Speech and Hearing after Cochlear Implantation in Children with Inner Ear Malformation and Cochlear Nerve Deficiency


Anomalies

Number of ears

Number of patients

Inner ear

Common cavitya

10

10

IP-I

13

11

IP-II

18

14

EVA

9

7

CH-IIIb

6

3

Lateral canal hypoplasia

1

1

unclassifiedc

3

3

Internal auditory canal

IAC stenosis

3

2

CNC stenosis

6

6

Total

69

57


CC common cavity, IP incomplete partition, EVA enlarged vestibular aqueduct, CH cochlear hypoplasia, IAC internal auditory canal, CNC cochlear nerve canal

aFive ears were with cochlear nerve deficiency

bTwo patients had CHARGE syndrome, three ears with IAC stenosis, one ear with CNC stenosis, and two ears with duplicate IACs

cWaardenburg syndrome, CHARGE syndrome, and Down syndrome with inner ear anomaly





12.2 Speech Perception in CC, IP-I, and IP-II



12.2.1 Introduction


Common cavity anomaly lacks separation between the cochlear and vestibular part of the inner ear. In contrast, the cochlear and vestibular regions are individually identified in the inner ear of IP-I and IP-II, but both lack bony partitions within the cochlea, partly or completely. While the osseous structure of the basal turn including the modiolus is formed in IP-II, the bony modiolus is missing in IP-I. Thus, the primary auditory neurons exist at the center of the cochlea in IP-II, while the distribution of auditory neurons of IP-I varies and is not always located at the central region in the cochlea. Since patients with common cavity and IP-I anomalies have profound deafness at birth, cochlear implantation is the only strategy for them to obtain auditory perception. In contrast, patients with IP-II anomaly often have residual hearing, primarily in low frequencies, at birth, and there are children who acquire spoken language with hearing aids. Their hearings, however, usually deteriorate with age, and cochlear implants take over the role of hearing aids. Anatomical differences among these anomalies influence postoperative hearing and spoken language development.


12.2.2 Speech Perception Test Results


We performed cochlear implantation in 69 ears of 57 pediatric patients with malformations in the inner ear and/or in the internal auditory canal. Among them, 27 patients reached the age range at which speech perception test was possible and had been followed up more than 1 year after surgery. The test results of 27 ears in these patients, 7 ears with CC, 9 with IP-I, and 11 with IP-II anomaly, were studied (Table 12.2). The results of 22 pediatric CI patients whose hearing loss had been confirmed to be due to GJB2 gene mutation and without inner ear malformation were used as controls. Children with mental retardation and pervasive developmental disorders were excluded from the current study.


Table 12.2
The subjects included in the present investigation













































 
Age at surgery (months)

Concomitant CND

Electrode array

Follow-up period (months)

CI-aided threshold (dB)

CC: 7 ears

30.4 ± 6.1

2 ears

CI24M: 1 ear, CI24RE(ST): 4 ears, CI422: 2 ears

35.8 ± 9.8

41.1 ± 3.9

IP-I: 9 ears

32.5 ± 20.4

None

CI24RE(ST): 8 ears, CI24R(CA): 1 ear

35.4 ± 9.1

34.9 ± 4.1

IP-II: 11 ears

71.1 ± 55.8

None

CI24M: 2 ears, CI24R(CS): 3 ears, CI24RE(CA): 5 ears, 90 K: 1 ear

35.8 ± 9.1

30.3 ± 4.1

Controls: 22 ears

32.8 ± 18.3

None

CI24R(CS): 1 ear, CI24RE(CA): 20 ears, 90 K: 1 ear

37.7 ± 13.9

28.4 ± 1.7


Aided thresholds = (500 Hz + 1,000 Hz + 2,000 Hz + 4,000 Hz)/4, controls: GJB2 gene mutation without anomaly

CND cochlear nerve deficiency, CI cochlear implant, CC common cavity, IPI incomplete partition type I, IPII incomplete partition type II

The mean age at implantation in IP-II was 71.1 months, which was much higher than the other groups (Table 12.2). The delay of CI surgery in IP-II children was due to their usable residual hearings that enabled them to, at least partly, acquire speech. But they lost hearing afterward and underwent cochlear implantation.


