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| Credit: Wikipedia.org |
Anotia ("no
ear") describes a rare, congenital deformity, that involves the complete absence
of the pinna, the outer projected portion of the
ear, and narrowing or absence of the ear canal. This contrasts with microtia, in
which a small part of the pinna is present. Anotia and microtia may occur
unilaterally (only one ear affected) or bilaterally (both ears affected). This
deformity results in conductive
hearing loss, deafness.
Developmental biology of the ear
Ear
development begins in about the third week of human embryonic development.
Beginning with the formation of the Otic Placodes which are an extension of the
early hind brain. By the fourth week of development the otic placodes
invaginate, or sink inward forming pits which close themselves off for the
outer surface ectoderm and begin forming the inner ear labyrinthe on the inside.
Outer ear development begins in about the fifth week of human embryonic
development. Upon the pharyngeal arches Auricle Hillocks begin to form.
By the seventh week the three pairs of hillocks' have enlarged differentiated
and fused together to start forming the Pinna, or out portion of the ear.
Throughout fetal development the hillocks' will move from the sides of the neck
to the sides of the head. simultaneously in the seventh week of development the
auditory tube begins to form out of the tympanic membrane.
The human ear and processing sound
The human
ear is divided into three sections. Each section has possesses its own
specialized function.
1. The outer
ear acts like a funnel and takes in the sound.
2. The
middle ear holds the tympanic membrane, or ear drum and several little
bones that are moved by the sound waves that have entered the ear via the
canal. These movements are very small, like vibrations and are transmitted to
the inner ear.
3. The inner
ear contains a structure called the cochlea, which contains small hair- like
cells that respond to sound information and transmits it via nerve impulses
down the auditory
nerve and to
the brain, where they are processed.
Defects of the ear: anotia/microtia
The isolated
cause, a cause not associated with a syndrome, of anotia or microtia is not
known, though it is believed to be of genetic basis. Developmentally
anotia/microtia occurs when certain tissues associated with the auricle do not
develop. This rare defect may occur as part of a syndrome or as an isolated
abnormality. This defect is able to be classified into four types depending on
the extent of the anomaly.
Type I: External portion of the ear is
small in size; auricle structure is normal
Type II: The auricle is in a hook or 'S'
shape; external ear is only moderately abnormal.
Type III: Small amount of basic, soft
tissue ear structure lacking cartilage; auricle is abnormal in appearance.
Type IV: Most severe type, Anotia; all
external structures of the ears are absent. Defects affecting the external ear
such as the auricle results from malformation or
suppression of the auricular hillocks, which are small swellings on the
embryonic visceral arches or the beginnings of the external ears; the small
swellings are derived from the first and second pharyngeal arches. Because the
ears and the kidneys develop simultaneously, children with ear defects are
often checked for kidney defects at birth.
Related syndromes
"20% to
40% of children with microtia/anotia will have additional defects that could
suggest a syndrome."
Treacher-Collins Syndrome: (TCS) A congenital disorder caused by a defective protein
known as treacle, and is characterized by craniofacial deformities; malformed
or absent ears are also seen in this syndrome. The effects may be mild,
undiagnosed to severe, leading to death. Because the ear defects are much
different in this disorder and not only affect the outer ear, but the middle
ear as well, reconstructive surgery may not help with the child's hearing and
in this case a Bone Anchored Hearing Aid would be best. BAHA will only work, however if the
inner ear and nerve are intact.
Goldenhar
Syndrome: A rare
congenital birth defect that causes abnormalities of facial development. also
known as Oculoauricular Dysplasia. The facial anomalies include underdeveloped,
asymmetric half of the face. The defect is capable of affecting tissue, muscle,
and the underlying bone structure of the side of the face with the abnormality.
Ablepharon-macrostomia
Syndrome: (AMS) A rare genetic disorder characterized by various physical anomalies
which affect the craniofacial area, the skin, the fingers, and the genitals.
Treatment
The
treatment will vary with the different grades, but the most common is a
surgical repair. The surgical option is cosmetic reconstruction of the external
ear's normal shape and repair of the ear canal. In less severe cases the
reconstruction will be sufficient to restore hearing. In grades of
anotia/microtia that affect the middle ear the surgery with the use of a Bone Anchored Hearing Aid (BAHA) will likely restore the hearing. The BAHA may be
surgically implanted onto the skull which would allow for some hearing repair
by conduction through the skull bone. "This allows sound vibrations to
travel through bones in the head to the inner ear."
BAHA: An
implantable hearing device. It is the only hearing aid device that works via
direct bone conduction. Most children with an isolated form of bilateral or
unilateral anotia/microtia do well after corrective surgery and there are no
adverse effects on the child's development, as this surgery is typically
performed in the child's early years. Common Complications Post
Surgery: Common obstacles in healing for those who received the corrective
surgery include: infections, poor wound healing, and excessive scarring.
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