array design has continuously evolved to reduce insertion trauma and improve
hearing conservation. However, one
downside of some delicate (smaller diameter, more flexible) electrodes has been
a tendency for tip fold-over. Tip
fold-over may occur during insertion when the electrode array tip impinges the
modiolar wall (or other structure) and is temporarily held stationary while the
more proximal electrode advances past it.
The phenomenon has also been called “tripping” and may be more common in
perimodiolar electrodes.1,2 Tip
fold-over may result in a variety of negative consequences, ranging from the
need to program-out electrode contacts all the way to removal and replacement
of the entire electrode array. Fold-over
is also associated with cochlear insertion trauma.
The American Cochlear Implant (ACI) Alliance is a not-for-profit
membership organization created with the purpose of eliminating barriers to
cochlear implantation. The ACI Alliance membership spans clinicians and
scientists from across the cochlear implant continuum of care including
otolaryngologists, audiologists, speech pathologists, educators, psychologists,
and others in cochlear implant teams. Parents of children with cochlear
implants, adult recipients, and other advocates for access to care are also
active members. Our activities include research, advocacy and awareness
initiatives designed to improve access to CI care. The ACI
Alliance sponsors an annual clinical research meeting that provides opportunities
for scientists, clinicians and others to share information.
Audiologic Management of CI Patients has become Increasingly Complex
Terry Zwolan, Ph.D.
Over the past 3 years, the Institute for Cochlear Implant Training (ICIT) Advanced Surgeons’ Training Course has provided in-depth education
for over 60 CI surgeons from the US and around the world, which could improve outcomes of thousands of CI recipients. Similar training and education needs to exist
for audiologists. This blog describes
some of the areas that are covered in the Advanced
Audiology CI Course(AAC), which was developed by ICIT to meet this
It is the responsibility of the cochlear implant (CI) team,
which typically includes the implant surgeon, audiologist, and speech-language
pathologist, as well as other professionals, to determine who is an appropriate
candidate to receive a CI. It is also
their responsibility to ensure the device is adequately placed, appropriately
programmed, and to monitor device function to ensure the patient is receiving
optimal benefit from its use. In recent
years, the responsibilities of CI audiologists have expanded considerably and
become increasingly complex as technological advances with external and
internal devices have accelerated at fast rates.
Delayed Hearing Loss after Hearing Conservation Surgery
Thomas J. Balkany, MD
of residual hearing during cochlear implantation has been a focused area of CI
research since the first report in 1989.1 Retention of low-frequency acoustic hearing
may allow fine structure processing, enhance speech understanding in noise,
sound localization, and music appreciation.
Hearing conservation has been made possible by advances in surgical
techniques, low-trauma electrodes and the use of steroids (see ICIT Surgeons’
Blog 7/1/15; 8/1/15; 12/1/15; 1/1/16; 2/1/16; 3/1/16; 12/5/16; 3/7/17).
residual hearing is frequently conserved (not destroyed) during implantation, at
this time there are no widely available methods to actively preserve it. Delayed loss of residual hearing after
implantation is known to occur in a substantial number of patients.
CI OUTCOMES: THE IMPACT OF SPIRAL GANGLION SURVIVAL
Thomas J. Balkany, MD
CI outcomes are generally good and consistently improving, there continues to
be a wide range of performance in speech recognition. Disparate outcomes have been attributed to several
clinical variables including:
of signed language
hearing aid use
position of electrode
in examining these factors a retrospective study of 2,251 CI recipients showed
that even a combination of the most significant variables accounted for only about 10 to 20% of outcome variability.1,2
Some other determinant(s) must have a substantial impact on performance.
Development and Validation of the Cochlear Implant Surgical Competency Assessment Instrument
Thomas Balkany, Kaming Lo, Howard Francis, Simon Angeli, Michael Novak, William Luxford, Rodney Lusk, and Heather Strader
present a new instrument for evaluation of cochlear implant (CI) surgical skills
and review its validation process.
instrument to assess CI surgical competency incorporated results of structured
surveys of comprehensiveness sent to 30 international CI experts and US
trainees. One-hundred evaluations of 28 residents, fellows, and practicing CI
surgeons were completed. Surgical skills were evaluated by four experienced
neurotologists (two raters per subject) using two temporal bones per subject. A
training session was completed by 24 subjects between the first and second
procedure. Comparison of two blinded rater’s scores per subject provided
information on interrater reliability. Correlation of competency scores with
degree of training and with improvement after a training session provided
information on construct validity.
levels of interrater reliability were confirmed by using the intraclass
correlation coefficient. Construct validity was demonstrated by correlation of
higher performance scores with increasing years of training, board certification,
and fellowship training. Construct validity is also supported by improvement in
scores after a CI training session as well as by acceptability surveys.
