The effect of the surgical approach and cochlear implant electrode on the structural integrity of the cochlea in human temporal bones

Abstract

Cochlear implants (CI) restore hearing of severely hearing-impaired patients. Although this auditory prosthesis is widely considered to be very successful, structural cochlear trauma during cochlear implantation is an important problem, reductions of which could help to improve hearing outcomes and to broaden selection criteria. The surgical approach in cochlear implantation, i.e. round window (RW) or cochleostomy (CO), and type of electrode-array, perimodiolar (PM) or lateral wall (LW), are variables that might influence the probability of severe trauma. We investigated the effect of these two variables on scalar translocation (STL), a specific type of severe trauma. Thirty-two fresh frozen human cadaveric ears were evenly distributed over four groups receiving either RW or CO approach, and either LW or PM array. Conventional radiological multiplanar reconstruction (MPR) was compared with a reconstruction method that uncoils the spiral shape of the cochlea (UCR). Histological analysis showed that RW with PM array had STL rate of 87% (7/8), CO approach with LW array 75% (6/8), RW approach with LW array 50% (4/8) and CO approach with PM array 29% (2/7). STL assessment using UCR showed a higher inter-observer and histological agreement (91 and 94% respectively), than that using MPR (69 and 74% respectively). In particular, LW array positions were difficult to assess with MPR. In conclusion, the interaction between surgical approach and type of array should be preoperatively considered in cochlear implant surgery. UCR technique is advised for radiological assessment of CI positions, and in general it might be useful for pathologies involving the inner ear or other complex shaped bony tubular structures.

Acute effects of cochleostomy and electrode-array insertion on compound action potentials in normal-hearing guinea pigs

“…We should note that of the steps investigated, nowadays, cochleostomy is the less common approach for cochlear implantation ( Kant et al, 2022b ). However, cochleostomy and extended round window (which is a related approach as it also requires drilling) are expected still to be used in the future as these approaches are preferred in certain anatomical conditions and for perimodiolar electrode arrays ( Garaycochea et al, 2020 ; Jwair et al, 2022 ).…”

Intracochlear Trauma and Local Ossification Patterns Differ Between Straight and Precurved Cochlear Implant Electrodes

“…Second, not only the surgical techniques but also the electrode designs have evolved over time resulting in lower insertional trauma rates, at least in acute insertion studies (28,(38)(39)(40)(41). Third and finally, the distribution of the different electrode insertion locations in this study is skewed toward ERW insertions, whereas it is known that the insertion location of the electrode may impact the electrode trajectory and trauma pattern (37,40,42). Future insertions may be even less traumatic with robotic insertion and the integration of insertion tools that can help direct the electrode array in the cochlea away from delicate structures in real time (43,44).…”

Models of Cochlea Used in Cochlear Implant Research: A Review

“…It is important to consider that the use of animal models is complementary to measures that can be conducted in human patients and cadaveric tissues. For instance, several studies have characterised the electrical properties [32,72] and conducted CI insertion studies [18,75,77] in both fresh-frozen and fixed human cochleae. Furthermore, many electrophysiological and psychoacoustic measures have been developed to test the CI-nerve interface in humans, which include contact impedance and trans-impedance measurements [59,87,138], electrically evoked compound action potentials (eCAPS) [27,41,42], and electrically evoked auditory brainstem responses (eABR) [17,36] which enable the evaluation of CI electrical characteristics (including fibrosis, positioning, and electrical faults), cochlear neural activation patterns, and propagation the CI stimulation to the brain, respectively.…”