James Prueter, DO
Southwest Ohio ENT Specialists
Acoustic neuromas (vestibular schwannomas) are slow-growing, non-cancerous tumors that derive from the balance and hearing nerves in the inner ear (also known as the vestibulocochlear nerve). The tumor is composed of the cells (Schwann cells) that typically wrap around and insulate nerve fibers.
How Do Acoustic Neuromas Develop?
Acoustic neuromas develop due to mutations in Schwann cells that cause uncontrolled cell division. As a result, a tumor forms. As these tumors grow, they can compress the vestibulocochlear nerve causing unilateral (one-sided) hearing loss, dizziness, and ringing in the ear (tinnitus). With continued growth, it can also compress the trigeminal nerve causing facial numbness. It is also capable of interfering with the nerves that control the facial muscles causing weakness or paralysis on the side of the tumor. If the tumor grows larger, it can threaten more vital functions, such as breathing, as it exerts pressure on the brainstem.
Although acoustic neuromas can be dangerous at larger sizes, it is important to note that many acoustic neuromas do not grow at all, and of those that do, they grow very slowly. They also do not typically destroy surrounding tissues like cancerous (malignant) tumors. Hearing loss and balance function can still worsen over time with a non-growing acoustic neuroma.
Unilateral acoustic neuromas account for 8% of all intracranial tumors and approximately one out of every 100,000 people develops an acoustic neuroma. Symptoms typically develop between the ages of 30 and 60 but can develop at any age. Unilateral acoustic neuromas develop from sporadic, non-hereditary mutations.
How Are Acoustic Neuromas Diagnosed?
Early diagnosis of a vestibular schwannoma can be difficult because patients may be asymptomatic in the tumor’s early stages. Another complication to finding an accurate diagnosis is the fact that many middle and inner ear disorders share similar symptoms.
When symptoms develop, a thorough ear exam, hearing, and balancing tests are needed for accurate diagnosis. Computed tomography (CT) scans or magnetic resonance imaging (MRI) are crucial for early detection of these tumors. These imaging exams help the physician determine the neuroma’s size and location, as well as create a plan for surgical removal if necessary. An early diagnosis provides the best opportunity for a successful treatment.
How Are Acoustic Neuromas Treated?
There are three treatment options for acoustic neuromas: surgery, radiation, and observation.
Sometimes, vestibular schwannomas must be surgically removed. The type of operation involved depends on the size of the tumor and the impact the tumor has had on the patient’s hearing. Hearing loss that has already occurred cannot be reversed, but remaining hearing can be preserved with tumor removal in some cases. Surgical removal can also improve balance problems and other symptoms caused by smaller tumors, but there is an increased risk of nerve damage during removal of larger tumors. In these cases, vestibular rehabilitation may help promote compensation by the brain for the inner-ear deficits.
Radiation therapy, or radiosurgery, may be used to decrease the size or halt the growth of the tumor. This is typically the preferred method for elderly patients, those in poorer health, or those with bilateral acoustic neuromas (a tumor in each ear). Protocols for managing acoustic neuromas can vary with providers or institutions. A study by Macielak, Thao, Borah, et al. investigated treatment strategies that would incur the lowest lifetime cost and allow for the best quality of life for patients with small- and medium-sized tumors. The results of this study found that observation with the use of radiosurgery for continued growth resulted in the highest quality of life and was most cost-effective, independent of the patient’s age at diagnosis. Upfront surgery was also found to result in a lower quality of life and higher costs. Most acoustic neuromas have a slow growth rate or do not grow at all, so surgery is not always indicated upfront, especially for small- and medium-sized tumors.
If the tumor is not growing, it may be preferred to observe the tumor for a period with repeated imaging exams. This will allow the physician to determine if the acoustic neuroma is growing and will assist them in deciding if the tumor will need to be removed in the future.
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Jackson, MD C, Creighton, Jr., MD FX. Acoustic neuroma(Vestibular schwannoma). Accessed September 12, 2021. https://www.hopkinsmedicine.org/health/conditions-and-diseases/brain-tumor/vestibular-schwannoma
Vestibular Schwannoma (Acoustic Neuroma) and Neurofibromatosis. NIDCD. Accessed September 12, 2021. https://www.nidcd.nih.gov/health/vestibular-schwannoma-acoustic-neuroma-and-neurofibromatosis
Macielak RJ, Thao V, Borah BJ, et al. Lifetime cost and quality-adjusted life-years across management options for small- and medium-sized sporadic vestibular schwannoma. Otology & Neurotology. 2021;42(9):e1369-e1375. doi:10.1097/MAO.0000000000003266 https://journals.lww.com/otology-neurotology/Abstract/2021/10000/Lifetime_Cost_and_Quality_Adjusted_Life_Years.46.aspx