External Ear Aural Atresia

Etiology

Acquired aural atresia, although rare, usually occurs following external ear trauma, such as motor vehicle collisions, gunshot wounds, radiation therapy, or otologic surgery.[6][7][8] Canal stenosis and atresia are also associated with neoplasms and idiopathic inflammation.[9] Conversely, the causes of congenital aural atresia are often multifactorial. Several defined syndromes are associated with ear malformations, but most cases are idiopathic.[10] Atresia results from a disruption of normal embryonic development, beginning as early as the sixth week of gestation.[4] This disruption affects the development of the first pharyngeal cleft, from which the external auditory canal develops. The malformation can occur sporadically but is usually associated with conditions such as Goldenhar, Treacher Collins, and Crouzon syndromes. The etiology of Goldenhar syndrome remains unknown; however, an early vascular insult to the stapedial artery, which supplies the first and second pharyngeal arches, is a potential cause.

In this condition, the right ear is most commonly affected, and the patient may present with orbital, mandibular, vertebral, or other extracraniofacial manifestations.[11] Goldenhar syndrome has an autosomal dominant or recessive inheritance pattern, indicating multiple genetic abnormalities.[12][13] Treacher Collins syndrome is caused by a mutation in the TCOF1 gene and is associated with aural atresia. The TCOF1 gene regulates early craniofacial development, including the formation of the first and second pharyngeal arches. Crouzon syndrome is caused by a mutation in the FGFR2 or FGFR3 gene on chromosome 10 and is inherited in an autosomal dominant manner, often resulting in craniosynostosis and occasionally aural atresia.[14] Aural atresia may also be a component of Möbius, Klippel-Feil, Fanconi, DiGeorge, and Pierre Robin syndromes.[15] However, the distal 18q22.3 deletion is the only known genetic cause of congenital aural atresia, presenting with normal auricles, bilateral complete aural atresia, and other characteristic craniofacial abnormalities.[15] Several risk factors have also been identified, including maternal isotretinoin or thalidomide use, vascular insults due to maternal cocaine use, and maternal diabetes.[16]

Epidemiology

Congenital aural atresia occurs in 1 out of 10,000 to 20,000 births. The condition is usually unilateral, often right-sided, and is 2.5 times more common in men than women.[16] Microtia may be associated with atresia, and the severity of the deformity may correlate with concomitant middle or inner ear deformities.[4] Children with unilateral aural atresia typically experience normal speech development if the other ear remains unaffected. Patients usually have normal hearing and ear development in the unaffected ear.

However, patients are at increased risk of delayed language development due to functional monaural hearing, and early identification of this is essential. Normal language development is supported through preferential positioning, speaking toward the unaffected ear, and preferential classroom seating that directs the unaffected ear towards the teacher. Contralateral routing of signal hearing aids can also be considered.[17]

Pathophysiology

Understanding the embryological development of the human ear to comprehend the pathogenesis of congenital aural atresia, whether it occurs in isolation or in conjunction with other craniofacial abnormalities, is essential. The external ear develops from the first and second pharyngeal arches and the first pharyngeal cleft.[15] The auricle begins to develop during the sixth week of gestation. The 6 hillocks of His are small buds of mesenchyme arising from the first and second pharyngeal arches. Each hillock contributes to the formation of a corresponding structure of the auricle.[16] Additionally, the first pharyngeal arch develops into the malleus, incus, mandible, and the muscles of mastication. In contrast, the second pharyngeal arch develops into the stapes, stapedius, and muscles of facial expression.[18] 

During the fourth week of gestation, the external auditory canal arises from the first pharyngeal cleft (or groove). This ectodermal structure migrates towards the endoderm of the pharyngeal pouch until the mesoderm interrupts.[18] This migration creates the 3 layers of the tympanic membrane. By the eighth week, the concha cavum of the auricle invaginates inward, forming the outer fibrocartilaginous portion of the external auditory canal.[16] At this time, an epithelial plug fills the canal, and by the 28th week, medial-to-lateral recanalization occurs, resulting in a patent external auditory canal. [18] Furthermore, an atretic external ear canal may be associated with microtia or congenital cholesteatoma due to aberrant interactions between the pharyngeal arches and clefts.[19] Similarly, other pharyngeal arch abnormalities may include mandibular hypoplasia, cleft palate, profound hearing loss, and, in some cases, airway compromise.

