Download Total # Spiral Ganglion Cells

Patterns of neural degeneration in the human
cochlea and auditory nerve: Implications for
cochlear implantation
JOSEPH B. NADOL, Jr, MD, Boston, Massachusetts
Although the identity of all the variables that may influence speech recognition after
cochlear implantation is unknown, the degree of preservation of spiral ganglion cells is
generally considered to be of primary importance. A series of experiments in our laboratories, directed at quantification of surviving spiral ganglion cells in the profoundly deaf,
evaluation of the predictive value of a variety of clinical parameters, and the evaluation of
the consequences of implantation in the inner ear, is summarized. Histologic study of the
inner ears of patients who were deafened during life demonstrated that the cause of deafness accounted for 57% of the variability of spiral ganglion cell counts. Spiral ganglion cell
counts were highest in individuals deafened by aminoglycoside toxicity or sudden idiopathic deafness and lowest in those deafened by postnatal viral labyrinthitis, congenital or
genetic deafness, or bacterial meningitis. Study of the determinants of degeneration of the
spiral ganglion revealed that degeneration is most severe in the basal compared with the
apical turn and more severe when both inner and outer hair cells are absent. Unlike the
findings in some experimental animal studies, no survival advantage of type II ganglion
cells could be identified. There was a strong negative correlation between the degree of
bony occlusion of the cochlea and the normality of the spiral ganglion cell count.
However, even in specimens in which there was severe bony occlusion, significant numbers
of spiral ganglion cells survived. A strong positive correlation between the diameter of the
cochlear, vestibular, and eighth cranial nerves with the total spiral ganglion cell count (p <
0.001) was found. This would suggest that modern imaging techniques may be used to predict residual spiral ganglion cell population in cochlear implant candidates. Trauma from
implantation of the electrode array was studied in both cadaveric human temporal bone
models and temporal bones from individuals who received implants during life. A characteristic pattern of damage to the lateral cochlear wall and basilar membrane was identified in the upper basal turn. New bone formation and perielectrode fibrosis was common
after cochlear implantation. Despite this significant trauma and reaction, there is no firm
evidence that further degeneration of the spiral ganglion can be predicted as a consequence. (Otolaryngol Head Neck Surg 1997;117:220-8.)
A
l thet identity
h ofo all uthe variables
g hthat may
influence the success of speech recognition after
cochlear implantation is unknown, the degree of preset-
Supported by grant no. 5P01 DC00361 from the National Institute on
Deafness and Other CommunicationDisorders, National Institutes
of Health.
Presented at the Sixth Symposiumon CochlearImplants in Children,
Miami Beach, Fla., Feb. 2-3, 1996.
Reprint requests: Joseph B. Nadol, Jr, MD, Department of
Otolaryngology,Massachusetts Eye and Ear Infirmary,243 Charles
St., Boston, MA 02114.
Copyright © 1997 by the American Academy of OtolaryngologyHead and Neck SurgeryFoundation, Inc.
0194-5998/97/$5.00 + 0 23/1/75094
220
vation of spiral ganglion cells is generally considered to
be of primary importance. 1 Therefore an understanding
of the degenerative patterns of the spiral ganglion in the
multiple causes that result in profound deafness would
be useful. Based on correlation between spiral ganglion
cell counts from temporal bone studies and premortem
clinical parameters such as age, sex, comorbidity, cause
of deafness, radiologic findings, and duration of deafness, a formula for predicting spiral ganglion cell counts
in implant candidates could theoretically be developed,
The strength of correlation between performance of
cochlear implant recipients, as judged by speech-recognition scores, and predicted spiral ganglion cell counts
could then be calculated. Finally, if such correlations are
OtolaryngologyHead and Neck Surgery
NADOL 221
Volume 117 Number 3 Part 1
strong, prognostication of success of cochlear implantation in a given candidate might be possible, based on
predicted spiral ganglion cell counts.
Insertion of an implant electrode will result in trauma to the inner ear. Based on limited human and animal
temporal bone data, the long-term consequences of
implantation on survival of spiral ganglion cells remain
controversial.
