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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 29  |  Issue : 1  |  Page : 67-73

Inner ear computed tomography findings among children with audiometry proven sensorineural hearing loss in a special needs school in South-West, Nigeria


1 Department of Radiology, Everight Diagnostic and Laboratory Services Limited, Center for Molecular Science and Genetic Study, Abuja, Nigeria
2 Department of Radiology, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria
3 Department of Otorhinolaryngology, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria
4 Department of Speech, Language and Hearing Sciences, University of Health and Allied Sciences, Ho, Volta Region, Ghana
5 Department of Radiology, Obafemi Awolowo University, Ile – Ife, Osun State, Nigeria
6 Department of Radiology, Ladoke Akintola University of Technology Teaching Hospital, Ogbomoso, Oyo State, Nigeria
7 Department of Radiology, University of Sao Paulo, Sao Paulo, Brazil

Date of Submission01-Feb-2022
Date of Acceptance29-Sep-2022
Date of Web Publication15-Nov-2022

Correspondence Address:
Dr. Olawale Ogundiran
University of Health and Allied Sciences, Ho
Ghana
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/wajr.wajr_2_22

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  Abstract 


Background: Hearing loss is a major problem in children because of its devastating effect on education and cognitive development. Clinicians rely on pure-tone audiometry (PTA) to determine the types and degrees of hearing loss; however, the test is subjective and cannot determine the cause of the hearing loss.
Computed tomography (CT) of the temporal bone is important for evaluating hearing loss, due to its ability to identify bony ear malformations and to examine pathologies of the middle and the inner ear. The objective of this study was to determine bony labyrinthine anomalies in a group of children with profound and severe hearing loss.
Materials and Methods: This was a descriptive cross-sectional study conducted among students from a school with special needs in Osogbo, Osun State, Nigeria. One hundred and twenty students with hearing loss selected by stratified systematic random sampling participated in this study. There were 66 (55%) males and 54 (45%) females. Demographic data were collected from the participants and from the school records. All the participants went through audiometry so as to determine and confirm their thresholds and a high-resolution CT scan of the temporal bone to determine bony labyrinthine abnormalities.
Results: One hundred and twenty participants making 240 ears were studied, with a mean age of 12.1 ± 2.3 years. Ninety-five participants (79.2%) had prelingual hearing loss while 25 (20.8%) had acquired postlingual hearing loss. Nine participants (7.5%) had abnormalities of the bony labyrinth; seven of which had bilateral and two unilateral bony abnormalities, and thus 16 (6.7%) out of 240 ears had such abnormalities. The most common cochlear abnormality was hypoplasia 6 ears (37.5%), followed by type I incomplete cochlear partitions 3 ears (18.7%).
Conclusion: This study found that the bony labyrinth was normal in 93.3% of ears, and the most common bony anomaly was cochlear hypoplasia.

Keywords: Hearing loss, high-resolution computer tomography, pure-tone audiometry


How to cite this article:
Akindokun SS, Bello TO, Olaosun AO, Ogundiran O, Ayoola OO, Oyedepo VO, Alagbe OA. Inner ear computed tomography findings among children with audiometry proven sensorineural hearing loss in a special needs school in South-West, Nigeria. West Afr J Radiol 2022;29:67-73

How to cite this URL:
Akindokun SS, Bello TO, Olaosun AO, Ogundiran O, Ayoola OO, Oyedepo VO, Alagbe OA. Inner ear computed tomography findings among children with audiometry proven sensorineural hearing loss in a special needs school in South-West, Nigeria. West Afr J Radiol [serial online] 2022 [cited 2022 Dec 1];29:67-73. Available from: https://www.wajradiology.org/text.asp?2022/29/1/67/361183




  Introduction Top


Hearing loss can be defined as the inability to perceive sound frequency in the normal hearing range.[1]In infants and children, hearing impairment prevents the acquisition of language and educational skills, while in adults, it causes difficulties in both professional and social life as well as stigmatization.[2] In addition to these, it also leads to high economic costs to society and constitutes a significant public health problem in developing countries.[3],[4]

