Cochlear implant 1

cochlearimplant

1. Cochlear implant DR DISHA SHARMA JR ENT-HNS IGMC,SHIMLA

2. Definition Cochlear implants are surgically placed electrical device that receive sound and transmit the resulting electrical signals to electrodes implanted in the cochlea of the ear. The signals stimulate cochlea, allowing patient to hear. It is also known as Bionic ear.

3. HISTORY

4. 1790 -Alessandro Volta electric signal in auditory system can create perception of sound. 1957 - (French-Algerian surgeons Andre Djourno and Charles Eyries ) ; They were the first who attempted to produce the first cochlear implant It was single channel device .

5. 1961 - Dr. William F. House , an Otologist considered the inventor of the cochlear implant along with John Doyle (a neurosurgeon) and James Doyle (an electrical engineer) commenced work on a single-channel device. It was a single channel device but speech was modulated by 16 hz carrier.

6. December 1984 , the Australian cochlear implant was approved by the United States Food and Drug Administration to be implanted in adults in the United States. 1964 - Blair Simmons at Stanford University implanted some recipients with a six-channel device . However, it was Dr. Michelson's patent and ultimate device, which are thought of as the first cochlear implants

7. 1990 the FDA lowered the approved age for implantation to two years, then 18 months in 1998, and finally 12 months in 2000, although off-label use has occurred in babies as young as 6 months. Cochlear Implant in India-1996 Prof Mohan Kaneswaran in Madras ENT Research foundation Chennai Cochlear Implant Group of India-Nov 2003

8. Selection criteria - children child above 12months below 7 years in pre – lingually deaf children. At birth the cochlea is fully formed but the auditory pathway is not. Auditory pathway is dependent on stimulation for its maturation and this stimulation is vital to acquisition of speech and language skill as well as amount of cognitive development. Post lingual deaf no age limit

9. degree of deafness- profound >90dB SNHL with poor discrimination in both ears with cochlear nerve. Respond to hearing aid- in those who do not benefit from a hearing aid ,at least 3 to 6 months of use. Absence of contraindications- cochlear aplasia or absent cochlear nerves are absolute contraindications to cochlear implantation.

10. Selection criteria- adult Severe or profound hearing loss with PTA of 70dB or greater heaing level. Little or no benefit from hearing aids Aided scores on open-set sentence test of less than 50%. No evidence of central auditory lesions or lack of an auditory nerve. No medical or radiological contraindications for surgery .

11. PREOPERATIVE EVALUATION

12. Medical evaluation History genetic hearing loss auditory neuropathy\ dyssynchrony Acquired deafness Physical examination-

13. Audiological e valuation to determine the type and severity of hearing loss testing the unaided air and bone conduction thresholds, unaided speech discrimination, speech recognition threshold, speech detection threshold, tympanometry and acoustic reflexes. The degree of hearing loss The duration of hearing loss Benefit from hearing aids

14. Electrophysiological test Auditory brainstem response (ABR)- a)verify audiometric test result b)identify patient with auditory dyssynchrony c)rule out possibility of functional deafness

15. Speech perception test in adult Monosyllabic test-a)north western university(NU-6)monosyllabic word test. b)consonant nucleus test(CNC) Sentence material- a)hearing in noise test(HINT) b)City university of New York(CUNY)

16. Speech perception test in children The Early Speech Perception (ESP): (Moog & Geers , 1990) The Low Verbal version of the test is administered to young children (2yrs and up) The Standard version is used with older children .

17. MeaWord intelligibility by picture identification ( Wipi ) test; (Ross & Lerman , 1979)   Craig lip inventory meaningful auditory integration scale(MAIS

18. Monosyllabic Trochee Spondee Test (MTS); Erber And Alencewics ; 1976Assesses the closed set word identification in children with hearing impairment Lexical Neighborhood Test (LNT) (Kirk, Pisoni , and Osberger , 1993 ) Test (MLNT) Multisyllabic Lexical NeighborhoodThis is an open-set test of multisyllabic word recognition.

19. Imaging High resolution temporal bone computed tomography Inner ear morphology Patency of cochlea Position of facial nerve Location of large mastoid emissary veins Size of facial recess Height of jugular bulb

20. Magnetic resonance imaging Labyrinthine ossifican Cochlear nerve CNS abnormalities

21. Psychological evaluation No unrealistic expectations, by both family and the patient. The necessary cognitive and behavioral skills should been developed for successful programming . The revised form of Wechsler intelligence scale is available for this purpose. If skills not developed –postpone the procedure - help him to develop the skills

22. Factors that affect pediatric cochlear implant performance. Age of implantation Hearing experience Training with amplification in case of some residual hearing Presence of other disabilities Parent and family support.

23. Three modes of stimulation of auditory system involving cochlear implant Electrical stimulation -complete electric stimulation when there is no residual hearing in both ear Electroacoustic stimulation- ( hybrid implants) lower frequencies stimulated acoustically via hearing aid while higher frequencies electrically via cochlear implant. Bimodal stimulation-one ear uses implant while use a high gain hearing aid on other ear

24. Bilateral cochlear implant Localisation Head shadow Squelch Summation Head shadow effect – when the sound has to cross the head to reach the other side of the ear. 6dB loss in sound intensity occurs.

