Auditory Brainstem Implant

Question 1

What is an ABI?

Answer 1

A surgically implanted device that provides auditory sensation to individuals who cannot benefit from a cochlear implant by directly stimulating the cochlear nucleus of the brainstem

Question 2

When was the ABI developed?

Answer 2

1979
By the House Ear Institute for patients deafened by bilateral vestibular schwannomas (NF2)

Question 3

When was the first multichannel ABI developed?

Answer 3

1995
Developed by Laszig and colleagues
8 platinum disk electrodes

Question 4

When did the ABI receive FDA approval for clinical use?

Answer 4

2000

Question 5

What are the current ABIs like?

Answer 5

21 electrodes arranged in 3 rows
Over 1000 ABI procedures performed worldwide

Question 6

What are the FDA approved indications for ABI?

Answer 6

12+ years
Must meet both: NF2 and those who are rendered deaf due to bilateral resection of neurofibromas of the auditory nerve

Question 7

When can implantation of ABI occur?

Answer 7

During the first or second side tumor removal
Or in patients with previously removed tumors

Question 8

What is NF2?

Answer 8

Neurofibromatosis type 2
AD disorder
Cause by pathogenic variants in the NF2 gene, leading to bilateral vestibular schwannomas and multiple nervous system tumors (meningiomas, ependymomas, schwannomas)
Often with ocular and cutaneous manifestations

Question 9

What is the treatment plan for NF2?

Answer 9

Surgical resection, radiosurgery, and general medical management for the acoustic neuroma
Implantation of ABI
Rehabilitation

Question 10

Can ABI also be used off-label?

Answer 10

Yes
May be considered for adults or children who lost their hearing in different ways
Ex. cochlear nerve injury secondary to a temporal bone fracture, cochlear ossification secondary to bacterial meningitis or otosclerosis, fibrous tissue growth in the cochlea, children with congenital cochlear aplasia or cochlear aplasia (strong family support is important)

Question 11

Should children who are being considered for an ABI typically undergo a failed trial with a cochlear implant?

Answer 11

Yes

Question 12

What do you do when the electrode array is causing facial stimulation?

Answer 12

Go to upper stimulation levels and stimulate each electrode one by one
Lower the level of the electrode that is causing the facial nerve issue (gets less and if you still see it, keep dropping it)
Can increase pulse width for that electrode so it is perceived as louder by the patient
Turn off electrode if issue cannot be resolved and increase band width of the other electrodes
Can switch stimulation if this issue persists for many electrodes - from monopolar (broad response) to bipolar (smaller response bc the distance between the ground and the stimulating electrode is much smaller) - this could focus the stimulation so it doesn’t activate the facial nerve

Question 13

Are focused stimulation levels higher?

Answer 13

Yes, bipolar stimulation
Requires higher stimulation levels because of it’s focused nature
Different stimulation levels than monopolar

Question 14

What is triphasic/tripolar?

Answer 14

Med-El specific
More focused than bipolar
Gives part of the return or ground capabilities to each adjacent electrode (or two electrodes around the stimulated electrode)

Question 15

Can triphasic also be used for those with facial nerve stimulation?

Answer 15

Yes
Especially for use when you have tried to troubleshoot and cannot
If the whole electrode array is involved or a large number of the electrodes

Question 16

What does focusing do?

Answer 16

Causes less current to spread and will make facial nerve stimulation less likely if it is directly impacting one area

Question 17

What determines candidacy in global clinical practice for ABIs?

Answer 17

Complete cochlear ossification
Severe auditory neuropathy
Skull trauma/cochlear nerve avulsion
Cochlear nerve aplasia; malformation of the auditory nerve
Severe cochlear malformation
Patients as young as 14 months old were implanted

Question 18

What are factors that can influence ABR benefit?

Answer 18

Motivation to hear
Psychological readiness
Acceptance of device limitations
Anatomical status
Family and support system
Commitment to rehabilitation
Limited facilities that support ABI
Cost of implant and contracted specialists
Patients with usable hearing in one ear (may not use ABI consistently if implanted early)
Tumor resection is a long procedure and duration must be considered for patient safety

Question 19

What is done during pre-op ABI counseling?

