Acoustic Neuroma

Courtney Clark Bilodeau, M.D.

Basic Information

Definition

Acoustic neuroma is a benign proliferation of the Schwann cells that cover the vestibular branch of the eighth cranial nerve (CN VIII). Symptoms are commonly a result of compression of the acoustic branch of CN VIII, the facial nerve (CN VII), and the trigeminal nerve (CN V). The glossopharyngeal nerve (CN IX) and vagus nerve (CN X) are less commonly involved. In extreme cases, compression of the brain stem may lead to obstruction of cerebrospinal fluid (CSF) outflow and elevated intracranial pressure (ICP).

Synonyms

Vestibular schwannoma

ICD-10CM CODES
D33.3	Benign neoplasm of cranial nerves

Epidemiology & Demographics

Overall incidence is approximately 1.2 in 100,000 person-years, with a higher incidence in patients with neurofibromatosis type 2 (NF2). The prevalence is 2 in 10,000 people. The tumor most commonly presents in the fifth and sixth decades.

Physical Findings & Clinical Presentation

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Most frequently unilateral hearing loss and/or tinnitus. Also balance problems, vertigo, facial pain (trigeminal neuralgia) and weakness, difficulty swallowing, fullness or pain of the involved ear. Headache may occur.
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With elevated ICP, patients may also have vomiting, fever, and visual changes.
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Hearing loss is the most common presenting complaint and is usually high frequency.

Etiology

The etiology is incompletely understood, but long-term exposure to acoustic trauma has been implicated. Bilateral acoustic neuromas may be inherited in an autosomal-dominant manner as part of NF2. This disease is associated with a defect on chromosome 22q1. Childhood exposure to low-dose radiation for benign head and neck conditions may increase risk for acoustic neuromas. There is inconclusive evidence to link chronic exposure to radiofrequency radiation from cellular telephone use and the risk for developing brain tumors.

Diagnosis

Differential Diagnosis

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Benign positional vertigo
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Menière’s disease
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Trigeminal neuralgia
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Cerebellar disease
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Normal-pressure hydrocephalus
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Presbycusis
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Glomus tumors
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Vertebrobasilar insufficiency
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Ototoxicity from medications
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Other tumors:
1. 1.
  
  Meningioma, glioma
2. 2.
  
  Facial nerve schwannoma
3. 3.
  
  Cavernous hemangioma
4. 4.
  
  Metastatic tumors

Workup

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A detailed neurologic examination with special attention to the cranial nerves is crucial.
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Common office balance tests (i.e., Romberg, Dix-Hallpike) are typically normal.
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Otoscopic evaluation may help rule out other causes of hearing loss.

Laboratory Tests

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Audiometry is useful, often showing asymmetric, sensorineural, high-frequency hearing loss.
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CSF protein may be elevated.

Imaging Studies

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MRI with gadolinium (Fig. 1) is the preferred test. It can detect tumors as small as 2 mm in diameter.

FIG.1

MRI with enhancement shows bilateral acoustic neuromas.

Coronal view.

From Kanski JJ, Bowling B: Clinical ophthalmology, a systematic approach, ed 7, Philadelphia, 2011, Saunders.
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High-resolution CT scan with and without contrast can detect tumors 1 cm in diameter or larger.
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Treatment decisions should be based on the size of the tumor, rate of growth (older patients tend to have slower-growing tumors), degree of neurologic deficit, desire to preserve hearing, life expectancy, age of the patient, and surgical risk. A combination of treatments can also be used.

Treatment

Nonpharmacologic Therapy

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Surgery is the definitive treatment. Choice of approach (middle cranial fossa, translabyrinthine, or retromastoid suboccipital) may vary depending on the size of the tumor, amount of residual hearing desired, and degree of surgical risk that can be tolerated. Partial resection is sometimes undertaken to minimize the risk of injury to nearby structures. Intraoperative facial nerve monitoring is recommended.
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Radiation therapy (stereotactic radiotherapy, stereotactic radiosurgery, or proton beam radiotherapy) is useful for tumors <3 cm in diameter or for those in whom surgery is not an option. Radiotherapy after partial resection has also been used to minimize complications.
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Age alone is not a contraindication to surgery.

General Rx

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Bevacizumab, an antivascular endothelial growth factor (VEGF) monoclonal antibody, has been shown to improve hearing and reduce the volume of growing acoustic neuromas in some neurofibromatosis type 2 patients.
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Observation with MRI every 6 to 12 mo may be appropriate for frail patients with small tumors, but risk of unrecoverable hearing loss may increase if surgery is delayed. Also, progressive hearing loss may occur despite absence of growth on subsequent imaging.

Disposition

Hearing can be preserved at near-preoperative levels in more than two thirds of patients with small- to medium-sized tumors. Occurrence of secondary radiation-related tumors following radiosurgery is rare. There are no standard posttreatment follow-up recommendations. Therefore, an individualized approach to follow-up imaging and audiometry is recommended.

Referral

Prompt referral to an otolaryngologist or neurosurgeon who is facile with all three surgical approaches is recommended.

Pearls & Considerations

Comments

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Presents most commonly as unilateral, sensorineural hearing loss.
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Treatment outcomes are excellent, with surgical cure rates greater than 95%.
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Of those who are managed with observation only, approximately half have continued enlargement and approximately one fifth eventually have a surgical intervention.

Patient/Family Education

Acoustic Neuroma Association: https://www.anausa.org/

Ferri – Acoustic Neuroma