The purpose of this article is to summarize a series
of experiments in our laboratories, directed at quantification of surviving spiral ganglion cells in the profoundly deaf, evaluation of the value of a variety of
clinical parameters in predicting residual spiral ganglion cell counts, and evaluation of the consequences of
implantation on the inner ear.
METHODS AND MATERIAL
Archival Temporal Bone D a t a b a s e
From the temporal bone collection at the
Massachusetts Eye and Ear Infirmary, 93 temporal
bones from 66 patients who, during life, had documented profound sensorineural loss were used for this
study. Of these, nine temporal bones were from six
patients who in life suffered profound sensorineural
loss as a result of bacterial meningitis. To evaluate the
correlation between the diameter of the cochlear nerve
and the survival of spiral ganglion cells, 47 temporal
bones were analyzed. Of these, 42 were from patients
with a clinically documented history of profound deafness, and five were from patients with normal hearing.
In each instance only one temporal bone per individual
was evaluated. For each patient the cause of deafness,
age at onset of hearing loss, duration of hearing loss,
age at onset of total deafness, and duration of total
deafness were documented.
In an effort to understand the implications of the
presence of labyrinthitis ossificans for spiral ganglion
cell survival, a quantitative study of six temporal bones
from individuals who were profoundly deafened by
bacterial meningitis was evaluated. The severity of
labyrinthitis ossificans was quantified by estimating the
percentage of the volume of the membranous labyrinth
replaced by new bone. The segmental and total spiral
ganglion cell counts were compared with age-matched
control subjects to determine the percent normality of
residual spiral ganglion counts per segment and in
total. 2
All temporal bones were fixed in Heidenhain-Susa
solution or 10% buffered formalin, decalcified in
trichloroacetic acid or ethylenediamine tetraacetic acid
(EDTA), and embedded in celloidin. The temporal
bones were sectioned at a thickness of 20 gm in the
Table 1. Pearson c o r r e l a t i o n coefficients with spiral
g a n g l i o n c o u n t ( o n e e a r from e a c h person)
Variable
Correlation
Sex
Age at death
Age at onset of hearing loss
Duration of hearing loss
Age at onset of deafness
Duration of deafness
-0.10
-0.24
0,22
-0.41"
0.18
-0.401-
From NadolJB Jr, YoungYS, Glynn RJ. Ann Otol RhinolLaryngol
1989;98:414-6.
*p < 0.001.
tp < 0.01.
horizontal plane. Every tenth section was stained with
hematoxylin and eosin and mounted on glass slides.
To understand the cellular patterns of degeneration
of the spiral ganglion better, an additional 12 human
pathologic specimens and two normal neonatal specimens, in which fixation was achieved within 4 1/2
hours after death, were evaluated. All specimens were
fixed in 2% paraformaldehyde and 2% glutaraldehyde
in 0.1 mol/L phosphate buffer at pH 7.2 by perilymphatic perfusion through the oval and round windows
before necropsy. After removal of excess bone, the otic
capsule was thinned with a power drill and the specimens were decalcified i t 0.1 mol/L disodium EDTA
with 1.25% glutaraldehyde in 0.1 mol/L phosphate
buffer. The tissue was then stained en bloc with aqueous uranyl acetate, dehydraded in graded alcohols,
and embedded in epon resin. For these studies, sections were cut at 2 gm and stained with 1% toluidine
blue.
