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Medicine, Neuroscience, Otolaryngology

Treatment of pediatric hearing loss with cochlear implantation

Lee Ware, Dasha Kenlan, John Penn, Kendra Campbell, Tara Shrout, Keith Albrektson, Jason Chisholm, Daniel Hudson

Introduction

Cochlear implants, approved for children by the FDA in 1990, are implantable, 2-component devices designed to transmit sound information from the external environment to a patient’s auditory processing circuitry. The external component (placed behind the ear) and internal component (beneath the scalp) work in conjunction to detect and convert sound, to transmit the signal, and ultimately stimulate the auditory nerve by way of a multichannel electrode array embedded in the patient’s cochlea.

Relevant Anatomy

Structure-Of-Ear-Diagram-image-ojbRRelevant ear anatomy includes the external pinna, to which the speech processor and microphone are attached; the temporal scalp, onto which the external component is anchored; the mastoid and temporal bones against which the internal component is placed; the bony labyrinth, with it’s cochlear and vestibular chambers and organs, where the cochleostomy is performed and electrode array inserted into the cochlea’s scala tympani. Because the facial nerve’s (CN VII) path is variable, intra- and extratemporal landmarks are critical to ensure safe and successful surgical implantation (Cochlear Implants, 2012).

Common Anatomical Pathology

  • Mondini dysplasia
    • Congenital malformation in which the cochlea has only 1 and a half coils rather than the usual two (Rarediseases.info.nih.gov, 2014)
  • Enlarged vestibular aqueduct (EVA)
    • Not believed to actually cause deafness, but often seen alongside it. Both EVA and the deafness are thought to be cause by a mutation in the SLC26A4 gene (Nidcd.nih.gov, 2014)
  • Labyrinthitis ossificans
    • Ossified cochlea that results in loss of hearing. Often seen as a sequela of bacterial meningitis (Emedicine.medscape.com, 2014)
    • Prior to the operation, imaging is used to assess abnormal anatomy. CT scans are often implemented initially, while MRIs can be used as well. Below is a good image of an ossified cochlea from a 6 year-old boy recovering from bacterial meningitis: http://www.mypacs.net/cases/OSSIFICATION-OF-THE-BASAL-TURN-OF-THE-COCHLEA-80373.html (Mypacs.net, 2014)

How do cochlear implants work?

A cochlear implant is a device that is surgically implanted into a patient with profound to complete sensorineural hearing loss, meaning that the function of the cochlea has been disrupted and it is no longer properly transmitting externally matched impulses to the brain along the auditory nerve.  This is normally due to hair cell function loss, which severs the connection between peripheral and central hearing.  These implants are used to reestablish this connection, and restore a form of functional hearing to recipients.

 

US20130023967A1-20130124-D00002The typical cochlear implant consists of numerous parts, both internal and external:

  • Microphone (external): Picks up sound from the environment
  • Speech Processor (external): Selectively filters sound received by the microphone and then splits it into separate channels.  This processor uses an algorithm, developed internally by each manufacturer, to select which sounds and frequencies to be broken down and delivered to these channels.  These electrical sound signals are sent to the transmitter.
  • Transmitter (external): A coil held in place behind the external  ear, uses electromagnetic induction to transmit the electrical sound signals across the skin to the internal receiver/stimulator
  • Receiver/Stimulator (internal):  This device is implanted into the temporal bone above the ear.  It receives the electrical signal and converts it into an electrical stimulus that is sent to a certain region of the electrode array.
  • Cable (internal):  Carries the output from the receiver/stimulator to the electrode array.
  • Electrode array (internal):  This array (20 or more) of electrodes is surgically wound through the cochlea and implanted in the scala tympani.  These electrodes directly stimulate nerves of the spiral ganglia at different locations throughout the cochlea, conveying rudimentary sound to the auditory nerve.
    • Electrodes are organized according to the tonotopy of the normal cochlea.
      • High-frequency sounds will stimulate more basally positioned electrodes.
      • Low-frequency sounds will stimulate more apically positioned electrodes

Who receives an implant, when, and why?

Cochlear implantation is a surgical procedure that has become the standard of care for pediatric patients with severe to profound sensorineural hearing loss. As of December 2012, the FDA estimates that more than 38,000 children in the United States have received an implant. The inclusion criteria for implantation has expanded over recent years to also include those with auditory neuropathy spectrum disorder (ANSD), cochleovestibular malformations, cochlear nerve deficiency, associated syndromes, as well as various developmental and medical disabilities. Guidelines, though, still indicate there should be demonstration of severe to profound hearing impairment in both ears, with no appreciable improvement from hearing-aid amplification during a trial period of four to six months. Although cochlear implantation can serve as second-line treatment in many cases, all candidates for the surgery must have intact auditory nerve fibers in order for the device to have clinical benefits.

