AUTHOR AND EDITOR INFORMATION

Section 1 of 8  

• Authors and Editors
• Introduction
• Preoperative Considerations
• Etiologies of Severe to Profound Hearing Loss
• Bilateral Implants
• Outcomes
• Multimedia
• References

INTRODUCTION

Section 2 of 8  

• Authors and Editors
• Introduction
• Preoperative Considerations
• Etiologies of Severe to Profound Hearing Loss
• Bilateral Implants
• Outcomes
• Multimedia
• References

Background

Hearing loss is one of the most common sensory impairments and affects 28 million Americans. Approximately 1-3 out of 1000 newborns has hearing impairment. The elderly are more commonly affected with 40-50% of people over age 75 having hearing loss. Depending on the degree of hearing loss, many affected individuals can be successfully fitted with hearing aids. For patients with hearing loss that is not mitigated with hearing aids, a cochlear implant may provide an opportunity for hearing. 

The cochlear implant is a surgically placed device that converts sound to an electrical signal. This electrical signal is transmitted via electrodes to the spiral ganglion cells in the cochlear modiolus. As of 2005, an estimated 85,000 patients worldwide have received cochlear implants. However, this number represents only a small number of individuals with hearing impairment who may potentially benefit from implantation (an estimated 250,000 people). Many candidates for cochlear implants often do not have access to this procedure due to failure of recognizing appropriate candidates or because of inadequate healthcare resources.

Although individual responses to cochlear implants are highly variable and depend on a number of physical and psychosocial factors, the trend toward improved performance with increasingly sophisticated electrodes and programming strategies has dramatically expanded indications for cochlear implantation. Although cochlear implants originally were touted as an aid to speech reading for individuals with profound hearing impairment, a growing population of implanted patients are exceeding their preoperative hearing performance (which was aided with conventional hearing aids). Due to the overall success of cochlear implants and ongoing advances in performance, an article addressing indications for cochlear implantation attempts to describe a target that moves almost yearly.

For excellent patient education resources, visit eMedicine's Ear, Nose, and Throat Center. Also, see eMedicine's patient education article Hearing Loss    

Throughout the 1970s, the Food and Drug Administration (FDA) recommended that devices be implanted only in adults with profound hearing loss. In 1980, the FDA allowed children at least 2 years of age to be implanted. The age limit has recently been lowered to 12 months for all 3 devices available in the United States (Advanced Bionics, Med-El, and Cochlear Corporation devices). Over time, indications have been broadened to include adults with severe hearing loss who may achieve some benefit from conventional amplification.

PREOPERATIVE CONSIDERATIONS

Section 3 of 8  

• Authors and Editors
• Introduction
• Preoperative Considerations
• Etiologies of Severe to Profound Hearing Loss
• Bilateral Implants
• Outcomes
• Multimedia
• References

Cochlear implantation is a collaborative effort involving patients, families, schools, audiologists, speech/hearing therapists, and surgeons. A patient with hearing impairment does not have a surgical problem that responds to the simple intervention of an implant surgeon. Because preoperative expectation affects the patient's postoperative satisfaction and use of the implant, all patients and families require attention and counseling from an implant team before they embark on the life-changing journey of cochlear implantation.

Pure-tone audiometry

The human ear is capable of hearing frequencies from 20-20,000 Hz. Pure-tone audiometry is used to assess a subject’s response to a frequency at a specific intensity measured in decibels. In most cases, frequencies from 250 Hz to 8000 Hz are assessed, as these are most important for speech perception. 

Speech audiometry

Although a number of speech-recognition tests are currently used for different reasons, one of the most common speech-recognition tests is the hearing in noise test (HINT), which tests speech recognition in the context of sentences. In determining cochlear implant candidacy, HINT is performed without background noise, despite its name. HINT measures word-recognition abilities to assess the patient's candidacy for cochlear implantation, in conjunction with conventional pure-tone and speech audiometry. The HINT consists of 25 equivalent 10-sentence lists that may be presented in quiet or noise to assess the patient's understanding of sentences.