Finally, temporal bones from humans who had
received a cochlear implant during life and cadaveric
human temporal bones in which cochlear implantation
was done postmortem were evaluated by light
microscopy to assess patterns of cochlear injury
induced by the implantation process. These specimens
were fixed in 10% buffered formalin, decalcified in
buffered EDTA, stained en bloc with aqueous uranyl
acetate, and embedded in araldite to allow serial sectioning of the temporal bone at a thickness of 35 gm
with the electrode array maintained in situ. 3,4
Data Analysis
Graphic reconstruction of serial sections by a
method described previously5,6 were done. Statistical
methods included analysis of variance, t tests, Pearson
correlation coefficients, and multiple linear regression
analysis with the BMDP statistical software. 7
Quantification of spiral ganglion cell counts was done
by segmental analysis 6 or segmental density measurements, s
OtolaryngologyHead and NeckSurgery
September 1997
222 NADOL
Total # Spiral Ganglion Cells
35,000
Sudden idiopathic SNHL ( n - 6)
30,000
Aminoglycoside ototoxicity (n - 8)
25,000
Normal hearing (n : 5)
20,000
t
15,000
10,000
5,000
-
m
m
Neoplasm of temporal bone (n = 8)
Bacterial labyrinthitis (n 11)
Congenitalor genetic (n 9)
Postnatalviral labyrinthitis (n 8)
Fig. 1. Means and standard deviations of spiral ganglion cell counts in six most common
diagnostic categories and five individuals with normal hearing. (SNHLSensorineural hearing
loss.) (From Nadol JB Jr, Young Y-S,Glynn RJ. Ann Otol Rhinol Laryngol 1989:98;411-6.)
Table 2, Summary of multiple linear regression
analysis predicting total spiral ganglion cell c o u n t
for ears from diagnostic groups 1, 3, 5, 6, 8, a n d 10"
Variable
Diagnostic group 3t
Diagnostic group 51Diagnostic group 6t
Diagnostic group 81Diagnostic group 10t
Age at death (yr)
Age at deafness (yr)
Sex++
Constant
Coefficient
Standarderror
14,795'
5,293
11,029§
2,871
12,524~
-36.2
-14.8
400
9,283
4,452
3,458
4,934
3,510
4,271
56.5
55.9
2,259
--
Reprinted with permission from Nadol JB Jr, Young Y-S, Glynn RJ. Ann
Otol Rhinol Laryngol 1989;98:414-6.
R2 = 0.446; R2 for a model containing only the five indicators of diagnostic groups = 0.425.
*One ear was chosen from each patient for a total of 49 ears (one ear
was deleted because age of deafness was unknown).
1Coefficients for a diagnostic group estimate the mean difference in
counts between ears from that diagnostic group and ears from diagnostic group 1.
::p < 0.01.
§p < 0.05.
++The coefficient of sex estimates the mean difference in counts
between ears of men and ears of women.
RESULTS
Correlation of Survival of Spiral Ganglion Cells
with Age, Duration, and Cause of Deafness
The results of bivariate analysis of the correlation of
total spiral ganglion cell counts with a number of clinical variables is displayed in Table 1. Spiral ganglion
cell counts were generally lower in older compared
with younger deaf individuals. The total spiral ganglion
cell count tended to be negatively correlated with duration of hearing loss and deafness. The only correlations
that reached statistical significance were between total
spiral ganglion cell counts and duration of hearing loss
and duration of total deafness. 9
Analysis of variance indicated that the mean total
spiral ganglion cell counts were not equal across the six
most common diagnostic groups (postnatal viral
labyrinthitis, sudden idiopathic deafness, bacterial
labyrinthitis, tumor of temporal bone or cerebellopontine angle, congenital or genetic causes, and aminoglycoside ototoxicity). Multiple regression analyses were
performed with data from the 49 ears in the six most
common diagnostic categories. The diagnostic grouping accounted for 57% of the variability in spiral ganglion cell count. Thus the major determinant of spiral
ganglion cell count at death was the diagnostic category rather than the age at death, duration of deafness, or
duration of hearing loss (Table 2). The means and standard deviations of spiral ganglion cell counts in the six
most common diagnostic categories and five individuals with normal hearing are shown in Fig. 1. Thus spiral ganglion cells from individuals who were deafened
by sudden idiopathic sensorineural loss or aminoglycoside ototoxicity were among the highest, whereas those
from individuals deafened from congenital or genetic
causes or postnatal viral labyrinthitis were among the
lowest counts. In summary, the contribution of age and
duration of deafness were much less significant than the
OtolaryngologyHead and Neck Surgery
Volume 117 Number 3 Part 1
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Fig. 2. Scatter plot of percent survival of type II spiral ganglion cells and all spiral ganglion cells in 12 pathologic
and two normal human spiral ganglia, suggesting that
survival of type II cells is highly correlated with survival of
entire spiral ganglion. This suggests that there is no survival advantage for type II ganglion cells. (From
Zimmermann CE, Burgess BJ, Nadol JB Jr. Hear Res
1995:90;192-201.)
