Variation of the cochlear anatomy and cochlea duct length: analysis with a new tablet-based software

Abstract

Purpose In cochlear implantation, thorough preoperative planning together with measurement of the cochlear duct length (CDL) assists in choosing the correct electrode length. For measuring the CDL, different techniques have been introduced in the past century along with the then available technology. A tablet-based software offers an easy and intuitive way to visualize and analyze the anatomy of the temporal bone, its proportions and measure the CDL. Therefore, we investigated the calculation technique of the CDL via a tablet-based software on our own cohort retrospectively. Methods One hundred and eight preoperative computed tomography scans of the temporal bone (slice thickness < 0.7 mm) of already implanted FLEX28™ and FLEXSOFT™ patients were found eligible for analysis with the OTOPLAN software. Measurements were performed by two trained investigators independently. CDL, angular insertion depth (AID), and cochlear coverage were calculated and compared between groups of electrode types, sex, sides, and age. Results Mean CDL was 36.2 ± 1.8 mm with significant differences between sex (female: 35.8 ± 0.3 mm; male: 36.5 ± 0.2 mm; p = 0.037), but none concerning side or age. Differences in mean AID (FLEX28: 525.4 ± 46.4°; FLEXSOFT: 615.4 ± 47.6°), and cochlear coverage (FLEX28: 63.9 ± 5.6%; FLEXSOFT: 75.8 ± 4.3%) were significant (p < 0.001). Conclusion A broad range of CDL was observed with significant larger values in male, but no significant differences concerning side or age. Almost every cochlea was measured longer than 31.0 mm. Preoperative assessment aids in prevention of complications (incomplete insertion, kinking, tipfoldover), attempt of atraumatic insertion, and addressing individual necessities (hearing preservation, cochlear malformation). The preferred AID of 720° (two turns of the cochlea) was never reached, opening the discussion for the requirement of longer CI-electrodes versus a debatable audiological benefit for the patient in his/her everyday life.

Robotic Cochlear Implant Surgery: Imaging-Based Evaluation of Feasibility in Clinical Routine

“…The current results show that the mean CDL of analyzed ears was in the range with previously published data (24,25). Between well trained examiners, the CDL differed by 1.5 mm on average, which was reported by Canfarotta et al (28).…”

“…Although some image data with a slice thickness of up to 0.5 mm were sufficient enough to plan a trajectory, bad imaging resolution was the most frequent reason for a failure in planning, followed by software problems, failure in 3D ear reconstruction, and corrupted image data. A slice thickness of up to 1.3 mm might be enough for CDL planning in some cases (24,25), but based on the current data and our experience, sufficient visualization of the facial nerve or the chorda tympani is almost impossible. Even in imaging with a slice thickness of 0.3-0.5 mm, the chorda tympani can be only visualized if the angle of the Xray is in favor of the nerve's location and reconstruction allows for sufficient presentation on the image.…”

Vermessung der Cochlea mittels eines Tablet-basierten Softwarepakets: Einfluss der Bildgebungsmodalität und des Untersucherhintergrunds

“…Eine zu geringe Insertion hingegen kann zu einer Stimulation überwiegend oder sogar ausschließlich der Nervenfasern in den basalen Bereichen der Cochlea führen, was zu einer Komprimierung der Frequenzdynamik führt. Patienten erfahren dann initial aufgrund der fehlenden Übereinstimmung der Orts-Frequenz-Auflösung vermehrt eine "hochfrequente" Klangqualität, wobei Reiss et al dabei eine Plastizität der Hörbahn beschreiben, mit der dieses initiale Hörgefühl über die Zeit kompensiert werden kann [32] Die Größe der Cochlea ist individuell unterschiedlich, was sich in der großen Spannweite der Länge des Ductus cochlearis, definiert von rundem Fenster bis Helicotrema, abbilden lässt [36]. Dabei sind die Referenzpunkte der Messung zu beachten, da der Unterschied der gemessenen CDL auf Höhe der lateralen Wand der Cochlea (CDLLW), im Vergleich zu der CDL auf Höhe des Corti-Organs (CDLOC) mehr als 10 % betragen kann [31].…”

“…Die Unterschiede zwischen den Messungen der verschiedenen Untersucher waren für beide Bildgebungsmodalitäten klein und weder statistisch noch klinisch signifikant (M Differenz < 0,5 mm). [36].…”

“…Die Größe der Cochlea ist individuell unterschiedlich, was sich in der großen Spannweite der Länge des Ductus cochlearis, definiert von rundem Fenster bis Helicotrema, abbilden lässt [ 36 ]. Dabei sind die Referenzpunkte der Messung zu beachten, da der Unterschied der gemessenen CDL auf Höhe der lateralen Wand der Cochlea (CDL LW ), im Vergleich zu der CDL auf Höhe des Corti-Organs (CDL OC ) mehr als 10 % betragen kann [ 31 ].…”