Congenital Hearing Loss – Overview, Diagnosis, and Management Strategies

Abstract

Congenital hearing loss, i.e., hearing loss that presents during the perinatal period from the 20th week of gestation to the 28th day of birth, is a prevalent cause of physiological and social morbidity in pediatric patient development. Hearing loss may be hereditary or acquired, with the former including syndromic and nonsyndromic causes and the latter consisting of infections and ototoxic medication exposure. With the help of various diagnostic tools and universal newborn hearing screening programs, many of these patients may be identified early and intervened to improve long-term outcomes. Interventions may include amplification, otologic surgeries, cochlear implantation, and brainstem auditory implants.

1. Introduction

Hearing loss may result from disruption at any level of the auditory system. If the hearing loss results from abnormalities housed in the external ear (e.g., the auricle, the external acoustic canal) or the middle ear (e.g., the middle ear cavity, the ossicular chain, etc.), it is deemed a conductive hearing loss. On the other hand, if the abnormality is located in the inner ear (e.g., the cochlea, the spiral ganglion, or the distal afferent fibers of the cochlear nerve) or in proximal portions of the neural component of the auditory system (e.g., the cochlear nerve, higher-degree neurons in the brainstem projecting to cephalad parts of the auditory system), then it is called sensorineural hearing loss (SNHL). If both conductive and sensorineural components explain a patient’s hearing loss, it is considered a mixed hearing loss. The severity of the loss is categorized by hearing thresholds recorded as decibels. In pediatric patients, mild hearing loss corresponds to 20–39 dB, moderate hearing loss from 4069 dB, severe hearing loss from 70 to 89 dB, and profound hearing loss from values equal to or higher than 90 dB. Congenital hearing loss, i.e., hearing loss that presents during the perinatal period from the 20th week of gestation to the 28th day of birth, is a prevalent cause of physiological and social morbidity in pediatric patient development. Early diagnosis and intervention are critical to optimize the patient’s language and social development.

2. Epidemiology

Congenital hearing loss is considered the most common birth defect in the U.S., with estimates ranging from an average of 1.7 per 1000 infants [1]. However, not all infants are affected equally. Studies have shown that there are racial and ethnic disparities in the prevalence of congenital hearing loss, with higher rates disproportionately affecting minorities and infants from low-income neighborhoods compared to non-Hispanic white infants and those from more affluent communities [2].

3. Etiologies

Congenital hearing loss may be genetically inherited (50%) or acquired (50%) after exposure to infections or ototoxic medications. Hereditary hearing loss can be further divided into syndromic, i.e., as part of a condition involving a constellation of clinical symptoms affecting a patient, or non-syndromic, i.e., an isolated clinical finding in an otherwise healthy patient.

3.1 Inherited syndromic congenital hearing loss

3.1.1 Pendred syndrome

Pendred syndrome is one of the most common inherited syndromic forms of sensorineural hearing loss, accounting for 5–10% of cases of congenital hearing loss [3]. It results from mutations in the pendrin gene (SLC26A4/PDS) on chromosome 7q, which codes for a protein pump responsible for transporting chloride, iodine, and other anions in the cochlea and thyroid follicular cells [4]. Affected patients usually present during adolescence with bilateral, progressive, and profound SNHL with or without structural cochlear abnormalities (such as enlarged vestibular aqueduct and Mondini deformity) [5] and with diffuse thyroid goiter with or without hypothyroidism.

3.1.2 Waardenburg syndrome

The most common form of autosomal dominant syndromic congenital deafness is Waardenburg syndrome, accounting for 2–5% of congenital hearing loss cases [6]. Multiple genes have been described as responsible for the phenotype of this syndrome and involve the PAX3 gene (i.e., paired box 3 transcription factor) located on chromosome 2q37, MITF (microphthalmia-associated transcription factor), EDN3 (endothelin 3) and SOX10 (Sry bOX10 transcription factor).

