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An acoustic
neuroma is a Schwann cell–derived tumor of the 8th cranial nerve.
Symptoms include unilateral hearing loss. Diagnosis is based on
audiology and confirmed by MRI. Treatment is surgical removal, stereotactic radiotherapy,
or both.
Acoustic neuromas 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 meatus into the cerebellopontine angle and compresses the cerebellum and brain stem. The 5th cranial nerve and later the 7th cranial nerve are affected.
Bilateral acoustic neuromas are common in neurofibromatosis type 2.
Symptoms and Signs
Slowly progressive unilateral sensorineural hearing loss is the hallmark symptom. 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 of the facial nerve.
Diagnosis
An audiogram is the first test done (see Hearing Loss: Audiologic tests). 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. Acoustic reflex decay, the absence of waveforms, and increased latency of the 5th waveform in auditory brain stem response testing are further evidence of a neural lesion. Although not usually required in the routine evaluation of a patient with asymmetric sensorineural hearing loss, caloric testing demonstrates marked vestibular hypoactivity (canal paresis). Such findings indicate the need for imaging tests, preferably gadolinium-enhanced MRI.
Treatment
Small tumors may be removed with microsurgery that preserves the facial nerve. A middle cranial fossa or retrosigmoid approach may preserve remaining hearing; a translabyrinthine route may be used if no useful hearing remains. Large tumors are removed with the translabyrinthine approach regardless of the remaining hearing. Stereotactic radiation as the sole treatment modality is used predominantly in the management of small tumors in older patients; its long-term efficacy and adverse effects are under study.
Last full review/revision July 2007 by John S. Oghalai, MD
Content last modified July 2007
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