Scalar localization by cone-beam computed tomography of cochlear implant carriers: a comparative study between straight and periomodiolar precurved electrode arrays.

Objective: To compare using analyses of cone-beam computed tomography (CBCT) images, the incidence of scalar dislocation after cochlear implant surgery with a straight or a precurved electrode array. Study design: Consecutive non-randomized case comparison study. Settings: Tertiary referral center Patients: CBCT analysis of patients after cochlear implantation. Intervention(s): Precurved perimodiolar and straight electrode arrays from two different manufacturers were implanted. A pure round window insertion was performed in all cases, except two necessitating a cochleostomy. All patients had, CBCT imaging and the images were reconstructed in coronal oblique, sagittal oblique, and axial oblique section. Main outcome measures: Evaluation of the insertion depth angle and the occurrence of dislocation from the scala tympani to the scala vestibuli. Results: Fifty four patients and 61 implants were analyzed. Thirty one patients were implanted with a perimodiolar electrode array and 30 patients with a straight array. Nine (15%) scalar dislocations were observed, 8 (26%) in the perimodiolar array group and 1 (3%) in the straight array group. The dislocation occurred at an insertion depth angle between 170 and 190° in the perimodiolar array group, and around 370° in the straight array group. Conclusion: CBCT imaging is a reliable tool to assess the position of the electrode array in the cochlea and to detect a possible scalar dislocation. The dislocation usually occurs in the ascending part of the basal turn of the cochlea with a perimodiolar array. A straight flexible electrode array has a higher chance of an exclusive scala tympani positioning than a perimodiolar precurved array.