Fig. 3. Histogram of mean and standard deviation of spiral ganglion (SGC) cell count by maximum diameter of
cechelar nerve (C.N,). (From Nadol JB Jr, Xu W-Z.Ann Otol
Rhinol Laryngol ]992;]01:988-93.)
%NORMAL SPG
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cause of deafness. Insofar as the cause of deafness is
known in many candidates for cochlear implantation,
this clinical variable would seem to be a valuable prognosticator of spiral ganglion cell count and by extension, perhaps, valuable for prognostication of success
with cochlear implantation. However, there was considerable variability of total spiral ganglion cell count
within each diagnostic category. In addition, the minimum requisite number of functioning spiral ganglion
cells and their optimal distribution along the cochlear
partition is not known. Finally, the presence of the spiral ganglion cell as determined histopathologically does
not guarantee that it was functioning normally during
life. In an effort to validate the prognostic utility of estimating spiral ganglion cell count, the NU-6 scores of
i6 recipients of cochlear implants with greater than 6
months' experience with the speech processor were correlated with the spiral ganglion cell counts. The correlation was low (R = 0.32), suggesting that spiral ganglion cell count alone may be a poor predictor of success.
P a t t e r n s of D e g e n e r a t i o n
Ganglion
in t h e H u m a n Spiral
!n a study of 12 human pathologic specimens and
two normal neonatal specimens, the patterns of degeneration of the human spiral ganglion and their correlation with degeneration of the organ of Corti, age, sex,
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Fig. 4. There was negative correlation between spiral ganglion ($PG) count expressed as percentage of normal
and degree of bony occlusion expressed as percentage
of volume of cochlea. (From Nadol JB Jr, Hsu W. Ann Otol
Rhinol Laryngol 1991;100:712- 6.)
duration of deafness, and cochlear location were evaluated. 1° Degeneration of the spiral ganglion was significantly greater for the basal one half compared with the
apical one half of the cochlea (p < 0.001). Linear
regression analysis demonstrated a strong correlation
between the presence of the organ of Corti and the density of type I spiral ganglion cells. In the pathologic
specimens, the prevalence of type II ganglion cells as a
OtoiaryngologyHead and Neck Surgery
224 NADOL
September 1997
Table 3. C o r r e l a t i o n o f spiral g a n g l i o n c o u n t a n d n e r v e d i a m e t e r s w i t h h e a r i n g status ( t test)
Parameters
Spiral ganglion count
Maximum diameter of cochlear nerve (mm)
Maximum diameter of vestibular nerve (mm)
Maximum diameter of eighth cranial nerve (mm)
Normal (n = 5)*
27,304
1.04
0.98
2.02
+ 4,203 (23,103-31,932)
_+0.11 (0.90-1.20)
_+0.08 (0.90-1.10)
+ 0.08 (1.90-2.10)
15,463
0.81
0.76
1.57
Deaf (n = 42)*
p Value
+ 7,838 (0-29,997)
_+0.15 (0.50-1.20)
_+0.12 (0.50-1.00)
_+0.26 (1.00-2.10)
0.0008
0.0067
0.0019
0.0001
Reprintedwith permissionfrom Nadol JB Jr, Xu W-Z. Ann Otol Rhinol Laryngo11992;101:988-93.