Discussion: Data indicate
that this instrument is an objective, accurate, and dependable
procedure-specific instrument for evaluating CI surgical competency.
cochlear implant surgical competency assessment (CI-SCA) can be used to
establish CI surgical competency, identify surgical skills that require
remediation and demonstrate progress during training.
Vestibular Function and Development of Motor Skills in Implanted Children
Guest Author: Hamlet Suarez, MD
Progress in cochlear implantation programs allows a better
understanding of speech development in children with prelingual profound
hearing loss. Less understood is the impact of vestibular receptor disorders
which can be associated with congenital deafness. These disorders can be congenital
or result from the surgical procedure. Sensory preservation surgical techniques
are effective for residual hearing1-4 and have recently been
proposed for preserving vestibular function. (CI Surgery Blog 12.5.16).
Also, measurements of vestibular function5-7,
posture, and gait in these children has created a new area of interest,
generating other questions, such as:
1-Does the motor skill development in congenitally deaf
children have a similar process to that of normal hearing children?
2-How is the posture and gait performance in implanted
children with congenital deafness?
surgical techniques, low-trauma electrodes, and the use of steroids can be
effective in preserving residual hearing after cochlear implantation (ICIT CI
Surgery Blog: 9/16; 8/16; 6/16; 3/16; 2/16; 1.1/16…). However, less attention has been given to
preservation of vestibular function. This
is understandable because from a clinical practice perspective, post-CI
vestibular complaints are surprisingly uncommon; possibly due to the remarkable
capacity for central vestibular compensation and adaptation.
spontaneous complaints are few, when recipients are specifically questioned, post-CI
vestibular symptoms have been reported to be as high as 75%.1 And as surgical indications expand and
bilateral implantation becomes more common, preservation of vestibular function
may take on an important clinical role. Can
vestibular function be preserved by techniques used for hearing preservation?
et al, using a hearing preservation surgical technique including bony
cochleostomy, found that unilateral CI rarely results in significant adverse
effects on the vestibular system and that postural stability actually improved
post-implantation.2 Recent studies
tend to validate those findings.
the LASER has been described for use in treatment of acoustic neuromas, cholesteatomas,
and stapes surgery.1-4 A wide
variety of LASERs exist for otologic use; however, the most commonly used are
the carbon dioxide (CO2), potassium-titanyl phosphate (KTP), and argon LASERs.
Each of these LASERs has their strengths and weaknesses with surgeons
preferring one or the other based on cost, ease of use (i.e., flexible fiber
vs. micromanipulator), wavelength, and interaction with tissue. What is less
commonly discussed is use of the LASER in cochlear implant (CI) surgery.
Use of a KTP laser
in conjunction with fiberoptic endoscopy to remove bony obstruction of the
inferior segment of the cochlea was first documented by Balkany5 in
1990. Video of this procedure is
Additional studies were
performed by Kautzky et. Al., who attempted to recanalize the basal turn of a
human cadaveric cochlea that was artificially obliterated.6 Klenzner
et. Al. described the use of the CO2 laser for a high-precision cochleostomy in
an experimental model; the goal of the study was to reduce the trauma to the
cochlea during hearing preservation approaches in a contactless fashion.
Fishman et. Al. studied the CO2 laser in 18 guinea pig models. The authors
measured compound action potential (CAP) thresholds by acoustic tone pips and
noted little change after creating the cochleostomy with the LASER.7 Cipolla et. Al. performed standard drill and
CO2 laser cochleostomies on 30 cadaveric temporal bones.8 They felt that the operative times were
similar between the 2 techniques.
However, the LASER had an intracochlear sound level that was
significantly lower than the drill (54.9 vs. 89.9 dB, P<0.001). Other
authors have described a significant and marked energy transfer when allowing
the drill to touch the endosteum.9 This is something that should not
occur with the LASER, although the LASER can cause heat transfer to the
perilymph of the scala tympani.8
preservation of residual hearing during cochlear implantation (CI) was first described
in 19891, it has become clear that hearing preservation is possible
in most cases2,3 and that it can result in better CI outcomes.4,5
Over the last several years, slow electrode insertion speed has been evaluated
as a surgical technique to optimize hearing preservation.
