engleski

Modified surgical approach for cochlear implantation

Introduction Cochlear implantation is almost 30 years old procedure. The classical surgical approach was described by Clark in 19791, and until nowadays the technique has not changed much. Some of the authors introduced minimal changes in the skin incision, but mastoidectomy, posterior tympanotomy and cochleostomy remained constant parts of the surgical procedure. The established operation has lately begun to change. Kronenberg et al.2 have described the alternative approach, avoiding the transmastoid posterior tympanotomy described by Jansen3 in 1957. Since we have also realized that mastoidectomy is not necessary for the cochlear implantation, from 1999 we have introduced the bone tunnel, connecting the mastoid planum with the inner part of the bone ear canal, in our surgical procedure. Patients and methods Until today, 29 patients were operated on using the modified surgical technique of cochlear implantation. 24 patients were children between 2 and 7 years, 13 boys and 11 girls. They were all prelingualy deaf. 5 patients were adult, postlingualy deaf people. Retroauricular incision resembling the distended letter "J" is performed with electric knife in order to reduce bleeding. After the elevation of the tympanomeatal flap the middle ear is opened. The bone from the posterior part of the ear canal is drilled off, and the stapes and round window are presented. The oblique tunnel is made with 2 mm diamond drill in the region of the mastoid planum, behind the suprameatal spine, and about 10 mm behind the posterior edge of the bony meatus. The tunnel ends about 5 mm above the annulus tympanicus, in the posterior bony wall of the external auditory canal. In the extension of the tunnel, the bony canal directing to the future cochleostoma, is made. The dept of canal must be sufficient for the electrode. Using the 0.8 mm diamond drill, after the removal of the periost, the cochleostoma is made on the promontory. This aperture is temporary closed with the gel foam. After that, the second skin incision and preparation of the retroauricular flap is made. Under this flap a pouch for the cochlear stimulator on the temporal bone is drilled in a classical way, about 7 - 8 cm behind and above the auditory canal. From this pouch to the external meatus, the groove for the active electrode is drilled. The placement of the electrode through the tunnel and cochleostoma is very easy to perform. The stapes reflex is used to check the correct position and a proper function of the electrode. After that, a bit of muscle or connective tissue and some fibrin glue are put around for the fixation of the electrode. When the electrode is settled in its bed, the groove is covered with the bone dust (from the earlier drilling) mixed with the fibrin glue. The same thing is performed in the part of the canal that is previously formed on the posterior part of the bony meatus. Results Neither one case of the facial nerve paralysis, nor any other complication, was noticed in any of the 29 operated patients. The correct settlement of the electrode in the cochlea was checked by stapes reflex during the operation. This was later confirmed (24 hours after the surgery) with the X - ray imaging. The final proof of the correct procedure was given one month after the surgery, when the speech processor was turned on for the first time, and when the cochlear implant was functioning properly. Discussion The described technique is much faster than the classical method since we do not need to perform the mastoidectomy nor posterior tympanotomy. This method is very secure, and the danger of the facial nerve injury is very low. Furthermore, in comparison to the classical surgery, the electrode is more easily to put into the cochlea through the cochleostoma since it enters directly to the cochleostoma from the oblique placed tunnel without any angle. In the classical operation technique there is always an angle on the electrode on the place it enters the cochleostoma.

cochlear implantation; mastoidectomy

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