Congenital Malformation of the External Auditory Canal and Middle Ear

5

Congenital Malformation of the External Auditory Canal and Middle Ear Antonio De la Cruz and Karen B. Teufert     Videos corresponding to this chapter are available online at www.expertconsult.com.

Congenital aural atresia is characterized by aplasia or ­hypoplasia of the external auditory canal (EAC), often associated with absence or deformity of the auricle (microtia) and the middle ear, with occasional inner ear abnormalities. Aural atresia occurs in 1 in 10,000 to 20,000 live births1-5; unilateral atresia is three times more common than bilateral atresia. This disorder occurs more commonly in males and on the right side.1 EAC atresia is more often bony rather than membranous, and bony atresia is regularly accompanied by malformation of the middle ear cavity and structures of the middle ear.6-9 More severe forms of congenital microtia are usually associated with EAC atresia; rarely, canal atresia may be seen in patients with a normal pinna.10 Generally, a more severe external deformity implies a more severe middle ear abnormality.11,12 Kiesselbach, in 1883, is often credited with the first deep operation attempting to correct this malformation.8 Lascaratos and Assimakopoulos13 noted that the Byzantine physician Paul of Aegina performed a surgical treatment of congenital aural atresia.14 The procedure done by Kiesselbach resulted in facial paralysis. Because of the lack of middle ear microsurgery and the high complication rate, congenital aural atresia surgery was considered dangerous and to be avoided for the most part. In 1914, Page15 reported hearing improvement after surgery in five of eight patients. This report was followed in 1917 by Dean and Gittens,16 who reported an excellent hearing result in a patient and reviewed the various types of operations that had been tried by other surgeons. The prevailing attitude toward surgical correction in these cases remained generally pessimistic, however, despite these and other occasional reports of successful operations, until 1947. That year, Ombredanne17 in France and Pattee18 in the United States each reported a series of patients successfully operated on to improve hearing. Pattee’s technique included removal of the incus to “mobilize” the stapes18; Ombredanne17 added fenestration of the lateral semicircular canal. With the advent of tympanoplasty techniques in the 1950s, interest in atresiaplasty increased as the teachings of Wullstein and Zollner carried over into surgery of the congenital ear.8 Larger series with greater success rates

were reported as surgeons attempted to improve their results, using ossiculoplasty, mastoidectomy, differing degrees of bone removal, and different types and techniques of graft placement.2,4,17,19-26 Ombredanne27 went on to report on more than 600 aplasia cases by 1971 and 1600 cases with major and minor malformations by 1976.8 Gill’s report of 83 cases in 19692 and Jahrsdoerfer’s 1978 article8 are considered landmarks. Crabtree,28 Jahrsdoerfer,29,30 Marquet,31,32 and De la Cruz6,33 and their colleagues all reported on large surgical series, with modifications of classification and operative techniques. Although techniques of canalplasty, meatoplasty, tympanoplasty, and ossiculoplasty have improved considerably, surgical correction of congenital aural atresia remains one of the most challenging operations performed by otologists. This is a complex surgical problem, requiring application of all tympanoplasty techniques and a thorough knowledge of the surgical anatomy of the facial nerve, oval window, and inner ear, and their congenital variants.1,6,8,17,21,26,27,29-31,33-40 The temporomandibular joint is displaced posteriorly by the lack of development of the EAC, narrowing the distance between the glenoid fossa and the anterior wall of the mastoid tip.19,41 Fusion of the incus and malleus is common, but because of its dual origin, the stapes footplate is usually normal.4,42 The surgical repair of aural atresia is recommended at age 6 years.6 The timing of repair must take into account any planned auricular reconstruction procedures. Criteria for patient selection must be stringent when attempting to achieve closure of the air-bone gap to within 20 to 30 dB. Preoperative counseling and several postoperative visits are essential for optimal results. In this chapter, we discuss these issues and provide guidelines for patient evaluation and selection, surgical techniques, and postoperative management.

EMBRYOLOGY A review of the normal embryologic development of the ear aids in understanding the myriad of possible combinations of malformations encountered in congenital 55

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OTOLOGIC SURGERY

TABLE 5-1  Development of the Auricle First Branchial Arch

Second Branchial Arch

First hillock—tragus

Fourth hillock—antihelix

Second hillock—helical crus

Fifth hillock—antitragus

Third hillock—helix

Sixth hillock—lobule and lower helix

TABLE 5-2  De la Cruz Classification of Congenital

Aural Atresia

Minor Malformations 1. Normal mastoid pneumatization 2. Normal oval window/footplate 3. Good facial nerve–footplate relationship 4. Normal inner ear

aural atresia. The inner ear, middle ear, and external ear develop independently and in such a way that deformity of one does not presuppose deformity of another.9,43 Most frequently, abnormalities of the outer and middle ear are encountered in combination with a normal inner ear.44,45 Microtia is a result of first and second branchial arch anomalies. Growth of mesenchymal tissue from the first and second branchial arches forms six hillocks around the primitive meatus that fuse to form the auricle (Table 5-1). By the end of the third month, the primitive auricle has been completed. The external auditory meatus develops from the first branchial groove. During the second month, a solid core of epithelium migrates inward from the rudimentary pinna toward the first branchial pouch. This core, the precursor of the EAC, starts to hollow out and take shape in the sixth month. It canalizes in the seventh month, causing the developing mastoid to become separated from the mandible. Its subsequent posterior and inferior development carries the middle ear and facial nerve to their normal positions.1,43,46-48 Some of the literature supports the notion that microtia grade can indicate the status of middle ear development in aural atresia. The better developed the external ear is, the better developed is the middle ear. The first branchial pouch grows outward to form the middle ear cleft. The plaque of tissue where this cleft meets the epithelium of the EAC forms the tympanic membrane. While the pouch is forming the eustachian tube, tympanic cavity, and mastoid air cells, Meckel’s cartilage (first branchial arch) is forming the neck and head of the malleus and incus body. Reichert’s cartilage (second branchial arch) forms the remainder of the first two ossicles’ long processes and the stapes superstructure. The footplate has a dual origin from the second arch and the otic capsule. The ossicles attain their final shape by the fourth month. By the end of the seventh to eighth month, the expanding middle ear cleft surrounds the ossicles and covers them with a mucous membrane.1,45,49 The facial nerve is the nerve of the second branchial arch. At 4.5 weeks, this developing nerve divides the blastema, which is the condensation of the second arch mesenchymal cells, into the stapes, the interhyale (stapedius muscle precursor), and the laterohyale (precursor of the posterior wall of the middle ear). The nerve’s intraosseous course is dependent on this bony expansion.45,47 The membranous portion of the inner ear develops during

