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Deaf Child

Evaluation of Deaf Child. Early screening and assessment of hearing loss are vital for infants and children. Early identification can help to make early decisions about hearing rehabilitation including hearing aids, and cochlear implants. From birth to 5 years of age, the child develops speech and language. The child managed before 6 months of age develops good vocabulary and better expressive and comprehensive language skills. Therefore early identification of a child’s hearing impairment is important. Screening and surveillance is the most effective and cost-effective way to identify congenital hearing loss.

Definition of Deaf child. Children with profound (> 90 dB loss) or total deafness are termed deaf-mute or deaf and dumb. Risk factors for permanent congenital hearing loss are:

  • Child kept in the neonatal intensive care unit (NICU) for more than 48 hours.
  • Family history of early childhood deafness.
  • Craniofacial anomaly (e.g. cleft palate) associated with hearing impairment. 

AETIOLOGY. The onset of hearing loss may be before birth (prenatal), during birth (perinatal) or afterbirth (postnatal).

A. PRENATAL CAUSES

They may pertain to the infant or the mother.

1. Genetic defects. An infant may be born with inner ear anomalies due to genetic or nongenetic causes. Anomalies may affect inner ear only, involving only the membranous labyrinth or both the membranous and bony labyrinths. (nonsyndromic) or can be part of a syndrome (syndromic). It results in various forms of malformations. They include:

(i) Mondini dysplasia. There is dysplasia of bony and membranous labyrinth. It usually occurs bilaterally. This deformity may be seen in isolation or in association with other symptoms in certain syndromes like Enlarged vestibular aqueduct, Pendred, Klippel-feil, Waardenburg and Treacher-Collins. Anomalies of Cochlea usually seen are:

  • There may be only 1.5 cochlear turns present instead of 2.5 turns.
  • Basal coil is only present 
  • Absence of osseous spiral lamina.
  • Absence of modiolus.

(ii) Scheibe dysplasia. It is one of the most common inner ear deformity in deaf children. Bony labyrinth is normal. Utricle and semicircular ducts are normal. Anomalies usually seen are:

  • Marked dysplasia is seen in the membranous cochlea and saccule; hence also called as cochleosaccular dysplasia.
  • Hypoplastic cochlear nerve and inferior division of vestibular nerve is seen. 
  • Organ of corti may be absent. 

(iii) Alexander dysplasia. Basal turn of membranous cochlea is affected causing high-frequency hearing loss. Hearing can be improved by use of hearing aids, as lower frequencies are preserved. 

(iv) Michel aplasia. There is total aplasia of bony and membranous labyrinth. There is no inner ear development. The external ear and middle ear are completely normal. There is no role for hearing aids or cochlear implantation.

(v) Enlarged vestibular aqueduct. There is an enlargement of Vestibular aqueduct and endolymphatic sac. It causes early-onset progressive sensorineural hearing loss during childhood. Attacks of vertigo may be present. A Perilymph fistula may also be seen.

(vi) Common cavity: There is no division between cochlear and vestibular parts. There is only single cavity present.

(vii) Cochlear/ vestibular nerve aplasia or malformation.

(viii) Semicircular canal malformations.Malformations are related to superior and lateral semi-circular canals.

(ix) Bing-Siebenmann dysplasia.There is a complete absence or dysplasia of membranous vestibular labyrinth. Cochlea is normal.

2. Maternal. Factors affecting developing foetus during pregnancy.

  • Infections. Toxoplasmosis, rubella, cytomegaloviruses, herpes type 1 and 2 and syphilis. Remember mnemonic, TORCHES.
  • Drugs. Streptomycin, gentamicin, tobramycin, amikacin, thalidomide, quinine or chloroquine.
  • Radiation during first trimester.
  • Other factors. Nutritional deficiency, Alcohol intake, diabetes, toxaemia and thyroid deficiency. 

B. PERINATAL CAUSES

They relate to causes during birth or in early neonatal period. They are as follows.

