Inner Ear Malformations in Cochlear Implantation Candidates at Mother and Child Hospital of Bingerville (Côte d’Ivoire)

Introduction

Inner ear and vestibulocochlear nerve malformations may lead to congenital sensorineural hearing loss (SNHL).¹ Hearing loss is the most common sensory disability in children. It is considered that 1 in 1,000 children has severe or profound deafness at birth and 90% of birth hearing loss are sensorineural.²

The reported prevalence of inner ear malformations (IEMs) in individuals with congenital hearing loss varies from 2.3 to 28.4%.³ A variety of congenital anomalies are seen, syndromic and nonsyndromic.⁴ These anomalies have been grouped according to various classifications and the most used is proposed by Sennaroglu.^5,6

In cases of severe-to-profound deafness, cochlear implant is proven to be the most beneficial in children. For this management, IEMs may not only affect the decision to perform the implant procedure but also increase the risk of complications.¹ In Côte d’Ivoire, our cochlear implantation experience is recent (December 2015), and the first cochlear implantations at Bingerville Mother-Child Hospital were performed in 2020. Moreover, no study has been carried regarding the inner ear anomalies in our setting. The lack of data on malformations therefore justifies this study. Thus, the objectives were to determine the prevalence and the types of inner ear and/or cochlear nerve abnormalities in children with severe or profound SNHL in Côte d’Ivoire.

Methods

This is a descriptive cross-sectional study with a review of the medical files of children under 15 years old, candidates for cochlear implantation, who presented to our hospital for a preimplantation imaging assessment (computed tomography [CT] and magnetic resonance imaging [MRI]), from January 2019 to December 2021. All cochleovestibular or cochlear nerve malformations, isolated or associated, were included in the study. Malformations isolated from the windows, abnormal hyperdensity, or ossified lesions were not retained. They were categorized by side (unilateral, bilateral), site (cochlea, vestibule, semicircular canal, entire labyrinth), and Sennaroglu classification.^5,6

The variables to be studied were reason for consultation, risk factors, types of inner ear abnormalities classified and analyzed according to degree of SNHL, gender, and age at diagnosis. Significant risk factors and history corresponded to the presence of parameters that could impact the occurrence of cochleovestibular malformations: TORCH (TOxoplasmosis, Rubella, Cytomegalovirus, Herpes simplex virus) infection during pregnancy and other microorganisms; gestational age less than 34 weeks, birth defects of the head and neck.

After collection, data was tabulation using Microsoft Excel Worksheet and analyzed statistically using Statistical Package for Social Studies (SPSS) Version-23. Results were analyzed using descriptive statistic including frequencies, percentages, mean, and standard deviation. Chi-squared and Fischer's exact tests were used to see association (p-value < 0.05).

The study was conducted after administrative approvals were obtained; and the anonymity of the tools and data collected was ensured.

Results

Discussion

We found a prevalence of 11.1% of malformations in children's candidates for cochlear implantation, which is within the range of prevalence reported worldwide: 7.5 to 20%.^7-9 With a prevalence of 3.7% in cases of unilateral SNHL, the study by Masuda and Usui¹⁰ showed a significant increase in the prevalence of malformations in the case of bilateral SNHL.

Gender does not seem to be a predisposing factor for ear malformations either in our study or in the literature.^4,10 However, studies concerning the prevalence by sex of the different malformations in general are lacking, apart from those on the anomalies of the external ear that note a male predominance.¹¹ More than the age of the patients included, the present study demonstrated a significant correlation between IEMs and early age at diagnosis. The children were mostly the first born in the family (7/9 cases), like in other studies on deafness.^12,13 Children were mostly out of school, perhaps because of the hearing loss?

The main reason for consultation in children's SNHL was a language delay according to Ridal et al.¹⁴ The profound deafness would favor early diagnosis, even in under-equipped countries, because of the main impact on the language development of young children. We did not note any pathological history in our work, due to the size of our sample. However, the role of pregnancy and childbirth conditions as well as prenatal infections, in particular TORCH, are known to be responsible of congenital craniofacial malformations, including auricular. Indeed, ear malformations may have not only an acquired background (infections, chemical agents, irradiation, etc.) but also a genetic origin. Theses malformations can affect outer/mid- dle ant inner ear, sometimes in combination. But the different embryogenesis of the outer/middle ear and the inner ear explains malformations in outer and/or middle ear without IEMs.³ An association with other malformations (cervical, renal, cardiac, etc.) is noted in two patients, which may be part of so-called syndromic genetic deafness described in 10 to 30% of cases of genetic deafness.³ The IEMs were associated with profound and/or severe degree sensorineural deafness in majority of cases, with varying rates.^8,10

CT is the first-line examination in the exploration of the ear in children, but CT and MRI must be complementary in the preoperative assessment. MRI essentially makes it possible to look for an anomaly of the cochlear nerve or of the labyrinthine membranous structures and of the brain.^1,4 In most cases, the underlying disorders involve the membranous labyrinth at a microscopic level and therefore radiological examinations are entirely normal.¹ The most used classification is that in eight groups.^1,5,6 Majority of patients demonstrated multiple abnormalities.⁵ The prevalence of any type of IEMs is variable with large differences in the proportions reported by studies. In our series, the most common abnormalities were SCC malformations, including SCC hypoplasia and dehiscence of superior SCC bone capsule. In second position, we had cochlear malformations with cochlear hypoplasia type II or III (25%) while incomplete partitions were the most frequent malformations in studies by Sennaroglu and Sun.^7,15 Conversely, the most common malformations were dilated vestibules for other authors.^9,16 An enlarged vestibular aqueduct has been reported at high rates (40-56%) in several studies, whereas they represent only 2.5% of the malformations in our series.^9,15,17 No documented explanation could justify these significant differences.

Conclusion

This study shows that 11.1% of children with profound SNHL have inner ear malformations. SCC anomalies and cochlear hypoplasia were the most common. A precise description of these malformations during the imaging assessment is particularly useful for cochlear implantation, for better planning of this surgery.