Characterization of Tip Fold-Over Using Fluoroscopy and Intracochlear Pressure in Cadaver Specimens

Cochlear implant array malpositioning is associated with impaired speech perception, vertigo, and facial nerve stimulation. Tip fold-over is a subset of malpositioning that occurs more often with perimodiolar electrodes, but historically it has not been characterized due to lack of knowledge regarding electrode movements of the electrode within the cochlea. The aim of this study was to characterize the mechanics of tip fold-over events and their associated insertion pressure profiles.

Cadaveric human heads were surgically prepared with a mastoidectomy and facial recess. Fiberoptic pressure sensors were inserted into the scala vestibuli and tympani to measure intracochlear pressures. Perimodiolar CI electrodes (Cochlear Slim-Modiolar, CI532) were inserted via round window under fluoroscopy.

Three types of tip fold-over events were observed: anterior-posterior C-shaped, medial-lateral C-shaped, and S-shaped roll-overs. The largest transient pressures occurred with anterior-posterior and S-type roll-over, and were associated with rotation or twisting inside the cochlea.

Results demonstrate at least three subtypes of tip fold-overs. Elevated pressure transients were noted before and during the tip fold-over event related to electrode twisting. The characterization of tip fold-over into subtypes is novel and may aid identification of tip fold-over events intraoperatively in the future. It remains important to identify tip fold-over events, and they should be recognized early using a multimodal verification system. Further investigation is still required to determine the significance of these changes and other possible patterns of intracochlear electrode movement.

NA: Cadaver study Laryngoscope, 135:1795-1802, 2025.