Most cochlear implant centres confirm electrode position after surgery using X-rays to ensure optimal electrode placement. As well as transorbital view X-rays, this team check placement using impedance measures and neural response telemetry (NRT) performed intraoperatively. The former indicates whether the simulator receiver package and electrode array are intact and working and the latter looks at the electrically evoked compound action potential (e-ECAP) giving information about the response of the auditory nerve fibres and position of the array in the cochlear. The team investigated whether NRT would accurately confirm electrode position without the need to then subject the patient to another procedure involving radiation. They found that NRT was sensitive, and all but three of the 98 measurements obtained NRT when there was a full insertion of the electrode array. Specificity was also high as none of the six cases where electrodes were not fully inserted into the cochlea obtained the desired level of NRT. They found that X-ray imaging yielded similar results in determining whether there was a full insertion. Due to the high sensitivity and specificity of NRT, they felt that this technique was reliable in determining whether an electrode had been fully inserted. However, as this study was done retrospectively with Nucleus Freedom implants, these results may not be transferable to other Nucleus implant types or implants from other cochlear implant companies. The cases where the cochlear implant was not found to be fully inserted were also the cases where the cochlea was malformed and insertion depth may have had to be determined by the surgeon more accurately. Consideration also needs to be given to the time taken to perform the intraoperative measurements as this can be more time consuming than an X-ray. In addition, a postop X-ray can help determine if there has been electrode movement once the surgery is over. Therefore, it is unlikely that NRT measurements alone will become the gold standard to check electrode positioning, but they can provide useful additional information.
X-ray vs. intraoperative testing for determining cochlear implant placement
Reviewed by Kerri Millward and Morag Lockley
Accuracy of intraoperative electrophysiology testing in confirming correct cochlear implant electrode positions.
CONTRIBUTOR
Kerri Millward
Manchester Paediatric Cochlear Implant Programme, Manchester, UK.
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