Answer 19

ABI internal/external device schematic
Warranty and longevity
ABI surgical placement
Device verification during the resection
ABI function/failure rate
Adverse effects: non-auditory outcomes and potential complications
Care of implant site
Expected benefits and limitations
Rehabilitation plan

Question 20

What are the external components of the ABI?

Answer 20

Microphone
Speech processor
Power source
External transmitting coil and magnet

Question 21

What are the internal components of the ABI?

Answer 21

Internal receiving coil and magnet
Receiver-stimulator
Electrode lead
Paddle-shaped electrode array (surface electrodes or penetrating electrodes (discontinued))

Question 22

Does AB have an ABI device?

Answer 22

Not anymore
They used to
Implant had 16 electrode contacts which were housed on a paddle-shaped layer of silicone

Question 23

Is cochlear the only FDA approved ABI device?

Answer 23

Yes, so these are the only ones that can be used in the US
ABI24M first ABI approved by FDA (2000)
Nucleus 6 is the latest processor that is compatible for use with ABI24M implant
The FDA has also approved the Nucleus Profile ABI541; thinner and compatible with Nucleus 7

Question 24

What is the Med-El ABI device?

Answer 24

Synchrony ABI
Currently not FDA approved in the US
Approved for commercial distribution in Europe and in other countries around the world
Has 12 electrode contacts that are housed on a paddle-shaped layer of silicone which is held on the brainstem with surgical mesh

Question 25

Is a well-trained multi-disciplinary team essential for a successful ABI program?

Answer 25

Yes Neurotologist Neurosurgeon Electrophysiologist Audiologist Psychologist

Question 26

What is the implantation site of the surface array?

Answer 26

Places within the lateral recess of the 4th ventricle along the brainstem and directly stimulated the cochlear nucleus

Question 27

What are the components of the cochlear nucleus complex?

Answer 27

Dorsal cochlear nucleus Ventral cochlear nucleus

Question 28

Is the cochlear nucleus a very complex structure?

Answer 28

Yes Each nuclear group has its own sequence from low- to high-frequency representation Unlike the AN that has two types of cells, the CN has a number of different cell types

Question 29

What is the surgery like for ABI?

Answer 29

Completed under general anesthesia Takes substantially longer to complete than a CI surgery Hospitalization is required for several days to allow for recovery from the more invasive procedure Surgery requires the surgeon to perform a craniotomy to insert the electrode array through the fourth ventricle and onto the surface of the cochlear nucleus During auditory brainstem implant surgery, an electrophysiologist should be present to evaluate the integrity and function of nearby cranial nerves V, VII, VIII (if it is not already being monitored by the audiologist), IX, and XI

Question 30

What are the two surgical approaches?

Answer 30

Translabyrinthine - involves removal of the mastoid bone behind the auricle as well as the SCC in the inner ear (provides good visualization of the fourth ventricle and the facial nerve, eliminates the possibility of preserving residual hearing) Retrosigmoid - involves an incision made behind the auricle and accessing the brainstem and cerebellum through a small opening made near the base of the skull (less invasive, enables removal of skull-based tumors and provides visualization of cochlear nerve; requires retraction of the cerebellum and does not provide complete visualization of the facial nerve)

Question 31

What are some challenges related to electrode array placement?

Answer 31

The full surface of the CN is not visible during surgery No clear anatomical landmarks to define the exact periphery of the CN complex Anatomical variations between patients increase placement complexity Removal of large tumor can distort surrounding anatomy, making electrode placement more challenging

Question 32

Do you use intraoperative electrophysiology to guide electrode placement?

Answer 32

Yes Given the limited visibility and anatomical variability, visual guidance alone is not sufficient for accurate placement Techniques used: monitoring of neighboring cranial nerves, EABR

Question 33

Why is EABR used during ABI placement?

Answer 33

Confirms that stimulation from the electrode array activates the auditory brainstem pathway, as reflected in the eABR waveforms Assists in optimizing electrode placement by confirming effective stimulation of the cochlear nucleus

Question 34

How is intraoperative eABR used to position the ABI electrode?

