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Cochlear Implantation

last modified on: Tue, 01/16/2018 - 11:52

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Cochlear Implantation

return to: Otology - Neurotology

  1. GENERAL CONSIDERATIONS
    1. Indications
      1. Adults (at least 18 years of age)
        1. Bilateral severe-to-profound sensorineural hearing loss
        2. Post-lingual onset of deafness
        3. Little to no useful benefit with appropriately fit hearing aids and consistent use of amplification
        4. In best-aided condition (without lip-reading cues)
          1. <50% on open-set sentence recognition in quiet in ear to be implanted
          2. <60% on open-set sentence recognition in quiet in contralateral ear
        5. High motivation and realistic expectations for improving hearing
          1. Specific insurance company requirements and Medicare criteria are not addressed here, and are subject to change.
      2. Children
        1. Bilateral profound sensorineural hearing loss (12 months to 2 years old) or bilateral severe-to-profound sensorineural hearing loss (2 to 18 years old)
          1. Little to no useful benefit with appropriately fit hearing aids and consistent use of amplification
          2. Lack of progress in development of auditory skills despite appropriate hearing amplification
          3. In best-aided condition (without lip-reading cues), <30% on open-set word recognition test in quiet (performed on children old enough to complete the test)
          4. High motivation and realistic expectations from family
          5. Enrollment in an educational program that supports auditory development
      3. Additional comments
        1. The FDA (Food and Drug Administration) approved guidelines for cochlear implants in the United States vary slightly among the different implant manufacturers. The presented indications are intended to provide only a general overview for candidacy criteria. Additionally, criteria for cochlear implant candidacy by the FDA may differ from criteria for coverage of cochlear implantation by medical insurance.
        2. While cochlear implantation has been approved by the FDA only for those older than 1 year of age, children younger than this have been implanted off-label, especially when the hearing loss is secondary to meningitis (to allow for cochlear implantation before the development of intracochlear ossification).
    2. Contraindications
      1. Absolute contraindications
        1. Cochlear nerve aplasia
        2. Complete agenesis of the cochlea
      2. Relative contraindications
        1. Significant intracochlear ossification or fibrosis
        2. Other congenital malformations of inner ear
        3. Active chronic otitis media
        4. Medical contraindications, including relative inability to tolerate general anesthesia or psychiatric conditions that may result in inability to use cochlear implant
        5. Poor psychosocial environment
        6. Post-lingually deafened adult
    3. Anatomic considerations
      1. The presence of a cochlear nerve is essential for cochlear implantation. Confirmation of this (eg. via radiological imaging) is particularly important in pre-lingually deafened children who are candidates for cochlear implants.
      2. The patency of the cochlea and presence of inner ear malformations can result in modifications of the technique used for cochlear implantation.
      3. Abnormal facial nerve anatomy may place the facial nerve at greater risk during cochlear implantation. Additionally, the descending segment of the facial nerve tends to be located more laterally in children, who have not had full development of the mastoid tip, placing it at greater risk during the surgical incision.
      4. A poorly pneumatized mastoid cavity, low-lying tegmen, anteriorly-located sigmoid sinus, or high jugular bulb may make the surgical approach more difficult. Consideration may be given to sacrifice of the chorda tympani and/or a subtotal petrosectomy approach in cases where the mastoid cavity is significantly contracted.
  2. PREOPERATIVE PREPARATION
    1. Evaluation
      1. Complete history
        1. History of hearing loss in each/both ears, including progression and patient’s perceived usefulness of amplification.
          1. "Can you use the telephone?"
        2. Meningitis or post-traumatic SNHL: consider ossification of the cochlea and expedite evaluation.
        3. History of ear infections and previous ear surgeries
        4. Developmental delay/neurologic abnormalities
      2. Physical examination
        1. Craniofacial abnormalities: consider anomalous facial nerve anatomy
        2. Otomicroscopic exam of ears with pneumotoscopy
        3. Weber/Rinne tuning fork exam (256, 512, 1024 Hz)
        4. Documentation of facial nerve function (House-Brackmann Scale).
      3. Complete audiometric evaluation
        1. Hearing-aid verification
        2. Speech perception testing in the best-aided condition
        3. If not previously aided, a hearing aid trial with appropriately fit amplification (covers monaural and bilaterally fit hearing aids) for at least 3 months.
        4. Adults need a complete audiogram (including pure tones, speech perception)
        5. Children
          1. Age-appropriate audiometric testing (eg. behavioral observation, visual reinforcement, conditioned play, conventional, etc.)
          2. Immittance testing
          3. tympanometry
        6. Infants
          1. otoacoustic emission (OAE) hearing screening
          2. Auditory Brainstem Response (ABR) and Auditory Steady State Response (ASSR) testing
          3. tympanometry
          4. myringotomy and tubes prior to ABR if any middle ear effusion
      4. Caloric testing for bilateral cochlear implantation in adults
      5. Radiological examination
        1. In adults: High-resolution, thin-cut computed tomography (CT) scan without contrast of the temporal bone (axial, coronal).
