Approach Considerations

Many cochlear implantation surgeons have moved away from extensive dissection and drill-out of a receiver-stimulator well within the parietooccipital cortex in favor of less-invasive techniques of device stabilization.

Campisi et al (2005) studied the use of a proprietary anchor fixation device for stabilization of the receiver/stimulator in children. This system performed comparably to that of traditional suture ligature techniques of stabilization but required significantly thicker cortical bone thickness for successful stability of the proprietary anchors.^[1]

Davis et al (2004) reviewed 285 patients who underwent cochlear implantation with stabilization of the internal receiver/stimulator using polypropylene mesh and titanium screws and found no difference in safety profiles between this technique and standard drill-out of receiver/stimulator wells.^[2]

Limited-incision techniques forgo en face exposure of the parietooccipital cortex completely in favor of a restricted tangential exposure of just the cortical bone necessary to develop a limited well for the thickest portion of the receiver/stimulator package. While initially technically challenging, this technique preserves the integrity and tensile strength of the overlying periosteum, thereby maintaining inherent pressure over the receiver/stimulator and stabilizing it without the need for suture ligature or other synthetic anchoring devices.

Stratigouleas et al (2006) described a study of 176 patients in which a limited postauricular incision 1 cm posterior to the postauricular crease and 3-4 cm in length vertically was used. A subperiosteal pocket was raised in which the receiver/stimulator was placed. They reported a complication rate similar to that of standard cochlear implantation. This technique demonstrated comparable safety compared to standard approaches and has the added advantages of less dissection and postoperative edema, less venous stasis, decreased risk of pressure necrosis on the skin, and, subsequently, earlier mapping times (typically occurring on postoperative day one).^[3]

Likewise, Mann and Gosepath (2006) described a similar technique used in 52 patients with an average follow-up of 8.4 months in which no postoperative complications were reported.^[4]

Mack et al (2006) reported a similar approach in a large study of 808 patients. A small 5- to 6-cm postauricular incision was used, and the receiver/stimulator was accommodated with elevation of a subperiosteal plane. In all 808 patients, no wound infection and no skin flap complications were noted. The main advantages claimed by the authors included the lack of need for shaving of hair, lack of a visible scar, and no need to fix the implant with nonabsorbable sutures. However, the disadvantages included limited views of the implant bed (increased risk of CSF leak and tearing of emissary veins), requiring more careful drilling by the surgeon.^[5]

Davids et al (2009) reported results of the limited-incision/subperiosteal pocket technique in 462 pediatric patients undergoing cochlear implantation. Their results also demonstrated comparable safety and efficacy of this technique in pediatric patients, especially considering the thinner scalp and lower tensile strength of the overlying soft tissue envelope in children compared to adults.^[6]

Image-guided minimally invasive cochlear implantation

A more recent development involves the use of CT guidance for an even less-invasive technique for cochlear implantation.

Image-guided approaches to the middle ear were shown to be feasible prior to 2008; however, none demonstrated that cochleostomy was possible with this technique until this time.^[7]Nonetheless, Majdani et al (2008) performed a feasibility study in which they used flat-panel CT imaging to map out a drilling channel from the mastoid surface to the round window niche in 4 human temporal bones, all of which demonstrated (by both CT scan and mastoidectomy) a cochleostomy at the appropriate position as standard cochlear implantation would demonstrate.^[8]This study was limited because of the use of cadaveric temporal bones. Therefore, questions remain regarding how to control unexpected bleeding and how to insert the electrode through such a narrow canal.

A subsequent investigation by Majdani et al (2009) utilized the same image-guided technique described above and incorporated a robot to surgically drill along the preplanned pathway in 10 human cadaveric temporal bones. In 9 of the 10 specimens, successful cochleostomy was performed. However, stapes in 2 specimens and the chorda tympani in one specimen incurred damage. Again, this article demonstrated that an accurate pathway from the mastoid cortex to the cochlea is possible using CT guidance.^[9]

Clinical validation was undertaken by Labadie et al (2010) by showing that a single drill path from the lateral mastoid to the cochlea can be achieved via the facial recess in a clinical setting. This study utilized preoperative CT scanning and preplanning the course from the mastoid through the facial recess to the basal turn of the cochlea. This was successfully performed in 5 ears.^[10]

Limited Dissection Technique

The steps of the procedure are as follows:

A postauricular incision is performed without posterior extension
A small mastoidectomy is performed without saucerization of the cavity
The facial recess is dissected
Development of the facial recess is expedited by removal of the incus and dissection of the recess from a superior to inferior direction starting at the fossa incudis; the resulting recess provides a panoramic view, aiding in accurate identification of all middle ear structures and minimizing the risk of noncochlear placement
A subperiosteal pocket is developed over the parietooccipital cortical bone
A limited well is drilled out in a tangential fashion to accommodate the receiver/stimulator
An electrode channel is developed between the receiver/stimulator well and the mastoid cavity
Standard cochleostomy is performed
The implant device is inserted into the subperiosteal pocket and checked for stability within the receiver/stimulator well
The implant electrode array is inserted into the cochlea
Fascia is used to stabilize the electrode array cable at the cochleostomy, within the facial recess, and within the mastoid cavity
Complete two-layer closure of the periosteum and scalp over the implant device and mastoid cavity is critical to minimize risk of postimplantation infection and device extrusion