The clinical features of Waardenburg syndrome include unilateral or bilateral SNHL, pigmentary changes in the skin, hair, or eyes, and craniofacial dysmorphic features [7]. The pigmentary changes may consist of the following:

• A white forelock (a patch of white hair on the scalp hair).

• Heterochromia irides (heterogenous coloration of the iris).

• Premature graying of hair.

• Vitiligo.

Additionally, the craniofacial dysmorphic features may include:

• Dystopia canthorum (abnormal position of the medial canthi of the eyes).

• A broad nasal root.

• Synophrys (unibrow).

There are four different variants of Waardenburg syndrome, as summarized in Table 1.

Waardenburg syndrome types	Pattern of inheritance	Clinical features
Type I	Autosomal dominant	Sensorineural hearing loss, heterochromia irides, white forelock, patchy hypopigmentation, dystopia canthorum
Type II	Autosomal dominant	Type I, but without dystopia canthorum
Type III	Autosomal dominant	Type I with microcephaly, musculoskeletal abnormalities, intellectual; disability
Type IV	Autosomal recessive	Type II with Hirschsprung disease

Table 1.

The four subtypes of Waardenburg syndrome.

3.1.3 Usher syndrome

Another common syndrome causing inherited congenital sensorineural hearing loss is Usher syndrome. It is considered the most common cause of combined inherited vision and hearing loss, and up to 3–6% of cases of congenital hearing loss may be attributed to Usher syndrome [8, 9]. Mutations in several genes cause it; however, the most involved gene is MYO7A, which codes for a myosin protein in various tissues, most notably in the cochlea and retina [10]. Aside from SNHL, it is associated with retinitis pigmentosa (hereditary retinal dystrophy) and may be associated with or without vestibular system abnormalities. Retinitis pigmentosa initially manifested by nyctalopia (night blindness), progressing to peripheral vision impairment, and finally leading to blindness. Evaluation by an ophthalmologist is critical in the management of Usher syndrome.

There are four different types of Usher syndrome, as summarized in Table 2.

Usher syndrome types	Pattern of inheritance	Clinical features
Type I	Autosomal dominant	Most severe phenotype, clinical presentation during childhood, sensorineural hearing loss, vestibulopathy, retinitis pigmentosa
Type II	Autosomal dominant	Most common subtype, clinical presentation during adolescence, no vestibulopathy, retinitis pigmentosa
Type III	Autosomal dominant	Similar clinical features as Type I Usher syndrome but with milder symptoms

Table 2.

The three major different subtypes of Usher syndrome.

3.1.4 Branchio-oto-renal syndrome (Melnick-Fraser syndrome)

Branchio-oto-renal syndrome is an autosomal dominant inherited condition with complete penetrance and variable expressivity characterized by congenital hearing loss (may be conductive, sensorineural, or mixed), external ear deformities, branchial cleft anomalies, and renal abnormalities [11, 12]. The genetic mutations involve the EYA1 gene, intimately involved with the embryonal development of the auditory system, branchial arches, and the genitourinary system.

3.1.5 Jervell and Lange-Nielsen syndrome

Jervell and Lange-Nielsen syndrome is a rare genetic disorder resulting from mutations in the KCNQ1 or KCNE1 genes affecting the β-subunit of connexin 26 located in the marginal cells of the stria vascularis and heart, leading to sensorineural hearing loss and long QT syndrome [13]. This syndrome accounts for less than 1% of cases of congenital hearing loss. Episodes of arrhythmias characterize this syndrome due to a defect in cardiac conduction that can even terminate with sudden death. The degree of hearing loss is variable; however, it is usually severe to profound.

3.1.6 Other syndromes

These are just a few examples of the syndromes that can cause congenital hearing loss. Other syndromes associated with hearing loss include Alport syndrome, Treacher-Collins syndrome, CHARGE syndrome, and Stickler syndrome, as detailed in Table 3 [14, 15].