25. Device selection

26. Parts of cochlear implant External Microphone Speech processor Transmitter Internal Receiver and stimulator An array of up to 22 electrodes

27. Parts of cochlear implant External Microphone Speech processor Transmitter Internal Receiver and stimulator An array of up to 22 electrodes

28. Speech processor converts acoustical signal coded for transmission to the internal device. The signal is sent via a wire to the transmitter located on the implant users’ head. The method by which a signal sent to the implant recipient is derived is called the Coding strategy Most cochlear implant systems utilize either a filter bank or a feature extraction procedure for coding .

29. In filter bank procedure, the signal is separated into a number of frequency bands and transmitted as an analogue input. The feature extraction procedure focuses on the aspect of the signal that theoretically provide the greatest degree of speech recognition

30. Coding strategy Method by which pitch, loudness and timing of sound are translated into series of electrical impulses. Two types: Simultaneous Nonsimultaneous

31. Simultaneous strategies Activation of more than one electrodes at the same time. Only produced by advanced bionics Problem of signals interference Benefit from modiolus hugging electrode arrays

32. Nonsimultaneous strategies Continuous interleaved sampling strategies stimulate each electrode serially (one after another). No electrode is bypassed. Cochlea receive the complete information about the frequency composition of incoming signal. Faster sequential stimulation –better speech recognition. Available with all three devices .

33. Electrode Array Consists of electrodes and electrode carrier Electrode carrier is the wire which extends from the receiver to the electrodes Electrodes are of 2 types: Extracochlear electrodes and intracochlear electrodes

34. Type of electrodes Extra cochlear electrodes : Located outside the cochlea such as on the plate of the receiving coil or placed under the temporalis muscle. Used as a ground source for monopolar stimulation

35. Modiolus hugging electrode Modiolus – core of cochlear spiral-ganglion cells resides their. Electrodes in close approximation to modiolus are referred- modiolus hugging electrodes. Placed with stylette - keeps the electrodes straight, stiff - easily inserted- stylette withdrawn-springs back into its original configuration-tightly around the modiolus .

36. Electrodes are inserted next to modiolus

37. Special electrode arrays Compressed array -same no. of electrodes compressed into 60% of length. Useful for patients with labyrinthitis ossificans . Less overlap of electrodes using compressed electrodes array. Double arrays -designed for subjects with labyrinthitis ossificans . Separate cochleostomies are performed into the inferior and middle turn of cochlea.

38. Insertion depth: The mean length of human being cochlea is 33–36 mm. the implants don't reach to the apical tip . it may reach up to 25 mm which corresponds to a tonotopical frequency of 400hz

39. Nucleus 24 freedom N6 with contour advance electrode Manufactured by cochlear ltd. Sydney, Australia Uses flexible silicone housing surrounds titanium case for reciever / stimulator Age 12months Electrode arrray is curved consist of 22 half banded platinum electrodes space over 15mm MRI compatibility -1.5 T with replaceable magnet

40. Advanced bionics Hi Res Sylmar Electrode ( hifocus 1j) system –banana shaped curved towards Modiolus Age :12 months No. of electrodes: 16 spaced at 1.1mm over 17mm. No. channels :16 MRI compatibility-1.5 T with magnet removed

41. Med-el Pulsar Innsbruck ,Austria Age 12 yrs Reciever /stimulator housed in titanium case that is 25.4mm wide :45.7mm long. No.of electrodes:26 No. of channels:12 MRI compatibility-1.5T

42. vaccination Two vaccines available PPV-23( pneumoccocal polysacharide vaccine) PCV-13( pnemococcal conjugated vaccine) Children <2 yrs -receiving implant should receive PCV13 CHILDREN >2yrs who have completed PCV-13 should receive PPV23 Child planned for implant should be up to date on age-appropriate pnemococcal vaccination >2 weeks before surgery if possible.

43. all children should receive three doses of pneumococcal conjugated vaccine before age of one Children aged 24--59 months who have not received PCV13 should receive PCV13 2month apart and one dose of PPV23 2month later Children who have completed the PCV13 series should receive PPV23 > 2 months after vaccination with PCV13. Persons aged 5--64 years should receive PPV23 a single dose is indicated

44. Surgical procedure In cision and skin flap Incision may be C-shaped ,inverted U, J-shaped. The flap is elevated, it includes periosteum of the mastoid, temporalis fascia, and temporalis muscle. Flap thickness should not be greater than 6mm .

45. C- Shaped incision

46. Inverted U

47. INVERTED-J -INCISION

48. The well For the placement of stimulator. More superior placement in small children in the area temporal squama , in adults occipital portion of temporal bone. In children stimulator placed over exposed Dura. Channel formed over the bone to pass the electrode lead. During drilling the well and tie down holes the CSF leak may occur.

49. mastoidectomy It is performed after creating the site for well. The mastoidectomy cavity should not be saucerized as edges help to retain the electrode leads. Facial recess is identified and widely opened . Care should be taken of the anomalous facial nerve.. Or absent facial nerve. The most inferior part facial recess is important for visualization of round window niche.