*Data are expressedas mean + SD (range).
percentage of the total remaining spiral ganglion cell
population in each segment ranged from 0% to 17%,
with an average of 8.6%. There was no significant correlation between the prevalence of type II ganglion cells
and age, sex, or duration of deafness or the degree of
degeneration of the spiral ganglion as a whole. Similar
to the findings for type I ganglion cells, there was a
strong correlation between the survival of type II ganglion cells and the preservation of the organ of Corti. As
shown in Fig. 2, there was a strong correlation between
survival of type II cells with survival of the spiral ganglion as a whole and, hence, no obvious survival advantage for the type II cell, compared with the type I cell.
Correlation of the Diameter of the Nerve Trunks
of the Internal Auditory Canal with Remaining
Spiral Ganglion Cell Count
Given the sizeable variability of spiral ganglion cell
counts with other clinical parameters such as cause of
deafness, age, and duration of deafness, a histologic
correlation between the diameter of the eighth, auditory, and vestibular nerves in the internal auditory canal
with the total spiral ganglion cell count was done in 42
individuals with clinically documented profound deafness, who in life would have been candidates for
implantation, and in five temporal bones from patients
with normal hearing, u The diameters of the nerve
trunks were measured at their points of maximum
diameter in the internal auditory canal. As shown in
Table 3, the total spiral ganglion cell count and maximum diameters of the cochlear, vestibular, and eighth
cranial nerves were significantly smaller in the deaf
population than in the normal-hearing group.
According to the Pearson correlation, the maximum
diameter of the cochlear, vestibular, and eighth cranial
nerves was strongly correlated with the spiral ganglion
cell count (p = 0.0006, p = 0.0001, and p = 0.0003,
respectively, and Fig. 3). However, there is considerable
overlap in the range of diameters of cochlear nerves in
deaf and hearing ears. Nevertheless, it would seem reasonable that modern imaging techniques, which are
capable of demonstrating the soft tissue contents of the
internal auditory canal, may be considered a way of
evaluating residual spiral ganglion cell preservation.
Implications of the Presence of Labyrinthitis
Ossificans
Labyrinthitis ossificans, or new bone formation
within the cochlea, is a common finding in temporal
bones from individuals who were deafened by bacterial
meningitis. 12,13Despite the mechanical impediments to
implantation, the presence of labyrinthitis ossificans is
now considered only a relative, rather than absolute,
contraindication to cochlear implantation. 13,14 As
shown in Fig. 4, there was a statistically significant negative correlation between the percent bony occlusion
and the percent normal spiral ganglion cell count. In all
cases in which the segmental and total bony occlusion
was less than 10%, there was at least 30% of the normal
segmental and total spiral ganglion cell densities.
Expressed in another way according to Pearson correlations, a statistically significant negative correlation (p <
0.05) was found between spiral ganglion cell counts
and the presence of bony occlusion in segments 2 (7 to
15 mm) and 4 (23 mm to apex). For all four segments
of the cochlea there was a negative correlation, weakest
in segment 1 (0 to 6 mm; r = -0.30), between the degree
of bony occlusion and spiral ganglion cell counts.
Therefore because significant degrees of bony occlusion can be determined before surgery by computed
tomography, it is possible to predict before surgery that
severe degrees of bony occlusion will be correlated
with lower total spiral ganglion cell counts. Hence if the
hearing levels are comparable in both ears, this study
would predict that the ear with less bony occlusion
would have a higher spiral ganglion cell count and perhaps a highler likelihood of success with the cochlear
implant. However, it is important to recognize that even
in those specimens in which there was severe bony
occlusion, significant numbers of spiral ganglion cells
survived. Total absence of spiral ganglion cells was not
found in any specimen with labyrinthitis ossificans
after bacterial meningitis.
Evaluation of Implantation Trauma to the Inner
Ear
A major potential factor determining long-term survival of cochlear neurons, particularly in the pediatric
population, is the degree of trauma to the inner ear dur-
OtolaryngologyHead and Neck Surgery
NADOL 225
Vorume 117 Number 3 Part 1
Fig. 5. In cadaveric human temporal bone in which cochlear implanation was done postmortem, bone chips (BC) were carried into upper basal turn by advancing electrode array.
(Original magnification ×138.)
