Reconstruction of the Posterior Ear Canal

Peter S. Roland and Joseph L. Leach

The canal-wall-down (CWD) mastoidectomy finds favor with otologists primarily for one reason: the technique reduces the risk of persistent or recurrent cholesteatoma. Whether one takes the posterior canal wall down or not, there is a significant incidence of epithelial pearls that remain behind and can form the nidus of new disease.1 These pearls may or may not cause clinically detectable findings. Smythe1 reported that recurrent cholesteatoma from a retraction pocket occurred in 14% of intact canal-wall ears as compared with 1% of ears treated with mastoid obliteration and tympanic reconstruction. He concluded that the best way to reduce the incidence of cholesteatoma complications to the greatest possible degree long-term was to remove the posterior canal wall.

Nevertheless, after a CWD mastoidectomy, a patient is left with several problems inherent in the open cavity. The exposed bone of the mastoid leaks tissue fluid, which is a rich medium for bacterial growth. Unlike other areas of the head and neck, the mastoid, and in particular the sclerotic mastoid, is not particularly well vascularized.2 The combination of mediocre blood supply and weeping tissue fluid means that control of bacterial ingrowth can be challenging. Not only may healing be marginal or delayed, but also the patient may need to avoid moisture for life. Recurrent aural discharge afflicts 10 to 60% of patients with an open mastoid cavity.3,4 other complications, such as perichondritis of the pinna, have been reported.4 It is widely taught that the incidence of discharge or other infectious complications can be minimized by lowering the facial ridge, making the cavity large, and providing a generous meatal opening,3 but these maneuvers also have their drawbacks. For one, hearing aids are often required in these patients. Although it is undesirable to fit a hearing aid in a discharging mastoid cavity, it is also a problem to construct a mold for an enlarged meatus.3,5 In addition, lowering of the facial ridge may decrease the depth of the middle ear space, which makes ossicular reconstruction difficult and hearing less than optimal.6 Although a large meatus may reduce the incidence of postoperative drainage, it is often cosmetically unappealing (Fig. 12-1). A large mastoid cavity can draw the pinna inward, causing a noticeable deformity of the auricle. It may also draw the medial concha inward and displace the pinna laterally.

The dizziness associated with caloric stimulation is another drawback of a large open mastoid, and patients sometimes have to limit their exposure to water and wind. The ear loses its natural ability to clean itself, and wax and squamous debris build up over time. A foul smell can develop, which can be an irritation and source of embarrassment. In most cases, the mastoid bowl needs to be cleaned on a routine basis every 6 to 12 months. Water exposure can lead to infection. This is especially disappointing to patients who wish to swim regularly. In fact, it is not the size of the cavity that is crucial. In a comparative study, ears with a small open mastoid bowl have fared no worse than those with an obliterative flap.1 It is believed that the critical issue is the adequacy of the meatal opening as determined by the ratio of the meatal circumference to the volume to the mastoid cavity. One must have an opening sufficient to allow free circulation of air.

Therefore, many reasons exist not only for CWD mastoidectomy, but also for reconstruction of the posterior ear canal and obliteration of the mastoid. Hearing aids are easier to fit into an obliterated cavity than into an open cavity. The obliterated cavity is also more likely to retain its epithelial migratory potential and be self-cleaning because it is smaller.3 obliteration of the mastoid cavity leaves a smaller

Mastoidectomy
FIGURE 12-1 Typical appearance of an ear following canal-wall-down mastoidectomy with large meato-plasty.

surface area. Healing is therefore theoretically faster, and there is a reduced likelihood of developing granulations. Obliteration has been shown to significantly reduce the symptoms associated with the open mastoid. In a survey of patients with recurring mastoid disease, groups were treated either with revision mastoidectomy or obliteration.3 The pre-operative symptom scores were not significantly different, but the patients treated by obliteration had a significantly lower postoperative symptom score.3 Some recommend mastoid obliteration as a routine procedure in all mastoid surgery.7

Nevertheless, mastoid obliteration should not be undertaken lightly, because it carries a risk of enclosing cholesteatoma within the cavity. Computed tomography (CT) may or may not be effective in detecting these residua. A study was conducted in cadaver temporal bones in which cholesteatoma pearls were covered either with hydroxyapatite or muscle.8 Scanning was effective in detecting small pearls within the cavity obliterated with hydroxya-patite, but not so effective when muscle was used. In practice, however, obliteration has been safe. When CT was performed on 31 ears after mastoid obliteration with hydroxyapatite, there was no residual cholesteatoma in the obliterated area.8 A muscle flap may have an advantage over hard tissue replacement because an epithelial cyst may present as a swelling beneath the flap.

