Microtia is a congenital deformity where the auricle (external ear) is underdeveloped. A completely undeveloped pinna is referred to as anotia. Because microtia and anotia have the same origin, it can be referred to as microtia-anotia. Microtia can be unilateral (one side only) or bilateral (affecting both sides). Microtia occurs in 1 out of about 8,000–10,000 births. In unilateral microtia, the right ear is most commonly affected. It may occur as a complication of taking Accutane (isotretinoin) during pregnancy. Classification According to the Altman-classification, there are four grades of microtia: Grade I: A less than complete development of the external ear with identifiable structures and a small but present external ear canal Grade II: A partially developed ear (usually the top portion is underdeveloped) with a closed stenotic external ear canal producing a conductive hearing loss. Grade III: Absence of the external ear with a small peanut-like vestige structure and an absence of the external ear canal and ear drum. Grade III microtia is the most common form of microtia. Grade IV: Absence of the total ear or anotia. Causes and risk factors The etiology of microtia in children remains uncertain but there are some cases that associate the cause of microtia with genetic defects in multiple or single genes, altitude, and gestational diabetes. Risk factors gathered from studies include infants born underweight, male sex, women gravidity and parity, and medication use while pregnant. Genetic inheritance has not been fully studied but in the few studies available, it has shown to occur during the early stages of pregnancy. Diagnosis At birth, lower grade microtia is difficult to visually diagnose with a physical exam. While higher grade microtia can be visually diagnosed due to noticeable abnormalities. Infants that have noticeable abnormalities are closely monitored by physicians and hearing specialists. Treatment The goal of medical intervention is to provide the best form and function to the underdeveloped ear. Hearing Typically, testing is first done to determine the quality of hearing. This can be done as early as in the first two weeks with a BAER test (Brain Stem Auditory Response Test). At age 5–6, CT or CAT scans of the middle ear can be done to elucidate its development and clarify which patients are appropriate candidates for surgery to improve hearing. For younger individuals, this is done under sedation. The hearing loss associated with congenital aural atresia is a conductive hearing loss—hearing