MAJOR ABNORMALITIES OF THE OUTER EAR: MICROTIA AND ATRESIA Introduction
The development of the external ear is complex in embryological terms, and the final shape of the pinna, together with the patency of the ear canal and the formation of the tympanic membrane, results from the fusion and canalisation of a number of primitive swellings. As with any complex developmental process there is scope for abnormalities to develop due to failure of fusion, canalisation or growth. Abnormalities of the outer ear amounting to microtia (an abnormally-small or rudimentary pinna) and atresia (absence of the pinna or failure of development of an open ear canal) may occur on one or both sides, and they may sometimes occur as isolated defects, although it is more common for them to be associated with abnormalities of the middle ear, and sometimes with developmental abnormalities of the inner ear. The most important aspect of management of any infant born with one or two rudimentary ears is, therefore, to assess the hearing ability as rapidly as possible, and to provide appropriate rehabilitation where this is defective. In this section, only isolated abnormalities of the outer ear will be considered, and abnormalities of the middle and inner ears will be dealt with later.