Chapter 8 The canal-wall-up (CWU) mastoidectomy procedure was introduced by Jansen at the House Ear Clinic in 1958.1 His goal was to perform more conservative surgical excision of cholesteatoma or other chronic ear disease, preserving the normal anatomy of the external auditory canal. This procedure was developed as a way to address some of the disadvantages of radical and modified radical mastoidectomy, which can include a lifelong need for cleaning of the mastoid cavity and for avoidance of swimming and other water sports, and the possibility of caloric stimulation by cold air or water reaching the mastoid cavity.1 Additionally, the CWU procedure leaves the patient with more options for hearing aids postoperatively.2 The main disadvantage of CWU mastoidectomies is the higher postoperative rate of cholesteatoma as compared to canal-wall-down procedures. Postoperative cholesteatoma can represent either recurrent or residual disease. Residual disease is defined as the presence of cholesteatoma due to incomplete excision at the time of initial surgery, whereas recurrent disease represents new formation of a cholesteatoma from a new retraction pocket postoperatively. Published reports suggest that residual disease is more common following CWU mastoidectomy, but rates of recurrent disease are comparable to those following canal-wall-down surgery.3 Overall reported failure rates of the CWU procedure range from 3 to 62%; failure is more common in children.4 Results from Sanna et al,5 however, indicated that chances of failure can be decreased with certain preventative measures, including using Silastic sheeting, repairing bony defects of the posterior canal wall, performing a staged second look surgery, and placing pressure equalization tubes. Overall failure rates for the CWU procedure dropped to 5.2% with the use of these measures. Many surgeons perform a planned second-look surgery at 6 to 12 months postoperatively to evaluate for residual or recurrent disease, with or without reconstruction of the ossicular chain. Hearing results following wall-up versus wall-down mastoidectomies are difficult to interpret in the literature due to wide variation in reporting methods. Data are often not stratified to allow comparison between the two techniques, or between studies. There is evidence, however, that the status of the ossicular chain is more predictive of postoperative hearing than the type of mastoidectomy performed.2 Indications for a CWU mastoidectomy include complications of acute otitis media, chronic otitis media, cholesteatoma, exposure of structures within or deep to the temporal bone, cerebrospinal fluid otorrhea, facial nerve trauma, and neoplasm of the temporal bone.6 A canal-wall-down procedure should be performed if the disease is in the only hearing ear, severe complications of otitis media or cholesteatoma are present, the surgeon is unable to remove cholesteatoma completely with the posterior canal wall intact, the eustachian tube is nonfunctional, or the patient is noncompliant or a poor anesthesia risk. A contracted or sclerotic mastoid cavity is a relative indication for wall-down surgery.7 Preoperative preparation for the CWU mastoidectomy involves routine audiometry as well as imaging studies. High-resolution computed tomography (CT) of the temporal bones allowsfor intraoperative planning and can reveal features of surgical significance, such as a dehiscent facial nerve or tegmen tympani, but it is not routinely performed by all otologists prior to the procedure. The positioning of the patient is key in all otologic surgery. For the CWU mastoidectomy, the patient should be positioned on the operating table such that the head is located at the foot of the bed. This allows the surgeon’s knees to fit comfortably underneath the table when seated. Also, the bed controls should be easily within reach of the anesthetist, as rotation of the bed is necessary throughout the procedure. The patient should be securely strapped to the table to allow for rotation of the bed toward or away from the surgeon without endangering the patient. The patient’s head should be located at the very end of the bed, closest to the surgeon’s side, and the head should be rotated away from the surgeon. The facial nerve monitor, if it is to be used, should be placed following the induction of anesthesia. Three pairs of electrodes are used for monitoring. One pair is placed within the fibers of the orbicularis oris muscle, less than 1 cm apart; another pair is placed in the orbicularis oculi muscle. The last pair contains a ground and a stimulating electrode. These can be placed within the frontalis muscle on the patient’s forehead, or the ground electrode can be placed at the patient’s shoulder with the stimulating electrode below the sternal notch. The electrodes are connected to the facial nerve monitor, which is then turned on. Electrodes are checked for proper function prior to the case. The patient’s hair should be shaved approximately 3 cm behind and above the ear to be operated upon. The surgical field should be prepped widely with the surgeon’s choice of sterile solution, including inside the external auditory canal. Various methods are used to secure the patient’s hair away from the field, including painting the hair with Betadine, or taping it securely away with plastic tape and benzoin. The ear should then be draped with either an iodoform plastic drape or a head drape with an ear hole. The patient is then draped in the routine fashion and placed in a slight Trendelenburg position.
CANAL-WALL-UP MASTOIDECTOMY
POSITIONING AND PREPARATION
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