Fig. 11.1 Anatomical view of the inner ear scalae in relation to the ear canal, ossicles, and tympanic cavity. Note the extension of the basal turn of the cochlea inferior to the round window, and the hook of the scala media as it approaches the vestibule. The goal of cochlear implantation is atraumatic placement of the electrode array into the scala tympani. Whether this is performed through the round window or cochleostomy, a solid grasp of the location and interrelationships of the scalae is needed to avoid additional cochlear injury and potential reduction in performance. RW, round window.

Fig. 11.2 Planning the placement of the receiver–stimulator should allow sufficient room between the pinna and the headpiece to enable the comfortable use of a behind-the-ear processor and eyeglasses. Approximately 3 to 4 cm should be left between the ear canal and the anterior edge of the device, which then provides additional distance to the magnet and headpiece. The device is angled up at about 45 degrees from the linea temporalis, which places it behind the bulk of the temporalis muscle.

Fig. 11.3 A postauricular incision is most commonly used for cochlear implantation. The superior aspect of the incision can be continued anteriorly or extended superiorly. This modification can provide additional ease of exposure for creating a well to seat the receiver–stimulator. Minimal or no shaving of hair is required if drapes are secured sufficiently to adjacent skin. Sufficient space (at least 1.5 cm) between the incision and the anterior aspect of the implant should be allowed to minimize the chance of device extrusion through the incision.

Fig. 11.4 The skin incision is carried down to the level of the temporalis fascia and mastoid periosteum. Minimizing anterior dissection along the temporalis muscle can reduce postoperative facial edema. A separate anteriorly based periosteal flap is created, which can be closed over the mastoidectomy and device at the conclusion of the procedure. Avoiding electrocautery for this step minimizes tissue shrinkage and facilitates closure. In small children where the flap is quite thin, the periosteum and muscle can be left attached to the skin. An extension of the periosteal incision posteriorly, curving up along the linea temporalis, allows for retraction of the temporalis muscle superiorly. This can help when creating the soft-tissue pocket for the receiver–stimulator.

Fig. 11.5 A subperiosteal pocket is created to accept the receiver–stimulator. A device-specific template is used to gauge the size of the pocket, and to mark the location of a bony well to recess and stabilize the electronics case. The pocket should be kept just large enough to comfortably accept the template without the need for excessive force or bending. Using a periosteal elevator to make multiple parallel passes will create a rectangular pocket, and reduce the risk of excessive movement or migration. Care must be taken during this elevation in very young children or those with developmental abnormalities, since the cortical bone over dura may be quite thin or even dehiscent.

Fig. 11.6 Mastoidectomy is then performed. Unlike the conventional technique for chronic otitis media, the surrounding cortex is not “saucerized.” Instead, bony overhangs are left superiorly, posteriorly, and inferiorly to help retain the coiled electrode lead. The creation of such overhangs should not be performed at the expense of safety. By carefully controlling the angle of view, the surgeon can ensure that the burr is always seen, even while creating the overhang. Most cochlear implant recipients have normally developed and aerated mastoids. Some air cells can be left intact provided that adequate exposure to completely open the facial recess is provided. The facial recess is then performed as described elsewhere. Adequate middle ear exposure through the facial recess is critical for array insertion. The facial nerve is identified through thin bone, as is the chorda tympani. The removal of bone anterior to the facial nerve will enable optimal view of the round window niche. Exposure of the incudostapedial joint and stapedial tendon can provide valuable landmarks. The incudal buttress is left intact.

Fig. 11.7 Depiction of the importance of adjusting the surgical angle of view while leaving cortical overhangs during mastoidectomy. By moving the microscope appropriately, the surgeon can maintain continuous line-of-sight with the burr, ensuring that no structures are inadvertently injured.

Fig. 11.8 It is critical that the posterior external canal wall be adequately thinned to provide optimal exposure of the round window. The canal moves anteriorly as it extends medially, and following its contour to maintain uniform thickness is essential. Incomplete canal wall thinning will prevent identification of the chorda tympani, and leave the facial recess significantly smaller than it should be. Similarly, the persistence of medial canal bone can prevent sufficient exposure of the bone anterior to the facial nerve, and prevent the identification of the round window niche.