An acoustic neuroma is a slow-growing, noncancerous tumor that develops on the main nerve connecting your inner ear to your brain. Doctors now more commonly call it a vestibular schwannoma, which better describes what it actually is: a growth made entirely of Schwann cells, the insulating cells that wrap around nerve fibers. These tumors affect roughly 34 out of every million people per year, with a median age at diagnosis of about 60.
Despite being benign, acoustic neuromas can cause real problems. As they grow, they press on nearby structures and gradually affect hearing, balance, and sometimes facial sensation or movement. The good news is that up to 75% of these tumors show no measurable growth over time, and multiple effective treatment options exist for those that do.
Where the Tumor Comes From
Your eighth cranial nerve, called the vestibulocochlear nerve, carries signals for both hearing and balance from your inner ear to your brain. This nerve runs through a narrow bony channel called the internal auditory canal. An acoustic neuroma forms when Schwann cells along this nerve begin multiplying abnormally, creating a well-encapsulated mass.
Most acoustic neuromas occur spontaneously, without a clear genetic cause. A small percentage, however, are linked to a hereditary condition called neurofibromatosis type 2 (NF2), caused by a mutation in the NF2 gene on chromosome 22. People with NF2 typically develop tumors on both sides, which is unusual for the sporadic form. About half of NF2 cases are inherited from a parent, while the other half arise from new, spontaneous mutations.
How Symptoms Typically Appear
The hallmark symptom is hearing loss in one ear. In a large study of over 900 patients, 80% presented with one-sided hearing loss, and 90% of those described it as gradually worsening rather than sudden. You might first notice it when using a phone on one side or struggling to hear in noisy environments.
About half of patients also experience tinnitus, a ringing, buzzing, or hissing sound in the affected ear. For most people (81%), the tinnitus comes and goes rather than being constant. When it is present, it tends to be mild in roughly two-thirds of cases, moderate in about 30%, and severe in only 2%.
Balance problems are also common, though they tend to develop slowly enough that your brain partially compensates. Because the tumor grows gradually, you may feel a vague unsteadiness rather than sudden spinning vertigo. Larger tumors that press on the facial nerve or the nerve responsible for facial sensation can cause numbness, tingling, or weakness on one side of the face, though these symptoms are less common at initial diagnosis.
How Acoustic Neuromas Are Diagnosed
If you report one-sided hearing loss or tinnitus, a hearing test (audiometry) is typically the first step. This can reveal a specific pattern of high-frequency hearing loss that raises suspicion. But the definitive diagnostic tool is an MRI scan with a contrast dye called gadolinium, which makes the tumor light up clearly on imaging. Before MRI became widely available, CT scans missed about 30% of acoustic neuromas, and older screening methods could only reliably detect tumors larger than 5 millimeters.
Modern MRI is sensitive enough to catch very small tumors. Over the past four decades, the average tumor size at diagnosis has dropped from 26 millimeters to just 7 millimeters, largely because MRI access has improved and doctors are ordering scans earlier.
Growth Patterns and Observation
Not every acoustic neuroma needs immediate treatment. A systematic review of growth data found that the average growth rate across all tumors is only 1 to 2 millimeters per year. Among tumors that do actively grow, the rate is 2 to 4 millimeters per year. But up to 75% of tumors show no measurable growth at all on follow-up scans.
This is why many doctors recommend a “watch and scan” approach for small tumors, especially in older patients or those with minimal symptoms. You’ll get periodic MRI scans, often every 6 to 12 months initially, to track any changes. If the tumor remains stable, you may simply continue monitoring. There are currently no reliable predictors of which tumors will grow and which won’t, so consistent follow-up matters even when things look stable.
Surgical Treatment Options
When a tumor is large, growing, or causing worsening symptoms, surgery to remove it is one option. Surgeons use three main approaches, chosen based on tumor size, hearing status, and anatomy.
- Retrosigmoid approach: The most versatile option. Surgeons access the tumor through an opening behind the ear and can remove tumors of various sizes. This is the approach most likely to preserve remaining hearing, because it doesn’t disrupt the inner ear structures directly.
- Translabyrinthine approach: Preferred when useful hearing has already been lost. The surgeon goes through the inner ear itself, which sacrifices any remaining hearing on that side but provides early visibility of the facial nerve during the procedure and avoids the need to retract brain tissue.
- Middle fossa approach: Reserved for small tumors still confined within the bony ear canal. It has a more limited application but can offer hearing preservation for the right candidates.
The facial nerve runs right alongside these tumors, making its preservation a primary surgical concern. In one surgical series, the nerve was physically preserved in 97% of cases. However, temporary facial weakness after surgery is common. About 39% of patients in that study had some degree of facial nerve weakness immediately after the operation. At the one-year mark, 37% still had some lasting deficit, ranging from mild asymmetry to more significant weakness. Cerebrospinal fluid leaks occurred in about 4.5% of cases, most managed without additional surgery.
Radiation as an Alternative
Stereotactic radiosurgery delivers a focused, high-dose beam of radiation to the tumor in a single session or a small number of sessions. It doesn’t remove the tumor but aims to stop its growth. This is often recommended for small to medium tumors, for patients who aren’t good candidates for surgery, or for those who prefer a less invasive option.
Five-year tumor control rates with modern techniques are excellent, ranging from 91% to 99% when standard doses are used. That means the vast majority of treated tumors stop growing or shrink slightly over the following years.
The tradeoff is the effect on surrounding nerves over time. Hearing preservation rates at five years range from 41% to 79%, meaning a significant number of patients do lose functional hearing despite successful tumor control. Facial nerve function is preserved in 95% to 100% of cases, which is generally better than surgical outcomes for larger tumors. The nerve responsible for facial sensation is preserved in 79% to 99% of cases.
Choosing Between Treatment Approaches
There is no single best treatment for every acoustic neuroma. The decision depends on several overlapping factors: how large the tumor is, whether it’s actively growing, how much hearing you still have, your age, your overall health, and your own priorities regarding hearing preservation versus tumor removal.
Small, stable tumors in patients with good hearing are often best served by observation. Radiation tends to be favored for small to medium tumors where the goal is tumor control with less immediate risk. Surgery is typically the choice for larger tumors causing compression, tumors that have grown despite radiation, or cases where a definitive removal is preferred. Rigorous head-to-head comparison data between these approaches remains limited, so the decision is often made collaboratively between you and a skull base treatment team familiar with all three options.