**3.6 Electrode insertion**

*Advances in Rehabilitation of Hearing Loss*

tympani, each one having advantage and disadvantage:

drilling a bony well.

**3.5 Cochleostomy**

insertion.

window membrane.

was type IIa and IIb, while 7% was type III [37].

*3.5.1 Endoscopic cochlear implantation*

• 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

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

1.Traditional cochleostomy technique: in which there is a separate opening just inferior and slightly anterior to the RW membrane; it should be crated after good visualization of the RW membrane and lowering down the RW niche. The main advantages of this approach are avoiding the hook region of the basal turn, providing more effective sealing of both cochleostomy and RW by fibrous tissue, and providing appropriate angle of electrode insertion away from the osseous spiral lamina [5, 16], However, this approach entails more bone drilling on the cochlea that may expose the neuro-sensitive structures of

2.RW approach: in which the RW membrane is opened, better by using a sharp needle. This approach is the least traumatic approach; however, electrode insertion may be difficult, and electrode may be hanged in the hook region by a projecting crista fenestra, which will need further drilling to allow electrode

3.Extended RW approach: in which the round window membrane is opened and then the anterior-inferior margin of the RW is drilled till good visualization of the scala tympani is achieved. Through this approach, the hook region is avoided, electrode array insertion will be in the same trajectory line of the scala

The "best" type of cochleostomy is still a controversial issue; however, according

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%

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

tympani, and trauma to the osseous spiral lamina will be avoided.

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

the cochlea to traumatic and thermal effect of the drill [35].

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