Preoperative prediction of the expected opening width of the posterior tympanotomy using Otoplan

Background Access to the round window membrane (RF) via posterior tympanotomy (PT) in cochlear implantation (CI) varies interindividually. Despite computed tomographic (CT) imaging, the surgical field of view through the PT is difficult to anticipate for CI. Otoplan provides an automatic trajectory for CI using CT images. In the present study, we analyzed how much the bore channel of the PT, especially the chordo-facial angle, needs to be opened up depending on the anatomical relationships of the guide structures to the automatic trajectory in Otoplan.

Methods Computed tomography scans were obtained from 27 human temporal bone specimens. Using Otoplan, distances of the automatic trajectory to the guide structures and out-/in-plane angles were analyzed. The temporal bone preparation was used to measure how far the chordo-facial angle had to be reamed in relation to the parameters in the otoplan to ensure adequate visibility of the RF in CI. The results of the otoplan analysis were compared with those in the temporal bone preparation.

Results The greater the distance of the ideal trajectory to the auditory canal (p<0.05), to the chorda tympani (p<0.01) and to the facial recess (p<0.05) and the shorter the distance to the facial nerve (p<0.05), the further the chordo-facial angle had to be opened caudally. Distances to the other leading structures and out-/in-plane angles showed no significant correlation (p>0.05).

Conclusions In the present study, Otoplan showed potential as a tool for anticipating the expected drilling work at the chordo-facial angle in CI with respect to the anatomical relationships of the ideal trajectory to the guide structures.

Publication History

Article published online:
12 May 2023