Ear and Hearing Disorders

Normal Hearing

To understand the spectrum of permanent and transient hearing disorders that can be identified, it is necessary to understand the normal hearing pathway, which consists of transmission of sound energy from the environment via the outer ear through the middle ear, inner ear, auditory nerve, brainstem, and, finally the temporal lobe cortex, where the sound’s electrical energy is interpreted as language ( Table 97.1 ). Dysgenesis, disruption, or injury at any point in the pathway may result in a hearing loss that can have its onset in fetal life or during childhood. The auditory pathway develops embryologically very early in gestation. The inner ear develops first, at about 22 days, and is derived from the otic placodes on either side of the developing head. The middle ear and ossicles derive from the first and third pharyngeal pouches and begin to develop at about day 33. The outer ear develops from the dorsal portion of the first pharyngeal cleft. As a result, congenital hearing loss is often seen in conjunction with structural abnormalities of the head, eyes, ears, nose, and throat. In fact, the odds of having a hearing loss is significantly increased if a preauricular skin tag or pit is present. Atresia or microtia of the pinna are also strongly associated with a permanent hearing loss. Table 97.2 shows the area of pathology associated with the types of hearing loss. A standard medical assessment for every newborn/child should include both a family history of hearing loss and a comprehensive physical examination for minor or major congenital abnormalities and syndromes associated with hearing loss. The primary provider should be familiar with risk factors associated with hearing loss, particularly a family history of permanent hearing loss. Approximately 50% of children with permanent hearing loss, however, will not have associated stigmata. Every physical examination in childhood should include an evaluation for the presence of transient middle ear fluid. Once a child is diagnosed with a permanent hearing loss by an audiologist, additional consultation with ophthalmology, otolaryngology, genetics, and developmental behavioral specialists and a parent support group are recommended to ensure that both the hearing loss and associated diagnoses and challenges are addressed.

Permanent Hearing Loss—The Challenge

Hearing loss is one of the most common congenital abnormalities, occurring in approximately 1.5 to 2 per 1000 newborns screened. Subgroups of infants with risk factors for hearing loss, especially those requiring neonatal intensive care unit (NICU) care are at increased risk of hearing loss. Delayed identification of permanent hearing loss in infants is associated with significant delays in language development, literacy, and academic success. Prior to newborn screening, children in the United States in the 1980s who were deaf or hard of hearing achieved reading comprehension skills at the third grade level at the time of graduation from high school (Deaf Children in America, 1986). A method of identification trialed in the 1980s was the high-risk register. Physicians would be informed by the birthing hospital of infants who were considered at high risk of hearing loss. However, approximately 50% of infants with a permanent hearing loss identified in the newborn period do not have a known risk factor for hearing loss. Newborns were not routinely screened with technology for hearing loss at the time, because there was no effective physiologic method. This changed after a demonstration project in Rhode Island funded by the Department of Education and Health and Human Services in 1990–1991, which demonstrated the feasibility of newborn hearing screening with a new objective physiologic technique, called oto-acoustic emissions (OAEs). This was followed in 1993 by an NIH consensus conference (“NIH Consensus Statement. Early identification of hearing impairment in infants and young children”) recommending universal newborn hearing screening. Data from CDC indicates that in 2018 more than 98% of newborns were screened in the United States ( https://www.cdc.gov/ncbddd/hearingloss/2018-data/01-data-summary.html ).

Hearing Disorders

A hearing loss is secondary to interference in the transmission of sound from the outer ear (pinna and ear canal) to the middle ear (tympanic membrane, ossicles, middle ear space and Eustachian tube opening), the inner ear (cochlea and vestibular system), the central auditory pathway (nerve pathways that transmit to the brainstem and cortex, and the auditory cortex (temporal lobes) where sound information is processed. There are anatomical or neural problems that can develop at any point in this pathway that may interfere with the transmission of sound energy and result in a change in the hearing threshold. There are three types of permanent hearing loss that may be present in the neonate including sensorineural hearing loss, auditory neuropathy (neural hearing loss), and permanent conductive hearing loss, in addition to transient conductive hearing loss (middle ear fluid or debris in the ear canal). Some infants may have a mixed hearing loss, which is a combination of two or more types of hearing loss. Types of permanent and transient hearing loss are shown in Table 97.2 .

Degrees of hearing loss are determined using clinical audiograms, which evaluate the softest hearing level (HL) thresholds, in decibels (dB). Thresholds between –10 and +20 dB HL are considered to be in the normal range, while thresholds above 20 dB are considered diagnostic for mild (20 to 34 dB), moderate (35 to 49 dB), moderately severe (50 to 64 dB), severe (65 to 79 dB), and profound (>80 dB) hearing loss. Ear and frequency-specific behavioral response hearing testing using a visual reinforcement audiometry (VRA) protocol (conditioned response) can be accomplished beginning at approximately 5 to 6 months of age if this is consistent with the infant’s development status. Behavioral testing using conditioned play audiometry can be used in children with developmental ages of 3 to 5 years. The official definition of deafness from the Individuals with Disabilities Education Act is “a hearing impairment that is so severe that the child is impaired in processing linguistic information through hearing, with or without amplification.” Hard of hearing refers to a hearing loss where there may be enough residual hearing that an auditory device provides adequate assistance to process speech.

