Hearing Loss in Congenital Microtia

Congenital microtia occurs in approximately one in 10,000–20,000 live births as a result of the aberrant development of the first and second branchial arches. However, the exact pathogenesis of microtia remains unknown; it is considered a multifactorial disease where both environmental and genetic factors play a role. Microtia and aural atresia are known to be associated with conductive or mixed hearing loss caused by the developmental failure of the auricle, the external auditory canal (EAC), and middle ear structures. Cholesteatoma and mandibular dysplasia are also known to occur in microtia and atresia, as well as rare conditions, such as facial nerve paralysis, chorda tympani dysfunction, and inner ear deformity. The first branchial arch is the origin of the malleus head and the incus body as well as of the mandible, and the second arch derivatives include the stapes bone, the long process of the incus, and the manubrium of the malleus. It has been reported that the grade of microtia and the severity of middle ear abnormalities are correlated, and it is thought that better development indicates more developed middle ear structures. The existence of additional structural anomalies is suggestive of a broader developmental problem in most patients with microtia. This chapter will focus on hearing loss and structural anomalies in congenital microtia.