Acoustic Neuroma: Causes, Symptoms and Treatment
An acoustic neuroma is a benign, slow-growing tumor of the hearing nerve. It can cause gradual hearing loss, tinnitus, and balance problems.
Things worth knowing about "Acoustic neuroma"
An acoustic neuroma is a benign, slow-growing tumor of the hearing nerve. It can cause gradual hearing loss, tinnitus, and balance problems.
What Is an Acoustic Neuroma?
An acoustic neuroma (medically termed vestibular schwannoma) is a benign, slow-growing tumor that arises from the Schwann cells surrounding the eighth cranial nerve – the vestibulocochlear nerve. This nerve is responsible for both hearing and balance. Although non-cancerous, the tumor can cause significant symptoms as it expands and may, in advanced cases, compress vital brainstem structures.
Acoustic neuromas account for approximately 6–8% of all brain tumors and are most commonly diagnosed in middle-aged adults. In the vast majority of cases, the tumor occurs on one side only (unilateral). Bilateral acoustic neuromas are a hallmark of the rare genetic condition Neurofibromatosis Type 2 (NF2).
Causes
The exact cause of most acoustic neuromas remains unknown. Recognized risk factors and associations include:
- Neurofibromatosis Type 2 (NF2): A hereditary condition caused by a mutation in the NF2 gene on chromosome 22, almost always resulting in bilateral vestibular schwannomas.
- Prior radiation exposure: Low-dose radiation to the head and neck region, especially during childhood, has been identified as a potential risk factor.
- Spontaneous mutations: The majority of cases arise sporadically with no identifiable family history.
Symptoms
Symptoms of an acoustic neuroma typically develop gradually over months to years. The most common signs include:
- Unilateral hearing loss: Usually the first and most prominent symptom, often beginning with difficulty hearing high-pitched sounds.
- Tinnitus: Persistent ringing or buzzing in one ear on the affected side.
- Balance disturbances and dizziness: Unsteadiness when walking or episodic vertigo.
- Facial numbness or tingling: Larger tumors may press on adjacent nerves such as the facial nerve or trigeminal nerve.
- Headaches and pressure: In advanced cases due to increased intracranial pressure.
Diagnosis
Diagnosis is established through a combination of clinical evaluation and imaging studies:
- Audiometry (hearing test): Initial test to detect unilateral sensorineural hearing loss.
- MRI with contrast enhancement: The gold standard for visualizing the tumor and assessing its size and location.
- CT scan: May complement MRI to evaluate bony structures of the inner ear canal.
- Auditory brainstem response (ABR): Measures nerve conduction along the auditory pathway and helps identify lesions.
Treatment
Treatment strategy depends on tumor size, growth rate, location, and the age and overall health of the patient. The main options include:
Watchful Waiting (Watch and Scan)
For small, slowly growing tumors causing minimal symptoms, a strategy of regular MRI monitoring without immediate intervention may be appropriate. This is particularly suitable for older patients or those with significant comorbidities.
Microsurgical Removal
Surgery remains a well-established treatment for larger tumors or those causing significant symptoms. The goal is complete or near-complete tumor removal while preserving the facial nerve and, where possible, residual hearing.
Stereotactic Radiosurgery
Techniques such as Gamma Knife or CyberKnife deliver precisely focused high-dose radiation to the tumor while minimizing damage to surrounding structures. This is particularly effective for small to medium-sized tumors and is a preferred option for patients at higher surgical risk.
Medical Therapy
In patients with Neurofibromatosis Type 2, the VEGF inhibitor bevacizumab is being investigated in clinical trials as a means of inhibiting tumor growth. However, no pharmacological treatment is currently approved as a standard therapy for sporadic acoustic neuromas.
Prognosis
The overall prognosis for acoustic neuroma is favorable given its benign nature. With timely treatment, tumor growth can generally be controlled. However, some patients may experience permanent hearing loss or facial nerve weakness depending on tumor size and chosen treatment. Regular follow-up examinations are essential to monitor for recurrence or residual tumor growth.
References
- Stangerup SE, Caye-Thomasen P. Epidemiology and natural history of vestibular schwannomas. Otolaryngologic Clinics of North America, 2012; 45(2):257–268.
- Plotkin SR, Merker VL, Halpin C, et al. Bevacizumab for progressive vestibular schwannoma in neurofibromatosis type 2. Otology & Neurotology, 2012; 33(6):1046–1052.
- National Institute on Deafness and Other Communication Disorders (NIDCD). Acoustic Neuroma. U.S. National Institutes of Health, 2023. Available at: https://www.nidcd.nih.gov/health/acoustic-neuroma
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