Major Malformations 1. Poor pneumatization 2. Abnormal or absent oval window/footplate 3. Abnormal course of facial nerve 4. Abnormalities of inner ear From De la Cruz A, Linthicum FH Jr, Luxford WM: Congenital atresia of the external auditory canal. Laryngoscope 95:421-427, 1985.

the third to sixth week from an auditory placode on the lateral surface of the hindbrain. The surrounding mesenchyme transforms into the bony otic capsule.50 Congenital aural atresia can range in severity from a thin membranous canal atresia to complete lack of tympanic bone, depending on the time of arrest of intrauterine development.1,51,52 The common finding of a normal inner ear is explained because the inner ear is formed by the time of external/middle ear development arrest. Facial nerve course abnormalities are often seen.

CLASSIFICATION SYSTEMS Of historical significance is a classification in congenital aural atresia developed in 1955 by Altmann.51 In this system, atresias are categorized into three groups, as follows: Group 1 (mild): Some part of the EAC, although hypoplastic, is present. The tympanic bone is hypoplastic, and the ear drum is small. The tympanic cavity is either normal in size or hypoplastic. Group 2 (moderate): The EAC is completely absent, the tympanic cavity is small, and its content is deformed, and the “atresia plate” is partially or completely ­osseous. Group 3 (severe): The EAC is absent, and the tympanic cavity is markedly hypoplastic or missing. Altmann’s classification system is purely descriptive, and most surgical candidates fall into groups 2 and 3. The De la Cruz classification includes surgical feasibility guidelines using only high-resolution computed tomography (CT), taking into consideration mastoid pneumatization, inner ear normality, and facial nerve and footplate relationship.6 The malformations are divided into minor and major malformations (Table 5-2). The

Chapter 5  •  Congenital Malformation of the External Auditory Canal and Middle Ear TABLE 5-3  Jahrsdoerfer’s Grading System of

Candidacy for Surgery of Congenital Aural Atresia

Parameter

Points

Stapes present

2

Oval window open

1

Middle ear space

1

Facial nerve normal

1

Malleus-incus complex present

1

Mastoid well pneumatized

1

Incus-stapes connection

1

Round window normal

1

Appearance of external ear

1

Total available points

10

Rating

Type of Candidate

10

Excellent

9

Very good

8

Good

7

Fair

6

Marginal

≤5

Poor

From Jahrsdoerfer RA, Yeakley JW, Aguilar EA, et al: Grading system for the selection of patients with congenital aural atresia. Am J Otol 13:6-12, 1992.

clinical importance of this classification is that surgery in cases of minor malformations has a good possibility of yielding serviceable hearing, whereas cases of major malformations are frequently inoperable, but treatable with the bone-anchored hearing aid (BAHA) system.3 Jahrsdoerfer and colleagues53 developed a widely used point grading system to guide surgeons in preoperative assessment of the best candidates for hearing improvement (Table 5-3). This system takes into account the parameters of mastoid pneumatization, presence of the oval and round windows, facial nerve course, status of the ossicles, and external appearance. Point allocation is based primarily on the findings on high-resolution CT. Jahrsdoerfer and colleagues53 proposed that when the preoperative evaluation of the patient is itemized into this grading system, the best results (>80% success) are achieved with a score of 8 or better. A score of 7 indicates the patient is a fair candidate, a score of 6 indicates the patient is a marginal candidate, and with a score less than 5 the patient becomes a poor candidate. Ishimoto and associates54 evaluated the relationship between hearing level and temporal bone abnormalities in patients with microtia, using Jahrsdoerfer’s CT scoring system and high-resolution CT scans of the temporal bone. They found that the hearing level in microtic ears correlated with the formation of oval/round windows

57

and ossicular development, but not with the degree of middle ear aeration, facial nerve aberration, or severity of ­microtia. Schuknecht’s55 system of classification of congenital aural atresia is based on a combination of clinical and surgical observations. Type A (meatal) atresia is limited to the fibrocartilaginous part of the EAC. Meatoplasty is the surgical procedure of choice, and when performed in a timely fashion prevents formation of canal cholesteatoma and conductive hearing loss. In type B (partial) atresia, there is narrowing of the fibrocartilaginous and bony EAC, but a patent dermal tract allows partial inspection of the tympanic membrane. The tympanic membrane is small and partly replaced by a bony septum. Minor ossicular malformations exist, and hearing loss may be mild to severe. Type C (total) atresia includes all cases with a totally atretic ear canal, but a well-pneumatized tympanic cavity. There is a partial or total bony atretic plate, the tympanic membrane is absent, the heads of the ossicles are fused, there may be no connection to a possibly malformed stapes, and the facial nerve is more likely to have an aberrant course over the oval window. Type D (hypopneumatic total) atresia is a total atresia with poor pneumatization, common in dysplasias such as Treacher Collins syndrome. There are abnormalities of the facial nerve canal and the bony labyrinth. These patients are poor candidates for hearing improvement surgery. Chiossone’s56 classification is based primarily on the location of the glenoid fossa. In type I, the fossa is in the normal position; in type II, it is moderately displaced; in type III, the fossa overlaps the middle ear; and in type IV, in addition to the fossa overlapping the middle ear, there is lack of mastoid pneumatization. Patients with types I and II are ideal surgical candidates. Type III cases have a tendency toward graft lateralization. Patients with type IV are not surgical candidates. In atresiaplasty surgery, a classification scheme is useful for surgical planning, patient counseling, and comparison of outcomes.

