Cochlear Implant

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Cochlear Implant
2013-11-11 22:03:05

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  1. What are adult selection criteria for cochlear implant?
    • (1) severe or profound hearing loss with a pure-tone average of 70 dB HL
    • (2) use of appropriately fit hearing aids or a trial with amplification
    • (3) aided scores on open-set sentence tests of less than 50%
    • (4) no evidence of central auditory lesions or lack of an auditory nerve
    • (5) no evidence of contraindications for surgery in general or cochlear implant surgery in particular.
  2. Indications for cochlear implant evaluation for children
    • (1) unaided thresholds of greater than 90 dB HL at 2000 Hz and above in the better ear, even if hearing levels at 250 and 500 Hz are better
    • (2) aided thresholds in the better ear are greater than 35 dB HL, especially at 4000 Hz
    • (3) no response for ABR testing in both ears or no response for one ear and responses at elevated levels in the other ear
    • (4) parents are frustrated with their child's development of auditory and/or communication skills
    • (5) progressive hearing loss with detection levels at or near the profound range at 2000 Hz and above
    • (6) evidence of severely impairing auditory neuropathy/dys-synchrony.
    • There is no lower age limit for evaluation.
  3. The implant directly stimulates which cochlear structure?
    Bipolar spiral ganglion neurons. Majority of causes of deafness, the audi-tory hair cells are lost or dysfunctional. The bipolar spiral ganglion neurons and their primary afferent dendrites remain intact
  4. What percentage of congenital deafness is hereditary?
    60% of these children have hereditary causes of the deafness.
  5. What percentage of heritable hearing loss is nonsyndromic?
    • It is estimated that 70% of all hereditary hearing losses are nonsyndromic
    • 80% of nonsyndromic cases of heritable hearing loss are inherited in an autosomal recessive fashion.
  6. What percentage of congenital SNHL are due to connexion 26?
    50% of all NSHL cases are due to a mutation in a single gene encoding connexin 26 (Cx26). The gene coding for Cx26 (gap junction protein beta 2 or GJB2) is located at locus DFNB1 on human chromosome 13q12.
  7. Two most common recessive syndromes that cause congenital hearing loss?
    • Pendreds: enlarged vestibular aqueduct, thyroid dysfunction
    • Ushers: blindness due to retinitis pigmentosa, +- vestibular dysfunction
    • Also:
    • Jervell and Lange-Nielsen syndrome (deafness and sudden death syndrome due to prolonged QT interval)
    • NF2: phenotype of bilateral acoustic neuromas
  8. Three most common autosomal dominant syndromes causes of congenital deafness?
    Stickler syndrome, branchio-oto-renal syndrome, and Waardenburg syndrome
  9. When reviewing a temporal bone CT in a child with congenital hearing loss, what are some of the most important elements to assess?
    Determination of intact internal auditory canals, normalcy of the cochlea, primary or secondary bone diseases affecting the cochlea, and presence of a wide vestibular aqueduct
  10. What is auditory steady-state response (ASSR) testing?
    ASSR uses a continuous tone with a carrier frequency that is amplitude and frequency modulated. Similar to an ABR, ASSRrecordings show primary energy at the carrier frequency and two sidebands separated from the carrier by the modulation frequency. Recent studies have demonstrated correlation between the degree of hearing loss measured by standard PTA and ASSR at 500, 1000, 2000, and 4000 Hz
  11. Advantages of MRI in pre-implant evaluation of hearing loss in children?
    It is more effective in identifying fibrosis of the cochlea by assessing its patency, in identifying the presence and caliber of the cochlear nerve (especially on sagittal T2 imaging of the internal auditory canal), and in providing information about brainstem and cortical lesions. A study compared the ability of HRCT and MRI for identifying abnormalities of the cochlea and modiolus, and MRI was found to be superior.
  12. Where does cochlear ossification typically begin?
    ossification generally begins in the basal turn and proceeds apically.