Clinical syndrome	Predominant pattern of inheritance	Clinical key points
Alport syndrome	X-linked pattern	Progressive, bilateral SNHL resulting from defective collagen type IV synthesis (present in the basement membranes of the inner ear and kidneys).; Hearing loss occurs before the onset of kidney insufficiency. Renal disease results from progressive glomerulonephritis, mostly ending at end-stage renal disease.
Treacher-Collins syndrome (Mandibular Facial Dysostosis)	Autosomal dominant	Autosomal dominant craniofacial condition affecting the bones and tissues in the face leading to deformities of the ears, eyes, zygomatic bones, and chin, i.e., structures derived from the first and second pharyngeal arches during embryologic development.; Malformations of the ear may include microtia and aural meatal atresia leading to conductive hearing loss; however, bilateral SNHL may also be possible.
CHARGE syndrome	Sporadic (not inherited)	C (coloboma of the eye); H (heart disease); A (atresia of choanae); R (development and growth retardation); G (genitourinary abnormalities); E (ear abnormalities); The ear malformations may be associated with conductive or SNHL and are usually asymmetric.
Stickler syndrome	Autosomal dominant	Hearing loss, ocular abnormalities (e.g., retinal detachment, cataracts, and myopia), bone and joint abnormalities (e.g., arthritis and joint hypermotility), and Pierre Robin sequence.; Hearing loss is usually progressive sensorineural but also can be conductive due to abnormalities in the middle ear. There are several types of Stickler syndrome (Type 1, type 2, and type 3) due to mutations in different genes.

Table 3.

Other syndromes associated with congenital hearing loss.

3.2 Inherited nonsyndromic congenital hearing loss

Non-syndromic hereditary hearing loss can result from a functional or structural abnormality. Loss of function commonly results from mutations in proteins involved in the processing of sound signals. These conditions are inherited in an autosomal recessive manner in 80% of cases, and the remaining 20% in an autosomal dominant manner. Mutations in GJB2, which encodes for connexin 26, a gap junction protein that facilitates communication between cells in the stria vascularis, cause 50% of all autosomal recessive cases, leading to severe-profound bilateral sensorineural hearing loss [16]. Mutations affecting otoferlin are another important cause of non-syndromic SNHL. This transmembrane protein plays a crucial role in inner hair cell glutamate exocytosis at the synapse with the cochlear nerve ends [17].

On the other hand, structural malformations lead to hearing loss by disrupting the pathway of soundwaves. These malformations can affect the external, middle, or inner ear and can occur in isolation or as part of a syndrome. Examples of structural abnormalities leading to conductive hearing loss include: microtia, where the external ear is dysplastic or absent; stenosis or atresia of the external auditory canal; anomalies of the ossicular chain; and congenital cholesteatomas, which are benign tumors of keratinizing epithelium found in the middle ear cavity and can result in chronic inflammation. Sensorineural hearing loss can result from cochlear malformations such as enlarged vestibular aqueduct, cochlear hypoplasia, dysplasia, or aplasia. The most common cochlear anomaly is Mondini dysplasia, also known as type II dysplasia, where the cochlea has one and a half turns instead of the normal two and a half turns [18].

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3.3 Acquired congenital hearing loss due to infections

Hearing loss can be caused by infections occurring before or after birth. Therefore, infections play a major causative role in acquired congenital hearing loss, particularly TORCH infections, which include Toxoplasmosis, Other (such as Syphilis, Varicella-Zoster virus, Hepatitis B virus), Rubella, Cytomegalovirus, and Herpes simplex virus. Although we will only mention a few examples, many other viruses are associated with congenital hearing loss, including Lymphocytic choriomeningitic virus, Measles, and Human immunodeficiency virus [19].