Answer 34

Individual electrodes are stimulated and EABR waveforms are recorded Aim is to place the array at a location that will generate a robust ABR from the largest number of electrodes Results may indicate that the array needs a slightly different orientation or depth into the lateral recess of the fourth ventricle When all, or nearly all electrodes elicit auditory sensations, it can be assumed that whatever result the patient achieves is the best possible result Few or no eABR responses typically indicate inaccurate electrode positioning or insufficient contact with the cochlear nucleus surface Repositioning or repacking behind the ABI array may be considered to improve outcome

Question 35

Should stimulation always start at low intensities?

Answer 35

Yes Stimulation at high current levels may stimulate the vagus nerve causing heart arrest (reported in 2 cases using levels of 150 nC). The anesthesiologist should always be alerted to this possibility

Question 36

What can wide bipolar stimulation be used for?

Answer 36

To confirm approximate placement of an electrode array For more accurate placement of the electrode array, a combination of electrodes across the array should be stimulated

Question 37

What does a valid response look like?

Answer 37

Correctly positioned ABI electrodes typically elicit 1 to 4 positive peaks occuring withing about 4 ms from the start of the stimulus Waveforms vary across patients, but generally include three positive peaks between 1.2-4 ms, likely corresponding to waves III-VI of the traditional ABR, and an early peak around 0.4-0.9, respembling wave II (occasionally observed if an excitable stump of the auditory nerve is present - some of it is still there) Mainly looking at waves III, VI, and V

Question 38

How can you determine id a response is real?

Answer 38

After recording a response, the stimulus polarity should be inverted and then a second response obtained If the response if biological, the stimulus artifact will invert, but the neural response will remain unchanged

Question 39

What are some risks of ABI placement/surgery?

Answer 39

Standard surgical risk Meningitis (risk will all neurosurgery) Unsuccessful hearing enhancement (device failure, implant migration, limitations fo technology regarding tonotopic information, improper placement over CN, CN compromised (radiotherapy), head trauma and device damage) Unknown long-term effects of electrical stimulation

Question 40

When does activation occur for ABI?

Answer 40

4-8 weeks after surgery CT or MRI performed to confirm array placement (prior to activation)

Question 41

How long might the initial device activation take?

Answer 41

2-4 hours Follow up session the next day

Question 42

Is the entire procedure explained to the patient prior to activation?

Answer 42

Yes, visual support may also be used

Question 43

What sensations is the patient instructed to report?

Answer 43

Auditory perception Tinnitus or ringing sensation Other sensations (paresthesia, vertigo, dizziness) Any combination of auditory and non-auditory effects

Question 44

What is the activation protocol (for initial and subsequent programming sessions with untested electrodes)?

Answer 44

Programming should take place in a setting with immediate access to emergency medical services (risk of vagal nerve stimulation and serious non-auditory side effects) Patient must be connected to ECG monitoring equipment with a physician present in case resuscitation is required Vital signs must be continuously monitored (BP, pulse, oxygen) Clinicians should closely observe for non-auditory sensations during stimulation and stop immediately if adverse effects occur

Question 45

Why do non-auditory sensations occur?

Answer 45

The cochlear nucleus is located close to many other nerve nuclei and sites for vital body functions in the brainstem

Question 46

What are some examples of non-auditory sensations?

Answer 46

Facial movement Constriction or tickling in the throat Vertigo Tingling in the shoulder or arm Tingling in the leg Vibratory sensation in the eye Dizziness and nystagmus

Question 47

Is ABI programming generally more complex and time consuming than CI programming? Why?

Answer 47

Yes Presence of nonauditory sensations More central locus of stimulation Uncertainty and irregularity of tonotopic stimulation Potential central disease from NF-2 Recipients often in poor health and tire easily

Question 48

What happens during the mapping?

Answer 48

Once electrodes that produce auditory responses are identified, electrical threshold and maximum comfortable level are measured for all active electrodes ABIs are programmed using a combination of MP and BP stimulation (monopolar and bipolar) MP allows stimulation at lower current levels, which can result in fewer nonauditory sensation Speech coding strategies: Nucleus ABI 22: SPEAK Nucleus ABI 24: SPEAK or ACE

Question 49

Why are electrodes disabled?

Answer 49

Did not elicit auditory sensation Elicited non-auditory sensation

Question 50

If minor non-auditory sensations occur, what should be done?

