Anatomic correlates of noise induced hearing loss

Industrialization has taken its toll in creating a noise environment that has resulted in a man-made disease known as noise induced hearing loss or acoustic trauma. The characteristics of the noise exposure can vary widely, such as impulsive, intermittent, or continuous noise composed of ow (including infrasound), high, or mixed frequencies. Noise in the real world is often mixed not only in frequency but also in continuity. The mode and extent of noise induced inner ear damage are also dependent on the characteristics, level, and duration of exposure. Regardless of the type of noise, the basic mechanism involved in acoustic trauma is physical, physiochemical, or metabolic (stress(es) exerted on the auditory sensory organ. The end result is sensory cell injury or damage and even total destruction of the organ of Corti, which accounts for the resultant hearing loss. The hearing loss can be either temporary (temporary threshold shift) or permanent (permanent threshold shift), depending on the extent of injury. The purpose of this article is to review various kinds of morphologic damage in the cochlea due to noise exposure.