Sound is received by a microphone located on the BTE sound processor (1); it is processed and coded, then sent via the transcutaneous radiofrequency link to the implanted receiver-stimulator (2); data are decoded and sent to the multi-electrode array (3), stimulating spiral ganglion neurons, which then transmit the signal via the auditory nerve (4) toward higher processing centers
Current Implant TechnologyThree companies currently have FDA approved implants Advanced Bionics (California) —HR90 K Cochlear (Australia) —Nucleus 5 Med-El (Austria) —Sonata ti100
Candidacy for CI has changed gradually but significantly since the first multichannel devices were implanted in the late 1970s . Due to increasing experience, improvement of technology and the proven reliability, the selection criteria are broadened with shifting borders. Main extensions are related to age, additional handicaps, residual hearing & special etiologies of deafness.
The obvious goal for careful selection of CI patients is to never have a single patient perform more poorly with their CI than they did with their hearing aids (Gifford,H 2011).
Stages in Patient Selection I. Questionnaire Age - Aetiology Onset of HL ( pre , peri , postlingual ) Duration of sensory deprivation ( plasticity ) Hearing aid use II. Audiological investigations III. Language assessment IV. Radiological examination
V. Psychological assessment IQ testing VI. Vestibular testing VII. Medical & Otological examination VIII. Electrical stimulation of the cochlea Counseling…………..
FDA approval for implanting children: 1990 > 2 years 1998 = 18 months 2000 = 12 months
Changes in age of implantation are due to:1.Better / early identification of HL (universalhearing screening ) 2.Increased public awareness 3. Increased professional awareness 4.Changes in technology : Electrode array – Programming – Processors Telemetry
The literature has demonstrated that in terms of speech development and language acquisition , the best results come from children implanted under the age of 2 years similar to normal hearing children (Sharma et al ., 2002 ). All CI devices can be safely indicated for children 12 months or older . However, implanting children younger than 12 months remains controversial.
Further reductions in age at implantation are currently limited by the nature of audiologic testing in very young children. In cases of HL due to meningitis or hereditary hearing loss , implantation should be considered before the age of 12 months.
Audiological evaluation Behavioral audiometry ( age appropriate ) Tympanometry & acoustic reflexes ABR , ear specific & frequency specific ASSR OAE Aided free field testing Special tests : EABR , EMLR , ESR, Electrical late event related potentials.
Audiometric Thresholds For children aged 12-23 months hearing threshold for both ears should equal or exceed 90 dB. For individuals older than 24 months hearing threshold should equal or exceed 70 dB. Speech detection with best fit hearing aids in a sound field equal to or worse than 55 dB.
Hearing aid trial for 3 months. During HA trial , child should be making at least month to month auditory progress as well as speech and language progress. If this is not the case then, CI evaluation should be considered ( Gifford, H 2011 ). Teenagers ???
Speech & Language assessment Psychological assessment , IQ testing Counseling , family support , motivation & realistic expectations. Medical and Otological examination
Radiological assessment:CT scan traditionally is the gold-standard imaging modality Superior visualization of the bony structure of the otic capsule and the course of the facial nerve . Weakness: can miss cochlear fibrosis, retrocochlear pathology, CNS abnormalities, and cochlear nerve hypoplasia/absenceMagnetic resonance imaging (MRI) More effective at identifying cochlear fibrosis Able to identify presence/absence of cochlear nerve and caliber Weakness: inferior visualization of bony anatomy, inability to detect the presence of the round window, oval window, or an enlarged vestibular aqueduct; often requires anesthesia for young patients
Vaccination Children with cochlear implants are at higher risk for meningitis, though overall rate is low (<0.6%) Streptococcus pneumoniae has been the most common organism isolated in the children with cochlear implants who developed meningitis Current vaccine recommendations: Patients <2 years old Prevnar (7-valent) only Patients 2-5 years old Prevnar and Pneumovax (23-valent) Patients >5 years old Pneumovax only Additionally, all patients <5 year old should receive the Hib vaccine Vaccination should be completed at least 2 weeks prior to surgery
History : Onset & course of hearing loss Duration (plasticity) Aetiology ( fever , trauma ) History of HA use Means of communication Education Motivation , realistic expectations Prelingual adults ???????
