Aural Atresia 

Surgery to repair congenital aural atresia (CAA) is one of the most challenging operations the ear specialist faces. The goals of surgery are to provide the patient with a clean, skin-lined external auditory canal with long-term restoration or improvement in hearing.

In congenital aural atresia, the external auditory canal (EAC) and structures in the middle ear fail to develop completely. Development of the ear canal and middle ear may be arrested at any point in the process. Therefore, the clinician may encounter varying degrees of severity of this malformation. In the severe form of the disorder, no identifiable ear canal exists (complete atresia), and the middle ear and its structures (ossicles, or ear bones) may be absent or show significant underdevelopment. If a semblance of an external auditory meatus is present, the ear canal may end in a shallow blind pouch. In less severe forms of the disorder, the ear canal may be stenotic with a pinpoint aperture leading into the medial ear canal and, possibly, a rudimentary tympanic membrane. The tympanic membrane in these cases may or may not be attached to the ear bones (the ossicular chain).

Congenital aural atresia is commonly accompanied by microtia ("small ear"), or incomplete development of the auricle, which is also a surgical reconstructive challenge. The ear canal and auricle assume separate developmental and embryologic origins, yet the development of the auricle often mirrors that of the middle ear structures: A more developed auricle is generally accompanied by a more developed middle ear space and ossicular chain.^[1] The evaluation and care of the patient with microtia is another topic entirely and is addressed in a separate section (see the eMedicine topic Microtia).

An image depicting aural atresia can be seen below.

Our current understanding of the evaluation and management of patients with CAA stems from 3 significant advancements. First, detailed anatomic studies of the temporal bone have improved our knowledge of the sequence of events in the development of the different regions of the ear (ie, external ear, middle ear, and inner ear). Findings from these studies explain why some regions of the ear are more developed than others in patients with CAA and enhance our appreciation of the anatomical variations found in CAA.

Second, high resolution computed tomography (CT) scanning has allowed the otologist to "see" into the middle and inner ears to understand the internal anatomy. Before CT scanning, plain radiography and tomography were available, and surgeons could only surmise what the anatomy looked like inside without the ability to predict good surgical candidates.

Third, individuals such as Jahrsdoerfer, De la Cruz, and Lambert have gained vast experience in managing patients with CAA and have shared their insight into surgical candidacy, hearing restoration, surgical technique, and management of complications.

In CAA, the role of the otologist extends beyond diagnosis and treatment. The otologist must consider the hearing needs of the child, especially with regard to bilateral atresia, and must determine not only the appropriate treatment, but also the timing of that treatment. The otologist must work closely with the facial plastic surgeon to determine the optimal time for atresia repair.^[2] This decision making process usually occurs in the setting of anxious parents seeking answers as to how this deformity came about, what can be done to restore their child's hearing and appearance, and how soon treatment can be administered.

An important point to remember: Not all patients with CAA are candidates for surgical correction. Among patients with associated syndromes such as Treacher Collins or Hemifacial microsomia (HFM)/Goldenhar, approximately 50% of patients are not surgical candidates because of the existing anatomy. In isolated unilateral cases of CAA (most patients) approximately 65-75% will be surgical candidates.

For surgical candidates with favorable anatomy, the otologist must rely on the skills, techniques, and experience from middle ear and mastoid surgery to optimize the surgical result. Surgical success is based on restoration of useful hearing, long-term stability of hearing, and maintenance of a patent, skin-lined ear canal. Otologists agree that when these goals are achieved, few accomplishments are as gratifying as successfully treating a patient with CAA.

Although atresia of the external auditory canal has been recognized for over 70 years, reports of surgical repair of atresia did not surface until the late 1940s and 1950s. Nager advocated tailoring the surgical technique to open the ear canal and restore hearing to the severity of the atresia.^[3] For minor malformations (Group I; normal or stenotic canal with hypoplastic middle ear and some malformation of the ossicles), Nager described an endaural approach to widen the stenotic ear canal and address any middle ear abnormalities.

For Group II malformations (fistulous tract or complete atresia of the canal with a bony atretic plate and some degree of malformation of the middle ear structures), Nager recommended opening the mastoid to expose the lateral ossicular mass, freeing the ossicular chain, and using a split-thickness skin graft to the mucoperiosteal membrane on the undersurface of the bony atretic plate.

For more severe malformations (Group III; complete ear canal atresia with nonpneumatized mastoid and middle ear), he advised against surgery, or possibly creating a window into the lateral semicircular canal.^[3]

Schuknecht also divided aural atresia patients into 3 groups based on severity and reviewed 3 methods for surgical reconstruction: 1) creating a window into the lateral semicircular canal, 2) canaloplasty, and 3) type III tympanoplasty.^[4] In all of these, the mastoid cavity is opened to access the ossicles and middle ear space, leaving the patient at risk for postoperative drainage and other problems associated with a cavity.

