SRS FOR ACOUSTIC NEUROMA
RADIATION OVER SURGERY
Acoustic neuroma (vestibular schwannoma) was once routinely treated with open brain surgery — an approach that often damaged the facial nerve and hearing. Gamma Knife radiosurgery has largely replaced surgery for medium-sized tumours, offering equivalent tumour control with dramatically better preservation of facial function and a significantly safer profile.
analyticsAt a Glance
- check_circle10-year tumour control rate 90–95% with Gamma Knife SRS
- check_circlePermanent facial weakness: 0–1% (SRS) vs 5–20% (microsurgery)
- check_circleHearing preservation at 5 years: 50–70% (SRS) vs 30–50% (surgery)
- check_circleNo incision, no anaesthesia risk, outpatient single session
What Is an Acoustic Neuroma?
Acoustic neuroma (vestibular schwannoma) is a benign tumour arising from the Schwann cells of the vestibular nerve — one of the two components of the eighth cranial nerve that runs from the inner ear to the brainstem. Despite being benign, its location makes it clinically significant.
“Acoustic neuroma is not a cancer — it is a benign, slow-growing tumour. But "benign" does not mean harmless. It sits in the narrow internal auditory canal and cerebellopontine angle, adjacent to structures governing hearing, balance, and facial movement. Treatment decisions require extraordinary precision — both in diagnosis and in treatment choice.”
Symptoms
Progressive one-sided hearing loss — the most common presenting symptom, present in 95% of cases. Tinnitus (ringing in the affected ear). Imbalance or dizziness, which is often mild because the vestibular system adapts gradually. Facial numbness (involvement of the adjacent trigeminal nerve). Facial weakness is rare until tumours are large, because the facial nerve is separate from the tumour's origin. Headache or brainstem symptoms in large tumours causing compression.
Imaging and Diagnosis
MRI with gadolinium is the gold standard for diagnosis. Acoustic neuromas appear as a brightly enhancing, well-defined mass at the internal auditory canal (IAC) or cerebellopontine angle (CPA). Tumour size is classified by its CPA component: intracanalicular (confined to IAC), small (<1.5 cm CPA), medium (1.5–3 cm CPA), and large (>3 cm CPA). Size determines management: small tumours may be observed; medium tumours are the core SRS indication; large tumours with brainstem compression typically require surgery first.
Three Management Options: Observation, SRS, and Surgery
Not every acoustic neuroma requires immediate treatment. The three management options — active surveillance, SRS, and microsurgery — each have a defined role.
Active Surveillance: For Small, Asymptomatic Tumours
Many small acoustic neuromas grow very slowly — 0–2 mm per year — or not at all. For intracanalicular or small CPA tumours in older patients, active surveillance with serial MRI every 6–12 months is a legitimate first approach. Approximately 50–60% of observed tumours are radiologically stable at 5 years. Intervention is triggered by documented growth, worsening symptoms, or patient anxiety. Surveillance avoids the potential risks of both surgery and radiation for tumours that may never require treatment.
SRS: For Medium-Sized Growing Tumours (The Core Indication)
Tumours 1.5–3 cm with documented growth, progressive symptoms, or patient preference for definitive treatment. Single-session Gamma Knife (or CyberKnife) radiosurgery to the tumour margin. The standard dose is 12–13 Gy at the 50% isodose line — a dose that achieves tumour growth arrest and obliteration while minimising cranial nerve toxicity. No hospitalisation; outpatient procedure. The preferred treatment at most expert centres for this size range.
Microsurgery: For Large Tumours or Special Circumstances
Tumours >3 cm causing brainstem compression or obstructive hydrocephalus require surgical decompression before or instead of SRS. Three surgical approaches exist: translabyrinthine (no hearing preservation possible but lowest facial nerve risk), retrosigmoid (hearing preservation possible for some), and middle fossa (best hearing preservation for small intracanalicular tumours). Surgery is also preferred when histological confirmation is needed or when tumour cyst is causing acute expansion.
SRS Outcomes for Acoustic Neuroma
Long-term published outcomes from major Gamma Knife series for acoustic neuroma.
Tumour Control and Cranial Nerve Preservation
Tumour control = no further growth on MRI. Hearing preservation = maintained serviceable hearing (Gardner-Robertson class I–II). Facial nerve preservation = no permanent facial weakness.
- Tumour Control — 5 Years93–97%
- Tumour Control — 10 Years90–95%
- Facial Nerve Preservation (No Permanent Weakness)99–100%
- Serviceable Hearing Preservation at 5 Years50–70%
- Trigeminal Neuropathy (Numbness)1–4%
SRS vs Microsurgery: Cranial Nerve Outcomes
SRS consistently demonstrates superior facial nerve preservation and comparable hearing preservation vs microsurgery.
