SOURCE: Grand Rounds Presentation, UTMB, Dept. of Otolaryngology
DATE: November 17, 1999
RESIDENT PHYSICIAN: Stephanie Cordes, M.D.
FACULTY PHYSICIAN: Jeffrey Vrabec, M.D.
SERIES EDITOR: Francis B. Quinn, Jr., M.D.
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Congenital aural atresia is a birth defect characterized by hypoplasia of the external auditory canal, middle ear, and occasionally the inner ear. The anomalies occur in varying combinations and severity. The rate of occurrence is 1 in 10,000 to 1 in 20,000 live births. Unilateral atresia is three times more common than bilateral atresia, more common on the right side, and males are more commonly affected. Associated with a variety of syndromes and disorders as well as occurring in isolation, the severity of aural atresia can range from a mild malformation with a membranous external auditory canal narrowing and a normal middle ear to a severe malformation characterized by the complete absence of the external auditory canal, middle ear, and ossicles as well as an anomalous facial nerve. The challenge facing the otologic surgeon is to create a functional conductive pathway for sound, from the external ear to the cochlear fluids, while preserving the facial nerve and labyrinth function and avoiding postoperative canal stenosis or infection.
A general knowledge of the embryologic development of the ear is essential for understanding the altered surgical anatomy of congenital aural atresia. The inner ear, middle ear, and external ear develop independently and in such a way that deformity of one does not necessarily presuppose deformity of another. Usually, abnormalities of the outer and middle ear are encountered in combination with a normal inner ear structure. The external ear is derived from the first branchial cleft and pouch and begins development during the fourth week gestation. Growth of mesenchymal tissue from the first and second branchial arches forms the six hillocks around the primitive meatus that fuse to form the auricle. The primitive auricle has been completed by the end of the third month.
The external ear canal and tympanic membrane are derived from the first branchial cleft and initially is represented by a solid core of epithelial cells that extends down to the area of the tympanic ring and first pharyngeal pouch. This core of epithelial cells remains in place until the seventh month of fetal life. At this point, absorption of the epithelial cells begins, progressing in a medial to lateral direction. If this process is arrested early, it is possible to have a more normally developed tympanic membrane and bony external canal in association with an atretic or very stenotic membranous external canal. A stenotic external ear canal predisposes to formation of canal cholesteatoma as the trapped squamous epithelium continues to desquamate.
The medial portion of the external ear canal is formed by the tympanic bone. By the third embryonic month this structure begins to ossify and eventually forms the tympanic ring and osseous ear canal. The osseous ear canal continues its lateral growth during the first and second postnatal years. Malformation of the tympanic bone produces atretic bone at the level of the tympanic membrane and results in atresia of the ear canal.
The eustachian tube, middle ear, and mastoid air cells are derived from the first pharyngeal pouch. In patients with aural atresia the middle ear cavity and mastoid air cells are smaller than normal. Pneumatization of the mastoid is a late embryologic event that starts in the seventh or eighth fetal month and continues into postnatal life. Therefore, a well pneumatized mastoid usually indicates good middle ear development. The pharyngeal pouch grows outward to form the middle ear cleft. The expanding middle ear cleft surrounds the ossicles and covers them with a mucous membrane by the end of the seventh or eight fetal months.
The development of the ossicular chain begins within the first 4 weeks of embryogenesis. The ossicles, except for the footplate of the stapes, are formed from the first and second branchial arches. In congenital atresia, a bony fusion of the incudomalleolar joint is present. Of the two ossicles, the malleus is more deformed and usually smaller in size. The head of the malleus is fixed to the atretic bone by a bony union. The stapes footplate is formed in part from the lamina stapedialis of the otic capsule and is usually normally developed in congenital atresia ears. It is uncommon to encounter a fixed stapes in patients with aural atresia, although the superstructure is usually deformed. This is important because the stapes is often partially obscured by the lateral ossicular mass or facial nerve and the mobility may be difficult to assess.
