Conductive hearing loss
Any problem which blocks transmission of sound through the ear canal and/or
the middle ear will cause a conductive type of hearing loss. Therefore,
abnormalities of the ear canal, tympanic membrane, ossicular chain (little bones
in the middle ear) or middle ear space will cause this type of hearing loss.
The most common cause of conductive hearing loss is fluid in the middle ear
space (see section on otitis media). The presence of fluid instead of air in the
middle ear reduces efficient transmission of sound into the inner ear. Fluid can
persist in the middle ear after birth as the middle ear may not immediately fill
with air. Later in infancy and childhood, fluid in the middle ear occurs most
commonly secondary to an ear infection. Once the fluid is gone, the child's
hearing typically returns to normal.
Another acquired, reversable cause of hearing loss is wax or a foreign body
that completely blocks the ear canal. Conductive loss can also develop because
of abnormalities of the eardrum or the little bones in the middle ear. For
example, a large hole in the eardrum (tympanic membrane perforation) can cause
conductive hearing loss. Fortunately, small holes often do not cause hearing
loss. Holes in the drum can be repaired by a surgical procedure called
tympanoplasty. If the hole was the only cause of hearing loss, surgical closure
should improve hearing.
Abnormalities of the little bones can occur due to chronic middle ear and
mastoid infection and can occur due to cholesteatoma. Rarely, trauma to the ear
can disrupt the little bones, causing hearing loss.
A small number of children are born with middle ear bones that did not
develop normally. Their ossicles do not vibrate normally in response to sound
and, therefore, these children have a conductive hearing loss in the affected
ear. Some children are born with a condition known as aural atresia. In these
children, the ear canal, tympanic membrane, and ossicular chain does not fully
develop in one or both ears.
In the majority of cases, conductive hearing loss can be corrected
surgically. Conductive hearing loss can also be managed in many cases by use of
hearing aids.
A new implant system for children and adults who have conductive (middle ear)
hearing loss who cannot be successfully fit with hearing aids is the bone-anchored hearing device (BAHA, for its original name,
the bone-anchored hearing aid).
Hearing loss in babies
According to the National Institutes of Health (NIH), nearly 12,000 babies
are born each year in the United States with a permanent hearing impairment. It
is estimated that serious hearing loss occurs in about one to three of every
1,000 healthy newborns, and in two to four of every 100 babies in newborn
intensive care units. Without hearing testing, significant hearing loss may not
be noticed until the baby is over a year of age. Profound deafness is often not
recognized until 18 to 24 months of age. Lesser degrees of hearing loss may not
be recognized until 3 to 6 years of age. Although these children are not meeting
normal developmental milestones, this situation is often unrecognized, or
attributed to other causes.
The sooner hearing loss is identified and treated, the less likely there will
be a significant impact on development of language. Recent studies indicate that
intervention by 6 months of age is very beneficial in terms of prevention of
language delays in early childhood.
Because of the potential benefit of identifying hearing loss early in the
first year of life, many states have implemented universal infant hearing
screening of all children prior to discharge from the newborn nursery. Many
hospitals in Illinois currently perform newborn hearing screening. All hospitals
in Illinois are required by law to have newborn hearing screening programs in
place by the end of 2002.