Vestibular Schwannoma
Summary
Vestibular Schwannoma (formerly Acoustic Neuroma) is a benign, slow-growing tumour arising from the Schwann cells of the vestibular portion of the Vestibulocochlear Nerve (CN VIII). It is the most common tumour of the Cerebellopontine Angle (CPA) (80%). The classic presentation is Unilateral Sensorineural Hearing Loss and Tinnitus. Large tumours can compress the Brainstem, Facial Nerve (VII), and Trigeminal Nerve (V). [1,2]
Clinical Pearls
The Corneal Reflex: The loss of the corneal reflex (CN V1 afferent, CN VII efferent) is often the first sign of a large tumour. The tumour in the CPA compresses the Trigeminal nerve. Always check corneal reflexes in any patient with unilateral hearing loss.
Unilateral Tinnitus: Is Vestibular Schwannoma until proven otherwise. Any patient with asymmetrical tinnitus requires an MRI IAMs (Internal Acoustic Meatus) to rule this out.
Ice Cream Cone Sign: The appearance on MRI. The tumour fills the IAM (the cone) and bulges out into the CPA (the ice cream).
Demographics
- Incidence: 1 in 100,000 per year. (Increased detection due to MRI availability).
- Age: Peak 40-60 years.
- Gender: Female > Male slightly.
Neurofibromatosis Type 2 (NF2)
- Bilateral Vestibular Schwannomas are pathognomonic for NF2.
- Genetic mutation on Chromosome 22 (Merlin protein).
- Present earlier (20s-30s).
Anatomy (The CPA)
The Cerebellopontine Angle contains:
- CN V (Trigeminal): Compression -> Facial numbness / Loss of corneal reflex.
- CN VII (Facial): Compression -> Facial weakness (rare early due to motor fibre resilience).
- CN VIII (Vestibulocochlear): Origin of tumour -> Hearing loss / Vertigo.
- Brainstem/Cerebellum: Compression -> Ataxia / Hydrocephalus.
Histology
- Benign: WHO Grade I.
- Antoni A Areas: Dense, cellular, palisading nuclei (Verocay bodies).
- Antoni B Areas: Loose, myxoid tissue.
| Condition | Frequency | Key Features |
|---|---|---|
| Vestibular Schwannoma | 80% | Widens the IAM. Acute angle with petrous bone. |
| Meningioma | 10% | Dural tail. Obtuse angle. Does not usually widen IAM. |
| Epidermoid Cyst | 5% | "Pearls". Diffusion Restricted on MRI (DWI bright). |
| Arachnoid Cyst | less than 1% | CSF fluid signal on all sequences. |
Otological (Early)
Neurological (Late - >2cm)
Audiology
- Pure Tone Audiogram: Asymmetrical Sensorineural Hearing Loss. (High frequency loss is typical).
Imaging (Gold Standard)
- MRI Brain (IAM Protocol): with Gadolinium contrast.
- Shows enhancing mass in IAM/CPA.
- Koos Grading:
- Grade 1: Intracanalicular (inside IAM).
- Grade 2: Extending into CPA (less than 2cm). No brainstem contact.
- Grade 3: Touching brainstem.
- Grade 4: Compressing brainstem.
Management Algorithm
DIAGNOSED VESTIBULAR SCHWANNOMA
↓
ASSESS SIZE, AGE, HEARING, COMORBIDITIES
(Discuss in Skull Base MDT)
↓
┌─────────┼─────────┐
OBSERVATION RADIOTHERAPY SURGERY
(Wait & Scan) (Stereotactic) (Microsurgery)
↓ ↓ ↓
• Small (less than 1.5cm) • Medium (less than 3cm) • Large (>3cm)
• Elderly • Growing • Brainstem
• Non-growing • Preservation compression
of hearing • Young patient
1. Conservative (Watch, Wait & Rescan)
- Indication: Asymptomatic, Small (less than 1.5cm), Elderly.
- Rationale: 50% do not grow. Average growth often only 1-2mm/year.
- Protocol: MRI at 6 months, then annually.
2. Stereotactic Radiosurgery (Gamma Knife / CyberKnife)
- Indication: Tumours less than 3cm, Growing tumours, Unfit for surgery.
- Mechanism: Delivers high dose radiation to tumour, sparing surround.
- Goal: Local control (Stop growth). Does not remove tumour.
- Risk: Malignant transformation (very rare).
3. Microsurgery
- Indication: Large (>3cm), Brainstem compression, Cystic tumours (don't respond well to radiation), Patient choice.
- Approaches:
- Translabyrinthine: Sacrifices hearing (if already lost). Excellent facial nerve ID.
- Retrosigmoid: Hearing preservation possible. Headache risk.
- Middle Fossa: Small intracanalicular tumours only.
Pre-treatment
- Hydrocephalus: Shunt required.
- Tinnitus: Can be debilitating.
Post-Surgery
- Facial Nerve Palsy: (10-30%). May need gold weight implant for eyelid closure / nerve graft.
- CSF Leak: (10%) - Rhinoleak (down Eustachian tube).
- Meningitis.
- SSD: Single Sided Deafness.
- Tumour Control: >95% with Radiosurgery or Surgery.
- Hearing: Usually lost eventually in affected ear.
- Return to work: Generally good unless severe balance/facial nerve issues.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Skull Base Tumours | SBNS / ENT UK | Management must be via specialized Skull Base MDT. |
| Radiosurgery | Congress of Neurosurgeons | Radiosurgery recommended for tumours less than 3cm with documented growth. |
Landmark Evidence
1. Natural History Studies
- Many longitudinal studies have shown that ~50% of intracanlicular tumours show no growth over 5 years, supporting the "Watch and Wait" policy for small tumours.
What is an Acoustic Neuroma?
It is a benign (non-cancerous) growth on the hearing and balance nerve. It is relatively rare. It is not a brain tumour, but it grows in the space next to the brain.
Why do I have hearing loss?
The tumour grows on the nerve cable, pressing on the delicate fibers that carry sound to the brain.
Do I need an operation?
Not necessarily. Many of these tumours are very small and stop growing on their own. We often just monitor them with MRI scans every year. If it grows, we might beam radiation at it to kill it (Gamma Knife) or remove it with surgery.
What about my face?
The hearing nerve runs right next to the facial nerve (which moves your face muscles). If the tumour is large, or if we do surgery, there is a risk to this nerve, which could cause a facial droop. Surgeons use special monitors to protect this nerve.
Primary Sources
- Goldbrunner R, et al. EANO guidelines for the diagnosis and treatment of vestibular schwannoma. Lancet Oncol. 2020.
- Germano A, et al. Congress of Neurological Surgeons Systematic Review and Evidence-Based Guidelines on the Role of Radiosurgery and Radiation Therapy in the Management of Patients with Vestibular Schwannomas. Neurosurgery. 2018.
Common Exam Questions
- Diagnosis: "Unilateral hearing loss management?"
- Answer: MRI IAM (to exclude VS).
- Genetics: "Bilateral Acoustic Neuromas?"
- Answer: Neurofibromatosis Type 2 (NF2).
- Anatomy: "Nerves in CPA?"
- Answer: CN V, VII, VIII.
- Radiology: "Ice cream cone sign?"
- Answer: Vestibular Schwannoma.
Viva Points
- Facial Nerve Preservation: Why is it hard? Because the facial nerve is often splayed/stretched over the surface of the tumour and can be microscopic.
- Hitselberger's Sign: Loss of sensation in the posterior aspect of the ear canal (supplied by sensory branch of Facial nerve). An early sign.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.