The facial nerve begins its development from the acoustico-facial primordium. At about 5 weeks gestation, the cells of the primordium begin to differentiate into the neuroblasts of the geniculate ganglion, along with the main trunk of the facial nerve and chorda tympani. By the seventeenth week of development, all the neural components of the facial nerve have completed their connections. At this point the facial nerve is more anterior and superior than in the adult. As the tympanic ring and mastoid tip develop the facial nerve follows more of the adult course. Facial nerve abnormalities are common in cases of congenital ear malformations. In congenital aural atresia, the facial nerve is found to be displaced in 25% to 30% of all cases. Bony dehiscence of the fallopian canal is common. The facial nerve may also take an anomalous course that is usually more anterosuperior as compared to its normal course. Typically, the facial nerve makes an acute angle at the second genu, crossing the middle ear in a more anterior and lateral direction to exit into the glenoid fossa. In such cases, the facial nerve may lie just deep to the area of the tragus. A correlation between the degree of microtia and the extent of facial nerve abnormality has been noted.
Congenital aural atresia can therefore range in severity from a thin membranous canal atresia to a complete lack of tympanic bone, depending on the time of arrest of intrauterine development. The usual finding of a normal inner ear is explained by the fact that the inner ear has already formed by the time of external or middle ear development arrest. Only very severe congenital malformations of the external and middle ear are associated with inner ear deformities.
Altmann developed a widely used classification system in congenital aural atresia in 1955. In this system, atresia is categorized into three groups with attention given to the anatomical variations of the external auditory canal and middle ear. In group 1 or mild malformation, some part of the external auditory canal is present but hypoplastic. The tympanic bone is hypoplastic with possible ossicular malformation and the tympanic membrane is small. The tympanic cavity is either normal or hypoplastic in size. In group 2 or moderate malformation, the external auditory canal is completely absent. The tympanic cavity is small and its contents are deformed with malleus and incus fixation. The canal atresia is either partly or completely osseous. In group 3 or severe malformation, the external auditory canal is absent, and the tympanic cavity is markedly hypoplastic or missing. The ossicles may be absent.
Several other authors have developed classification systems similar to the Altmann system. De La Cruz has modified this system with more practical surgical guidelines. This modification involves only advanced Altmann groups 2 and 3 and divides the abnormalities into major and minor categories. Minor malformations consist of normal mastoid pneumatization, normal oval window, reasonable facial nerve-oval window relationship, and normal inner ear. The major malformations are poor pneumatization, abnormal or absent oval window, abnormal course of the horizontal portion of the facial nerve, and abnormalities of the inner ear. The clinical importance of this classification is that surgery on the cases of minor malformations has a good possibility of yielding serviceable hearing, whereas cases of major malformations are frequently inoperable.
There is however several other classification systems used by surgeons. The several classifications of congenital aural atresia that have appeared in the literature are based variously on temporal bone studies, clinical evaluations, surgical findings and type of repair, or a combination of these modalities. One other classification described by Schuknecht is based on a combination of both clinical and surgical observations, but is based principally on surgical observations. Type A or meatal atresia is limited to the fibrocartilaginous portion of the external auditory canal. The atretic area has an opening that is too small to permit the spontaneous egress of desquamated keratin and therefore is predisposed to cholesteatoma formation. Type B or partial atresia has a narrowing and sometimes toruosity of both the fibrocartilaginous and bony parts of the external auditory canal. The tympanic membrane size is often reduced and replaced at least in part by a bony septum. There are usually middle ear deformities including ossicular malformations. Hearing loss ranges from mild to severe. Type C or total atresia includes all cases that have a totally atretic canal, but well developed pneumatization of the tympanic cavity. There is a partial or complete bony atresia plate. Characteristically, the tympanic membrane is missing, the head of the malleus is slightly deformed with fixation to the atresia plate, and the head of the malleus and body of the incus are fused. The facial nerve occasionally takes a more anterior course, in which case it may partially overlap the oval window and proceed anteriorly within the atresia plate. Type D or hypopneumatic total atresia there is the full constellation of dysmorphic features listed in type C, as well as reduced pneumatization of the temporal bone. There is usually an abnormal course of the facial nerve as well as abnormalities of the bony labyrinth.