Fig. 6. Sixty-seven-year-old patient received cochlear implant in right ear 2 years before
death. Electrode array (EA) in midbasal turn is surrounded by fibrous tissue (F). (Original
magnification ×55.)
ing the process of implantation. This may not only
impact survival of spiral ganglion cells after implantation but also influence the ease of changing an electrode
array if necessary.
In a study of temporal bones in which cochlear
implantation was done, a characteristic pattern of damage to the lateral cochlear wall in the 8 to 15 mm region
was found. This consisted of damage to the spiral ligament and in some cases displacement or even disruption of the basilar membrane. Even without obvious
intracochlear mechanical impediment such as presence
of new bone, the electrode array may pass from the
scala tympani into the scala media or scala vestibuli. In
these cadaveric specimens, particles of bone from the
OtolaryngologyHead and Neck Surgery
226 NADOL
September 1997
Fig. 7. Seventy-two-year-old man received cochlear implant in his right ear 7 years before
death, Here in the basal turn of the cochlea, a bail electrode (BE) is encased in new bone
(NB) in the scala tympani, indicating that new bone formation occurred after implantation.
(Original magnification x55.)
round window cochleostomy were often carried deep
within the inner ear with the advancing electrode array
(Fig. 5). In an evaluation of in vivo implantations a similar pattern of damage to the cochlear wall was identified. Evidence for perielectrode fibrosis (Fig. 6) and
some degree of new bone formation after implantation
was also found (Fig. 7). However, despite this significant trauma, as judged from histopathologic study of
humans with implants, there is evidence that postimplantation degeneration of the spiral ganglion as a consequence of implantation is not severe. For example, in
one case in which implantation was done during life
and in which there was significant trauma to the basilar
membrane (Fig. 8) there was little apparent impact on
spiral ganglion counts (Fig. 9).
DISCUSSION
A l t h o u g h all the parameters that influence the success of cochlear implantation as judged by speech
recognition scores are unknown, the preservation of
spiral ganglion cells is considered to be of primary
importance. 1 Our ability to predict spiral ganglion cell
preservation accurately from individual to individual or
between ears in the same individual would therefore be
valuable clinical information for the purpose of prognosticating success or selecting the ear to be implanted.
Study of the temporal bone from humans who in life
were deaf has indicated that spiral ganglion cell count
decreases with age and the duration of deafness.
However, the most significant predictor of spiral ganglion cell count appears to be the cause of deafness.
Specimens from individuals who were deafened by
aminoglycoside ototoxicity or sudden idiopathic sensorineural hearing loss had significantly higher residual spiral ganglion cell counts than those deafened by
postnatal viral labyrinthitis or congenital or genetic
causes.
In evaluating the differential survival of types I and
II spiral ganglion cells, no survival advantage for type
II ganglion cells was identified in the human. This differs from the findings in some animal studies in which
a positive survival advantage of type II ganglion cells
was identified after trauma to the organ of Corti 15 or
ototoxic insult. 16 The finding in the human of no survival advantage of type II ganglion cells suggests that in
ears with reduced total spiral ganglion cell count
approximately 85% to 90% of the residual spiral ganglion cells will be of the type I variety, which are
thought to be of primary importance for the detection of
the acoustic signal.
The demonstration of a positive correlation between
the residual spiral ganglion cell population and the
diameter of the cochlear, vestibular, and eighth nerve
trunks in temporal bone specimens provides optimism
that preoperative imaging of potential candidates for
cochlear implantation may prove to be a useful prognostic tool.
The identification of labyrinthitis ossificans, or new
OtolaryngologyHead and Neck Surgery
NADOL 227
Volume 117 Number 3 Part 1
Fig. 8. Unstained 35 ~m axial section of implanted right ear in 62-year-olcl woman who
became deaf after intravenous gentamycin 5 years before implantation. Electrode array
(EA) was sectioned in situ. Disruption of basilar membrane (BM) is shown on left approximately 11 mm from round window membrane and displacement of basilar membrane is
shown on right approximately 18 mm from round window membrane. (Original magnification x28.) (From Nadol JB Jr, Ketten DR, Burgess BJ. Laryngoscope 1994;104:299-303.)
bone formation within the cochlea, as can be evaluated
before surgery by computed tomography, predicts a
reduced population of residual spiral ganglion cells.