The pathophysiology of acquired canal atresia is less well understood. Traumatic acquired atresia develops when circumferential scarring leads to narrowing and eventual obliteration of the canal lumen via scar contracture. Circumferential contraction of scar tissue progressively narrows the lumen, producing stenosis.[20]  Idiopathic acquired stenosis is thought to result from underlying canal skin or soft tissue inflammation, leading to repeated scar contracture and stenosis.[21] This inflammatory process is also the proposed mechanism for radiation-induced stenosis.[6]

History and Physical

Acquired aural atresia typically presents with progressive conductive hearing loss and a visible narrowing of the external auditory canal (EAC). A thorough physical examination is necessary to evaluate local causes of inflammation contributing to canal stenosis or fibrosis. A history of recent trauma, recurrent otitis media, or otologic surgery may suggest the diagnosis and underlying etiology. Without these external factors, idiopathic constriction of the EAC due to rheumatologic or autoimmune conditions should be considered.[9]

Clinical signs of congenital aural atresia may be evident during the first few days after birth. Initial evaluation requires a thorough examination of the external ear and other craniofacial structures, including the mandible, oral cavity, spine, and eyes, as well as assessment of facial nerve function.[4] The most common findings include an underdeveloped ear, which may appear as a small auricle or absent pinna. The external auditory canal may be stenotic, shortened, or absent. Examination should also include evaluation of extracranial structures. Any newborn with abnormal hearing screening results should be evaluated for EAC patency. Because this examination can be challenging in newborns, prompt referral to a pediatric otolaryngologist is warranted when abnormalities are identified.

Evaluation

Every infant with an ear deformity should undergo hearing diagnostics within the first few months of life. Auditory brainstem response testing is typically the first step in evaluating unilateral or bilateral aural atresia, as both conductive and sensorineural hearing loss may be present. Although conductive hearing loss accounts for up to 90% of the hearing loss, approximately 15% of cases involve sensorineural hearing loss.[16] If the hearing test result in the unaffected ear is normal, speech and language development generally progress appropriately, and additional testing may be deferred until the child is 6 months old. However, thorough repeat examination and prompt treatment of middle ear effusion are critical to preserving hearing in the unaffected ear.[16] 

An abnormal hearing test result should prompt auditory brainstem response testing to ensure the normal function of at least one ear and to support normal language development. Genetic testing may also be warranted in patients with possible genetic syndromes. A temporal bone computed tomography scan is generally not indicated until age 5 or when surgery is planned. The Jahrsdoerfer grading scale is a tool that can assess the need for surgical intervention. The scale ranges from 0 to 10, and 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. [22]

Treatment / Management

The gold standard treatment for acquired aural atresia is surgical repair. However, management during the early stages, or the "wet phase," is controversial. Some otologists recommend antibiotic and anti-inflammatory therapy, whereas others argue that delayed surgical intervention worsens medial canal fibrosis.[23][24] Close follow-up is essential, regardless of the approach, to prevent complications.[25] The laterality of the condition, the hearing status, the cosmetic needs, and the feasibility of hearing restoration determine the type of intervention. Bilateral aural atresia presents with abnormal audiological testing and typically requires early use of bone conduction hearing aids. However, recent studies emphasize that unilateral aural atresia may impact academic performance; thus, the decision to use a hearing aid remains controversial.[26]  In locations where hearing aids are widely available, they can significantly improve hearing and should be obtained as early as possible. The auditory benefits of hearing aids are well-documented, but in locations where hearing aids must be privately purchased, the costs may outweigh the potential benefits.[27] These patients may require close observation by teachers and speech therapists to ensure normal speech and language development. Repeat hearing testing and medical examinations every 6 to 12 months help ensure hearing preservation in the normal-hearing ear. Aggressive treatment for otitis media or effusion prevents further deterioration. (A1)