Aguilar and Jahrsdoerfer developed a rating point system to establish criteria by which to select surgical candidates. These criteria are based on anatomical variations of the external auricle, canal, middle ear, facial nerve course, and mastoid pneumatization. This point-grading system is a guide to surgeons in their preoperative assessment of the best candidates for hearing improvement. Point allocation is based primarily on the findings on high-resolution computed tomography. They have found that when the preoperative evaluation of the patient is incorporated into this grading system, the best results will be achieved with a score of 8 or better. A score of 7 implies a fair chance, 6 is marginal, and below 6 the patient becomes a poor candidate for hearing improvement.
In 1983, Chiossone presented a classification based primarily on the location of the glenoid fossa. In type I, the fossa is in normal position. In type II, the fossa is moderately displaced. In type III, the fossa overlaps the middle ear. In type IV, the fossa overlaps the middle ear and there is poor mastoid pneumatization. Cases with types I and II are ideal surgical candidates. Type III cases have a tendency for graft lateralization. Type IV cases are not surgical candidates.
Most cases of major congenital ear malformations are evident at birth because of microtia or other craniofacial abnormalities. Patients with a normal or only slightly deformed pinna and a stenotic or blindly ending external auditory canal may escape diagnosis for years. For parents, the discovery of congenital aural atresia in a newborn infant is a cause for great anxiety. A sense of frantic urgency for corrective surgery is followed by a period of emotional stress that demands thoughtful and realistic professional counseling.
All patients require formal assessment. When initially evaluating an infant or young child with congenital aural atresia, two principal objectives are 1) to assess the overall hearing status and need for immediate amplification and 2) to formulate a treatment plan that provides for consultation with members from other specialties and for acquisition of data necessary to make further recommendations for rehabilitation and possible surgery. The history should include any family history of atresia. In the case of a child, achievement of neurologic milestones, such as speech and ambulation, is assessed. This information can give insight into auditory and vestibular development. The physical examination should be performed by the otologist and evaluate overall craniofacial development looking for other syndromes involving the first or second branchial arches. Careful palpation of the mandible may reveal a mild hemifacial microsomia. Development of the palate and other intraoral structures should be assessed. The degree of aural development should be assessed. If atresia is present, it should be noted if the canal ends in a blind pouch or if the tympanic membrane is present. The tympanic membrane may reveal an anterior displacement of the malleus handle or a bony shelf extending from the posterior canal wall. If canal stenosis is present, it is important to note if cholesteatoma is forming medial to the narrowing. Each major division of the facial nerve should be carefully examined and any weakness or asymmetry noted. The most common anomaly of facial function is a congenital absence of the depressor anguli oris muscle.
Evaluation of auditory function follows. Behavioral audiometry can be used in most cases, but auditory brainstem response (ABR) testing may be necessary in young infants or children who are difficult to test. Patients with bilateral atresia present a difficulty in assessing their auditory function because of the masking dilemma. In such cases, it is essential to determine the level of cochlear function in each ear to prevent operating on an only-hearing ear or on an ear with little or no potential for hearing improvement. Bone conduction auditory brainstem response testing can provide information about both ears. The wave I response on the ABR is ear specific and allows differential assessment of cochlear function. If the ear canals are patent, electrocochleography can be used in a similar way to obtain ear specific information. Auditory testing determines the need for hearing aids.
Computed tomography (CT) of the temporal bone is necessary in all patients to determine the patients’ candidacy for surgical correction. Immediate CT scanning is required if sensorineural hearing loss is documented, otherwise defer scanning until the time of pre-surgical consultation (usually about age 4 or 5). To completely assess middle ear development, projections in the axial and coronal planes are necessary. The body of the malleus and incus, the incudostapedial joint, and the round window are best seen by axial scans, but the stapes, the oval window, and the vestibule are best delineated by coronal scans. Both projections are needed to follow the course of the facial nerve.