3.3.1 Cytomegalovirus infection

The most common cause of non-genetic congenital sensorineural hearing loss is congenital infection with cytomegalovirus (CMV), a member Herpesviridae family, which causes up to 40% of cases [19]. CMV infection in newborns is notorious for affecting the auditory system, as it is also the most common sequelae caused in this patient population. Contrary to other otologic viral pathogens (e.g., Rubella), maternal immunity does not confer immunity against vertical transmission to the fetus [20]. Thus, it may be transmitted through the placenta or by direct contact with infectious body fluids during labor or while breastfeeding. Hearing loss correlates with the degree of viral load and results from both, direct cytopathic effects of viral inclusions bodies and indirect effects induced by the host’s inflammatory response to the virus in the inner ear and cochlear nerve [19].

Primary CMV infection during pregnancy poses a 40% risk of intrauterine transmission. Approximately 90% of infants are asymptomatic at birth, but approximately 15% will develop hearing loss eventually. Therefore, asymptomatic babies can develop hearing loss several years after birth, making the diagnosis of congenital CMV infection challenging. On the contrary, symptomatic babies at birth can have the following: microencephaly, low birth weight, premature birth, jaundice, development delay, hepatosplenomegaly, petechiae, chorioretinitis, thrombocytopenia, hyperbilirubinemia, anemia, and hearing loss. The diagnosis in newborns requires a high index of suspicion by the clinician and is made by detection of CMV DNA in the urine, saliva or blood during the first 3 weeks of life [21].

3.3.2 Toxoplasmosis infection

Toxoplasmosis is caused by an intracellular protozoan parasite, Toxoplasma gondii, that infects humans and animals. Toxoplasmosis is acquired by exposure to cat feces, meat, soil, and water contaminated with the parasite. Intrauterine transmission can result in congenital hearing loss due to damage caused by the inflammatory response in the cochlea and cochlear nerve. This response its mainly triggered by the tachyzoite form of the parasite during active infection [22]. The cystic form (dormant form) of the parasite is not associated with pathological findings. The risk of SNHL following congenital Toxoplasmosis infection has been reported to be 27%, with patients having a 5-fold increased risk of abnormal neonatal hearing screening results compared to non-infected patients [23].

The primary infection during pregnancy carries a 30–50% risk of intrauterine transmission. However, 85% of infants with congenital toxoplasmosis at birth are asymptomatic. The manifestations of congenital toxoplasmosis include micro/macrocephaly, hydrocephalus, cerebral calcification, chorioretinitis, hepatosplenomegaly, jaundice, anemia, thrombocytopenia, petechiae, and lymphadenopathy. The diagnosis will require a high index of clinical suspicion plus positive laboratory serologic findings. Although treatment is not standardized, it is recommended that children receive treatment with pyrimethamine and sulfadiazine [24].

3.3.3 Rubella infection

Rubella virus, a member of the Togaviridae family of viruses, is another pathogen responsible for causing sensorineural hearing loss. It occurs as part of the broader Congenital Rubella Syndrome, which involves cataract formation, cardiac anomalies, intellectual disability, a characteristic “blueberry muffin” rash, and SNHL. First, the primary infection of an unvaccinated mother occurs during pregnancy, with subsequent vertical transmission to the fetus through the placenta. Following viremia, the virus invades the inner ear and directly damages the stria vascularis and Organ of Corti in the cochlea leading to SNHL [19]. If the pregnant mother is infected during the first 11 weeks of pregnancy the chance of congenital rubella syndrome is approximately 90%. Fortunately, Congenital Rubella Syndrome has plummeted since widespread vaccination programs against the Rubella virus began [25]. The Centers for Disease Control and Prevention (CDC) in the United States suggests administering the rubella vaccine, as part of the combined measles, mumps, and rubella (MMR) vaccine, between 12 and 15 months, followed by a booster shot at 4 to 6 years old.

3.3.4 SARS-CoV-2 infection

Coronaviruses, a family of enveloped, single-stranded RNA viruses, have the ability to invade the cranial nervous system through both anterograde and retrograde transport from nerve endings [26]. The recent epidemic caused by SARS-CoV-2, which emerged in 2019, has been linked to hearing loss in certain adults [27]. However, the impact of intrauterine transmission of SARS-CoV-2 on the inner ear development in embryos is still unclear. Despite limited research in this area, several retrospective multicenter cohort studies have investigated whether exposure to COVID-19 in utero increases the risk of hearing loss in infants. To date, these studies suggest that intrauterine exposure to COVID-19 is not a risk factor to the development of hearing loss [27, 28, 29].

