A vestibular schwannoma (acoustic neuroma) is a Schwann cell–derived tumor of the eighth cranial nerve. Symptoms include unilateral hearing loss. Diagnosis is based on audiometry and confirmed by MRI. When required, treatment is surgical removal, stereotactic radiation therapy, or both.
Vestibular schwannomas almost always arise from the vestibular division of the eighth cranial nerve and account for approximately 8% of all intracranial tumors (1). Based on incidence rates ranging between 3 and 21 per 100,000 individuals across all age groups, the lifetime prevalence of developing sporadic vestibular schwannoma appears to exceed 1 per 500 persons worldwide, which is higher compared with previous reports (2). Vestibular schwannomas originate from the perineural components of Schwann cells and share similar pathological characteristics with peripheral schwannomas. As the tumor expands, it projects from the internal auditory canal into the cerebellopontine angle, compressing the seventh and eighth cranial nerves. As the tumor continues to enlarge, the cerebellum, brain stem, and nearby cranial nerves (fifth and ninth through twelfth) can also become compressed.
Bilateral vestibular schwannomas are a common feature of neurofibromatosis type 2.
References
1. Carlson ML, Link MJ. Vestibular Schwannomas. N Engl J Med. 2021;384(14):1335-1348. doi:10.1056/NEJMra2020394
2. Marinelli JP, Beeler CJ, Carlson ML, Caye-Thomasen P, Spear SA, Erbele ID. Global Incidence of Sporadic Vestibular Schwannoma: A Systematic Review. Otolaryngol Head Neck Surg. 2022;167(2):209-214. doi:10.1177/01945998211042006
Symptoms and Signs of Vestibular Schwannoma
Slowly progressive unilateral sensorineural hearing loss is the hallmark symptom of a vestibular schwannoma. However, the onset of hearing loss may be abrupt, and the degree of impairment may fluctuate. Other early symptoms include unilateral tinnitus, dizziness, and dysequilibrium. Progressive mass effects can occur (eg, headache, a sensation of pressure or fullness in the ear, otalgia, trigeminal neuralgia, and numbness or weakness in the face due to involvement of the facial nerve).
Diagnosis of Vestibular Schwannoma
Clinical history
Audiogram
Gadolinium-enhanced MRI
Sometimes tympanometry, auditory brain stem response, and caloric testing
Sometimes genetic testing
A history of progressive unilateral hearing loss should raise clinical suspicion for a vestibular schwannoma. Most commonly, an audiogram is the first test done to diagnose vestibular schwannoma. It usually detects an asymmetric sensorineural hearing loss and a greater impairment of speech discrimination than would be expected for the degree of hearing loss. Such findings indicate the need for imaging tests, preferably gadolinium-enhanced MRI. However, some tumors are found incidentally when brain imaging is done for another reason.
Other findings include the presence of acoustic reflex decay on tympanometry. Auditory brain stem response testing may show the absence of waveforms and/or increased latency of the fifth waveform.
Although not usually required in the routine evaluation of a patient with asymmetric sensorineural hearing loss, caloric testing can show marked vestibular hypoactivity (canal paresis) on the affected side.
Patients under 30 years of age with unilateral schwannomas or those with bilateral schwannomas should undergo genetic testing for NF2 mutations to exclude neurofibromatosis (1).
Diagnosis reference
1. Pathmanaban ON, Sadler KV, Kamaly-Asl ID, et al. Association of Genetic Predisposition With Solitary Schwannoma or Meningioma in Children and Young Adults. JAMA Neurol. 2017;74(9):1123-1129. doi:10.1001/jamaneurol.2017.1406
Treatment of Vestibular Schwannoma
Observation
Sometimes surgical removal or stereotactic radiation therapy in selected cases
Sometimes rehabilitation
Small, asymptomatic, and nongrowing vestibular schwannomas do not require treatment; such tumors may be observed with serial MRI scans and treated if they begin growing or cause symptoms; this has been called the wait-and-scan approach (1). Whether to use stereotactic radiation therapy (eg, gamma knife or cyberknife radiation therapy) or conventional microsurgery depends on many factors, including the amount of residual hearing, tumor size, patient age and health, and patient preference. Stereotactic radiation therapy can be used in small or medium-sized tumors without significant brainstem compression. Radiation tends to be used for older patients, or those who cannot have surgery for medical reasons. Microsurgery can involve a hearing-preservation approach (middle cranial fossa or retrosigmoid approach) or a translabyrinthine approach if there is no useful residual hearing. Occasionally, certain patients need rehabilitative treatment, particularly those experiencing prolonged facial nerve paralysis, bilateral hearing loss, or persistent dizziness and imbalance.
Reference
1. Carlson ML, Link MJ. Vestibular Schwannomas. N Engl J Med. 2021;384(14):1335-1348. doi:10.1056/NEJMra2020394
Key Points
Vestibular schwannoma is usually unilateral but can be bilateral in neurofibromatosis type 2.
Unilateral hearing loss, sometimes with tinnitus and dizziness, is typical.
Larger and/or symptomatic tumors are treated with stereotactic radiosurgery or conventional microsurgery.
Small, asymptomatic, and nongrowing tumors can be observed with serial MRI scans.
