Development of the external ear (auricle) begins during the 5th week of gestation. Six hillocks from the first and second pharyngeal arches are responsible for the intricate anatomy and three-dimensional topography of the external ear. Underdevelopment (microtia) or absence (anotia) of the external ear comes in many different forms and has aesthetic and functional implications.
Aural atresia is the absence of the ear canal, and therefore the ability to hear. The majority of cases (~90%) of microtia are unilateral (one-sided) and the hearing in the unaffected ear is normal. Adequate hearing is important for the development of speech. Children with unilateral hearing loss are able to develop speech normally. However, their ability to localize sounds is dimished due to the lack of stereo sound.