Hearing loss is one of the most common medical conditions presenting to physicians.[5] It affects about 10% of the population worldwide[6] and is considered one of the most prevalent congenital abnormalities.[7] Congenital sensorineural hearing loss (SNHL) is one of the most common birth defects, with an incidence of approximately 1 in 1000 live births.[8] In Nigeria, the prevalence of hearing loss has been documented to affect one in seven children, which is about 14%.[9]

In recent years, substantial advances in radiological imaging have contributed significantly to the early identification and management of patients with hearing loss, especially those patients who may benefit from hearing implants or corrective surgeries.[10],[11],[12] These imaging modalities include high-resolution computed tomography (HRCT) and magnetic resonance imaging (MRI). Both imaging modalities are pertinent to correctly diagnosing children with hearing loss due to outer, middle, and inner ear abnormalities. HRCT is cheaper than MRI, readily available, and can detect bony anomalies of the auditory canal, middle ear, and inner ear.[13],[14],[15],[16] MRI on the other hand can visualize soft-tissue components of the ear and the associated nerves. MRI is the gold standard for evaluating SNHL due to inner ear abnormalities, but in our environment, that modality is not accessible to patients, mainly due to its high cost.[17],[18],[19]

In Nigeria, doctors rely solely on audiological investigations such as pure-tone audiometry (PTA) for diagnosing and differentiating the types of hearing loss. While this has its usefulness and established place, PTA alone cannot accurately localize inner ear pathologies. This study was therefore designed to evaluate the computed tomography (CT) features of the inner ears of children with hearing loss confirmed on PTA.


  Materials and Methods Top


This study was a cross-sectional survey conducted among students with hearing loss in the school for people with special needs in Osogbo, Osun State, Nigeria, over a 12-month period, from July 2015 to June 2016. The study took place at the Audiology Unit, ENT Department, and Radiology Department of LAUTECH Teaching Hospital, Osogbo (now University of Osun Teaching Hospital). Approval for the study was obtained from the ethical and research committee of the teaching hospital. The targeted students were between the ages of 8 and 15 years. School for people with special needs is a specialized school for the deaf and dumb, as well as other children with disabilities. This school is classified into different segments, and most of the students admitted into this school are mostly proven children with SNHL.

One hundred and twenty students were recruited by stratified systematic random sampling after informed consent had been obtained from the headmaster of the school and the parents. The participants were minors, and the decision for the participation in this study was based on the parents' and headmaster's consent, although the procedures were explained to each student through the help of their class teachers and audiologists. In each class, all the students were stratified into five groups and the 4th group was sampled for the study from primary 1 to 6. The sample size was calculated based on the prevalence of hearing loss which is one in seven children.[9] In this environment, children with hearing loss or any major disabilities are confined to this special school which is a true representation of the general population. Therefore, the prevalence of hearing loss among the children in the general population was used to calculate the study sample size. The margin of error was set at 7% because the participants were special students that needed more persuasion to participate in the study and also because of availability (some were day while others were boarding students). The sample size for the study-94-was calculated using the Cochran formula (sample size formula for single proportions). To allow for possible attrition, the number of participants recruited was increased to 120.

All the participants went through PTA to determine their degrees and types of hearing loss and a CT scan of the temporal bone to determine bony labyrinthine anomalies. PTA was performed with MA 53 Diagnostic Audiometer (MAICO, Germany) and temporal bone CT was by 16 Slice Scanner (Somatom Emotion, Siemens, Germany).

The audiologist who is one of the researchers of this study performed PTA on the participants and gave instructions to all the participants individually. Each one was taken into the soundproof booth so as to perform the hearing test without environmental noise, altering test results using a modified Hughson-Westlake procedure while the thresholds were determined by averaging decibels from 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz.

