External auditory canal atresia occurs in one of 10,000–20,000 births and is bilateral in approximately one third of patients . Patients with external auditory canal atresia experience conductive hearing loss. Given intact sensorineural hearing, surgical restoration of conductive hearing can be achieved. To obtain satisfactory results and prevent complications, physicians must select proper candidates for surgery. Preoperative high-resolution CT of the temporal bone plays a central role in evaluating surgical candidates and planning the operation. The purpose of this pictorial essay is to present a spectrum of isolated and complex patterns of external auditory canal atresia encountered on high-resolution CT and their implications in surgical planning.
Surgical Approach and Technique
Two surgical techniques have been established, the transmastoid and the anterior approaches. Both techniques are initiated with a postauricular incision and elevation of the auricle. After the transmastoid approach has been performed, the mastoid air cells are first removed, providing middle ear visualization during the subsequent dissection of the atretic plate . The drawback of this approach is a large mastoid defect, causing an increased risk of local infection problems . For the anterior approach, opening the mastoid cells is avoided by creating a cylindric canal through the atretic plate. Drilling is started posterior to the glenoid fossa and anterior to the mastoid cells and is continued in the direction of the middle cranial fossa to reach the epitympanum below the tegmen to avoid ossicle or facial nerve injury [1, 2]. Both transmastoid and anterior approaches are followed by mobilization of the ossicles attached to the atretic bone (usually the hammer neck). The temporalis fascia is grafted as a new tympanic membrane to the ossicles or to a stapes prosthesis. The newly generated canal is then covered with a skin graft [1, 2].
Although sensorineural hearing is usually maintained in patients without a major congenital syndrome, audiometric evaluation is indispensable to ensure that sufficient sensorineural hearing is present. Unlike unilateral atresia, in which normal speech development is ensured, bilateral atresia requires early amplification with a bone conduction hearing aid and surgery on the more suitable ear in childhood.
Yeakley and Jahrsdoerfer  described a 10-point rating scale for the selection of surgical candidates by comparing high-resolution CT findings to postsurgical hearing results. Using nine reproducible criteria, one calculates a score to predict postoperative improvement of the speech reception threshold. The criteria include assessment of the stapes, oval window and round window, middle ear space, mastoid pneumatization, facial nerve course, malleus–incus complex, and incus–stapes connection. One point is given for each item with correct or only slightly dysplastic appearance, with the exception of the stapes, which receives 2 points when presented. The final item consists in the clinical aspect of the external ear, which is added to the CT criteria. A point is assigned for a fairly developed auricle. Patients with more than 5 points on the grading system are considered candidates for surgical reconstruction.
High-Resolution CT Findings
Isolated External Auditory Canal Atresia
Atresia consists of an osseous plate with a varying degree of pneumatization superposed laterally to the tympanic cavity (Figs. 1 and 2). Accompanying middle ear dysplasias in patients without a further malformation syndrome are frequently of minor type and follow a typical pattern.
Incudomallear complex.—The incudomallear joint is usually normal (Figs. 1, 2, and 3A) with a rudimentary hammer handle attached to the atretic plate (Figs. 3A and 3B). Severe incudomallear dysplasia (Figs. 3C and 3D) is rare. A dysplastic incudomallear complex has to be resected and the stapes is grafted to the temporalis fascia.
Incudostapedial connection.—Integrity of the incudostapedial joint is best evaluated in the coronal planes (Figs. 3E and 4). Horizontal axis rotation of the long incus process with an obtuse angle to the lenticular process (Fig. 3E) may be seen, with both the incudomallear and the incudostapedial joint recognizable on the same axial slice (Fig. 2).
Oval window and round window.—Patients with an atretic oval window are not considered candidates for surgical repair . The vertical oval window diameter should measure at least 1 mm . A patent round window is essential for membranous wave transmission of the cochlea. Patients without a congenital syndrome usually show open windows, even with considerable middle ear dysplasia (Fig. 5A).
Middle ear cavity.—Aerated tympanic cavity with preserved function of the tuba auditiva (Fig. 5B) is indispensable for successful surgery. Reduced middle ear space was correlated with unfavorable outcome of surgery . A tympanic cavity width less than 3 mm from the promontory to the atretic plate in the coronal plane is considered inadequate for reconstruction (Figs. 5A, 6, and 7A).