INITIAL EVALUATION AND PATIENT SELECTION When aural atresia is noted in a newborn, several issues must be addressed. Where one congenital abnormality is found, others must be sought. A high-risk registry for hearing loss is helpful in this regard.57 After the degree of aural deformity is assessed by physical examination, evaluation of auditory function in unilateral and bilateral atresia should be performed using auditory brainstem response audiometry within the first few days of life. An 11% to 47% incidence of inner ear abnormality is associated with congenital aural atresia.12 Occasionally, in unilateral cases, there is a total sensorineural hearing loss (SNHL) on the side of the normal-appearing ear, which might otherwise be missed.6,33

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OTOLOGIC SURGERY

In bilateral cases, a bone-conduction hearing aid should be applied as soon as possible, ideally in the third or fourth week of life. In unilateral cases in which the opposite ear hears normally, a hearing aid is unnecessary. A child with aural atresia and associated cephalic abnormalities (e.g., hemifacial microsomia and Treacher Collins, Crouzon, or Pierre Robin syndrome) should be recognized.57-61 In this subset, surgical correction has poor results,55 and a long-term bone-conduction hearing aid or BAHA in these nonoperable bilateral congenital aural atresia situations is beneficial (see later).3 Prompt and careful counseling of the parents of a child with sporadic (nonsyndromal) congenital aural atresia is necessary to alleviate concerns regarding possible occurrence in subsequent children (no more than the general population), to answer questions regarding future auricular reconstruction, and, most important, to ensure that proper hearing amplification is instituted in a timely fashion. The child should be enrolled in special education at an early age to maximize speech and language acquisition, in preparation for “mainstreaming” at preschool age. Radiologic and surgical evaluations are deferred until the child is 6 years old (see later). In the initial evaluation of an older individual with congenital aural atresia, the most crucial elements remain the functional and anatomic integrity of the inner ear. Audiometry and high-resolution thin-section (≤1 mm) CT in coronal and axial views are necessary. Prognosis for hearing improvement depends on the presence and degree of malformations. Auricular reconstruction must be done before hearing reconstruction to avoid interfering with the blood supply to the surrounding soft tissue, which is indispensable for microtia repair. Reconstruction with alloplastic materials, such as porous high­density polyethylene (Medpor), can be done before or after atresiaplasty because intact blood supply is not indispensable. A patient with congenital aural atresia may present with an infected or draining ear or acute facial palsy; 14% have congenital cholesteatoma.6 The priority in these cases is removal of the cholesteatoma and resolution of the infection. Preoperative audiometry and highresolution CT scanning may be necessary at an earlier age in children with repeated infections in the atretic ear.6,55,62 There are two requirements for planning surgery in congenital aural atresia: radiographic three-­dimensional evaluation of the temporal bone and audiometric evidence of cochlear function.8,63 Other conditions mandating prompt surgical intervention are congenital cholesteatoma, a draining postoperative atretic ear, and acute facial palsy. The CT scan should always be reviewed for ­ cholesteatoma, which necessitates surgery at any age.55,62,64 It is not included in any of the grading systems because these are used only for predicting hearing results in elective atresiaplasty surgery.

TIMING OF AURICULAR RECONSTRUCTION AND ATRESIAPLASTY In bilateral or unilateral atresia, auricular reconstruction and atresiaplasty are recommended at 6 years of age. Before this age, there may be a tendency to form exostosis-like bony growth that may occlude the EAC, and there is less patient cooperation. By age 6, the costal cartilage has developed sufficiently to allow for reconstruction of the auricle, and the mastoid has become as pneumatized as possible. The microtia repair should be done first because the complex flaps and use of autologous rib graft demand excellent blood supply.65,66 Many surgeons do not perform cartilage microtia reconstruction on an ear with previous reconstruction attempts.64 The hearing restoration surgery is performed 2 months after the last step of the microtia repair. Rehabilitation of auricular defects can be done using an osseointegrated percutaneous mastoid implant prosthesis, with and without bone-conduction aids, such as BAHA.3,48,67-69 Alloplastic materials have been used for microtia repair in the past, but there is a high risk of extrusion associated with their use. Newer materials, such as Medpor, seem to be very well tolerated, however.70-72 As noted earlier, Medpor reconstruction can be done before or after atresiaplasty because intact blood supply is not indispensable. In unilateral cases, atresiaplasty surgery may be indicated in a patient with “minor” unilateral atresia with normal middle ear, ossicles, and facial nerve, and excellent pneumatization. In such patients, atresiaplasty may be offered in childhood with the parents’ consent.33 We often see older adults with unilateral atresia who request surgery when their normal ear begins having high­frequency hearing loss (presbycusis).

Bone-Anchored Hearing Appliances Implantable bone hearing aids available for clinical use were introduced in 1977 in Sweden. BAHA, using Branemark System implants in combination with a hearing aid, has proved to be a favorable means of providing hearing rehabilitation for certain groups of patients, including patients with a congenital ear malformation. BAHAs are suitable for patients who are poor atresiaplasty candidates because of the severity of their malformations. BAHA is a better alternative than a conventional bone hearing aid. Conventional bone hearing aids have several drawbacks: discomfort because of constant pressure from the steel spring, worse sound quality because of higher frequency attenuation by the skin, and poor esthetics and insecure positioning of the device. BAHA works without pressure on the skin and provides direct bone transmission without air interface. Other implants are discussed in detail elsewhere in this textbook. Surgery for BAHA can be performed under local or general anesthesia and is a one-stage procedure. To implant BAHA, a small transcutaneous titanium

Chapter 5  •  Congenital Malformation of the External Auditory Canal and Middle Ear