  • Anoxia. It damages the cochlear nuclei and causes haemorrhage into the ear. Placenta praevia, prolonged labour, cord round the neck and prolapsed cord can all cause fetal anoxia.
  • Prematurity and Low birth weight. Born before term or with birth weight less than 1500 g (3.3 lb).
  • Birth injuries. e.g. forceps delivery. They may cause intracranial haemorrhage with extravasation of blood into the inner ear.
  • Neonatal jaundice. Bilirubin level greater than 20 mg% damages the cochlear nuclei.
  • Neonatal meningitis
  • Sepsis
  • Time spent in neonatal icu
  • Ototoxic drugs. Used for neonatal meningitis or septicaemia.

C. POSTNATAL CAUSES

  • Genetic. It is seen in familial progressive sensorineural deafnessor may be associatedwith other syndromes, e.g. Alport, Klippel-Feil, Hurler, etc.Though it is termed genetic, but it manifests laterin childhood or adult life.
  • Nongenetic. The causes are similar to adults.
  • Neonatal  Jaundice & Meningitis 
  • Time Spent in Neonatal ICU
  • Ototoxic Drugs. 

EVALUATION OF A DEAF CHILD.

1.  History taking

Detailed history of prenatal, perinatal or postnatal period. 

  • Pregnancy delivery and postnatal period. 
  • Developmental milestones including speech and language and motor.
  • Noise exposure, 
  • Ototoxic medications
  • Head injuries, 
  • Infections. Ear disease, meningitis and viral illness
  • Immunization status 

Detailed Family history.  Hearing loss and other risk factors associated with hearing loss.

Physical examination. Inspection of any craniofacial anomalies, palatal abnormalities, branchial cysts, sinuses, heterochromia iridis, white forelock fistulae etc. 

Hearing tests. Depending upon the age.

Radiological Investigations. Magnetic resonance imaging of inner ears and/or computed tomography of petrous temporal bones. 

2.  Risk factors for permanent congenital hearing loss.

  • Child kept in neonatal intensive care unit (NICU) for more than 48 hours.
  • Family history of early childhood deafness.
  • Craniofacial anomaly (e.g. cleft palate) associated with hearing impairment. 
  • Prenatal infections (TORCHES).
  • Birth weight less than 1500 g (3.3 lbs).
  • Ototoxic medications
  • Bacterial meningitis
  • Hyperbilirubinemia.
  • Apgar score of 0–4 at 1 min or 0–6 at 5 min.

METHODS OF HEARING ASSESSMENT IN INFANTS AND CHILDREN

Accurate assessment of hearing is fundamental to diagnosis, investigation and rehabilitation. Choice of test to be done depends on the patient’s age and its ability to cooperate. It also depends on the skill and experience of the assessor. 

These tests should age-appropriate, specific, valid, adaptable. Use toys and smiles to make it a game so that child should not easily bored or frightened.

Children below 6 months are generally not able to cooperate and therefore require objective tests such as OAEs and BERA. These tests are also useful in young child or adult with special needs who not able to cooperate.

1. Electrophysiological testing. Key developmental age: 0–6 months, up to adult if appropriate.

They are done for screening andearly identification of hearing loss in neonates.. Both are electrophysiological tests.

A. OAE (Otoacoustic emissions).It is a fast, easy to obtain, minimally-invasive screening test, used for screening for hearing loss in early life. OAEs are low intensity sound signals produced by outer hair cells of the cochlea. These signals can be picked up from the external ear canal by a sensitive microphone. 

Pathophysiology:

The signals travelsin reverse direction from outer hair cells→ basilar membrane → perilymph → oval window  → ossicles → tympanic membrane → external ear canal. 

The OAE is quick, consumable costs are relatively low compared with AABR. OAEs detects outer hair cell dysfunction earlier than a pure tone audiogram.

