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Depth and quality of electrode insertion: a radiologic and pitch scaling assessment of two cochlear implant systems
1Department of Otolaryngology, Sunnybrook Women's College Health Science Centre, University of Toronto, Ontario, Canada.
Objective:
To compare the depth of electrode insertion in two types of cochlear implants, and to assess the ability of the implantees in each group to place-pitch during random electrical stimulation.
Study Design:
This was a prospective clinical study.
Setting:
This study was performed at an implant program within a university teaching hospital.
Patients:
Five consecutive patients with the Clarion (Advanced Bionics, Symlar, CA, U.S.A.) device and 5 with the Nucleus-22 (Cochlear Corporation, Sydney, Australia) implants were enrolled. All 10 implantees had fully active and functioning electrodes.
Interventions:
The depth of insertion was determined using plain anteroposterior skull film and high resolution computed tomography (CT). The quality of electrode insertion was assessed by pitch scaling; electrodes were randomly stimulated to generate subjective pitch responses.
Outcome Measures:
The depth of electrode insertion was measured radiographically as degrees of angular rotation within the cochlea. For pitch scaling, the averaged responses to electrical stimulation was plotted against the "place" of the electrodes along the array. Pitch range, plateauing, and reversal of pitches were also noted. Insertion depth was correlated with the result of pitch scaling and open-set speech discrimination at 3 months.
Results:
The mean insertion depth was 406 degrees for the Clarion device and 254 degrees for the Nucleus device. CT was used to confirm the intracochlear placement of the electrodes and their relationships to the cochleostomy site. It did not confer more information than the plain films unless kinking had occurred. Pitch perception was consistent with the tonotopic organization of the cochlea. The Nucleus-22 recipients displayed a broader range of pitches with less plateaus and reversals than the Clarion implants. The depth of insertion did not compare well with the outcome of pitch scaling or with open-set speech discrimination scores in either group of implantees.
Conclusion:
The preformed spiral array of the Clarion device allowed deeper electrode insertion compared to the Nucleus-22 device. However, depth of insertion did not translate into better pitch placement.