Can fresh frozen heads be used to perform hydraulic pressure measurements during cochlear implant electrode insertion?

Objective: Intracochlear hydraulic pressure change that occurs during cochlear implant surgery is thought to play a role in hearing preservation. Presence of intracochlear air might be a problem when performing pressure measurements in temporal bones. In this study, we aimed to examine if air could enter the cochlea due to decomposition through the opening of the labyrinth and through electrode insertion. Furthermore, the effect of a large amount of insufflated intracochlear air on peak hydraulic pressure during electrode insertion was also examined in fresh frozen heads (FFHs). Methods: Three human FFHs were used. An electrode was inserted three consecutive times, while the peak hydraulic pressure was measured. Air was then insufflated, and a second series of electrode insertions was performed. Computed tomography scans were performed on each FFH before each experiment and after insufflation of air. Volume in mm3 and location of air were reported. Results: All FFHs had air, especially in the subarachnoid and intravascular space. One FFH had air in both cochleae (3–5 mm3). All FFHs showed air near the stapes footplate (1–3 mm3) after opening of the labyrinth. Air was present in the vestibule and scala vestibuli (1–23 mm3) of all FFHs after the electrode insertions and removal of the pressure sensor. The mean peak hydraulic pressure during electrode insertion decreased with insufflation of air (from 0.68 mmHg (standard deviation [SD] 0.34) to 0.24 mmHg (SD 0.14). Conclusion: Future studies on FFH or temporal bones should consider intracochlear air when performing hydraulic pressure measurements.