Acoustic neuroma: Year of the Zebra 2024

Acoustic neuroma, also known as vestibular schwannoma, is a benign tumor arising from Schwann cells—the cells responsible for producing the myelin sheath that insulates nerve fibers. Schwannomas can develop along any nerve in the body, but they have a predisposition for the 8th cranial nerve, also called the vestibulocochlear nerve, which sends sensory information about hearing and balance from the inner ear to the brain.

The cause of acoustic neuroma isn’t clear; however, a small number are related to a condition called neurofibromatosis type 2, which causes a mutation that allows Schwann cells to start dividing uncontrollably.

The most common symptoms of acoustic neuromas are tinnitus, or a ringing sound in the ears, and gradual hearing loss on one side. For individuals with neurofibromatosis type 2, acoustic neuromas typically occur bilaterally, so individuals tend to have hearing problems in both ears.

Peripheral vertigo, often described as a sense of imbalance or unsteadiness, can also occur; and it typically has a mild, gradual onset. This is because acoustic neuromas grow slowly, so the central nervous system has time to compensate for the loss of balance function, making the symptoms very subtle. As a result, individuals are more likely to notice symptoms like hearing loss and tinnitus earlier than vertigo.

Acoustic neuromas don’t typically spread to other tissues, but if they grow large enough, they can compress nearby structures, particularly the facial nerve, causing facial weakness and paralysis.

Diagnosis of acoustic neuroma is suspected in individuals with tinnitus, one-sided sensorineural hearing loss, and peripheral vertigo. Follow-up evaluation may include assessment by an ENT specialist, who may order hearing tests and other specific exams to assess the integrity of the vestibulocochlear nerve.