The decision to operate depends primarily on the degree of middle ear development. The CT also is good for assessing the development of the cochlear and vestibular labyrinths because their appearance can influence middle ear surgery. CT usually can delineate the course of the facial nerve. The inability to define this structure precisely is not a contraindication to surgery, assuming the other criteria for middle ear development are met. CT can also reveal cholesteatoma formation, which would necessitate surgical intervention. Almost all patients with cholesteatoma formation are older than 3 years.
The decision regarding surgery to restore hearing should be delayed until the process of pneumatization of the temporal bone is well advanced, which would be about 5 years old. For patients with unilateral involvement, some otologists advise against surgery, while others recommend that the decision for surgery be delayed until adolescence or adulthood, when the patient can make the decision on the basis of their perceived handicap and a realistic appraisal of expected surgical results. The audiologist can provide amplification and assistive auditory devices, lip reading instruction, special education, and parental guidance from infancy to age 5. Given good cochlear function, such children should experience normal intellectual growth.
Medical management consists of listening devices and hearing aids. No medical intervention needed in the patient with unilateral atresia and normal hearing in the contralateral ear. The parents can be reassured that speech, language, and intellectual development will proceed normally. Preferential seating in school is advised. Many adults find the consequences of unilateral hearing loss from unilateral atresia to be a significant aggravation at work and in social settings, and more readily accept hearing aids. In patients with atresia of the ear canal, a bone-conduction hearing aid must be used. If the canal is only stenotic, an air-conduction aid is preferred because of cosmesis, improved sound localization, broader frequency response, and less sound distortion. Early amplification in children with bilateral atresia is essential. A bone-conduction hearing aid should be applied as soon as possible, ideally in the third or fourth week of life. The use of implantable hearing aids are controversial because the surgical scars preclude future microtia repair.
Although most otologic surgeons would consider atresia repair in bilateral cases, many are reluctant to operate on unilateral atresia. The concern is the degree and predictability of hearing improvement that can be achieved, potential lifetime care of a mastoid cavity, and the risk to the facial nerve in atresia surgery. These concerns have prompted many surgeons to recommend delaying surgery in unilateral cases until adulthood, when patients can make their own decision. An improvement in the hearing threshold to 25dB or better eliminates the handicap of unilateral hearing loss. This degree of hearing improvement is not possible in all atresia cases, but it can be achieved in at least 50% of carefully selected patients. The recent trend among authors is to operate on "properly selected" cases at the age of 5 or 6 years. Citing the importance of binaural hearing, they operated on patients selectively who were more likely to achieve a residual conductive deficit of 30dB or less after surgery. This prediction of postoperative success depended on meeting certain criteria developed by each surgeon based on the surgeon’s personal experience.
Patients with bilateral atresia present less of a surgical dilemma. The goal in these cases is to restore sufficient hearing so that amplification is no longer needed. Most surgeons recommend operating as the child approaches school age and, depending on the hearing result, on the second ear within the next several years. Although the selection criteria are not as stringent as in unilateral cases, careful patient screening is essential for routinely satisfactory results. Patients with cholesteatoma, regardless of CT or audiometric findings, should undergo surgery to eradicate the disease process and, if possible, improve hearing. Patients with stenosis of the external canal who are at risk for cholesteatoma should be considered for surgery.
