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Previously on ENT Weekly, we discussed various types of hearing loss (noise induced versus conductive), as well as ways to diagnose hearing loss. These topics, however, only scratch the surface as we explore asymmetric hearing loss and the possibility of acoustic neuromas.

Asymmetric hearing loss occurs when hearing is worse in one ear than the other.

Image Source: Bloomberg

At its most basic definition, asymmetric hearing loss occurs when hearing is worse in one ear than the opposite ear due to nerve damage. Diagnosed on a formal audiogram, this contrasts with symmetrical hearing loss, in which hearing decreases equally on both sides over time. Otolaryngologists (ear-nose-throat doctors) and audiologists become concerned when one side worsens faster as the cause dictates the appropriate follow-up plan. The following are some possible etiologies:

  1. Noise induced hearing loss: When taking the patient’s history, unequal exposure to loud noises may lead to this type of hearing loss. For example, for a right-handed shooter, hunting with a rifle may cause the left ear to repetitively get noise-induced damage from the gunshot.
  2. Acoustic neuroma: A tumor can be pressing against the hearing nerve causing it to fail faster than the other ear’s nerve which is not compressed.
  3. Bad luck: Sometimes the hearing nerve may be damaged from a viral attack such as a cold.

If there is a 20 decibel difference at two adjoining frequencies or a 30 decibel at one frequency, most doctors will order a MRI of the IACs (magnetic resonance imaging of the internal auditory canals) to rule out the presence of an acoustic neuroma. The image formed would clearly define an acoustic neuroma if present, identifying tumors measuring only a few millimeters in diameter. As a note, an acoustic neuroma is also known as a vestibular schwannoma as the tumor arises from the vestibulocochlear nerve and is a cancer of the Schwann cells in the peripheral nervous system.

There are three main treatment options available to a patient, which include observation, microsurgical removal, and radiation therapy. Determining which treatment is best involves careful consideration of factors such as the size of the tumor, its location, the patient’s age, physical health, and current symptoms. About 25% of all acoustic neuromas are treated with medical management that consists of periodic monitoring of the patient’s neurological status, serial imaging studies, and usage of hearing aids when appropriate.

Stay tuned for next week when we delve further into the types of hearing loss as we look into congenital hearing loss and its management options.

Feature Image Source: Justin Chin

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