Jahrsdoerfer first described the anterior approach, avoiding opening the mastoid air cells, in 1978.^[5] This approach, the standard in atresia surgery today, keeps the drilling anterior and superior by following the bone separating the ear canal from the brain and the jaw (temporomandibular) joint through the nonpneumatized bone of the atretic plate directly into the epitympanum and middle ear space. The atretic bone is carefully picked away, the ossicles are freed, and temporalis fascia is used as an eardrum graft with preservation of the native ossicular chain. Placement of a split-thickness skin graft and opening the meatus complete the procedure. With a few minor modifications, this technique is used today and continues to deliver significantly improved hearing results without a mastoid cavity and with fewer complications.

The main anatomic deformity in CAA is failure of the external ear canal to complete development. The severity of the deformity is variable. The anatomy of the ear depends on the point along the embryological pathway where development is arrested. In the most severe form of CAA (ie, when development of the ear is halted early), the ear canal cannot be identified. Bone fills the region the ear canal normally occupies, and no external opening (meatus) is present. In mild cases, the ear canal is present, but it is stenotic and markedly narrowed. A rudimentary tympanic membrane may be present, and it may or may not be connected to the ossicular chain. In these cases, the ear has developed more than in other cases.

Interestingly, the inner ear develops much earlier in the fetus than the ear canal and middle ear. In addition, the inner ear develops from a completely separate structure from the middle and outer ears. As such, most patients with CAA have normal inner ear (cochlear) function. The problem is simply that the sound energy is not being transmitted or conducted to the inner ear. Ways to improve the transmission of sound to the healthy inner ear include the bone conducting hearing aid, the BAHA system, and surgery to open the ear canal and restore the natural sound conducting mechanism to the inner ear (atresia repair or atresia surgery).

Frequency

The incidence of CAA is 1 in 10,000-20,000 live births. Unilateral CAA is more common than bilateral cases with an approximate ratio of 3-4:1. For unknown reasons, right ears are more commonly affected than left ears.

Factors that cause the developmental sequence of the ear canal and middle ear to cease in CAA are not known. Regions adjacent to the ear canal, including the jaw bone (mandible) may be affected as well. In general, the inner ear (cochlea and hearing nerve) is not affected because its development is from a completely separate set of structures from the ear canal and middle ear, and the development of the inner ear is complete by the time the ear canal begins to form. In general, the middle ear, ossicles, and the auricle are affected because their development is concurrent with that of the ear canal. Recent studies have linked mutations in chromosome 18 to some cases of aural atresia.^{[6, 7]}

Intimate knowledge of the anatomy and development of the ear is essential to understanding the clinical manifestations of CAA. The development of the ear consists of a complex series of events. The inner ear, middle ear cleft, ossicles, ear canal, and auricle each are derived from the 3 embryonic germ layers (ie, ectoderm, mesoderm, endoderm). These structures assume individual paths of growth and maturation.

Embryology of the ear

The ear canal and middle ear develop from the branchial apparatus, a series of ectodermal outpouchings (arches) and indentations (clefts/grooves) on the lateral surface of the embryo that are first clearly seen at 24 days gestation. The formation of the ear canal begins with the invagination of the first branchial groove (ie, primary meatus). This area is located between the first branchial arch rostrally (toward the head) and the second branchial arch caudally (toward the tail).

The branchial groove invaginates and advances medially as an epithelial plate as early as the second month of fetal life. Its ingrowth temporarily meets the lateral growth of the first pharyngeal pouch. The first pharyngeal pouch is derived from endoderm and subsequently develops into the middle ear cleft and Eustachian tube. The union between the ingrowth of the first branchial groove and first pharyngeal pouch forms the meatal plate, which is the precursor to the tympanic membrane. At 6 months of fetal life, the epithelial plate begins to canalize (open) from a medial to lateral direction (from the inside out) to meet the primary meatus.

At birth, the ear canal comprises the bony tympanic ring medially and a membranous cartilaginous portion laterally. Postnatally, the bony tympanic ring lengthens and transforms from a ring into a bony cylinder. Thus, the ear canal increases in length and reaches adult proportions by the age of 4-5 years.

In CAA, development of the ear may be interrupted at any point. If the process is halted before canalization of the ear canal, total atresia occurs. If development is halted during canalization, the patency of the external ear canal varies depending on how far canalization has progressed.

