Hearing Loss and Deafness 169Categories of Hearing Loss
There are three general categories of hearing loss: conductive, sensorineural, and mixed.
Conductive hearing loss results from impaired functioning of the external or middle ear.
Sensorineural hearing loss is due to impaired functioning of the cochlea or cranial nerve VIII.
Mixed hearing loss involves both conductive and sensorineural components. In addition, auditory
pro cessing disorders concern perception and association of auditory stimuli due to neurological
damage or abnormalities in the brainstem or higher cortical levels. Each is discussed in detail next.
Typical Causes of Hearing Loss and Deafness
Otitis media is the most common cause of conductive hearing loss in children. Otitis refers to
inf lammation, and media indicates its location at the level of the middle ear. (Otitis externa, also
known as swimmer’s ear, is inf lammation of the external ear.) Often in otitis media, the eustachian
tube does not equalize pressure between the middle ear and the external atmosphere. In middle
ear infections, the tympanic membrane does not function properly and may rupture. A myrin-
gotomy tube can be placed in the tympanic membrane to equalize pressure.
Recently, there has been controversy about the placement of myringotomy tubes; some pedia-
tricians believe they are unnecessary, easily dislodged, and have little medical benefit. By contrast,
some otologists believe they reduce symptoms and prevent hearing loss. Otitis media also occurs
in adults, but otosclerosis— calcification and fixation of the ossicles—is another frequent cause of
conductive hearing loss. Other causes include prolonged impacted cerumen, narrowing (stenosis)
of the external ear canal, and trauma.
Sensorineural hearing loss is frequently caused by excessive and prolonged exposure to noise.
Noise- induced hearing loss may also occur as a result of sudden loud noises such as gunshots,
bombs, and industrial explosions. The terms barotrauma and acoustic trauma are sometimes used
to refer to hearing loss due to sudden explosive noise. “As a rule, the amounts of hearing loss are
similar in both ears when individuals acquire noise- induced hearing losses in the workplace. Rif le
shooters generally show more hearing loss in the ear opposite the shoulder to which the rif le stock
is held, that is, right- handed shooters will have more hearing loss in the left ear” (Martin & Clark,
2003, p. 298). Other causes of sensorineural hearing loss include toxins, meningitis, presbycusis
(a progressive hearing loss in both ears occurring with aging), and Meniere’s disease (a sudden
disorder of the inner ear characterized by tinnitus and progressive low- frequency hearing loss).
Meniere’s disease is also associated with dizziness and nausea and can be considered a syndrome.
Mixed hearing loss can result from combinations of the aforementioned conductive and senso-
rineural etiological factors. Traditionally, the hallmark of mixed hearing loss is depressed air and
bone conduction thresholds and the air– bone gap discussed in the section Audiograms and Types
of Hearing Loss.
Tumors, trauma, strokes, aging, and disease pro cesses can cause auditory pro cessing disorders,
and because definitions of the nature and symptoms of dif fer ent disorders vary, the etiology of
many cases is idiopathic. The term auditory pro cessing disorders, formerly referred to as central
auditory pro cessing disorders, is a vague diagnostic label and can include auditory and acoustic
agnosia. When addressed by an audiologist, auditory pro cessing disorders are part of aural habili-
tation or rehabilitation; when considered by a speech- language pathologist, they are a component
of agnosia or aphasia therapy.
Tinnitus
Tinnitus is usually described as the sensation of ringing in the ear. A more precise definition
is the sensation of noise in the head without external stimulation through the ear. The noise can
also be described as buzzing, whistling, roaring, and so forth. The condition is associated with