a­ butment is implanted behind the ear, where it osseointegrates to the mastoid bone. After a 3-month healing period the BAHA processor can then be connected. Audiologic indications for BAHA include a pure tone average bone-conduction threshold better than or equal to 45 dB hearing level (HL) (average 500 Hz, 1000 Hz, 2000 Hz, and 3000 Hz). A maximum speech discrimination score better than 60% when using PB (Phonetically Balanced) word lists is recommended. From an audiologic point of view, the side with the best cochlear function (the best bone-conduction threshold) should be used. Patients with a bone-conduction threshold of 25 to 45 dB HL would be expected to improve, but might not achieve levels in the normal range. Patients with a bone-conduction threshold of less than 30 dB HL (similar to most atresias) can be expected to experience hearing improvements that restore hearing levels to normal ranges. Patients must be able to maintain the abutmentskin interface of BAHA. Careful consideration must be given to the patient’s psychological, physical, emotional, and developmental capabilities to maintain hygiene. Titanium implants can be installed in most patients because allergy to titanium is extremely rare. Alternative treatments should be considered for patients with a disease that might jeopardize osseointegration. For patients with bilateral hearing loss, BICROS (Bilateral Contralateral Routing of Signal) hearing aid is an additional microphone that can be used as an accessory to an implanted BAHA fixture and sound processor to overcome the head shadow effect. The accessory microphone is placed in the contralateral ear to the BAHA fixture. The signal is routed from the accessory microphone to the BAHA sound processor via a wire worn behind the neck. It is intended to improve hearing by eliminating the head shadow effect, but it does so with little success and is not well accepted by patients.73 We do not generally recommend implantable hearing aids in children because the surgical scars may preclude any future microtia repair. However, the BAHA titanium implant is ideally placed 5 to 6 cm behind and 3 cm above the ear canal in a hair-bearing area. This placement seems to allow for the possibility of transplanting costal cartilage to an area with unscarred skin for future microtia repair. On the other hand the titanium implants for a boneanchored ear epithesis are ideally placed 18 to 20 mm behind the (future) ear canal; this interferes with the skin of a future auricle, if reconstruction is contemplated.73 Numerous studies have reviewed results with BAHA in atresia patients.3,74-77 In one series, 45 atresiaplasty surgeries were compared with 39 BAHA surgeries.3 Of 44 ears followed for more than 2 years after atresiaplasty, hearing gain was less than 10 dB in 55% and 10 to 30 dB in 43%. Surgical outcome correlated with Altmann classification: the worse the Altmann classification stage, the worse the surgical outcome. Within 5 years, 24 ears were reoperated on. Of the 39 patients supplied with BAHA, 16 had had prior atresiaplasty

59

work. All BAHA patients in the series considered the implant to be superior to conventional bone-conduction hearing aids, and superior to hearing improvement obtained surgically, for the difficult cases for whom atresiaplasty had been unsuccessful. Van der Pouw and colleagues74 described experience with bilateral BAHA in four patients with bilateral inoperable congenital aural atresia, three of whom had Treacher Collins syndrome. Bilateral BAHA application resulted in improved performance in all tested audiologic parameters, including sound localization, speech recognition in quiet, speech recognition in noise, and a cued listening task. Kunst and associates75 reported on the audiologic outcome of BAHA in 20 patients with congenital unilateral conductive hearing impairment, with a mean air-bone gap of 50 dB. Small, although not statistically significant, improvements in localization scores were observed in favor of BAHA. Some patients with congenital unilateral conductive hearing impairment had such good directional hearing and speech-in-noise scores in the unaided situation that no overall significant improvement occurred after BAHA fitting. Compliance with BAHA use was remarkably high, however, suggesting patient perceived benefit. House and Kutz76 reported the incidence of complications associated with implantation of BAHA in 149 patients and the management of these complications. There were no intraoperative or perioperative complications. Significant postoperative complications ­requiring intervention occurred in 12.8% of patients. Skin ­ overgrowing the abutment occurred in 7.4%, and all but one of these patients required revision in the operating room. Skin overgrowth was a late complication, occurring an average of 12 months (range 3 months to 2 years) after the initial procedure. Implant extrusion from failure to osseointegrate occurred in 3.4%. Two patients had local wound infections requiring oral antibiotics. One study evaluated hearing results in pediatric patients managed with EAC reconstruction or BAHA.77 The investigators also evaluated the medical cost­effectiveness of each procedure. They reviewed 36 ears that underwent surgical canal reconstruction and 6 patients who underwent BAHA placement. Most (93%) of the patients undergoing EAC reconstruction required some form of amplification postoperatively. The investigators concluded that BAHA can achieve acceptable hearing (<15 dB) in school-aged children with normal bone curves, and it can match the bone curves for children with SNHL. The two-staged BAHA system placement may be provided at almost one third the cost to the medical system of surgical EAC reconstruction, on a decibel-for-decibel basis, with single-stage placement yielding even greater cost savings. Implantable hearing appliances seem to offer a good alternative for patients with inoperable atresia and for patients in whom the operative prognosis is poor.

60

OTOLOGIC SURGERY

PREOPERATIVE EVALUATION AND PATIENT COUNSELING Early diagnosis with auditory brainstem response and auditory enhancement with bone-conduction hearing aids in bilateral cases should be done in the first weeks of life.78 Corrective surgery begins at 6 years of age. Imaging is deferred until age 6. Microtia repair is performed before atresiaplasty. The size of the mastoid on physical examination can be estimated by palpation of the mastoid tip, suprameatal spine of Henle (if present), condyle, and zygomatic arch. This is a useful measure because the new ear canal is constructed at the expense of the mastoid air-cell system. The preoperative imaging study is a high-resolution CT scan of the temporal bone in coronal and axial planes (Fig. 5-1).5,12,63,79 The CT scan must be examined ­ carefully by the otologic surgeon together with the otoradiologist.41,80 The four important imaging elements that are most helpful to the surgeon planning reconstruction of a congenitally malformed ear are (1) the degree of pneumatization of the temporal bone; (2) the course of the facial nerve, including the relationship of the horizontal portion to the footplate, and the location of the vertical segment; (3) the presence of the oval window and stapes footplate; and (4) the status of the inner ear.5,6,63 CT also provides information on thickness and form of the atretic bone, size and status of the middle ear cavity, and soft tissue contribution to the atresia,6 but these are less critical for the repair. Proponents of three-dimensional reconstruction CT for preoperative evaluation believe that three-dimensional imaging clearly shows the relationships between the condyle, zygomatic arch, temporal bone, temporomandibular joint, and fallopian canal. We have not found it to be of practical use, however. Lack of pneumatization is the major cause of inoperability in congenital aural atresia.6,33 Normal

I G H T

Y LIN R RED OM: 2 D: 400 V: 500

FIGURE 5-1.  Congenital aural atresia, right ear. Coronal high-resolution CT shows atretic external auditory canal and normally developed mastoid system, with normal inner ear.