Evolution of Cochlear Implant Electrodes: Straight vs. Pre-Curved
Thomas J. Balkany, MD
Early intra-cochlear electrodes were simply
straight, short wires. The House
single-channel electrode was a somewhat variable length (around 4 mm) of copper
wire with a flame-balled tip.1
Preserving hearing was not a priority for the anacusic or profoundly
deaf patients implanted in the 1960s and 1970s and short electrodes seemed
appropriate to the expectations of single channel implantation.
Extra-cochlear electrodes were also in common use at
that time. Douek et al2 implemented
a steel, flame-tipped electrode that was initially placed on the round window
membrane in 1976. It was later placed on
the promontory after surgical collapse of the tympanic membrane (tympano-cochleopexy)
where it was held in place by spring-loading it to a hearing aid mold. Other unilateral extra-cochlear systems were
used in a number of centers including Portmann3 in Bordeaux and by
Burian and Hochmaier4 in Vienna.
Banfai et al5 in Cologne-Duren used a
16-channel extra-cochlear electrode nicknamed the Hedgehog. Anatomic studies allowed promontory surface
projections of the scalae. Bone was
thinned in the areas to be stimulated and a plate was wedged against the
promontory with 16 metal projections in corresponding locations.
As it became clear that extra-cochlear and single channel
intra-cochlear devices provided limited benefit, the push was on to optimize multi-channel
devices with intra-cochlear electrodes. Two outstanding electrode engineers,
among others, who played a critical role in the evolution of CI electrodes
deserve recognition for their work:
Janusz Kuzma and (Melbourne, Valencia), Claude Jolly (Vienna).
Multichannel electrodes were first used in the 1960s
by House and Simmons (later abandoned). More successful prototypes were
developed in the 1970s by Michelson and Schindler (San Francisco), Eddington
(Salt Lake City), Chouard (Paris), the Hochmairs (Vienna), and Clark
(Melbourne), et al.
The most commonly used commercially available
multi-channel electrodes of the 1980’s were straight, bulky, stiff, and
traumatic.6 In comparison,
early peri-modiolar electrodes of the 1980s were less traumatic and had the putative
advantage of being close to ganglion cells, limiting current spread during
bipolar stimulation. However, the
industry has leaned to monopolar stimulation, largely to increase battery life,
thereby increasing current spread and reducing some potential benefits of
peri-modiolar electrodes. Straight,
flexible, low-trauma electrodes came into common use in the 1990s.
The current emphasis in electrode development is on
reducing electrode insertion trauma.
Doing so helps preserve residual hearing and improve CI outcomes (with
and without electro-acoustic stimulation).
The very short, very delicate hybrid electrodes developed by Gantz are
the best example of low-trauma electrodes.7
Over the last decade, advanced imaging techniques
have been used to estimate scalar location (S. tympani vs. S. vestibuli) in
living subjects. It is generally thought
that electrode location in S. vestibuli may be a surrogate for cochlear trauma
and appears to correlate with poorer hearing outcomes and reduced hearing
Very-long CI electrodes (28mm, 31 mm), elegantly flexible and
minimally traumatic, are designed to be deeply inserted into the low-frequency areas
of the upper cochlear turns. However, it
is not yet clear whether this additional depth of insertion provides outcomes
superior to standard-length electrodes (< 24 mm). This is important because reaching the upper
turns comes at a potential cost.
electrodes have previously been associated with greater loss of residual hearing and balance1 as well as
a higher rate of incomplete insertion
(18%) than standard-length electrodes.2 (CI Surgeons Blog 12/1/15)
Do Current Guidelines Prevent Access to Cochlear Implantation?
Thomas J. Balkany, MD
In the era of single channel cochlear implants, nothing
less than bilateral profound deafness was an indication for surgery. But as CI performance improved, auditory guidelines
for candidacy expanded. And as safety
and efficacy of implantation were confirmed, young children and older adults
were included. It has been anticipated
that, consistent with improving outcomes, the candidate field would continue to
So it is not surprising that in clinical practice, hearing
impaired people with conditions that once contraindicated implantation are now candidates.
