Physiology of hearing & approach to hearing loss in a child


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Physiology of hearing & approach to hearing loss in a child

  1. 1.  Outer Ear Middle Ear Inner Ear
  2. 2.  Pinna (Auricle, Ear) External Auditory Meatus (Ear canal)
  3. 3.  Tympanic Membrane (ear drum) Ossicles Middle ear cavity Eustachian tube Muscles
  4. 4.  Thin membrane separates the outer ear from middle ear Transmits sound from air to ossicles
  5. 5.  Malleus (hammer), Incus (anvil), & Stapes (stirrup) Vibrate in response to sound
  6. 6.  Equalizes pressure and allows drainage
  7. 7.  Stapedius and Tensor Tympani Retract to loud sounds to protect hearing (acoustic reflex)
  8. 8.  Oval window/Round window Cochlea 8th nerve Semicircular canals
  9. 9.  Tube divided into 3 fluid- filled chambers ◦ Scala vestibuli ◦ cochlear duct ◦ scala tympani
  10. 10.  Oval window attached to scala vestibuli (at base of cochlea) ◦ Vibrations at oval window induce pressure waves in perilymph fluid of scala vestibuli Scalas vestibuli and tympani are continuous at apex ◦ waves in scala vestibuli pass to scala tympani and displace another membrane, round window (at base of cochlea)  Necessary because fluids are incompressible and waves would not be possible without round window
  11. 11.  Low frequencies – travel all the way through scala vestibuli and back to scala tympani As frequencies increase they travel less before passing directly thru vestibular and basilar membranes to scala tympani
  12. 12.  High frequencies produce max stimulation ◦ of Spiral Organ (of Corti) ◦ closer to base of cochlea and ◦ lower frequencies stimulate closer to apex
  13. 13.  Frequency or pitch – how many waves/sec a note has High frequency – high number of frequencies/sec Low frequency – low number of frequencies/sec
  14. 14.  Where sound is transduced Sensory hair cells – located on basilar membrane ◦ 1 row of inner cells extend length of basilar membrane ◦ Multiple rows of outer hair cells embedded in tectorial membrane
  15. 15.  Pressure waves moving thru cochlear duct ◦ create shearing forces between basilar and tectorial membranes ◦ moving and bending stereocilia ◦ causing ion channels to open ◦ depolarizing hair cells ◦ the greater the displacement, the greater the amount of NT released and action potentials produced
  16. 16.  Information from CN VIII goes to medulla, then to inferior colliculus, then to thalamus, and on to auditory cortex
  17. 17.  Neurons in different regions of cochlea stimulate neurons in corresponding areas of auditory cortex ◦ called tonotopic organization ◦ where each area of the cortex represents a different part of cochlea ◦ and thus a different pitch
  18. 18.  Vestibular (balance) system ◦ perceive a sense of balance and perception in space
  19. 19.  Auditory nerve ◦ sound information to the brain Vestibular nerve ◦ position and balance information to brain
  21. 21.  Conductive Sensorineural Mixed
  22. 22. • Sound is not normally conducted through the outer or middle ear or both• Sound can be picked up by a normally sensitive inner• Often only mild and temporary• Caused by any of the following: – Ear infections, otosclerosis, excessive wax, etc.
  23. 23.  Damage of the cochlea or auditory nerve It can be mild, moderate, severe, or profound, to the point of total deafness Permanent Can be caused by hair cell damage, noise exposure, medicines, genetics, trauma, illness, etc.
