Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature. Congenital Aural Atresia The first mention of attempts to surgically correct congenital aural atresia was made by Thomson in 1843 in England. Although 2 out of the three cases were aborted when a thick atresia plate was encountered, a third record documented what was presumably a tympanic membrane, although it appears that stenosis became a problem postoperatively. In 1883, Kiesselbach attempted an atresia repair on a child that resulted in facial paralysis. It was not until 1947 and the work of Pattee and Ombredonne that a significant improvement in hearing could be obtained with surgery. Pattee reported that fixation of the stapes via the lateral chain to the atresia plate was responsible for these patients' deficits. Ombredonne devised an approach through the mastoid in order to fenestrate the lateral semicircular canal, with reportedly good hearing results. Using Wullstein and Zollner's tympanoplasty techniques, Bellucci reported a 30 decibel gain in hearing level in 50% of his cases. Shambaugh, in 1967, recommended surgery in unilateral cases only if the cochlear reserve allowed hearing improvement to approach that of the normal ear by 25dB. Several studies by Gill, Naumann and Schuknecht reported their individual experiences adding minor variations to the basic transmastoid approach. With the advent of polytomography and subsequently, computed tomography, finer detail of middle and inner ear structures could be obtained and used to select patients for surgery. Jahrsdoerfer, in 1978, reported the first large series using the anterior approach for congenital aural atresia repair, whereby the middle ear cavity was entered directly via a newly-created external canal without performing a mastoidectomy. An appreciation of the events that occur during embryogenesis with regard to the inner, middle and external ear is requisite to understanding the trends that occur in atresia. The inner ear, including all of the components of the membranous labyrinth, develops from an invagination of ectoderm, the otic placode, at approximately 3 week's gestation, and achieves adult dimensions at midterm. Further elaboration on inner ear development and abnormality is the subject of Congenital Sensorineural Hearing Loss. The middle ear space, including the mastoid air cell system, the Eustachian tube and the inner surface of the tympanic membrane derive from endoderm of the first pharyngeal pouch. Most of these elements complete their development by the 30th week, excepting the mastoid system in which pneumatization can progress well into adulthood. Due to the late development of the mastoid system, several authors have pointed out that patients with atresia who maintain a well-developed mastoid generally manifest greater development of their middle ear space and ossicles, thus making them better surgical candidates. Ossicular development, which progresses from the 8th through the 26th week, derives from the mesoderm of the first and second branchial arches. The malleus head and body and the short process of the incus arise from the first branchial arch (Meckel's) cartilages. Second branchial (Hyoid) arch derivatives include the manubrium of the malleus, the long process of the incus and the stapes superstructure. The footplate derives from both the second arch and the lamina stapedialis of the otic capsule. Ossification occurs through endochondral bone growth. Release of the ossicles except at their ligamentous attachments occurs by endodermal resorption as it gives rise to the tympanic cavity. Ectoderm of the first branchial cleft gives rise to the external auditory canal, which develops as an invagination at the site of the future auricle at the fourth gestational week. By the eighth week, a solid core of epithelium arises and extends to the area of the middle ear space, separated from it by a thin layer of mesoderm. At approximately 28 weeks, this core begins to recanalize from medial to lateral until the surface ectoderm is reached giving rise to the external auditory canal. At its medial extent, ectoderm persists as the outermost layer of the TM, with the mesodermal layer reduced to a fibrous sheet interposed between outer ectoderm and inner cuboidal endoderm. Mesoderm from the tympanic ring serves as the primary impetus for the formation of the tympanic bone and the osseous portion of the external auditory canal, starting at about the 12th week. Finally, the auricle is the result of the fusion of six hillocks (His) from the first and second branchial arches, which is usually complete by the 12th week as well. Malformations are graded I through III, with Grade I manifesting as a small, but well-formed auricle; Grade II representing a recognizable auricle with varying degrees of anomaly; and Grade III, which describes a rudimentary appendage or none at all. Auricular anomalies are the subject of Microtia. Congenital aural atresia has a reported incidence that varies between 1 in 10 to 1 in 20,000. Congenital aural atresia is usually found in isolation and in these instances patterns of inheritance have not been seen. Its association with several known craniofacial syndromes is well known. Aural atresia has been found in association with 22 of the 71 known craniofacial syndromes. The most common of these are Treacher-Collins (mandibulofacial dysostosis), Nager (acrofacial dysostosis), Crouzon's (craniofacial dysostosis), hemifacial microsomia, and the first and second branchial arch syndromes including Goldenhar's (oculoauriculovertebral dysplasia). In unilateral cases, Jafek et al and others have cited an increased incidence of atresia on the right. Bilateral atresia has been reported to occur in approximately 30% of cases. Establishing a classification system of the congenital ear malformations has been