Parental concern about a child’s hearing should precipitate an immediate referral to an audiologist.
Audiologists can test the hearing of children at any age.
A child who has suspected or diagnosed global delays or speech and language delays should be referred promptly for audiologic testing.
Children who have severe emotional or neurological impairment can be tested accurately by using evoked response testing.
Early diagnosis and management of children who have all degrees and types of hearing impairment can be attained through heightened awareness of physicians and other health professionals to the indicators for hearing loss and the need to develop a strong coalition with a licensed audiologist.
The prevalence of hearing loss among newborns and infants in the United States is estimated to be 1.5 to 6 per 1,000 live births. This estimate, however, is based on the number of children who are profoundly deaf and does not account for infants who are mildly or moderately to severely hearing impaired. Thus, the true prevalence is no doubt much higher. More alarming is the fact that the average age at which a child who has a profound, bilateral, sensorineural hearing loss is identified is 24 months, while hearing impairments of lesser degrees often are identified at an average age of 48 months of age. The impact of these statistics is disturbing because the critical period for language learning is within the first 36 months of life. Thus, undetected or late detection of significant hearing impairment in infants and young children results in lifelong disability.
Early Detection and Intervention Efforts
Late detection of significant hearing impairment not only affects a child’s speech and language learning, but it can result in academic failure, which in turn severely limits career options. Ultimately, the independence of the hearing impaired individual is compromised. One nationwide focus of health professionals and the federal government is to improve methods for early identification of hearing impairment. In 1990, as one of the initiatives in the Healthy People 2000 document, the United States Department of Health and Human Services stated that by the year 2000, identification of children who are hearing impaired will be reduced to 12 months of age or younger. In accordance with this initiative, the National Institutes of Health, in a consensus statement, and the Joint Committee on Infant Hearing endorsed universal detection of and intervention for hearing impaired infants. In addition, amendments to the Education of the Handicapped Act (PL 99-457) mandate services for children who have handicaps (including hearing loss) as part of a comprehensive, multidisciplinary early intervention effort. Despite these initiatives, many caregivers remain unaware of the laws that support them in acquiring early intervention services for their children. In these cases, health professionals have a responsibility to inform caregivers of their rights and to advocate for them and their child.
Factors Contributing to Delays in Diagnosis
Physicians and other health professionals need to work with each other and with caregivers to identify hearing loss and provide intervention. Pediatricians have the opportunity to evaluate infants on multiple occasions in early infancy and several more visits before the age of 24 months. During these visits, the physician can listen to parental concerns about a child’s speech, language, and auditory development. Parental concern is of greater predictive value than the informal behavioral examination performed in the physician’s office. According to one investigation, parents are usually 12 months ahead of physicians in identifying their child’s hearing loss. In addition, knowledge of the associated hearing loss that occurs in craniofacial syndromes, among children who have developmental (especially speech) delays, and in other medical conditions that place children at risk for hearing loss will ensure the earliest possible diagnosis and contribute greatly to successful management of the hearing disorder. There is no place for the “wait and see” approach in diagnosing hearing loss.
The purpose of this review is to provide clinicians with information about: the development of the ear and the onset of hearing that is necessary to identify audiologic health care needs of infants and children; indications for referral for audiologic evaluation; the components of audiologic testing; degrees and types of hearing loss; and management of the hearing impaired child.
Development of the Ear and the Onset of Hearing in Humans
DEVELOPMENT OF THE EAR
The first signs of ear development occur at about the third week of gestation, when the neural tube is forming. The five branchial arches noted at this time encompass five branchial grooves or “gill slits” and their corresponding pharyngeal pouches. As the ear begins to take its final shape, the outer ear forms from ectodermal tissue of the first and second branchial arches. The middle ear ossicles (malleus, incus, and stapes) arise from mesodermal tissue. The malleus and incus arise from mesoderm of the first branchial arch, and the stapes arises from the second branchial arch. The middle ear lining and eustachian tube develop from endodermal tissue of the first pharyngeal pouch. The auditory structures and organ systems of the body associated with the three germ layers from which all systems and structures develop are shown in Table 1⇓ . (See Suggested Reading for detailed reviews of auditory development by Peck and by Northern and Downs.)
