Hearing and ENT

Newborn Hearing Screening Tests

Newborn hearing screening is a universal programme that aims to identify permanent moderate, severe and profound deafness and hearing impairment in newborn babies. The test can be done on babies up to the age of 3 months.

Early detection and early intervention of hearing problems will lessen the impact of deafness on the child, the child’s family and society. All well babies undergo an automated otoacoustic emission test (aOAE). If this is not “passed” after two attempts, then the baby has an automated auditory brainstem response test (aABR). Babies in the neonatal intensive care or at high risk and have both an aOAE and an aABR test.

Acoustic emissions are sounds that are produced by the outer hair cells of the inner ear in response to a noise stimulus and can be measured by placing a small probe in the ear canal. Since the sounds are only produced by normal outer hair cells, their detection correlates highly with normal hearing. The vast majority of hearing impairment is due to damage of these cells and the test therefore provides a sensitive and accurate means of screening for cochlear hearing impairment.

Auditory brainstem response is an electrophysiological response that measures the function of the auditory pathway from the external ear to the brainstem when sounds are presented to the ear. It can determine hearing thresholds allowing targeted treatment depending on the severity of the hearing thresholds.

Visual Reinforcement Audiometry

The test provides a “visual reward” when a child responds correctly by turning their head to sound played from headphones or field speakers on either side of the child and hearing thresholds are determined at different frequencies and amplitudes.

Play Audiometry

This test requires the child to respond to a sound by performing a simple task such as putting a ball in a bucket. This is repeated across different frequencies and at different volumes to determine the hearing thresholds.

Pure Tone Audiometry

The child usually wears headphones and is asked to respond when they hear the sound by pressing a button. The volume and frequency of the sound is adjusted to determine the hearing thresholds.

Tympanometry

The test assesses the status of the middle ear by measuring mobility of the eardrum. It is not a hearing test but an assessment of the compliance of the eardrum.

Conductive Impairment

Conductive hearing loss occurs when there is impairment of the sound transmission through either the outer or middle ear or both. Formal testing demonstrates that the bone conduction thresholds are better than air conduction thresholds. Conductive hearing loss produces losses of up to 50–60 dBHL.

The causes include:

• ear canal obstruction—atresia, wax, foreign body

• perforation of tympanic membrane

• otitis media with effusion

• Down syndrome

• cranio-facial anomalies—Pierre Robin syndrome, cleft palate

Sensorineural Impairment (SNHL)

Sensorineural hearing loss is due to impairment within the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII). Formal testing demonstrates that both bone conduction and air conduction thresholds are poor. It can be more severe than conductive impairment and can also be progressive.

The causes include:

• congenital SNHL

  • genetic—syndromic or nonsyndromic

  • infection—congenital infections

  • prematurity

  • hypoxic ischaemic encephalopathy

• acquired SNHL

  • ototoxic drugs—aminoglycosides, furosemide

  • meningoencephalitis

  • head injury

  • neurodegenerative disorders

  • hyperbilirubinemia

The hearing loss in sensorineural impairment is usually profound and usually greater than 90 dBHL. The children need prompt referral to ENT services for a more detailed assessment and consideration of the need for a hearing device. Aminoglycosides classically induce a high-tone hearing loss with a ‘ski slope’ appearance on the audiogram.