3.4 Acquired congenital hearing loss due to ototoxic medications

Another important cause of acquired congenital hearing loss is ototoxic medication exposure. For example, aminoglycosides (antibiotics commonly used to treat severe neonatal infections such as meningitis) are notorious for causing sensorineural hearing loss. Cochlear hair cells are terminally differentiated cells without the capability of regenerating following insults. Drugs may reach the inner ear through the blood-labyrinth barrier or topically through the middle ear and the round or oval windows. However, regardless of how they reach the inner ear, aminoglycosides tend to concentrate in the endolymph of the inner ear and cause direct cytotoxic damage through the chelation of iron, the increased signaling of NMDA receptors, and creation or reactive oxygen species, ultimately affecting the stria vascularis and outer hair cells [30]. As it more commonly affects the inner row and basilar turn of the cochlea first and later progresses towards the apex, ototoxicity caused by aminoglycosides manifests as high-frequency hearing loss. Other medications can also induce SNHL, such as systemic chemotherapy (e.g., cisplatin), macrolides antibiotics, salicylates, and loop diuretics.

4. Screening and diagnostic approach

A child who is deaf or hard of hearing in infancy is at increased risk for delays in speech and language development, academic achievement, and social outcomes without early recognition [31]. Before the advent of universal neonatal screening programs, the average age of diagnosis of congenital hearing loss was two years old [32]. U.S. states and territories, as well as other international jurisdictions, have implemented Early Hearing, Detection, and Intervention (EHDI) programs to maximize the number of newborn patients screened for hearing loss [33]. The specific goals by age are summarized in the “1–3-6” guideline, i.e., screening all newborns within 1 month of age, evaluating and establishing a diagnosis in all newborns that failed the hearing screening tests within 3 months of age, and starting therapeutic hearing intervention within 6 months of age in those patients with confirmed hearing loss. These interventions have been correlated with improved language outcomes.

4.1 Neonatal hearing screening

The screening consists of two electrophysiological tests that must permit detecting hearing thresholds deficits of equal or more than 35 dB and that may be used in infants less than or equal to 3 months of age, e.g., Automated auditory brainstem responses (AABR) and Otoacoustic emissions (OAE) [34]. The most commonly used test for neonatal hearing screening is the AABR, which estimates the integrity of the entire auditory pathway by using a series of electrodes placed in the patient’s skull to detect electrical signal changes recorded as a waveform in response to 35 dB click. In AABR, the generated waveform from the patient is compared to that of a standard control sample. Like the conventional auditory brainstem response (ABR) test, the generated waveform consists of a series of peaks corresponding to different events in the auditory pathway. However, the comparison in AABR is made in an all-or-none binary fashion, with a pass-fail type of result. Thus, even though the estimated accuracy for identifying patients with decreased hearing thresholds under 35 dB between an AABR and an Auditory Brainstem Response is 98% [35], further characterization of the hearing loss must be done after a neonate fails a test.

Otoacoustic emissions (OAE) is another commonly employed objective screening test, which registers changes in the tympanic membrane compliance in response to acoustic signals generated from the cochlea’s outer hair cells. It is worth mentioning that the middle ear must be cleared of existing pathologies (e.g., middle ear effusion) to use OAE as an indicator for cochlear function. Both tests, AABR and OAE, are performed sequentially [34].

4.2 Evaluation of an infant after a failed hearing screening test

Providers must conduct a comprehensive audiological assessment for patients who do not pass the screening test, including otoscopic examination, audiometric tests, and Auditory Brainstem Responses.

