External Ear Aural Atresia

Etiology

Acquired aural atresia, although rare, is most often seen following external ear trauma, such as motor vehicle accidents, gunshot wounds, or otologic surgery. In rare instances, canal stenosis and atresia have been described in the setting of neoplastic changes and idiopathic inflammatory processes.[4] The exact cause of congenital aural atresia is often multifactorial. Several defined syndromes are associated with ear malformations, but most cases are idiopathic. It ultimately results from disruption of the normal embryological development beginning as early as the sixth week of gestation.[2] This disruption affects the development of the first pharyngeal cleft, which is responsible for the development of the external auditory canal. Most often, this disruption occurs randomly, but it is related to several syndromes, including Goldenhar, Treacher Collins, and Crouzon. The etiology of Goldenhar syndrome is unknown; however, the most widely accepted theory is an early vascular insult to the stapedial artery, which is responsible for the development of the first and second pharyngeal arches. In this condition, the affected ear most commonly occurs on the right and may present with orbital, mandibular, vertebral, or other extra-craniofacial features.[5] 

It may also demonstrate an autosomal dominant or recessive inheritance pattern, suggesting multiple genetic aberrations as potential causes. Treacher-Collins syndrome is commonly caused by a TCOF1 gene mutation and is associated with aural atresia. The TCOF1 gene involves various aspects of early craniofacial development, including the first and second pharyngeal arches. Crouzon syndrome is caused by an FGFR2 or FGFR3 mutation on chromosome 10. It is inherited in an autosomal dominant syndrome fashion, often causing craniosynostosis and occasionally causing aural atresia.[6] Aural atresia may also be seen in Mobius, Klippel-Feil, Fanconi, DiGeorge, and Pierre Robin syndromes.[7] However, the distal 18q22.3 deletion is the only known, isolated genetic cause of congenital aural atresia, presenting with normal auricles and bilateral complete aural atresia and other characteristic craniofacial abnormalities.[7] Several external risk factors have also been identified. These include maternal isotretinoin use, maternal thalidomide use, vascular insults often due to maternal cocaine abuse, and maternal diabetes.[8]

Epidemiology

Congenital aural atresia occurs in 1 of 10,000 to 20,000 births. It is unilateral in most cases, with an unexplained predilection for the right ear in some studies, and is 2.5 times more likely to affect males than females.[8] It is often associated with varying degrees of microtia, which may correlate to the extent of concomitant middle ear deformity.[2] Children with unilateral aural atresia typically have normal speech development so long as the other ear is unaffected and typically have normal hearing and ear development in the unaffected ear. They are at increased risk of delayed language development due to functional mono-aural hearing, and early identification of this is essential. Normal language development is fostered via preferential positioning/speaking into the unaffected ear and preferential school seating placement of the child to facilitate the unaffected ear being directed towards the teacher.[9]

Pathophysiology

It is essential to understand the embryological development of the human ear to understand the pathogenesis of congenital aural atresia, whether in isolation or conjunction with other craniofacial abnormalities. The external ear collectively develops from contributions of the first and second pharyngeal arches and the first pharyngeal cleft.[7] The auricular portion of the external ear begins to develop during week 6 of gestation. The 6 hillocks of His are 6 small buds of mesenchyme, which arise from the first and second pharyngeal arches. Each of these 6 hillocks is believed to be responsible for developing a portion of the auricle.[8] In addition, the first pharyngeal arch is responsible for the development of the malleus, incus, mandible, and muscles of mastication; the second pharyngeal arch is responsible for the stapes, stapedius, and muscles of facial expression.[10] 

During the fourth week of gestation, the external auditory canal portion of the external ear begins to arise from the first pharyngeal cleft (or groove). This ectodermal structure begins to migrate towards the pharyngeal pouch endoderm until it is interrupted by mesoderm.[10] This migration is ultimately responsible for developing the 3 layers in the tympanic membrane. At week 8, The concha cavum of the auricle invaginates inward, forming the outer fibrocartilaginous portion of the external auditory canal.[8] At this time, an epithelial plug fills the canal, and by week 28, a true canal forms with the recanalization of the external auditory canal in a medial-to-lateral direction.[10] As evidenced by the intricate orchestration of the embryologic derivatives, an atretic external ear canal can also present with microtia through aberrant interactions of the pharyngeal arches and clefts. Similarly, other pharyngeal arch abnormalities may be present, such as mandibular hypoplasia, cleft palate, profound hearing loss, and, in some cases, airway compromise.