Interpretation:

OAEs are present when

  • Outer hair cells are normal and healthy. 
  • VIIIth nerve lesion as cochlear hair cells are normal thus helps to test the function of VIIIth nerve.

OAE’s are absent when. 

  • Outer hair cells are damaged or non-functional thus helps to test the function of cochlea.
  • Hearing loss more than 30 dB.
  • In 50% of normal individuals.
  • Lesions of cochlea.
  • Middle ear disorders i.e. effusion, as sound signals coming back cannot be picked up by the microphone.
  • Debris in the outer ear.

B. BERA (Brainstem evoked response audiometry). 

It is an objective, non-invasive test which can be used as both screening test and hearing assessment test in infants and young children. It may require sedation in children.

Principle. BERA assess the structural integrity and functional status of the central auditory pathway through the VIIIth nerve, pons and midbrain. A series of electrical activity (potentials) generated by the activation of different parts of the auditory systemin response to sound stimulus presented to the ear. The sound stimulus is in the form of clicks and tone-bursts. These potentials are recorded/ measured by placing surface electrodes on the scalp. 

It correlates well with the pure-tone thresholds. It gives more accurate results than OAE’s but takes longer time.To measure hearing threshold in an infant, ABR tracing is obtained first at higher sound stimulus and then gradually lowered till wave V is just identifiable but repeatable. BERA gives more accurate results than OAE’s but takes longer time and general anaesthesia is also sometimes required. Infants or baby who fails the BERA twice is referred for further assessment and early intervention.

Indications for BERA in screening.

  1. Child who fails the OAEs test on two occasions.
  2. Child kept in neonatal intensive care unit, both OAEs and BERA performed.

Interpretations.

  1. ABR waves are usually absent when a patient has a severe or profound hearing loss. 
  2. Identifiable waveforms are generally seen 10–20 dB above behavioural threshold.
  3. Hearing is regarded normal with a response of 30–35 dB nHL. 

C. Arousal test. Method. When the infant is in light sleep. A narrow band noise of high-frequency isdelivered three times for 2 seconds. Interpretation. Infant having normal hearing will get aroused minimum of two times. 

D. Auditory response cradle (ARC) is a fully automated screening device for newborns. In this test, infant is placed in a cradle and his behavioural responses (head jerk or turn, body movements, and respiration) in response to sound stimulus (high pass noise). 

The responses are monitored by transducers. The transducer is a polyethylene band placed around the infant’s abdomen. ARC is a useful test for screening moderate, severe or profound hearing loss in babies.

2. Behaviour Observation Audiometry. Key developmental age: 0–6 months 

The idea is to check behavioural responses to sound stimulus delivered to an infant. The responses can be eye blink (auro-palpebral reflex), alteration in sucking response, alerting, cessation of an activity, widening of eyes or facial grimacing. Although BOA is not preferred over electrophysiological tests. But may be of particular value in infants having auditory neuropathy spectrum disorder when ABR is a poor indicator of functional hearing levels. 

  • Moro’s reflexis a reflex reaction of infants in response to sound of 80–90 dB. It is characterized by sudden extension of arms and legs away from the body and then drawing back. Extension of head in also present. 
  • Cochleo-palpebral reflex, there is contraction of the orbicularis muscle causing blinking of the eye in response to loud sound. 
  • Cessation reflex, In response to a sound of 90 dB, an infant stops activity or starts crying.

3. Distraction Test. Key developmental age: 06-18 months 

The test incorporates the principle that young children at this age, turns there head to locate the source of auditory stimulus. 

Method. In this test, the child sits on the parent’s lap or on an infant seat. Child is lightly distracted by an assistant sitting directly in front who holds their attention. While the examiner produces a sound for <2 seconds. The sound is delivered from a distance of 15 cm and should be out of peripheral vision of the child. or delivered via insert earphones. Both distractor and examiner can observe the response.

