Chapter 030. Disorders of Smell,
Taste, and Hearing
(Part 9)

Disorders of the Sense of Hearing
Hearing loss can result from disorders of the auricle, external auditory
canal, middle ear, inner ear, or central auditory pathways (Fig. 30-4). In general,
lesions in the auricle, external auditory canal, or middle ear cause conductive
hearing losses, whereas lesions in the inner ear or eighth nerve cause
sensorineural hearing losses.

Figure 30-4 An algorithm for the approach to hearing loss. HL, hearing loss; SNHL,
sensorineural hearing loss; TM, tympanic membrane; SOM, serous otitis media;
AOM, acute otitis media; *, CT scan of temporal bone; t , MRI scan.

Conductive Hearing Loss
This results from obstruction of the external auditory canal by cerumen,
debris, and foreign bodies; swelling of the lining of the canal; atresia or neoplasms
of the canal; perforations of the tympanic membrane; disruption of the ossicular
chain, as occurs with necrosis of the long process of the incus in trauma or
infection; otosclerosis; or fluid, scarring, or neoplasms in the middle ear. Rarely,
inner-ear malformations may present as conductive hearing loss beginning in
adulthood.
Cholesteatoma, stratified squamous epithelium in the middle ear or
mastoid, occurs frequently in adults. This is a benign, slowly growing lesion that
destroys bone and normal ear tissue. Theories of pathogenesis include traumatic
implantation and invasion, immigration and invasion through a perforation, and
metaplasia following chronic infection and irritation. On examination, there is

of the temporal bone, meningitis, cochlear otosclerosis (see above), Ménière's
disease, and aging. Congenital malformations of the inner ear may be the cause of
hearing loss in some adults. Genetic predisposition alone or in concert with
environmental exposures may also be responsible.