ONSET OF HEARING
Around the 20th week of gestation, the outer ear has developed and taken on its adult shape. It will continue to grow in size, however, until a child reaches age 9 years. The middle ear ossicles are almost completely ossified, and the inner ear has achieved adult size, although differentiation of the sensory cells (outer and inner hair cells) in the organ of Corti is still underway. By 24 weeks, the human cochlea and its end organ have matured structurally. Myelination of the ganglion nerves at this same time may be taken as evidence that the onset of hearing probably occurs in the sixth month of gestation.
Knowledge of normal human embryology and the associations of each organ system with its respective developmental germ layer enables the health-care professional to be alert to the presence of physical anomalies and the possibility of related structural defects that include ear and hearing abnormalities. For example, hypertelorism and abnormal pigmentation of the skin, hair, or eyes (eg, Waardenburg syndrome) may be associated with cochlear pathology because these anomalies are related to disturbances of the surface ectoderm during development. Anomalies associated with the first and second branchial arches may include mandibular hypoplasia, an abnormally formed external ear, and the presence of preauricular pits or tags. In one study, nearly 50% of 46 children who were diagnosed with permanent hearing loss showed signs of associated structural deformities and related visible physical anomalies.
Referral for Audiologic Evaluation
Children who have structural anomalies or syndromes known to be associated with hearing impairment should be referred promptly for audiologic evaluation. Other referral criteria include significant perinatal events and medical history that may be associated with sensorineural hearing impairment. Further, children who have suspected global delays or speech and language delays should be referred. The high-risk indicators identified by the Joint Committee on Infant Hearing can guide physicians for referral of infants and children for hearing assessment (Table 2⇓ ). Awareness of expected speech/language/auditory milestones is helpful in noting lack of achievement or delayed attainment of specific milestones (Table 3⇓ ). A checklist can aid professionals in obtaining important information from parents and medical records.
Recent advances in technology have made available an extensive battery of tests for evaluating all parts of the auditory system. A test battery, rather than a single test, is necessary for pediatric assessment to compare and perform a “cross-check” of all test results.
The outer ear is evaluated both visually and by otoscopic examination. The size and shape of the pinnae should be observed, as should the presence or absence of skin tags or ear pits on or near the pinnae. The examiner also should note the presence of abnormal skin growths, debris, or excessive cerumen that may block the auditory signal from reaching the inner ear. Finally, the examiner should visualize the familiar landmarks on the tympanic membrane (TM) (cone of light, umbo, long and short crus of the malleus).
The middle ear status and function are evaluated via acoustic immittance testing. The complete acoustic immittance test procedure consists of tympanometry, the physical volume test, and stapedial reflex measures.
Tympanometry measures the energy transfer of the ear as a function of air pressure. It involves sealing the external auditory canal (EAC) with a tightly fitting probe tip that contains three tubes: one connected to an oscillator-receiver for the presentation of a tone, one connected to a microphone for monitoring sound pressure level (SPL), and one leading to a pump-manometer that both varies and measures air pressure in the ear canal. A fixed-frequency tone is presented to the ear while ear canal air pressure is varied from+ 200 mm to −400 mm H2O. Sound reflection is monitored continuously as a function of TM compliance or mobility, which is related directly to the artificial variation of ear canal air pressure. With extremely positive or negative ear canal pressures, the compliance of the TM is reduced and the majority of the sound energy presented to the ear is reflected to the measuring microphone in the probe. As the pressure in the ear canal approaches the value of the pressure in the middle ear, the tympanic membrane becomes more compliant until it reaches a point of maximum compliance, where the pressure in the canal is equal to that in the middle ear space. At maximum compliance, sound energy is transmitted through the TM, and little acoustic energy is reflected. The measurement of ear canal SPL as a function of pressure changes provides a direct assessment of TM compliance, which is plotted as a tympanogram.