Therefore if other indications are equal, the ear with the
smaller amount of new bone formation would be predicted to have the higher spiral ganglion cell count. On
the other hand, the presence of even severe labyrinthitis
ossiflcans does not predict total loss of the spiral ganglion population.
Cochlear implantation in the human results in a predictable pattern of trauma to the inner ear. Previous
studies have demonstrated significant trauma to the spiral ligament and basilar membrane near the site of
insertion and at the 8 to 15 mm region or ascending segment of the basal turn. 17-21 In addition, in human temporal bone specimens from individuals who received a
cochlear implant during life, there is evidence to suggest that new bone formation may occur after implantation. This may be due to the original cause of deafness,
new bone introduced into the cochlea at the time of
implantation, or damage to the cochlear blood supply
from trauma to the lateral cochlear wall or basilar membrane at the time of implantation.
The effects of implantation on the spiral ganglion
cell count are less clear. In some studies 2°22 a decrease
in the number of spiral ganglion cells on the implanted
side compared with the nonimplanted side was identi-
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Fig. 9. Calculated segmental spiral ganglion cell counts
for imlanted and unimplanted side of patient described
in Fig. 8, compared with average data for normal adult
cochleae, patients with ototoxic deafness, and predicted
counts for patient calculated by regression analysis. 8,9
(From Nadol JB Jr, Keften DR, Burgess BJ. Laryngoscope
1994; 104:299-303.)
fled. In other studies no signficant effect of implantation was identified in either in humans 4J9,23 or animals. 24,25 However, some reports have demonstrated
improved survival of residual spiral ganglion cell
228 NADOL
counts on the implanted versus nonimplanted side in
the experimental animal. 26,27
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1. Clopton BM, Spelman FA, Miller JM. Estimates of essential
neural elements for stimulation through a cochlear prosthesis.
Ann Otol Rhinol Laryngol Suppl 1980;89:5-7.
2. Nadol JB Jr, Hsu W. Histopathologic correlation of spiral ganglion cell count and new bone formation in the cochlea following meningogenic labyrinthitis and deafness. Ann Otol Rhinol
Laryngol 1991;100:712-6.
3. Ketten DR, Nadol JB Jr, Burgess BL Short-term effects of multiple electrode implants. Abstracts of the Fourteenth Midwinter
Research Meeting, Association for Research in Otolaryngology,
1991:114.
4. Nadol JB Jr, Ketten DR, Burgess BJ. Otopathology in a case of
multichannel cochlear implantation. Laryngoscope 1994;104:
299-303.
5. Schuknecht HF.,Techniques for study of cochlear function and
pathology in experimental animals: development of the anatomical frequency scale for the cat. Arch Otolaryngol 1953;58:37797.
6. Otte J, Schuknecht I-IF, Kerr AG. Ganglion cell populations in
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7. Dixon WJ, editor. BMDP statistical software. Berkeley,
California: University of California; 1985.
8. Nadol JB Jr. Quantification of human spiral ganglion cells by
serial section reconstruction and segmental density estimates.
Am J Otolaryngol 1988;9:47-51.
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10. Zimmerman CE, Burgess BJ, Nadol JB Jr. Patterns of degeneration in the human cochlear nerve. Hear Res 1995;90:192-201.
11. Nadol JB Jr, Xu WZ. Diameter of the cochlear nerve in deaf
humans: implications for cochlear implantation. Ann Otol
Rhinol Laryngol 1992;101:988-93.
12. Eisenberg LS, Luxford WM, Becker TS, House WE Electrical
sltimulation of the auditory system in children deafened by
meningitis. Otolaryngol Head Neck Surg 1984;92:700-5.
O|olaryngologyHead and NeckSurgery
September 1997
13. Balkany T, Gantz B, Nadol JB Jr. Multichannel cochlear
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