Surgical candidates must have normal bone conduction thresholds and good speech discrimination, and no inner ear abnormalities. Patients who on CT scan have little or no pneumatization of the middle ear and mastoid are not surgical candidates. There are two basic surgical approaches for repair of aural atresia: the mastoid approach and the anterior approach. For both operations general anesthesia with no paralysis is used. The patient is placed in the otologic position and the head is turned away. Facial nerve monitoring is used in all cases. The postauricular area is shaved and the patient is prepped and draped. Additionally, the lower abdomen is shaved, prepared, and draped for the skin graft donor site. A postauricular temporo-occipital incision is made. In cases with previous microtia repair, care is taken not to expose the grafted costal cartilage. Subcutaneous tissue is elevated anteriorly to the temporomandibular joint. A T-shaped incision is made in the periosteum, which is elevated, exposing the mastoid cortex and temporomandibular joint space. Care must be taken to not injure an anomalous facial nerve that could be exiting the temporal bone in this area. A large piece of temporalis fascia is harvested 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 anterior approach begins drilling at the remnant of the tympanic bone and if there is no such remnant then drilling is begun at the linea temporalis, just posterior to the glenoid fossa. By use of cutting and diamond burrs, the dissection is carried anteriorly and medially. The middle cranial fossa dura is the superior landmark and the temporomandibular joint is the anterior landmark. The bone that is removed is usually solid, but may be cellular in areas. The posterior wall of the glenoid fossa should be very thin to maximize anterior exposure and to limit opening into the mastoid air cells. The middle fossa dura is followed medially to the epitympanum, where the fused malleus and incus heads are identified. Care is taken not to drill on the ossicular mass so there will not be transmission of the high-speed drill energy. Concentrating the drilling superiorly along the middle fossa dura has the advantage of protecting the facial nerve because that structure always lies medial to the ossicular mass in the epitympanum. The facial nerve is vulnerable to injury as the external canal is enlarged in the posteroinferior direction because it may lie lateral to the middle ear cavity. To ensure proper draping of the fascia and split-thickness skin graft, the canal walls should be smooth and without ledges lateral to the ossicular mass. Drilling is continued to create a new ear canal measuring about 1.5 times the normal size, with the surgeon being careful not to violate the temporomandibular joint space or to expose an excessive number of mastoid air cells.
The epitympanic ossicular mass is dissected free of the atresia plate and is left intact. The atresia plate is removed with diamond drill and curettes to completely expose the ossicles. Periosteum underlying the atretic bone is still attached to the malleus and should be sharply excised with a microknife or microscissors. Except for the fossa incudis, which may be left intact, bone should be completely removed around the ossicles, leaving at least a 2-3 mm space between these structures and the adjacent canal wall. The ever-present fibrous ligaments and adhesions are better vaporized with a carbon dioxide laser in the final phases of ossicular dissection; to avoid delayed refixation of the ossicles. The atretic bone should be removed so that the ossicular mass is centered in the new canal. Ossicular reconstruction with the patient’s intact ossicular chain is preferred to the use of a prosthesis. When the ossicular chain is not intact, ossiculoplasty is performed with a partial or a total ossicular reconstruction prosthesis to either a mobile footplate or to the stapes head. The prosthesis is covered with cartilage prior to the grafting of the new tympanic membrane.
The previously prepared skin graft donor site (upper arm or upper thigh) is exposed. A 0.012-inch thick, 6cm x 6cm split-thickness skin graft is taken with a dermatome. To determine the proper configuration of the skin graft, several measurements of the canal are made. The temporalis fascia is trimmed to size. Small tabs are cut into the anterior and superior aspects of the fascia to prevent lateralization of the tympanic membrane graft. The fascia is placed over the ossicular chain, medial to the malleus, or over the cartilage covering the prosthesis. The tabs are placed medially into the protympanum and epitympanum in an attempt to prevent lateralization. The new ear canal is circumferentially lined with the pie crusted split-thickness skin graft; small wedges are excised from the portion that overlaps the fascia graft. All of the bone of the new ear canal is lined. It is important to assure that none of the skin is folded on itself. Two to three cm of skin graft should remain lateral to be tacked down later. A disk of 0.020-inch reinforced silicone sheeting is placed over the tympanic membrane to reproduce the tympanomeatal angle. Stabilization of the skin graft within the canal can be achieved by several techniques. One-quarter inch Nu-gauze impregnated with an antibiotic ointment can be layered into the canal, or Merocel wicks may be placed within the canal and hydrated with Cortisporin suspension.
The attention is then turned to the meatoplasty. The auricle is undermined and the deep soft tissue is debulked from the approximate area of the meatus. A circular meatal opening about twice the normal size is created because 30% of the diameter will eventually reduce as a result of the normal healing process. Leaving only a small amount of subcutaneous tissue around the meatus limits the length of the membranous canal and helps prevent stenosis. The auricle is returned to its normal anatomical position to check for alignment of the meatus and bony canal. Further undermining of the auricle may be necessary so that it can be positioned in the proper location without tension. The postauricular incision is close. Working through the meatus, the lateral end of the split-thickness skin graft is grasped and pulled through the meatal opening. It is trimmed as necessary and sutured into place to the meatal skin. The lateral portion of the external canal and meatus are packed. A mastoid dressing is applied and the patient is woken up from anesthesia.
