Distance to Rosenthal’s Canal is a Moderate Predictor of Intraoperative Electrical Compound Action Potential Thresholds in Contour Advance Electrode Arrays

Background

It is generally assumed that decreasing the distance from a stimulating contact to Rosenthal’s canal results in lower monopolar current thresholds for neural excitation. However, no studies have yet demonstrated a significant correlation for in vivo measured distances, when all intracochlear electrode contacts along the array are considered.

Objective

To examine the 3-dimensional position of all electrode contacts along the array with respect to Rosenthal’s canal, and to determine whether a correlation exists with intraoperative current thresholds from electrically evoked compound action potential (ECAP) measurements.

Methods

In a retrospective study, cone-beam computed tomography (CBCT) scans and intraoperative ECAP thresholds (T-NRT) from 16 subjects with a Contour Advance array were analyzed. Intracochlear anatomy and the position of electrode contacts were segmented from pre- and postoperative CBCT. To overcome poor soft-tissue delineation in CBCT, the location of Rosenthal’s canal was estimated by non-rigidly co-registering a micro-computed tomography atlas with the in-vivo scans.

Results

A moderate positive correlation (R = 0.46, P<0.001) was found between the distance to Rosenthal’s canal and ECAP thresholds. When the correlation was calculated per case, a significant positive correlation (P<0.05) could be shown in 14 out of 16 patients.

Conclusion

The distance to Rosenthal’s canal is a moderate predictor for ECAP thresholds in Contour Advance electrode arrays. Placement closer to Rosenthal’s canal results in lower currents necessary for evoking a neural response.