The document discusses congenital hearing loss, including that it exists at birth or within the first six to twelve months. Congenital hearing loss creates lifelong disabilities if not detected early. The embryology of the inner ear is reviewed, starting as an auditory placode that develops into otocysts and eventually the mature inner ear structures. Early intervention is important for children with congenital deafness. Causes of congenital deafness include genetic factors, elimination of rubella, and cytomegalovirus.

1. Congenital means “existing at
birth”.
However, with hearing loss,
congenital includes an onset
prior to speech/language
development– usually within
the first six to twelve months
(post-natal).

2. Congenital hearing loss
creates a lifelong disability.
When detected late in early
childhood development, it can
create delays in language
development which may never
be corrected to normal.

3. It is important to recognize
congenital conductive hearing
loss, because amplification
often leads to normal levels of
hearing.

4. Children with corrected
congenital conductive hearing
loss, have the potential for
normal speech/language
development.

5. Let’s review the embryology
of the inner ear.

6.  First Appearances/otocysts
The inner ear first appears as a
thickening of ectoderm—the
auditory placode.
In the twenty-fourth day of
embryo formation hollow cysts
have formed-- otocysts (auditory
vesicles)

7.  First Appearances/otocysts
The otocysts soon become
detached from the ectoderm
from which they arose.
At that point where the otocyst
has detached from the ectoderm,
the endolymphatic sac begins to
extend in the medial direction.

8.  First Appearances/Cochlear
Duct
It continues to dilate; and this
slender medial endolymphatic
sac becomes the cochlear duct.
The dorsal portion begins to
show indications of developing
the semicircular canals (for
balance).

9.  First Appearance/Cochlea
By the end of the seventh week,
the otocyst has been modeled
roughly into the membranous
labyrinth with its semicircular
canals and a cochlea with one
turn.

10.  First Appearance/Cochlear Duct
In the eighth week, the
endolymphatic duct with the
three semicircular canal are well
defined and utricle and saccule
have been divided.
The cochlear duct has begun to
coil into its familiar snail shell
shape.

11.  First Appearance/Cochlear Duct
By the third month, the adult
form of the inner ear has been
nearly completed.
Its further development results in
complete separation of the
utricle and saccule which
remains attached to the
endolymphatic duct by a short
slender canal.

12.  First Appearance/Tectorial
Membrane
With the development of the
membranous labyrinth, the spiral
organ divides into an inner and
outer ridge.
Both ridges become covered with
an increasingly prominent
tectorial membrane.

13.  First Appearance/Hair Cells
In the area between these two
ridges the epithelial cells begin
to form the sensory hair cells.

14.  First Appearance/Bony Labyrinth
The mesoderm surrounding the
membranous (epithelial)
labyrinth becomes differentiated
into a fibrous membrane and
later into cartilage.

15.  First Appearance/Perilymph
At about the tenth week, the
cartilage immediately
surrounding the membranous
labyrinth undergoes a peculiar
reversal of development.
It returns to a precartilaginous
condition in which the cells lose
their boundaries.

16.  First Appearance/Perilymph
This loose network of cells
becomes the perilymphatic
space surrounding the
membranous labyrinth.
When this has taken place, the
membranous labyrinth becomes
suspended in the fluid of the
perilymphatic spaces.

17.  First Appearance/Perilymph
The perilymphatic spaces
continue to develop above and
below the cochlear duct creating
the upper (scala vestibuli area)
and the lower (scala tympani
area).

18.  First Appearance/Bony Labyrinth
By the fifth month, the cartilage
surrounding the membranous
labyrinth has become the bony
labyrinth (the hardest bone in the
human body).
Thus, by the middle of fetal life,
the inner ear has attained its full
adult size.

19. Now that we are aware of how
the inner ear is formed inside the
womb, we can become more
aware of how the mother’s health
conditions may affect the
development of the fetus’s inner
ear.