          1. If concerns about the patency of the cochlea exists, MRI is a better tool to assess fluid in the cochlea. A CT will reveal ossification but not fibrosis
        2. In children: a non-enhanced fine-cut high-definition T2 (CISS or FIESTA) magnetic resonance imaging (MRI) scan of the temporal bone (axial, coronal, and oblique cuts perpendicular to the internal auditory canal)
          1. Assess for presence of cochlear nerve.
          2. Cochlear architecture
          3. Middle ear fluid
      6. A psychosocial evaluation may be useful in children to assess factors that may influence the amount of benefit received from cochlear implantation in kids and to provide appropriate counseling
    2. Determination of which ear to implant
      1. If both ears have similar hearing levels, the "better" ear (eg. ear with shorter duration of deafness or more consistent use of hearing aid) is implanted.
      2. The ear with more favorable radiological anatomy.
      3. The ear free of chronic or acute otitis media.
      4. If there is not a clearly "better" ear, then the ear the patient prefers is implanted.
      5. If one ear has still aidable acoustic hearing, the other, "worse" ear, may be implanted.
      6. Benefits of bilateral cochlear implantation in adults and children are beyond the scope of this medium.
    3. Immunization against ''S. pneumonia'' must be documented prior to cochlear implantation.
      1. Vaccination must occur greater than two weeks from date of implantation
        1. The following are the currently recommended vaccination guidelines from the Centers for Disease Control (https://www.cdc.gov/vaccines/vpd/mening/hcp/dis-cochlear-gen.html)
          1. Children < 2 years
            1. pneumococcal conjugate vaccine (PCV-7) (Prevnar®)
          2. Children > 2 years who have completed the PCV-7 series
            1. one dose of the pneumococcal polysaccharide vaccine (PPV-23) (Pneumovax® 23).
            2. If they have just received PCV-7, they should wait at least two months before receiving PPV-23.
          3. Children 24-59 months of age who have never received either PCV-7 or PPV-23
            1. should receive two doses of PCV-7 two or more months apart and then receive one dose of PPV-23 at least two months later.
          4. Persons aged 5 years and older
            1. one dose of PPV-23.
            2. Revaccination is not indicated.
      2. Chronic otitis media
        1. Cochlear implantation is contraindicated during ongoing middle ear infections.
        2. Patients who continue to have ear infections or otorrhea despite ventilation tubes should have a staged implantation
          1. subtotal petrosectomy (involving plugging of the eustachian tube with muscle/fascia, obliteration of mastoid cavity, taking the canal wall down, and closure of the external auditory canal)
          2. cochlear implantation a month later.
        3. Previous canal-wall down tympanomastoidectomy
          1. staged subtotal petrousectomy with closure of EAC
          2. cochlear implantation 2 months later.
  3. CONSENT
    1. Benefits
      1. To provide hearing to deaf individuals via electrical stimulation of the cochlea
      2. A wide range of hearing abilities is obtained with a cochlear implant, with most cochlear implant listeners able to obtain good open-set speech recognition in quiet.
        1. For adults, performance with a cochlear implant generally improves rapidly over a few months and then more slowly over several years.
        2. For children, performance usually improves with development of the child over many years.
    2. Alternatives
      1. Observation
      2. Hearing amplification (although cochlear implant candidates typically receive little to no benefit from hearing aids)
      3. Sign language and assist devices in home/workplace
    3. Risks
      1. Bleeding
      2. Wound infection, either immediate or delayed
        1. Includes device extrusion
        2. Meningitis
      3. Facial nerve
        1. Paralysis
        2. Facial stimulation by device
        3. Taste changes (chorda tympani)
      4. Inner ear changes
        1. Loss of residual acoustic hearing (expected)
        2. Tinnitus
        3. Vertigo or vestibulopathy
      5. Ear numbness
      6. CSF or perilymph leak
      7. Device failure or migration
      8. Complications of general anesthesia including heart attack, stroke, and death
      9. Need for further surgeries, including removal and/or reimplantation of device.
    4. Warnings
      1. The magnet contained in the internal part of the cochlear implant needs to be surgically removed prior to any MRI undertaken by the patient (see cochlear implant manufacturer guidelines)
      2. The following therapies are contraindicated in patients with a cochlear implant
        1. electrosurgery (monopolar cautery)
        2. electroconvulsive therapy
        3. neurostimulation over the cochlear implant
        4. ionizing radiation therapy over the cochlear implant
        5. diathermy using electromagnetic radiation
      3. Head trauma may result in damage to the cochlear implant
  4. NURSING CONSIDERATIONS
  5. MEDICATION: see OTOLOGY ANTIBIOTIC ADMINISTRATION GUIDELINES
  6. ANESTHESIA CONSIDERATIONS: see General Considerations of Otologic Surgery
  7. OPERATIVE PROCEDURE
    1. Positioning: see General Considerations of Otologic Surgery
      1. For bilateral cochlear implantation
        1. ETT taped to midline (RAE tube works well)
        2. ETT not secured to blanket/straps
        3. Double check ETT to assure that rotating head during surgery will not result in extubation
    2. A C-shaped post-auricular incision with a posterosuperior extension, is made down to the level of the superficial layer of the deep temporalis fascia. For cochlear implantation, a post auricular incision is designed approximately 3-5 mm just behind the post-auricular crease.