The FDA has stipulated the minimum age for cochlear implantation for pediatric patients to be twelve months, although some exceptions to this have occurred in unusual circumstances. This age limit is also expected to evolve, with improved surgical technology, and techniques. Despite the relatively poor success of cochlear implantation seen in prelingual adults, children with no language speaking ability have been found to display notable speech production, and high levels of speech recognition within a few years post implantation. The mechanisms surrounding the discrepancy between adults and children are poorly understood, but point to a difference in neural plasticity. In general, higher levels of implantation success are associated with prior language ability, and younger age. Currently, several studies are striving to find further factors that will allow physicians to better predict the potential benefit of a patient’s cochlear implantation.

A variety of other considerations affect why certain pediatric patients are implanted, while others are not. Notably, parents are concerned with risks of the surgical implantation, which include bleeding, infection, injury to the facial nerve, anesthesia concerns, post-surgical dizziness, mechanical or electrical failure of the device, rejection, and other complications that would require removal or replacement of the implant. Despite these concerns, a majority of candidates for the procedure are implanted, and retrospective studies show that parents’ decisions are influenced by the multidisciplinary team approach. With otologic surgeons, pediatric audiologists, communication therapists, and more, the goal of the cochlear implantation approach is to improve the child’s quality of life through hearing, understanding, speech, and social interaction.

What should parents expect?

Evaluation & Pre-Implantation Steps

As seen in the previous section, a cochlear implant is not recommended for every child. An intensive evaluation procedure includes several appointments with a pediatric cochlear program, usually at a university or large medical center, and includes various members of the team such as a financial counselor, surgeon, pediatrician, audiologist, and speech therapist.  The goals of these evaluations and preparation appointments are:

  • Obtain insurance approval/coverage for the surgery and equipment
    • The average cost of the procedure, including the rehabilitation process and programming, is in excess of $40,000.  Insurance companies are increasingly likely to cover implants due to cost effectiveness studies that have found unilateral cochlear implantation to be cost effective in both children and adults.
  • Obtain a medical history including cause for hearing loss and fitness for surgery
  • Perform a current hearing, speech and language evaluation
  • Select a device – there are 3 companies currently making cochlear implants
  • Vaccinate the child against meningitis causing bacteria
  • Provide parents with information regarding the cost and long term commitment of the process

Surgery & Post-Operation Requirements

The cochlear implant is typically a 3-4 hour surgery with same-day discharge unless there are complications. Complications include the usual issues such as infection, bleeding and device malfunction, along with region specific complications such as facial nerve weakness, dizziness, ringing in the ear, and poor hearing. The recovery period is approximately 4 weeks before the device is utilized.

Approximately 4 weeks after surgery, the initial appointment is scheduled where the cochlear device is first mapped and the internal processor is tested. The mapping process is essentially the process by which the audiologist calibrates the device. Specifically, the audiologist will increase or decrease the amount of electrical stimulation delivered from the electrode to the nerve, ensuring that the patient has maximum hearing capability. The family is also taught how to use, troubleshoot, and care for the device. The family also receives training on how to incorporate the child back into the ’hearing’ world. Many programs have mandatory appointment schedules with a speech therapist that are weekly at first, then follow up at 3 mo, 6 mo, 9 mo, and 12 mo.Six mo and 1 year followups start after a year of therapy. These followup appointments also include further mapping of the device for up to 2 years. The commitment to so many appointments  has significant impact on the family.

Research is being conducted to understand which pediatric patients have the best outcomes from a cochlear implant, and the best ways to educate children with implants.

Hearing & Lifestyle

One of the biggest questions regarding what to expect after a cochlear implant is “what does it sound like?” The answer is, it varies. Multiple research papers will indicate that some people have good hearing, others feel like it is ok, and others do not have improved quality of life based on the implant. It has been described as beeps, like people talking under water, or like people talking through a radio. The auditory system adapts rapidly, and generally the hearing becomes better with mapping and over time. The stage of previous hearing and learning that a patient had prior to the surgery is also a factor in ‘what it sounds like’ and what kind of therapy is needed. Many pediatric patients are born deaf, so they would have never experience the world through sound before, and most learn to associate language, visual cues, and sound into meaning.

Other lifestyle factors to consider:

  • A child going through airport security should carry an implant card
  • No MRIs
  • Cell phone usage is variable
  • Lots of copays for appointments
  • Not recommended to play contact sports
  • Must always wear helmet
  • Insurance policy on outer portion of device (warranty only 3-5 years)

Resources

Rarediseases.info.nih.gov. (2014). Mondini dysplasia | Disease | Overview | Office of Rare Diseases Research (ORDR-NCATS). [online] Retrieved from: http://rarediseases.info.nih.gov/gard/8215/mondini-dysplasia/resources/1 [Accessed: 9 Apr 2014].

