ear, nose, and throat disorders
Hearing Loss
Pathophysiology of Hearing Loss
Hearing loss can be classified as conductive, sensorineural, or both (mixed loss). Conductive hearing lossoccurs secondary to lesions in the external auditory canal, tympanic membrane (TM), or middle ear. These lesions prevent sound from being effectively conducted to the inner ear. is caused by lesions of either the inner ear (sensory) or the auditory (8th) nerve (neural). This distinction is important because sensory hearing loss is sometimes reversible and is seldom life threatening. A neural hearing loss is rarely recoverable and may be due to a potentially life-threatening brain tumor—commonly a cerebellopontine angle tumor. An additional type of sensorineural loss is termed auditory neuropathy spectrum disorder, when sound can be detected but the signal is not sent correctly to the brain, and is thought to be due to an abnormality of the inner hair cells or the neurons that innervate them within the cochlea ( Pathophysiology reference ). may be caused by severe head injury with or without fracture of the skull or temporal bone, by chronic infection, or by one of many genetic disorders. It may also occur when a transient conductive hearing loss, commonly due to Otitis Media (Acute) , is superimposed on a sensorineural hearing loss. Test Sensory Hearing Loss Neural Hearing Loss Speech discrimination Moderate decrement Severe decrement Discrimination with increasing sound intensity Usually improves up to a point, depending on the severity and distribution of loss of sensory elements Deteriorates Recruitment in which the perception of sound is exaggerated, especially at high sound levels Present Absent Acoustic reflex decay in which the acoustic reflex response is reduced over time during a measurement Absent or mild Present Waveforms in auditory brain stem responses Well formed with normal latencies for mild to moderate hearing losses; reduced for more severe losses Absent or with abnormally long latencies Otoacoustic emissions Absent Present 1.Pham NS: The management of pediatric hearing loss caused by auditory neuropathy spectrum disorder.Curr Opin Otolaryngol Head Neck Surg25(5):396-399, 2017. doi: 10.1097/MOO.0000000000000390 