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Microtia is a congenital deformity where the pinna (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.〔Pretest self assessment and review for the USMLE, pediatrics, 12th edition, question 84, general pediatrics〕 ==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 () 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Microtia」の詳細全文を読む スポンサード リンク
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