When to refer an Adult for a CI?• Bilateral severe to profound sensorineural hearing loss• Limited benefit from appropriate hearing aids i.e. poor speech recognition• Telephone use is difficult, limited or impossible• Patient relies heavily on speech reading or note writing to understand speech• Patient is distressed by the inability to communicate efficiently on a daily basis• No medical contraindications
Speech recognition testing is the cornerstone in adult CI patient selection, Where the best-aided scores on open-set sentence tests of <50% in the ear to be implanted and <60% in contralateral ear is considered as an indication for implantation.
Choosing the most appropriate ear Audiological factors :1. Residual hearing In the early years of CI , the audiologically worse ear was chosen so that (un) expected iatrogenic cochlear damage would have fewer consequences. In the late 1990s the better ear with the most residual hearing was preferred as studies had shown that better preserved peripheral neural pathways would lead to better results after CI.
2. Duration of HLIt is generally accepted that duration of deafness hasa negative effect on CI performances.Most clinicians choose the ear with the shortestduration of deafness. 3. Only functioning labyrinth
Surgical Factors 1.Anatomic variations : cochlear ossification, cochlear malformation and cochlear nerve malformation. 2.Otological medical history : otitis media , cholesteatoma and temporal bone fracture. Personal factors Handedness , (right ear advantage)
Contraindications for implantation Completely atretic VIII nerve Small internal auditory canal syndrome Agenesis of cochlea: Michel deformity Active middle ear/mastoid infection Tympanic membrane perforation Severe organic brain dysfunction Severe mental retardation Psychosis, unrealistic expectations
Hybrid CI (Electro Acoustic Stimulation) The expanded criteria have led to research questions centering on advanced uses of the technology. Specifically, could an implant benefit other users previously not considered to be a candidate? A group that was felt to be underserved with conventional amplification were those patients with the following audiometric profile
Audiogram Below 1.5 kHz – No or moderate HL Above 1.5 kHz – Severe to profound sensorineural hearing impairment. Dead regions of the cochlea (elderly) . Speech scores The patients monosyllable word score should be ≤ 60% at 65dB SPL in the best aided condition.
Hearing preservation surgery Two methods are commonly used for inserting the electrode into the cochlea: Round-window insertion VS Cochleostomy insertion. Round-window insertion has found a wider acceptance because it is considered to be less traumatic (controversial).
EAS electrodes for cochlear implants : Long-term research has shown that mechanical flexibility of the electrode array is one of the key factors for preserving residual hearing. Studies with different lengths of electrodes have shown that an insertion depth of 10 mm has a good chance of preserving residual. Electrodes that can be inserted to a depth of 18– 22 mm are a good compromise.
EAS audio processors Combines cochlear implant technology with a digital hearing aid. This device uses one microphone for the input, but has two separate digital sound processors for differentiated processing. The parallel processing of these signals, however, is performed separately and optimized for both acoustic hearing (focusing on low-frequency hearing) and cochlear implant stimulation (focusing on high- frequency hearing).
The hearing aid is integrated in the ear hook and the amplified signals are forwarded to the auditory pathway via an ear mould. The ear mould used for the acoustic component is similar to a conventional hearing aid ear mould and can be exchanged.
Bilateral CI Recent Trend towards BILATERAL use of CI/s -- 1992: 0-1% -- 2007: 14-15% 70% of bilateral CI usage is among 18 years and under age group. Simultaneous CI Sequential CI
Advantages of bilateral implantation Improved hearing in quiet (binaural summation) Improved hearing in noise (binaural squelch, head shadow effect, and binaural redundancy) Improved sound lateralization Improved sound localization Assurance that the ―better hearing ear‖ is implanted/‖captured‖ Qualitative listening improvement (more ―balanced‖; ―richer quality‖; more ―confident‖ feeling; and less fatigued)
Disadvantages Increased costs (2 devices, batteries, etc.) Multiple pieces of equipment to manage Surgical and medical risks Future developments No or limited ―natural‖ hearing remaining Different processing strategies & speech processors (with sequential bilateral CIs)
Bimodal stimulation CI in one ear and HA in the other. Binaural stimulation Residual hearing in contralateral ear After established electrical stimulation Balancing between the two ears Future technology Cost effectivness
Meningitis: 9% of childhood deafness. Commonest organism to cause HL is S pneumoniae. Labyrinthitis ossificans. Implantation before 12 months of age.Trauma: BILATERAL OTIC CAPSULE FRACTURES ARE UNCOMMON Intraluminal fibrosis or ossification may occur which makes electrode insertion difficult.
