What is a vestibular schwannoma and how should it be assessed and treated in a 54‑year‑old woman with persistent tinnitus?

What is a Vestibular Schwannoma?

A vestibular schwannoma is a benign, slow-growing tumor arising from Schwann cells of the eighth cranial nerve (vestibulocochlear nerve), representing the third most common intracranial nonmalignant tumor and the most common cerebellopontine angle tumor in adults. 1

Tumor Origin and Location

• Vestibular schwannomas arise from Schwann cells anywhere along the eighth cranial nerve, with approximately 80% originating from the vestibular portion and 20% from the cochlear portion 1, 2
• The tumor typically presents as a solid nodular mass with an intracanalicular component in the internal acoustic canal (IAC), often causing widening of the canal 1, 3
• Larger lesions protrude into the cerebellar pontine cistern, while smaller tumors may be confined to the IAC or labyrinth 1, 3

Clinical Presentation in Your 54-Year-Old Patient

Your patient's persistent tinnitus is a classic presenting symptom, occurring in 83% of vestibular schwannoma patients. 1

The typical symptom profile includes:

• Unilateral sensorineural hearing loss (94% of patients) 1
• Tinnitus (83% of patients) 1
• Vestibular symptoms including vertigo and unsteadiness (17-75% of patients, though likely underreported) 1
• Large tumors may cause trigeminal and facial neuropathies, brainstem compression, and hydrocephalus 1

Critical Diagnostic Pitfall

No clinical features can reliably distinguish sudden sensorineural hearing loss caused by vestibular schwannoma from idiopathic varieties, and hearing recovery does not predict whether hearing loss results from a tumor. 2 This means your patient requires imaging regardless of symptom characteristics.

Diagnostic Assessment

Imaging Protocol

MRI with gadolinium-enhanced T1-weighted sequences is the gold standard for diagnosis, with sensitivity and specificity approaching 100%. 1, 4

The complete MRI protocol should include 1:

• Standard T1- and T2-weighted sequences
• Diffusion-weighted imaging (DWI) to differentiate VS from arachnoid or epidermoid cysts
• Fluid-attenuated inversion recovery (FLAIR) sequences
• Axial submillimetric heavily T2-weighted sequences (FIESTA, CISS, or DRIVE) to evaluate the vestibulocochlear nerve
• Axial T1-weighted sequences before and after gadolinium administration

Characteristic imaging findings: 1, 3

• Isointense on T1-weighted imaging with strong gadolinium enhancement
• Heterogeneously hyperintense on T2-weighted imaging
• Larger lesions may show scattered cystic degenerative changes and hemorrhagic areas
• Calcifications are typically absent

Audiologic Testing

Complete audiometric evaluation is mandatory, as approximately 50% of patients lose functional hearing within 3-4 years of diagnosis. 2

Key audiologic assessments include 2:

• Pure tone audiometry and speech discrimination testing
• Full speech discrimination score at initial diagnosis is a good predictor for preservation of functional hearing
• Progressive hearing loss >10 dB in 2 or more frequencies or word recognition score drop >10% warrants further evaluation
• Auditory Brainstem Response (ABR) testing has limitations, missing 8-42% of intracanalicular tumors and is not possible when hearing loss exceeds 80 dB in the 2000-4000 Hz range

When to Consider Neurofibromatosis Type 2 (NF2)

NF2 should be considered when a patient presents with unilateral vestibular schwannoma at age <30 years. 1

Your 54-year-old patient is outside this age range, but NF2 should still be considered if she has 1:

• Two or more NF2-related tumors (meningioma, glioma, neurofibroma, schwannoma, posterior subcapsular cataracts)
• Family history of NF2
• Bilateral vestibular schwannomas (hallmark of NF2, occurring in 4-6% of VS cases) 1

Treatment Approach Based on Tumor Size

Small Tumors (Koos Grade I-II, <1.5 cm)

For small, asymptomatic tumors, observation is appropriate, with stereotactic radiosurgery (SRS) as an alternative when preserving facial nerve and hearing function is the primary goal. 1

• Observation protocol: MRI at 6,12,24, and 36 months, then annually if stable 1
• Without intervention, 29-54% of tumors will grow and 16-26% of patients require additional treatment 5
• With observation, 54-63% preserve functional hearing 5
• SRS achieves tumor control with only 2-4% requiring additional treatment and hearing preservation in 44-66% of cases 5

Medium Tumors (Koos Grade III-IV, <3 cm)

Both surgery and radiosurgery can be recommended at similar levels, though SRS has a lower risk profile while surgery offers complete tumor removal. 1

• Most patients present with vestibular or cochlear symptoms 1
• Subtotal resection to preserve function followed by SRS of growing tumor remnant is a valid option 1
• The decision should be discussed meticulously with the patient, explaining all options 1

Large Tumors with Brainstem Compression (Koos Grade IV, >3 cm)

Surgery is mandatory for large tumors causing brainstem compression, as it is the only option for decompression of the brainstem and stretched cranial nerves. 1

• Patients typically suffer from eighth cranial nerve symptoms for extended periods 1
• Many present with additional symptoms including facial nerve paresis and gait ataxia 1
• Tumor mass reduction by incomplete resection followed by SRS or observation is valid when complete resection risks significant cranial nerve dysfunction 1
• Surgery carries considerable risk for loss or deterioration of cranial nerve function 1
• With microsurgery, fewer than 2% require additional treatment, but risks of hearing loss, facial neuropathy, and other morbidities are relatively high 5

Follow-Up Monitoring

Annual follow-up with MRI and audiometry is recommended for conservatively treated, radiated, and incompletely resected vestibular schwannoma for 5 years. 2

• If tumor size remains stable for 5 years, follow-up intervals can be doubled thereafter 2
• Serial audiometry is important for monitoring, though less sensitive than MRI 2
• Risk for tumor regrowth rises with residual tumor volume 1

Common Pitfalls to Avoid

Do not rely on clinical features alone to rule out vestibular schwannoma in patients with hearing loss and tinnitus. 2 Associated events like barotrauma or recent viral infection are present in approximately one-third of patients with VS, potentially misleading clinicians. 2

Do not assume ABR testing is sufficient for diagnosis. 2 ABR misses 8-42% of intracanalicular tumors and has reduced sensitivity with milder hearing losses. MRI with gadolinium remains the gold standard. 1, 2

Incomplete resection carries significant risk of tumor regrowth. 6 When surgery is chosen, complete resection with periodic follow-ups is essential, or planned subtotal resection with subsequent SRS should be considered. 1