Vestibular Schwannoma

A vestibular schwannoma, also known as an acoustic neuroma, is a noncancerous tumor that develops on the nerve leading from the inner ear to the brain. Most of these tumors are not emergencies and grow slowly over time. The expertise of the multidisciplinary team is essential for selecting and performing the appropriate treatment.

What Is a Vestibular Schwannoma?

A vestibular schwannoma is a slow-growing, benign tumor that arises from Schwann cells — the cells that form the insulating sheath around the vestibular portion of the eighth cranial nerve. It typically grows inside the internal auditory canal and can push out into the cerebellopontine angle, where it can press on the facial nerve, trigeminal nerve, cerebellum, and eventually the brainstem itself.

These tumors are not cancer. They grow slowly — on average less than 1–2 mm per year. Most are found in adults between 40 and 60 years old, almost always on one side. Bilateral tumors are a hallmark of neurofibromatosis type 2 (NF2).

At a Glance

A vestibular schwannoma is a benign (non-cancerous) tumor that grows from the insulating cells of the balance nerve (cranial nerve VIII)
The most common first symptom is one-sided hearing loss, often with ringing (tinnitus) in that ear
Many small tumors never need treatment — careful MRI surveillance is the right answer for most patients with small, stable tumors
When treatment is needed, the three choices are stereotactic radiosurgery, microsurgical removal, or continued observation
Facial nerve preservation and hearing preservation are the two outcomes that matter most, and both are strongly tied to surgical experience

Symptoms

The classic early symptoms

One-sided hearing loss — often first noticed on the phone or trouble understanding speech in a noisy room
Tinnitus (ringing or buzzing) in one ear
Imbalance or unsteadiness, especially in the dark or on uneven ground; true spinning vertigo is less common
A feeling of fullness or pressure in one ear

When the tumor gets larger

Numbness or tingling on one side of the face (from pressure on the trigeminal nerve)
Facial weakness or twitching (less common)
Headaches, especially in the back of the head
Unsteady walking or coordination problems (from pressure on the cerebellum)

Diagnosis

Workup usually starts with an audiogram. Any asymmetric sensorineural hearing loss in an adult is a reason to image the inner ear and brainstem.

Thin-slice MRI of the internal auditory canals with gadolinium contrast

The gold standard test. Even tumors just a few millimeters across show up clearly. The tumor is measured in its largest dimension outside the internal auditory canal (drives Koos grade and treatment decisions).

Additional testing

Repeat audiometry — AAO-HNS 50/50 rule: pure-tone average better than 50 dB and word recognition better than 50% is considered 'serviceable'
Balance testing (VNG or rotary chair) in some cases
Facial nerve function grading using the House-Brackmann scale (I = normal to VI = complete paralysis)
Genetic testing for NF2 if young, bilateral, or with family history

Types

Koos Grades

Grade I — Intracanalicular

Tumor sits entirely inside the internal auditory canal. Usually the smallest and most likely to be watched safely.

Grade II — Small extension into the cerebellopontine angle

Extends out of the canal into the CPA but does not touch the brainstem. Typically less than 2 cm extrameatal. Good candidate for observation, radiosurgery, or hearing-preserving microsurgery.

Grade III — Touches the brainstem, no compression

Now reaches the brainstem but does not deform it. Usually 2-3 cm extrameatal. Often treated with radiosurgery or microsurgery.

Grade IV — Compresses and displaces the brainstem

Largest tumors. Push the brainstem out of position and can obstruct spinal fluid flow. Microsurgical resection is usually the first choice — too large for radiosurgery alone.

Treatment

1. Observation ('wait and scan')

For small, newly-diagnosed tumors — especially Koos I and II. Many small tumors grow slowly or not at all. MRI at 6 months, then yearly, then spacing out if stable. Treatment recommended if tumor grows meaningfully, hearing declines quickly, or new symptoms develop.

2. Stereotactic radiosurgery (SRS)

Gamma Knife or CyberKnife focuses a single targeted dose of radiation on the tumor in a one-day outpatient treatment. Does not remove the tumor — it stops it from growing. Long-term tumor control rates ~94–97% at 5 and 10 years for tumors up to ~3 cm. Modern low-dose protocols (~12-13 Gy) have made facial and trigeminal nerve complications rare. Hearing tends to decline over the decade following SRS.

3. Microsurgical resection

For larger tumors (especially Koos IV), younger patients who want the tumor gone, and tumors that failed radiosurgery. Three standard approaches:

Retrosigmoid approach — Behind the ear, through the back of the skull. Most flexible corridor, usable for any size. Preserves option of hearing preservation.
Translabyrinthine approach — Through the mastoid bone. Sacrifices residual hearing by design, but gives unobstructed view of facial nerve at brainstem. Used for larger tumors when hearing is already lost.
Middle fossa approach — From above, through the floor of the temporal bone. Reserved for small, mostly intracanalicular tumors when hearing preservation is the main goal.

Every modern microsurgical resection uses intraoperative facial nerve monitoring and, when hearing preservation is the goal, auditory brainstem response monitoring.

Outcomes

Treatment	Serviceable hearing preserved (short term)	Notes
Observation	~50-70% at 5 years	Depends on starting hearing and tumor growth
Gamma Knife SRS	~55-75% early, <25% at 10 years	Hearing declines gradually after radiosurgery
Middle fossa (small tumor)	~60-75%	Best for intracanalicular tumors <1.5 cm
Retrosigmoid (small-medium)	~40-60%	Declines as tumor size grows beyond 1.5-2 cm
Translabyrinthine	0% by design	Best facial nerve exposure; used when hearing already gone

Tumor control: ~97% at 5 years and ~94% at 10 years after SRS; ~95-99% long-term control after complete microsurgical removal.

Facial nerve preservation: ~85-90% retain House-Brackmann grade I or II at long-term follow-up in experienced microsurgical series. For small tumors (<2 cm), that approaches 95%.

References

Carlson ML, Link MJ. Vestibular Schwannomas. NEJM. 2021;384(14):1335-1348. PMID: 33826821
Marinelli JP, et al. Long-term natural history and patterns of sporadic vestibular schwannoma growth: 952 patients. Neuro-Oncology. 2022;24(8):1298-1306. PMID: 34964894
Hadjipanayis CG, et al. CNS Systematic Review and Guidelines on Surgical Resection for Vestibular Schwannomas. Neurosurgery. 2018;82(2):E40-E43. PMID: 29309632
Germano IM, et al. CNS Guidelines on Radiosurgery for Vestibular Schwannomas. Neurosurgery. 2018;82(2):E49-E51. PMID: 29309637
Johnson S, et al. Long term results of primary radiosurgery for vestibular schwannomas. J Neuro-Oncol. 2019;145(2):247-255. PMID: 31535315
Starnoni D, et al. Surgical management for large vestibular schwannomas: systematic review and consensus statement. Acta Neurochir. 2020;162(11):25

Our Specialists

Peleg Horowitz, MD, PhD

Neurosurgery

Paramita Das, MD, MS

Neurosurgery

Request an Appointment

We are currently experiencing a high volume of inquiries, leading to delayed response times. For faster assistance, please call 1-773-702-2123 to schedule your appointment.

If you have symptoms of an urgent nature, please call your doctor or go to the emergency room immediately.

By submitting this form you acknowledge the risk of sending this information by email and agree not to hold the University of Chicago or University of Chicago Medical Center liable for any damages you may incur as a result of the transfer or use of this information. The use or transmittal of this form does not create a physician-contact relationship. More information regarding the confidentiality of this request can be found in our Privacy Policy.

* Indicates required field