Arrangement of distraction test

A range of sound stimuli may be employed, including voice or noisemakers but ideally calibrated narrow-band,. Sounds used are calibrated narrow-band noise (500–4000 Hz), high frequency rattle (8 kHz), low-frequency hum, warble tones or ling sounds, whispered sound as “S, S, S”, xylophone.

4. Visual reinforcement audiometry (VRA). Key developmental age: 05-36 months.

It is a conditioning technique in which child is trained to look for visual stimulus in response to a sound stimulus by turning his head. It is commonly used test battery for hearing assessment in preschool children.

This test uses standard audiometric methods to determine the hearing threshold. The sound is delivered by headphones or earphones. 

Arrangement of  Visual reinforcement audiometry test

5. Play audiometry. Key developmental age: 2–5 years

The test follows principle that the child is conditioned to wait for a sound signal and then to respond byperforming a specific task. Simple tasks which involve a simple repetitive activity such as placing a toy in a box, putting a ring on a stick or putting balls in a bucket each time when the child hears a sound signal. Hearing thresholds can be determined by 10dB down, 5dB-up/ descending-ascending technique as described for pure tone audiometry. Each correct response is reinforced with vocal praise, clapping or reward. 

6. Pure tone audiometry: Key developmental age: 3 years onwards.

If the child has conditioned adequately to PTA test. And using play audiometry technique it is often possible to measure hearing thresholds through PTA close to adult levels.

7. Speech audiometry.

In a quiet room, using live voice,the child is asked to repeat thenames of toys or point picturesplaced on a table. The live voice level is gradually lowered. In this way, hearing thresholds and speech discrimination threshold or score is recorded. 

Speech discrimination threshold. Hearing threshold at which the child correctly identifies 80% (score) of the toys. A child with normal hearing is expected to identify 80% of the toys or pictures at ≤40dB(A). The ability of a child to discriminate speech signals is an important measure of functional hearing with normal to moderate degrees of hearing loss. 

8. The cooperative test. Key developmental age18–30 months

It is an valuable alternative test where equipment and facilities are limited. The child is asked to discriminate three different simple instructions, for instance having been handed a small toy, asked to ‘give it to Mummy’ or ‘give it to daddy’ or ‘give it to baby’. Starting at a supra-threshold level, the voice is then dropped. A child with normal hearing may discriminate the instruction at 35–40dB(A). 

9. Objective tests

A. Evoked response audiometry.

(i) Electrocochleography. It can detect hearing threshold in the young infants and children within 5-10 dB. 

Procedure : It is an invasive procedure. The electrical activity can be detected by inserting a needle like thin, active recording electrode through the tympanic membrane and placing onto the promontory or round window. The reference and ground electrodes are placed on the mastoid process and on the forehead respectively. It is usually done under sedation or local anaesthesia . But requiring placement of electrodes through the tympanic membrane.It measures the summated intracellular potentials of the outer hair cells seen in response to an auditory stimulus. The electrical response is either due to cochlear microphonic potentials (electrical activity in the cochlea), summating potentials (complex measurement of many electrophysiological parameters taken together) or electrical activity due to action potential of 8th nerve. It is an objective test that provides reasonably accurate measurement of hearing threshold between 1000 to 8000 Hz. No masking in contralateral ear is required.

(ii) Auditory brainstem response. It is an objective, non-invasive test which can be used as both screening test and hearing assessment test in infants and young children. It may require sedation in children.

Principle. BERA assess the structural integrity and functional status of the central auditory pathway through the VIIIth nerve, pons and midbrain. A series of electrical activity (potentials) generated by the activation of different parts of the auditory systemin response to sound stimulus presented to the ear. The sound stimulus is in the form of clicks and tone-bursts. These potentials are recorded/ measured by placing surface electrodes on the scalp. 

