Assessment of electrode placement and audiological outcomes in bilateral cochlear implantation

Abstract

Objective: The goal of this study was to use highly accurate nonrigid algorithms to locate the position of cochlear implant (CI) electrodes and correlate this with audiological performance.

Patients: After obtaining institutional review board approval, adult patients who had bilateral CIs were identified, and those with preoperative temporal bone computed tomographic scans were asked to return for a postintervention computed tomography. Sixteen adult patients agreed. Demographics, cause of deafness, length of auditory deprivation, and audiological performance were recorded.

Intervention: Using a nonrigid model of the shape variations of intracochlear anatomy, the location of the basilar membrane was specified in relationship to the electrode array. The number of electrodes within each compartment of the cochlea was correlated with hearing in noise and consonant-noun-consonant scores for the known confounding variable: length of deafness.

Main outcomes: Mann-Whitney U tests of differences were used to compare the hearing performance resulting from implants completely in the scala tympani (ST) versus those not completely in the ST.

Results: Of all implants, 62.5% were fully inserted in the ST; 34.4% were partially inserted into the ST and 3.1% was fully inserted in the scala vestibuli. Controlling for the known contributing variable of length of auditory deprivation, our results show that the location of electrodes in relationship to the scala is not predictive of audiological performance.

Conclusion: We have assessed electrode placement and correlated it with audiological outcome. The presence of the electrodes solely in the ST was not predictive of outcome. We estimate that it would take analyzing data of thousands of CI patients before any valid correlations can be made.

Figure 1

A. Post-op CT of a patient with full electrode insertion in ST. Note that ST is contoured by red and SV contoured in blue. Figure 1B. Reconstructed CT in the same patient with full ST insertion. (ST shadowed in red; SV shawdowed in blue).

Figure 2

A. Post-op CT of a patient with the electrode crossing from ST to SV. (ST contoured in red; SV contoured in blue). Figure 2B. Reconstructed CT in the same patient with the electrodes starting in ST and then crossing to SV at approximately 180 degrees. (ST-red, SV-blue).

Figure 3

Comparison of CNC word scores for bilaterally implanted patients with complete versus incomplete ST insertion. The data is shown as a horizontal median value with 25–75th percentiles shown in the gray box and complete data shown between the whiskered lines.