The transmastoid approach has not been used by many for several years. Exposure of the mastoid cortex and glenoid fossa is obtained as for the anterior approach. Dissection is then begun at the level of the linea temporalis, well posterior to the temporomandibular joint. The sinodural angle is identified and then followed medially to the antrum. The lateral semicircular canal, the malleus-incus complex, and the atresia plate are identified. The atresia plate is removed very carefully with the drill. Mastoid air cell removal and lowering of the facial ridge to the facial nerve allow access and creation of an external auditory canal with a canal wall down technique. The remainder of the operation proceeds as previously described. Bone pate or other soft tissue is used to obliterate the mastoid cavity before meatoplasty and canal skin grafting are performed.
A modified anterior approach is used in patients with a thick atretic plate because orientation may be difficult during the medial dissection. Dissection too far in either the inferior or the posterior direction risks inadvertent carotid, lateral canal, or facial nerve injury. Orientation is achieved in these cases with initial posterior dissection and limited posterior antrotomy at the sinodural angle only, enabling identification of the levels of the lateral semicircular canal and the ossicular mass. A new ear canal is then created in a method similar to that used for the anterior approach by drilling just posterior to the glenoid fossa and following an intact canal wall mastoidectomy approach. The lateral canal, which was previously exposed, is used as a landmark. The remainder of the surgery proceeds as described earlier.
The mastoid dressing is removed on the first postoperative day. The patient is counseled to keep the surgical site dry and to change the cotton ball in the meatus once or twice a day. The patient is given a 5 day course of antistaphylococcal antibiotics. At three weeks postoperatively, the packing and silicone disk are removed. The canal can be repacked if necessary. The first postoperative audiogram is obtained at 6 – 8 weeks postoperatively. Subsequent audiograms are obtained at 6 months, one year, and then yearly. Postoperative office care is very important. An infected graft in a patient is a serious and difficult problem. If the meatus appears to be narrowing, usually at the third month, it can be dilated every two weeks and restented effectively with the large wicks and gelatin sponge for 12 to 24 months.
It is difficult to compare hearing results from various series because of differences in classifying congenital ears, in selection criteria, in reporting hearing results, and in the length of follow up. In general, an initial postoperative hearing level of 30dB or better can be achieved in approximately 50% to 75% of major congenital atresia patients. A hearing level of 20dB or better is possible in 15% to 50% of these patients.
Schuknecht reported a hearing level of at least 30dB in 50% of 55 patients followed for an average of 5.5 years. Thirty percent of Schuknecht’s patients has a hearing level of 20dB or better. De la Cruz et al. reported 56 patients with a 6-month follow up and observed that 53% had a conductive deficit of 20dB or less. In a follow up series of 24 patients, similar results were obtained. Jahrsdoerfer found that 65% of 17 patients followed for 2 months to 8 years had a pure-tone average of 30dB or less. In a more recent series of 86 patients, Jahrsdoerfer reported a postoperative hearing level at 1 month of 25dB or better in 71% of patients. Lambert reported that 67% of 15 patients followed for at least one year had a speech reception threshold of 30dB or better and the mean improvement in the hearing level was 30dB.
Given the fact that near-normal hearing is not universally achieved even in carefully selected patients, the surgical complications must be carefully compared with the merits of atresia surgery. The two potential serious complications are sensorineural hearing loss and facial nerve paralysis. Other complications that can occur include canal stenosis, chronic infection, graft failure, and recurrent conductive hearing loss.
The potential for labyrinthine injury via the horizontal semicircular canal is minimized by the anterior surgical approach because of limited exposure of the mastoid air cells. High-frequency sensorineural hearing loss has been noted in some patients postoperatively, although a loss in the speech frequencies has not been recorded in recent series. This seems to be caused by acoustical energy from the drill and direct manipulation of the ossicles. Because the ossicular mass is connected to the atretic bone, energy from drilling will be transmitted to the inner ear in all atresia cases regardless of the approach. This may be of less consequence than direct manipulation of the ossicular chain by instruments. Care must be taken when removing the ossicular mass from the atretic bone.
