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Human Cochlear Implant Histopathology
Xu XH1,2, MD, Cureoglu S2, MD, Maher S1, MD, Pollak N2,MD, Froymovich O2, MD,
Paparella MM2, MD
1Department
of Otolaryngology, H & N Surgery, Loma Linda University Medical Center, Loma Linda, CA
2Paparella Ear, Head and Neck Institute, Minneapolis, MN
2 International Hearing Foundation, Minneapolis, MN
Abstract
A
C
.
Objectives:
1) to examine the histopathology of multi-channel cochlear implant temporal bones
2) to evaluate the relationship of residual spiral ganglion cell counts and clinical hearing
performance
Methods:
Eight temporal bones from 4 cochlear implant patients were prospectively examined histologically.
Paired comparisons were made between implanted and non-implanted temporal bones. Clinical
performance data was obtained from patient charts.
Results:
There were varying amounts of inflammation (fibrosis and ossification) at the basal turn of the cochlea
in all 4 implanted temporal bones. Compared to non-implanted sites, two implanted bones with less than
a 10 year duration of implantation had no significant changes of spiral ganglion cell population. One
case with prolonged implant duration (15 years) showed a 36% decrease of spiral ganglion cells at the
implanted site. The case with the best speech recognition (89% with CID sentence) had the lowest
residual spiral ganglion cells (30% of normal spiral ganglion cell population). Two cases with poor
clinical performance (<10% with CID sentence) had residual spiral ganglion cells of 11% and 22%. The
case with moderate clinical performance (30% with CID sentence) had 14% of normal spiral ganglion
cell population. Surviving dendritic cells varied from 5% to 30% among 4 cases with no relationship to
clinical performance.
Conclusion:
Our findings suggest prolonged implantation may affect spiral ganglion cell population. Although our
data does show a trend toward a reverse relationship between residual spiral ganglion cells in implanted
temporal bones and speech performance (as previously reported), we were unable to obtain statistical
significance due to small sample size
B
Fig. 2. a. This section (case 2, left ear) shows an
electrode tract (A) inside the scala tympani at the
basal turn of cochlea at the level of round window .
There is extensive fibrous reaction inside scala
tympani (B). (Hematoxylineosin, magnification x 2). A
coincidental finding of cochlear otosclerosis (C)
Fig. 2. b. Higher magnification ( x 4 ) of the framed
area shows significant inflammatory reaction around
the electrode with inflammatory cell infiltration and
neovasculization. Organ of Corti and Stria vascularis
appear atrophic with a decrease of type II and type III
fibrous cells in the spiral ligament.
Case 3. This patient had a history of bilateral Meniere’s disease and several endolymphatic sac
surgeries. He eventually lost hearing completely in both ears. He received his cochlear implant on
the left ear 10 years after deafness at the age of 67. Following implantation, he continued to have
difficulty with vertigo and had no improvement of hearing.
A
Introduction
A
A
Patients with severe to profound sensorineural hearing loss will benefit from cochlear implantation
for speech perception. However, this benefit varies significantly from patient to patient. Many
studies have been conducted to try to identify possible predictors for improved clinical performance,
but at present, no definitive factors have been found for this variation. Studying the histopathology
of temporal bones from living donors who have received cochlear implants will help to elucidate
this matter further.
Methods and Materials
A total of eight temporal bones from four patients with unilateral cochlear implants were studied.
Clinical information was retrieved from chart review. For each implanted temporal bone, the
following data was evaluated: trauma at the cochleostomy site; damages to basal membrane, Organ
of Corti, spiral ligaments and stria vascularis; inflammatory reaction including new bone formation
and fibrosis; as well as viable spiral ganglion cell counts and dendrites. The implanted bones were
compared with the non-implanted bones in each case. Spiral ganglion cells and dendrite cell counts
were measured. The relationship between SGC counts and auditory outcomes was also studied.
Results
TABLE 1
Clinical Information of Patients
Case
Side
No. Gender of CI
Etiology
of Deafness
Deaf
Duration
(yr)
Age at Duration Age at
CI of CI (yr) Death
1
M
L
Unknown
5
70
2
72
2
3
4
F
M
M
L
L
R
Ototoxicity
Meniere’s
Cochlear Otosclerosis
50
10
3
46
58
51
7
9
15
53
67
66
Cause of
Death
Unknown
S/p bypass
surgery
Heart attack
Stroke
B
A
Fig. 3. (case 3, left ear) In this implanted temporal
bone section at the level of the round window, the
electrode path (A) is seen in scala tympani at the
basal turn of the cochlea. Severe new bone
formation (B) and a fibrous sheath around the
electrode occupy the entire scala tympani.