Methods for Newborn Hearing Screening

The current methods readily available for newborn screening do not independently differentiate permanent hearing loss from transient conductive hearing loss. Since the primary objective of newborn hearing screening is to identify permanent hearing loss, this limitation results in an ongoing challenge of false positive newborn screens, and at times, a delay in the diagnosis of a permanent hearing loss. There are currently two objective, non-invasive physiologic measures, OAEs, either transient or distortion product, and automated auditory brainstem response (AABR) that are available and reliable for screening newborns and young infants.

There are important differences between the two measures as shown in Table 97.3 . OAE measures a physiologic response from the cochlear outer hair cells, while AABR measurements reflect both cochlear status, as well as auditory neural function beyond the cochlea to the brainstem. Thus, the AABR response reflects activity from a greater portion of the auditory pathway than OAE and will detect auditory neuropathy, whereas OAE screening will not. Therefore, because of the higher incidence of auditory neuropathy among NICU infants AABR is recommended for screening in the NICU. Both methods will screen positive for sensorineural hearing loss and permanent conductive hearing loss. Permanent conductive hearing loss is caused by abnormalities of the ossicular chain or eustachian tube anatomy and is more often associated with unilateral hearing loss. Relative to screen fail rates, AABR is more likely to miss borderline or mild hearing loss because of the higher threshold for a pass resulting.

In addition, both methods screen false positive for permanent hearing loss in the presence of transient retained fluid in the ear canal or middle ear fluid with transient conductive hearing loss. It is important to note that there is an increased incidence of transient middle ear fluid among high-risk infants cared for in the NICU. Uncertainty also may arise with mixed hearing loss which is a combination of sensorineural or neural hearing loss in conjunction with transient conductive hearing loss. Therefore, although the methods continue to improve, limitations remain, supporting the need for ongoing surveillance in the medical home. Hearing loss missed by both methods may include mild hearing loss, hearing loss in an isolated frequency range, progressive hearing loss and late onset hearing loss. A study of a large longitudinal cohort in the United Kingdom of over 17,000 neonates born from 2013 to 2014 reported that 24% of infants who did not pass an TEOAE screen but passed an AABR screen were subsequently diagnosed with a hearing loss greater than 45 dB HL using diagnostic auditory brainstem response (ABR). Although current screen methods have limitations, tremendous headway has been made in lowering the age of diagnosis, and newborn hearing screening is recommended for all infants prior to discharge from the birthing hospital. In an effort to facilitate diagnosis of the highest risk in a timely fashion, a current recommendation is for NICU infants who do not pass their hearing screen to have a diagnostic ABR performed prior to discharge. This approach facilitates the current JCIH early hearing detection and intervention (EHDI) recommendation to screen by 1 month, diagnose by 3 months and provide intervention services by 6 months of age.

Risk Factors for Permanent Hearing Loss in Infants and Children

Although approximately 50% of infants with an identified hearing loss have a risk factor for hearing loss ( Table 97.4 ), 50% do not. Therefore, ongoing surveillance and rescreening of all infants/toddlers is recommended with added diligence to those who pass the screen but have a risk factor. Most birthing hospitals currently report risk factors to the primary care provider. However, it may be incomplete since family history is often reported after discharge, and diagnosis of a congenital syndrome may occur postdischarge. Therefore a complete physical and comprehensive review of history of hearing loss with the family after discharge is recommended for all infants.

Identifying risk factors among all newborns and structured monitoring for late onset or progressive hearing loss allows early recognition of children who will not be identified through robust newborn hearing screening programs. As many as 1 in 5 children who are ultimately diagnosed with hearing loss may pass their hearing screening. It is important to perform a complete family history and risk factor query in addition to a comprehensive physical examination. Having a monitoring system for risk factors, including developmental delays within an electronic health record can provide a reminder to the medical home provider to ensure earlier recognition of childhood hearing needs.

Table 97.4 shows the list of risk factors for permanent hearing loss. Although all infants require ongoing surveillance of auditory and speech language skills, infants who pass the newborn screen and have a risk factor will benefit from enhanced surveillance. Within the 2019 Joint Committee on Infant Hearing (JCIH) position statement, monitoring for hearing status noted specific intervals by risk factor. For many risk factors, completing an audiology evaluation with an audiologist experienced in assessing children by 9 months of age is recommended. Children who have been on ECMO and those with congenital cytomegalovirus (CMV) should have a hearing evaluation by 3 months of age. For children with culture positive infections (meningitis), ototoxic medications (such as chemotherapy) and head trauma should receive a hearing assessment no later than 3 months from the event. Most importantly, any time a family or caregiver has a concern about a child’s hearing or speech/language development, referral for hearing testing should be immediate. It is important to remember that passing a newborn hearing screen does not protect a child from later onset hearing loss. Surveillance is especially important since it is well documented that the rate of identified childhood deafness and hearing loss increases from approximately 1.2/1000 in newborns to 3/1000 in early school age. In a 2015 report the prevalence of children confirmed as deaf or hard of hearing by school age was 3.65 per 1000.