**2. Congenital auris atresia (CCA)**

Congenital aural atresia is an ear malformation that may have different severity and may affect the external ear only or the middle ear too. The ear malformation may be a single problem or be part of a syndromic picture. An altered development of the first and second branchial arches and the first branchial cleft may be responsible for the CCA [5].

Schuknecht [6] classified four degree of severity based on the combination of high-resolution computer tomography (CT) scan and surgical findings: (1) Type

#### **Figure 1.**

*The image shows the four types of CAA as described by Schuknecht. In Type A, the yellow indicates the presence of the cholesteatoma behind the meatal stenosis. The gray areas in Types B, C, and D represent the portion with bone atresia. The red dot in type D shows the aberrant exit of facial nerve.*

**75**

*Congenital Aural Atresia: Hearing Rehabilitation by Bone-Anchored Hearing Implant (BAHI)*

A: narrowing of the fibrocartilaginous canal and presence of cholesteatoma distal to the stenotic area. (2) Type B: narrowing and tortuosity of fibrocartilaginous and bony part of the canal, commonly associated with abnormal tympanic membrane and malleus. (3) Type C: complete atresia with different combination of fibrous tissue and bone. Typically, malleus and incus are fused together, the manubrium and the tympanic membrane are missing, and the stapes is mobile. (4) Type D: totally atresia with decreased pneumatization of mastoid. More severe ossicular anomalies

than type C and frequently the facial nerve being aberrant (**Figure 1**).

type II based on the surgical findings and functional outcome [9].

**3. Embryology and etiopathogenesis of CAA**

Other authors classified the CAA; one of the most famous is Weerda [7] that classified these malformations in three types (A, B, and C), while Altmann described a histopathological classification correlating the severity of CAA [8] by identifying three categories: mildly, moderately, and severely malformed types. Many authors have since modified this classification system, further subclassifying

The mandibular (I) and the hyoid (II) branchial arches contribute to the auricular development, and both may be involved in the etiopathogenesis of CAA. Auricular pinna starts to develop between the third to sixth weeks of embryonic life, when hillocks appear on the arches, and its formation is complete at the fourth month of gestation. The basis of tragus, the helical root, and the superior part of the helix comes from the anterior three hillocks, derived from the first arch. The posterior hillock that derives from second arch is responsible for the formation of the antihelix, antitragus, and lobule. The middle ear cavity derives from the first pharyngeal arch starting from 4 weeks of gestation. The pinna develops around the external meatus which becomes canalized at week 28 of embryologic life. At 8 weeks the middle ear cleft is formed, and the cavity is complete developed at 30 weeks. The first arch cartilage generates malleus and incus by 8 weeks of gestation that start to ossify at the 4 months of pregnancy. From the second arch, cartilage comes out the stapes except the medial lamina of the footplate which derives from the otic capsule [10]. At week 9, ectodermal cells proliferate, fill the meatus lumen, and form the "meatal plug" (MP); then on week 10, the MP extends in a disclike fashion by following a horizontal plane, and the internal part of MP starts to thin for generating the future tympanic membrane. At the same time, the plug in the proximal portion of the neck starts to be resorbed. At week 13 the MP is in contact with the primordial malleus, and this contact will contribute to the thinness of internal part of MP that will create the tympanic membrane at week 15. At week 16 the external ear canal is fully patent but still narrow and curved. At week 18 the meatus is fully

extended and starts its opening that will be completed at 28 weeks [11].

disease (deficiency of thyroid hormone or diabetes) [12].

Any type of adverse event that occurs during the 4 and 25 weeks of gestation and interrupts one of more of these developments may be responsible for one of the different types of CAA. The adverse event may be related to genetic aberrations, vascular accident (fetal hypoxia), teratogenic substances (aminoglycoside antibiotics, hydantoin, alcohol, nicotine, herbicides), maternal infection (rubella, *Cytomegalovirus*, measles, hepatitis, toxoplasmosis, lues), and maternal metabolic

CAA may be a single malformation or be associated with other malformations as in the case of oto-facial dysostosis (Treacher-Collins syndrome, Goldenhar syndrome), craniofacial dysostosis (Crouzon syndrome, Apert syndrome), otocervical dysostosis (Klippel-Feil syndrome, Wildervanck syndrome), oto-skeletal

*DOI: http://dx.doi.org/10.5772/intechopen.88201*

*Congenital Aural Atresia: Hearing Rehabilitation by Bone-Anchored Hearing Implant (BAHI) DOI: http://dx.doi.org/10.5772/intechopen.88201*

A: narrowing of the fibrocartilaginous canal and presence of cholesteatoma distal to the stenotic area. (2) Type B: narrowing and tortuosity of fibrocartilaginous and bony part of the canal, commonly associated with abnormal tympanic membrane and malleus. (3) Type C: complete atresia with different combination of fibrous tissue and bone. Typically, malleus and incus are fused together, the manubrium and the tympanic membrane are missing, and the stapes is mobile. (4) Type D: totally atresia with decreased pneumatization of mastoid. More severe ossicular anomalies than type C and frequently the facial nerve being aberrant (**Figure 1**).

Other authors classified the CAA; one of the most famous is Weerda [7] that classified these malformations in three types (A, B, and C), while Altmann described a histopathological classification correlating the severity of CAA [8] by identifying three categories: mildly, moderately, and severely malformed types. Many authors have since modified this classification system, further subclassifying type II based on the surgical findings and functional outcome [9].