­ neumatization is present in most cases. The facial nerve p over the oval window may prevent ossiculoplasty and hearing improvement. If the oval window or footplate are absent, surgery with fenestration of the lateral semicircular canal or placement of a hearing aid is indicated. There is potential for facial nerve injury in atresia surgery.81 The nerve may describe a more acute angle rather than its usual 90 to 120 degrees at the mastoid genu, and often lies more lateral than usual (Fig. 5-2).82 On high-resolution CT, it is important not to “identify” mistakenly the vertical lie of the facial nerve in the marrow bone leading to the styloid process and the hypoplastic mastoid process (Fig. 5-3).83 Even in atretic ears in which the facial nerve does not have an abnormal course, a significantly reduced distance is found between the facial canal and the ­temporomandibular joint,41 and the facial canal and the posterior wall of the cavum tympani.47 To be considered a surgical candidate, the patient must have sufficient cochlear function as determined by auditory brainstem response or routine audiometry; a ­normal-appearing inner ear on CT scan; and, preferably, a well-developed mastoid, and good oval window/footplate and facial nerve relationship. The patient and parents are counseled regarding the success of atresiaplasty repair and the chances of successful hearing improvement. Patients with a degree of malformation equivalent to an 8 or better on the Jahrsdoerfer grading scale are given a greater than 80% chance of hearing improvement. The risk to the facial nerve is small, made more so by the use of the facial nerve monitor intraoperatively.33,82 Patients are informed that a split-thickness skin graft (STSG) from the hypogastrium is used to line the new EAC. Initially, frequent postoperative visits are necessary. The possibilities of a facial nerve paralysis (<1%), profound SNHL (approximately 7%, no dead ears), postoperative canal stenosis (<4%), tympanic membrane graft lateralization (<4%), and ossicular chain refixation (<4%) are noted.84,85

SURGICAL APPROACH Early atresiaplasty operations failed because of poor tympanoplasty techniques, large mastoidectomies, and faulty skin grafting techniques.18 Advances in meatoplasty added to the success rate of atresiaplasty surgery, ­however.19,86 Although fenestration remains a rare option in bilateral congenital absence of the oval window, modern methods of ossiculoplasty are used preferentially and yield superior results.6,8,19,23,26,28,31,34-36,87-89 General endotracheal anesthesia is used; muscle relaxants are avoided. Facial nerve monitoring is used in all cases. The patient is in the otologic position, and the head is turned away. A large shave of the postauricular area is performed, and the auricle and postauricular area are prepared with povidone-iodine and draped. Additionally, the hypogastrium is shaved, aseptically prepared, and draped for the skin graft donor site.

Chapter 5  •  Congenital Malformation of the External Auditory Canal and Middle Ear

Oval window

61

Fused malleus-incus

Normal 95° to 120° 60°

A B FIGURE 5-2.  Facial nerve in congenital aural atresia. A, Normal intratemporal facial nerve anatomy. B, Intratemporal facial nerve anatomy in congenital aural atresia.

Care is taken to avoid injury to an anomalous facial nerve exiting the temporal bone in this area. Temporalis fascia is harvested, trimmed of excess soft tissue if needed, and placed aside to dry. The temporomandibular joint space is explored to verify that the facial nerve or tympanic bone is not lying within it. The literature has fostered the belief that there are separate and distinct approaches to the bony work necessary in atresiaplasty: the anterior approach, the transmastoid approach, and modification of the anterior approach.6,8,24, 33,35,57,64 We believe that strict distinction between these surgical approaches is unnecessary because each can be used alone or in combination to facilitate the ­atresiaplasty.

Surgical Technique FIGURE 5-3.  Pitfalls in congenital aural atresia surgery: facial nerve on coronal high-resolution CT. Arrows point to a vertical segment of the facial nerve in the left ear.

A postauricular temporo-occipital incision is made. In cases in which microtia repair has been done, care is taken not to expose the costal cartilage graft or alloplastic material used in the auricular reconstruction. Subcutaneous tissue is elevated anteriorly to the temporomandibular joint. An incision is made in the periosteum, which is elevated forward exposing the mastoid cortex and, anteriorly, the temporomandibular joint space (Fig. 5-4).

If a remnant of tympanic bone is present, drilling for the new ear canal begins at the cribriform area. If no such remnant exists, drilling of a 12 mm cylindrical-shaped canal begins at the level of the linea temporalis, just ­posterior to the glenoid fossa. Dissection proceeds anteriorly and medially, keeping in mind the lack of landmarks in atretic bone. The middle fossa plate is identified and followed to the epitympanum, where the fused malleus head/incus body mass is identified (Fig. 5-5). Care is taken to avoid exposure of the temporomandibular joint space or to avoid opening an excessive number of mastoid air cells. A radical mastoidectomy–like approach should be avoided. When the ossicular mass is identified,

62

OTOLOGIC SURGERY Mastoid periosteum reflected TMJ Cribriform area Temporalis fascia

FIGURE 5-4.  Incision, harvesting temporalis fascia, T-incision, and elevation of periosteum. TMJ, temporomandibular joint.

12 mm Ant.

12 mm

Sup.

outer diameter

inner diameter

Inf.

Removal of atretic plate

Post.

FIGURE 5-5.  Removal of atretic plate and adhesions, exposing the ossicles, and drilling for the new ear canal.

the atretic bone is removed with diamond microdrills and curettes to expose the ossicles completely (Fig. 5-6A). It is important to minimize drilling on the ossicular mass because transmission of high-speed drill energy to the inner ear may result in high-tone SNHL. An argon laser is used to free the malleus-incus complex from its soft tissue attachments to reduce potential drill trauma to the inner ear. The ossicular mass in the epitympanum is meticulously dissected free of the atresia plate and left

intact. Although the temporomandibular joint often limits anterior dissection, particular effort is made to try to create a space of 2 mm or greater, anterior to the ossicular mass (Fig. 5-6B). The horizontal facial nerve always lies medial to the ossicular mass. While dissecting the inferior and posterior aspect of the canal, an aberrant facial nerve may be encountered as it passes laterally through the atretic bone. Drilling for the new ear canal continues until it measures about 12 mm. This circumference is

Chapter 5  •  Congenital Malformation of the External Auditory Canal and Middle Ear

63

A

A Atretic plate

I

S

S

MF plate

Mastoid genu of facial n. (Fallopian canal) 2 mm space

A

P

B

P

FIGURE 5-6.  A and B, The ossicular mass is dissected free of the atretic plate, and a 2 mm space is created around the ossicles. MF, middle fossa.

