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).

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.

It is important to recognize

congenital conductive hearing

loss, because amplification

often leads to normal levels of

hearing.

Children with corrected

congenital conductive hearing

loss, have the potential for

normal speech/language

development.

Let’s review the embryology

of the inner ear.

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)

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.

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).

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.

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.

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.

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.

First Appearance/Hair Cells

In the area between these two

ridges the epithelial cells begin

to form the sensory hair cells.

First Appearance/Bony Labyrinth

The mesoderm surrounding the

membranous (epithelial)

labyrinth becomes differentiated

into a fibrous membrane and

later into cartilage.

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.

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.

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).

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.

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.

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

Embryology Summary

During the formation of the

embryo, an abnormal formation of

one organ will many times indicate

the abnormal formation of another.

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.

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.

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.

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!

Because of the importance of early

intervention for children with

congenital deafness, several

approaches have been tried over

the years.

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.

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).

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).

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

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.

Three factors have influenced the

prevalence of congenital deafness

in the United States.

1. Genetic factor

2. New vaccine factor

3. Cytomegalovirus (CMV) factor

Genetic Factor

If one excludes the environmental

causes of hearing loss, over fifty

percent are felt to have a genetic

etiology.

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.

Cytomegalovirus (CMV) factor

Many genetists believe that this is

one of the leading causes of

congenital hearing loss previously

described as “unknown etiology”.

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.

Let’s review Northern page

#194 for described etiology of

severe to profound congenital

hearing loss.

Let’s review Northern pages

#194—195 for a list of

syndromes commonly

associated with hearing loss.

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.

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.

Today, the most common cause

of post-natal severe to

profound deafness is bacterial

meningitis.

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.

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.