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Sensorineural and conductive hearing loss

last modified on: Wed, 10/21/2020 - 18:28

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See also Cisplatin Ototoxicity

Overview:

Three major types of hearing loss:

  • Conductive hearing loss (CHL)
  • Sensorineural hearing loss (SNHL)
  • Mixed: both CHL and SNHL components

Hearing Fork Tests:

  • Can help to determine type and laterality of loss
  • Types of tests:
    • Weber test
      • place tuning fork at the midline of the patient's forehead
      • Normal or equal bilateral loss: localizes to midline
      • CHL: localizes to the affected ear
      • SNHL: localizes to better ear
    • Rinne test
      • place tuning fork on patient's mastoid bone (bone conduction) and then in front of the patient's ear (air conduction)
      • Normal or SNHL: air conduction > bone conduction
      • CHL: bone conduction > air conduction
      • A normal test is termed as a 'positive Rinne', and an abnormal test is termed 'negative'

Audiogram:

  • Pure-tone audiometry which tests hearing threshold (dB) for different frequencies (Hz)
  • Tests each ear for bone conduction and air conduction
  • Hearing loss types:
    • CHL: 'air-bone gap'; difference in threshold for a given frequency in the same ear
    • SNHL: >25 dB for a given frequency
    • Mixed: Higher thresholds as well as an air-bone gap

Conductive Hearing Loss: 

  • Trouble conducting sound, from the auricle to the inner ear 
  • Location of abnormality:
    • EAC
    • Tympanic membrane
    • Middle Ear Space
    • Ossicles
  •  Causes:
    • Cerumen impaction
    • Otitis Media 
    • Tympanic membrane perforation
    • Otosclerosis
    • Foreign body
    • Otitis externa
    • Tumors
  • Findings:
    •  Physical abnormality
      • EAC obstructed (tumor, otitis externa)
      • TM perforation
      • Change in TM mobility
      • Fluid in ME
      • Cholesteatoma 
    • Negative Rinne (BC>AC), Weber localizing to affected ear
    • Audiogram showing air-bone gap

 

Sensorineural Hearing Loss:

  • Trouble sending neural signals, from the cochlea to CNVIII to the brain 
  • Location of abnormality:
    • Inner ear
    • Eighth cranial nerve
  • Causes:
    • Presbycusis
    • Noise exposure
    • Congenital
    • Infection
    • Meniere's disease
    • Ototoxicity
  • Findings:
    • No physical abnormality
    • Positive Rinne (AC>BC)
    • Audiogram showing increase in hearing thresholds with no air-bone gap