Temporal bone pneumatization.—Aeration of the mastoid cells frequently correlates to pneumatization of the atretic plate (Figs. 2 and 3B). Poor pneumatization of the temporal bone results in reduced space for surgical approach. The temporomandibular joint is displaced posteriorly with close relationship to the tympanic cavity (Fig. 7B). The middle cranial fossa shows a deep position (Fig. 6) in reduced or absent temporal bone aeration. The postoperative coronal plane view provides the steep drilling pathway to avoid opening the middle cranial fossa (Fig. 7C).
Stapes.—Stapes has a significant impact on surgery planning. Although the intact stapes can be anchored to the fascia graft (Figs. 7C and 7D), the dysplastic or absent stapes has to be replaced with a prosthesis  with a less predictable outcome .
Facial nerve.—The course of the facial nerve is often altered and is one of the most important aspects to be considered when planning the surgical approach [1–3]. Unfavorable or undefined nerve course precludes surgical repair . The descending segment is frequently displaced in the ventral and lateral directions with the facial nerve passing along or through the atretic plate (Figs. 3B, 3C, and 5B). Anterolateral displacement of the stylomastoid foramen (Figs. 5A and 6) may lead to extracranial facial nerve injury during elevation of the auricle . In its tympanic segment, the facial nerve may be displaced caudally, overlying the oval window (Figs. 5A and 8A). Typically, the pyramidal eminence with the second genu is displaced anteriorly in the tympanic cavity (Fig. 8B).
External Auditory Canal Atresia in Congenital Malformation Syndromes
Contrary to patients with isolated external auditory canal atresia, patients with an underlying congenital syndrome show a higher degree of external and middle ear deformity  and achieve low scores on the Yeakley-Jahrsdoerfer grading system . Inner ear pathologic changes can occur in certain syndromes.
Goldenhar's syndrome.—Goldenhar's syndrome is part of the craniofacial anomaly spectrum with malformation of the first and second branchial arch derivatives, characterized by facial and temporal bone hypoplasia but also involving ectodermal structures such as the otic placode . Severe dysplasia occurred in the external and middle ear of the patient in Figure 9A, 9B, 9C. The middle ear cavity was not aerated (Fig. 9A) because of obliteration of the eustachian tube (Fig. 9B). No ossicle structure is visible (Fig. 9A). Mastoid pneumatization was absent, causing a deep middle cranial fossa (Fig. 9C). The most important finding, however, is an atretic oval window (Figs. 9A and 9C). A closed oval window and obliteration of the eustachian tube exclude surgical repair.
Treacher Collins syndrome.—Similar to Goldenhar's syndrome, Treacher Collins syndrome is part of the craniofacial dysplasia complex caused by a malformation of the first and second branchial arch derivatives, but represents an inherited disorder with bilateral midface hypoplasia, micrognathia (Fig. 10A), and external and middle ear deformity . Surgical exclusion criteria here include small, nonaerated middle ear rudiments, unrecognizable windows, undefined facial nerve course, and a deep middle cranial fossa (Figs. 10B, 10C, 10D, 10E).
Pierre Robin sequence.—The Pierre Robin sequence comprises the bilateral cleft palate, retrognathia (Fig. 11A), and glossoptosis . To our knowledge, middle and inner ear deformities have not yet been described. Figure 11A, 11B, 11C presents a patient with evidence of a Pierre Robin sequence and external auditory canal atresia. Despite having normal ossicles and patent windows, our patient had a dehiscent facial nerve in the middle ear cavity and reduced tympanal width (Fig. 11B). The dehiscent facial nerve represents an unpredictable risk for surgical reconstruction. Our patient showed an unusual labyrinthine malformation with absent posterior semicircular canal (Fig. 11C) as a possible hint for further membranous labyrinthine deficiency.
Presented at the 2002 annual meeting of the Radiological Society of North America, Chicago, IL.
Address correspondence to E. M. Gassner.
Lambert PR, Dodson EE. Congenital malformations of the external auditory canal. Otolaryngol Clin North Am 1996; 29:741 –760