The otoscopic evaluation may reveal important causes of hearing loss, including external ear canal stenosis or middle ear effusion. Concerning audiometric testing, providers must tailor these tests based on the patient’s neurodevelopmental age. For instance, trained audiologists can conduct a Behavioral Audiological evaluation for patients younger than 6 months. During this examination, patients are placed in a sound-controlled room and are presented with various tone stimuli, such as speech and warbled tones, through an earphone. The audiologist records the patient’s minimal response level (MRL), which may include behaviors like eye widening and head movements and traces the patient’s response as a function of the frequency at which the stimuli were presented, which ranges from 500 Hz to 4000 Hz. However, due to the subjective nature of this evaluation and its inherent variability, other objective audiological assessments are more commonly utilized in this patient population, e.g., Auditory Brainstem Responses.

Visual Reinforcement Audiometry is another audiological evaluation used to screen for congenital hearing loss in children, although suitable for patients older than 6 months but younger than 30 months. This test involves placing the patient in a sound-controlled environment like a Behavioral Audiometric evaluation. However, operant conditioning is employed by associating different sound levels with a playing video or moving toy, creating a conditioned behavioral response (e.g., head movements).

Upon objective confirmation of hearing loss, patients require further investigations and ongoing monitoring [36]. It is imperative to conduct genetic testing to identify common genetic mutations associated with congenital hearing loss with an unknown etiology. Prompt screening for potential causative infections, such as cytomegalovirus, is also essential. Obtaining head and neck imaging studies, including Computerized Tomography (CT) and/or Magnetic Resonance Imaging (MRI), is highly recommended to assess the presence of structural ear abnormalities and other pertinent features (e.g., state of cochlear nerves to evaluate candidacy for cochlear implants, later detailed). Moreover, considering the increased likelihood of accompanying ophthalmological abnormalities, an ophthalmological evaluation is advised for individuals with congenital sensorineural hearing loss.

5. Management strategies

Management of congenital hearing loss is done by providing the best hearing amplification option personalized to the specific auditory necessity of a given patient. It is also primarily dictated by addressing what caused it in the first place. Early intervention with hearing amplification (ideally before 6 months of age) is critical for infants with congenital hearing loss for their language and communication development.

5.1 Nonsurgical management

5.1.1 Hearing amplification

Hearing aids are small electronic devices that amplify sound and deliver it to the ear, and in infants, they may be used as young as a few weeks old. They consist of a microphone, an amplifier, and a speaker. For infants with hearing loss, the behind-the-ear (BTE) hearing aid is preferred as it is cheaper (parents only need to change the ear mold as the external ear grows) and a safer (lower risk for swallowing) alternative to in-the-ear (ITE) hearing aids. Fitting should be done every 3 months during the first 2 years of use due to the relatively rapid remodeling that the external ear undergoes during development [37]. The clinician and the audiologist should be aware that infants (children younger than 2 years), children from mothers with no college education, and children with mild hearing loss have been known to report less compliance with hearing aid daily use. Thus, increased surveillance and intervention is required to avoid poor outcomes in these patients.

5.1.2 Assistive listening devices

Assistive-learning technologies (e.g., personal amplifiers, FM systems) are devices consisting of a microphone and a speaker that aim to optimize the acoustic signal-to-noise ratio that patients experience during spoken language [38]. It may be particularly useful in specific situations like, for example, for children struggling in their academic performance due to poor comprehension. In these situations, the teacher would have a microphone and the student would possess the assisted listening device in the better hearing ear, in conjunction with his or her hearing aid.

5.1.3 Auditory-verbal therapy

Auditory-verbal therapy is a type of therapy that serves as adjuvant therapy to hearing aids, cochlear implants, or assistive listening devices to improve spoken language skills. It has been shown to increase receptive language skills and improve speech production in infants with hearing loss [39]. Therapies involve the patient and his or her family, which play a central role. A trained speech and language pathologist conducts the therapy, or other trained personnel (e.g., a teacher for the deaf, audiologist) excludes non-verbal means of communication (e.g., sign language) to achieve competency in spoken language.