History and Physical

Acquired aural atresia is typically identified in progressive, conductive hearing loss and a visible narrowing of the EAC. A thorough physical exam is required to evaluate for local causes of inflammation contributing to canal stenosis or fibrosis. A history of recent trauma, recurrent outer ear infections, or otologic surgery often suggests the diagnosis and underlying etiology. Without these external factors, idiopathic constriction of the EAC should be investigated as a potential rheumatologic/autoimmune condition.[4]

Clinical suspicion for congenital aural atresia may begin during the first few days of life in a newborn. Initial evaluation requires thoroughly examining the external ear and other craniofacial features such as the mandible, oral cavity, spine, eyes, and facial nerve function.[2] The most common findings include an underdeveloped ear, which may appear as a small auricle or absent pinna. An external auditory canal may be stenotic, shortened, or absent. Evaluation of extra-cranial features should also be included in the examination. Any child who fails their newborn hearing screening should be more thoroughly investigated to ensure the patency of the EACs. This can be a challenging examination to perform on a newborn, and prompt referral to a pediatric otolaryngologist is therefore warranted if there is any concern.

Evaluation

Every child with an ear deformity should have comprehensive hearing diagnostics within the first few months of life. Auditory brainstem response testing is generally the first step in evaluating patients with unilateral or bilateral aural atresia because both conductive and sensorineural hearing loss may be present in either ear. Although conductive hearing loss accounts for up to 90% of the hearing loss, up to 15% of cases may have sensorineural hearing loss requiring further workup.[8] If the hearing test in the unaffected ear is normal, speech and language development occurs normally, and further testing can be delayed until 6 months of age. However, thorough routine examination and prompt treatment of middle ear effusion are critical to preserving normal hearing in the unaffected ear.[8] 

An otherwise abnormal hearing test requires auditory brainstem response testing to ensure the normal function of at least 1 ear and allow for normal language development. Genetic testing may also be warranted in suspected syndromic patients. A temporal bone computed tomography scan is generally not indicated in the initial workup until age 5 or unless surgery is warranted, as suggested by the Jahrsdoerfer grading scale. The Jahrsdoerfer grading scale attributes 2 points for the presence of a stapes bone and 1 point each for the presence of an open oval window, middle ear space, facial nerve, malleus-incus complex, mastoid pneumatization, incus-stapes connection, round window, and external ear. There are 10 possible points.[11]

Treatment / Management

The gold standard treatment for acquired aural atresia is surgical repair. However, management during the early stages is controversial. Some otologists recommend antibiotic/anti-inflammatory treatment, while others argue that delayed surgical intervention results in the progression of medial canal fibrosis. Extremely close clinical follow-up is essential, regardless.[12] Intervention for congenital forms is driven by the laterality of the condition, the hearing status, the cosmetic desires, and the feasibility of hearing restoration. Bilateral aural atresia presents with failed audiological testing and requires early bone conduction hearing aids. However, recent studies have shown that unilateral aural atresia may have some bearing on academic performance; thus, the decision to place a hearing aid is controversial. Financial constraints complicate this; in locations where such hearing aids are widely available, the answer is clear: they maximize the patient's hearing status and should be obtained as early as possible. The auditory benefits are clear, but it is very situation-dependent in locations where these hearing aids must be privately purchased, as the costs to the family of such a hearing aid must outweigh the potential benefits for the child.[13] These patients may require close observation by teachers and speech therapists to ensure normal speech and language progression. A routine medical examination is recommended, with repeat hearing testing every 6 to 12 months to ensure hearing preservation in the normal hearing ear. Aggressive treatment for a middle ear infection or effusion is warranted. (B2)

In the setting of microtia-atresia, the timing of canal atresia repair must be coordinated with pinna reconstruction. There are no definite guidelines, and hearing restoration trumps cosmesis. Many surgeons advocate for canal atresia repair before pinna reconstruction/creation. In contrast, others advocate for a bone-conduction hearing aid until the child is old enough to undergo multi-staged atresia and pinna repair.[14] Rib cartilage is typically not used for grafting/microtia repair until 5 or 6 years, as the contralateral ear has now reached >85% of its adult size. For this reason, alloplastic repair, such as Medpor, is often postponed until this age to maximize auricular symmetry. This needs to be timed appropriately with school and maturation to minimize psychological anguish. Before surgical repair, patients benefit from bone-conducting hearing aids. The preferred age of surgical intervention for bilateral aural atresia is around 5 or 6 years of age for several reasons. One reason is to allow maturation of the eustachian tube and pneumatization of the temporal bone to prevent complications of the middle ear. Another reason is improved patient understanding and compliance with postoperative management.[15] An exception to this age is the development of an external canal cholesteatoma, a known complication that can result in irreversible damage to the middle ear.[16] 