In 1970, Jerger described a classification system for determining the status of the middle ear based on the tympanogram and maximum compliance values (peak amplitude measures) (Fig. 1⇓ ). Type A tympanograms are characterized by a maximum compliance peak at or near 0 mm H2O (also measured as 0 daPa) and are measured consistently in normal ears. Type A tympanograms also are measured in otosclerotic ears, but peak amplitude measures may be reduced due to the increased stiffness of the ossicular chain. These reduced compliance tympanograms also are referred to as type AS. In cases of ossicular discontinuity, the compliance of the TM is increased, often beyond the limits of the equipment, resulting in a tympanogram classified as type AD. Type B tympanograms are characterized by their “flat line” appearance, which indicates immobility of the TM, resulting in no recording of a maximum compliance peak in the tracing. Middle ear effusion is the most consistent diagnosis associated with a type B tympanogram, although TM perforations also generate this type. Type C tympanograms are similar to type A, but the maximum compliance peak is shifted to the left, beyond −100 mm H2O. This tympanometric function indicates significant negative middle ear pressure and usually is recorded just prior to, or during resolution of, otitis media with effusion. Type C tympanograms also may be recorded in circumstances in which eustachian tube dysfunction, an inability to aerate the middle ear space efficiently, is suspected.
According to recent studies, and as stated in the American Academy of Audiology Position Statement on identification of hearing loss and middle ear dysfunction in preschool and school-age children, measures of tympanic width in conjunction with static compliance and peak pressure measures “may improve the sensitivity of middle ear screening.” Generally, normal tympanic width measures for children should be less than 150 daPa. Children who have a history of middle ear disease, however, often exhibit “wide” tympanograms (>150 daPa), even in the absence of middle ear pathology. Thus, peak pressure, tympanic width, and static compliance measures should be viewed together, along with acoustic reflex data and physical volume measures, to determine any middle ear pathology.
Physical Volume Test
The physical volume test enables calculation of the physical volume of the EAC and is extremely useful in determining TM integrity or ventilation tube patency. When the ear canal is sealed, the SPL measured in the enclosed cavity is related directly to cavity size. Normal physical volume measures in infants and children range from 0.3 to 1.0 mL and depend on ear canal diameter and probe tip insertion. Volumes less than 0.3 mL may indicate either that the probe tip is malpositioned against the ear canal wall or that excessive cerumen is present. In both instances, a tympanogram that displays a type B function (flat line) may be recorded. Physical volumes larger than 1.0 mL indicate TM perforation or ventilation tube patency. In these cases, a tympanogram cannot be recorded, yet a type B function still might be drawn. Thus, knowledge of the normal physical volumes expected for a child’s ear help to clarify the etiology of a type B tympanogram recording.
Acoustic Reflex Test
The acoustic reflex test in immittance measurement is a powerful diagnostic tool used to help determine degree, type, and site of hearing loss. It cannot be substituted for conventional audiometry, however, because it is not a test of hearing. The acoustic reflex threshold is a measure of the lowest signal intensity that elicits a measurable contraction of the stapedius muscle in the middle ear. In persons who have normal hearing, tonal signals of 70 to 100 dB HL presented to one ear elicit this muscle reflex, while white noise signals of 65 dB HL induce contraction of the stapedius muscle. Because it is a bilateral response, the acoustic reflex threshold can be measured with the stimulus presented to one ear and the reflex measured from either the ipsilateral or the contralateral ear. Helpful guidelines for interpretation of findings for the acoustic reflex threshold test, physical volume test, and tympanometry are found in Table 4⇓ .
The hearing status of the pediatric patient can be assessed by subjective (behavioral) or objective testing (which does not require an overt behavioral response from the child). The type of testing used depends on the child’s developmental age and abilities (Table 5⇓ ).
The behavioral hearing test allows graphing of a child’s response thresholds to tonal stimuli of different frequencies or pitches on an audiogram (Fig. 2A⇓ ). Frequency is expressed on the abscissa from low to high frequencies. The intensity or loudness level in dB HL (referenced to the hearing levels of normally hearing individuals) is plotted on the ordinate, with the lowest intensity sounds at the top and the highest intensity sounds at the bottom. A key of symbols is on the form. Several different techniques can be used to obtain audiometric information from children, depending on the child’s developmental, not chronologic age. Behavioral testing techniques include sound field testing and conventional audiometry.
Testing in the sound field (a sound-treated room) is conducted with the infant seated independently or held on the caregiver’s lap and centered between two loudspeakers. Primary methods of sound field testing include behavioral observation audiometry (BOA) and visual reinforcement audiometry (VRA).
