**3.4 Drilling a bony well for the RS**

The trends in manufacturing recent CI devices is toward making the RS as thin as possible, so that recent devices are thinner and need drilling a shallower bony well for RS. For example, the thickness of the RS of the CI532® (Cochlear Corp) is 3.9 mm, while the thickness of the RS of the older generation of the same company such as CI124RE® is 6.9 mm. Drilling a bony well with depth equal to 3 mm is usually enough to accommodate most of recent implants.

Some surgeons advocate the tight "temporalis pocket" technique in fixating the body of the implant; this technique entails elevation of small tight periosteal pocket that can just lodge the device tightly without the need of drilling a well for the RS [31]. Although slim devices can be fixed easier with tight temporalis pocket technique, still most of surgeons prefer drilling a well for stabilization of the RS [16].

Other methods for RS fixation:


• Some CI devices, such as the Neuro Zti® (Oticon Corp), are manufactured with two titanium screws that can be fixed during surgery without the need for drilling a bony well.

### **3.5 Cochleostomy**

Insertion of the electrode into the scala tympani is the goal of standard cochlear implantation. To achieve this goal, there are three possible approaches to the scala tympani, each one having advantage and disadvantage:


The "best" type of cochleostomy is still a controversial issue; however, according to the meta-analysis conducted by Santa Maria et al., hearing preservation rates were higher in cochleostomy than in RW approach [36]. Whatever the surgical approach used for cochleostomy, the key point for successful scala tympani insertion with minimal trauma is good access and visualization of the whole round window membrane.

However, the RW visibility through the surgical microscope through MPTA is variable. St Thomas' Hospital introduced a classification for the visibility of the RW during CI as follows: type I, the RW membrane is entirely exposed; type IIa, more than 50% but less than 100% of the RW membrane is exposed; type IIb, the exposure of RW membrane is less than 50% but more than 0%; and type III, the RW membrane could not be identified. Most of the adult cases (76%) were type I, 17% was type IIa and IIb, while 7% was type III [37].

#### *3.5.1 Endoscopic cochlear implantation*

Otoendoscopy can be used, instead of surgical microscope, to solve the problem of "difficult RW." Marchioni et al. [38] has described the surgical technique of endoscopic CI. They used 3 mm rigid otoscope through the EAC, after elevation of an intact tympanomeatal flap, without incising the EAC skin, and then endoscopic cochleostomy is performed through the RW membrane. However, they did not use

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*Advances in Surgical and Anesthetic Techniques for Cochlear Implantation*

particularly useful for malformed or abnormal cochlea [39–41].

drilling a bony grove in the posterior wall of EAC [38].

MPTA for electrode insertion; instead of that, they used pericanal approach by

However, due to the advantages of the standard MPTA, the use of endoscope in CI became mainly limited to help the surgeons in accurate identification of the RW membrane and precise electrode placement; also this technique appears to be

According to the method of insertion of the CI electrode array, there are three main types of CI electrode arrays that vary in the design and the method of the

1.The lateral wall (LW) electrode: Such as the K electrode of the Nucleus® (Cochlear Corp, Lane Cove, Australia), all MED-EL electrodes (MED-EL Corp, Innsbruck, Austria), and the HiFocus™ 1 J Electrode (Advanced Bionics Corp, Sylmar, CA). The lateral wall electrode, with exception of the 1 J electrode, is usually inserted by using micro forceps with or without the guide of claw instrument. The 1 J Electrode is better to be inserted with its specific

2.The midscalar (MS) electrode: such as Mid-Scala Electrode of HiFocus™

3.The perimodiolar (PM) electrode: such as HiFocus Helix™ electrode (Advanced Bionics Corp) and the Contour® electrode (Cochlear Corp). Both of these electrodes have a stylet that is removed during insertion by the off-stylet technique. The recent CI532® (Cochlear Corp) is a PM slim electrode (0.7 mm); during insertion the electrode is loaded in its sheath, the stopper is kept at the cochleostomy opening, and then the electrode array is slowly advanced out of the electrode sheath. The electrode sheath was then removed,

after seeing the three white markers at the cochleostomy site [43].

they can also have the disadvantages of both of them [44–46].

*3.6.2 Depth of insertion of the CI electrode array*

Each of the three types of electrode array has advantages and disadvantages. In general, the LW electrodes are usually slimmer and are assumed to have less traumatic effect on the cochlea during insertion, but they are usually rest away from the spiral ganglia which are the target of the electrodes' stimulatory impulses. The PM electrodes can hug the modiolus and became very close to the spiral ganglia; but because of the need of stylet, they are usually more stiff and thick, except the new PM electrode generations such as CI532® (Cochlear Corp), so that PM electrodes usually have more traumatic potentials on the cochlea during insertion. The MS electrodes are assumed to have the advantages of both LW and PM electrodes, but

Proper electrode insertion is achieved by both making full insertion, which entails inserting all active electrodes into the scala tympani, and by making appropriate depth of insertion. Regarding the depth of insertion, Yukawa et al.

(Advanced Bionics Corp,). This type of electrode is usually inserted through a specific applicator using the off-stylet technique (that was originally described

pre-loaded metal tube connecting to its specific applicator.

for the Contour Advance electrode® (Cochlear Corp) [42].

*DOI: http://dx.doi.org/10.5772/intechopen.88380*

**3.6 Electrode insertion**

insertion:

*3.6.1 Types of CI electrode arrays*

*Advances in Surgical and Anesthetic Techniques for Cochlear Implantation DOI: http://dx.doi.org/10.5772/intechopen.88380*

MPTA for electrode insertion; instead of that, they used pericanal approach by drilling a bony grove in the posterior wall of EAC [38].

However, due to the advantages of the standard MPTA, the use of endoscope in CI became mainly limited to help the surgeons in accurate identification of the RW membrane and precise electrode placement; also this technique appears to be particularly useful for malformed or abnormal cochlea [39–41].
