Benign but Not Harmless: The Symptoms of Acoustic Neuroma

When a patient presents with one-sided hearing loss, the causes can range from asymmetric noise exposure to injury or illness, among others. Froedtert & the Medical College of Wisconsin specialists caution that one-sided hearing loss could also be a symptom of acoustic neuroma. Medical College of Wisconsin faculty members Nathan Zwagerman, MD, neurosurgeon, and Michael Harris, MD, otolaryngologist and neuro-otologist, discussed the nuances of diagnosing and treating this benign tumor.

Besides Asymmetric Hearing Loss, What Are Other Symptoms of Acoustic Neuroma?

Dr. Zwagerman: Symptoms can include one-sided tinnitus, balance issues, dizziness, facial numbness, tingling or weakness — even swallowing problems.

Dr. Harris: If someone has hearing loss in one ear and not the other, it’s a red flag that deserves investigation. Rarely, vertigo, or a room spinning sensation, may also be a symptom. When the tumor is large enough to compress the brain stem, headaches and other symptoms can arise.

How Common Are Acoustic Neuromas?

Dr. Harris: Historically, acoustic neuromas have been estimated to affect about one in 100,000 people. Newer studies suggest these tumors may affect one in 500. The upward trend may be due to greater awareness of the condition, more frequent hearing screenings or more frequently performed MRIs that result in an incidental finding of acoustic neuroma.

Dr. Zwagerman: We see patients with acoustic neuromas every week in our clinic. We have one of the busiest practices in Wisconsin for this condition. Our team-based approach considers patients’ needs and life situations to ensure they receive excellent care.

How Is Acoustic Neuroma Diagnosed?

Dr. Harris: A contrast-enhanced MRI is the gold standard.

Dr. Zwagerman: We typically recommend a follow-up MRI scan at three to six months. If there’s no change, patients come in for a follow-up once a year. If there’s still no change, we see them every two years and then every several years to monitor the condition.

Where Does Acoustic Neuroma Arise? What Nerves Are Involved?

Dr. Harris: They originate at the lateral skull base where the cranial nerves that exit the brain stem enter the internal auditory canal, the bony channel that travels through the ear.

Dr. Zwagerman: Cranial nerve eight has three parts — one for hearing and two for balance. The biggest risk of treatment is injury to the facial nerve, the seventh cranial nerve that goes into the auditory canal next to nerve eight.

Dr. Harris: Over time, acoustic neuromas can grow into the brain space. Symptoms that occur and the risks we weigh before recommending treatment are related to what’s occurring in the internal auditory canal.

Dr. Zwagerman: In extreme cases, these tumors can compress the cerebellum, push over the brain stem and collapse the ventricle that allows for cerebrospinal fluid flow. They can become life-threatening.

Dr. Harris: From the point they’re detected, half of the tumors don’t continue to grow, so in some situations, observation is all that’s ever needed. However, in 50% of patients they do grow. The average rate over a one-year period is 1 millimeter.

Dr. Zwagerman: Most of the time acoustic neuromas are not an emergency. There is time to plan ahead.

What Advantages Does the Froedtert & MCW Health Network Offer People With Acoustic Neuromas?

Dr. Zwagerman: Patients benefit from a collaborative, multidisciplinary approach. Our team includes neurosurgery, neuro-otology, physical therapy, audiology and radiation oncology. This extensive team meets weekly to discuss cases.

Dr. Harris: We truly take every patient and every tumor and its unique characteristics into account in formulating a management strategy. This approach gives patients access to different viewpoints and perspectives so they can make informed decisions. We’re not locked into a single treatment approach.

How Is an Acoustic Neuroma Treated?

Dr. Zwagerman: There are two standard modalities: radiation therapy, which stops tumor growth in 90% of patients, and surgery, which removes the lesion. Observation alone can also be an option for certain patients. We tailor treatment to each patient.

Dr. Harris: Other factors influencing management decisions for acoustic neuroma are the tumor’s size and location and the patient’s symptoms, age and overall health. These are not age-related tumors, but if the patient is 80 or older, age is considered. Older patients require a different approach.

Dr. Zwagerman: If the tumor is small, our practice is to observe it. They frequently grow slowly. If it is growing and putting pressure on the brain, we suggest treatment.

Dr. Harris: Some people are not comfortable with the concept of observation; therefore, they may choose to treat early. Others are of the mindset that as long as it won’t cause imminent problems, they’re comfortable with a minimalist approach and treating as necessary. If patients are making informed decisions about the options and implications, we’re supportive.

What Kind of Radiation Therapy Is Used?

Dr. Harris: Gamma Knife^®, or stereotactic radiation therapy, is different from radiation therapy most patients are familiar with if they know someone who has gone through radiation therapy for cancer. Gamma Knife therapy is not accompanied by chemotherapy and does not take multiple sessions. It’s a one-time, single-session treatment.