12.2.2.1 CI-Aided Thresholds


The CI-aided thresholds in CC, IP-I, IP-II, and control group are listed in Table 12.2. The thresholds of patients were highest in CC group, followed by IP-I. The aided thresholds of IP-II group were significantly lower than those of CC and IP-I, exhibiting no significant difference between controls.


12.2.2.2 Monosyllable Perception Scores


The monosyllable perception scores in each group are shown in Fig. 12.1. The scores were lowest in CC, followed by IP-I. The scores in IP-II and the control groups were about 80–90 % and did not differ from each other. The scores in CC and IP-I groups were significantly lower than those in IP-II and control groups.

A395951_1_En_12_Fig1_HTML.gif


Fig. 12.1
Monosyllable perception scores


12.2.2.3 Word Perception Scores


Figure 12.2 shows the word perception scores of CC, IP-I, IP-II, and control groups. The results are similar to monosyllable perception scores. The mean score of IP-II was 93.7 %, which was very close to 95.3 % in controls. The scores for IP-I and CC were 82.2 % and 54.3 %, respectively, which were lower than those of IP-II and controls, but the difference between each group is smaller compared to monosyllable tests.

A395951_1_En_12_Fig2_HTML.gif


Fig. 12.2
Word perception scores


12.2.2.4 CAP Score and SIR Scale


To assess the spoken language development in daily life situations, we examined Categories of Auditory Performance (CAP) and Speech Intelligibility Rating (SIR) Scale .

Categories of Auditory Performance (CAP) is an index consisting of eight performance categories arranged in order of increasing difficulty [1]. The category 0 means no awareness of environmental sound, 1 awareness of environmental sounds, 2 response to speech sounds, 3 identification of environmental sounds, 4 discrimination of speech sounds, 5 understanding of phrases without lip reading, 6 understanding of conversation without lip reading, and 7 use of the telephone. The mean CAP score in IP-II group was 6.4, which was the same as in control group, corresponding to the level of understanding conversation without lip reading, and sometimes telephone can be used. The mean scores of IP-I and CC children were 5.7 and 4.5, respectively, which were one and two levels below that of IP-II and controls (Fig. 12.3).

A395951_1_En_12_Fig3_HTML.gif


Fig. 12.3
CAP scores

The Speech Intelligibility Rating (SIR) Scale is used as a framework to rank the child’s spontaneous speech production into one of five hierarchic categories: (1) pre-recognizable words in spoken language, (2) connected speech is unintelligible but is developing for single words, (3) connected speech is intelligible to a listener who concentrates and lip-reads within a known context, (4) connected speech is intelligible to a listener who has little experience of a deaf person’s speech (the listener does not need to concentrate unduly), and (5) connected speech is intelligible to all listeners (the child is easily understood in everyday contexts). SIR is not a performance test and was designed as a time-effective global outcome measure of speech production in real-life situations [2]. The mean SIR scores were as high as 4.8 and 4.6 in IP-II and control groups, and, again, the scores were 1 and 2 points lower in IP-I and CC groups, respectively (Fig. 12.4).

A395951_1_En_12_Fig4_HTML.gif


Fig. 12.4
SIR scale scores


12.2.3 Mapping Characteristics in Children with an Inner Ear Anomaly


The CIs used in the current pediatric patients were all cochlear devices. In principle, electrode arrays with straight configuration (CI24M, CI24RE-ST, CI422) were selected in CC and IP-I patients, with an exception in which pre-curved electrode (CI24R-CS) was used in one IP-I patient. In contrast, pre-curved arrays (CI24R-CS, CI24RE-CA) were used more in IP-II and in control group with three exceptions in which straight-type electrode arrays (two CI24M and one CI422) were selected. The initial values of mapping parameters, pulse width, stimulation rate, and maxima (the number of electrodes for stimulation to extract sound features), are set at 25 μs, 900 Hz, and 8, respectively. The map for each patient is created by gradually raising the sound intensity from the T level (threshold level) until the charge reaches the C level (maximum comfort level) by observing the responses to the sound. If the charge amount corresponding to T level and C level is not attainable within default current range, a pulse width is widened to create a map at lower current levels. Such adjustments are often necessary in anomalous inner ears, and there are even cases in which certain electrodes are determined to be unusable due to lack of auditory responses in spite of thorough adjustments.


