Audiologic Evaluation and Radiologic Procedures

axial

• looks at brain from below starting from chin

• R and L are flipped

coronal

• looks at brain from behind starting at back of head

• divides into front and back

• R and L are flipped

sagittal

• looks at brain from side starting at one ear

Speech threshold

speech recognition threshold (SRT)/ speech detection threshold - to cross check with pure tone average for patient reliability

word recognition score

• assess how well speech understanding is at conversational level

• site of lesion estimation: roll over

acoustic reflex threshold and decay

objectively asseses the middle ear muscle reflex (MEMR) pathway

• provide cross-check for audio when patient reliability is questionable

• used to eval central pathology

OAEs

DPOAE/TEOAE

• suggests OHC function and cross check with standard audio

• determine if SNHL is cochlear or neural in origin

ABR

• estimate hearing thresholds

  • assess functional status of the auditory neural pathway

Type A

• normal hearing or SNHL

• TM and ME work most efficiently at ambient E

type As

• otosclerosis

• TM and ME have abnormally reduced efficiency at ambient EC pressure

• normal ECV, abnormally small Adm

Type Ad

• ossicular discontinuity

• TM and ME have abnormally high efficiency at ambient pressure

• normal ECV, abnoramally lard Adm

Type B

• otitis media

• TM and ME are not efficient at any EC pressure

• Normal ECV, abnormally low Adm and no peak

Type C

• ET dysfunction/TM retraction

• TM and ME are most efficient at negative EC pressure

• normal ECV normal/abnormally low Adm and peak at negative pressure

Large ECV

• TM perforation

• artifactual appearance of inefficient TM and ME

• abnormally large ECV

X-Ray

• radiation through a single beam

• cant see small injuries

• grey/black = soft tissue

• white = bone

computed tomography (CT)

• bony labyrinth

• IAC

• CPA

• radiation rotates around body

• multiplanar slices

• looks at bone structure

• grey/black = soft tissue

• white = bone

Magnetic Resonance Imaging (MRI)

• membranous labyrinth

• detailed IAC

• detailed CPA

• neural branches

• grey/black = bone

• white = soft tissue

with no magnet, protons are randomly positioned; magnet on, mostly aligned in the same direction; radio pulse, moved orthogonally (90 degrees from aligned position); protons relax, protons release a radio signal

• weighted with gadolinium (contrast agent): helps see breakdown in blood brain barrier which can detect new lesions

HRCT (high res CT)

• 3D

• multiplanar reconstructions

• SSCs; vestibular aqueduct; oval window; round window

T2-weighted brain study

• detecting fluid-filled structures and lesions that alter fluid signal: SNHL (unexpected), vertigo, secondary tinnitus, exclude central lesion (tumor, demyelination, stroke)

• CSF is bright

unenhanced T1-weighted images

anatomy, fat, blood products, certain masses

• hyperintensities in membranous labyrinth, IAC, CPA

• schwannomas

• lipoma: fatty growth

• vascular trauma, cholesterol granuloma, vascular malfomration

• high-protein fluid

• CSF appears dark

GAD-enhanced T1

highlighting abnormal tissue where the blood-labyrinth or blood-brain-barrier is disrupted

• pathologies in membranous labyrinth, IAC, CPA

• schwannomas

• labyrinthitis, vestibular neuritis

neurofibromatosis

• genetic disorder leading to vestibular shwannomas

• NF2 - bilateral, grow at same rate, may be sequential

• NF1 - unilateral