Answer 50

Reduce current level (loudness) Increase the pulse width Change the electrode coupling mode (switch to a more focused mode) to avoid nonauditory side effects Reduce pulse rate

Question 51

What happens if those adjustments don't help?

Answer 51

Disable the affected electrodes Note: Non-auditory sensations often decrease over time; 9% of patients experience persistent nonauditory sensation

Question 52

Do you have to map pitch with ABI?

Answer 52

Yes It is different than CI because each structure has its own tonotopic organization Not as predicable

Question 53

What is the audiologists goal with mapping pitch?

Answer 53

Aim to ensure that pitch perception progresses in a consistent and orderly manner across active electrodes Accurate pitch ranking is more critical than the total number of electrodes activated The ability to reliably differentiate pitch across electrodes is associated with improved speech recognition

Question 54

What are the two procedures that can be used to determine appropriate tonotopic order or the electrodes?

Answer 54

Pitch scaling and ranking Ranking may not be reliable in children (age limitation)

Question 55

Should audiologists ensure that loudness is balanced at upper-stimulation levels across all active electrodes?

Answer 55

Yes Upper-stimulation levels should then be globally adjusted in live speech mode to the recipient’s most comfortable listening level During live speech, the patient should be closely monitored for non-auditory sensations or aversive effects If any issue is noted, the audiologist should sweep at upper stimulation levels across the electrode array to identify and address the problematic electrode

Question 56

Should ABI patients be seen frequently for follow-ups?

Answer 56

Yes Follow-up should occur several times during the first few months of device use and at least twice a year after the first year of use Young children should be seen at least quarterly for the first several years after implantation to ensure that progress is optimized Additional sessions do not require medical personnel and ECG monitoring

Question 57

How well do adults perform with ABI?

Answer 57

Most performed slightly above chance on recognition of common environmental sounds ABI improved speech understanding by an average of 26% when speechreading cues were available (audio+visual vs. visual-only); the ABI functioned primarily as an aid to support speechreading Only 4 of 61 scored above 20% in audio-only open-set sentence recognition; one exceeded 60% The NF2 group had a mean open-set sentence recognition score of 10% and the non-tumor group achieved a mean score of ~ 60%, with some scoring as high as 100% *NF2 results in poorer outcomes

Question 58

What are the overall outcomes and benefits of ABI?

Answer 58

Improves awareness of environmental and speech sounds, enhancing daily communication and quality of life Provides cues for rhythm, stress, and intonation that support lip-reading Helps recipients function more effectively in an auditory environment Only a few ABI recipients were able to understand speech without lip-reading Outcomes are generally poorer that that obtained with CI, especially in NF2 patients This poor outcome in NF2 recipients was attributed to neural degeneration in the brainstem from tumor growth

Question 59

What are the two hypotheses for differences in performance between ABIs and CIs?

Answer 59

Difference in speech understanding between CI and ABI is caused by the ABI bypassing or distorting activation of specialized neural circuitry occurring in the CN ABI does not make selective contact with the tonotopic dimension of the CN which limits the number of independent channels of spectral information

Question 60

What is a penetrating ABI?

Answer 60

PABI A hybrid consisting of 8-10 penetrating microelectrodes and standard surface electrodes Intended to utilize the tonotopic organization of the CN, which is organized from the surface (LF) toward the center (HF)

Question 61

What did PABI result in?

Answer 61

Lower thresholds Increased pitch range High selectivity *did not result in improved speech recognition

Question 62

Was the PABI discontinued?

Answer 62

Yes Due to serious side effects

Question 63

What is an auditory midbrain implant?

Answer 63

AMI Central auditory prosthesis designed to stimulate the inferior colliculus (IC) in patients with neural deafness caused by bilateral vestibular schwannomas (mainly NF2) It was developed in response to the limited outcomes of ABI in NF2 patients and the complexity of the surgical procedure

Question 64

What does the AMI result in?

Answer 64

Provides loudness, pitch, temporal, and directional cues important for speech perception Recipients show improvements in lip-reading, environmental sound awareness, and speech perception comparable to ABI users with NF2 Open-set speech recognition without visual cues remains limited