most difficult to achieve medially, where the facial nerve, temporomandibular joint capsule, and middle fossa plate limit larger exposure. Reconstruction with the patient’s own ossicular chain is performed in almost all cases, even if the ossicular chain is deformed. If the ossicular chain is intact, it is left in place and used for ossicular reconstruction. When this is impossible, a total or partial ossicular reconstruction prosthesis to either a mobile footplate or the stapes head is used for reconstruction. The prosthesis is covered with cartilage before grafting the new drum. Occasionally, the stapes footplate may not be seen well because of anomalous facial nerve anatomy, making placement of an ossicular prosthesis difficult or dangerous. In these instances, gentle transposition of the facial nerve has been described, but more commonly hearing restoration can be accomplished with lateral semicircular canal fenestration or the patient can be counseled to use a hearing aid only.4,8,17,26,31,36,42 Drilling continues to create an EAC. It must be one and one third times the size of a normal canal (12 mm versus 9 mm) to allow for contracture healing in the postoperative period. While creating the EAC, care is taken not to open mastoid cells or enter the temporomandibular joint unnecessarily. A dermatome is used to obtain a 0.008-inch thick, 6 × 6 cm STSG from the hypogastrium. Pressure with a gauze sponge soaked in 1% lidocaine with epinephrine 1:100,000 and thrombin solution aids hemostasis of the donor site. When dry, the donor site is dressed with a sterile Tegaderm dressing.90 This dressing reduces most

of the pain associated with other methods of donor site care. One edge of the skin graft is cut in a zigzag fashion to create four or five triangular points (Fig. 5-7). To assist inspection of the skin graft in the final stages of the procedure, the tips of each point and the two corners on the opposite edge are colored with a skin marker. The dried temporalis fascia is trimmed to size, ideally a 20 × 15 mm oval, and a small 4 mm “tab” is cut into the anterior-inferior aspect of the graft in an attempt to prevent lateralization.91 Nitrous oxide is discontinued 30 minutes before grafting begins. The fascia is placed over the ossicular chain medial to the malleus, if present, or over the cartilage that covers the prosthesis (Fig. 5-8). The tab of the graft is placed medially into the protympanum to help prevent lateralization of the new eardrum. Next, the new ear canal is circumferentially lined with the STSG so that all the bone is completely covered (Fig. 5-9). The triangular corners of the skin graft are placed medially and partially overlap the fascia. The colored points help ensure that no skin lies folded on itself, and that the entire width of the graft is used. A single layer of antibiotic-soaked absorbable gelatin sponge (Gelfoam) holds the fascia and skin graft in place. To reproduce the anterior tympanomeatal angle, a disk of absorbable gelatin film (Gelfilm) is placed over the fascia and skin graft. Lateralization is the most common delayed cause of a poor hearing outcome, usually occurring in the first 12 months after surgery. When the graft starts lateralizing, it pulls away from the ossicles, and the original good hearing results slowly deteriorate. After the fascia

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and skin graft are in proper position, three 0.020 inch silicone elastomer (Silastic) strips are placed to line the skin (Fig. 5-10). The Silastic strips help prevent adhesions between the skin graft and the ear canal packing, and ensure good contact between the skin graft and ear canal bone. A 9 × 15 mm Merocel wick is placed in the bony canal. A 12 mm meatus is created, anticipating that a third of its diameter will reduce because of normal healing. Before starting the meatoplasty, the ear is turned back, and the periosteum is brought back in place with one absorbable suture at the superior level of the new ear canal; this stabilizes the pinna and helps ensure that the meatus is at the same level as the new ear canal. Skin, subcutaneous tissue, and cartilage are removed in a 12 mm diameter core over the new meatus. An attempt is made to avoid exposing

6 cm

Lateral end Blue lines

Shape of STSG when in EAC

6 cm

Split-thickness skin graft

Medial end

Blue dots

FIGURE 5-7.  Split-thickness skin graft (STSG) used to line new external auditory canal (EAC).

the grafted cartilage or other materials used for auricular reconstruction. The lateral edge of the STSG is brought through the meatoplasty, and the lateral portion of the new ear canal and the meatus are packed with a large 15 × 25 mm Ambrus wick (Ambrus Merocel, Medtronic Xomed Surgical Products, Jackonsiville, Florida) this applies diffuse pressure over the entire lateral skin graft and widely packs the meatoplasty. Five tacking sutures of 5-0 braided polyester (Ticron) attach the lateral edge of the skin graft circumferentially to the meatal skin. Finally, 6-0 fast-absorbing plain gut is used in a running manner between each Ticron suture (Fig. 5-11). The periosteum is sutured back into position. The postauricular incision is closed using absorbable sutures (3-0 polyglactin 910 [Vicryl]). Steri-Strips cover the incision, a mastoid dressing is applied, anesthesia is reversed, monitoring equipment is removed, and the patient leaves the operating room. Silastic sheets and Merocel wicks have helped decrease the incidence of tympanic membrane lateralization by maintaining the tympanic membrane graft in position and the incidence of postoperative EAC stenosis by covering all exposed areas of bone that may cause granulation tissue formation.85 The Merocel wicks, which are now available in many sizes for canal stenting, help prevent postoperative infection and granulation tissue by allowing administration of topical antibiotics to the entire EAC.

12 mm

I (F) A

P

S Temporalis fascia (F)

FIGURE 5-8.  Temporalis fascia graft with tab used over an ossicular mass or a partial ossicular replacement prosthesis and cartilage. F, temporalis fascia.

Chapter 5  •  Congenital Malformation of the External Auditory Canal and Middle Ear

65

Running suture

STSG

(Enlargement)

Fascia (F) Gelfilm (G)

G F

B

A FIGURE 5-9.  A and B, Split-thickness skin graft (STSG) in place over fascia, lining new external auditory canal, and disk of Gelfilm over fascia and skin graft.

Transmastoid Approach (Canal Wall Down Technique) The transmastoid approach is of historical interest only (Fig. 5-12). It has not been used since 1975. In this approach, the drilling starts as posterior as possible from the temporomandibular joint. It starts at the linea ­temporalis and follows the sinodural angle to the ossicular mass. Mastoid air cell exenteration and lowering of the facial ridge to the facial nerve allows the creation of an EAC with a canal wall down technique. Bone pâté and soft tissue obliteration of the large mastoid cells is performed before undertaking meatoplasty and canal skin grafting. The transmastoid approach resulted in a large mastoid cavity with frequent postoperative drainage, and patients were not allowed to swim.

