of Hearing Loss
HEARING LOSS: Sound waves are conducted into and
through the hearing system in a variety of ways. The term conductive
hearing loss refers to a disruption or mechanical blockage of
the movement of sound waves (vibrations) at some point in the
hearing system before they reach the inner ear. A conductive
loss occurs in the outer and/or middle ear.
Sound is first conducted through the air into the ear canal and then transmitted
further via vibration of the middle ear bones. This conduction of sound can be
disrupted by something as simple as a build-up of wax in the ear canal. It can
also be disrupted by a hole in the ear drum, or by the presence of fluid in the
Otitis Media is a common cause of conductive hearing loss associated with children
who have frequent ear infections. Normally, the air pressure in the middle ear
should be equal to the air pressure on the outer side of the eardrum. The Eustation
Tube, which connects the middle ear and the back of the throat, helps to maintain
this balance of pressure. Allergies, a cold, or a nose and throat infection might
close the Eustation Tube and will block the exchange of pressure. Nature will
complain, and can cause a painful earache or a plugged ear. Fluid can also build
up in the middle ear. If this condition is not treated, infection can spread
to the inner ear (through the mastoid bone) and/or cause the eardrum to burst.
Children are more susceptible to middle ear infections because their Eustation
Tubes are straighter and shorter than those in an adult. Often a tiny cut, called
a myringotomy, is made in the eardrum and a small ventilating tube is inserted.
The tube usually remains within the ear for 2 to 8 months. Normally, it works
it way out naturally during the healing process. Hearing loss can fluctuate anywhere
from a 20 dB to 40 dB loss when a child is suffering from an infection.
Many conductive losses can be treated and eliminated with medication or surgery.
But conductive loss can occur due to malformations of the outer or inner ear.
If the conductive hearing loss occurs because the bony or soft tissues of the
outer ear have not fully developed, it is known as microtia. If there is no visible
canal opening, there is atresia of the ear canal. These types of problems do
not allow enough sound to the ear drum for the middle and inner ear to detect
sound. The three small bones in the middle ear may be fused, or stuck together
so that they cannot carry the sound from the eardrum to the cochlea. This is
most common with the last ossicle, or the stapes. If the rest of the middle and
outer ear are working well, a surgeon may be able to go into the middle ear cavity
and loosen the stuck bones. These procedures are usually done after a child is
at least four years old, and the procedures may not completely correct the hearing
SENSORI-NEURAL HEARING LOSS: This
type of hearing loss is caused by a problem with the reception
of sound in the inner ear or in the transmission of electrical
impulses along the auditory nerve to the brain.
Possible causes of sensorineural hearing loss are: heredity; drugs; permanent
damage due to excessive noise; prenatal exposure to rubella, cytomegelovirus;
RH incompatibility at birth; low birth weight caused by prematurity; elevated
biliruben levels (jaundice); meningitis; and some infectious diseases such as
A sensor-neural loss implies damage to the sensors or nerve fibers which connect
the inner ear to the hearing center in the brain. Since damaged nerve fibers
do not regenerate or repair themselves like some other parts of the body, this
damage is permanent.
MIXED HEARING LOSS: This
is a combination of conductive and sensor-neural hearing losses.
The conductive loss often masks the sensorineural loss. It is
important to have a child with a conductive loss tested for the
presence of a sensorineural loss. There is often some improvement
in the hearing of a child with a mixed hearing loss when the
conductive loss is corrected or improved upon.
UNILATERAL HEARING LOSS: This
type of hearing loss only affects one ear and may range from
mild to profound. Most children with unilateral loss have problems
localizing or locating the source of sound. Others may have difficulty
with paying attention in noisy situations and language-based
AUDITORY NEUROPATHY (AN): Auditory
neuropathy is a type of hearing loss where the cochlea, or organ
of hearing, appears to be functioning normally. However, sound
cannot travel to the hearing centers of the brain because the
auditory nerve is not working properly. Children with AN sometimes
can hear sounds but cannot understand what those sound mean or
hear better on different days, with no obvious reason for the
difference. And, most children, even those that can discriminate
words in a quiet environment, cannot use their residual hearing
in noise. Doctors don’t know the exact cause of this type
of hearing loss, but there seems to be an increased risk for
children who have a brother or sister with AN or babies who were
born premature or had severe jaundice.
Illustration Source: MED-EL