Predicting depth of electrode insertion by cochlear measurements on computed tomography scans.

OBJECTIVES/HYPOTHESIS: To evaluate the effectiveness of cochlear measures obtained by high-resolution computed tomography (HRCT) scan in predicting depth of cochlear implant insertion.

STUDY

DESIGN

Retrospective case review.

METHODS

Patients who underwent cochlear implantation in an academic referral center between 2010 and 2013 were considered. Inclusion criteria included available preoperative HRCT scan and complete operative data. Subjects with labyrinthitis ossificans, cochlear hypoplasia, or major inner ear malformations were excluded. Subsequently, measures of cochlear height in the coronal plane and basal turn width in the axial plane were obtained using electronic calipers of the stored digital HRCT images by a blinded investigator. The insertion was considered deep when the electrode was placed at least 23 mm into the cochlea. Subjects were divided into those who had a deep insertion and those who did not. Regression analyses were done to associate cochlear measures with deep insertion.

RESULTS

A deep insertion was possible in 25 patients out of 35. There was no statistically significant association between deep insertion and age at implantation, gender, and type of cochleostomy. The mean cochlear height was 6.22 mm (standard deviation [SD] = 0.32 mm) and 5.80 mm (SD = 0.3mm) in subjects with and without deep insertion, respectively (Student t test, P = .0015). Only cochlear height showed an association with deep insertion (logistic regression, P = .0007). For a cochlear height of 6.27 mm, the probability of deep insertion was 0.90.

CONCLUSIONS

Linear measurements of standard CT scans of the cochlea can predict the depth of insertion and may help the selection of the appropriate electrode array preoperatively.

LEVEL OF EVIDENCE: 4. Laryngoscope, 126:1656-1661, 2016.