  24. 24.  Demonstration
  25. 25.  a condition in which a child or adolescent is unable to detect or distinguish the range of sounds at the level normally possible by the human ear Hearing loss: results from damage to the outer, middle, or inner ear, or the auditory nerve Auditory processing disorder: hearing loss resulting from damage to the processing centers of the brain
  26. 26.  Location of damage (outer, middle, inner, auditory nerve) Whether it affects one or both ears ◦ Unilateral or bilateral Extent of impact on communication Chronicity ◦ Short-term, fluctuating, permanent or progressive Timing ◦ Congenital, prelingual, acquired, postlingual
  27. 27.  Hearing loss varies in the extent to which it affects speech, language, and communication Affects ability to develop relationships, succeed academically, and be involved with extracurricular activities Can result in delayed receptive and expressive speech and language development, can affect any domain of language
  28. 28.  Family needs to respond early, proactively, and responsively Newborn hearing screenings increase likelihood of early identification Parental decisions: communication mode, communication “orientation” (Deaf vs. deaf) Best age for identification and initiation of intervention: prior to six months
  29. 29.  Early Hearing Detection and Intervention (EDHI) program: 5 to 6 out of every 1000 infants born with hearing loss Eight percent of school-age children have “educationally significant” hearing loss ◦ Includes cases of acquired hearing loss due to middle ear infections (35% children experience ongoing middle ear infections throughout childhood) ◦ Also includes cases of congenital hearing loss due to pre-, peri-, or post-natal genetic influences, injuries or illnesses
  30. 30.  Classified by either etiology, manifestation and impact, or severityA. ETIOLOGY For characterizing the cause of the hearing loss: a. Genetic or environmental cause b. Age of onset c. Type of loss
  31. 31.  Genetic: ◦ Transmitted from parents to offspring  autosomal dominant  autosomal recessive Environmental: ◦ Exposure to noise (e.g., ventilator system in NICU) ◦ Sudden exposure to noise or sudden change in air pressure (barotrauma)
  32. 32.  Developmental: present at birth ◦ Common causes: genetic disorders, Rh incompatibility, infection or disease, trauma, anoxia, ototoxic drugs, prematurity Acquired: occurs sometime after birth ◦ Common causes: trauma, ototoxic drugs, middle ear infections, infection, noise, systemic illness, barotrauma Prelingual vs. postlingual
  33. 33.  Identifies the auditory structures that are affected Conductive loss: damage to the outer or middle ear Sensorineural loss: damage to the cochlea or auditory nerve Mixed loss: simultaneous damage to the conductive and sensorineural mechanisms
  34. 34.  Classification based on the aspects of audition that are impacted Loss of hearing acuity: loss of precision of hearing at different levels of loudness Decrease in language comprehension (occurs with sensorineural loss) ◦ more difficult to manage
  35. 35.  Classification based on severity using decibel system (dB) Hearing loss is represented by identifying the threshold of hearing: where a person just begins to hear ◦ Normal hearing: -10 to 15 dB ◦ Mild hearing loss: 26 to 40 dB ◦ Moderate hearing loss: 41 to 55 dB ◦ Severe hearing loss: 71 to 90 dB ◦ Profound hearing loss: 91 dB or higher
  36. 36.  Attenuation or reduction of the sounds heard in the environment However, exaggerates sound of one’s voice and chewing, because of bone conduction Slight to moderate loss in one or both ears, typically not severe Medical or surgical intervention is usually successful, so loss is usually temporary
  37. 37.  Most CHL is acquired, with middle ear fluid the most common cause. Congenital causes include anomalies of the pinna, external ear canal, TM, and ossicles. Rarely, congenital cholesteatoma or other masses in the middle ear may present as CHL. TM perforation (trauma, OM), ossicular discontinuity (infection, cholesteatoma, trauma), tympanosclerosis, acquired cholesteatoma
  38. 38.  masses in the ear canal or middle ear (Langerhans cell histiocytosis, salivary gland tumors, glomus tumors, rhabdomyosarcoma) may also present as CHL. Uncommon diseases affecting the middle ear and temporal bone that may present with CHL include otosclerosis, osteopetrosis, fibrous dysplasia, and osteogenesis imperfecta.
  39. 39.  CHL can also be genetic. Conditions, diseases, or syndromes that include craniofacial abnormalities are often associated with conductive hearing loss and possibly with SNHL. Pierre Robin, Treacher Collins, Klippel-Feil, Crouzon, and branchio- otorenal syndromes and osteogenesis imperfecta . malformations of the ossicles and middle-ear structures and atresia of the external auditory canal.
  40. 40.  Most common cause: middle ear infections (otitis media) ◦ Angle and shortness of Eustachian tube in children allows organisms to enter easily ◦ Allergens (e.g., cigarette smoke) make more susceptible ◦ Interactions with other children spread infections (e.g., child-care centers) Other causes: ear wax (cerumen) blockage, foreign objects, congenital malformations
  41. 41.  Most common type of hearing loss – slight to profound loss of hearing in one or both ears Decrease in loudness, also decrease in speech perception and ability to distinguish speech from background noise Some also experience reduced tolerance for loud noises or ringing in the ears (tinnitus)
  42. 42.  SNHL may be congenital or acquired. Causes of SNHL include genetic, infectious, autoimmune, anatomic, traumatic, ototoxic, and idiopathic factors. The most common infectious cause of congenital SNHL is cytomegalovirus (CMV), which infects 1/100 newborns in the United States. Of these, 6,000-8,000 infants per year will have clinical manifestations, including approximately 75% with SNHL.