almost as difficult as the operative procedures themselves. Several schemes have been proposed over time, one the first being that proposed by Marx in 1926 for auricular anomalies, which were graded I - III for mild to severe deformities. Altmann in 1955 proposed the first schema based on the temporal bone itself, looking at the status of the canal, tympanic bone, drum and ossicles. Lapchenko in 1967 and Gill in 1969 both set up a four tier scale, examining the degree of middle ear and external canal development, and the presence of ossicular abnormality. Additionally, Gill incorporated into his system, the degree of pneumatization of the mastoid, as this seemed to predict the relative success of operative interventions. Ombredonne and Nager and Colman each tried to establish simplified and clinically practical systems based on Altmann's original scheme, but these were inconsistent at predicting outcome in those cases of major aplasia or group II anomalies. Jahrsdoerfer in 1992 established not so much a classification system, but rather a grading scale as a means selecting patients that would most likely benefit from attempts at repair of their atresias. This system of grading allows for a quantitative analysis of the temporal bone and those structures that are considered vital to the success of an operation. Whereas prior systems were excellent descriptions of surgical and anatomical findings, they lacked predictive power and were subject to interobserver bias. This scale, which is based on temporal bone CT findings, assesses nine different parameters that are used in making the determination of candidacy for surgery. Of note, the stapes and oval window complex account for 3 out of the 10 points possible in the scale. Other parameters include the middle ear cleft, facial nerve position, status of the ossicles and round window, and pneumatization of the mastoid. Scores of 6 through 10 range from marginal to excellent candidates for surgery while a score of 5 or less usually anticipates a poor outcome. In general, patients with congenital aural atresia are seen in referral from neonatologists in those cases where gross craniofacial anomalies are present. However, many cases of isolated atresia or even those with very mild head and neck syndromes may be delayed until later in development and may be referred by pediatricians for either atresia or for problems relating to a stenotic canal. As is usual, a thorough history is important in the initial evaluation of these patients, including questions relating to the gestation of the infant. Specifically, issues of drug utilization, toxic exposures, prior family history of hearing impairment and developmental craniofacial disorders and maternal infections should be probed as possible etiologies. A thorough physical exam of the head and neck as well as of other organ systems should be performed, especially the spine, extremities and genitourinary systems as these develop concurrently with those of the head and neck. Associated anomalies of the midface and mandible should be noted. Position of the auricle and the degree of external canal development should be checked. The degree of mastoid prominence should be noted as this may give an early insight to the operative potential of the patient. Cranial nerve function, especially that of the facial nerve should be assessed. An audiologic evaluation is essential in the initial assessment of these patients. A screening ABR should be obtained for several reasons. The first is to establish the presence of a functional inner ear. In very young patients this is accomplished with multichannel air and bone conduction ABR. In cases of bilateral atresia, this form of ABR will also allow one to establish with greater certainty the ear with greater cochlear function by examining the response obtained in wave I, which is indicative of ipsilateral cochlear status only. The second reason for early ABR is that if an intact inner ear is present, the child can be fitted early on with a bone-conducting device. The usual finding is that of moderate to maximal conductive loss, although mild conductive losses are sometimes seen in cases with membranous atresia. A third reason for early ABR is to assess the functional status of the contralateral ear in unilateral atresias. Several cases of sensorineural or mixed losses in the contralateral, normal-appearing ear have been reported and should be ruled out. Having ascertained the functional status of the inner ear, diagnostic imaging is used to assess the degree and nature of the temporal bone deformity. With CT scanning, an assessment of the ossicular mass, the nature of the atretic plate (whether bony or soft), the position and course of the facial nerve, the degree of external canal development and mastoid pneumatization is possible. The presence of a cholesteatoma, which has a slight predilection for stenotic ears, can also be ruled out. Current recommendations for the timing of CT scan is at approximately 4 years when mastoid pneumatization is most complete. A review of the literature by Cressman et al has shown that approximately 50% of patients seen for this condition are ultimately found to be candidates for reconstruction based on CT scan findings. The current consensus among those who undertake these procedures is that surgery on cases of either bilateral or unilateral atresia should be deferred until the patient is at least 4 to 6 years of age, with an additional delay to consenting age espoused by others for those cases of unilateral atresia. The need to foster continued mental development and the evolution of speech skills requires that interim bone conducting appliances be provided for these patients with bilateral atresias that have documented cochlear function on ABR. Unilateral atresia patients usually do not require any intervention