Sensorineural Hearing Loss and Cochleovestibular Malformations in Children in Côte d’Ivoire

Introduction

Deafness is one of the most common sensory disabilities in children. It is estimated that one child in a thousand has severe or profound deafness at birth [1]. Most congenital hearing loss (90%) is caused by sensorineural impairments in the inner ear, cochlear nerve, and/or central auditory pathway [2].

Detectable inner ear malformations (IEMs) and cochlear nerve deficiencies, identifiable with computed tomography (CT scan) and/or magnetic resonance imaging (MRI), are responsible for 15–40% of pediatric sensorineural hearing loss (SNHL) cases [2, 3]. The etiology of these malformations is usually unknown [4]. Taking these IEMs into account in the assessment is essential because they present specific challenges in therapeutic management.

The lack of epidemiological data related to cochleovestibular malformations causing sensorineural hearing loss in our context justifies this study. The aim of our study was to find the distribution of various malformations and to report the clinical features of commonly encountered IEMs in our practice.

Methods

The study was conducted in the ENT departments of the Abidjan University Hospitals (CHU), the Dominique Ouattara Mother and Child Hospital in Bingerville and a private medical group in Abidjan. This was a retrospective cross-sectional study. The study took place over a period of 14 months (January 2019 to March 2020).

All patients aged up 15 years, who had a cochleovestibular malformation related to sensorineural hearing loss and/or predominantly sensorineural mixed hearing loss confirmed during the study period were included. Other types of hearing loss and malformations of outer or middle ear were not included. Sampling was non-probability for convenience, with an exhaustive collection of patients followed during the study period and meeting the selection criteria.

Data collection was carried out using the medical records of children, consultation registers and imaging registers.

All studied variables, reported in the documents used, have been listed. The total number of consultants in ENT departments for sensorineural hearing loss and/or mixed sensorineural hearing loss during the study period was recorded.

The variables to be studied were age at diagnosis, gender, ethnicity, level of education. Clinically: the reason for consultation, associated signs (language delay, hearing loss, behavioral problems, balance disorders), risk factors and pathological history (embryo-fetopathies, gestational age less than 34 weeks, congenital malformations of the head and neck, meningitis, neonatal jaundice, consanguineous marriage), clinical data (ENT examination), etiologies of deafness (acquired, congenital), results of objective or subjective audiometry, characteristics of the deafness (side and degree according to the BIAP classification [5]), IEMs detected by imaging (CT scan and MRI of inner ear and brain) were classified according to the side (right, left) and the site (cochlea, vestibule, internal auditory canal).

Data collection and statistical analysis were done in CSPRO VERSION 6 and exported to SPSS 23 for data analysis. All p-values less than 0.05 were considered statistically significant.

Discussion

Out of the 160 patients identified for this study, we found 6 patients with cochleovestibular malformations (3.75%). This rate remains below those reported in the literature: 40% for Sarioglu, et al. [6]; 20% for Sennaroglu, et al. [4] and 10% for Adibelli, et al. [7]. A bias might be created by the small sample size in our study. Sensorineural hearing loss of malformative origin does not appear to be related to sex: sex ratio 1 in our study and 0.95 in Masuda, et al. study [8]. The size of the sample does not allow us to conclude that there is a link between ethnic origin and the existence of IEMs. However, the presence of the Akan’s group, an indigenous population of Abidjan and its surroundings, would probably be linked to the location of the study. Unlike the group from Northern Mande, for which ethnic origin could be incriminated, due to the frequent existence of consanguineous marriage. According to an observation made in several studies on deafness, the hearing-impaired child is the eldest of the siblings in most cases (46 to 53% of cases) [9, 10]. The patients were mostly under 4 years old, so they were not in school.

These SNHL with malformative origin are sometimes syndromic (2 cases in our study). Petit [11] states that 30% of genetic deafness is associated with other symptoms or malformations, therefore called syndromic, when Denoyelle, et al. [12] report that genetic SNHL is syndromic in 10 -15% of cases. To explore deafness, objective audiometry was mainly performed in our study, probably related to the young age of the patients. Some authors note that behavioral audiometry, generally gives reliable answers in children over 4 years old [13]. We noted a preponderance of profound deafness and bilateral deafness (5/6 cases); while Masuda, et al. [8] had identified profound deafness in 46% of cases, bilateral in 49% of cases. Adibelli, et al. [7] found different levels of hearing loss (severe and profound) in their study. The difference in the size of the study populations could explain these results, even though our study seems to link cochleovestibular malformation and the degree of deafness.

The risk of having profound deafness is estimated at 1.9.

Once the diagnosis of sensorineural deafness had been made, an imaging assessment was carried out in some patients. This assessment most often consisted of CT scans. This is consistent with data from the literature and in the work done by Er-Raji I [14] especially. According to him, computed tomography should be the first-line examination in the exploration of the ear in children, whatever the type of malformation; MRI is only complementary. Essentially, it is used to look for an abnormality of the cochlear nerve or labyrinthine structures. The proportions of the different abnormalities identified vary from one study to another. In Masuda, et al. [8] report the authors cite in order of frequency, IAC abnormalities, cochlear malformations then the vestibule anomalies. In our study, these are mainly the SCC hypoplasia, then IAC abnormalities and finally, cochlear malformations. The description and classification of these abnormalities also vary. Some studies separate inner ear malformations from third window abnormalities [6]. In this context, some malformations including EVA are classified for certain authors as IEMs [4] and for others, as abnormalities of the third window [6]. These abnormalities of the third window bring together disorders which result in abnormal communications between the inner and the middle ear, as well as cerebrospinal fluid and vascular structures. Superior semicircular canal (SCCs) dehiscence, posterior SCC (SCCp) dehiscence, enlarged vestibular aqueduct (EVA), X-linked stapes gusher, perilymph fistula (PLF), and bone dyscrasias of the temporal bone comprise the third window abnormalities [15].

Three cases are reported in our study: SCCs dehiscence, enlarged vestibular aqueduct, bone dysplasia of the utricle. Different types of hearing loss were considered for third window abnormalities [6].

Conclusion

Sensorineural deafness linked to cochleovestibular malformations in children appears to be uncommon in our practice, sometimes associated with malformations of other organs. However, they are associated with a risk of profound SNHL, for which the only alternative is cochlear implant surgery. It is therefore important, in the face of any sensorineural hearing loss in the child, to systematically carry out an imaging assessment, including at least a CT scan of the inner ear, even in our countries.