As noted earlier, when used to assist in the determination of cochlear implant candidacy, the HINT is currently performed in quiet. (HINT sentences are found in the Minimum Speech Perception Test Battery for Adult Cochlear Implant Users CD.) Administer the first test in quiet by using 2 lists of 10 sentences, which are scored for the number of words correctly identified.

Criteria

For adults and children who can respond reliably, standard pure-tone and speech audiometry tests are used to screen likely candidates. For children aged 12-23 months, the pure-tone average (PTA) for both ears should equal or exceed 90 dB. For individuals older than 24 months, the PTA for both ears should equal or exceed 70 dB. If the patient can detect speech with best-fit hearing aids in place, a speech-recognition test in a sound field of 55-dB HL sound pressure level (SPL) is performed. A number of speech recognition tests are currently in use.

Current US Food and Drug Administration (FDA) guidelines permit implantation in patients whose open-set sentence recognition (eg, HINT) is 60% or less in the best-aided condition. However, for patients receiving Medicare benefits, the current cutoff for cochlear implant candidacy is a HINT score of 40% or less. For Medicare patients enrolled in an acceptable clinical trial or study, the cutoff is 60% or less. Guidelines for other third-party payers may vary and should be consulted.

Other tests

In children with prelingual deafness, cochlear implant candidacy is established when auditory skills fail to develop after amplification and aural rehab over a 3-month time period. Progress is typically monitored with the Meaningful Auditory Integration Scale or the Early Speech Perception test. Other scales of auditory benefit may be used in older children.

Imaging

Imaging with CT or MRI is performed prior to implantation to evaluate the inner ear, facial nerve, cochleovestibular nerve, brain, and brainstem. MRI may reveal hypoplasia or aplasia of the cochleovestibular nerve, whereas CT may show a narrow internal auditory canal or absence of the bony cochlear nerve canal at the modiolus. Inner ear malformations ranging from the rare cases of cochlear aplasia to the more common enlarged vestibular aqueduct are easily visualized on CT or MRI. Such results may alter the choice of side of implantation or raise other issues such as electrode selection.

Patients with cochlear malformations are still candidates for cochlear implantation, but they may require a different type of electrode, a different surgical approach (ie, drill out), and may be more at risk for meningitis or cerebrospinal fluid gusher. Surgeons should be prepared for a cerebrospinal fluid leak caused by incomplete partition between the cochlea and the internal auditory canal. Absence of the cochlea or the cochlear nerve can usually be confirmed with imaging and are absolute contraindications for cochlear implantation.

Clinicians must take extra caution to identify the cochleovestibular nerve complex; auditory stimulation with a cochlea implant in patients with supposed cochlear nerve aplasia has been reported. These cases may be more appropriately labeled cochlear nerve hypoplasia. Families and patients must be adequately counseled and fully informed about the variable performance of patients with dysplastic cochleae and the potential risk of cerebrospinal fluid leakage and meningitis.

In pediatric or young adult patients with progressive hearing loss, exclude neurofibromatosis II by performing MRI before proceeding with implantation. MRI has more recently become the imaging study of choice at some institutions because the inner ear, cochleovestibular nerve, brain, and brainstem can all be visualized. MRI, unlike CT scanning, is also very useful in identifying early labyrinthitis ossificans, which typically begins with endoluminal fibrosis of the scala tympani at the basal turn.

Preoperative counseling and education

In addition to the purely audiologic criteria discussed above, pediatric candidates must be enrolled in an educational program that supports listening and speaking with aided hearing. For patients of all ages, no medical contraindications (eg, cochlear or auditory nerve aplasia, active middle-ear infection) may be present. Communication among patients, families, schools, audiologists, therapists, and surgeons is required.