POSTOPERATIVE CARE The mastoid dressing is removed on the first postoperative day. The Steri-Strips are left in place over the postauricular incision for 7 days. The patient is counseled to keep the operative site dry and to change the cotton ball over the canal/meatus packing four times daily. The Tegaderm over the skin graft donor site is left on for at

least 3 weeks and requires no special attention. Epithelialization occurs under the plastic, and the typical pain associated with older methods of donor site dressing is absent.90 The patient is given a 5-day course of oral ­antibiotics. The patient is seen 1 week after surgery, at which time the postauricular strips and the tacking Ticron sutures at the meatus are removed. Any dried blood or crusting on the lateral end of the meatus pack should be trimmed. The donor site is inspected. The postauricular site can now be washed, but water precautions continue to apply to the ear canal. We continue to see the patient on a weekly basis. At 2 weeks, the Merocel packs and Silastic are removed, and the meatus is repacked with antibiotic-soaked Gelfoam. At this point, the patient should apply antibiotic suspension to the packing in the ear canal twice a day for 8 to 12 weeks. Usually by 3 weeks, the abdominal donor site has completed the initial re-epithelialization, and the Tegaderm may be removed. By 6 to 8 weeks postoperatively, nearly all of the Gelfoam is usually gone, and the canal is healing well. The first postoperative audiogram is obtained at that time and repeated in 6 months, at 1 year, and yearly thereafter.

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6. 1. 2. 3. 4. 5. 6.

5. 4.

Fascia STSG Gelfilm Silastic sheets ´ 3 1st wick 9 ´ 15 mm 2nd wick 15 ´ 25 mm

Enlargement

4.

5.

4.

2.

4.

2. 3.

2.

2.

1.

3. 1.

A Ant.

Sup.

B

2.

Inf. 1.

4. 4.

Silastic strips

4.

C

Post.

FIGURE 5-10.  A-C, Split-thickness skin graft (STSG) and Silastic strips with ear wicks to maintain contact with bony external auditory canal and wide meatus.

PITFALLS Clear communication between the surgeon and the anesthesiologist ensures that the patient is not paralyzed during the procedure, so that facial nerve monitoring, which is essential in these cases, can be effective. When the monitor is turned off transiently owing to the use of electrocautery, we monitor the facial nerve manually with

a hand on the patient’s face. In a poorly pneumatized mastoid, the otic capsule may be difficult to distinguish from surrounding bone, so care is taken not to fenestrate the semicircular canals accidentally. Postoperative care is crucial to achieve proper healing. Patients should understand beforehand that they must follow the postoperative instructions strictly, and that they must keep all scheduled postoperative visits. We check the circumference of

Chapter 5  •  Congenital Malformation of the External Auditory Canal and Middle Ear

the pack each week and allow air to enter the EAC. If the meatus appears to be narrowing, usually at the third month, it should be dilated every 2 weeks and restented with a Merocel wick for a period of several months to 2 years. This practice usually eliminates the need of reoperation. Early identification and treatment of infection is also necessary to prevent graft failure and canal stenosis.

STSG sutured to new EAC

Wick

FIGURE 5-11.  Skin graft sutured into place at meatus. EAC, external auditory canal; STSG, split-thickness skin graft.

RESULTS Numerous publications have described atresiaplasty results in more than 500 patients from our institution over time.6,33,84,85,92 Our most recent reviews were published in 2003 and 2004 and included 116 atretic ears operated at the House Ear Clinic.84,85 Closure of the airbone gap to 30 dB at short-term (<6 months) ­ followup occurred in 58.5% of primary surgeries and 56% of revisions.84 The long-term (≥6 months) postoperative air-bone gap was 30 dB or less in 50.8% and 39.1% respectively. There was no significant change in air-bone gap from short-term to long-term follow-up for either primary or revision cases. Soft tissue stenosis occurred in 8% of primary surgeries and 3.4% of revisions, and tympanic membrane lateralization occurred in 3.4% and 3.4% respectively, an improvement from the previous series reported in 1995. The lower complication rates resulted from anchoring the fascia graft medial to the malleus handle, placing the tabs created in the graft into the hypotympanum and protympanum, using a Gelfilm disk to form an anterior tympanomeatal angle and to keep the graft in position, and using thinner STSG and Merocel Ambrus ear packs. One of the most common causes of postoperative hearing loss after congenital aural atresia surgery is ossicular chain refixation; this occurred in 11.5%

Transmastoid approach

Tympanic bone remnant

Middle fossa plate

67

TMJ

Deformed malleus Normal incus Stapes Horizontal canal

Posterior canal wall created Sinodural angle

FIGURE 5-12.  Transmastoid approach: of historical interest only. TMJ, temporomandibular joint.

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OTOLOGIC SURGERY

of primary cases and 6.9% of revision cases. To try to avoid refixation, we vaporize fibrous ligaments and bony adhesions with argon laser in the final phases of ossicular dissection. By 1994, all the modifications used in current practice (use of argon laser, thinner STSG, Silastic sheets in the EAC, and Merocel wicks) were routinely being employed. On this basis, the patients were divided into two groups: old cases performed before the changes in surgical technique (n = 36), and new cases that included surgeries performed after these changes were introduced (n = 80).85 We compared complication rates and hearing results before and after the introduction of the new techniques. Overall, the new group had better hearing results and lower rates of complications. Closure of the air-bone gap to 30 dB or less at short-term follow-up occurred in 63.1% of surgeries performed after modifications in the surgical technique and 44.5% of surgeries performed before the modifications. Soft tissue stenosis and bony growth of the EAC were seen in 3.8% of surgeries performed after and 13.9% of surgeries performed before the surgical technique changes. Tympanic membrane lateralization occurred in none of the cases performed after and in 11.1% of the surgeries performed before the surgical technique changes. Ossicular chain refixation occurred in 3.8% of surgeries performed after and 25% of surgeries performed before the modifications. There were no dead ears and no facial palsies in either group. Shih and Crabtree93 reviewed long-term surgical results for 39 ears. Hearing averages of 25 dB, 40 dB, and 46 dB were achieved for mild, moderate, and severe atresia. Restenosis occurred in 33%, and 31% had recurrent cavity/canal skin infections. This rate was reduced with the use of STSG. Digoy and Cueva94 reviewed their short-term (<1 year) and long-term (>1 year) surgical and hearing results for congenital aural atresia in 45 patients (54 ears). Approximately 50% of their patients achieved a speech reception threshold of 30 dB or better in the short term and long term. The average improvement in air-bone gap was 22 dB. Short-term and long-term outcomes were not significantly different. Patients with an intact ossicular chain did not seem to have a significant advantage in hearing compared with patients with a reconstruction prosthesis. They reported meatal stenosis in 7% and tympanic membrane lateralization in 18% of the cases. Persistent or recurrent conductive hearing loss after an initial satisfactory improvement can occur after this procedure and is usually secondary to lateralization of the tympanic membrane or ossicular chain refixation. Modifications used in the surgical technique, such as Silastic sheets, Merocel wicks, Gelfilm disks and tabs in the fascia graft placed in the protympanum, have helped decrease the incidence of these two complications and achieve better hearing results. Stenosis of the ear canal