In cases of microtia associated with atresia, the timing of canal repair must be coordinated with the reconstruction of the pinna. There are no definitive guidelines, and hearing restoration takes precedence over cosmesis. Many surgeons advocate for canal atresia repair before pinna reconstruction. In contrast, others recommend a bone-conduction hearing aid until the child is old enough to undergo multistage atresia and pinna repair.[28] Rib cartilage is typically used for microtia repair after age 5 or 6, when the contralateral ear has reached more than 85% of its adult size. For this reason, alloplastic repair, such as Medpor, is often postponed until this age to maximize auricular symmetry.[29] Surgical intervention should be timed appropriately with the school schedule and developmental stage to minimize psychological complications. Before undergoing surgical repair, patients often benefit from bone-conduction hearing aids.[30] The preferred age for surgical intervention in bilateral aural atresia is around 5 or 6 years. One reason is to allow maturation of the eustachian tube and the pneumatization of the temporal bone, thereby reducing the risk of complications in the middle ear. Another reason is to allow improved understanding of and compliance with postoperative care.[31] An exception is the presence of an external canal cholesteatoma, a known complication that can result in irreversible damage to the middle ear and requires earlier intervention.[32] 

In unilateral cases, several factors must be considered, including speech, language, and academic development, as well as the child's maturity level and hearing ability in the contralateral ear. With a normally developed contralateral ear, some clinicians delay surgery until adolescence, when the patient has the maturity to choose between atresiaplasty and bone-anchored hearing aids. Surgical approaches vary. For example, lateral atresia is often repaired with a meatoplasty, whereas more medial atresia is repaired with a canalplasty. The decision to undergo atresiaplasty is guided by the Jahrsdoerfer grading scale, which assigns points for the presence of various anatomic features.[33] Higher scores correlate with improved audiometric outcomes. Study results show that patients with a score of 7 or higher (out of 10) have up to a 90% chance of achieving near-normal hearing after atresia surgery. In contrast, patients with a score of 6 or lower have a 40% chance of attaining near-normal hearing after atresia surgery.[28] A Jahrsdoerfer score of less than 5 indicates poor candidacy for atresiaplasty. The benefits of surgery over hearing aids include improved sound localization and the ability to differentiate speech from background noise.[34](B3)

Differential Diagnosis

The differential diagnosis includes congenital aural stenosis, characterized by the narrowing of the external auditory canal. Congenital aural atresia is classified as either nonsyndromic or syndromic. Most cases are due to nonsyndromic causes of unknown etiology. Goldenhar syndrome, also known as oculoauriculovertebral dysplasia or hemifacial microsomia, is one of the most common syndromes associated with aural atresia.[35] This syndrome results from injury to the stapedial artery, affecting the first and second pharyngeal arches. Clinical manifestations include craniofacial, cardiac, renal, vertebral, and neurologic abnormalities. Goldenhar syndrome is usually sporadic but can rarely be inherited in an autosomal dominant pattern.[36] 

Treacher Collins syndrome is a rare autosomal dominant disorder caused by neural crest dysfunction. This syndrome is characterized by zygomatic bone and mandibular hypoplasia, hearing loss, and airway compromise.[37] Assessment for craniofacial abnormalities has significant implications for diagnosis and anesthetic management, particularly in preventing perioperative airway obstruction. Crouzon syndrome, caused by mutations in FGFR2 or FGFR3, is characterized by craniosynostosis, hypertelorism, proptosis, a flattened forehead, a beaked nose, midface hypoplasia, and occasionally aural atresia. Patients with Möbius, Klippel-Feil, Fanconi, DiGeorge, De Grouchy, branchio-oto-renal, and Pierre Robin syndromes may also present with aural atresia.[16][38]

Prognosis

Prognosis for both acquired and congenital aural atresia varies based on the severity and associated malformations. In most cases, the overall prognosis is favorable.[39] Complete or near-complete canal atresia produces hearing loss at a threshold of 40 to 60 dB, nearing maximal conductive hearing loss.[16] The mean postoperative threshold is 25 to 35 dB, representing mild hearing loss with improved sound localization and background differentiation.[22] Thus, children can experience appropriate hearing and speech development with timely intervention; however, their hearing may never reach the level of an anatomically normal ear. Moreover, the rate of restenosis after repair is nearly 40%, depending on the etiology of the atresia.[40] 

Acquired, nonautoimmune atresia has the best prognosis. Conversely, congenital atresia associated with superimposed autoimmune or genetic conditions has the worst prognosis. If congenital atresia is complicated by cholesteatoma, surgical repair is warranted; otherwise, bone-conduction hearing aids are required 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 into the middle ear and require surgical intervention.[41] The most common 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%).[16] Other complications include taste disturbance, sensorineural or conductive hearing loss, infection, and vertigo.