Immunization

A study published in 2003 reported that pediatric and adult patients with cochlear implants are at increased risk of acquiring S. pneumoniae meningitis.¹ In 2002, the CDC issued age-appropriate immunization guidelines for patients who have a cochlear implant or are going to be the recipient of a cochlear implant. These vaccines include the 7-valent pneumococcal conjugate vaccine (PCV7; Prevnar), and the 23-valent pneumococcal polysaccharide vaccine (PPV23; Pneumovax).

The following recommended schedule was recommended:

• Children aged less than 24 months with cochlear implants should receive PCV7. If a vaccination is missed, the appropriate catch-up schedule should be used.
• Children aged 24 to 59 months with cochlear implants who have not received PCV7 should be vaccinated according to the high-risk schedule. Children who have missed a vaccination should be vaccinated according to the catch-up schedule. PPV23 should be given to children 2 months after they have completed the PCV7 series.
• Patients between the ages of 5 and 64 with cochlear implants should receive PPV23.
• An age-appropriate pneumococcal vaccination series should be completed at least 2 weeks before surgery (see Table).

Recommended Pneumococcal Vaccination Schedule for Persons With Cochlear Implants²

ETIOLOGIES OF SEVERE TO PROFOUND HEARING LOSS

Section 4 of 8  

• Authors and Editors
• Introduction
• Preoperative Considerations
• Etiologies of Severe to Profound Hearing Loss
• Bilateral Implants
• Outcomes
• Multimedia
• References

Genetic

Genetic hearing loss is the most common etiology of childhood deafness (33-50%); and many of these cases can be attributed to single gene mutations. Seventy five to eighty percent of genetic deafness is secondary to autosomal recessive gene defects, 18-20% is secondary to autosomal dominant gene defects, and the remainders are X-linked gene defects. Another potential cause of genetic deafness is mitochondrial gene defects. Genetic hearing loss is generally divided into nonsyndromic and syndromic, with the former being twice as common as the latter.

To date, 25 autosomal recessive loci, 21 autosomal dominant loci, and 1 x-linked loci have been reported for nonsyndromic hearing loss. The GJB2 gene encodes for the protein Connexin 26, and mutations in GJB2 account for the most common cause of nonsyndromic autosomal recessive deafness, which is thought to be responsible for 20% of hereditary hearing loss in children. Connexins are transmembrane proteins that form gap-junction channels. These channels allow ion transport and cell-to-cell communication. Syndromic hearing loss conditions include but are not limited to Waardenburg, Stickler, Brachio-oto-renal, Treacher Collins, Neurofibromatosis, Usher, Jervell Lange-Neilsen, Alport, and Pendred syndromes.

Infectious

• Nonmeningitis
• • Nongenetic or environmental causes generate 25-33% of childhood deafness. Congenital cytomegalovirus is the most common environmental cause of hearing impairment in children.
  • Ten to fifteen percent of patients with asymptomatic congenital CMV infections develop mild to profound sensorineural hearing loss. Other potential infectious agents include rubella, syphilis, toxoplasmosis, mumps, and measles.
• Meningitis
• • Meningitis causes approximately 9% of childhood deafness and can make implantation difficult. Organisms commonly causing meningitis (from most to least common) include Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis.
  • The organism causing the highest incidence of hearing loss is S pneumoniae (31%). Patients with meningitis are predisposed to developing obstruction of the cochlear lumen (ie, labyrinthitis ossificans; see Image 3), especially when S pneumoniae is the causative organism.

Although 12 months is the current age limit the FDA has established for implantation, other factors may cause the implant team to treat infants younger than 12 months. In particular, a child with deafness due to meningitis may develop labyrinthitis ossificans, filling the cochlear duct or the entire cochlear labyrinth and usually the scala tympani starting near the round window, with bone. In cases of labyrinthitis ossificans, special techniques may be needed for successful cochlear implantation. However, even with special techniques, this condition often leads to a suboptimal outcome.

