Downs, Brian W. MD; Buchman, Craig A. MD
Cochlear implantation has become an increasingly common operation for sensorineural hearing loss, with thousands of implantations having been performed worldwide. In most cases, the transmastoid, facial recess approach facilitates entry into the middle ear and usually allows visualization of the round window (RW) niche.1–3 Occasionally, the relationships of the osseous external auditory canal (EAC), RW niche, and facial nerve may impair adequate visualization for creation of a cochleostomy. In this situation, a transcanal approach, canal wall down mastoidectomy, or moving the cochleostomy to an alternative location may be necessary.
The present report describes a case in which visualization of the RW niche was impaired despite standard mastoidectomy, facial recess techniques. The posterior wall of the osseous EAC was translocated anteriorly, keeping the canal skin intact. After this maneuver, the cochleostomy was easily drilled and the implant electrode inserted without difficulty. The advantages and potential complications of this technique are discussed.
A 3-year-old girl with profound sensorineural hearing loss diagnosed at birth was taken to the operating room for cochlear implantation. A preoperative computed tomography (CT) scan showed no middle or inner ear abnormalities. Transmastoid facial recess approach to the posterior mesotympanum revealed a posterior sloping EAC and a relatively posteriorly placed RW niche. Despite thinning the EAC, sacrificing the chorda tympani nerve, and identifying the tympanic annulus, the RW niche could not be visualized. Thus, using a 1.0-mm diamond bur, osteotomies were carried out through the posterosuperior and posteroinferior EAC, with care taken to stay in a subcutaneous plane (Fig 1). Liberal elevation of the canal skin including the tympanic annulus inferiorly and up to the malleus superiorly allowed wide exposure of the posterior mesotympanum. A Perkins retractor maintained anterior translocation of the EAC contents, and the cochleostomy and electrode insertion were carried out without difficulty (Fig 2). Following insertion, mastoid cortical bone pate was used to fill the osteotomy sites, and the wound was closed in a routine fashion. The EAC was packed firmly with moist Gelfoam, and a mastoid dressing was placed.
| Fig. 1. Round knife pushes translocated external auditory canal anteriorly, demonstrating intact canal skin and improved visualization of round window niche. |
| Fig. 2. Retractor secures translocated external auditory canal before cochleostomy. |
The patient had an uneventful postoperative course. The EAC was unpacked at 3 weeks and was found to be widely patent. Three months after surgery, the EAC remains normal in appearance. The patient successfully underwent fitting of her processor and initial stimulation.
The transmastoid facial recess approach is a safe and widely used technique for cochlear implantation. This access depends on the size and shape of the chorda tympani–facial nerve angle, as well as the inter-relationships of the mastoid segment of the facial nerve, EAC, chorda tympani nerve, and RW niche. In most cases, the facial recess is ample for safe cochleostomy and electrode insertion. Occasionally, posterior sloping of the EAC, an anteriorly placed descending facial nerve, or a posteriorly located RW niche may obscure the line of sight for cochleostomy placement anteroinferior to the RW membrane. In these cases, options for access include combined transcanal-transmastoid approach, canal wall down mastoidectomy with blind sac closure of the EAC, or placement of the cochleostomy in a different location. In the transcanal approach, the cochleostomy and insertion angle, as well as line of sight, are altered in a way that may require bending of the implant electrode array to avoid contact with the undersurface of the tympanic membrane. Moreover, canal wall down mastoidectomy with blind sac closure requires more extensive drilling, creates difficulty for electrode fixation, and poses some small risk for delayed cholesteatoma formation. In the present report, we describe posterior EAC translocation with reconstruction as another option for this anatomical situation. Moving the posterior EAC wall anteriorly allows a wide view of the posterior mesotympanum. Moreover, the line of sight can be directed posteriorly into the middle ear space allowing correct identification of the RW niche anterior to the mastoid segment of the facial nerve.
Theoretical complications from anterior translocation of the EAC could include canal stenosis or canal wall skin perforation and subsequent cholesteatoma formation or electrode extrusion. To date, these complications have not been observed.
Translocation of the posterior, osseous EAC is a reasonable option for cochlear implantation when temporal bone anatomy limits adequate visualization through the standard facial recess. Long- term follow-up with a greater number of patients will be necessary to validate the safety and efficacy of this technique.
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