Microtia is a developmental abnormality in which the external part of the ear (the pinna or auricle) has not fully developed. There are varying degrees of microtia depending on how well developed the auricle is. The degree of auricle development can range from simply a small ear that has all the proper cartilage (grade I) to a small "nubbin" or peanut ear that has little or no cartilage and only a mound of skin and soft tissue (grade III). Rarely, people are born without an auricle, a condition called anotia.
A plastic surgeon skilled in microtia repair can often rebuild the auricle to a very favorable appearance using a prosthesis, the person's own rib cartilage, or an implant made of a porous plastic material.
Auditory canal atresia is the partial or total failure of the ear canal to develop. Absence of the ear canal is usually associated with absence of the eardrum (tympanic membrane) and underdevelopment of the middle ear and middle ear bones (hammer, anvil, and stirrup bones). Children with auditory canal atresia have hearing loss because sound is not efficiently carried, or conducted, into the middle and inner ear. Usually the inner ear (cochlea) is healthy and normally developed in these children.
In some children, doctors can surgically open the ear canal, build an eardrum, and restore the natural sound-conducting pathway of the ear canal and middle ear to the healthy inner ear. Although surgical correction of auditory canal atresia, called canalplasty, can improve hearing, it seldom results in normal hearing at all pitches (frequencies) of sound.
Bone-conducting hearing devices can also be used to treat auditory canal atresia. These devices conduct sound to the inner ear by vibrating the bone of the skull. These hearing devices are attached to a hard metal or soft band that is worn tightly around the head. A bone-conducting hearing device is important for normal development of speech and language in children with auditory canal atresia in both ears.
Special implantable bone-anchored devices are becoming popular as an alternative to bone-conducting hearing devices worn on a soft or hard band. These devices are attached to titanium posts or magnetic plates that are surgically anchored into the skull bone (hence the term, "bone anchored hearing device"). In the United States, the Food and Drug Administration (FDA) approved these surgically placed devices for children 5 years and older.
The key feature of these devices is that they must make close contact with the bone of the skull to conduct sound efficiently to the inner ear.