Microtia and atresia: When ears don't develop fully
Microtia is a rare birth defect in which the external ear is not completely developed. It affects about one of every 3,800 babies born annually, according to the US Centers for Disease Control and Prevention. Microtia usually occurs with atresia, also known as aural atresia, a condition in which the auditory ear canal is either underdeveloped, absent or closed. When this happens, a child will likely have severe conductive hearing loss in the affected ear.
Source: Healthy Hearing