Otorhinolaryngology (ENT)
Audiology and Hearing Assessment
Audiology for MBBS ENT: pure tone and speech audiometry, tympanometry types, otoacoustic emissions, BERA and newborn hearing screening, mapped to NMC codes EN2 and EN4.
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Audiology and Hearing Assessment
Audiology for MBBS ENT: pure tone and speech audiometry, tympanometry types, otoacoustic emissions, BERA and newborn hearing screening, mapped to NMC codes EN2 and EN4.
This chapter covers how hearing is measured objectively and subjectively. It explains pure tone and speech audiometry, tympanometry and the acoustic reflex, otoacoustic emissions and evoked response audiometry, and how each test contributes to grading and localising hearing loss, including newborn screening.
High-yield: Audiology and Hearing Assessment
- Pure tone audiometry measures air and bone conduction thresholds across frequencies and is the core test of hearing.
- An air-bone gap on the audiogram indicates conductive hearing loss, while air and bone thresholds falling together indicate sensorineural loss.
- Normal hearing threshold is 0 to 25 decibels; mild loss is 26 to 40, moderate 41 to 55, severe 71 to 90 and profound above 90 decibels.
- Tympanometry measures middle ear pressure and compliance: type A is normal, type B is flat (fluid or perforation), type C shows negative pressure.
- Otoacoustic emissions test cochlear outer hair cell function and are widely used for newborn hearing screening.
- The brainstem evoked response audiometry (BERA) is an objective test of the auditory pathway, useful in infants and in retrocochlear lesions.
- Speech audiometry assesses how well spoken words are heard and understood, complementing pure tone results.
- A rollover phenomenon on speech audiometry, where scores fall at higher intensity, suggests a retrocochlear lesion.
- Impedance audiometry also elicits the acoustic (stapedial) reflex, which is absent in facial nerve palsy proximal to the stapedius branch.
- Free field and behavioural tests are used in young children who cannot cooperate with pure tone audiometry.
- A carhart notch, a dip in bone conduction at 2 kilohertz, is a classic audiometric sign of otosclerosis.
- The audiogram plots frequency on the horizontal axis and hearing level in decibels on the vertical axis, with worse hearing lower down.
- Noise-induced hearing loss classically shows a notch at 4 kilohertz on the audiogram.
- Newborn hearing screening aims to detect congenital hearing loss early so that intervention can begin within the first months of life.
Tympanometry types
- **Type A:** Normal peak at atmospheric pressure. Normal middle ear.
- **Type B (flat):** No peak. Middle ear fluid or perforation.
- **Type C:** Peak shifted to negative pressure. Eustachian tube dysfunction.
- **Acoustic reflex:** Absent in significant conductive loss and in facial palsy above the stapedius branch.
NMC competencies in this chapter
- **EN2.4:** Assessment of hearing and interpretation of hearing tests
- **EN2.8:** Interpret audiological investigations including audiometry and tympanometry
- **EN4.16:** Newborn and infant hearing screening
- **EN4.17:** Rehabilitation of hearing loss including hearing aids
Frequently Asked Questions
How does the audiogram distinguish conductive from sensorineural loss?
An air-bone gap, where bone thresholds are better than air, indicates conductive loss. When air and bone thresholds fall together with no gap, the loss is sensorineural.
What is tympanometry used for?
It measures how the eardrum and middle ear move under changing pressure. A flat type B trace suggests fluid or perforation, and a type C trace suggests Eustachian tube dysfunction.
Why are otoacoustic emissions used in newborns?
They test cochlear outer hair cell function quickly and without the baby's cooperation, so they are ideal for universal newborn hearing screening to detect congenital deafness early.
What is a Carhart notch?
A dip in the bone conduction threshold around 2 kilohertz, a characteristic audiometric feature of otosclerosis that often improves after successful surgery.
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