12.2.3.1 Number of Usable Electrodes


The numbers of usable electrodes that elicited auditory responses ranged from 8 to 22 in CC group, 18–22 in IP-I group, and all 22 in IP-II group (Table 12.3). The numbers of usable electrodes were less in patients with smaller cavities in CC group.


Table 12.3
Mapping parameters





























































Groups

Number of functioning electrodes

Amount of charge per phase for T and C levels (nC)a (mean ± SD)

Pulse width and facial stimulation below C level

T level

C level

Pulse width =25 μs

Pulse width >25 μs without facial nerve stimulation

Facial stimulation below C level

CC (7 ears)

8 (1 ear)

26.3 ± 13.4b

66.3 ± 35.1b

1 ear (14.3 %)

2 ears (28.6 %)

4 ears (57.1)%

17 (2 ears)

22 (4 ears)

IP-I (9 ears)

18 (1 ear)

12.8 ± 3.3b

29.3 ± 5.3b

1 ear (11 %)

6 ears (67 %)

2 ears (22 %)

22 (8 ears)

IP-II (11 ears)

22 (all 11 ears)

5.6 ± 1.8

15.4 ± 6.5

11 ears (100 %)

None

None

Controls (22 ears)

22 (all 22 ears)

4.7 ± 1.3

12.7 ± 3.4

22 ears (100 %)

None

None


CC common cavity, IPI incomplete partition type I, IPII incomplete partition type II

aAmount of charge in nanocoulomb (nC) = amount of current (μ A) × pulse width (μs) × 1000

b P < 0.01 larger than controls (Kruskal-Wallis, Mann-Whitney U test, Bonferroni correction)


12.2.3.2 The Amount of Charge Used in Electrodes


The amount of charge per phase for T levels (mean ± standard deviation) was 26.3 ± 13.4 nC for the CC group, 12.8 ± 3.3 nC for the IP-I group, 5.6 ± 1.8 nC for the IP-II group, and 4.7 ± 1.3 nC for the control group (Table 12.3). The amount of charge used in the CC and IP-I groups was significantly greater than that of the control group (p < 0.01). There was no significant difference between the IP-II and control groups.

The amount of C level charge was 66.3 ± 35.1 nC for the CC group, 29.3 ± 5.3 nC for the IP-I group, and 15.4 ± 6.5 nC for the IP-II group, while it was 12.7 ± 3.4 nC for the control group (Table 12.3). Charge in CC and IP-I groups was significantly greater than that in the control group (p < 0.01). Again, there was no significant difference between the IP-II and control groups.


12.2.3.3 Modification of Routine Mapping Procedures


Our initial setting for pulse width was 25 μs, which was sufficient for one ear in the CC group (14.3 %), one ear in the IP-I group (11 %), and all ears in the IP-II and the control groups (Table 12.3). There was a need to set the pulse width wider than 25 μs in six ears in the CC group and eight ears in the IP-I group. Of these 14 ears, for two ears in the CC group and for six ears in the IP-I group, it was possible to ensure the appropriate amount of charge corresponding to C level by expanding the pulse width from 37 to 88 μs and without encountering facial nerve stimulation. Nevertheless, for four ears in the CC group and two ears in the IP-I group (Table 12.3), increasing the current level stimulated the facial nerve, and securing a charge amount corresponding to the C level was challenging. As a result of re-adjusting the map through further expansion of pulse width, for five out of the six ears, we were able to reach C level before encountering facial nerve stimulation. Nevertheless, for the one remaining ear, it was not possible to suppress the facial nerve stimulation, and maximum stimulation remained at a lower value than the charge amount corresponding to the C level.

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Oct 3, 2017 | Posted by in OTOLARYNGOLOGY | Comments Off on Speech and Hearing after Cochlear Implantation in Children with Inner Ear Malformation and Cochlear Nerve Deficiency
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