Acoustic Neuroma (Vestibular Schwannoma): Symptoms, Causes & Treatment

An acoustic neuroma, more precisely termed vestibular schwannoma (VS), is a benign encapsulated tumor arising from the Schwann cells of the inferior or superior vestibular nerve as it traverses the internal auditory canal. It constitutes 8–10% of all intracranial tumors and is the most common cerebellopontine angle (CPA) tumor. VS typically presents in the fifth decade of life; 95% are unilateral and sporadic. Bilateral VS is pathognomonic of neurofibromatosis type 2 (NF2) — a genetic syndrome caused by NF2 gene mutation.

The tumor grows slowly (1–2 mm/year on average, though up to 30–40% remain stable), extending from the internal auditory canal into the CPA cistern. As the tumor grows, it compresses the cochlear nerve (sensorineural hearing loss, tinnitus), vestibular nerve (imbalance), facial nerve (CN VII — facial weakness in large tumors), and ultimately the brainstem and cerebellum — causing hydrocephalus if very large. Despite being histologically benign, VS is locally destructive through compression.

Management is individualized: observation with serial MRI for small/elderly/asymptomatic; microsurgical resection for young patients, large tumors, or progressive growth; stereotactic radiosurgery (Gamma Knife) for tumors <3 cm in patients unsuitable for or declining surgery — provides excellent local tumor control (90–95%) with hearing preservation in 40–60%.

• Unilateral sensorineural hearing loss (95%): usually progressive over months to years; may present as sudden sensorineural hearing loss (10%)
• Unilateral tinnitus: typically high-pitched and constant in the affected ear; may be the only symptom for years
• Imbalance and unsteadiness: vestibular dysfunction; overt vertigo less common as central compensation occurs
• Aural fullness in the affected ear
• Large tumor (>3 cm) symptoms: facial weakness (CN VII compression), headache, dysphagia, dysarthria, hydrocephalus

• Sporadic loss of function of the NF2 tumor suppressor gene in a single Schwann cell — in 95% of cases; no identified environmental cause
• Neurofibromatosis type 2 (NF2 syndrome): germline NF2 mutation (chromosome 22q12) — bilateral VS are diagnostic; autosomal dominant; onset in 20s–30s
• Prior ionizing radiation to the head (low-dose radiation therapy in childhood) — small increased risk
• Cell phone use: extensive epidemiological studies (including INTERPHONE and Million Women Study) have not established a causal link despite proximity

MRI with gadolinium contrast of the internal auditory canal and CPA: the gold standard for diagnosis — sensitivity >99% for detecting VS; shows characteristic enhancing mass in the internal auditory canal or CPA with 'ice cream cone' morphology. Pure-tone audiometry and speech discrimination: characterizes hearing level (guide to treatment and outcome expectation). Auditory brainstem response (ABR): prolonged wave V interpeak latency is suggestive but has lower sensitivity than MRI. CT of temporal bone: shows internal auditory canal widening in advanced cases; useful for surgical planning.

Three management strategies: (1) Observation (watchful waiting): serial MRI every 6–12 months — for small (<1.5 cm) asymptomatic or minimally symptomatic tumors, elderly patients, or favorable tumor biology; 50–60% of small VS remain stable or regress. (2) Microsurgical resection: definitive treatment for large tumors (>3 cm), young patients, rapidly growing tumors; approaches: retrosigmoid, translabyrinthine, or middle fossa (depending on hearing status and tumor location); facial nerve monitoring essential; hearing sacrifice unavoidable in translabyrinthine. (3) Stereotactic radiosurgery (SRS — Gamma Knife, CyberKnife): for tumors 1–3 cm not immediately threatening brainstem — single-fraction radiation achieving local control in 90–95% at 10 years; hearing preservation 40–60%; facial nerve function preserved in >95%; not surgery, no incision, day procedure.

• Complete hearing loss in the affected ear (from tumor progression or treatment — especially translabyrinthine surgery)
• Facial nerve palsy: most feared surgical complication; experienced surgeons achieve grade I–II facial function in >90% for medium tumors
• Brainstem compression and obstructive hydrocephalus in very large tumors (>4 cm)
• Chronic imbalance from vestibular nerve damage — most patients compensate over 1–2 years
• Tumor recurrence after subtotal resection (~5–10% — less common after SRS)

• No known prevention for sporadic VS
• Genetic counseling and NF2 gene testing for families with bilateral VS or NF2 syndrome
• Early audiological screening in NF2 patients — bilateral VS often presents in 20s–30s