Chapter 14 Canal Wall Reconstruction Tympanomastoidectomy
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The primary goal in the surgical management of chronic otitis media with cholesteatoma is the creation of a dry, safe ear through removal of disease and the alteration of anatomy to prevent recurrence. This goal can be accomplished effectively with preservation (canal wall up) or removal (canal wall down) of the posterior canal wall, both of which are described in other chapters 16 and 17. This chapter describes the technique of canal wall reconstruction tympanomastoidectomy with mastoid obliteration. Canal wall reconstruction tympanomastoidectomy combines elements of the canal wall up and canal wall down procedures to optimize surgical exposure for removal of disease, and creates a blockage of the attic that prevents recurrence of retraction pockets and recurrence of cholesteatoma.
Many authors have described reconstruction of the posterior canal wall and mastoid obliteration using various methods, including composite osteoperiosteal flaps,1 composite cartilage/titanium grafts,2 ceramic alloplasts,3–7 bone pâté,8–10 costal cartilage,11 and bone cements.12–14 Canal wall reconstruction tympanomastoidectomy with mastoid obliteration was originally described by Mercke in 1987.15 Important modifications to the Mercke technique have been have been published by the senior author16 and are described in detail in this chapter.
ADVANTAGES AND DISADVANTAGES OF CANAL WALL UP AND CANAL WALL DOWN TECHNIQUES
Canal wall down tympanomastoidectomy is the gold standard for surgical management of cholesteatoma.17,18 The enhanced exposure to the attic, antrum, and middle ear afforded by removal of the posterior canal wall provides for optimal visualization and removal of disease in cases of extensive cholesteatoma. Removal of the canal wall and lateral attic also prevents retraction and recurrent cholesteatoma formation. In addition, all nitrogen-absorbing mucosa of the mastoid cavity and epitympanum is removed, and ultimately is replaced by stratified squamous epithelium after healing has occurred. When performed properly, the canal wall down procedure can result in a recidivism rate of 2%.17
Preservation of the posterior canal wall in cholesteatoma surgery has many advantages, including the elimination of the need for periodic cleaning and avoiding the need for water restrictions. The recidivism rate has been reported to be 36% in adults and 67% in children,19 however, higher by many reports than the incidence of recurrent disease seen with canal wall down procedures.18,20 The high rate of recidivism seen in canal wall up procedures can be due to numerous factors. First, exposure of the attic, antrum, and facial recess is more limited in canal wall up procedures compared with canal wall down approaches, which may lead to difficulty in complete removal of all involved air cell tracts and elimination of cholesteatoma at the initial procedure. Second, the epitympanum and mastoid cavity are ultimately relined with nitrogen-absorbing cuboidal mucosal epithelium after canal wall up procedures. The presence of this nitrogen-absorbing mucosa is thought to lead to negative middle ear and mastoid pressures, especially when continued inflammation with associated hypervascularity affects the mucosal layer.21 This large surface area of nitrogen-absorbing epithelium along with underlying eustachian tube dysfunction can lead to progressive retraction of the tympanic membrane postoperatively, and ultimately to recurrence of cholesteatoma.16 Eustachian tube dysfunction exacerbates this scenario in children.
RATIONALE FOR CANAL WALL RECONSTRUCTION TYMPANOMASTOIDECTOMY WITH MASTOID OBLITERATION
Canal wall reconstruction tympanomastoidectomy with mastoid obliteration is a technique in which the posterior canal wall is removed en bloc using a microsagittal saw to provide canal wall down–like exposure and ensure optimal visualization, aiding complete elimination of disease. The canal wall is replaced after the disease has been removed. The attic and mastoid cavity are isolated from the middle ear using pieces of cortical bone and are obliterated using bone pâté. Replacement of the posterior canal wall allows for preservation of near-normal middle ear anatomy, which can aid with ossicular reconstruction and avoid the need for routine cavity cleanings. Blocking the attic and mastoid cavities prevents re-retraction of the tympanic membrane by eliminating the negative pressure associated with a nitrogen-absorbing mucosa lining the cavity and physically limiting tympanic membrane retraction into the middle ear only.
PATIENT SELECTION
Canal wall reconstruction is indicated in patients of all ages with congenital or acquired cholesteatoma of the middle ear with extension to the attic, antrum, or mastoid not amenable to simple tympanoplasty or atticotomy. Canal wall reconstruction can be performed in patients who have had prior mastoid surgery, unless the posterior canal wall has been removed, or the lateral portion of the posterior canal wall drilled away in a prior canal wall up procedure. The procedure is not contraindicated in patients with facial paralysis, labyrinthine fistula, or an encephalocele. Canal wall reconstruction can be performed in patients with extensive scutum erosion or destruction of the medial aspect of the posterior canal wall from cholesteatoma or prior surgery, although there are additional reconstructive considerations in these circumstances. Canal wall reconstruction is contraindicated in patients with severe mastoid cholesteatosis that cannot be cleared from all mastoid air cell tracts, as sometimes occurs in young children. Care should be taken in the use of the canal wall reconstruction technique in patients with an extensive infectious component, although infection in general is not a contraindication to the procedure.
PATIENT PREPARATION
The patient is placed in the supine position on the operating room table with the head turned away from the side to be operated on. Facial nerve monitoring electrodes are applied to the orbicularis oris and orbicularis oculi muscles. Hair is clipped from the postauricular area, and a C-shaped incision 3 to 4 cm behind the pinna and within the hairline is marked. A solution of lidocaine 1% with epinephrine 1:100,000 is injected, and povidone-iodine solution is applied to the area, including the external auditory canal (EAC).
Sterile towels are placed around the prepared area, being careful to include the face on the involved side in the field. A large sterile adhesive drape is applied over the field and surrounding towels followed by application of a split drape to the torso and surrounding area. A sterile irrigation/drainage bag is applied after trimming the adhesive drape around the auricle and postauricular area.
SURGICAL TECHNIQUE
Mastoidectomy: Special Considerations
A postauricular incision is made approximately 2 cm behind the hairline and carried to the level of the temporalis fascia superiorly. Dissection of the skin flap is carried anteriorly to within 2 to 3 mm of the EAC. A wide (3 to 4 cm) anteriorly based musculoperiosteal (Palva) flap is incised, elevated, and retracted anteriorly with the pinna. Bone pâté is collected from the mastoid cortex and squamous temporal bone using a large cutting burr and suction using a bone pâté collector (Otomed Corporation, Lake Havasu City, AZ, or Anspach, Palm Beach Gardens, FL). Bone pâté collection is stopped if an air cell becomes exposed. After collection, the bone pâté is soaked in bacitracin solution placed aside until the reconstruction. Calvarial bone slices approximately 4 × 10 × 0.5 mm in size are harvested from the mastoid tip or retrosigmoid area using an osteotome and are placed aside.
An intact canal wall mastoidectomy and facial recess are performed as described in Chapter 16
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