  43. 43.  Congenital CMV warrants special attention because it is associated with hearing loss in its symptomatic and asymptomatic forms; the hearing loss may be progressive. Some children with congenital CMV have suddenly lost residual hearing at age 4-5 yr. Other less common congenital infectious causes of SNHL include toxoplasmosis and syphilis.
  44. 44.  Congenital CMV, toxoplasmosis, and syphilis may also present with delayed onset of SNHL, months to years after birth. Rubella, once the most common viral cause of congenital SNHL, is now very uncommon because of effective vaccination programs. Prenatal infection with herpes is rare, and hearing loss as the only manifestation is very unusual
  45. 45.  Other postnatal infectious causes of SNHL include Group B streptococcal sepsis in newborns and bacterial meningitis. Streptococcus pneumoniae is the most common cause of bacterial meningitis that results in SNHL after the neonatal period; this cause may become less frequent with the routine administration of pneumococcal conjugate vaccine.
  46. 46.  Haemophilus influenzae, once the most common cause of meningitis resulting in SNHL, is now rare owing to the Hib vaccine. Uncommon infectious causes of SNHL include Lyme disease, parvovirus B19, and varicella. Mumps, rubella, and rubeola, all once common causes of SNHL in children, are rare owing to vaccination programs
  47. 47.  Genetic causes of SNHL are probably responsible for as many as 50% of SNHL cases. These disorders may be associated with other abnormalities, may be part of a named syndrome, or may exist in isolation. SNHL often occurs with abnormalities of the ear and eye and with disorders of the metabolic, musculoskeletal, integumentary, renal, and nervous systems. Autosomal dominant hearing losses account for about 10% of all cases of childhood SNHL.
  48. 48.  Waardenburg (types I and II) and branchio- otorenal syndromes represent two of the most common autosomal dominant syndromic types of SNHL. Autosomal recessive genetic SNHL, both syndromic and nonsyndromic, accounts for about 80% of all childhood cases of SNHL.
  49. 49.  Usher syndrome (types I, II, and III), Pendred syndrome, and the Jervell and Lange-Nielsen syndromes (a form of the long Q-T syndrome) are three of the most common syndromic recessive types of SNHL. Whereas children with an easily identified syndrome or with anomalies of the outer ear may be identified as being at risk for hearing loss and monitored adequately,
  50. 50.  nonsyndromic children present greater difficulty. Mutations of the connexin-26 and -30 genes have been identified in autosomal recessive and autosomal dominant and in sporadic nonsyndromic patients with SNHL. Sex-linked disorders associated with SNHL, thought to account for 1-2% of SNHL, include Norrie disease, the otopalatal digital syndrome, and Alport syndrome.
  51. 51.  Chromosomal abnormalities such as 13-15- trisomy, 18-trisomy, and 21-trisomy can also be accompanied by hearing impairment. Patients with Turner syndrome have monosomy for all or part of one X chromosome and may have CHL, SNHL, or mixed hearing loss. The hearing loss may be progressive. Mitochondrial genetic abnormalities may also result in SNHL.
  52. 52.  Agenesis or malformation of cochlear structures, including the Scheibe, Mondini, Alexander, and Michel anomalies, and enlarged vestibular aqueducts and semicircular canal anomalies may be genetic. These anomalies probably occur before the 8th wk of gestation and result from arrest in normal development, aberrant development, or both. Many of these anomalies have also been described in association with other congenital conditions such as intrauterine infections (CMV, rubella).
