Pediatric Hearing Loss

Etiology

Hearing loss can be broadly characterized as congenital or acquired in the pediatric population.

Congenital Causes

Congenital hearing loss can be classified as genetic and non-genetic in etiology. The former category is responsible for greater than half of congenital causes and can be due to either an autosomal dominant, recessive, or sex-linked mutation.[1] Genetic causes are often further subdivided into syndromic versus non-syndromic categories based on whether the patient suffers from an underlying genetic syndrome. Approximately 30% of the genetic causes of hearing loss are syndromic.[2] The most common cause of congenital hearing loss is autosomal recessive non-syndromic hearing loss. 

TORCH organisms (toxoplasmosis, rubella, cytomegalovirus (CMV), and herpes) have been identified as key infective causative agents. CMV is the most common cause of congenital non-genetic hearing loss in the developed world. Other congenital causes include trauma, ototoxic medications used in the antenatal period, and several perinatal risk factors such as prematurity, low birth weight, and hyperbilirubinemia.

Acquired Hearing Loss

Otitis media with effusion is the number one cause of acquired hearing loss in children. It is beyond the scope of this article to cover this in detail, but it classically has a bimodal peak at 2 years and 5 years of age and is characterized by a conductive hearing loss associated with a flattened tympanogram.[3] It typically resolves without intervention as the eustachian tube matures or following the insertion of a ventilation tube in the middle ear.[4] Adenoidal hypertrophy can contribute to this clinical picture.[5] Infections also present another major category for acquired hearing loss, with a particularly strong link with bacterial meningitis, mumps, and measles. Other reasons include primary otological pathologies such as cholesteatoma, impacted wax, and otosclerosis, as well as trauma.

High-risk factors in neonates:

• Congenital infections
• Family history
• Craniofacial anomalies
• Hyperbilirubinemia
• Birth weight 1500 g
• Low Apgar
• Bacterial meningitis
• Need prolonged intubation

Epidemiology

Hearing loss occurs in 1-3 newborns per 1000 births,[6] with 1-2 per 1,000 suffering from permanent childhood hearing impairment.[7] There is a slightly increased prevalence of hearing loss in boys compared to girls, with a ratio of 1.16:1.0.[7] There are around 45,000 children with hearing loss in the UK, half of which are congenital in origin.[8] 

Pathophysiology

Any condition that lowers the transmission of sound from the external space to the cochlea will cause conductive hearing loss. This includes cerumen, abnormalities of the helix or auricle, effusions, and fixed ossicular chain. Besides cholesteatoma, other masses include glomus tumors, schwannomas of the facial nerve, and hemangiomas.

Sensorineural hearing loss is due to interruption of sound transmission after the cochlea. This may be due to damage to the hair cells or damage to the 8th cranial nerve. Even mild distortions in the hair cells can result in severe hearing loss.

Categories of hearing loss are as follows:

• Slight hearing loss: 16-25 dB
• Mild hearing loss:    26-40 dB
• Moderate hearing loss: 41-55 dB
• Severe hearing loss: 71-90 dB
• Profound hearing loss: 90 dB

History and Physical

Hearing loss can present in different ways depending on the age of the child. Hearing loss in neonates is almost exclusively picked up via newborn screening program assessments. In older children, parents or other professionals, such as school teachers, may notice delayed language skills, behavioral problems, or listening to the television at raised volumes. In the history, it is important to ascertain whether there are any associated otological symptoms such as otorrhoea, otalgia, tinnitus, or vertigo. A thorough history is required, including asking about any other neurological symptoms, and medical history, including drug history and precipitating events such as trauma, recent viral infections, or new medications.

The examination will involve assessing the ear, including the appearance of the pinna, particularly inspecting for any deformities such as microtia or anotia. Otoscopic examination of the external auditory canal and tympanic membrane is crucial, with special attention on the attic for cholesteatoma. An examination should also include assessment of cranial nerves, a full neurological assessment, and assessment of balance, depending on the age of the child.

With the implementation of the Universal Newborn Hearing Screening program, today, most patients are identified within a few months after birth, with intervention started by 6 months.

Evaluation

Hearing assessment in children is age and ability dependent and will be addressed per age group here.[9]

Neonates

Otoacoustic Emissions

In the UK, all newborns and those who require less than 48 hours of special care in neonatal intensive care (NICU) are offered evoked otoacoustic emission (OAE) testing within the first 4-5 weeks of birth as part of a Newborn Hearing Screening Programme.[9] Otoacoustic emissions are outer hair vibrations that are detected in the external auditory canal in response to a click stimulus. This test is easy to perform and does not involve a general anesthetic.

Automated Auditory Brainstem Response

This investigation is offered to all newborns who have spent over 48 hours in the neonatal intensive NICU and is also offered to those who do not pass two OAE tests.[9] It involves measuring brainstem electrophysiological responses to click stimuli using electrodes placed on the scalp. This assesses hearing throughout the entire hearing pathway, from the external ear through to the brainstem.

