8.18\ Cochlear Implant

Complications

8.18.1\ Discussion

Complications related to cochlear implantation include infection, perilymphatic fistula from the round window or cochleostomy site with pneumolabyrinth, extrusion, erosion of the hardware into the intracranial compartment, device malposition, and extrusion of the electrode out of the cochlea. (Figs. 8.81, 8.82, 8.83, 8.84, 8.85, 8.86, 8.87, 8.88, and 8.89). Malposition of the electrode is a significant cause for cochlear implant malfunction and can be evaluated via dedicated radiographs or temporal bone CT. Potential malpositions to consider include “false insertion” of the electrode into hypotympanic air cells, Eustachian tube, or carotid

canal, coiling or buckling of the electrode array within the cochlea, incomplete insertion into the cochlea, and “transcalar insertion” with violation of the basilar membrane and osseous spiral lamina such that the electrode extends from scala tympani into scala vestibuli. Transcalar insertion will result in loss of any residual natural hearing by damaging the delicate neurosensory elements and also will result in postoperative new bone formation that will require excessive high power settings/ battery requirements to overcome resulting high impedance. If a congenital cochlear anomaly is present, it is possible for the electrode array to breach the deficient modiolus and extend into the internal auditory canal. A defect in the otic capsule can allow the electrodes to contact the labyrinthine segment of the facial nerve, which can result in unwanted stimulation of the facial nerve.

Fig. 8.81  Receiver-stimulator hardware erosion into the skull. Axial CT image shows a defect (arrow) in the squamous temporal bone under the receiver-stimulator hardware

Fig. 8.82  Perilymphatic fistula. Axial CT image shows pneumolabyrinth (arrow) following cochlear implantation

Fig. 8.83  Electrode malpositioning. Coronal CT image shows the “false insertion” of the electrode passing through hypotympanic air cells into the petrous apex and clivus (arrow)

Fig. 8.84  Lateral cochlear implant electrode malpositioning. Axial CT image shows the distal end of the cochlear implant coiled on itself within the vestibule (arrow)

Fig. 8.85  Incomplete cochlear implant electrode insertion. Axial CT image shows the electrodes only partially inserted into the basal turn of the cochlea due to obstruction by labyrinthitis ossificans (encircled)

Fig. 8.89  Transcalar electrode array insertion. Axial CT images at two different levels (a, b) show that the cochlear implant is properly positioned within the scala tympani in

the basal turn (arrow), but winds up in the scala vestibuli in the middle turn (arrowhead)