Superior Canal Dehiscence Similarly Affects Cochlear Pressures in Temporal Bones and Audiograms in Patients.
Y Song Cheng, Stefan Raufer, Xiying Guan and 3 others
PMID 31688316WHAT IT FOUND
Superior canal dehiscence lowers air-conduction hearing mainly at low frequencies.
Six temporal bones and 53 patient audiograms showed the same pattern. Testing below 250 Hz may catch cases missed by routine audiograms.
Key findings
01In six temporal bones, creating superior canal dehiscence progressively reduced the cochlear pressure difference as frequency fell; at 20 Hz the decrease was 12 to 22 dB.
02In 53 patients with unilateral superior canal dehiscence, air-conduction thresholds were higher in the affected ear at 250, 500, and 1 kHz, but not at 2, 4, or 8 kHz.
03Temporal bone pressure changes and patient air-conduction threshold changes showed a similar low-frequency pattern, with about a 6 dB per octave increase as frequency decreased.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The temporal bone work used only six specimens, so individual variation was large and the small number limits certainty. The dehiscence made in temporal bones was 1.25 mm, smaller than the average 4.0 mm clinical dehiscence, so the pressure effect may not match patients exactly. Patient thresholds were not measured below 250 Hz; the estimate that 20 Hz testing would show 35 to 40 dB loss was extrapolated, not observed. The analysis assumed the opposite ear was a normal baseline and that superior canal dehiscence did not affect sensorineural hearing. The study excluded patients with known profound sensorineural hearing loss, so it cannot address whether some patients have both conditions. The cadaveric model does not capture living factors such as dura or brain tissue that may plug a dehiscence.
Declared interests
The authors declared no conflict of interest. Publication types indicate NIH extramural and non-U.S. government research support, but the text does not say how the funders were involved.
The easy way to misread this
Do not conclude that low-frequency audiometry has been shown to improve diagnosis of superior canal dehiscence. The paper did not measure patient air-conduction thresholds below 250 Hz; the suggestion to test lower frequencies was based on cadaveric pressure changes and extrapolation.