In unilateral cases, many factors need to be considered, including the child's speech, language, academic development, maturity level, and hearing ability in the contralateral ear. With a normal hearing contralateral ear, some delay surgery until the patient is of adolescent age and can partake in the decision for surgery, which includes atresiaplasty versus bone-anchored hearing aids. Surgically, there are different types of atresiaplasty. Lateral atresia is often repaired with a meatoplasty, and a more medial atresia is repaired with a canalplasty. The decision to undergo surgical repair atresiaplasty is based on the Jahrsdoerfer grading scale, which assigns points for the presence of various anatomical features.[17]  Higher scores are related to better audiometric outcomes. Some studies have shown that patients with a score of 7/10 or greater had up to a 90% chance of achieving near-normal hearing with atresia surgery. In contrast, patients with a score of 6/10 or less had a 40% chance of attaining near-normal hearing with atresia surgery.[14] A Jahrsdoerfer score of less than 5 suggests poor candidacy for atresiaplasty. The benefits of surgery over the continuing use of hearing aids include improved sound localization and better hearing in background noise.(B3)

Differential Diagnosis

The differential diagnosis includes congenital aural stenosis and the narrowing of the external auditory canal. For congenital aural atresia, it can be characterized as nonsyndromic versus syndromic. Most cases are due to unknown, nonsyndromic causes. Goldenhar syndrome, known as oculoauriculovertebral dysplasia or hemifacial microsomia, is among the most common syndromes associated with aural atresia. It is believed to be caused by stapedial artery injury, affecting the first and second pharyngeal arch. Clinical manifestations include craniofacial, cardiac, renal, vertebral, and neurological abnormalities, often following an autosomal inheritance pattern.[18] 

Treacher-Collins syndrome is a rare autosomal dominant neural crest dysfunction leading to zygomatic bone and mandibular hypoplasia, hearing loss, and airway compromise.[19] Assessment for craniofacial abnormalities has important implications in diagnosis and anesthetic management, particularly for perioperative airway obstruction. Crouzon is caused by an FGFR2 or FGFR3 mutation that leads to craniosynostosis, hypertelorism, proptosis, a flattened forehead, a beaked nose, midface hypoplasia, and occasionally aural atresia. Aural atresia may also be seen in Mobius, Klippel-Feil, Fanconi, DiGeorge, De Grouchy, branchio-oto-renal syndrome, and Pierre Robin syndromes.[8][20]

Prognosis

Determining prognosis for both acquired and congenital aural atresia is challenging as it depends on the severity of the condition and associated abnormalities. In a majority of cases, the overall prognosis is favorable.[21] Hearing loss in aural atresia is expected to be at a threshold of 40 to 60 dB, approaching maximal conductive loss given a total or near-total canal atresia.[8] The mean postoperative threshold is 25 to 35 dB, categorized as mild hearing loss with improved sound localization and background differentiation.[11] Thus, children can develop appropriate hearing and speech with timely intervention; however, the hearing may never be at the level of normally developed ears. A significant rate of re-stenosis of a repaired atretic canal is approaching 40%.[22] This depends on the initial cause of the atresia/stenosis. Acquired atresia that is non-autoimmune has the best long-term results. Congenital atresia in the setting of concurrent autoimmune or genetic conditions carries the worst prognosis. It may be better treated with surgery solely to eliminate cholesteatoma but with bone-conduction hearing aids for hearing restoration.

Complications

Complications of untreated congenital aural atresia include delayed language development and severe learning disabilities. Patients with stenotic ear canals are also at increased risk of external canal cholesteatomas, which can erode through the middle ear and thus require surgical intervention.[23] The most common postoperative complications of aural atresia repair include lateralization of the tympanic membrane graft (25%), restenosis of the canal (8%), temporomandibular joint dysfunction (2%), and facial nerve paralysis (1%).[8] Other complications include taste disturbance, sensorineural hearing loss, conductive hearing loss, infection, and vertigo.