  1. monopolar electrocautery contraindicated if a cochlear implant is already in place (eg. for patients with planned bilateral cochlear implantation or a revision surgery)
  2. In children without a well-developed mastoid tip, care must be taken in making the incision to avoid damaging the descending portion of the facial nerve inferiorly, which may be located more laterally than in adults.
  3. An anteriorly-based, Palva flap (approximately 4 x 4 cm) is created, composed of temporalis fascia, muscle, and periosteum. The superior extent of the Palva flap should consist of the inferior border of the temporalis muscle and the linea temporalis.  This will prevent significant bleeding from the muscle.
    1. The spine of Henle is the landmark for the anterior border of the flap.
    2. Design your Palva flap so that it is set off from the skin incision, and to afford complete coverage of the receiver/processor and the electrodes.
  4. A limited cortical mastoidectomy is performed, with identification of the tegmen, sigmoid sinus, antrum, incus, and lateral semicircular canal.
    1. Keep a shelf of cortical bone posteriorly and superiorly.  This helps to maintain placement of the electrodes in the mastoid cavity.
    2. Open the facial recess to provide adequate exposure to the round window.
      1. Do not sacrifice the chorda tympani nerve
      2. Expose the entire round window niche, and visualize the stapes as well
        1. The incal butress is preserved in hearing preservation cases.
  5. Drill the well for the device.
    1. The receiver/stimulator should be located approximately 45 degrees from the sinodural angle.
    2. Avoid placing the CI too anteriorly, as this may cause the internal device to rub against the postauricular skin or eyeglasses.
    3. Elevate the posterior periosteum and temporalis. Use the implant template to determine that this has been done sufficiently.
    4. Drill the well as recommended for the individual device.
      1. Emphasis should be on a well that accommodates the implant completely with preserved bone anteriorly to prevent device migration.
      2. In children, the cortical bone may be thin and require exposure of dura with a central island of bone for adequate seating of the internal device.
      3. Different means of securing the CI exist.
        1. If suture is used, drill the holes to accommodate the sutures and place the sutures in anticipation of implantation
        2. If plating system is used, drill the screw holes now.
  6. The cochleostomy
    1. Recommend using a 1 mm diamond burr on high magnification.
    2. Place cochleostomy anterior and inferior to the round window.
      1. Emphasis on opening cochleostomy on the floor of the basal turn, in the scala tympani.
      2. High cochleostomy or placement through the round window is not recommended.
    3. Cochleostomy size as recommended by specific device manufacturer.
    4. Soft surgery technique for hearing preservation
      1. Blue line the cochlea
      2. Enter cochlea with footplate rasp
      3. Smallest cocheostomy possible for device insertion (0.5 mm for Hybrid cochlear implant
      4. Do not suction perilymph.
    5. In cases with intracochlear ossification a drillout procedure may be necessary.
      1. Take down canal wall and close off external auditory canal.
      2. Drill out basal turn until lumen noted
      3. May need two separate cochleostomies in the basal and apical turns
      4. Anticipate the need for a split electrode array, and have on-hand
      5. Fluoroscopy for insertion may be helpful.
  7. Introducing device.
    1. Introduce device and place into well.
    2. Secure as preferred.