50. cochleostomy Round window niche is clearly seen after opening the facial recess. Cochleostomy is created inferior to inferior attachment of round window membrane. The size of cochleostomy varies between 0.8 mm to 1.2mm in diameter.

51. Insertion of electrode array When device is brought into operative field the monopolar cautery is to be removed. The electrode array is inserted into the cochleostomy . The tip of the electrode array should be directed inferiorly so that it will slide along the lateral wall of the scala tympani. Lubricant like healon and mixture of water and glycerine is used . Incomplete insertion may occur in cases of labyrinthine ossificans .

52. fixation The stimulator is fixed to skull with sutures. Drill holes are made above and below the receptacle site and sutures are passed through them. It can cause perforation and CSF leak in children. Alternatevely a strip of material is placed over the stimulator secured with miniplates . Nonabsorbable material like gortex or absorbable material like alloderm can be used .

53. The skin incision is closed in layers. From Advanced Bionics

54. Device should be handled gently. Monopolar cautery should be discarded when device is brought into operative field. Surgeon should have the clear view of round window and should be assure about scala tympani. Precautions:

55. Middle Cranial Fossa approach Number of surgeons capable of performing this approach are limited. Post lingually deafened adult Individuals who have open canal wall down mastoidectomy cavities.

56. Veria technique Non mastoidectomy technique Done through endaural route for cochleostomy Transcanal tunnel drilled in the posterior canal wall Faster healing,ealier fitting of the processor Minimise trauma to facial nerve

57. Post-op complication Facial nerve injury- ,incidence is less than 1%.however minor paresis of facial nerve is uncommon. May occur in patients with anomalous facial nerve associated with dysplastic semicircular canal. Taste disturbance due to injury to chorda tympani. Hematoma - formation of more than 10cc requires evacuation.

58. Generally trivial and can be handled by gently opening the wound and treating with antibiotics. Device removal is not required. Infections:

59. If small can be left to heal by secondary intention or secondary closure can be done. Flap necrosis-most serious complication –device removal may be required. It occurs in cases of aggressive thining of flap. Scalp rotation flap , temporoparietal facial flap can be required. Wound dehiscence:

60. Early Device Failure : Out of box failure Due to factory defects or during surgical manipulation. Extracochlear implantation can occur when hypotympanic cells are mistaken for scala tympani. The electrode array may get migrated after correct placement. Most common cause of displaced electrode is movement of electrodes array after drill out procedure

61. Cerebrospinal fluid leak: Can occur when placing the stimulator, more likely in young children as skull is very thin. Also occurs during drilling for tie down sutures. Can also occur during opening the scala tympani. Chances are increased when cochlear dysplasia is there .

62. This can be treated by packing the common cavity with muscle tissue. If this does not controls the leak the ear must be closed by plugging the eustachian tube filling the middle ear and mastoid with fat.

63. Balance disturbances : Incidence is less than 10%. It gets resolved with in few weeks by itself .

64. Meningitis: Individuals with CSF leak and inner ear malformations are at more risk. Lumbar puncture is required for diagnosis. Broad spectrum antibiotics are started.

65. Extrusion or exposure of the device: Suture line should be kept away from the edges of the implant. Repair must remove skin to avoid suture line that parallel the implant edge closer than 1-1/2 cm A pericranial flap should be rotated to fully cover the device with or without a temporoparietal flap . Late complication

66. Displacement : Due to physical injury. During scar formation. Assessed by fine cut CT of the temporal bone .

67. Late device failure: Usually due to internal device failure-due to trauma or spontaneously. External component is first replaced, sometimes that solves the problem - fine cut CT of temporal bone to look for the position of stimulator and electrodes.

68. Device activation 2 to 4 weeks postoperatively, referred as hook up” Determine stimulation mode- a)bipolar mode –active electrode paired with another electrode in intracochlear electrode array,narrow band of stimulation. b)monopolar mode-electrode in cochlea is grounded to extracochlear electrode,resulting in wide current spread.

69. Programming of device requires-threshold level and most comfortable loudness level for each active electrode. Objective method to assess threshold- a)neural response telemetry(NRT)-use radiofrequency telemetry to measure the action potential in auditory nerve. b)Electrical ABR c)Stapedius reflex-stapedius reflex correlate with most comfortable loudness level.

70. Auditory rehabilitation after cochlear implant Development of speech preception with training in implant listeners. Programs of auditory training in children are with implant are often organised with hierarchic approach by which the child learns to associate meaning with unfamiliar and unnatural sounds

71. Auditory training in children with cochlear implant Detection Discrimination Identification Comprehension Auditory feedback loop (imitation or approximation of speech sound)

72. Children with implants need the implant system to be working well, and it should be worn consistently in good listening conditions when good communication opportunities are available. Keep all external parts in good functioning order and working with an audiologist who specializes in CI on a regularly scheduled basis .

73. to be successful in mainstream education classroom situation should be appropriate and has good acoustic and the technology is successfully managed .