(Hemtoxylineosin, magnification x 2)
Fig. 4. This section of a temporal bone (case 3, left side)
shows evidence of endolymphatic hydrops with
distortion of Reissner’s membrane (A).
Case 4. This patient had a history of
progressive hearing loss secondary to noise
exposure according to clinic history.
However the temporal bone study shows
the true cause of deafness to be bilateral
severe cochlear otosclerosis. He
underwent an attempted right cochlear
implant at age of 51, 3 years after bilateral
deafness. At the time of surgery, entrance
into the cochlea was hindered by bony
obstruction at the level of the round
window. Three months later, right cochlear
implantation was completed with direct
drilling into the promontory. The patient
benefited from cochlear implantation with
improvement of his CID sentences scores
from 5% to 50% post-implantation .
D
E
A
B
C
Fig. 5. This is a section of an implanted temporal
bone (case 4, right ear) at the level of the
cochleostomy site (A) shows surgical trauma at the
promontory following cochleostomy. Initial attempt
at electrode insertion at the routine cochleostomy
site failed. The scala tympani is completely
occluded with bony structures (B), severe and
extensive cochlear otosclerosis is shown in otic
capsule (C). The electrode tract (D) appears within
the scala vestibuli with significant new bone
formation (E) around the electrode which extends
onto the cochleostomy site.
TABLE 2.
Spiral Ganglion Cell (SGC) Counts of implanted bones and non-implanted bones
CI = cochlear implant.
Case 1. This is a patient who is status post right acoustic neuroma resection via a
translabyrinthine approach at the age of 63. He had progressive hearing loss of his left ear
within 5 years prior to cochlear implantation due to unknown etiology. His pure tone average
(PTA) of the left ear was 100dB with 28% SDS prior to implantation. The patient received a
Clarion AB 5000 cochlear implant at the age of 70. He was doing very well with his cochlear
implant. CID Sentences scores improved from 18 to 68 after implantation.
Basal turn
Middle turn
Apex
case No. implant non-imp implant non-imp implant
1
2826
N/A
2556
N/A
1098
2
7614(1%) * 7722 4968
4221
288
3
5346(24%) * 7074 3726
4068
693
4
3537(36%)* 5553 1233
5022
0
Total
non-imp implant non-imp
N/A
6480
N/A
549
12492
891
9765
12033
360
4770
12870
* (%): SGC counts decrease in percentage compared with non-implant bone
Case 2. This is a young woman who lost her hearing at 3 years of age secondary to drug induced
ototoxicity. She received her cochlear implant at the age of 46. The patient showed significant
benefit from the cochlear implant: Her post implant CID everyday sentence test after 12 months
improved from 6% to 89%.
Case #4
20
80
00
70
00
60
00
0
50
00
Fig. 1. b. Higher magnification (x10) of the area
C shows an empty appearance of Rosenthal
canal at ascending limb of basal turn of
cochlear. This is the case with the lowest spiral
ganglion cells in our series.
Case #3
40
40
00
Fig 1a. Midmodiolar histologic section of
temporal bone (case 1, left ear) showing
distortion of basal membrane (A) and fracture of
osseous spiral lamina (B) at basal turn of
cochlear caused by electrode insertion. Spiral
ligament, stria vascularis and organ of Corti
appear atrophic. (Hematoxylineosin,
magnification x 2).
Case #2
30
00
C
Case #1
60
20
00
B
80
10
00
A
100
0
Post-implant Best CID sentence score
(%)
Relationship Between Speech Perception Score and Basal
Turn SGC Counts
SGC counts at basil turn of cochlear
Conclusions
1. Cochlear implants caused varied degrees of inflammation and trauma to cochlea
2. Prolonged implantation may affect spiral ganglion cell population
3. There is no reverse relationship between residual spiral ganglion cells in implanted temporal
bones to clinical speech performance observed from our limited cases. Studies of a larger number
of cases are needed.