Six hillocks derived from the first and second branchial arches fuse to form the auricle. By the end of the third month the primitive auricle is completed. The external auditory meatus develops from the first branchial groove. It takes shape in the sixth month. Its canalization takes place in the seventh month. The subsequent inferior and posterior development of the external auditory meatus carries the middle ear and the facial nerve to their normal positions.

The middle ear cleft develops from the first branchial pouch. The tympanic membrane is formed by the junction between the middle ear cleft and the epithelium of the external auditory canal. The first branchial pouch forms the eustachian tube, tympanic cavity, and mastoid air cells. Meckel’s cartilage forms the head of the malleus and body of the incus. Reichert’s cartilage forms the remainder of the first two ossicles and the stapes superstructure. The footplate has a dual origin from the otic capsule and the second arch. The ossicles attain their final shape by the fourth month. By the end of the seventh or eighth month, the expanding middle ear cleft surrounds the ossicles and covers them with a mucous membrane (1,20).

The facial nerve is the nerve of the second arch. The membranous portion of the inner ear develops during the third to the sixth week from an auditory placode on the lateral surface of the hindbrain (21,22).

Congenital aural atresia can present in different forms depending on the time of the arrest of intrauterine development. The usual finding of a normal inner ear is explained
by the fact that the inner ear is already formed by the time the external/middle ear development arrests. Only severe congenital malformations of the external and middle ear are associated with inner ear deformities (23).

De la Cruz et al. (2) modified Altmann’s descriptive system to include practical surgical guidelines. They divided these malformations into minor and major malformations. Minor malformations include (i) normal mastoid pneumatization, (ii) normal oval window footplate, (iii) favorable facial nerve-oval window footplate relationship, and (iv) normal inner ear. Major malformations include poor pneumatization, abnormal or absent oval window footplate, abnormal course of the horizontal portion of the facial nerve, and abnormalities of the inner ear. The clinical importance of this classification is that surgery in cases of minor malformations has the best chance of yielding a good functional result, whereas major malformations are often inoperable.

Jahrsdoerfer et al. (24) developed a point grading system (from 0 to 10) to identify good candidates for surgery. This system takes into consideration mastoid pneumatization, presence of the oval and round windows, course of the facial nerve, status of the ossicles, and external appearance. Allocation of points is based on the results of high resolution computed tomography (CT). They allocate two points for the presence of the stapes and one point for each one of the following parameters: oval window open, middle ear space present, facial nerve course normal, malleus-incus complex present, mastoids well pneumatized, incus-stapes connection present, round window normal, and appearance of the external auditory canal acceptable. A score of eight or better predicts a good surgical result. A score of seven implies a fair chance, six is marginal, and below that the patient becomes a poor candidate for surgery.

In 1955, Altmann (25) developed a widely used classification system that categorizes congenital aural atresia into three groups. Group 1 includes mild deformities; the external auditory canal, although hypoplastic, is present, the tympanic bone is hypoplastic, and the ear drum is small; the tympanic cavity is either normal or hypoplastic. Group 2 includes moderate deformities; the external auditory canal is completely absent, the tympanic cavity is small and its content deformed, and the atresia plate is partially or completely osseous. Group 3 includes severe deformities; the external auditory canal is absent, and the tympanic cavity is markedly hypoplastic or missing.

Schuknecht’s system of classification of congenital aural atresia is based on a combination of clinical and surgical observations (26). Type A (meatal) atresia is limited to the fibrocartilaginous part of the external auditory canal and is corrected easily with a meatoplasty. In type B (partial) atresia, there is a narrowing of the cartilaginous and bony external auditory canal. A patent tract allows inspection of the tympanic membrane, which is small and may be partly replaced by a bony septum. Minor ossicular malformations exist, and hearing loss could be mild to severe. Type C (total) atresia includes cases of totally atretic ear canal with a well-pneumatized tympanic cavity. There is a partial or a total atretic plate, the ossicles are fused and most probably not connected to a malformed stapes, and the facial nerve may follow an aberrant course over the oval window. Type D (hypopneumatic total) atresia is a total atresia with poor pneumatization. These patients are poor surgical candidates for hearing improvement.

Chiossone’s classification is based on the location of the glenoid fossa (27). In type 1 the fossa is in a normal position, in type II the fossa is slightly displaced, in type III the fossa overlaps the middle ear, and in type IV the fossa overlaps the middle ear and there is poor mastoid pneumatization. Patients with types I and II are ideal surgical candidates, whereas those with type IV are not.

Aural atresia diagnosed in the newborn mandates the search for other abnormalities. When aural atresia is associated with cephalic abnormalities, a full genetic workup is recommended to rule out the possibility of a syndromic child. The most commonly associated syndromes are Treacher Collins, Crouzon’s, Klippel-Feil, Pierre Robin, Goldenhar’s, drug teratogenicity, and hemifacial microsomia (28). Auditory function is evaluated using auditory brainstem response audiometry during the first few days of life whether the malformation is unilateral or bilateral. In bilateral cases, a boneconduction hearing aid should be applied as soon as possible. In unilateral cases in which the hearing is normal in the opposite ear, a hearing aid is not indicated.

The incidence of inner ear abnormality associated with congenital aural atresia could be as high as 47% (5). In some unilateral cases, an anacusis may occur on the normal-appearing ear (2,17). It is necessary to counsel the parents and answer their questions regarding the possibility of occurrence of an aural atresia in their subsequent children (no more than the general population), future auricular reconstruction, and daily use of proper amplification. The child should be enrolled in special education at an early age to maximize speech and language acquisition. Radiologic and surgical evaluations are deferred until the child reaches the age of 6 years.

The evaluation includes a hearing test and high resolution CT of the temporal bone in coronal and axial views to assess the degree of the deformities. Auricular reconstruction must be done before hearing reconstruction to avoid interfering with the blood supply to the surrounding soft tissue, which is indispensable for microtia repair.

A patient with congenital atresia may present with a recurrently infected or draining ear or an acute facial palsy. Congenital cholesteatoma is present in 14% of the cases (2).
The priority in these cases is removal of the cholesteatoma and resolution of the infection. The presence of a cholesteatoma necessitates surgery at any age in unilateral and bilateral atresias.

Before undertaking surgery for congenital atresia, two requirements are necessary: the radiologic presence of an inner ear and the audiometric evidence of cochlear function.

In bilateral cases of congenital atresia, auricular reconstruction and atresiaplasty are recommended when the patient is age 6 years. By this time, the costal cartilage has developed sufficiently to allow for harvesting and transfer to the auricle, and the mastoid pneumatization is nearly complete. In unilateral cases, atresiaplasty is indicated only in minor deformities. The microtia repair is done first because of the need of an excellent blood supply to cover the autologous rib graft (29,30). The hearing restoration surgery is performed 2 months after the last step of the microtia repair. Rehabilitation of severe auricular defects can be done using an osseointegrated percutaneous mastoid implant prosthesis, with and without bone-conduction aids, such as a bone-anchored hearing aid (BAHA) (31).

Early diagnosis with auditory brainstem response audiometry and bone-conduction hearing aids in bilateral cases should be done in the first weeks of life. Radiologic evaluation can be deferred until age 6 years, using high resolution CT in coronal and axial planes of the temporal bone (Figs. 24.1, 24.2 and 24.3). Four anatomic parameters as visualized radiographically are crucial for surgical planning. These include the degree of pneumatization of the mastoid, the course of the facial nerve (both the relationship of the horizontal segment to the oval window and the location of the mastoid segment), the presence or absence of the oval window and stapes footplate, and the status of the inner ear.