Acoustic neuroma, also known as a vestibular schwannoma, is a benign tumor that grows on the vestibulocochlear nerve (cranial nerve VIII). Such tumors tend to grow very slowly, and, depending on their size, might cause decreased hearing with tinnitus (usually a high-pitched ringing in the ear), pressure in the ear, dizziness and/or imbalance. Larger tumors may cause numbness or weakness of the face on the affected side, altered taste, or trouble swallowing.
Acoustic neuromas occur spontaneously in most cases, about 5% are related to a genetic condition, neurofibromatosis, and in cases associated with neurofibromatosis type 2, may be bilateral (involve both vestibular nerves).
Diagnosis is suspected based on audiogram revealing unilateral (one-side) hearing loss, specifically sensorineural hearing loss, and vestibular function testing abnormalities. Vestibular function testing abnormalities may include caloric weakness on the same side as the hearing loss, spontaneous nystagmus typically in the direction opposite the affected side, reduced VEMP respose on the affected side, and rotary chair abnormalities including reduced VOR gain, VOR asymmetry and phase lead. MRI of the brain or IACs (Internal Auditory Canals) with contrast is the best way to confirm the presence of an acoustic neuroma.
Treatment depends on the size of the tumor and the age of the patient. Periodic monitoring every 6-12 months may be the only necessary action, as 45% of tumors have little to no growth over a 3-5 year monitoring period. Radiation therapy, often in the form of gamma-knife radiosurgery, may be performed, or, in certain cases, surgical removal of the tumor is necessary.
Below is the result of caloric testing of a patient with an acoustic neuroma/vestibular schwannoma. Note that the nystagmus elicited by cool and warm air blown into the ear canal is much less on the left side, indicating reduced function of the left vestibular nerve.
To the right are two sequences of an MRI scan of the brain, the first without contrast, the second, with contrast. The red arrow points to the acoustic neuroma. As you can see, without contrast, an acoustic neuroma might evade detection.
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Below is the result of rotational chair testing of a patient with an acoustic neuroma/vestibular schwannoma. Note reduced VOR gain with VOR asymmetry and phase lead, indicative of a unilateral vestibular nerve weakness.