Hearing Loss Caused by Auditory Nerve Damage

The auditory nerve is the 8^th cranial nerve. It connects the inner ear to the brain. The auditory nerve divides into two branches: the cochlear nerve and the vestibular nerve. The former receives auditory information from the inner ear. The latter receives information about balance.

When the auditory nerve is damaged, the primary symptoms are sensorineural deafness and/or vertigo. Additionally, people with damage to the cochlear part of the nerve (known as retrocochlear damage) tend to score lower on speech intelligibility (clarity) tests than people with the same degree of hearing loss originating in the cochlea itself.

Auditory nerve damage can be caused by several factors. For instance, nerve injury may occur after trauma, an infection (such as meningitis) or even the use of ototoxic medications like high-dose antibiotics or certain cancer drugs.

Additionally, an acoustic neuroma, also known as a vestibular schwannoma, may form on the auditory nerve. This is a benign tumour on the vestibular or cochlear part of the nerve that appears spontaneously, without an associated family history. It affects one or two in 100,000 people. The most common symptoms are unilateral deafness on the side of the tumour, unilateral tinnitus and vertigo.

Another, less common cause is auditory neuropathy, which is characterized by damage to the auditory nerve or the junction between the auditory nerve and internal cilia despite the external cilia working properly. This condition is characterized by difficulty understanding speech in silence, and even more difficulty doing so in noisy environments despite sound amplification.

In short, the auditory nerve plays a key role in transmitting auditory information to the brain and in maintaining balance. Damage can therefore cause significant hearing and vestibular (balance) problems.