- Permanent Facial Weakness — SRS0–1%
- Permanent Facial Weakness — Microsurgery5–20%
- Hearing Preservation — SRS (5 years)50–70%
- Hearing Preservation — Surgery (retrosigmoid)30–50%
Acoustic Neuroma Treatment Selection by Clinical Scenario
How the MDT approach typically maps clinical characteristics to management options.
| Clinical Scenario | Preferred Management | Rationale |
|---|---|---|
| Small tumour (<1.5 cm), older patient, no growth on serial MRI | Active surveillance | High probability of stability; avoid treatment risk for tumour that may never require it |
| Small tumour with documented growth, younger patient | SRS | Prevent further growth; excellent long-term control; preserve nerve function |
| Medium tumour 1.5–3 cm, growing, useful hearing present | SRS | Superior hearing and facial nerve preservation vs surgery; equivalent tumour control |
| Medium tumour, patient wants definitive surgical resection | Microsurgery (retrosigmoid) | Patient preference for surgical certainty; full counselling on facial nerve risk required |
| Large tumour >3 cm, brainstem compression | Surgery first; SRS to residual | Brainstem decompression cannot wait; SRS after debulking controls residual |
| NF2-associated bilateral acoustic neuromas | Individualised — SRS for smaller/growing, surgery for dominant or cystic side | Bilateral disease; hearing preservation on at least one side critical |
| Tumour with cystic component, rapid expansion | Surgery | Cystic tumours may expand further after SRS before stabilising — surgical risk manageable |
The SRS Procedure for Acoustic Neuroma: What to Expect
For most patients, the Gamma Knife procedure for acoustic neuroma is a same-day outpatient experience. Understanding what happens reduces anxiety.
Pre-Procedure MRI (Day Before or Morning Of)
A dedicated MRI with gadolinium is performed in the planning position with the stereotactic frame (or thermoplastic mask for frameless systems) attached. The neurosurgeon, radiation oncologist, and medical physicist review the MRI together — delineating the tumour margin, the internal auditory canal, the facial nerve canal, the cochlea, and the brainstem. The dose plan is designed to deliver 12–13 Gy to the tumour margin while constraining cochlear dose (to preserve hearing) and brainstem dose.
Frame Placement (For Frame-Based Gamma Knife)
A lightweight aluminium stereotactic frame is applied under local anaesthesia with four pin sites — two at the forehead, two at the back of the skull. This takes approximately 20 minutes. The frame provides sub-millimetre positional accuracy for the duration of treatment. Most patients describe the pin placement as mild pressure and brief sting from the local anaesthetic.
Treatment Delivery (45–90 Minutes)
The patient lies on the Gamma Knife table with the frame locked to the treatment couch. The helmet (containing the 192 cobalt-60 sources) moves into position and treatment begins. The patient is alone in the room but continuously monitored via camera and intercom. There is no sensation from the radiation — no pain, no heat, no sound from the beams.
Recovery and Discharge
The frame is removed after treatment. Most patients experience mild headache or scalp tenderness at the pin sites for 1–3 days, managed with paracetamol. A short course of dexamethasone may be prescribed to reduce temporary swelling around the treatment site. Most patients go home the same day. Return to normal activity the following day for the majority.
Explore the SRS Knowledge Base
Related SRS and acoustic neuroma topics.
- What Is SRS and How Is It Different from Regular Radiation?
- Gamma Knife vs CyberKnife vs TrueBeam: How to Choose
- SRS for Brain Metastases: The Evidence That Changed Standard of Care
- SRS vs WBRT: Understanding the Neurocognitive Trade-Off
- Stereotactic Radiosurgery — Full Treatment Page
- Osteoid Osteoma RFA: The Minimally Invasive Cure
Frequently Asked Questions
Common questions about SRS for acoustic neuroma.
About Outcomes
After Gamma Knife, will my acoustic neuroma disappear?
Gamma Knife does not typically cause the tumour to disappear. The goal is tumour growth arrest — preventing further enlargement. Most tumours either remain stable in size or show gradual shrinkage on serial MRI over 2–5 years. Complete tumour obliteration eventually occurs in approximately 10–20% of treated tumours at long-term follow-up. The critical endpoint is control — no further growth — which is achieved in 90–95% of cases at 10 years. If your MRI shows a slightly enlarged tumour at 6–12 months after Gamma Knife, this can reflect post-treatment swelling rather than failure — most transient enlargements stabilise by 18–24 months.
Can I have SRS for acoustic neuroma if I've already had surgery?
Yes. SRS for residual or recurrent acoustic neuroma after prior surgery is a well-established indication. Surgery often leaves a small residual tumour attached to the facial nerve that the surgeon deliberately leaves to protect nerve function. This residual is typically treated with adjuvant SRS — achieving control rates similar to primary SRS. CancerFax can assess your post-surgical MRI to evaluate whether residual tumour is present and whether SRS is appropriate.
About the Decision
My surgeon says I need surgery. Should I get a second opinion on SRS?
Yes, absolutely. For medium-sized acoustic neuromas (1.5–3 cm) without brainstem compression, the evidence does not show microsurgery to be superior to SRS in any key outcome category — and surgery carries substantially higher facial nerve risk. Any patient being recommended microsurgery for a medium-sized acoustic neuroma is entitled to a radiation oncology consultation specifically assessing SRS candidacy. A second opinion at a centre with a dedicated skull base radiosurgery programme is standard of care in many countries.
How CancerFax Helps
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CancerFax does not guarantee treatment access, eligibility, or clinical outcome. Our role is to help patients access accurate information, structured review, and appropriate specialist pathways.
Acoustic Neuroma Diagnosed? SRS May Be the Right Choice.
Upload your MRI and audiology reports. Our neuro-oncology team will assess whether SRS is appropriate for your tumour size and hearing status — and identify the most experienced Gamma Knife centre for your case.
For informational purposes only. Acoustic neuroma treatment decisions require multi-disciplinary neuro-otology and radiation oncology evaluation.