Acoustic Neuroma Explained: Causes, Symptoms, And Treatments

An acoustic neuroma is a rare type of brain tumor (per the Acoustic Neuroma Association). Acoustic neuromas got their name because doctors and scientists originally thought that the tumors grew from the acoustic nerve, though later research showed that they come from Schwann cells of the vestibular nerve. Therefore, vestibular schwannoma is a more appropriate name, but the term acoustic neuroma is more common.

Schwann cells form a sheath around nerves, insulating them and increasing nerve impulse conduction (via the National Library of Medicine). Acoustic neuromas form when Schwann cells surrounding the vestibular nerve form a benign, or non-cancerous tumor, according to the Acoustic Neuroma Association. The vestibular nerve is "responsible for both hearing and balance" (per Healthline), so the first signs of an acoustic neuroma are typically problems with hearing function and balance. 

These tumors tend to be slow growing, although they grow rapidly in some cases. Acoustic neuromas do not spread throughout the body but because they press on the brain as they grow, they can cause symptoms and health problems. Let's take a closer look at the causes, symptoms and available treatments. 

A 2021 review in the International Journal of Molecular Sciences describes neurofibromatosis type 2 (NF2) as a genetic disorder caused by a mutation in the NF2 gene, which encodes a tumor-suppressing protein known as Merlin. The mutation causes the NF2 gene to lose its tumor-suppressing function, and so the NF2 disorder is characterized by the formation of tumors in the "central and peripheral nervous system." Roughly one in 25,000 people have NF2.

People with NF2 are more likely to develop acoustic neuromas and they develop these tumors at an early age. By age 20, roughly 90% of patients with NF2 develop "bilateral vestibular schwannomas." These tumors may recur even after treatment. Half of NF2 patients will also develop meningiomas, which are tumors that form from the meninges — "the membranes that surround the brain and spinal cord" (per the Cleveland Clinic). Many patients also develop spinal schwannomas, a type of spinal cord tumor, according to the Mayo Clinic, ependymomas, a type of tumor in the brain or spinal cord (via the National Cancer Institute), and dermal schwannomas, a type of tumor of the nerve sheath that forms beneath the skin, explains a 2010 case report in the American Journal of Dermatopathology.

Because people with NF2 develop so many types of tumors at an early age, they require a team of specialists to manage their condition. This team may include family physicians, neurogeneticists, neuro-oncologists, neuro-otologists, neurosurgeons, neuro-ophthalmologists, neuroradiologists, social workers, and audiologists — along with speech, physical, and occupational therapists.

Acoustic neuromas are slow-growing tumors, so their symptoms may take years to appear, according to the Mayo Clinic. When they do show up, these symptoms are easy to miss. As the tumor grows, it will start to press on nearby nerves, blood vessels, and muscles, making symptoms more apparent.

Because the vestibular nerve affects hearing, many symptoms of an acoustic neuroma involve hearing. Hearing loss on one side is the most common symptom of an acoustic neuroma. Patients may also experience a feeling of fullness in the affected ear. Others develop tinnitus, which is a ringing, roaring, clicking, buzzing, or hissing sound in one or both ears, according to the National Institute on Deafness and Other Communication Disorders.

The vestibular nerve also plays a role in balance, so patients with acoustic neuromas may feel unsteady or lose their sense of balance and develop vertigo. Pressure from the tumor on other nerves or muscles may lead to facial numbness or weakness, loss of muscle movement, difficulty swallowing, headaches, a feeling of pressure in the head, a change in taste, and a change in tear production.

According to Johns Hopkins Medicine, death is a rare but potential outcome of an acoustic neuroma. Untreated tumors can "compress the cerebellum and brain stem" or cause an increase of fluid on the brain.

Proper testing and diagnosis are necessary to rule out other conditions with symptoms similar to symptoms of an acoustic neuroma. The National Organization for Rare Disorders provides information about conditions, such as Bell's palsy, Meniere's disease, and meningioma, that can look like an acoustic neuroma.