BOA is used with neonates and infants up to 6 months of age. Typically, two audiologists or observers are needed to determine the presence or absence of a response to presentations of warbled pure tones, speech, or white and narrow-band noise at varying intensity levels through the loudspeakers. Toy noisemakers of known frequency and intensity also may be used, although the primitive nature of this test makes it of very little diagnostic use. Responses, which depend heavily on the child’s physical state prior to stimulation, include arousal, startle, eye-widening, cessation of movement, and auropalpebral reflex (closing of the eyes or tightening of the lids if eyes already are closed).
VRA is the sound field procedure used most commonly for testing or screening children from 6 months to 2 years of age. It involves conditioning the child to respond, usually with a head turn toward the active speaker, when the stimulus is heard. Responses are reinforced visually by the examiner activating a lighted toy animal stationed near or on the speaker. A variation of VRA testing is called conditioned orientation reflex (COR) and involves correct identification of the speaker from which the signal is emanating. The difference between VRA and COR is that any overt response to the stimulus (head turning, pointing, or mimicking the sound) is acceptable in VRA testing, whereas correct head turning in response to the stimulus is required with COR. One limitation of both techniques is the inability to assess each ear separately because both ears can listen in the sound field environment. Therefore, results reflect the sensitivity of the better hearing ear. Only when the child can tolerate wearing earphones can ear-specific results be obtained with this method.
The conventional audiometric test battery includes testing via air conduction and bone conduction, obtaining speech recognition thresholds (SRT), and assessing speech discrimination ability. Air conduction testing involves the presentation of pure tone stimuli to one ear at a time through earphones. The intensity of the tones is decreased gradually until the lowest intensity that elicits a response is determined and recorded as the child’s threshold. The need for sound waves to travel through the air of the EAC and middle ear space before reaching the inner ear is the source of the term air conduction testing. It is possible to bypass the EAC and middle ear and stimulate the cochlea directly via bone conduction. This method requires placement of a bone oscillator on the child’s forehead or mastoid. It often is necessary to mask the ear not being tested because vibration of the skull may elicit a response from both cochleas. This is accomplished by presenting a narrow band noise to the nontest ear to “keep it busy” while responses from the test ear are being recorded.
Play audiometry may be used for children 2 to 5 years of age to obtain threshold information via air and bone conduction mechanisms. The child is taught to place a peg in a board whenever a tone is heard through the earphones or the bone oscillator. Thus, ear-specific information can be obtained. Speech testing (Fig. 2B⇓ ) also may be initiated in children in this age range. SRT is the clinical measure of speech perception obtained most routinely. It is recorded as the lowest intensity level at which a listener can repeat 50% of the speech material presented. The SRT should be in close agreement with pure tone thresholds at 500, 1,000, and 2,000 Hz because the speech material includes phonemes that have most of their energy in this frequency range. Children who cannot repeat words for SRT testing may point to pictures on a board to indicate recognition of the speech stimulus. Younger children who cannot participate in a pointing or repeating task still may respond to speech with a head turn. The lowest level of speech that elicits this type of response from the child is recorded as the speech detection threshold (SDT).
Children ages 5 years or older usually can respond with the conventional hand raising technique that is used with adults to obtain ear-specific threshold information across the frequency range for pure tones and SRT. Speech discrimination ability (the ability to understand and discriminate speech material) also may be assessed. Typically, phonetically balanced words are presented to the listener at an average conversational level (45 dB HL) or at higher levels, and the percentage of words correctly identified and repeated by the listener is recorded (Fig. 2B⇓ ). Speech discrimination ability often is reduced significantly in the presence of sensorineural hearing loss.
Auditory brainstem response (ABR) and otoacoustic emissions (OAE) are objective tests of peripheral function that can be administered to individuals of all ages. ABR, also commonly referred to as BAER (brainstem auditory evoked potentials), and OAE are particularly useful with people who are unable or unwilling to respond behaviorally or when ear-specific or reliable results are not obtained with conventional audiometric techniques.
ABR testing employs several electrodes on the surface of the person’s scalp to record the synchronous firing activity of the auditory nerve and brainstem auditory neurons in response to brief tonal or click stimuli. Over the past 25 years ABR has achieved universal acceptance as an important screening and diagnostic tool for assessing peripheral and brainstem auditory integrity. Because it has high sensitivity and specificity (98% and 96%, respectively), one of its most recognized uses is in the detection of hearing impairment in neonates within the first few hours of life.
