‘Cochlear view’ plain radiograph: A simple reliable positioning method

A new method of preoperative assessment of correct electrode array alignment based on post-operative measurements in a cochlear implanted cohort

PURPOSE

During cochlear implantation surgery, a range of complications may occur such as tip fold-over. We recently developed a method to estimate the insertion orientation of the electrode array. The aim of the study was to determine the optimal angle of orientation in a cohort of cochlear implanted patients.

METHODS

On eighty-five CT scans (80 uncomplicated insertions and 5 cases with tip fold-over), location of the electrode array's Insertion Guide (IG), Orientation marker (OM) and two easily identifiable landmarks (the round window (RW) and the incus short process (ISP)) were manually marked. The angle enclosed by ISP-RW line and the Cochlear™ Slim Modiolar electrode array's OM line determined the electrode array insertion angle.

RESULTS

The average insertion angle was 45.0-47.2° ± 10.4-12° SD and was validated with 98% confidence interval. Based on the measurements obtained, patients' sex and age had no impact on the size of this angle. Although the angles of the tip fold-over cases (44.9°, 46.9°, 34.2°, 54.3°, 55.9°) fell within this average range, the further it diverted from the average it increased the likelihood for tip fold-over.

CONCLUSION

Electrode array insertion in the individually calculated angle relative to the visible incus short process provides a useful guide for the surgeon when aiming for the optimal angle, and potentially enhances good surgical outcomes. Our results show that factors other than the orientation angle may additionally contribute to failures in implantation when the Slim Modiolar electrode is used.

Accuracy of intraoperative electrophysiological testing in confirming correct cochlear implant electrode positions

Objective: To investigate the accuracy of intraoperative electrophysiological studies in detecting incorrectly positioned electrodes in cochlear implant surgery. Study design: A retrospective chart review. Setting: Tertiary referral centre. Patients: In total, 104 consecutive patients with a mean age of 5 years underwent cochlear implant surgery at our centre between January 2012 and December 2013. All patients were implanted with Cochlear Nucleus Freedom implants. Method: A retrospective study to compare intraoperative neural response telemetry (NRT), impedance and electrode position using Stenver's transorbital plain X-ray view. Results: Intraoperative electrophysiological tests for patients with Cochlear Nucleus Freedom implants showed 97% sensitivity and 100% specificity compared with postoperative X-ray imaging. Conclusion: NRT results for the position of cochlear implants were very accurate when checked by X-ray imaging showing that this technique is sufficient in most cases. Stenver's plain X-ray view is needed in complicated cases with abnormal NRT testing or difficult electrode insertion.