• Rupture of a delicate membrane in your inner ear, in a "weak" place from birth that bursts and allows the potassium-rich endolymph to spill into the perilymph space and come into contact with the "hair cells" that are responsible for hearing and damage them. This causes the sudden loss of hearing, but may also cause a feeling of fullness, noise in the ear, and loss of balance or dizziness. If these ruptures heal, some or all of the hearing may return. Most do not heal, and then little or no hearing returns. The loss of balance, dizziness, fullness, and noise eventually subsides.
• Viral upper respiratory infections, such as a cold, flu, sinusitis, etc., which spreads to the inner ear. High-dose steroids plus anti-viral medication as well as transtympanic perfusion with dexamethasone may help.
• Loss of circulation to the inner ear from blockage of an artery (a “stroke” of the inner ear). Most patients with sudden hearing loss due to loss of circulation have evidence of poor circulation in other parts of the body, especially the brain, such as a prior stroke.

There are about 25,000 cases of sudden hearing loss in the United States each year, most of which do not recover with or without treatment. The chance of having a sudden hearing loss is approximately 1 in 10,000 each year. After you have had one such sudden hearing loss in one ear, the chance of another sudden hearing loss in the other ear is much greater, perhaps as much as 1 in 100. Special tests must be done, including MRI of the brain with gadolinium, to rule out a tumor on the balance nerve (acoustic neuroma) as a cause of the sudden hearing loss.

Such a "spontaneous" sudden hearing loss, without obvious cause, must be distinguished from a "traumatic" or other type of hearing loss due to a known cause, such as a loud noise, sudden pressure change, head injury, medication, Meniere's Disease, autoimmune inner ear disease, etc., for which the treatment is very different.

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	Sudden Hearing Loss: A Detailed Look