20. Embryology Summary
The human embryo has three
primitive tissue layers from which
all organs of the body are formed.
They are:
1. The ectoderm
2. The entoderm
3. The mesoderm

21.  Embryology Summary
During the formation of the
embryo, an abnormal formation of
one organ will many times indicate
the abnormal formation of another.

22.  Embryology Summary
For example, a congenital anomaly
of the eye involves the ectoderm,
as does the endolymphatic portion
of the inner ear.
Therefore, a congenital anomaly of
the eye suggests the infant may
also have a congenital inner ear
abnormality.

23.  Embryology Summary
Timing of the embryonic insult will
also determine which organs may
possess abnormal formation.
Examples of embryonic insult
include: X-rays, viruses, drugs,
and environmental toxins.

24.  Embryology Summary
For example, the timing of
embryonic exposure to maternal
rubella within the first trimester
may cause cardiac defects,
cataracts, mental retardation, and
hearing loss.
However, if exposure occurs within
the second or third trimester, only
hearing loss may result.

25. While there continues to be
controversy about the best way to
habilitate a hearing impaired child,
it is generally accepted that early
intervention is extremely
important!

26. Because of the importance of early
intervention for children with
congenital deafness, several
approaches have been tried over
the years.

27. Over the past few decades,
identifying congenitally deaf
children through the use of a high-
risk register (HRR) has become a
common method.
The HRR is based on birth factors
often associated with childhood
deafness.

28. The infants identified as having
factors on the high-risk register
(HHR), are to be screened by three
months and placed into a
habilitation program by six months
of age.
New testing technology supports
the HHR through objective
assessment (ABR and EOAE).

29. In 1994, the Joint Committee on
Infant Hearing recommended
universal hearing screening upon
all infants prior to three months of
age using either auditory
brainstem response (ABR) or
evoked otoacoustic emissions
(EOAE).

30. Let’s review some HHR indicators
in Northern page #192.

31. The management of the hearing
impaired child involves several
members of the hearing health
care team.
The pediatric audiologist must
accurately measure the hearing
loss. The otologist must rule out
treatable disease . The speech
pathologist must assess the child’s
communication skills.

32. Three factors have influenced the
prevalence of congenital deafness
in the United States.
1. Genetic factor
2. New vaccine factor
3. Cytomegalovirus (CMV) factor

33.  Genetic Factor
If one excludes the environmental
causes of hearing loss, over fifty
percent are felt to have a genetic
etiology.

34.  New Vaccine Factor
Maternal rubella has essentially
been eliminated.
On the other hand, small
premature infants are surviving
and many of them are at an
increased risk for hearing loss.

35. Cytomegalovirus (CMV) factor
Many genetists believe that this is
one of the leading causes of
congenital hearing loss previously
described as “unknown etiology”.

36. Most congenital hearing loss is
nonsyndromic or not associated
with any other abnormalities of the
ear.
Genetic deafness is very difficult
to recognize when the family
history is negative.

37. Let’s review Northern page
#194 for described etiology of
severe to profound congenital
hearing loss.

38. Let’s review Northern pages
#194—195 for a list of
syndromes commonly
associated with hearing loss.

39. As stated earlier, congenital
hearing loss is often
associated with other medical
problems.
For example, a steeply sloping
high frequency hearing loss is
suggestive of perinatal
etiology.

40. With this revealed precipitous HL
and twelve months post-natal, an
MRI may reveal periventricular
leukomalacia.
Children with this “signature
audiogram” may have an increased
risk of cerebral palsy, mental
retardation, attention-deficit
disorder, and seizures.

41. Today, the most common cause
of post-natal severe to
profound deafness is bacterial
meningitis.

42. NOTE: The deaf population are
rarely concerned about having a
deaf child. They have their own
language and culture which
contributes to little concern
regarding the birth of a hearing
impaired child.

43. In contrast, a deaf child born into a
family not familiar with the
communication challenges of
deafness; may require that family
to learn the “language of the deaf”
for adequate communication
development of the child.