Anotia

Ear development

Ear development begins in about the third week of human embryonic development, beginning with the formation of the otic placodes, 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 auricle, or outer 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.

Processing sound

The human ear is divided into three sections. Each section has 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.

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.