Rehabilitation of hearing by cochlear implantation

A cochlear implant (CI) is a surgically implanted electronic device that transmits sounds directly to the auditory nerve through electrical stimulation of the cochlea. It has become the standard of care for severe or profound losses in hearing and indeed has produced the irst substantial restoration of a lost or absent human sense using a medical intervention. It has proven to be a useful treatment option for individuals with severe-to-profound hearing loss by providing improved access to one’s surrounding auditory environment. Both postlingually deafened adults and prelingually deafened children can bene it from a CI [1]. The goal of the present study is to describe the epidemiological characteristics, the surgical approach and the outcomes of our experience regarding the aural rehabilitation by cochlear implantation.


Introduction
A cochlear implant (CI) is a surgically implanted electronic device that transmits sounds directly to the auditory nerve through electrical stimulation of the cochlea. It has become the standard of care for severe or profound losses in hearing and indeed has produced the irst substantial restoration of a lost or absent human sense using a medical intervention. It has proven to be a useful treatment option for individuals with severe-to-profound hearing loss by providing improved access to one's surrounding auditory environment. Both postlingually deafened adults and prelingually deafened children can bene it from a CI [1]. The goal of the present study is to describe the epidemiological characteristics, the surgical approach and the outcomes of our experience regarding the aural rehabilitation by cochlear implantation.

Materials and Methods
We completed a retrospective study of children with profound hearing loss implanted in our department between 2007 and 2018. The data were collected from patients records and from the speech-language evaluation forms completed in the presence of surgeons, speech therapists and parents of children .The patients were assessed regularly during the irst 1-3 months and every 6 months after cochlear implantation. Communication abilities of the children are studied, on base of the APCEI-score. It evaluates ive components of the language: cochlear implant acceptance, perceptive language performance, comprehension of the oral orders, expressive language and speech intelligibility. Scores for each item range from 0 to 5. The highest possible score on the APCEI-scale is 25 ( Figure 1). Among all patients 103 had prelingual deafness. The implant in children progressively increased through the considered time interval (Figure 2).
The average age of implantation was 5,25 years old, with a minimum of 18 months old and a maximum of 16 years old. The majority of patients were female (57.5%).In the majority of cases (89.5%) the CI was performed before 5 years old. Several causes of deafness were also identi ied (Table 1). However, the majority of the cases were unknown.

Pre-implant assessment
All patients bene ited from a pre-implant assessment (clinical, audiological, radiological, orthophonic and psychological evaluation). There was no contraindication for cochlear implantation.
Otitis media with effusion (OME) was identi ied in 8 patients, treated before surgery (medical treatment in 4 cases, adenoidectomy in 1 case, adenoidectomy +ear tube ventilation in 3 cases). The hearing aids were used in 10 patients. The associated comorbidities in the patients were: heart disease (2 cases), unilateral blindness (1 case) paresis of the left hemibody (1 case) and anemia (1 case). A unilateral complex cochlear malformation was identi ied by imaging in two patients implanted on the versus side.

Surgical approach
All Patients were preoperatively vaccinated (pneumococcal vaccination) for meningitis prophylaxis. Implantation was unilaterally in all cases: 100 cases in the right ear and 13 cases in the left one. Surgical revision with reimplantation was performed in 3 cases due to device failure. One of the cases had the irst implantation in our department.
The surgery was performed under general anesthesia with monitoring of the facial nerve. A mastoidectomy with facial recess approach was performed in all cases to access the round window for placing the electrode ( Figure 3). In all our patients the electrode arrays were fully inserted into the scala tympani except for two cases: reimplantation (1case) and post meningitis hearing loss (1case). Impedance testing and neural response telemetry (NRT) were performed to test the integrity of the device. There was no peroperative complication.

Follow-up
The duration of hospitalization was 48 hours in average. X-ray Sternvers view was performed systematically, it showed the correct location of the cochlear implant in all patients. No post implantation complication was noted.
The "initial stimulation" and device programming, were conducted after 4-6 weeks of recovery with regular speech therapy at an average of 2 sessions per week. The adjustments were regular and modi ied afterwards according to the evolution in speech therapy, schematically at 1, 2, 3, 6, 9, 12, 18, 24 months then yearly.

Evaluation of communications abilities after cochlear implantation
The speech-language assessment by the APCEI scale was Figure 1: The APCEI-scale evaluates fi ve components of the language: cochlear implant acceptance, perceptive language performance, comprehension of the oral orders, expressive language and speech intelligibility [18].  conducted in pre-implantation and during follow-up. All patients had a score of 0 prior to cochlear implantation in all areas of the used scale. The evaluation was done monthly during the irst 6 months, and there after every 6 months. Figure 4 illustrates the evolution of the APCEI scale during the last control and according to the length of cochlear implant use.
All patients in our experience bene ited from their implants with a mean follow-up of 37.54 months. The communications abilities improved during the period of use of the cochlear implant. Results showed high interindividual variability (age of implantation, the duration of implant use, motivation, rhythm of speech therapy). Figure 5 represents the average APCEI score of children with prelingual deafness according to the age of implantation. Good results were found to be correlated with early implantation.
Children with a signi icant parental investment and good follow-up of speech therapy had the best results compared to children with low or moderate follow-up Figure 6.
The oral environment had a positive in luence on the results unlike the signed communication Figure7.
Regarding our global results, all patients accepted the use of the cochlear implant with an acquisition of sound alertness from the irst months. The words recognition started from 1 year of use, and the possibility to understand a conversation from the 3rd year. The cochlear implant has allowed a schooling rate of 80,95% in our population with a failure rate of 1,85%.