Mastoid obliteration may be contraindicated if there has been removal of a malignant tumor, if there are otogenic intracranial complications, if cholestea-toma has not been totally removed, or when air cell removal has been incomplete.9 Although there are many options for mastoid obliteration, all depend on a rich blood supply for success. Well-vascularized flaps are the best options when there has been extirpative surgery for cancer or osteoradionecrosis.

The goal of reconstruction of the posterior external auditory canal is to provide a safe, dry mastoid and restore hearing to near-normal levels. No single procedure has yet been devised that entirely accomplishes these purposes consistently. Various materials have been used to fill the mastoid, including fascia, fat, muscle, cartilage, bone paste, cancellous bone strips, bioactive glass ceramics, Proplast (a combination of polytetrafluoroethylene and glassy carbon fibers) methylmethacrylate, and ionomer-based bone substitutes.5 Most biologic tissues have a tendency to atrophy over time, and some otologists recommend overfilling the cavity to compensate for the expected loss of the volume of the obliterating tissues over time.10 Because the final shape and size of the obliterated mastoid cavity cannot be predicted, using biologic tissues for obliteration can be a drawback.

The earliest obliteration techniques involved flaps of local tissue. One of the early methods was that of Mosher11 in 1911. He used soft tissues from the back of the auricle and pedicled toward the temporalis muscle. Mosher always performed a simple mastoi-dectomy first, and then lowered a greater part of the posterior canal wall, leaving a bridge of bone external to the aditus in place. Popper12 described another early method in which he used periosteum to line the mastoid. He made a postauricular incision through the skin and subcutaneous tissues, retracting the posterior skin flap as far back as possible. He then made a horseshoe-shaped incision through the periosteum, creating an anteriorly based flap. Popper's aim was not to entirely obliterate the cavity but to provide a viable lining with good blood supply to facilitate healing. Meurman and Ojala13 described filling the lower part of the cavity by using an inferiorly and caudally based postauricular muscu-loperiosteal flap. Guilford14 attempted a more complete obliteration by combining the Meurman and Ojala flap with a superiorly pedicled postauricular flap.

These early flaps all demonstrated variable viability and some atrophy of tissue over time. In an effort to provide more consistent and longer-lasting results, Palva15 in the early 1950s began using a meatally based musculoperiosteal flap for obliteration and simultaneous reconstruction of the posterior canal wall. This flap retained the essential form of Popper's flap but included all the tissues between the skin and bone. For the Palva flap, the skin incision is made 1.0 to 1.5 cm behind the postauricular fold to facilitate liberation of the tissues posteriorly (Fig. 12-2). The horseshoe-shaped incision includes all the subcutaneous tissues from the retroauricular area down to the bone, theoretically preserving the facial nerve branches to the postauricular muscles and forestalling atrophy of the tis-sues.7,15 The flap could be made broad and long to allow obliteration of even large mastoid cavities.

Despite its good viability, the Palva flap demonstrated gradual atrophy in patients over years of follow-up. New methods of obliteration were sought. The soft tissue flaps mentioned above are all based on a random-pattern blood supply. If they are raised with a length-to-width ratio of greater than 1:1, ischemia of the distal portion is a risk, and subsequent necrosis and contraction of the flap would result in inadequate coverage and fill of the cavity.4 Another drawback to these local flaps is that they rarely have sufficient bulk or plasticity to completely line and fill a large mastoid.4 Another flap used to obliterate the mastoid has been the temporalis muscle flap, which is pedicled anteriorly.

