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.
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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.
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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.
Imaging Studies
Traditionally, high-resolution CT scanning of the temporal bone has been the mainstay of the preoperative radiographic workup of cochlear implant candidates.
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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.
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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.
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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Postauricular incision for cochlear implant.
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Mastoidectomy has been performed, as well as facial recess approach. Attention is now turned to marking the site for implant-well drilling.
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Tie-down holes have been created and 2-0 nonabsorbable sutures have been placed through 1-mm holes drilled into the ledge of bony well.
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Cochleostomy is performed (upper left hand corner) prior to placing implant into receiver well (main photo).
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Once electrodes are placed into cochleostomy and extracochlear electrode lead is placed under temporalis muscle, closure of periosteal tissue can begin.
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A water-tight periosteal closure is performed, and skin closure begins with a subcutaneous absorbable suture line.
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Implant well is drilled down to the dura.
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Cochlear Implant is secured into the skull via suture. The ground electrode is placed under the temporalis muscle and the electrode array is inserted into the scala tympani. The stylet is then removed.
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Depicts patient prepped out in sterile techique. Post-auricular incision marked
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Dummy template helps determine drill site for cochlear implant
