**2. Clinical characteristics and embryology of congenital microtia**

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. We investigated 172 patients (191 ears) who underwent reconstructive surgery for their external ear malformations at our university. Consistent with a previous study [1], there was a predominance of right-sided microtia (62%) and boys (64%) (**Table 1**). Although the basis for the sex discrepancy in microtia incidence has not been determined, the difference appears to be more common in Asia. Only 11% of patients had bilateral involvement. **Figure 1** shows the distribution of microtia according to severity using the Marx system proposed by Marx in 1926 [6]. Briefly, grade I microtia corresponds to a normal-shaped but small pinna, grade II to a residual vertical ridge of the tissue, and grade III to the complete absence of the pinna or the presence of only rudimentary soft tissue. The distribution was as follows: 3% was classified as grade I, 27% as grade II, and 78% as grade III (**Table 1**). It has been reported that 74% of cases of microtia are complicated with narrow external auditory atresia [2, 3], and one in five cases with congenital external auditory stenosis are complicated with ear canal cholesteatoma [6]. In our patients, narrow external auditory atresia described as complete atresia was present in approximately 70%, and external auditory stenosis affected 30%. Careful observation is required to detect external auditory stenosis patients with ear canal cholesteatoma.

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 branchial arch.


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

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

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

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

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 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. We investigated 172 patients (191 ears) who underwent reconstructive surgery for their external ear malformations at our university. Consistent with a previous study [1], there was a predominance of right-sided microtia (62%) and boys (64%) (**Table 1**). Although the basis for the sex discrepancy in microtia incidence has not been determined, the difference appears to be more common in Asia. Only 11% of patients had bilateral involvement. **Figure 1** shows the distribution of microtia according to severity using the Marx system proposed by Marx in 1926 [6]. Briefly, grade I microtia corresponds to a normal-shaped but small pinna, grade II to a residual vertical ridge of the tissue, and grade III to the complete absence of the pinna or the presence of only rudimentary soft tissue. The distribution was as follows: 3% was classified as grade I, 27% as grade II, and 78% as grade III (**Table 1**). It has been reported that 74% of cases of microtia are complicated with narrow external auditory atresia [2, 3], and one in five cases with congenital external auditory stenosis are complicated with ear canal cholesteatoma [6]. In our patients, narrow external auditory atresia described as complete atresia was present in approximately 70%, and external auditory stenosis affected 30%.

**2. Clinical characteristics and embryology of congenital microtia**

their lives, requiring up-to-date and unbiased patient information.

facial nerve.

48 An Excursus into Hearing Loss

to them throughout their lives.

the care of patients with these conditions.

**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.