Experience has shown that these flaps have a tendency to undergo atrophy, and the majority shrink down to the point that the resulting cavity is as large as it was originally.9 This is probably because the muscle becomes denervated and the blood supply becomes compromised, making the flap in effect a free muscle graft.4

In an effort to overcome such problems, practitioners have advocated the use of vascularized temporalis fascia. Both the deep and superficial temporalis fascia have been used. The deep tempor-alis fascial flap, ''the Hong Kong flap,'' is based on the middle temporal artery. It is thin, strong, and pliable, with more than adequate surface area to line the entire mastoid cavity.16 Its proponents claim that because it is translucent in nature, detection of recurrent disease is not compromised.16 Although the flap is adequate for achieving a healthy dry ear, it does not completely obliterate the mastoid or reconstruct the posterior canal wall.

The superficial temporalis or temporoparietal fascial flap is a good option for mastoid obliteration. The flap is thin, pliable, and can accept skin grafts.17 It also provides enough bulk for the obliteration of large mastoid defects.17 To avoid compression on the pedicle of the flap when it is rotated into the cavity, the middle fossa dura can be skeletonized above the ear canal at the ridge formed by the root of the zygomatic arch.4 A vertical incision is made through the scalp in the temporal area. Dissection is carried out just deep to the hair follicles, and bipolar cautery is used to avoid damage to the vessels. Care must be

Skeletonized Fascia
FIGURE 12-2 The Palva flap.

taken not to damage the frontal branch of the facial nerve. The flap incorporates an area of temporoparietal fascia 8 x |7 cm.4 A small absorbable tacking suture is used to anchor the flap to the temporalis muscle so that it will not pull away from the mastoid cavity. The temporoparietal fascia flap has shown its utility in patients who have undergone partial temporal bone resection for the treatment of a variety of neoplasms and revision surgery for chronic otitis media.17 In these cases, the standard pedicled muscle and periosteal flap reconstruction was not possible due to scarring, radiation damage, and disruption of vascularity resulting from previous surgery.17 Because the flap does not contain muscle, it should not shrink, but experience shows that some shrinkage can occur.4,18

Because vascularized tissue may not provide adequate long-term obliteration of the mastoid cavity and secure reconstruction of the posterior ear canal, biologic and nonbiologic implants have been used to afford bulk and stability. Fat grafts to the mastoid were first described in the late 1940s, but consistent success was not reported in subsequent articles.19 Guilford20 found that diced cartilage was effective in reducing the size of fenestration cavities, but not helpful following mastoidectomy for chronic otitis media. Dornhoffer6 has had success using cartilage for partial mastoid obliteration. Mastoid disease is removed, and the cavity is contoured. Cartilage is harvested from the concha and the meatus, and perichondrium is included. The cartilage is pressed and morcellized with a scalpel. obliteration is carried out only to the level of the facial ridge. Although reconstruction of the posterior auditory canal and complete mastoid obliteration were not attempted, problems with an open mastoid such as drainage or debris collection were ameliorated. After 2 years, it appeared that the cartilage became well incorporated into the mastoid, and ingrowth of fibrous tissue took place between the cartilage chips, which increased the volume of obliteration.6 Dorn-hoffer thought that the contour of the cavity was more critical than the amount of obliteration achieved. one disadvantage with this technique is that the amount of cartilage that can be obtained from the concha and tragus is limited. The use of autogenous iliac bone strips for cavity obliteration has been reported to be successful, but problems in resorption of the bone grafts were reported.18,21 There is associated incapacitating pain at the donor site, and prolonged bed rest of 12 to 14 days was recommended.18,21

