Vestibular schwannomas almost always arise from the vestibular division of the 8th cranial nerve and account for about 7% of all intracranial tumors. As the tumor expands, it projects from the internal auditory canal into the cerebellopontine angle, compressing the 7th and 8th cranial nerves. As the tumor continues to enlarge, the cerebellum, brain stem, and nearby cranial nerves (5th and 9th to 12th) can also become compressed.
Bilateral vestibular schwannomas are a common feature of neurofibromatosis Neurofibromatosis Neurofibromatosis refers to several related disorders that have overlapping clinical manifestations but that are now understood to have distinct genetic causes. It causes various types of benign... read more type 2.
Symptoms and Signs of Acoustic Neuroma
Slowly progressive unilateral sensorineural hearing loss Pathophysiology Worldwide, about half a billion people (almost 8% of the world's population) have hearing loss (1). More than 10% of people in the US have some degree of hearing loss that compromises their... read more is the hallmark symptom of 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, headache, 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 Acoustic Neuroma
If asymmetric hearing loss, gadolinium-enhanced MRI
Most commonly, an audiogram Testing Worldwide, about half a billion people (almost 8% of the world's population) have hearing loss (1). More than 10% of people in the US have some degree of hearing loss that compromises their... read more is the first test done as part of the evaluation to diagnose vestibular schwannoma. It usually reveals 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 presence of acoustic reflex decay on tympanometry. Auditory brain stem response testing may show the absence of waveforms and/or increased latency of the 5th waveform. Although not usually required in the routine evaluation of a patient with asymmetric sensorineural hearing loss, caloric testing shows marked vestibular hypoactivity (canal paresis) on the affected side.
Treatment of Acoustic Neuroma
Sometimes surgical removal or stereotactic radiation therapy in selected cases
Small, asymptomatic (ie, discovered incidentally), 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. 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, and patient age and health. Stereotactic radiation therapy tends to be used for older patients, those with smaller tumors, or those who cannot undergo 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.
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.