The impact of round window vs cochleostomy surgical approaches on interscalar excursions in the cochlea: Preliminary results from a flat-panel computed tomography study

Abstract

Objective: To evaluate incidence of interscalar excursions between round window (RW) and cochleostomy approaches for cochlear implant (CI) insertion.

Methods: This was a retrospective case-comparison. Flat-panel CT (FPCT) scans for 8 CI users with Med-El standard length electrode arrays were collected. Surgical technique was identified by a combination of operative notes and FPCT imaging. Four cochleae underwent round window insertion and 4 cochleae underwent cochleostomy approaches anterior and inferior to the round window.

Results: In our pilot study, cochleostomy approaches were associated with a higher likelihood of interscalar excursion. Within the cochleostomy group, we found 29% of electrode contacts (14 of 48 electrodes) to be outside the scala tympani. On the other hand, 8.5% of the electrode contacts (4 of 47 electrodes) in the round window insertion group were extra-scalar to the scala tympani. These displacements occurred at a mean angle of occurrence of 364° ± 133°, near the apex of the cochlea. Round window electrode displacements tend to localize at angle of occurrences of 400° or greater. Cochleostomy electrodes occurred at an angle of occurrence of 19°-490°.

Conclusions: Currently, the optimal surgical approach for standard CI electrode insertion is highly debated, to a certain extent due to a lack of post-operative assessment of intracochlear electrode contact. Based on our preliminary findings, cochleostomy approach is associated with an increased likelihood of interscalar excursions, and these findings should be further evaluated with future prospective studies.

Keywords: Cochlear implantation; Cochleostomy; Electrode position; Flat-panel computed tomography; Interscalar excursion; Round window insertion; Surgical approach.

Fig. 1

Delineation of scala tympani versus scala vestibuli using 3D curved multiplanar reformation analysis and window level/window width settings. The white arrows note the osseous spiral lamina and the red arrows highlight the basilar membrane. A typical WL/WW bone setting on CT is 300/1500. Abbreviations: WW, Window width; W, Window level.

Fig. 2

Electrode intracochlear position on secondary flat-panel CT reconstructions. (A), Sagittal oblique section of the cochlea (B), and cross section of cochlea at the center of the modiolus. Abbreviations: ST, Scala tympani; SV, Scala vestibuli; BM, Basilar membrane.