1.  Language is learned through sound.
2.  The goal of infant auditory screening is to detect and start habilitation by six months of age.
3.  The high-risk registry is the first line of defense in the detection of hearing loss.  Risk factors are: low birth weight, elevated bilirubin, severe congenital infection, head and neck anomalies, meningitis, ototoxic drugs, consanguinity and anoxia.

Some degree of hearing loss affects 7.5% of the population of the United States.  In adults the most common cause is sensorineural hearing loss (inner ear pathology) from presbycusis (hearing loss associated with aging) and noise exposure.  In the pediatric age group the most common cause is a conductive impairment (middle ear pathology) from otitis media.  Sensorineural loss also occurs and may be acquired during the first months of life or congenital in nature.  Noise induced hearing loss in the adolescent is also an important entity.  This type of hearing loss is preventable but not curable.

The early diagnosis of hearing loss is important since it allows intervention aimed at preventing second tier disabilities.  Hearing is used to monitor speech, both loudness and quality, and its loss can result in the deterioration of speech skills with loss of the ability to communicate.  For this reason we speak of speech and hearing handicaps and rarely just speech handicaps.  In the child, deafness creates a severe handicap that can hinder language acquisition.  A child learns language in the following steps.  First a child learns to listen and understand, then to speak, read and write.  If the child never hears the spoken word, he will have difficulty acquiring language and may never learn to speak, read, or write.  Thus, many deaf individuals cannot read and have difficulty in the job market place.  A deaf eight-year-old child will be several years behind the hearing child in math and verbal skills.  Unfortunately, there is no cure for deafness.  Sign Language is not a word for word translation of English.  It has a different syntax and some researches debate whether it is a true language.  Relatively few deaf individuals master lip reading and hearing aids cannot totally relieve the handicap of a severe sensorineural hearing loss.

Helen Keller stated, "I am just as deaf as I am blind.  The problems of deafness are deeper and more complex, if not more important than those of blindness.  Deafness is a much worse misfortune.  For it means the loss of the most vital stimulus, the sound of the voice that brings us language, sets thought astir and keeps us in the intellectual company of man."

It is not universally held that mild hearing losses caused by otitis media will have an impact on language and learning.  Randomized prospective studies to determine the long term affects of untreated and treated otitis media on children can not easily be undertaken because careful controls to prevent the possible long term deleterious effects on the untreated group of children would have to be instituted.  On the average, otitis media causes approximately 20 - 40% dB (decibels) hearing loss.  This deficit is comparable to one caused by a well-placed foam earplug designed to prevent noise induced hearing loss.  The clinician who wishes to determine the impact of such a loss on learning skills should wear these plugs during an educational session.  He/she could then better judge if the learning child, who has a shorter attention span than most physicians, will be affected.

Although the effects of mild hearing losses on children are debated, the effects of severe hearing loss are not.  Approximately 1/1000 newborns have congenital deafness and many neonatal ICU graduates have acquired this disability.  Whenever possible, the diagnostic process should be completed and habilitation begun by the age of 6 months.  The first line of defense in detecting childhood deafness is the High Risk Registry.  The following items are usually included:

            1.         Family history of hearing loss
            2.         Congenital virus/infection
            3.         ENT defects
            4.         Elevated Bilirubin > 20 mg/100 ml serum
            5.         Low birth weight < 1500 gms
            6.         Neonatal meningitis

Other risk factors include consanguinity, ototoxic drugs, respiratory distress syndrome, sepsis, APGAR < 6, and a difficult delivery.

Hearing loss in early childhood can be categorized as acquired or inherited.

Acquired:
- TORCH--Toxoplasmosis, Rubella, CMV and Herpes Virus.
- Meningitis (10% of all deafness).
- Mumps--most common cause of unilateral deafness.
- Syphilis--Onset 8 to 20 years, usually presents as bilateral endolymphatic hydrops.
- Ototoxins.
- Asphyxia:  Outer hair cells are more sensitive, than the inner hair cells or CNS.
- Measles, elevated bilirubin, etc.

Inherited:
- CHARGE Association (Coloboma, Heart disease, choanae Atresia, Retarded development & CNS Abnormalities, Genital hypoplasia, Ear anomalies.
- Inner ear dysplasias
    Michel:  Complete failure of development of the labyrinth.
    Mondini:  Abnormality of the osseous labyrinth.  Associated with Down's Syndrome and Klippel-Feil.  There is a high incidence of perilymphatic fistulas and some authorities recommend surgically patching the oval and round window on all children with this syndrome.
    Bing-Siebermann:  Abnormality of the membranous cochlear and vestibular labyrinth
    Scheibe:  Abnormalities of the cochlear and saccular membranous labyrinth
    Alexander:  Abnormalities of the cochlear membranous labyrinth

Other Syndromes
- Alports:  Renal disease progressing to renal failure in early adulthood.
- Jervell's:  Cardiac abnormalities (prolonged QT interval and sudden death)
- Apert's, Crouzon's, Treacher-Collin's  (First Arch Syndrome) have middle ear abnormalities.
- Waardenburg's Syndrome: white forelock and SNHL.
- Usher's Syndrome.
- Pendred's Syndrome: Goiter
- Renal Abnormalities are frequently associated with otological abnormalities.

It is important to remember that congenital hearing loss can be associated with abnormalities of almost every organ system and a thorough laboratory evaluation and physical examination by the primary care physician is indicated.  Useful laboratory tests in the evaluation of these patients have included: CBC, U/A, BUN, FTA, PBI, T4, Perchlorate, EKG, Urine mucopolysaccharides, buccal smear (genetics work up), Serum pyrophosphate, uric acid, temporal bone films.