A Somatom Emotion Siemens 16 Slices CT Machine was used to acquire images of the ear. Participants lay supine on the examination table in a neutral position. After scanogram, axial scanning was performed in planes parallel to the infra-orbitomeatal line with a slice thickness of 0.625 mm, and this was obtained from the top of the petrous apex to the inferior tip of the mastoid bone. The gantry was not angulated. The raw axial image data were reconstructed at 0.6 mm to obtain high-quality coronal and sagittal reformations. A 512 × 512 matrices were used, and all images were reviewed with a high-resolution bone algorithm, and a small field of view for separate documentation of the right and left ears was also used. Axial sections showed external, middle, and inner ear components while coronal sections showed details of cochlea turns and semicircular configurations.

Data collected from audiometry and CT were analyzed quantitatively through percentages, means, and standard deviation using SPSS 20 (IBM, Armonk, New York, USA).


  Results Top


Sociodemographic characteristics of the study population

A total of 120 participants were recruited for this study. There were 66 (55%) males and 54 (45%) females. The children's ages ranged from 8 to 15 years with a mean age of 12.1 ± 2.3 years. The age at diagnosis of hearing loss (for both congenital and acquired hearing loss) ranged from 1 to 6 years with a mean of 1.3 ± 0.9 years. Ninety-five (79.2%) had congenital hearing loss while 25 participants (20.8%) had acquired hearing loss [Table 1].
Table 1: Age, sex, and onset of hearing loss

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Pure-tone audiometry of the participants

SNHL was noted in 176 (73.3%) ears while 64 (26.7%) ears had mixed hearing loss. There was no participant with isolated conductive hearing loss. In most ears, 154 (64.2%) demonstrated a profound degree of hearing loss (worst degree of all degrees of hearing loss; 91 dB and above) while 86 (35.8%) showed a severe degree of hearing loss (71 dB–90 dB) [Table 2].
Table 2: Pure-tone audiometry findings among right and left ears of the participants (n=240)

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Temporal bone computed tomography

Normal inner ear bony labyrinth was noted in 111 participants, 92.5%. [Table 3] shows the abnormal bony labyrinthine findings observed in nine (7.5%) participants, comprising bilateral abnormalities in seven participants and unilateral abnormalities in two participants. Thus, of the 240 ears examined, 16 (6.7%) had abnormalities on HRCT. There was the involvement of the cochlea in 12 (75%) of the ears [examples shown in [Figure 1] and [Figure 2]]. Cochlea hypoplasia with varying degrees of the deformed vestibule and internal acoustic meatus (IAM) was the most common abnormality [Figure 3] and [Figure 4], occurring in 6 (37.5%) ears, followed by type I incomplete partition in 3 ears (18.7%). Cochlear aplasia was noted in one participant [Figure 1]. IAM hypoplasia was seen in two (12.5%) participants with normal cochlear structures [Figure 5]. [Table 3] and [Table 4] showed the aforementioned bony abnormalities.
Figure 1: HRCT axial section showing the right cystic dilatation of cochlea (arrow) and the vestibule [[Figure 8] configuration of Type I incomplete partition]. HRCT – High-resolution computed tomography

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Figure 2: HRCT coronal section showing the cystic dilatation of the cochlea apex, the basal turn is normal. (Type II incomplete partition i.e., Mondini dysplasia). HRCT – High-resolution computed tomography

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Figure 3: HRCT coronal section showing hypoplasia of the left cochlea, vestibule, semicircular canals, and IAM. HRCT – High-resolution computed tomography, IAM – Internal acoustic meatus

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Figure 4: HRCT axial section (Bone window) showing ectasia of the right internal acoustic meatus. HRCT – High-resolution computed tomography

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Figure 5: HRCT axial section (Bone window) showing atresia of the right internal acoustic meatus. HRCT – High-resolution computed tomography

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Table 3: Computerized tomographic findings (summary) on the inner ears (n=16)

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Table 4: High-resolution computed tomography findings in the right and left inner ears of participants (n=120)

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  Discussion Top


The external and middle ear develop from the first and second branchial arches.[20]

The inner ear arises from the otic placode in a process that begins early in the 3rd week of gestation and by the 8th week, the development of the cochlea is complete while the vestibule is completely developed by the 11th week, and the semicircular canals, between the 19th and 22nd weeks, the lateral canal or duct is the last to form. Ossification of the labyrinth is complete by the 23rd week.

