Cochlear implant

Last revised by Andrew Murphy on 7 May 2023

Cochlear implants (CI) are surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. Unlike conventional hearing aids, the cochlear implant does not amplify sound but works by directly stimulating any functioning auditory nerves inside the cochlea with an electric field.

External components of the cochlear implant include a microphone, a speech processor and a radiofrequency (RF) transducer or primary headpiece coil. A secondary coil is implanted beneath the scalp and inductively coupled to the primary headpiece coil.

The implant gives recipients additional auditory information, which may include sound discrimination fine enough to understand speech in quiet environments. Post-implantation rehabilitative therapy is often critical to ensuring successful outcomes.

Radiographic features

The electrodes should be intracochlear; the radial position of the tip determines the depth. Complications observed postoperatively include electrode 13:

  • tip fold over

    • can result in the rupture of the basilar membrane

  • basal fold over

    • fold over at the basal portion of the array

    • can result in the rupture of the basilar membrane

  • under-insertion or extrusion

    • electrode contacts are sitting outside of the cochlear

  • over-insertion

    • most proximal electrode contact is >3mm from the round window

  • kinking or pinching

  • scalar translocation

    • electrode is translocated from the scala tympani into the scala vestibuli

    • can result in basilar membrane injury

  • tympanic cavity placement

    • typically seen in the context of CHARGE syndrome where the array can't make the basal turn and sits in the tympanic cavity

  • placement in the internal auditory canal

  • placement in the vestibulum and semi-circular canals

Regular electrode

Before assessing post operative imaging it is important to note the route in which the implant has been inserted, it can be one of three ways via the 12:

  • round window (the preferred method)

  • extended round window (where the round window is enlarged and opened via drilling of the anterior-inferior margin)

  • cochleostomy

Split electrode

The split electrode (used in patients with otosclerosis) implant comprises two electrodes in the cochlear, one in the basal turn and one in the second turn.

Retrograde electrode

Patients with basal turn ossification require insertion via cochleostomy.

Plain radiograph

Post operative plain film radiography of the temporal bones are sufficient in a majority of patients. Plain radiography is the most helpful modality to assess for extrusion and superior in assessing the number of inserted electrodes. Typically a modified Stenvers view is performed, which has succeeded the original Stenvers view

Correct placement of the electrodes are within the scala tympani regions 11

CT

Particularly useful when postoperative radiographs fail to demonstrate the location of the electrode array adequately or if postoperative infection is suspected 1

Usually thin-collimation (≤1 mm) scanning performed contiguously or with a 0.5–1-mm overlap is required. 

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