Bell's palsy is a neurological disorder that affects the seventh cranial nerve. It is non-progressive, meaning that it does not get worse with time. There is no known cause of Bell's palsy, although it may be linked to a viral infection, an immune disorder, or family history. Bell's palsy causes a sudden onset of facial paralysis, which may look like the facial weakness sometimes caused by an acoustic neuroma.

Meniere's disease affects the inner ear and can cause episodes of vertigo or dizziness, low-frequency hearing loss, tinnitus, and a feeling of fullness or pressure in the ear, all symptoms of an acoustic neuroma. People with Meniere's disease may experience symptoms daily or occasionally, although hearing loss and tinnitus can become permanent.

Meningiomas are benign tumors of the meninges, which is the membrane lining the brain and spinal cord. Meningiomas can occur anywhere in the brain or spinal cord, but if they develop near the nerves affecting balance and hearing they can cause the same symptoms as an acoustic neuroma. Common symptoms include hearing loss, dizziness, problems with balance, facial numbness, and difficulty swallowing.

Your doctor will advise you on the best surgical approach based on the size of your tumor and its location. Here is more information from the Cleveland Clinic about surgical options.

With the middle fossa approach, the surgeon removes the tumor from the inner ear through an incision in the side of your head. This approach works well for small tumors inside the bony ear canal. It may preserve hearing and facial nerve function.

With the retrosigmoid approach, the surgeon makes an incision behind the ear to remove the tumor from the inner ear canal and a part of the skull called the cranial fossa. This approach works best for medium to large tumors that are pressing on the brain. It may preserve hearing and prevent facial paralysis.

With the translabyrinthine approach, "The surgeon makes an incision behind the ear, removing bones of the inner ear for a better view of the tumor" (via the Cleveland Clinic). This process causes total hearing loss on the affected side, so surgeons typically use this approach on patients who have already lost their hearing. This approach can be used for tumors of any size. While it does cause hearing loss, it preserves facial nerve function.

Your surgical team will attempt to remove the entire tumor but may choose to leave some of the tumor behind to protect the facial nerve. According to a 2020 review published in the journal Neuro-Oncology, residual tumors can lead to recurrence of the acoustic neuroma.

Patients with NF2 often develop acoustic neuromas on both sides, which can lead to complete deafness. Because of this risk, observational management is not the best approach for patients with NF2. The Acoustic Neuroma Association recommends that these patients work closely with their team of specialists to preserve their hearing for as long as possible.

The current recommended strategy for NF2 patients is to remove the smaller of the two tumors first, because removing smaller tumors typically preserves hearing on that side. If the surgery works and preserves hearing, patients should have the other tumor removed. If the surgery does not preserve hearing, observational management should be used on the other tumor to avoid losing hearing in both ears. However, if the second tumor continues to grow or starts to damage hearing on that side, it should be removed as well.

While stereotactic radiosurgery is an option, it is not always the best choice for NF2 patients. The cell type of acoustic neuromas in NF2 patients can be resistant to radiation and more likely to become malignant.

According to the Cleveland Clinic, most patients can expect to stay in the hospital for two to three days after undergoing surgery to remove an acoustic neuroma. In the days and weeks following the surgery, patients will need to go through several tests. Your doctor may recommend an MRI or other imaging scans to confirm tumor removal and monitor the area. They will also order tests to see how the surgery affects your hearing, facial nerve function, and balance.

A 2022 study in the Journal of Clinical Neuroscience found that frail patients, defined as patients with exhaustion, low physical activity, weakness, slowness, and shrinking, experience worse outcomes after surgery. They are more likely to experience complications such as post-operative infection, facial paralysis, urinary tract infections, and hydrocephalus. They also tend to have longer hospital stays and higher rates of readmission.

Patients who have trouble with balance may need to go through vestibular rehabilitation therapy (VRT). According to the Vestibular Disorders Association, VRT is an exercise-based therapy performed by a specialized occupational or physical therapist. It can help patients through habituation, gaze stabilization, and balance therapy. Habituation reduces dizziness caused by quick movements, changes in posture, or visual stimuli. Gaze stabilization helps patients by improving their eye control. Balance training provides patients with customized exercises to help reduce their risk of falling and improve their ability to walk on uneven surfaces.