  13. What is the risk of losing residual hearing in the implanted ear?
    risk of losing residual hearing during electrode insertion is estimated at 50% to 70%
  14. Which pneumococcal vaccination is given to children below the age of 2 years?
    • Prevnar, the heptavalent pneumococcal conjugated vaccine, which contains seven pneumococcal serotypes conjugated to a nontoxic variant of diphtheria toxin
    • 23-valent vaccine (pneumovax) composed of pure capsular antigen is not recommended for children younger than 2 years of age because of immaturity of their immune systems.
  15. How thin should you make the skin flap overlying the device?
    Current devices require that the flap be less than 10 to 12 mm thick. Significant risk is inherent whenever a skin flap must be thinned. It is recommended to avoid thinning the skin flap to less than 0.8 cm
  16. Where do you make your cochleostomy?
    The cochleostomy is drilled through the promontory just anterior and inferior to the round window membrane
  17. In a patient with predominantly high frequency hearing loss, what is the benefit of a short or hybrid implant?
    Short implant doesn't reach the apex, thus low frequencies are likely to be preserved. A hybrid implant relays combined electric and acoustic stimulation.
  18. Children who have received implants by what age acquire language at approximately the same rate as children without implants.
    2 years
  19. Compared to an adult cochlea, how large is a newborn's cochlea?
    The cochlea is full size at birth
  20. Auditory neuropathy (AN) or dyssynchrony is associated with hearing loss in which _____ hair cells function but _____ hair cells or the cochlear nerve are dysfunctional.
    Outer hair cells function, inner hair cells or cochlear nerve don't
  21. When is auditory neuropathy suspected?
    • When the audiogram shows dispro-portionately low word recognition scores and the MRI is normal.
    • It is critical to provide an adequate trial of hearing aids and auditory verbal therapy because, despite an absent ABR, some children will have adequate benefit from hearing aids alone.
  22. When do you implant children who are deafened by meningitis?
    • May regain some of their hearing, immediate implantation is not recommended.
    • Fibrosis and ossification of the cochlea may occur within a few months after meningitis, and follow-up with serial MRIs performed at 2- to 3-month intervals may be done. If the perilymph/endolymph signature is lost, fibrosis and eventual ossification may be occurring. In such cases, hearing does not return, and early implantation may be indicated.
  23. Is CI recommended in pts with Mondini malformation? Common cavity? Michel's deformity?
    • Mondini's dysplasia (incomplete partition), large vestibular aqueduct, and other, less severe forms of dysplasia—are associated with excellent results.
    • Common cavity deformity has highly variable results that are generally not as good as those seen in children with normal cochlea.
    • Aplasia of the cochlea (Michel's deformity) or absence of the auditory nerve are absolute contraindications to implantation of the affected ear.
  24. Absence of the cochlear nerve is suspected in anacusic patients with internal auditory canal (IAC) of what diameter?
    • Diameters of 1.5 mm or less. When a stenotic bony IAC is found, sagittal high-resolution MRI with heavily T2-weighted images is indicated.
    • Electrical auditory brainstem responses may be performed to document the presence of the auditory nerve when there is doubt
  25. T/F. After encountering a CSF gusher, a lumbar drain should be placed to make it easier to seal the cochleostomy.
    A lumbar drain should not be used before sealing the cochleostomy, because it reduces the CSF pressure head, thereby making it impossible to determine whether the tissue seal is adequate.
  26. How is hearing enhanced with placement of b/l CI as opposed to unilateral?
    • Head shadow effect: improved hearing in background noise
    • Sound localization
  27. The most common indications for revision surgery in a 2008 report was what?
    • “hard failure” or device malfunction that occurred in 46% of the cases of revision surgery.
    • Medical-surgical reasons (e.g., wound healing, electrode malposition, cholesteatoma) occurred in 37% of cases.
    • A “soft failure” (decrease in auditory performance or aversive symptoms in a device that performs within manufacturer specifications) occurred in 15% of cases.
  28. Two interoperative considerations when performing a cochlear implant on patients with a cochlear malformation.
    • facial nerve anomalies
    • CSF leaks through the cochleostomy