The abnormal development of the temporal bone in cases of congenital aural atresia places the facial nerve at increased risk for damage. The risk can be minimized by understanding the anomalies of the facial nerve that are likely to be encountered and by using the facial nerve monitor during all surgical cases. Temporary facial paralysis has occurred rarely. This most commonly has occurred when the facial nerve has been transposed to gain access to the oval window. Facial paralysis has not been observed in recent series when facial nerve monitoring has been used. By adhering to several surgical guidelines, potential damage to the facial nerve may be minimized. First, as the atretic bone is removed, the drilling should be concentrated superiorly along the middle cranial fossa dural plate, entering the middle ear first in the epitympanum. The facial nerve is protected in this approach, since it will always lie medial to the ossicular heads in this location. Second, care should be exercised as the canal is enlarged in the posterior-inferior direction because of the more anterior and lateral course of the mastoid segment. Injury to the facial nerve can also occur in its extratemporal segment, as the postauricular incision is made, or as the auricle is undermined to align the soft tissue meatus and the newly created external auditory canal.
Some narrowing of the new external auditory canal develops in as many as 25% of patients. This narrowing is of little significance if a large meatus has been made. Occasionally, a significant stenosis occurs that traps squamous epithelium and causes infection. In such cases, secondary meatoplasty is required to solve the problem. This potential problem can be minimized by generously debulking soft tissue from the auricle before the meatoplasty, thus decreasing the length of the membranous canal. Coverage of all exposed bone by skin graft is also essential to prevent granulation tissue formation and subsequent stricture. In some patients, the lateral canal may be narrowed by displacement of the pinna. Because the reconstructed auricle has more mass and less muscular and soft tissue support than the normal pinna, it can shift after surgery. This newly created pinna usually shifts anteriorly and inferiorly. This shift causes a malalignment of the meatus and bony canal. Occasionally, a permanent suspension suture from the framework of the auricle to the mastoid periosteum or a hole drilled in the mastoid cortex is necessary for proper realignment of the soft tissue and bony canals.
The incidence of canal infections is increased in the newly created external ear canal. This is because the normal migration of keratin debris is lacking in the skin-grafted ear canal and protective secretions from sebaceous and apocrine glands are absent. The cylindrical contour of the canal and the absence of a mastoid defect achieved with the anterior approach minimize debris accumulation. A widely patent meatus and membranous canal are important for aeration and cleaning. Most patients are not restricted with regard to water activities.
Persistent or recurrent conductive hearing loss is the most common negative outcome in aural atresia surgery. The causes of persistent conductive hearing loss are inadequate mobilization of the ossicular mass from the atretic bone, an unrecognized incudostapedial joint discontinuity, or a fixed stapes. Wide exposure of the ossicular mass at surgery is necessary to ensure chain mobility and to facilitate assessment of chain integrity. Recurrent conductive hearing loss after an initial satisfactory improvement in air-conduction thresholds is usually secondary to refixation of the ossicular chain or to the tympanic membrane lateralization. At least a 2 to 3mm wide area of bone removal around the ossicular mass is desirable, since bony regrowth can occur. Care at the time of surgery can help minimize the incidence of lateralization. Anchoring the fascia graft beneath a bony ledge and the use of a Silastic button helps minimize graft lateralization. The patient must be followed carefully for at least 12 to 16 months because lateralization has been known to occur up to 12 months postoperatively. The incidence of tympanic membrane perforation or middle ear adhesions approximates that encountered in routine tympanoplastic procedures.
The objective in congenital ear surgery is to create a functional pathway by which sound can reach the cochlear fluids. A thorough knowledge of the anatomic variations that can occur with abnormal development of the temporal bone is essential. Hearing results that are consistently excellent cannot yet be achieved in atresia surgery, but with adherence to strict selection criteria and with further refinements in surgical technique, this goal is realistic.
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