Brainstem Test Helps Predict Who Keeps Useful Hearing After Vestibular Schwannoma Radiosurgery

A 86-patient retrospective study finds that a pretreatment auditory brainstem response, combined with how good a patient's hearing was before treatment, predicts whether useful hearing survives two years after Gamma Knife radiosurgery.

A vestibular schwannoma is a slow-growing benign tumor that arises from the nerve connecting the inner ear to the brain. It is rare, but for the people who are diagnosed with one, the central question after the tumor is controlled is often the same: will I still be able to hear out of that ear?

A new retrospective study from a tertiary referral center in Switzerland looked at 86 patients who underwent stereotactic radiosurgery between 2010 and 2019 and tries to answer that question. The team identifies two pretreatment markers that, together, can flag which patients are most at risk of losing useful hearing within two years.

Background: Why the Researchers Looked at This

Vestibular schwannomas grow on the eighth cranial nerve, which carries both hearing and balance information from the inner ear into the brainstem. As the tumor enlarges it can press on the nerve, gradually erode hearing on that side, and produce tinnitus and dizziness. Treatment options include observation with regular imaging, microsurgery, or stereotactic radiosurgery, a focused form of radiation that aims to halt tumor growth without removing it.

Stereotactic radiosurgery, often delivered with a Gamma Knife device, has become a popular option because it is non-invasive and tumor control rates are high. The trade-off is that the same nerve carrying hearing signals sits inside or near the radiation field, so some patients lose useful hearing in the treated ear over time even though the tumor is contained. Predicting in advance who is most likely to lose hearing would help patients and clinicians make better decisions about timing and treatment choice.

The auditory brainstem response, abbreviated ABR, is a non-invasive test that measures the electrical signal traveling from the cochlea up through the brainstem in response to sound. The earliest peak in that signal, called Wave I, reflects activity at the level of the auditory nerve itself. The Gardner-Robertson, or GR, scale is a four-tier classification clinicians use to summarize how useful a patient's hearing is, where class 1 and class 2 are considered serviceable.

How the Study Was Done

The team reviewed records from 86 patients treated with Gamma Knife radiosurgery at their center between 2010 and 2019. To be included, patients had to have serviceable hearing at the time of diagnosis and had to have undergone an ABR along with pure-tone audiometry and speech audiometry both before treatment and again at two years after radiosurgery.

Pure-tone audiometry measures how soft a tone a person can detect across a range of frequencies. Speech audiometry measures how clearly the person can recognize spoken words at comfortable loudness levels. The team combined these into a Gardner-Robertson class at each time point and looked for pretreatment factors that predicted whether a patient was still in class 1 or 2, the serviceable range, two years out.

What the Researchers Found

Most patients did keep useful hearing two years after treatment. Using pure-tone audiometry to define the cutoff, 77.9 percent of the 86 patients were still in Gardner-Robertson class 1 or 2 at the two-year mark. When the team used speech audiometry, the figure was higher at 86.7 percent. The gap between the two numbers reflects the fact that some patients lose tone sensitivity faster than they lose word recognition, or vice versa.

Two pretreatment markers stood out as significant predictors of losing useful hearing by two years. The first was a pathologic ABR Wave I, meaning the earliest peak of the brainstem response was already abnormal before treatment, suggesting that the auditory nerve at that level was under stress. The second was an initial Gardner-Robertson class of 2 rather than class 1. Patients who entered treatment with already-borderline hearing on the GR scale were more likely to drop below the serviceable threshold afterward.

Put together, these two factors give clinicians a pretreatment warning signal. A patient with normal Wave I morphology and starting GR class 1 has a relatively high probability of retaining useful hearing at two years; a patient with an abnormal Wave I and starting GR class 2 should be counseled that hearing loss in the treated ear is more likely.

What It Means for People with Hearing Loss

If you or a family member has been diagnosed with a vestibular schwannoma, this study supports asking your team specifically about your ABR Wave I and your Gardner-Robertson class before any treatment decision. Those two pieces of information can change the conversation about whether to observe the tumor a little longer, choose radiosurgery, or consider microsurgical options.

For people who do lose useful hearing after treatment, the situation is workable. Asymmetric hearing loss, where one ear hears normally and the other does not, is well understood and well addressed today. Modern hearing technology can route sound between ears, support phone calls and television streaming, and restore much of the spatial hearing that asymmetric loss tends to disrupt.

Restoring Clinical-Grade Hearing After Treatment-Related Loss

When the goal is to recover clinical-grade performance, particularly for adults who need clear speech, dependable phone calls, and reliable streaming for television and music, the device should be doing more than amplifying. The Panda Quantum is a 16-channel receiver-in-canal hearing aid with adaptive noise reduction, Bluetooth for calls, music, and TV streaming, and up to 80 hours of total battery life when used with its charging case.

The Panda Quantum also includes the Panda app-based in-ear hearing test. After delivery, the user pairs the device with the Panda app, the app runs a frequency-specific hearing test through the hearing aid itself, and then automatically programs the device's gain and frequency response to match the user's audiogram. The result is similar to what an audiologist does at a clinical fitting, but performed at home with the device the user actually wears.

The Panda Quantum carries a 5-year warranty and a 45-day return window, which gives someone adjusting to a new hearing aid time to live with it in real environments. OTC hearing aids are approved for adults with mild-to-moderate hearing loss; severe or profound losses, including the deeper losses that sometimes follow radiosurgery, often benefit most from a clinical fitting and possibly other technologies such as bone-conduction or contralateral routing devices.

Limitations of This Research

This was a retrospective single-center review with 86 patients, and the authors classify the work as Level 3 evidence. Findings from one tertiary center may not match those at other centers using different radiosurgery devices, dosing protocols, or follow-up schedules. The two-year endpoint also leaves open the question of how hearing evolves over five or ten years, which matters for younger patients especially.

The team did not report external industry funding for this analysis. One coauthor is affiliated with a center that performs radiosurgery commercially, which is worth keeping in mind when weighing the conclusions.

Where This Leaves Us

For most patients with serviceable hearing at the time of vestibular schwannoma diagnosis, Gamma Knife radiosurgery preserves useful hearing at two years, and a pretreatment ABR plus Gardner-Robertson grading helps identify who is at higher risk. For the smaller group whose hearing changes meaningfully after treatment, today's hearing technology offers a real path back to clear speech and connected listening.

Beharry A, Tuleasca C, Faouzi M, Levivier M, Maire R. Auditory Brainstem Response as a Predictor of Hearing After Vestibular Schwannoma Radiosurgery. Otology & Neurotology. 2026. Retrieved from PubMed. https://doi.org/10.1097/MAO.0000000000004937