The development of inner ear malformations may result from developmental arrest at any of these stages. The type and severity of malformation depend on the gestational age at which the arrest occurs.[21]

A key observation is that all our participants were having CT of the temporal bone for the first time; we believe if PTA and cross-sectional imaging were performed within the first 6 months of diagnosis of hearing loss, some of these individuals may be able to benefit from medical management and cochlear implants.

The demographic data shows that there were more males than females in this study and that congenital hearing loss was more common than acquired, as was the case in studies by Eziyi et al., 2008 in Nigeria and Brobby, 1988 in Ghana.[17],[18]

The prevalence of congenital bony labyrinthine anomalies has been reported to be between 6.8% and 37%.[22],[23],[24],[25],[26] This study found that 7.5% of the cases being bony abnormalities consistent with what has been documented. The wide range of the percentages of bony labyrinthine abnormalities might be due to differences in study design, the severity of hearing loss, or genetics.

The bony abnormalities seen on CT images of the inner ears of the participants in this study include cochlear hypoplasia, type 1 and 11 incomplete partitions, abnormal vestibule and semicircular canal, and IAM with normal cochlear, enlarged vestibular duct with normal cochlea and semicircular canal and cochlea aplasia.

From all 16 bony inner ear anomalies, cochlear hypoplasia was seen in 37.5% where cochlea had rudimentary appearances with associated vestibular and semicircular canal hypoplasia. About 18.9% of cochlea showed type 1 incomplete partition, in which there were cystic dilatations with no modiolus and no turns, and these were accompanied by cystic dilatation of the vestibules and dilatation of the internal acoustic canal. Likewise, 12.5% of cochlea showed type II incomplete partition (Mondini dysplasia), in which the apical and middle turns showed cystic dilatation, with normal basal turn (1 half turns); and in 6.3% out of the inner ear anomalies, the cochlea was absent (aplasia). These findings were contrary to previous studies by Haidar et al.[23] and Agarwal et al.[27] that showed that Mondini dysplasia was the most common cochlea anomalies, 25% and 41% out of bony inner ear anomalies, respectively, among children with congenital SNHL. However, in this study, cochlea hypoplasia was the most common inner ear abnormality. These disparities might be due to their concentration on children with congenital hearing loss while this study was conducted on children with both acquired and congenital hearing loss. Racial differences might also be responsible for variations in these findings.

In addition, the term Mondini dysplasia has been used in the past for various forms of cochlear pathologies and the disparity may be due to different usage of terminologies.[16],[17],[18],[19]

Cochlear aplasia was noted in one participant (6.3%). It causes profound sensorineural deafness, and it is associated with abnormalities of the vestibule and semicircular canals.[16] These patients usually do not benefit from cochlear transplants due to the absence of the cochlear nerve.[28]

Vestibular anomalies were seen in 11 ears (4.6%) out of the total population and this corresponds to 68.8% of inner ears anomalies. These anomalies include cystic dilatation, hypoplasia, and aplasia. About 18.8% of vestibules showed cystic dilatation out of a total of 16 inner ear anomalies and they were associated with type 1 and type 11 incomplete cochlea partition. About 43.8% of the population was seen to have vestibules although the vestibules appeared rudimentary which is suggestive of hypoplasia while the vestibule was absent in 6.25% of the population found to have inner ear anomalies. These findings are lower to a previous study by Agarwal et al., 2014[27] which reported vestibular anomalies in 87.1% of the inner ear anomalies among children with SNHL.