A simpler method of adding bulk to the reconstruction is to collect bone chips and bone paste during the mastoidectomy. To avoid collecting any cholesteatoma matrix or infected tissue, it is important to collect the bone before entering the diseased portion of the mastoid. Along with a large cutting bur and continuous irrigation and suction, the paste is collected in a specialized bone paste collector or in an ordinary trap bottle connected to the suction tubing within the sterile field.18,22 Covering the walls of the mastoid with bone paste may inhibit the process of transudation of tissue fluid and reduce the risk of subsequent infection.3 In addition to bone paste, bone chips from the mastoid have been used. Guilford20 reported using bone chips taken from the mastoid for obliteration prior to 1957. He felt that they acted as foreign bodies, however, and discontinued their use. Despite Guilford's experience, others have continued to use native bone fragments with better results.23 Bone fragments are mixed with either fibrin glue24 or bone paste15 to add stability. Some advocate keeping periosteum to the bone chips to enhance survival.15,25 With this technique, a new bony posterior canal has been observed after 6 to 8 weeks.25 To harvest the bone, undermining is carried out posteriorly, allowing removal of cortex over a broad area with a chisel.25 Bone from the mastoid tip can be removed by a rongeur. Removing bone in this area has the added benefit of allowing the mastoid cavity to partially collapse.

Reconstructing the posterior ear canal with an autogenous, bilaminar membrane (soft wall reconstruction) has also been described.26 This method, unlike others, allows inspection of the underlying cavity for residual or recurrent disease due to the fact that the soft canal wall is semitransparent. The canal is reconstructed in such a way as to allow aeration of the mastoid from the middle ear. A large fascia graft is draped from the tympanic membrane underneath the posterior canal skin, which is preserved (Fig. 12-3). The mastoid cavity is packed with gelatin foam, which supports the fascia graft. Laterally, a Palva flap underlies and supports the fascia. Over 2 years, retraction of the posterior canal wall was observed in about half the cases, but functional results were good.26 In some of these cases, significant eustachian tube dysfunction persisted and the soft wall retracted into the mastoid defect, but the ear usually remained dry. The resulting cavity tended to be smaller than the classic modified radical mastoidectomy cavity.26 The technique is not recommended for patients with extremely small, sclerotic mastoids or for those with aggressive cholesteatomas involving multiple small cell tracts, or if there was hypertrophy of the mucosa of the protympanum.26

The mastoid contains not only bone but also air. Intuitively, it would seem difficult, at best, to restore t'alva flap

Skin/vascular strip

Hastia graft t'alva flap

Skin/vascular strip

Hastia graft

Ridge Bridge Radical Mastoidectomy

Facial nerve ridge and Vit

FIGURE 12-3

ior canal.

Ossicles

Eustachian luhe

Facial nerve ridge and Vit

FIGURE 12-3

ior canal.

Ossicles

Eustachian luhe

"Soft wall'' reconstruction of the poster-

the entire volume of the mastoid by replacing only the native bone, whether that would be in the form of paste or chips, and given that it could be collected efficiently and free of disease. Adding local cartilage grafts might help, but their volume is limited as well. Fascia, fat, and muscle are often not sufficiently bulky or long lasting to sufficiently reconstruct the posterior canal in the long term. In the past this problem was dealt with by use of homograft cartilage and bone, but the fear of transmitting infectious diseases, especially AIDS, has curtailed their use.6 Citing the fact that obliteration of the mastoid with bone makes sense because it utilizes the material natural to the area, Shea et al used bone chips from the femoral heads in bone banks. They broke the bone up into chips about 3 mm in diameter, and applied a layer of autogenous bone paste to the surface of the bone chips to develop a hard smooth surface on the new posterior canal wall. It resulted in a canal wall with a natural texture and appearance. Guilford20 used heterogeneous bone paste for mastoid obliteration, but found it to be unsatisfactory. These experiences with homograft tissues laid the groundwork for the later use of allografts.

Most alloplastic implant materials, such as plastic mesh, Proplast, and porous polypropylene, have not been successful long-term due to difficulties in the face of infection.5,28 Although there was initial enthusiasm for Proplast, it was subsequently discovered that the material caused a lasting giant cell reaction.28 Antibiotics could not clear the infection when the organisms became harbored in the pores.29 A two-stage tympanoplasty was necessary so that the area could be relatively sterile. Postauricular fistulas, persistent drainage, and purulent granulation tissue led to gradual disuse of plastics.2 The mastoid bone is a problematic site for alloplasts because it is devoid of cancellous bone and its stem cells and has marginal vascularity.2 An implant that elicits a marginal foreign body reaction cannot stimulate neovascularity by intimation in such an environment.2