Development of the middle ear is closely aligned with the development of the ear canal, from the branchial apparatus. The middle ear space arises from lateral growth of the first pharyngeal pouch. The middle ear eventually envelops the ossicles and incorporates them into the middle ear space. The ossicles are derived from both first and second branchial arches, specifically Meckel and Reichert cartilages, respectively. Arrest in the development of the ear canal affects the middle ear to the extent that the growth and maturation of the middle ear will also be incomplete, and the middle ear space is contracted. The ossicular chain is usually deformed, typically featuring a fused malleus-incus complex, shortened malleus, and occasionally, hypoplastic stapes suprastructure. The malleus neck may be fused to the bony atretic plate. In cases of complete atresia, the tympanic membrane is absent.

The inner ear begins development as early as the third week of fetal life with the formation of the otic placode, a local thickening of the ectoderm. The otic placode invaginates to form the otic pit. The epithelium of the otic pit fuses to become the otic vesicle, which forms the membranous labyrinth of the inner ear. A series of infoldings of the otic vesicle compartmentalizes the membranous labyrinth into the vestibule, cochlea, and endolymphatic regions. The inner ear completes its development by the 20th week of fetal life, which predates the formation of the ear canal and explains why patients with CAA generally have a cochlea that is functional and able to be stimulated.

CAA commonly coexists with microtia. However, rarely, CAA may occur alone with an auricle that appears healthy. The embryologic precursors of the auricle are the axonal hillocks, a series of ectodermal elevations derived from the first and second branchial arches located along the rostral end of the branchial apparatus. The axonal hillocks fuse with each other around the primitive ear canal. Each of the 6 hillocks is responsible for forming a distinctive part of the auricle. Hillock 1 forms the tragus; hillock 2 forms the crus helicis; hillock 3 forms the helix; hillock 4 forms the antihelix; hillock 5 forms the antitragus; and hillock 6 forms the ear lobule. The auricle assumes adult shape (but not size) by the 20th week of fetal life. Microtia ("small ear") results when the development of these hillocks is arrested. In general, the middle ear is less developed when microtia is severe than when it is not.^[1]

The patient with CAA may present with unilateral or bilateral atresia. If the deformity is present in both ears, the severity of the deformity may vary between the ears. Hearing evaluation and hearing rehabilitation, generally with a bone conducting hearing aid, is critical early in life in children with bilateral CAA.

Colman graded the severity of CAA into 3 categories: minor, moderate, and severe. Patients with severe CAA have total canal atresia and usually present with unfavorable middle ear anatomy and temporal bone development for reconstruction. In comparison, patients with moderate CAA have more favorable anatomy (ie, an identifiable ear canal with deformed ossicles and an aerated middle ear space). Most patients with CAA present with this moderate form. In minor cases, the ear canal is present but narrowed, and the middle ear is better developed.

CAA may coexist with syndromes that feature first and second branchial arch deformities (eg, Treacher-Collins syndrome, hemifacial microsomia, Goldenhar syndrome, and other craniofacial abnormalities).

The patient with CAA may present to the otologist in any of the scenarios discussed next.

Detection at birth

If the anatomic abnormality is detected at birth, the otologist meets the newborn and parents in consultation. The parents are usually anxious and eager to have their many questions answered. Reassurance and parent education are critical during this time. Regardless of whether this condition is present in 1 or both ears, cochlear function must be assessed in both ears by means of specialized audiologic testing, such as auditory-evoked brainstem responses (ABR or BAER testing) elicited from both air-conducted and bone-conducted signals. If bilateral CAA and good cochlear function are present, the infant needs amplification with a bone-conducting hearing aid (eg, BAHA Softband) until a decision is made to pursue surgical correction just before the child starts school.

Amplification is generally not recommended in children with unilateral CAA as long as the contralateral ear functions well. This recommendation may change as researchers are discovering some of the more subtle problems associated with unilateral hearing loss, especially in school-age children.^[8] In general, normal hearing in one ear is enough hearing to support normal speech and language development.

Detection in the older child just before microtia repair

The otologist may encounter the older child with unilateral CAA before a plastic surgeon repairs microtia. In these patients, coordination of care between the plastic surgeon and otologist are important to delineate a clear surgical plan and schedule to prevent confusion and unrealistic expectations.^[2] Using the patient's own rib ("autologous"), the plastic surgeon sculpts an auricle and pockets it under the skin, moves the lobule, elevates the sculpted rib off the skull with a skin graft, and creates a tragus in a multistage (3-4 operations over a one year period) procedure. The otologist opens the new ear canal, frees the ossicular chain so the ear bones can vibrate, constructs a tympanic membrane, lines the ear canal with a skin graft, and opens the meatus in continuity with the new ear canal in a single stage procedure.

A porous polyethylene implant (Medpor) has recently been established as a viable means of reconstructing the auricle. No long-term data have been published on the durability of this implant. The implant in the setting of atresia can be problematic if the atresia repair is performed after the implant has been placed. In these cases, the implant is at risk for exposure, infection, and extrusion. Anecdotally, some patients have undergone atresia repair before Medpor implantation with some success. Revision atresia repair in these patients again puts the Medpor implant at risk.

