Sudden Sensorineural Hearing Loss

Sudden sensorineural hearing loss is hearing loss that results from damage to either the cochlea or the cochlear nerve.

Etiology for Sudden Sensorineural Hearing Loss

Viral Infection

The viral infection manifested by a cold may propagate into the inner ear or cause an inflammatory reaction in the inner ear that is harmful to hearing. Other viruses such as Herpes viruses may also have a role.

Idiopathic

This occurs for unknown reasons and an instigating event is never identified. There are two theories for why this develops.

Membrane Break Theory

Here you can see a panned out view of the cochlea.  In the next picture, you will see a zoomed in cross-section of the cochlea shown.

This shows a cross-section of the cochlea with the vestibular membrane, the membrane that separates endolymph and perilymph, in its proper position.

The inner ear has an intricate structure of membranes that separate two different kinds of fluids, the endolymph and the perilymph. These fluids vary in their electrolyte composition and produce an electrochemical gradient across membranes. This gradient is vital to the electrical activity of the inner ear. The membrane-break theory assumes that for some reason there is a break that occurs in the membranes that causes mixing of the two fluids. This produces electrical chaos and resultant hearing loss. Inflammation occurs with migration of cells that mediate inflammation into the inner ear. The initial cells that migrate there are destructive in nature; this is the basis for steroid treatment.

Mini-stroke Theory

The blood supply to the inner ear comes from the labyrinthine artery which is a tiny branch off the anterior inferior cerebellar artery. This theory assumes that a clot or spasm of this tiny branch causes decreased blood supply to the inner ear. Again, inflammatory cells migrate to the inner ear. They are initially destructive, and this is the basis for steroid treatment. Medications that dilate blood vessels have also been found to have some utility. Niacin is a naturally occurring vitamin that causes vasodilation.

There is no known correlation between development of strokes in general and sudden hearing loss. In another words, patients who develop sudden hearing loss do not have an increased chance for developing other kinds of strokes. Patients who develop other kinds of strokes do not have an increased chance of developing sudden hearing loss, either.