This comprehensive review explains that vestibular schwannomas (non-cancerous inner ear tumors) are more common than previously thought, affecting approximately 1 in 500 people during their lifetime. Modern MRI scanning has led to earlier detection of smaller tumors in older patients, with current management favoring observation for many cases. Treatment options include careful monitoring, radiation therapy, or surgery, with the best approach depending on tumor size, patient age, and symptoms.
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Understanding Vestibular Schwannomas: A Comprehensive Patient Guide
Table of Contents
- Introduction: What Are Vestibular Schwannomas?
- Current Understanding of How Common These Tumors Are
- Disease Presentation and Symptoms
- Diagnostic Evaluation and Testing
- Treatment Options and Approaches
- Wait-and-Scan Approach (Active Monitoring)
- Radiosurgery Treatment Option
- Source Information
Introduction: What Are Vestibular Schwannomas?
Vestibular schwannomas (sometimes historically called acoustic neuromas) are non-cancerous tumors that account for 8% of all intracranial tumors. They are the most common type of tumor found in the cerebellopontine angle area of the brain in adults.
These tumors develop from the Schwann cells that protect the vestibular nerve, which is part of the eighth cranial nerve responsible for balance and hearing. Although often considered rare, recent research shows they actually affect approximately 1 in 500 people during their lifetime.
The management of these tumors remains controversial due to their unpredictable behavior and the importance of preserving quality of life. Treatment approaches vary significantly across different medical centers and countries.
Several important developments have changed how these tumors are diagnosed and treated. Widespread access to sensitive MRI scanning has led to increased detection, with more cases being discovered incidentally when tumors are small and patients are older. There has been a shift toward conservative management that prioritizes preserving neurological function over completely removing the tumor.
Current Understanding of How Common These Tumors Are
The increased detection of vestibular schwannomas is primarily due to better diagnostic technology rather than a true increase in the actual occurrence of these tumors. From the early 1900s through the 1970s, the incidence remained stable at about 1 case per 100,000 people per year.
Current incidence rates range from 3 to 5 cases per 100,000 person-years, with sustained increases over the most recent decade. This increase has been most dramatic among people over age 70, where incidence rates now approach 20 cases per 100,000 person-years.
Today, cases are commonly diagnosed when patients are in their 60s or 70s, with tumors that are just millimeters in size. Analysis of data from Denmark's national registry spanning four decades showed that the average age at diagnosis increased from 49 to 60 years, while the mean tumor size decreased from 2.8 cm to 0.7 cm.
In regions with widespread access to MRI, up to 25% of all new cases are discovered incidentally during imaging performed for unrelated reasons such as headaches. Some researchers have suggested environmental exposures like cell phone use or long-term noise exposure might increase risk, but large studies have not confirmed these associations.
Disease Presentation and Symptoms
The most common symptoms patients experience include:
- Ipsilateral sensorineural hearing loss in more than 90% of patients
- Dizziness or imbalance in up to 61% of patients
- Asymmetric tinnitus (ringing in one ear) in 55% of patients
Hearing loss is often subtle initially and may first become apparent when using the telephone or lying in bed with the unaffected ear covered. Over time, many people experience increasing difficulty with sound localization and understanding speech in noisy environments due to loss of binaural hearing.
Interestingly, despite arising from the vestibular nerves, symptoms of vertigo and continuous dizziness occur in only about 8% and 3% of cases respectively. This discrepancy likely reflects the slow progression of vestibular loss that allows the brain time to compensate.
Patients with large tumors that compress the brain stem and cerebellum may experience numbness in parts of the face, facial pain (trigeminal neuralgia), coordination problems, or slowly progressive hydrocephalus. Importantly, there is limited association between tumor size and severity of hearing loss, tinnitus, or dizziness at diagnosis.
Diagnostic Evaluation and Testing
Thin-slice, gadolinium-enhanced MRI of the head is the standard diagnostic approach for detecting vestibular schwannomas as small as 2 mm in diameter. The imaging features are highly sensitive and specific, resulting in accurate diagnosis in most cases without needing a biopsy.
