Medihub - Medical Information - ENT

Sound is normally transmitted from the environment to the external ear where it hits the eardrum which causes it to vibrate. This in turn causes the 3 ossicles (ear bones) in the middle ear to vibrate. These vibrations are carried through to the inner ear which in turn results in a displacement of the inner ear fluids. This displacement results in the excitement of the organ of hearing and electrical impulses are generated which are carried to the hearing centres in the brain via the hearing (cochlear) nerve. Deafness can result when there is a breakdown in this process.

Deafness can be divided into two main types; conductive and sensorineural. Conductive deafness results when there is a failure of sound conduction from the environment to the inner ear. This generally means a problem in the external and middle ear. Sensorineural deafness indicates disease affecting the organ of hearing (sensory) or the hearing nerve (neural). The most common cause of conductive hearing loss is a build up of wax.

Conductive deafness can also result from external ear infections, bony tumors of the external ear, perforation of the ear drum (figure 2), fluid or pus collection in the middle ear or disease that affects the mobility of the ossicular chain (eg. otosclerosis)

Sensorineural deafness is most commonly seen in presbycusis. Certain drugs, noise or acoustic trauma can permanently damage the organ of hearing. Sensorineural deafness can be part of a myriad of symptoms such as dizziness and tinnitus. When affecting only one ear, an MRI must be performed to exclude tumors arising from the hearing and balance nerve (Fig 3).