Image 3 depicts a CT scan of a child with deafness due to meningitis whose left cochlea has ossified. In this patient, successful implantation of the patent right cochlea was accomplished. For patients at risk of labyrinthitis ossificans, implantation may be indicated soon after early ossification or fibrosis is diagnosed. Early implantation in the setting of labyrinthitis ossificans may allow a full electrode insertion and obviate the need for performing a cochlear drill-out procedure.

Using serial imaging, implant teams may monitor patients with new deafness due to meningitis and perform implantation at the first sign of replacement of the scala tympani with fibrous tissue or bone. Several reports have described spontaneous hearing improvement after meningitis in patients with residual hearing. In patients with profound hearing loss after meningitis, the chance of hearing improvement is unlikely and cochlear implantation should proceed as soon as possible. Ossification can begin as early as 2 weeks after meningitis. In the setting of bilateral labyrinthitis ossificans, expeditious placement of bilateral implants should be considered as these patients are not likely to benefit from future technology.

Ototoxicity

Numerous medications can cause hearing loss. Perhaps the most well known ototoxic medications are the aminoglycoside antibiotics. Other commonly cited ototoxic medications include loop diuretics, erythromycin, salicylates, vancomycin, cisplatin, and quinine.

Trauma

Hearing loss from temporal bone trauma is most commonly conductive secondary to hemotympanum, tympanic membrane perforation, or ossicular discontinuity. The otic capsule is fairly resistant to trauma but occasionally fractures may involve the cochlear or labyrinth. Injuries to the otic capsule almost always results in profound sensorineural hearing loss. Bilateral otic capsule fractures are very uncommon but would be an indication for cochlear implantation. Intraluminal fibrosis or ossification may occur in the setting or otic capsule fractures, which can make electrode insertion more difficult. Preoperative imaging may provide additional information of fibrosis or ossification has occurred.

Hyperbilirubinemia

In the setting of neonatal jaundice, bilirubin may cross the blood-brain barrier. Bilirubin can deposit in the ventral cochlear nucleus and cause sensorineural hearing loss. Transient loss of wave IV and V on an ABR is seen in 33% of neonates with bilirubin levels of 15-25 mg/dL. Hyperbilirubinemia is also a risk factor of auditory neuropathy.

Auditory neuropathy/dyssynchrony

Patients with auditory neuropathy are characterized by intact outer hair cell function with abnormal or absent ABR, implicating the vestibulocochlear nerve as the site of pathology in this condition. Outer hair cell function can be assessed with otoacoustic emissions, the cochlear microphonic or pure-tone audiometry. A defect in inner hair cells, spiral ganglion cells or the synapse between the two is the cause of auditory neuropathy.

Auditory neuropathy occurs in both adults and children. Pure-tone audiometry may reveal normal to profound hearing loss, but poor performance of speech discrimination testing is the common denominator in patients with auditory neuropathy. Anoxia, hyperbilirubinemia, and prematurity are potential risk factors for auditory neuropathy. Several recent reports described hereditary forms of auditory neuropathy, including a nonsyndromic autosomal dominant condition that progresses to outer hair cell involvement with eventual decline of pure-tone hearing. Some patients may benefit from FM devices or hearing aids, but in some cases a cochlear implant may provide the only means to communicate.

Ménière disease

Meniere disease is characterized by room spinning vertigo, fluctuating hearing, tinnitus, or aural fullness. The diagnosis is made with a thorough history and physical examination, as well as imaging studies to rule out retrocochlear pathology. Histology of postmortem temporal bones in subjects with Meniere disease reveals dilation of the endolymph compartment. Histologic endolymphatic hydrops may be the end result of some other pathologic process that is causing the symptoms of Meniere disease or may be the actual cause of the symptoms.

