Introduction:
The electrode position within the cochlea plays an important role for the interaction
between electrode contacts and spiral ganglion cells. It is determined by the form
of the electrode carrier. Straight electrode arrays (Nucleus™ 522 „SRA“) are pressed
against the lateral wall of the cochlea, while precurved arrays (Nucleus™ 532 „SMA“
and 512 „Contour“) curl around the modiolus and ideally have no contact to the lateral
wall. Recent improvements in postoperative CBCT (cone beam computational tomography)
imaging resolution now allow accurate determination of the space between each electrode
contact and the medial wall of the cochlea and to observe correlations between this
distance and electrophysiological and psychophysical measurement values.
Methods:
Postoperative high resolution CBCT-images of 30 patients with Cochlear® Nucleus™ 532,
522 and 512 implants were evaluated using the Comet (Cochlea Measurement Tool) program
to determine the distance between the 22 electrode contacts and the medial wall. During
the first fitting week after the initial activation ECAPs, T- and C-levels and spread
of excitation (SOE) were measured.
Results:
Patients with perimodiolar electrode arrays (Nucleus™ 532 and 512) had significantly
lower ECAP thresholds, T- and C-levels as well as SOE widths than patients with the
straight des Nucleus™ 522 implant.
Conclusion:
Our results show that the electrode position has a significant effect on both electrophysiological
and psychophysical parameters. Low psychophysical thresholds are among other aspects
relevant for prolonging battery life by decreasing energy consumption. No significant
differences in speech test performance were notable at the end of the first fitting.
