**Hearing Loss in Congenital Microtia**

**Hearing Loss in Congenital Microtia**

#### Kenichi Takano Kenichi Takano Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72429

#### **Abstract**

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.

DOI: 10.5772/intechopen.72429

**Keywords:** microtia, atresia, facial nerve, taste disorder, hearing

### **1. Introduction**

Congenital microtia occurs in approximately one in 10,000–20,000 live births as a result of aberrant development of the first and second branchial arches [1]. The exact pathogenesis of microtia remains unclear, but it is considered to be a multifactorial disease in which both environmental and genetic factors are thought to be associated with its pathogenesis. Microtia and aural atresia are known to be associated with conductive or mixed hearing loss and are caused by developmental failure of the auricle, the external auditory canal (EAC), and structures

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

of the middle ear [2, 3]. Other complications, such as cholesteatoma and mandibular dysplasia, are also known to occur in microtia and atresia, as well as rare conditions such as inner ear deformity, facial nerve paralysis, and chorda tympani dysfunction [4, 5]. It is well known that the first branchial arch is the origin of the head of the malleus, body of the incus, and the mandible, and the derivatives of the second arch include the stapes bone, the long process of the incus, and the manubrium of the malleus [2, 3]. Developmental abnormalities of the first and second branchial arches can give rise to congenital microtia and atresia, which have a significant effect on the development of the ear, including the course of the facial nerve.

Careful observation is required to detect external auditory stenosis patients with ear canal

Hearing Loss in Congenital Microtia http://dx.doi.org/10.5772/intechopen.72429 49

Embryologically, the auricle is formed from several protuberances in the first and second branchial arches. These protuberances, known as auricular hillocks, surround the first branchial cleft, which is the space between the first and second branchial arches [8]. Each of the hillocks contributes to a specific component of the auricle, and those in the second branchial arch form most of the ear structure. The external auditory canal and lateral tympanic membrane are derived from the ectoderm of the first branchial cleft and the epithelium of the middle ear cavity, which is derived from the endoderm of the first pharyngeal pouch. The ossicles develop from the mesenchyme of the proximal area of the branchial arches, and the malleus and incus both derive from the first branchial arch (mandibular area and maxillary area, respectively), while the stapes is formed from the second bran-

**Figure 1.** Marx system. Grade I: A normal-shaped but small pinna. Grade II: A residual vertical ridge of the tissue. Grade

III: Complete absence of the pinna or the presence of only rudimentary soft tissue.

cholesteatoma.

chial arch.

**Sex**

**Laterally**

**Marx's classification %** Grade I 3 Grade II 27 Grade III 78

Male 64 Female 36

Right 62 Left 27 Bilateral 11

**Table 1.** Characteristics of patients with congenital microtia.

Most children with congenital microtia are identified by an obvious anomaly at birth; however, they do not always receive the necessary medical care. Although otolaryngologists frequently examine only the hearing level of patients with microtia, those born with both microtia and aural atresia have a complex craniofacial condition that may affect all aspects of their lives, requiring up-to-date and unbiased patient information.

Patients with microtia are unable to undergo corrective plastic surgery until they are in their early teens since their rib bones need to be of a sufficient size for harvesting in order to create an adequately sized graft. Otolaryngologists are responsible for providing care and support to them throughout their lives.

In this chapter, we present the clinical characteristics of congenital microtia and atresia and associated complications observed at our hospital for the benefit of medical staff involved in the care of patients with these conditions.
