Otosclerosis

Question 1

What is otosclerosis

Answer 1

Disease process unique to the temporal bone that only involves the otic capsule. There is abnl removal of mature dense otic capsule bone by OC and replacement with woven bone of greater thickness, cellularity, and vascularity

Question 2

Where does it usually occur

Answer 2

The anterior border of the oval window (fissula ante fenestram)

Question 3

What type of HL is seen?

Answer 3

• CHL when dz involves the annular ligament of the oval window and stapes footplate
• SNHL when other parts of the otic capsule involved (also get vestibular sx)

Question 4

Epidemiology

Answer 4

• Whites in 3rd and 4th decade with family hx
• 2:1 F:M
• 13% subclinical dz
• 0.5-1% clinical dz

Question 5

Pathogenesis

Answer 5

• Otic capsule and stapes form from cartilaginous anlage which begins endochondral ossification by 19th wk and complete by 1st year of life
• Vestibular surface of footplate remains cartilaginous
• Bone turnover DOES NOT occur in healthy otic capsule
• w/ otosclerosis, inc OB and OC activity and vascular proliferation
• As dz “burns out” the nl otic capsule bone is replaced by metabolically quiescent dense mineralized bone

Question 6

What is the only way to dx otosclerosis

Answer 6

Histopathology

Question 7

Define otospongiosis

Answer 7

The histologic appearance of the bone

Increased bony turnover and metabolic activity

Question 8

What is the genetic component

Answer 8

Auto dom
Incomplete penetrance
Variable expressivity

Question 9

Presentation

Answer 9

Slowly progressive b/l asymmetric HL
Difficulty understanding speech once 25-30 dB loss
Tinnitus
Fluctuations in hearing are uncommon but can be linked to hormonal instability (e.g. preg)

Question 10

What is paracusis of Willis

Answer 10

a paradoxical phenomenon seen with otosclerosis where pts report improved hearing in background noise

Question 11

What is the Schwartze sign?

Answer 11

Reddish blush over both the promontory and oval window niche owing to the prominent vascularity a/w an otospongiotic focus

Question 12

Typical physical exam

Answer 12

• Normal otoscopic exam (excludes other causes of CHL like cholesteatoma, tympanosclerosis, ME effusion/mass)
• Possibly Schwartze sign
• TF: weber lateralizes to worse ear, BC>AC

Question 13

Classic audiometric findings

Answer 13

1. Low freq CHL
2. Carhart notch
3. Type A or As tymp
4. Biphasic or absent reflexes (often precedes AB gap)
5. Negative Rinne (BC>AC)

Question 14

Imaging modality of choice

Answer 14

CT

Question 15

CT findings

Answer 15

• Subtle areas of demineralization, typically just anterior to the oval window (fissula ante fenestram)
• Thickening of footplate
• With cochlear involvement: demineralization of otic capsule yielding halo sign or double ring sign seen on CT as a low density zone outlining the basal turn of cochlea
• In the sclerotic phase of dz or after fluoride Rx, remineralization may occur and CT may look nl

Question 16

When to obtain CT

Answer 16

When pt has

• vertigo
• SNHL
• poor word recognition
• concern for SSCCD
• pedi pt (bc typically no dz b4 20 yo and higher risk of otic capsule and t bone malformations in these pts)

Question 17

MRI

Answer 17

Provides limited info
Not obtained routinely

• T1: loss of nl signal void from otic capsule
• Contrast T1: enhancement of pericochlear otic capsule

Question 18

What is the Carhart notch

Answer 18

• A mechanical phenomenon from the disruption of normal ossicular resonance (which is approx 2 kHz)
• Elevation of bone conduction thresholds of 5, 10, and 15 dB at 500, 1000, and 2000 Hz
• It reverses after surgery