A recent study showed 11% of patients presented with bilateral disease and another 12% eventually developed symptoms in their unaffected ear.⁴ The progression of hearing loss is difficult to predict but may result in bilateral profound loss. A recent series of 9 patients with bilateral Ménière disease who underwent cochlear implant showed overall excellent performance results with at least one year of follow-up. Some patients in this series experienced fluctuations in their implant performance associated with episodic vertigo attacks.

Noise-induced hearing loss                            

According to the National Institute of Deafness and Communication Disorders, 10 million American have noise induced hearing loss and an additional 30 million are exposed dangerous noise levels daily.⁵ Hearing loss secondary to noise exposure can be temporary (temporary threshold shift) or permanent (permanent threshold shift). Acoustic trauma is the immediate, permanent onset of hearing loss after exposure to sounds louder than 140 dB, such as explosions or firearm discharge. Outer hair cells are the most susceptible to noise exposure. The outer hair cells typically swell with excessive noise exposure, but may normalize if the noise exposure ceases. A notch at 4000 Hz on pure-tone audiometry is fairly common in the setting of noise-induced hearing loss, but hearing loss may progress to a level where even amplification provides little benefit.

Presbycusis

Hearing loss associated with aging initially begins with loss of high frequencies, with eventual progression to include lower frequency loss. Thirty to thirty five percent of 65 year olds have some hearing loss; this figure rises to 40-50% of individuals over 70 years. Men are more commonly affected with age-related hearing loss. Hearing aids often provide meaningful benefit for patients with presbycusis, but only one in five individuals who would benefit from a hearing aid actual wear one. Patients with severe to profound hearing loss who are unable to hear with traditional amplification may benefit from a cochlear implant. In cases where residual low frequency hearing is found, some individuals may benefit from a combined hearing aid /cochlear implant that provides both electrical and acoustic stimulation.

Residual hearing

Short implant electrodes that are under development may allow for implantation in patients with good low-frequency hearing and poor high-frequency hearing. Placing the electrode atraumatically in the basal turn of the cochlea through a small cochleostomy may preserve residual hearing, and a conventional hearing aid (for low-frequency hearing amplification) could be worn simultaneously. This approach allows for the auditory rehabilitation of patients who are not candidates for conventional implants because their low-frequency hearing exceeds current guidelines. These hybrid implants are a current focus of research.

BILATERAL IMPLANTS

Section 5 of 8  

• Authors and Editors
• Introduction
• Preoperative Considerations
• Etiologies of Severe to Profound Hearing Loss
• Bilateral Implants
• Outcomes
• Multimedia
• References

Patients with unaided unilateral hearing loss often have difficulty in everyday listening situations. Significant disadvantages to unilateral hearing loss are well known and include the head shadow effect, difficulty with hearing in noise, and sound localization. Amplification for unilateral hearing loss is routinely recommended in children and adults. A multitude of studies have demonstrated significant performance improvement in patients with bilateral cochlear implants.

A number of arguments have been made against bilateral implantation, including saving the ear for future technology or using a hearing aid with residual hearing. No one knows when future technologies (ie, gene therapy) will become available for clinical use, and a critical time period for auditory development remains. A recent study showed that a second critical time period in regards to bilateral implantation may exist. Significant delay between the first and second implant may significantly decrease future benefit.⁶ A formal position statement supporting bilateral cochlear implants as accepted medical practice has been issued by the William House Cochlear Implant Society. This position statement was issued after pertinent literature was reviewed in regards to bilateral cochlear implants.⁷ 

OUTCOMES

Section 6 of 8  

• Authors and Editors
• Introduction
• Preoperative Considerations
• Etiologies of Severe to Profound Hearing Loss
• Bilateral Implants
• Outcomes
• Multimedia
• References

Critical outcome factors for pediatric patients receiving implants include (1) age at onset of deafness and duration of deafness prior to implantation, (2) progression of hearing loss, and (3) educational setting.