Vestibular aqueduct (VA) anomalies were seen in 8 ears (3.3%) out of a total of 240 ears and correspond to 50% of inner ear anomalies. These anomalies include hypoplasia, ectasia, and aplasia. About 25.0% of VAs out of the 16 inner ear anomalies appeared rudimentary in keeping with hypoplasia in association with cochlear and vestibular hypoplasia. About 12.5% of VAs out of inner ear anomalies were dilated in association with cochlea type I incomplete partition. Furthermore, no VAs were seen in 12.5% of ears with inner ear anomalies. These findings were different from studies performed previously by Haidar et al.[23] and Agarwal et al.[27] that showed more of vestibular duct dilatations, in which VA ectasia was 50.0% and 51.5% of the inner ear anomalies, respectively. However, this study is similar to the same studies by Haidar et al.[23] and Agarwal et al.[27] in terms of multiple anomalies. Nevertheless, in 84% of cases in other studies, it is associated with other inner ear anomalies.[29],[30]

Semicircular canal anomalies were seen in 9 ears (3.8%) of the total population and correspond to 56.3% of the inner ear anomalies in this study. These anomalies include hypoplasia, ectasia, and aplasia. About 37.5% of ears out of inner ear anomalies showed hypoplasia of the semicircular canals. About 12.5% of ears out of all inner ear anomalies showed ectasia while 6.25% of ears showed aplasia of the semicircular canals. These findings were different from previous studies by Haidar et al.[23] and Agarwal et al.[27] that showed 26.9% and 16.7% of inner ear anomalies with semicircular canal malformations, respectively. However, these semicircular canal anomalies occurred with other inner ear anomalies and agree with the same studies.[12],[23],[27] Likewise, groups of patients with isolated semicircular anomalies in theory are well suited for cochlear implants as the nerve is usually present.[28]

The internal auditory canal (IAC) anomalies were seen in 3 ears (1.3%) out of 240 ears and correspond to 18.8% of the inner ear anomalies. These anomalies include ectasia and atresia. About 12.5% of inner ear anomalies showed dilations of IAC (>8 mm) which were associated with type 1 incomplete partition, while 6.3% showed a narrowed canal, i.e., atresia (<2 mm). These findings were different from a previous study by Agarwal et al.[27] that showed 30.7% of inner ear anomalies with malformations of the IAC. However, 6.3% of inner ears with atresia of IAC agree with previous studies among children with SNHL by Haidar et al.[23] and Mafong et al.[25] These disparities in these findings might be due to geographical or racial differences. It has been shown that IAC narrowing is usually associated with aplasia or hypoplasia of the vestibulocochlear nerve as a cause of SNHL and this anomaly is a contraindication for cochlear implants.[30]

The role of PTA is to identify the type and severity of hearing loss, although it cannot localize the pathology.[9],[10],[17] Modern imaging using CT and MRI can identify pathologies in both bony and membranous labyrinths, and therefore, PTA and cross-sectional imaging play crucial roles in the management of patients with hearing loss. CT was able to identify structural anomalies in about 6.7% of the ears in this study. A major drawback of CT is that it cannot visualize the membranous labyrinth and the cochlear nerve which are major origins of SNHL. Therefore, MRI is essential in identifying pathologies of the cochlear nerve and in selecting patients for cochlear implants.


  Conclusion Top


This study found that the bony labyrinth was normal in 93.3% of ears, the most common bony anomaly was cochlear hypoplasia. Pure Tone Audiometry showed more profound hearing loss among the participants, thus the findings in this study suggest that most of the participants would have benefitted from cochlear implants if hearing loss is detected early. We therefore advocate for early hearing loss detection and intervention.

Limitations of the study

The first difficulty we encountered was getting accurate past medical history from the school of people with special needs.

Another limitation of this study was that the cost of doing the study was so high.

We also had problems of getting a big sample size.

Finally, we were limited because we could not have access to MRI which is important for the assessment of vestibule-cochlea nerves and other inner ear structures in preparation for the cochlear implant.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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