Cochlear implant (CI) electrode migration is generally considered to be very uncommon, the subject of few clinical reports and often not considered when discussing CI complications with patients. However, partial electrode extrusion from the cochlea, enough to reduce function and cause aversive stimuli, may not be so unusual.
Rivas et al.1 described electrode migration as an important cause of cochlear reimplantation, second only to device failure at Hopkins. And Connell et al.2 reported a ten year period during which the United States Food and Drug Administration MAUDE database3 showed 151 reported instances of electrode extrusion (presumably underestimated due to the voluntary nature of reporting and the tendency to report only major extrusions).
Electrode extrusions are thought to have been more common in the generation of stiff, straight electrodes some two decades ago. To reduce the rate of electrode migration at that time, Cohen and Kuzma introduced a titanium clip that attached the electrode cable to the incus bridge (buttress)4 and Balkany and Telischi described the split bridge technique (a slot in the incus bridge) to fixate the cable in the same location.5 Both were effective in reducing electrode extrusion.6 However, the advent of pre-curved electrodes and more flexible cables reduced the tendency for electrode migration.
With the current predominance of thin straight electrodes, which have reduced frictional forces to resist extrusion, it is time to reconsider the frequency of CI electrode migration/partial extrusion. Recently, Dietz et al.7 from the Kuopio University Hospital, the University of Eastern Finland, and Helsinki University Central Hospital reported on electrode migration with straight flexible electrodes. In that study, prospectively collected data on 201 implantations performed between 2002 and 2014 were analyzed. Patients with less than full insertion were excluded. Eighteen devices were noted to have large, progressive increases in impedance values (>75%) or aversive stimuli from the basal electrodes. Cone-beam CT demonstrated extrusion of basal electrodes in 12 of 201 subjects (6%). (This total includes both straight and pre-curved.)
Sixty-three ears were implanted with the Cochlear Corporation CI422 (Slim Straight electrode) and 64 with the Contour Advance (pre-curved electrode array). Seventy-four ears were implanted with variable lengths of the Med El electrode.
Five of 63 (8%) of Cochlear Corporation CI422 (Slim Straight) electrodes showed partial migration/extrusion compared to 0 of 64 (0%) of Contour Advance (pre-curved) electrodes.
Seven of the 74 (9%) Med El electrodes partially extruded as well.
This paper demonstrates that straight flexible electrodes have a high rate of partial extrusion (12 of 137 = 9%). This figure includes all straight electrodes. A contemporaneous cohort of 64 pre-curved electrodes, inserted by the same surgeons, can be seen as a comparison group. In the pre-curved electrode group, there were no extrusions.
It is hoped that this research can be replicated soon to determine generalizability. Nonetheless, based on this paper, surgical precautions to prevent electrode extrusion from the cochlea should be reconsidered.
The authors used tight fascia packing of the cochleostomy sealed with fibrin glue in the middle ear and bone paté and fibrin glue in the facial recess and mastoid cavity. These were not effective.
Methods used prior to the advent of pre-curved electrodes may once again be considered: the split-bridge technique, titanium clip, coiling a loop of electrode cable against the mastoid tegmen, focus on mastoid overhangs. Newer techniques developed for insertion of hybrid electrodes, such as passing the electrode through a loop of suture in the tegmen that is snugged after insertion (suggested by Bruce Gantz) or manufacturing a tab on the cable near the electrode array to lock into the facial nerve-chorda tympani angle (suggested by Thomas Lenarz), might also be considered.
The Dietz study contains clinically important information regarding a high rate of partial electrode extrusion with straight, flexible electrodes. Although not yet replicated, these findings should be disseminated to cochlear implant surgeons.
1. Rivas A, Marlowe AL, Chinnici JE, Niparko JK, Francis HW. Revision cochlear implantation surgery in adults: indications and results. Otol Neurotol. 2008 Aug;29(5):639-48.
2. Connell SS1, Balkany TJ, Hodges AV, Telischi FF, Angeli SI, Eshraghi AA. Electrode migration after cochlear implantation. Otol Neurotol. 2008 Feb;29(2):156-9.
3. US Food and Drug Administration. Manufacturer and User Facility Device Experience (MAUDE) Database Search. Available at: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/search.cfm. Accessed March 1, 2007.
4. Cohen NL, Kuzma J. Titanium clip for cochlear implant electrode fixation. Ann Otol Rhinol Laryngol Suppl 1995;104:402-3.
5. Balkany T, Telischi FF. Fixation of the electrode cable during cochlear implantation: the split bridge technique. Laryngoscope 1995;105:217-8.
6. Roland JT Jr, Fishman AJ, Waltzman SB, et al. Stability of the cochlear implant array in children. Laryngoscope 1998;108:1119-23.
7. Dietz A , Wennström M, Lehtimäki A, Löppönen H, Valtonen H. Electrode migration after cochlear implant surgery: more common than expected? European Archives of Oto-Rhino-Laryngology and Head & Neck 2015:3716. Epub before print: DOI: 10.1007/s00405-015-3716-4