ABSTRACT
Sensorineural hearing loss refers to a corresponding decrease in both air and bone conduction thresholds and can be sensory (for example, cochlear) or neural (eighth cranial nerve) in nature. Sensory hearing loss is often associated with damage to the sensory hair cells in the cochlea. This can be caused by noise exposure, ototoxic drugs (for example, aminoglycosides), or normal aging. Because of their location at the basal end of the cochlea, hair cells associated with highfrequency hearing are more vulnerable to impairment. Consequently, sensorineural hearing loss from cochlear pathologies often affects high-frequency hearing (for example, greater than 1000 Hz) more than low-frequency hearing. The elderly individual with a high-frequency sensorineural hearing loss, known as presbycusis, will frequently report difficulty hearing consonant sounds, especially in the presence of background noise. This is because consonant sounds contain high-frequency information, which is typically less intense than low-frequency vowel sounds and more likely to be masked in the presence of background noise. Because the hearing test does not distinguish between sensory and neural contributors to a sensorineural hearing loss, clinicians may use other tests, including otoacoustic emissions (OAE), which assess the integrity of outer hair cell motility. Absence of OAEs is consistent with a cochlear (sensory) hearing loss. Other sources of cochlear pathology resulting in unilateral and/ or bilateral sensorineural hearing loss include childhood illnesses, such as mumps and meningitis, as well as congenital malformations of the cochlea.
