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Intact Canal Wall Tympanomastoldectomy
In discussing intact canal wall tympanomastoidectomy, we would be remiss in not acknowledging the otologic pioneers that elucidated and refined the general principles of this procedure. This chapter reviews the application of these principles and focuses on new technologies that have improved the quality of care for our patients.
The decision to proceed with mastoidectomy evolves from the need to eradicate disease extending into the mastoid cavity, improve exposure of the middle ear space, improve aeration of the middle ear space, and at times to provide a pathway for drainage. In the debate on canal wall up versus canal wall down techniques, the performance of a particular mastoid procedure should be individualized based on patient and disease variables. A dry, safe ear with maximization of hearing remains the goal.
The intact canal wall procedure should be attempted initially in the majority of pediatric and adult patients. Removal of the canal wall, if necessary, is based on intraoperative findings and in certain cases described following here. The advantages of the intact canal wall approach in terms of more rapid healing, reduced maintenance requirements, and absence of postoperative water precautions outweigh the possible increased incidence of recurrent disease associated with this technique.1
It is our experience that the presence or absence of the canal wall does not significantly impact on the visualization of the sinus tympani when otoendoscopyis employed as an adjuvant. Furthermore, the use of otoendoscopy allows visualization of areas of the epitympanic space that remained obscured through the operating microscope with the canal wall intact. Because our practice is located in a tertiary referral center, many of our patients have had previous middle ear and mastoid surgeries. We have found that the presence of recurrent or persistent disease in ears previously treated with an intact canal wall operation is often amenable to a revision procedure leaving the canal wall in place.
The specifics of the disease identified during intra-operative evaluation will at times necessitate removal of the posterior canal wall, such as in cases of a significant labyrinthine fistula, recurrent extensive cholesteatosis, or extensive posterior external auditory canal wall destruction. Likewise, patients with evidence of severe permanent eustachian tube dysfunction (syndromic or cleft palate patients) or a very small contracted mastoid cavity are often treated with removal of the canal wall in our practice.
Preoperative factors favoring canal wall down surgery include mastoid disease in the only hearing ear, prior canal wall down in the opposite ear, concern regarding reliability for follow-up examinations, and associated medical comorbidity limiting subsequent general anesthesia.
■ Preoperative Evaluation
The decision to proceed with a mastoidectomy in most cases is made during the initial documentation of the clinical history and the results of the physical exam. At times the need for a mastoidectomy will only become evident intraoperatively. Therefore, consideration for the requirement of a mastoidectomy must be entertained in all cases of middle ear disease and the patient appropriately counseled.
Audiometric evaluation preoperatively impacts directly on the surgical approach and allows for more detailed informed discussion with the patient. Preoperative audiometric evaluation is performed within the month preceding the surgical procedure.
The role of preoperative computed tomographic (CT) imaging remains a topic of debate. CT is somewhat limited in delineating recurrent or residual disease from scar tissue or fluid.2 Preoperative imaging is not required for uncomplicated cholesteatoma workup. Intraoperative findings have far greater influence on our decision toward a particular surgical technique. Imaging does, however, have a role in specific instances in our practice. In clean retraction pockets in which the base cannot be clearly visualized, CT scanning can be of assistance in delineating whether the pocket merely represents a small retraction or is the narrow isthmus of an extensive cholesteatoma. CT imaging also has a role in pregnant patients, in those with medical comorbidi-ties, and in only hearing ear patients with evidence of cholesteatoma to assess whether the risk of complications from the cholesteatoma is greater than that posed by surgical therapy. If there is a history of intratemporal or intracranial complications from otologic disease, CT and magnetic resonance imaging are obtained to evaluate for possible aberrant anatomy or dehiscence along the intracranial margins. If the preoperative history and examination are suggestive for evidence of a labyrinthine fistula, imaging is ofvalue to facilitate safe dissection and allows informed preoperative counseling.
■ Consent
Before scheduling surgery, a thorough discussion is performed with patients concerning the benefits and risks of the proposed procedure. Patients are informed that the primary objective of the operation is to obtain a dry and safe ear. Patients are informed that reconstruction of the hearing mechanism either during the initial surgery or during a subsequent operation will depend on the extent of mucosal disease, probability of residual cholesteatoma, or fixation of the stapes footplate. No specific percentages are quoted to represent the likelihood of hearing improvement because individual disease states greatly impact the reconstruction potential. Patients are given a summary document describing the risks of injury to the hearing mechanism, vestibular labyrinth, and facial nerve. Similarly, patients are counseled regarding disturbances in taste, postoperative infections, and dural/intracranial complications.
■ Medical Preparation of the Draining Ear
Effort is made to resolve any associated discharge prior to surgery. This attempt to bring about resolution of inflammatory tissue preoperatively will allow improved hemostasis and enhanced surgical dissection. The authors believe that control of environmental allergies prior to surgical intervention improves the probability of successful control of the disease process. Smoking is prohibited for 2 weeks prior to surgery and for at least 2 weeks following surgery, and cessation is strongly encouraged.
Meticulous debridement of the external canal down to the tympanic membrane under microscopic visualization is performed. If the ear is activelydraining, patients are begun on a regime of twice daily irrigations with half strength white vinegar solution and a course of a fluoroquinolone topical antimicrobial. If cholesteatoma is present, surgery is scheduled because resolution of the otorrhea is unlikely. If no cholesteatoma is present, patients are seen the following week, and surgery is scheduled if the drainage has cleared. Cultures are not routinely obtained because of the mixed flora in the external auditory canal. Quite often chronically draining ears will already have been treated with multiple courses of both oral and topical antibiotics prior to referral and will remain recalcitrant to medical treatment because of loculated infection, thereby requiring surgical treatment.
■ Facial Nerve Monitoring
Although we do not believe that facial nerve monitoring represents the standard of care in surgery for all chronic ear disease, this technology does have a role as an adjunctive measure to facilitate facial nerve dissection. Facial nerve monitoring offers assistance in the identification of anatomical distortions from chronic ear disease, improves identification of unexpected anatomical variations, and provides assistance in the dissection of extensive granulation tissue.3 We employ this technology in all revision procedures and in cases with evidence of anomalous anatomy on preoperative imaging or in patients with syndromic features. Emphasis should here be given to the danger in dependence upon the nerve monitor. The monitor is only of value when a positive response is obtained from electrical or mechanical stimulation. A lack of response cannot be safely interpreted as a lack of facial nerve stimulation. Facial nerve monitors cannot safely replace anatomical knowledge of the course of the facial nerve and the ability to identify and follow the nerve, even under diseased conditions.
■ Principles of Surgical Technique
Preparation
The technique discussed here is applicable to those ears either involved with chronic mucosal disease or those involved by cholesteatoma. Detailed in the following text are the highlights of the authors’ technique and maneuvers we have found to be of assistance in performing intact canal wall tympanomastoidectomy.
The ear to be operated on is verified with the patient and after reviewing the patient’s chart prior to the patient receiving any sedation. This ear is clearly marked to prevent the possibility of a surgical misadventure. One inch of hair is shaved to allow placement of drapes. The postauricular incision is injected with 1% lidocaine with 1:100,000 epinephrine.
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