    3. Insert the electrode array into the scala tympani of the basal turn of the cochlea, with the goal of a full insertion of all electrodes.
    4. See manufacturer’s instructions for specifics as to different devices.
    5. Soft surgery:
      1. prior to drilling cochleostomy, place small washer of pressed fascia onto implant, all the way to the silastic hub.
      2. Have everything ready for immediate insertion upon opening the cochlea.
      3. Slow advancement performed with ABR (noise bands) monitoring over approx 45 seconds.
    6. A small piece of temporalis muscle (MRH) or fascia (BJG) is used to plug the cochleostomy around the device. An additional piece of temporalis can be placed between the electrode and the annulus and the electrode and facial nerve if either is exposed (MRH).
    7. Place the ground electrode, if present, into the zygomatic root,
    8. Curl the excess electrode into the attic.
    9. Hemostasis should now only be achieved with bipolar and not monopolar cautery, to avoid damage to the implant.
      1. Have your scrub nurse throw the monopolar off the surgical field.
  8. Intraoperative measurements
    1. neural response telemetry to assess for proper function of the device may be obtained during closure.
    2. We routinely do this only with children, and not for second sided implants.
    3. Some institutions shoot a plain film during closure to document position. We do not.
  9. Closure
    1. The Palva flap is closed. Care is taken to completely cover the electrode and hub of the device.
    2. The wound is then closed in two layers, without placement of a drain
    3. A standard mastoid dressing is applied
  10. POSTOPERATIVE CARE
    1. Patients are typically discharged home on the same day of surgery (MRH) or after 23-hour inpatient observation (BJG))
    2. Postoperative antibiotics for 7-days: see OTOLOGY ANTIBIOTIC ADMINISTRATION GUIDELINES
    3. Patients are instructed to remove their mastoid dressing the morning after they are discharged home.
    4. The patient may shower and get the incision wet after 3 days, but are instructed to avoid submersion.
    5. Non-absorbable sutures (if present) are removed on post-operative day 7
    6. The cochlear implant is activated approximately 4 weeks following surgery by the audiologist.
    7. Regular follow-up visits for additional adjustments to the signal processor programs (MAPs) are planned as follows:
      1. Adult appointments
        1. 2 weeks, 1 month, 3 months, 6 months, & 12 months after initial fit; annually afterwards
        2. Expect a stable MAP within 6-12 months
      2. Child appointments
        1. 1 day, 2 weeks, 1 month, 2 months, & then every other month for the 1st year after initial fit; 18 months, 24 months, & then annually afterwards
        2. Expect a stable MAP within 8-18 months

REFERENCES

Clark GM, Pyman BC, Bailey QR. The surgery for multiple-electrode cochlear implantations. J Laryngol Otol. 1979;93:215-228.
Coker NJ, Jenkins HA, Fisch U. Obliteration of the middle-ear and mastoid cleft in subtotal petrosectomy- indications, technique, and results. Ann Otol Rhinol Laryngol. 1986;95:5-11.
Gantz BJ, McCabe BF, Tyler RS. Use of multichannel cochlear implants in obstructed and obliterated cochleas. Otolaryngol Head Neck Surg 1988;98:72-81
Lenarz T, Lesinski-Schiedat A, et al. The Nucleus double array cochlear implant: a new concept for the obliterated cochlea. Otol Neurotol. 2001;22:24-32.
Luxford WM, Mills D. Cochlear implantation in adults. In Jackler RK, Brackmann DE (eds): Neurotology, 2<sup>nd</sup> ed. New York, Mosby, 2004, pp 1309-1314.
Ying YM, Toh EH. Cochlear implantation. In Myers EN (ed): Operative otolaryngology, 2<sup>nd</sup> ed. Philadelphia, Elsevier, 2008, pp 1377-1384.