6-8 months                                               

Distraction techniques

An assistant engages the child’s attention, and the tester, whilst placed behind and to the side of the child, makes sounds of different intensities. The child is assessed to see whether they turn to the side of the noise.

9 – 36 months

Visual Reinforcement Audiometry

The child is placed at a table with some toys with two speakers on either side that produce sounds. If the child looks towards the speaker playing a sound, they are delivered a visual reinforcement (such as a flashing light).[10]

24-60 months

Conditioned Play Audiometry

The child is conditioned to perform a task in response to an auditory stimulus, such as placing a ball in a cup. Once the task is learned, the sound volume is reduced in order to determine their hearing threshold.

Over 60 months

Pure Tone Audiometry

A 5 years of age, most children can undergo pure tone audiometry. Hearing thresholds are determined by presenting sounds of various frequencies and at various intensities until the quietest sound is reliably detected 50% of the time. This test requires a higher level of attention and therefore is rarely done below the age of 5 years.

Other investigations

Additional investigations will be tailored to the precise clinical picture. In syndromic children, chromosomal testing is advised. There is also a role for imaging in the form of either computed tomography (CT) or magnetic resonance imaging (MRI)

Some authors advocate the measurement of renal function and testing for connexin-26, which is a marker who sensorineural hearing loss. In some children, imaging studies may prove useful and detect abnormalities of the cochlea or the cochlear nerve. Finally, ECG may be useful in children with Jervell Lange Nelsen syndrome. The ECG will reveal a prolonged QT interval, which can lead to syncopal attacks and death.

Treatment / Management

Treatment for hearing loss depends on the type of hearing loss present, the underlying cause and often there is an element of patient/parent preference.

Conductive hearing loss due to otitis media is treated with antibiotics. Some children may benefit from a myringotomy tube. Sensorineural loss cannot be treated with medical measures. Mild cases may be treated with amplification aids, and speech therapy is useful. However, amplification of sound can result in ear pain and discomfort.

Conservative management

A key element to managing hearing loss is family support and advice. There are a number of behavioral measures that can be used to improve hearing without the need for adjuncts or surgical intervention. The principles of this are rooted in creating a deaf-friendly environment, such as limiting background noise, talking face-on, and clear intonation. There are also a range of hearing assist devices that can be used, such as television listeners. It is also crucial that the child's educational support which could be in the form of special equipment or positioning in the classroom.

Hearing Aids

There are a variety of hearing aid types that are used in specific situations. Each type will be briefly covered here.

Binaural air conduction hearing aids rely on at least a partially functioning inner ear and central auditory processing system. They work by converting sound detected by a microphone into digital signals, which can then be amplified and re-converted into audible sounds that are transmitted to the ear. They can be classified based on whether these key parts are housed in an earpiece that sits externally (behind the ear), inside the canal (in-the-canal), or further inside the canal (in the ear). 

Bone conduction hearing aids are typically used in conductive hearing loss when there are ear problems that impede the use of a regular air conduction hearing aid, such in children with external ear deformities (anotia, microtia) or when there are chronic ear infections. Bone-anchored hearing aids (BAHA) are fitted surgically under general anesthetic over two stages. A titanium implant is fixed into the temporal bone. Through this setup, a sound is conducted directly to the inner ear by way of the bone, bypassing the middle ear. Typically the BAHA is fitting from 4 years of age once the temporal bone has developed. However, soft-band bone conducting aids can be used from several weeks of age.

Contralateral routing of sound (CROS) hearing aids are used when there is unilateral sensorineural hearing loss. The sound in the problem ear is diverted to the better hearing ear without amplification. In cases where neither ear has normal hearing but one side is significantly better, a variation on this can be used called a BiCROS.

Cochlear Implant

Cochlear implants work by converting sound into digital signals that are transmitted directly to the auditory nerve via an electrode array. In the UK, the National Institute of Clinical Excellence (NICE) recommends cochlear implants in children who have severe to profound deafness in one or two ears with minimal benefit from conventional hearing aids after 3 months of use.[11](B3)

Other options

Ventilation tubes are indicated in conductive hearing loss secondary to fluid ear or less frequently in the context of recurrent otitis media. They are inserted surgically and typically self-extrude on average a year of insertion. Children found to have cholesteatoma invariably require surgical clearance of the disease via a mastoidectomy.

Differential Diagnosis

• Acute otitis media

• Cholesteatoma

• Congenital stenosis

• Exostoses

• Foreign body

• Hemotympanum

• Impacted cerumen

• Keratosis obturans

• Middle ear tumour

• Otitis externa

Prognosis

The prognosis of hearing loss will vary considerably based on the underlying etiology. Congenital sensorineural hearing loss left untreated will invariably not improve or can progress, such as in the case of congenital CMV. On the other side of the spectrum, glue ear shows an excellent prognosis with the resolution of symptoms even without intervention.[12]