is one of the most common postoperative complications. The subsequent routine use of STSG, covering all exposed bony and soft tissue surfaces, allows for quicker epithelialization and healing with a reduction in postoperative infection and stenosis. The use of Merocel packs and Silastic sheets has also helped decrease soft tissue stenosis. The Merocel wick placed in the EAC exerts enough pressure to hold the skin graft against the bone, and the Silastic sheets used to line the ear canal make the skin look smooth, with no bubbles, after the packing is removed.

COMPLICATIONS AND THEIR MANAGEMENT Complications of atresiaplasty at our institution for cases operated with the most current technique include lateralization of the tympanic membrane in 3.4%, stenosis of the meatus in 3.8%, high-tone SNHL in 7.5%, and facial nerve palsy in less than 1%.84,85 Other authors have reported meatal stenosis in 7% and tympanic membrane lateralization in 18% of their cases.94 Care is taken at the time of surgery to help minimize the incidence of lateralization. Modern techniques of tympanoplasty are applied during the reconstruction. Nitrous oxide is discontinued 30 minutes before grafting. The graft is anchored medially to the malleus, and tabs are placed into the protympanum. An accurately sized Gelfilm disk is used in an attempt to recreate an anterior tympanomeatal angle, minimizing blunting and keeping the graft in position. Silastic sheets and Merocel wicks placed in the EAC also help minimize the incidence of lateralization. The patient must be followed carefully for at least 24 months because lateralization has been known to occur up to 12 months postoperatively. The incidence of stenosis has been greatly reduced with the use of one-piece STSG covering all exposed bone, and Silastic sheets and Merocel wicks in the EAC.85 Local care and prevention of infection avoid graft failure and early restenosis. Careful inspection of the meatus and early restenting with large Merocel wicks can obviate reoperation. Bony EAC stenosis with a “bumpy” exostosis-like appearance tends to occur more frequently in young patients84; this is probably due to active bone growth at this age, resulting in an exuberant bone regrowth in the newly created EAC. This problem seems to be greatly underreported in the literature. Although laser is used in an attempt to reduce noise trauma to the inner ear and manipulation of the ossicular chain, cases with SNHL and noise-induced hearing loss are still observed. To reduce the risk of inner ear trauma, it is crucial to minimize drilling on the ossicular chain when dissecting it away from the atretic bone, but noise transmission during ear canal creation cannot be completely avoided.

Chapter 5  •  Congenital Malformation of the External Auditory Canal and Middle Ear

With high-resolution CT, the oval window can be identified, and problems of SNHL resulting from oval window drill-out can be anticipated. Patients with severe malformations, in whom surgery would be fraught with problems, can be counseled against surgical intervention and fitted with hearing aids or BAHA. With CT, the facial nerve position and trajectory inside the temporal bone can be identified, and, along with facial nerve monitoring, use of this information can reduce the incidence of facial nerve paralysis further.

UNILATERAL ATRETIC EAR Controversy remains over whether children with unilateral atresia should undergo surgery. Jahrsdoerfer8 and De la Cruz and coworkers6 have argued for atresia surgery in selected patients with unilateral atresia. Other authors support this position.95 In the past, Schuknecht,96 Crabtree,28 and Bellucci52 recommended against operating on children with unilateral atresia. These authors argued that the benefit to be gained is minimal in the presence of a contralateral normal-hearing ear. Hearing results at that time were unpredictable and often did not approach the 20 dB air-bone gap needed for useful hearing in the atretic ear. Risks of surgery, including facial nerve injury, also precluded operating on the unilateral atretic ear. In a review of more than 1000 operations for aural atresia with and without cholesteatoma, however, Jahrsdoerfer and Lambert97 showed that the risk was minimal (1%). The incidence of major complications (total SNHL and facial nerve injury) and of other complications (tympanic membrane graft lateralization and restenosis) has decreased over the years, but these are still potential complications. The decision to operate on the unilateral atretic ear must weigh these potential complications along with the possibility of a draining ear. Nevertheless, with excellent preoperative imaging, improved surgical techniques, and advances in technology, we believe the results of atresia surgery are now more predictable. Closure of the air-bone gap to within 30 dB in a properly selected patient can be consistently achieved, and hearing remains stable over the length of follow-up.84 A review examining long-term stability of hearing results in patients operated on for aural atresia does show some drop-off in hearing thresholds (speech reception threshold) over time, ­ however.84,85,98 In the hands of an experienced otologic surgeon with an anatomically favorable patient who (with the parents) understands the risks of potential complications and the need for postoperative care, atresiaplasty in the patient with unilateral atresia is a rewarding operation for the surgeon and the patient. Surgical correction of unilateral atresia offers the benefits of a clean, dry ear with binaural hearing, including sound localization and improved hearing in noise.

69

SUMMARY The treatment of congenital aural atresia poses a challenge. Early identification, appropriate hearing amplification, and speech and language therapy are crucial in bilateral cases. Cooperation with the auricular reconstruction surgeon allows for the best esthetic and functional success. Strict radiologic and clinical criteria are necessary to select appropriate candidates for atresiaplasty. Classification of patients into categories of minor and major malformations provides a guide for prognosis for hearing improvement and potential risks of surgery. A thorough understanding of the embryologic development of the ear and adherence to the surgical principles of tympanoplasty, canalplasty, and facial nerve surgery enable optimal and safe hearing restoration. Maintenance of good initial surgical results and avoidance of late compli­ cations require diligent postoperative office care. BAHAs provide a good alternative for patients who are poor atresiaplasty candidates.

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