Angular Insertion Depth in Inner Ear Malformations, Relationship to Cochlear Size, and Implications for Electrode Selection.

Objective: The objectives were to determine the interrater agreement of the Skull AP X-ray in measuring angular insertion depth (AID), to provide descriptive information about the insertion depths of different electrodes used in inner ear malformations (IEMs), to investigate the effect of cochlear size and electrode length on AID, and to guide clinicians in electrode selection in IEMs.

Study design: Retrospective case review.

Setting: Tertiary referral center.

Patients: A total of 198 IEMs (n = 169 patients) and 60 cochleae with normal anatomy (n = 60 patients) were selected from patients with severe mixed or sensorineural hearing loss who presented to our clinic and underwent cochlear implantation (CI) between January 2010 and December 2022.

Interventions: Three neurotologists independently measured AID on Skull AP X-rays. Basal turn length of the cochlea was measured in axial and coronal oblique reformatted sections on HRCT images.

Main outcome measures: Interrater reliability (ICC) of the AID measurements on Skull AP X-ray, determining the impact of cochlea size and electrode length on AID measurements.

Results: The interrater reliability (ICC) test showed a high level of consistency in measuring AID in the Skull AP X-ray ( R = 0.906, p < 0.001). In the control group, a negative correlation was observed between the AID and the basal turn length of the cochlea, while a positive correlation was found between electrode length and AID ( R = 0.947, p < 0.001).

Conclusions: The Skull AP X-ray appears to be a dependable tool for measuring AID. In cases of IEMs, it is important to select an electrode of appropriate length, considering the dimensions of the cochlea.