Some of these prior contraindications include 1:
Significant residual hearing
Auditory neuropathy spectrum disorder
Pre-linguistically deaf adolescents and
Non-auditory developmental or cognitive delay
Single sided deafness
Unfortunately, written guidelines for candidacy may
not reflect best practices, which tend to respond quickly to evidence-based,
peer-reviewed research. Too often, CI professionals must challenge regulatory
and insurance authorities in the best interest of their patients. As a result, inappropriate guidelines and
regulations tend to prevent access to CI for many candidates who could be
expected to benefit. A special issue of
Cochlear Implants International (ed., John Graham) addresses this concern 2.
is associated with accelerated cognitive decline, dementia and depression. Affected individuals suffer difficulty
communicating, social isolation, loss of autonomy and general psychological
involution. Memory and concentration
decline 30 – 40% faster in older adults with hearing loss than in those with
normal hearing1,2. Further, the risk of developing dementia
increases proportionately with the amount of hearing loss.
Preservation of Residual Hearing: Pharmaceutical Agents
Thomas J. Balkany, MD
Electrode insertion trauma (EIT) is thought to be a primary
cause of loss of residual hearing during cochlear implantation (CI). Over the past three decades, improved surgical
techniques and electrode design have partially preserved residual hearing and
improved CI outcomes in many recipients.
Although EIT may cause loss of residual hearing through
immediate tissue disruption and necrosis, histological studies suggest that the
preponderance of damage results from secondary inflammation, fibrosis/osteogenesis,
oxidative stress and apoptosis. In some
cases, these programmed pathways may be blocked to varying extents by
medications. Some of the pharmaceuticals
currently under investigation for preservation of residual hearing in CI
Dexamethasone (Dex) has anti-inflammatory and
anti-apoptotic characteristics. For
example, Dex can suppress inflammatory cytokines, interleukins and TNF-alpha,
increases expression of anti-apoptosis genes and decreases expression of
pro-apoptosis genes in the cochlea. A single
dose of systemic and/or topical steroids is often given just prior to implantation
and has also been delivered orally in a two-week clinical trial (1).
Neuroprotective growth factors such as brain derived
neural growth factor (BDNF), insulin-like growth factor (ILGF), hepatic growth
factor (HGF) and neurotrophin-3 (NT3) have been used experimentally to enhance
ganglion cell survival after cochlear implantation. Delivery methods include osmotic pumps (2)
and drug eluting electrodes. Neurotrophins have also been delivered with gene
therapy via viral vectors (3) and cell therapy in alginate microspheres (4).
N-acetyl cysteine (NAC) is a free radical scavenger
that replenishes glutathione and L-cysteine.
NAC provides protection against hydroxyl radicals and lipid peroxidase
and blocks the MAPK/JNK apoptotic pathway in the cochlea.
Mannitol reduces oxidative stress by stabilizing
blood flow, especially in ischemia-reperfusion injury that may result from
EIT. It has been shown to protect hair
cells from acoustic trauma, gentamicin toxicity and TNF alpha mediated hair
RW Cochleostomy: A Cause of Progressive Hearing Loss?
Thomas J. Balkany, MD
Up to one-third of recipients who retain residual hearing
after CI have progressive low-frequency loss in the weeks or months after
One common theory is that following CI electrode insertion,
intra-scalar histiocytic and giant-cell infiltration (foreign body reaction),
fibrosis and osteoneogenesis lead to the progressive loss.3,4 These
inflammatory reactions may destroy residual neural elements or interfere with
the fluid-pressure wave as well as basilar membrane vibration. But are
intra-cochlear factors the only causes of progressive loss and does the
location of the cochleostomy make a difference?
The key neural elements that are stimulated by
cochlear implants (CI) are spiral ganglion cells (SGC). So it would seem logical that the more SGCs that
survive, the better CI performance would be.
Nonetheless, histopathologic studies have suggested that SGC survival ratesdo not correlate with CI performance. 1,2
However, prior temporal bone studies could not control
for variables that might affect performance (age, cause of deafness, degree of
hearing loss, duration of deafness, cognitive ability, etc.) Failure to control these variables cast some
doubt on the validity of the findings above.
In short, the best data available over the past 25
years indicated that SGC survival did not correlate with CI performance, but those
studies created an intuitive dissonance.