as long as normal hearing is present in the contralateral ear. Once the decision to proceed with surgery has been made, a consideration of both the functional and cosmetic aspects of the operation needs to be taken together. Close coordination with the plastic surgeon reconstructing the auricle is needed and usually takes place as a multi-staged procedure. Because of problems relating to healing in a fibrotic, previously-operated area, current practice is to allow the plastic surgeon to operate first with the implantation of an auricular framework of autogenous rib graft in a subcutaneous pocket. Stage II consists of lobule transposition and remnant excision. Correction of the atresia with the creation of a new external meatus, canal, drum and conducting mechanism in continuity with the stapes and inner ear is completed in Stage III along with alignment of the new auricle to the meatus. Stages IV and V usually consist of the creation of a new tragus and the elevation of the auricle off the post-auricular skin. Contrary to the standard practice of operating on the poorer hearing ear first, as is the case with chronic ear infection, cholesteatoma and otosclerosis, the better hearing ear is operated on first in CAA as this will afford the best chance for an optimal outcome. Two general approaches to the repair of atresia are currently described, both of which commence with postauricular incisions. The first of these is the transmastoid approach that makes use of the familiar landmarks of the tegmen and sinodural angle to approach the mastoid antrum and the bony atresia plate. This dissection is conducted with the aid of a facial nerve monitor, as the course of this nerve is commonly aberrant owing to the anomalous development of the tympanic bone and mastoid. Some surgeons opt to perform incudostapedial dislocation if this is feasible in order to prevent transmitted acoustic trauma to the inner ear with resultant sensorineural loss. Once the plate is removed, a canal wall down mastoidectomy is completed leaving an open cavity. A second, newer, approach described by Jahrsdoerfer and known as the Anterior Approach involves exposure of the tympanum and ossicular mass by directly removing bone from lateral to medial between the glenoid fossa and the middle cranial fossa dura. Drilling begins just posterior to the condyle, and proceeds medially using the middle fossa dura as a superior guide. An anterior and superior approach presents the least risk in injuring an anomalous facial nerve. This usually leads to an ossicular mass consisting of a fused incus and malleus attached to the atretic plate. Once identified, the atretic plate can be taken down with diamond burrs and curettes, taking care to avoid contact with the ossicular mass. Mobility of the stapes and the status of the oval and round windows is checked. Middle ear reconstruction with a prosthesis is performed if necessary. Otherwise, temporalis fascia and split-thickness skin grafting is performed to create a new eardrum and line the newly-created canal. A meatoplasty completes the procedure and places the canal in continuity with the auricular meatus. Modification of this approach has been described including a canal wall-up approach that allows the surgeon to identify the nerve and atresia plate prior to opening a canal. The goal of attaining hearing improvement in an ear with a previously moderate to maximal conductive loss varies from persistent maximal conductive loss to cases of near-total closure of the air-bone gap. Although different parameters for successful improvement in hearing have been reported, according to Cressman et al, if one chooses a speech reception threshold of 25 decibels or less, then anywhere from 20 to 80% of patients will have a successful operation. Much of this range hinges on patient selection, experience and technique. Crabtree, de la Cruz and Glasscock have each reported varying degrees of success with this operation. However, this may reflect the utilization of different parameters and definitions by each of these authors. Jahrsdoerfer reported in 1992 on his results based on patients selected using a 10-point grading system. He reported achieving speech reception thresholds of 25 decibels or less in 75% of 86 cases operated on. Several authors have noted that cases requiring a prosthesis for ossicular reconstruction tend to have greater air-bone gaps postoperatively than those receiving grafts over a mobile ossicular mass. Complications relating to CAA repair can be divided into intraoperative and postoperative categories. Intraoperative complications include facial nerve injury, sensorineural deafness, and perilymph fistula. Although cited as a potential complication, permanent facial paralysis is exceedingly rare despite its aberrant course through atretic temporal bones. High frequency sensorineural loss secondary to transmitted vibrations has been reported with both approaches. Postoperative or delayed complications for the most part include stenosis and chronic drainage, more common with the transmastoid approach, and graft lateralization that plagues both approaches as well. This can be prevented by the creation of a bony ledge medial to the ossicular mass wherein the graft can be placed, or through the use of a silastic button just lateral to the graft. Bilateral atresia patients that are either unable or unwilling to undergo surgery have the option of being fitted with a bone-conducting hearing appliance. Both percutaneous and transcutaneous devices have been developed; however, only the transcutaneous version is FDA approved. Older devices that are held to the head by a tight-fitting headband are unsightly and uncomfortable. Despite the advances that have been made in technique and imaging over the past twenty years, several issues regarding the timing