The pediatric patient must sleep during testing because the ABR is very sensitive to muscle contraction and movement. ABR testing may be scheduled around sleeping times for infants younger than 6 months. Children older than 6 months often require conscious sedation with chloral hydrate (50 mg/kg or 75 mg/kg administered orally, not to exceed 100 mg/kg or 1,000 mg total) or an intramuscular injection of a mixture of meperidine, promethazine/phenylephrine, and chlorpromazine. Sedation is administered only under the specific orders of a physician and when medical support is available for monitoring the physical condition of the child before, during, and after emergence from sedation.
The measurement of OAE is now recognized as a powerful method for assessing the status of the cochlea and the outer hair cells of the organ of Corti. OAE are acoustic signals generated from within the cochlea that travel in a reverse direction through the middle ear space and TM out to the ear canal. These signals are usually inaudible to the unaided human ear, but they may be detected with a very sensitive microphone/probe system placed in the ear canal, much like that used in immittance testing. Although 50% of normal hearing ears generate OAE spontaneously, nearly 100% generate OAE in response to an evoking stimulus. Thus, evoked OAE, including transient evoked OAE and distortion product OAE, are used most frequently in clinical settings to determine the status of the cochlea. Similarly to ABR, OAE can be measured in infants within the first few days after birth. Because OAE testing is relatively quick, noninvasive, and does not require sleep or sedation, it is an attractive technique for infant screening. Its limitations involve an inability to quantify hearing loss or hearing threshold levels. However, because the response is eliminated in the presence of a hearing loss greater than 35 dB HL, middle ear pathology, or debris in the EAC, it is an excellent screening measure for normal versus abnormal hearing.
ABR and OAE are tests of auditory structural integrity, but are not true tests of hearing. Even in the presence of a normal ABR and normal OAE, there is no way to guarantee that a child “hears” until he or she is mature enough to indicate so behaviorally. Thus, follow-up evaluations should be scheduled until a reliable audiogram can be obtained.
Degrees and Types of Hearing Loss
Normal hearing is defined as thresholds of 15 dB HL or better (lower intensities) for children who are 18 months to school age (Fig. 2A⇓ ). Thresholds greater (worse) than 15 dB HL can handicap a child educationally. Most children who present with acute otitis media have worse thresholds than the 15 dB HL normal limits for hearing. They frequently appear to ignore people and activities in the classroom or at home, often turn up the volume while watching television, and may ask constantly for repetition from persons who are speaking to them. Children who have greater hearing loss may become withdrawn and isolated from peers because of the difficulty in communication. Hearing loss also causes fatigue because additional effort is needed to listen in the typically noisy classroom. Varied degrees of hearing loss are associated with characteristic handicapping effects (Table 6⇓ ).
Three major types of hearing loss are named for their sites of pathology: sensorineural (involving the sensory end organ of hearing or cranial nerve VIII), conductive (of or having to do with the air conduction pathways of the EAC and/or middle ear space), and mixed (sensorineural hearing loss with an additional conductive component) (Fig. 3⇓ ). In cases of normal hearing or sensorineural impairment, bone conduction thresholds closely agree with air conduction thresholds (within 10 dB) (Figs. 3A⇓ and 3C⇓ ). When pathology of the EAC or middle ear space effectively obstructs the air conduction pathway, air conduction thresholds are poorer compared with bone conduction thresholds (>10 dB); the difference between the two scores is described as an air-bone gap, indicating the presence of conductive pathology (Fig. 3B⇓ ). In some instances, bone conduction thresholds may be reduced (<15 dB HL) in combination with an air-bone gap. This is characteristic of a mixed type of hearing loss (Fig. 3D⇓ ).
Hearing loss rarely affects all portions of the cochlea equally, producing a flat type of hearing impairment. For example, the majority of sensorineural hearing impairments affect the base or high frequency end of the cochlea first; most conductive pathologies have a greater effect on low frequency hearing abilities. Different strategies are used to manage the hearing impaired child, depending on the type, degree, and configuration of the loss.
Management of the Hearing Impaired Child
Most children have at least some degree of usable hearing, which makes “deaf” an incorrect label because it implies a lack of any measurable hearing. Recent advances in amplification technology have enabled audiologists to access usable hearing, beginning at the earliest age of identification. Personal FM amplification devices, hearing aids, and cochlear implants are used to access sounds for children who have varying degrees and types of hearing impairment. A complete discussion of each type of amplification is beyond the scope of this article, but amplification alone will not ensure that the child identified as having significant hearing loss will develop speech, language, and social/emotional skills normally.
