Cochlear Implant Surgery Workup

Updated: Oct 13, 2017
  • Author: Cliff A Megerian, MD, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Workup

Laboratory Studies

Preoperative laboratory studies include those germane to any standard otologic procedure. These studies include CBC count, electrolytes, and clotting time studies.

Controversy exists regarding the preoperative laboratory workup with respect to issues particular to patients with severe sensorineural hearing loss.

  • If the patient has rapidly progressive hearing loss or other signs or symptoms of autoimmune hearing loss, an immunologic workup is often indicated during the evaluation of the patient. Treatment of autoimmune inner-ear disease should be instituted in patients with bilateral progressive hearing loss in the event that the hearing loss is rapid over weeks. The immunologic workup may include a Western blot analysis for antibodies to the heat shock protein. Failure to achieve serviceable hearing after a course of steroid therapy is often an indication for cochlear implantation.
  • If syndromic causes of hearing loss are suggested (eg, Pendred syndrome, Alport syndrome), obtain appropriate complementary serologic tests (eg, thyroid studies, renal studies).

Although genetic testing regarding the molecular basis for a patient's deafness most likely would not change the plans for cochlear implantation, obtaining available blood tests for genetic markers of specific mutations known to cause sensorineural hearing loss, such as the test for connexin 26 mutations, is helpful for counseling reasons.

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Imaging Studies

Traditionally, high-resolution CT scanning of the temporal bone has been the mainstay of the preoperative radiographic workup of cochlear implant candidates.

  • This study helps determine the absence of malformations that contraindicate implantation (eg, cochlear aplasia, absence of the auditory nerve). Additional relative contraindications, such as chronic otitis media, are revealed with high-resolution CT.
  • CT scanning also reveals abnormalities that alter the standard insertion procedure of the electrode array. These abnormalities include Mondini dysplasia, common cavity, and cochlear ossification. Suspect cochlear ossification in patients with a history of meningitis.

In some centers, high-resolution T2-weighted fast spin echo MRI is complementing and even replacing CT scanning because of its increased ability to reveal cochlear ossification.

In patients older than 40 years, preoperative chest radiography is performed as per protocol in most hospitals. In addition, before leaving the operating room after cochlear implantation, plain film radiography of the cochlea in the anteroposterior plane (transorbital) is useful to confirm correct placement of the electrode array, but, more importantly, chest radiography is used to provide evidence and confirmation of correct initial placement in the event that delayed implant malfunction arises and electrode migration is suspected.

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Other Tests

Intra-operative fluoroscopy is not only beneficial to confirm placement but also guides the right trajectory of placement in cases of malformed cochlear anatomy where inadvertent entry into the internal auditory canal (IAC) because of modiolar deficiency is a potential challenge.

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