Infant Toddler Development Training
Module 6, Lesson 3
A summary of the causes of hearing impairment is as follows:
- Lack of anatomy for hearing is one cause of conductive loss. Some syndromes are manifested through the lack of an outer ear or ear opening, however, the internal structure is intact. In cases like this the child will need a bone conduction hearing aid until surgical correction is performed.
- Conductive loss due to structural abnormalities is common in many syndromes and can be worsened with middle ear infections.
- Genetic causes are the most common with 1 in 2000 children who have a genetic disorder affected with a sensorineural hearing loss. Genetic hearing loss may have a late onset after birth or can cause congenital hearing loss.
- Acquired causes include congenital infections or bacterial meningitis in neonatal or infancy periods, high bilirubin levels, exposure to ototoxic drugs, perinatal depression (low Apgar scores), and brain abnormalities that can cause sensorineural hearing loss.
- Structural causes include malformations that are present from conception. They can also cause sensorineural hearing loss if malformations exist in the inner ear.
It is critical for audiological evaluation to occur by three months of age so that a child with significant hearing loss will be identified and SHINE services can begin. Listening typically begins before birth. Research suggests that the brain development of children with hearing loss will be affected when no auditory stimulation is consistently received. Thus, it is very important for appropriate intervention (hearing aids, SHINE) to be provided prior to six months of age. If consistent auditory stimulation and quality early intervention to develop communication skills is provided after the age of 6 months, a child will learn skills but there may be delays in communication that cannot be effectively habilitated.
By performing a battery of tests, the audiologist can gather information to differentiate between possible sensorineural hearing loss and conductive hearing loss due to the presence of ear infections. During the test, clicks or tones can be presented through earphones (air conduction) and then tones can be sent through a small vibrator placed behind the ear that will direct sound to the inner ear that is embedded in bone (bone conduction). In this way a definitive test to identify permanent hearing loss can be obtained, even if a child is experiencing an ear infection.
When a child is at a developmental age of 5-6 months, he or she has the ability to look around and identify the source of sounds. When a child is 6 months of age or older, the child should be evaluated by an audiologist who will observe the child's reinforced behavioral responses to sound. If the child fails this exam then the child's ears will be tested with a tympanometer to determine if the cause of the hearing problem could be due to ear infection. An otoacoustic emissions (OAE) test may then be done as a means to determine inner ear/cochlear problems. If the child appears to have hearing difficulty that is not related to ear infection, the audiologist may schedule the child to return for an auditory brainstem response (ABR) test. The ABR is for diagnosing auditory nerve and associative cortex issues of the brain. With this test battery, the audiologist is able to determine when a child has a hearing loss and the location of the cause of the hearing loss within the auditory system.
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