  53. 53.  Many genetically determined causes of hearing impairment, including both syndromic and nonsyndromic, do not express themselves until some time after birth. Alport, Alström, and Down syndromes, von Recklinghausen disease, and Hunter-Hurler syndrome are genetic diseases that may have SNHL as a late manifestation
  54. 54.  SNHL may also occur secondary to exposure to toxins, chemicals, and antimicrobials . Early in pregnancy, the embryo is particularly vulnerable to the effects of toxic substances. Ototoxic drugs, including aminoglycosides, loop diuretics, and chemotherapeutic agents (cisplatin) may also cause SNHL. Congenital SNHL may occur secondary to exposure to these drugs as well as to thalidomide and retinoids. Certain chemicals, such as quinine, lead, and arsenic, may cause hearing loss both prenatally and postnatally
  55. 55.  Trauma, including temporal bone fractures, inner ear concussion, head trauma, iatrogenic trauma (surgery, extracorporeal membrane oxygenation [ECMO]), radiation, and noise may also cause SNHL. Other uncommon causes of SNHL in children include immune disease (systemic or limited to the inner ear), metabolic abnormalities, and neoplasms of the temporal bone
  56. 56.  Usually is present at birth as a congenital hearing loss Half of the causes are unknown, the other half are caused by genetics and heredity, infection, otitis media, prematurity, pregnancy complications, trauma Risk factors: influenced by maternal health, birth process, hereditary factors, exposure to medications, and disease
  57. 57.  Both permanent reduction of sound (sensorineural) and additional temporary loss of hearing (conductive)
  58. 58.  Identification: often begins with routine screening, (e.g., newborn screening) Ongoing monitoring: understanding hearing loss changes over time and to measure effects of intervention
  59. 59.  Referral Screening Comprehensive Audiological Evaluation Hearing Aid Evaluation
  60. 60.  EDHI programs are present in most states, with the goal to detect hearing loss while the infant is still in hospital after birth Toddlers and preschoolers are referred if: ◦ show developmental delay ◦ have hereditary disposition for hearing loss ◦ develop disease or disorder that affects the auditory mechanism All children are evaluated routinely in kindergarten, and 1st-3rd grades, and 7th and 11th grades
  61. 61.  Infant Screening: ◦ Completed at birth in the hospital ◦ Typically uses otoacoustic emissions or evoked auditory potentials as test measures Conventional Hearing Screening: ◦ Require the child to respond when a soft tone is presented and heard (behavioral testing) ◦ Children who fail are either re-screened in two weeks or referred for a comprehensive examination
  62. 62.  Assesses the type and degree of hearing loss, speech discrimination, and auditory perception Case history Interview and observation Otoscopic examination Audiometry Objective measures ◦ Immitance, otoacoustic emissions (OAEs), evoked auditory potentials (EAPs)
  63. 63.  12No differentiated babbling or vocal imitation 18No use of single words 24Single-word vocabulary of ≤ 10 words 30Fewer than 100 words; no evidence of two-word combinations; unintelligible 36Fewer than 200 words; no use of telegraphic sentences, clarity < 50% 48Fewer than 600 words; no use of simple sentences; clarity ≤ 80%
  64. 64. An audiogram provides the fundamental description of hearing sensitivity. Hearing thresholds are assessed as a function of frequency using pure tones (sine waves) at octave intervals from 250-8,000 Hz.Earphones are typically used, and hearing is assessed independently for each ear.Air-conducted signals and bone-conducted signals are elicited.
  65. 65.  In a normal ear, the air and bone conduction thresholds are the same; they are also the same in those with SNHL. In those with CHL, the air and bone conduction thresholds differ. This is called the air-bone gap; it indicates the amount of hearing loss attributable to dysfunction in the outer and/or middle ear. With mixed hearing loss, both the bone and air conduction thresholds are abnormal, and there is an air-bone gap.
  66. 66.  Another measure useful in describing auditory function is the speech recognition threshold (SRT), which is the lowest intensity level at which a score of approximately 50% correct is obtained on a task of recognizing spondee words. Spondee words are two-syllable words or phrases that have equal stress on each syllable (baseball, hotdog, pancake). Listeners must be familiar with all the words for a valid test result to be obtained.
  67. 67.  The SRT should correspond to the average of pure-tone thresholds at 500, 1,000, and 2,000 Hz, the pure-tone average (PTA). The SRT is relevant as an indicator of a childs potential for development and use of speech and language; it also serves as a check of the validity of a test because children with nonorganic hearing loss (malingerers) may show a discrepancy between the PTA and SRT
  68. 68.  Hearing testing is age-dependent. For children at or above the developmental level of a 5 or 6 yr old, conventional test methods can be used. For children 2½-5 yr old, play audiometry can be used. Responses in play audiometry are usually conditioned motor activities associated with a game, such as dropping blocks in a bucket, placing rings on a peg, or completing a puzzle.
