Hearing loss can be classified as conductive or sensorineural, although both may occur after certain types of head injuries. Conductive hearing loss can be due to mechanical disruption of the ossicles, impedance with noise conduction to the eardrum, or a blockage in the middle ear or external auditory canal (e.g. blood clot). Sudden neurosensory hearing loss (NSHL) is defined as loss of hearing due to pathology within or medial to the cochlea (disorders involving the acoustic nerve or hair cell function).

If a patient presents with a chief complaint of loss of hearing, first verify the presence of a real hearing loss. Use the 512 Hz tuning fork to perform a Weber and Rinne test. Beware of inconsistent responses and have a high index of suspicion for malingerers. If the 512 Hz tuning fork test is consistent with a conductive hearing loss, check for effusions, retraction, chronic ear disease, and perforation. Also perform valsalva testing. The cause of a conductive hearing loss is usually evident by history or exam and it is rarely of sudden onset unless it occurs with barometric pressure changes.

On the other hand, if the tuning fork test is consistent with sensorineural hearing loss, then confirmatory audiometric testing is mandatory. Any sudden onset of sensorineural loss should be referred within 24 hours for evaluation by an otolaryngologist because rapid intervention (medical or surgical) is associated with higher rates of recovery. Sudden sensorineural hearing loss secondary to perilymphatic fistulas is surgically treatable.

All other forms of inner ear injury causing sudden sensory loss, with the exception of decompression illness, are treated with oral steroids, bed rest, and fluids. There are many protocols using inhaled gases and vasodilators, but the clinical efficacy is statistically no greater than with steroid therapy alone. Prompt treatment is more important than which treatment, as most studies show that the prognosis for saving hearing deteriorates beyond the 7th day following onset of symptoms.

Remember that 10 percent of patients with acoustic neuromas present with sudden sensorineural hearing loss. Imaging with MRI or CT scan should be performed to rule out the likelihood of a mass lesion.

Special consideration must be given to patients with sudden sensorineural hearing loss following barometric pressure changes like diving or aerospace accidents. The probability of perilymph rupture is greater in these patients and rapid diagnosis and institution of bedrest with fluids will improve chances of spontaneous closure. If bedrest does not relieve symptoms surgical intervention is warranted. Decompression illness can also cause cochlear gas emboli with hearing loss. Perform a careful neurologic exam and always consult with a diving medical officer (DMO) or otolaryngologist.

Sudden sensorineural hearing loss is often misdiagnosed due to the failure of evaluating the patient with tuning forks. Perform a methodical exam of the ears and related structures. If hearing can be saved, intervention must be initiated early following symptom onset. Consultation with an otolaryngologist is very important as well as MRI and CT imaging to rule out mass lesions.

Reference

1. DeWeese and Saunders, Textbook of Otolaryngology