Hydroxyapatite is the main constituent of living bone and is a natural choice as a bone substitute for mastoid obliteration and canal-wall reconstruction. The use of hydroxyapatite avoids donor-site morbidity and is well tolerated in an infected field. Ideally, it osseointegrates into surrounding bone, leaving a stable canal wall that does not retract with time. Because hydroxyapatite is bioactive, graft failure and extrusion in the long term should not be observed. Unlike bone paste, there is no risk of implanting cholesteatoma. Hydroxyapatite has been used in four different forms, including granules, cement, preformed canal-wall prostheses, and in a block form, which is sculpted to fit the individual defect. The most common complication that accompanies the use of hydroxyapatite is incomplete covering of the material with viable tissue in the healing phase.23

Hydroxyapatite cement, unlike granules, can be confined relatively easily to the operative site. The cement comes as a powder that is mixed with sterile water and hardens within 20 minutes.30 Risk to the surrounding tissue is minimal, because the reaction is essentially isothermic and occurs at a physiologic pH.30 Hydroxyapatite cement is microporous, with a pore size of approximately 8 to 12 mm.30 When implanted in a subperiosteal location, new bone formation occurs.30 When exposed to cerebrospinal fluid or blood, conventional hydroxyapatite cement takes a long time to set, but this can be reduced to 5 to 8 minutes when the calcium phosphate powder is mixed with a phosphate solution instead of water.31 The material was used in a series of 21 patients, including two involving the mastoid, with no com-plications.31 With a mean follow up of 15 months, there were no infections or extrusions.

Blocks of ceramic hydroxyapatite share the excellent tissue compatibility and osseointegrative potential found with hydroxyapatite granules and cement. The blocks, however, are brittle, and the material is difficult to contour. Sculpting the blocks takes additional operating room time. Nevertheless, sculpted hydroxyapatite blocks were used in a series of nine patients with 78% success.5 There was one failure due to granulation and one due to stenosis. Canal-wall reconstruction with the preformed hy-droxyapatite prostheses should overcome the problem of sculpting encountered with hydroxyapatite blocks. Nevertheless, the prostheses generally do require some amount of shaping. Instability has also been a problem.5 This is especially true when attempting to reconstruct a previously drilled radical cavity when the tegmen and the inferior tympanic bone were smoothed appropriately. In these cases, a notch can be drilled in the zygomatic area to stabilize the prosthesis. Although some prefer hy-droxyapatite reconstruction at a second stage if the ear is free of cholesteatoma,32 others implant the material at the time of mastoidectomy.5,33 Reconstruction of the posterior canal with the hydroxya-patite prosthesis without obliteration is possible, but there is the risk that retraction will occur and that the hydroxyapatite will cut through the skin of the auditory canal.33

When reconstructing the posterior ear canal at the time of CWD mastoidectomy, it is helpful to leave the facial ridge high, if this is possible without compromising disease eradication. The high facial ridge acts as a posterior margin for the obliteration and helps to retain the obliteration material. As a general rule, one should ensure that the middle ear is sealed off with a temporalis fascia graft.18 If a CWD mastoi-dectomy is already present, the flap of skin that used to line the mastoid cavity is used to line the reconstructed posterior ear canal wall. The edge of the mastoid cavity is then identified, and the skin lining is carefully elevated forward to a point just short of the facial ridge. Any excess or poor-quality skin is excised. Filler (bone chips, bone paste, hydroxyapatite granules, or hydroxyapatite cement) is then placed into the mastoid cavity, behind the skin flap and fascial lining, so as to fill the cavity and leave an ear canal of near-normal size (Fig. 12-4).