The main reason for obtaining a screening MRI is sudden or asymmetric sensorineural hearing loss detected through hearing tests. With such a history, the probability of identifying a vestibular schwannoma is between 1% and 5%.
Widely adopted screening protocols specify that MRI should be considered when there is any difference between ears of 10 dB or greater in two consecutive frequencies or 15 dB or greater in any single frequency. Guidelines for performing MRI to investigate unilateral tinnitus or asymmetric vestibular dysfunction are less well defined.
Patients with an isolated, unilateral vestibular schwannoma who have no other signs of neurofibromatosis type 2 and no affected relatives generally do not need genetic testing.
Treatment Options and Approaches
Treatment strategies for vestibular schwannomas include:
- Observational wait-and-scan approach
- Radiation therapy (radiosurgery)
- Microsurgical removal
- Combination of these methods
Several new drug therapies that aim to halt tumor growth, including aspirin and monoclonal antibodies, have been explored but remain investigational. To date, no high-level evidence indicates that one treatment approach is unequivocally superior to others.
Each strategy has advantages and limitations, and research shows that the diagnosis itself and patient-related factors affect quality of life more than treatment choice. Tumor size primarily drives treatment recommendations, but decision-making is also guided by subtle patient- and provider-related factors.
Wait-and-Scan Approach (Active Monitoring)
The wait-and-scan approach has gained popularity because many tumors are now discovered when they are small in older patients with mild symptoms. Studies over the past 15 years have shown that only 22% to 48% of tumors show growth (defined as an increase of 2 mm or more in diameter) during follow-up periods averaging 2.6 to 7.3 years.
Typically, tumors with a maximal diameter of less than 1.5 cm in the cerebellopontine angle are considered for observation. The most consistent predictor of future growth is larger tumor size at diagnosis.
Imaging and hearing evaluation are commonly performed 6 months after the initial MRI to identify fast-growing tumors. If no growth is detected at 6 months, assessments are typically performed annually until year 5, then every other year. Given the unpredictable nature of tumor growth, lifelong follow-up is recommended.
Hearing loss progression is expected during observation. Population data from Denmark showed that of 636 patients with useful hearing at diagnosis (speech discrimination score >70%), only 31% retained hearing above this threshold after 10 years of observation. However, 88% of patients who started with perfect speech comprehension (100% score) still had good hearing (>70%) at 10 years.
Radiosurgery Treatment Option
Stereotactic radiosurgery typically involves highly focused radiation delivered in 1 to 5 treatments to the tumor while sparing surrounding tissue. Gamma-knife radiosurgery is one common type that uses 192 cobalt-60 sources to deliver precise radiation.
Treatment usually involves a stereotactic head frame and specialized imaging to target the tumor in three-dimensional space. Unlike surgical removal, the tumor remains in place after radiosurgery but typically stops growing and may gradually shrink over years.
Patients with tumors less than 3.0 cm in diameter are usually considered candidates for radiosurgery, though tumors less than 2.5 cm are preferred to minimize risks. Single-fraction stereotactic radiosurgery with a marginal dose of 13 Gy or less is associated with less than 1% risk of permanent facial nerve weakness and less than 5% risk of trigeminal nerve problems.
Contemporary radiosurgery series report tumor control in more than 90% of cases at 10 years of follow-up. The risk of developing a secondary cancer from radiosurgery is approximately 0.02%.
Source Information
Original Article Title: Vestibular Schwannomas
Authors: Matthew L. Carlson, M.D., and Michael J. Link, M.D.
Publication: The New England Journal of Medicine, April 8, 2021
DOI: 10.1056/NEJMra2020394
This patient-friendly article is based on peer-reviewed research originally published in The New England Journal of Medicine. The information has been translated into accessible language while preserving all scientific data, study results, and clinical recommendations from the original research.