In general, early implantation facilitates rapid development of oral communication ability. Progressive hearing loss, which allows for the development of speech-reading skills, favors performance after implantation. Placement in a school setting that stresses oral versus signed communication is important for optimal implantation outcome. However, many variables remain unknown because approximately one half of the variance in performance after implantation cannot be predicted.

Children should be receptive to wearing a hearing aid before cochlear implantation because all current implants require an external processor. A period of hearing aid use to ascertain development of aided communication ability is an important criterion in determining candidacy of young children.

After audiologic criteria have been met, parental expectations and attitudes must be assessed and addressed. Unrealistic expectations can frustrate the efforts of the child and the implant team. Families must be appropriately counseled about the need for long-term therapy, variable outcome of implantation, and the limitations of implantation.

MULTIMEDIA

Section 7 of 8  

• Authors and Editors
• Introduction
• Preoperative Considerations
• Etiologies of Severe to Profound Hearing Loss
• Bilateral Implants
• Outcomes
• Multimedia
• References

Media file 1:  Cochlear implant electrode passing through the facial recess to the scala tympani.
	View Full Size Image
Media type:  Photo

Media file 2:  Cochlear malformations. Neural foramen on the right is absent. Right arrow indicates a rudimentary vestibule. On the left is a severe cochlear malformation (large arrow). Small arrow indicates the internal auditory canal.
	View Full Size Image
Media type:  CT

Media file 3:  Labyrinthitis ossificans. Cochlea on the left is obliterated by bone after meningitis. Scala tympani of the cochlea on the right was patent, and the patient underwent successful implantation with complete electrode insertion.
	View Full Size Image
Media type:  CT

Media file 4:  This axial FIESTA image of the basal turn of the cochlea demonstrates loss of T2 signal in the scala tympani. This patient has a history of pneumococcal meningitis with profound hearing loss.
	View Full Size Image
Media type:  MRI

REFERENCES

Section 8 of 8

• Authors and Editors
• Introduction
• Preoperative Considerations
• Etiologies of Severe to Profound Hearing Loss
• Bilateral Implants
• Outcomes
• Multimedia
• References