When using hydroxyapatite granules, Yung10 advocates covering them with an inferiorly based periosteal flap that can incorporate temporalis fascia at its superior margin. He also recommends soaking the granules in an antibiotic solution for 10 minutes. When a hydroxyapatite canal-wall prosthesis is used, it should be burred to the exact size using a diamond bur. One should then fashion a groove in

Gelatin film (optional)

/ Fascia graft or canal Palva flap / j wa,] prosthesis

FIGURE 12-4 A typical method of reconstructing a posterior ear canal. EAC, external auditory canal.

the residual bony buttresses, which allows for dovetailing of the prosthesis and stabilizing it. Estrem and Highfill5 recommend covering the prosthesis with fascia and skin or fascia or homograft dura. Grote32 recommends covering the canal-wall prosthesis at the canal side with a cranial-based perios-teal flap, which is then covered by the vascular strip and the tympanomeatal flap. In the case of previous CWD mastoidectomy, the mastoid lining and a vein graft are used anterior to the periosteal flap.28 Gelatin film is placed on the other side of the prosthesis. Grote and Van Blitterswijk28 warn that if the periosteal flap is not used, and if poor attention is paid to the epithelial remnants, there can be erosion between the implant and the bony canal.

Postoperatively, the principles of wound care that are followed with other otologic procedures make good sense for the patient who has undergone posterior ear canal reconstruction. A good postauricular closure and a mastoid dressing are used. Although there is some argument that keeping packing in place for 3 weeks may allow better epithelialization than removing the packing at the usual 7 to 10 days,23 one has to keep in mind the

Posterior Ear Canal

FIGURE 12-4 A typical method of reconstructing a posterior ear canal. EAC, external auditory canal.

Ossicics

Eustachian lube

Ossicics

Eustachian lube possibility of overgrowth of organisms in the dressing. Eardrops are generally used to maintain an acidic pH in the ear, prevent infection, and promote rapid healing. When granulation tissue forms in the ear canal postoperatively, it is sometimes necessary to treat these patients with application of dilute silver nitrate solution.

When implants are used in the mastoid along with a flap, there is always the possibility that partial or total loss of the flap could occur or that the implant could become exposed. These complications seem to be more common if obliteration is attempted in an old open mastoid.4,23 Local wound debride-ment, cleaning, and otic drops may alleviate the problem, but occasionally reoperation is necessary. Retraction pockets and recurrent cholesteatomas are occasional reported complications of the various obliteration techniques described.5,33

Experience has shown that with long-term follow-up, random, muscle, and fascia flaps undergo atrophy, retraction, and fibrosis.18,22 Temporal muscle flaps in particular tend to retract away from the cavity and do not form good support of the canal wall.15 Despite the claim to contain innervated muscle, the Palva flap atrophies over time. Over a 13-year period, mastoid volumes were noted to increase significantly in cavities obliterated by this method.1,9,33 Nevertheless, retraction pockets and other hidden cavities were uncommon.33 significantly, no recurrence of cholesteatoma was seen in more than 2000 ears that used the flap.15

With obliteration with bone chips alone, a significant increase in the cavity size has been observed long-term.33 Some of these lost their self-cleaning ability and had to be taken care of as radical cavities.33 obliteration with bone paste, on the other hand, has demonstrated decrease of the cavity size due to osteoneogenesis.34 Obliteration of the mastoid with hydroxyapatite granules has shown greater than 85% long-term success.5,10 Water has been tolerated in the cavities in most patients, and the majority report no aural discharge or need to use eardrops.10 Long-term success with hydroxyapatite canal-wall prostheses is a bit lower, at about 75%.5,32 Although extrusion and recurrent cholesteatoma may compromise the implant, the main cause of failure in one series was recurrent middle ear infection.32 When the implants are retrieved, they tend to show good remodeling with living bone tissue.32 Retroauricular fistulas have occurred with hydroxyapatite prostheses, one appearing 3 years postoperatively.33 Nevertheless, the general rule is that the cavities remain dry long-term.33

Because CWD mastoidectomy continues to be a commonly performed procedure, the open cavity will continue to pose problems. Mastoid obliteration and reconstruction of the posterior canal eliminate many of these problems in a majority of patients. Techniques that incorporate well-vascularized tissues into the area will continue to supplant those that do not. Exciting new materials, particularly the several forms of hydroxyapatite, hold great promise in restoring these patients to better function and appearance.

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