It correlates well with the pure-tone thresholds. It gives more accurate results than OAE’s but takes longer time.To measure hearing threshold in an infant, ABR tracing is obtained first at higher sound stimulus and then gradually lowered till wave V is just identifiable but repeatable. BERA gives more accurate results than OAE’s but takes longer time and general anaesthesia is also sometimes required. Infants or baby who fails the BERA twice is referred for further assessment and early intervention.

Indications for BERA in screening.

  • Child who fails the OAEs test on two occasions.
  • Child kept in neonatal intensive care unit, both OAEs and BERA performed.

Interpretations.

  • ABR waves are usually absent when a patient has a severe or profound hearing loss. 
  • Identifiable waveforms are generally seen 10–20 dB above behavioural threshold.
  • Hearing is regarded normal with a response of 30–35 dB nHL. 

B. Otoacoustic emissions. It is a fast, easy to obtain, minimally-invasive screening test, used for screening for hearing loss in early life. OAEs are low intensity sound signals produced by outer hair cells of the cochlea. These signals can be picked up from the external ear canal by a sensitive microphone. 

Pathophysiology:

The signals travelsin reverse direction from outer hair cells→ basilar membrane → perilymph → oval window  → ossicles → tympanic membrane → external ear canal. 

The OAE is quick, consumable costs are relatively low compared with AABR. OAEs detects outer hair cell dysfunction earlier than a pure tone audiogram.

Interpretation:

OAEs are present when

  • Outer hair cells are normal and healthy. 
  • VIIIth nerve lesion as cochlear hair cells are normal thus helps to test the function of VIIIth nerve.

OAE’s are absent when. 

  • Outer hair cells are damaged or non-functional thus helps to test the function of cochlea.
  • Hearing loss more than 30 dB.
  • In 50% of normal individuals.
  • Lesions of cochlea.
  • Middle ear disorders i.e. effusion, as sound signals coming back cannot be picked up by the microphone.
  • Debris in the outer ear.

C. Impedance audiometry. It is based on the fact that a loud sound 70–100 dB above hearing threshold of one ear, causes bilateral contraction of the stapedius muscle (which pulls the stapes slightly outward and upward) & and tensor tympani muscle (pulls the tympanic membrane slightly inward). The effect is more pronounced on the stapedius muscle than on tensor tympani. It is very simple to perform, requires a few minutes, is non-invasive, objective test (does not depend upon subjective responses from the patient). Absence of acoustic reflex indicates middle ear disorder, retrocochlear hearing loss or severe to profound SNHL. It differentiates cochlear and retro-cochlear pathology. In cochlear lesion, stapedial reflex is present at lower intensities, e.g. 40–60 dB than the usual 70 dB(recruitment phenomenon). Absence of acoustic reflex but an abnormal tympanogram generally indicates conductive loss. Since ABR and OAEs provide more information, use of acoustic reflexes in assessment of paediatric testing is not done commonly.

OAEs and ABR have been used both in screening programmes and in hearing evaluation in infants and children.

——– End of the chapter ——–

Reference Textbooks.

  • Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
  • Glasscock-Shambaugh, Textbook of Surgery of the Ear.
  • Susan Standring, Gray’s Anatomy.
  • Frank H. Netter, Atlas of Human Anatomy.
  • B.D. Chaurasiya, Human Anatomy.
  • P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
  • Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
  • Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck Surgery
  • Hans Behrbohm, Textbook of Ear, Nose, and Throat Diseases With Head and Neck Surgery.
  • Salah Mansour, Middle Ear Diseases – Advances in Diagnosis and Management.
  • Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
  • Rob and smith, Textbook of Operative surgery.
  • Anirban Biswas, Textbook of Clinical Audio-vestibulometry.
  • Arnold, U. Ganzer, Textbook of  Otorhinolaryngology, Head and Neck Surgery.
  • Ganong’s Review of Medical Physiology.
  • Guyton & Hall Textbook of Medical Physiology

Author:

Acoustic Neuroma

Dr. Rahul Bagla
MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Renowned Teaching Faculty
Mail: msrahulbagla@gmail.com
India

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