w8

Question 1

where are the windows?

Answer 1

Temporal bone, perilymphatic space, membranous labyrinth containing endolymph
- Either high or low impedance

Question 2

What are these windows?

Answer 2

Small holes, channels and ducts in inner ear that may be covered (by membrane)

Question 3

low impedance windows

Answer 3

oval and round window
- Connect perilymph to air in ME cavity
- Large in area & mobile
- Low impedance allows transmission of sound from ME air space to inner ear fluids
- Movement of these 2 windows allow for bulk movement of inner ear fluids with sound vibrations

Question 4

oval window

Answer 4

covered by stapes footplate & ligament

Question 5

round window

Answer 5

covered by membrane

Question 6

high impedance windows

Answer 6

• Perilymphatic space is embedded within temporal bone but not entirely enclosed
• Small openings and channels in temporal bone
  o Connect perilymph to the cranial cavity containing CSF (cochlear aqueduct)
  o Allow blood vessels and nerves to connect inner ear & brain

Question 7

• Habenula perforate:

Answer 7

holes” allow nerve fibers & blood vessels to pass into cochlea

Question 8

Abnormal windows can develop and cause inner ear dysfunction when:

Answer 8

1. High impedance windows/channels/ducts become enlarged
   a. High impedance window change & become low impedance
2. New holes or weaknesses develop in temporal bone or membranous labyrinth
   a. New holes/channels appear in inner ear forming extra low impedance windows
   b. Normally there are only 2 low impedance windows: oval and round

Question 9

Low impedance 3rd window mechanisms

Answer 9

Characteristic low frequency air-bone gap due to
- Decreased (Worse) air conduction
- Increased (better than normal) bone conduction
Unusual types of tinnitus: increased sensitivy to internal sounds

Question 10

Normal air conduction with normal ear 2 low impedance windows

Answer 10

difference in vibration between the oval & round window generates a pressure gradient across the BM activating haircells and creating perception of sound

Question 11

Third window air conduction

Answer 11

incoming acoustic energy from oval window is shunted away decreasing transmission to round window and decreasing pressure gradient across the BM, resulting in reduced air conduction thresholds

Question 12

Normal BC mechanism

Answer 12

Bc vibrations produce outward motion of oval and round windows (round window is greater) this is due to unequal impedances oval window is higher impedance bc covered by bony footplate of stapes
Normal ear 2 low impedance windows: vibrations produce unequal outward motion of oval and round windows, pressure difference across BM creates BM vibrations and perception of sound by BC

Question 13

underlying mechanisms: tinnitus

Answer 13

• Tinnitus rupture in bone or enlargement of high impedance windows creates low impedance connections b/w inner ear fluids and CSF surrounding bone
• Pressure changes in cerebral spinal fluid with changes to heartbeat
• If connection between perilymph and CSF the pressure changes can flow into cochlea and into BM causing pulsatile tinnitus or ringing in ear, likely as pulsatile and rhythmic to heartbeat,
• Increase in pressure differential so vibrations are being detected by cochlea whereas in normal patients it is not

Question 14

Perilymphatic Fistula

Answer 14

rupture in oval or round window creating an abnormal connection b/w inner ear perilymph and ME space
- can be aquired, congenital or ideopathic

Question 15

Abnormal ear with enlarged window (3rd window BC)

Answer 15

energy shunting across 3rd window decreases motion of higher impedance oval window, motion of round window unchanged, elevating pressure difference across BM, increasing BM displacement and improving BC sound perception

Question 16

acquired perilymphatic fistula

Answer 16

surgery (stapedectomy) head trauma, barotrauma, erosion in the bony labyrinth (cholesteatoma)

Question 17

congenital perilymphatic fistula

Answer 17

TB malformation

Question 18

Perilymphatic fistula: idiopathic

Answer 18

• No specific diagnostic test
• Reliability of observed leaks on exploration of ME space (OW or RW)
• Without inciting event (surgery, barotrauma) does it even exist

Question 19

pathologic 3rd window

Answer 19

• Defect in the bony labyrinth can create new low impedance window
• Disruption of high impedance window (converted to a low impedance window, new fistulas (holes) or weakness can reduce impedance)

Question 20

pathologic third window symptoms

Answer 20

variable depending on size and location in membranous labyrinth; extra low impedance window renders the membranous labyrinth to sound and pressure changes

Question 21

Pathological 3rd window clinical presentation

Answer 21

often mimics ME disoreders (ex., otosclerosis)
- Auditory & vestibular symptoms
- Sensitive to loud sound & pressure change
- HL with conductive component (normal tests of ME function)
If no genetic deafness or congenital malformation may be otologic mysteries
Hypothesis: inner ear lesions induce inner ear CHL, caused by defects in otic capsules of inner ear

Question 22

Superior semicircular canal dehiscence (SSCD)

Answer 22

• Temporal bone around SSCC is unusually absence
• SSCD forms a 3rd window into inner ear

Question 23

Superior semicircular canal dehiscence (SSCD) prevelance
20-50% bilateral
Etiology: idiopathic

Answer 23

0.5-0.6%

Question 24

Superior semicircular canal dehiscence (SSCD) mean age

Answer 24

45 years old

Question 25

SSCD causes

Answer 25

congenital malformation with underdevelopment of bone around SSC (1-2% pop), bone thinning associated with aging, head trauma affecting temporal bone, increase pressure/barotrauma, erosion of bone by vascular pulsations

Question 26

SSCD Symptoms auditory

Answer 26

aural fullness, tinnitus (constant, pulsatile), HL (low freq conductive or mixed), internal amplification (autophony: perception of one’s own body sounds at abnormally high levels)

Question 27

SSCD Symptoms vestibular

Answer 27

: unsteadiness, oscillopsia (objects in visual field appear to oscillate caused by loud sounds or pressure changes), tullio phenomenon (vertigo & nystagmus caused by loud sound(, hennebert sign (vertigo and nystagmus caused by increased pressure)

Question 28

how is SSCD diagnosed

Answer 28

case history and symptoms, audiologic and vestibular testing, CT scan
Ct scan of temporal bone shows opening or thinning of bone around SCC

Question 29

audiologic assessment of SSCD

Answer 29

Otoscopy: unremarkable
History and complaints
Audiogram: conductive or mixed HL, excellent BC
Acoustic immittance: normal Type A tymps, AR present but sound stimulation can cause nystagmus or vertigo

Question 30

Treatment/management of SSCD

Answer 30

Avoid: Nosie or pressure triggers or activities that increase risk of head trauma or barotrauma
Surgery: tympanostomy tube for patients with pressure incided symptoms
- Resurfacing or plugging of temporal bone in SCC
- Surgery may be necessary if patients QOL sig impacted but risk of HL in affected ear or vestibular complications

Question 31

other 3rd window disorders

Answer 31

Various conditions can involve (1) enlargement of existing high impedance bony channels (2) deficits in the bony labryith producing low impedance 3rd windows
Symptoms anc clinical presentation can vary: b/w different sites of lesions, b/w different individuals with same condition, may be asymptomatic
Auditory features: HL any type, variable degree, low frequency air-bone gap is a classic sign, autophony
Vestibular complaints similar to SSCD

Question 32

symptoms of other 3rd window disorders

Answer 32

Symptoms anc clinical presentation can vary: b/w different sites of lesions, b/w different individuals with same condition, may be asymptomatic
Auditory features: HL any type, variable degree, low frequency air-bone gap is a classic sign, autophony
Vestibular complaints similar to SSCD