In order to settle the issue, the critical variables would need to be
Long Cochlear Implant Electrodes: Incomplete insertion, loss of residual hearing and balance
Thomas J. Balkany, MD
Preservation of residual
hearing has been a goal of CI surgery since it was first reported in 1989.1
It is an indication of good surgical technique and may result in enhanced
speech perception in conventional2 and hybrid devices.3 Very-long
electrodes (> 28 mm) have been used successfully for over two
decades, but continue to be debated due to anecdotal inferences of loss of residual
hearing and vestibular function, as well as a high incidence of insertion
In early stages of development, peripheral stimulation
helps organize the sensory cortex, a process commonly referred to as neural
plasticity. Neural plasticity may be
best thought of as continuous reorganization throughout early life in which
neural pathways are formed, but abandoned if not frequently used, in favor of
other more active pathways.
In the auditory and visual systems, sensory
deprivation during CNS development causes deficient organization, or
detrimental reorganization of the cortex that may lead to permanent deficits.1 For example, in amblyopia (“lazy eye”),
affecting about 2% of children, one eye is less functional than the other. If untreated, the visual cortex will “ignore”
the less-coherent signals from the lazy eye and its neural pathways will
degenerate, leading to blindness of that eye.
The central auditory system likewise undergoes sensory-deprivation-based
detrimental reorganization in the event of peripheral deafness. In the absence of peripheral stimuli, the
auditory cortex can be subsumed by the more active processes of the visual
system, especially in signers. This
cross-modal adaptation has been associated with poor outcomes when cochlear implantation
is delayed.2 Although electrical stimulation with cochlear
implants can establish central auditory pathways and diminish takeover by the
visual system early in development, after 5 years of age, restitution of the
auditory cortex may be minimal.3,4
Clinical experience has
demonstrated the value of cochlear implantation prior to the age of 18 months
and many feel that the ideal age is less than 12 months. Controlled studies confirm the time-sensitive
nature of successful implantation. Based
on ABR findings, Sharma, Dorman and Spahr demonstrated that progressively worse
CI outcomes occur in prelinguistically deaf children who had delayed
Ninety-six percent (96%) of early implanted (age
less than 3.5 years) children had normal P1 latencies. Only 5% of late implanted children (age
greater than 7 years) had normal P1 latencies.5
Over the past three decades, several papers have
demonstrated positive as well as negative effects of cochlear implantation (CI)
·Pre-operative tinnitus in CI candidates
has been estimated at 65 – 100%.1, 2
·The rate of tinnitus improvement following
CI ranges from 50 – 90%.4,5
·Tinnitus may be generated or made worse by
CI in 0 – 28% of recipients.5, 6
Theoretical mechanisms of CI effects on tinnitus
include electrical stimulation and electrode insertion trauma (EIT). Electrical effects may reduce tinnitus by
masking (creating an auditory percept that makes tinnitus inaudible),
electrical suppression (directly altering the generation or neural transmission
of the tinnitus signal) or by other mechanisms.
EIT may cause increasing tinnitus due to neural or metabolic organelle
damage that may cause abnormal signal generation. The following discussion addresses a series
of patients in whom traumatic, scala transgressing insertion exacerbated
tinnitus in comparison to another cohort in whom non-scala transgressing
electrodes did not.
High Rate of Migration/Partial Extrusion of Straight Cochlear Implant Electrodes
Thomas J. Balkany, MD
implant (CI) electrode migration is generally considered to be very uncommon,
the subject of few clinical reports and often not considered when discussing CI
complications with patients. However,
partial electrode extrusion from the cochlea, enough to reduce function and
cause aversive stimuli, may not be so unusual.
Rivas et al.1
described electrode migration as an important cause of cochlear reimplantation,
second only to device failure at Hopkins. And Connell et al.2 reported a ten
year period during which the United States Food and Drug Administration MAUDE
database3 showed 151 reported instances of electrode extrusion
(presumably underestimated due to the voluntary nature of reporting and the
tendency to report only major extrusions).
extrusions are thought to have been more common in the generation of stiff,
straight electrodes some two decades ago.