Hyperbilirubinemia risk of auditory neuropathy.Auditory neuropathy /dyssynchrony: Many clinicians have been conservative about the outcome. Sydney CIC has the most experience. They reported variable outcome due to wide variability of impairments.
Many of the children had successful implantation with a smaller number failing to gain significant benefit.75 % of the patients benefited from the CI due to surviving OHCs when IHCs are compromised.Patients who did not benefit ,may have dysfunction in afferent neural synapses, CN or higher auditory systems.During patient selection, electrically evoked CAP should be tested .
Usher Syndrome Most common cause of blindness in humans. Autosomal recessive Type I (USH1) most severe 30- 40 % : Severe to profound congenital HL , motor developmental delay & progressive retinopathy. Early implantation is critical to developing effective oral – auditory skills prior to visual loss.
Keratitis Icthiosis Deafness Syndrome (KID)Rare congenital disorder of the ectoderm.Heterogeneous mutation in the Connexin 26 geneAutosomal dominant.Congenital icthyosis , vascular keratits , SNHL , alopecia and squamous cell carcinoma may occur.CI produces good audiological results BUT Wound complications are very common , failure to heal, partial extrusion of the implant.
Multi handicapped Patients with additional disabilities such as mild motor disability, cerebral palsy , cognitive disabilities, specific learning disabilities, behavioral disorders and sight impairment have been implanted. Multi-handicapped children receive benefit from cochlear implantation. The rate of this improvement is slow but offers better quality of life due to better auditory-communication skills, better self- independence and social integration.
C I in Unilateral Deafness Up to now treatment modalities for single sided deafness are; NO treatment , Conventional contralateral routing of signal or BAHA. CI makes a new treatment modality for those patients. Study done by Arndt et al., 2011 revealed that CI improved hearing abilities in single sided HL & superior to alternative options. CI didn’t interfere with speech understanding in the normal ear.
CI in Unilateral deafness and tinnitus Tinnitus is a frequent often disabling condition. In patients who are deaf with tinnitus in the affected ear, treatment based on acoustic input are impossible. Tinnitus suppression using electric stimulation has been reported to be successful (Buechner et al.,2010). Several studies (Kleinjung 2009: Van de Heyning et al., 2008 and Moller 2003 ) concluded that CI may represent a chance for complete suppression of tinnitus in selected cases.
Audiological Mapping very young children: difficulty in obtaining behavioral results’ evolution of recent technology helps assist in mapping through the use of ECAP measurements. Mapping the multi handicapped.
Surgical Challenges Implanting very young children Children below 12 months usually have poorly pneumatized mastoid bones leading to greater intraoperative blood loss and risk of facial nerve injury. Greater anesthesia risk ,size of airway & difficulty maintaining cardiovascular fluid & temp homeostasis. Thin scalp : care in drilling well for body of device. Increased incidence of otitis media Fortunately, cochlea is adult size at birth.
Hearing preservation surgery A special surgical technique to preserve the residual hearing of the patient (in most routine cochlear implant surgeries, any residual hearing will likely be destroyed). This is a very realistic goal for many patients with sloping hearing loss (EAS ). Achieved by performing ―Soft surgery‖
Dysplastic CochleaDue to increased knowledge of temporal bone anatomy and improved imaging techniques more patients with Mondinin dysplasia , Common cavity, hypoplastic cochlea and large vestibular aqueducts are implanted.Modifications in surgical techniques.Likelihood of CSF gusher .
Labyrinthitis OssificansConsequence of meningitisOssification partially or completely block the lumen of scala tympani & or scala vestibuli.Several techniques:Drilling a basal tunnel , circum-modiolar drill-out, use of double or split electode array.
Bilateral ImplantationLengthy, bilateral loss of vestibular function , contamination of the field.Monopolar cautery can not be used for the second side
New DevicesIf and when the totally implantable cochlear implant (TICI) becomes a reality, it will require a modification of current surgical techniques to implant a microphone and possibly adding hardware to the ossicles.
Overall the selection criteria have been broadened with increasing experience and technological improvement. This development may continue and the borderline between HA & CI will shift further. However, the basis for success still remains good rehabilitation, a team approach and the willingness of the patient to undergo the whole process of CI.