of surgery in general, when to operate on cases of unilateral atresia, and the operability of cases with severe craniofacial malformations remain difficult questions. The issue of when to operate on these patients is a difficult one because many surgeons with considerable experience in this area maintain such varied opinions. Generally speaking, most would agree that the earliest age at which to proceed is at 4 to 5 years of age, thereby allowing time for adequate mastoid and middle ear pneumatization and increasing patient compliance with the postoperative care that is required. Also, most authors state that in cases of unilateral atresia with evidence of cholesteatoma, infection or with very thin atresia plates, surgery should be undertaken earlier. However, there are differing opinions regarding cases of grade II and III unilateral atresia in patients with normal hearing in the other ear. Jahrsdoerfer finds that the benefit of binaural hearing far exceeds the risk of facial nerve injury and other complications. De la Cruz also favors operating earlier on unilateral atresias if a good outcome can be expected based on CT findings. Others, including Crabtree, Bellucci, Glasscock and Fisch, favor waiting until the patient is of consenting age at which point an individually informed decision can be made. All points considered, the decision to proceed with early intervention ultimately depends on the experience of the surgeon and the relative degree of malformation that the individual patient has and with which the surgeon is comfortable. In summary, congenital aural atresia is a congenital developmental anomaly of the middle ear that manifests with varying degrees of external auditory canal stenosis or atresia, ossicular derangements, poorly developed mastoid and tympanic cavities and is characterized by a conductive hearing loss that is of a moderate to maximal degree. Heritable forms of CAA are found in association with many of the craniofacial syndromes, but nonheritable, isolated CAA is more frequent. History and physical exam findings are important in the early identification of the problem complemented by audiometric/ABR evaluation in order to allow speech development. CT scanning to assess operative potential is then performed at about 4 years of age, with an approximate yield of 50%. Grading of the patient based on CT findings has been shown to be predictive of outcome. Success rates of as high as 75% have been reported with speech reception thresholds of 25dB or less. Historically, a transmastoid approach has been used, but the problems of stenosis, drainage and long-term care of a mastoid cavity have favored the anterior approach. Issues regarding the timing of unilateral cases are complex and the decision to operate early on in these cases ultimately depends on the experience of the surgeon and the degree of malformation present. Case Presentation A 2-year and 9-months-old male, former 36-week premature infant that at birth was noted to have midfacial and mandibular hypoplasia consistent with the diagnosis of Treacher-Collins Syndrome. The family history was negative for relatives with craniofacial or auricular malformations. His past medical history was notable for uncomplicated neonatal jaundice. Medical work-up for congenital cardiac and renal anomalies was negative. On exam, the patient is noted to have malar hypoplasia, absent zygomatic arches, hypoplasia of the mandible with Class III occlusion, and bilateral Grade III microtia with aural atresia. The mastoids, however, are well developed bilaterally. A tracheotomy is present in the neck. The remainder of the physical exam was unremarkable. Upper airway obstruction secondary to severe mandibular hypoplasia necessitated elective tracheotomy in the first week of life. A gastrostomy tube was placed secondary to poor oral intake. At two months of age, he underwent audiometric evaluation consisting of air and bone conduction multichannel ABR. The patient was fitted with a bone-conducting type hearing aid at age four months. Subsequently, the patient underwent repair of his palatal defect at age two, and most recently underwent bilateral Ilizarov mandibular distraction procedures. After more than two years with his bone-conducting aids, he has acquired comprehensible speech and a vocabulary comparable to that of children with normal hearing. Bibliography Andrews JC, Anzai Y, Mankovich NJ, Favilli M, Lufkin RB, Jabour B. Three-dimensional CT scan reconstruction for the assessment of congenital aural atresia. Am J Otol 1992;13:236-240. Chang SO, Min YG, Kim CS, Koh TY. Surgical management of congenital aural atresia. Laryngoscope 1994;104:606-611. Cole, RR. The "buttock sign" in congenital aural atresia. Otolaryngol Head Neck Surg 1993;109:140-141. Cole RR, Jahrsdoerfer RA. 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Surgical approaches to congenital atresia of the external auditory canal. Otolaryngol Head Neck Surg 1990;103:991-1001. Pattee GL. An operation to improve hearing in cases of congenital atresia of the external auditory meatus. Arch Otolaryngol 1947;46:568-580. Patten BM. Human Embryology. New York: McGraw-Hill, 1968:335-344. Schuknecht HF. Congenital aural atresia. Laryngoscope 1989;99:908-917. Shambaugh GE. Surgery of the Ear. Philadelphia: Saunders, 1959:493-523. Shih L, Crabtree JA. Long-term surgical results for congenital aural atresia. Laryngoscope 1993; 103:1097-1102. Swartz JD, Harnsberger HR. Imaging of the Temporal Bone. New York: Thieme Medical Publishers, 1992:20. Portmann M, Guillen G, Richards AE. The Ear and Temporal Bone. New York: Masson, 1979:382-384. Grand Rounds Archive | Department Home page BCM Public | BCM Intranet | Privacy Notices | Contact BCM | BCM Site Map | ©2001-2006 Baylor College of Medicine
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