Congenital aural atresia results from a failure of canalization of a solid core of epithelial cells that extends from the developing auricle to the tympanic ring and middle ear cleft. The incidence of congenital aural atresia is 1 per 10,000 to 20,000 live births.1 Approximately one-third of cases are bilateral.2 The child with unilateral congenital aural atresia and a normally-functioning contralateral ear will develop language normally and have no significant cognitive, developmental, or social deficits, even without the use of a hearing aid in the affected ear.1, 11, 12 As such, the decision to operate on the child with unilateral atresia is controversial.
Most cases of atresia of the external auditory canal are accompanied by some form of microtia, although isolated middle ear ossicular anomalies do occur and may not be diagnosed until the child is several years old. Aural atresia can be associated with other craniofacial anomalies (e.g., Treacher Collins, hemi-facial microsomia) or can occur as an isolated congenital anomaly. Jafek reported a 14% positive family history;2 atresia is seen in families, although no genetic inheritance pattern has been demonstrated.
Surgery for aural atresia involves a number of steps, with the ultimate goal of creating a healed, dry ear canal with liberation of the ossicles to restore the middle ear conductive mechanism. The following steps give a general overview of the procedure:
A postauricular incision followed by standard T-shaped periosteal incision is made to identify the atretic bone.
Using surface landmarks, including the glenoid fossa, linea temporalis, and cribriform areas, the new ear canal is drilled.
The middle ear ossicles are identified and freed from the surrounding bone.
A tympanic membrane graft is fashioned from temporalis fascia and lain over the mobile ossicles.
A split thickness skin graft is used to line the new bony ear canal.
A meatoplasty is created and the skin graft pulled through and sutured to the skin of the native or reconstructed auricle.
Children with bilateral aural atresia have maximal conductive hearing deficits (50 to 60 dB hearing loss [HL]), and if the anatomy is favorable, surgery at age 6 is performed in an attempt to gain hearing. Cholesteatoma will be found in 8 to 14% of children with atretic ear canals.3, 4 Stenosis of the external auditory canal is associated with a higher incidence of cholesteatoma than is complete atresia. One series of 50 patients (54 ears) with an average canal diameter of 4 mm found a 50% incidence of cholesteatoma.5 No cholesteatoma was found in patients less than 3 years old. The more stenotic (especially < 2 mm) canals had the greater incidence of cholesteatoma. Regardless of middle and inner ear anatomy, patients with cholesteatoma require an operation to clean the ear and eradicate the disease.
Controversy exists, however, in the management of the unilateral atretic ear without cholesteatoma, as the surgery itself is challenging and has potential complications. In addition, the predictability of the final hearing result has been questioned. Improvement in the hearing threshold to 20 dB eliminates the handicap of unilateral hearing loss;6 achieving that result cannot be guaranteed. The heart of the issue lies in the ability to predict preoperatively which patients have the potential to achieve closure of the air–bone gap to within 20 to 30 dB.
Although the incidence of major complications (total sensorineural hearing loss, facial nerve paralysis, restenosis) has decreased significantly over the years, other complications (high-tone sensorineural hearing loss [SHL], tympanic membrane lateralization) have essentially remained the same. The postoperative ear must be cleaned and debrided regularly (every 6 to 12 months). The postoperative draining ear requires extra attention and cleanings along with restrictions on swimming, exercise, and moisture/water in the ear. An argument can easily be made against operating on the unilateral atretic ear, so long as the contralateral ear is in good health and functioning well.
Nevertheless, thoughtful evaluation and preparation before surgery and advances in surgical techniques have made atresia surgery results more predictable. Patients are carefully chosen for surgery on the basis of motivation, cooperation, and anatomy, as demonstrated on high-resolution computed tomography (CT) scanning. The well-healed postoperative ear is treated normally; we even allow patients to swim. Older patients who have developed presbycusis or patients who suffer hearing loss in the unaffected ear are potentially excellent candidates and may reap the rewards of surgery. Given the improved predictability of results of atresia surgery, we feel that the benefits of binaural hearing, sound localization, and improved hearing in noise outweigh the risks of surgery. In the hands of an experienced atresia surgeon, we favor atresiaplasty in the unilateral atretic ear, if the patient is motivated, cooperative, and a good candidate (minor malformations) anatomically.
Embryology
The human external auditory canal is derived from the first branchial groove. A primitive meatus is initially formed in the fifth week of gestation from an invagination of ectoderm medi-ally toward the endoderm of the first pharyngeal pouch. This primitive meatus becomes the cartilaginous ear canal. The surface ectoderm also gives rise to a core of epithelial cells called the meatal plate which extends medially toward the tympanic cavity (pharyngeal pouch). The most medial ectodermal cells of the meatal plate form the superficial layer of the tympanic membrane. A layer of mesenchymal growth between the meatal plate and pharyngeal endoderm forms the middle fibrous layer of the tympanic membrane. Pharyngeal endoderm contributes to the medial mucosal layer.
In the third month of gestation, the medial canal is formed by ossification of the tympanic bone around the core of epithelial cells. Malformation of this bone medially results in atretic bone at the tympanic membrane and atresia of the bony ear canal. Similarly, if the core of epithelial cells does not grow toward the pharyngeal groove, tympanic bone is allowed to ossify producing atretic bone. The epithelial core canalizes late in development—the seventh month. Failure of these cells to absorb can result in a normal tympanic membrane and bony canal, with an atretic or stenotic cartilaginous ear canal. In 313 patients with major congenital ear malformations, Jahrsdoerfer,1 found atresia far more common than stenosis, in a ratio of 7 : 1. Pneumatization of the mastoid bone is also a late embryologic event and continues into postnatal life. As discussed later, size of the mastoid air cell system and tympanic cleft are crucial in evaluating candidacy for atresia surgery.
The pharyngeal pouch persists medially as the tubotympanum and widens laterally to form the tympanic cavity. Interestingly, the eustachian tube generally develops normally, and patients with aural atresia have no increased incidence of eustachian tube dysfunction.6 The ossicles develop from the first and second branchial arches. The head of the malleus and body of incus are formed from Meckel’s cartilage of the first branchial arch, while the manubrium of the malleus, long process of incus, and stapes superstructure are derived from Reichert’s cartilage of the second branchial arch. The stapes footplate is a product of Reichert’s cartilage and otic capsule bone; it develops normally, and is rarely fixed in aural atresia. Ballachandra7 gives an excellent review of developmental anatomy of the outer and middle ears.
The derivation of inner ear structures including the membranous labyrinth is from the ectodermal otocyst and is completely separate from the embryology of the middle and outer ears. As a result, vestibular function and sensorineural hearing in these patients is usually normal. Inner ear abnormalities, both anatomic and functional, can exist in patients with aural atresia, however, and may be a relative contraindication to atresiaplasty.
Patient Evaluation
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