  69. 69.  The technique can be used to obtain a reliable audiogram for a preschool child. For those who will not or cannot repeat words clearly for the SRT and word intelligibility tasks, pictures can be used with a pointing response.
  70. 70.  For those between the ages of about 6 mo and 2½ yr, visual reinforcement audiometry (VRA) is commonly used. In this technique, the child is observed for a head-turning response upon activation of an animated (mechanical) toy reinforcer. If infants are properly conditioned, by giving sounds associated with the visual toy cue, VRA can provide reliable estimates of hearing sensitivity for tones and speech sounds.
  71. 71.  In most applications of VRA, sounds are presented by loudspeakers in a sound field, so no ear-specific information is obtained. Assessment of an infant is often designed to rule out hearing loss that would affect the development of speech and language. Normal sound field response levels of infants indicate sufficient hearing for this purpose despite the possibility of different hearing levels in the two ears.
  72. 72.  Used as a screening device for infants younger than 5 mo, behavioral observation audiometry (BOA) is limited to unconditioned, reflexive responses to complex (not frequency-specific) test sounds, such as noise, speech, or music presented using calibrated signals from a loudspeaker or uncalibrated noisemakers. Response levels can vary widely within and among infants and usually do not represent a reliable estimate of sensitivity
  73. 73.  This is a standard part of the clinical audiologic test battery and includes tympanometry. Acoustic immittance testing is a useful objective assessment technique that provides information about the status of the middle ear. Tympanometry can be performed in a physicians office and is helpful in the diagnosis and management of OM with effusion, a common cause of mild to moderate hearing loss in young children
  74. 74.  This technique provides a graph of the ability of the middle ear to transmit sound energy (admittance, or compliance) or impede sound energy (impedance) as a function of air pressure in the external ear canal. Abnormalities of the TM can dictate the shape of tympanograms and thus obscure abnormalities medial to the TM.
  75. 75.  Children with OME often have reduced peak admittance or high negative tympanometric peak pressures . The more rounded the peak (or "flat" in an absent peak), the higher is the probability that an effusion is present .
  76. 76. FIGURE 2 Typical tympanograms showing, for each, the estimated probability of MEE Smith, C. G. et al. Pediatrics 2006;118:1-13Copyright ©2006 American Academy of Pediatrics
  77. 77.  Reflexes are usually absent in those with CHL due to the presence of an abnormal transfer system; thus, the ART is useful in the differential diagnosis of hearing impairment. ART also is used in the assessment of SNHL and the integrity of the neurologic components of the reflex arc, including cranial nerves VII and VIII.
  78. 78.  The ABR test is used for newborn hearing screening, to confirm hearing loss in young children, to obtain ear-specific information in young children, and to test children who cannot, for whatever reason, cooperate with behavioral test methods. It is also important in the diagnosis of auditory dysfunction and of disorders of the auditory nervous system. The ABR test is a far- field recording of minute electrical discharges from numerous neurons
  79. 79.  As an audiometric test, it provides information on the ability of the peripheral auditory system to transmit information to the auditory nerve and beyond. It is used also in the differential diagnosis or monitoring of central nervous system pathology. For audiometry, the goal is to find the minimum stimulus intensity that yields an observable ABR
  80. 80.  Plotting latency versus intensity for various waves also aids in the differential diagnosis of hearing impairment The ABR is recorded as 5-7 waves. Waves I, III, and V can be obtained consistently in all age groups; Waves II and IV appear less consistently
  81. 81.  The ABR test has two major uses in a pediatric setting. As an audiometric test, it provides information on the ability of the peripheral auditory system to transmit information to the auditory nerve and beyond. It is used also in the differential diagnosis or monitoring of central nervous system pathology.
  82. 82.  During normal hearing, OAEs originate from the hair cells in the cochlea and are detected by sensitive amplifying processes. They travel from the cochlea through the middle ear to the external auditory canal, where they can be detected using miniature microphones. Transient evoked OAEs (TEOAEs) may be used to check the integrity of the cochlea.
  83. 83.  In this test, a hand-held instrument is placed next to the opening of a childs ear canal and 80-dB sound is delivered that varies in frequency from 2,000-4,500 Hz in a 100-msec period. The instrument measures the total level of reflected and transmitted sound. Some physicians have found this device useful to help gauge the presence or absence of middle-ear fluid