Number of ears
Number of patients
Lateral canal hypoplasia
Internal auditory canal
12.2 Speech Perception in CC, IP-I, and IP-II
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.
The subjects included in the present investigation
Age at surgery (months)
Follow-up period (months)
CI-aided threshold (dB)
CC: 7 ears
30.4 ± 6.1
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
CI24RE(ST): 8 ears, CI24R(CA): 1 ear
35.4 ± 9.1
34.9 ± 4.1
IP-II: 11 ears
71.1 ± 55.8
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
CI24R(CS): 1 ear, CI24RE(CA): 20 ears, 90 K: 1 ear
37.7 ± 13.9
28.4 ± 1.7
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.
220.127.116.11 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.
18.104.22.168 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.
Monosyllable perception scores
22.214.171.124 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.
Word perception scores
126.96.36.199 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 . 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).
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 . 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).
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.
188.8.131.52 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.
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
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 %)
Controls (22 ears)
22 (all 22 ears)
4.7 ± 1.3
12.7 ± 3.4
22 ears (100 %)
184.108.40.206 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.
220.127.116.11 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.