1. Reefhuis J, Honein MA, Whitney CG, et al. Risk of bacterial meningitis in children with cochlear implants. N Engl J Med. Jul 31 2003;349(5):435-45. [Medline].
2. Smith PJ, Nuorti JP, Singleton JA, et al. Effect of vaccine shortages on timeliness of pneumococcal conjugate vaccination: results from the 2001-2005 National Immunization Survey. Pediatrics. Nov 2007;120(5):e1165-73. [Medline].
3. www.cdc.gov/mmwr/PDF/RR/RR4909.pdf.
4. House JW, Doherty JK, Fisher LM, Derebery MJ, Berliner KI. Meniere's disease: prevalence of contralateral ear involvement. Otol Neurotol. Apr 2006;27(3):355-61. [Medline].
5. Noise-Induced Hearing Loss. Available at http://www.medhelp.org/NIHlib/GF-331.html.
6. Gordon KA, Valero J, Papsin BC. Auditory brainstem activity in children with 9-30 months of bilateral cochlear implant use. Hear Res. Nov 2007;233(1-2):97-107. [Medline].
7. Balkany T, Hodges A, Telischi F, Hoffman R, Madell J, Parisier S. William House Cochlear Implant Study Group: position statement on bilateral cochlear implantation. Otol Neurotol. Feb 2008;29(2):107-8. [Medline].
8. Brown KD, Balkany TJ. Benefits of bilateral cochlear implantation: a review. Curr Opin Otolaryngol Head Neck Surg. Oct 2007;15(5):315-8. [Medline].
9. Camp GV, Smith R. Hereditary Hearing Loss Homepage. Hereditary Hearing Loss Homepage. Available at http://webh01.ua.ac.be/hhh/. Accessed February 2008.
10. CMS. Centers for Medicare and Medicaid Services. Medlearn matters: information for Medicare providers. Cochlear implantation. No. 3796. Revised August 1, 2005. Available at: www.cms.hhs.gov/medlearn/matters/mmarticles/2005/MM3796.pdf. [Full Text].
11. Cohen NL, Waltzman SB, Fisher SG. A prospective, randomized study of cochlear implants. The Department of Veterans Affairs Cochlear Implant Study Group. N Engl J Med. Jan 28 1993;328(4):233-7. [Medline].
12. El-Kashlan HK, Ashbaugh C, Zwolan T, et al. Cochlear implantation in prelingually deaf children with ossified cochleae. Otol Neurotol. Jul 2003;24(4):596-600. [Medline].
13. Gantz BJ, Turner C, Gfeller KE. Acoustic plus electric speech processing: preliminary results of a multicenter clinical trial of the Iowa/Nucleus Hybrid implant. Audiol Neurootol. 2006;11 Suppl 1:63-8. [Medline].
14. Gantz BJ, Tyler RS, Knutson JF, et al. Evaluation of five different cochlear implant designs: audiologic assessment and predictors of performance. Laryngoscope. Oct 1988;98(10):1100-6. [Medline].
15. Gantz BJ, Woodworth GG, Knutson JF, et al. Multivariate predictors of audiological success with multichannel cochlear implants. Ann Otol Rhinol Laryngol. Dec 1993;102(12):909-16. [Medline].
16. Grundfast KM, Lalwani AK. Pediatric Otology and Neurotology. Philadelphia, PA: Lippincott-Raven; 1998.
17. Havlik R. Aging in the eighties: impaired senses for sound and light in persons age 65 and over. Preliminary data from the supplement on aging to the National Health Interview Survey. Advance data from vital and health statistics. DHHS (PHS) Publication No. 125. Jan-Jun 1984;86-1250.
18. Luetje CM, Thedinger BS, Buckler LR, et al. Hybrid cochlear implantation: clinical results and critical review in 13 cases. Otol Neurotol. Jun 2007;28(4):473-8. [Medline].
19. Murphy J, O'Donoghue G. Bilateral cochlear implantation: an evidence-based medicine evaluation. Laryngoscope. Aug 2007;117(8):1412-8. [Medline].
20. Nilsson M, McCaw V, Soli S. Minimum Speech Test Battery for Adult Cochlear Implant Patients: User Manual. Los Angeles, CA: House Ear Institute; 1996.
21. Nilsson M, Soli SD, Sullivan JA. Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise. J Acoust Soc Am. Feb 1994;95(2):1085-99. [Medline].
22. Papsin BC, Gordon KA. Cochlear implants for children with severe-to-profound hearing loss. N Engl J Med. Dec 6 2007;357(23):2380-7. [Medline].
23. Parry DA, Booth T, Roland PS. Advantages of magnetic resonance imaging over computed tomography in preoperative evaluation of pediatric cochlear implant candidates. Otol Neurotol. Sep 2005;26(5):976-82. [Medline].
24. Pneumococcal vaccination for cochlear implant candidates and recipients: updated recommendations of the Advisory Committee on Immunization Practices. MMWR Morb Mortal Wkly Rep. Aug 8 2003;52(31):739-40. [Medline].
25. Roland PS, Wright CG, Isaacson B. Cochlear implant electrode insertion: the round window revisited. Laryngoscope. Aug 2007;117(8):1397-402. [Medline].
26. Wei BP, Robins-Browne RM, Shepherd RK, et al. Assessment of the protective effect of pneumococcal vaccination in preventing meningitis after cochlear implantation. Arch Otolaryngol Head Neck Surg. Oct 2007;133(10):987-94. [Medline].
27. Wolfe J, Baker S, Caraway T, et al. 1-year postactivation results for sequentially implanted bilateral cochlear implant users. Otol Neurotol. Aug 2007;28(5):589-96. [Medline].

Article Last Updated: Jul 8, 2008