Successful communication is an active process for the hearing impaired child, fostered by therapeutic, parental, and educational acceptance, patience, and hard work compared with the ease with which most children who have normal hearing learn to communicate. No single“ miracle” method can be used to teach a hearing impaired child to communicate. Educational methods range from the use of sign language in which the child does not depend on any auditory information to the auditory/verbal method in which the child is forced to access any and all usable hearing to communicate and is not allowed to lip-read or use signs to a method of total communication in which auditory information, lip-reading, and signs all are used to communicate. Although many biases for or against each method exist among hearing professionals, caregivers ultimately must decide which method is best for their child.
Success with any of the methods depends on several important variables that include, but are not limited to: 1) the degree and type of hearing impairment, 2) parent and family motivation, 3) presence of a healthy emotional support network for the family, and 4) development of realistic goals and expectations for the parents and the child. The day that a child who has significant hearing loss receives amplification should be considered by parents and professionals to be the first day of that child’s hearing life. Thus, a child who receives amplification at 1 year of age or older would be expected to have speech, language, and auditory skills equivalent to that of a newborn.
When children who have severe hearing impairments reach school age, they usually are placed in special classrooms with some integration into regular classrooms. This is typically part of the individualized education plan. Some children, however, can be mainstreamed completely, with classroom amplification or personal FM amplification systems used to enhance the teacher’s voice relative to the background noise. These amplification systems can be useful for children who have all degrees of hearing loss.
The child who has a unilateral loss or a mild-to-moderate hearing impairment often is seated preferentially. Seating in close proximity to the teacher may help the child hear what is being said, although this is ineffective by itself unless the teacher stands in one spot the entire day. Personal FM amplification systems require the teacher to wear a remote microphone approximately 6 inches from the mouth; the signal is transmitted via FM (radio frequency) waves to a receiver worn by the child. The receiver may be connected directly to the child’s hearing aids or the child may wear some form of headphones, similar to portable audiocassette headphones. The advantage of the FM system is that the remote microphone can, in essence, place the teacher’s voice 6 inches from the child’s ear (the distance of the microphone from the teacher’s mouth) no matter where the teacher is located in the room. This enhances both the speaker-to-noise ratio (SNR) and the sound quality for the child.
Unfortunately, state and school officials appear to be reluctant to accept recommendations for use of an FM unit for children who have mild hearing impairments and unilateral losses. Physicians, case workers, parents, teachers, and audiologists must advocate proactively for these children. Section 504 of the Rehabilitation Act of 1973 states that all children have the right to an appropriate education. With the support of this legislation, professionals can advocate confidently for the provision of SNR-enhancing technology. Flexer recommends “stating that the child’s hearing problem interferes with his or her access to spoken instruction; therefore, the child is being denied an appropriate education.”
Early identification of and intervention for all children who have hearing impairments remain unattained goals in the United States. Physicians typically are the first persons to obtain the medical and family history of infants and children and are the primary professionals confronted with parental concerns about hearing loss. Heightened awareness of the common causes of hearing loss in infants and children can facilitate prompt and appropriate referrals to audiologists when hearing loss is suspected. A strong and interactive relationship between physician and audiologist is needed to attain the common goals of providing the earliest and best possible diagnosis of and optimal management for hearing impaired pediatric patients.
The authors thank D. Blackmore, B. Lasky, T. Mancuso, L. Segal-Pallas, S. Seidenberg, and V. Shields-Haseley, members of the Speech-Language-Hearing Department, who contributed to the research for this manuscript.
Bess F, Hall JW III, eds. Screening Children for Auditory Function. 1992 Nashville, Tenn.: Bill Wilkerson Center Press
Flexer C. Facilitating Hearing and Listening in Young Children. 1994 San Diego, Calif.: Singular Publishing Group, Inc
Hayes D, Northern J. Infants and Hearing. 1996 San Diego, Calif.: Singular Publishing Group, Inc
Northern J, Downs M. Hearing in Children. 4th 1991 Baltimore, Md.: Williams and Wilkins
- Copyright © 1998 by the American Academy of Pediatrics