurgery?

Radiation treatment requires ongoing follow-up and annual scans to watch for tumor regrowth. Parts of the tumor unaffected by the radiation may give rise to new growth. Signs of an acoustic neuroma coming back could include facial muscle weakness and spasms that slowly worsen, and new growth can often be seen on an MRI scan. Few studies have documented the effects of radiation beyond five years.

Repeated radiation for an acoustic neuroma that comes back after radiosurgery is typically unsafe, and the doctor may recommend surgery. Acoustic neuroma surgery after radiotherapy treatment can be complicated by scar tissue (fibrosis) that can make it difficult to separate the tumor from adjacent nerves.

What determines the acoustic neuroma treatment?

Factors such as the tumor size, your age, tumor growth rate and severity of symptoms help the doctor decide which treatment options are appropriate.

Acoustic Neuroma Size

The size of the acoustic neuroma is something your doctor will consider. Larger tumors are more likely to continue to grow, and surgical removal is often recommended. Small tumors that are not growing and do not cause disruptive symptoms might not require immediate treatment.

Doctors may use different measurements to determine the size of an acoustic neuroma. The tumors look like ice cream cones, so the measurement varies depending on whether the tumor is measured vertically or horizontally. The diameter of the “ice cream on top” — the part of the tumor that pushes into the brain stem and cerebellum — is what matters, and it should determine the treatment. Proper assessment of the tumor’s size is one reason to choose a doctor who has experience treating these tumors.

If the brain tumor is larger than 20 to 25 millimeters at the time of diagnosis, your doctor may consider treatment even if your symptoms aren’t worrisome. Larger tumors can make surgery more complex and raise the risk of damaging hearing, balance and facial nerves.

Severe or Worsening Symptoms

Sometimes a larger acoustic neuroma can cause only minor symptoms, and a small tumor can be incapacitating. Severe facial pain, balance issues and falls can affect quality of life, and treating the tumor might be the best option.

Worsening symptoms may be a good reason to move from watching an acoustic neuroma to treatment. If you have been diagnosed with an acoustic neuroma and you notice that symptoms such as imbalance, facial numbness, weakness or hearing loss are becoming worse, contact your doctor.

Tumor Growth

If the doctor is monitoring an acoustic neuroma and MRI exams show that the tumor is growing, it might be time for treatment, depending on the rate of growth, the tumor’s shape, size and location, and your overall health.

Hearing Loss and Other Complications After Acoustic Neuroma Treatment

After treatment for acoustic neuroma, some patients experience hearing loss, cerebrospinal fluid leak, damage to facial nerves and other problems.

• Facial nerve damage is usually only temporary, and most patients recover in several months to a year. If the damage is thought to be permanent, a facial plastic surgeon can perform nerve transfer surgery or other procedures to help restore movement in the face.
• Cerebrospinal fluid leaks are caused by a hole or tear in the dura, a membrane that covers the brain and spinal cord. If a leak occurs, a doctor can perform a procedure to block the hole that is leaking cerebrospinal fluid.
• For ongoing hearing issues after acoustic neuroma surgery, a doctor may recommend a bone-anchored hearing aid, cochlear implant or a regular hearing aid.
• For patients with neurofibromatosis type 2 who develop acoustic neuromas in both ears, causing deafness, cochlear implants or auditory brain stem implants can help provide a sense of sound and possibly help them understand speech.

Acoustic Neuroma Treatment — Choosing Your Care Team

Because acoustic neuroma tumors are rare, it is important to choose a doctor with experience treating them. Asking a doctor how many acoustic neuroma patients he or she sees annually, and how many surgeries the doctor performs, may be a good start. Visiting a specialty center with a dedicated, multidisciplinary acoustic neuroma team might give you the best chance of a positive outcome.