Dr. Zwagerman: Gamma Knife offers a quick recovery, and patients return to their regular activities the next day. We favor this for people with advanced age or those who cannot have surgery. We also may recommend it for patients with tumors of less than 3 centimeters.

Dr. Harris: Patients are fitted with a frame to keep their head from moving, and an MRI is used to map the tumor and plan the radiation therapy dose. Using that data, we focus multiple beams of radiation from different angles, delivering a therapeutic dose precisely to the tumor alone.

Dr. Zwagerman: Focused radiation therapy spares surrounding structures from getting a large dose of radiation therapy. Because Gamma Knife offers precise targeting, the exposure to healthy structures is minimal.

Dr. Harris: Radiation therapy puts the brakes on the tumor, so to speak. In some cases, radiation makes these tumors dramatically smaller. A patient who receives radiation therapy will usually need periodic scans to check for regrowth of the tumor.

When Is Surgery Recommended and What Are the Approaches?

Dr. Harris: This is where we consider the patient’s age and their tumor’s likely growth rate. As the disease is benign, the patient has the option, in many cases, of observation, surgery or radiation therapy. When tumor growth is demonstrated, radiation therapy or surgery is warranted. If a tumor is large, surgery may be the best option. The general trend is for younger patients to skew more toward surgery. For this group, tumor regrowth and other considerations with radiation therapy may be more significant. Older patients skew more toward radiation therapy. However, this is not a hard-and-fast rule, and the treatment plan is tailored for each individual.

Dr. Zwagerman: For example, a young person who has a tumor that is growing may have 60 years ahead of them, but if the tumor causes brain issues like hydrocephalus, it can be fatal. If the tumor is not treated, there’s also the risk of other problems like facial pain, worsening hearing loss and balance problems.

Dr. Harris: There are three surgical approaches to remove these tumors, and we’re well-versed in all. We use the retrosigmoid approach, toward the back of the skull, for larger tumors. The translabyrinthine approach, from directly behind the ear and into the internal auditory canal, minimizes retraction of the brain. Approaching from the middle fossa, above the ear, to uncover the internal auditory canal, is appropriate for small tumors and hearing preservation. The approach is selected based on the individual’s tumor, symptoms and wishes. Patients do share in the decision-making.

Dr. Zwagerman: Each approach has risks and benefits. If the patient presents with normal or functional hearing, for example, our goal is to save it. This is dictated by how big the tumor is. If the primary issue is balance, we use the approach that best addresses that symptom.

How Is the Surgery Performed?

Dr. Zwagerman: It is microsurgery. We use a series of microscopes to see the nerves, brain tissue and blood vessels. The operations can be quite lengthy, so in the majority of cases, Dr. Harris and I work together, each taking turns with the various stages.

Dr. Harris: We follow the contemporary philosophy of prioritizing facial nerve function above achieving a gross total resection. We don’t hesitate to leave a small veil of tumor behind if we think chasing that last 1% of tumor would risk a good, long-term facial outcome.

Dr. Zwagerman: If the tumor is too large, we concentrate on debulking. If it is old and we are unable to remove the whole tumor, we may use radiation therapy for the residual tumor tissue, but this is uncommon.

What Are the Outcomes of Surgery and Radiation Therapy?

Dr. Harris: Outcomes for radiation therapy and surgery are similar. With surgical resection, the control rate is great because we’re actually removing the tumor. With radiation therapy, the control rate is very good and often equivalent to surgical control rates.

Dr. Zwagerman: If no growth is evident after an adequate series of follow-up scans, we space follow-ups out seven to 10 years. The longer we go without growth, the less likely the tumor will come back.

Dr. Harris: Our hope and expectation for all patients is that the facial expression is symmetrical and strong.

What Ongoing Services Are Available to Acoustic Neuroma Patients?

Dr. Zwagerman: We teach people how to compensate for the aftereffects of treatment until the brain can heal. People who do physical therapy prior to surgery do better dealing with post-surgery balance issues.

Dr. Harris: Regarding hearing loss and vestibular function, there are ways we can help beyond just radiating or resecting these tumors. When traditional hearing aids are not effective, specialized strategies exist for routing sound from the bad ear to the good ear. Cochlear implants are a potential option for people whose hearing nerve has been preserved. And facial plastic surgery offers options for people with residual facial weakness, paralysis, asymmetry or eyelid closure problems. We really look at all aspects of our patients’ quality of life.

How Does the Acoustic Neuroma Team Work With Physicians Who Refer Patients?

Dr. Harris: Treatment for acoustic neuroma involves a long-term relationship with patients, and referring physicians are considered part of the team. Our specialists keep providers apprised of treatments and next steps. When patients come from outside Wisconsin, their local physicians may order follow-up MRIs and have them reviewed by our team. Referring physicians can rely on their Froedtert & MCW counterparts as much as they desire. Partnership is key.