Discussion
Severe to profound hearing loss affects 1 of 1000 newborn each year. Recent studies show that this incidence could reach 2-3 births on thousand [2] .It is one of the major disabilities that adversely affect the development of speech and cognitive abilities in children.
CIs work by substituting the sensory hair cells within the cochlea with electrodes that stimulate electrically the auditory nerve ibers [3].
Pediatric CI candidates are in the majority of cases prelingual deafened children, who are born with SNHL due to genetic mutations, perinatal environmental exposures, or unidenti ied (idiopathic) causes. According to Nicholas et al. [1] these patients often obtain good speech outcomes after implantation with the best results, occurring when implanted within 1 to 2 years of age [1]. Table 2 provides a broad overview of conventional CI indications [3].
The FDA requires children to be 12 months of age. However several centers in the U.S. and Europe are implanting children as young as 6 months old [5]. Colletti and et al. [6] reported on 12 children implanted at or before the age of 6 months; four years after implantation, these children had receptive and expressive language skills similar to normal-hearing peers. However, Tajudeen and et al. [4], did not con irm clear evidence of improved outcomes in children implanted in the irst year of life compared with those im-planted a year later [4].   There has been an expansion in CI candidacy criteria. For example, children with auditory neuropathy spectrum disorder (ANSD) have shown to achieve reliable open-set speech recognition and the majority of patients with cochlear malformations (e.g. Mondini deformity), who were previously not implant candidates are now being implanted safely [7].
Cochlear implant candidacy has been extended also to some children with signi icant residual hearing [8]. An example is a bilateral and asymmetric SNHL, in which signi icant bene it can derive from cochlear implantation in the worse hearing ear in combination with a hearing aid in the better ear [9].
In addition, there is growing interest in implanting patients with single-sided deafness (SSD). At present time, implantation for SSD is not currently FDA approved, but increasing evidence suggests that this may be a viable option in the future [10].
Before implantation several factors must be considered to establish whether a child is suitable or not; thus, for a successful cochlear implantation the patient selection is of outstanding importance. A complete evaluation should comprise a series of tests, including audiologic, medical and imaging studies, as well as speech and language evaluation; furthermore, patient/ family counseling is fundamental to explain them the potential bene its and to create realistic expectations [1,3].
Contraindications to implantation, such as complete labyrinthine aplasia, cochlear aplasia, cochlear nerve aplasia, and complete cochlear ossi ication should be eliminated by radiographic assessment. According to Parry et al. [11], magnetic resonance imaging (MRI) is the best modality for con irming a luid-illed cochlear duct to receive the electrode, as well as the presence of a cochlear nerve to carry the signal to the brainstem and auditory cortex. Importantly, in older patients, obtaining an MRI prior to CI provides them with their last opportunity to obtain a high-quality brain image without artifact or the need to remove a magnet [11]. High resolution computed tomography (HRCT) also has utility, particularly for surgical planning in cochlear malformations, and can also be done in a faster, more cost effective manner compared with MRI [12].
Cochlear implantation is usually performed under general anesthesia without muscle relaxation to allow for facial nerve monitoring. Selected elderly patients have also been safely implanted under conscious sedation [13]. Patients should be preoperatively vaccinated according to Centers for Disease Control and Prevention (CDC) guidelines for meningitis prophylaxis [14]. CIs are placed through small skin incision in the retroauricolar region; a surgical opening is made in the mastoid to provide access to the cochlea from behind. Once identi ied the round window, the latter is opened and the electrode array is inserted into the cochlea. After the implant has been secured in place and before closing the surgical access, intraoperative electrophysiological testing is performed to verify the correct functioning of the device and to record the neural responses to the electrical stimuli. In standard cases, the procedure takes about 2 hours; children are generally discharged from hospital within 2-3 days [1,3].
The activation of the implant is usually done 2-4 weeks after surgery, when healing is complete, and consists in setting the sound levels presented to each electrode within the cochlea. During the irst year after activation, the cochlear implant is periodically tuned according to the child responses in order to maintain optimal stimulation levels [3].
There are remarquable results regarding the acquisition of spoken language in implanted children with profound deafness. Prelingually deaf children develop signi icant speech perception and production abilities over time. According to O'Donoghue et al. 1998 [16], these achievements may appear limited in the irst two years, but show signi icant improvement after the second year of implantation, and do not reach a plateau, even 5 years following implantation.
Prelingually deaf children also develop signi icant speech intelligibility, but a long period of cochlear implant use is needed prior to the emergence of intelligible speech [17].
Nevertheless, children with CI show an important variability. According to Gerard et al. and Clark et al. [18,19], several factors, such as the aetiology of deafness, the age of the child at the time of the CI, the presence of residual hearing, the process of the auditory rehabilitation, the family participation in the therapeutic process, all may in luence the inal performance.
The protocols of evaluation in post-implantation are multiple [17][18], varying from one center and one country to another (TEEP, MUSS, APCEI, CAP, MAIS, SIR.). There is no Word recognition Limited benefi t from binaural amplifi cation defi ned by 50% sentence recognition in the ear to be implanted (or 40% by CMS criteria) and 60% in the contralateral ear or binaurally.
Limited benefi t from binaural amplifi cation trial based on the MAIS.
Abbreviations: CMS, centers for medicare and medicaid services; dB, decibels; SNHL, sensor neural hearing loss; MAIS, meaningful auditory integration scale standardized protocol adapted to our culture. Despite being subjective, the APCEI scale was chosen in our evaluation but it remains a simple test, quick to perform and explores the different areas of speech assessment.

Conclusion
Cochlear implantation is worldwide considered a safe and highly effective technique in rehabilitating children with severe to profound SNHL. Its effectiveness has already been demonstrated and our results are in agreement with those of the literature. Its Bene its include not only better abilities to hear and to develop speech and language skills, but also improved academic attainment, improved quality of life, and better employment status.