Clinical picture with canal stenosis

A child with canal stenosis (mild atresia) may present to the clinician with or without associated hearing loss in the ear. These patients with narrowed canals (generally less than 2 mm are at risk of canal cholesteatoma.^[9] Cholesteatoma is a pocket or cyst of skin that grows and expands as dead skin cells fill the cyst. Careful observation, follow-up, and microscopic examination and cleaning may ensure the patient does not develop a canal cholesteatoma. However, when the opening to the ear canal is too small to permit examination or when the patient's history (eg, otorrhea, otalgia) suggests a cholesteatoma, radiographic imaging with CT scanning is used to evaluate the possibility of a canal cholesteatoma CT scan image of a patient with canal cholesteatoma is seen below.

Children with canals 2 mm or smaller in diameter develop canal cholesteatoma more frequently than do other children. In addition, canal cholesteatomas are rarely, if ever, observed to occur in children younger than 3 years. Cole and Jahrsdoerfer reported these findings and noted that 50% of 54 stenotic ears with canals smaller than 4 mm developed canal cholesteatoma.^[9] Clinicians should readily incorporate CT scanning into their diagnostic workup to ensure that no canal cholesteatoma, medial to the stenosis, is present.

Clinical picture in the adult with CAA

Adults with CAA who present to the otologist usually have a unilateral condition that was not corrected in childhood. In some patients, the condition was unnoticed, especially in those with stenotic ears. If it was noticed, the patients may have been told that their condition was inoperable or too risky to repair in light of possible facial nerve injury. This is especially true if the contralateral ear was morphologically and functionally normal. In this situation, the patient may make an informed decision to proceed with an evaluation for surgery with the hopes of obtaining binaural hearing.

Before surgical correction is considered, the patient must fulfill 2 criteria. First, the patient with congenital aural atresia (CAA) must have normal cochlear function, as demonstrated on audiologic examination and normal bone conduction thresholds in the atretic ear. Second, CT scanning must demonstrate normal inner ear and internal auditory canal morphology.

If patients meet these criteria, the next step is to identify patients with favorable anatomy who have a reasonable chance of success with surgical correction. Jahrsdoerfer devised a 10-point grading scheme, based on features from the CT scan and appearance of the external ear, that reflects the likelihood of success (see Imaging Studies).^[10] Patients who have a score of 7 or higher are good candidates for surgery. Patients must also be motivated to undergo the surgery and postoperative care and must be willing to have the ear cleaned of dead skin once or twice a year for the rest of their lives.

Numerous studies now show that in patients with favorable anatomy, repair of unilateral CAA is a viable and successful undertaking.^{[11, 12]}

Critical assessment of the anatomy is necessary in the evaluation and treatment of the patient with congenital aural atresia (CAA). Even if surgical correction is not sought, the otologist must understand the patient's anatomy and be able to assess the CT scan to explain the nature of the deformity to the parents or patient. Each case of CAA is different.

The relevant anatomy includes the patency (or lack thereof) of the ear canal. In the absence of an ear canal, the atretic plate is the bony region just lateral to the middle ear space. Assessment of the middle ear space should include the appearance of each of the 3 ossicles and the incudostapedial joint and the position and course of the facial nerve through all of its segments. The course of the facial nerve is often aberrant in CAA, as the nerve typically courses more anterior and lateral in its proximal mastoid segment just after the second genu.

In addition, the second genu takes a more acute bend than normal. Patency of the round and oval windows must be ensured. The otologist should evaluate the size and pneumatization of the middle ear cavity and mastoid. Relationship to the jaw joint is also important to determine the amount of room for drilling the ear canal. The position of the tegmen is important, as the "roof" of the ear may hang down too far inferior to open an ear canal Very low tegmen is seen in the image below. The morphology of the inner ear is also evaluated for concurrent inner ear dysplasia.

An absolute contraindication to surgical correction of congenital aural atresia (CAA) is lack of cochlear function in the involved ear as evidenced by repeated audiologic examination. CT scan may reveal a dysplastic or aplastic inner ear (rare). Surgical correction of CAA is pointless if the patient has no cochlear function. However, if microtia is present, reconstruction of the auricle may be undertaken for cosmetic purposes.

Lack of middle ear aeration is another contraindication to surgery. Without an air space, the ossicles cannot vibrate, and the sound conducting mechanism of the middle ear will not be restored.

The tegmen is the bone that separates the brain from the ear. If the tegmen hangs too low, not enough space exists to open an ear canal; brain injury is a risk during the drilling. The patient is not a candidate for atresia surgery (see the image below).

Although some authors have advocated transposition of the facial nerve in some situations, a facial nerve coursing over the oval window or in direct line of canal drilling would be a relative contraindication.^[13]