To reduce the rate of electrode migration at that time, Cohen and Kuzma
introduced a titanium clip that attached the electrode cable to the incus
bridge (buttress)4 and Balkany and Telischi described the split
bridge technique (a slot in the incus bridge) to fixate the cable in the same
location.5 Both were
effective in reducing electrode extrusion.6 However, the advent of pre-curved electrodes and
more flexible cables reduced the tendency for electrode migration.
cochleostomy is the concept that a single type of cochleostomy is not ideal in
all cases. Rather, the type of
cochleostomy used should be selected based on the anatomy of the patient and
the physical characteristics of the electrode to be inserted. In short, the cochleostomy should be adapted
to the patient’s anatomy and the electrode used. Cochleostomy is used here to mean an
enduring opening into the cochlea through which an electrode is inserted.
round window membrane (RWM), extended RWM and bony cochleostomy approaches have
claimed that their preferred technique is best.
Support for each is provided in the literature.1-4 RWM insertion may minimize drill trauma, prevent
bone dust and blood from entering the scala and reduce leakage of perilymph; extended
RWM cochleostomy may provide a more favorable insertion trajectory when the RWM
is angled too inferiorly; and bony cochleostomy allows better electrode
alignment with the axis of the scalar lumen, especially important when
inserting larger, stiffer or pre-curved electrodes.1 However, the one-size-fits-all arguments do
not take into account common variations in patient anatomy and electrode
presented the concept of Adaptive Cochleostomy at CI2012 in Baltimore5,
proposing that no single method of cochleostomy was ideal in all cases. Shapira et
al.6 had already demonstrated a normal variation in angulation
of the RWM of 27 – 65°. RWM
insertion in the case of angulation >45° (13% of patients) can
result in modiolar trauma, insertion into the vestibule and electrode
transposition into S. vestibuli. In such
cases, bony cochleostomy is preferred.
hearing after CI is a notable accomplishment.
Although current studies suggest that CI outcomes may not be improved by
hearing preservation (unless there is aidable hearing, especially speech
recognition), there is evidence that the electrical dynamic range is larger
when some hearing is preserved, which could be advantageous.1 Current methods of preserving residual hearing
after CI include surgical technique, electrode design and the use of
Cochleostomy is used here to mean an enduring opening into the cochlea through which a CI electrode is inserted. There are currently three leading categories of cochleostomy:
The original round window cochleostomy used with short, single channel implants by Wm. House and currently used with certain electrodes to conserve residual hearing,
Traditional bony cochleostomy, suggested by Graeme Clark to avoid misdirection of long multichannel electrodes by the crista fenestra,
Extended RW cochleostomy, consisting of extension of the RW by drilling labyrinthine bone antero-inferiorly in cases where the RWM is too small or angled too inferiorly to use effectively.
Helge Rask-Andersen and his colleagues at Uppsala University continue their remarkable work on the anatomy of the hook portion of the cochlea that is relevant to hearing conservation during cochlear implantation. In their detailed description of the hook region in 2014, they conclude that there may be anatomic reasons to prefer RW insertions in hearing conservation cases.1
The Impact of Maturational Changes in Cochlear Position on Cochlear Implantation
Thomas J. Balkany, MD
Three dimensional CT imaging provides good data regarding
the positional changes in normal temporal bone development. Attention has been focused on the position of
the basal turn in relation to other structures of the temporal bone. The
following studies demonstrate that such changes occur rapidly between birth and
4 years of age and then may occur slowly until adulthood with a possible bump
McRackan et al (2012) found age-related variation between
adults and children in the orientation of the facial recess to the round window
membrane (RWM). 1 Children had greater angulation than adults
averaging 6.2°(p=0.01) between adults and children. Thus surgeons can expect a narrower view of
the RWM in children and may find slightly more difficulty in electrode
insertion. The authors also showed that
maturation of the EAC over time simplifies the approach to the facial recess
and RWM. The angle between the facial
recess and EAC is more acute (tighter) in young children. This supports the findings of Lloyd et al
(2010) who showed that the axis of the inferior segment of the basal turn
becomes more parallel to the axis of the trans-mastoid approach angle over time.2
clinical term cochlear nerve deficiency has been established in the otologic
literature to indicate a small or absent cochlear nerve on MR imaging. To the
best of my knowledge it was first described by the Antwerp cochlear implant group in 1997.1
More recently, Buchman, Adunka and colleagues at UNC have shown that
cochlear nerve deficiency (CND) is more common than previously recognized in CI
candidates. CND may account for up to
20% of those with OAE/SP/ABR indications of auditory neuropathy spectrum