Nidcd.nih.gov. (2014). Enlarged Vestibular Aqueducts and Childhood Hearing Loss [NIDCD]. [online] Retrieved from: https://www.nidcd.nih.gov/health/hearing/pages/eva.aspx [Accessed: 9 Apr 2014].

Emedicine.medscape.com. (2014). Medscape: Medscape Access. [online] Retrieved from: http://emedicine.medscape.com/article/857018-overview [Accessed: 9 Apr 2014].

Mypacs.net. (2014). OSSIFICATION OF THE BASAL TURN OF THE COCHLEA. [online] Retrieved from: http://www.mypacs.net/cases/OSSIFICATION-OF-THE-BASAL-TURN-OF-THE-COCHLEA-80373.html [Accessed: 9 Apr 2014].

Hang, A.X., et al., (2013). Cochlear Implantation in Unique Pediatric Populations. Current Opinions in Otolaryngology, Head and Neck Surgery. 20(6):507-517.

Copeland, B.J., and Pillsbury, H.C. (2004). Cochlear Implantation for the treatment of deafness. Annual Reviews of Medicine. 55:157-167.

Hardonk S, Bosteels S, Desnerck G, Loots G, Van Hove G, Van Kerschaver E, Vanroelen C, Louckx F.(2010). Pediatric cochlear implantation: a qualitative study of parental decision-making processes in Flanders, Belgium. Am Ann Deaf.155(3):339-52. PubMed PMID: 21138046.

Cochlear Implant Program, The Children’s Hospital of Philadelphia. Retrieved 4/8/2014 from http://www.chop.edu/service/cochlear-implant-program/home.html.

Anna’s Story,The Children’s Hospital of Philadelphia. Retrived 4/8/2014 from http://www.chop.edu/service/neonatology/patient-stories/anna-niicu-cochlear-implant.html

Cochlear Implants, The National Institute on Deafness and Other Communication Disorders (NIDCD). Retrived on 4/8/2014 from https://www.nidcd.nih.gov/health/hearing/pages/coch.aspx.

Cochlear Implants. (2012). Available at: http://emedicine.medscape.com/article/1982450-overview. Accessed April 9, 2014.

Spencer, L. J., et al. (2003). “Exploring the language and literacy outcomes of pediatric cochlear implant users.” Ear Hear 24(3): 236-247.

Damen, G. W. J. A., et al. (2010). Cochlear Implantation and Quality of Life in Deafness. Handbook of Disease Burdens and Quality of Life Measures. V. Preedy and R. Watson, Springer New York: 3887-3904.

Cochlear Implants. (n.d.). Retrieved from https://www.bcm.edu/healthcare/care-centers/otolaryngology/procedures/cochlear-implants

Pediatric Cochlear Implants (CCCDP) — UNC School of Medicine. (n.d.). Retrieved from https://www.med.unc.edu/earandhearing/pediatric-services/pedscis

Dorman M, Wilson B: The Design and Function of Cochlear Implants. American Scientist 2004, 92:436

Dorman M, Wilson B: Cochlear Implants: Current Designs and Future Possibilities. Journal of Rehabilitation Research & Development 2008 45(5):695-730

Spencer, L. J., et al. (2003). “Exploring the language and literacy outcomes of pediatric cochlear implant users.” Ear Hear 24(3): 236-247.

Damen, G. W. J. A., et al. (2010). Cochlear Implantation and Quality of Life in Deafness. Handbook of Disease Burdens and Quality of Life Measures. V. Preedy and R. Watson, Springer New York: 3887-3904.

Cochlear Implants. (n.d.). Retrieved from https://www.bcm.edu/healthcare/care-centers/otolaryngology/procedures/cochlear-implants

Pediatric Cochlear Implants (CCCDP) — UNC School of Medicine. (n.d.). Retrieved from https://www.med.unc.edu/earandhearing/pediatric-services/pedscis

Cochlear Implant Frequently Asked Questions – National Speech Language Hearing Association. Retrieved from

http://www.asha.org/public/hearing/Cochlear-Implant-Frequently-Asked-Questions/

Bond, M., et al. (2009). “The effectiveness and cost-effectiveness of cochlear implants for severe to profound deafness in children and adults: a systematic review and economic model.” Health Technol Assess 13(44): 1-330.

Frequently Asked Questions – Cochlear Implants – Callier Center at UT Dallas. Retrieved from

http://www.utdallas.edu/calliercenter/evaluation-and-treatment/cochlear/faq.php#q4

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