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

Disadvantages of the canal wall down technique include the accumulation of debris in the mastoid cavity necessitating periodic débridement and potentially the need for ongoing water restrictions to help avoid bowl infections. The middle ear space that results after the canal wall down technique is narrower than that after the canal wall up technique, which can make ossicular reconstruction more difficult. The wide meatoplasty, which is a crucial component in the canal wall down technique, can present difficulties in the placement of a hearing aid, and may have an unacceptable esthetic appearance to some patients.

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