1. PERIPHERAL AND CENTRAL AUDITORY ASSESSMENT Ravi Pachigolla, MD Jeffery T. Vrabec, MD

2. Introduction zPure tone audiometry zTympanometry zAcoustic reflex measurements zECochG zAuditory Brainstem Response (ABR) zOtoacoustic Emissions

3. Pure Tone Audiometry zMost common test zThreshold of audibility zActivation of auditory system zEnergy formatted into neural code zAir conduction assesses entire system zBone conduction assesses cochlea onwards

4. Pure Tones zAuditory acuity zSpectrally specific zHigh frequency tones stimulate basal turn of the cochlea zLow frequency tones stimulate apical turn of the cochlea

5. Decibel Scales zSound Pressure Level (SPL) zHearing Level (HL) zSensation Level (SL)

6. Assessment of thresholds zOctave frequencies tested zBone conduction thresholds zMastoid or forehead used zMastoid preferred because less intensity required zOcclusion effect zAscending series of tone presentations

7. Speech Audiometry zSpeech Reception Threshold using spondaic words zStandardized word lists zFamiliarization with spondees zAscending series of presentation zExcellent speech discrimination in conductive hearing loss patients zPoor speech discrimination in cochlear hearing loss patients zPoorest speech discrimination in retrocochlear hearing loss patients

8. Clinical Masking zNontest ear can influence thresholds of test ear zShadow curve apparent without masking zInteraural attenuation varies from 40 to 80 dB with air conduction zInteraural attenuation is about 0 dB with bone conduction

9. Shadow Curve

10. Clinical Masking cont. zCompare bone conduction threshold of nontest ear with air conduction threshold of test ear to determine whether masking is necessary

11. Masking using narrow bands of noise

12. Plateau method zMask nontest ear with progressively greater amounts of sound until threshold does not rise. zMasking Dilemma

13. Acoustic Immitance zImpedance zReflected energy zTympanometry zAcoustic Reflex

14. Tympanometry configurations

15. Acoustic Reflex Threshold zStapedial muscle contraction zTemporary increase in middle impedance zBilateral Stimulation zAdaptation zNeural network in lower brainstem

16. Clinical application of ASR zMiddle Ear Disease zOtosclerosis zCochlear hearing loss and loudness recruitment zRetrocochlear lesions may abolish the ASR zBrainstem lesions may abolish the contralateral reflexes zDetermination of site of a seventh nerve lesion zAcoustic Reflex Decay

17. Electrocochleography zCochlear Microphonic zSummating Potential zCompound Action Potential zIncreased SP/AP ratio suggests hydrops zAbility to enhance wave I of the ABR in patients with severe high frequency hearing loss

18. Electrocochleography setup

19. ECochG and Meniere’s zIncreased SP/AP ratio zLatency not important zRatio greater than 0.45 suggests meniere’s zHydrops affects elasticity of the basilar membrane

20. Auditory Brainstem Response zAuditory evoked potential zFarfield recording zAcoustic clicks or tonal stimuli used zRate of stimulus presentation

21. ABR continued zWaves I - V zUnaffected by sleep and pharmacotherapy zABR latencies decrease from birth until 2 years zWave V used for threshold testing (most robust) zABR thresholds about 10 to 20 dB poorer than behavioral measures

22. Latency of response

23. ABR continued zLesions of the eighth cranial nerve zInterwave latency zInteraural latency difference zAbsolute latency zAmplitude ratio

24. Retrocochlear lesion

25. Otoacoustic Emissions zEnergy leakage zEvidence of a healthy, functioning cochlea zSpontaneous and evoked emissions zEvoked emission seen only in cochleae with thresholds less than 20 to 30 dB zConductive losses affect emissions zScreening tool in infants

26. Central Auditory Function zComprehension zBackground noise zBehavioral tests zMonotic vs. dichotic zMonaural vs. binaural

27. Case Presentation z31 yo male with left sided hearing loss noticed when listening to portable radio zNo other otologic complaints, no pmh or contributory family or social history zPE normal

28. Audiogram

29. Assessment zMild high frequency sensorineural hearing loss zSmall amount of rollover zIpsi reflexes elevated in left ear zContra reflexes elevated in left ear suggesting retrocochlear pathology zMRI showed 5 mm acoustic neuroma

30. Analysis zAbnormal reflex responses in left ear indicate 7th nerve affected zElevated contralateral thresholds in right ear means that decussating pathways from left VCN to right brainstem affected