The High Risk Registry registers 10% to 20% of all well babies and detects hearing loss in 50% of all deaf well babies.  Thus, one half of the deaf children will not be initially diagnosed before they leave the hospital and will have to be detected by the primary care physician by evaluating the child's acquisition of language milestones.  The High Risk Registry registers 64% of all ICU babies and detects almost all hearing losses in this population.

Hearing evaluations in the very young include: Behavioral Testing, Brainstem Auditory Evoked Response and Crib-o-gram evaluations.  Behavioral testing evaluates the child's response to sound as observed by the examiner.  The validity of the test increases with the experience of the examiner and age of the child.  Visual response audiometry is a type of behavioral test that can reliably determine the magnitude of the hearing loss.  It cannot reliably detect a unilateral loss or test each ear separately because an awake young child rarely tolerates the placement of earphones.  Also, children less than one year of age cannot always be tested by this method.  Brainstem Auditory Evoked Response measures brain waves elicited by sound and can usually be performed without sedation in children less that one-year of age.  This test is expensive and requires trained personnel.  It is excellent at determining normality and can test each ear separately.  It has limited reliability in determining the magnitude of the hearing loss.  Jerger found the standard error in predicting sensory hearing losses to be 15 to 16 dB.

Crib-o-gram testing automatically measures the child's movement to a 3000 HZ 90 dB tone pip via a pressure transducer.9  It only reliably detects bilateral hearing losses greater than 45 dB and can only be used on children weighing less than 12 lbs.  It cannot detect a unilateral loss.

All of the above tests are non-invasive.  In a child at risk for a severe hearing loss there is little reason to delay testing and initiation of habilitative measures.

Standard Auditory Testing in Children and Adults: The two most common audiometric tests are the pure tone audiogram and tympanometric testing.  During a pure tone audiogram stimuli are presented through earphones, and a bone oscillator placed on the mastoid.  The bone oscillator transmits sounds to the inner ear through the cranial vault, bypassing the middle ear.  Diseases of the middle ear (e.g. serous otitis, perforated tympanic membrane, ossicular disruption) can cause a conductive hearing loss.  Audiometric testing will show normal hearing to bone conduction and not air conduction producing an air bone gap on the audiogram.  A sensorineural hearing loss is caused by pathology in the inner ear or auditory nervous system.  In these cases the hearing loss is equal for both air and bone conduction.  Discrimination scores for the patient's understanding of speech are often determined during audiometric testing.  A nerve or severe sensorineural hearing loss will often have poor discrimination.  This is the reason a hearing aid will not totally compensate the disability created by sensorineural hearing losses.  

In young children, the auditory stimulus is delivered through speakers mounted on the wall.  Both ears are tested at the same time.  The child is trained to respond to the auditory stimulus by associating it with a novel visual reward (moving animals behind smoked glass).  This type of testing is referred to as Visual Response Audiometry (VRA) and is a type of Conditioned Oriented Response (COR) testing.

Tympanometry evaluates the compliance of the tympanic membrane.  In this test, a probe is inserted into the external ear canal and a tone is delivered.  The loudness of the tone is recorded as a function of various canal air pressures.  The transmission of sound into the middle ear results in the dampening of the sound in the external ear canal.  If the air pressure in the ear canal equals the pressure in the middle ear maximum sound transmission takes place.  A normal middle ear will produce a peaked graph, with the peak's position approximating zero (Type A).  Normally there is a wide variation of middle ear air pressure that occurs with swallowing and air absorption.  Negative middle ear pressure is diagnosed when the tympanometric peak is from -150 to-200 cm H20 (Type C).  Middle ear fluid will produce a flat graph (Type B).

In general, tympanometry should be used as an aid and not a replacement to pneumatic otoscopy.  In infants and young children, this technique is often unreliable.  The mobile canal wall of the young child can produce a Type A graph with middle ear fluid or a Type B results with a normal ear drum.  Also, the test requires a cooperative quite child.  It is unfortunate that this test is not totally reliable in the patient population where otoscopy is the most difficult to perform.

References:

1.  Helen Keller is Scotland.

2.  Fria, T.J., Cantekin, E.I., and Eichler, J.A.  Hearing acuity of children with otitis media with effusion.  Archives of Otolaryngology  111:10-16, 1985.

3.  Joint committee on infant hearing position statement 1982.  Ear and Hearing.  4:3-4, 1983.

4.  Pappas, D.G.  A study of the high risk registry for sensorineural hearing impairment.  Otolaryng. Head and Neck Surgery.  91:41-44, 1983.

5.  Alberti, P.W., Hyde, M.L., Riko, K. et al.  Issues in early identification of hearing loss.  The Laryngoscope.  95:373-381, 1985.

6.  Wright, C.G., Brown, O.E., Meyerhoff, W.L. and Rutledge, J.C.  Auditory and temporal bone abnormalities in CHARGE association  Ann. Otol. Rhinol. Laryngol. 95:480-486, 1986.

7.  Suehiro, S. and Sando, I.  Congenital anomalies of the inner ear.  Introducing a new classification of labyrinthine anomalies.  2-24.

8.  Jerger, J.J., and Mauldin, L. Prediction of sensorineural hearing level from the brain stem evoked response.  Archives of Otolaryngology,  104:456-461, 1978.

9.  Simmons, B.F., et al.  An automated hearing screening technique for newborns.  ACTA Otolaryngol.  87:1-8, 1979.