5.2 Surgical management

5.2.1 Otologic surgeries

The appropriate management approach primarily of congenital conductive hearing loss revolves around addressing the underlying causes of the hearing loss [40]. For instance, in external auditory canal atresia without ossicular chain pathology, patients may benefit from remodeling the external canal shape through an atresiaplasty after they reach 6 years of age. For patients with microtia who have significant hearing loss and psychological distress from cosmetic deformity, surgical intervention can provide substantial benefit. Alloplastic implants, i.e., made from artificial materials, can be used as early as 3 years of age. If the option of using autologous rib harvest is being contemplated, it is generally preferred to wait until the patient’s ear reaches full adult size, which typically occurs around the age of 6 years. If the tympanic membrane or ossicles house any abnormality that would deem them amenable for surgical correction (e.g., chronic suppurative otitis media, ossicular chain fixation), a tympanoplasty with or without ossicular chain reconstruction, for example, may be indicated to restore the function of the middle ear.

A common finding in neonates that fail newborn hearing screening is Otitis Media with Effusion. The Academy of Otolaryngology and Head and Neck Surgery recommends ensuring adequate follow-up for neonates failing the newborn hearing screening with Otitis Media with Effusion, as it does not necessarily rule out the possibility of another co-existing cause of hearing loss [41]. Usually, otitis media with effusion resolves by itself within three months. For those patients who do not resolve after such a period, tympanostomy with ventilation tube placement can be considered. Additionally, for patients with congenital aural atresia, other forms of congenital conductive hearing loss not amenable to the surgeries mentioned above, or sensorineural hearing loss not amenable to cochlear implants, a bone-anchored hearing aid (BAHA) provides an excellent alternative [42]. It involves an osseointegrated titanium implant inserted into the temporal bone and a percutaneous abutment for the bone-conduction hearing aid.

5.2.2 Cochlear implantation

Patients with profound bilateral sensorineural hearing loss and an intact cochlear nerve may be candidates for cochlear implantation [43]. In the United States, the Food and Drug Administration (FDA) has approved cochlear implants for patients as young as 9 months of age, with device-specific approval granted recently [44]. Lowering the minimum age for consideration is supported by evidence showing that early implantation enhances quality of life, improves language skills, and promotes auditory development. Bilateral cochlear implantation is advocated as it further improves language skills and sound localization. The anatomy and integrity of the vestibulocochlear nerve are confirmed through imaging, including Magnetic Resonance Imaging (MRI) and Computerized Tomography (CT) scans of the temporal bone. Prior to surgical consideration, patients should be up to date with their vaccinations.

5.2.3 Brainstem auditory implantation

In cases with profound sensorineural hearing loss in which the cochlear nerve is absent or damaged or in cases where cochlear implantation cannot be done, an auditory brainstem implant (ABI) can be considered [45]. The implant is placed along the lateral recess of the fourth ventricle, and its electrode directly stimulates the cochlear nucleus, effectively bypassing the vestibulocochlear nerve and more distal portions of the auditory apparatus. In the United States, ABIs are only approved for patients older than 12 years of age and suffer from Neurofibromatosis type 2, a rare condition caused by mutations in the Merlin protein gene located in chromosome 22 that results in multiple nerve tumors, including bilateral vestibular nerve schwannomas. However, in recent years other applications have been described, such as in post-meningitis bilateral total ossified cochlea, various inner ear malformations, and trauma.

6. Conclusions

Congenital hearing loss is a common factor contributing to both physical and social challenges in the development of pediatric patients. This type of hearing loss can be either inherited or acquired, with inherited causes encompassing syndromic and non-syndromic, while acquired causes include infections and exposure to ototoxic medications. Through the utilization of various diagnostic tools and the implementation of universal newborn hearing screening programs, many of these patients can be identified early on and receive appropriate interventions to enhance long-term outcomes.

Conflict of interest

The authors declare no conflict of interest.